Ultracompact multibound-state-assisted flat-band lasers
Jieyuan Cui, Song Han, Bofeng Zhu, Chongwu Wang, Yunda Chua, Qian Wang, Lianhe Li, A. G. Davies, E. H. Linfield, Qijie Wang, Qijie Wang, Qijie Wang
Abstract
Highly compact lasers with a low threshold and stable single-mode operation are in great demand for integrated optoelectronics. However, considerable side leakages and radiation losses in small cavities substantially degrade the quality (Q) factor, posing a substantial obstacle in pursuing high-performance miniature lasers. Here we propose and experimentally demonstrate a flat-band laser supplemented by multiple bound states in the continuum. By simultaneously confining light in all three dimensions, a high Q factor of ~1,440 in an ultracompact terahertz quantum cascade laser cavity with a lateral size of ~3λ is reported. The field confinement makes it possible to realize an electrically pumped single-mode terahertz laser with a low threshold current density, despite the small device footprint. This surface-emitting laser emits a well-defined beam with good directionality. The demonstrated multibound-state-assisted flat-band design is also applicable to other wavelength regimes, offering a route to energy-efficient, monolithically integrated and ultracompact laser sources that suit a wide range of applications. A laser design that exploits multiple bound states on a flat band to tightly confine light in three dimensions yields an ultracompact terahertz quantum cascade laser cavity with a lateral size of ~3λ.