Patent ID: 7453612

Claim:
An optical device including an optical waveguide upon which a group of parallel light beams different in traveling direction from each other are incident and from which the group of parallel light beams go out after propagated by repeated total reflection through it, the optical waveguide comprising: a first reflection-type volume hologram grating to diffract and reflect, in the light beam-incident section thereof, the group of parallel light beams as they are so as to meet internal total reflection condition in the optical wave guide; a second reflection-type volume hologram grating to diffract and reflect, in a section thereof from which the group of parallel light beams are to go out, the group of parallel light beams as they are so as to go out of the optical waveguide; a plurality of pitches of interference fringes on the hologram surfaces of the first and second reflection-type volume hologram gratings being equal to each other; in at least the second reflection-type volume hologram grating, an angle formed between the interference fringes and hologram surfaces being varied continuously or stepwise within the hologram in relation to the main incident light beam so as to meet the Bragg condition; and at least parts of the group of parallel light beams different in traveling direction from each other and propagated from the incident to outgoing section in the optical waveguide by repeated total reflection have different numbers of total reflection respectively depending upon the difference in traveling direction, wherein, in the first reflection-type volume hologram grating, the number of stacked hologram layers or interference fringes laid side by side in each hologram layer is varied in a direction perpendicular to the interference fringes on the surface of the first reflection-type volume hologram grating.