Optics express最新文献

Mamyshev oscillators (MO) can be equivalently regarded as passively mode-locked fiber lasers, but this equivalence is achieved solely through spectral broadening and filtering. Therefore, the formation mechanism of its pulse patterns is different from that of other passively mode-locked fiber lasers. In this study, an MO with narrowband filters was constructed. By comparing the differences between the oscillator output spectrum and the amplified spontaneous emission spectrum, the key spectral conditions for MO self-starting were clarified. The self-start law was revealed at the experimental level, and stable single soliton output was achieved simultaneously. Further exploration reveals that the formation of pulse patterns such as soliton clusters, bound state soliton clusters, and harmonic mode locking in MO is not dominated by the previous study's believed peak-power-clamping effect in the cavity, but rather the result of the synergistic effect of narrowband filtering and self-phase modulation effects. This effect transforms MO from a single soliton operating state to a multi-soliton pulse patterns operating state. This discovery breaks through the previous explanations based on the peak-power-clamping effect, providing what we believe to be a new mechanism for the formation of MO pulse patterns, offering strong support for the construction of a complete MO theoretical system and the advancement of fundamental research in this field.

All-optical computing offers ultra-high speed, low-power consumption, and parallel processing capabilities, crucial for overcoming Moore's Law limitations. However, conventional single-wavelength diffractive deep neural networks (D²NN) face significant challenges in achieving synergistic optimization between high-precision optical edge-feature extraction and classification tasks. Here, an edge-detecting spin-differential diffractive neural network (ESD-DNN) is proposed for single-wavelength all-optical object classification. The network architecture is implemented through a Pancharatnam-Berry phase gradient metasurface to achieve rapid edge-feature extraction, while classification inference is accomplished by utilizing a spin-differential mechanism based on left-/right-handed circularly polarized (LCP/RCP) components. Through end-to-end optimization of the diffractive layers, the ESD-DNN achieves co-optimization of edge-feature extraction and classification, significantly improving accuracy while reducing computational costs. Numerical validations reveal that the single-layer ESD-DNN attains 97.5% (MNIST) and 87.5% (Fashion-MNIST) classification accuracy, surpassing traditional single-wavelength D²NN by 10.2% and 5.2%, respectively. Meanwhile, it achieves 5-fold higher computational efficiency while reducing time complexity by 80% compared to a four-layer D²NN. Remarkably, under extreme conditions such as moderate turbulence intensity or thermal lensing effects, the network maintains >90% classification accuracy (MNIST), demonstrating its exceptional environmental robustness. These findings pave the way for applications in artificial intelligence, satellite remote sensing, intelligent industrial inspection, and space optical communications.

This work presents a random laser (RL) based on natural biomaterials, specifically poplar catkin fibers (PCFs), used as a biodegradable scattering matrix in a solution-processed gain medium with Rhodamine 6G. Five samples with PCF concentrations ranging from 1.5 to 5.5 mg/mL were prepared, and the lasing threshold reached a minimum of 8.21 µJ/pulse at 4.5 mg/mL-attributed to optimal multiple scattering provided by the hierarchical fibrous network. At this concentration, the emission spectrum narrowed from 14.8 nm to 0.8 nm at 584 nm, accompanied by nonlinear intensity growth and a 4 nm redshift from lower concentrations, indicating enhanced scattering strength. The system maintained stable output over 1,200 pump pulses, and replica symmetry breaking analysis confirmed the emergence of reproducible coherent modes above threshold. Owing to its low spatial coherence, the device achieved a speckle contrast of only 0.0755-significantly lower than that of a conventional 532 nm laser (0.2118)-enabling high-fidelity speckle-free imaging of both a USAF 1951 target and a dragonfly wing. This work establishes PCFs as a green, low-cost, and high-performance RL platform, offering a promising route toward speckle-free imaging applications in bioimaging, environmental sensing, and flexible photonics.

Broadband nonlinear optical devices play a critical role in both classical and quantum optics. Here, we design and fabricate a 6.82-mm-long step-chirped periodically poled lithium niobate (CPPLN) waveguide on lithium niobate on insulator, which enables quasi-phase matching over a broad bandwidth for second-harmonic generation (SHG) and spontaneous parametric down-conversion (SPDC). The SHG achieves an average efficiency of 91%/W/cm² over the first-harmonic wavelength range of 1510 nm-1620 nm, paving the way for realizing SPDC across a wide range of pump wavelengths. For SPDC, by tuning the pump wavelength to 775 nm, 780 nm, and 785 nm, we achieve broadband photon-pair generation with a maximum full bandwidth and brightness up to 99 THz (846 nm) and 21 MHz/mW/nm, respectively. Our findings provide an efficient and experiment-friendly approach for generating broadband photon pairs, which holds significant promise for advancing applications in quantum metrology.

