Vortex Laser at Exceptional Point

TL;DR

This paper demonstrates that a micro-laser operating at an exceptional point can directly emit vortex beams with tunable orbital angular momentum, using specific gratings to modulate the eigenmodes.

Contribution

It introduces a novel method to generate vortex lasers directly from a micro-laser at the exceptional point with tunable OAM by employing dual gratings for mode modulation.

Findings

Micro-laser at EP can emit vortex beams with arbitrary OAM.

Dual gratings enable precise control of vortex mode.

Analytical and simulation results confirm the approach.

Abstract

The optical vortices carrying orbital angular momentum (OAM) are commonly generated by modulating the available conventional light beam. This article shows that a micro-laser operates at the exceptional point (EP) of the non-Hermitian quantum system can directly emit vortex laser with well-defined OAM at will. Two gratings (the refractive index modulation and along azimuthal direction and the grating protruding from the micro-ring cavity) modulate the eigenmode of a micro-ring cavity to be a vortex laser mode. The phase-matching condition ensures that we can tune the OAM of the vortex beam to be arbitrary orders by changing the grating protruding from the micro-ring cavity while the system is kept at EP. The results are obtained by analytical analysis and confirmed by 3D full wave simulations.