Shozo Murata

High-Speed Recording up to 15,000 rpm Using Thin Optical Disks

We propose a high-speed optical disk system using thin flexible optical disks (HS-FOD) recording up to 15,000 rpm. The thin optical disk system is composed of three technical elements: media employing a thin and flexible substrate 0.1 mm thick, a mechanical stabilizer, and a high-speed tracking servo employing a feed-forward control with zero phase error tracking (ZPET-FF control). The HS-FOD system has an optical head with numerical aperture (NA) of 0.85 and is compatible with the optical system of a Blu-ray disc or a broadcast-use optical disk. We have successfully performed disk rotation stably and have performed precisely a focus servo and a tracking servo at 15,000 rpm. We also achieved writing and reading data at 15,000 rpm and recording 252 Mbps of random pattern data and could get small values of jitter below the tolerance. These results are enough to record professional high-definition television (HDTV) video signals in formats such as HD-D5 for broadcast-use.

A 252-Mb/s Recording Experiment Using Flexible Optical Disks for Broadcast Use

Flexible optical disks (FOD) have a feasibility of their high data-transfer rate and large capacity for archival storage. We have been developing the FOD in order to replace as the media with a current professional video cassette recorder (VCR) of HD-D5 format which have a data-transfer rate of more than 250 Mb/s. Here, we developed the FOD with the high recording sensitivity for high-speed recording, and succeeded to record the 252 Mb/s data with the high-speed tracking control method and optimized write strategy. We also employed the partial response maximum likelihood (PRML) read channel for playback data. We could get and achieve the low byte-error rate (BER) below 2 times 10-4 at the recording speed of 252 Mb/s, enough to record the video signals of HD-D5 VTR for professional broadcast use.

High Speed Flexible Optical Disk with Cylindrically Concaved Stabilizer

We developed a brand-new stabilizer with a cylindrically concaved active surface for a flexible optical disk system. The unique design enabled extremely stable driving of the flexible disk at rotational speeds over 10,000 rpm. We actually demonstrated the driving at rotational speeds of up to 15,000 rpm, the spindle motor limit of our optical disk tester. This highest rotational speed promises a maximum data transfer rate of more than 600 Mbps for the recording density of a Blu-ray Disc. This stable state was achieved using a simple control that just adjusts the relative axial position of the stabilizer against the flexible disk. Once the adjustment was made, high stability was maintained over a wide rotational speed, ranging from 4,000 to 15,000 rpm. In this stable state, the axial runout on the pickup scanning line was suppressed to less than 10 µm at all rotational speeds. By achieving this high performance with simplified stabilizer control, we have come close to putting our system into practical use.

Effect of Stabilizer in Reducing Effects of Axial Runout on a Flexible Optical Disk

We have been studying a new optical disk system constructed from a flexible disk and stabilizer. The feature of the system is the extremely small axial runout that is reduced by the aerodynamic effect of the stabilizer. We experimentally demonstrated that the system had the capability of achieving an axial runout of less than 5 µm across a radial region from 35 to 55 mm at a linear velocity of 13 m/s.

Aerodynamic Stabilization of Flexible Optical Disk with Triangularly Arranged Stabilizer System

We have developed a flexible optical disk (FOD) system comprising a flexible disk and stabilizer, which can achieve a small axial runout of the disk through simplified stabilizer control. The approach adopts a new stabilizer system made up of triangularly arranged stabilizers (TASs), which consists of one main stabilizer (MS) that stabilizes the pickup focus area on the disk and two auxiliary stabilizers (ASs) that control the balancing conditions around the MS. We experimentally demonstrated that the TAS system could effectively stabilize a flexible disk even under conditions with no active stabilizer adjustments, such as axial position control and tilt control, which could not be eliminated in our previous single-stabilizer system. The suppressed axial runout without active adjustments was sufficiently small of less than 5 µm at linear velocities from 5.7 to 13.0 m/s up to double the speed of Blu-ray disk system. The results indicated that the FOD system with the TASs, which is easily operated, could be implemented in high-density optical disk systems with a high numerical-aperture (NA) pickup.

Improvement of Aerodynamic Stability in Flexible Optical Disk System with Cylindrically Concaved Stabilizer

To improve the aerodynamic stability in a flexible optical disk system with a cylindrically concaved stabilizer, the effects of the curvature of the stabilizer, disk thickness, and disk materials on aerodynamic stability were investigated. We clarified that these factors affect the effective working area of the stabilizer. This result shows that the effective working area of the stabilizer could be expanded by adjusting the curvature of the stabilizer, disk thickness, and disk material. We also demonstrated recording and reproduction at 4× speed for Blu-ray disc density using flexible optical disks with various thicknesses.

High-density recording on air-stabilized flexible optical disk

We have developed an optical disk system constructed from a flexible disk and a stabilizer. The key feature of the system is an extremely small axial runout that has been reduced by 5 /spl mu/m as a result of the aerodynamic effect of the stabilizer. The system can achieve an axial runout of less than 5 /spl mu/m and enables a recording signal at a density of 0.13 /spl mu/m/bit. This system is stable in various curvature disks.

Semi transparent Recording Stack with Fast-Crystallization Phase-Change Material for Dual-Layer Optical Disk

We report the experimental results of a semi transparent recording stack with a fast-crystallization (FC) phase-change material for a dual-layer optical disk, using a pickup with a blue laser diode at 405 nm and a lens numerical aperture (NA) of 0.85 to achieve the highest capacity. The transmittance of 47% and the clock-to-data jitter of approximately 9% were obtained from the semi transparent recording stack. We confirmed that the FC phase-change material could be applied to a high-capacity dual-layer recording system.

High-speed blue-laser recording on the double-decker phase change disk with high-reliability

In this paper, we report the feasibility of 100 Mbps data transfer-rate with high reliability and wide-power margin that media can apply to double-deck high density recording of 42 GB capacity corresponding to an optical recording disk system (K. Schep et al, ISOM Tech. Dig., p. 210, 2000) using a blue laser diode at 405 nm, and NA (numerical aperture) of 0.85.

Characteristics of Flexible-Film Disks

To achieve high-density recording with a high numerical aperture (NA) pickup, we produced a flexible optical disk system that has a small axial runout, enabling the pickup to follow the focal servo more easily. Youngs modulus, the film thickness, and the position of the radius determine the rigidity of a film. Therefore, we defined the length to which a stabilizer pushing on a disk deformed the disk as the repellent force of the film and investigated the relationship between this repellent force and the axial runout of the disk. Consequently, by developing films with a specific repellent force, the axial runout of a variety of disks was reduced to less than 10 µm and high-density recording was achieved at a linear velocity of 13 m/s.