Exceptional points at bound states in the continuum in photonic integrated circuits

We propose the realization of exceptional points (EP) at bound states in the continuum (BIC), with two coupled strips, made of an electron-beam resist and patterned on the thin film photonic integrated platform, which makes possible etchless photonics integrated circuits (PIC). The loss rate of the EP can be significantly decreased through merging the BIC peaks in the dual-BIC scheme. The orthogonality of the eigenvectors is retrieved for evaluating the Hermitian orthogonal eigenvectors and the non-Hermitian EP features. We also find that engineering the dimension of the dual-BIC scheme enables a transition between the coalesced eigenvectors in the EP and the orthogonal eigenvectors in the Hermitian system. This work is of great significance for the exploration on BIC-based directional coupling with ultralow-loss phase matching conditions, special coupling conditions of EPs and BICs with coupled quasi-BIC systems, dynamical EP encircling, and EP topology, in PICs.