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

Abstract

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.

Metamaterials – from fundamentals and MEMS tuning mechanisms to applications

“…However, their performances can be further enhanced with the integration of the metamaterial perfect absorbers, which offer almost unity absorption and satisfying wavelength selectivity [50]. Comparing to the conventional nondispersive infrared system (NDIR) which involves the Fabry Perot filters [156][157][158], the plasmonically enhanced radiation sensors integrate the spectral filter with the detectors without significantly increasing the fabrication difficulties. It shows great potentials in the ultracompact MIR spectroscopic sensing.…”

Optical Microelectromechanical Systems Technologies for Spectrally Adaptive Sensing and Imaging

“…The simulations of optical transmittance presented in this review were carried out using the basic optical matrix method [ 15 ] which has been extended to the particular case of imperfect FP cavities. [ 16 ] The transmittance of a FP cavity with imperfections can be estimated by segmenting the cavity into infinitely small, ideal cavities and integrating over the total cavity area. [ 17 ] This approach corresponds to a convolution with an imperfection distribution function that characterizes the imperfection type and forms the essence of all simulated transmittance spectra presented in this review demonstrating agreement with measured filter characteristics, even for imperfections relatively large in magnitude.…”

“…In comparison to the single‐layer suspended membrane mirrors developed for multispectral imaging, narrower FWHM and improved out‐of‐band rejection of the FP filter have been achieved utilizing the increased reflectivity of a 3‐layer DBR. The MEMS approach shown in Figure 3b was used to realize suspended Si‐air‐Si 3‐layer DBRs for use in the SWIR and MWIR bands, [ 16 ] as well as suspended Ge‐BaF 2 ‐Ge 3‐layer DBRs for use in the LWIR band. [ 29,30 ] For each IR application band, the optical area of the fabricated filters consisted of a 1 mm × 1 mm square aperture.…”

Ge/BaF2 thin-films for surface micromachined mid-wave and long-wave infrared reflectors

“…25 In this configuration, λ∕4-thick optical films are deposited, where the thickness of each optical layer is equivalent to one quarter of the wavelength for which the DBR is designed. 12,26,27 High reflectivity of the DBRs is assured if there is a high contrast between the refractive indices of the high-and low index materials, which provides a pathway toward the realization of narrowband FPIs. In this paper, germanium (Ge) and barium fluoride ðBaF 2 Þ∕air have been considered as the high and low refractive index materials/media, respectively, for the fabrication of DBRs.…”