Abstract
Wavelength-scale lasers provide promising applications through low power consumption requiring for optical cavities with increased quality factors. Cavity radiative losses can be suppressed strongly in the regime of optical bound states in the continuum; however, a finite size of the resonator limits the performance of bound states in the continuum as cavity modes for active nanophotonic devices. Here, we employ the concept of a supercavity mode created by merging symmetry-protected and accidental bound states in the continuum in the momentum space, and realize an efficient laser based on a finite-size cavity with a small footprint. We trace the evolution of lasing properties before and after the merging point by varying the lattice spacing, and we reveal this laser demonstrates the significantly reduced threshold, substantially increased quality factor, and shrunken far-field images. Our results provide a route for nanolasers with reduced out-of-plane losses in finite-size active nanodevices and improved lasing characteristics.
Highlights
Wavelength-scale lasers provide promising applications through low power consumption requiring for optical cavities with increased quality factors
The intrinsic topological nature of BICs splits them into a few groups, with two of the most conventional kinds represented by symmetry-protected BICs, existing at high-symmetry points of the momentum space, and accidental BICs, which can be realized for an arbitrary in-plane wavevector
The design of the laser cavity is based on an infinite-size InGaAsP photonic crystal slab structure with a thickness of 650 nm modulated with a squarelattice array of air holes
Summary
Wavelength-scale lasers provide promising applications through low power consumption requiring for optical cavities with increased quality factors. Various mechanisms for strong light confinement were proposed and demonstrated in subwavelength and wavelength-scale optical cavities used to decrease their lasing threshold[1,2,3,4] Nanolasers such as defect-type photonic crystal lasers and plasmonic lasers possess limited output power and exhibit instability to the structural disorder[5,6]. Optical bound states in the continuum (BICs) were shown to be a versatile tool for substantial suppression of out-of-plane radiative losses and dramatic enhancement of the quality factor (Q factor) in infinite periodic structures to provide low-threshold lasing and high-output powers[8,9,10]. Our study presents the direct observation of all the BIC lasers simultaneously and provides an efficient recipe to reduce the optical loss in active nanocavities with finite sizes
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