# Chiral orbital lasing in a twisted bilayer metasurface

## TL;DR

Researchers demonstrated chiral orbital lasing using a twisted bilayer photonic structure, enabling new applications in optical communication and diagnostics.

## Contribution

The novel contribution is achieving orbital chiral lasing via helical and non-Hermitian couplings in a twisted bilayer metasurface.

## Key findings

- A Moiré-type structure of semiconductor metasurfaces enables single-mode lasing over a 250 nm spectral range.
- Chiral orbital characteristics are confirmed through polarization-resolved imaging and self-interference measurements.
- The lasing arises from helical and non-Hermitian couplings of clockwise and counterclockwise resonances.

## Abstract

Chirality is a fundamental concept in physics, core to many phenomena in nonlinear optics, quantum physics and topological photonics. Photons are intrinsically chiral when carrying spin angular momentum, whereas orbital angular momentum can induce chirality when photons interact with structures with broken mirror symmetry. Here, we observe orbital chiral lasing from a twisted bilayer photonic structure, by leveraging its inherent structural chirality. We design and fabricate a Moiré-type optical structure consisting of two semiconductor membrane metasurfaces. By optically pumping the twisted bilayer, we achieve single-mode lasing over a broad spectral range of 250 nm. The lasing emission exhibits chiral orbital characteristics, arising from helical and non-Hermitian couplings between collective guided resonances rotating clockwise and counterclockwise and confirmed by polarization-resolved imaging and self-interference measurements. The observed chiral orbital lasing from a twisted photonic structure can contribute to diverse applications of chiral light in diagnostics, optical manipulation and communication with light.

Photons carrying orbital angular momentum inherit chirality from their twisted wavefront. Here, authors propose a twisted bilayer photonic structure - consisting of semiconductor membrane metasurfaces - where helical wavefronts are combined with non-Hermitian coupling, yielding orbital chiral lasing at telecom wavelengths.