Tunable mid-infrared filter based on Fabry-Perot interferometer with two movable reflectors

Abstract

A tunable IR filter based on a Fabry-Perot interferometer with two movable reflectors is reported. The infrared filter can be tuned over a wavelength range from 8 m to 11 m with voltages lower than 63 V. The FWHM bandwidth is lower than 200 nm and the peak transmittance is larger than 70 %. Simulation and practical shock test, both showed that the device can withstand 1500 g, 0.5 ms shocks according to Mil-Std-883G, method 2002.4, test condition B. The new infrared filter measures 8.5 mm x 8.5 mm and is suitable for the integration in a TO-8 housing in combination with a broadband infrared detector. The design benefits from relatively low stiffness of the mirror suspensions, compensation of vibration and gravitation induced forces possibly influencing the central wavelength and much lower actuation voltages as a result. Both reflector carriers are movable and are actuated by electrostatic forces

Characterization of the tuning performance of a micro-machined Fabry–Pérot interferometer for thermal infrared

“…Poly2 top surface features isolated crystallite protrusions which evolve semispherically through the 5 μm deposition of the λ/2 sacrificial SiO 2 . This mechanism, supported by a 5-10 nm extra roughness of the LTO deposition, generate the overall 50 nm unevenness to the gap thickness t. The inclusion, through (7), of the small bow of type A does not affect much whereas the stronger bowing of type B brings the FWHM behavior to the overall shape of the measured data. Further contribution by the 50 nm waviness, as δ r = 50 nm/(2 sqrt(2)) in equation ( 6), brings the FWHM curves very close to the data.…”

“…First, we modify the prediction by the concept of defected finesse by using equations ( 4)- (7). The stylus profilometry suggests δ t = 20 nm upward bow for the nonactuated (0 V) UM over the 800 μm aperture area of both designs A and B.…”

“…The prior art in the micro-electro-mechanical system (MEMS) FPI has concentrated on the near and medium infrared range below λ < 5 μm, as reviewed in [4,5] and compared with our work in [3]. The closest match of performance to compare with seems to be a bulk-micromachined TIR FPI that is assembled through wafer bonding [6,7].…”

Optical transmission performance of a surface-micromachined Fabry–Pérot interferometer for thermal infrared

“…Our technology naturally results in a very small height and the optical axis in the wafer-normal direction. Among the related works to compare with, there are the TIR-FPI realizations based on MEMS mirrors on separate wafers then bonded into the complete device [3,4]. Comparable performance in similar footprint was achieved, but, compared with our single-wafer process, the final unit cost in a high-volume production remains a challenge.…”

Large-area narrowband Fabry–Pérot interferometers for long-wavelength infrared spectral sensing

“…[20][21][22][23] On the other hand, bulk micromachined narrowband LWIR FPIs have also been fabricated by a group of researchers from InfraTec, and have achieved an FWHM of 105 to 250 nm in the LWIR region. [24][25][26][27][28][29] Another research group from Teledyne has reported an FWHM of 90 to 120 nm in the LWIR region. 30,31 Thus, in general, bulk micromachined FPIs have been able to provide narrower FWHM in comparison to surface micromachined FPIs.…”