Tunable infrared detector with integrated micromachined Fabry-Perot filter

We report the 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 movable reflectors and spring configurations are 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 are designed for the spectral ranges of 3 to 4.3 m and 3.7 to 5.0 m, respectively. The tunable filter is arranged on top of a current mode pyroelectric detector with a flat spectral response. It is shown that the main challenge is to achieve a high finesse in spite of nonperfect parallelism, mirror curvature, and the additional phase shift caused by the Bragg reflectors.