JPH07249228A - Optical recording medium reproducing device - Google Patents

Abstract

PURPOSE:To obtain an information signal having a low noise by obtaining the information signal while adding a sum signal in which a first detection signal obtained from one of two photodetectors and a second detection signal obtained from the other photodetector are summed and a difference signal in which the first detection signal and the second detection signal are subtracted from each other. CONSTITUTION:A first read-out signal R1 and a second read-out signal R2 are added by a first addition means 21 to become a sum signal SUM. Moreover, the first read-out signal R1 and the second read-out signal R2 are subtracted from each other by a subtraction means 22 to become a difference signal DIFF. In a frequency area where the sum signal SUM is having a higher C/N, the sum signal SUM is utilized and in a frequency area where the difference signal DIFF is having a higher C/N, the difference signal DIFF is utilized by obtaining the sum signal between the sum signal SUM and the difference signal DIFF by using a second addition means 23. Thus, the information signal having the waveform of good continuity and also having a low noise can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium reproducing apparatus for reproducing information recorded on an optical recording medium having phase pits, and more specifically, the wavelength of read light at the time of reproduction and the aperture of an objective lens. The present invention relates to an optical recording medium reproducing device capable of reproducing information having a frequency higher than a spatial frequency determined by the number.

[0002]

2. Description of the Related Art Conventionally, an optical disc and a reproducing apparatus for realizing so-called super-resolution reproduction capable of reproducing information having a frequency higher than a spatial frequency determined by the wavelength of read light and the numerical aperture of an objective lens have been developed. ing. An optical disc that realizes this super-resolution reproduction has two or more mutual optical spots inside a light spot corresponding to the temperature distribution on the optical disc generated by the irradiation of the reading light from the outside on the substrate on which information is held by the phase pits. A polarization state change layer having a characteristic of generating read light having different polarization states is formed. The reproducing apparatus for super-resolution reproducing the information recorded on the optical disc is provided with a reproducing circuit of a differential optical system composed of a subtractor in order to reproduce the read light having different polarization states. ing. The purpose of using the reproducing circuit of the differential optical system is to detect different polarization components of the read light.

[0003]

However, since the signal component of the read signal originally obtained from the phase pit is the in-phase component included in the two read lights, this in-phase component is used in the reproducing circuit of the differential optical system. However, there is a problem that the level of the read signal becomes low as a whole.

FIG. 18 shows an output example of a reproducing circuit in a conventional optical recording medium reproducing apparatus. As shown in FIG.
In a conventional optical recording medium reproducing apparatus using a reproducing circuit of a differential optical system, a sufficient C / N ratio (Carrier to Noise) is exhibited particularly in a region where the recording mark length is long (reproduction frequency is low).
Ratio) cannot be obtained.

Therefore, an object of the present invention is to provide an optical recording medium reproducing apparatus for performing super-resolution reproduction, which can obtain a high C / N ratio in a wide frequency band including a low frequency band. Especially.

[0006]

In order to solve the above problems, the invention described in claim 1 is, as shown in FIG.
Information is held by the phase pits, and two or more regions with different polarization states of reflected light or transmitted light appear in the light spot of the reading light, corresponding to the temperature distribution accompanying the irradiation of the reading light emitted from the outside. At least two photodetectors that separate the reflected light or transmitted light of the reading light from the optical recording medium into two reading lights according to the polarization state, receive the two reading lights, and obtain detection signals respectively. In an optical recording medium reproducing apparatus provided with the first detection signal R ₁ obtained from one photodetector of two photodetectors for detecting two reading lights, and the other photodetection of the two photodetectors. Adder 21 for adding the second detection signal R ₂ obtained from the detector to generate the sum signal SUM, and subtraction for generating the difference signal DIFF between the first detection signal R ₁ and the second detection signal R _2. Means 22
And second adding means 23 for adding the sum signal SUM and the difference signal DIFF to generate the information signal S.

