High-order mode suppression in double-clad optical fibers by adding absorbing inclusions

Svetlana S Aleshkina,Denis S Lipatov,Alexey N Guryanov,Mikhail Yu Salganskii,Mikhail M Bubnov,Mikhail E Likhachev,Tatiana A Kochergina,Mikhail V Yashkov,Vladimir V Velmiskin,Konstantin K Bobkov

doi:10.1038/s41598-020-63969-7

Abstract

We proposed and experimentally demonstrated a technique for the suppression of unwanted modes in double-clad fibers with a high core-to-clad diameter ratio by introducing high-index absorbing inclusions into the first cladding of the fibers. These inclusions disturb the shape of undesirable modes, and a noticeable part of the power becomes localized inside the inclusion, resulting in an increase in the propagation loss of these modes. Two fiber designs were studied and realized: one with cylindrical symmetry and an absorbing high-index ring as the inclusion and another with high-index absorbing rods inserted around the fiber core. In both cases, the possibility of achieving perfect single-mode propagation was demonstrated both theoretically and experimentally.

Highlights

We proposed and experimentally demonstrated a technique for the suppression of unwanted modes in double-clad fibers with a high core-to-clad diameter ratio by introducing high-index absorbing inclusions into the first cladding of the fibers
In the most common case, the core diameter Dcore is an order of magnitude smaller than the first cladding diameter Dclad, so the major part of the power in the high-order modes (HOMs) is localized in the first cladding, and only a small part is still confined in the fiber core
We proposed a new approach for the suppression of undesirable modes in DC optical fibers with an increased core-to-cladding diameter ratio

Summary

Introduction

We proposed and experimentally demonstrated a technique for the suppression of unwanted modes in double-clad fibers with a high core-to-clad diameter ratio by introducing high-index absorbing inclusions into the first cladding of the fibers. Two fiber designs were studied and realized: one with cylindrical symmetry and an absorbing high-index ring as the inclusion and another with high-index absorbing rods inserted around the fiber core In both cases, the possibility of achieving perfect single-mode propagation was demonstrated both theoretically and experimentally. In the most common case, the core diameter Dcore is an order of magnitude smaller than the first cladding diameter Dclad, so the major part of the power in the high-order modes (HOMs) is localized in the first cladding, and only a small part is still confined in the fiber core For this reason, these modes have negligible gain in fiber amplifiers and are not excited during fusion splicing of DC fiber with conventional single-mode fiber. By optimizing the inclusion parameters, we succeed in increasing the propagation losses of the HOMs and simultaneously keep a reasonably low optical loss for the fundamental mode

Methods

Findings

Conclusion