High-Q quasi-BIC in photonic crystal nanobeam for ultrahigh sensitivity refractive index sensing
Bing Duan, Songyi Liu, Xiao Liu, Xiao‐Chong Yu, Chuan Wang, Daquan Yang
Abstract
We propose and numerically demonstrate the existence of bound state in the continuum (BIC) in silicon-based one-dimensional photonic crystal nanobeam (1D-PCN). The 1D-PCN is formed by introducing rectangular air nanoholes in a simple 1D nanobeam waveguide. By engineering the structure parameters, an ideal BIC with infinite quality (Q) factor is demonstrated in 1D-PCN. On this basis, we further investigate the refractive index sensing performance with quasi-BIC by introducing defects into the aforementioned 1D-PCN structure, and an ultrahigh Q factor of ∼ 4.1 × 107 is obtained. Compared to the conventional sensing mechanism based on the shift of forbidden bands modes, the 1D-PCN sensor based on quasi-BIC has a comparable figure of merit (FOM) higher than 106. It is worth mentioning that the quasi-BIC can be directly excited by external light sources without the special coupling mechanism, which provides a new method for ultrasensitive refractive index sensing.