Efficient generation and control of different order orbital angular momentum states for communication links

TL;DR

This paper introduces a novel optical device that efficiently encodes and decodes two bits of information into specific orbital angular momentum states of a beam, enabling high-bandwidth optical communication.

Contribution

The paper presents a new optical setup using spin-to-orbital angular momentum conversion and a q-plate to generate and switch between multiple OAM states for communication.

Findings

Generates four OAM states of order ±2 and ±4

Achieves high switching speed with electro-optical components

Enables multi-bit information transfer using OAM states

Abstract

We present a novel optical device to encode and decode two bits of information into different Orbital Angular Momentum (OAM) states of a paraxial optical beam. Our device generates the four angular momentum states of order $\pm 2$ and $\pm4$ by Spin-To-Orbital angular momentum Conversion (STOC) in a triangular optical loop arrangement. The switching among the four OAM states is obtained by changing the polarization state of the circulating beam by two quarter wave plates and the two-bit information is transferred to the beam OAM exploiting a single $q$-plate. The polarization of the exit beam is left free for additional one bit of information. The transmission bandwidth of the device may be as large as several megahertz if electro-optical switches are used to change the beam polarization. This may be particularly useful in communication system based on light OAM.