Moire-enabled optical vortex with tunable topological charge in twisted bilayer photonic crystals

TL;DR

This paper demonstrates a novel method to generate and tune optical vortex beams with adjustable topological charge using twisted bilayer moire photonic crystals, combining moire physics with optical vortex control.

Contribution

It introduces a new class of moire-induced Bessel-type modes enabling tunable optical vortex generation in layered photonic structures.

Findings

Vortex beams with OAM orders from -3 to 4 were experimentally demonstrated.

Selective excitation of specific topological charges was achieved by tuning interlayer parameters.

Localized modes enable vortex array generation across the moire superlattice.

Abstract

The orbital angular momentum (OAM) of light is a versatile degree of freedom with transformative impact across optical communication, imaging, and micromanipulation. These applications have motivated a growing demand for compact, reconfigurable vortex arrays with tunable topological charge, yet integrating these functionalities into nanophotonic platforms remains elusive. Among possible strategies to meet this challenge is exploiting the twist degree of freedom in layered structures, which enables both emerging moire physics and unprecedented reconfigurability of photonic and electronic properties. Here, we harness these capabilities in twisted bilayer moire photonic crystals (TBMPCs) to realize vortex array generation with tunable OAM, demonstrated both analytically and experimentally. Central to this advancement is a new class of quasi-bound state in the continuum: Bessel-type modes emerging from moire-induced interlayer coupling, which generate vortex beams with tailored spiral phase distributions. We experimentally demonstrate vortex beams spanning eight OAM orders, from -3 to 4, and achieve selective excitation of distinct topological charges at a fixed telecommunication wavelength by tuning the interlayer separation and twist angle. Furthermore, localized Bessel-type modes at AA stacking regions can be excited nonlocally across the moire superlattice, enabling vortex array generation. Our work offers new insights into moire physics and introduces an innovative approach for future multiplexing technology integrating OAM, wavelength, and spatial division.