JPS6223378B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for optically reading information from a recording medium such as an optical video disk, and more particularly to an apparatus for reading information without being affected by the surface condition of the recording medium.

Conventionally, in this type of device, reading is difficult because the irradiated light beam is scattered by the surface condition of the recording medium, such as unevenness of the surface due to unevenness of the surface of the substrate or uneven reflection due to non-uniformity of the material. The problem was that the information signals received were degraded.
Note that related devices of this type include, for example, Japanese Patent Publication No. 52-32931, Japanese Patent Publication No. 53-30453,
There is Japanese Patent Publication No. 49-94304.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and provide an information reading device capable of detecting a reproduced signal with a good S/N ratio regardless of the surface condition of a recording medium. Hereinafter, the present invention will be explained with reference to the drawings.

1, 3, and 4 are diagrams for explaining the principle of the present invention, and show two information reading light beams irradiated onto a recording medium and information recorded on the recording medium. It shows the relationship between pits. In the figure, 100 to 103 indicate information pits, and 30
A and 30B indicate light beams. Signal existing areas on the recording medium, that is, information pits 100 to 10
Since the portion 3 and the other portions have different reflectances or transmittances, the two light beams 30A and 30B are directed to track A as shown in the figure.
When the light beams 30A and 30B are irradiated at the same time while partially overlapping each other in the direction of , the light intensity of the reflected light or the transmitted light of the light beams 30A and 30B changes as shown in the signals 41A and 41B shown in FIG. 2a, respectively. By taking the difference between the signals 41A and 41B, a signal 41 shown in FIG. 2b is obtained. The signal 41 is
Since this method detects the difference in the light intensity of the reflected light or transmitted light from two light beams irradiated onto a partially overlapping area of information pits existing in the track direction, it is possible to eliminate the influence of the surface condition of the recording medium. This is a signal that has been almost completely removed, that is, a signal that detects only the change in light intensity caused by the information pit. Therefore, if the above signal 41 is integrated, the reproduced signal 42 (Fig. 2 c
). In addition, in FIGS. 2a to 2c, the horizontal axis represents time, and the vertical axis represents light intensity.

Alternatively, as shown in FIG. 3, two light beams 30A and 30B may be applied to the track A in a direction perpendicular to each other so as to partially overlap each other. Obviously in this case the difference signal from the two light beams provides the tracking signal. To reproduce the information signal, it is sufficient to detect the signal from one of the light beams or the sum signal from the two light beams.

Further, as shown in FIG. 4, two light beams 30A and 30B may be irradiated in a direction inclined at an angle of about 45 degrees to the track A so as to partially overlap each other. In this case, the difference signal from the two light beams provides an information signal and a tracking signal simultaneously. Information signals and tracking signals can be distinguished by frequency band. That is, the high frequency component of the difference signal provides the information signal, and the low frequency component of the difference signal (corresponding to the envelope of the information signal) provides the tracking signal.

In the above description, two light beams were irradiated simultaneously, but the two light beams may be irradiated alternately in time. In this case, two light beams are applied alternately at a repetition frequency that is sufficiently higher than the temporal variation of the signal to be read. Furthermore, in the present invention, one light beam may be irradiated with a slight oscillation sufficiently earlier than the temporal change of the signal to be read. In these cases, if a signal obtained by detecting reflected light or transmitted light from the recording medium is synchronously detected using a predetermined signal, a signal equivalent to the difference signal in the above explanation can be obtained. For example, when one light beam is slightly vibrated along the track direction, that is, when the areas irradiated by the light beams 30A and 30B in FIG. 1 are vibrated and irradiated, the reflected light Alternatively, the light intensity of the transmitted light changes like the signal 43 shown in FIG. In the figure, the horizontal axis shows time and the vertical axis shows light intensity. If the signal 43 is synchronously detected with a signal for vibrating the light beam, a signal 41 shown in FIG. 2b can be obtained.

As explained above, by irradiating a light beam onto a close area on a recording medium, it is possible to detect an information signal or a tracking signal with a good S/N ratio, or even both an information signal and a tracking signal. I can do it.

