We report an experiment of incoherent beam combining based on a 7×1 all-fiber signal combiner with output power up to 6.08 kW. Properties of transmission efficiency and beam quality are analyzed by beam propagation method. Based on the calculative results, a 7×1 all-fiber signal combiner is fabricated. The handle power capacity is tested with average transmission efficiency of 98.9% and beam quality of M2≈10.
A high-efficiency pump-signal combiner for high power fiber amplifiers based on thermally expanded core (TEC)
technique is reported in this paper. TEC technique is used to fabricate mode-field adapter which allows optimization of
signal fibers in a monolithic (6+1) ×1 fiber combiner. The combiner is fabricated by connecting a tapered fiber bundle
(TFB) to a passive 25/250 (NA=0.06/0.46) double-clad fiber (DCF). By this method, the coupling efficiency of SMF-28
signal fiber at 1064nm improves from 54% to 92.7%. The average pump coupling efficiencies of six 105/125 (NA=0.15)
fibers are measured to be 96.7% at 976nm. Furthermore, the average signal transmission efficiency is around 93.3%. The
fabricated fiber combiner is spliced to an Yb-doped DCF for use as an all-fiber amplifier. The slope efficiency is
measured to be 71.6%.
We study the mode evolution properties in a 3 x 1 adiabatic tapered single-mode fiber combiner (ATSMFC) in theory. The fabrication of the combiner for single mode fibers based on adiabatic tapered fused bundle (TFB) technique with the assistant of low index glass capillary is introduced. The whole taper region can be seen as three phase: single-mode fibers, multi-core fiber and multi-mode fiber. Supermodes of three-core fiber with scalar mode results are derived based on coupling mode theory. The analysis is verified with numerical examples by fully vectorial finite element mode solver (Cosmol Multiphysics). Simulation results show that the three input core modes in single-mode fibers gradually evolve into three supermodes in three-core fiber and then evolve into three low-order modes in the multi-core fiber. Effective indices for different modes are calculated which can depict the evolution process vividly. The results may be useful for practical high power fiber laser systems.
Pumping coupler technology is one of the critical technologies for high power laser and amplifier. Side-pumping
technology can couple pumping beam into inner cladding of the double-clad fiber through the side of the fiber.
Compared to the end-pumping technology by tapered fused bundle (TFB), it has many superiorities. That the signal fiber was not disconnected guarantees high transmission efficiency, providing the possibility of transmitting a high power signal. Additionally, the pump light is coupled into the double-cladding fiber all along the coupler’s body (~5-10 cm long), which reduces the thermal effects caused by leakage of pumping light, resulting in high pump power handling capabilities. 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 developed. The complete simulations were carried out for the process of side-pumping. From detailed information about simulations, we found that the pump efficiencies, one of the vital parameters of pumping coupler, have a significant influence with coupling length, the numerical aperture (NA) and taper ratio of pump fiber. However, the diversification of the parameters drops the high transmission efficiency barely. Optimized the parameters in the simulations, the pump and signal coupling efficiencies are 97.3% and 99.4%, respectively. Based on theoretical analysis, the side-pumping coupler was demonstrated at the pump and signal coupling efficiencies are 91.2% and 98.4%, respectively. This fiber coupler can be implemented in almost any fiber laser or amplifier architecture.