Effects of Random Birefringence in Multimode Fibers on Nonlinear Ultrashort Pulse Propagation

TL;DR

This paper studies how random birefringence in multimode fibers affects nonlinear ultrashort pulse propagation, revealing complex interactions and conditions under which certain nonlinear phenomena persist despite birefringence.

Contribution

It introduces a modified model to analyze the impact of random birefringence on nonlinear pulse dynamics in multimode fibers, focusing on beam self-cleaning and soliton propagation.

Findings

Random birefringence generally weakens nonlinearity in MMFs.

Soliton self-frequency shift can be affected by birefringence.

Beam self-cleaning can survive high birefringence at high powers.

Abstract

Nonlinear pulse propagation in multimode fibers (MMFs) has attracted significant attention recently due to the rich spatiotemporal nonlinearities and promising applications. In practical scenarios, random birefringence in MMFs cannot be neglected, affecting the polarization-dependent nonlinear pulse propagation. This paper investigates the influence of random birefringence in MMFs on nonlinear ultrashort pulse propagation using a modified generalized multimode nonlinear Schr\"odinger equation. Two scenarios, spatial beam self-cleaning and multimode soliton propagation, are specifically examined. It is found that while random birefringence typically weakens nonlinearity in MMFs, certain nonlinear processes such as soliton self-frequency shift caused by intra-pulse Raman effect exhibit a complex relationship with random birefringence. Moreover, the study reveals that beam self-cleaning can endure random birefringence at high input peak powers. This research provides guidance for practical applications that utilize the nonlinear transmission of ultrashort pulses in MMFs.