JPS6142751A - Information reader - Google Patents

Abstract

PURPOSE:To eliminate a need to record a decision signal on a recording medium by irradiating the recording medium with laser light and deciding on the kind of a recording medium according to a difference in refractive index of the recording medium, and outputting an output of a photodetector to a differential type reproducing circuit or nondifferential type reproducing circuit selectively. CONSTITUTION:A sensor 13 is equipped with a light emission part and a photodetection part and supplies its output having a level corresponding to reflected light from a disk 5 to a command part 12. The command part 12 having a voltage comparator decides on a recording medium such as a compact disk when said output is larger than a specific threshold value and applies, for example, an L-level signal to a connection part 11, thereby supplying outputs of the 1st and the 2nd photodetectors 8a and 8b to an adder 10. When the output is smaller than the specific threshold value, the command part decides on a photomagnetic recording medium and supplied an H-level signal to the connection part, thereby supplying the outputs of the detectors 8a and 8b to a differential amplifier 9. Thus, information is read out without recording any decision signal on the recording medium previously.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application This invention relates to an information reading device that reads information recorded on a recording medium.

B) Prior Art Generally, when reproducing information recorded on a recording medium such as an optical video disk, the recording medium is irradiated with laser light and the reflected or transmitted light is detected.

Recently, information has been magnetically recorded on magneto-optical recording media by applying the phenomenon in which the plane of polarization rotates due to the magnetic Kerr effect when linearly polarized light is reflected off the surface of a magnetic material or transmitted through a magnetic material. This type of magneto-optical recording medium is used for reading.

In order to increase the density of information recording and to make the magnetic Kerr effect noticeable, it is constructed of a perpendicularly magnetized film having perpendicular magnetic anisotropy, that is, the axis of easy magnetization in the direction perpendicular to the substrate surface.

By the way, when recording information on a magneto-optical recording medium such as the one described above, the entire recording area of the medium must be uniformly distributed in the same direction in advance! l! After being directly magnetized, a laser beam is irradiated to a specific region of the perpendicularly magnetized region to heat it to the Curie temperature or compensation temperature, and information is recorded by reversing the direction of magnetization in the heated region. .

In addition, when reading information recorded on a magneto-optical recording medium as described above, the original i' in which the plane of polarization rotates due to the magnetic Kerr effect is applied, and the medium is irradiated with a laser beam. Receives reflected light from.

Information is read by detecting how much the plane of polarization of reflected light is rotated. Conventionally, information reading devices that read information recorded on magneto-optical recording media in this way have, for example, The information reading device is configured as shown in the figure, and will be explained next.

In FIG. 3, (1) is a semiconductor laser, and (2) is a polarizer that converts the laser light from laser (1) into linearly polarized light.

(3) is the first half mirror that transmits the linearly polarized light from the polarizer (21); (4) is the convex lens that condenses the linearly polarized light that has passed through the first half mirror (3); (5) is the magneto-optical recording medium. It is a magnetic material made of rare earth-transition metal-based amorphous alloys such as manganese-bismuth, i-dovnic A-iron, f-ruhinium-iron, and gadolinium-muterubikmu-iron, which have high coercive force and perpendicular magnetic anisotropy. As shown by the arrows in Figure 1, desired information is recorded above and below the magnetization direction of the magnetic thin film, and the linearly polarized light irradiated through the lens (4) reflected by the medium (5).

The reflected light flux passes through the lens (4) @1 half mirror (3)
reaches and is reflected.

(6) is an I11 half mirror (3) that transmits and refracts the reflected light beam from the medium (5) and branches it into two directions.@2 Half mirror 1 (7a), (71)) is a polarizer ( @1,32 analyzers set at the same angle on opposite sides with respect to the polarization plane of linearly polarized light, (8
1L) and (811) are bilateral photons (7a) and C7, respectively.
@1 and the second photodetector (9), which is the detection unit that detects the light incident through the 'b) and outputs an electric signal, are differential amplifiers that are differential regeneration circuits. Terminals (c), C+) are both party detectors (8 &), (
8)) to differentially amplify those detection signals.

Figure 'WI4 shows the rotation of the plane of polarization when linearly polarized light is reflected by the medium (5). When linearly polarized light having a polarization plane in the direction of the solid arrow in the figure is irradiated, due to the magnetic Kerr effect, when the linearly polarized light is reflected by the medium (5), the polarization plane changes according to the direction of magnetization. The polarization plane of linearly polarized light is rotated in the direction of the dashed arrow and the dashed-dotted arrow in the figure, respectively.

