Avalanche Pumping of Thulium Doped S-Band Fiber Amplifiers

In the last years a lot of different pump configurations were investigated for thulium doped fiber amplifiers (TDFA) in the S-band. Since the TDFA is using a four-level transition with long lifetime of the lower amplifier level, it turned out, that pumping with two wavelengths was most effective. Comparing the results of fluoride fibers doped with 2000 ppm and 5000 ppm thulium, we show that an avalanche effect significantly improves the efficiency of TDFAs with the highly thulium doped fiber when pumped at 1050 nm only and at the same time makes the dual-pump configuration 790/1050 nm inefficient. For the measurements we used self-made fluoride fibers