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We have developed a magneto optical disk system, having the recording density of 7.1 Gbit/in2, by using zero-field type MAMMOS technology and an in-groove structured disk with a 635 nm laser diode and a 0.60 N.A.objective lens. We demonstrated that the system has enough margins for read/write powers, tilt, detrack anddefocus. On the other hand, the dependence of polarization direction of the incident beam on read/write characteristics was a problem, but was solved by optimizing the groove width.

A new type of MAMMOS (Magnetic amplifying magneto-optical system), which operates under the DC magnetic field in reproducing process, was proposed and evaluated. In this system, the CNR of 43 dB was obtained for 0.25 μm packed domains by applying 10 kA/m of DC magnetic field. Compared with conventional CAD (Center aperture detection)−MSR (Magnetically induced super resolution) disk, it was shown that the CNR for domain size below 0.4 μm was greatly improved.

MAMMOS (Magnetic Amplifying Magneto-Optical System) is a technology for reproducing a large signal during MO readout from a small magnetic domain. It has hitherto been considered that the domain recorded on the recording layer is copied to and expanded on the readout layer by irradiating the readout layer with a laser beam and applying a perpendicular magnetic field. However, we discovered that it is very effective for readout of small magnetic domains to apply an in-plane magnetic field. Under conditions where λ = 635 nm and NA = 0.55, the bit error rate (BER) of 0.15μm packed domains was improved to 2×10-4, while the BER of 0.2 μm packed domains was 2 × 10-4 when an in-plane magnetic field was not applied.

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/.

IFN療法によりC型肝炎ウイルス(HCV)が駆逐されたにもかかわらず,約1年6カ月後に細小肝癌が発見されたC型慢性肝炎の1例を報告した.症例は52歳男性.昭和40年輸血を受け,輸血後肝炎となり,その後C型慢性肝炎活動型(CAH2B)として加療をうけていた.平成4年IFN療法を行い,血中HCV-RNAは持続陰性化し著効となった.しかし,IFN投与終了約1年6カ月後に肝S7に17mm大の占拠性病変を認め,中分化型肝細胞癌と診断された.C型慢性肝炎に対してIFN療法を施行するに際し,血中HCV-RNAが陰性化した著効例であっても1年以上経過して肝細胞癌が発見される症例があり,長期的に厳重な経過観察が必要であると考えられた.

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.

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.

MAMMOS (Magnetic AMplifying Magneto-Optical System) is one of the highest density readout methods for storage media. The signal is directly amplified on the medium and its amplitude is just the same as that from a long domain. Even at a 0.04 μm domain, the signal was large enough. At a 0.2 μm packed domain, CNR was more than 50 dB and BER was in the 10-4 range. By employing a MAMMOS readout with magnetic field modulation (MFM-MAMMOS), the signals have both very high resolution and large amplitude characteristics.