Abstract

We report a technique which allows any germanium doped fiber to be made highly and reproducibly photosensitive. Using this technique allows UV writing of phase gratings in virtually any fiber, resulting in greatly increased design flexibility for devices such as fiber filters, and pump reflector gratings. Fibers were saturated with H₂ by soaking in hydrogen at high pressures, (typically 20-800 atm) and at low temperatures (typically 20-100°C). Subsequent exposure to UV in the region of 240nm then caused large permanent refractive index changes to occur rapidly in the fiber cores. Fig. 1 shows a UV induced space average Δn of 10⁻² for a grating in a 14% GeO₂ fiber. Fig. 2 shows spectra for gratings written in standard (2.8% GeO₂) and high (14%) GeO₂ fibers which were hydrogen loaded, with UV induced maximum core Δn’s of 4×10⁻³ and 1.5×10⁻², and spectral widths of 2.5 and 10nm (FWHM), respectively. Index changes of order 2×10⁻² have been achieved in fibers with 18% GeO₂. We have also observed that substantial index changes (e.g. Δn=7.4×10⁻³ in a 10% GeO₂ fiber) can be thermally induced in a H₂ loaded fiber-e.g. by flame or CO₂ laser heating.

© 1993 Optical Society of America