Reliable femtosecond laser bonding of glass and metal is urgently required for extreme-service optical components, yet severe thermal expansion mismatch and roughness-induced interfacial air gaps severely degrade joint performance. This work systematically investigates plasma behaviors and welding property control in metal-glass laser welding under non-optical-contact conditions based on the regulation of metal surface roughness. Four gradient-roughness specimens are prepared via grinding and opal polishing suspension (OPS) polishing, with Sa ranging from 439.33 to 13.42 nm. High-speed imaging verifies that microgrooves on ground steel trigger lateral plasma escape and insufficient interfacial fusion, yielding a shear strength below 0.56 MPa. By contrast, OPS nanopolishing eliminates interfacial gaps to realize optical contact, confining plasma vertically and boosting joint strength to 16.73 MPa. Scanning electron microscope (SEM) characterizations confirm wider Si-Fe-O interdiffusion zones and cohesive fracture inside fused silica for polished samples, where longitudinally constrained high-density plasma provides persistent vertical action to drive sufficient bidirectional melt interpenetration at the interface. This study reveals the full correlation among surface topography, plasma dynamics, elemental diffusion, and mechanical performance, offering a pretreatment strategy for high-strength transparent-metal joints.

This paper presents a transformation-optics framework for comparing four-direction, twisted, radial, and circular-core field concentrators using a common finite-difference frequency-domain (FDFD) model. The mappings are evaluated in terms of field enhancement, concentration ratio, field uniformity, material complexity, and attainable compression. At a common compression of ΓA,ref≈2.56, the four-direction mapping gives the highest ηH=1.6635 and CH=5.3578% but requires the highest tensor magnitude. The radial mapping gives the lowest UH=0.0213 and max|μij|=2.2527 and is selected for its best overall balance. Robustness analysis shows that material loss mainly reduces concentration performance, coarse discretization degrades uniformity, and geometric variations affect both concentration and field distribution. This framework provides a consistent basis for selecting concentrator mappings for different design objectives.

In this work, we propose an eye-shaped microring resonator (E-SMRR)-based photonic biosensor on a silicon-on-insulator (SOI) substrate. The device is modeled using variational finite-difference time-domain (Var FDTD) simulations. Furthermore, the Mason's gain rule is employed to analytically determine the optical transfer function for the drop port of the E-SMRR system. The proposed E-SMRR biosensor offers a bulk sensitivity of 460.829 nm/RIU, an FSR of 27.535 nm, a quality factor of 1070.677, and a figure of merit equal to 341.308. Additionally, the device has been evaluated for its ability to detect the anemia by assessment of varying hemoglobin concentrations, demonstrating a significant shift in resonant wavelength with a high sensitivity of 7.378×10[-2]nm/gL[-1] and an intrinsic limit of detection (iLOD) of 4.325×10[-3]RIU. Thus, the design of the proposed E-SMRR biosensor on the SOI substrate is promising for the development of futuristic on-chip optical biosensors.

The design of a dual-port antenna with decreased RCS and circular polarization is presented in this study. A cylindrical silicon dielectric resonator is excited via an asymmetrical plus-shaped aperture-coupling device to produce circularly polarized radiation (3.45-3.85 THz). An EBG metasurface integrated on the underside of the substrate provides two significant advantages. First, it effectively reduces the monostatic radar cross-section (RCS), achieving values below -25dBsm. Second, it substantially improves the isolation between antenna ports, resulting in an isolation level that exceeds 25 dB. The suggested antenna works well in the 3.25-4.0 THz frequency band, according to CST/HFSS EM simulation. Throughout the operational band, the antenna exhibits steady radiation performance with a broadside peak realized gain of around 7.0 dBi. The suggested radiator is a feasible choice for THz radar and wireless transmission due to its directed broadside radiation characteristics and superior diversity performance.

Accurate two-dimensional image reconstruction in compact resonant electromagnetic microelectromechanical system (MEMS) scanning confocal microscopy depends on segmenting a continuously acquired one-dimensional detector stream into image lines and estimating the scan parameters. Mismatch between nominal drive timing and actual fast-axis motion can cause line dislocation and geometric distortion, whereas additional sensing hardware, external synchronization, or image-domain estimation may increase instrument size and implementation complexity. We present a method that obtains the required line-data information directly from the fast-axis back electromotive force (back-EMF). Under constant-current H-bridge drive, the fast-axis coil-terminal voltage was acquired by pseudo-differential sampling and processed to extract the back-EMF waveform. From the extracted waveform, a field-programmable gate array (FPGA) generated center-aligned line data, the line-scan period, and the optical scan amplitude in real time. The host computer used these outputs to perform scan-parameter-based two-dimensional image reconstruction. For a standard square-grid target, the line-offset standard deviation decreased from 4.397 to 0.618 pixels, a reduction of approximately 86%. The mean grid-cell aspect ratio improved from 1.1282 to 1.0074, closer to the ideal value of unity, while its mean absolute error (MAE) relative to unity decreased from 0.1282 to 0.0082, a reduction of approximately 93.6%. Imaging of a plant leaf showed improved interline continuity and local morphological consistency in complex cellular structures. The current system displayed 1000×1000-pixel images in real time at 30 fps, demonstrating the feasibility of this route for acquiring back-EMF-derived line-data information and applying it to image correction in a compact high-frame-rate imaging configuration.

