SBIR Phase II: A Large Mosaic Liquid Crystal Fabry-Perot Etalon for Atmospheric Sensing

Scientific Solutions Incorporated, North Chelmsford MA

Investigators

Abstract

This Small Business Innovation Research (SBIR) Phase II project addresses the traditional size limit of the Fabry-Perot interferometer (FPI) input aperture. This limit (approximately 8-inches) is imposed by (1) practical fabrication limits to the size of glass flats that can be polished to a surface figure of lambda/100 and (2) by cost limitations. Although an array of smaller glass plates might be used to expand the collecting area of the FPI, coordination of spectral scans over the array elements requires unwieldy control systems or else is not possible with conventional barometric or piezo-electric FRI systems. This research establishes arrays of innovative FPI etalons that use liquid crystal (LC) in the FPI resonant cavity. Spectral scanning of these devices is accomplished by application of a low current to conducting layers applied to the glass substrates. The electric field imposed upon liquid crystal in the resonant cavity alters the orientation of the LC, and thus the index of refraction of the material in the resonant cavity. The ease of electronic control over the refractive index in the FPI cavity permits simple, low weight, low power coordination of multiple LC filled cells and thus makes possible a large array of FPI cells, scanning a spectrum in unison. Phase II will design and fabricate two 10-inch diameter arrays of LC FPI (LCFP) filters. One array will be configured for Doppler measurements of atmospheric emissions and the other for 0.16-nanometer spectral resolution. Potential commercial applications are expected in (1) atmospheric lidar, (2) space-based environmental sensing, (3) passive airglow sensing, (4) clear-air turbulence detection, and (5) target detection.