Topological Photonic States at a 1-D Binary-Quaternary Interface

TL;DR

This paper investigates topological interface states at the boundary between binary and quaternary photonic crystals, identifying conditions for their existence and analyzing how they evolve with geometric changes.

Contribution

It introduces conditions for topological states at a 1-D binary-quaternary interface and explores their behavior as the quaternary crystal's geometry varies.

Findings

Topological interface states occur when the binary and quaternary crystals have opposite surface impedance signs.

Band gap closing conditions depend on optical path ratios.

Interface states evolve with geometric modifications of the quaternary crystal.

Abstract

The existence of topological interface states is investigated at the boundary between a binary photonic crystal and a quaternary photonic crystal, with each possessing inversion symmetric unit cells. Conditions are established that describe where the quaternary crystal can exist in parameter space subject to constraints. The closing of band gaps is discussed for different optical path ratios. When the binary and quaternary crystals share an interface, optical states appear at the interface when the two crystals have different signs for the surface impedance. The evolution of the states is displayed as the geometry of the quaternary crystal changes.