A Brillouin random fiber laser (BRFL) based on a low-concentration erbium-doped fiber is proposed as an active distributed feedback medium. Using a 980 nm pump source, a custom-made 25 m erbium-doped fiber with an ion mass fraction of 0.0035% serves as the Rayleigh scattering medium, providing distributed random feedback to achieve laser resonance. Compared to a traditional 20 km single-mode fiber (SMF), the erbium-doped fiber significantly enhances the distributed Rayleigh scattering intensity by approximately two orders of magnitude. This compact BRFL, leveraging the low-concentration erbium-doped fiber, demonstrates excellent laser noise suppression and frequency stability. Experimental results indicate that the proposed BRFL reduces relative intensity noise by about 20 dB and decreases frequency jitter over time by 64.3% compared to a BRFL using 20 km of SMF as the feedback medium. The active amplification of Rayleigh scattering in the erbium-doped fiber introduces optically controllable disorder, enabling the BRFL photonic system to display manipulated statistical properties of the dynamic spin glass phase. Moreover, the experimental observation of optically controlled replica symmetry breaking offers new avenues for exploring laser physics and nonlinear phenomena.

We report an orthogonally polarized dual-frequency continuous-wave (CW) Er∶?YAG laser that can simultaneously output laser with wavelengths of 1617 nm and 1645 nm. Polarization beam splitter (PBS) prism and etalons are inserted into the cavity to generate an orthogonally polarized dual-frequency mode. The maximum output power of the S-polarized 1645 nm and the P-polarized 1617 nm lasers is 1.074 W and 0.242 W, respectively. We measure the longitudinal mode spectrum of the output laser using a Fabry?Perot (FP) interferometer and prove that the lasers at both wavelengths are single longitudinal mode. The M2 factors of the 1617 nm and 1645 nm lasers are 1.32 and 1.87 in the x direction and 1.38 and 2.06 in the y direction, respectively, and the frequency difference is 3.28 THz.

Optical vortices have demonstrated significant potential in diverse applications, including particle micromanipulation, optical communication, and optical imaging. Among these, the generalized perfect optical vortex (GPOV) has emerged as a focal area of research due to its highly customizable intensity profiles and beam radius that remain independent of topological charges. These attributes have established GPOV as a versatile tool in advanced optical micromanipulation. In this paper, we employ blazed grating technology to enhance the generation of GPOV and integrate them into manipulation experiments involving polystyrene fluorescent microspheres. Through theoretical and experimental validation, we demonstrate the feasibility and precision of transporting particles along customizable paths. This research advances the integration of light field modulation and optical micromanipulation, paving the way for potential applications in microscale delivery systems.

A 1.3 μm high-speed, double-junction cascaded quantum-dot (QD) active-region vertical-cavity surface-emitting laser (VCSEL) is designed using PICS 3D simulation software. The impact of the tunnel-junction cascaded QD active region on the high-speed performance of the VCSEL is investigated. The tunnel-junction cascade structure effectively enhances both the output power and the small-signal modulation bandwidth of the QD VCSEL. Under continuous-wave conditions, a double-junction cascaded VCSEL not only reduces the threshold carrier density but also improves the quantum-well differential gain compared with a single-junction QD VCSEL. The results show that doubling the number of active regions increases the modulation bandwidth, decreases the threshold current, and exponentially enhances the output power and slope efficiency. For a double-junction cascaded QD VCSEL with a 12 μm oxide aperture at a current of 10 mA, the small-signal modulation bandwidths at 25 °C and 85 °C are 28.0 GHz and 17.8 GHz, respectively. This represents improvements of 16.67 % and 22.76% over single-junction QD VCSEL. The output power of the double-junction cascaded QD VCSEL reaches 17.3 mW at room temperature with an injection current of 10 mA. Further reduction of the number of logarithmic DBRs on top of the double-junction cascaded QD VCSEL increases the small-signal modulation bandwidths to 29.6 GHz and 18.0 GHz at 25 ℃ and 85 ℃, respectively. The designed double-junction cascaded 1.3 μm QD VCSEL provides data and theoretical support for epitaxial-material preparation.

