0.8-Numerical-Aperture Two-Element Objective Lens for the Optical Disk

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Abstract
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 spherical aberration compensation mechanism. We designed a two-element objective lens rather than a conventional singlet objective lens in order to increase the fabrication tolerance of the objective lens for high NA. A disk substrate which is thinner than that of the digital video disk (DVD) was adopted to increase the disk tilt tolerance. A spherical aberration compensation mechanism was realized by controlling the distance between the two lenses of the objective using an actuator in order 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 objective lens.