Writing Bragg gratings in optical waveguides

DETAILED DESCRIPTION It is an object of the present invention to provide a method of writing a Bragg reflection grating in an optical waveguide using a diffraction grating located at a sufficient distance from the waveguide as to make it readily possible to include aperture defining means to control the illumination of the waveguide so as to provide a high visibility fringe pattern, and at the same time to use separated portions of the diffraction grating for the generation of that fringe pattern.
Particularly in the case of the writing of long Bragg reflection gratings, such use of two separated zones of illumination of the diffraction grating has the advantage of reducing the deleterious effects in the optical performance of the resulting Bragg reflection grating caused by the presence of random stitch errors in the diffraction grating used to write that Bragg reflection grating.
According to a first aspect of the present invention there is provided a method of writing a Bragg grating in a photosensitive optical waveguide by irradiating the waveguide with an interference fringe pattern generated by the passage of electromagnetic radiation in two spatially separated zones via a diffraction grating oriented to have diffracting elements of the diffraction grating extending at an angle to the waveguide axis.
According to a second aspect of the present invention there is provided a method of writing a Bragg grating in a photosensitive optical waveguide by irradiating the waveguide with an interference fringe pattern generated by the passage of electromagnetic radiation via a diffraction grating oriented to have diffracting elements of the diffraction grating extending at an angle to the waveguide axis, wherein a beam of light is divided into two spatially separated components arranged to be incident upon the diffraction grating in two spatially separated zones, and the fringe pattern is generated by interference between one diffracted order of one of the two components and one diffracted order of the other component