Intrinsic mechanism for spectral evolution in single-frequency Raman fiber amplifier

TL;DR

This paper analyzes the spectral evolution in single-frequency Raman fiber amplifiers, revealing how pump configurations and pump source stability influence spectral broadening and single-frequency operation through gain dynamics.

Contribution

It introduces a theoretical analysis of gain dynamics in RFA, highlighting the natural low-pass filter effect in counter-pumped configurations and the impact of pump source stability.

Findings

Counter-pumped RFA exhibits a natural low-pass filter effect.

Pump source fluctuations cause spectral broadening in co-pumped RFA.

Stable laser sources improve single-frequency operation in both pump manners.

Abstract

In this work, the spectral evolution properties in single-frequency Raman fiber amplifier (RFA) with different pump manners are analyzed theoretically for the first time based on the gain dynamics. The analysis of gain dynamics reveals that the walk-off effect in counter-pumped manner produces a natural low-pass filter in single-frequency RFA. When applying rare-earth doped fiber lasers as the pump source, the strong temporal fluctuations in the pump source lead to spectral broadening in co-pumped manner, while the natural low-pass filter in countered-pumped case can still ensure single-frequency operation. Furthermore, applying temporal stable laser, such as single-frequency fiber laser or narrow band fiber laser spectral broadened by phase modulation technique, as the pump source would be superior for high-performance single-frequency RFA for the both two pump manners.