| As a typical integrated optics device,microring resonators(MRRs)are widely used in optical delay lines,optical frequency combs,optical filters and sensors featuring compact structure,high Q-factor and easy integration.The resonance structure of MRR can increase the effective length of light-matter interaction,which is conducive to ultra-high sensitivity sensing and has important application prospects in the field of label-free optical biosensing.MRR sensors based on Silicon-on-insulation(SOI)integrated optical waveguide utilize evanescent field to detect external sensing medium,but their sensitivity is limited due to the high mode field confinement of SOI waveguide,so how to realize highsensitivity MRR sensors is a hot research topic.In this paper,we design high-sensitivity slot microring resonator(SMRR)sensos and photonic crystal concentric dual-microring resonators(PhCCDMRR)sensor by three-dimensional time-domain finite-difference method,and improve the sensitivity of MRR sensors significantly with enhanced light-matter interaction inside resonance cavity.The main work of the essay is as follows:1.By introducing an air slot into the ring waveguide of the SMRR sensor,the light field energy is strongly confined to the slot area,which enhances the lightmatter interaction and improves the sensitivity of the SMRR sensor.Optimal geometrical values of the SMRR sensor are obtained by studying the influence of the sensor structure parameters on the transmission spectrum of resonance peak and the mode field distribution.The bent asymmetric directional coupler is employed to realize efficient coupling between the bus waveguide and resonance cavity,which significantly reduces the footprint of the SMRR sensor.The SMRR sensor achieved a concentration sensitivity of 725.71 pm/%for NaCl solution in biological bodies,corresponding refractive sensitivity is 403 nm/RIU,which is approximately six times greater than that of traditional strip waveguide microring resonator sensor.A low detection limit of 0.129%is also achieved.2.The PhCMRR sensor was designed by combining the whispering-gallery mode resonance effect of a microring with the slow-light effect in photonic crystal waveguide to enhance the light-matter interaction.By optimizing the structure parameters,a photonic crystal waveguide with a group index of 18.2 and a slowdown factor of 5.3 is obtained,and the sensitivity of the PhCMRR sensor is improved to 300 nm/RIU.Based on the PhCMRR structure,a small photonic crystal concentric microring waveguide is introduced for designing a PhCCDMRR sensor.A high extinction ratio of more than 22 dB and a refractive index sensitivity of 265 nm/RIU are achieved.This sensitivity is approximately four times greater than that of conventional strip waveguide MRR sensors.The high-sensitivity SMRR sensor and PhCCDMRR sensor proposed in this paper have potential applications in the field of label-free optical biosensing,which play a key role in the development of on-chip integrated sensing systems. |
