Dynamic information storage or retrieval – Specific detail of information handling portion of system – Radiation beam modification of or by storage medium
Patent
1988-12-12
1991-12-03
Envall, Jr., Roy N.
Dynamic information storage or retrieval
Specific detail of information handling portion of system
Radiation beam modification of or by storage medium
369122, 250205, G11B 700
Patent
active
050704966
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a laser reproducing apparatus that reproduces recorded data recorded on a recording medium such as an optical disc, a magneto-optical disc or the like by the irradiation of a laser beam.
2. Background Art
As data recording and reproducing means in which data is rewritable, there has been recently developed a magneto-optical disc.
Data recorded on this magneto-optical disc is reproduced therefrom by means of such a pickup as, for example, shown in FIG. 7. When the recorded data is reproduced from a magneto-optical disc 11 on which data were already recorded by virtue of the change of the magnetization direction, a laser beam emitted from a laser diode 12 is irradiated on the magneto-optical disc 11 through a collimator lens 13, a beam splitter 14 and an objective lens 15 and a reflected light from the magneto-optical disc 11 is again introduced into the beam splitter 14 through the objective lens 15, whereby the reflected 1 light is changed by the beam splitter 14. A portion of the thus reflected light is introduced through an analyzer 16 and a lens 17 into a light receiving element 18.
The condition of the magneto-optical disc 11 can be known by detecting the polarized state of the light incident on the light receiving element 18 so that the recorded data can be reproduced.
When the data is reproduced by using the pickup shown in FIG. 7, however, a so-called reflected-back light occurs, in which the laser beam from the laser diode 12 is reflected by the magneto-optical disc 11 and a part thereof is passed through the beam splitter 14 and is returned to the laser diode 12. This reflected-back light makes the oscillation mode of the laser diode 12 unstable, causing a waveform of the reproduced signal to be distorted. Also, there occurs a mode-hopping noise or the like in which a plurality of longitudinal modes concur, unstably, thus making it impossible to properly the data. Specifically, in the case of the above-mentioned optical system in which the outward and backward paths of the laser beam re changed by the beam splitter, as compared to an optical system in which a polarizing beam splitter is employed as a beam splitter and a 1/4 wavelength plate is provided between this beam splitter and an objective lens, from a construction standpoint, the reflected-back light occurs frequently so that the waveform distortion of the reproduced signal, the mode-hopping noise and so on occur frequently.
To solve this problem, such a technique is proposed in Official Gazette of Japanese Patent Publication No. 59-9086 (published on Feb. 29, 1984) in which a high frequency signal of about 700 MHz is superimposed upon a laser drive signal supplied, for example, to a semiconductor laser and a multi-mode laser is outputted from this semiconductor laser thereby removing the influence caused by the reflected-back light. However, since a circuit for superimposing a high frequency signal requires a signal of a relatively large power, the arrangement thereof is complicated. Also, this circuit cannot be matched with the laser diode in impedance without difficulty so that the mode-hopping noise and waveform distortion cannot be sufficiently removed.
DISCLOSURE OF INVENTION
In view of the above-mentioned aspect, the present invention is to provide a laser reproducing apparatus of simple arrangement which can reproduce data satisfactorily, without the problems of the reflected back light.
A laser reproducing apparatus of the present invention is constructed as, for example, shown in FIG. 1. In this laser reproducing apparatus which reproduces data recorded on a recording medium by the irradiation of a laser beam emitted from a laser diode 12, the current value of a drive signal of the laser diode 12 is set near a value at which the irradiated state of the laser beam is changed the least by the reflected-back light. The irradiation of the laser beam from the laser diode 12 by the thus set current value is intermittently carried out at a predetermined cycle. Also, the
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patent: 4580044 (1986-04-01), Hongo et al.
patent: 4692606 (1987-09-01), Sakai et al.
patent: 4701609 (1987-10-01), Koishi et al.
patent: 4754460 (1988-01-01), Kimura et al.
patent: 4788674 (1988-11-01), Maeda et al.
Horimai Hideyoshi
Ogawa Hiroshi
Envall Jr. Roy N.
Nabil Hindi
Shaw, Jr. Philip M.
Sony Corporation
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