Improved MEMS based FT-IR spectrometer: Position encoding and closed loop control

We discuss recent improvements of our MEMS-based FT-IR spectrometer. A novel MEMS actuator design of the translational mirrors features an increased mirror surface of 7 mm2 and enables larger translation amplitudes (up to ±250 m), leading to improved performance of the spectrometer. Furthermore we present a new method for accurate position detection of the MEMS device, thus enabling the implementation of closed-loop control. A dedicated circuit demodulates the reference signal and generates a highly accurate control signal returning the zero-crossing position of the mirror. The implementation of a closed-loop control ensures optimally stable MEMS mirror movement and maximal mechanical amplitude, even under varying environmental conditions allowing building robust MEMS-based Fourier-transform infrared (FT-IR) spectrometers with large mechanical amplitudes and thus good spectral resolutions.