Hideki Akasaka

Direct Overwrite by Light Power Modulation on Magneto-Optical Multi-Layered Media

The present authors have developed a new direct overwrite method on multi-layered Magneto-optical(MO) memory media by light power modulation [1]. (In this experiment double-layered MO memory media are used.) The key points were the media constituing of a memory layer and a reference layer, and an auxiliary magnet which initializes the reference layer. The materials of the two thin film layers we have tested were TbFe/TbFeCo and TbFe/GdTbFe. The both combinations worked well. The former conbination gave us the following result; media velocity = 13.4m/sec, readoput C/N (RBW = 30kHz) = 54dB, 47dB, 44dB for 1MHz, 6MHz, 8MHz respectively.

Recording power characteristics of 130 mm overwritable MO disk by laser power modulation method

The authors investigate the recording power characteristics of 130 mm overwritable MO disk by laser power modulation method. At 2400 rpm, the laser power of 11 mW on disk is enough to record marks on our disk. When we choose the recording conditions properly, PL power margin of ±20% is attained at overall area of the disk.

2 GB/130 mm Capacity Direct-Overwrite Magneto-Optical Disk

Precise mark-edge recording on a high signal-to-noise ratio (S/N) exchange-coupled direct overwrite magneto-optical (MO) disk provides 2 GB capacity on a 130 mm disk with a sufficient edge jitter margin. Write compensation technology was proven to be effective for both non- and direct-overwrite MO disks.

2-GByte/130-mm capacity direct overwrite magneto-optical disk and drive

We have modified drives of 2Gbyte/130 mm non-DOW MO disk to be drives of 2GByte/130 mm DOW-MO disk. We have demonstrated that we have already reached the practical stage showing that it is possible to produce 2 GByte/130 mm DOW-MO disk and drive.

Direct overwritable magneto-optical exchange-coupled multilayered disk by laser power modulation recording

In 1987, we presented a direct overwritable Magneto-Optical exchange coupled Multilayered (DOW) disk by laser power modulation recording. Since then two major improvements of DOW were announced, namely 3- layered and 4-layered DOW disks, based on the 2-layered DOW disk, From the view point of merits and demerits, we compare the DOW disk with other direct overwritable optical disks, magnetic field modulation recording type of MO disk and phase change type of optical disk. As a latest topic, the recording power margin of the DOW scheme is explained. Adding metal coat to the DOW MO thin films is effective to expand the recording power margin. We have achieved (+/- 10%)2 allowance for direct overwriting power margin of PH and PL. Perspectives of the DOW disk for the next generation MO disk memory system are mentioned.

Optimum Recording Conditions of Direct Overwrite Magneto-Optical Disk Drive for the Widest Power Margin

The write laser power margin of magneto-optical (MO) disks is determined by, for example, the disk sensitivity and various conditions of MO drive. Especially when the multipulse writing method is used for mark edge recording, the drive conditions influence the writing power margin. The drive conditions include both the write channel conditions, such as the writing waveform and the writing power, and the read channel conditions, such as the readout equalizer. When these conditions are optimal, the drive has the widest power margin possible for the object disk. We used the multipulse writing method on direct overwrite (DOW) MO disks and examined the optimum write power condition and the optimum readout equalizer condition. As a result, the correlation between those parameters has been clarified.

Overdrivability of Red Laser Diode Pulse Power for Recording on Direct Overwrite Magneto-Optical Disk

We measured electric current and light power diagrams of red laser diodes with a pulse power condition, and performed a life test of red laser diodes with the pulse power condition. From these experimental results, we conclude that these red laser diodes are overdrivable in pulsing, far exceeding their specification of DC rated power. We also conclude that direct overwrite magneto-optical (DOW-MO) disks with red laser diodes can achieve next-generation large capacity, with current disk rotation speed, which means, a data transfer rate equal to or greater than that of the current disk memory.

High-speed response to laser heating and cooling in thermo-magnetic writing on magneto-optical disk memory

In order to use Magneto-Optical (MO) media for multi media applications, it is necessary to achieve higher density, higher data transfer rate and lower cost technologies than current MO media. MO recording is thermo- magnetic recording. MO recordings makes use of temperature modulation caused by light intensity modulation from the laser diode for recording. So, it is important to realize high speed response to the light intensity modulation for high data transfer rate recording. The high speed response is also indispensable to make small magnetic domains. So, it is important for high density recording, too. We investigate the temperature response to the light intensity modulation on MO disk. consequently, we found that MO medium shows the high speed response when the laser spot scanning velocity is large.