Imaging detectors under intense light suffer from local saturation and reduced visibility. We propose a co-design methodology for active front-end interference suppression. This framework formulates the coupled physical constraints of beam separation, conjugate transfer, and non-rotationally symmetric aberration correction inherent to tilted modulation planes. By integrating digital micromirror device (DMD) spatial modulation with a two-stage off-axis freeform four-mirror architecture, we reveal the joint governing mechanisms of local masking, plane orientation, and aberration correction. Simulations over 0.35-1.0 µm yield a full-field MTF above 0.725 at 50 lp/mm and a maximum distortion of 2.29%. Independent validation of the second-order DMD-to-detector mapping yields residuals of 0.407 µm RMS and 0.763 µm maximum. An ideal 20×20µm OFF-state mask rejects 89.07% of selected interference energy, corresponding to 9.61 dB suppression and demonstrating system-level feasibility.

Underwater wireless optical communication (UWOC) can effectively provide high-bandwidth wireless connectivity for underwater scenarios; however, its performance is worsened by multiplicative fading and additive system noise. Traditional denoising methods for UWOC typically rely on handcrafted rules and empirical parameter selection, with limitations to the complex and variable underwater optical channel. Here, we propose a three-branch physics-informed network (TBPIN) to suppress the multiplicative noise of UWOC effectively. By embedding the UWOC channel equation into a composite loss function, the proposed network explicitly decouples the distorted received signal into three physically constrained components. This network is verified both on simulated and experimental UWOC datasets. The results show that TBPIN achieves advanced performance in signal-to-noise ratio gain and mean squared error reduction compared with traditional and other deep learning methods. This method provides an accurate and interpretable solution for multiplicative noise suppression in UWOC.

To address challenges such as weak pipeline leakage signal characteristics and the difficulty of leakage identification, this study explores the application of distributed acoustic sensing (DAS) technology in pipeline leakage monitoring. Specifically, leakage signal denoising, condition identification, and spatial localization were investigated, and an integrated pipeline leakage monitoring method comprising signal enhancement, condition identification, and spatial localization was developed. First, variational mode decomposition (VMD)-based denoising was combined with wavelet decomposition (WD)-based mode screening to suppress background noise. Second, a backpropagation (BP) neural network optimized by the sparrow search algorithm (SSA) was developed for leakage identification. Finally, accurate leakage localization was achieved using the high-to-low-frequency energy ratio as the primary criterion. Experimental results showed that with the leak location fixed and tested under three different flow-rate conditions, the maximum absolute positioning error was estimated at 0.4 m, corresponding to a positioning accuracy of 98.1%. Under the experimental setup and test conditions described in this paper, the proposed method demonstrates effective leak localization capabilities; it successfully enhances leak characteristics, improves the accuracy and stability of identifying various leak states, and achieves precise leak point localization, thereby offering significant value for engineering applications.

Conventional monocular polarimetric imaging in turbid underwater environments suffers from severe particulate interference, leading to unreliable polarimetric parameter estimation and loss of image detail. This paper proposes AM-PDC, a multi-view polarimetric restoration framework based on sequential 5×5 spatial sampling using a single translated polarimetric camera. Feature alignment and pixel-level median fusion suppress stochastic noise, while multi-view variance characteristics enable automatic background extraction for estimating the background polarization direction. Backscatter suppression is performed through orthogonal polarization decomposition guided by the estimated background polarization direction, followed by contrast-truncated histogram stretching (CTHS) and contrast-limited adaptive histogram equalization (CLAHE) applied to the luminance channel. Experimental results demonstrate that AM-PDC recovers structural and textural information across varying turbidity levels and achieves improved structural preservation, visual quality, and detail enhancement under the evaluated medium-to-high turbidity conditions.

In this work, we confirm the polarization-independent and enhanced GH shifts can be achieved in a monolayer-graphene-based disordered and defective photonic crystal at the working wavelength for both transverse electric and magnetic polarized waves. Additionally, the changed chemical potential of monolayer graphene in a monolayer-graphene-based disordered and defective photonic crystal heterostructure yields polarization-independent and controllable GH peak values. Notably, the changed thickness of the defect layer can engineer both the values and positions of the GH peaks. This strategy offers a fresh platform for realizing the polarization-independent GH shifts, with potential applications for polarization-independent photonic devices, such as optical sensors and switches.

