FORMATION OF BRAGG GRATINGS IN GERMANIUM DOPED OPTICAL FIBERS USING A PRISM INTERFEROMETER

Bragg gratings have been written in Germanium doped core silica fibers by transversally exposing the fibers to fringe patterns produced by a pair of coherent U.V. pulsed beams combined inside a prism interferometer. The transmission spectra of the gratings have been recorded at various times of irradiation. The drop in transmission near resonance wavelength may be as large as 100%, depending on the experimental conditions of the writing experiment. The thermal annealing behavior of different gratings shows that the evolution of the fiber transmittivity recovery versus temperature depends upon the number and the energy of the laser pulses applied to form the grating and upon the nature of the fiber.