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 Tm³⁺-doped fluorotellurite fibers (FTFs) with a Tb³⁺-doped cladding by using a 1212 nm fiber laser as the pump source. The FTFs based on TeO₂-BaF₂- Y₂O₃ glasses were fabricated by using a rod-in-tube method. The doping concentration of Tm³⁺ ions in the core was about 4000 ppm and that of Tb³⁺ ions in the fiber cladding was about 10,000 ppm. By introducing the Tb³⁺ ions into the cladding, the emission in the long-wavelength region (>1750 nm) originating from the transition ³F₄→³H₆ of Tm³⁺ ions was suppressed efficiently by broadband absorption (1700-2100 nm) originating from the transitions ⁷F₆→⁷F_0,1,2 of the Tb³⁺ 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 Tm³⁺-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 Tm³⁺-doped FTFs with a Tb³⁺-doped cladding are promising gain media for constructing fiber amplifiers and lasers in the wavelength region of 1600-1700 nm.