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, as shown in Figure 2. The proposed bi-direction deliverable PSC chains including 6 PSCs and 10s meters of gain fiber, as shown in Figure 2 (b), are able to deliver total pump power of about 14.4 kW, assuming 1.2kW output power from each diode laser. In principle, assuming 80% efficiency, the total power of fiber amplifier would reach 11.5kW.  Our novel fiber pump signal combiner structure shows several advantages: Effectively shrink the total fiber length of fiber amplifier and reduce the nonlinear effect. The ultimate limitation of single-frequency fiber amplifiers is the nonlinear effect of stimulated Brillouin scattering (SBS). A shorter fiber length is highly desired in the amplifier design to lower the SBS effect. The distributed design allows fewer input pumps for individual fiber combiner. Compared with traditional (6+1)X1 structure, individual fiber combiner in the distributed design could have lower number of input pump fibers like (2+1)X1 or even (1+1)X1, which not only simplify the fabrication but also provide the better thermal management on either conjunction section of the combiner and the gain fiber due to lower pump power delivered or fiber combiner itself due to pump light leakage.