Kousei Sano

Novel one-beam tracking detection method for dual-layer blu-ray discs

In this paper, we propose a new advanced push–pull (APP) method as a new one-beam tracking detection method suitable for a dual-layer Blu-ray disc (BD) system. This method overcomes two issues. One of them is tracking error signal (TES) offset at the boundary between recorded tracks and unrecorded tracks, and the other is TES offset caused by the stray lights from the other layer of dual-layer discs. The new APP-TES is stable at the boundary in the dual-layer BD system, because the dividing area of a far-field pattern is optimized and the detecting areas are allocated to avoid stray lights from the other layer. Its stable characteristics are confirmed experimentally.

One-Head Near-Field Writing/Erasing on a Rewritable Dual-Layer Optical Disk Having High-Index Cover and Separation Layers

Near-field writing and erasing on a rewritable dual-layer optical disk with a single solid immersion lens (SIL) optical head is demonstrated for the first time. A novel beam expander enabled access to both information layers of the disk without exchanging two individual optical heads. A rewritable dual-layer disk having high-index (n=1.8) cover and separation layers was newly developed. By using the SIL optical system and the disk, an effective numerical aperture (NA) of 1.42 is achieved and a recording capacity of 180 Gbyte for the dual-layer rewritable disk is expected.

Application of a Polarizing Holographic Optical Element to a Recordable Optical Head

A polarizing holographic optical element (HOE) with compensating grooves on the surface of a LiNbO 3 substrate has good polarizing beam-splitter characteristics. This polarizing HOE was applied to a recordable optical head with an integrated laser and photodetector unit. In the optical head, a correct far-field tracking method is constructed by setting the polarizing HOE and a quarter-wave plate right under the objective lens, which can be moved with the objective lens. A holographic pattern of the polarizing HOE is divided into 20 portions along a disc track direction for spot size focus error detection and far field tracking detection. With this optical head, conventional CD play-back and recording signals on phase change discs were performed. Then the tracking offset caused by objective lens shift was measured and determined to be markedly decreased. Signal degradation by the ±1st light diffracted by a polarizing HOE was not observed. Good characteristics of recording and play-back for phase change discs were also obtained. This recordable optical head was found to have desirable characteristics and high productivity.

Optical Pickup for Recording to Dual-Layer 2x-Speed Blu-Ray Disc, DVD and Compact Disc

An ordinary half-height size optical pickup with high light-use efficiency for Blu-ray Discs (BDs) has been realized. It has two objective lenses arranged tangentially. Although one of the objective lenses, BD objective lens, does not follow the line that passes thorough the center of the spindle motor, stable tracking-error detection has been achieved by enhancing a one-beam method. This pickup has a beam shaper which changes a divergent angle of light with high magnification. Although beam shapers are sensitive to a positional error, our pickup accomplished stable positioning by introducing a new structure.

Development of Integrated Optical Unit for Large Storage Capacity Floppy Disk

A small integrated optical unit suitable for a large storage capacity floppy disk drive is proposed. The optical unit is 6.8 mm wide, 3.3 mm deep, and 3.0 mm high. The distance between the laser diode and the focused beam on the disk is only 4.0 mm. The optical unit consists of two components, a lens unit and a laser-detector unit. In this optical unit, with the beam slanting incident on the disk, the reflected beam takes another path. Thus, a diffraction grating, a lens, and a deflector can be integrated into one component. The optical unit allows wide disk tilting of up to 2.4 degrees.

Optical Pickup for Recording to Dual-Layer High-Speed Blu-ray Disc

A compact BD optical system with high light use efficiency that enables high-speed recording to a dual-layer BD is reviewed. It also achieves stable tracking-error detection on a dual-layer BD using a stray-light-free one-beam method.