0.8-NUMERICAL-APERTURE 2-ELEMENT OBJECTIVE LENS FOR THE OPTICAL DISK

A high-numerical-aperture (NA) optical pick-up for an optical disk was developed using a two-element lens, a thin disk substrate and a spher ical aberration compensation mechanism. We designed a two-element obje ctive lens rather than a conventional singlet objective lens in order to increase the fabrication tolerance of the objective lens for high N A. A disk substrate which is thinner than that of the digital video di sk (DVD) was adopted to increase the disk tilt tolerance. A spherical aberration compensation mechanism was realized by controlling the dist ance between the two lenses of the objective using an actuator in orde r to cancel the aberration due to the variations in the disk thickness . In the experiment, we fabricated a two-element lens according to our design and confirmed that it performed as a high-quality 0.8-NA objec tive lens.