Permanent Refractive Index Modification in GE-doped Optical Fibers Using Red Light

Intense radiation from the UV to green spectral region is known to permanently change the optical properties of silica fibers. This photosensitivity can be used to induce periodic changes in the refractive index along the fiber length, which results in an intracore Bragg grating. In 1978, Hill et. al. observed this effect in germanium-doped silica fibers using 488-nm and 518-nm light from an intense argon-ion laser beam. The progress on the photosensitivity of Andrew elliptical-core Ge-doped birefringent silica optical fiber due to cw krypton-ion laser light is explained.