JP2986639B2 - Crosstalk reduction device for optical information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information input / output device for recording and reproducing information by using light, and more particularly to a crosstalk reduction device for an optical information reproducing device.

[0002]

2. Description of the Related Art In order to increase the density of an information storage medium, if the track pitch is made smaller than the diameter of a spot where a light beam is converged, the information is reproduced adjacent to a desired track. The effect of the information recorded on the track appears strongly. This leakage of information recorded on an adjacent track is generally called crosstalk, and degrades information reproduction characteristics. As a method of reducing crosstalk, information recorded on tracks adjacent to each other is read, and a signal mainly including information recorded on a desired track is used to include information recorded on adjacent left and right tracks. A method of multiplying a signal by an appropriate coefficient and subtracting the signal has been devised, and is disclosed in, for example, JP-A-57-58248.

FIG. 12 shows an example of the configuration of the signal processing circuit. In FIG. 12, among the three detectors, the central detector 5
2 outputs a signal mainly including information recorded on a desired track, and two outer detectors 51 and 53 output signals including information recorded on a track adjacent to the desired track. . The signals obtained from the two outer detectors 51 and 53 are attenuated by the attenuator 54 to a signal having the same magnitude as the amount of crosstalk contained in the signal obtained from the central detector 52, It is subtracted from the signal obtained from the central detector 52.

[0004]

However, in the above-described configuration, the information storage medium which records information by a change in complex reflectivity, such as a change in reflectivity due to a phase change or the presence or absence of a pit, causes crosstalk. It cannot be removed effectively. For this reason, there has been a problem that an eye used when performing signal detection with a partial response is not sufficiently opened, and jitter caused by crosstalk is not reduced.

In view of the foregoing, the present invention provides a cross-section of an optical information reproducing apparatus which effectively removes crosstalk, increases the aperture ratio of an eye used when detecting a signal by a partial response, and further reduces jitter caused by crosstalk. An object is to provide a talk reduction device.

[0006]

According to the present invention, there is provided a crosstalk reducing apparatus for an optical information reproducing apparatus for reproducing information using a light beam, wherein a series of tracks on which information is recorded and reproduced are arranged so as to be adjacent to each other. Pickup that optically reads information recorded on an information storage medium and outputs a first signal mainly containing information recorded on a desired track and a second signal mainly containing information recorded on an adjacent track A head device, a variable gain amplifier circuit that receives the second signal and controls the level or polarity of the second signal, and is directly obtained from amplitude information of the first signal.
A value, comprising a signal processing circuit for outputting a signal for controlling at all times the gain of the variable gain amplifying circuit, an arithmetic circuit, for adding or subtracting a signal output from the first signal and the variable gain amplifier circuit , A crosstalk reducing device of the optical information reproducing device.

[0007]

According to the present invention, there is provided a light source capable of obtaining a signal free of crosstalk by controlling the gain of a variable gain amplifying circuit according to a mark or a space recorded on a desired track. It becomes a crosstalk reduction device of the information reproducing device.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a crosstalk reducing device of an optical information reproducing apparatus according to the present invention will be described in detail with reference to FIGS.

(First Embodiment) As an embodiment of the present invention, three beams are irradiated on a desired track and a track adjacent to the desired track as shown in FIG. 1 to be recorded on each track on the information storage medium. 1 shows the configuration of an optical system of a crosstalk reducing device of an optical information reproducing device that reads out and calculates information and reduces crosstalk. The configuration of this optical system is well known. For example, a configuration in which three beams are generated by three semiconductor lasers is disclosed in JP-A-57-58248, in which three beams are formed by one semiconductor laser and one diffraction grating. A configuration for generating the information is disclosed in Japanese Patent Application Laid-Open No. 60-69842.

