A method of writing of bragg - reflection gratings in light waveguides

摘要

Instead of a single beam, two coherent beams of light (10',10") are used to illuminate a phase grating (11) in spatially separated zones for writing a Bragg reflection grating in an underlying optical (fibre) waveguide (12). Close proximity between phase mask and waveguide is not required. This facilitates the use of masking so that only two different diffracted orders (10'c,10"a) contribute to the fringe pattern that generates the Bragg grating, by cutting off the zero order (10'b,10"b) with field stop (24), thereby improving fringe contrast and reducing the deleterious spectral effects upon the reflectivity of the Bragg reflector occasioned by the presence of stitch errors in the phase grating. The beam (10) is split into two by beam splitter and the two beams (10',10") are reflected by mirrors (21,22) so they pass through grating (11).