According to a second aspect of the present invention, as shown in FIG. 4, in the optical recording medium reproducing apparatus of the first aspect, the C / N of the sum signal SUM of the signal components of the difference signal DIFF is used.
The filter means 24 is configured to remove a signal component of the difference signal DIFF corresponding to a frequency band lower than the frequency at which the ratio and the C / N ratio of the difference signal DIFF are substantially equal.

According to a third aspect of the present invention, as shown in FIG. 5, in the optical recording medium reproducing apparatus according to the first aspect, the first waveform shaping means 25 for shaping the sum signal SUM and the difference signal DIFF. Second waveform shaping means 26 for shaping the waveform of
It is configured with.

According to a fourth aspect of the present invention, as shown in FIG. 7, the optical recording medium reproducing apparatus according to the first aspect is provided with a third waveform shaping means 27 for shaping the waveform of the information signal S _4. To be done.

According to a fifth aspect of the present invention, as shown in FIG. 6 or 8, in the optical recording medium reproducing apparatus according to the third or fourth aspect, among the signal components of the difference signal DIFF, the sum signal SUM is included. The difference signal D corresponding to a frequency band lower than the frequency at which the C / N ratio and the C / N ratio of the difference signal DIFF are almost equal.
It is configured by including a filter means 24 for removing the signal component of the IFF.

According to a sixth aspect of the present invention, for example, as shown in FIG. 9, in the optical recording medium reproducing apparatus according to the fifth aspect, crosstalk removing means 30 for removing the crosstalk included in the sum signal SUM is provided. It is equipped with.

[0012]

According to the first aspect of the present invention, as shown in FIG. 2, the first adding means 21 is obtained from one photodetector of the two photodetectors for detecting the two readout lights. The first detection signal R ₁ and the second detection signal R ₂ obtained from the other photodetector of the two photodetectors are added to add the sum signal SUM.
To generate.

The subtracting means 22 includes a first detection signal R ₁ and a second detection signal R ₁ .
A difference signal DIFF from the detection signal R ₂ is generated. The second adding means 23 adds the sum signal SUM and the difference signal DIFF to generate the information signal S ₀ .

Therefore, the sum signal SUM is combined with the sum signal SUM in the frequency band having a higher C / N ratio, and the difference signal DIFF is combined with the difference signal DIFF in the frequency band having a higher C / N ratio. An information signal S ₀ having a high C / N ratio is obtained in all frequency bands.

According to the second aspect of the present invention, as shown in FIG. 4, the filter means 24 includes the difference signal DIFF and the C / N ratio of the sum signal SUM among the signal components of the difference signal DIFF.
Since the signal component of the difference signal DIFF corresponding to the frequency lower than the frequency band in which the C / N ratio of
When the sum signal SUM and the difference signal DIFF are added, the information signal S ₁ with less noise is obtained.

According to the third aspect of the invention, as shown in FIG. 5, the first waveform shaping means 25 waveform-shapes the sum signal SUM. The second waveform shaping means 26 determines the difference signal DIFF.
Shape the waveform.

Therefore, when the sum signal SUM and the difference signal DIFF are added, the information signal S having a waveform with good continuity
You get ₂ . According to the invention described in claim 4, as shown in FIG. 7, the third waveform shaping means 27 shapes the waveform of the information signal S ₄ .

Therefore, since the waveform shaping can be performed by one waveform shaping circuit, the information signal S ₅ having a waveform with good continuity can be obtained with a simple circuit configuration having a small number of elements.

According to the fifth aspect of the present invention, as shown in FIG. 6 or 8, the filter means 24 includes the difference signal DIF.
Of the signal components of F, the signal component of the difference signal DIFF corresponding to the frequency band lower than the frequency where the C / N ratio of the sum signal SUM and the C / N ratio of the difference signal DIFF are almost equal is removed, so that the sum signal SUM When the difference signal DIFF and the difference signal DIFF are added, the information signal S ₃ with less noise is obtained.

