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 3+ -doped fluorotellurite fibers (FTFs) with a Tb 3+ -doped cladding by using a 1212 nm fiber laser as the pump source. The FTFs based on TeO 2 –BaF 2 – Y 2 O 3 glasses were fabricated by using a rod-in-tube method. The doping concentration of Tm 3+ ions in the core was about 4000 ppm and that of Tb 3+ ions in the fiber cladding was about 10,000 ppm. By introducing the Tb 3+ ions into the cladding, the emission in the long-wavelength region (>1750 nm) originating from the transition 3 F 4 → 3 H 6 of Tm 3+ ions was suppressed efficiently by broadband absorption (1700–2100 nm) originating from the transitions 7 F 6 → 7 F 0,1,2 of the Tb 3+ 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 3+ -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 3+ -doped FTFs with a Tb 3+ -doped cladding are promising gain media for constructing fiber amplifiers and lasers in the wavelength region of 1600–1700 nm.