Patent ID: 7418170

Claim:
An optical device comprising: an optical waveguide to guide parallel pencil groups meeting a condition of internal total reflection inside the optical waveguide by internal total reflection of the parallel pencil groups; a first reflection volume hologram grating to diffract and reflect the parallel pencil groups incident upon the optical waveguide from outside and traveling in different directions as they are so as to meet the condition of internal total reflection inside the optical waveguide; and a second reflection volume hologram grating to project the parallel pencil groups guided by internal total reflection inside the optical waveguide as they are from the optical waveguide by diffraction and reflection thereof so as to depart from the condition of internal total reflection inside the optical waveguide, some parallel pencils of the parallel pencil groups guided through the optical waveguide being totally reflected different numbers of times for a period from external incidence upon the optical waveguide until outgoing from the optical waveguide, the first reflection volume hologram grating having recorded thereon first interference fringes having a first slant angle, the second reflection volume hologram grating having recorded thereon second interference fringes having a second slant angle, the first and second slant angles being identical to each other, and the first and second interference fringes being symmetrical with each other with respect to a predetermined plane of symmetry.