US Patent 7502168 Optical device and image display apparatus

An optical device includes a light guide plate, and first and second reflective volume hologram diffraction grating members. The first member has interference fringes extending from therewithin towards surfaces thereof and arranged at an equal pitch. Each interference fringe and each surface of the first member form an inclination angle therebetween. The first member has the following conditions. (a) In an outer region positioned farther away from the second member than a minimum inclination angle region having a minimum inclination angle, the inclination angles of the interference fringes increase with increasing distance from the minimum inclination angle region. (b) In an inner region positioned closer to the second member than the minimum inclination angle region, the inclination angles of the interference fringes 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.