This work investigates spatial evolution characteristics during second-harmonic generation (SHG) through numerical and experimental study by employing a dual-pass Nd: YLF amplifier chain. Through simultaneous monitoring of conversion efficiency dynamics and beam profile evolution, we demonstrate that the spatial uniformity follows deterministic transformation patterns during nonlinear frequency conversion. Notably, optimization of beam uniformity was achieved at the fundamental power density of 0.478 GW/cm2 in our configuration, while maintaining conversion efficiency exceeding 85%.

Airy wavepackets, distinguished by their unique self-accelerating, self-healing, and nondiffracting properties, have found extensive applications in particle manipulation, biomedical imaging, and material processing. Investigations into Airy waves have predominantly concentrated on either spatial or temporal dimensions, whereas studies on spatiotemporal Airy wavepackets have garnered less attention owing to the intricate nature of their generation systems. In this study, we present the generation of spatiotemporal Airy wavepackets by employing discrete frequency modulation and geometric phase modulation of pulses from a mode-locked fiber laser. The properties of Airy wavepackets are dictated by the imparted cubic frequency phase, geometric phase, and polarization state, resulting in controllable spatiotemporal profiles. The self-healing properties of spatiotemporal Airy wavepackets have been confirmed in both temporal and spatial dimensions, demonstrating substantial potential for applications in dynamic microscopy imaging and high-speed optical data transmission.

Spatiotemporal mode-locked (STML) fiber lasers have emerged as a novel platform for investigating spatiotemporal solitons and three-dimensional nonlinear phenomena. In this work, we report the generation of synchronous dual-wavelength STML noise-like square pulses in a few-mode fiber laser, characterized by distinct pulse durations at each wavelength. To further explore the experimental results, numerical simulations are conducted, where the mode-related and wavelength-related characteristics of the dual-wavelength noise-like pulses are revealed. It is found that different modes have distinct transient time-frequency characteristics, and a broader spectrum correlates with a longer duration of the pulse envelope and a shorter duration of the sub-pulses. These findings enhance our understanding of the underlying mechanisms and characteristics of noise-like pulses in STML fiber lasers for better exploration of their potential applications.

We report continuous operation of stimulated Raman scattering at 1.9 µm wavelength based on hydrogen-filled anti-resonant hollow-core fibers (AR-HCFs) for the first time, to the best of our knowledge. Using a single-frequency fiber laser at 1 µm as the pump source, a Stokes laser with a maximum power over 25 W is measured in a 47 m nested type of AR-HCF filled with hydrogen gas at 10 bar pressure, corresponding to a power conversion efficiency of 40% and a quantum efficiency of 72.5%. Backward stimulated Raman scattering is observed at the same time and a maximum power of over 5 W is measured at a higher pressure of 30 bar. This work demonstrates the potential of gas-filled AR-HCF in high-power nonlinear wavelength conversion in the mid-infrared spectral region.

A spectrum-tunable 650 nm semiconductor laser dense spectral beam combining (DSBC) system has been successfully realized for the first time, to the best of our knowledge. This system is constructed based on a dual-grating DSBC (DG-DSBC) module, which can realize DSBC with any preset spectrum width under ideal conditions. In this paper, three sets of spectrum-tunable examples are finally given. The combined spectra are stabilized at 4.89, 8.04, and 10.17 nm, with a maximum beam combining efficiency of about 88.27%. The brightness of this system is improved by more than 71% compared with that of the traditional DSBC structure.

Microscale covert photonic barcodes demonstrate exceptional potential in anti-counterfeiting and information security applications due to their advanced security characteristics. However, the current methods suffer from spectral overlap and low concealment of security, restricting encoding capacity and requiring a high security level. These inherent drawbacks significantly restrict both the encoding capacity and the achievable security level. Here, we proposed a strategy to construct the high-security photonic barcodes via photomerization manipulation based on an excited-state intramolecular proton transfer (ESIPT) process in dye-doped whispering gallery mode (WGM) microcavities. The WGM microcavity is composed of highly polarized organic intramolecular charge-transfer (ICT) dye molecules, which have two cooperative gain states. Moreover, the light-manipulated covert photonic barcodes have further been obtained through an ESIPT energy-level process between the trans-excited state and cis-excited state. The WGM lasing spectrum constitutes the fingerprint of the corresponding microsphere, which can be modulated through tuning the dimensions of the microspheres. These results offer a promising route for exploring the light-manipulated security platform for advanced information anticounterfeiting.

Photonic crystal (PC) laser diodes (LDs) exhibit high power and narrow divergence angle output. Enhancing their thermal characteristics is critical for improving device performance and reliability. In this study, we develop a 3D heat dissipation model for 976 nm PC LDs packaged in conduction-cooled heat sink mounts (CS-mounts). The steady-state thermal characteristics are simulated using the finite element method (FEM) to optimize heat sink dimensions and transition heat sink design. Through optimization, the heat sink volume is reduced by 83.3%, while heat dissipation efficiency is improved by 18.2%. Under 60 A continuous-wave operation, the PC LD with the optimized heat dissipation structure achieves an output power of 48.2 W at 20°C with the thermal resistance of 1.17 K/W, and an output power of 54.5 W at 5°C with the maximum power conversion efficiency of 62.4%.

A high-power single-mode semiconductor laser with a photonic crystal structure is demonstrated. The high-order surface gratings are designed as longitudinal photonic crystals to introduce distributed reflection defects. A broad ridge is employed to enhance output power, accompanied by two sets of transverse photonic crystals on either side to filter out high-order lateral modes. At an injection current of 700 mA, the output power of the laser reaches 120 mW, featuring a single-flap horizontal far-field (HFF) distribution with a full width at half-maximum (FWHM) of only 8.8°. The lasing wavelength is 1.3 µm with a side-mode suppression ratio (SMSR) of up to 41.74 dB. The fabrication process is based on standard lithography, and it avoids the need for high-precision lithography and regrowth techniques and provides a cost-effective and simple-process solution for single-mode lasers.

In order to balance the suppression of stimulated Raman scattering (SRS) and transverse mode instability (TMI) in high-power fiber lasers, in this Letter, a new type of spindle-shaped ytterbium-doped fiber (YDF) with asymmetric longitude distribution was designed and produced, which had a small-sized input end, large-sized transmission section, and moderate output end, enabling a good fit with a seed laser and mitigating SRS as well as TMI effects. A counter-pumped fiber laser amplifier was established using this YDF, and two kinds of laser diodes (LDs) were adopted for increasing the TMI threshold. Finally, the maximum output power reached 6 kW, and the beam quality (M2 factors) indicated near-single-mode output. The SRS suppression ratio under 6 kW output power was 36 dB, and no dynamic TMI was observed, which revealed that further enhancement of output power was limited only by pump power.

The nonlinear Schrödinger equation (NLSE) is extensively used to numerically study pulse evolution dynamics in ultrafast fiber lasers. Yet, the computational speed of the NLSE is relatively slow, restricting its applications in systems that rely on real-time computation for dynamic control and operation. In this work, we propose and demonstrate a deep learning approach for the prediction of Stokes pulses’ evolution in a Raman fiber amplifier based on nonlinear optical gain modulation (NOGM). A four-layer fully connected neural network is developed to predict the spectral evolution of the first-order Stokes light in fiber amplifiers using different types of Raman gain fibers. The model achieves high prediction accuracy with normalized root mean square errors below 0.1, while providing up to 86 times faster computation compared to conventional NLSE methods. The network demonstrates reliable generalization capability for parameter combinations beyond the training dataset.

In this Letter, we propose and experimentally demonstrate, to the best of our knowledge, a novel compact power-equalized multi-wavelength laser (MWL) source for optical I/O technology. This multi-wavelength distributed feedback (DFB) laser array is used to achieve simultaneous emission of multiple wavelengths with balanced output power and stable single-mode operation. The reconstruction equivalent chirp technique is used to design and fabricate the π-phase shifted DFB laser array to achieve precise wavelength spacing. The power equalizers (PEs) are monolithically integrated in front of the laser unit to equalize the output power. The experimental results show that the wavelength spacing of the proposed eight-channel MWL is 100 G ± 4.38 G, and the maximum deviation of the intensity (MDOI) is 1.00 dB under a 25°C working environment. Compared with the traditional MWL structure, the wavelength spacing error is reduced from 0.32 to 0.035 nm, and the MODI is reduced from 3.8 to 1.0 dB. The output power exceeds 25 mW when the current injected into the semiconductor optical amplifier (SOA) is 150 mA. Besides, the relative intensity noise (RIN) of all wavelengths is below -138 dB/Hz, and clear 25 Gb/s non-return-to-zero (NRZ) eye diagrams are obtained for the eight wavelengths with the external lithium-niobate Mach–Zehnder modulator. The superior performance of the proposed MWL makes it a promising method for low-bit-error optical I/O links and high-density chip interconnection systems.

In this paper, an all-optical tuning scheme of a multi-walled carbon nanotube (MWCNT)-coated microcavity is introduced, achieving high-speed precise resonance control across the free spectral range (FSR). A modulation laser input through the microcavity tail fiber adjusts the resonance peak position, achieving a tuning efficiency of 107.3 pm/mW below 15 mW, with a maximum range exceeding one FSR and a response time of ∼20 ms. Combined with a fixed-wavelength pump, this scheme can precisely control the microcomb states. The scheme offers high tuning efficiency, simple fabrication, and low cost, making it suitable for applications in microcomb control and optical filters.

We propose a method for generating an all-fiber cylindrical vector beam (CVB) using a fiber Bragg grating (FBG) inscribed in a ring core fiber (RCF). The FBGs are inscribed using the femtosecond laser phase mask scanning technique, chosen for its large ring core diameter and low photosensitivity of the RCF. Additionally, a lateral offset splicing spot is introduced to couple the fundamental mode to the second-order modes. Switchable LP01 and LP11 mode lasers can be achieved. Meanwhile, azimuthally and radially polarized CVBs are successfully realized by adjusting the polarization controllers.

A high-quality 1% (atom fraction) Ho3+:BaF2 crystal was successfully grown using the temperature gradient technique (TGT). The optical properties of the crystal were investigated, and continuous-wave (CW) laser operation of Ho3+ ions in the 2 µm range was successfully demonstrated for the first time in the BaF2 crystal, to the best of our knowledge. Spectral parameters such as Ωt (t = 2, 4, 6) and radiative lifetimes were calculated and studied by the Judd–Ofelt (J–O) theory. The quality factor was calculated to be Q = 6.60 × 10-20 cm2·ms, and the full width at half-maximum (FWHM) was fitted to be 134.5 nm, indicating that the Ho:BaF2 crystal has a low laser threshold and broadband tunability. A maximum output power of 1.5 W and a slope efficiency of 29.3% were achieved by the 1908 nm fiber laser as the pumping source, with a relatively low threshold of 399 mW. Additionally, the Ho:BaF2 crystal achieved a tunable laser output with a bandwidth of 166.4 nm, which is the widest as reported for other 2 µm band Ho-doped fluoride crystals to the best of our knowledge. These results suggest that the Ho:BaF2 crystal has the potential to achieve femtosecond ultrafast pulse laser output through mode-locking operation.

We presented a repetition-rate tunable Yb-doped fiber laser system, which used a chirped fiber Bragg grating as a fiber stretcher designed to match the second- and third-order dispersion of the transmission grating compressor. The system delivered 1-µJ, 143-fs pulses at a 2 MHz repetition rate and 10-µJ, 157-fs pulses at a 200 kHz repetition rate, respectively. The pulse repetition rate can be tuned from 200 kHz to 2 MHz while the pulse duration maintains <180 fs. This compact fiber laser source was built for applications in ophthalmology, such as corneal flap cutting and tissue vaporization. Furthermore, it can be applied in micro-machining applications, such as laser marking, scribing, and drilling.

We demonstrate a versatile bismuth-doped fiber pulse source that is seeded by a mode-locked fiber laser operating in different regimes with different net dispersions in the same cavity, including the square-wave noise-like pulse regime with anomalous net dispersion at 1331 nm and the multi-pulse soliton regime with normal net dispersion at 1320 nm. The versatile pulse evolutions and the multi-pulse dynamics in these two regimes are investigated under different pump powers or polarization states. The seed pulses are then amplified by a bismuth-doped fiber amplifier, which boosts the pulse energy to 21 nJ with a slope efficiency of 21.3% without power saturation and is anticipated to be useful for practical applications.

We report a high-power, all-fiber Tm-doped laser system operating at 1908 nm, based on a master-oscillator power amplifier (MOPA) configuration. The oscillator utilizes two polarization-maintaining (PM) fiber Bragg gratings (FBGs) with orthogonal principal axes to achieve single-polarization output. The system generates a linearly polarized output power of 12.6 W, with a slope efficiency of 40.6%. The power is subsequently scaled to 207.6 W through a primary amplifier, which uses a large mode area (LMA) fiber while maintaining single-mode operation. The amplifier achieves a beam quality factor (M2) of 1.36 and a polarization extinction ratio (PER) exceeding 18.3 dB.

In this Letter, we demonstrate high-energy and high-peak-power nanosecond pulse generation aiming at the 2.94 µm water absorption peak, from a 980 nm diode-clad-pumped actively Q-switched Er3+/Dy3+-codoped fluoride fiber oscillator. Operating at the 2943 nm wavelength locked by a diffraction grating in a Littrow configuration, stable Q-switching with the shortest temporal width of 41 ns has been obtained at a low repetition rate of 100 Hz. The maximum pulse energy of 108 µJ and peak power of 2.48 kW are primarily limited by the thermal damage of the bare fluoride fiber facet for pump coupling and represent the records of pulsed fiber oscillators around 2.94 µm, to the best of our knowledge. This advanced nanosecond laser source provides an optional promising tool for laser medical applications.

In this Letter, we designed a random laser based on a nematic liquid crystal with titanium nitride nanoparticles, which has low spatial coherence, and its spatial coherence can be dynamically manipulated by the applied voltage. In a scattering environment, the speckle effect can be effectively suppressed using the random laser as the light source, and the speckle degree is controlled by the applied voltage. Moreover, with the decrease of the spatial coherence of the random laser, the imaging edges become blurred. We provided a quantitative way to optimize the image quality between uniformity and edge sharpness while improving the signal-to-noise ratio.

High-power diode-pumped solid-state lasers (DPSSLs) can support many important applications owing to their simple setup and high efficiency. However, the thermal effect in the laser crystal is a major limiting factor for laser power improvement. Here, we originally present a quasi-continuous-wave (QCW) diode-pumped monolithic Yb3+-doped YCa4O(BO3)3 (Yb:YCOB) laser and realize the power scaling at room temperature by removing the heat efficiently. The Yb:YCOB laser at 1024 nm is designed with a quantum efficiency of 95%. A high-power QCW laser is realized with an output peak power of up to 226.7 W, a pulse energy of 12.2 mJ, and an optical-to-optical efficiency of 41.2%. To the best of our knowledge, this result represents the record peak power in Yb:YCOB lasers and should have promising applications in some modern devices requiring high-power and large-energy lasers.

We present a novel all-fiber ultrahigh-repetition-rate pulse (UHRP) source based on ultrafast pulse-stimulated dissipative four-wave mixing (FWM). By injecting an ultrafast seed pulse into a dissipative ring cavity equipped with a spectral shaper, a comb-like nonlinear response is generated. The high peak power of the seed pulse reaches the FWM threshold, stimulating a 0.275 THz pulse with an output power of 0.5 W. The gain and spectral shaper in the fiber ring cavity form a dissipative system that modifies the initial field both temporally and spectrally, ensuring UHRP stability even after the pulse is turned off.

In this Letter, we studied a kilohertz nanosecond 1645 nm optical parametric oscillator (OPO) for methane detection. The OPO pump source was an electro-optical Q-switched 1064 nm oscillator, followed by a preamplifier and two Innoslab amplifiers. Two KTiOAsO4 crystals with type II angular phase matching were used as the nonlinear working materials, and two plane mirrors were used for the OPO cavity. We achieved the signal light with an average power of 9.32 W and a minimum pulse duration of 1.8 ns at a repetition rate of 8 kHz for a 54.1 W pump power, and the optical-optical conversion efficiency was 17.3%. The beam quality was measured as Mx2 = 1.08 and My2 = 1.22. The wavelength of the signal light was continuously tunable from 1641.9207 to 1648.1791 nm. To the best of our knowledge, this is the highest average power achieved at the kilohertz regime of a 1645 nm laser.

We demonstrate a 202 W all polarization-maintaining (PM) single-frequency fiber amplifier operating at the C band. Simulations show that the length of the output fiber pigtail following the gain fiber critically has a great impact on stimulated Brillouin scattering (SBS), posing a major obstacle for high-power single-frequency amplification. Optimizing the length to suppress the backward SBS by ∼10 dB, we experimentally achieved a maximum output power of 202 W, yielding an optical-to-optical efficiency of 42%. The signal-to-noise ratio (SNR) of signal light, relative to amplified spontaneous emission (ASE) in Er3+ and Yb3+ bands, was measured to be 23 and 32 dB, respectively, and it can be further improved by ASE suppression and filtering techniques during amplification. To the best of our knowledge, this is the all-PM single-frequency fiber amplifier with the highest power reported in the C band.

In this paper, we demonstrate the single-fiber and two-wavelength time transfer (SFTWTT) over a 2061 km field fiber loop-back link network with a synchronous wavelength-division and time-division multiplexing access (WD-TDMA). This system utilizes wavelength-division multiplexing to avoid the impact of backscatter. In order to achieve high-precision time transfer, time-division multiplexing access is employed. This approach facilitates multiple bidirectional comparisons between local and remote devices. A digital phase-locked loop (PLL), which matches the bandwidth of the transfer system, and precision temperature control technology have been proposed to enhance the high stability of the fiber-optic time and frequency transfer system. The first on-site high-precision fiber-optic time transfer system exceeding 2000 km has been validated. Experimental results show that the stabilities of 5.6 ps@1 s and 3.1 ps@40,000 s can be achieved. The precision of time transfer over a 2061 km fiber-optic network, employing a single-fiber and two-wavelength approach, has been significantly enhanced. This study presents an average time difference of 52 ps across the distance, with a system uncertainty budgeted at 41.8 ps. This achievement signifies a substantial advancement in the realms of stability and reach for optical fiber time transfer, facilitating the development of a high-precision ground-based time service system.

A multistage amplifier system based on high-power end-pumped two-segmented Nd:YVO4 is developed, which realizes the effective beam quality management in high-power lasers. Because of the severe thermal effect caused by high-power end pumping, both the appropriate crystal and beam filling factor (the ratio of the laser beam radius to the pump beam radius) are important in the amplifier. The multisegmented doped crystal is controlled in cooperation with the beam filling factor to realize high output power and maintain good beam quality. To study the thermal effect in the end-pumped crystal, the temperature distributions of end-pumped single-segmented and two-segmented Nd:YVO4 are theoretically calculated. In the experiment, a probe laser is employed to measure the spherical aberration coefficient and the beam quality of the laser at the rear end of the two end-pumped crystals, respectively, and the experimental results are in good agreement with the theoretical results. In the power amplification, a seed laser is employed in the experiment. The appropriate gain medium and beam filling factor are determined by considering the spherical aberration coefficient, beam quality, and power extraction efficiency. Based on the reasonable layout of the power amplification for each stage amplifier, the multistage amplifier system outputs a 280.2 W picosecond laser with the beam quality factors of Mx2 = 1.28 and My2 = 1.32.

In this paper, we proposed and experimentally demonstrated an 8-channel O-band distributed feedback (DFB) laser array with highly uniform 400 GHz spacing and high output power for optical input/output (I/O) technology. The grating phase is precisely controlled, and an equivalent π phase shift is implemented in the laser cavity via the reconstruction equivalent chirp (REC) technology. Anti-reflection (AR) and high-reflection (HR) films are coated on the front and rear facets, respectively, to enhance output power. The equivalent π phase shift is strategically placed near the HR film facet to improve the yield of the single longitudinal mode. Operating with a 400 GHz wavelength spacing, the proposed DFB laser array meets the continuous wave-wavelength division multiplexing multi-source agreement (CW-WDM MSA) specifications. The proposed DFB laser array is flip-chip bonded to a thin-film circuit with an aluminum nitride (AlN) submount to reduce the thermal resistance and enhance the output power. Compared to the p-side-up structure, the flip-chip bonding design significantly reduces junction temperature by 28% and increases maximum output power by approximately 20%. This design effectively lowers the thermal resistance of the chip and enhances its heat dissipation properties. At a bias current of 110 mA, the laser demonstrates wavelength deviations below 1.579 GHz and side-mode suppression ratios above 50 dB. The far-field divergence is measured at 25.8° × 30.1°, and the Lorentzian linewidth is 3.28 MHz. Increasing the bias current to 250 mA results in a laser output power exceeding 80 mW. Furthermore, the relative intensity noise (RIN) for all 8 channels is below -135.3 dB/Hz. The proposed flip-chip bonded 8-channel high-power DFB laser array demonstrates uniform wavelength spacing, high output power, and stable single longitudinal mode performance, making it a promising candidate for multiple wavelength laser sources in optical I/O technology.