The divergent beam 70 having linear polarization emitted from the semiconductor laser light source 1 is transmitted through the diffraction grating 10 and
It becomes three beams of the first order diffracted light 70 and ± first order diffracted lights 71 and 72. The three beams 70 to 72 become parallel beams after passing through the collimating lens 2, and become polarized beam splitters 3.
After passing through, the light passes through the λ / 4 plate 9 to become a circularly polarized beam, passes through the objective lens 8, and is focused on the information storage medium 4. Information represented by marks or spaces is formed on the information storage medium 4 to form a track, and the beams 70 to 72 condensed by the lens 8 are optically designed so as to be positioned on the track. I have. Information storage medium 4
The beams 70 to 72 reflected and diffracted by the
After passing through the λ / 4 plate 9, the beam becomes a linearly polarized beam having a polarization direction different from that of the beam emitted from the light source 1 by 90 degrees, and is incident on the polarization beam splitter 3. The beams 70 to 72 incident on the polarizing beam splitter 3 are reflected and guided to the cylindrical lens 6, and the beams 7 transmitted through the cylindrical lens 6.
0 to 72 are beams having astigmatism, which are condensed by the lens 7 and received by the photodetector 5.

The track and beam 70 on the information storage medium 4
2 are shown in FIG. FIG. 2 shows the information storage medium 4 on an enlarged scale, where n-2, n-1, n, n + 1, n
+2 indicates a track, and 70 to 72 indicate condensed beams. Information is recorded on the track as marks and spaces. Information of a desired track recorded on the information storage medium 4 is read using the beam 70, and in FIG. 3, information recorded on the track n is read. As the track pitch tp becomes smaller, the beam 70 simultaneously reads not only the information recorded on the track n but also the information recorded on the adjacent tracks n-1 and n + 1. This causes crosstalk, and the beam 70 is read by the beam 70. The quality of the information recorded on the track n is deteriorated. The beam 71 and the beam 72 are condensed on tracks n-1 and n + 1, respectively, and are arranged so that information of each track is read. Beam 70-7
2 are arranged apart from each other by a distance L with respect to the track direction in order to enable beams 70 to 72 to be received by different light receiving units using a simple optical system as shown in FIG. is there.

FIG. 3 shows the relationship between the photodetector 5 and the beams 70 to 72 received by the photodetector 5 in the optical system shown in FIG. 1 and the configuration of an electric circuit system of the crosstalk reduction device.
The photodetector 5 includes light receiving units 501 to 506. Beam 7
0 is the light receiving units 501 to 504, and the beam 71 is the light receiving unit 50.
At 5, the beams 72 are respectively received by the light receiving units 506. By performing a desired operation on the signals output from the light receiving units 501 to 504, a focus error signal and a tracking error signal can be obtained. Here, the focus error signal is obtained by the astigmatism method, and the tracking error signal is obtained by the push-pull method. Although an arithmetic circuit for obtaining the focus error signal and the tracking error signal is omitted because it is difficult to understand the gist of the present invention, the focus error signal is obtained by summing the signals output from the light receiving units 501 and 503 and the light receiving unit 502. By performing a differential operation of the sum of the signals output from the light receiving unit 504 and the sum of the signals output from the light receiving unit 5
The signals are obtained by performing a differential operation on the sum of the signals output from 01 and 502 and the sum of the signals output from the light receiving units 503 and 504, respectively. The focus error signal and the tracking error signal are respectively applied to the actuators 91 and 9 shown in FIG.
2 for focus and tracking control.

Information recorded on a desired track n on the information storage medium 4 is obtained by adding signals output from the light receiving units 501 to 504 by an adding circuit 61, and the adjacent tracks n-1 and n + 1 are obtained. Are obtained from signals output from the light receiving units 505 and 506, respectively.

