Extraction of optical Bloch modes in a photonic-crystal waveguide

TL;DR

This paper introduces a method to extract and analyze optical Bloch modes in photonic-crystal waveguides using phase-sensitive near-field microscopy and Fourier analysis, enabling detailed mode characterization and behavior near band edges.

Contribution

The paper presents a novel reconstruction algorithm to decompose near-field measurements into superpositions of Bloch modes, advancing mode analysis in photonic-crystal waveguides.

Findings

Successfully decomposed measured fields into guided modes.

Observed mode extension near the band edge.

Enhanced understanding of mode behavior in photonic crystals.

Abstract

We perform phase-sensitive near-field scanning optical microscopy on photonic-crystal waveguides. The observed intricate field patterns are analyzed by spatial Fourier transformations, revealing several guided TE- and TM-like modes. Using the reconstruction algorithm proposed by Ha, et al. (Opt. Lett. 34 (2009)), we decompose the measured two-dimensional field pattern in a superposition of propagating Bloch modes. This opens new possibilities to study specific modes in near-field measurements. We apply the method to study the transverse behavior of a guided TE-like mode, where the mode extends deeper in the surrounding photonic crystal when the band edge is approached.