Patent ID: 7420894

Claim:
An optical pickup device for irradiating a recording medium with laser beams having different wavelengths, comprising: a semiconductor laser that houses plural laser elements having different emission wavelengths in a single package; and a diffraction grating for substantially matching by an diffraction effect, optical axes of laser beams among laser beams emitted from the laser elements except a reference laser beam whose optical axis conforms to an optical axis of an optical system with the optical axis of the reference laser beam, wherein the diffraction grating is individually prepared corresponding to laser beams subjected to optical axis correction and is arranged at a position on the optical axis of the optical system at an optical path length L′ expressed by the following expression from a laser element for emitting the reference laser beam: L ′ = ( L - Z ) ⁢ ( 1 + ( 2 ⁢ X · Δ ⁢ ⁢ X + 2 ⁢ Y · Δ ⁢ ⁢ Y + Δ ⁢ ⁢ X 2 + Δ ⁢ ⁢ Y 2 ) / ( X 2 + Y 2 ) - Δλ / ( λ + Δλ ) ) + Z + Δ ⁢ ⁢ Z ( A ) where: when a travelling direction of the reference laser beam is set as Z axis of a three-dimensional orthogonal coordinate and the laser element for emitting the reference laser beam is arranged at its origin, X, Y, and Z denote coordinate positions on a coordinate axis of the laser element for emitting an optical axis adjustment target laser beam as designed values for the semiconductor laser; ΔX, ΔY, and ΔZ denote variations between the designed values and the coordinate positions on the coordinate axis of the laser element for emitting the optical axis adjustment target laser beam as values of the X, Y, and Z axes of the coordinate axis; λ denotes a wavelength of the optical axis adjustment target laser beam as designed values for the semiconductor laser; Δλ denotes a wavelength variation between the wavelength of the optical axis adjustment target laser beam and the designed values of the semiconductor laser; and L =Λ·ROOT( X 2 +Y 2 )/( m·λ )+ Z (Λ denotes a grating pitch, and m denotes a diffraction order).