# Layered Photonic Topological Insulators

## TL;DR

This paper introduces layered photonic topological insulators using all-dielectric bilayer photonic crystals, enabling advanced control of light states and promising applications in integrated photonics and information processing.

## Contribution

It presents the concept of layered photonic topological insulators based on all-dielectric bilayer structures, incorporating layer pseudospin for enhanced dispersion engineering and novel topological phases.

## Key findings

- Demonstration of layer-polarized and layer-mixed topological insulators.
- Observation of layer-direction locking behavior.
- High transmission maintained across domain walls despite defects.

## Abstract

The recent realization of photonic topological insulators has brought the discovery of fundamentally new states of light and revolutionary applications such as non-reciprocal devices for photonic diodes and robust waveguides for light routing. The spatially distinguished layer pseudospin has attracted attention in two-dimensional electronic materials. Here we report layered photonic topological insulators based on all-dielectric bilayer photonic crystal slabs. The introduction of layer pseudospin offers more dispersion engineering capability, leading to the layer-polarized and layer-mixed photonic topological insulators. Their phase transition is demonstrated with a model Hamiltonian by considering the nonzero interlayer coupling. Layer-direction locking behavior is found in layer-polarized photonic topological insulators. High transmission is preserved in the bilayer domain wall between two layer-mixed photonic topological insulators, even when a large defect is introduced. Layered photonic topological insulators not only offer a route towards the observation of richer nontrivial phases, but also open a way for device applications in integrated photonics and information processing by using the additional layer pseudospin.

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Source: https://tomesphere.com/paper/1812.09169