Currently, most quantum holography schemes adopt reconstructing images from the second-order correlation information or fiber scanning, which are both non-visualized, meanwhile making three-dimensional (3D) quantum holography a big challenge. Here, we implement the visualized quantum 3D orbital-angular-momentum (OAM) holography in the twin photon system, where the OAM-multiplexing hologram within two imaging planes and three OAM channels in the signal arm is selectively read out and directly displayed on an intensified CMOS camera by switching the OAM state in the idler arm. A thousands-of-times acceleration of the holographic reconstruction process is achieved with the maintenance of the OAM feature for each pixel compared to the scanning approach. The 3D imaging feature in a quantum holography system provides additional freedom for further improving the capacity of holographic information transmission and encryption.

Vector vortex beams (VVBs) have attracted considerable attention due to their unique polarization distribution and helical phase wavefront. We first attempt to retrieve the modal coefficients of hybrid VVBs measured by their multiplex polarized intensities using the deep learning (DL)-based stochastic parallel gradient descent (SPGD) algorithm. The Xception-based DL model with multi-view images can make an accurate prediction of modal coefficients that are validated by the theoretical calculations of the waveplate angles, demonstrating a high correlation of 99.65%. The universality of the algorithm to high-order vector-eigenmodes (VMs) decomposition is proved to enable the precise reconstruction of modal patterns generated by mode-selective couplers, which promotes the accurate characteristics of VVBs in laser beam characterization and fiber mode-division multiplexing.

The 6G transport network will be intricately designed as an integrated carrier, seamlessly integrating computing and networking capabilities. Leveraging the network as its foundation, it aims to deliver differentiated computing power services through supercomputing/intelligent computing and capability resource pooling. This study proposes an advanced modulation format, alternating polarization chirped return-to-zero frequency shift keying (Apol-CRZ-FSK), specifically designed to meet the integrated computing and networking carrying requirements of future 6G. Furthermore, comprehensive comparison and analysis of the transmission performance of 100 Gbps Apol-CRZ-FSK, CRZ-FSK, and differential quadrature phase shift keying (DQPSK) are conducted under identical conditions. The research indicates the high nonlinearity resistance capability exhibited by Apol-CRZ-FSK, highlighting its superior transmission performance.

The intermodal nonlinear coefficient is an important parameter to analytically describe few-mode fiber (FMF) nonlinearity when the nonlinear interaction arising in the FMF is exploited for various applications. Here, we experimentally characterize the intermodal nonlinear coefficient based on continuous-wave cross-phase modulation, without a priori knowledge of the intramodal nonlinear coefficient for the FMF under test. Based on the derived equation, we examine the impact of the pump modulation scheme and the wavelength spacing between the probe and pump on the precise measurement of the intermodal nonlinear coefficient. Compared with double sideband (DSB) modulation, the pump modulated with carrier-suppressed DSB scheme leads to an underestimation of measurement results, due to the coexistence of unnecessary nonlinear interactions. Finally, the intermodal nonlinear coefficient of a 1.9-km FMF supporting two mode groups is experimentally characterized and is in good agreement with the theoretically calculated values. Due to the random birefringence fluctuation, the average value of 4/3 to describe the intermodal nonlinear interaction arising in weakly coupled FMF by the commonly used Manakov equation is experimentally verified.

Study on optical correlation function initiates the development of many quantum techniques, with ghost imaging (GI) being one of the great achievements. Upon the first demonstration with entangled sources, the physics and improvements of GI attracted much interest. Among existing studies, GI with classical sources provoked debates and ideas to the most extent. Toward better understanding and practical applications of GI, fundamental theory, various designs of illumination patterns as well as reconstruction algorithms, demonstrations and field tests have been reported, with the topic of GI very much enriched. In this paper, we try to sketch the evolution of GI, focusing mainly on the basic idea, the properties and superiority, progress toward applications of GI with classical sources, and provide our discussion looking into the future.

Coherent control of terahertz (THz) wave radiation with two-color laser excitation requires good temporal overlap with good dispersion control of both the fundamental (ω) and the second harmonic (2ω). Herein, we experimentally determined the temporal overlap of the ω and 2ω pulses in the time-domain, which was corroborated by theoretical calculations. Furthermore, the coherent control of THz radiation of ZnSe also proves the good temporal overlap of two-color femtosecond lasers. This work provides an experimental tool for finding temporal overlap and realizing the dispersion control of two femtosecond lasers.

A biosensor featuring an S-tapered fiber (STF) with a composite bio-sensitive film comprising graphene oxide and gold nanoparticles, has been proposed for the rapid, highly sensitive, and label-free detection of pseudomonas exotoxin (PE). The STF was created using a fusion splicer. Subsequently, the composite film and nanobody were successively assembled onto its surface. The detection mechanism relies on monitoring changes in the external refractive index induced by the specific binding of PE to the nanobody. The developed STF biosensor exhibited a remarkable sensitivity of 0.28 nm/(ng/mL) and a limit of detection as low as 0.21 ng/mL for PE.

