Fabrication of high-efficiency pump and signal combiner based on a thermally expanded core technique

• We have fabricated a high-efficiency (6+1) ×1 pump–signal combiner based on the thermally expanded core technique.
• The signal coupling efficiency of combiner increases dramatically from 51% to 94% by the thermally expanded core technique.
• We have measured the enlarged mode field diameters of SMF-28 with different heating times and measured the signal loss of each combiners fabricated by using the TEC fibers as signal fibers.

We have developed a high-efficiency (6+1)×1 pump–signal combiner for high power fiber lasers and amplifiers based on a thermally expanded core technique. The thermally expanded core technique can control the dopant concentration of the signal fiber, which can realize mode field match between the mode field sizes of the signal fiber and the output fiber. Using a thermally expanded core method, signal coupling efficiency is increased from 51% to 94% at the wavelength of 1064 nm. And we experimentally demonstrate that the optimal heating time for our signal fiber is around 30 min at a temperature around 1500 °C. At the same time, the pump coupling efficiency ranges from 96% to 99% at 976 nm. The high-efficiency pump and signal combiner can be implemented in many fiber laser or amplifier architectures.