35-dB gain Tm-doped ZBLYAN fiber amplifier operating at 1.65 μm

We demonstrate the first high gain rare-earth-doped fiber amplifier operating at 1.65 μm. It consists of ZBLYAN fiber with a Tm/sup 3+/-doped core and Tb/sup 3+/-doped cladding, pumped by 1.22 μm laser diodes. It is possible to achieve efficient amplification with Tm/sup 3+/ ions if their amplified spontaneous emission (ASE) in the 1.75 to 2.0 μm wavelength region is suppressed by doping Tb/sup 3+/ ions in the cladding. A two-stage-type fiber amplifier is constructed and a signal gain of 35 dB is achieved for a pump power of 140 mW. A gain over 25 dB is realized in the 1.65 μm to 1.67 μm wavelength region.