Asymmetrical Fabry-Perot cavity slot micro⁃ring resonator and its sensing characteristics

To achieve high quality factor and high-sensitivity refractive index sensor, a slot micro-ring resonator(MRR) based on asymmetric Fabry-Perot (FP) cavity was proposed. The structure consisted of a pair of elliptical holes to form an FP cavity and a micro-ring resonator. The two different optical modes generated by the micro-ring resonator were destructively interfered to form a Fano line shape, which improved the system sensitivity while obtaining a higher quality factor and extinction ratio. The transmission principle of the structure was analyzed by the transfer matrix method. The transmission spectrum and mode field distribution of the proposed structure were simulated by the finite difference time domain(FDTD) method, and the key structural parameters affecting the Fano line shape in the device were optimized. The simulation results show that the quality factor of the device reached 22 037.1, and the extinction ratio was 23.9 dB. By analyzing the refractive index sensing characteristics, the sensitivity of the structure was 354 nm·RIU^-1, and the detection limit of the sensitivity was 2×10^-4 RIU. Thus, the proposed compact asymmetric FP cavity slot micro-ring resonator has obvious advantages in sensing applications owing to its excellent performance.