We have improved the phase-shift differential push-pull (PS-DPP) tracking method with a multidivision phase-shift grating, which is applicable to various optical disks with different track pitches and does not require the accurate alignment of the three-spot position on a disk. In this paper we presented the properties of this method in recordable optical disks such as phase-change or dye media in which reflectivity greatly changes after recording. In particular, we found the cause of a radial tracking error signal offset occurring at the boundary between recorded and unrecorded tracks. To resolve this issue, we proposed two solutions: one is the optimum calculation procedure for the PS-DPP signal, and another is a newly designed phase-shift grating for recordable disks. We demonstrated the offset cancellation effect of this improved PS-DPP method using a new hologram laser unit for various types of digital versatile discs (DVDs) and showed its applicability to the Blu-ray Disc (BD).

Three-dimensional microstructures with aspect ratios larger than 20 and a solidified wall with a thickness down to 2.0 µm have been fabricated by the one-photon absorption photopolymerization technique. Lateral and longitudinal spatial resolutions in a single-line scanning process of as high as 1.0 µm and 0.3 µm, respectively, are reproducible. An experimental system consisting of a common picosecond pulsed laser and an optical microscope makes laser microfabrication easy to realize, implying a broad application potential.

For a high-numerical-aperture (NA) optical pickup system, the spherical aberration (SA) caused by cover layer thickness error should be corrected. We detected the SA error signal using a newly designed hologram optical element (HOE). The HOE has both sufficient signal sensitivity and constant signal level independent of objective lens shift. In addition, we fabricated on SA servo for a dual-layer Blu-ray disc.

A newly optical pickup using integrated optical unit (IOU) which can detect spherical aberration error signal (SAES) and control light intensity distribution is described. In this IOU, the SAES is detected by hologram and light intensity distribution is controlled by grating. In addition, spherical aberration (SA) servo for a dual-layer Blu-ray disc is demonstrated by using this SAES.

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