Photonic-Crystal Waveguides with Disorder: Measurement of a Band-Edge Tail in the Density of States

TL;DR

This paper experimentally measures the density of states near the band edge in disordered photonic-crystal waveguides, revealing the formation of a Lifshitz tail due to Anderson localization, which was previously unobserved.

Contribution

It provides the first experimental observation of the DOS tail in a disordered photonic system, confirming theoretical predictions about localization effects.

Findings

Van Hove singularity is suppressed by disorder

Localized states form a Lifshitz tail in the DOS

High-resolution band structures were successfully measured

Abstract

We measure localized and extended mode profiles at the band edge of slow-light photonic-crystal waveguides using phase-sensitive near-field microscopy. High-resolution band structures are obtained and interpreted, allowing the retrieval of the optical density of states (DOS). This constitutes a first observation of the DOS of a periodic system with weak disorder. The Van Hove singularity in the DOS expected at the band edge of an ideal 1D periodic structure is removed by the disorder. The Anderson-localized states form a "tail" in the density of states, as predicted by Lifshitz for solid-state systems.