Subwavelength gratings micro-resonator for gas sensing applications

Subwavelength Gratings (SWG) waveguides are gaining significant interest in evanescent field sensing, which has a wide range of applications including biomedical and gas sensing. This interest arises from the gratings structure in the subwavelength regime where the optical properties of the waveguide can be controlled by the geometry through varying the gratings period and duty cycle to ensure higher overlap between the propagating mode and the material subjected to index change (sensing medium). This paper proposes an optical gas sensor based on the emerging SWG technology in a silicon-on-insulator platform, operating in the near-infrared region around the 1550 nm wavelength. The sensor design is based on a micro-resonator structure characterized by its small footprint. To achieve higher sensitivities, the SWG resonator's duty cycle should be decreased, increasing radiation losses. Conversely, increasing the resonator radius lowers the quality factor, reducing the sensor’s detection limit. An optimal design is chosen to ensure high sensitivity and low detection limits, defining a figure of merit for the sensor.