Resonantly pumped amplification in a Tm-doped large mode-area photonic crystal fiber

摘要

Ultra-large mode area thulium-doped photonic crystal fibers (Tm:PCF) have enabled the highest peak powers in 2 micron fiber laser systems to date. However, Tm:PCFs are limited by slope efficiencies of ＜50% when pumped with 790 nm laser diodes. A well-known alternative is pumping at 1550 nm with erbium/ytterbium-doped fiber (Er/Yb:fiber) lasers for efficiencies approaching ～70%. However, these 1550 nm pump lasers are also relatively inefficient themselves. A recently demonstrated and more attractive approach to enable slope efficiencies over 90% in thulium-doped step-index fibers is resonant pumping (or in-band pumping). This utilizes a high power thulium fiber laser operating at a shorter wavelength as the pump. In this manuscript, we describe an initial demonstration of resonant pumping in Tm:PCF. While the extracted power was still in the exponential regime due to pump power limitations, slope efficiencies in excess of ～64 have been observed, and there is still room for improvement. These initial results show promise for applying resonant pumping in Tm:PCF to improve efficiencies and facilitate high power scaling in ultra-large mode area systems.