Therefore, an information signal S3 having a waveform with good continuity and little noise can be obtained. Further, according to the portion of the invention according to claim 5 related to the invention according to claim 4, as shown in FIG. 8, since waveform shaping can be performed by one waveform shaping circuit, the number of elements is reduced. Waveform shaping can be performed with a simple circuit configuration with few

According to the sixth aspect of the present invention, for example, as shown in FIG. 9, the crosstalk removing means 30 removes the crosstalk included in the sum signal SUM. Therefore, a good information signal S without crosstalk can be obtained.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. (I) Device Configuration of the Present Invention First, the overall device configuration of the optical recording medium reproducing device of the present invention will be described with reference to FIG.

An optical disc D, which is a recording medium for recording information reproduced by the optical recording medium reproducing apparatus according to the present invention.
K is an optical disc for super-resolution reproduction, and on the substrate on which information is held by the phase pits, corresponding to the temperature distribution on the optical disc caused by the irradiation of the reading light from the outside, inside the optical spot, A polarization state change layer having a characteristic of generating a read region and a non-read region (mask region) that generate read light having two or more different polarization states is formed.

An optical recording medium reproducing apparatus 10 shown in FIG. 1 has a laser diode 11 for emitting a laser beam as a reading light.
A beam splitter 12 that transmits the laser light incident from the laser diode 11 and reflects the laser light incident from a mirror 13, which will be described later, a mirror 13 for guiding the laser light, and an information recording surface of the optical disk DK. A dichotomy for adjusting the ratio of the amount of reflected light and the amount of transmitted light of a laser beam from the mask region (a reproducing light) reflected by the objective lens 14 that is focused on the upper part and the beam splitter 12 to a polarization beam splitter 16 described later. One-wave plate 15
If, transmits only polarized light having a predetermined polarization state, the polarization beam splitter 16 for reflecting the other light, receiving the polarized light reflected by the polarized beam splitter 16, the outputs as a first read signal R ₁ 1 A photodetector 17a, a second photodetector 17b which receives the light transmitted through the polarization beam splitter 16 and outputs it as a second read signal R ₂ , and a reproducing circuit 18 which converts the read signal into an information signal and outputs it. , Magnet M
It is composed of G ₁ .

Here, the magnet MG ₁ is for aligning the perpendicular magnetization direction of the optical disk DK to a fixed direction, and may be unnecessary depending on the super-resolution reproducing system of the optical disk DK.

The present invention relates to the internal structure of the reproduction circuit 18 described above. (II) Principle of the Present Invention Next, the principle of the present invention will be described with reference to FIGS.

In FIG. 2, the first read signal R ₁ and the second read signal R ₁
The read signal R ₂ is added by the first adding means 21 and becomes the sum signal SUM. This sum signal SUM is shown in FIG.
It has a waveform as shown in (a).

Further, the first read signal R ₁ and the second read signal R ₂ are subtracted by the subtraction means 22, and the difference signal DI
It becomes FF. This difference signal DIFF has a waveform as shown in FIG.

3A and 3B are compared with each other, the sum signal SUM shown in FIG. 3A is determined by the wavelength of the laser light and the numerical aperture of the objective lens 14. Most of the frequency band lower than the spatial frequency fc has a C / N ratio higher than that of the difference signal DIFF, but no output signal is obtained in the frequency band higher than the spatial frequency fc.

On the other hand, the difference signal D shown in FIG.
The IFF has a lower C / N ratio than the sum signal SUM in most of the frequency band lower than the spatial frequency fc, but since it has a signal by super-resolution reproduction, the spatial frequency f
Output can be obtained even in a frequency band higher than c.

Therefore, in the present invention, by obtaining the addition signal of the sum signal SUM and the difference signal DIFF using the second adding means 23, in the frequency region where the sum signal SUM has a higher C / N ratio, The sum signal SUM is used, and the difference signal DIFF is used in the frequency region where the difference signal DIFF has a higher C / N ratio.

As a result, as shown in FIG. 3 (c), an information signal S ₀ having a high C / N ratio can be obtained in a wide frequency band including a high frequency equal to or higher than the spatial frequency fc. The above is the principle of the present invention. (III) First Embodiment Next, a first embodiment of the present invention will be described with reference to FIGS. 9 to 14.