Light receiving section 506, adding circuit 61, light receiving section 50
The signals output from 5 are input to delay circuits 62 to 64, respectively. The delay circuits 62 to 64 correct a time delay of information caused by the beams 70 to 72 focused on the information storage medium 4 being separated from each other by a distance L in the track direction. As disclosed in Japanese Patent Application Laid-Open No. 61-287056, a beam for reading information recorded on a desired track and a beam for reading information on an adjacent track are arranged so as to have no distance in the track direction. In this case, the delay circuits 62 to 64 become unnecessary. The signal output from the delay circuit 63 has a component of information recorded on a desired track, and is amplified by the amplifier circuit 65 before being input to the signal processing circuit 67 and the differential operation circuit 69. The signal processing circuit 67 receives a signal output from the amplification circuit 65 and outputs a control signal for controlling the gain of the variable gain amplification circuit 68. The signals output from the delay circuits 62 and 64 have information components recorded on tracks adjacent to the desired track, respectively, and are added by the addition circuit 66 to adjust the gain from positive to negative. After being amplified by the variable gain amplifier circuit 68, it is input to the differential operation circuit 69. The differential operation circuit 69 performs a differential operation, and a signal output from the differential operation circuit 69 is obtained from a terminal 80.

In this embodiment, the signal processing circuit 67 controls the gain of the variable gain amplifier circuit 68 to change as a linear function of the signal obtained from the amplifier circuit 65. This is shown in FIG. 4, the horizontal axis represents the signal strength obtained from the amplifier 65, and the vertical axis represents the gain of the variable gain amplifier 68. In the figure, S1 is the signal strength when a space is continuously recorded on a desired track n, k1 is the gain determined by the amount of crosstalk from an adjacent track at that time, and S2 is a mark having a continuous mark on the same track n. K2 is the signal strength when the signal was recorded as the data, and the gain is determined by the amount of crosstalk from the adjacent track at that time. FIG. 5 shows changes in signal strength (middle in the figure) and gain (lower in the figure) of a signal obtained from the amplifier circuit 65 when the mark 81 and the space 82 are arranged on the desired track n as shown in the upper part of the figure. Correspond to the positions of the mark and the space. S1, S2, k1, and k2 are symbols common to FIG. Controlling the gain of the variable gain amplifier circuit 68 in the crosstalk reduction device of the present invention is equivalent to changing the coefficient in the conventional crosstalk reduction device.

An optical system having a light source wavelength λ = 680 nm and an objective lens NA = 0.6, and a track pitch tp = 0.5
μm, basic period T = shortest mark length = shortest space length =
FIG. 6 shows an eye pattern obtained by using the crosstalk reducing device described in this embodiment when reproducing digital information recorded at 0.425 μm. In FIG. 6, the gain of the amplifier 65 is set to 1, and the gain of the variable gain amplifier 68 is set to k1 = 0.17 and k2 = 0.08. On the other hand, FIG.
1 shows an eye pattern obtained when a crosstalk reducing device having a signal processing circuit having the configuration of FIG. Here, in the conventional example, the detector 51 is
The signal from 53 is multiplied by 0.13. In FIGS. 6 and 13, the area A is an eye used when performing normal signal detection, and the areas B and C are eyes used when performing signal detection with a partial response. When the information is a digital signal, the timing at which normal signal detection is performed is t0, the timing shifted by T / 2 from t0 is t1, and the timing shifted by T / 4 before and after t1 is t2. The amplitude of the entire signal is I, and the amplitude of the area A at the timing t0 is I
A, the amplitudes of the timing t1 of the regions B and C are IB and I, respectively.
C, the amplitude of the timing t2 of the regions B and C is IB1, IC
1 and the eye aperture ratios are IA / I, IB / I, and IC, respectively.
/ I, the aperture ratio at the timing t2 of the regions B and C is IB1 /
Let I, IC1 / I be the eye aperture ratios of 13% and 34, respectively, when the crosstalk reduction device of this embodiment is used.
% And 32%, and the eye aperture ratios when the conventional crosstalk reduction device is used are 13%, 29% and 27%, respectively.
It is. Further, the aperture ratio at the timing t2 of the regions B and C is 16% and 17% in the case of the present embodiment, respectively, and 12% and 12% in the case of the conventional example. When the crosstalk reducing device shown in the present embodiment is used, crosstalk is effectively removed, and the aperture ratio of an eye used when performing signal detection with a partial response is improved as compared with the conventional example, so that a noise margin is increased. In other words, the error rate when reproducing the information recorded on the information storage medium is reduced. In addition, areas B and C
The aperture ratio at the timing t2 is greatly improved. When the aperture ratio at a position (for example, timing t2) shifted from the timing t1 of the regions B and C increases, a margin for jitter when performing signal detection with a partial response increases, and the error rate during reproduction decreases.