We experimentally developed massive parallel chaotic sources for random bit generation, based on a monolithically integrated amplified-feedback laser (AFL) array using the reconstruction-equivalent chirp technique. Proof-of-concept experiments demonstrate that using our method, eight independent random bit streams with 100 GSa/s and uniform wavelength spacing could be obtained. In addition, there is a low correlation between different bit-stream channels. Our approach enables scalable integration for large-scale parallel chaotic channels, potentially achieving throughput capacities of up to Tb/s for random bit generation.

Chip-based frequency combs have attracted increasing attention in recent years due to the advantages of small size, integrability, low power consumption, and large re-frequency range. Continuous and deterministic generation of optical frequency combs is critical for the development of diverse applications. In this work, an integrated design of a computer-program-controlled optical frequency comb generation scheme is developed, whereby the optical frequency comb generation and monitoring units are housed inside an aluminum box. Through this improvement, an optical frequency comb with a free spectral range (FSR) of 100.3 GHz can be generated and maintained continuously for a duration of >48 h. It is varied that the control method is highly effective during 1000 startup tests. With statistical analysis, the startup probability and mean time of the single-soliton state is 100% and as short as 1.5 s, respectively. Besides, chaotic states with a startup probability of 100% and a mean time of 0.31 s are also generated with the same program. The self-injection-locked generation method is still less stable and shorter in duration, and it requires a different state for each generation, which is capable of generating the Kerr optical frequency comb more consistently and more rapidly.

The mode selection ability of whispering gallery mode (WGM) microcavities is crucial in applications such as sensors, lasers, and nonlinear optics. Though various shapes of microcavities have been studied for mode suppression, single-mode operation is still difficult to realize. Here, we demonstrate a Reuleaux-triangle resonator (RTR) with corner-cuts, which can reconstruct phase space to realize single-mode control. According to classical ray dynamics, the boundary of the RTR is optimized to obtain the stable 9-period islands with the consideration of suppression of standing waves and strong light scattering. The single-mode characteristic of the RTR is experimentally verified under the optimal coupling position, with a Q factor of 1.1 × 104. Our investigation reveals a new thread for mode suppression with potential in the fields of single-mode lasers and nonlinear optics.

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.

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.

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.

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.

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.

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.

Black silicon materials prepared via microstructuring and hyperdoping by ultrafast laser irradiation have attracted immense attention owing to their high absorption and photon sensitivity across a broadband spectral range. However, a conflict exists between the repair requirements for the high amount of laser-induced damage and the thermally unstable hyperdoped impurities, resulting in low photon sensitivity and rapid decay at subbandgap wavelengths for the annealed black silicon. In this work, the properties of titanium (Ti) hyperdoped silicon have been explored using first-principle calculations. The findings of the study reveal that the interstitial Ti atoms exhibit a deep impurity band and low formation energy in silicon, which may be responsible for the stable subbandgap absorption that is achieved. Furthermore, femtosecond laser irradiation and rapid thermal annealing have been applied to manufacture Ti-hyperdoped black silicon (b-Si:Ti). The b-Si:Ti compound prepared by hyperdoping displayed high absorption across the visible and infrared ranges, with absorptance exceeding 90% for visible lights and 60% for subbandgap wavelengths. Additionally, the subbandgap absorption remains high even after intense thermal annealing, indicating a stable deep-level impurity of Ti in silicon. The experimental findings are consistent with the simulation results and complement each other to reveal the physical mechanisms responsible for the high performance of b-Si:Ti. The results thus demonstrate promising prospects for the application of black silicon in high-efficiency solar cells, photoelectric imaging, and flip-chip interconnection systems.

Vector vortex beams (VVBs), novel structured optical fields that combine the polarization properties of vector beams and phase characteristics of vortex beams, have garnered widespread attention in the photonics community. Capitalizing on recently developed metasurfaces, miniaturized VVB generators with advanced properties have been implemented. However, metasurface-empowered VVB generators remain static and can only generate one pre-designed structured light. Here, we propose a kind of phase change metasurface for tunable vector beam generation by utilizing anisotropic Ge2Sb2Se4Te1 (GSST) unit cells with tunable phase retardation when GSST transits between two different phase states. By properly rotating the orientations of the tunable GSST unit structures that transit between quarter-wave plates and half-wave plates, we can effectively transform incident plane waves into vector beams with distinct topological charges and polarization states. When GSST is in the amorphous state, the designed metasurface can transmit circularly polarized light into VVBs. In the crystalline state, the same GSST metasurface converts linearly polarized light into second-order radially polarized (RP) and azimuthally polarized (AP) beams. Our phase-change metasurface paves the way for precise control over the polarization patterns and vortex characteristics of beams, thereby enabling the exact manipulation of beam structures through the alteration of their phase states.

Recently, artificial intelligence has been proven as an effective modeling tool in ultrafast optics; its application in the design of ultrafast laser systems is a promising issue. In this Letter, a method based on a feed-forward neural network (FNN) model with a simple structure is adopted to inversely predict the full-field supercontinuum generation and recover the initial pulse. The performance of the FNN and its dependence on the predicted pulse features are further explored by a reconstruction test. The generalization ability of the proposed method is further demonstrated in the case with an initial chirp.

