Patent ID: 7245432

Claim:
An optical dual grating device comprising: a transmittive grating formed of segments of non-transparent material deposited on a flat planar surface of a transparent substrate, said transmittive grating having a first grating pitch and adapted to selectively transmit a first incident radiation beam to produce a transmitted beam corresponding to a first interference pattern; and a reflective grating formed of segments of a reflective material deposited upon the non-transparent segments of said transmittive grating, said reflective grating having said first grating pitch and adapted to selectively reflect a second incident radiation beam to produce a reflected beam corresponding to a second interference pattern; wherein said transmittive and reflective gratings are arranged such that said transmitted and reflected beams, when produced simultaneously, interfere to produce a combined interference pattern corresponding to a combined grating having a second grating pitch equal to about half of said first grating pitch, wherein the combined interference pattern is of an order lower than the orders of said first and second interference patterns.