Mitigating of Modal Instabilities in Linearly-Polarized Fiber Amplifiers by Shifting Pump Wavelength

TL;DR

This paper explores how shifting the pump wavelength in high power linearly-polarized fiber amplifiers can significantly suppress modal instabilities, combining theoretical modeling and experimental validation to identify optimal wavelengths for stability.

Contribution

The study introduces a semi-analytical model for MI frequency coupling and demonstrates effective MI suppression by pump wavelength tuning, validated through experiments.

Findings

Pumping at 915nm doubles the MI threshold compared to 976nm.

Experimental results agree with theoretical predictions.

MI suppression effectiveness decreases with larger core-to-cladding ratios.

Abstract

We investigated the effct of pump wavelength on the modal instabilities (MI) in high power linearly-polarized Yb-doped fiber amplifiers. We built a novel semi-analytical model to determine the frequency coupling characteristics and power threshold of MI, which indicates promising MI suppression through pumping at an appropriate wavelength. By pumping at 915nm, the threshold can be enhanced by a factor of 2.36 as compared to that pumped at 976nm. Based on a high power linearly-polarized fiber amplifier platform, we studied the influence of pump wavelength experimentally. The threshold has been increased by a factor of 2 at 915nm, which agrees with the theoretical calculation and verified our theoretical model. Furthermore, we show that MI suppression by detuning the pump wavelength is weakened for fiber with large core-to-cladding ratio.