Sensitivity of an IGI fiber with a germanium-oxide-doped silica core to refractive index changes of the optical cladding

Fibers with inverted-graded index (IGI) profiles in the core with all refractive-index values above that of silica were drawn from performs doped in the core with germanium oxide which were prepared by the MCVD method. The sensitivity of the fibers to refractive-index changes of the optical cladding was theoretically determined on the basis of measured refractive-index profiles by using ray optics and assuming axial excitation of the fibers. The theoretical results are compared with experimental data measured in model immersing experiments.