Bound States in the Continuum with Giant Q-factor Generating from One-Dimensional Symmetric Defect Ring Optical Waveguide Networks

In this paper, we focus on achieving bound states in the continuum (BICs) in optical waveguide networks. For this purpose, we design a one-dimensional symmetric defect ring optical waveguide networks (1D SDROWNs) and extensively investigate the propagation characteristics of electromagnetic waves in this network. The results indicate that 1D SDROWNs can effectively generate BICs. By varying parameters such as the ratio of the waveguide length of the lower arm to that of the upper arm(RWLLAUA), the ratio of the refractive index of the lower arm to that of the upper arm (RRILAUA), or the number of cells of the system, we not only realize a giant quality factor (Q-factor), but also reveal the angular frequency and quantity characteristics of quasi-BICs. Remarkably, the optimally designed network in this study theoretically realizes a huge Q-factor exceeding 109, which is at least three orders of magnitude higher than the maximum Q-factor achieved in the reported experiments. Furthermore, we observe two types of electromagnetic wave singularities at the quasi-BICs angular frequencies: the quasi-BICs-induced periodic transmission oscillation varying with the number of unit cells, and the quasi-BICs-induced high transmittance and low transmittance varying with the RWLLAUA. These results have broad application prospects in fields such as optical information storage, optical logic and computation, optical modulators and switches, optical sensor networks, optical filters and multi-channel selectors.