A single slot micro-ring structure for simultaneous CO2 and CH4 gas sensing

Abstract

In this paper, we proposed a single silicon-on-insulator micro-ring structure for detecting two different gas components in the same time from one output spectrum. By introducing slot structure, the sensitivity and selectivity of sensor are improved. Specifically, two different sensing mechanisms are synthesized in this structure, thus output spectrum is impacted by varying concentrations of CH4 and CO2 respectively. The resonant wavelength of micro-ring resonator is the absorption peak of CH4, the concentration of CH4 can be measured with the light intensity change. Simultaneously, the combined action of CH4 and CO2 can cause the shift of resonant wavelength, and the total concentration of CH4 and CO2 gas can be obtained through the shift amount. For enhancing the evanescent field fraction in slot area and tuning the resonant wavelength of micro-ring being located on the absorption peak of CH4 (around 3.31 µm), the parameters of slot micro-ring structure, including height of slot in silicon, slot width, radius of micro-ring, waveguide width and the gap distance in coupling section, are well tailored, meanwhile, the quality factor Q of micro-ring is considered for ensuring a satisfied accuracy of sensor. A simulation based on the finite difference time domain method is implemented and the analysis results show that the sensitivity of sensor reaches 2308 nm/refractive index unit.