Studies have been conducted of emission characteristics directly related to the mode composition of radiation such as the spatial distribution of radiation and generation spectra of lasers with a radiation aperture of 20 µm and different cavity lengths, made on the basis of an AlGaInAs/InP heterostructure with an ultra-narrow waveguide. It is shown that there are two ranges of pump currents in which the laser characteristics behave differently. The first range of currents corresponds to operation in a few-mode lasing mode and switching between modes. The characteristics of every individual sample have a strong influence on mode competition, which leads to a spread of characteristics between identical samples in this region. In the second range, the laser operates in a multimode lasing mode, and the spread of characteristics between samples practically degenerates.

We propose and experimentally demonstrate the monolithic dual-waveguide (DW) distributed feedback (DFB) laser with tunable wavelength spacing. The differences in the chirp sampled grating with various index modulation amplitudes are theoretically elaborated. The wavelength spacing properties of the DW laser at different Bragg spacings are compared and analyzed. To validate the numerical investigation, the DW laser consisting of three sections is fabricated and implemented, where the chirp sampled grating with two equivalent π phase shifts is located. The simulated relationship between the Bragg wavelength spacing and the mode spacing is consistent with the experimental results. Owing to the prominent contribution of the three-section structure and chirp sampled grating, the tuning range of the wavelength spacing is extended significantly, and the cavity of the DW laser becomes compact. The experimental results indicate that the proposed scheme achieves a tuning range from 59.50 to 116.25 GHz. The proposed scheme paves an extraordinary avenue for the integration of laser devices in the applications of optical sensing and THz communication.

In this work, we report on the recent research progress on watt-level all-solid-state single-frequency Pr:LiYF4 (YLF) lasers in the orange spectral region. Combining dual-end pumping and ring-cavity technologies, we have achieved a maximum single-frequency output of 1.19 W at 607 nm with a linewidth of about 20.3 MHz. Based on this study, by inserting a 0.15 mm etalon inside the ring cavity, we find that the 607 nm lasing can be completely suppressed and a single-frequency laser at 604 nm with a 0.69 W output power and a linewidth of about 16.7 MHz can also be obtained. Moreover, the wavelengths of the two single-frequency lasers can be tuned from 607.16 to 607.61 nm and from 603.99 to 605.02 nm, respectively. Furthermore, the single-frequency Pr:YLF laser can also operate in a state of the two orange wavelengths, simultaneously, with a maximum output power of 0.97 W. We believe that this is the highest output power of a direct generation of single-frequency orange lasers and the first demonstration of the wavelength-tuned operation of the achieved single-frequency orange lasers, which could bring opportunities for the application of single-frequency orange lasers.

In this Letter, a homemade bismuth-doped germane silica fiber (BGSF) with a high gain coefficient is fabricated. Based on this fiber, a single-frequency fiber laser (SFFL) operating at 1440 nm is successfully realized. A ring cavity with a short BGSF of 10 m and two cascaded sub-ring cavities ensures the single-longitudinal-mode (SLM) operation. The maximum SLM laser output power of about 6 mW is obtained with the optical signal-to-noise ratio (OSNR) of more than 75 dB. The linewidth of the stable SLM laser is about 745 Hz, measured by the delayed self-heterodyne method. To the best of our knowledge, this is the first SFFL operating at 1440 nm based on the bismuth-doped fiber (BDF), demonstrating the great potential of BDF in expanding the operating band of SFFL.

In this paper, to reduce the damage or absorption caused by radiation to optical fibers, we study lightweight and flexible anti-radiation films based on optical precision deposition technology. At first, anti-radiation composite thin films based on Kapton, ITO, and Cu (or Al) are designed and homemade with different structures. Subsequently, polarization-maintaining (PM) Yb-doped fiber (Yb-fiber) samples protected by these different kinds of anti-radiation films are irradiated with a dose of ∼150 kGy. At last, we comparatively investigate (1) the radiation-induced attenuation (RIA) of these PM Yb-fiber samples and (2) the lasing performance (threshold and slope efficiency) and gain performance of a 1064 nm fiber laser and amplifier using these irradiated PM Yb-fibers as the gain medium, respectively. The results show that such a film can reduce the RIA of the irradiated Yb-fiber by up to 2.84 dB/m and increase the output power by up to 75.3% at most. In addition, we also study the optical recovery of the PM Yb-fibers after radiation.

In this Letter, we report a 2-kW all polarization-maintaining (PM) fiber ultrafast laser from a single fiber link, which has a center wavelength of 1064 nm and a repetition rate of 1.39 GHz. To the best of our knowledge, this is the highest average power from all PM fiber lasers at 1.0 µm. Its beam quality (M2) is measured to be <1.2, and the pulse width after compression is measured to be ∼855 fs.

We propose a dual feed-forward neural network (DFNN) model, consisting of a cavity parameter feature expander (CPFE) and a dynamic process predictor (DPP), for predicting the complex nonlinear dynamics of mode-locked fiber lasers. The output of the CPFE, following layer normalization, is combined with the pulse complex electric field amplitude and then fed into the DPP to predict the dynamics. The pulse evolution process from the detuned steady state to the steady state under different cavity configurations is rapidly calculated. The predicted results of the proposed DFNN are consistent with the numerical split-step Fourier method (SSFM). The simulation speed has been greatly improved with low computational complexity, which is approximately 152 times faster than the SSFM and 4 times faster than the long short-term memory recurrent neural network (LSTM) model. The findings provide a new low computational complexity and efficient machine learning approach to model the complex nonlinear dynamics of mode-locked lasers.

A high-energy and high-efficiency 2 µm nanosecond optical parametric oscillator (OPO) with excellent energy stability is reported. The cavity adopts a plane–plane configuration with two potassium titanyl phosphate (KTP) crystals inserted using a spatial walk-off compensated orientation. The KTP-OPO is pumped by a 1064 nm Nd:YAG Q-switched laser at a repetition rate of 10 Hz and produces a maximum pulse energy of 162.6 mJ at a pump energy of 431 mJ, corresponding to an optical conversion efficiency of 37.7% and a slope efficiency of 45.2%. The energy stability shows a record root mean square (RMS) of 0.4% over 30 min. To our knowledge, this represents the highest 2 µm pulse energy achieved via the 1 µm laser-pumped KTP-OPO scheme, which could be an excellent laser source for driving extreme ultraviolet (EUV) radiations in the subsequent demonstration experiments.

We present the dispersion-managed mode-locked pulse generation in the Er-doped fiber laser in this work. The linear cavity laser scheme is implemented with an all-fiber ring serving as the total reflection mirror and a semiconductor saturable absorber mirror (SESAM) as the mode-locker and non-transparent mirror. The dispersion compensation is applied to change the net dispersion from anomalous to normal dispersion, which integrates mode-locked regimes in the -0.495-+0.197 ps2 net-cavity-dispersion range by incorporating different lengths of the dispersion compensating fiber (DCF). The noise-like mode-locked pulse and conventional soliton are observed during the net-cavity-dispersion variation process. In addition, the homemade mode-selective couplers (MSCs) are utilized to realize high-mode-purity orbital angular momentum (OAM) outputs based on the mode superposition principle.

In this paper, a polarization full-feedback open-loop spectral beam combining (PFF-SBC) structure based on double-ridge stripe semiconductor parity-time-symmetric laser diodes (PTLDs) is proposed and demonstrated. The beam quality of the PTLD is optimized, and the combining efficiency is improved using the methods of polarization separation and full feedback. The maximum output power is up to 2.71 W, which leads to a spectral beam combining efficiency of 83.4% and a grating diffraction efficiency of 95.51% under continuous current operation at a current of 2.3 A. Additionally, the brightness of the SBC module is 116.2 MW·cm-2 sr-1 at a current of 1.6 A, which is 3.5 times that of a single PTLD. The PFF-SBC strategy provides, to our knowledge, a new approach for increasing the beam brightness of PTLDs.

We demonstrate a quantum cascade laser (QCL) emitting at around 5.0 µm with a peak power of 4.7 W at room temperature (298 K) continuous-wave (CW) operation. The cavity length and the ridge width are 7.5 mm and 6.5 µm, respectively. The active core was grown by molecular beam epitaxy (MBE) with high-AlAs quantum barrier layers designed to suppress the current leakage. The device achieved the maximum power of 10.2 W and the maximum wall plug efficiency (WPE) of 22.7% in the pulsed mode. High beam quality is achieved by a single transverse mode (measured M2 < 1.5) with a CW power of 4 W at 298 K.

Photonic-crystal surface-emitting lasers (PCSELs) are considered as next-generation semiconductor lasers because they can operate in a high-power single mode. However, these devices are not suitable for low-threshold high-speed operation because they often require a long cavity length to achieve low loss. In this paper, we break this limit and demonstrate very low-threshold operation of the PCSELs for their high-speed application, using a triple-lattice photonic-crystal structure with a 100 µm cavity length. Low threshold currents of 29 mA at 10°C and 36 mA at 25°C under continuous wave (CW) operation were realized, which is comparable to the traditional high-speed distributed feedback (DFB) Bragg edge-emitting lasers. The far-field divergence angles defined by 1/e2 power were respectively 3.84° and 1.63° along the x- and y-directions. A small-signal modulation bandwidth of 5.8 GHz was obtained. By further optimizing the mesa size, the threshold current was decreased to 12 mA, which, to the best of our knowledge, is the lowest threshold current reported for PCSELs so far.

In this paper, a digital laser with a dual-cavity configuration for the pattern control of a Q-switched pulsed laser is presented. The dynamic pattern control of the pulsed laser from the primary cavity is generated and controlled by simply manipulating the projected phase of the spatial light modulator (SLM) in the secondary cavity. The proposed digital laser design provides a solution for a flexible pulsed laser source while preventing damage to the SLM from high-peak light pulse flux density, benefiting structured laser applications that require high-peak laser power.

We demonstrated a divided pulse amplification of burst pulse trains. The intraburst rate is 1 GHz, and the burst rate ranges from 1.5 kHz to 15 MHz. Under the pump power of 100 W, the burst pulse energy is adjustable from 2.2 µJ to 22 mJ. The pulse width of combined and compressed pulses is 275 fs with beam quality M2 of 1.2.

Ultrastable continuous-wave lasers are one of the important elements for space-based gravitational wave detection. Here we present a Pound–Drever–Hall laser frequency-locked system based on a field-programmable gate array, demonstrating its potential to achieve 10-16 levels of frequency stability for space applications. The system is employed to lock a space-qualified 1064-nm neodymium-doped yttrium aluminum garnet laser to a laboratory-operated 20-cm ultrastable optical cavity. Major noise contributors are identified as laser intensity fluctuation and residual amplitude modulation. The heterodyne beat measurement shows that the frequency noise spectral density of a single laser is reduced to 2.5 Hz/√Hz at a Fourier frequency of 1 mHz, and the frequency instability is 2.1 × 10-16 at 1 s and remains below 3.5 × 10-16 up to 6000 s.

A diode-pumped mode-locked (ML) Tm,La:CaF2 crystal laser is reported in this paper. This laser system delivers stable continuous-wave ML pulses, achieving a maximum output power of 143 mW at a fundamental frequency of 96.2 MHz. Moreover, the signal-to-noise ratio in the stabilized single-pulse regime reaches as high as 75 dB. The central wavelengths of the laser are located at 1886.5 and 1886.7 nm, which further advances the development of ultrafast lasers in the water absorption band of 1.8–1.9 µm.

Mode-locked lasing operations at 1064 and 910 nm wavelengths are demonstrated, respectively, in two all-fiber laser oscillators using our homemade Nd3+-doped silica fiber (NDF) as the gain medium. The Al3+/Nd3+ co-doped silica core glass was fabricated by the modified sol–gel method with 18,300 × 10-6 Nd3+ doping concentration. The NDF drawn by the rod-in-tube method has a core of 4 µm in diameter and a numerical aperture (NA) of 0.14. At 1064 nm, we measure an average laser output power of 18 mW with a pulse duration of 5.75 ps, a pulse energy of 1.14 nJ, and a slope efficiency of 7.2%. Using the same NDF gain fiber of a different length, a maximum average laser output power is 3.1 mW at 910 nm with a pulse duration of 877 ns, a pulse energy of 2.7 nJ, and a slope efficiency of 1.44%.

Ultra-short pulse, ultra-intense (USUI) lasers have become indispensable tools for scientific research. High-energy pump lasers are crucial for ensuring adequate energy and beam quality of these USUI lasers. Pump lasers with rod amplifiers are a cost-effective and reliable option for meeting high-energy pump requirements. However, there is a notable dearth of comprehensive reports on the design of high-energy rod amplifiers. This study provides a detailed analysis of rod amplifiers, focusing primarily on the pump unit utilized at SULF-10 PW and SEL-100 PW prototypes. The analysis covers aspects such as gain management, thermal effects, and spatiotemporal evolution.

Pulse duration is considered as one of the most important characteristics of high-power femtosecond lasers. However, pulses output from the laser system are susceptible to ambient changes and manifest the instability of pulse durations in an open environment. In this paper, incorporating the algorithmic framework of the improved stochastic hill-climbing search and incremental proportional-integral controller, temperature-induced fluctuations of pulse duration can be effectively compensated by an automatic feedback control in an all-fiber chirped-pulse amplification system. In the experiment, sub-hundred femtosecond fluctuation of pulse duration is introduced to verify the performance robustness of the proposed pulse-duration feedback control (PDFC). The stability of pulse duration is obviously higher than the case without the feedback control, and the peak-to-peak fluctuation of pulse duration is reduced to 6.5%. Furthermore, the robust switching between different pulse durations proves the versatility of the PDFC. We expect that the proposed feedback control method could provide a novel insight into high-power femtosecond lasers widely applied in fundamental researches and industrial fields.

We report on a compact, high-efficiency mid-infrared continuous-wave (CW) Fe:ZnSe laser pumped by a 2.9 µm fiber laser under liquid nitrogen cooling. A maximum output power of 5.5 W and a slope efficiency of up to 66.3% with respect to the launched pump power were obtained. The overall optical-to-optical (OTO) conversion efficiency, calculated from the output of the 2.9 µm fiber laser to the 4 µm laser, was as high as ∼54.5%. The OTO efficiency and the slope efficiency are, to the best of our knowledge, the highest ever reported in Fe:ZnSe lasers. A rate-equation-based numerical model of CW operation was established, and the simulation agreed well with the experiment, identifying the routes used in the experiment for such high efficiency.

Lasers from 1I6 to 3F4 transitions were first demonstrated in a Pr3+:YLF crystal by inserting a birefringent filter. Output powers up to 2.44 W, 2.10 W, 2.01 W, and 2.42 W were obtained at 691.7 nm, 701.4 nm, 705.0 nm, and 708.7 nm, respectively. Their slope efficiencies were 19.8%, 16.5%, 15.8%, and 19.4%, respectively. The Mx2 and My2 factors were measured to be 2.29 and 2.03 at 691.7 nm, 2.23 and 1.86 at 701.4 nm, 2.31 and 2.08 at 705.0 nm, and 2.41 and 2.04 at 708.7 nm, with corresponding power fluctuations of less than 5.3%, 5.6%, 5.8%, and 2.9%.

We demonstrated an actively acousto-optic Q-switched pulsed laser based on Pr:YLF at 604 nm. A 604 nm continuous-wave (CW) laser with a maximum output power of 3.84 W was achieved for the first time, to the best of our knowledge. The Q-switched laser with a maximum average output power of 0.384 W, a narrowest pulse duration of 44.5 ns, a maximum single pulse energy of ∼64.1 µJ, and a maximum peak power of ∼1.44 kW was obtained at a repetition rate of 6 kHz. As far as we know, this was the first report of such a narrow pulse duration, high-power, and high-energy Q-switched pulsed laser at 604 nm. The beam quality factors Mx2 and My2 were measured to be 2.87 and 2.40, respectively. The results show that acousto-optic Q-switching is a promising method for obtaining pulsed lasers.

The evolution dynamics of mode locking for a solid-state femtosecond Yb:KGW laser is demonstrated and detected with time-stretch dispersive Fourier transform (DFT) technique for the first time, to the best of our knowledge. The Yb:KGW laser is constructed first with a classical X-shaped cavity, and SESAM-assisted Kerr lens mode locking is obtained. Then, a DFT device is built to record the buildup and extinction dynamics of the mode-locked laser. The results suggest that the time of extinction is slightly shorter than the buildup time and both of them experience complex transitions. The results indicate that DFT could also be suitable to detect the transient buildup and extinction process in solid-state lasers, which would help investigate both the evolution of mode locking and characteristics determination for solid-state lasers.

An 8-channel hybrid-integrated chip for 200 Gb/s (8 × 25 Gb/s) signal transmission has been demonstrated. The channels are all within the O-band, and with a spacing of 800 GHz. The core of this chip is a monolithic integrated multi-wavelength laser array of 8 directly-modulated distributed feedback (DFB) lasers. By using the reconstruction equivalent chirp technique, multi-wavelength integration and asymmetric phase shift structures are achieved in the laser array. The output laser beams of the array are combined by a planar light-wave circuit, which is hybrid-integrated with the laser array by photonic wire bonding. Experiment results of this transmitter chip show good single-mode working of each unit laser, with a side-mode suppression ratio above 50 dB, and the modulation bandwidth is above 20 GHz. Clear eye diagrams are obtained in the lasers for 25 Gb/s non-return-to-zero modulation, which implies a total 200 Gb/s transmission rate for the whole chip.

Soliton generation schemes have attracted considerable scholarly attention. This paper introduces a novel backward tuning method for the reversible generation of dissipative Kerr solitons (DKSs). Reversible soliton generation relies on the thermal stabilization of the auxiliary laser, coupled with backward tuning of the pump laser, significantly increasing the range of soliton steps by over 10 times. Moreover, the method alleviates the stringent auxiliary laser detuning requirement. By adjusting the detuning of the auxiliary laser, diverse numbers of solitons can be deterministically generated, enhancing both flexibility and precision.

We demonstrate an all-polarization-maintaining (APM) fiber mode-locked laser based on nonlinear polarization evolution (NPE). A well-designed Sagnac fiber loop is employed to establish the nonlinear polarization evolution process in a polarization beam splitter (PBS) figure-8 fiber laser. Nonlinear loss curves are calculated to verify the saturable absorption characteristic of this NPE-based APM oscillator. Then, we simulate the pulse propagation process in the cavity to demonstrate the pulse mode-locked formation. Finally, we also design a realizable compact scheme to further reduce noise disturbances, achieving a 101-fs mode-locked pulse train with a 0.3-mrad integrated phase noise and a 0.006% integrated relative intensity noise (RIN). This figure-8 fiber laser provides a new scheme for compacting low-noise compact APM fiber lasers based on the NPE mode-locked mechanism.

A 2 × 3 kW-level bidirectional output fiber oscillator is realized by combining the specially designed spindle-shaped ytterbium-doped fiber, non-wavelength-stabilized 976-nm LDs, and grating bandwidth optimization to balance transverse mode instability and stimulated Raman scattering. The maximum output powers at both ends are 3265 and 2840 W, respectively, with a total efficiency of 73.2%. The M2 factors of the lasers at both ends are about 1.98 and 2.38, respectively. The beam profile at both ends shows that a bidirectional output annular beam fiber oscillator has been realized, which has great potential in practical applications.

We have experimentally presented a watt-level noise-like (NL) pulse mode-locked all-polarization-maintaining (PM) fiber laser centered at ∼1995 nm, which can directly generate stable NL pulses with a maximum output power of ∼1.017 W and pulse energy of ∼0.61 µJ, representing the highest output power of mode-locked NL pulse at 2 µm from any fiber oscillators, to the best of our knowledge. The mode-locked NL pulse laser exhibits an excellent stability with a power fluctuation of ∼0.1% in 8 h of monitoring, and a signal-to-noise ratio of ∼83 dB at a fundamental frequency of ∼1.662 MHz. Moreover, the pulse envelope and coherence spike width of the NL pulse can be widely tuned from ∼4.5 ns to ∼16 ns, and ∼364 fs to ∼323 fs, respectively, with the enhancement of the pump power. Such an all-PM fiber oscillator is the ideal seed source for the implementation of a high-power NL pulse laser and has potential valuable applications in mid-infrared spectroscopy and industrial processing.

