Large Area Silicon-Air-Silicon DBRs for Infrared Filter Applications

This paper presents the design, fabrication, and optical characterization of silicon-based thin film Fabry-Pérot filters for spectroscopic sensing applications at short-wave infrared (SWIR: 1.5-2.5 μm) and mid-wave infrared (MWIR: 3-5 μm) wavelengths. Filter performance is enhanced using distributed Bragg reflectors composed of silicon and air-gap layers for enhanced refractive index contrast. A peak-to-peak surface variation of less than 20 nm in the fabricated micromachined structures was achieved across a large spatial area of 1 mm × 1 mm. Spectral measurements on released Fabry-Pérot filters show excellent agreement with optical simulations. The fabricated Fabry-Pérot filters demonstrate peak transmittance values greater than 50% across all spectral ranges, with measured full width at half maximum values in the range of 50 nm rendering them suitable for use in spectral sensing and imaging in the SWIR and MWIR wavelength ranges.