Two-element objective lens and spherical aberration correction for DVR

This paper describes the advancement we made in developing objective lenses and actuators for DVR, which we see as the next generation in optical disk recording. Data capacity is primarily determined by the laser wavelength and the numerical aperture (NA) of the objective. In the DVR system, a blue (400 nm) semiconductor laser and a NA=0.85 two-lens objective are used, to achieve a capacity of 22 GB on a single layered optical disk with CD-like dimensions. The disk cover layer is only 0.1 mm thick, to achieve sufficient robustness against optical aberrations (coma) from disk tilt. Cover layer thickness variations result in spherical aberrations. For a user bitrate of 50 Mb/s, the required linear velocity of the track is 9 m/s. Given the manufacturing tolerances of the disk, the accelerations of the track in focus and radial direction can then be computed. Furthermore, there is an optical requirement on the maximum allowable error in spot position relative to the track, resulting in a minimum required bandwidth for focusing and radial tracking (3.6 kHz and 5.0 kHz).