We present the design, fabrication, and optical characterization, of silicon-air-silicon based distributed Bragg reflectors or quarter wavelength mirrors, in sizes ranging from 200 µm × 200 µm to 5 mm × 5 mm. Such mirrors can be used in conjunction with either single-element photodetectors or large-area focal plane arrays to realise tunable multispectral sensors or adaptive focal plane arrays from the shortwave infrared wavelength ranges (1500-3000 nm) to mid-wave infrared wavelength (3000-6000 nm) ranges. Surface optical profile measurements indicate a flatness of the order of 20-30 nm in the fabricated structures across several millimetres. Single point spectral measurements on devices show excellent agreement with simulated optical models. The fabricated distributed Bragg reflectors show around 94% reflectivity, which is in close agreement with theoretical reflectivity. The demonstrated high reflectivity across a wide wavelength range, renders them suitable as broadband reflectors. Finally we present optical transmittance modelling results for Fabry-Pérot filters based on these distributed Bragg reflectors.
This paper presents the design, fabrication, and optical characterization of silicon-based thin film Fabry-Pérot filters for spectroscopic sensing applications at shortwave 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-topeak 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.
Evolving from past black‐and‐white images, through present red‐green‐blue spectral colors, future remote imaging systems promise spectroscopic functionalities extending well beyond the visible wavelengths. This allows real‐time spectral information to be gathered from multiple wavelength bands that is applicable to numerous remote sensing spectroscopy/imaging applications and aids target recognition. This paper reviews the wavelength tunable microelectromechanical systems (MEMS) optical filter technologies developed for the important infrared and the emerging terahertz wavelength bands of the electromagnetic spectrum with the fabrication effort being enabled by the Western Australian Node of the Australian National Fabrication Facility. A low size, weight and power (SWaP) platform solution is demonstrated delivering mechanically robust, field‐portable, spectroscopic, chem/bio sensing suitable for deployment in remote sensing and imaging applications.
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