Discovery of high-Q Fabry–Pérot supercavity modes

We report on a high-quality Fabry–Pérot supercavity mode observed in the terahertz frequency range. The experiment is carried out on a silicon chip with metallic gratings of equal period lithographically fabricated on both sides of the substrate. We show that the supercavity mode arises from interference between the Fabry–Pérot and substrate waveguide modes. As a result, Q factors as high as 880 are achieved at the terahertz frequency band. Possible applications of surface-enhanced electromagnetic field amplification are discussed and demonstrated experimentally.