Design And Research Of Gas Sensor Based On Single Micro-Ring Resonator

Excessive methane and carbon dioxide in coal mine will increase the risk factor of underground workers.Therefore,it is necessary to monitor the concentration of methane and carbon dioxide in coal mine production in time to avoid serious safety accidents and ensure safe production.In recent years,optical sensors have received extensive attention and practical applications in gas species and concentration detection due to their stability and accuracy.With the development of photonic chips and integration processes,the application of photonic devices with the dimensions of micrometers and nanometers in sensing has attracted the researchers' attention,among which the micro-ring resonator has important application and development potential in the field of optical sensing due to its unique transmission characteristics.In this paper,we proposed a single silicon-on-insulator?SOI?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,the resonant wavelength shift method and the intensity variation method,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 ?m?,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?FDTD?method is implemented,the analysis results show that the sensitivity Sn based on the resonant wavelength shift method is 2308 nm/refractive index unit?RIU?and the sensitivity Si based on the intensity variation method is 5.59×10-7 ppm-1 for the sensor designed in this paper.The single micro-ring structure designed in this paper can realize the work of two micro-rings,which saves the space and time of optical sensing and has great significance for the integration of large-scale sensor arrays with other devices in the SOI chip in the future.Finally,the slot waveguide structure with Ag is analyzed.The numerical result shows that the slot waveguide structure with Ag can achieve high intensity light limitation due to reflection of metal,and the evanescent field fraction increases significantly in slot area.The maximum evanescent field fraction is about 86.17%,which is significantly higher than that of the slot waveguide structure without Ag.And it is beneficial to enhance the interaction between light and matter and improve the sensitivity of the sensor.