Jiacheng Zhu

The arrayed waveguide grating (AWG) is a core dispersive component in on-chip spectroscopic detection systems, but its polarization sensitivity can degrade spectral calibration and reconstruction accuracy. In this Letter, we propose a synchronous phase-matching method for polarization-insensitive AWG design, which is related to the propagation phases at both the center wavelength and the whole range of the working wavelength. Two different cross-sections of double-layer silicon nitride (Si ₃ N ₄ ) waveguides were designed to achieve polarization-insensitive outputs for a coarse and a fine AWG, respectively. Numerical simulations demonstrate that polarization-dependent wavelength shift (PDWS) below 0.165 nm with polarization-dependent loss (PDL) less than 0.214 dB has been obtained for TE and TM polarizations on a nine-channel AWG under a spectral channel spacing of 2.74 nm. Furthermore, a PDWS below 17.1 pm with a PDL less than 0.169 dB has been obtained for a seven-channel fine AWG with a channel spacing of 0.12 nm.

High-throughput microscopic imaging is essential for applications such as gene sequencing and semiconductor inspection. The requirements for high numerical aperture (NA) and ultraviolet broadband performance introduce substantial challenges in controlling spherical aberration and chromatic aberration. To address these challenges, this study proposes and fabricates a single-material high-throughput catadioptric objective that offers high NA, a wide field of view (FOV), and a wide wavelength range. Through ray tracing and numerical analysis, conditions for aberration correction and apochromatism are derived, and a computational model for the initial structure of this catadioptric objective is established. Based on this model, a broadband objective (0.360–0.600 µm, 0.9 NA, 5.0 mm focal length, and 1.0 mm FOV) is designed, and only fused silica is used. An objective prototype is developed and tested. The results show that the root mean square (RMS) of the wavefront error is below 0.068 λ at 0.365 µm test wavelength across the whole FOV. The objective achieves a high resolution of 3300 lp/mm, field curvature less than 150 nm, and relative distortion below 0.08%. Chromatic aberration is effectively controlled, and imaging quality approaches the diffraction limit. These results confirm the validity of the proposed aberration correction conditions and the initial-structure model. This work establishes a systematic technical approach for developing high-NA, broadband, and non-immersion microscope objectives.

High-throughput microscopic objectives require simultaneously a high numerical aperture (NA) and a large field of view (FOV), posing significant challenges in aberration correction. This paper presents a coaxial four-mirror all-reflective microscope objective that achieves a high NA, a large FOV, and a long working distance (WD). Based on ray-tracing analysis and analytical derivation, the geometric constraints, flat-field condition, and spherical aberration correction criteria are established, and a method for determining the initial structure is developed. The designed objective operates over a wavelength range of 0.260–0.450 µm, achieving an NA of 0.85, an FOV of 1 mm, and a WD of 2 mm. At the primary wavelength of 0.260 µm, the RMS wavefront error over the full FOV is below 0.045 λ , the field curvature is below 200 nm, and the relative distortion is less than 0.15%, demonstrating near-diffraction-limited imaging performance. Furthermore, simulations using black-and-white line-pair targets with different obscuration ratios reveal that central obscuration has a limited influence on resolution. This work provides a practical design approach for high-NA, large-FOV, and long-WD all-reflective microscope objectives.

This paper presents a UAV-based hyperspectral imaging system that can simultaneously capture a frame image and three hyperspectral images, providing an efficient and precise approach to hyperspectral data acquisition. By utilizing the frame image to preserve relative pose information across consecutive frames, the system simplifies geometric correction and eliminates the need for high-precision directional geo-referencing devices, ground control points, or gimbal systems. At the same time, the system employs a multi-slit time-sharing sampling strategy to enable repeated spectral measurements while reducing sampling loss and maintaining data authenticity. A matched geometric correction algorithm, which combines single-slit image mosaicking and multi-slit fusion, is proposed to ensure precise spatial alignment even under challenging conditions. Furthermore, a robust radiometric calibration framework, incorporating cross-calibration and real-time corrections via a downwelling radiance measurement device, mitigates errors caused by variable solar illumination. These features enable reliable reflectance measurements and high-quality hyperspectral images. A rigorous evaluation framework, including both ground-based and UAV-based experiments, is conducted to comprehensively assess system performance. The results demonstrate superior sampling efficiency, improved geometric alignment accuracy, and greater radiometric consistency compared to conventional methods. The proposed system offers a cost-effective, lightweight, and versatile solution for hyperspectral imaging applications in agriculture, environmental monitoring, target exploration, and other fields, effectively addressing key limitations of existing technologies.

In this paper, the principles of spectral data cube reconstruction based on an integral field snapshot imaging spectrometer and GPU-based acceleration are presented. The primary focus is on improving the reconstruction algorithm using GPU parallel computing technology to enhance the computational efficiency for real-time applications. And the computational tasks of the spectral reconstruction algorithm were transferred to the GPU through program parallelization and memory optimization, resulting in significant performance gains. Experimental results indicate that the average processing time of the GPU-based parallel algorithm is approximately 29.43 ms, showing a substantial acceleration ratio of about 14.27 compared to the traditional CPU serial algorithm with an average processing time of around 420.46 ms. The study aims to refine the GPU parallelization algorithm for continued improvement in computational efficiency and overall performance. The anticipated applications of this research include providing crucial technical support for the perception and monitoring of crop growth traits in agricultural production, contributing to the modernization and advancement of intelligence in the field.

The increasing demand for accurate imaging spectral information in remote sensing detection has driven the development of hyperspectral remote sensing instruments towards a larger view field and higher resolution. As the core component of the spectrometer slit, the designed length reaches tens of millimeters while the precision maintained within the μm level. Such precision requirements pose challenges to traditional machining and laser processing. In this paper, a high-precision air slit was created with a large aspect ratio through MEMS technology on SOI silicon wafers. In particular, a MEMS slit was prepared with a width of 15 μm and an aspect ratio exceeding 4000:1, and a spectral spectroscopy system was created and tested with a Hg-Cd light source. As a result, the spectral spectrum was linear within the visible range, and a spectral resolution of less than 1 nm was obtained. The standard deviation of resolution is only one-fourth of that is seen in machined slits across various view fields. This research provided a reliable and novel manufacturing technique for high-precision air slits, offering technical assistance in developing high-resolution wide-coverage imaging spectrometers.

The optical system of an imaging spectrometer working on a geostationary earth orbit (GEO) covering a full optical spectrum of 0.3–12.5 μm is analyzed and designed. It enables a ground coverage of 400 × 400 km by internal scanning and achieves a high spatial resolution of 25 m. The full spectrum is divided into five sub-bands, and each band adopts four spectrometers to splice in the field of view to achieve the ultra-long slit required by the wide swath. The total length of the slit is up to 241.3 mm. This paper focuses on compact spectrometers with long slits that can meet the splicing requirements and points out that low spectral distortions, low stray light, high signal-to-noise ratio, and uniform spectral response are necessary for high-fidelity performance. The Offner and Wynne–Offner high-fidelity spectrometers based on convex blazed gratings are designed, and prototypes of each band are developed as well. The properties of long slits and convex blazed gratings are presented. The maximum length of a single slit is 61.44 mm. The groove density of gratings for five bands ranges from 8.8 lp/mm to 312.1 lp/mm, and the peak efficiency is up to 86.4%. The alignment and test of the spectrometers are introduced. Results show that the developed spectrometers have high fidelity and fulfill all requirements.