Germanate-tellurite composite fibers for supercontinuum generation in the mid-infrared

The fabrication process and characterization of composite step-index fibers with a large refractive index difference between the tellurite glass-made core and the germanate-tellurite glass-made cladding are presented. In order to fabricate these composite fibers, the composition of the cladding glass was optimized to match its thermal and optical properties to those of the core glass. This work demonstrates that even if these two glasses have relatively different chemical compositions, their association results in a good quality fiber. This fiber design combines strong confinement of the optical modes inside its core and good environmental stability for nonlinear applications in the mid-infrared. Supercontinua were generated in these fibers by pumping with a femtosecond laser source.