In recent years, semiconductor memories have become inexpensive, and as disclosed in Japanese Patent Application Laid-Open No. 2-257474, an optical system for emitting one beam and a semiconductor for storing information for three tracks are disclosed. Using a memory, a configuration equivalent to a configuration in which three beams are irradiated can be realized. There is no problem at all when the crosstalk reducing device shown in the present embodiment is applied to the optical system and the electric circuit system having such a configuration. In the configuration of the optical system that irradiates the information storage medium with three beams, the information storage medium has a large eccentricity, or in the case of a disc-shaped information storage medium, the curvature of the track at the inner circumference and the outer circumference of the information storage medium is different. Due to the difference, the relationship between the three beams and each track fluctuates, and crosstalk may not be sufficiently reduced. At this time, for example, SPIE Proceeding Vol. 1316 p35-p39
It is effective to rotate the positions of the three beams by using an image rotation prism to keep the relationship between the three beams and each track constant, as disclosed in US Pat. When an optical system that emits one beam and a semiconductor memory that stores information for three tracks are used to realize a configuration equivalent to a configuration that irradiates three beams, the information storage medium is irradiated with three beams. Unlike the case of the configuration described above, the crosstalk can always be sufficiently reduced. Also, since there is no need to irradiate three beams and no image rotation prism,
The optical system is simplified.

(Second Embodiment) As a second embodiment, the optical system is the same as that of the first embodiment, but the variable gain amplifying circuit 68
Here are the different ways of changing the gain. In the present embodiment, control is performed so that the gain of the variable gain amplifier 68 changes in a step function type depending on whether a signal obtained from the amplifier 65 is larger or smaller than a certain threshold. This is shown in FIG.
7, the horizontal axis represents the signal strength obtained from the amplifier 65, and the vertical axis represents the gain of the variable gain amplifier 68. In the figure, S1 is the signal strength when the space is continuously recorded on the desired track n, k1 is the gain determined by the crosstalk amount from the adjacent track at that time, and S2 is the mark on the same track n. Signal strength when it was recorded as
k2 is a gain determined by the amount of crosstalk from the adjacent track at that time, and S3 is a threshold value set between S1 and S2. FIG. 8 shows the signal strength of the signal obtained from the amplifier circuit 65 when the mark 81 and the space 82 are arranged on the desired track n as shown in the upper part of FIG.
And changes in gain (lower part in FIG. 3) correspond to the positions of marks and spaces. S1, S2, S3, k1, k
2 is a symbol common to FIG.

As in the first embodiment, the wavelength of the light source is λ = 6.
When reproducing digital information recorded with an optical system of 80 nm, NA of an objective lens = 0.6, track pitch tp = 0.5 μm, basic period T = shortest mark length = shortest space length = 0.425 μm, FIG. 9 shows an eye pattern obtained when the crosstalk reducing device shown in the embodiment is used. In FIG. 9, the gain of the amplifier 65 is set to 1, and the gain of the variable gain amplifier 68 is k1 = 0.17, k2 = 0.08,
The signal intensity of the specular reflection is normalized to S1 = 1.0 and S3 =
0.5. In FIG. 9, an area A is an eye used when performing a normal signal detection, and areas B and C are eyes used when performing a signal detection with a partial response. When the information is a digital signal, the timing for performing normal signal detection is t0, and the timing shifted from T0 by T / 2 is t1,
The timing shifted by T / 4 before and after t1 is represented by t2.
And The amplitude of the entire signal is I, and the timing t0 of the region A is
IA, the amplitude of the timing t1 in the areas B and C is IB and IC, the amplitude of the timing t2 in the areas B and C is IB1 and IC1, and the eye opening ratios are IA / I and I, respectively.
Assuming that the aperture ratios at timing t2 of B / I, IC / I, and regions B and C are IB1 / I and IC1 / I, the aperture ratios of the eyes when the crosstalk reduction device of the present embodiment is used are each 0.
%, 26%, and 20%, and the aperture ratios at the timing t2 in the regions B and C are 18% and 17% in the case of the present embodiment. This is because when the conventional crosstalk reduction device is used, the aperture ratio at the timing t2 of the regions B and C is 12%, 1%.
This is very good as compared with 2%, and an even larger aperture ratio is obtained as compared with 16% and 17% in the first embodiment. That is, the aperture ratio of the partial response eye and the jitter margin are significantly increased. It is possible to do.

