Miniaturized quasi-BICs based on a two-dimensional heterostructure to realize a low-threshold nanolaser.

Bound states in the continuum (BICs) have been demonstrated as an effective mechanism to achieve high quality (Q)-factor cavities for nanolasers. However, the development of a compact BIC laser with a low threshold has remained elusive. Here, we numerically report lasing action from symmetry-protected BICs in a two-dimensional heterostructure, which consists of compound gratings with finite cells surrounded by orthogonal distributed Bragg reflectors (DBRs). The compound grating is used to excite quasi-BIC resonance with a high Q-factor, and DBRs enable light confinement and localized electric fields to enhance light-matter interaction. The nanolaser with a threshold of 16.8 µJ/cm is achieved within a footprint as small as 3.35 × 3.35 µm. By changing the phase adjusting gap or asymmetry degree, it is possible to control the lasing emission. This work reveals a new, to our knowledge, path toward compact BIC lasers with a simple scheme for applications that require a small footprint and low threshold.