We demonstrate an intracavity self-synchronized multi-color Q-switched fiber laser using a parallel-integrated fiber Bragg grating (PI-FBG), fabricated by a femtosecond laser with a point-by-point parallel inscription method. The multi-color Q-switched pulses can be always self-synchronized when the group delay differences between neighboring spectra range from -3.4 to 3.4 ps. The starting and evolution dynamics indicate that the saturable absorption effect of the carbon nanotube plays a dual role: synchronously triggering the startup of the pulse at successive colors by active Q-switching and spontaneously compensating to some extent the temporal walk-off of the multi-color pulses through the cross saturable absorption modulation. This work unveils the intracavity self-synchronization mechanism of the multi-color Q-switched pulses and also demonstrates the potential of PI-FBGs for the customizable generation of the synchronized multi-color pulse in a single cavity.

The Raman random fiber laser (RRFL) is a typical complex physical system due to the intrinsic random feedback of the fiber, which causes complexity in the RRFL output. So far, the time-domain statistical attributes of the RRFL are still not fully characterized. In this paper, the temporal statistical properties of the RRFL are investigated comprehensively for the first time under the full bandwidth condition. First, the time-domain intensity statistical characteristics of the RRFL under the full bandwidth condition are theoretically studied: the results demonstrate that the intensity probability density function of the RRFL is related to the pump power and observing position and deviates inward from the exponential distribution, indicating that correlation exists between the different frequency components in the spectrum. Afterward, in the validation experiment, an elaborate structure is designed to realize a narrow-bandwidth 1053 nm RRFL, and its full bandwidth temporal intensity statistical features manifest an identical variation pattern to the simulation results. This work fills a vacancy in the study of RRFL temporal statistical features and rigorously reveals the different physical mechanisms between RRFL and amplified spontaneous emission light sources, providing instructions for the application of the RRFL.

To the best of our knowledge, this is the first time that a mid-infrared Er3+:CaF2-SrF2 laser has achieved continuous-wave mode-locked operation by a semiconductor saturable absorber mirror. The laser emits a maximum output power of 93 mW at 2.73 µm with a repetition rate of approximately 69 MHz and demonstrates a high signal-to-noise ratio of around 71 dB. In addition, a MgF2 birefringent plate was utilized to enable wavelength tuning of the Er3+:CaF2-SrF2 laser, resulting in operation at approximately 2.73 µm, 2.75 µm, 2.79 µm, and 2.81 µm. These results demonstrate that Er3+:CaF2-SrF2 is a promising alternative for the generation of efficient diode-pumped mode-locked lasers around 2.8 µm.

In this paper, a spectral beam combining (SBC) structure of multi-single emitters laser diode based on a polarization full feedback (PFF) external cavity is proposed and demonstrated. The maximum combining efficiency is 75.6%, which leads to an output power of 38.48 W, a degree of polarization (DOP) of 99.42%, and electro-optical conversion efficiency of 35.63% under continuous wave operation at a current of 8 A. Compared to the conventional SBC, the output power, the combining efficiency, the electro-optical conversion efficiency, and the DOP of the PFF-SBC structure present improvements of 5.73 W, 11.26 percentage points, 5.3 percentage points, and 7.26 percentage points, respectively. The results show that this SBC method can achieve a high efficiency and linearly polarized laser output of SBC, thereby making the subsequent polarization beam-combining efficiency approach the limit.

In this research, we report the latest progress in the suppression of nanosecond prepulses from regenerative amplifier and multipass amplifiers in the SULF-1PW laser. The prepulse generated from the Pockels cell (PC) in a regenerative amplifier is delay-shifted by enlarging the distance between the PC and the nearby cavity mirror, and then removed by the extra pulse pickers outside the regenerative amplifier. The prepulses arising from multipass amplifiers are also further suppressed by adopting a novel amplifier configuration and properly rotating the Ti:sapphire crystals. After the optimizations, the temporal contrast on a nanosecond time scale is promoted to be better than a contrast level of 10-9. This research can provide beneficial guidance for the suppression of nanosecond prepulses in the high-peak-power femtosecond laser systems.

We experimentally demonstrate tunable dual-comb soliton rains in a polarization multiplexing fiber laser based on a single-walled carbon nanotube. The repetition frequency difference of dual-comb pulses is about 39 Hz, with a maximum extinction ratio of 29 dB. With suitable polarization states, one of the dual-comb pulses switches into soliton rain sequence with chirped isolating soliton trains. The signal-to-noise ratio reaches 61 dB, which is 11 dB higher than that of the normal dual-comb pulses. The intervals between chirped isolating solitons are distributed progressively, and the number of isolating solitons can be flexibly tuned from 2 to 11 by adjusting polarization state or pump power. Our work will provide support for further understanding of interaction dynamics of solitons and give a new route to the application of precision measurement.

An unstable resonator with seven large aperture ceramic disks and intra-cavity adaptive correction is presented. The composite ceramic disks with absorption rings were adopted to suppress amplified spontaneous emission. An intra-cavity aberration non-conjugate correction based on round-trip wavefront and relaxation iteration was applied in the resonator. After tilt and defocus were corrected in turn, an average output power of 4.5 kW was obtained. The corresponding beam quality factor β was 19.5. After tilt, defocus, and high order aberrations were corrected, the average output power was increased to 5.4 kW, and the beam quality factor β was improved to 6.8.

To ensure the frequency accuracy of a heterodyne laser source in the ambient temperature range of -20°C to 40°C, a dual-longitudinal-mode thermally stabilized He–Ne laser based on non-equilibrium power locking was designed. The ambient adaptive preheating temperature setting scheme ensured the laser could operate normally in the range of -20°C to 40°C. The non-equilibrium power-locked frequency stabilization scheme compensated for the frequency drift caused by different stabilization temperatures. The experimental results indicated that the frequency accuracy of the laser designed in this study could reach 5.2 × 10-9 in the range of -20°C to 40°C.

We demonstrate a stable narrow linewidth single-frequency erbium-doped fiber laser (EDFL) operating at 1.6 µm. A Fabry–Perot fiber Bragg grating and two cascaded subrings are incorporated in the main ring cavity to achieve single-frequency operation. The experimentally measured optical signal-to-noise ratio is greater than 73 dB. Furthermore, the linewidth of the EDFL is measured to be about 480 Hz by the self-built short-delayed self-heterodyne interferometry device. The laser shows superior stability, with no mode-hopping during the 60-min observation period. The proposed EDFL provides a new experimental idea for realizing a single-frequency fiber laser in the L-band.

A low-numerical-aperture (NA) concept enables large-mode-area fiber with better single-mode operation ability, which is beneficial for transverse mode instability and nonlinear effects suppression. In this contribution, we reported a high-power fiber amplifier based on a piece of self-developed large-mode-area low-NA fiber with a core NA of 0.049 and a core/inner cladding diameter of 25/400 µm. The influence of the pump wavelength and fiber length on the power scaling potential of the fiber amplifier is systematically investigated. As a result, an output of 4.80 kW and a beam quality factor of ∼1.33 were finally obtained, which is the highest output power ever reported in a fiber amplifier exploiting the low-NA fiber. The results reveal that low-NA fibers have superiority in power scaling and beam quality maintenance at high power levels.

High-power ultrafast laser amplification based on a non-polarization maintaining fiber chirped pulse amplifier is demonstrated. The active polarization control technology based on the root-mean-square propagation (RMS-prop) algorithm is employed to guarantee a linearly polarized output from the system. A maximum output power of 402.3 W at a repetition rate of 80 MHz is realized with a polarization extinction ratio (PER) of > 11.4 dB. In addition, the reliable operation of the system is verified by examining the stability and noise properties of the amplified laser. The M2 factor of the laser beam at the highest output power is measured to be less than 1.15, indicating a diffraction-limited beam quality. Finally, the amplified laser pulse is temporally compressed to 755 fs with a highest average power of 273.8 W. This is the first time, to the best of our knowledge, that the active polarization control technology was introduced into the high-power ultrafast fiber amplifier.

The 1.4–1.8 µm eye-safe lasers have been widely used in the fields of laser medicine and laser detection and ranging. The diamond Raman lasers are capable of delivering excellent characteristics, such as good beam quality concomitantly with high output power. The intra-cavity diamond Raman lasers have the advantages of compactness and low Raman thresholds compared to the external-cavity Raman lasers. However, to date, the intra-cavity diamond cascaded Raman lasers in the spectral region of the eye-safe laser have an output power of only a few hundred milliwatts. A 1485 nm Nd:YVO4/diamond intra-cavity cascaded Raman laser is reported in this paper. The mode matching and stability of the cavity were optimally designed by a V-shaped folded cavity, which yielded an average output power of up to 2.2 W at a pulse repetition frequency of 50 kHz with a diode to second-Stokes conversion efficiency of 8.1%. Meanwhile, the pulse width of the second-Stokes laser was drastically reduced from 60 ns of the fundamental laser to 1.1 ns, which resulted in a high peak power of 40 kW. The device also exhibited single longitudinal mode with a narrow spectral width of < 0.02 nm.

All-fiber few-mode erbium-doped fiber amplifiers (FM-EDFAs) with isolation and wavelength division multiplexers (IWDMs) have been developed to enable flexible pumping in different directions. The FM-EDFA can achieve >30 dB modal gain with <0.3 dB differential modal gain (DMG). We experimentally simulate the DMG performance of a cascade FM-EDFA system using the equivalent spectrum method. The overall DMG reaches 1.84 dB after 10-stage amplification. We also build a recirculating loop to simulate the system, and the developed FM-EDFA can support transmission up to 3270 km within a 2 dB overall DMG by optimizing the few-mode fiber length in the loop.

We demonstrate the generation of a unique regime of multiple solitons in a Tm-doped ultrafast fiber laser at ∼1938.72 nm. The temporal pulse-to-pulse separation among the multiple solitons, 10 in a single-pulse bunch, increases from 0.89 ns to 1.85 ns per round trip. In addition, with the increasing pump power, the number of bunched solitons increases from 3 up to 24 linearly, while the average time separation in the soliton bunch varies irregularly between ∼0.80 and ∼1.52 ns. These results contribute to a more profound comprehension of nonlinear pulse dynamics in ultrafast fiber lasers.

We report a high-stability ultrafast ultraviolet (UV) laser source at 352 nm by exploring an all-fiber, all-polarization-maintaining (all-PM), Yb-doped femtosecond fiber laser at 1060 nm. The output power, pulse width, and optical spectrum width of the fiber laser are 6 W, 244 fs, and 17.5 nm, respectively. The UV ultrashort pulses at a repetition rate of 28.9 MHz are generated by leveraging single-pass second-harmonic generation in a 1.3-mm-long BiB3O6 (BIBO) and sum frequency generation in a 5.1-mm-long BIBO. The maximum UV output power is 596 mW. The root mean square error of the output power of UV pulses is 0.54%. This laser, with promising stability, is expected to be a nice source for frontier applications in the UV wavelength window.

A passively switchable erbium-doped fiber laser based on alcohol as the saturable absorber (SA) has been demonstrated. The SA is prepared by filling the gap between two optical patch cords with alcohol to form a sandwich structure. The modulation depth of the alcohol–SA is measured to be 6.4%. By appropriately adjusting the pump power and the polarization state in the cavity, three kinds of mode-locked pulse patterns can be achieved and switched, including bright pulse, bright/dark soliton pair, and dark pulse. These different soliton emissions all operate at the fundamental frequency state, with a repetition rate of 20.05 MHz and a central wavelength of ∼1563 nm. To the best of our knowledge, this is the first demonstration of a switchable soliton fiber laser using alcohol as the SA. The experimental results further indicate that organic liquid-like alcohol has great potential for constructing ultrafast lasers.

A high-power CW Yb:YAG slab laser amplifier with no adaptive optics correction has been experimentally established. At room temperature, the amplifier emits a power of 22 kW with an average beam quality (β) of less than 3 in 0.5 min. To our knowledge, this is the brightest slab laser without closed-loop adaptive optics demonstrated to date. In addition, an extracted power of 17 kW with an optical extraction efficiency of 33%, corresponding to a residual optical path difference of less than 0.5 µm, is achieved with the single Yb:YAG slab gain module. The slab gain module has the potential to be scalable to higher powers while maintaining good beam quality. This makes a high-power solid-state laser system simpler and more robust.

A whispering gallery mode resonator (WGMR) filter can narrow laser linewidth while significantly changing the output power characteristics of fiber laser system. It is found that traditional laser output power model is invalid. We report a correction model of a narrow linewidth fiber laser filtered with a WGMR to analyze its power. We believe that the loss of the laser system and the threshold gain increase caused by the WGMR filter lead to the predominate amplified spontaneous emission during the original laser period. According to that, we assume the correction coefficient is an exponential decay related to the Er-doped fiber length in the large loss situation, and we verify it experimentally. As a result, the correction model is valid for WGMR-filtered fiber laser.

The dynamic gain of a few-mode erbium-doped fiber amplifier (FM-EDFA) is vital for the long-haul mode division multiplexing (MDM) transmission. Here, we investigate the mode-dependent dynamic gain of an FM-EDFA under various manipulations of the pump mode. First, we numerically calculate the gain variation with respect to the input signal power, where a mode-dependent saturation input power occurs under different pump modes. Even under the fixed intensity profile of the pump laser, the saturation input power of each spatial mode is different. Moreover, high-order mode pumping leads to a compression of the linear amplification region, even though it is beneficial for the mitigation of the differential modal gain (DMG) arising in all guided modes. Then, we develop an all-fiber 3-mode EDFA, where the fundamental mode of the pump laser can be efficiently converted to the LP11 mode using the all-fiber mode-selective coupler (MSC). In comparison with the traditional LP01 pumping scheme, the DMG at 1550 nm can be mitigated from 1.61 dB to 0.97 dB under the LP11 mode pumping, while both an average gain of 19.93 dB and a DMG of less than 1 dB can be achieved from 1530 nm to 1560 nm. However, the corresponding signal input saturation powers are reduced by 0.3 dB for the LP01 mode and 1.6 dB for the LP11 mode, respectively. Both theoretical and experimental results indicate that a trade-off occurs between the DMG mitigation and the extension of the linear amplification range when the intensity profile of pump laser is manipulated.

The high-power mode-programmable orbital angular momentum (OAM) beam has attracted significant attention in a wide range of applications, such as long-distance optical communication, nonlinear frequency conversion, and beam shaping. Coherent beam combining (CBC) of an optical phased array (OPA) can offer a promising solution for both generating the high-power OAM beam and rapidly switching the OAM modes. However, achieving real-time phase noise locking and formation of desired phase structures in a high-power CBC system faces significant challenges. Here, an internal phase-sensing technique was utilized to generate the high-power OAM beam, which effectively mitigated thermal effects and eliminated the need for large optical devices. An OPA with six elements was employed for experimental demonstration. The first effective generation of over 1.5 kW mode-programmable OAM beam in a continuous-wave domain was presented. Moreover, the results demonstrated that the generated OAM beam could be modulated with multiple dimensions. The topological charge can be switched in real time from -1 to -2. Notably, this OAM beam emitter could function as an OAM beam copier by easily transforming a single OAM beam into an OAM beam array. More importantly, a comprehensive analysis was conducted on power scaling, mode switching speed, and expansion of OAM modes. Additionally, the system’s compact design enabled it to function as a packageable OAM beam emitter. Owing to the advantages of having high power and programmable modes with multiple dimension modulation in phase structures and intensity distribution, this work can pave the way for producing high-power structured light beams and advancing their applications.

We demonstrate a high power, Er:LuAG single-longitudinal-mode laser in an anti-misaligned resonator. Based on the Faraday effect, a 1.61 W single-longitudinal-mode (SLM) laser is obtained with the double corner-cube-retroreflector (CCR) structure, and the tunable wavelength is 1649.2–1650.3 nm. Additionally, we investigate the anti-misalignment characteristics when the CCR moves and rotates along the optical axis. Furthermore, by utilizing the Er:LuAG amplifier, the maximum 2.32 W single-longitudinal-mode laser at 1649.6 nm is achieved. The beam quality factors M2 of the 2.32 W Er:LuAG single-longitudinal-mode laser are 1.23 and 1.25 along the horizontal (x) and vertical (y) directions, respectively.

In this paper, we experimentally investigate the tuning characteristics of laser modes for an ultrahigh-Q Er3+-doped microbottle resonator (MBR) based on the whispering gallery mode (WGM). Thanks to the optimized Er3+ doping technique, the laser threshold could be as low as 70 µW. Benefiting from the abundant axial modes and radial modes of the MBR, our experiments demonstrate that the number of laser modes can be flexibly controlled by varying the pump power, adjusting the coupling positions along the axis of the MBR, as well as modifying the coupling diameter of the tapered fiber. The laser mode switching is performed from single-mode to multimodes. Furthermore, different from the traditional external tuning method, we propose a simple and stable approach for continuous wavelength tuning of the laser mode based on the thermal effect associated with the high Q MBR. By precisely adjusting the pump laser wavelength, the emitted laser wavelength can be tuned over a range of 0.102 nm with a high linearity of 99.96%. The engineering of laser mode switching and precise wavelength tuning of the Er3+-doped MBR is expected to have promising applications in miniature tunable single-mode lasers, laser precision measurement, and so on.

A mode-switchable femtosecond vortex laser is innovatively developed in a Yb:KGW-based resonator. The unique structure is designed to achieve a transition between different transverse modes. In a normal cavity, 416 fs TEM00 mode is obtained. With a 50 µm defect spot mirror, the resonator delivers LG0,1 mode with a pulse duration of 476 fs. Under off-axis pumping, LG0,1 mode is switched to a two-vortex array. The pulse width of the two-vortex array is as short as 520 fs. The maximum output power is 401 mW with a pulse energy of 4.15 nJ. To the best of our knowledge, this is the first realization of a femtosecond vortex array from resonators.

We experimentally demonstrate a Yb-doped all-fiber mode-locked laser based on the Mamyshev mechanism. The entire experimental setup operates only by injecting pump powers and adjusting polarization controllers (PCs), which realizes self-starting. Two types of pulse patterns are observed at different pump powers and polarization states, including single pulses and up to eight-pulse bound-state pulses. The operating wavelength of single-pulse mode-locking switching between 1072.3 and 1043.1 nm can be realized by increasing the pump power while keeping the PCs in a fixed state. The design can provide an attractive experimental model for all-fiber and self-starting Mamyshev oscillators.

A hybrid cavity structure based on individual laser diode integrating coherent beam combining (CBC) and spectral beam combining (SBC) is demonstrated. The CBC structure is used to enhance laser output power while optimizing beam quality, and the SBC structure is employed to further increase laser output power. An output power of 1.42 W was obtained at 0.55 A, with a high combining efficiency of 87.2%. Additionally, the brightness of this structure is 58.65 MW·cm-2·sr-1, which is 3.66 times that of a single laser diode. The entire structure provides a new approach for increasing the output power and optimizing the beam quality of the laser diode.

Statistical properties of the erbium-doped random fiber laser (ERFL) play an important role in studying its physical attributes and advancing profound applications. Thus, there is an obvious need for thorough characterization and effective tailoring. Here, we investigate the full-bandwidth time-domain statistical properties of ERFL and achieve its tailoring through the aspect of fiber dispersion. Particularly, a narrowband ERFL is delicately designed to guarantee full-bandwidth measurement. The intensity probability density function (PDF) employed to analyze time-domain characteristics exhibits an inward deviation from the exponential distribution, indicating that correlations exist among different wavelength components. Furthermore, the effect of fiber dispersion on the temporal characteristics of ERFL is explored. The results demonstrate that dispersion accumulation breaks correlations among wavelength components, making its time-domain characteristics closer to the amplified spontaneous emission source. Conversely, dispersion compensation makes the PDF distribution converge further, leading to a more stable temporal output compared to the ERFL seed source. This work reveals the intrinsic time-domain dynamics of ERFL and provides new insights into tailoring demand-oriented temporal characteristics.

