Loop-Terminated Mach-Zehnder Interferometer Integrated with Functional Polymer for CO₂ Gas Sensing

Abstract

In this work, a numerical study on the loop-terminated Mach-Zehnder interferometer (LT-MZI) structure for CO2 gas sensing application is carried out via the finite element method. The sensing arm is covered with a polyhexamethylene biguanide (PHMB) polymer which is highly receptive to CO2 gas. The refractive index of the host material decreases due to the absorption of the CO2 gas resulting in a shift in the interference pattern of the LT-MZI structure. As a result, a redshift in the wavelength is observed in the transmission spectrum of the device. The sensitivity of the device is estimated at 7.63 pm/ppm, 34.46 pm/ppm and 74.78 pm/ppm for the sensing arm length of 5 µm, 10 µm, and 15 µm, respectively. The sensitivity can be further enhanced, however at the cost of the bigger footprint of the device. Utilizing the innovative sensor design, a comprehensive range of CO2 gas concentrations spanning from 0 to 524 ppm is successfully detected. This compact and highly sensitive device serves as a vital tool for monitoring indoor CO2 levels, fostering a healthier breathing environment for all occupants.

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

“…This absorption causes measurable changes in the light's intensity, which can be correlated to gas concentration. On the other hand, the wavelength interrogation method involves observing shifts in the wavelength of light that resonate within the WG, often using structures like Mach-Zehnder interferometer (MZI) [13] or ring resonators [56]. In this case, functional polymers like polyhexamethylene biguanide (PHMB) play a crucial role in enhancing the sensitivity and selectivity of gas sensors.…”

“…In a recent study, M.A. Butt conducted a numerical analysis on the loop-terminated Mach-Zehnder interferometer (LT-MZI) structure aimed at CO2 gas detection applications (Refer to Figure 5 (i) [13]). The sensing arm was treated with a PHMB polymer, known for its high sensitivity and selectivity to CO2 gas.…”

“…environmental surveillance, industrial safety, and medical diagnostics [13]. For instance, detecting trace levels of dangerous gases in industrial environments can avert accidents and ensure worker safety.…”

“…Photonic sensors based on the wavelength interrogation method represent a cutting-edge approach to gas detection, capitalizing on the interplay between light and gas molecules. This method encompasses monitoring shifts in the wavelength of light as it passes through or interacts with a gas sample[13]. Functional polymers that are sensitive to gas absorption play a crucial role in the development of advanced photonic gas sensors.…”