(Third Embodiment) As still another embodiment of the present invention, FIG. 10 shows the configuration of an optical system of a crosstalk reduction apparatus for irradiating a desired track with one beam to reduce crosstalk. . The concept of the configuration of this optical system is disclosed in Japanese Patent Application Laid-Open No. 61-131245. FIG.
In the optical system shown in FIG. 1, those optical elements that can use the same optical elements as those shown in FIG. 1 are denoted by the same reference numerals as the optical elements shown in FIG. The optical system shown in the present embodiment is different from the optical system shown in the first embodiment in that the diffraction grating 10 is not provided and one beam 70 is focused on the information storage medium 4, and the optical detector The arrangement of the light receiving unit 50 is different from the arrangement of the light receiving unit of the photodetector 5. FIG. 12 shows the arrangement of the light receiving units on the photodetector 50. Photodetector 50
Is composed of eight light receiving units 507 to 514, and the focus error signal is the sum of the signals output from the light receiving units 509, 510, 511, 512 and the light receiving units 507, 508, 513, 5
By performing a differential operation on the sum of the signals output from the light-receiving units 507, 508,
Sum of signals output from 511 and 512 and light receiving unit 50
9, 510, 513, and 514, respectively, by performing a differential operation with the sum of the signals output from the signals. Also,
The crosstalk reduction device inputs the sum of the signals output from the light receiving units 508, 509, 512, and 513 to the amplification circuit 65 shown in FIG.
7, 510, 511, and 514. In the case of this embodiment,
Since the delay circuits 62, 63 and 64 become unnecessary, the circuit configuration is simplified. Further, even when the rotation speed of the information storage medium 4 changes, there is no need to vary the delay time because no delay element is required.
In an optical information reproducing apparatus in which the relative speed with respect to 0 changes according to the partial area of the information storage medium 4, the crosstalk can be stably reduced.

The optical system shown in this embodiment can be applied to the first and second embodiments without any problem. The crosstalk reduction device according to the present invention may be any optical pickup head device that outputs a signal including information recorded on a desired track and a signal including information recorded on a track adjacent to the desired track. Things can be tolerated. It goes without saying that the detection method of the focus error signal and the tracking error signal of the optical pickup head device is not restricted at all.

Although the embodiment has shown two types of gain control characteristics of the variable gain amplifier circuit, variable gain amplifier circuits having other characteristics may be used.

In the embodiment, all signals including information recorded on the adjacent tracks are added and then input to the variable gain amplifier circuit. However, a plurality of signals including information recorded on the adjacent tracks can be independently obtained. In this case, the signals can be input to different variable gain amplifier circuits, amplified, and then added together by an adder circuit. In that case, independent coefficients increase, and the effect of canceling crosstalk further increases.

In this embodiment, only signals mainly containing information recorded on a desired track are considered as signals for controlling the variable gain amplifier circuit. However, control using other signals such as a tracking error signal is also allowed. A configuration is also possible.

[0025]

As described above, according to the present invention,
Controls the gain of the variable gain amplifier circuit according to the mark or space recorded on the desired track, and amplifies a signal containing information recorded on an adjacent track with different gains when the mark is used and when the space is used. Then, by adding or subtracting a signal mainly including information recorded on a desired track, a signal from which crosstalk has been removed can be obtained, and the eye pattern of the signal can be used for signal detection with a partial response. Greatly increases, and jitter caused by crosstalk can be reduced, and information can be reproduced at a low error rate.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system of a crosstalk reduction device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship between a track on an information storage medium and a focused beam according to the embodiment.

