Donor and acceptor modes in photonic band structure

TLDR

Photonic crystals are 3‑D periodic dielectric structures with a photonic band gap, and introducing a local defect creates modes inside this forbidden gap. Adding dielectric locally creates donor modes, while removing dielectric locally creates acceptor modes. These donor and acceptor modes enable high‑Q dielectric cavities of roughly one cubic wavelength, spanning from millimeter waves to ultraviolet, where metallic cavities are ineffective.

Abstract

Three-dimensionally periodic dielectric structures, photonic crystals, possessing a forbidden gap for electromagnetic wave propagation, a photonic band gap, are now known. If the perfect 3D periodicity is broken by a local defect, local electromagnetic modes can occur within the forbidden band gap. Addition of extra dielectric material locally, inside the photonic crystal, produces ``donor'' modes. Conversely, local removal of dielectric material from the crystal produces ``acceptor'' modes. It is now possible to make high-Q electromagnetic cavities of \ensuremath{\sim}1 cubic wavelength, for short wavelengths at which metallic cavities are useless. These new dielectric cavities can cover the range from mm waves to UV wavelengths.