Optical devices and methods of manufacture thereof

A method of forming an optical device that exhibits a variable optical effect upon illumination, the method comprising:

• providing a portion of a first full kinoform representation, wherein the first full kinoform representation contains a complete phase function to produce an electric field propagating from a first image object and thereby encodes a first image;
• providing a portion of a second full kinoform representation, wherein the second full kinoform representation contains a complete phase function of an electric field propagating from a second image object and thereby encodes a second image;
• forming a diffractive structure in a carrier layer, wherein the diffractive structure comprises
• a first diffractive region corresponding to the portion of the first full kinoform representation whereby the first diffractive region defines a perceived motion and depth of the first image upon tilting the device in the form of a replayed image of the first image, and
• a second diffractive region corresponding to the portion of the second full kinoform representation whereby the second diffractive region defines a perceived motion and depth of the second image upon tilting the device in the form of a replayed image of the second image;
• wherein
• the first image is different from the second image;
• the portion of the first full kinoform representation and the portion of the second full kinoform representation are such that the perceived motion and/or depth of the replayed first and second images upon tilting the device are different;
• the first diffractive region and the second diffractive region are laterally separate;
• each of the first diffractive region and the second diffractive region are discernible to the naked human eye;
• and
• the optical device is a security device.