JPH0772949B2 - Reproducing apparatus for magneto-optical recording medium - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a magneto-optical disk reproducing apparatus capable of reproducing by increasing a signal-to-noise ratio.

[Technical background of the invention and its problems]

In recent years, instead of a recording or reproducing device that records and reproduces using a magnetic head, an optical recording that enables high-density recording using a light beam or high-speed reproduction of information recorded at high density Or, playback devices have been developed.

As a device capable of optically erasing both recording and reproducing, there is a device utilizing a magneto-optical effect.

In this magneto-optical device, recording can be performed without any problem, but when reproducing, depending on the direction of magnetization of the portion of the magneto-optical disk exposed to the laser beam,
The fact that the vibrating surface of the reflected light rotates in the opposite direction and returns is used, but since the rotation angle of the reflected light at this time is generally about 1 °, unevenness of the magnetic film of the disk and The signal-to-noise ratio (hereinafter C / C
N) is extremely low, and it is difficult to reproduce recorded information without error.

Therefore, IEICE Technical Report Vol.83, No.197,19
The conventional apparatus shown in 83 has improved the C / N at the time of reproduction by the optical system shown in FIG. 5 and the (electrical) signal processing circuit shown in FIG.

The above optical system is configured as follows.

A magneto-optical pickup 3 is provided so as to face one surface of a magneto-optical disk 2 fixed to a rotation shaft of a spindle motor 1. The pickup 3 is fixed to a carriage 4, which can be moved in the radial direction of the disk 2 by a voice coil motor or the like.

A laser diode 5 is housed in the pickup 3 as a monochromatic light source. The light from the laser diode 5 is collimated by a collimator lens 6 and then shaped into a shaping prism 7.
The cross section of the light beam is changed into a circularly polarized light beam and a polarized wave, and the light beam that has passed through the beam splitter 8 is focused and irradiated in a spot shape on the disk 2 surface through the objective lens 9. A field coil 10 is provided so as to face the surface of the disk 2 opposite to the pickup 3, and a magnetic field in a predetermined direction is formed in the case of erasing and recording.

The light beam applied to the disk 2 depends on whether the irradiated part is magnetized to the S pole or the N pole.
Due to the magnetic Kerr effect, the oscillating planes of the reflected waves rotate in opposite directions by a small angle θ, and the reflected waves pass through the objective lens 9 and are partially reflected by the beam splitter 8 and are incident on the half-wave plate 11. It Since the vibrating surface is set by the half-wave plate 11 so as to face an intermediate direction between the S axis and the P axis of the polarization beam splitter 12, the polarization beam splitter 12 depends on whether it is reflected by the S pole or the N pole. The intensity of light incident on the side is shown by A ₊ or A ₋ as shown in FIG.
Therefore, the polarizing beam splitter 12 that functions as an analyzer
As a result, the P-axis component and the S-axis component are received by the pin photodiodes 13a and 13b, respectively. By the way, since the disk 2 is rotationally driven by the spindle motor 1, the direction of magnetization is reflected in accordance with the recorded information, so that the pin photodiode 13a has a difference between the P-axis components of A ₊ and A ₋ (indicated by the symbol Ap). A varying modulated light is incident,
The pin photodiode 13a outputs a photoelectric conversion signal a corresponding to the intensity difference Ap as shown in FIG. On the other hand, from the other pin photodiode 13b A _-,
Modulated light corresponding to the difference between the S-axis components of A ₊ (denoted by the symbol As) is input, and the photoelectric conversion signal corresponding to the intensity difference As is input from the pin photodiode 13b as shown in FIG. 8 (b). b is output.

By the way, these signals a and b are shown in FIGS. 8 (a) and 8 (b).
As shown in Fig. 6, noise mainly composed of in-phase components is mixed in. Therefore, signal processing is performed by the signal processing circuit shown in Fig. 6.
A good signal output of C / N was obtained.

That is, the signals a and b output from the pickup 3 are input to the adder 15 and the subtracter 16, respectively, and as shown in FIGS. 8C and 8D, almost no components corresponding to Ap and As are present. 0
The signal c and the components corresponding to Ap and As become a doubled signal d and are input to the adder 17. In this case, since the medium noise component is mainly in-phase, as shown in FIGS. 8 (c) and 8 (d), the in-phase component appears approximately twice in the signal c, and the noise component is almost eliminated in the signal d. Mostly erased (noise is sufficiently small-the above research report).

By the way, when recording information on the disc 2, it is necessary that the track number and the sector number of the track to be recorded are recorded on the disc 2 in advance.