FIG. 3 is a configuration diagram of an electric circuit system of a crosstalk reduction device according to an embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between the gain of a variable gain amplifier circuit according to an embodiment of the present invention and the signal strength entering a signal processing circuit for controlling the gain;

FIG. 5 is a diagram showing a relationship between information recorded on an information storage medium, a gain of a variable gain amplifying circuit, and a signal strength entering a signal processing circuit for controlling the gain, showing an embodiment of the present invention.

FIG. 6 is an eye pattern obtained by using the crosstalk reducing device according to the embodiment of the present invention.

FIG. 7 is a diagram showing the relationship between the gain of the variable gain amplifier circuit and the signal strength entering the signal processing circuit for controlling the gain, showing the second embodiment of the present invention;

FIG. 8 is a diagram showing a relationship between information recorded on an information storage medium showing the embodiment, a gain of a variable gain amplifier circuit, and a signal strength entering a signal processing circuit for controlling the gain.

FIG. 9 is an eye pattern obtained by using the crosstalk reducing device shown in the embodiment.

FIG. 10 is a configuration diagram of an optical system of a crosstalk reduction device according to a third embodiment of the present invention.

FIG. 11 is a diagram showing the relationship between a photodetector and a received light beam according to the embodiment.

FIG. 12 is a configuration diagram of an electric circuit system of a conventional crosstalk reduction device.

FIG. 13 is an eye pattern obtained using a conventional crosstalk reduction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser light source 2 Collimating lens 3 Polarization beam splitter 4 Information storage medium 5 Photodetector 6 Cylindrical lens 7 Lens 8 Lens 9 λ / 4 plate 10 Diffraction grating 50-54 Photodetector 54 Attenuator 55 Addition / subtraction circuit 61, 66 Adder circuit 62 to 64 Delay circuit 65 Amplifying circuit 67 Signal processing circuit 68 Variable gain amplifying circuit 69 Differential operation circuit 70 Beam (0th order diffracted light) 71 Beam (1st order diffracted light) 72 Beam (1st order diffracted light) 80 Output terminal 81 Mark 82 Space 91 Focus Control Actuator 92 Tracking Control Actuator 501-514 Light Receiver A, B, C Eye I Signal Amplitude IA, IB, IC Eye Amplitude IB1, IC1 Eye Amplitude L Beam Distance tp Track Pitch T Basic Period k1 Gain k2 Gain S1 Signal strength Each T / 4 shifted by the timing before and after the signal S2 intensity S3 threshold t0 timing t2 t1 which is shifted from the timing t1 t0 of normal signal detection by T / 2

Claims (3)

(57) [Claims] 1. A crosstalk reducing device for an optical information reproducing apparatus for reproducing information using a light beam, wherein a series of tracks on which information is recorded and reproduced are recorded on an information storage medium arranged adjacent to each other. An optical pickup head device that optically reads information and outputs a first signal mainly including information recorded on a desired track and a second signal including information recorded on an adjacent track; A variable gain amplifier circuit that receives a signal and controls the level or polarity of the second signal; and a value directly obtained from amplitude information of the first signal.
In the variable gain gain of the amplifying circuit and the signal processing circuit for outputting a signal for controlling at all times, the first signal and the variable gain amplifier arithmetic circuit for adding or subtracting a signal output from the circuit, the light with a capital Crosstalk reduction device for information reproducing device. 2. The optical information reproducing apparatus according to claim 1, wherein the gain of the variable gain amplifier circuit changes as a linear function of a first signal mainly including information recorded on a desired track. Talk reduction device. 3. The gain of the variable gain amplifier circuit changes stepwise depending on whether the first signal mainly containing information recorded on a desired track is larger or smaller than a certain threshold. 2. The crosstalk reducing device of the optical information reproducing device according to 1.