Fabrication of 2 × 1 signal combiner for high power lasers based on D-shaped fiber pair

Abstract

The all-fiber signal combiner based on incoherent beam combination is the key component to realize the power amplification of fiber laser. At present, the all-fiber combiner is generally fabricated by splicing a tapered fused fiber bundle with an output fiber. During the tapering process, the size of the cladding and core of the input fiber will become smaller at the same time, which will inevitably cause the core mode to change to the cladding mode. To reduce the degree of taper, the method of hydrofluoric acid corrosion is generally used to remove part of the cladding of the input fiber to make the diameter of the optical fiber smaller. Even so, the tapering process is still unavoidable. Therefore, we have proposed a new manufacturing method for the all-fiber signal combiner. This method uses a CO2 laser to ablate part of the cladding of the input optical fiber to produce a D-shaped fiber. Then, the planes of the two D-shaped optical fibers are pressed tightly and then heated to get fused. Finally, the D-shaped fiber pair is cut and spliced with an output fiber to form an all-fiber combiner. This novel method avoids the tapering process and hardly changes the core size of the input fiber. The relationship between the core distance of the input fiber and the beam quality of the signal combiner manufacturing by the new method is studied by the finite-difference beam propagation method. We also compared the combining ability and beam quality of the combiner made based on the D-shaped fiber and that made by the tapered fiber bundle. Both the simulation and experimental results showed that the beam quality of the combiner made based on the D-shaped fiber was better than that made by the traditional method.