Silicon-Air-Silicon DBRs for Electrostatically Actuated Infrared Filter Applications

This paper presents the design, modeling, fabrication and optical characterization of electrostatically-actuated silicon-based thin film Fabry-Pérot filters for spectroscopic sensing applications at mid-wave infrared (MWIR: 3–5 $\mu \text{m}$ ) wavelengths. The distributed Bragg reflectors of the FP filters consist of silicon and air-gap layers in order to enhance the refractive index contrast and performance of the filter. A peak-to-peak surface variation of less than 30 nm in the fabricated micromachined structures was achieved across a large spatial area of 1 $\text{m}\text{m}$ × 1 $\text{m}\text{m}$ . Although, spectral measurements on released Fabry-Pérot actuated filters show good agreement with optical simulations the filter performance indicates there is a significant peak-to-peak surface variation within the main air optical cavity. The fabricated Fabry-Pérot filters demonstrate peak transmittance values between 38% and 50%, with measured full width at half maximum values in the range of 70 $\mathrm{n}\text{m}$ making them promising devices for use in spectral sensing and imaging in the MWIR wavelength range.