Design and modeling of eye-shaped double-slot GaAs microring resonator for CO₂ sensing

Monitoring of CO₂ is crucial because of its profound impact on both environmental and human health. A novel highly sensitive refractive index (RI) sensor, utilizing a double-slot microring resonating structure, has been designed and numerically assessed for the sensitive detection of gas media. The structure consisted of a circular microring resonator nested in a racetrack resonating configuration mimicking the structure of an eye-shaped microring resonator (ESMRR). This system was simulated and designed for a GaAs double-slot core waveguide deposited on a suitable Al_0.5Ga_0.5As substrate. Optical transfer function of ESMRR and related equations were derived using Mason rule, while the numerical analysis was performed using the variational finite difference time domain (var- FDTD) method. The free spectral range (FSR) was extended to 137.68 nm that led to a remarkable bulk sensitivity of 1217.39 nm/RIU and a resolution of 4.93 × 10⁻⁶ RIU. The proposed sensing structure was envisioned for CO₂ sensing and demonstrated an impressive sensitivity of 24.4 pm/ppm for CO₂ detection with an estimated detection limit of 0.82 ppm.