β-Ga₂O₃ is a promising ultrafast semiconductor scintillator, but its efficiency is hindered by low light yield and slow decay components. Here, high-quality β-Ga₂O₃:In single crystals were grown by the optical floating-zone method. In³⁺ incorporation narrows the bandgap (4.76 eV to 4.72 eV), redshifts photoluminescence, strengthens electron-phonon coupling, and accelerates recombination, with a 91 meV activation energy for blue-to-ultraviolet energy transfer. Compared to unintentionally doped (UID) β-Ga₂O₃, the β-Ga₂O₃:In bulk single crystal demonstrates enhanced light yields of (3348 ± 310) ph/MeV and (5664 ± 710) ph/5.5 MeV under 662 keV γ-ray and 5.5 MeV α-ray excitation, respectively, using Bi₄Ge₃O₁₂ (BGO) as the reference scintillator, together with a markedly faster nanosecond-scale decay. The improved performance is attributed to enhanced charge transport and carrier recombination, highlighting its potential for ultrafast radiation detection.

We propose a directional single-photon routing scheme based on waveguide quantum dynamics in the absence of a unidirectional waveguide or a circulator. The model consists of two 2-level atoms coupled to a one-dimensional waveguide. The interaction between the two atoms and the waveguide is controlled by dynamically tuning their coupling strengths, with which we have one of the atom acts as a reflector and enforce the directionality of the emission. However, we find that this mechanism prevents the emission of the reflector atom, which we address by introducing direct coupling between the two atoms tuned within a specific range. By carefully designing the functions of the couplings, we show that full directional emission of a single photon can be achieved. This finding offers a promising solution to the challenge of directionally routing microwave photons and provides crucial support for large-scale quantum information processing networks.

This paper describes dynamic spectro-ellipsometric interferometry (DSEI), which simultaneously measures ultra-thin film thickness and surface profile non-destructively. The proposed snapshot-scheme DSEI system can provide a cross-sectional image of a sub-100 nm non-uniform thin film object deposited on a warped substrate. This unique measurement capability is enabled by combining spectral interferometry (SI) with dynamic spectroscopic imaging ellipsometry (DSIE) employing a monolithic spectral polarizing interferometric module. In this study, we present a method for obtaining a real cross-sectional thickness line profile by compensating for the nonlinear phase term introduced by the ultra-thin film. To evaluate the effectiveness of the proposed compensation method and measurement reliability, a SiO₂/Si step-shape sample is measured and analyzed. We demonstrate that the proposed DSEI system can provide non-uniform thin film thickness and substrate warpage profiles with nanometer-level vertical resolution and a large field of view of 10 mm.

Snapshot compressive imaging has emerged as a powerful framework for acquiring high-dimensional data efficiently in a single exposure. Despite significant advances in spectral and temporal imaging, capturing a full-spectral video in a single snapshot remains challenging, as conventional approaches typically rely on multiple acquisitions to separately capture spectral and temporal dimensions. To address this limitation, we propose a single-shot compressed dynamic color-coded spectral video system that employs a windowed temporal encoding approach that improves pixel-intensity uniformity and dynamic range. The proposed compressive coding scheme synchronizes a liquid crystal tunable filter with a coded aperture device to encode and acquire the spectral video within a fixed exposure time. We develop and implement a plug-and-play alternating-direction multiplier method (PnP-ADMM) to efficiently recover the four-dimensional data cubes. Extensive simulations and proof-of-concept experiments demonstrate the effectiveness of the proposed system in capturing and reconstructing compressed spectral video efficiently.

Tip, tilt (TT) and focus modes cannot be directly measured from a laser guide star (LGS). For optical communications, residual TT errors in the pre-compensation of a ground-to-satellite optical communications link will lead to beam wander, resulting in signal fades at the receiver. We describe a method for retrieving the full TT solely with LGSs. This method uses trilateration, in which the differential arrival times of a pulsed LGS at ≥3 detectors at different locations around the laser transmitter are used to find the position of the LGS, and therefore the TT from only the uplink path of the LGS. We study the feasibility of this method and the technological developments needed to enable it. The simulation results show that, given a detector with a timing resolution t_res =10^-12 s, and ≥ 10⁸ photons s^-1 are collected at each detector, the tip and tilt modes can be measured to an accuracy of θ ≈ 0.45 arcsec. For pre-compensation to a low earth orbit (LEO) satellite, this can increase the power received at the satellite by over 2 dB when compared to pre-compensation using the TT from the downlink beam.

Single-photon avalanche diode (SPAD)-based light detection and ranging (LiDAR) introduces significant pileup errors at high echo photon flux due to the SPAD's dead time. To expand the application of single-photon LiDAR in the field of remote sensing, autonomous driving, etc., it is crucial to perform rapid and accurate ranging within an echo photon flux of a wide dynamic range. Emerging SPAD array detectors combined with specific photon detection modes attempt to strike a balance between photon detection efficiency and hardware resources, necessitating the development of appropriate dead time compensation methods. Therefore, we experimentally investigated a synchronous single-photon ranging LiDAR operating in a mode where up to two photons are detected per laser cycle, and proposed dead time compensation methods based on forward modeling of the photon detection process. The results show that, using a wide laser pulse of 3.5 ns, the compensated ranging error is less than 4.2 cm, while the uncompensated ranging error is as max as 17.96 cm. Our method provides a reference for dead time compensation in single-photon LiDAR that requires comprehensive consideration of detection efficiency and hardware resources.