Manabu Tani

0.04 µm Domain Expansion Readout for the Magnetic Amplifiying Magneto Optical System

Read/write characteristics of the magnetic amplifying magneto optical system (MAMMOS) with alternative readout fields such as carrier to noise ratio (C/N), eye pattern, jitter and bit error rate (BER), are investigated with a 640 nm wavelength laser diode and 0.55 numerical aperture of the objective lens. The C/N value of 0.12 µm is 50 dB and is independent of the mark length. A very clear eye pattern was observed. The results show that the jitter value is less than 3% compared with the window width and it is only dependent on the switching speed of the readout field. The error rate is improved by using a thin recording layer of 50 nm in thickness. The minimum domain length which yields a BER of less than 1×10-4 is 0.045 µm (45 nm); the minimum space length is 0.10 µm (100 nm). These results are confirmed at a track pitch of about 0.40 µm. By using a digital versatile disk (DVD) pickup, the areal density can be estimated to be about 23 Gbit/in2 with the user data capacity of 30 GB/120 mmφ. By using a 400 nm blue laser diode, these values are estimated as 59 Gbit/in2 and 77 GB/120 mmφ.

20 nm domain expansion readout by magnetic amplifying MO system (MAMMOS)

Very small domains are recorded on the MAMMOS disk and they ran be detected using RF readout field. The MO signal amplitude of 20 nm domains can be enhanced to the saturated signal level. For these small domains, the thermal stability problem is investigated. Even if high laser power for readout is irradiated to the small domains, the reproduced signal was maintained. The result indicates that the recording layer of TbFeCo possesses an advantage for paramagnetic limit problem over 100 Gbits/in/sup 2/.

Basic Characteristics and Predicted Lifetime of Stacked Volumetric Optical Disks

A stacked volumetric optical disks (SVOD) system has been developed to achieve an over 1 Tbytes cartridge capacity using a commercialized drive and conventional recording layers. To confirm the reliability of thin optical disks in SVOD, several feasibility tests were conducted. The recording power margin, tilt margin and read stability of the thin optical disks were measured, and the lifetime of the thin optical disks was estimated. The results were similar to those of conventional 1.2-mm-thick optical disks regardless of the disk thickness.

Zero-Field Magnetic Amplifying Magnetooptical System Applied to Next Generation “iD PHOTO” System

We investigated very high-density recording performance of the zero-field magnetic amplifying magnetooptical system (MAMMOS) with a 635 nm laser diode and a 0.60 N.A. objective lens. It was shown that the linear bit length of 0.13 µm was successfully reproduced with sufficient readout margins. The recording density up to 7.1 Gbit/in2 was demonstrated by combining the zero-field (ZF)-MAMMOS with an in-groove disk structure.

Thermal stability evaluation of 0.03/spl mu/m MO domains in MAMMOS

~, ~~ the future of high density MO recording. The problem should be investigated not only for HDD, but also for MO. There are few reports concerning this thermal stability problem for MO. The reason is due to the difficulty in detecting MO signals for the very tiny domains involved, less than 0.1 pm. As one solution for this small domain detection, we proposed a magnetic domain expansion detection named MAMMOS (Magnetic AMplifying MO System). By using this technique, very tiny MO signals reproduced from small domains less than 0.1 vm in length can be enhanced to the saturated signal level”. ’I. In this paper, the thermal stability of these very tiny domains is discussed. Experimental Drocedures The readout layer (GdFeCo:20nm) and recording layer (TbFeCo50nm) were prepared by a magnetron sputtering process on a Poly-Carbonate substrate. The typical TbFeCo for MO recording layer is an amorphous rare earth transition metal alloy. The coercive force at room temperature is quite large (over 20kOe). From this characteristic, it seems that very small domains could be recorded very stable. However, the experimental data were not reported. A non-magnetic intermediate layer separated each magnetic layer. In order to investigate the thermal stability for very small domains, a read-write tester was used with 680nm wavelength, with an objective lens of numerical apeaure, 0.55. The linear disk velocity was 0.8dsec. Exoerimental results and discussions Generally, high readout laser power irradiation causes reformation of the recorded domains because of decreased thermal stability of the domains. This leads to data error. We investigated the change in readout signal before and after irradiation of high laser power to the recorded areas in a MAMMOS disk. In one example, repetition patterns of 0.031.” (30nm) domains and 0.97pm spaces were recorded and the readout waveforms, observed. After this, the high lascr power was irradiated several times onto the recorded areas and the readout waveforms were observed again. In this way, we measured the irradiation number of the high laser power until an error MAMMOS signal was observed. The relation between the laser power and maximum temperature of the recording layer in the laser spot was estimated. According to this, the readout laser powers were transformed to the maximum temperature of the laser spot. The resulting thermal stability is shown in Fig.]. This is a typical graph of Anhenius plot to illustrate the thermal stability. The plots show a linear relation between the inverse temperature and the number of high power laser irradiation corresponding to when error a peared. In the case of a MAMMOS readout temperature region around 1.97e-3 K- , the laser P irradiation number indicates over le10. This is sufficient for actual data reproduction. Also, in the region of 373K (lOOC), the thermal stability of 0.03pm domains was investigated. The laser irradiation number was over le50. This number corresponds to at least over 100 years of archival data storage. In the figure, there are two symbols. The closed squares correspond to the result of the 0.03pm domains and the triangles are those of the 0.10 pm domains. However, there is no apparent difference between them. Conclusion Thermal stability of 0.03pm recorded domain on the MAMMOS disk was investigated. The results indicated that the readout cycle is over le10 times and the archival life at around lO0C is beyond 100 years

0.04-um domain expansion readout for the MAMMOS

Magneto-Optical (MO) disk possesses a very high advantage of high density recording compared to non magnetic optical disk, because MO recording is almost same as a perpendicular magnetic recording However, the high density recording is recorded by very tiny domains, so the readout MO signal decreases and the correct data reproduction becomes impossible. In order to amplify the small MO signal, one new idea has been proposed.