Mitigating of modal instabilities in linearly-polarized fiber amplifiers by shifting pump wavelength

Abstract

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