[Invited paper] Hybrid silicon-on-chip lasers based on quasi-bound states in the continuum

Abstract

Bound states in the continuum (BICs) in photonic crystal slabs represent the resonances with an infinite quality(Q)-factor, occurring above the light line for an infinitely periodic structure. We show that a set of BICs can turn into quasi-BICs with a very high Q-factor even for two or three unit cell structures. They are explained by a viewpoint of BICs originating from the tight-binding of individual resonances of each unit cell as in semiconductors. Combined with a reciprocal-space matching technique, the microcavities based on quasi-BICs can achieve a Q-factor as high as defect-based PhC microcavities. Few experimental studies have been done for BIC lasers. In this work, based on our finding on quasi-BICs, we have designed silicon-on-chip micro-cavity lasers, which integrates a BIC structure onto a combination of a 1-micron-thick oxide layer and a silicon substrate. Then, laser samples were fabricated by using a low-temperature wafer bonding technique and characterized with optical pumping method. The laser sample exhibits a clear evidence of lasing and a strong single mode operation. We note that the lasing action has a good tolerance over fabrication error, which is an experimental evidence of the theoretically anticipated conservation of topological charges. Detailed discussion on the laser characteristics will be presented in the talk.