Theoretical study of the effect of pump wavelength drift on mode instability in a high-power fiber amplifier

Abstract

This paper presents an investigation of the effect of pump wavelength drift on the threshold of mode instability (MI) in high-power ytterbium-doped fiber lasers. By using a semi-analytical model, we study the effects of pump wavelength drift with a central pump wavelength around 976 nm and 915 nm, respectively. The influences of the pump absorption coefficient and total pump absorption are considered simultaneously. The results indicate that the effect of pump wavelength drift around 976 nm is stronger than that around 915 nm. For more efficient suppression of MI by shifting the pump wavelength, efficient absorption of pump power is required. The MI thresholds for fibers with different total pump absorptions and cladding diameters are compared. When the total pump absorption is increased, the gain saturation is enhanced, which results in the MI being mitigated more effectively and being more sensitive to pump wavelength drift. The MI threshold in gain fibers with larger inner cladding diameter is higher but more dependent upon pump wavelength. The results of this work can help in optimizing the pump wavelength and fiber parameters and suppressing MI in high-power fiber lasers.

Experimental study of transverse mode instability threshold dependence on seed wavelength in high power ytterbium-doped fiber amplifiers

“…With an understanding of TMI mechanism, much experimental and theoretical work has been carried out to understand its impact on fiber laser performance, and most importantly, to demonstrate methods of mitigating the TMI in fiber lasers. With the help of theoretical models and numerical work [21,22], several approaches to improve the TMI threshold have been proposed and successfully demonstrated, including optimizing numerical aperture [19], tailoring the Yb-ion distributions [23], optimizing bend diameter of the active fiber [18], enlarging core/inner cladding diameter ratio of the active fiber [23], shifting the pump or signal wavelength [24], increasing the bending loss of high order mode [25], employing counter/bi-direction pumping technique [26] and etc.…”