In this work, polarization mode dispersion (PMD) in polarization-maintaining (PM) fibers, to the best of our knowledge, is first proposed and experimentally proved to be responsible for severe spectral modulations in ultrafast PM fiber amplifiers, the introduction of which can give reasonable explanation for the dense spectral ripples imposed on the spectra of amplified lasers from the commonly used all-PM-fiber or hybrid “PM-fiber + bulk crystal” amplifiers, including both high-power amplifiers with remarkable nonlinear effects (self-phase modulation, SPM) and even low-power amplifiers with negligible nonlinear effects.

The mid-infrared (MIR) pulsed laser, operating at around 2.8 µm, holds great significance due to its strong water absorption and the characteristic fingerprint spectra it provides for essential molecules. Nevertheless, the challenge of achieving stable MIR pulses persists, primarily due to the limited availability of reliable components operating in the MIR range. In this work, a La3Ga5SiO14 (LGS) crystal is used as the electro-optical modulator within the laser cavity constituted by an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber, successfully generating Q-switched MIR lasing. This achievement is characterized by a low pump threshold, high slope efficiency, and adjustable repetition rate within the 2.8 µm wavelength range. Stable pulses are attainable with long-term stability at a repetition rate of 18 kHz and a modest pump power of 0.6 W, and the maximum output power reaches 451 mW, featuring a pulse width of 64 ns at a pump power of 4.4 W, along with a slope efficiency of approximately 11.4%. It represents the highest efficiency in an electro-optical Q-switched laser operating around 2.8 µm. Our research introduces an innovative active Q-switching approach to enhance the performance of MIR pulsed fiber lasers, thus advancing the development of MIR coherent sources and their associated applications.

On-demand and real-time generation of arbitrary complex fields directly from the laser source holds significant appeal for myriad applications. In this Letter, we demonstrate a ring laser configuration capable of dynamically generating arbitrary transverse fields. In a ring laser resonator, two cascaded phase modulations are utilized, which permits the control of two beams with high efficiency and high fidelity. The zeroth-order beam is a fundamental Gaussian field that self-reproduces itself in the resonator. The first-order beam serves as the desired output field, which is separated from the self-reproduction mode to facilitate the on-demand manipulation of amplitude and phase. In the verification experiments, a series of typical Hermite–Gaussian (HG) modes, Laguerre–Gaussian (LG) modes, flat-top mode, and amplitude-only pattern “A” are generated from the ring laser configuration. This innovative ring laser resonator may open up new perspectives for the design of structured-light lasers, with potential impacts in applications such as particle manipulation, advanced microscopy, and next-generation optical communication.

Dynamic beam shaping is of importance for a wide range of applications, such as light field regulation, laser processing, and advanced manufacturing. In this paper, an internal phase-sensing tiled-aperture coherent beam-combining system with seven beam elements was constructed for dynamic beam shaping. This system could be performed as a digital laser, where each laser beamlet functioned as an individual laser pixel. The amplitude and phase of each laser pixel could be adjusted independently in real time. In our experiment, the laser array was operated in three different configurations: the triangular, pentagonal, and hexagonal laser arrays, while each laser pixel was modulated with a different piston phase of nπ (where n was an integer). We demonstrated various beam-shaping patterns based on this system with output powers scaling over 1 kW. Additionally, the energy distribution of the emitted laser could be flexibly varied and customized. These results highlighted that our dynamic beam-shaped laser exhibited excellent performance in both dynamic beam-shaping and power-scaling capabilities. This work holds great potential for numerous applications involving beam shaping.

A high-speed distributed feedback laser based on the reconstruction equivalent chirp technology has been proposed and demonstrated. Due to the enhanced detuned loading and the photon–photon resonance effect, the 3-dB modulation bandwidth is improved to 29 GHz. Utilizing the proposed method, the relative intensity noise is reduced to below -156.37 dB/Hz, and the frequency chirp is decreased from 4.74 to 2.58. Moreover, the modulation maintains excellent linearity, with a 1-dB compression point of more than 18 dBm.

The realization of single-frequency fiber lasers requires high-gain media. In this work, an Er:YAG crystal-derived silica fiber (EYDSF) was prepared using the melt-in-tube method, whose gain coefficient was up to 2.11 dB/cm using a pump power of 1480 nm. A linearly polarized single-frequency fiber laser was constructed based on a 2-cm-long EYDSF. The optical-to-optical conversion efficiency was 27.0%. A fiber mirror was used at the end of the cavity to reflect the residual pump, which can be absorbed by the EYDSF to further increase the output power. The maximum output power and the slope efficiency of the proposed laser were over 100 mW and up to 22.4%, respectively. To the best of our knowledge, it has the highest output power and the largest slope efficiency, compared with the previous single-frequency fiber lasers based on EYDSFs. In addition, the laser had good polarization and noise performance with a polarization extinction ratio of 25 dB and a relative intensity noise of <-139 dB/Hz. The performance of the proposed fiber laser demonstrates its great potential as a seed source for coherent optical communications, laser combining systems, and other fields.

Directly modulated vertical-cavity surface-emitting lasers (VCSELs) have long dominated the data center optical interconnect market, attributed to VCSELs’ cost-effectiveness and energy efficiency. However, numerous challenges are currently being addressed to enhance device characteristics and modulation speed, aligning with the evolving trends in next-generation data centers that underscore the need for enhanced communication rates and extended transmission distances. This review delves into VCSEL structure design, methods for achieving single-mode control, techniques for fabricating long-wavelength VCSELs, and advanced packaging technology for VCSEL arrays, offering insights into recent research on high-speed single-mode VCSEL development and related technologies.

We demonstrate, for the first time and to the best of our knowledge, a continuous-wave and broadly tunable Cr:ZnSe bulk crystal laser pumped by a Tm:YLF bulk laser with 1845 nm and 1887 nm wavelengths. We compare the output characteristics and wavelength-tuning properties of the continuous-wave operation at the two pump wavelengths. In the continuous-wave operation, the maximum output power is 1.79 W with a slope efficiency of 28.8%, which is achieved at the pump wavelength of 1887 nm. In addition, a tuning range of ∼700 nm (696 nm) from 2040 nm to 2736 nm by using a reflective diffraction grating is realized. To the best of our knowledge, this is the widest tuning range realized so far for Cr:ZnSe bulk crystal tuned by gratings.

We explore for the first time the real-time spectra of dissipative soliton (DS) and noise-like pulse (NLP) inter-switching by adjusting the pump power, as well as the dual-pulse collision dynamics for three modes: dual-NLP, NLP-DS, and dual-DS in a single-/dual-wavelength mode-locked fiber laser. Different types of dual-pulses differ in collision duration. During spectral reconstruction, dual-pulses exchange energy twice due to their respective accumulation dynamics. Additionally, collision-induced soliton explosions have chaotic properties, leading to each collision being random. The experimental results advance the study of the dynamics of different pulse types and also contribute to the conduction of in-depth investigations on dual-comb sources.

By combining the thermally-induced spectral broadening of Er3+/Yb3+ co-doped crystal and the high ratio of cavity gain to loss, a high-power broadband continuously tunable 1.5-1.6 µm laser was successfully demonstrated in an Er:Yb:YAl3(BO3)4 crystal. End-pumped by a continuous-wave 975.6 nm laser diode, three discrete tunable laser bands at 1483–1488, 1495–1503, and 1521–1612 nm were realized at an incident pump power of 7.7 W. The maximum continuously tunable bandwidth was 91 nm at 1521–1612 nm, and the maximum output power was 474 mW at 1551 nm. The output power was generally higher than 100 mW in the whole tunable range.

In this Letter, we realized the phonon-assisted Q-switched laser operation in Yb:YCOB crystal. Differing from previous laser wavelengths below 1.1 µm, we extended the wavelength to 1130 nm by amplifying multiphonon-assisted electronic transitions. At a repetition rate of 0.1 kHz, the laser output power was 82 mW with a pulse width of 466.1 ns, corresponding to a high peak power of 1.76 kW and a single pulse energy of 0.82 mJ, respectively. To the best of our knowledge, this represents the highest pulse energy among all Yb3+-doped crystal lasers at the wavelength beyond 1.1 µm. Such a large pulse energy could be explained by the laser rate-equation theory. These results indicated that the electron-phonon coupling effect not only extends the lasing wavelengths but also enables a fast temporal response to support nanosecond, picosecond, even femtosecond pulse laser operation.

We present our efforts towards power scaling of Er:Lu2O3 lasers at 2.85 µm. By applying a dual-end diode-pumped resonator scheme, we achieve an output power of 14.1 W at an absorbed pump power of 59.7 W with a slope efficiency of 26%. In a single-end pumped resonator scheme, an output power of 10.1 W is reached under 41.9 W of absorbed pump power. To the best of our knowledge, this is the first single crystalline mid-infrared rare-earth-based solid-state laser with an output power exceeding 10 W at room temperature.

We present a study on a watt-level acousto-optically Q-switched Pr:YLF laser at three different repetition rates (10 kHz, 20 kHz, and 50 kHz) for the first time, to the best of our knowledge. The corresponding average output powers and pulse widths were measured to be 1.14 W, 1.2 W, and 1.32 W, and 40 ns, 52 ns, and 80 ns, respectively. A maximum pulse energy of 0.11 mJ was obtained, corresponding to a peak power of up to 2.8 kW at a repetition rate of 10 kHz. The simulated dynamics of a fast Q-switched Pr:YLF laser is in agreement with the experiment. The laser’s ability to generate stable pulses with high peak power and short pulse width makes it highly desirable for various practical applications, such as laser machining and material processing.

The dual-mode stabilization scheme has been demonstrated as an efficient way to stabilize laser frequency. In this study, we propose a novel dual-mode stabilization scheme that employs a sizable Fabry–Pérot cavity instead of the microcavity used in previous studies and has enabled higher bandwidth for locking. The results demonstrate a 30-fold reduction in laser frequency drift, with frequency instability below 169 kHz for integration time exceeding 1 h and a minimum value of 33.8 kHz at 54 min. Further improvement could be achieved by optimizing the phase locking. This scheme has potential for use in precision spectroscopic measurement.

A high efficiency, low threshold, high repetition rate H-β Fraunhofer line light at 486.1 nm was demonstrated. A high-efficiency KTP optical parametric oscillator was achieved by double-pass pumping with a high-maturity 5 kHz 532 nm laser. Thanks to the efficient intracavity frequency doubling of the circulating signal wave by a BIBO crystal, the threshold pump power of the 486.1 nm output was 0.9 W, and the maximum output power of 1.6 W was achieved under the pump power of 7.5 W. The optical–optical conversion efficiency was 21.3%, with the pulse duration of 45.2 ns, linewidth of ∼0.12 nm, and beam quality factor M2 of 2.83.

In this work, we demonstrate the phonon-assisted vibronic lasing of a Yb-doped sesquioxide Yb:LuScO3 crystal. The electron–phonon coupling process was analyzed and the Huang-Rhys factor S was calculated to be 0.75 associated with the fluorescence spectrum at room temperature. By a rational cavity design to suppress lasing below 1100 nm, a continuously spectral tunability from 1121 to 1136 nm was realized in a Yb:LuScO3 laser, which represents the longest achievable wavelength in the Yb-doped sesquioxide lasers. Moreover, the Raman spectrum indicated that the Eg phonon mode with a frequency of 472 cm-1 was mainly devoted to the phonon-assisted transition process. This work broadens the achievable laser spectrum of Yb-doped sesquioxide, and suggests that the multiphonon–electron coupling strategy should be universal for other laser materials.

In this work, we demonstrate the spectral manipulation in an ultrafast fiber laser system that generates ultrashort pulses with a repetition rate of 1.2 GHz and two switchable modes—a 1064-nm fundamental laser mode with a maximum output power of 66.6 W, and a 1125-nm Raman laser mode with a maximum output power of 17.23 W. The pulse width, beam quality, and power stability are carefully characterized. We also investigate a method to switch between the two modes by manipulating the duty cycle of the modulation signal. It is anticipated that this bi-mode ultrafast fiber laser system can be a promising ultrafast laser source for frontier applications, such as micromachining, bioimaging, and spectroscopy.

We experimentally demonstrated a cascaded internal phase control technique. A laser array with 12 channels was divided into three sub-arrays and a stage array, and phases of the sub-arrays and the stage array were locked by four phase controllers based on the stochastic parallel gradient descent (SPGD) algorithm, respectively. In this way, the phases of the whole array were locked, and the visibility of the interference pattern of the whole emitted laser array in the far field was ∼93%. In addition, the technique has the advantage of element expanding and can be further used in the high-power coherent beam combination (CBC) system due to its compact spatial structure.

An immersed liquid cooling slab laser is demonstrated with deionized water as the coolant and a Nd:YAG slab as the gain medium. Using waveguides, a highly uniform pump beam distribution is achieved, and the flow velocity distribution is also optimized in the channels of the gain module (GM). At various flow velocities, the convective heat transfer coefficient (CHTC) is obtained. Experimentally, a maximum output power of 434 W is obtained with an optical–optical efficiency of 27.1% and a slope efficiency of 36.6%. To the best of our knowledge, it is the highest output power of an immersed liquid cooling laser oscillator with a single Nd:YAG slab.

We demonstrate spectral-furcated vector solitons in normal-dispersion fiber lasers comprising a section of polarization-maintaining fiber. The spectrum of each orthogonal-polarized component is confined by the birefringence-related phase-matching principle, and the bicorn spectral structure corresponds to the zero-order sidebands of two vector modes. Due to the Hopf bifurcation effect, the vector soliton evolves into a breathing state at the higher pump level, accompanied by an extra set of sub-sidebands that continuously exchange energy with the zero-order sidebands. Simulation results fully reproduce experimental observations of the spectral furcation and soliton breathing, offering comprehensive insights into the pulse-shaping mechanism of the birefringence-managed soliton.

We have successfully generated a 1.3/1.4 µm random fiber laser (RFL) using bismuth (Bi)-doped phosphosilicate fiber. The Bi-doped RFL has shown excellent long-term operational stability with a standard deviation of approximately 0.34% over 1 h at a maximum output power of 549.30 mW, with a slope efficiency of approximately 29.21%. The Bi-doped phosphosilicate fiber offers an emission spectrum ranging from 1.28 to 1.57 µm, indicating that it can be tuned within this band. Here, we demonstrated a wavelength-tuning fiber laser with a wavelength of 1.3/1.4 µm, achieved through the using of a fiber Bragg grating or a tunable filter. Compared to traditional laser sources, the RFL reduces the speckle contrast of images by 11.16%. Due to its high stability, compact size, and high efficiency, this RFL is highly promising for use in biomedical imaging, communication, and sensor applications.

We report a Yb-doped mode-locked fiber laser based on a nonlinear amplifying loop mirror (NALM), which is all-normal-dispersion (ANDi), and allows the output wavelength to be tunable. The laser can generate a stable femtosecond dissipative soliton with a maximum output power of 196 mW. Its repetition rate is 112.4 MHz, and the final pulse duration is 236 fs. By adjusting the angle of the reflective diffraction grating, the mode-locked fiber laser was realized to tune the output with a tuning range of 54 nm from 1011.8 nm to 1065.6 nm. To the best of our knowledge, this is the widest tuning range of an ANDi Yb-doped mode-locked fiber laser based on NALM.

High-order dispersion introduced by Gires–Tournois interferometer mirrors usually causes spectral sidebands in the near-zero dispersion region of mode-locked fiber lasers. Here, we demonstrate a sideband-free Yb-doped mode-locked fiber laser with dispersion-compensating Gires–Tournois interferometer mirrors. Both the simulation and the experiment demonstrate that the wavelength and energy of the sidebands can be tuned by changing the transmission coefficient of the output mirror, the pump power, and the ratio of the net cavity dispersion to the net third-order dispersion in the cavity. By optimizing these three parameters, the laser can generate a sideband-free, Gaussian-shaped spectrum with a 13.56-nm bandwidth at -0.0232 ps2 net cavity dispersion, which corresponds to a 153-fs pulse duration.

The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion. This paper presents the intracavity frequency tripling in a self-mode-locked semiconductor disk laser, and a picosecond pulse train at 327 nm wavelength is achieved. The pulse repetition rate is 0.49 GHz, and the pulse width is 5.0 ps. The obtained maximum ultraviolet output power under mode locking is 30.5 mW, and the corresponding conversion efficiency is obviously larger than that of continuous-wave operation. These ultraviolet picosecond pulses have high spatial and temporal resolution and can be applied in some emerging fields.

A monolithic visible supercontinuum (SC) source with a record average output power of 204 W and a spectrum ranging from 580 nm to beyond 2400 nm is achieved in a piece of standard telecom graded-index multimode fiber (GRIN MMF) by designing the pumping system. The influence of the GRIN MMF length on the geometrical parameter instability (GPI) effect is analyzed for the first time, to the best of our knowledge, by comparing the SC spectral region dominated by the GPI effect under different fiber lengths. Our work could pave the way for robust, cost-effective, and high-power visible SC sources.

High-repetition rate femtosecond lasers are shown to drive heat accumulation processes that are attractive for femtosecond laser-induced subwavelength periodic surface structures on silicon. Femtosecond laser micromachining is no longer a nonthermal process, as long as the repetition rate reaches up to 100 kHz due to heat accumulation. Moreover, a higher repetition rate generates much better defined ripple structures on the silicon surface, based on the fact that accumulated heat raises lattice temperature to the melting point of silicon (1687 K), with more intense surface plasmons excited simultaneously. Comparison of the surface morphology on repetition rate and on the overlapping rate confirms that repetition rate and pulse overlapping rate are two competing factors that are responsible for the period of ripple structures. Ripple period drifts longer because of a higher repetition rate due to increasing electron density; however, the period of laser structured surface is significantly reduced with the pulse overlapping rate. The Maxwell–Garnett effect is confirmed to account for the ripple period-decreasing trend with the pulse overlapping rate.

A high-energy 100-Hz optical parametric oscillator (OPO) based on a confocal unstable resonator with a Gaussian reflectivity mirror was demonstrated. A KTA-based OPO with a good beam quality was obtained when the magnification factor was 1.5, corresponding to the maximum signal (1.53 µm) energy of 56 mJ and idler (3.47 µm) energy of 20 mJ, respectively. The beam quality factors (M2) were measured to be M2x = 5.7, M2y = 5.9 for signal and M2x = 8.4, M2y = 8.1 for idler accordingly. The experimental results indicated that the beam quality positively changed with the increase of magnification factors, accompanied by an acceptable loss of pulse energy.

We first study the effect of cavity modes propagating in the lateral dimension on high-power semiconductor lasers with a large stripe width. A sidewall microstructure was fabricated to prevent optical feedback of lateral resonant modes. Theoretically, we demonstrate the existence of lateral resonant modes in the Fabry–Perot cavity with a large stripe width. Experimentally, we design the corresponding devices and compare them with conventional broad-area diode lasers. About a 15% reduction in threshold current and a 27% increase in maximum electro-optical conversion efficiency are achieved. The amplified spontaneous emission spectrum is narrowed, which proves that lateral microstructures suppress optical feedback of lateral resonant modes. Under a large continuous-wave operation, the maximum output power of laser device is 43.03 W, about 1 W higher than that of the standard broad-area laser at 48 A.

We demonstrated an electrically pumped InP-based microcavity laser operating in continuous-wave mode. The active region is designed with antimony surfactants to enhance the gain at 2 μm, and a selective electrical isolation scheme is used to secure continuous-wave operation for the microcavity laser at room temperature. The lasers were fabricated as a notched elliptical resonator, resulting in a highly unidirectional far-field profile with an in-plane beam divergence of less than 2°. Single-mode emission was obtained over the entire dynamic range, and the laser frequencies were tuned linearly with the pumping current. Overall, these directional lasers pave the way for portable and highly integrated on-chip sensing applications.

We report continuous-wave deep red lasers at 696.6 and 698.6 nm in a Pr3+:YLF crystal pumped by an InGaN laser diode. A Lyot filter was inserted into the cavity as a birefringent filter to select wavelength; the lasers at 696.6 and 698.6 nm were obtained with a maximum output power of 1.36 and 3.11 W, separately. To the best of our knowledge, the output powers of these two lasers are the highest to date, and this is the first scaling of the output power of the Pr3+:YLF laser to the watt level at around 696 nm. In addition, the corresponding theoretical analysis and simulation were carried out to explain the experimental phenomena.

