LAUSR

A tunable Fabry-Perot interferometer (FPI) can be used as an optical band-pass filter. This type of filter is used in spectrometers and spectral imagers. The transmitted wavelength depends on the optical cavity adjusted by an electronic controller. This cavity, or the gap between the FPI mirrors, is measured using capacitive sensing. The performance of the FPI controller directly affects the FPI transmission spectrum and thus the quality of the spectral data. This work describes the design of the FPI controller for the ultraviolet channel of the ALTIUS hyperspectral imager. The ALTIUS mission is part of the Earth Watch program managed by the European Space Agency, ESA. This article presents a novel combination of building blocks to implement a low-noise, high-stability controller for piezo-actuated FPIs. Special care was taken to guarantee temperature stability and to minimize fluctuation of the FPI gap caused by the controller electronics. With the controller design presented in this paper, temperature variations ranging from–50 to $+ 50\,\,^{\circ }\text{C}$ induce FPI gap deviations of less than 0.1 nm at an electrode distance of 3000 nm, corresponding to a relative temperature drift of 0.3 ppm/°C.