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

TL;DR

This paper experimentally investigates slow light in glide-symmetric photonic-crystal waveguides, revealing enhanced chiral light-matter interactions and the impact of backscattering, with potential applications in slow-light and quantum optics.

Contribution

It provides the first experimental analysis of slow light and backscattering interplay in glide-symmetric photonic-crystal waveguides, confirming theoretical predictions.

Findings

Group indices exceeding 90 were measured.

Backscattering effects increase with higher group index.

Excellent agreement between experimental data and theory.

Abstract

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.