To enhance the temperature uniformity and stability of the constant-temperature cavity during the static calibration of ultra-high-temperature sensors, this paper proposes a structural design method for a dual-layer temperature-controlled laser thermostatic chamber (LTC) based on laser heating. Using ZEMAX software, laser beam shaping is simulated to achieve energy redistribution from a Gaussian spot to a square uniform spot, thereby improving the spatial distribution characteristics of laser energy at the source. Furthermore, a heat conduction model of the LTC is established using COMSOL Multiphysics to systematically analyze the effects of spot morphology, laser irradiation mode, and thermal insulation structure on the temperature field distribution within the LTC. Simulation results indicate that double-sided symmetric square uniform spot irradiation combined with a graphite felt insulation structure can effectively suppress temperature gradients, reducing the temperature non-uniformity of the LTC to approximately 4.25%. On this basis, an experimental platform for an ultra-high-temperature laser heating static calibration system is constructed. Experimental results show that, under a laser power of 1000 W, the proposed structure achieves a minimum temperature non-uniformity of 4.89% and maintains a steady-state fluctuation of ±5.5[∘]C at 2100°C. The results demonstrate that the synergistic optimization of beam shaping and the dual-layer temperature control structure can significantly improve the temperature field distribution within the LTC, providing reliable technical support and a theoretical basis for the high-precision static calibration of ultra-high-temperature sensors.

To address sub-meter space debris monitoring demands in the geosynchronous belt, this paper proposes a wide-field unobscured off-axis freeform four-mirror reflective optical system. A parametric mathematical model derived from the detection signal-to-noise ratio mechanism is established to correlate the threshold entrance pupil diameter, observation phase angle, focal length, and detectable debris radius, supporting rational matching and selection of core specifications. A joint merit function is constructed by combining an independent obscuration penalty function and low-order distortion-free aberration terms derived under the pupil-field four-dimensional ray propagation framework, enabling rapid initial configuration screening and efficient system design. The system features a 400-700 nm band, a 300 mm aperture, a 620 mm focal length, and a 15[∘]×12[∘] FoV, achieving <5% distortion and >95% encircled energy in 20µm×20µm binned four-pixel areas. Modeling confirms its capability to detect 0.5 m radius debris in dawn-dusk sun-synchronous orbits. This work meets the detection requirements and provides a reference for similar developments.

This study proposes an all-dielectric near-infrared metasurface composed of a quartz substrate and dual silicon square cavities. By introducing an incident beam tilt (out-of-plane symmetry breaking) and rotating the right cavity (in-plane geometric asymmetry), precise dual regulation of quasi-bound states in the continuum (Q-BICs) is achieved. Under normal incidence, the symmetric structure supports a symmetry-protected BIC. At a 2° incident angle, out-of-plane symmetry breaking couples the dark BIC to radiation channels, exciting a high-Q resonance. Benefiting from C4 spatial symmetry, the metasurface is polarization-independent, and its resonance wavelength symmetrically blue-shifts then red-shifts as the cavity rotates from 0° to 90°. At 2° incidence and 0° rotation, the Q factor reaches 13,343.11, strictly satisfying an inverse-square dependence on the asymmetry parameter. This work provides a novel approach, to our knowledge, for manipulating high-Q resonances and lays a theoretical foundation for dynamically tunable, polarization-independent near-infrared micro-nano optical devices.

Spectral gain characterization of erbium-doped fiber amplifiers (EDFAs) routinely uses broadband ASE loading, which saturates the amplifier but presents a continuous spectrum, not a defined channel set. A saturation tone with a weak probe offers a defined-load alternative, yet its fidelity to a multi-channel load, and its dependence on the pumping architecture, remain experimentally unestablished. We compare tone-based and nine-channel WDM gain spectra for a C-band EDFA across six pumping configurations at -10 and 0 dBm. The closest agreement reaches 0.23 dB RMSE; the optimal tone is set by the pumping configuration but independent of pump direction under 980 nm. Saturation removes the correctable level offset, leaving a shape-limited residual.

Bound states in the continuum (BICs) have attracted extensive attention in nanophotonics and sensing because they support exceptional optical confinement and ultrahigh quality factors. Dielectric BIC platforms based on high-refractive-index materials are particularly appealing because of their low radiative loss, strong field localization, and rich multipolar responses. Here, we propose a symmetry-protected quasi-BIC metasurface based on the anisotropic dielectric material α-MoO3 for mid-infrared (mid-IR) sensing. By introducing an in-plane symmetry-breaking perturbation through the displacement of the central cylinder within the unit cell, an anisotropic quasi-BIC resonance is excited in the mid-IR regime. Near-field distributions and multipole decomposition reveal that the resonance originates from the hybrid contribution of the electric quadrupole (EQ) and magnetic dipole (MD) modes. The optimized device exhibits a high sensitivity of up to 6000 nm/RIU and a Q factor of 553. These results deepen our understanding of anisotropic BICs and provide theoretical guidance for the design of compact photonic devices with enhanced sensing functionality.