Dynamic information storage or retrieval – Storage medium structure – Optical track structure
Reexamination Certificate
1996-02-09
2002-06-25
Neyzari, Ali (Department: 2651)
Dynamic information storage or retrieval
Storage medium structure
Optical track structure
C369S044260, C369S275300
Reexamination Certificate
active
06411592
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical information recording medium and an optical information recording and reproducing apparatus for recording and reproducing information by using a light beam. More particularly, the present invention relates to an optical information recording medium and an optical information recording and reproducing apparatus allowing for obtaining a higher track density by recording a signal on both lands and grooves of the guide grooves thereof.
2. Description of the Related Art
Optical disks, optical cards, optical tapes and the like are well-known as recording mediums (or recording members) for recording and/or reproducing information by the use of an optical means. In order to record information on such a recording medium, a laser beam is generally used as a light source. More specifically, information is recorded by precisely focusing a light beam through a lens so as to irradiate the light beam on a recording thin film of the recording medium.
An optical disk, one of the above-cited recording media, includes a circular substrate on which spiral or concentric guide grooves having a plurality of convex portions and concave portions are provided, and a recording thin film formed thereon. By irradiating a light beam, which is intensity-modulated in accordance with each information signal, along the direction of these guide grooves, information is recorded on the recording thin film.
The recording thin film is required to exhibit such characteristics that the physical properties thereof are varied upon the-irradiation of light, and that the difference between the states before and after the variation may be optically detected. The variations in the physical properties of the recording thin film, are for example, the deformation of the thin film owing to the absorption of the light, the phase change of the thin film owing to the light irradiation, and the like. The recording media showing such variations are known as a deformation type recording medium and phase-change type recording medium, respectively. A signal indicating the variations of the physical properties as difference in the amounts of the reflected light is reproduced.
A magnetooptic recording medium is also well-known as another optical type recording medium. In a magnetooptic recording medium, information is recorded thereon by the application of a magnetic field as well as light irradiation, and the difference in the magnetization directions on the recording thin film is detected by utilizing a Kerr effect, thereby reproducing a signal.
Optical type recording media such as those described above have been put into practical use depending on the respective applications thereof. In addition, in order to further increase the memory capacity for information, various kinds of researches on the increase of the recording density have been earnestly conducted.
As an exemplary method for increasing the recording density of an optical type recording medium, a method for recording a signal both on the convex portions and concave portions of the guide grooves is proposed so as to replace a conventional method for recording a signal on either the convex portions or the concave portions of the guide grooves (e.g., Japanese Journal of Applied Physics, Vol. 32 (1993), pp. 5324-5328). According to the method disclosed therein, by using a substrate in which the width of a concave portion of each guide groove is approximately equal to that of a convex portion thereof, and the depth of the concave portion is optimized, an information signal may be recorded and reproduced on/from both of the concave portion and the convex portion. In this specification, a convex portion with respect to the light incident direction is called a “groove”, and the operation of recording information on a convex portion is called a “groove recording”. In the same way, a concave portion with respect to the light incident direction is called a “land”, and the operation of recording information on a concave portion is called a “land recording”. If a method for recording a signal on both of lands and grooves is employed, a track density is considered to become double as compared with a conventional method in which information is recorded on either one side of each guide groove.
In recording and reproducing information in accordance with this method, the same kinds of optical systems and optical type recording systems as conventional ones may be used in principle. This method may be realized easily by additionally providing a tracking polarity switching means so as to correspond to each concave portion and each convex portion of the guide grooves, and by irradiating an intensity-modulated light beam on the two kinds of regions based on the information signals. However, the comparison of the two kinds of signals recorded on the two kinds of portions of the recording medium reveals that difference exists in the amplitude and the frequency characteristics of the two kinds of reproduced signal corresponding to a land and a groove, respectively. Such difference in the amplitude of the signals is also caused depending on the configuration of the respective recording thin films;. Therefore, even if a signal recording may be satisfactorily performed on either one of a land track and a groove track during a step of demodulating a reproduced signal, a great deal of error is generated on the other kind of track in some cases. Also, even in recording thin films having the same configuration, if the shape of the edges of the guide grooves or the groove width become different from each other, the levels of the reproduced signals become different on the two kinds of tracks.
Accordingly, in a conventional recording medium for performing a land/groove recording, there exists problems to be solved in that the configuration of a recording thin film is required to be optimized and that the guide grooves on the substrate must be shaped with high precision.
SUMMARY OF THE INVENTION
An optical information recording and reproducing apparatus for recording and reproducing an information signal on/from both concave portions and convex portions of guide grooves formed on a recording medium is provided. The recording medium has: a substrate on which the guide grooves consisting of the concave portions and the convex portions are formed; and a recording thin film, formed on the guide grooves, on which variations to be detected optically are generated by irradiation of light is provided. The optical information recording and reproducing apparatus of the invention includes: an optical portion, having a light source, for focusing a light beam emitted from the light source on the recording medium using an objective lens; a focusing control portion for controlling so as to make a focal point of the light beam correspond to a position of the recording thin film; a tracking control portion for controlling a position of the light beam in a direction substantially vertical to the guide grooves go that the light beam tracks the guide grooves; a selection portion for selecting which of the concave portions and the convex portions of the guide grooves are used for recording a information signal thereon or reproducing a recorded information signal therefrom; a polarity inverting portion for inverting the polarity of an output signal from the tracking control portion depending on a result selected by the selection portion; a waveform setting portion for setting a modulation pattern for the light beam to be irradiated on the recording medium in accordance with the information signal; and a signal reproduction portion for demodulating the information signal from a light reflected or transmitted by recorded marks recorded on the recording medium; wherein at least one of the focusing control portion, the tracking control portion, the waveform setting portion and the signal reproduction portion has at least two kinds of operation conditions for recording and reproducing the information signal on/from the concave portions and
Akahira Nobuo
Miyagawa Naoyasu
Nishiuchi Ken'ichi
Ohno Eiji
Neyzari Ali
Ratner & Prestia
LandOfFree
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