As shown in FIG. 9, the reproducing circuit of the present embodiment has an adder 21 as a first adding means, a crosstalk canceller 30 as a crosstalk canceling means, a delay circuit 29, and a first waveform shaping. Equalizer 25 as a means
And a subtractor 22 as a subtraction means and an A / D converter 28
And an HPF (High Pass Filter) 24 as a filter means
And an equalizer 26, which is a second waveform shaping means, and an adder 23, which is a second adding means.

The crosstalk canceller 30 comprises an A / D converter 31, 1-track memories 32 to 34, and a canceller 35. Next, the operation and the signal waveform of each part will be described.

The adder 21 adds the first read signal R ₁ and the second read signal R ₂ and outputs a sum signal SUM. The subtractor 22 outputs a difference signal DIFF from the first read signal R ₁ and the second read signal R ₂ .

The crosstalk canceller 30 outputs the sum signal S
Remove crosstalk contained in UM. As the crosstalk canceller 30, a known technology can be used.

Here, the sum signal SUM and the difference signal DIFF
An example of the waveform of the signal of is shown in FIG. In FIG. 10, the frequency fa is a graph showing the sum signal SUM and the difference signal DIFF.
Is the frequency corresponding to the intersection of the graphs
c is the spatial frequency. Note that FIG. 10 shows the results when the wavelength of the laser light is 680 nm, the numerical aperture of the objective lens 14 is 0.55, and the linear velocity of the optical disk DK is 5 m / s.

As can be seen from FIG. 10, the sum signal SUM has a higher C / N ratio in the frequency band lower than the frequency fa, and the spatial frequency f in the frequency band higher than the frequency fa.
Including the frequency band higher than c, the difference signal DIFF has a higher C / N ratio.

The sum signal SUM whose crosstalk has been canceled by the crosstalk canceller 30 is input to the delay circuit 29. The delay circuit 29 includes an adder 23
It is for synchronizing the sum signal and the difference signal at the time of combining. Therefore, in the present embodiment, it is inserted on the path of the sum signal, but it may be inserted on the path of the difference signal when the difference signal precedes the sum signal.

Sum signal SUM passed through delay circuit 29
₁ is input to the equalizer 25. Equalizer 25
Waveform-shapes the sum signal SUM ₁ so that the combined waveform in the adder 23 is a continuous waveform. As the equalizer 25, an equalizer having the characteristics shown in FIG. 12B may be used.

The sum signal SUM ₂ passed through the equalizer 25.
Changes from the waveform shown in FIG. 13 (a) to the waveform shown in FIG. 13 (e). In FIG. 13E, the solid line shows the sum signal SUM ₂ and the broken line shows the sum signal SUM ₁ .

Furthermore, the positions of the equalizer 25 and the delay circuit 29 may be interchanged. A / D converter 28
Performs A / D conversion of the difference signal DIFF and outputs the digitized difference signal DIFF.

The HPF 24 has a frequency f of the difference signal DIFF.
This is a digital filter for removing a portion corresponding to a frequency band lower than a, and its characteristic example is shown in FIG. Using the HPF 24 to remove the portion corresponding to the frequency band lower than the frequency fa is to remove the sum signal SU without removing it.
This is because, if M and the difference signal DIFF are simply added, they may become noises, resulting in a noisy information signal.

After passing through the HPF 24, the difference signal DI
When the FF is A / D converted, the HPF 24 uses an analog filter, and its characteristics are, for example, the frequency fa.
The following may use a filter having a characteristic of −12 db / oct.

Difference signal DIFF passed through HPF 24
₁ changes from the waveform shown in FIG. 13 (b) to the waveform shown in FIG. 13 (c). Incidentally, in FIG. 13C, the solid line shows the difference signal DIFF ₁ , and the broken line shows the difference signal DIFF.

The equalizer 26 uses the difference signal D in order to make the combined waveform in the adder 23 a continuous waveform.
Shape the waveform of IFF ₁ . As the equalizer 26, an equalizer having the characteristics shown in FIG.

Difference signal DIFF passed through the equalizer 26
₂ changes from the waveform shown in FIG. 13 (c) to the waveform shown in FIG. 13 (d). In FIG. 13D, the solid line shows the difference signal DIFF ₂ , and the broken line shows the difference signal DIFF _1.
Is shown.

