Patent ID: 7764413

Claim:
An optical device comprising: a substrate of optical material having a first surface and an opposing second surface; a first diffractive element disposed on the substrate configured to receive a light beam; a second diffractive element disposed on the substrate in relationship with the first diffractive element and having substantially the same grating line orientation as the first diffractive element; and an intermediate diffractive element disposed between the first and the second diffractive elements, wherein the first diffractive element is configured to diffract at least part of the received light beam within the first and second surfaces for providing a diffracted light component to the intermediate diffractive element in an incident direction substantially, the intermediate diffractive element is configured to couple by diffraction substantially between the first and second surfaces at least part of the diffracted light component for providing a coupled diffracted light component to the second diffractive element, and the second diffractive element is configured to couple at least part of the coupled diffracted light component to exit the substrate by diffraction in the second diffractive element, wherein the intermediate diffractive element has a substantially periodic pattern composed of substantially linear elements along a pattern direction for producing conical diffraction.