Use of CsCl to enhance the glass stability range of tellurite glasses for Er³⁺ doped optical fiber drawing

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.