Optical amplification ranging from 1600 to over 1680 nm in thulium-doped fluorotellurite glass fibers with a terbium-doped cladding.

We demonstrated optical amplification ranging from 1600 to over 1680 nm in Tm-doped fluorotellurite fibers (FTFs) with a Tb-doped cladding by using a 1212 nm fiber laser as the pump source. The FTFs based on TeO-BaF- YO glasses were fabricated by using a rod-in-tube method. The doping concentration of Tm ions in the core was about 4000 ppm and that of Tb ions in the fiber cladding was about 10,000 ppm. By introducing the Tb ions into the cladding, the emission in the long-wavelength region (>1750 nm) originating from the transition F→H of Tm ions was suppressed efficiently by broadband absorption (1700-2100 nm) originating from the transitions F→F of the Tb ions in the cladding. As a result, a positive net gain ranging from 1600 to over 1680 nm was achieved in a 1.5 m long Tm-doped FTF as the launched power of the 1212 nm laser was about 3 W. The gain value at 1675 nm was about 19.7 dB for an input signal power of ∼0 dBm (or 1 mW). The gain was gradually reduced for shorter wavelengths, but it was still above 10 dB at ∼1644 nm. Our results show that Tm-doped FTFs with a Tb-doped cladding are promising gain media for constructing fiber amplifiers and lasers in the wavelength region of 1600-1700 nm.