Patent ID: 7502168

Claim:
An optical device comprising: a light guide plate which receives a collimated beam group including a plurality of collimated beams traveling in different directions, the collimated beam group traveling through the light guide plate while undergoing total reflection therein and then exiting from the light guide plate; a first diffraction grating member including a reflective volume hologram diffraction grating that diffracts and reflects the collimated beam group incident on the light guide plate so as to allow the collimated beam group to undergo total reflection within the light guide plate; and a second diffraction grating member including a reflective volume hologram diffraction grating that diffracts and reflects the collimated beam group transmitted through the light guide plate and directly emits the collimated beam group from the light guide plate, wherein the first diffraction grating member is provided with interference fringes extending from within the first diffraction grating member towards surfaces thereof, the interference fringes on the surfaces of the first diffraction grating member being arranged at an equal pitch, wherein when an angle formed between each of the interference fringes in the first diffraction grating member and each surface of the first diffraction grating member is defined as an inclination angle, the first diffraction grating member has the following conditions, (a) the first diffraction grating member has a minimum inclination angle region having an interference fringe with a minimum inclination angle; and an outer region positioned farther away from the second diffraction grating member than the minimum inclination angle region, and the inclination angles of the interference fringes in the outer region increase with increasing distance from the minimum inclination angle region, and (b) the first diffraction grating member has an inner region positioned closer to the second diffraction grating member than the minimum inclination angle region, and the inclination angles of the interference fringes in the inner region include a maximum inclination angle in an inner area disposed adjacent to the minimum inclination angle region and decrease with increasing distance from the minimum inclination angle region.