HOLOGRAM UNIT OF OPTICAL PICKUP AND METHOD FOR MOUNTING HOLOGRAM ELEMENT BY USING THE SAME

PROBLEM TO BE SOLVED: To exactly align an LD and a hologram element by aligning this hologram element in such a manner that the light emitting point of the LD is image-formed at the center of many projected light emitting points. SOLUTION: The hologram unit of optical pickup has a main hologram 19 arranged at the center of the hologram element 18 and a holograms 20 for alignment formed on the periphery of this main hologram 19 so as to act as orthogonal signals corresponding to the reference coordinates of a monitor 12. The holograms 20 for alignment serve to allow the transmission of the reference light diffracted at a specified angle of the light emitting point 13a of the LD and are so formed as to have the optical axes from the light emitting points of the positions apart a specified distance in +x, -x, +y, -y directions respectively from the light emitting point of the LD 13 on the plane of the light emitting point of the LD 13.