Intrinsic improvement of diffraction-limited resolution in optical MEMS fourier-transform spectrometers

High resolution MEMS FTIR spectrometers are now of growing interest on both the academic and industrial levels. Such spectrometers are characterized by their small compact size, high speed of response and the use of optical fiber coupling. The main optical MEMS engine of the spectrometer is an interferometer with a moving mirror displaced using a MEMS actuator. The resolution of the FTIR spectrometer is related to the travel distance of the moving mirror but with a lower limit restricted by the divergence angle of the input light to the spectrometer; an effect called self-apodization. In this work, we analyze this effect within the MEMS systems, in which the size of the optical components is in the order of 50-300 μm limited by the microfarbication technology. We show analytically and experimentally that the resolution is intrinsically improved 5-10 times relative to the values directly predicted by the input light divergence angle.