The sum signal SUM ₂ and the difference signal DIFF ₂ whose waveforms have been shaped by the equalizers 25 and 26 are added by the adder 2
3 is added to produce an information signal S, which is output from the reproducing circuit. The change in the waveform at this time is obtained by synthesizing the difference signal DIFF ₂ having the waveform shown in FIG. 13D and the sum signal SUM ₂ having the waveform shown in FIG. 13E.
The information signal S has the waveform shown in FIG.

In FIG. 13 (f), the solid line shows the information signal S, and the broken line shows the difference signal DIFF ₂ and the sum signal SUM _2.
Is shown. Next, in order to facilitate understanding of changes in signals of respective parts in the reproducing circuit of the present embodiment, FIG.
Shows the waveform of the signal of each part in the relationship between intensity and time.

Now, in the super-resolution optical disk DK, as shown in FIG.
Assume that two simple sinusoidal superposition signals are recorded, as shown in (a). Further, among the superimposed sine waves, the frequency of the high frequency sine wave is higher than the spatial frequency fc and is a frequency that can be reproduced only in super-resolution reproduction.

The read light including the original signal shown in FIG. 14A is dispersed by the polarization beam splitter 16 and detected by the photodetectors 17a and 17b, whereby the first read signal R ₁ and the second read signal are obtained. It becomes the signal R ₂ . And
The first read signal R ₁ and the second read signal R ₂ are added by the adder 21.
Are added to form a sum signal SUM. This sum signal SUM
Has the waveform shown in FIG. As can be seen from FIG. 14B, the sum signal SUM includes a signal having a frequency lower than the spatial frequency fc among the signals recorded on the optical disc DK.

Thereafter, the sum signal SUM is delayed by the delay circuit 29 in order to synchronize with the difference signal DIFF, and becomes the sum signal SUM ₁ shown in FIG. 14 (d). On the other hand, the first read signal R ₁ and the second read signal R ₂ are subtracted by the subtractor 22 and a difference signal DIF having a reproduced signal by super-resolution reproduction is obtained.
It becomes F. Here, as shown in FIG. 14C, the difference signal DIFF includes all the spectra included in the original signal, but the in-phase component is subtracted from the signal having a frequency lower than the frequency fa. Therefore, only a low intensity signal can be obtained. In the conventional super-resolution reproduction, this signal is used to obtain an information signal.

The difference signal DIFF shown in FIG. 14C is H
The PF 24 removes low-frequency components, and FIG.
The difference signal DIFF ₁ shown in FIG. And the sum signal SUM
₁ and the difference signal DIFF ₁ are waveform-shaped by the equalizers 25 and 26, and then added by the adder 23 to become the information signal S shown in FIG. As can be seen from FIG. 14 (f), the information signal 8 becomes a signal closer to the original signal shown in FIG. 14 (a). (IV) Second Embodiment FIG. 15 shows a second embodiment of the present invention.

In this embodiment, a cross beam canceller of the 3-beam type is used, and the adder 23 is used.
In (1), the waveform is shaped after adding the sum signal and the difference signal. When the 3-beam type crosstalk canceller is used, in addition to the photodetector shown in FIG. 1, two photodetectors for two sub-beams (leading sub-beam and trailing sub-beam) are required. .

In this embodiment, the same parts as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted. As shown in FIG. 15, in the present embodiment, a crosstalk canceller 40 is provided instead of the crosstalk canceller 30 of the first embodiment. The crosstalk canceller 40 outputs the detection signal R ′ by the preceding sub-beam to A
A / D converter 41 that performs A / D conversion, delay circuit 43 that delays sum signal SUM that is A / D converted in order to synchronize with other detection signals, and detection signal R ″ by the trailing sub-beam A / D converter 42 for A / D conversion, delay circuit 44 for delaying A / D converted detection signal R ″ in order to synchronize with other detection signals, detection signal R ′ and detection signal R ″ Is used to cancel the crosstalk included in the sum signal SUM.

