Transverse mode instability, thermal lensing and power scaling in Yb3+-doped high-power fiber amplifiers

Zervas, Michalis N. (2019) Transverse mode instability, thermal lensing and power scaling in Yb³⁺-doped high-power fiber amplifiers. Optics Express, 27 (13), 19019-19041. (doi:10.1364/OE.27.019019).

Record type: Article

Abstract

Transverse mode instability (TMI) is compared to thermal lensing (TL) power threshold and used to derive power scaling limits in high-power fiber amplifiers. The TMI power threshold is shown to be ~65% of the TL one and dominates power scaling. In addition to commonly used limiting effects, we introduce a bend-induced mechanical reliability criterion, which limits the maximum allowable cladding diameter to ~600μm. This also results in the introduction of a critical pump brightness, the minimum required pump brightness at which the maximum signal power is achieved. The maximum achievable power depends primarily on the choice of pumping wavelength, amplifier gain and heat coefficient. Maximum signal powers of ~28kW to ~38kW, for diode pumping (λ_p = 976nm), and ~35kW to ~52kW, for tandem pumping (λ_p = 1018nm), are predicted for single-mode fiber amplifiers operating at signal wavelength λ_s = 1070nm, when the amplifier gain is increased from 10dB to 20dB. For an amplifier gain of 10dB, the maximum achievable signal power varies from 85kW to 25kW for tandem pumping and 35kW to 20kW for diode pumping, when the heat coefficient varies from 1% to 15% and 5.5% to 20%, respectively. The corresponding critical pump brightness varies from ~0.50 W/(μm² sr) to ~0.14 W/(μm² sr) for tandem pumping and ~0.25 W/(μm² sr) to ~0.13 W/(μm² sr) for diode pumping.