Realization of bound states in the continuum in anti-PT-symmetric optical systems

TL;DR

This paper demonstrates a novel integrated photonic system that simultaneously achieves bound states in the continuum and anti-PT symmetry, enabling advanced optical functionalities like ultralow-linewidth lasing and enhanced sensing.

Contribution

It introduces a cascaded-resonator design that realizes both BICs and anti-PT symmetry simultaneously, a first in the field, with robustness to fabrication imperfections.

Findings

Achieved simultaneous BICs and anti-PT symmetry in a cascaded-resonator system

Demonstrated robustness of the system to fabrication imperfections

Potential applications include ultralow-linewidth lasers and enhanced optical sensors

Abstract

Novel physical concepts that originate from quantum mechanics, such as non-Hermitian systems (dealing mostly with PT and anti-PT symmetry) and bound states in the continuum (BICs), have attracted great interest in the optics and photonics community. To date, BICs and anti-PT symmetry seem to be two independent topics. Here, we for the first time propose a parallel cascaded-resonator system to achieve BICs and anti-PT symmetry simultaneously. We found that the requirements for the Fabry-P\'erot BIC and anti-PT symmetry can both be satisfied when the phase shift between any two adjacent resonators is an integer multiple of {\pi}. We further analyzed the cascaded-resonator systems which consist of different numbers of resonators and demonstrated their robustness to fabrication imperfections. The proposed structure can readily be realized on an integrated photonic platform, which can have many applications that benefit from the advantages of both BICs and anti-PT symmetry, such as ultralow-linewidth lasing, enhanced optical sensing, and optical signal processing.