Observation of slow light in glide-symmetric photonic-crystal waveguides

We report optical transmission measurements on suspended silicon photonic-crystal waveguides, where one side of the photonic lattice is shifted by half a period along the waveguide axis. The combination of this glide symmetry and slow light leads to a strongly enhanced chiral light-matter interaction but the interplay between slow light and backscattering has not been investigated experimentally in such waveguides. We build photonic-crystal resonators consisting of glide-symmetric waveguides terminated by reflectors and use transmission measurements as well as evanescent coupling to map out the dispersion relation. We find excellent agreement with theory and measure group indices exceeding 90, implying significant potential for applications in slow-light devices and chiral quantum optics. By measuring resonators of different length, we assess the role of backscattering induced by fabrication imperfections and its intimate connection to the group index. (C) 2022 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

Automated summary

We report optical transmission measurements on suspended silicon photonic-crystal waveguides with a glide symmetry and slow light. The chiral light-matter interaction is strongly enhanced by this combination, but the interplay between slow light and backscattering has not been experimentally investigated in such waveguides. Photonic-crystal resonators consisting of glide-symmetric waveguides terminated by reflectors were built, and transmission measurements and evanescent coupling were used to map out the dispersion relation. The results show excellent agreement with theory and reveal the potential of these waveguides for applications in slow-light devices and chiral quantum optics.