Confining Light in Hexagonal Boron Nitride Photonic Resonators

Abstract van der Waals (vdWs) materials have been highly regarded in optoelectronics and nanophotonics, given that they exfoliate effortlessly and offer precise control over light–matter interactions. When constructed as metasurfaces, all-dielectric vdWs are capable of hosting tailored Mie responses across the visible-NIR spectra. However, typically Mie resonances are associated with low quality factors due to the inverse correlation between refractive index and bandgap energy. Here we demonstrate the existence of quasi-bound states in the continuum (qBIC) in a square array of tapered cylindrical resonators in the vdW hexagonal boron nitride. The mode frequency and quality factor are shown to be substantially modified by introducing vertical dielectric symmetry after coating the resonator array with PMMA. Our experimental study is supported by extensive optical simulations of transmittance for different structure parameters and environments. The agreement between theory and experiment is excellent. Our results confirm the potential of using qBICs in low-index materials with controllable features.