Measuring the spatial extent of individual localized photonic states

TL;DR

This study measures the size of individual localized photonic states in a photonic crystal waveguide using near-field techniques, revealing states not visible in transmission and providing quantitative size estimates.

Contribution

It introduces a perturbation-based method to directly measure the spatial extent of localized photonic states and validates it with near-field measurements.

Findings

Localized states are shorter than the waveguide.

Some localized states are not observable in transmission.

Participation ratio measurements agree with perturbation results.

Abstract

We measure the spatial extent of individual localized photonic states in a slow-light photonic crystal waveguide. The size of the states is measured by perturbing each state individually through a local electromagnetic interaction with a near-field probe. We find localized states which are not observed in transmission and show that these states are shorter than the waveguide. We also directly obtain near-field measurements of the participation ratio, from which the size of the states can be derived, in quantitative agreement with the size measured with the perturbation method.