Universal behavior of the scattering matrix near thresholds in photonics

TL;DR

This paper reveals a universal behavior of the scattering matrix near thresholds in photonics, supported by a model and demonstrated across various optical systems, enhancing understanding of spectral properties in photonic structures.

Contribution

It introduces a simple universal model for the scattering matrix near thresholds, validated across multiple photonic systems, based on fundamental symmetry principles.

Findings

Universal scattering matrix behavior near thresholds

Model validated in photonic crystal slab, dielectric interface, metallic waveguides

Provides insights into spectral properties in photonics

Abstract

Scattering thresholds and their associated spectral square root branch points are ubiquitous in photonics. In this Letter, we show that the scattering matrix has a simple universal behavior near scattering thresholds. We use unitarity, reciprocity, and time-reversal symmetry to construct a two-parameter model for a two-port scattering matrix near a threshold. We demonstrate this universal behavior in three different optical systems, namely a photonic crystal slab, a planar dielectric interface, and a junction between metallic waveguides of different widths.