Compound optical device, compound optical unit including the compound optical device, and optical pickup apparatus including the compound optical unit

A compound optical device comprising:

• an incidence surface to which laser beams of different wavelengths are applied, the laser beams having optical axes parallel to each other;
• an emission surface from which the laser beams applied to the incidence surface are emitted;
• a returning light incoming surface to which returning light beams of the laser beams emitted by the emission surface are applied;
• a returning light emitting surface to emit the returning light beams applied to the returning light incoming surface;
• and
• a returning light reflecting surface to reflect the returning light beams applied to the returning light incoming surface toward the returning light emitting surface,
• the returning light incoming surface including a first diffraction element to diffract and direct the returning light beams to a position on the returning light reflecting surface, and the returning light reflecting surface including a second diffraction element to correct for a difference of incidence angle, with respect to the returning light reflecting surface, between the returning light beams and direct the returning light beams toward the returning light emitting surface along the same optical axis, whereby the returning light emitting surface emits the returning light beams along the same optical axis.

A method of positioning light beams of different wavelengths returning from an optical apparatus comprising:

• diffracting the returning light beams on a first surface of a compound optical device;
• reflecting the diffracted light beams on a second surface of the compound optical device;
• and
• correcting a trajectory of the diffracted light beams by re-diffracting the diffracted light beams to direct the light beams onto a light receiving device.