# Direct generation of tunable orbital angular momentum beams in microring lasers with broadband exceptional points

## TL;DR

This paper introduces a robust, broadband exceptional point in microring lasers with unidirectional coupling, enabling stable, tunable generation of orbital angular momentum beams for advanced optical applications.

## Contribution

It presents a novel broadband exceptional point design using unidirectional coupling in microring lasers, allowing stable and tunable OAM beam generation.

## Key findings

- Unidirectional coupling enhances robustness against perturbations.
- Broadband exceptional points enable stable OAM beam generation.
- Potential applications in telecommunications and quantum computing.

## Abstract

Non-Hermitian exceptional points (EPs) represent a special type of degeneracy where not only the eigenvalues coalesce, but also the eigenstates tend to collapse on each other. Recent studies have shown that in the presence of an EP, light-matter interactions are profoundly modified, leading to a host of novel optical phenomena ranging from enhanced sensitivity to chiral light transport. As of now, however, in order to stabilize a system at the vicinity of an exceptional point, its related parameters must be carefully tuned and/or continuously controlled. To overcome this limitation, here we introduce a new family of broadband exceptional points based on unidirectional coupling, implemented by incorporating an Sshaped waveguide in a microring cavity. In active settings, the resulting unidirectionality exhibits unprecedented resilience to perturbations, thus providing a robust and tunable approach for directly generating beams with distinct orbital angular momentum (OAM). This work could open up new possibilities for manipulating OAM degrees of freedom in applications pertaining to telecommunications and quantum computing, while at the same time may expand the notions of non-Hermiticity in the orbital angular momentum space.

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Source: https://tomesphere.com/paper/1903.10108