Tunable infrared detector with integrated micromachined Fabry-Perot filter

This paper reports design, fabrication and test results of a tunable pyroelectric detector with an integrated micromachined Fabry-Perot (FP) filter for gas analysis in the Mid-Wave Infrared (MWIR). The new approach is based on a bulk micromachined Fabry-Perot interferometer with an air cavity, which is electrostatically tuned. Various types of moveable reflectors and spring configurations have been fabricated to determine the optimum solution with respect to maximum tuning range, low gravity influence on center wavelength and suitable filter bandwidth. Short and long cavity filters were designed for the spectral ranges of 3...4.3 m and 3.7...5.0 m respectively. The tunable filter is arranged on top of a current mode pyroelectric detector with a flat spectral response. It could be shown that the main challenge is to achieve a high finesse in spite of non-perfect parallelism, mirror curvature and additional phase shift caused by the Bragg reflectors.