This paper reviews tellurite-based fibers and their applications to optical communication networks. First, an investigation of tellurite-based glass and the fabrication of conventional step-index fibers and photonic crystal fibers (PCF) are described. By purifying the raw materials and employing a novel PCF fabrication process, low background losses were achieved for an Er³⁺-doped, an undoped tellurite-based fiber and a tellurite-based PCF. Second, the optical properties of Er³⁺-doped tellurite-based glass and fiber, and the gain characteristics of erbium doped tellurite fiber amplifiers (EDTFAs) were studied. A seamless, low noise and gain flattened C + L band EDTFA was realized, and an S + C + L band amplifier was constructed by combining an EDTFA and a thulium-doped fluoride fiber amplifier (TDFFA) in parallel. Third, it is confirmed that the Raman scattering characteristic of tellurite-based fiber has such a large gain coefficient and Stokes shift that it is possible achieve a wideband tellurite-based fiber Raman amplifier. To overcome several problems, a distributed/discrete hybrid tellurite- and silica-based fiber Raman amplifier (FRA) was constructed as an S + C + L band WDM repeater with a gain bandwidth of 127-nm. Fourth, Brillouin amplification and the simulated performance of slow light generation in a tellurite-based fiber were investigated. The fiber exhibits the largest time delay per unit power of 19.9 ns/mW. Finally, a carrier-envelope offset (CEO)-locked frequency comb with low fiber coupling pulse energy (230 pJ) was demonstrated by using a tellurite-based PCF. This method has the potential to lock the CEO with a lower pulse energy and thus provide a low-noise and high-accuracy optical frequency comb at telecommunication wavelengths. These tellurite-based fibers with low background loss thus offer attractive functions for applications in the optical communication field.