The simplified mode method (SMM) is used for the optimization design of gratings with different functionalities, typically focusing on the intensity prediction of diffracted light without considering phase information. In this paper, the SMM is, for the first time, applied to phase calculations and a detailed derivation process is provided. Using this method, we designed a grating-based quarter-wave plate which accumulates pi/2 phase difference between TE and TM polarizations in both 0th and -1st diffraction orders under Littrow configuration. The results are compared with those obtained from the rigorous coupled- wave analysis method (RCWA), which are remarkably consistent, indicating that the SMM can be used for complex diffracted field calculations. The diffraction characteristic of the proposed grating-based quarter-wave plate is studied in detail, which will have application potentials in optical communication and other polarization modulation fields.

In this work, we propose and design a polarization beam splitter based on two-dimensional grating operating under the Littrow incidence condition. The transmission grating exhibits excellent polarization-splitting performance at the wavelength of 780 nm. For TE polarization, the -1st diffraction order achieves an efficiency of 96.63%, while for TM polarization, the 0th diffraction order efficiency reaches 97.89%. Further analysis indicates that the extinction ratio (ER) at the target wavelength can reach 26.8 dB. The proposed two-dimensional grating features a simple and fabrication-friendly structure, offering a new approach to high-efficiency polarization beam splitters. Such strong polarization selectivity that enables efficient separation of different polarization states with high energy allocation has not been reported with two-dimensional gratings, and will have potential applications in two-dimensional displacement measurement, polarization imaging, optical communications, and other fields.

The Talbot effect is a classic optical phenomenon in which periodic structures achieve self-imaging under monochromatic illumination. However, at fractional Talbot distances, the fringe contrast often degrades. To address this, this paper proposes and experimentally verifies an enhanced Talbot self-imaging method via linear holographic picometer comb gratings. The resulting stable pattern is referred to as the "Talbot comb". The linear holographic picometer comb grating is a 1D grating that is exposed twice to a picometer-differential grating field. This proposed structure achieves high-contrast coherent enhancement and stable Talbot patterns, compared with the traditional Talbot effect. Theoretical analysis shows that the structure effectively stretches the Talbot distance while enhancing its ability to sharpen spatial fringes over a long distance. Under 633 nm He-Ne laser illumination, clear, well-symmetric, and uniformly energy-distributed fringe patterns were obtained at several typical Talbot distances (including ZT/8, ZT/4, and ZT), achieving a Michelson contrast of up to 0.9534 at ZT/4. Moreover, high-fidelity output was maintained even after propagation over 6 m in free space, retaining a high contrast of 0.5753. The proposed configuration exhibits the unique characteristics of a high-contrast fringe and excellent stability, providing a new approach for a variety of applications such as high-resolution lithography, high-precision measurement, long-range interferometry, and wavefront control.

We presented analytical sine-square-addition equations for rectangle fused silica grating diffraction under second Bragg incidence with unequal refractive indices of three modes. We found that the efficiencies of diffraction orders can be described by the analytical equations consisting of the sine-square summation based on refractive indices differences of any two modes. We matched the coefficient values of analytical equations and compared with the results of Rigorous Coupled Wave Analysis. The results show that the differences between them are less than 3% for TE polarization, and less than 2% for TM polarization. For the first time, these analytical equations reflect the internal physical mechanism in general case where mode refractive indices are not equal, which will provide a powerful tool to obtain a new series of analytical equations for extending grating theory.

To achieve accurate and efficient measurement of large-scale, high-density grating periods, this study presents a prism-grating interferometer and an improved measurement algorithm. The high-density grating was fixed on a translation stage; a laser interferometer collected the stage's real-time displacement data, which were jointly processed with interference signals from the prism-grating interferometer to solve the grating period accurately. Based on a first-order Taylor expansion least-squares iterative mechanism, the improved algorithm optimizes nonlinear models via linearization, ensuring measurement accuracy while reducing single-iteration time to 62.9% of the traditional least-squares method and significantly cutting iteration counts. Experimental verification conducted on a reflective grating with a period of 833 nm and a clear aperture of 360×20mm shows that within the 360 mm measurement range (covering 360 groups of 1 mm intervals), the average grating period is 833.3367±15.7pm, and the average relative repeatability reaches 4.2 ppm. This combined scheme offers high precision and efficiency, providing a reliable technical solution for large-scale, high-density grating period measurement and adapting to diverse precision scenarios in semiconductor manufacturing and ultra-precision machining.

