J. Allen Cox Honeywell Technology Ctr. (United States) David C. Dobson Texas A&M Univ. (United States) Thomas R. Ohnstein Honeywell Inc. (United States) J. David Zook Honeywell Technology Ctr. (United States)
The analysis of an IR tunable filter that uses a transmission grating with variable spacing is extended to include incident spherical waves instead of plane waves and to illustrate specifically the effects of finite conductivity in the metal. The model is based on a rigorous vector solution of Maxwell’s equations implemented in a finite elements solver. The modeling results based on tabulated optical properties of nickel are compared with experimental measurements made with filters fabricated in permalloy by the lithographie, galvanoformung, abformung (LIGA) process. The theoretical and experimental results compare quite well and suggest that the resolution of the filter is severely reduced at the shorter wavelengths (less than 4 ?m). At longer wavelengths, the resolution is limited by the aspect ratio of the LIGA structures. A spectral resolution of 0.1 ?m appears to be practical.