Generally, from the viewpoint of mass productivity of the disc 2, the disc 2
In many cases, uneven information pits are formed on the surface (formed by pressing with a female die on the stamper) (hereinafter referred to as prepits).

When the optical system having the above-mentioned configuration is used, the information based on the pre-pits is the information only on the intensity modulation, and therefore becomes the vector as indicated by the symbol I in FIG. Therefore, in this case, the light intensities input to the photodiodes 13a and 13b are the same as those shown in FIG.
The signals output from the photodiodes 13a and 13b are represented by the symbols Ip and Is (indicated by the same symbols) in FIGS. 8A and 8B.

As can be seen from the waveforms shown in FIGS. 8 (a) and 8 (b) above, a large amount of in-phase components are included, so the output of the adder 15 is small (contrary to the case of magneto-optically modulated light depending on the magnetization direction). 8 (c)), the output of the subtractor 16 is large (FIG. 8 (d)).
See).

The information read from the disk 2 does not depend on the track information (which becomes the light intensity modulation method), the sector information, and the reproduction information of the recording (data) which becomes the magneto-optical modulation method. Since it is necessary to send the signal to the signal c, d in the adder 17 as shown in FIG.
Is added to obtain a signal e having substantially the same amplitude as shown in FIG. 8 (e), and this signal e is applied to one input terminal of the comparator 19 to generate a reference voltage applied to the other input terminal. A binarized output was obtained from the potential of the container 21, and it was sent to the controller 18.

However, since the output signal c of the adder 15 contains a lot of noise, it causes deterioration of C / N earned by the differential optical system.

Further, if the outputs of the adder 15 and the subtracter 16 are binarized and then added, the above problem can be solved, but signal processing such as low-pass filter, waveform equalization, AGC, etc. not shown in FIG. 6 is solved. Two systems are required, which causes a problem in terms of cost. In addition, due to imbalance of the optical system and the like, erroneous information may occur due to noise mixed in prepits when binarizing magneto-optical information, or vice versa. In some cases, there are drawbacks.

[Object of the Invention]

The present invention has been made in view of the above-mentioned points, and it is determined whether the read-out area is the pre-pit portion is the magneto-optical recording portion, and based on this determination, the selector is switched so that the magneto-optical information can be reproduced. It is an object of the present invention to provide a reproducing apparatus for the above magneto-optical recording medium.

[Outline of Invention]

The present invention receives the P-polarized component and the S-polarized component of the reflected light from the magneto-optical recording medium, respectively, and adds the P-polarized component output and the S-polarized component output to obtain the recording signal of the prepit portion. , P polarization component output and S polarization component output are subtracted to obtain the recording signal of the magneto-optical recording portion, while the reproduction start timing and the reproduction end timing of the pre-pit portion are detected. Since the recording signal of the pre-pit portion is connected to the signal processing circuit and the recording signal of the magneto-optical recording portion is connected to the signal processing circuit when the reproduction end timing is detected, the reproduction signal from the magneto-optical recording medium is formed. We have realized the playback device at low cost while preventing the deterioration of C / N.

Example of Invention

 Hereinafter, the present invention will be specifically described with reference to the drawings.

1 to 3 relate to a first embodiment of the present invention.
The figure shows the configuration of the signal processing circuit in the first embodiment,
FIG. 2 shows signal waveforms for explaining the operation of FIG. 1, and FIG. 3 shows the structure of the data selector.

Since the optical system of the reproducing apparatus in the first embodiment is the same as that in FIG. 5, the explanation of the optical system will be omitted.

Further, the signal processing circuit 31 constituting the first embodiment is constructed as shown in FIG.

That is, as shown in FIGS. 2A and 2B, the output signals a and b of the pickup 3 include signals Ap and As whose phases are opposite to each other according to the direction of magnetization of the recorded information, and track numbers,
Includes intensity modulated information signals Ip, Is reflected from the prepit portion representing the sector number.

The output signals a and b are adjusted so that the amplitudes of the signals Ap and As are adjusted so that the optical system shown in FIG. Is set to the minimum. In this state, the intensity modulated light signal I due to the pre-pit
p and Is do not have the same size (Ip> Is in the figure).