FIG. 6 is a diagram showing the configuration of an embodiment of the present invention, in which two light beams are irradiated simultaneously. Reproduction light source 1 (for example, randomly polarized light source
A light beam 20 from a He--Ne gas laser is split by a beam splitter 2 into two light beams 20A and 20B having different polarization states. The beam splitter 2 is, for example, a Wallaston prism, and in this embodiment, the polarization directions of the light beams 20A and 20B are perpendicular to each other. Both of the beams are reflected by the mirror 4, pass through the lens 5, and are irradiated onto the recording medium 12 as light beams 30A and 30B that partially overlap each other. At this time, the light beams 30A and 30B are directed in the same direction, at right angles to the track, as shown by the light beams with the same symbols in FIG. 1, FIG. 3, or FIG.
Alternatively, the angle of the beam splitter 2 is set in a direction of about 45 degrees. In this example, approximately 45
This is the case when the light is irradiated in the direction of °. The two reflected lights 40A and 40B from the recording medium 12 are guided by the half mirror 6 to the photodetectors 8A and 8B. In this case, the reflected lights 40A and 40B are separated by the polarizing prism 7 inserted into the optical path, and only the reflected light 40A is guided to the photodetector 8A, and only the reflected light 40B is guided to the photodetector 8B. be guided. The output signals 50A and 50B from the photodetectors 8A and 8B are supplied to a differential amplifier 9, and the output signal 60 is passed through an integrating circuit 10, where an information signal 70 is detected. A tracking signal 80 is obtained by passing the output signal 60 from the differential amplifier 9 through the low-pass filter 11, and this signal 80 drives the mirror 4 to perform tracking.

FIG. 7 is a diagram showing the configuration of another embodiment of the present invention, in which two light beams are irradiated alternately in time. In the figure, 16 is a Zeeman laser and 2 is a Wallaston prism. The plane of polarization of the light beam 20 from the Zeeman laser 16 rotates at a frequency that depends on the strength of the magnetic field applied to the Zeeman laser 16, so the Wallaston prism 2 splits the light beam 20 into two light beams 20 with different polarization states.
A and 20B are sent out alternately in time. The light beams 20A and 20B are reflected by the mirror 4, pass through the lens 5, and are irradiated alternately in time as light beams 30A and 30B that irradiate partially overlapping areas on the recording medium 12, respectively. As in the embodiment of FIG. 6, the light beams 30A and 30B may be directed in the same direction, perpendicular to the track on the recording medium 12, or in a direction at approximately 45 degrees, depending on the angle of the Wallaston prism 2. It is irradiated so that In this example, the light is irradiated in a direction of about 45 degrees. After the reflected lights 40A and 40B from the recording medium 12 pass through the lens 5 and the mirror 4, they are sent to the photodetector 8 by the half mirror 6.
be led to. Signal 5 detected by the photodetector 8
0 is supplied to the synchronous detection circuit 14. A signal for synchronous detection is obtained by extracting a part of the light beams 20A and 20B by a half mirror 23 inserted in the optical path, and by polarizing plate 24, either one of the light beams 20A and 20B is converted into a signal. Signal 90 detected by the photodetector 25 of a change in the light intensity of the beam
given by. The signal 60 synchronously detected by this signal 90 is passed through the integrating circuit 10 to generate the information signal 7.
0 is detected. A tracking signal 80 is obtained by passing the signal 60 through the low-pass filter 11, and this signal 80 drives the mirror 4 to perform tracking.

FIG. 8 is a diagram showing a main part of the configuration of another embodiment of the present invention, in which one light beam is vibrated and irradiated. A light beam 20 from the reproduction light source 1 is deflected by an optical deflector 3 (for example, an acousto-optic optical deflector) according to a signal 91 from an oscillator 13. That is, the light beam 20 is connected to the dotted line 2
0' and a solid line 20''.The direction in which the light beam 20 oscillates can be adjusted to the track on the recording medium (not shown) by appropriately setting the inclination of the optical deflector 3. It is set in the same direction, perpendicular direction, or about 45 degrees.For example,
If the light beam 20 is slightly oscillated in a direction of about 45 degrees, that is, the light beam 30A in FIG.
and 30B, the oscillated light beam 20 performs substantially the same function as the light beams 20A and 20B in the embodiment of FIG. .
Therefore, the oscillator 13 is used as a signal for synchronous detection.
By using the signal 91 from , it is possible to detect the information signal and the tracking signal with the same configuration as the embodiment shown in FIG.

In addition, in the embodiment shown in FIGS. 7 and 8,
As described above, it is preferable to change the light beam irradiated onto the recording medium faster than the temporal change of the signal to be read. For example, in an optical video disc, the playback signal is about 10MHz, so the 7th
In the example shown in the figure, in order to reproduce the signal with a good S/N ratio, it is necessary to
It is preferable to rotate the plane of polarization.

