Theoretical design of coupled high contrast grating (CHCG) waveguides to enhance CO2 light-absorption for gas sensing applications

Abstract

In this work, we present a theoretical study on using high contrast grating (HCG) designs to enhance light–gas interaction in the mid-infrared range. The optical behavior of a single layer HCG was studied under the presence of CO2 gas. Through optimizing the structure parameters, we could confine an intense electric field over the grating layer. Consequently, about 200 times of light-absorption enhancement was observed. To further improve the performance, a coupled HCG (CHCG) was proposed to introduce another vertical photonic confinement mechanism. We found that CHCG can restrict much intense light energy in the structure leading to over 600 times of light-absorption enhancement. However, it is noticed that a significant part of the concentrated electric field was still trapped in the high index areas, where the gas cannot interact. To address this issue, a modified CHCG with a thin substrate thickness was proposed. Through the optimization (T=1.149μm), we were able to redistribute most of the light energy into the void space of the CHCG layer which resulted in close to 1400 times of improvement. This work clearly demonstrates that using HCG for enhancing light–gas interaction is a promising approach to make on-chip gas sensing devices. Furthermore, it can also be integrated into other photonic components, e.g., fibers for advanced sensing system development.

On-Chip Optical Gas Sensors Based on Group-IV Materials

“…Besides the two-dimensional PhC waveguide devices, grating structures were also studied for sensing applications. For example, Hemati et al 106 reported a design of a high contrast grating (CHCG) device for carbon dioxide (CO 2 ) sensing. The authors theoretically showed that the CHCG devices could restrict much intense light energy in the structure leading to 1400× light-absorption enhancement for developing gas sensors based on infrared absorption spectroscopy.…”

“…Besides the total-internal-reflection waveguide and subwavelength waveguide devices, PhC waveguide devices also attract great attention in developing optical gas sensors due to their compact device footprints and excellent ability in the light confinement. ,,,,,,,− On the one hand, PhC waveguide devices are used for developing gas sensors based on enhanced infrared absorption spectroscopy, ,,,,, since slow-light effects in PhC waveguide devices could result in the absorption cross-section enhancement . For example, Lai et al used a silicon PhC slot waveguide, as shown in Figure a, for methane (CH 4 ) molecules detection at 1.55 μm wavelengths.…”

Selective H2 sensing using lanthanum doped zinc oxide thin film: A study of temperature dependence H2 sensing effect on carrier reversal activity

“…Recently, there are various reports that highlighted the inevitability of the gas sensors at different fields of applications. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] However, gas sensors are extremely necessary for the early detection of gas leakage. Compared to other gas species, detection of hydrogen is highly desirable as H 2 leakage is harmful to human safety and can be flammable and explosive when mixed with air.…”