Analysis of Bending-Induced Degradation of Orbital Angular Momentum Modes in Optical Fibers

Lee Lee,Song Song,Kim Kim

doi:10.3390/photonics6030097

Abstract

In this work, bending-induced deterioration of orbital angular momentum (OAM) modes in ring core fiber (RCF), photonic crystal fiber (PCF), and vortex fiber (VF) was theoretically investigated: Bending losses, coupling losses, and intermodal crosstalk at the interface between straight and bent optical fibers were investigated from the modal analysis of those three types of OAM mode fibers. In addition, the degradation of a topological charge number of an OAM mode due to the bending-induced birefringence and horizontal mode asymmetry was also investigated. Our investigation revealed that, in all aspects, the PCF is most robust to bending among the three types of optical fibers, and the most serious bending-induced problem in the VF and the RCF is the degradation of the topological charge number. The allowed minimum bending radii of VF and RCF appeared to be ~15 and ~45 mm, respectively, for the specific structures considered in this work. We expect that the methodology and results of our quantitative analysis on bending-induced degradation of OAM modes will be of great use in the design of OAM mode fibers for practical use.

Highlights

In accordance with increasing traffic on optical communication networks, a spatial mode division multiplexing scheme based on orbital angular momentum (OAM) modes have attracted great attention in recent years [1,2,3,4]
In spite of the fact that the fiber bending is inevitably involved in practical uses of the optical fibers, the effect of the fiber bending on OAM mode propagation has not been studied sufficiently with theoretical and numerical bases
Since the OAM mode is basically composed of two degenerate eigenmodes of opposite spatial symmetry which are excited with a relative phase difference of 90◦, the additional phase difference caused by the effective index variation of the eigenmodes in the bent fiber will impair the OAM mode

Summary

Introduction

In accordance with increasing traffic on optical communication networks, a spatial mode division multiplexing scheme based on orbital angular momentum (OAM) modes have attracted great attention in recent years [1,2,3,4]. By taking advantage of its unique property, that is, a helical phase front expressed as exp(-ilφ), where l is a topological charge number, and φ is an azimuthal angle, an OAM beam can have numerous modes distinguished by the topological charge number l To exploit this characteristic, there have been various theoretical and experimental studies on the generation, coupling, and multiplexing of OAM modes in fiber-optic communication [5,6,7,8,9]. The mode profile deformation in the bent optical fibers will cause intermodal crosstalk and coupling loss at the intersection between the bent and the straight parts of fibers All these impairments should be investigated quantitatively for the practical use of OAM fibers

Methods

Results

Conclusion