With the rapid advancement of infrared focal plane device technology, broadband infrared imaging detection devices have been developed to meet the increasing demand for higher sensitivity and enhanced adaptability in adverse environments, such as nighttime or inclement weather conditions. Compared to traditional single-wave infrared imaging, broadband infrared polarization imaging enriches detection dimensions and improves the contrast between targets and their surroundings. As the demand for dynamic target infrared polarization imaging grows, the development of focal plane polarization imaging technology and devices has become a prominent research area. In this paper, we process wire grid microstructures on each pixel of an infrared focal plane array detector, achieving simultaneous detection of information in various polarization directions and states with high real-time performance and resolution. Despite advancements, the design of broadband infrared micro-polarization arrays remains underexplored both domestically and internationally. Therefore, researching and designing focal plane micro-nano polarization wire grids suited for broadband infrared is of great significance for advancing infrared imaging technology.

In this paper, we address the demand for broadband infrared real-time polarization imaging by modeling and optimizing the structure of a double-layer slit metal wire grid micro-polarization array. A time-domain finite difference (FDTD) method is employed to simulate and analyze the performance of these arrays. Based on equivalent medium theory, we analyze the wire grid using Maxwell’s equations to establish a theoretical foundation for selecting suitable materials. The periodic structure of the wire grid ridges is modeled as an anisotropic uniform thin film, enabling the creation of a uniform medium model. A novel double-layer slit metal wire grid is proposed. Structural optimization of the metal wire grids is conducted, including analyzing the influence of different incident angles on polarization performance. A cross-shaped aluminum isolation strip is designed to effectively suppress polarization crosstalk between pixels. This approach demonstrates the broad potential applications of the proposed micro-polarization array in broadband infrared polarization imaging devices.

The double-layer slit metal wire grid (Fig. 2) incorporates a similar double-layer metal structure within the gaps between the wire grid ridges. The top and bottom metal wire grid layers are arranged in a periodic pattern, forming a structure akin to a Fabry-Pérot (F-P) resonant cavity. The transmittance and extinction ratio of the metal wire grid collectively determine its polarization performance. However, these parameters are often inversely proportional, making it essential to prioritize maximizing the extinction ratio while minimizing the reduction in transmittance. 1) Common metals such as gold, silver, and aluminum, with high concentrations of free electrons, are ideal for wire grid structures in the infrared range. Aluminum, used as the grid material, has a larger imaginary dielectric constant, which significantly attenuates TE transmittance waves (Fig. 4), resulting in a higher extinction ratio. 2) Transparent, non-metallic materials with low refractive indices are selected for the base and dielectric layers. Aluminum oxide serves as the base material, while silicon nitride is the dielectric. These materials enhance polarization performance by increasing transmittance. 3) Subwavelength metal wire grids operate in zero-order diffraction, with grid periods smaller than the critical value of 1.755 μm. As the duty cycle increases, TM transmittance decreases, while TE transmittance attenuates more strongly, thus improving the extinction ratio. 4) The metal wire grid consists of three layers: metal, non-metal, and metal. Analyses (Figs. 12 and 13) reveal that the height of the metal layer is directly proportional to both transmittance and extinction ratio, whereas the height of the non-metal layer inversely affects transmittance. 5) For oblique incidence in an uncooled broadband infrared detection system, performance improves at larger angles (Fig. 15), but the enhancement is not substantial.

In this paper, we propose a novel double-layer slit metal wire grid polarization array capable of achieving high transmittance and extinction ratio. The integration of optimized materials resolves the valley phenomenon at 9 μm, increasing TM transmittance by 47%. In the broadband infrared range of 3 μm to 12 μm, the transmittance achieved is between 75% and 95%, with a maximum extinction ratio of 88 dB, an improvement of 43% compared to traditional designs. We introduce a cross-shaped metal isolation band with widths of 260 nm and 40 nm, effectively suppressing pixel crosstalk within the micro-polarized array. The inclusion of the isolation band increases the electric field strength of the wire grid by 0.26 V/m, further enhancing the extinction ratio of the double-layer slit metal wire grid. The designed micro-polarization array is optimized for a broadband uncooled infrared focal plane array detector, featuring a resolution of 640×512 and a pixel size of 17 μm. The design offers significant reference value and provides a theoretical foundation for the development of next-generation infrared imaging devices.