Photo-masks and methods of fabricating periodic optical structures

An apparatus for producing a periodic optical structure, the apparatus comprising:

• a photo-mask comprising a set of diffractive elements and/or refractive elements disposed on a body element and/or within the body element;
• and
• a recording material;
• wherein the set of diffractive elements and/or refractive elements is configured to produce three or four non-coplanar beams of light when a beam of light is passed therethrough such that the three or four non-coplanar beams of light interferometrically produce a periodic optical structure at a specific location in the recording material.

A method of fabricating a periodic optical structure, the method comprising:

• generating a light beam;
• directing the light beam into a photo-mask having a set of diffractive elements and/or refractive elements to produce three or four non-coplanar beams of light;
• and
• focusing the three or four non-coplanar beams of light in a photosensitive recording material to interferometrically produce a periodic optical structure in the photosensitive recording material.