Kilowatt Class Side-pumped Thulium Fiber Amplifier

Q-Peak proposes a high power Thulium (Tm) doped fiber amplifier design operating at 2 µm wavelength utilizing a novel lateral fiber fusion side-pumping method and a nanoparticle doping technique to generate significant signal power and performance.  The proposed fusion side-pumping method will distribute the pump power along the length of the active fiber, allowing the high power amplifier to yield a relatively uniform gain distribution and a distributed thermal load. The fusion side-pumping method, consisting of fusing a coreless passive fiber to a Tm-doped double clad fiber, will provide significant cross-coupling between the input pump power and the cladding of the active fiber. This high power amplifier model will avoid thermal loading issues seen experimentally in end-pumping high power Thulium fiber lasers.  Q-Peak’s high power amplifier design will utilize a fusion region between the two fibers long enough to be able to efficiently pump bi-directionally without damaging any pump diode lasers. Additionally, the proposed nanoparticle doping method, developed by NRL, will intentionally cluster Tm ions into intimate contact in order exploit the “two-for-one” cross-relaxation phenomena observed in Thulium ions in close proximity.  The location of the Tm ions will be effectively controlled, causing the cross-relaxation process to require less ions.  Therefore, there is less absorption and less thermal load on the active fiber.  Utilizing these two methods will allow for a novel amplifier prototype capable of signal power in excess of 1 kW without having significant thermal load issues in the active fiber.