The development of laser systems leads to an increasing threat to photoelectric imaging sensors. A cubic phase plate wavefront coding imaging system is proposed to reduce the risk of damage owing to intense laser radiation. Based on the wavefront coding imaging model, the diffracted spot profile and the light intensity distribution on the observation plane are simulated. An experimental device is set up to measure the laser-induced damage thresholds and investigate the morphology of laser-induced damage patterns of the conventional and the wavefront encoding imaging system. Simulations and experimental results manifest the superior laser suppression performance of the proposed method, which can help diminish the undesirable effects of laser irradiation on an imaging sensor.

In this Letter, we report on widely tunable pulse generation from a red-diode-clad-pumped mid-infrared (mid-IR) Er3+/Dy3+ codoped ZrF4 fiber laser, for the first time, to the best of our knowledge. Using a Fe2+:ZnSe crystal, continuously tunable Q-switched pulses across the range of 3.06–3.62 µm have been attained, which not only represents the widest range (in wavelength domain) from a pulsed rare-earth-doped fiber laser at any wavelength, but also almost entirely covers the strong absorption band of C-H bonds in the mid-IR, providing a potential way for gas detection and polymer processing. In addition, the commercial InAs quantum-well-based saturable absorbers (SAs) have been employed instead, and the obtained longest Q-switching wavelength of 3.39 µm is slightly shorter than 3.444 µm determined by its nominal direct bandgap of 0.36 eV.

Wavelength-tunable dissipative solitons and amplifier similaritons have been obtained by inserting all-fiber Mach–Zehnder interferometer (MZI) filters with different free spectral ranges (FSRs) in a Yb-doped mode-locked fiber laser. The MZI filter is fabricated by splicing one segment of seven-core fiber (SCF) between two segments of single-mode fibers. The bandwidth of the filter depends on the FSR of the modulated interference curve and consequently depends on the tapered fiber diameter. Inserting MZI filters with bandwidths in a fiber laser and applying a tensile strain on the tapered SCF, both wavelength-tunable dissipative solitons and amplifier similaritons have been obtained.

We investigate the mechanisms to realize the Raman laser switching in a silica rod microresonator with mode-interaction-assisted excitation. The laser switching can be triggered between two whispering gallery modes (WGMs) with either the same or distinct mode families, depending on the pumping conditions. The experimental observations are in excellent agreement with a theoretical analysis based on coupled-mode equations with intermodal interaction terms involved. Additionally, we also demonstrate switching of a single-mode Raman laser and a wideband spectral tuning range up to ∼32.67 nm by selective excitation of distinct mode sequences. The results contribute to the understanding of Raman lasing formation dynamics via interaction with transverse mode sequences and may extend the microcavity-based Raman microlasers to potential areas in switchable light sources, optical memories, and high sensitivity sensors.

A Q-switched Nd:YAG laser has been actively mode-locked at a subharmonic frequency for the first time, to the authors’ knowledge. The laser operation mode is provided by a combination of a traveling wave acousto-optic modulator and a spherical cavity mirror. The dynamics of laser generation is investigated. Pulses with a duration of 70 ps and a peak power of about 10 MW were obtained. Also presented are new results on obtaining high-power (∼60 kW) picosecond tunable radiation in the ∼620 nm region based on frequency conversion of a superluminescent parametric generator pumped by such a laser.

With the rapid development of laser technology, laser as the light source of night vision illuminating can realize long-distance and clear imaging, which has been widely used in laser active illuminating field. A high-power diode laser with a wavelength of 808 nm was designed as the laser active illuminating source, and the output power of no less than 100 W was obtained by spatial beam multiplexing, polarization multiplexing, and high efficiency fiber coupling techniques. In view of the beam homogenization of illuminating source, a novel beam homogenization system based on waveguide is proposed in this work. A square spot with a horizontal divergence angle of 40°, a vertical divergence angle of 10°, and an illuminating power ratio of 4:1 was obtained by a collimating lens. Comparing with the traditional circular illuminating beam, the square illuminating beam can match the illuminating angle of CCD camera better, and the energy utilization rate is higher. In addition, by optimizing the structure of waveguide and collimating lens, the illuminating angle can be changed to meet the illuminating requirements under different conditions theoretically.

We demonstrate an ultrastable miniaturized transportable laser system at 1550 nm by locking it to an optical fiber delay line (FDL). To achieve optimized long-term frequency stability, the FDL was placed into a vacuum chamber with a five-layer thermal shield, and a delicate two-stage active temperature stabilization, an optical power stabilization, and an RF power stabilization were applied in the system. A fractional frequency stability of better than 3.2×10-15 at 1 s averaging time and 1.1×10-14 at 1000 s averaging time was achieved, which is the best long-term frequency stability of an all-fiber-based ultrastable laser observed to date.

In an acousto-optic modulator, the electrode shape plays an important role in performance, since it affects the distribution of the acoustic field. The acousto-optic modulator based on the conventional rectangular electrode has the problems of low energy efficiency and small modulation bandwidth due to an imperfect acoustic field. In this paper, a new serrated periodic electrode has been proposed for using acousto-optic modulator transducers. The proposed electrode has the following advantages. By using serrated periodic electrodes to suppress the sidelobes, the collimation of the acoustic field in the direction perpendicular to the light incidence is improved. This makes the acousto-optic modulator have a stable diffraction efficiency fluctuation and high energy efficiency. In addition, the electrode has a large divergence angle in the direction of light incidence, so a large bandwidth can be obtained. The simulations and experiments demonstrate that the serrated periodic electrode has an increased bandwidth and high energy efficiency.

We have observed various polarization domains and a giant self-mode-locked pulse in a 130 m long erbium-doped fiber laser without any mode-locking devices. By adjusting the intracavity polarization controller, we investigated the evolution process of the polarization domain with the varying cavity birefringence. When the birefringence was close to zero, the polarization domains split into multidomains, and finally a giant self-mode-locked pulse formed for the first time. We analyzed that the generation of the self-mode-locked pulse was related to the multiple subdomains ascribed to the strong coherent cross coupling between the orthogonal polarization light components in the long fiber cavity.

A diode-pumped continuous-wave Tm:YVO4 laser operating on the H34→H35 and F43→H36 transitions was demonstrated for the first time, to the best of our knowledge. An a-cut Tm:YVO4 crystal with 1.5% (atomic fraction) Tm3+ ion concentration was used to characterize the laser behavior. A common commercial laser diode with a central wavelength of 790 nm and a bandwidth of 3.2 nm was utilized as a pump source. With an output coupler for the H34→H35 and F34→H36 transitions, simultaneous three-wavelength laser operation was achieved. The laser emissions at 2292 and 2363 nm in π-polarization and at 2108 nm in σ-polarization were realized. With an incident pump power of 22 W, the total output power of 1.17 W at 2292, 2363, and 2108 nm was obtained. The output power at 2292 and 2363 nm was measured to be 750 mW, and the output power at 2108 nm was measured to be 420 mW.

Based on the Rydberg cascade electromagnetically induced transparency, we propose a simultaneous dual-wavelength locking method for Rydberg atomic sensing at room temperature. The simplified frequency-locking configuration uses only one signal generator and one electro-optic modulator, realizing real-time feedback for both lasers. We studied the effect of the different probe and coupling laser powers on the error signal. In addition, the Allan variance and a 10 kHz amplitude-modulated signal are introduced to evaluate the performance of the laser frequency stabilization. In principle, the laser frequency stabilization method presented here can be extended to any cascade Rydberg atomic system.

An all-fiberized random distributed feedback Raman fiber laser (RRFL) with LP11 mode output at 1134 nm has been demonstrated experimentally, where an intracavity acoustically induced fiber grating is employed for modal switching. The maximum output power of LP11 mode is 93.8 W with the modal purity of 82%, calculated by numerical mode decomposition technology based on stochastic parallel-gradient descent algorithm. To our best knowledge, this is the highest output power with high purity of LP11 mode generated from the RRFL. This work may pave a path towards advanced fiber lasers with special temporal and spatial characteristics for applications.

In this paper, we report on a wide wavelength tuning optical vortex carrying orbital angular momentum (OAM) of ±ħ, from a thulium-doped yttrium aluminum perovskite (YAP) laser employing a birefringent filter. The OAM is experimentally found to be well maintained during the whole wavelength tuning process. The Laguerre–Gaussian (LG0,+1) mode with a tuning range of 58 nm from 1934.8 to 1993.0 nm and LG0,-1 mode with a range of 76 nm from 1920.4 to 1996.6 nm, are, respectively, obtained. This is, to the best of our knowledge, the first experimental implementation of wavelength tuning for a scalar vortex laser in the 2 µm spectral range, as well as the broadest tuning range ever reported from the vortex laser cavity. Such a vortex laser with robust structure and straightforward wavelength tuning capability will be an ideal light source for potential applications in the field of optical communication with one additional degree of freedom.

We fabricate a pair of fiber Bragg gratings (FBGs) by a visible femtosecond laser phase mask scanning technique on passive large-mode-area double-cladding fibers for multi-kilowatt fiber oscillators. The bandwidth of high-reflection (HR) and low-reflection (LR) FBG is ∼1.6 nm and 0.3 nm, respectively. The reflection of the HR-FBG is higher than 99%, and that of the LR-FBG is about 10%. A bidirectional pumped all-fiber oscillator is constructed using this pair of FBGs, a record output power of 5027 W located in the signal core is achieved with a slope efficiency of ∼82.1%, and the beam quality factor M2 is measured to be ∼1.6 at the maximum power. The FBGs are simply fixed on a water cooling plate without a special package, and the thermal efficiency of the HR-FBG and the LR-FBG is 2.76°C/kW and 1°C/kW, respectively. Our research provides an effective solution for robust high-power all-fiber laser oscillators.

We present a continuously tunable high-power continuous wave (CW) single-frequency (SF) Nd:YAlO3/lithium triborate (Nd:YAP/LBO) laser with dual-wavelength output, which is implemented by combining an optimized and locked etalon with an intracavity nonlinear loss. The obtained output powers of the stable SF 1080 and 540 nm lasers are 2.39 and 4.18 W, respectively. After the etalon is locked to an oscilating mode of the laser, the wideband continuous frequency tuning and long-term stable single-longitudinal-mode operation of the laser are successfully realized, which can be well used for the applications of quantum information and quantum computation. To the best of our knowledge, this is the first realization of the continuously tunable high-power CW SF 1080/540 nm dual-wavelength laser.

MXene V2CTx has great practicability because it is not easy to degrade under ambient conditions. In this paper, a V2CTx saturable absorber (SA) was firstly applied to a passively Q-switched (PQS) laser, to the best of our knowledge. The V2CTx-SA was prepared by the spin-coating method. The linear absorption of the V2CTx-SA in the 1000–2200 nm region and the nonlinear absorption near 2 µm were studied. With the V2CTx-SA, a typical PQS operation at 1.94 µm was realized in a Tm:YAlO3 laser. The minimum pulse width produced by the PQS laser was 528 ns, and the peak power, repetition rate, and average output power were 10.06 W, 65.9 kHz, and 350 mW, respectively. Meanwhile, the maximum pulse energy was 6.33 µJ. This work demonstrates that the V2CTx can be used as an effective SA to obtain nanosecond pulses with high peak power and high repetition rate simultaneously.

We report a wavelength-tunable multi-point pump scheme of the semiconductor disk lasers (SDLs). By designing an external cavity of SDL with an intra-cavity transmission grating, multiple pump gain regions share the same resonator. The effect of the intra-cavity grating on the output laser power, wavelength, and beam quality was investigated. The emission wavelength could be tuned over a bandwidth of ∼18 nm. With multi-point pumping, we achieve the laser output power with almost no loss, and further improvement is limited by the thermal effect. The changes in the beam are due to the mode selectivity by the intra-cavity grating.

In this work, we demonstrated the double-cladding Tm/Al co-doped photonic crystal fiber (PCF) by laser additive manufacturing. The measurements show that the fiber was heavily doped with a Tm3+ concentration of 2.13% (mass fraction) without any crystallization. The splicing property of PCF was studied, and the integrity of the PCF air holes was maintained during the splicing process. The PCF with combiner pigtail has a splice loss of 0.23 dB. The all-fiber Tm/Al co-doped PCF amplifier system achieves a slope efficiency of 13% at 1948 nm with an output laser power of nearly 1.59 W. An upconversion process was also observed under laser excitation with a 1064 nm pulse. This method provides a new idea to deal with Tm-doped PCF fabrication and promotes the promising application of 2 µm fiber lasers.

In this paper, the frequency difference of the eigen polarization modes of the Nd:YAG crystal laser at different polarization ratios is experimentally studied, and to the best of our knowledge, the correlation between the frequency difference of the eigenmodes and the output polarization degree is reported for the first time. Combined with the analysis of the polarization beam profile, it is proved that the polarized laser produced by the isotropic crystal is due to the frequency locking of the eigen polarization modes. The weak birefringence in the crystal causes the round-trip phase difference of the orthogonal polarization modes, which leads to the frequency difference between the polarization modes. By the adjustment of the cavity mirror, the anisotropic loss will interact with the round-trip phase difference. The eigen polarization modes can reach frequency degeneration, and then be coherently combined to produce linearly polarized laser output. This work provides a useful reference for understanding the physical mechanism of polarized lasers realized by isotropic crystals.

We reporte and demonstrate a solid-state laser to achieve controlled generation of order-switchable cylindrical vector beams (CVBs). In the cavity, a group of vortex wave plates (VWPs) with two quarter-wave plates between the VWPs was utilized to achieve mode conversion and order-switch of CVBs. By utilizing two VWPs of first and third orders, the second and fourth order CVBs were obtained, with mode purities of 96.8% and 94.8%, and sloping efficiencies of 4.45% and 3.06%, respectively. Furthermore, by applying three VWPs of first, second, and third orders, the mode-switchable Gaussian beam, second, fourth, and sixth order CVBs were generated.

We report on the design and fabrication of a dual-wavelength switchable quantum cascade laser (QCL) by optimizing the design of a homogeneous active region and combining superposed distributed feedback gratings. Coaxial, single-mode emissions at two different wavelengths were achieved only through adjusting the bias voltage. Room temperature continuous-wave operation with output powers of above 30 mW and 75 mW was realized for single-mode emission at 7.61 µm and 7.06 µm, respectively. The simplified fabrication process and easy wavelength control of our designed dual-wavelength QCL make it very attractive for developing miniature multi-species gas sensing systems.

Swept source optical coherence tomography (SS-OCT) is a new noninvasive technique for assessing tissue. Although it has advantages, such as being label-free, noninvasive, and with high resolution, it also has drawbacks: there has been no in-depth research into identifying the driving of swept source. Based on preliminary research, we demonstrate a novel driving modulation method of a fiber Fabry–Perot tunable filter ranging phase adjustable as a tool for making bandwidth compensation of a swept laser source. This novel method is analyzed in detail; a swept laser source with a sweep rate of 100.5 kHz over a range of 152.25 nm and at a center wavelength of 1335.45 nm is demonstrated.

A wideband wavelength-tunable 4×5 distributed feedback (DFB) semiconductor laser array based on the reconstruction-equivalent-chirp (REC) technique using a simple tuning scheme is demonstrated. It consists of 20 DFB lasers with 4×5 matrix interleaving distributions, two-level cascaded Y-branch optical combiners, and one active semiconductor optical amplifier (SOA), all in-series integrated on one chip. Unlike the traditional thermal-electric cooler (TEC)-based wavelength-tuning scheme, the tunable 4×5 REC-DFB laser array achieves a faster and broader continuous wavelength-tuning range using TaN thin-film heaters integrated on the AlN submount. By changing the injection current of the TaN resistor from 0 to 190 mA, the proposed tunable laser achieves a wavelength-tuning range of ∼2.5 nm per channel and a total tuning of over 50 nm. This study opens up new avenues for realizing cost-effective and wide-tuning-range semiconductor lasers.

Based on the Nd-doped single-mode fiber as the gain medium, an all-fiber 12th harmonic mode-locked (HML) laser operating at the 0.9 µm waveband was obtained for the first time, to the best of our knowledge. A mandrel with a diameter of 10 mm was employed to introduce bending losses to suppress mode competition at 1.06 µm, which resulted in a suppression ratio of up to 54 dB. The 1st–12th order HML pulses with the tunable repetition rate of 494.62 kHz–5.94 MHz were obtained in the mode-locked laser with a center wavelength of ∼904 nm. In addition, the laser has an extremely low threshold pump power of 88 mW. To the best of our knowledge, this is the first time that an HML pulse has been achieved in a 0.9 µm Nd-doped single-mode all-fiber mode-locked laser with the advantages of low cost, simple structure, and compactness, which could be an ideal light source for two-photon microscopy.

The idea of a slot waveguide amplifier based on erbium-doped tellurite glass is first theoretically discussed in this work. Choosing the horizontal slot for low propagation loss, the TM mode profile compressed in the insertion layer was simulated, and the gain characteristics of the slot waveguide amplifier were calculated. Combining the capacity to confine light locally and the merits of tellurite glass as an emission host, this optimized amplifier shows enhanced interactions between the electric field and erbium ions and achieves a net gain of 15.21 dB for the 0.01 mW input light at 1530 nm, implying great promise of a high-performance device.

In this Letter, we proposed and experimentally demonstrated a directly modulated tunable laser based on the multi-wavelength distributed feedback (DFB) laser array. The lasers are placed in series to avoid the usage of an optical combiner and additional power loss. A three-section design is utilized to reduce the interference from other lasers and improve the electro-optic response bandwidth. Besides, the reconstruction-equivalent-chirp technique is used to simplify the grating fabrication and precisely control the grating phase. We realized 12 channels with 100 GHz spacing with high side mode suppression ratios of above 50 dB. The output power of all the channels is above 14 mW. The 3 dB electro-optic bandwidth is above 20 GHz at a bias current of 100 mA for all four lasers. A 25 Gb/s data transmission over a standard single-mode fiber of up to 10 km is demonstrated for all 12 channels, and 50 Gb/s data per wavelength is obtained through the four-level pulse amplitude modulation. The proposed directly modulated tunable in-series DFB laser array shows the potential for a compact and low-cost light source for wavelength division multiplexing (WDM) systems, such as next-generation front-haul networks and passive optical networks.

We report the InAs/GaAs quantum dot laterally coupled distributed feedback (LC-DFB) lasers operating at room temperature in the wavelength range of 1.31 µm. First-order chromium Bragg gratings were fabricated alongside the ridge waveguide to obtain the maximum coupling coefficient with the optical field. Stable continuous-wave single-frequency operation has been achieved with output power above 5 mW/facet and side mode suppression ratio exceeding 52 dB. Moreover, a single chip integrating three LC-DFB lasers was tentatively explored. The three LC-DFB lasers on the chip can operate in single mode at room temperature, covering the wavelength span of 35.6 nm.

A 222 nm all-solid-state far-ultraviolet C (UVC) pulse laser system based on an optical parametric oscillator (OPO) and second-harmonic generation (SHG) using β-Ba2BO4 (BBO) crystals was demonstrated. Pumped by a Nd:Y3Al5O12 laser with a repetition rate of 100 Hz at 355 nm, the maximum signal laser pulse energy of 1.22 mJ at 444 nm wavelength was obtained from the BBO-OPO system, corresponding to a conversion efficiency of 27.9%. The maximum output pulse energy of 164.9 µJ at the 222 nm wavelength was successfully achieved, corresponding to an SHG conversion efficiency of 16.2%. Moreover, the tunable output wavelength of UVC light from 210 nm to 252.5 nm was achieved.

Beam quality improvements by a large margin for signal and idler beams of a high energy 100 Hz KTiOAsO4 (KTA) non-critical phase matching (NCPM) optical parametric oscillator (OPO) were demonstrated using an unstable resonator configuration instead of a plane-parallel one. Theoretically, influences of cavity lengths and transmission of an output coupler on the OPO conversion efficiency for both were numerically simulated. For OPO based on an unstable resonator with a Gaussian reflectivity mirror, the maximum pulse energies at the signal (1.53 µm) and idler (3.47 µm) were about 75 mJ and 26 mJ, respectively. The corresponding beam quality factors of the signal were Mx2 = 9.8 and My2 = 9.9, and Mx2 = 11.2 and My2 = 11.5 for the idler. As a comparison, 128 mJ of signal and 48 mJ of idler were obtained with the plane-parallel resonator, and the M2 factors of the signal were Mx2 = 39.8 and My2 = 38.4, and Mx2 = 32.1 and My2 = 31.4 for the idler. Compared with a plane-parallel cavity, over eight times and three times brightness improvements were realized for the signal and idler light, respectively.

