Observation of nonlinear bands in near-field scanning optical microscopy of a photonic-crystal waveguide

TL;DR

This study uses near-field scanning optical microscopy to measure the photonic bandstructure of GaAs photonic-crystal waveguides, revealing nonlinear bands caused by a tip-induced phase modulation effect, which was previously unreported.

Contribution

It identifies a waveguide-specific near-field tip effect causing additional nonlinear bands, expanding understanding of near-field optical measurements in photonic structures.

Findings

Detection of unexpected nonlinear bands in the bandstructure

Power-dependent behavior of the additional bands

Identification of a tip-induced phase modulation effect

Abstract

We have measured the photonic bandstructure of GaAs photonic-crystal waveguides with high energy and momentum resolution using near-field scanning optical microscopy. Intriguingly, we observe additional bands that are not predicted by eigenmode solvers, as was recently demonstrated by Huisman et al. [Phys. Rev. B 86, 155154 (2012)]. We study the presence of these additional bands by performing measurements of these bands while varying the incident light power, revealing a non-linear power dependence. Here, we demonstrate experimentally and theoretically that the observed additional bands are caused by a waveguide-specific near- field tip effect not previously reported, which can significantly phase-modulate the detected field.