Tellurite glasses are important as a host of Er3+ ions because of their great solubility and because they present broader gain bandwidths than Er3+-doped silica, with promise to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good quality optical fibers. CsCl acts as a network modifier in glass systems, weakening the network by forming Te-Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi2O3 content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er3+-doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO2-ZnO-Li 2O-Bi2O3-CsCl glasses. Far infrared spectra of the glass samples exhibit absorption bands of the Te-Cl bond.6469Mori, A., Ohishi, Y., Sudo, S., Erbium-doped tellurite glass fibre laser and amplifier (1997) Electron. Lett, 33 (10), pp. 863-864Sekiya, T., Mochida, N., Ohtsuka, A., Tonokawa, M., Raman-spectra of Mo-TeO2 (M = Mg, Sr, Ba and Zn) glasses (1994) J. Non-Cryst. Solids, 168, pp. 1-2,106-114Bindra, K.S., Bookey, H.T., Kar, A.K., Wherrette, B.S., Liu, X., Jha, A., Nonlinear optical properties of chalcogenide glasses: Observation of multiphoton absorption (2001) Appl. Phys. Lett, 79 (13), pp. 1939-1941Wang, J.S., Vogel, E.M., Snitzer, E., Jackel, J.L., da Silva, V.L., Silbergerg, Y., 1.3 μm emission of neodymium and praseodymium in tellurite-based glasses (1994) J. Non-Cryst. Solids, 178, pp. 109-113Shen, S., Jha, A., Zhang, E., Wilson, S.J., Compositional effects and spectroscopy of rare earths (Er3+, Tm3+, and Nd 3+) in tellurite glasses (2002) C.R. Chim, 5 (12), pp. 921-938Yamada, M., Mori, A., Ono, H., Kobayashi, K., Kanamori, T., Ohishi, Y., Broadband and gain-flattened Er3+-doped tellurite fibre amplifier constructed using a gain equaliser (1998) Electron. Lett, 34 (4), pp. 370-371Mori, K., Kobayashi, M., Yamada, T., Kanamori, K., Oikawa, Y., Nishida, Y., Ohishi, Y., Low noise broadband tellurite-based Er3+-doped fibre amplifiers (1998) Electron. Lett, 34 (9), pp. 887-888Snitzer, E., Vogel, E.M., Wang, J.S., Tellurite glass and fiber amplifier (1993), US Patent 5,251,062Aitken, B.G., Ellison, A.J.G., Tellurite glasses and optical components (2001), US Patent 6,194,334Ding, Y., Jiang, S., Hwang, B.C., Luo, T., Peyghambarian, N., Himei, Y., Ito, T., Miura, Y., Spectral properties of erbium-doped lead halotellurite glasses for 1.5 μm broadband amplification (2000) Opt. Mater, 15 (2), pp. 123-130Keiser, G., (1999) Optical Fiber Communication, , Mac-Graw Hill, New YorkBarbosa, L.C., Cesar, C.L., Mazali, I.O., Barbosa, L.C., Alves, O.L., Spectroscopic and thermal properties of Ga2S 3-Na2S-CsCl glasses (2006) J. Am. Ceram. Soc, 89 (3), pp. 1037-1041Mazali, I.O., Barbosa, L.C., Alves, O.L., Preparation and characterization of new niobophosphate glasses in the Li2O-Nb 2O5-CaO-P2O5 system (2004) J. Mater. Sci, 39 (6), pp. 1987-1995El-Kheshen, A.A., Zawrah, M.F., Sinterability, microstructure and properties of glass/ceramic composite (2003) Ceram. Int, 29 (3), pp. 251-257A. Hruby, Evaluation of glass-forming tendency by means of DTA, Czech. J. Phys. B, B22 1187-& (1972)Burger, H., Vogel, W., Kozhukharov, V., IR transmission and properties of glasses in the TeO2-[RNOM, RNXM, RN(SO4)M, RN(PO3)M and B2O3] systems (1985) Infr. Phys, 25 (1-2), pp. 395-409Higazy, A.A., Bridge, B., Infrared-Spectra of the vitreous system CO 3O4-P2O5 and their interpretation (1985) Jour. Mat. Sci, 20 (7), pp. 2345-2358Bridge, B., Round, R., Computation of the bulk modulus of the high temperature ceramic superconductor YBa2Cu3O7-X from unit-cell data (1988) Jour. Mat. Sci. Lett, 7 (1), pp. 63-65Reynoso, V.C.S., Barbosa, L.C., Alves, O.L., Aranha, N., César, C.L., Preparation and characterization of heavy-metal oxide glasses - Bi2O3-PbO-B2O3-GeO 2 system (1994) J. Mater. Chem, 4 (4), pp. 529-532Canale, J.E., Condrate, R.A., Nassau, K., Cornilsen, B.C., Characterization of various glasses in the binary PbO-GeO2 and Bi2O3-GeO2 systems (1986) J. Can. Ceram. Soc, 55, pp. 50-56Adams, D.M., Lloyd, M.H., Far-Infrared reflectance spectra of some hexachlorotellurates and other hexachlorometallates (1971) Jour. Chem. Soc. A.-Inorganic Phys Theor, 7, p. 878Gloge, D., Weakly guiding fibers (1971) Appl. Opt, , 10 [10] 2252-