Dissipative Kerr cavity solitons (CSs) are localized temporal structures generated in coherently driven Kerr resonators which have attracted widespread attention for their rich nonlinear dynamics and key role in the generation of optical frequency combs. Akin to the complexity of the dissipative solitons in mode-locked lasers, the nonlinear dynamics of the CSs present distinctive evolutionary behaviors that may create new potential for understanding interdisciplinary nonlinear problems. Here, we leverage real-time spectroscopy to study the transient behaviors of the CSs in a Kerr fiber cavity with coherent driving. The real-time spectroscopy is implemented with the emerging dispersive Fourier transform (DFT) technology with a large dispersion of -10.2 ns/nm, which provides a sampling spectral resolution of ∼1 pm. Under perturbations, the complete birth-to-annihilation process of the CS is visualized in real time as the Kerr fiber cavity specifically locked around the boundary of modulation instability (MI) and bistable regimes. Fruitful transient dynamics are observed, including MI, soliton breathing, stationary CS, and its annihilation. The mechanism of the observed transient dynamics is theoretically studied through numerical simulation, and we find that the cavity detuning variation resulting from the external perturbation plays a dominant role in the evolution of the CS. More importantly, there exists a visible energy drop accompanied by the CS breathing, wherein the collision between the solitons triggers the subsequent drift and annihilation of the CS. The spectral interferograms of multiple CSs that are analyzed by their field autocorrelation also verify the annihilation of the CS.

The dependence of nonlinear optical absorption and carrier dynamics on the thickness of chromium thiophosphate (CrPS4) is investigated. Utilizing the I-scan system, we have observed the typical two-photon absorption (TPA) at 780 nm for three different thicknesses. The TPA coefficient, third-order nonlinear optical susceptibility Imχ(3), and the figure of merit have been obtained by fitting the I-scan data. Using nondegenerate pump-probe measurements, the photoinduced absorption has been observed, and the carrier relaxation processes are phonon-assisted. This study provides deep insights into the nonlinear optical properties of CrPS4, which is of great significance for potential applications in ultrafast optical devices.

A high-performance grating coupler (GC) operating at a wavelength of 1550 nm is proposed by utilizing the adjoint-based inverse design algorithm on a 220 nm silicon-on-insulator (SOI) substrate. The grating scheme offers several advantages, including simple structure, large minimum feature size (MFS), manufacturing friendliness, support for large-scale production and multi-project wafer (MPW) runs, etc., while simultaneously maintaining exceptional coupling performance and fabrication tolerance. The design process incorporates various fabrication constraints to satisfy the specifications of different foundry processes. The optimized GC demonstrates excellent coupling performance and 3 dB bandwidth within the MFS range of 60 to 180 nm. The simulated coupling efficiency (CE) of the GC with 130 nm MFS is -1.69 dB, whereas the experimentally measured CE of the fabricated GC using electron beam lithography (EBL) is -2.83 dB. Notably, the experimental CE of the GC with 180 nm MFS fabricated using 248 nm deep ultraviolet (DUV) lithography is -2.77 dB, representing the highest experimental CE ever reported for a single-layer etching C-Band GC supported by MPW runs fabricated on 220 nm SOI without utilizing any back reflector, multi-etch layer, or overlay. The manufacturing outcomes of the same GC structure employing different manufacturing processes are discussed and analyzed, providing valuable insights for the fabrication of silicon photonics devices.

In this Letter, we demonstrate ultraviolet (UV) spot position measurement based on the 4 H-SiC quadrant photodetectors (QPDs). The 4 H-SiC QPD with an 8 mm × 8 mm active area exhibits high uniformity across four quadrants, with a consistent low dark current of ∼18 pA and a responsivity of 0.111 A/W at 275 nm. Based on the QPD, the prototype system shows high positioning capability with a slight inherent nonlinearity. Correspondingly, the measurement error is analyzed and a calibration method utilizing the Boltzmann function is developed for the error correction. Evident improvement in positioning accuracy of the measurement system has been realized, achieving a position resolution of 0.3 µm and a mean positioning error of ∼28.5 µm.

Ghost imaging (GI) is a novel imaging technique that has garnered widespread attention and discussion since its inception three decades ago. To this day, ghost imaging has become an effective bridge between the advantages of quantum light sources and the field of imaging. This article begins by tracing the origin of ghost imaging and reviewing its development journey. Subsequently, we introduce some recent and important achievements and research interests of the field, which mainly include two aspects. First, we review recent works that extend GI from the intensity-only target to the complex field domain, that is, ghost holography. Using quantum correlation, traditional holographic techniques have been reproduced at the single-photon level. Second, we review the recent development of GI with the implementation of the intensified charge-coupled device (ICCD). As detection efficiency improves, ghost imaging will gradually become an important platform for studying physical mechanisms and achieving quantum advantage in imaging.