Regular Article

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

Faculty of electrical engineering and computer science, Ningbo University, Ningbo 315211, PR China

^* e-mails: zhangxin_nbu@163.com, jianjiawen@nbu.edu.cn

Received: 16 March 2018
Received in final form: 29 June 2018
Accepted: 30 July 2018
Published online: 10 October 2018

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.