Flexible generation conversion and exchange of fiber guided orbital angular momentum modes using helical gratings

TL;DR

This paper introduces a flexible method using helical gratings for generating, converting, and exchanging fiber-guided orbital angular momentum modes with high efficiency and tunable spectral bandwidth.

Contribution

It presents a novel approach employing helical gratings for efficient, flexible OAM mode manipulation in fibers, including mode exchange and spectral filtering capabilities.

Findings

High conversion efficiency close to 100%

Conversion bandwidth of about 10 nm in transmission

Less than 1 nm bandwidth in reflection

Abstract

By exploiting helical gratings (HGs), we propose and simulate flexible generation, conversion and exchange of fiber guided orbital angular momentum (OAM) modes. HGs can enable the generation of OAM modes, and the OAM conversion between two arbitrary modes guided in fibers. A specific HG can exchange the OAM states of a couple of OAM modes, i.e, OAM exchange. In addition, a Fabry Perot cavity cascaded with two identical reflective HGs can reflect converted OAM modes with a comb spectrum. The HGs based generation conversion and exchange of OAM modes are dependent on helix period, orientation, and the fold number of helical fringes. The proposed method of generation, conversion, and exchange of fiber guided OAM modes using HGs is flexible and well compatible with OAM fibers, featuring a high conversion efficiency close to 100% and a conversion bandwidth about 10 nm in transmission spectra, while less than 1 nm in reflection spectra.