COMPATIBLE OBJECTIVE LENS UNIT, THE METHOD OF DESIGNING THE SAME AND COMPATIBLE OPTICAL PICK-UP

摘要

A compatible objective lens unit, a design method thereof, and a compatible optical pickup are provided to prevent wave front aberration from deteriorating due to optical axis interlacing even though a laser beam of wavelength except approximately 405nm wavelength is used, thus optical axis adjustment while assembling is not necessary. A hologram device(25) is equipped. An objective lens(30) condenses the first laser beam into the first optical disk. A hollow-type case(35) receives the objective lens(30) and the hologram device(25). With regard to the second optical disk where the second laser beam having a central wavelength equal to or larger than a central wavelength of the first laser beam is condensed, the hologram device(25) has patterns of a phase delivery function which makes tertiary coma aberration of the second laser beam a zero at an eccentric position by tolerance generated when the objective lens(30) and the hologram device(25) are received in the case(35). The objective lens(30) has an operating distance with which the tertiary coma aberration of the second laser beam becomes a zero.