METHOD OF FABRICATING MULTIPLE SUPERIMPOSED FIBER BRAGG GRATINGS

摘要

A method of fabricating multiple superimposed Bragg gratings in the core of a portion of a photosensitive fiber is provided where only one common phase-mask is used. The multiple superimposed Bragg gratings are inscribed in the portion of the photosensitive fiber by applying different predetermined longitudinal stresses to the portion for each corresponding writing. The different predetermined longitudinal stresses are applied to the portion of the photosensitive fiber by stretching the portion along its longitudinal axis bi-directionally and simultaneously such that the centers of all fiber Bragg gratings imprinted in the portion are substantially superimposed at the center of the portion of the photosensitive fiber. The wavelength interval of two superimposed fiber Bragg gratings can be finely tuned to a required value and the wavelength intervals of three or more superimposed fiber Bragg gratings can be optimally tuned to a required wavelength grid, either even or uneven, by changing the effective refractive index of a portion of a photosensitive fiber covering the multiple fiber Bragg gratings inscribed.