By using a self-reference transfer oscillator method, two individual 1560 nm lasers with about 1.2 GHz frequency difference were phase locked to a 729 nm ultra-stable laser at two preset ratios. By measuring the beat frequency of the two 1560 nm lasers, fractional instabilities of 2×10-17 at 1 s and 2×10-20 at 10,000 s averaging time were obtained, and the relative offset compared with the theoretical value was 4.2×10-21±4.5×10-20. The frequency ratio of them was evaluated to a level of 1.3×10-20 in one day’s data acquisition. This work was a preparation for remote comparison of optical clocks through optical fiber links. The technique can also be used to synthesize ultra-stable lasers at other wavelengths.

The dispersive Fourier transform technique provides feasibility of exploring non-repetitive events and the buildup process in ultrafast lasers. In this paper, we report a new buildup process of dissipative solitons in a simplified mode-locked Yb-doped fiber laser, which includes more complex physics stages such as the Q-switching stage, raised and damped relaxation oscillation stages, noise-like stage, successive soliton explosions stage, and soliton breathing stage. Complete evolution dynamics of noise-like pulse and double pulse are also investigated with dispersive Fourier transform. For the noise-like pulse dynamics process, it will only experience the Q-switching and relaxation oscillation stages. In the case of dissipative soliton and noise-like pulse, the double pulse buildup behavior is manifested as the replication of individual pulses. A weak energy migration occurs between two pulses before reaching steady state. Meanwhile, real-time mutual conversion of the dissipative soliton and noise-like pulse has been experimentally observed, which appears to be instantaneous without extra physical processes. To the best of our knowledge, this is the first report on these physical phenomena observed together in a mode-locked fiber laser. The results further enrich the dynamics of mode-locked fiber lasers and provide potential conditions for obtaining intelligent mode-locked lasers with controllable output.

In this research, the highly efficient external cavity feedback technology based on volume Bragg grating (VBG) is studied. By using the structure of a fast axis collimating lens, the beam transformation system, a slow axis collimating lens, and VBG, the divergence angle of the fast and slow axes of the diode laser incident on the VBG is reduced effectively, and the feedback efficiency of the external cavity is improved. Combined with beam combining technology, fiber coupling technology, and precision temperature control technology, a high-power and narrow-linewidth diode laser pump source of kilowatt class is realized for alkali metal vapor laser pumping. The core diameter of the optical fiber is 1000 µm, the numerical aperture is 0.22, the output power from the fiber is 1013 W, the fiber coupling efficiency exceeds 89%, and the external cavity efficiency exceeds 91%. The central wavelength is 852.052 nm (in air), which is tunable from 851.956 nm to 852.152 nm, and the spectral linewidth is 0.167 nm. Research results can be used for cesium alkali metal vapor laser pumping.

A high peak power density and low mechanical stress photonic-band-crystal (PBC) diode laser array based on non-soldered packaging technology is demonstrated. The array consists of the PBC diode laser bars with small fast axis divergence angles. Meanwhile, we design the non-soldered array structure that realizes mechanical stacking of 10 bars in the vertical direction. In the experiment, the peak power density of the PBC array is about 1.75 times that of the conventional array when the same total power is obtained. The peak power of the non-soldered array is 292.2 W, and the “smile” effect is improved by adjusting the mechanical fixing force of the array.

An actively mode-locked fiber laser with controllable pulse repetition rate and tunable pulse duration is presented, in which an optical delay line (ODL) is used to adjust the cavity length precisely for regulating the repetition rate, and a semiconductor optical amplifier (SOA) is introduced for enabling the pulse duration control. Experimentally, continuous tuning of the repetition rate from 2 GHz to 6 GHz is realized, which is limited by the availability of an even higher repetition rate radio-frequency (RF) source. Specifically, when the repetition rate is fixed at 2.5 GHz, the pulse duration can be tuned from 4 ps to 30 ps, which is, to the best of our knowledge, the widest tuning range of pulse duration ever achieved in a gigahertz (GHz) repetition rate actively mode-locked 1.5 µm fiber laser oscillator.

Continuous operation of fiber gas Raman lasing at the 1135 nm wavelength is experimentally demonstrated with an output power exceeding 26 W. Rotational stimulated Raman scattering (Rot-SRS) is generated in the hydrogen gas filled 50 m homemade anti-resonant hollow-core fiber (AR-HCF). A single-frequency fiber laser at the 1064 nm wavelength is used as the pump source, and a minimum threshold of 31.5 W is measured where the core diameter of AR-HCF reaches 37 µm. Up to 40.4% power conversion efficiency of forward Rot-SRS is achieved in the single-pass configuration, corresponding to a quantum efficiency of 43.1%. Over 1 W strong backward Rot-SRS is observed in the experiment, ultimately limiting the further increase of Rot-SRS generation in the forward direction.

We studied the spectral beam combining (SBC) of a large optical cavity (LOC) laser array to achieve high-power and high-brightness laser output. We discussed the characteristics of the external cavity feedback efficiency and the focal length of the transform lens for lasers with different waveguide thicknesses. We have found that using LOC laser diodes can increase the proportion of external cavity feedback, thereby improving the SBC efficiency. At a current of 90 A, the CW output power of the SBC system is 59.2 W, and the SBC efficiency reaches up to 102.8%. All emitters of the laser array have achieved spectral locking with a spectral width of 11.67 nm, and the beam parameter product is 4.38 mm·mrad.

We report a 1.65 µm square-Fabry–Pérot (FP) coupled cavity semiconductor laser for methane gas detection. The laser output optical power can reach 7.4 mW with the side mode suppression ratio about 40 dB. The wavelength tuning range is 2 nm by adjusting the FP cavity injection current, covering the methane absorption line at 1653.72 nm. The lasing wavelength can also be tuned by adjusting the square microcavity injection current or temperature, respectively. Methane gas detection is successfully demonstrated utilizing this laser.

We fabricate a high-performance Bi/Er/La co-doped silica fiber with a fluorescence intensity of -33.8 dBm and a gain coefficient of 1.9 dB/m. With the utilization of the fiber as a gain medium, a linear-cavity fiber laser has been constructed, which exhibits a signal-to-noise ratio of 74.9 dB at 1596 nm. It has been demonstrated that the fiber laser has a maximum output power of 107.4 mW, a slope efficiency of up to 17.0%, and a linewidth of less than 0.02 nm. Moreover, an all-fiber single-stage optical amplifier is built up for laser amplification, by which the amplified laser power is up to 410.0 mW with pump efficiency of 33.8%. The results indicate that the laser is capable of high signal-to-noise ratio and narrow linewidth, with potential applications for optical fiber sensing, biomedicine, precision measurement, and the pump source of the mid-infrared fiber lasers.

The spectral linewidth of a transversely excited pulsed CO2 laser is broadened at high working pressures. This phenomenon causes a decrease in the upper-level lifetime such that the pulse width is significantly compressed. Although the tail part of CO2 laser pulses owns a non-negligible proportion of total energy, it has minor effects during the interaction process between photons and materials due to its low amplitude. Thus, it is of great significance to yield the tail part and generate a narrow pulse in most applications. In this study, a continuously tunable pulsed CO2 laser with a low nitrogen proportion in the mixture is developed to generate tail-free short pulses; a minimum pulse width of 30.60 ns with a maximum pulse energy of 481 mJ is synchronously achieved at a pressure of 7 atm, and the estimated peak power is above 15 MW. A numerical simulation is also conducted for comparison with the experimental results. The contribution of the spectral gain toward the compression of the pulse width is discussed in the last section of this paper.

Multi-beam laser processing is a very popular method to improve processing efficiency. For this purpose, a compact and stable multi-beam pulsed 355 nm ultraviolet (UV) laser based on a micro-lens array (MLA) is presented in this Letter. It is worth noting that the MLA is employed to act as the spatial splitter as well as the coupling lens. With assistance of the MLA, the 1064 nm laser and 532 nm laser are divided into four sub-beams and focused at different areas of the third-harmonic generation (THG) crystal. As a result, the multi-beam pulsed 355 nm UV laser is successfully generated inside the THG crystal. The measured pulse widths of four sub-beams are shorter than 9 ns. Especially, the generated four sub-beams have good long-term power stability benefitting from the employed MLA. We believe that the generated stable multi-beam 355 nm UV laser can meet the requirement of high-efficiency laser processing, and the presented method can also pave the way to generate stable and long-lived multi-beam UV lasers.

Copper welding with an infrared (IR) Gaussian laser beam usually shows obvious instability, spatters, and worse surface morphology due to the Gaussian distribution, temperature-dependent IR absorption, and high thermal conductivity in copper. In this paper, the IR quasi-continuous-wave Gaussian beam was converted into a vortex ring beam with a phase-plate and then applied to the micro-spot-welding of copper sheets. The welding with the vortex beam demonstrated a significantly improved welding performance, smoother surface morphology, and higher welding stability. Besides, no spatters appeared in the welding process.

We demonstrate a novel approach to achieve wavelength-tunable ultrashort pulses from an all-fiber mode-locked laser with a saturable absorber based on the nonlinear Kerr beam clean-up effect. This saturable absorber was formed by a single-mode fiber spliced to a graded-index multimode fiber, and its tunable band-pass filter effect is described by a numerical model. By adjusting the bending condition of the graded-index multimode fiber, the laser could produce dissipative soliton pulses with their central wavelength tunable from 1040 nm to 1063 nm. The pulse duration of the output laser could be compressed externally to 791 fs, and the signal to noise ratio of its radio frequency spectrum was measured to be 75.5 dB.

A single-frequency 1645 nm pulsed laser with frequency stability close to 100 kHz was demonstrated. The laser oscillator is injection-seeded by a single-frequency narrow linewidth Er:Y3Al5O12 (Er:YAG) nonplanar ring oscillator and frequency stabilized by the modified Pound–Drever–Hall method. The pulse repetition rate can be set from 100 to 500 Hz with the frequency stability from 82.72 kHz to 134.44 kHz and pulse energy from 9.84 mJ to 19.55 mJ. To our knowledge, this is the best frequency stability of a single-frequency pulsed laser with injection-seeding.

Monolithic integration of III-V lasers with small footprint, good coherence, and low power consumption based on a CMOS-compatible Si substrate have been known as an efficient route towards high-density optical interconnects in the photonic integrated circuits. However, the material dissimilarities between Si and III-V materials limit the performance of monolithic microlasers. Here, under the pumping condition of a continuous-wave 632.8 nm He–Ne gas laser at room temperature, we achieved an InAs/GaAs quantum dot photonic crystal bandedge laser, which is directly grown on an on-axis Si (001) substrate, which provides a feasible route towards a low-cost and large-scale integration method for light sources on the Si platform.

Direct current pulsed discharge is a promising route for producing high-density metastable particles required for optically pumped rare gas lasers (OPRGLs). Such metastable densities are easily realized in small discharge volumes at near atmospheric pressures, but problems appear when one is trying to achieve a large volume of plasma for high-power output. In this work, we examined the volume scalability of high-density metastable argon atoms by segmented discharge configuration. Two discharge zones attached with peaking capacitors were connected parallelly by thin wires, through which the peaking capacitors were charged and of which the inductance functioned as ballasting impendence to prevent discharging in only one zone. A uniform and dense plasma with the peak value of the number densities of Ar (1s5) on the order of 1013cm-3 was readily achieved. The results demonstrated the feasibility of using segmented discharge for OPRGL development.

A multi-lens retroreflector with field curvature compensation was designed and used in an alignment-free distributed-cavity laser with a long working distance for resonant beam charging applications. The multi-lens design, which makes use of off-the-shelf components, also allows a large field of view (FoV) without requirement of large element aperture. By implementing this design, an end-pumped 1063 nm Nd:GdVO4 laser could deliver over 5 W continuous-wave output power over a large range of working distances (1–5 m) and with ±30° receiver FoV under an incident diode pump power of 16.6 W. The output power fluctuation was less than 10% when moving and tilting the receiver over such a large range, without requiring any realignment of the cavity.

We report on a conceptually new type of waveguide in glass by femtosecond laser direct writing, namely, photonic lattice-like waveguide (PLLW). The PLLW’s core consists of well-distributed and densified tracks with a sub-micron size of 0.62 µm in width. Specifically, a PLLW inscribed as hexagonal-shape input with a ring-shape output side was implemented to converse Gaussian mode to doughnut-like mode, and high conversion efficiency was obtained with a low insertion loss of 1.65 dB at 976 nm. This work provides a new freedom for design and fabrication of the refractive index profile of waveguides with sub-micron resolution and broadens the functionalities and application scenarios of femtosecond laser direct-writing waveguides in future 3D integrated photonic systems.

Cylindrical vector beams (CVBs), with non-uniform state of polarizations, have become an indispensable tool in many areas of science and technology. However, little research has explored high power CVBs at the femtosecond regime. In this paper, we report on the generation of high quality CVBs with high peak power and femtosecond pulse duration in a fiber chirped-pulse amplification laser system. The radially (azimuthally) polarized vector beam has been obtained with a pulse duration of 440 fs (430 fs) and a maximum average output power of 20.36 W (20.12 W). The maximum output pulse energy is ∼20 μJ at a repetition rate of 1 MHz, corresponding to a high peak power of ∼46 MW. The comparison between simulated intensity profiles and measured experimental results suggests that the generated CVBs have a remarkable intensity distribution. The proposed configuration of our laser system provides a promising solution for high quality CVBs generation with the characteristics of high peak power, ultrashort pulse duration, and high mode purity.

Conventional ultrashort pulsewidth measurement technology is autocorrelation based on second-harmonic generation; however, nonlinear crystals and bulky components are required, which usually leads to the limited wavelength range and the difficult adjustment with free-space light alignment. Here, we proposed a compact all-fiber pulsewidth measurement technology based on the interference jitter (IJ) and field-programmable gate array (FPGA) platform, without requiring a nonlinear optical device (e.g., nonlinear crystal/detector). Such a technology shows a wide measurement waveband from 1 to 2.15 µm at least, a pulsewidth range from femtoseconds to 100 ps, and a small relative error of 0.15%–3.8%. In particular, a minimum pulse energy of 219 fJ is experimentally detected with an average-power-peak-power product of 1.065×10-6 W2. The IJ-FPGA technology may offer a new route for miniaturized, user-friendly, and broadband pulsewidth measurement.

We demonstrate an all-solid-state continuous-wave (CW) single-frequency tunable 1.08 µm laser, which is realized by employing a disordered laser medium Nd:CaYAlO4 (Nd:CYA) crystal. The maximal output power of single-frequency 1.08 µm laser is 1 W. By rotating the incident angle of the intracavity etalon (IE), the maximal tuning range of 183.71 GHz is achieved. After the IE is locked to the oscillating longitudinal mode of the laser, the continuous tuning range of 60.72 GHz for 1.08 µm laser is achieved by scanning the cavity length. To the best of our knowledge, this is the first demonstration of a CW single-frequency widely tunable 1.08 µm laser based on Nd:CYA crystal.

The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers (VCSELs) to enhance the laser power. In this work, we propose GaN-based VCSELs with the p-AlGaN/p-GaN structure as the p-type hole supplier to facilitate the hole injection. The p-AlGaN/p-GaN heterojunction is able to store the electric field and thus can moderately adjust the drift velocity and the kinetic energy for holes, which can improve the thermionic emission process for holes to travel across the p-type electron blocking layer (p-EBL). Besides, the valence band barrier height in the p-EBL can be reduced as a result of usage of the p-AlGaN layer. Therefore, the better stimulated radiative recombination rate and the increased laser power are obtained, thus enhancing the 3 dB frequency bandwidth. Moreover, we also investigate the impact of the p-AlGaN/p-GaN structure with various AlN compositions in the p-AlGaN layer on the hole injection capability, the laser power, and the 3 dB frequency bandwidth.

A good thermo-optic property of strontium dodeca-aluminum oxide (SrAl12O12, SRA) host material is very advantageous to the development of high-performance lasers by doping rare-earth ions for gain medium. In this work, we report on diode-end-pumped high-performance continuous-wave and passively Q-switched Nd:SRA lasers. For continuous-wave operation, a maximum output power of 6.45 W is achieved at 1049 nm with a slope efficiency of about 41.6%. Using a Y3Al5O12 (YAG) etalon, we have firstly achieved a 1066 nm laser with a maximum output power of 4.15 W and a slope efficiency of about 27%, to the best of our knowledge. For passively Q-switched operation, with Cr4+:YAG as a saturable absorber, a maximum average output power of 1.82 W was achieved with the shortest pulse width of 18.2 ns at pulse repetition rate of 22.9 kHz. The single-pulse energy and pulse peak power were 79.4 μJ and 4.3 kW. This work has further verified that the Nd:SRA crystal is very promising for high-performance laser generation.

In this paper, the high-repetition-rate passively Q-switched (PQS) and the femtosecond continuous-wave mode-locked (CWML) lasers are successfully obtained with 2D black arsenic-phosphorus (b-AsP) nanosheets as saturable absorber (SA) at 1 μm for the first time, to the best of our knowledge. The saturable absorption properties and ultrafast carrier dynamics of the 2D b-AsP SA are explored by Z-scan and pump-probe techniques. Moreover, according to the measurement of desired nonlinear optical characteristics of the relaxation time of 27 ps and the modulation depth of 7.14%, the PQS and CWML lasers are demonstrated with the highest repetition rate of 2.26 MHz in the PQS laser and the pulse width of 470 fs in the CWML laser. The results show 2D b-AsP SA has enormous potential for pulse modulation in solid-state bulk lasers.

A hertz-linewidth ultra-stable laser (USL), which will be used to detect the clock transition line, in a strontium optical clock will be launched into the China Space Station (CSS) in late 2022. As the core of the USL, an interference-filter-based external-cavity diode laser (IF-ECDL) was developed. The IF-ECDL has a compact, stable, and environmentally insensitive design. Performances of the IF-ECDL are presented. The developed IF-ECDL can pass the aerospace environmental tests, indicating that the IF-ECDL can be suitable for space missions in the CSS.

We demonstrate an all-fiber-based photonic microwave generation with 10-15 frequency instability. The system consists of an ultra-stable laser by optical fiber delay line, an all-fiber-based “figure-of-nine” optical frequency comb, a high signal-to-noise ratio photonic detection unit, and a microwave frequency synthesizer. The whole optical links are made from optical fiber and optical fiber components, which renders the whole system compactness, reliability, and robustness with respect to environmental influences. Frequency instabilities of 3.5×10-15 at 100 s for 6.834 GHz signal and 4.3×10-15 at 100 s for 9.192 GHz signal were achieved.

We proposed an aperiodic laser beam distribution, in which the laser beams are placed along a Fermat spiral, to suppress the sidelobe power in the coherent beam combining. Owing to the changed distances between two consecutive beams, the conditions of the sidelobe suppression are naturally satisfied. The Fermat spiral array was demonstrated to achieve a better sidelobe suppression than the periodic arrays, and the effects of various factors on the sidelobe suppression were analyzed numerically. Experiments were carried out to verify the sidelobe suppression by different Fermat spiral arrays, and the results matched well with the simulations.

We report on a high-power diode-pumped Yb:KG(WO4)2 (Yb:KGW) mode-locked laser with a semiconductor saturable absorber mirror (SESAM). For 32.7 W of incident pump power, we generate 261 fs pulses with the maximum average output power of up to 13.0 W and spectrum centered around 1039 nm at 68.4 MHz, corresponding to 190 nJ of single pulse energy and 0.72 MW of peak power. The optical-to-optical conversion efficiency is 39.8%, and the slope efficiency is 64.4%. The Yb:KGW laser exhibits a power stability better than 0.543% of the root-mean-square in 2 h.

A single-resonant low-threshold type-I β-Ba2BO4 (BBO) optical parametric oscillator (OPO) with tunable output from 410 nm to 630 nm at 5 kHz repetition rate is reported. By taking the noncollinear phase matching method, low-threshold OPO operation could be obtained compared with the configuration of collinear phase matching, and the maximum optical–optical conversion efficiency of 11.8% was achieved at 500 nm wavelength when 0.4 mJ pump pulse energy was applied. When the noncollinearity angle was preset at 1.6°, 4.8°, and 6.3°, a continuously tuning output with a total spectral range of 220 nm was successfully obtained by adjusting the phase matching angle of the BBO crystal.

