Mixed-gas CH4/CO2/CO detection based on linear variable optical filter and thermopile detector array

Abstract

This paper presents the design, fabrication, and characterization of a middle-infrared (MIR) linear variable optical filter (LVOF) and thermopile detectors that will be used in a miniaturized mixed gas detector for CH4/CO2/CO measurement. The LVOF was designed as a tapered-cavity Fabry-Pérot optical filter, which can transform the MIR continuous spectrum into multiple narrow band-pass spectra with peak wavelength in linear variation. Multi-layer dielectric structures were used to fabricate the Bragg reflectors on the both sides of tapered cavity as well as the antireflective film combined with the function of out-of-band rejection. The uncooled thermopile detectors were designed and fabricated as a multiple-thermocouple suspension structure using micro-electro-mechanical system technology. Experimentally, the LVOF exhibits a mean full-width-at-half-maximum of 400 nm and mean peak transmittance of 70% at the wavelength range of 2.3~5 μm. The thermopile detectors exhibit a responsivity of 146 μV/°C at the condition of room temperature. It is demonstrated that the detectors can achieve the quantification and identification of CH4/CO2/CO mixed gas.

Near‐Infrared InGaAs Intelligent Spectral Sensor by 3D Heterogeneous Hybrid Integration

“…The applied LVF is a thin‐film filter deposited with an energetic physical vapor deposition process, and its central wavelength linearly changes with position from 900 to 1700 nm. [ 28–31 ] The applied linear InGaAs FPA employs a hybrid structure, in which the photodiode array used as the photosensitive area and…”

“…The applied LVF is a thin-film filter deposited with an energetic physical vapor deposition process, and its central wavelength linearly changes with position from 900 to 1700 nm. [28][29][30][31] The applied linear InGaAs FPA employs a hybrid structure, in which the photodiode array used as the photosensitive area and CMOS readout integrated circuit (ROIC) are implemented in separate chips and vertically mounted by using bumps. Since the wavelength range of InGaAs FPA matches up to the working region of LVF perfectly, no additional cut-off filter is required to suppress the bypass band.…”

Chip-scale short-wavelength infrared InGaAs microspectrometer based on a linear variable optical filter

“…19 In addition, transmission through the multilayered F–P filter under normal incidence is associated with the reflectivity of the DBR and the physical parameters of the SiO 2 cavity. 20 where R 1 and R 2 denote the reflectivities of the top and bottom DBRs, respectively; F is the cavity's coefficient of finesse, with a higher value indicating a sharper transmission peak and a wider tuning range; and θ is the electric field phase shift after one round trip inside the cavity. The total phase shift is described by , where φ 1 and φ 2 denote the phase shifts related to the reflection off the top and bottom DBRs, respectively, and λ is the incident wavelength.…”

Replicable Quasi-Three-Dimensional Plasmonic Nanoantennas for Infrared Bandpass Filtering

“…Bandpass filters that allow through a specific band of light wavelengths serve as a critical optical element of spectral imaging for broad applications including space-based imaging, remote sensing, military target tracking, land mine detection, diagnostic medicine, and environmental monitoring. − The bandpass filters are typically composed of coupled half-wavelength resonators and multilayer mirrors using alternating dielectric thin films with high and low refractive indices to form a Fabry–Perot optical cavity. , Effective bandpass filtering occurs through the constructive interference of light when a phase difference coincides with incoming and reflected light waves . Narrow bandpass filtering with tunable spectral selectivity occurs using hybrid metal–dielectric plasmonic nanoarchitectures (i.e., nanoantennas) with various structural configurations such as metal disks, metal holes, metal coaxial apertures, split-ring resonators, coherent perfect absorbers, and quasi-three-dimensional (quasi-3D) crystals. − These plasmonic nanoantennas enable a surface-plasmon-enhanced light transmission through a subwavelength aperture (i.e., extraordinary optical transmission) …”

“…1−5 The bandpass filters are typically composed of coupled halfwavelength resonators and multilayer mirrors using alternating dielectric thin films with high and low refractive indices to form a Fabry−Perot optical cavity. 6,7 Effective bandpass filtering occurs through the constructive interference of light when a phase difference coincides with incoming and reflected light waves. 8 Narrow bandpass filtering with tunable spectral selectivity occurs using hybrid metal−dielectric plasmonic nanoarchitectures (i.e., nanoantennas) with various structural configurations such as metal disks, metal holes, metal coaxial apertures, split-ring resonators, coherent perfect absorbers, and quasi-three-dimensional (quasi-3D) crystals.…”