Photoinscription of Bragg gratings within a germanosilicate fiber subjected to a high static electric field

The kinetics of Bragg grating growth in germanosilicate fibers subjected to a high static electric field are compared with those obtained without any electric field. The gratings were written by exposure of the fiber core to laser light at 244 or 193 nm. These experiments gave some clues about the m echanisms responsible for both the photosensitivity in germanosilicate fibe rs and the nonlinear second-order UV-induced susceptibility in silica glass es. The refractive-index modulation proved to be significantly higher in th e fibers subjected to an electric field. Furthermore, the change in the fib er's mean effective refractive index as a function of exposure time was not monotonic. This evolution can be explained by the assumption that some ele ctric-field-induced diffusion of electron trapped centers [Ge(1) and Ge(2)] from the fiber core is involved. (C) 1999 Optical Society of America.