Active Distributed Pump Signal Combiner for High Power Fiber Laser

To realize a continuous-wave (CW) fiber laser operating at the kilowatt (kW) level, the integration of pump signal combiners becomes a critical necessity. These combiners play a pivotal role in coupling multiple pump lights into a double-cladding fiber, where the total power of the pump lights also reaches the kW level.In this SBIR program, we propose a distributed active fiber pump signal combiner using side-pump fiber combiner technology and the pump fibers are directly attached to the gain fiber. Moreover, the fiber combiners are distributed over the gain fiber to avoid the overheating of the gain fiber due to absorption of pump power. The proposed distributed active fiber pump signal combiners are going to demonstrate their performance in a 10KW level tandem pumped fiber amplifier.This approach offers the following key benefits:Extraordinary thermal management A recent theoretical study shows that the TMI threshold increases linearly as the active PSCs deployed along the gain fiber increases. When the number of pump points is four, the threshold can be increased by 50% as compared to that achieved with only one fiber PSC. The more active PSCs used, the higher increase of the TMI threshold. Reduced Nonlinear Effects. The distributed active fiber PSCs effectively reduces the total fiber length of the fiber amplifier, mitigating nonlinear effects. The primary limitation of single-frequency fiber amplifiers lies in the nonlinear effect of SBS. A shorter fiber length is paramount in the amplifier design to diminish the impact of SBS.Preservation of Beam Quality. It is well-known that side-pumping PSC avoids directly modifying the core's mode field, minimizing distortion of the signal beam. With distributed active PSC structure, this uniform excitation ensures that the amplified signal maintains high beam quality, crucial for applications requiring diffraction-limited outputs.Flexibility in Laser Design. A laser system with multiple active fiber PSCs offers greater design flexibility. Engineers can tailor the configuration to specific application requirements, such as beam combining, power scaling, or spectral broadening. The modular scalability makes it easier to upgrade systems incrementally without redesigning the entire architecture.