Low-threshold Optical Bistability Based on Bound States in the Continuum

Low-threshold optical bistability is essential for practical nonlinear optical applications. Many bi-stable optical devices based on high-quality-factor resonators have been proposed to reduce the thresh-old intensity. However, demonstrating high-quality-factor resonance requires complex fabrication tech-niques. In this work, we numerically demonstrate optical bistability with bound states in the continuum in a simple one-dimensional Si photonic crystal. The designed structure supports bound states in the continuum, producing an ultrahigh quality factor without tough fabrication conditions. The threshold intensity of the designed device is 150 MW/cm2 at the optical communication wavelength. This scheme may lead to a new class of nonlinear photonics.