A hundred-watt-level spatial mode switchable all-fiber laser is demonstrated based on a master oscillator power amplifier scheme. The performance of the amplifier with two seed lasers, i.e., with the acoustically induced fiber grating (AIFG) mode converter inside and outside the seed laser cavity, is investigated. Real-time mode switching with millisecond scale switching time between the LP01 and LP11 modes while operating in full power (>100 W) is realized through an AIFG driven by radio frequency modulation. This work could provide a good reference for realizing high-power agile mode switchable fiber lasers for practical applications.

Side pumping combiners are widely used in fiber laser schemes for their high coupling efficiency, low insertion loss, and multi-point pumping capability. However, side pumping combiners perform differently in coupling efficiency when pumping with a laser diode (LD) and a high-brightness 1018 nm Yb-doped fiber laser (YDFL). In this paper, for the first time, to the best of our knowledge, we investigated the different parameters to fabricate the (2+1)×1 combiner with high coupling efficiency when pumping with an LD and a YDFL, respectively. After optimization, the maximum coupled pump power from one single-pump port of the combiner was 1200 W and 2730 W when pumping with a LD and a YDFL, respectively.

A continuous-wave (CW) π-polarized 1084 nm laser based on Nd:MgO:LiNbO3 under 888 nm thermally boosted pumping is reported. According to the absorption spectrum and energy level structure of Nd:MgO:LiNbO3, the 888 nm laser diode (LD) is used for thermally boosted pumping. This pumping method eliminates the quantum defect caused by the nonradiative transition in Nd:MgO:LiNbO3 under the traditional 813 nm pumping and effectively improves the serious thermal effect of the crystal. The unmatched polarized 1093 nm laser is completely suppressed, and the π-polarized laser output of 1084 nm in the whole pump range is realized by the 888 nm thermally boosted pumping. In the present work, we achieved the CW π-polarized 1084 nm laser with a maximum output power of 7.53 W and a slope efficiency of about 46.1%.

A highly efficient milli-joule-level Q-switched Tm,La:CaF2 laser is experimentally demonstrated. By employing an acousto-optic modulator, the diode-pumped pulsed lasers are stably operated at repetition rates ranging from 500 Hz to 10 kHz. Dual-wavelength operation of 1881.7 nm and 1888.5 nm is achieved with slope efficiency of 64.7%. Up to 1.89 mJ of pulse energy is obtained at a pulse width of 100 ns, corresponding to a peak power of 18.88 kW. These results verified that the Tm,La:CaF2 crystal could be a promising candidate for achieving highly efficient and high-energy pulsed lasers.

We demonstrate a simple method to obtain accurate optical waveforms with a gigahertz-level programmable modulation bandwidth and a watt-level output power for wideband optical control of free atoms and molecules. Arbitrary amplitude and phase modulations are transferred from microwave to light with a low-power fiber electro-optical modulator. The sub-milliwatt optical sideband is co-amplified with the optical carrier in a power-balanced fashion through a tapered semiconductor amplifier (TSA). By automatically keeping TSA near saturation in a quasi-continuous manner, typical noise channels associated with pulsed high-gain amplifications are efficiently suppressed. As an example application, we demonstrate interleaved cooling and trapping of two rubidium isotopes with coherent nanosecond pulses.

The generation of supercontinuum (SC) often requires ultrashort pulsed lasers with high peak power and gain media with large nonlinear coefficients, such as a long piece of fiber or photonic crystal fiber. In this Letter, we propose and demonstrate that high-power SC can be generated through a simple narrow-bandwidth fiber Bragg gratings (FBGs)-based laser cavity without any modulation, based on the mechanism of intense nonlinear effects induced by the inherent self-pulsation generated inside the cavity. In the experiment, an ∼80 W SC laser with the spectrum range from 600 nm to 1600 nm was achieved. To the best of our knowledge, this is the first report about SC generation through a simple fiber laser cavity. This work enriches the research content of SC and provides a cost-effective method for high-power SC lasers.

We report on a mid-infrared fiber laser that uses a single-walled carbon nanotube saturable absorber mirror to realize the mode-locking operation. The laser generates 3.5 µm ultra-short pulses from an erbium-doped fluoride fiber by utilizing a dual-wavelength pumping scheme. Stable mode-locking is achieved at the 3.5 µm band with a repetition rate of 25.2 MHz. The maximum average power acquired from the laser in the mode-locking regime is 25 mW. The experimental results indicate that the carbon nanotube is an effective saturable absorber for mode-locking in the mid-infrared spectral region.

In this paper, a high-power and high-efficiency 4.3 µm mid-infrared (MIR) optical parametric oscillator (OPO) based on ZnGeP2 (ZGP) crystal is demonstrated. An acousto-optically Q-switched Ho:Y3Al5O12 laser operating at 2.1 µm with a maximum average output power of 35 W and pulse width of 38 ns at a repetition rate of 15 kHz is established and employed as the pump source. A doubly resonant OPO is designed and realized with the total MIR output power of 13.27 W, including the signal and idler output power of 2.65 W at 4.07 µm and 10.62 W at 4.3 µm. The corresponding total optical-to-optical and slope efficiencies are 37.9% and 67.1%, respectively. The shortest pulse width, beam quality factor, and output power instability are measured to be 36 ns, Mx2=1.8, My2=2.0, and RMS1.9% at 8 h, respectively. Our results pave a way for designing high-power and high-efficiency 4–5 µm MIR laser sources.

A tunable multi-wavelength erbium-doped fiber laser with precise wavelength interval control is reported theoretically and experimentally in this paper. It is made up of a Mach–Zehnder interferometer (MZI) filter and a Sagnac filter and supplemented by the four-wave-mixing effect. Compared with other filters, the proposed MZI filter based on the fused taper technology can change the wavelength interval more flexibly. The experiment result shows that wavelength tuning can be achieved, and the tuning range can reach ∼15 nm. Moreover, the variation in the number of wavelengths is also realized. The maximum side-mode suppression ratio can reach 39 dB.

As a universal phenomenon in nonlinear optical systems, intermittency is usually accompanied by the coherence loss such as soliton explosions in fiber lasers. Based on real-time spectroscopy, we revealed the coherent dissipative soliton intermittency in normal-dispersion fiber lasers. By increasing the pump strength, the intermittency transforms from the transient pulsation to the bi-stable soliton. It is demonstrated that the slow-gain effect dominates such coherent intermittency. Our results provide novel insights into laser physics, offering a promising approach for studying the bi-stable dissipative soliton.

Mid-infrared (MIR) laser sources operating in the 2.7–3 µm spectral region have attracted extensive attention for many applications due to the unique features of locating at the atmospheric transparency window, corresponding to the “characteristic fingerprint” spectra of several gas molecules, and strong absorption of water. Over the past two decades, significant developments have been achieved in 2.7–3 µm MIR lasers benefiting from the sustainable innovations in laser technology and the great progress in material science. Here, we mainly summarize and review the recent progress of MIR bulk laser sources based on the rare-earth ions-doped crystals in the 2.7–3 µm spectral region, including Er3+-, Ho3+-, and Dy3+-doped crystalline lasers. The outlooks and challenges for future development of rare-earth-doped MIR bulk lasers are also discussed.

We report on diode-pumped continuous-wave Pr-doped yttrium lithium fluoride (Pr:YLF) laser and its frequency doubling to 320 nm. The maximum output power of the 640 nm fundamental wave reached 3.44 W with a slope efficiency of about 48.3%. Using a type-I phase-matched lithium triborate (LBO) crystal as a frequency doubler, we have achieved 320 nm ultraviolet radiation with a maximum output power of 1.01 W, which is the highest power ever reported under diode pumping, to the best of our knowledge.

The population trapping effect of the F34 level is an important factor limiting the power scaling of the 2.3 μm thulium (Tm) laser on the H34→H35 transition. In this Letter, we demonstrate a novel scheme of ground state absorption (GSA) (H36→H34) and excited state absorption (ESA) (F34→H34) dual-wavelength pumped 2.3 μm Tm lasers. Introducing an ESA pumping process can accurately excite the Tm3+ ions accumulated in the F34 level to the H34 level, constructing a double populating mechanism for the upper laser level H34. A proof-of-principle experimental demonstration of the GSA (785 nm) and ESA (1470 nm) dual-wavelength pumped 2.3 μm Tm:LiYF4 (Tm:YLF) laser was realized. A maximum continuous-wave output power of 1.84 W at 2308 nm was achieved under 785 and 1470 nm dual-wavelength pumping, increased by 60% compared with the case of 785 nm single-wavelength pumping under the same resonator condition. Our work provides an efficient way to achieve higher output power from 2.3 μm Tm-doped lasers on the H34→H35 transition.

We propose an effective way to achieve an enhanced optical absorption surface of titanium alloy 7 (Ti7) fabricated by a femtosecond (fs) laser assisted with airflow pressure. The effect of laser scanning speed and laser power on the surfaces’ morphology and average reflectivity was studied. In order to further reduce the surface’s reflectivity, different airflow pressure was introduced during the fabrication of Ti7 by a fs laser. Furthermore, the average reflectivity of samples fabricated under different laser parameters assisted with airflow was presented. In addition, the high and low temperature tests of all samples were performed to test the stability performance of the hybrid micro/nanostructures in extreme environments. It is demonstrated that the airflow pressure has an important influence on the micro/nanostructures for light trapping, the average reflectivity of which could be as low as 2.31% over a broad band of 250–2300 nm before high and low temperature tests, and the reflection for specific wavelengths can go below 1.5%.

In this paper, we report a passively mode-locked Nd:Y3Sc2Al3O12 (Nd:YSAG) laser using a periodically poled LiNbO3 (PPLN) superlattice. Nonlinear mirror mode locking based on PPLN intracavity frequency doubling was theoretically analyzed. The modulation depth of nonlinear reflectivity of the nonlinear mirror is approximately 8.8%. Optical performances of the mode-locked laser including output power, radio frequency spectrum, and optical spectrum were experimentally investigated. An average output power of 710 mW with a slope efficiency of 14.6% was obtained at the pump power of 6.5 W. The repetition rate is 101.7 MHz, and the signal-to-noise ratio of the mode-locked pulse is 45 dB. The mode-locked pulse width was approximately 9 ps.

A stable noise-like (NL) mode-locked Tm-doped fiber laser (TDFL) relying on a nonlinear optical loop mirror (NOLM) was experimentally presented. Different from the previous NL mode-locked TDFL with NOLM, the entire polarization-maintaining (PM) fiber construction was utilized in our laser cavity, which makes the oscillator have a better resistance to environmental perturbations. The robust TDFL can deliver stable bound-state NL pulses with a pulse envelope tunable from ～14.1 ns to ～23.6 ns and maximum pulse energy of ～40.3 nJ at a repetition rate of ～980.6 kHz. Meanwhile, the all-PM fiber laser shows good power stability (less than ～0.7%) and repeatability.

We report a high power fiber amplifier based on nonlinear chirped-pulse amplification (NCPA). To manage the nonlinearity, pulse shaping is introduced by self-phase modulation in the fiber stretcher with the help of spectral filtering. The third-order dispersion is compensated for by the nonlinear phase shift in the NCPA. With optimization, the system can output 382 fs pulse duration with 20 W average power at 1 MHz repetition rate. The long-term average power fluctuation is measured to be 0.5% in 24 h, and the beam quality factor (M2) is 1.25.

A 125 MHz fiber-based frequency comb source in the mid-infrared wavelength region is presented. The source is based on difference frequency generation from a polarization-maintaining Er-doped fiber pump laser and covers a spectrum between 2900 cm-1 and 3400 cm-1 with a simultaneous bandwidth of 170 cm-1 and an average output power up to 70 mW. The source is equipped with actuators and active feedback loops, ensuring long-term stability of the repetition rate, output power, and spectral envelope. An absorption spectrum of ethane and methane was measured using a Fourier transform spectrometer to verify the applicability of the mid-infrared comb to multispecies detection. The robustness and good long- and short-term stability of the source make it suitable for optical frequency comb spectroscopy of hydrocarbons.

As one of the greatest inventions in the 20th century, ultrafast lasers have offered new opportunities in the areas of basic scientific research and industrial manufacturing. Optical modulators are of great importance in ultrafast lasers, which directly affect the output laser performances. Over the past decades, significant efforts have been made in the development of compact, controllable, repeatable, as well as integratable optical modulators (i.e., saturable absorbers). In this paper, we review the fundamentals of the most widely studied saturable absorbers, including semiconductor saturable absorber mirrors and low-dimensional nanomaterials. Then, different fabrication technologies for saturable absorbers and their ultrafast laser applications in a wide wavelength range are illustrated. Furthermore, challenges and perspectives for the future development of saturable absorbers are discussed and presented. The development of ultrafast lasers together with the continuous exploration of reliable saturable absorbers will open up new directions for the mass production of the next-generation optoelectronic devices.

In this paper, the absorption and fluorescence spectra of Er3+, Pr3+ co-doped LiYF4 (Er,Pr:YLF) crystal were measured and analyzed. The Pr3+ co-doping was proved to effectively enhance the Er3+:I411/2→I413/2 mid-infrared transition at the 2.7 μm with 74.1% energy transfer efficiency from Er3+:I413/2 to Pr3+:F34. By using the Judd–Ofelt theory, the stimulated emission cross section was calculated to be 1.834×10-20 cm2 at 2685 nm and 1.359×10-20 cm2 at 2804.6 nm. Moreover, a diode-end-pumped Er,Pr:YLF laser operating at 2659 nm was realized for the first time, to the best of our knowledge. The maximum output power was determined to be 258 mW with a slope efficiency of 7.4%, and the corresponding beam quality factors Mx2=1.29 and My2=1.25. Our results suggest that Er,Pr:YLF should be a promising material for 2.7 μm laser generation.

The influence of nodule defects on the characteristics of femtosecond laser-induced damage has not been fully investigated. In this study, two types of 800 nm/1064 nm dual-band HfO2/SiO2 high-reflection films with different configurations were analyzed. Combined with finite-difference time-domain electric field simulation and focused ion beam analysis, the initial state and growth process of femtosecond laser damage of nodules were explored. In particular, the sequence of blister damage determined by the film design and the inner damage caused by nodules were clarified. The rule of the laser-induced damage threshold of different size nodules was obtained. The difference in the damage behavior of nodules in the two types of films was elucidated.

The spatial distribution of the forward-propagating amplified spontaneous emission (ASE) of nitrogen molecular ions during femtosecond laser filamentation in air is studied via numerical simulations. The results suggest that the divergence angle and signal intensity are extremely sensitive to the external focal length. Concurrently, we show that the optical Kerr effect plays a significant role in concentrating the directivity of ASE signals, particularly in cases of loose focusing. Furthermore, the simulations demonstrate that ASE signals are enhanced for a tight focus, although the corresponding filament length is shorter. The main physical mechanism underlying this process is the competition between the plasma defocusing and optical Kerr effects. The result is important for filamentation-based light detection and ranging applied to remote sensing.

We propose a design of single-mode orbital angular momentum (OAM) beam laser with high direct-modulation bandwidth. It is a microcylinder/microring cavity interacted with two types of second-order gratings: the complex top grating containing the real part and the imaginary part modulations and the side grating. The side grating etched on the periphery of the microcylinder/microring cavity can select a whispering gallery mode with a specific azimuthal mode number, while the complex top grating can scatter the lasing mode with travelling-wave pattern vertically. With the cooperation of the gratings, the laser works with a single mode and emits radially polarized OAM beams. With an asymmetrical pad metal on the top of the cavity, the OAM on-chip laser can firstly be directly modulated with electrical pumping. Due to the small active volume, the laser with low threshold current is predicted to have a high direct modulation bandwidth about 29 GHz with the bias current of ten times the threshold from the simulation. The semiconductor OAM laser can be rather easily realized at different wavelengths such as the O band, C band, and L band.

We propose and demonstrate the cascaded multi-wavelength mode-locked erbium-doped fiber laser (EDFL) based on ultra-long-period gratings (ULPGs) for the first time, to the best of our knowledge. Study found that the ULPG can be used as both a mode-locker for pulse shaping and a comb filter for multi-wavelength generation simultaneously. Using the dual-function of ULPG, three-, four-, five-, six-, and seven-wavelength mode-locked pulses are obtained in EDFL, seven of which are the largest number of wavelengths up to now. For the four-wavelength soliton pulses, their pulse width is about 7.8 ps. The maximum average output power and slope efficiency of these pulses are 8.4 mW and 2.03%, respectively. Besides the conventional pulses, hybrid soliton pulses composed of a four-wavelength pulse and single soliton are also observed. Finally, the effect of cavity dispersion on the multi-wavelength mode-locked pulses is also discussed. Our findings indicate that apart from common sensing and filtering, the ULPG may also possess attractive nonlinear pulse-shaping property for ultrafast photonics application.

We demonstrate a three-nanosecond equidistant sub-pulse multi-step Q-switched Nd:Y3Al5O12 (Nd:YAG) laser. In the time interval of 100–1000 ns, three pulses with the same nanosecond interval and the same peak power are obtained at the pulse width of 24 ns, 28 ns, and 36.6 ns, respectively. The energy is 32.5 mJ, and the optical efficiency is 10.8%. The multi-step Q-switched method does not require the insertion of other optical elements into the traditional Q-switched laser, and it is very suitable to obtain pulse group output with several nanosecond pulse intervals.

In modern optics, particular interest is devoted to the phase singularities that yield complicated and twisted phase structures by photons carrying optical angular momentum. In this paper, the traditional M-line method is applied to a vortex beam (VB) by a symmetric metal cladding waveguide chip, which can host numerous oscillating guided modes via free space coupling. These ultrahigh-order modes (UOMs) result in high angular resolution due to the high finesse of the resonant chip. Experiments show that the reflected pattern of a VB can be divided into a series of inner and outer rings, whilst both of them are highly distorted by the M-lines due to the UOMs’ leakage. Taking the distribution of the energy flux into account, a simple ray-optics-based model is proposed to simulate the reflected pattern by calculating the local incident angle over the cross section of the beam. The theoretical simulations fit well with the experimental results, and the proposed scheme may enable new applications in imaging and sensing of complicated phase structures.

End-pumped by a 976 nm diode laser, a high-repetition-rate Er:Yb:YAl3(BO3)4 microchip laser passively Q-switched by a Co2+:MgAl2O4 crystal is reported. At a quasi-continuous-wave pump power of 20 W, a 1553 nm passively Q-switched laser with the repetition rate of 544 kHz, pulse duration of 8.3 ns, and pulse energy of 3.9 μJ was obtained. To the best of our knowledge, the 544 kHz is the highest reported value for the 1.5 μm passively Q-switched pulse laser. In the continuous-wave pumping experiment, the maximum repetition rate of 144 kHz with the pulse duration of 8.0 ns and pulse energy of 1.7 μJ was obtained at the incident pump power of 6.3 W.

In this paper, we demonstrated a series of short-living mode-locking (ML) states (each lasting a few to a hundred microseconds) that happened before a fiber laser reached a steady ML state. With time-stretched dispersion Fourier transform spectroscopy, a rich diversity of transient multi-pulse dynamics were revealed spectrally and temporally. As a result, we found that the formation of the short-living ML states was related to abundant pump power, and their decaying evolution dynamics were possibly governed by gain depletion and recovery. Our results revealed unexpected transient lasing behaviors of a soliton laser and thus might be useful to understand the complex dynamics of mode-locked lasers.

An effective and simple method is proposed for fabricating the micro/nano hybrid structures on metal surfaces by adjusting femtosecond laser fluence, scanning interval, and polarization. The evolution of surface morphology with the micro/nano structures is discussed in detail. Also, the mechanism of light absorption by the micro/nano hybrid structures is revealed. Compared with the typical periodic light-absorbing structures, this type of micro/nano hybrid structures has an ultralow average reflectivity of 2% in the 250–2300 nm spectral band and the minimum 1.5% reflectivity in UV band. By employing this method, large areas of the micro/nano hybrid structures with high consistency could be achieved.

Gas sensing for measurement of gas components, concentrations, and other parameters plays an important role in many fields. In this Letter, a micro-ring resonator laser used for gas sensing is experimentally demonstrated. The multi-quantum-wells micro-ring laser based on whispering-gallery modes with an annular resonator and an output waveguide was fabricated. A single-mode laser with a wavelength of 1746.4 nm was fabricated for the first time, to the best of our knowledge, experimentally. The output power of 1.65 mW under 40 mA injection current was obtained with a side-mode suppression ratio over 33 dB.