For example, set the polarization plane of the s1 analyzer (7a) to be perpendicular to the dashed arrow as shown by the two-dot chain line in the figure, and set the polarization plane to the left as shown by the one-dot chain line in the figure. The rotating light is set to pass through the first analyzer (71L), and in the same way, the second analyzer (7b) transmits the light whose polarization plane rotates clockwise as shown by the broken line in the figure. By setting it to transmit, when the reflected light beam of the medium (5) has a plane of polarization as shown by the dashed line in the figure,
The reflected light flux passes only through the first analyzer (7a) without passing through the second analyzer (711I) and reaches the @1 photodetector (1), where it is detected by both detectors (8&) and (811). ), for example, logic 1" and -0° signals are respectively routed to a differential amplifier (
9) is input to both input terminals (→, (+)).

Conversely, when the reflected light beam from the medium (5) has a plane of polarization as shown by the broken line in the figure, the reflected light beam does not pass through the first analyzer (7a) and passes through the $2 analyzer (7'b). ) and reaches the $2 photodetector (8b). Contrary to the case of pressure circumference, the logic signals of 0° and 1m are sent to the differential amplifier (9) from the second photodetector (8B, ) (811).
Input to both input terminals ←) and (+).

Next, the differential amplifier (9) detects both photodetectors (8&),
(81)) are calculated, and the signals from the medium (5) are
Information recorded in the form of vertical fluctuations of magnetization is reproduced as a digital signal of logic 1", 0° and output, and the information is read based on the reproduced digital signal.

By the way, the information reading device shown in Fig. 3 uses a magnetic Kerr effect.
It is a device that reads information recorded on a magneto-optical recording medium (5) that is reproduced by applying the optical technology, and is used to read information recorded on a magneto-optical recording medium (5) that is reproduced by applying the optical technology. Optical recording medium t-@
Even if an attempt is made to reproduce the data using the apparatus shown in FIG. Since no signal is output from the differential amplifier (9), reproduction is impossible, and it is necessary to prepare an information reading device according to the type of recording medium to be reproduced.

Therefore, in Utility Application No. 58-179!171, the applicant previously recorded a signal indicating that the recording medium is a magneto-optical medium in the innermost circumferential glue-in signal area of the magneto-optical recording medium. , and selects a reproducing circuit for the magneto-optical recording medium by determining the signal.

If this signal is not detected, the photodetector (8a
), CB'D), a technique for selecting a regeneration circuit having an adder circuit for adding signals from CB'D) and CB'D) is proposed. However, this method requires that a signal for discrimination be recorded on the magneto-optical recording medium in advance.

On the other hand, Japanese Patent Publication No. 58-51351 discloses a technique for distinguishing between an audio disc and a video disc on which a synchronization signal and an encoded audio signal are recorded based on the synchronization signal. However, in a device that can share a rewritable and recordable magneto-optical recording medium with a playback-only video disk, methods using synchronization signals etc. are not effective because there may be cases where no data is recorded on the magneto-optical recording medium.

(c) Problems to be Solved by the Invention As mentioned above, the conventional technology has the drawback that it is difficult to determine whether a discrimination signal needs to be recorded in advance or whether discrimination can be made effectively.

The present invention has been made in consideration of the above points, and it is an object of the present invention to provide a novel information reading device that automatically discriminates between a magneto-optical recording medium and a recording medium that is optically reproduced. .

B) Means for Solving the Problems The present invention utilizes the difference in reflectance between a magneto-optical medium and an optically reproduced recording medium. That is, light of a constant intensity is irradiated and the type of recording medium is determined according to the level of one reflected light.

(E) Operation There is a difference in reflectance between a magneto-optical recording medium and a recording medium that is optically reproduced, and if the intensity of incident light is constant, a difference occurs in the detection level of reflected light. One type of medium is determined based on this level difference.

(f) Examples Examples will now be described with reference to the drawings. FIG. 1 is a block diagram of an embodiment. (8&), (81)) are first and second photodetectors, and (9) is a differential amplifier (differential regeneration circuit), which are the same as those in FIG. C1 (It is an adder (non-differential reproducing circuit) used for an optically reproduced recording medium 1 such as an optical video disc or a compact disc.

αυ is the first. This is a connection section (selection means) that selectively supplies the output of the second photodetector (81L) (81) to the differential amplifier (9) or the adder (L/K) 11. (121 is the connection part aD
The command section (121 is supplied with a signal from the sensor r13 (the sensor and the command section constitute a determining means). The sensor αJ includes a light emitting section and a light receiving section. and supplies the command unit with an output at a level corresponding to the reflected light from the disk (recording medium) (5).
The sensor (13) is fixed at a position where it does not interfere with the movement of the pickup that reproduces signals from the disk (5) and at a position where it can irradiate light onto the surface of the recording medium.

The command unit 17J outputs a signal from the sensor (H depending on the level of the output 13).
A 1L level control signal is output to the connection part α1.

