Patent ID: 8810878

Claim:
An optical device comprising: a light source; a light guide plate configured to receive light, and to guide the received light; a first grating configured to diffract light entering the light guide plate; and a second grating configured to diffract light which has been propagated through the light guide plate, wherein a peak wavelength of the light source is closer to a central diffraction wavelength of the light with a first view angle having a given magnitude in a first angular direction relative to a zero degree viewing angle and which is diffracted a higher number of times in the second grating than a central diffraction wavelength of the light with a second view angle having the same given magnitude in a second angular direction opposite to the first angular direction and relative to the zero degree viewing angle and which is diffracted a lower number of times in the second grating, and wherein a diffraction efficiency at the first view angle of the first grating is higher than a diffraction efficiency at the second view angle of the first grating.