On-chip Light Trapping in Bilayer Moir\'e Photonic Crystal Slabs

Abstract

There has been remarkable recent progress in the formation of nano-resonators that support ultra-low-loss, compact dielectric photonic crystals with exceptional high-Q modes that operate at visible or telecom wavelengths. New insights into modal engineering have recently emerged from researchers exploring exotic electronic phases in 2D materials. The phenomenon relates to a twist in the angle between two layers of materials with high periodic spatial ordering, such as graphene. A moire pattern forms, and at a particular magic angle of twist, the electronic behavior significantly changes, enjoying a flat energy-momentum dispersion relationship. There is an optical analog to the electron twistronics: bilayer moire photonic crystal slabs can realize a flat-band condition. Under these conditions, the propagating modes have zero group velocity, thus giving rise to momentum-free trapping of Bloch waves in both transverse and vertical directions, creating high quality-factors and exceptionally small modal volumes that eventually lead to the enhancement of the Purcell effect. The dramatically different means of light-localization afforded by moire-structured cavities, very small mode volumes, and spatial determination by the overall moire pattern can manipulate spontaneous emission. This provides many opportunities for applications such as low-threshold lasing, single-photon source, quantum electrodynamics, photonic circuit, and quantum information processing.