Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
1999-09-16
2002-09-24
Hindi, Nabil (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S121000
Reexamination Certificate
active
06456575
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus and method for recording information in a recordable optical information medium in which information can be additionally written only once and for reproducing information from the optical information medium.
When information are recorded or reproduced from an optical information medium, a recording beam, a tracking beam, a focusing beam and a reproduction beam are utilized. These optical beams are emitted from the same light source.
Among conventional optical recording/reproducing apparatuses, there is known an apparatus that can record and reproduce information with reference to various types of optical information mediums. To enable this, the apparatus is provided with a number of light sources for emitting optical beams of different wavelengths. The apparatus selects an optical beam that has the wavelength corresponding to the type of optical information medium in use, and uses the selected optical beam for the recording and reproduction of information. Even when this type of apparatus records and reproduces information with reference to an optical information medium, the optical beams used by the apparatus are from the same light source.
In recent years, the information-oriented society makes further progress, and the information processing apparatuses that are in general use can process information far faster than before. In accordance with this trend, there is a demand for recording/reproducing apparatuses that can record and reproduce information at far higher speeds. However, in the case of an optical recording/reproducing apparatus which is of a write-once type, the recording speed of the recording unit is slower than that the reproduction speed of the reproducing unit. As can be seen from this, the recording speed is generally lower than the reproduction speed in the present circumstances.
When information are recorded in a recordable optical information medium, the optical beam used for recording is of high energy, and the recording layer of the recording medium corresponds to such a wavelength as provides a great light absorption coefficient. Accordingly, recording pits can be formed with a low level of outputs. The reason for this will be described in more detail.
Let us assume that the moving speed of a recording head is V (m/s), the width of the recording light beam is D (m), the irradiation time of the recording light beam is &Dgr;T (s), the output of the recording light beam is P (J/s), and the absorption coefficient of the recording layer of a recording beam is A. In this case, the amount of energy absorbed during the irradiation time &Dgr;T (s) is represented as P×A×&Dgr;T, and the area in which the energy is absorbed during the irradiation time &Dgr;T is represented as V×D×&Dgr;T. Accordingly, the average surface density W (J/m□) of the energy absorbed in area S is as follows:
(P×A×&Dgr;T)/(V×D×&Dgr;T)=(P×A)/(V×D)
Given that the value of D is constant, the average surface density of the energy absorbed in the recording layer is in proportion to the absorption coefficient and in inverse proportion to the moving speed of the recording head.
As can be seen from the above, higher recording density can be obtained by increasing the output of the recording optical beam or by applying a recording optical beam having such a waveform as provides high absorption coefficient.
When information are reproduced from a recordable optical information medium, the optical beam radiated to the medium must have such a wavelength as provides a high contrast between the beam reflected from the recording pits of the recording layer of the medium and the beam reflected from the areas other than the recording pits of the recording layer. The higher the contrast the optical beam provides, the higher will be the S/N ratio (signal-to-noise ratio) of a reproduction signal. The factors that should be considered to obtain a high contrast include the reflection factor of an optical beam, the polarization angle thereof, etc.
In general, optical beams of the same wavelength do not satisfy both the requirements of a recording beam and those of a reproducing beam.
Among commercially-available recordable mediums, there is a medium whose recording layer is made up of a transparent support member arranged on the light-incident side, a metallic reflecting film, and a recording layer located between the support member and the metallic reflecting member and containing an organic pigment. When a light beam is radiated onto the recording layer, the energy the light beam has when it has passed the support member thermally changes the nature of the organic pigment. Since recording pits are thereby formed, information can be written only once. As shown in
FIG. 2
, the recording layer of this type of recording medium shows greatly different reflection factors between the case where a light beam having a wavelength close to that of near infra-ray light is incident on the recording pits and the case where the same light beam is incident on the areas other than the recording pits. When information are reproduced from this write-once recordable medium, a light beam which has a wavelength close to that of infra-red light and which does not vary in intensity with time is radiated onto the medium, and the amount of light reflected from the medium is monitored so as to check the difference between the amount of light reflected from the recording pits and the light reflected from the areas other than the recording pits. By monitoring the amounts of light reflected from the medium in this manner, the length of time during which the reflected light is intense and the length of time during which it is feeble are measured. In principle, the reflection factor of the above medium is about 80% when near infra-red light having a wavelength of 800 nm or thereabouts is incident on the areas other than the recording pits (i.e., unrecorded areas, curve b), and is about 40% when the same infra-red light is incident on the recording pits (i.e., the recording areas curve a). (These values of reflection factors are based on the assumption that the recording layer is a flat and smooth base member.)
If a near infra-red light of the same wavelength as the reproducing beam described above is used for recording information in the unrecorded areas of the above recordable information medium, the absorption coefficient of the light beam is as low as 20% or so, as indicated by curve b in
FIG. 3
(100%—[reflection factor]—[transmittance]) (the transmittance can be regarded 0% or so). With such a low absorption coefficient, the recording speed cannot be improved.
The write-once recordable information medium described above exhibits a small reflection factor for an optical beam having a wavelength which is within the wavelengths of visible light; in other words, it exhibits a great energy absorption coefficient for that optical beam. This means that, when used for the recording of information, the optical beam provides a high energy efficiency and consequently speeds up the recording speed. At the same time, however, the optical light-does not produce a significant difference between the amount of light reflected from the recording pits and the amount of light reflected from the areas other than the recording pits. This being so, an optical beam having the same wavelength as the recording beam cannot be used as a reproducing beam.
To solve this problem, Jpn. Pat. Appln. KOKAI Publication No. 2-187937 discloses a technique wherein information is recorded in a recording layer by using a recording beam whose wavelength provides the recording layer with a high optical absorbing coefficient and wherein the recorded information is reproduced from the recording layer by using a reproducing beam whose wavelength provides the recording layer with a low optical absorbing coefficient.
Even when the recording/reproducing method disclosed in KOKAI Publication No. 2-187937 is used, howev
Hindi Nabil
Kabushiki Kaisha Toshiba
Pillsbury & Winthrop LLP
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