The reflectance of optically reproduced recording media such as optical video discs and compact discs is 70% or more according to standards.
It is specified as 90%. on the other hand.

The reflectance of materials used in magneto-optical recording media is low, for example, terbium-iron has a reflectance of 45% (IEEJ Study Group Materials,
"Photothermal magnetic recording and reproducing properties of amorphous TbFe film",
Tanaka et al., MAG-8!1-45), and there is a noticeable difference from compact discs and the like.

Therefore, the level of the signal from the sensor blade differs depending on the type of recording medium. A command unit having a voltage comparator determines that the voltage is a recording medium such as a compact disk when the voltage is higher than a predetermined threshold, and determines that it is a magneto-optical recording medium when the voltage is smaller than a predetermined threshold. When it is determined that the recording medium is a compact disc or the like, for example, the command unit α2 applies a shim level signal to the connection unit αD, and the first. Second photodetector (8&)
(8b) The output is supplied to the adder (1G. Conversely, when the magneto-optical recording medium is determined and the R level signal is applied to the connection συ, the differential amplifier (9) is supplied to the photodetector (8B). −)(
91)) is provided.

FIG. 2 shows a second embodiment. r13 is the sensor, 0 is 181. The command unit consisting of the second voltage comparator QD and the microcomputer, (8 &) (8b) is the 1-1
2nd photodetector, (23r24 is a preamplifier, (c) is an amplifier, (to) is a differential amplifier, Qη is a changeover switch.

■ is a playback output terminal.

sensor (13 is a light emitting diode (LIn) which is a light emitting part
D), a photodiode (Dt) which is a light receiving section, and an amplifier @. The outputs of the amplifiers are the first and second amplifiers, each having a different threshold value. It is applied to the second voltage comparison circuit TJJc+n.

Each voltage comparator @c! n obtains an H level output when the input voltage is lower than the respective threshold value. The first voltage comparator screen indicates the type of disk (5); when the output is at H level, it indicates a magneto-optical disk, and when it is at L level, it indicates an optical video disk, etc.

The second voltage comparator r21) determines whether the disk (5) is mounted or not, and when it is at H level.

This indicates that a disc is not loaded, and when it is at L level, it indicates that a disc is loaded.

That is, it is determined that no disk is loaded when the incident light to the 7-otodiode (Dl) is weak.

The output of each photodetector (8&)'(81)) is the preamplifier c! 3c! 4'f, the output of the preamplifier (product) is input to differential amplifier 4 with its level adjusted by a variable resistor (V'RI).The output of the preamplifier (to) is input to the amplifier (c). The selector switch Qη selects one of the amplifier (c) output and the differential amplification and amplifier (c) output and supplies it to the playback output terminal example. Controlled by the output wheel.

Next, the operation will be explained. When the second voltage comparator (21) determines whether a disk is attached, the apparatus can operate for the first time, and power is supplied to the laser, reproduction circuit, etc. by performing a reproduction operation, for example.

At this time, if the output of the '@1 voltage comparator (to) is at H level (discrimination of magneto-optical disk), the output of the microcomputer (to) causes the selector switch (27) to output the output of the differential amplifier (c). Select. If it is L level, the amplifier (
c) is selected, and compact discs etc. can be played. In the second embodiment, the type of disc and the presence/absence of the disc are determined by a common sensor a3.
The circuit configuration is simplified.

(g) Effects of the Invention As described above, according to the present invention, one type is automatically discriminated using the difference in reflectance of the recording medium, so there is no need to record a discrimination signal on the recording medium in advance. Therefore, it is effective for use in devices for recording and reproducing recording media such as magneto-optical recording media, optical video discs, and compact discs.

[Brief explanation of the drawing]

? Figure J1 is a block diagram of the embodiment, Figure 2 is a circuit block diagram of the second embodiment, Figure 3 is a block diagram of an information reading device for a magneto-optical recording medium, and Figure 4 is the ninth diagram explaining the operation. be. (8 &) (811)...Photodetector, (9)(a)...
・Differential regeneration circuit, (1(1@...non-differential regeneration circuit,
α2a3...Discrimination means. (11) (2η... selection means.

Claims (1)

[Claims] (1) In an information reading device that reproduces information by irradiating a recording medium on which information is recorded with a laser beam and detecting a reflected beam from the recording medium, the information reading device includes first and second photodetectors; a differential regeneration circuit receiving the outputs of the first and second photodetectors; a non-differential regeneration circuit receiving the output of at least one of the first and second photodetectors; a discriminating means for discriminating the type of recording medium based on the difference in reflectance of the recording medium, the discriminating means having a section and a light receiving section; An information reading device comprising: selection means for substantially selecting.