Further, an equalizer 27, which is a third waveform shaping means for shaping the sum signal and the difference signal added by the adder 23 and outputting the information signal S, is provided. Next, the operation and the signal waveform of each part will be described.

The first read signal R ₁ and the second read signal R ₂ are added by the adder 21, and the crosstalk canceller 40 is added.
Since the crosstalk is removed by the delay circuit 29 and the signal is delayed by the delay circuit 29 and the sum signal SUM ₁ is obtained, it is the same as that of the first embodiment, and therefore detailed description thereof will be omitted.

Further, the first read signal R ₁ and the second read signal R
₂ is subtracted by the subtractor 22, and the HPF 24 removes the component corresponding to the frequency lower than the frequency fa,
The process of obtaining the difference signal DIFF ₁ is also the same as that of the first embodiment, and detailed description thereof will be omitted.

The sum signal SUM ₁ and the difference signal DIFF ₁ are added by the adder 23 to form a signal S '. The change in the waveform at this time is the sum signal SU having the waveform shown in FIG.
M ₁ and the difference signal DIF having the waveform shown in FIG.
F ₁ is combined into a signal S ′ having the waveform shown in FIG. In FIG. 17D, the solid line shows the signal S ′, and the broken lines show the sum signal SUM ₁ and the difference signal DIFF.
₁ is shown.

Next, the signal S'is waveform-shaped by the equalizer 27 and becomes an information signal S having good continuity. As the equalizer 27, an equalizer having the characteristics shown in FIG. 16 may be used. The change in the waveform at this time is
The waveform shown in FIG. 17 (d) changes to the waveform shown in FIG. 17 (e). In FIG. 17E, the solid line shows the signal S and the broken line shows the signal S ′.

According to the above-described first embodiment and second embodiment.
For example, the sum signal S in the frequency band lower than the frequency fa
Difference between UM and frequency band higher than frequency fa
Since the information signal S is obtained by combining with the signal DIFF,
High C / N ratio in wide frequency band including wave number fc
And an information signal S with good continuity and low noise can be obtained.
To be (V)Other embodiments of the invention In the above description, detailed examples have been described.
However, the present invention is shown below in addition to those shown in the above examples.
Various modes are possible. (I)First embodiment In the first embodiment, as shown in FIG. 4, the first read signal R₁
And the second read signal R₂Is the first addition means for adding
Device 21 and first read signal R₁And the second read signal R ₂Subtract
The subtractor 22 which is a subtraction means for
Of the obtained signals, the signal obtained by the adder 21
C / N ratio of and the C / N of the signal obtained by the subtractor 22.
It corresponds to the frequency band lower than the frequency where the ratio is almost equal.
HPF24 which is a filter means for removing the signal component
And the signal obtained by the adder 21 and the HPF 24
Addition, which is the second addition means for adding the signals thus obtained
The device 23 is provided. (Ii)Second embodiment In the second embodiment, as shown in FIG. 5, the first read signal R₁
And the second read signal R₂Is the first addition means for adding
Wave for shaping the output signal of the adder 21 and the adder 21
An equalizer 25, which is a shape shaping means, and a first read signal R₁
And the second read signal R₂Subtractor 2 which is a subtraction means for subtracting
2 and a second waveform shaping for shaping the output signal of the subtractor 22.
Output of the equalizer 26 and the equalizer 25
The signal and the output signal of the equalizer 26 are added to obtain the information signal.
Issue S₂And an adder 23 which is a second adding means for outputting
Configure. (Iii)Third embodiment In the third embodiment, as shown in FIG. 6, the first read signal R₁
And the second read signal R₂Is the first addition means for adding
Wave for shaping the output signal of the adder 21 and the adder 21
An equalizer 25, which is a shape shaping means, and a first read signal R₁
And the second read signal R₂Subtractor 2 which is a subtraction means for subtracting
2 and an adder of the signals obtained by the subtractor 22
21 and the C / N ratio of the signal obtained by
The frequency at which the C / N ratios of the obtained signals are almost equal
A filter that removes signal components corresponding to lower frequency bands
The output signal of the HPF 24 and the
An equalizer 26 which is a second waveform shaping means for shaping the shape;
The output signal of the equalizer 25 and the output signal of the equalizer 26
Information signal S₃With the second addition means that outputs
And a certain adder 23. (Iv)Fourth embodiment In the fourth embodiment, as shown in FIG. 7, the first read signal R₁
And the second read signal R₂Is the first addition means for adding
Device 21 and first read signal R₁And the second read signal R ₂Subtract
Output signal from the adder 21
No. 2 and the output signal of the subtractor 22
A certain adder 23 and the output signal of the adder 23 are waveform-shaped
Information signal S_FiveWhich is the third waveform shaping means for outputting
And a riser 27. (V)Fifth embodiment In the fifth embodiment, as shown in FIG. 8, the first read signal R₁
And the second read signal R₂Is the first addition means for adding
Device 21 and first read signal R₁And the second read signal R ₂Subtract
The subtractor 22 which is a subtraction means for
Of the obtained signals, the signal obtained by the adder 21
C / N ratio of and the C / N of the signal obtained by the subtractor 22.
It corresponds to the frequency band lower than the frequency where the ratio is almost equal.
HPF24 which is a filter means for removing the signal component
And the output signal of the adder 21 and the output signal of the HPF 24
An adder 23 which is a second adding means for adding, and an adder 23
Information signal S after waveform shaping of the output signal of₃Output the third
And an equalizer 27 which is a waveform shaping means.
It