This paper presents a method for suppressing parasitic oscillations in crystalline waveguides, resulting in actively Q-switched laser output with high peak power and high optical-to-optical efficiency. The structural optimization of the Yb∶YAG/Er∶YAG single-clad crystalline waveguide incorporates three key enhancements: first, a highly absorptive Ge infrared coating applied to the cladding surface absorbs amplified spontaneous emission (ASE) photons in the cladding, effectively blocking parasitic oscillation pathways; second, the implementation of a slight refractive index differential between core and cladding increases the critical angle for total internal reflection of ASE at the interface, thereby reducing the grazing angle and decreasing the number of ASE reflections to block the reflection path within the core; third, the incorporation of a 0.5° tilt angle at the crystalline waveguide end faces eliminates residual ASE end-face reflections. Experimental data demonstrates that with an absorbed pump power of 67 W, the actively Q-switched crystalline waveguide generates an average output power of 15 W, a pulse energy of 1.5 mJ@10 kHz, a pulse width of 10 ns, and a peak power of 150 kW, achieving an optical-to-optical efficiency of 22% and a dynamic-to-static ratio of 57.7%. The beam quality factors in the x and y directions are 1.15 and 1.10, respectively, which are better than those of the conventional crystalline waveguides. Additionally, the crystalline waveguide maintains consistent output power without saturation at high pump power, confirming the effectiveness of parasitic oscillation suppression. This methodology establishes a novel approach for designing Q-switched/mode-locked lasers utilizing crystalline waveguides, offering substantial applications in laser processing, remote sensing, and related fields.

Polarization singularities are constructed by superposing orthogonal polarization circular Airyprime beams carrying different topological charges, generating a variety of initial polarization singularity structures such as quasi-lemon, V-point, and quasi-high-order polarization singularities. Numerical simulations are employed to investigate the evolution of these structures during free-space propagation. The results show that, for elliptical polarization fields, although the topological charges of the polarization structures remain invariant, their polarization states undergo significant evolution, characterized by changes in ellipticity, polarization handedness, and the transformation from quasi-singularities to standard polarization singularities. In contrast, for vector optical fields, the V-point structure remains topologically stable during propagation, while low-order vector fields can also evolve into stable polarization singularities. This work enriches the understanding of the formation and evolution mechanisms of polarization singularities and provides a theoretical basis for the precise control of polarization fields, with potential applications in optical micromanipulation, polarization encoding, and structured light field modulation.

A novel method for square wave pulse shaping based on field-programmable gate array (FPGA) is proposed. Aiming at the waveform distortion problem of square wave pulses caused by an erbium-doped fiber amplifiers (EDFA), a high-quality square wave pulse with a repetition frequency of 91.27 kHz and a pulse width of 650 ns is successfully obtained by using an extra-cavity pulse-shaping system. The experimental results show that the system can effectively suppress the distortion caused by gain saturation during the amplification process of the square pulse, and the consistency between the spectral envelope of the square pulse after shaping and the sinc function envelope of the ideal square wave pulse is significantly enhanced. This study applies FPGA to distortion correction after amplification of square pulses with a pulse width of hundreds of nanoseconds, and the results can provide technical support for the acquisition of high-energy and high-quality square wave pulses, and further promote their wide application in fields such as supercontinuum generation.

An optical frequency comb is a wideband light source consisting of stable frequency and evenly spaced comb teeth, manifesting as periodic ultrashort pulse outputs in the time domain. The inverse of pulsation period corresponds to the frequency spacing of the comb teeth in the frequency domain, known as the repetition rate. Over the past two decades, optical frequency combs have found wide applications in fields such as precision measurement and advanced manufacturing. Against the backdrop of pursuing faster measurement speeds and higher processing quality, optical frequency combs with high repetition rates have gradually attracted attention. Thanks to the excellent device integration and scene compatibility, optical frequency comb sources based on fiber schemes have developed rapidly in recent years. This review focuses on high-repetition-rate fiber-based optical frequency comb technology. We first briefly introduce the basic concepts and principles of fiber-based optical frequency combs, then review the diverse technical approaches for directly generating high-repetition-rate optical frequency combs in fiber schemes, analyzing their development history, current research status, and the challenges. Finally, based on the technical performance indicators of existing high-repetition-rate fiber-based optical frequency combs, we offer in-depth outlook of their future prospects in application fields.

We introduce a unique type of partially coherent light (PCL) that simultaneously carries a vortex phase and exhibits a special spatial correlation structure, known as radially polarized multi-Gaussian Schell-model fractional vortex (RP-MGSM-FV) beams. We outline the fundamental requirements for generating such light beams and derive the analytical expression for their cross-spectral density matrix after transmission through ABCD optical systems. We further examine the influence of the topological charge magnitude, sign, and coherence width of its vortex phase component on the intensity distribution at the focal plane. The results indicate that as the coherence width increases, the intensity distribution at the focal plane translates from a flat-top to a Gaussian-like shape, then to a flat-top, and ultimately to a ring pattern. An increase in the topological charge numbers leads to a distinct separation in the spatial distribution of the beam at the focal plane. Additionally, changes in the sign of the topological charge cause an inversion in the spatial distribution pattern, allowing for the detection of both the magnitude and sign of the topological charge in RP-MGSM-FV beams. These findings are significantly valuable in applications such as free-space optical communications and particle trapping in micro domains.