FIG. 9 is a diagram showing the main part of the configuration of another embodiment of the present invention, in which two semiconductor lasers are used as the reproduction light source. In the figure, one semiconductor laser 1A is intensity-modulated by a signal 92 from an oscillator 18, and the other semiconductor laser 1B transmits a signal 92 from the oscillator 18 to a phase inversion circuit 19.
The intensity is modulated by a signal 93 whose phase is inverted by 180°. If the light beams 21A and 21B from the two semiconductor lasers are combined by the mirror 22 so that they are in the same direction as the light beams 20A and 20B in the embodiment of FIG. 7, the light beam in the embodiment of FIG. A light beam is obtained that performs the same function as 20A and 20B. Therefore, if the signal 92 from the oscillator 18 or the signal 93 from the phase inversion circuit 19 is used as a signal for synchronous detection, the seventh
Information signals and tracking signals can be detected with the same configuration as the embodiment shown. Note that since semiconductor lasers can easily be directly modulated at several hundred MHz, it is possible to easily obtain light beams that alternately irradiate adjacent areas on the recording medium at several hundred MHz. Also,
In the embodiment shown in FIG. 9, two semiconductor lasers may be caused to oscillate simultaneously, and their polarization states may be different. That is, if the two semiconductor lasers are linearly polarized lights that are orthogonal to each other, the combined light beams 20A and 20B perform the same function as the light beams with the same symbols in the embodiment shown in FIG.

In the embodiment, only the case where reflected light is detected has been described, but transmitted light may also be detected.

As explained above, according to the present invention, even if there is a signal component of about 10 MHz as in an optical video disk, a reproduced signal with a sufficiently good S/N ratio can be detected without being affected by the surface condition of the recording medium. In particular, if the light beam is irradiated in a direction of about 45 degrees to the track, a tracking signal can be obtained at the same time. Furthermore, if the light beam is irradiated onto the track in the same direction or in a perpendicular direction, in this case only one of the reproduction signal and the tracking signal can be obtained.

[Brief explanation of the drawing]

FIGS. 1, 3, and 4 are diagrams showing the relationship between two light beams irradiated onto a recording medium and information pits recorded on the recording medium, and FIGS. 2 and 5 6 and 7 are diagrams each showing an embodiment of the present invention, and FIGS. 8 and 9 are diagrams illustrating the configuration of an embodiment of the main part of the present invention. FIG.

Claims (1)

[Claims] 1. A light source, an optical device that irradiates a light beam from the light source onto two partially overlapping areas on a predetermined recording medium on which information is recorded, and a light beam emitted from the light source from the two partially overlapping areas. a first detection means for spatially or temporally separating and detecting the obtained light beams to obtain a signal indicating the intensity difference between the two; and a second detection means for obtaining an information signal and/or a tracking signal from the output of the detection means. An information reading device comprising a detection means. 2. Two light beams with different polarization states are used as the light beams, and the two light beams are irradiated onto the two areas that partially overlap, and the first detection means is configured to irradiate the two areas that partially overlap. It is characterized by comprising a polarization separation means for separating light beams from two regions, a photodetector for receiving each of the lights separated by the polarization separation means, and means for obtaining a difference in the outputs of the photodetectors. An information reading device according to claim 1. 3 A laser light source that outputs a randomly polarized light beam is used as the light source, and the optical device converts the light beam from the laser light source into two different polarization states.
3. The information reading device according to claim 2, further comprising separating means for separating the book light beam into light beams. 4 Using two semiconductor lasers as the light source,
Claim 2, wherein the optical device has a combining means for combining the light beams from both the semiconductor lasers, and the combined light beam is irradiated onto the two partially overlapping regions. The information reading device described. 5. Using two light beams that alternately irradiate the two partially overlapping areas as the light beam, the first detection means receives the light beams from the two partially overlapping areas. Claim 1 comprising: a detector; and synchronous detection means for synchronously detecting the output of the photodetector using a signal indicating the intensity of one of the two light beams.
Information reading device described in section. 6 A laser light source that outputs a light beam with a rotating plane of polarization is used as the light source, and the optical device includes an optical element that receives the light beam from the laser light source and alternately emits two light beams with different polarization states. An information reading device according to claim 5, characterized in that the information reading device has: 7 The optical device emits light from the optical element 2
Claims characterized by having an optical element that extracts either one of the light beams of the book, and synchronously detecting the output of the photodetector using a signal detected by a photodetector of the extracted light beam. The information reading device according to item 6. 8 Using two semiconductor lasers as the light source,
6. The information reading device according to claim 5, wherein the two light beams are alternately outputted by driving the two semiconductor lasers with signals having a phase difference of 180 degrees. 9. The information reading device according to claim 8, wherein the output of the photodetector is synchronously detected by one of the signals for driving the two semiconductor lasers. 10 The optical device has a deflection means for deflecting the light beam from the light source, and vibrates and irradiates the light beam between the two partially overlapping regions, and the first detection means includes: It is characterized by comprising a photodetector that receives a light beam from between the two partially overlapping areas, and synchronous detection means that synchronously detects the output of the photodetector using a signal that drives the deflection means. An information reading device according to claim 1.