Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2000-06-29
2003-11-11
Psitos, Aristotelis M. (Department: 2653)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S013050
Reexamination Certificate
active
06646968
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a testing process for magneto-optical recording for presetting optimum recording power in magneto-optical medium of the domain wall displacement type, and to a magneto-optical recording-reproducing apparatus.
2. Related Background Art
In magneto-optical media, a multi-layer film comprising a magneto-optical layer and a reflection film has heretofore been formed on a transparent substrate through an insulating film. In general, land (or surface) portions and groove portions are used as data recording regions for storing information, and guiding grooves are used for tracking of a light beam, respectively, in magneto-optical recording. Magneto-optical medium capable of conducting high-density recording have been required with the increase in the quantity of information processing in recent years, and the idea to narrow a track pitch to meet such a requirement quickly has been forwarded. Research at a track pitch of 0.7 to 0.9 &mgr;m in a land (groove) type medium has been forwarded, and research to obtain a more narrow track pitch by shortening a laser wavelength has been advanced.
With the requirement of high-density recording, magneto-optical medium of the so-called land & groove type, in which grooves are formed as grooves sufficiently wide in width to write information not only into land portions; but also into groove portions, have also been developed. In the case of the land & groove type magneto-optical media, a pitch between land portions or between grooves can be made wider compared with the land (groove) type media, and so the restriction of a servo system for a light beam can be relaxed to form tracks as narrow as 6.4 to 0.7 &mgr;m, in terms of a track pitch.
As described above, information is recorded into the groove and land portions in a land & groove recording, and borders between land portions and groove portions are only slope portions of a substrate in which the land portions and groove portions have been formed, searches of formation of deep grooves, and the like are also collectively forwarded to provide longer slope portions.
On the other hand, in order to prevent destruction of data recorded on adjacent tracks, it is necessary to adjust power of a light beam in recording with high accuracy so as to form separately recorded domains of optimum sizes within land portions and groove portions constituting respective tracks. If the recording power is too high, in the case of a land recording, cross writing that a domain stored in the land portion extends beyond a groove to an adjacent land portion so as to destroy information recorded on the adjacent track occurs. In the case of a land & groove recording, cross writing that a domain stored in the land portion (or groove portion) extends beyond a slope portion of a border to an adjacent groove portion (or land portion) so as to destroy information recorded on the adjacent track occurs.
On the other hand, since magneto-optical recording is heat mode recording, the size of a magnetic domain recorded varies due to the influence of the temperatures of a recording apparatus and a medium used even when recording is conducted under the same recording conditions. Therefore, it is necessary to conduct recording while feeding back the influence of the temperatures of the recording apparatus and the medium into the recording conditions. In addition, individual differences between recording apparatuses due to differences in the form of a light spot caused by aberration of an optical head and defocusing, differences in characteristics between laser light sources, and the like, or scattering of the production of recording media, or the like, also greatly affects recording conditions.
As a method for preventing such cross writing, for example, Japanese Patent Application Laid-Open No.10-134354 has proposed a method for determining an optimum quantity of light for recording. According to this publication, a test pattern A is first recorded on an Nth track in a predetermined quantity of light for recording, and test patterns B are separately recorded on an (N+1)th track and an (N−1)th track in such various quantities of light for recording that a part of the test pattern A is sandwiched between them. Among data recorded on the Nth track, a difference between a reproduction signal from the portion of the test pattern A sandwiched between the test patterns B and a reproduction signal from the portion of the test pattern A not sandwiched between the test patterns B is determined every quantity of light for recording of the test patterns B to define the maximum quantity of light for recording from among the quantity of light for recording the test patterns B, in which the difference between the reproduction signal from the portion of the test pattern A sandwiched between the test patterns B and the reproduction signal from the portion of the test pattern A not sandwiched between the test patterns B falls within a prescribed range, as an optimum quantity of light for recording. Here, as a method for determining the difference between the reproduction signals, there is adopted a method in which a difference between the amplitude of the reproduction signal from the portion of the test pattern A sandwiched between the test patterns B and the amplitude of the reproduction signal from the portion of the test pattern A not sandwiched between the test patterns B, or a difference between standard deviation values of the respective signal levels or between error rates of reproduction is determined.
The linear recording density of an optical disk such as a magneto-optical medium greatly depends on the laser wavelength and the numerical aperture of an objective lens of an optical system for reproduction. More specifically, since the laser wavelength &lgr; and the numerical aperture NA of the objective lens of the optical system for reproduction determine the diameter of a beam waist, the detectable range of the spatial frequency upon reproduction of magnetic domains recorded is limited to about 2NA/&lgr;. Therefore, in order to achieve higher recording density with a conventional recording medium, it is necessary to shorten the laser wavelength &lgr; or enlarge the numerical aperture NA of the objective lens in the optical system for reproduction. However, improvements in the laser wavelength &lgr; and the numerical aperture NA of the objective lens are limited naturally. Therefore, techniques in which the structure and reading method of a recording medium are devised to improve the recording density have been developed.
For example, in Japanese Patent Application Laid-Open No. 6-290496, the present applicants have proposed a signal-reproducing method, in which signals are recorded in a memory layer of a multi-layer film having a displacement layer and the memory layer magnetically connected to each other, and recorded domains of less than the diffraction limit of an optical system are reproduced by displacing domain walls of the recorded domains in the displacement layer without changing record data in the memory layer by utilizing a temperature gradient caused by irradiation of a light beam for heating, and detecting a change in the polarization direction of reflected light of the light beam. According to this method, recorded domains of frequency of less than the diffraction limit of the optical system can be reproduced without decreasing the amplitude of reproduction signals, whereby recording density and transfer speed can be greatly improved. Such a magneto-optical medium will hereinafter be referred to as a domain wall displacement type magneto-optical medium.
Even when such a domain wall displacement type magneto-optical medium is used, research in which a track pitch is narrowed, thereby enhancing a track density in the magneto-optical medium, like the conventional magneto-optical medium, has been forwarded. In this case as well, the problem of cross writing due to formation of narrow tracks, like the conventional magneto-optical medium, or
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Psitos Aristotelis M.
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