Yasuo Nakata

Optical Pickup using Integrated Optical Unit for Blu-ray Disc

This paper reports the developed optical pickup for blu-ray disc which uses the integrated optical unit to detect the spherical aberration error signal. This study has obtained the prospect of the high efficiency for detection using the segmented wave plate by the photonic crystal structure

New Tracking Servomechanism Using Phase-Shift Differential Push-Pull Method for Recordable Optical Disks

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).

Spherical aberration error detection for blu-ray disc optical pickups

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.

Development of Optical Pickup for Mini Disc Drives

In order to miniaturize optical disc drives, it is important to miniaturize and thin the optical pickup. We have developed two new optical parts: the hologram laser and the actuator. By optimizing the hologram pattern of the hologram laser, optical path length is shortened. The frequency characteristics of the actuator have been stabilized by improving the damping characteristics. Thus, we have developed a compact optical pickup for Mini Disc drives, and the pickup shows high performance when it reads out an optical disc.

Integrated optical unit employing two-wavelength laser diode for digital versatile disc/compact disc optical pickup

We have developed an integrated optical unit employing a two-wavelength laser diode for a digital versatile disc (DVD)/compact disc (CD) optical pickup. In this paper, we propose a new design method to share a holographic optical element for 780 and 650 nm light beams in an integrated optical unit. To share the holographic optical element, we have introduced an additional aberration to reduce the focusing error signal offset of the 780 nm light beam. Moreover, we have introduced the phase-shift differential push–pull (PS-DPP) method for both the 650 and 780 nm light beams. We have evaluated the performance of this integrated optical unit and confirmed that the performance of this unit is sufficient for both DVD and CD systems.

Integrated Optical Unit for Magneto-Optical Pickups

We have developed an integrated optical unit for magneto-optical (MO) pickups which contains three polarized holograms for detecting MO signals and servo error signals. In this study, we modify the integrated optical unit so that it can reproduce two types of discs using two photo detectors. The phase-shift differential push-pull method is used for the radial servo and it is compatible with different track pitches. We also discuss the quality of the reproduced MO signals.

Optical Detection System of Defects in Multi Layered Optical Device

We developed a new optical detection method for defects in multilayered optical devices. An optical detection is achieved by sensing the scattering twinkle points of guided light in a multilayered optical device and by analyzing the scattering properties of the twinkle points. We found a difference in scattering property between defective points and nondefective points, and developed a check system for the scattering direction from a scattering twinkle point. By this optical defect detection method, we realize a decrease in defect detection error.