Metasurface lasers based on bound states in the continuum (BICs) have recently garnered plenty of research attention. In theory, a true photonic BIC is characterised by complete decoupling from the radiation continuum, implying infinite radiative lifetime and Q-factor. Interestingly, a slight perturbation can cause a true BIC to collapse to a Fano-like resonance and become what is known as a quasi-BIC with very high and controllable Q-factor. Metasurfaces with large ensemble of unit cells supporting such quasi-BIC modes are therefore excellent candidates for low-threshold laser cavity. 

Thus far, all the quasi-BIC metasurface lasers that have been demonstrated in the literature are fabricated through conventional top-down fabrication processes. In this project, we aim to demonstrate lasing in a bottom-up metasurface device supporting a perturbed symmetry-protected, quasi-BIC mode. The unit cell of the metasurface consists of a pair of InP nanosheet structures that are grown with the selective area epitaxy technique. The excellent sidewall facet quality of the nanosheets is expected to minimise scattering losses in the laser cavity and lead to ultra low threshold lasing at room temperature.