Method and apparatus for writing gratings

A method for creating a grating structure in a photosensitive material comprising the steps of:

• utilizing a single coherent beam of light and a diffraction grating to create two coherent working beams of light;
• propagating the two working beams around a plurality of reflective elements, the plurality of reflective elements comprising an even number greater than or equal to four, each of the beams being reflected by each of the reflective elements, so that the beams interfere at an initial predetermined position;
• positioning the photosensitive material at a first position so as to produce an initial portion of the grating structure in a predetermined portion of the photosensitive material;
• translating the diffraction grating and the photosensitive material in a direction substantially perpendicular to the single coherent beam so as to produce the grating structure in the photosensitive material;
• and
• simultaneously translating the reflective elements relative to the photosensitive material so as to maintain the interference pattern at a position determined in accordance with requirements for the grating structure;
• whereby said period of said interference pattern or said position of said interference pattern, or both said period and said position of said interference pattern can be controlled.

An apparatus for writing gratings comprising:

• a source for providing an input beam of coherent (UV) light;
• a phase mask for dividing the input beam of light into two coherent working beams of light;
• an even number of rotatable reflective elements greater than or equal to four, each of the reflective elements positioned to reflect each of the beams, so that the beams interfere at an initial predetermined position;
• a photosensitive waveguide positioned for exposure to an interference pattern, whereby the rotation of the reflective elements independently controls the period of the interference pattern and the position of the interference pattern.