Fabrication and testing of finite aperture polarizers for determination of edge termination effects on polarimetric imaging applications at midwave infrared

Abstract

Polarimetric imaging applications at the 2-to-5-µm or midwave infrared range use large pixel-count focal plane arrays (FPAs) with small pixel sizes. We report on the design, fabrication, and characterization of micropolarizers for the 2-to-5-µm regime. These micropolarizers will be used in conjunction with a FPA and will be in the near field of the imaging device. The pixel pitches for some commercial FPAs are small enough that the finite apertures of the polarizing devices may significantly affect their performance, because their aperture dimension varies between three and five waves. We are interested in understanding the effect on the extinction ratio due to variations in the edge terminations of a polarizer with a small aperture. Edge terminations are the spaces between the first and last wire with the perimeter of the aperture of the polarizer. To verify these effects, we fabricated micropolarizers with apertures of 5 to 20 µm and with termination edge spaces of one-quarter and three-quarters of the wiregrids period. The devices measured extinction ratios from 50:1 for the smallest aperture to 200:1 for the largest. Simulations and measurements show that the extinction ratio is larger for the smaller termination edge spacing.