Optical amplification covering the entire S-band in Tm³⁺/Er³⁺ co-doped fluorotellurite fibers

We demonstrated optical amplification covering the entire S-band in Tm³⁺/Er³+ co-doped fluorotellurite fibers by using a 1410 nm fiber laser as the pump source. Tm³⁺/Er³+ co-doped fluorotellurite fibers were fabricated by using a rod-in-tube method. A 10 dB gain bandwidth of ∼87 nm (1455-1542 nm) and a maximum gain of ∼ 21.7 dB at 1520 nm were achieved from a 3 m long Tm³⁺/Er³⁺ co-doped fluorotellurite fiber (the doping concentration of Tm³⁺ and Er³⁺: 4000 and 750 ppm) for a pump power of ∼ 1.7 W and an input signal power of ∼ 0 dBm (1 mW). In comparison with that in Tm³⁺-doped fluorotellurite fibers without Er³+ doping, the 10 dB gain bandwidth for the above Tm³⁺/Er³⁺ co-doped fluorotellurite fiber was improved from 67 nm (1455-1522 nm) to 87 nm (1455-1542 nm, covering the entire S-band), which was due to optical amplification in the long wavelength region of S-band originated from the transition ⁴I₁₃/₂→⁴I₁₅/₂ of Er³⁺ ions combining with that in S-band from the transition of ³H₄→³F₄ of Tm³⁺ ions. Our results show that Tm³⁺/Er³⁺ co-doped fluorotellurite fibers are promising gain media for constructing broadband S-band fiber amplifiers.