The development trend of microwave photonics systems is towards integration and miniaturization. In this work, we demonstrate a highly integrated narrowlinewidth microwave photonic emission front-end operating at 1550 nm band. The module simultaneously delivers high-performance characteristics, including a narrow laser linewidth, high output optical power, and broad modulation bandwidth, offering a compact and efficient alternative for microwave photonic transmitters. The monolithic integration of a thin-film lithium niobate (TFLN) microring resonator with an electro-optic modulator enables simultaneous external cavity linewidth narrowing and high-speed signal modulation on a single chip. Experimental results show a laser linewidth of 942.5 Hz, a maximum output power of 8.9 dBm, and a modulation bandwidth of 26.8 GHz. To validate its practicality, the module was employed in a frequency-modulated continuous-wave (FMCW) LiDAR system, achieving a ranging standard deviation of 1.2 cm. This integration significantly simplifies the architecture of photonic ranging systems while improving overall efficiency. The successful realization of this device provides a promising platform for future microwave photonic systems, with considerable application potential in areas such as remote sensing, LiDAR, and high-speed coherent optical communications.

This paper proposes a quarter-wave phase retarding device based on a one-dimensional (1D) reflective grating. This device achieves equal amplitudes and a pi/2 phase difference for transverse electric (TE) and transverse magnetic (TM) polarization components in both f1st orders. We utilize rigorous coupled wave analysis (RCWA) method and simulated annealing (SA) algorithm to obtain the optimized numerical results. Under optimal condition, the diffraction efficiencies of f1st orders for both TE and TM polarizations can reach 43%, and the phase difference is - 90.2 degrees. The influence of structural parameters on the performance of the grating is analyzed in detail. This grating integrates beam splitting and quarter wave plate functionalities, and can output two circularly polarized light beams at f1st orders. This compact and efficient design has significant potential for applications in optical communication systems and polarization-sensitive technologies.

Objective The fabrication of two-dimensional diffraction gratings-critical optical components in numerous optical systems-is inherently complex. However, surface defects introduced during each fabrication stage can significantly degrade grating performance. These imperfections are unavoidable, and their quantitative evaluation remains challenging, as conventional detection methods often fail to provide accurate assessments. Consequently, there is an urgent need for an efficient, non-contact characterization technique capable of quantifying the effects of grating defects and morphological deviations on diffraction efficiency. Methods To address the aforementioned issues, this paper presents the development of a diffraction efficiency detection device for Littrow reflective 2D metal gratings, designed to measure diffraction efficiency under Littrow configuration conditions. Based on experimental data obtained from this device, a grey wolf optimized particle swarm optimization (GWPSO) algorithm is integrated with a backpropagation (BP) neural network model to efficiently predict the diffraction efficiency of gratings containing surface defects, achieving a mean absolute percentage error (MAPE) below 3.416%. Due to the high sensitivity of diffraction efficiency to defects and morphology, the study predicts the minimum diffraction efficiency within defective regions based on macroscopic defect characterization, and a dataset is constructed for model training and validation. By employing the GWPSO-BP neural network model, with adaptive weights determined via the grey wolf optimizer (GWO), the approach enables accurate and efficient prediction of diffraction efficiency at defect sites on the grating surface. This methodology facilitates rapid assessment of grating quality, providing a novel technological solution for industrial inspection applications. Results and Discussions As a high-precision optical component, the fabrication of two-dimensional gratings must satisfy stringent optical performance requirements. The distribution density and geometric dimensions of surface defects are governed by process parameters such as coating uniformity and etching precision. To quantify the impact of different defect types on optical performance, this study constructs a weighted dataset based on the statistical frequency of grating manufacturing defects observed in real-world production environments. Predictive modeling is performed using three neural network architectures: GWPSO-BP, PSO-BP, and conventional BP. The predicted diffraction efficiency values in the 0 degrees direction and the 90 degrees direction are comparatively analyzed. Using a diffraction efficiency threshold of 65%, the GWPSO-BP neural network demonstrates superior predictive accuracy, effectively identifying and filtering out defect configurations that fail to meet performance criteria. Conclusions A diffraction efficiency detection experimental setup was constructed, enabling automated scanning of the grating under test and yielding its spatial diffraction efficiency distribution map, thereby further validating the effectiveness of the neural network model. Multiple training experiments conducted under identical dataset conditions demonstrate that the GWPSO-BP neural network model exhibits superior stability and reliability in predicting the diffraction efficiency associated with surface defects on gratings, compared to both the PSO-BP and BP neural network models. Notably, the GWPSO-BP model is less sensitive to initial parameter selection and achieves rapid convergence toward the global optimum. Owing to these performance advantages, the model is well-suited for analyzing various types of three-dimensional surface defects on gratings. Therefore, the GWPSO-BP neural network model provides a robust scientific foundation for theoretical research on large-size grating manufacturing and for optimizing engineering experimental processes, holding significant application potential in enhancing the dimensional accuracy and optical performance of two-dimensional gratings.

