Mode instability thresholds for Tm-doped fiber amplifiers pumped at 790 nm

TL;DR

This paper models mode instability thresholds in Tm-doped fiber amplifiers pumped at 790 nm, revealing higher thresholds than Yb-doped counterparts due to longer wavelength and gain saturation effects.

Contribution

It provides a detailed numerical analysis of mode instability thresholds in Tm-doped fiber amplifiers, highlighting the impact of cross-relaxation and heat load on stability.

Findings

Higher mode instability thresholds in Tm-doped fibers compared to Yb-doped fibers.

Thresholds are influenced by longer signal wavelength and gain saturation.

Tm-doped amplifiers achieve 60% efficiency with strong cross-relaxation.

Abstract

We use a detailed numerical model of stimulated thermal Rayleigh scattering to compute mode instability thresholds in Tm$^{3+}$-doped fiber amplifiers. The fiber amplifies 2040 nm light using a 790 nm pump. The cross-relaxation process is strong, permitting power efficiencies of 60%. The predicted instability thresholds are compared with those in similar Yb$^{3+}$-doped fiber amplifiers with 976 nm pump and 1060 nm signal, and are found to be higher, even though the heat load is much higher in Tm-doped amplifiers. The higher threshold in the Tm-doped fiber is attributed to its longer signal wavelength, and to stronger gain saturation, due in part to cross-relaxation heating.