# Turbulence-Resistant All Optical Relaying Based on Few-Mode EDFA in Free-Space Optical Systems

## TL;DR

This paper explores a few-mode EDFA based all-optical relay system for free-space optical communication, demonstrating improved power budget and BER performance over single-mode systems, especially with zero mode-dependent gain.

## Contribution

It introduces a dual-hop free-space optical model using few-mode EDFA, showing enhanced power budget and BER performance compared to single-mode EDFA systems.

## Key findings

- Power budget increased by up to 11.5 dB at BER=1E-4
- Optimal relay placement is slightly backward from the midpoint
- BER performance is best with zero mode-dependent gain

## Abstract

We investigate the communication performance of a few-mode EDFA based all-optical relaying system for atmospheric channels in this paper. A dual-hop free space optical communication model based on the relay with two-mode EDFA is derived. The BER performance is numerically calculated. Compared with all-optical relaying system with single-mode EDFA, the power budget is increased by 4 dB, 7.5 dB and 11.5 dB at BER = 1E-4 under the refractive index structure constant Cn2 = 2E-14, 5E-14 and 1E-13 respectively when a few mode fiber supporting 4 modes is utilized as the receiving fiber at the destination. The optimal relay location is slightly backward from the middle of the link. The BER performance is the best when mode-dependent gain of FM-EDFA is zero.