# Topological Ring-Cavity Laser Formed by Honeycomb Photonic Crystals

## TL;DR

This paper theoretically demonstrates that topological interface modes in honeycomb photonic crystals can be used to create stable, high-intensity, single-mode lasers with controllable orbital angular momentum, suitable for advanced photonic applications.

## Contribution

It introduces a novel topological ring-cavity laser design based on honeycomb photonic crystals, exploiting topological interface states for stable, single-mode lasing with enhanced intensity.

## Key findings

- TRC modes achieve higher intensity than whispering-gallery modes
- Modes are separated in frequency, enabling intrinsic single-mode operation
- Circularly polarized injection can selectively stimulate specific modes

## Abstract

We clarify theoretically that the topological ring-cavity (TRC) modes propagating along the interface between two honeycomb-type photonic crystals distinct in topology can be exploited for achieving stable single-mode lasing, with the maximal intensity larger than a whispering-gallery-mode counterpart by order of magnitude. Especially, we show that the TRC modes located at the bulk bandgap center benefit maximally from the gain profile since they are most concentrated and uniform along the ring cavity, and that, inheriting from the Dirac-like dispersion of topological interface states, they are separated in frequency from each other and from other photonic modes, both favoring intrinsically single-mode lasing. A TRC mode running in a specific direction with desired orbital angular momentum can be stimulated selectively by injecting circularly polarized light. The TRC laser proposed in the present work can be fabricated by means of advanced semiconductor nanotechnologies, which generates chiral laser beams ideal for novel photonic functions.

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Source: https://tomesphere.com/paper/1906.02464