Encapsulated Void Resonators in Van der Waals Heterostructures

Confining light in nanoscale air voids can enable new photonic applications by eliminating the requirement of low loss in traditional dielectric resonators. Van der Waals materials are uniquely suited for this purpose as they offer a tailored assembly of different materials and the ability to fully enclose air voids through transfer techniques. Here, highly lossy van der Waals materials are leveraged to demonstrate optical resonances that confine light in encapsulated air voids. Void resonances are theoretically designed in the visible spectrum and resonant modes supported by void arrays are identified. Experimentally, void arrays are fabricated in tungsten diselenide and the confined resonances are characterized using far-field reflectance measurements and scanning near-field optical microscopy. Using van der Waals heterostructure assembly, the voids are encapsulated with hexagonal boron nitride and tungsten diselenide, which substantially reduces the void volume causing a large spectral blue shift of the void resonance exceeding 150 nm. The work demonstrates a versatile optical platform for lossy materials, opening a new regime of material space for photonic devices.