Compact gas cell integrated with a linear variable optical filter

Abstract

A miniaturized methane (CH 4 ) sensor based on nondispersive infrared absorption is realized in MEMS technology. A high level of functional integration is achieved by using the resonance cavity of a linear variable optical filter (LVOF) also as a gas absorption cell. For effective detection of methane at λ = 3.39 µm, an absorption path length of at least 5 mm is required. Miniaturization therefore necessitates the use of highly reflective mirrors and operation at the 15th-order mode with a resonator cavity length of 25.4 µm. The conventional description of the LVOF in terms of the Fabry-Perot resonator is inadequate for analyzing the optical performance at such demanding boundary conditions. We demonstrate that an approach employing the Fizeau resonator is more appropriate. Furthermore, the design and fabrication in a CMOS-compatible microfabrication technology are described and operation as a methane sensor is demonstrated. 1-3), 191-197 (2000). 604-606 (1990). 42. T. T. Kajava, H. M. Lauranto, and R. R. E. Salomaa, "Fizeau interferometer in spectral measurements," J. Opt. ©2016 Optical Society of AmericaSoc. Am. B 10(11), 1980-1989 (1993). 43. P. Langenbeck, "Fizeau interferometer-fringe sharpening," Appl. Opt. 9(9), 2053-2058 (1970) Characteristics," Appl. Opt. 6(8), 1343-1351 (1967). 49. J. Altmann, R. Baumgart, and C. Weitkamp, "Two-mirror multipass absorption cell," Appl. Opt. 20(6), 995-999 (1981

Two-groove narrowband transmission filter integrated into a slab waveguide

“…LVF is a bandpass filter that is intentionally wedged in one direction, providing a position-dependent dispersive optical element. Typically, LVF corresponds to a Fabry-Pérot etalon with varying thickness between two Bragg reflectors [21][22][23][24]. On the basis of the proposed TGPF, a waveguide-integrated LVF can be created, in which the spectral shift of the transmittance peak can be achieved by changing one of the parameters of the structure, e.g.…”

Functionalizing a Tapered Microcavity as a Gas Cell for On-Chip Mid-Infrared Absorption Spectroscopy

“…The peak transmittance and resolution of the transmission curves can be improved with oblique incidence due to the nonparallel configuration of the mirrors [ 26 ]. At every detector plane position ( z ), there is an incidence angle that provides the identical optimum transmission for a specific wavelength [ 27 ]. For the LVOF design in the 3.2 to 3.4 wavelength range, this angle of incidence varies between −1.38 and −1.85 at .…”

CMOS-compatible mid-IR metamaterial absorbers for out-of-band suppression in optical MEMS

“…These changes cause a non-constant gas composition and necessitate composition measurement for burner control at industrial facilities, gas distribution points, and households for safe and clean combustion [2]. These users combined constitute a high-volume application, which favors the use of a technique such as CMOS that offers costs advantages in batch fabrication [3]. The characteristic absorption lines of the hydrocarbons are in the mid-infrared (mid-infrared) spectral range between about 3.1 μm and 3.5 μm (Free Spectral Range, FSR = 400 nm at λ o = 3300 nm) and should be measured with a Full-Width Half-Magnitude resolution, FWHM, in the range between λ FWHM = 2 and 5 nm for effective composition measurement [4].…”