Immersion gratings, a combination of reflective grating layers and a prism, enable spectrometers to achieve high dispersion and throughput. However, existing immersion gratings still face limitations in terms of operating bandwidth and preparation costs. Here, we propose a broadband internally reflective super-wavelength immersion grating (SWIG) with a deep-layer structure, which operates over a 400-1000 nm wavelength range. The SWIG shows several advantages throughout the operating band: first, unpolarized efficiencies exceeding 44.7% (up to 85%); second, polarization sensitivity suppression within 9%; third, incidence angle tolerance greater than 20 degrees; and fourth, good dispersion uniformity. In addition, we demonstrate in detail a low-cost fabrication scheme for SWIGs using imprint replication techniques. Optical measurements of the SWIG samples show good agreement with theoretical calculations, proving the feasibility of the fabrication scheme. This work provides strong support for promoting the wide application of high-performance and low-cost grating components in hyperspectral cameras.

In this work, we propose a two-dimensional grating under Littrow configuration, featuring high diffraction efficiency (DE), polarization insensitivity, a broad wavelength band, and large incident angle tolerance. The grating has a simple structure consisting of dielectric nano-cylinder arrays and a silver (Ag) reflective layer, with its geometric parameters optimized using rigorous coupled-wave analysis method. Over the incident wavelength range of 1016 nm to 1087 nm, the diffraction efficiencies of the (-1, 0) order for both transverse electric and transverse magnetic polarizations exceed 90%. Specifically, at a wavelength of 1064 nm, for the incident angle range from 17.32 degrees to 37.52 degrees, the DE of the (-1, 0) order exceeds 90%. Moreover, an analysis of the grating fabrication tolerances confirms its manufacturing feasibility and application potential in grating interferometers and spectral beam combining systems.

Digital holographic microscopy (DHM) has shown great potential in biomedical imaging and quantitative phase analysis due to its wide field of view, non-contact operation, and high measurement sensitivity. However, in practical DHM systems, the quality of the recorded holograms is not only limited by the optical imaging conditions but also constrained by the finite pixel pitch and pixel integration effect of the image sensor. These factors may reduce the spatial resolution of holographic fringe images, making it difficult to capture high-frequency information from the sample and thereby affecting the accuracy of phase reconstruction. To address this issue, we propose a multi-stage perceptual super-resolution network with directional variance attention for hologram enhancement under digital sampling constraints. The proposed method aims to improve the quality of holographic fringe patterns from low-resolution holograms, thereby enhancing the accuracy of phase reconstruction. Experimental results demonstrate that the proposed algorithm can effectively improve the quality of holographic fringe patterns in holographic imaging systems without requiring any advanced physical hardware and achieve more accurate phase reconstruction than competing methods. These results indicate that the proposed framework serves as an effective computational enhancement tool for improving phase reconstruction quality in DHM.

All-dielectric metasurface (ADM) absorbers driven by quasi-bound states in the continuum (BIC) are critical for high-performance optoelectronic devices due to their ability to offer high Q-factor absorption. However, these all- dielectric metasurfaces usually require the aid of degenerate critical coupling schemes or back-metal reflective layers to achieve high absorption, which often suffers from limitations such as sensitive geometrical parameters, ohmic losses, and low Q-factors. This work presents an ADM for high-Q near-perfect light absorption, which consists of double Si nanorods and SiO2/Ta2O5 multilayers. By breaking the symmetry of the length of the Si nanorods, this ADM can excite a single quasi-BIC resonance corresponding to the electric dipole. Without introducing a metal layer, we realize the highly asymmetric coupling of quasi-BIC by only 6 layers of SiO2/Ta2O5 films. It is theoretically and numerically demonstrated that the quasi-BIC has more than 98% absorption at 943.68 nm and a Q-factor as high as 2842. In addition, the ADM exhibits excellent tolerance to geometrical parameters while ensuring high absorption performance. Our results provide new ideas for the design of all-dielectric perfect absorbers with large tolerances and high Q-factors and also open up new possibilities for optical filtering, optical sensing, and photon detection devices. (c) 2024 Optica Publishing Group. All rights, including for text and data mining (TDM), Artificial Intelligence (AI) training, and similar technologies, are reserved.