[0062]

As described above, according to the first aspect of the invention, the first adding means is obtained from one of the two photodetectors for detecting the two read lights. A first detection signal and a second detection signal obtained from the other photodetector of the two photodetectors are added to generate a sum signal,
The subtraction unit generates a difference signal between the first detection signal and the second detection signal.

Since the second adding means adds the sum signal and the difference signal to generate the information signal, the sum signal is the sum signal in the frequency band having a higher C / N ratio and the difference signal. An information signal having a high C / N ratio in the entire frequency band can be obtained by synthesizing the difference signal in the frequency band having a higher C / N ratio.

According to the second aspect of the present invention, the filter means has a frequency band lower than a frequency at which the C / N ratio of the sum signal and the C / N ratio of the difference signal in the signal components of the difference signal are substantially equal to each other. Since the signal component of the difference signal corresponding to is removed, an information signal with less noise can be obtained as compared with the case where the sum signal and the difference signal are simply added.

According to the third aspect of the invention, the first waveform shaping means shapes the sum signal, and the second waveform shaping means shapes the difference signal. Therefore, when these signals are added, In addition, an information signal having a waveform with good continuity can be obtained.

According to the invention described in claim 4, the third waveform shaping means shapes the waveform of the information signal. Therefore, since the waveform is shaped by one waveform shaping means, it is possible to obtain an information signal having a waveform with good continuity with a simple circuit configuration having a small number of elements.

According to the fifth aspect of the invention, the filter means sets the frequency of the signal components of the difference signal to a frequency lower than the frequency at which the C / N ratio of the sum signal and the C / N ratio of the difference signal are substantially equal. Since the signal component of the corresponding difference signal is removed, an information signal with less noise can be obtained when the sum signal and the difference signal are added.

Therefore, an information signal having a waveform with good continuity and little noise can be obtained. Further, according to the part of the invention of claim 5 related to the invention of claim 4, since waveform shaping can be performed by one waveform shaping circuit, a simple circuit configuration with a small number of elements is provided. It is possible to obtain an information signal that can be waveform-shaped, has a waveform with good continuity, and has little noise.

According to the sixth aspect of the invention, for example, as shown in FIG. 9, the crosstalk removing means 30 removes the crosstalk included in the sum signal, so that a good information signal without crosstalk can be obtained. can get.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of an optical disc reproducing apparatus of the present invention.

FIG. 2 is a diagram showing the principle of the present invention.

FIG. 3 is a diagram showing a waveform of each part according to the principle of the present invention.

FIG. 4 is a diagram showing a first embodiment of the present invention.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a diagram showing a third embodiment of the present invention.

FIG. 7 is a diagram showing a fourth embodiment of the present invention.

