| Photosensitivity in germanium-doped silica glass fibers attract tremendous interest, since it allows the fabrication of many in-fiber Bragg grating-based optical devices. Photosensitivity can be estimated through the measurement of refractive index modulation induced in the fiber after UV exposure.; In the present project, we have made an experimental study of tapered fiber photosensitivity for different inverse taper ratios. To analyze their transmission before and after UV exposure, we have realized a tapered structure similar to a Mach-Zehnder interferometer. In this manner, we measured the right movement of wavelength response peaks as a function of exposure time and intensity of light beam. By correlating the experimental and computed results we have estimated the variation of refractive index.; In standard telecommunication fibers, the photosensitivity is function of mechanical and thermal history of the fiber. Heating and tapering fiber technique change the refractive index profile by diffusion of core dopants. In addition, the tapering using a flame brushing technique induces OH absorption loss near 1390 nm. The diffusion of moisture into the taper region can be responsible for the photosensitivity of thinning tapered fiber.; A controlled UV-induced refractive index modulation may be used in adjustment of optical devices wavelength response. |
