Infrared polarization detection technology, beyond mere intensity detection, enables the extraction of the polarization characteristics of infrared radiation from targets. These characteristics reveal the material properties, surface morphology, and physicochemical traits of the target and its surroundings, making this technology essential for military, civilian, and medical applications. In particular, focal plane array-based infrared polarization detectors have garnered significant attention from researchers owing to their high level of integration and real-time imaging capabilities. However, as the pixel size of infrared focal plane arrays continues to shrink, approaching the scale of the characteristic wavelength, there is an increasing demand for efficient polarization decoupling at the pixel level using microstructures. Furthermore, polarization structures must be vertically integrated at the pixel level with the pixel arrays to ensure accurate and efficient transmission of polarization components to the absorption region. These requirements place stringent demands on the design and integration of polarization micro- and nano-structures.

It is a significant challenge for traditional imaging systems to capture the polarization information of a target’s light field, which typically requires bulky optical components and time-domain multiplexing. Conventional polarization-detection technologies, such as time-division, amplitude-division, and aperture-division schemes, suffer from drawbacks such as large size, system complexity, and low stability. In response to the demand for lightweight, highly integrated, stable, and real-time full-polarization infrared detection, pixel-level polarization-sensitive structures in infrared focal-plane array polarization detectors have become a key development direction for next-generation infrared detection technologies. Emerging technologies have driven significant advances in polarization filter devices with innovations such as metal wire grids, photonic crystals, and metasurfaces, enabled by nanofabrication technologies. These micro- and nano- structures, with immense potential for optical field manipulation, have become mainstream technologies in polarization detection devices. Currently, relatively mature polarization-integrated focal-plane arrays typically rely on subwavelength metal wire grids to achieve strong polarization sensitivity. These grids offer advantages such as high polarization selectivity, customizable broad operational bandwidth, miniaturization, high stability, and ease of integration. However, when the operational wavelength extends into the infrared range, the extinction ratio of the integrated polarization devices declines significantly compared to that of standalone wire grid arrays. Several researchers have analyzed the impact of key parameters such as pixel size, pixel pitch, distance between the polarizer and the photosensitive area, and alignment errors in integration on the polarization extinction ratio. All conclusions indicate that optical crosstalk between adjacent pixels becomes particularly severe in the infrared wavelength range, where the operational wavelength is comparable to the pixel size, resulting in diffraction effects that severely limit the extinction ratio of focal-plane infrared polarization devices.

To address this issue, researchers have begun incorporating directional light field focusing into pixel-level micro and -nano-structures to reduce crosstalk between adjacent pixels. They are also advancing polarization multiplexing techniques to enhance energy utilization efficiency in weak-light infrared detection. These efforts are aimed at accelerating the practical applications of infrared polarization imaging devices. This paper reviews a series of notable works on polarization filtering/multiplexing and the implementation of pixel-level light field focusing (see Table 1), comparing key metrics such as operational wavelength range, energy utilization efficiency, number of polarization-encoded channels, unit cell size, and focal length. Given the impact of pixel-level discretized phase control and micro-nano fabrication errors, there is significant interest in ensuring the extinction ratio and other performance parameters of focal-plane array polarization detectors. New approaches, including the inverse design of novel microstructures, the integration of microstructures with pixel arrays, and the correction and reconstruction of readout signals, are being explored. These methods hold promise for driving efficient device optimization and achieving performance improvements beyond the limitations imposed by design and fabrication errors.

This study reviews research progress on focal-plane array integrated infrared polarization detectors based on polarization-sensitive microstructures. It focuses on key issues such as improving energy utilization, reducing crosstalk between adjacent pixels, increasing the number of multiplexing channels, and enhancing structural design efficiency. This review discusses various design approaches and advancements in pixel-level polarization-sensitive microstructures. Additionally, from the perspective of integrated polarization devices, this study analyzes the key technologies related to polarization decoupling and reconstruction that affect polarization detection capabilities. The proposal and optimization of these design methods have facilitated a series of concept-level experimental validations of on-chip polarization imaging, thereby accelerating the development of application-grade integrated devices.

Advancing the development of on-chip infrared polarization imaging devices based on micro- and nano-structures is of significant importance. Future research and applications should focus on several key innovations: AI-driven design of micropolarizers, designing pixel-level microstructures and key parameters of pixel arrays from an integrated device perspective, and establishing comprehensive polarization component transmission models for polarization calibration and reconstruction. By aligning with practical requirements and integrating multidisciplinary design approaches, this field offers new technological pathways for the development and application of miniature optical imaging systems in infrared polarization and spectroscopy.