Design Simulation of Gradient Photonic Crystal Slot Nanobeam Cavities for Refractive Index Sensing

In this study, we report the design simulation of photonic crystal slot nanobeam cavity sensors by utilizing the theory of electromagnetic wave dynamics that implemented in the finite element (FE) method. In the present work, the photonic crystal defect structure is designed to serve as the resonant cavity for light waves. Distinct resonant optical modes can be localized in the cavity by the photonic band gap to achieve efficient optical confinement. Accordingly, light waves of different wavelengths are respectively incident into the cavity structure immersed in a sensing fluid to obtain the resonance spectrum. By changing the surrounding fluids with different refractive indices, the offsets of the resonance wavelengths in the spectrum are observed and used for the refractive index sensing. We calculate the evaluation parameters, including the sensitivity, quality factor, and figure of merit, to evaluate the sensing performance of the device. It is expected that our results can provide a reference for the design and development of photonic crystal sensors.