The output signals a and b of the pickup 3 are input to the adder 15 and the subtractor 16, and the adder 15 and the subtractor 16 output the signals c and d shown in (c) and (d) of FIG. . The intensity modulation signal is separated and extracted by passing through the adder 15. By passing through the subtractor 16, a signal whose main component is a substantially magneto-optical modulation signal is separated and extracted. This signal d
As described above, since Ip> Is, the pre-pit information is included. However, this amplitude is the modulation component due to magneto-optical
It is smaller than | Ap-As |. The signal d has a good C / N with almost no noise.

The output of the adder 15 is input to the peak hold circuit 32, and the peak hold (integration) signal f ₁ as shown by the solid line in FIG. 2 (f) is output. This signal f ₁ is applied to one input end of the comparator 33, and the other input end of the comparator 33 is supplied with a constant voltage from the reference voltage generator 34 (indicated by a chain line f ₂ in FIG. 2 (f)). (Shown) is being applied. Since this constant voltage is set to be sufficiently higher than the noise level in the signal c output from the adder 15 and considerably smaller than the amplitude of the intensity modulated light, the adder 15 outputs the intensity modulated light. Then, the peak hold signal f ₁ immediately exceeds the reference voltage level, and the comparator 33 causes the second voltage
As shown in FIG. 6G, a prepit detection signal g which changes from low level to high level is output. (Note that when the pickup 3 passes through the prepit portion, the peak hold signal f ₁ shifts from the high level to the low level.) The output signal of the comparator 33, that is, the prepit detection signal g
Is applied to the switching control terminal of the data selector 36, and the signal c input to the data selector 36 from the adder 15 and the subtracter 16
The signal d input from is switched and selected.

That is, when the pre-pit detection signal g is not output (or when the signal g is at a low level), the signal d output from the subtracter 16 is switched to the signal d of the next stage.
19 while the signal g is output (or the signal g
Is high level), it is switched to the side of the signal c output from the adder 15, and the signal c is controlled so as to be guided to the comparator 19 in the next stage.

Therefore, the data selector 36 has, for example, a circuit configuration shown in FIG.

That is, the output signal c of the adder 15 is the first analog switch.
The output signal d of the subtractor 16 is input to the adder 42 via 41, and is input to the adder 42 via the second analog switch 43.

The output signal g of the comparator 33 is the second analog switch.
It is applied to the switching control end of the first analog switch 41 through the inverter 44 while being applied to the switching control end of 43. When the output signal g is low level, the first analog switch 41 is turned on and the second analog switch 43 is turned off. On the other hand, when the output signal g becomes high level, the output signal g is switched to the opposite state. .

Therefore, as shown in FIG. 2 (g), the first analog switch 41 is turned on and the output signal d of the subtractor 16 is input to the adder 42 while the output signal g is at the low level, The adder 42 outputs the output signal d of the subtractor 16 as shown in FIG. Then, as shown in FIG. 2 (g), the second analog switch 43 is turned on during the period when the output signal g is at the high level, and the adder is turned on.
The output signal c of 15 is input to the adder 42, and the output signal c of the adder 15 is output from the adder 42 as shown in FIG.

The output signal h of the data selector 36 is binarized by being applied to the other input end of the comparator 19 to which the voltage of the reference voltage generator 21 is applied to one input end, as in the conventional example. The output of the binarized signal is sent to the controller 18.

According to the first embodiment described above, a circuit for separating and extracting the output signal of the differential optical system through the subtracter 16 to extract the magneto-optical modulation signal with a small number of nozzles, and the adder 15 for the prepit portion having a large signal component with respect to noise. And a circuit for separating / extracting the signal of (1) and a detecting means for the prepit portion, and selecting the magneto-optical modulation signal and the intensity modulation signal respectively output from the circuit for separating / extracting based on the output signal of this detecting means. Then, a signal processing circuit 31 is formed so as to switch so as to take in. Therefore, it is possible to perform favorable reproduction of C / N with less noise on the magneto-optical modulation information. Further, since the information in the pre-pit portion and the magneto-optical information are output via the adder 42 without being influenced by each other, information reproduction with few errors can be performed. It can be realized at low cost without requiring a plurality of signal processing circuits for handling the magneto-optical and intensity-modulated signals respectively.

FIG. 4 shows a signal processing circuit according to the second embodiment of the present invention.

The signal processing path 51 in the second embodiment is promptly operated in the period in which the magneto-optical modulation signal is input after the peak hold circuit 32 in the first embodiment becomes high level by the signal of the prepit portion. It is for low level. Therefore, the output side of the subtractor 16 is also provided with a second peak hold circuit 52, etc., and the peak hold circuit 52 etc. is provided with a detecting means for the magneto-optical modulation signal. Reset means 53 for clearing the circuit 32 is provided.

