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 μm) 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.