Compatible objective lens unit, the method of designing the same and compatible optical pick-up

摘要

compatible objective lens unit, the design method and the optical pickup is disclosed. As disclosed compatible objective lens unit, compatible objective lens unit to record / reproduce information by condensing laser light on the different types of the optical disk, and a hologram element; A first objective lens for condensing the laser light; A hollow case which the holographic optical element and the objective lens receiving; includes a hologram element is, for the first second optical disk to which the second laser light of equal to or greater than the laser light center wavelength large center wavelength than the light-converging hologram element and the objective lens has a pattern of a phase transfer function for the second laser light cubic coma aberration in the eccentric position by the tolerance which occurs when accommodated in a hollow case to zero, the objective lens is the second laser light cubic coma It characterized in that the operation has a distance that is zero. ; According to the above structure, the objective lens unit is compatible and does not require adjustment of the optical axis when assembled also the NA is about 0.85 of the objective lens with the optical axis misalignment is difficult to occur.