A Fused Side-pumping Optical Fiber Coupler Based On Twisting

Pumping coupler technology is one of the key technologies for high power laser and amplifier. Side-pumping technology couples pumping beam into inner cladding of the double-clad fiber through the side of the fiber and is a potential candidate since it can be easily extended to cascaded pumping technology. Compared with the end-pumping technology by tapered fused bundle(TFB), it has the salient superiority that the signal fiber would not be disconnected, providing the possibility of transmitting a high power signal and not introducing any other loss. For the realization of reliable, rugged and efficient high power fiber amplifiers and fiber laser systems, a novel kind of fused side-pumping coupler based on twisting is researched and developed. The primary coverage as follows: 1. Fiber taper technology and twist manage technology are vital, as the foundation of the paper research. The transmission feature of light in tapered fiber was analyzed in detail through Geometrical Optical Method and Wave Optical Method. The relationship between the transmission feature and the parameters of tapered twisted fiber was given by simulations. 2. Simulations were carried out for the process of side-pumping and the energy distribution of pump light. Results show that the coupling length, the numerical aperture(NA), number and taper ratio of pump fiber have a significant influence on the pump efficiencies and the heat loss. With optimized parameters, the pump coupling efficiencies for the side-pumping couplers of single and 6 pump fiber are 97.3% and 87.2% respectively, and both signal coupling efficiencies are above 99%. Simulations also show that the isolation of the side-pumping coupler is good. 3. Based on the theoretical analyses and simulation results, the side-pumping coupler of single pump fiber was manufactured through fusing and twisting method with optimized parameters. The measured pump and signal coupling efficiencies are 91.2% and 98.4%, respectively. The side-pumping coupler of 2 pump fibers also was investigated experimentally.