Hiromichi Kobori

New magnetooptic head with a built-in generator for a bias magnetic field.

A high performance magnetooptic head, which generates a bias magnetic field itself, has been developed. It has a moving magnet actuator to drive an objective lens. The moving magnets have two functions. One is to apply a constant magnetic field on the recording medium. The other is to comprise a magnetic circuit for focusing and tracking control. This magnetooptic head is suitable for use in the two-head erase and write method, in which it is not necessary to change the polarity of the bias magnetic field. Moreover, it enables designing a small-sized magnetooptic disk drive, because a bias magnetic field generator is built into the optical head.

High-Density Recording Capability of Five-Layered Phase-Change Optical Disc

High-density recording capability of the five-layered phase-change disc has been examined from the viewpoints of optical simulation and disc performance. The optical simulation showed that the temperature rise in the amorphous state balanced that in the crystal state for the case when the thickness of the lower protective layer was adjusted from 70 nm to 120 nm. Carrier-to-noise ratio (CNR), overwriting erase ratio and jitter were measured by the optical recording system using a laser diode with a wavelength of 636 nm and an objective lens of 0.6 numerical aperture. Track-pitch was fixed at 0.6 µm and bit length was varied at a linear velocity of 6 m/s. CNR of 52 dB, overwriting erase ratio of more than 35 dB, and overwriting jitter of less than 10% were obtained on both land and groove at a bit length of 0.34 µm/bit.

High-density recording for greater than 1-GByte capacity using a 90-mm phase-change optical disk

The mark edge recording characteristics of a new thermally balanced phase-change optical disk operating at a wavelength of 690 nm have been studied, especially from the viewpoint of designing an optical disk drive. As a recording method, the multi-pulse write compensation method with constant duration of the read power level immediately after every multi-pulse, called the off-pulse, was applied. A high carrier-to-noise ratio (CNR) of 54 dB, a high erasability of 35 dB, and an overwrite power margin from -15% to +5% were obtained for a bit length of 0.5 micrometers and a track pitch of 1.0 micrometers at 14.7 m/s linear velocity. These results mean that it is possible to design an optical disk drive providing a capacity of 1.1 GBytes using a 90 mm double-sided disk. Further, it has been found that the off-pulse plays a very important role in controlling the precision of mark edge recording.

Computational Analysis of Cross-Erase Phenomenon for High-Density Phase-Change Recording

In order to increase the recording density and decrease the track pitch of the digital versatile discs (DVD) media using the land-and-groove recording format, it is essential to suppress the magnitude of the cross-erasure of the recorded marks. A computational analysis to estimate the mark and erasure shapes was carried out, and comparisons with the experimental results have shown good agreement. The cross-erasure was reduced under the conditions given in this paper by increasing the duty ratio of land width to groove width (L/G) while keeping the groove pitch constant.

Rewritable Optical Head Using ± First-order Diffracted Beams of a Holographic Optical Element

A new focusing error detection method using ±first-order diffracted beams of a holographic optical element (HOE) is proposed. We fabricate the proposed HOE and measured the focus offset between a land a groove. According to the measurement results, the focus offset of the proposed HOE was smaller than that of an astigmatic focusing error detection.

A Partial Response Maximum Likelihood Simulator to Evaluate the Effects of Various Deterioration Factors in Optical Disks

For higher density optical disks, it has been examined whether the partial response maximum likelihood (PRML) method can be used for signal detection. There have been, however, few theoretical studies about this method under the condition that the readout signal is deteriorated by various kinds of factors. We have developed a PRML simulator for optical disks to evaluate the PRML method theoretically taking, for example, crosstalk and disk tilt into account. We report the configuration of this PRML simulator and some results the simulator has yielded.

High-density mark position recording on a 90-mm phase-change optical disk

The attainable recording density of a thermally balanced phase-change optical disk with the mark position recording method have been studied, focusing on the viewpoint of designing an optical disk memory system. A new recording method with constant duration of the read power level after every write-pulse, called the off-pulse, was applied. A wide overwrite power margin from -20% to +10% was obtained for a bit length of 0.63 micrometers and a track pitch of 0.9 micrometers . These results mean that it is possible to attain 1.3 GByte capacity in a 90 mm double-sided disk with the zoned constant angular velocity format.

130mm.PHI. magneto-optic disc memory.

光磁気ディスクメモリーが現行の磁気メモリーと同様に世の中で広く使われるためには, 記録媒体の信頼性ならびに情報の重ね書きの問題を解決することが現在最も重要な技術課題となっている.我々は, 従来のFe系記録材料に比べて長寿命のTbCo膜を記録膜に用いることで媒体の信頼性向上を図り, 消去用と記録用の2光磁気ヘッド方式とすることで磁気メモリーと同様に情報の重ね書きを可能にした130mmφ光磁気ディスクメモリー装置を開発した.光磁気ヘッドの小型化, セクタ構造と2ヘッドのアクセス方向の工夫により, 装置全体を5.25インチ標準磁気ディスクドライブと同じサイズに収めている.本装置は2ヘッド構成でほぼ実時間で情報の重ね書きができることから, 卓上型や個人用のコンピュータの汎用外部メモリーのみならず, 書き換え可能なコンパクトディスク (CD) やビデオディスク (VD) へも応用できる.