Dual-band MEMS Fabry-Pérot filter with two movable reflectors for mid- and long-wave infrared microspectrometers

Abstract

A tunable dual-band MEMS Fabry-Pérot filter for simultaneous use of the spectral ranges from 8 µm to 10.5 µm and from 4 µm to 5 µm is reported. A peak transmittance of at least 75 % and a FWHM of less than 200 nm were measured. The maximum control voltage is 41 V. Two movable reflector carriers compensate the influence of gravitational force on the central wavelength. The device can withstand mechanical shocks according to Mil-Std-883G, method 2002.4, test condition B. The filter is integrated in a tiny, robust and fast microspectrometer module with the size of a TO-8 housing.

Micro-machined Fabry-Pérot interferometer for thermal infrared

“…1) through a single-wafer process. Earlier results at TIR parallel our device performance in a two-chip assembly based on bulk micro-machining [6]. The majority of the works [7] in the single-wafer FPI are limited to the transparent range of Si 3 N 4 and SiO 2 at < 5 µm.…”

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

“…The use of air as the low refractive index material in the top DBR has allowed this current work to attain the narrowest FWHM in the SWIR (27 nm) and MWIR (38 nm) wavelength ranges compared to all the previous works reported in Table III. Using the same number of layers for DBR formation (3layers) over the same wavelength range, the peak transmittance reported in earlier works ranged from 50% -80% [13], [23], [19], [24], [25], [12], while filters reported in this paper have demonstrated comparable or better transmittance, with 61% -74% peak transmittance (excluding the peak positioned at 4193 nm due to carbon dioxide absorption). Our use of air as the low index material has resulted in narrow-band, high throughput FP filters with the possibility to achieve comparable or larger tuning ranges compared to previously reported studies.…”

“…It must be clarified that this work used fabricated fixed filters for proof of concept to estimate the tuning range and the expected performance, whereas all the other filters presented in Table III were fabricated as electrostatically-actuated filters. Table III also provides details of materials used for the top suspended DBRs of the filters, which clearly indicates that use of silicon dioxide and silicon monooxide as the low index DBR material resulted in a reported FWHM of 50-100 nm [13], [23] in the SWIR wavelength range and 57-200 nm [19], [24], [25], [12] in the MWIR wavelength range. The use of air as the low refractive index material in the top DBR has allowed this current work to attain the narrowest FWHM in the SWIR (27 nm) and MWIR (38 nm) wavelength ranges compared to all the previous works reported in Table III.…”

MEMS-Based Tunable Fabry–Perot Filters for Adaptive Multispectral Thermal Imaging

“…Whilst MEMS-based LWIR Fabry-Perot filters have been previously reported [9]- [13], these published works concentrate on achieving high spectral resolution by incorporating highly reflective multilayer Bragg mirrors. These studies include Teledyne [9] with 120 nm FWHM, and InfraTec [10], [11] who report a 200 nm FWHM using multilayer Ge/ZnSbased mirrors. Any top mirror deformation arising from stress mismatch between different mirror layers will degrade filter transmission [14], [15], and in particular, cause pixel-to-pixel transmission peak wavelength non-uniformity, and therefore, complicates fabrication of these filters.…”

“…To control stress gradients induced mirror deformation, very thick, mechanically stiff carrier wafers have also been used [10], [11]. However, this increases the chip size considerably.…”