Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters

Abstract

In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH4) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based light emitting diode (LED)/photodiode (PD) light source/detector optopair, enhancing the NDIR CH4 sensor performance. The BPFs, deposited using a novel microwave plasma-assisted pulsed DC sputter deposition process, provide room temperature deposition directly onto the temperature-sensitive PD heterostructure. BPFs comprise germanium (Ge) and niobium pentoxide (Nb2O5) alternating high and low refractive index layers, respectively. Two different optical filter designs are progressed with BPF bandwidths (BWs) of 160 and 300 nm. A comparison of the modelled and measured NDIR sensor performance is described, highlighting the maximised signal-to-noise ratio (SNR) and the minimised cross-talk performance benefits. The BPF spectral stability for various environmental temperature and humidity conditions is demonstrated.

Design and Fabrication of a patterned dual colour filter using Microwave plasma assisted Sputtering and Photolithography

“…It can be used across a wide range of wavelengths from visible to mid-wave infrared [5,6]. Due to the low temperature of deposition it has also been shown to be compatible with deposition directly onto detector surfaces [7]. This current work demonstrates compatibility of the MPAS process with conventional photolithography and the successful design and fabrication of a dual-color optical filter.…”

Miniaturised Infrared Spectrophotometer for Low Power Consumption Multi-Gas Sensing

“…The fixed pass band filters are modelled to match ideal band pass characteristics suited for improved gas sensitivities, as well as to emulate available commercial fixed filter specifications [ 36 ].…”

“…The transmittance at the centre of each of the detector element is averaged to yield a spectrum shown in Figure 9-with lower average transmittance, as expected, at the lower end of the wavelength range and higher average transmittance at upper wavelengths [35]. The fixed pass band filters are modelled to match ideal band pass characteristics suited for improved gas sensitivities, as well as to emulate available commercial fixed filter specifications [36].…”

Optical and Mechanical Properties of Layered Infrared Interference Filters

“…The study [ 8 ] proposed a rating design consisting of a cylindrical matrix of high-performance waveguides based on graphene, which can be used for the manufacture of optical devices in the mid-infrared range (filters and refractive index sensors), and is also promising for future photonic integrated circuits. The paper [ 9 ] describes measures aimed at improving the performance of a non-dispersive infrared methane gas sensor by using multilayer thin-film bandpass filters containing germanium (Ge) and niobium pentoxide (Nb 2 O 5 ) and based on alternating layers with a high and low refractive index, respectively. The researchers [ 10 ] developed a highly sensitive plasmonic layered structure containing layers of chromium, gold, chromium, and silicon dioxide deposited on a BK7 base for measuring a liquid analyte.…”