A High-Performance and High-Resolution Optical Refractive Index Sensor Using a Compact Photonic Crystal Ring Resonator

In this study, we present an optical gas sensor (OGS) utilizing a remarkably compact photonic crystal ring resonator. Our novel design boasts an impressive resolution of 0.002 refractive index units (RIU). The sensor is ingeniously engineered by optimizing an add-drop filter with circular rods in a square lattice, which is then followed by the development of a new two-port resonator tailored for precise gas detection. By incorporating a novel circular ring at the resonator’s core, we achieve exceptional performance metrics, such as a narrow full width at half maximum (FWHM) and a high Q-factor. To comprehensively analyze the sensor’s behavior, we employ the two-dimensional finite difference time domain (FDTD) method to investigate the transmission spectrum and electromagnetic field distribution. The resulting design demonstrates remarkable attributes, including a remarkable transmission efficiency of 98%, an impressive Q-factor of 3040, and a sensitivity of 940 nm/RIU. Moreover, it offers a free spectral range of 100 nm and an outstanding figure of merit of 2186 RIU^− 1. These exceptional evaluation parameters unequivocally establish the superior performance of our optical sensor. Furthermore, our sensor’s compact footprint of merely 105.26 µm² positions it ideally for integration into optical integrated circuits (PICs). With its cutting-edge capabilities and small form factor, our optical gas sensor holds great promise for diverse real-world applications in gas sensing and related fields.