That is, the output signal d of the subtractor 16 is input to the peak hold circuit 52 which forms the reset means 53, and this output is the comparator.
54 is applied to one input terminal of 54, and a reference voltage generator is applied to the other input terminal of this comparator 54 (both are indicated by battery symbols).
The reference voltage E of 55 is applied, and the output of the comparator 54 is input to the one-shot multivibrator 56. (Note that the value of the voltage E is set higher than the level of the pre-pit signal in FIG. 2 (d).) In the above wasshot multivibrator 56, the output of the comparator 54 changes from low level to high level. At this time, a pulse having an appropriate width is output, the peak hold circuit 32 on the adder 15 side is cleared by this pulse, and its output is set to a low level.

The other structure is the same as that of the first embodiment.

According to the second embodiment, when the magneto-optical modulation signal changes to the pre-pit signal or vice versa, the switching can be performed quickly without delay.

In the signal processing circuit 31 shown in FIG. 1, for example, the output signal c of the adder 15 is not input to the data selector 36, but the output signal d of the subtractor 16 is input to the data selector 36 via an amplifier. You can also do it. In this case, the amplification factor (gain) of the above-mentioned amplifier is such that the voltage level at the high level of the pre-pit signal shown in FIG. 2 (d) is substantially the same as that of the magneto-optical modulation signal when passing through this amplifier. Just do it.

Incidentally, as shown in FIG. 4, it is also possible to provide a detecting means for the magneto-optical modulation signal and switch the data selector 36 shown in FIG. 1 based on the output signal of this detecting means.

The present invention also includes a combination of some of the above-described embodiments and the like.

〔The invention's effect〕

As described above, the P-polarized component and the S-polarized component of the reflected light from the magneto-optical recording medium are received, and the P-polarized component output and the S-polarized component output are added to obtain the recording signal of the prepit portion. At the same time, the P-polarized component output and the S-polarized component output are subtracted to obtain the recording signal of the magneto-optical recording portion, while the reproduction start timing and the reproduction end timing of the prepit portion are detected, and when the reproduction start timing is detected, Since the recording signal of the pre-pit portion is connected to the signal processing circuit and the recording signal of the magneto-optical recording portion is connected to the signal processing circuit when the reproduction end timing is detected, a good C / N reproduction is achieved. It can be performed. or,
A plurality of signal processing circuits for intensity modulation and magneto-optical modulation are not required, and the cost can be reduced.

[Brief description of drawings]

1 to 3 relate to an embodiment of the present invention, FIG. 1 is a block diagram showing the configuration of a signal processing circuit in the embodiment, and FIG. 2 is a timing for explaining the operation of the embodiment. FIG. 3 is a block diagram showing the configuration of a data selector, FIG. 4 is a block diagram showing the configuration of a signal processing circuit according to the second embodiment of the present invention, and FIG. FIG. 6 is a configuration diagram showing an optical system used, FIG. 6 is a block diagram showing a configuration of a signal processing circuit in a conventional example, FIG. 7 is an explanatory diagram showing directions of a vibrating surface of light reflected by a disk, and FIG. FIG. 7 is a timing chart diagram for explaining the operation of the conventional example. 1 …… Spindle motor, 2 …… Disk, 3 …… Pickup, 13a, 13b …… Photodiode, 15,42 …… Adder 16 …… Subtractor, 19,33 …… Comparator, 32 …… Peak hold Circuit, 36 …… Data selector, 41,43 …… Analog switch.

Claims (1)

[Claims] 1. A magneto-optical recording medium for reproducing recorded information from a magneto-optical recording medium having a pre-pit portion recorded by a light intensity modulation method having a different reflectance and a magneto-optical recording portion recorded by a magneto-optical modulation method. In a reproducing apparatus for a recording medium, a light receiving unit that receives a P-polarized component of reflected light from the magneto-optical recording medium, a light receiving unit that receives an S-polarized component of the reflected light, and P output from these light receiving units. A first calculation means for adding a polarization component output and an S polarization component output to obtain a recording signal of the pre-pit portion, and subtracting the P polarization component output and the S polarization component output to obtain the magneto-optical recording portion. When the reproduction start timing is detected by the detection means for detecting the reproduction start timing and the reproduction end timing of the prepit portion Connect the output of the first calculating means to the signal processing circuit,
A reproducing apparatus for a magneto-optical recording medium, comprising: data selector means for connecting the output of the second arithmetic means to the signal processing circuit when the detecting means detects the reproduction end timing.