Abstract In this paper, we introduce a micro-ring resonator-based highly sensitive carbon dioxide sensor. For this purpose, a valley is created in the core of the ring, and then PbSe quantum dots (QDs) are deposited in the valley and the sensor is exposed to CO2 gas. In this way, the refractive index of the PbSe QDs increases with an increase in the concentration of CO2 gas flow, which shifts the resonant frequency of the micro-ring resonator accordingly. The designed sensor operates almost linearly over a wide range of CO2 gas concentrations and shows a high shift in resonance frequency at different concentrations of CO2 gas. The detection limit for the designed sensor is 10 ppm of CO2 gas, which is more sensitive than previously reported sensors based on microring resonators. The resonance frequency shifts are investigated by changing the width of the valley. The minimum width of the valley was determined for the evanescent field in which only the outer core of the ring affects the resonant frequency. Also, the modal analysis of the waveguide of the designed micro-ring resonator is investigated to determine the core width. The radius of the micro-ring resonator is also investigated to determine the length of the straight waveguide at 193.41 THz.
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