Design and Integration of an Adaptive Controller for a Fourier Transform Spectrometer

This paper presents the design and integration of an adaptive controller for CIRIS (Compositional InfraRed Interferometric Spectrometer) on a stand-alone field programmable gate array (FPGA) architecture. CIRIS is a novel take on traditional Fourier Transform Spectrometers (FTS) and replaces linearly moving mirrors (characteristic of Michelson interferometers) with a constant-velocity rotating refractor to variably phase shift and alter the path length of incoming light. This design eliminates the need for periodically accelerating/decelerating mirrors inherent to canonical Michelson designs and allows for a compact and robust device, making it ideal for spaceborne measurements in the near-IR to thermal-IR band (2-12 mu m) on planetary exploration missions. The instrument's embedded microcontroller is implemented on a VIRTEX-5 FPGA with the aim of sampling the instrument's detector and optical rotary encoder in order to construct an interferogram. Subsequent signal processing, including resampling, Fast Fourier Transform (FFT), filtering, and dispersion correction techniques are applied in real-time to compose the sample spectrum. The instrument's FPGA controller is demonstrated with the FTS to highlight its suitability for implementation in space systems.