New Spherical Aberration Compensator for Blu-Ray Disc

In high numerical aperture optical disc systems, a spherical aberration compensator is required to accomodate thickness deviations of the cover layer and the space layer. In some cases, a liquid crystal (LC) plate is employed as a spherical aberration compensator and it is generally attached to the objective lens actuator coaxial with the objective lens. It is useful to put the LC plate in a fixed part of the optical head to cope with high-speed disc rotation and to reduce the size of the objective lens actuator, but additional objective lens decentering against the LC plate is caused by the tracking operation. In this paper, a new spherical aberration compensator for Blu-ray Disc optical systems is introduced to decrease the wavefront aberration caused by objective lens decentering.