After the three-dimensional self-affine fractal random surface simulation, we use the optical scattering theory to calculate the deep Fresnel region speckle (DFRS) under consideration of the more strict shadowing effect. The evolution of DFRS with the scattering distance and the intensity probability distribution are studied. It is found that the morphology of the scatterer has an antisymmetric relationship with the intensity distribution of DFRS, and the effect of micro-lenses on the scattering surface causes the intensity probability distribution of DFRS to deviate from the Gaussian speckle in the high light intensity area.

We experimentally demonstrate an all-fiber supercontinuum source that covers the spectral region ranging from visible to mid-infrared. The ultra-broadband supercontinuum is realized by pumping a cascaded photonic crystal fiber and a highly nonlinear fiber with a 1/1.5 μm dual-band pump source. A maximum output power of 9.01 W is achieved using the system, which is the highest power ever achieved from a supercontinuum source spanning from the visible to mid-infrared.

In order to reveal the evolution mechanism of repaired morphology and the material’s migration mechanism on the crack surface in the process of CO2 laser repairing surface damage of fused silica optics, two multi-physics coupling mathematical models with different scales are developed, respectively. The physical problems, such as heat and mass transfer, material phase transition, melt flow, evaporation removal, and crack healing, are analyzed. Studies show that material ablation and the gasification recoil pressure accompanying the material splash are the leading factors in forming the Gaussian crater with a raised rim feature. The use of low-power lasers for a long time can fully melt the material around the crack before healing, which can greatly reduce the size of the residual air layer. Combined with the experimental research, the methods to suppress the negative factors (e.g., raised rim, deposited debris, air bubbles) in the CO2 laser repairing process are proposed.

We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.

This paper proposes a hybrid layered asymmetrically clipped optical (HLACO) single-carrier frequency-division multiplexing (SCFDM) scheme for dimmable visible light communication. It designs a signal structure that combines layered asymmetrically clipped optical (LACO)-SCFDM and negative LACO-SCFDM in proportion for improving the inherent weaknesses of orthogonal frequency-division multiplexing (OFDM)-based dimmable schemes and further enhancing the system performance. Compared to the HLACO-OFDM-based dimming scheme, it obtains a lower bit error ratio and enables efficient communication over broader dimming range. Its spectral efficiency realizes 2.875 bit·s-1·Hz-1 within the dimming range of 30%–70%, and the attainable average spectral efficiency gains exceed at least 19.21% compared to other traditional dimmable schemes.

On the basis of a home-made femtosecond Yb-doped fiber laser, we designed a compact and efficient third harmonic generation scheme by a simple compensation plate of β-BaB2O4 crystal. The compensation plate is optimized through its thickness and cutting angle to reverse both spatial and temporal walk-off. By optimizing the parameters of the compensation plate and incident light intensity, a maximum output of 2.23 W with a repetition rate of 1 MHz at 345 nm is obtained, which implies a conversion efficiency of 23% from the infrared to ultraviolet.

Two-dimensional (2D) Te nanosheets were successfully fabricated through the liquid-phase exfoliation (LPE) method. The nonlinear optical properties of 2D Te nanosheets were studied by the open-aperture Z-scan technique. Furthermore, the continuous wave mode-locked Nd:YVO4 laser was successfully realized by using 2D Te as a saturable absorber (SA) for the first time, to the best of our knowledge. Ultrashort pulses as short as 5.8 ps were obtained at 1064.3 nm with an output power of 851 mW. This primary investigation indicates that the 2D Te SA is a promising photonic device in the fields of ultrafast solid-state lasers.

To obtain short pulse width and high peak power laser, a 7 kHz sub-nanosecond microchip laser amplified by a grazing incidence double pass slab amplifier is experimentally demonstrated in this Letter. We use a compact side-pumped Nd:YVO4 bounce amplifier with grazing incidence beam for achieving high gains and power extraction. Laser output power of 7.37 W at 7 kHz, 1.2 MW pulse peak power with 877 ps duration and 1.05 mJ energy, 25 pm spectral width, and near diffraction limited mode beam quality are achieved, and the optical-to-optical efficiency is 18%. The laser is packaged in a volume of 356 mm × 226 mm × 84 mm and may be used for applications such as laser altimeters and ladar systems.

In this Letter, we experimentally investigate fast temporal intensity dynamics and statistical properties of the cladding-pumped Er/Yb co-doped random Rayleigh feedback fiber laser (EYRFL) for the first time, to the best of our knowledge. By using the optical spectral filtering method, strong and fast intensity fluctuations with the generation of extreme events are revealed at the output of EYRFL. The statistics of the intensity fluctuations strongly depends on the wavelength of the filtered radiation, and the intensity probability density function (PDF) with a heavy tail is observed in the far wings of the spectrum. We also find that the PDF of the intensity in the central part of the spectrum deviates from the exponential distribution and has the dependence on the laser operating regimes, which indicates some correlations among different frequency components exist in the EYRFL radiation and may play an important role in the random lasing spectrum stabilization process.

The behavior of self-polarization emission in Nd:Y3Al5O12(YAG)/Cr4+:YAG lasers has been proved in some cases. However, the degree and direction of polarization were often sensitive and unstable. We experimentally observed different beam profiles versus the angle of the polarizer relative to the polarization direction of the laser. In order to explore the polarization mechanism, the dynamics of intracavity polarized eigenmodes was analyzed theoretically. Simulative results were well consistent with our experimental observations. It indicated that the linear self-polarization emission was a composite state rather than an intrinsic state. This study contributed to the improvement of the polarization stability in Nd:YAG/Cr4+:YAG passively Q-switched lasers.

Optically pumped magnetometers (OPMs) have developed rapidly in the bio-magnetic measurement field, which requires lasers with stable frequency and intensity for high sensitivity. Herein we stabilize a vertical-cavity surface-emitting laser (VCSEL) without any additional setup except for the parts of an OPM. The linewidth of the absorption spectrum as a frequency reference is broadened to 40 GHz owing to pressure broadening. To enhance performance, the VCSEL injection current and temperature are tuned simultaneously using a closed-loop control system. The experiments reveal that the VCSEL frequency stability achieves 2×10-7 at an average time of 1 s, and the intensity noise is 1×10-6 V/Hz1/2 at 1–100 Hz. This approach is useful for suppressing OPM noise without additional sensor probe parts.

Different laminated structures of TiO2/SiO2 composite film were prepared via atomic layer deposition (ALD) on alumina substrates. The effect of the annealing temperature in the air on the surface morphologies, crystal structures, binding energies, and ingredient content of these films was investigated using X-ray diffraction, field emission scanning electron microscopy, and X-ray photoelectron spectroscopy. Results showed that the binding energy of Ti and Si increased with decrease of the Ti content, and the TiO2/SiO2 nanolaminated films exhibited a complex bonding structure. As the annealing temperature increased, the thickness of the nanolaminated films decreased, and the density and surface roughness increased. An increase in the crystallization temperature was proportional to the SiO2 content in TiO2/SiO2 composite film. The annealing temperature and thin thickness strongly affected the phase structure of the ALD TiO2 thin film. To be specific, the TiO2 thin film transformed into an anatase phase from an amorphous phase after an increase in the annealing temperature from 400°C to 550°C, and the TiO2 film exhibited an anatase phase until the annealing temperature reached 850°C, owing to its extremely small thickness. The annealing process caused the Al ions in the substrate to diffuse into the films and bond with O.

We report a long-term frequency-stabilized optical frequency comb at 530–1100 nm based on a turnkey Ti:sapphire mode-locked laser. With the help of a digital controller, turnkey operation is realized for the Ti:sapphire mode-locked laser. Under optimized design of the laser cavity, the laser can be mode-locked over a month, limited by the observation time. The combination of a fast piezo and a slow one inside the Ti:sapphire mode-locked laser allows us to adjust the cavity length with moderate bandwidth and tuning range, enabling robust locking of the repetition rate (fr) to a hydrogen maser. By combining a fast analog feedback to pump current and a slow digital feedback to an intracavity wedge and the pump power of the Ti:sapphire mode-locked laser, the carrier envelope offset frequency (fceo) of the comb is stabilized. We extend the continuous frequency-stabilized time of the Ti:sapphire optical frequency comb to five days. The residual jitters of fr and fceo are 0.08 mHz and 2.5 mHz at 1 s averaging time, respectively, satisfying many applications demanding accuracy and short operation time for optical frequency combs.

Absorption induced by activated magnesium (Mg) in a p-type layer contributes considerable optical internal loss in GaN-based laser diodes (LDs). An LD structure with a distributed polarization doping (DPD) p-cladding layer (CL) without intentional Mg doping was designed and fabricated. The influence of the anti-waveguide structure on optical confinement was studied by optical simulation. The threshold current density, slope efficiency of LDs with DPD p-CL, and Mg-doped CL, respectively, were compared. It was found that LDs with DPD p-CL showed lower threshold current density but reduced slope efficiency, which were caused by decreasing internal loss and hole injection, respectively.

We demonstrate the non-mechanical beam steering and amplifier operation of a vertical cavity surface emitting laser (VCSEL) integrated Bragg reflector waveguide amplifier with a cut-off wavelength detuning design, which enables unidirectional lateral coupling, continuous electrical beam steering, and diffraction-limited divergence angle. We present the modeling of the proposed structure for unidirectional coupling between a seed single-mode VCSEL and slow-light amplifier. We also present the detailed operating characteristics including the near-field and far-field patterns, light/current characteristics, and lasing spectrum. The experimental measurements exhibit a single-mode output of over 8 mW under CW operation, a continuous beam steering range of 16°, and beam divergence below 0.1° as an optical beam scanner. The integrated amplifier length is as small as 0.9 mm, and thus we could expect much higher powers and higher resolution points by increasing the amplifier lengths.

We report Q-switched mode-locked (QML) pulses generation in an Yb-doped multimode fiber (MMF) laser by using a graphene-deposited multimode microfiber (GMM) for the first time, to the best of our knowledge. The single-wavelength QML operation with the central wavelength tunable from 1028.81 nm to 1039.20 nm and the dual-wavelength QML operation with the wavelength spacing tunable from 0.93 nm to 5.79 nm are achieved due to the multimode interference filtering effect induced by the few-mode fiber and MMF structure and the GMM in the cavity. Particularly, in the single-wavelength QML operation, the fifth harmonic is also realized owing to the high nonlinear effect of the GMM. The obtained results indicate that the QML pulses can be generated in the MMF laser, and such a flexible tunable laser has promising applications in optical sensing, measuring, and laser processing.

The dissipative Kerr soliton microcomb provides a promising laser source for wavelength-division multiplexing (WDM) communication systems thanks to its compatibility with chip integration. However, the soliton microcomb commonly suffers from a low-power level due to the intrinsically limited energy conversion efficiency from the continuous-wave pump laser to ultra-short solitary pulses. Here, we exploit laser injection locking to amplify and equalize dissipative Kerr soliton comb lines, superior gain factor larger than 30 dB, and optical-signal-to-noise-ratio (OSNR) as high as 60 dB obtained experimentally, providing a potential pathway to constitute a high-power chip-integrated WDM laser source for optical communications.

In this Letter, we demonstrated the switchable single- and dual-wavelength femtosecond soliton generation in single-mode Er-doped fiber lasers with the usage of carboxyl-functionalized graphene oxide (GO-COOH) saturable absorbers (SAs) for the first time, to the best of our knowledge. The fiber laser generated a stable single-wavelength conventional soliton at 1560.1 nm with a pulse duration of 548.1 fs. The dual-wavelength solitons centered at 1531.9 nm and 1555.2 nm with a spacing of approximately 23 nm can be obtained by adjusting the pump power of the cavity. Our experimental results indicated the GO-COOH has great potential to be used in ultrafast fiber lasers as broadband SAs.

In this paper, we demonstrate a scheme to tailor both longitudinal and transverse modes inside a laser cavity and constitute an eye-safe single longitudinal mode Er:Y3Al5O12 (Er:YAG) vector laser. A q-plate is employed as a spin-orbital conversion element to modulate the transverse mode and obtain cylindrical vector beams. An optical isolator is employed as a non-reciprocal element for the ring cavity to enforce unidirectional operation and achieve single longitudinal oscillation. The characteristics of power, transverse intensity, and polarization spectrum of the output beams are observed. The observed typical single longitudinal mode and highly matched special polarizations prove the successful tailoring of both longitudinal and transverse modes.

In this paper, we propose and demonstrate an adjustable-free and movable Nd:YVO4 thin disk laser based on the telecentric cat’s eye cavity. We design a V-shaped laser cavity containing two reflectors with Nd:YVO4 thin disks as the gain medium. The experimental results from the traditional plane-plane cavity, plane-telecentric cat’s eye cavity, and double telecentric cat’s eye cavity are compared. They show that plane-telecentric cat’s eye cavity laser can keep operating at the adjustable-free range of -6° to +6°, which is up to 60 times better than that of traditional plane-plane cavity. In the double telecentric cat’s eye case, the adjustable-free range is improved to -13° to +13°. Additionally, in the case of the double telecentric cat’s eye cavity, the output telecentric cat’s eye can achieve free movement within the horizontal range of ±20 mm.

We demonstrate a high-resolution frequency-modulated continuous-wave dual-frequency LIDAR system based on a monolithic integrated two-section (TS) distributed feedback (DFB) laser. In order to achieve phase locking of the two lasers in the TS-DFB laser, the sideband optical injection locking technique is employed. A high-quality linear frequency-modulated signal is achieved from the TS-DFB laser. Utilizing the proposed LIDAR system, the distance and velocity of a target can be measured accurately. The maximum relative errors of distance and velocity measurement are 1.6% and 3.18%, respectively.

We propose and demonstrate the generation of wideband chaos based on a dual-mode microsquare semiconductor laser with optical feedback. By adjusting the dual-mode intensity ratio and the feedback strength, wideband chaos covering more than 50 GHz in the RF spectrum is achieved. The standard and effective bandwidths of the chaotic signal are 31.3 GHz and 30.7 GHz with the flatness of 8.3 dB and 6.1 dB, respectively.

An improved self-mixing grating interferometer based on the Littrow structure has been proposed in this Letter to measure displacement. The grating is integrated inside the interferometer to reduce the impact on the vibration parameters of the object caused by the grating attached to the vibrating object. The +1st diffracted light returns to the laser cavity after being reflected by the target object, and self-mixing interference occurs. The displacement can be reconstructed by processing the self-mixing signals. The feasibility of the proposed interferometer is demonstrated by experimental measurements, and results show that it can achieve micro displacement measurement with the maximum absolute errors of less than 50 nm.

We design a 645 nm laser diode (LD) with a narrow vertical beam divergence angle based on the mode expansion layer. The vertical beam divergence of 10.94° at full width at half-maximum is realized under 1.5 A continuous-wave operation, which is the smallest vertical beam divergence for such an LD based on the mode expansion layer, to the best of our knowledge. The threshold current and output power are 1.07 A and 0.94 W, limited by the thermal rollover for the 100 µm wide and 1500 µm long broad area laser, and the slope efficiency is 0.71 W/A. The low coherence device is fabricated with the speckle contrast of 3.6% and good directional emission. Such 645 nm LDs have promising applications in laser display.

A novel tiled Ti:sapphire (Ti:S) amplifier was experimentally demonstrated with >1 J amplified chirped pulse output. Two Ti:S crystals having dimensions of 14 mm× 14 mm× 25 mm were tiled as the gain medium in a four-pass amplifier. Maximum output energy of 1.18 J was obtained with 2.75 J pump energy. The energy conversion efficiency of the tiled Ti:S amplifier was comparable with a single Ti:S amplifier. The laser pulse having the maximum peak power of 28 TW was obtained after the compressor. Moreover, the influence of the beam gap on the far field was discussed. This novel tiled Ti:S amplifier technique can provide a potential way for 100 PW or EW lasers in the future.

Noise-like pulses having a pedestal of 690 fs and a spike of 59.6 fs were generated in a nonlinear Yb-doped fiber amplification system. The seed source is a mode-locked Yb-doped fiber laser by nonlinear polarization rotation, and dissipative soliton pulses were obtained in it. Then, the dissipative soliton pulses passed through a 7.6 m dispersive fiber to enhance the dispersion and nonlinearity. Further on, the dissipative soliton pulses were launched into a Yb-doped fiber nonlinear amplifier, and stable noise-like pulses with a pedestal of 6.26 ps and a spike of 227 fs were achieved. Finally, by a grating pair, the pedestal and spike of the noise-like pulses were effectively compressed to 690 fs and 59.6 fs, respectively. To the best of our knowledge, this is the shortest pedestal demonstrated in noise-like pulses operating at 1 μm.

We report on a simultaneous generation of double white light lasers through filamentation by focusing a femtosecond laser pulse. The appearance of the two white light lasers can be controlled by tilting the focusing lens. The spectral bandwidth and the pulse energy of the double white light lasers were controlled by tuning laser filamenting pulse energy and polarization. Two white light lasers with pulse energies of 1.54 mJ and 1.84 mJ, respectively, were generated with the pump laser energy of 7.43 mJ. Besides being beneficial in understanding the multiple white light lasers generation process through multiple filamentation and its control, the results are also valuable for white light laser-based applications.

A rotating neodymium-doped yttrium aluminum garnet (Nd:YAG) disk laser resonator for efficiently generating vector beams with azimuthal and radial polarization is demonstrated. In the study, the laser crystal rotary for thermal alleviation and polarization discrimination uses c-cut ytterbium vanadate (YVO4). The laser output could be switched between azimuthal and radial polarizations by simply adjusting the cavity length. The laser power reached 4.38 W and 4.64 W for azimuthally and radially polarized beams at the slope efficiencies of 45.3% and 48.5%, respectively. Our study proved that an efficient, high-power vector rotary disk laser would be realistic.

A modulation classification method in combination with partition-fractal and support-vector machine (SVM) learning methods is proposed to realize no prior recognition of the modulation mode in satellite laser communication systems. The effectiveness and accuracy of this method are verified under nine modulation modes and compared with other learning algorithms. The simulation results show when the signal-to-noise ratio (SNR) of the modulated signal is more than 8 dB, the classifier accuracy based on the proposed method can achieve more than 98%, especially when in binary phase shift keying and quadrature amplitude shift keying modes, and the classifier achieves 100% identification whatever the SNR changes to. In addition, the proposed method has strong scalability to achieve more modulation mode identification in the future.

In this Letter, we firstly, to the best of our knowledge, demonstrated the influence of pre-pulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9 nm by employing an alumina capillary having an inner diameter of 4.8 mm. Specifically, the delay time was changed from 8 to 520 μs in small intervals. The pre-discharge current was increased from 25 A to 250 A through small steps, while keeping the main discharge current constant. Usually, a small pre-discharge current is applied to an Ar-filled capillary to attain a plasma column having sufficient pre-ionization before the injection of the main current. The pre-discharge current of 140 A was declared the best current to obtain lasing with a 4.8 mm diameter capillary. The laser spots were captured at best time delays for the pre-discharge currents of 25, 45, 80, 140, and 250 A, which support the experimental results. We observed that by applying the pre-discharge current of 140 A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140 A is cylindrically symmetric and has a better structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for the applications of the 46.9 nm laser. Results of this Letter might open a new way to enhance applications of a 46.9 nm capillary discharge soft X-ray laser.

A range-extended acidity detector based on Nile red was designed and analyzed in this work. In light of the good lasing property and solvatochromism characteristic of Nile red/ethanol solution, we have obtained laser spectra of sulfuric acid in different concentrations doped in this substrate. Moreover, to expand the acidity detection range, we proposed a tandem cuvette system containing rhodamine 6G/ethanol and Nile red/ethanol. Consequently, the detection range could be enlarged from 26 nm to 40 nm, by changing not only the wavelength peak but also by the intensity ratio of dual-wavelength laser output. In addition, by changing the detection and substrate materials, the whole detection range could be expanded, and therefore a wide range of applications in polarity and acidity detection could be implemented via this method.

A continuous-wave Nd:YVO4/BaWO4 Raman laser generating simultaneous multi-wavelength first-Stokes and second-Stokes emissions is demonstrated for the first time, to the best of our knowledge. Investigations concerning different pump spot sizes and crystal lengths were conducted to improve the thermal effect and pump absorption. Three first-Stokes lasers at 1103.6, 1175.9, and 1180.7 nm and two second-Stokes lasers at 1145.7 and 1228.9 nm are obtained simultaneously using the Raman shifts of 925 cm-1 and 332 cm-1 in BaWO4 and 890 cm-1 in YVO4. At the incident pump power of 23.1 W, 1.24 W maximum Raman output power is achieved, corresponding to an optical conversion efficiency of 5.4%. We also present a theoretical analysis of the competition between different Stokes lines.