Silicon Waveguide Sensors for Carbon Dioxide Gas Sensing in the Mid-Infrared Region

Abstract

Two optical waveguide sensors based on SOS (silicon-on-sapphire) for detecting CO2 are theoretically proposed. The operational wavelength is 4.23 μm, which is the maximum absorption line of CO2. The power confinement factor (η) value is over 40% and 50%, the propagation loss is 0.98 dB/cm and 2.99 dB/cm, respectively, in the slot waveguide and SWGS (subwavelength grating slot) waveguide. An inverted tapered structure is used for the transition from strip waveguide to slot waveguide and constitutes the sensing absorption region, with the coupling efficiency that can reach more than 90%. When the optimal absorption length of the slot waveguide and SWGS waveguide is 1.02 cm and 0.33 cm, respectively, the maximum sensitivity can reach 6.66 × 10−5 (ppm−1) and 2.60 × 10−5 (ppm−1). Furthermore, taking the slot waveguide as an example, spiral and meander structures enable the long-distance sensing path to integrate into a small area.

Integrated Photonic Sensors for The Detection of Toxic Gases - A Review

“…Integrated photonic sensors utilizing the EFA mechanism represent a sophisticated approach to gas detection, leveraging the interplay between light and gas molecules at the interface of a WG [61]. In these sensors, light is guided through a photonic WG, and a small portion of the light, known as the evanescent field, extends beyond the surface of the WG into the surrounding medium [62].…”

“…Two theoretical proposals for optical WG sensors based on slot WG and subwavelength slot (SWGS) utilizing SOS (silicon-on-sapphire) were introduced by Song et al for CO2 detection as presented in Figure 3 (c, d) [61]. The operational wavelength stands at 4.23 μm, corresponding to the maximal absorption line of CO2.…”