Laser active imaging technology has important practical value and broad application prospects in military fields such as target detection, radar reconnaissance, and precise guidance. However, factors such as uneven laser illuminance, atmospheric backscatter, and the imaging system itself will introduce noise, which will affect the quality of the laser active imaging image, resulting in image contrast decline and blurring image edges and details. Therefore, an image denoising algorithm based on homomorphic filtering and total variation cascade is proposed in this paper, which strives to reduce the noise while retaining the edge features of the image to the maximum extent. Firstly, the image type is determined according to the characteristics of the laser image, and then the speckle noise in the low-frequency region is suppressed by adaptive homomorphic filtering. Finally, the image denoising method of minimizing the total variation is adopted for the impulse noise and Gaussian noise. Experimental results show that compared with separate homomorphic filtering, total variation filtering, and median filtering, the proposed algorithm significantly improves the contrast, retains edge details, achieves the expected effect. It can better adjust the image brightness and is beneficial for subsequent processing.

Aiming at the application of laser active imaging detection technology, this paper studied the beam homogenization system of a semiconductor laser based on a homogenizing pipe. Firstly, the principle of the homogenizing pipe was introduced. Secondly, the homogenization effect, which was influenced by several geometric parameters (aperture size, length, and taper) of the homogenizing pipe using the optical design software, was simulated for the fiber-coupled semiconductor laser. Finally, according to the simulated results, a laser illumination system composed of a fiber-coupled semiconductor laser, a homogenizing pipe, and an aspheric lens was designed, which can obtain a rectangular uniform light spot in a long distance. The effectiveness of the illumination system was verified by simulation and experiment, respectively. Simulation results suggested that the uniformity of the spot at a distance of 20 m was 85.6%, while divergence angle was 10 mrad. The uniformity of the spot at a distance of 120 m was 91.5%, while divergence angle was 10 mrad. Experimental results showed that the uniformity of the spot at a distance of 20 m was 87.7%, while divergence angle was 13 mrad. The uniformity of the spot at a distance of 120 m was 93.3%, while divergence angle was 15 mrad. The laser illumination system designed in this paper was simple and easy to assemble, and has strong practicability. The results in this paper have certain reference value and guiding significance for the homogenization design of semiconductor lasers.

With the flourish of deep learning, transformer models have achieved remarkable performance in dealing with many computer vision tasks. However, their applications in infrared small target detection is limited due to two factors: (1) the high computational complexity of the conventional transformer models reduces the efficiency of detection; (2) the small target is easily left out in the visual environment with complex backgrounds. To deal with the issues, we propose a lightweight infrared small target detection method based on a linear transformer named IstdVit, which achieves high accuracy and low delay in infrared small target detection. The model consists of two parts: a multi-scale linear transformer and a lightweight dual feature pyramid network. It combines the strengths of a lightweight feature extraction module and the multi-head attention mechanism, effectively representing the small targets in the complex background at an economical computational cost. Additionally, it incorporates rotational position encoding to improve understanding of spatial context. The experiments conducted on the NUDT-SIRST and IRSTD-1K datasets indicate that IstdVit achieves a good balance between speed and accuracy, outperforming other state-of-the-art methods while maintaining a low number of parameters.

As a novel solid-state active steering beam chip, the integrated optical phased array (OPA) has been widely utilized in light detection and ranging (LiDAR), free-space optical communication, and biological imaging. In this study, we design and experimentally demonstrate a 16-channel OPA featuring a Taylor amplitude distribution to achieve an ultralow sidelobe level, implemented using a cascaded array of arbitrary ratio power splitters (ARPSs) on a silicon nitride (SiN) strip-loaded thin-film lithium niobate (TFLN) platform. The ARPSs are introduced to manipulate the amplitude distribution among the channel array, thereby suppressing sidelobe levels. The proposed TFLN-SiN OPA, utilizing a Taylor amplitude distribution, achieves a peak sidelobe level (PSLL) of 20.3 dB at 0°, an average sidelobe suppression ratio (SLSR) of 15.8 dB across the entire field of view (FOV), a two-dimensional beam steering capability with a FOV of 62° × 7.6°, and a beam divergence of 3.2° × 1.4°. This work highlights the significant advantages of the TFLN-SiN hybrid integrated OPA with a Taylor amplitude distribution, including low sidelobe levels, low power consumption, and high-speed beam steering.

Microelectromechanical system (MEMS) grating modulators enable versatile beam steering functions through the electrostatic actuation of movable ribbons. These modulators operate at ultrahigh frequencies in the hundred kHz range, and their micromirror-free configuration simplifies the fabrication process and reduces costs compared to micromirror-based modulators. However, these modulators are limited in their optical efficiency and aperture. Here, we present a MEMS grating modulator with a notably extendable aperture and a high optical efficiency that benefits from the adoption of a tunable sinusoidal grating. Instead of end-constrained movable ribbons, we constrain the MEMS grating modulator through broadside-constrained continuous ribbons. The end-free grating enables improved scalability along the ribbons, and the continuous sinusoidal surface of the grating allows an increased fill factor. As an example, we experimentally demonstrate a MEMS grating modulator with a large-scale aperture of 30 × 30 mm and an optical efficiency of up to 90%. The modulation depth enables intensity modulation across a broad wavelength range from 635 to 1700 nm. The experimental results demonstrate that the reported modulator has a mechanical settling time of 1.1 μs and an extinction ratio of over 20 dB. Furthermore, it offers a dynamic modulation contrast of over 95% within a 250 kHz operating frequency and achieves full modulation within a field of view (FOV) of ±30°. The reported MEMS grating modulator holds promise for application in high-speed light attenuation and modulating retroreflector free-space optical (MRR-FSO) communication systems. Our device also paves new ways for future high-speed, energy-efficient, and cost-effective communication networks.

The free space optical communication technology based on a cat-eye modulating retro-reflector has great advantages as compared to the classical free space optical communication technology. In this paper, the principle of free space optical communication technology based on modulating retro-reflector is described and its main construction is introduced. Then, the research status of the technology in modulator characteristics, cat-eye optical systems and technology used in foreign countries is reviewed, and the technology development in China is introduced briefly. The key points of the technology are analyzed. Finally, the application trends and developing prospects are viewed.