Tetsuo Saimi

Reproducing-only and recordable-reproduceable optical discs and common optical disc player therefor

The combination of recordable-reproduceable optical discs and reproducing-only optical discs and an optical disc player which is capable of reproducing recorded signals both from the recordable-reproduceable optical disc possessing pregrooves and the reproducing-only optical disc possessing recording pits by means of a common optical system. The common optical system has a common laser for irradiating both types of discs with a laser beam used for reading the discs. The wavelength of the laser is λ and the depth or height of the pregrooves of the recordable-reproduceable optical disc is made equal to or less than λ/8n, and the depth or height of the recording pits of the reproducing-only optical disc is made equal to or greater than λ/8n but less than λ/4n, wherein n is the refractive index of the substrate of the disc or the protective layer provided on the surface thereof.

4.7 GB Phase-Change Optical Disk for an Authoring System of Digital Versatile Disc

A phase-change optical disk that has an optical phase-shift signal reproducing structure and the same physical specifications as the 4.7 GB read-only digital versatile disc (DVD) was developed. A minimum jitter of 9% and a wide tilt tolerance for the jitter were obtained under DVD reproducing conditions of λ=650 nm and NA=0.60. This new medium can be used as an inspection tool for DVD authoring. It was also confirmed that this optical disk had a potential for use as a rewritable 4.7 GB DVD medium that has compatibility with the read-only DVD.

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.

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.

Dual-Layer Volume Holographic Optical Elements for Three-Wavelength Optical Disk Pickup

A dual-layer volume holographic optical element is proposed as a beam-splitting element for a three-wavelength (?=0.4 ?m, 0.65 ?m and 0.8 ?m) optical disk pickup. We fabricated it for normal incidence using photopolymer film via an inexpensive laminate process. It is demonstrated that it exhibited excellent wavelength selectivity (extinction ratio ?~100) with a high diffraction efficiency of 99.7%. This element could be a key device in a next-generation multi wavelength optical disk pickup.

Holographic Servo-signal Detection Stabilized to the Wavelength Fluctuation and the Mechanical Misalignment in the Optical Heads.

Compact holographic heads using the spot size detection of double beams with linear photodetector-elements are proposed to attain highly reliable performances under considerable optical misalignment. Acceptable amount of misalignment could be expanded by a factor of ten compared with that in an astigmatic system. Mechanical accuracy of the integrated head is also discussed.

Recording and Playing (R/P) System Having a Compatibility with Mass Produced Replica Disc

It has now been several years since the first laser video disc system made its debut on the market and the years since then have seen the development of many new applications utilizing various features of the system. The most outstanding features of the laser video disc system are high recording density, high speed of information retrieval, and high speed of copying of information.