Hiromichi Ishibashi

Overview and the Future of Phase-Change Optical Disk Technology

Phase-change optical disk technology in the early days dealt with three issues: cyclability, erase characteristics and sensitivity. These were resolved by materials development, and disk layer structure technologies. This paper shows the high (carrier to noise ratio) C/N recording characteristics of a multi-level phase-change optical disk. Multi-level mark radial width modulation (MRWM) recording experiments have demonstrated 4-level (level 0, level 1, level 2 and level 3) recording capability. Even level 1 marks with a radial width of 200 nm have a high C/N ratio of more than 50 dB. The laser pulse width and laser power assigned MRWM, M-level recording is expected the potential for marks storing density proportionally to log 2M. This technology offers the feature of enhanced density and compatibility with a digital versatile disk (DVD) pick-up.

Wobble-Address Format of the Blu-ray Disc

We explain a new address format that is adapted in the Blu-ray Disc Rewritable format. The address information is prerecorded by wobbling the groove track. It is based on a single tone carrier to obtain a stable and accurate write clock. The modulation scheme is a combination of minimum shift keying (MSK) that is strong for media noise and saw tooth wobble (STW) that is strong for wobble shift. The robustness of the format is demonstrated by measurement of the system margins.

Practical study of saw-tooth wobble addressing by theoretical and experimental approaches

We have proposed a new concept of addressing in optical disks, the saw-tooth wobble (STW) groove. In this paper, the practical study of the STW by theoretical and experimental analyses is described. The address information corresponds to an even ordered-harmonic, so the write clock has no jitter factor. A 30 dB of carrier-to-noise ratio is sufficient for achieving 1E-2 of address error. Using a practical detection system, a radial tilt margin of more than ±0.6 degree is achieved.

Signal Qualification Method for Partial-Response Maximum-Likelihood Read/Write Channel

The partial-response maximum-likelihood (PRML) signal processing technique is effective for high-density recording media. However, there are few omit evaluation methods for qualifying the played-back signal using a simple measurement tool such as a jitter meter. We propose a simpler PRML qualification method, the so-called maximum-likelihood sequence error (MLSE) detection method. In this paper, we show the validity of the new method for dual-layer Blu-ray Disc read channel and, furthermore, show the method for optimizing the write channel.

Optical disk recording system of 25-GB capacity

A new in-groove format with Saw-Tooth wobble (STW) for blue laser and high NA system is proposed. The STW is designed in order to satisfy for high reliability of the addressing, continuous generation of system clock and easy linking of write data. The format efficiency is high, and moreover, it is confirmed capability for not only single-layer but also dual-layer phase change optical disk. In the conditions of the disk diameter of 120mm, track pitch of 0.32 micrometers and data bit length of 0.116micrometers /bit, the user capacity per layer is achieved 25G-bytes using D8-15 codec and PR(3443)ML channel. The bottom jitter of 9.4 percent by level-slice and the bit-error-rate of 6.0E-6 after PRML are obtained. In addition, the wide stress margins, as the radial/tangential tilt and the defocus tolerances, demonstrate to be enough to realize consumer optical disk systems of the next generation.

Enhanced 8-10 conversion code for high density recording

A modulation code suitable for magneto-optical recording has been studied. The 8-10 code, proposed in this paper, is written in a 5/10, 2/10 or 8/10 code. The study clarifies that the 8-10 code enables high density recording in noisy conditions.

High-Density Recording on a Phase-Change Rewritable Disk using a 405 nm Blue Laser Diode

The possibility of a 28 GB capacity/layer has been studied using a blue laser diode and high-NA objective lens. Under the conditions of the disk diameter of 120 mm, cover layer thickness of 0.1 mm, track pitch of 0.32 µm and data bit length of 0.104 µm/bit, a low bit error rate (ber) of 10-5 was obtained in both modulations of D8-15 and RLL(1,7) with partial response maximum likelihood (PRML). A wide tilt margin comparable to that in the case of DVD-RAM was obtained in RLL(1,7).

Magneto-Optic Disk Drive of High Speed Track Accessability

This paper describes 5 1/4-in. high track-access performance magneto-optic disk drive. The drive employs a split optical system with a swing-arm actuator, the inertia of which is 160 g cm2(equivalent to a linear actuator of 10 g weight). An avarage seek time was estimated less than 35ms in the absence of latency. It is noticeable that both its mechanism and control systems are very simple.

New Prml for Asymmetrical Signals in High-Density Optical Disks

The partial response maximum-likelihood (PRML) signal processing technique is effective for high-density recording media. However, asymmetry in the playback signal, which is caused not only by inter-symbol interference, but also by mismatched recording power in phase-change optical disks, markedly degrades the quality of PRML signal processing. In this paper, we propose an adaptive equalizer with a LMS algorithm for asymmetrical signals. We show the improved results in recording and playback experiments.

Lens Shift Correction in Tracking Servo System for Digital Versatile Rewritable Disc

In this paper the development of tracking offset correction for playback of a digital versatile rewritable disc (so called DVD-RAM), is described. The slim drive, having a small optical pick-up head with a small objective lens, is easily influenced by the deviation of the push-pull tracking error signal due to lens shift. The DVD-RAM disk format provides information not only on the amount of lens shift using the push-pull tracking error signal of address marks to correct tracking deviation, but also an opportunity to determine the optimum initial lens position using the differential phase tracking error signal.