Polarization-State Degradation and Compensation of Folding Mirrors in Polarization-Encoded Detector-Multiplexed Infrared Imaging

Polarization-encoded detector multiplexing has recently shown promise for compact wide-field infrared imaging, where multiple field-of-view (FOV) regions are mapped onto a shared detector area and distinguished through Stokes-vector decoding. The practical implementation of this architecture, however, requires reflective folding components for optical path compression and detector reuse. Oblique metallic reflection introduces unequal amplitude attenuation and phase retardation between the p- and s-polarized components, which can deform the designed polarization code before it reaches the polarization-resolved detector. This work establishes a coordinate-consistent Jones–Mueller model for eight peripheral reflections from the internal octagonal mirror and one central direct path. The model distinguishes deterministic polarization-state transport from true depolarization and compares detector-side calibration, encoder pre-compensation, one shared liquid-crystal polarization retarder (LCPR), and a segmented-LCPR upper bound. Using a unified aluminum model at 4.0 um, the mirror displaces the encoded states by several degrees but does not depolarize a fully polarized monochromatic ray. Across 60 Monte Carlo trials with 2000 samples per channel, all principal methods remain approximately 100% accurate at an additive Gaussian-noise standard deviation of σ = 0.02, normalized relative to unit S0. At σ = 0.15, the ideal-codebook, calibrated-codebook, and pre-compensated decoders achieve 90.87%, 91.24%, and 89.87%, respectively. A shared LCPR provides little global benefit, whereas segmented settings recover individual states at the cost of channel-resolved hardware. The results show that mirror-aware calibration, code-space separation, and physically implementable compensation must be considered jointly.