Analysis of daytime star observation capability based on SWIR subwavelength metal grating polarizers

To solve the problems of limited detection capability and low utilization rate of optical information of the existing all-time star sensors in near-Earth space, the concept of polarization star sensor based on subwavelength metal gratings is proposed, which can obtain the polarization information of the starry sky through only one exposure, and the detection model of polarization star sensor is constructed. According to the application requirements of the star sensor in the SWIR band, a subwavelength metal grating polarizer with extinction ratios reaching 19.92 dB, 22.97 dB and 24.35 dB respectively in the JHKs band is designed. An analytical model for the detection capability based on degree of polarization star maps is proposed to characterize the optical visibility of stars. Combining the advantage that the polarization star sensor can utilize the three-dimensional information of Stokes vectors, four detection modes are proposed, and a comprehensive improvement model for the detection performance of the polarization star sensor is proposed by integrating the respective advantages of different detection modes. Analysis shows that when the sky polarization degree rises from 0.1 to 0.9, the comprehensive enhancement ability of the observable limit magnitude increases from 1.4 magnitude to 3 magnitude. Combined with the sky polarization simulation data, the influences of different observation scenarios, the performance and pointing deviations of micro-polarizers on the detection performance are analyzed, and the boundary for the improvement of detection performance is given. The research results can provide theoretical references for the optimal design and performance improvement of all-time star sensors in near-Earth space.