FIG. 8 is a diagram showing a fifth embodiment of the present invention.

FIG. 9 is a diagram showing a reproducing circuit according to a first embodiment of the present invention.

FIG. 10 is a diagram showing waveform examples of a signal SUM and a signal DIFF.

FIG. 11 is a diagram showing a characteristic example of the HPF 24.

FIG. 12 is a diagram showing a characteristic example of each equalizer.

FIG. 13 is a diagram showing a signal waveform (I) of each part in the reproducing circuit of the first embodiment.

FIG. 14 is a diagram showing a signal waveform (II) of each part in the reproducing circuit of the first embodiment.

FIG. 15 is a diagram showing a reproducing circuit according to a second embodiment.

FIG. 16 is a diagram showing a characteristic example of the equalizer 27.

FIG. 17 is a diagram showing a signal waveform of each part in the reproducing circuit of the second embodiment.

FIG. 18 is a diagram showing an output waveform example of a reproducing circuit in a conventional optical recording medium reproducing apparatus.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Optical recording medium reproducing device 11 ... Laser diode 12 ... Beam splitter 13 ... Mirror 14 ... Objective lens 15 ... Half wave plate 16 ... Polarization beam splitter 17a ... 1st photodetector 17b ... 2nd photodetector 18 ... Reproducing circuit 21 ... First adding means (adder) 22 ... Subtracting means (subtractor) 23 ... Second adding means (adder) 24 ... Filter means (HPF) 25 ... First waveform shaping means (equalizer) 26 ... 2 waveform shaping means (equalizer) 27 ... third waveform shaping means (equalizer) 28, 31, 41, 42 ... A / D converter 29 ... delay circuit 30, 40 ... crosstalk canceller 32, 33, 34 ... 1 track memory 35, 45 ... canceller 43 and 44 ... delay circuit R ₁ ... first read signal R ₂ ... second read signal sUM, sUM _1, sUM ₂ ... sum signal DIF , DIFF _1, DIFF ₂ ... difference signal S ₀ to S ₆ ... information signal S '... signal DK ... optical disc MG ₁ ... magnet

Claims (6)

[Claims] 1. Information is held by phase pits, and the polarization state of reflected light or transmitted light is different from each other in the light spot of the reading light in accordance with the temperature distribution accompanying the irradiation of the reading light emitted from the outside. The reflected light or the transmitted light of the reading light from the optical recording medium in which two or more areas appear is separated into two reading lights according to the polarization state, the two reading lights are received, and the detection signals are respectively received. In an optical recording medium reproducing apparatus having at least two photodetectors to be obtained, a first detection signal obtained from one photodetector of the two photodetectors for detecting the two reading lights, and the two First addition means for adding a second detection signal obtained from the other photodetector of the photodetectors to generate a sum signal, and a difference signal between the first detection signal and the second detection signal Subtraction means and the above Further comprising a second adding means for generating an information signal by adding the difference signal to the optical recording medium reproducing apparatus according to claim. 2. The optical recording medium reproducing device according to claim 1, wherein among the signal components of the difference signal, a frequency at which the C / N ratio of the sum signal and the C / N ratio of the difference signal are substantially equal to each other, An optical recording medium reproducing apparatus comprising a filter means for removing a signal component of the difference signal corresponding to a low frequency band. 3. The optical recording medium reproducing apparatus according to claim 1, further comprising: a first waveform shaping means for shaping the waveform of the sum signal, and a second waveform shaping means for shaping the waveform of the difference signal. An optical recording medium reproducing device characterized by. 4. The optical recording medium reproducing apparatus according to claim 1, further comprising a third waveform shaping unit that shapes the waveform of the information signal. 5. The optical recording medium reproducing apparatus according to claim 3, wherein among the signal components of the difference signal, the C / N ratio of the sum signal and the C / N ratio of the difference signal are substantially equal to each other. An optical recording medium reproducing apparatus comprising a filter means for removing a signal component of the difference signal corresponding to a frequency band lower than the frequency. 6. The optical recording medium reproducing apparatus according to claim 5, further comprising a crosstalk removing unit that removes crosstalk included in the sum signal.