JP2710709B2 - Optical recording / 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 optical recording / reproducing apparatus for detecting a change in reflected light from an optical recording medium to obtain a reproduced signal.

[0002]

2. Description of the Related Art In recent years, an optical recording / reproducing apparatus for digitizing information such as code data, video, music, and the like, optically recording the information, and reproducing the recorded information has been developed. Such an optical recording / reproducing apparatus usually reproduces an information signal by irradiating a laser beam onto an optical recording medium so as to be in a focused state and detecting a change in light reflected from the optical recording medium. ing. Recently, as an optical recording medium, a rewritable type capable of rewriting information in an information recording area many times has been proposed. As this rewritable optical recording medium, a phase change recording type and a magneto-optical recording type are mainly adopted.

A phase-change recording type optical recording medium records information using a phase change between a crystal and an amorphous phase of a recording material. The recording material has different reflectances in a crystalline state and an amorphous state. doing. The information bits are recorded by a change in the reflectance of the recording material. In an optical disk using such phase change recording, if a laser beam is focused on the disk and follows an information track, the intensity of light reflected from the disk changes depending on the presence or absence of an information bit. The recorded information is reproduced by detecting the change of the information.

In magneto-optical recording, Tb, Fe, Co
Information is magnetically recorded on a magneto-optical medium such as that described above to form information bits. When the linearly polarized laser light is made to follow the information track in a focused state, the polarization direction of the reflected light from the disk changes depending on the presence or absence of the information bit, so the change in the polarization direction is converted into a change in light intensity. By doing so, the recorded information is reproduced. In such a magneto-optical recording type optical disc, continuous guide grooves and discontinuous pre-pit rows for track servo are provided.

FIG. 9 shows an example of a conventional optical recording / reproducing apparatus for a phase change type optical recording medium. The laser light emitted from the laser light source 80 passes through the collimator lens 81, becomes parallel light, and is irradiated on the half prism 82. The half prism 82 refracts the irradiated laser light at a right angle, and the refracted light is condensed by the objective lens 83 and irradiated on the optical disc 84. The laser light reflected by the optical disk 84 is converted into parallel light by the objective lens 83, passes through the half prism 82, and irradiates the photodetector 85. Photo detector
The output of 85 is amplified by an amplifier 86 and reproduced as an information signal.

FIG. 10 shows an example of an optical recording / reproducing apparatus for a magneto-optical recording medium. The laser light emitted from the laser light source 90 passes through the collimator lens 91 and becomes parallel light, and is applied to the beam splitter 92. The beam splitter 92 refracts the irradiated laser light at a right angle, and the refracted light is condensed by the objective lens 93 and irradiated on the optical disc 84. The laser light emitted from the laser light source 90 is transmitted to the beam splitter 92 by the S beam.
It has a plane of polarization perpendicular to the outgoing direction so as to correspond to polarized light (electric field component perpendicular to the plane of incidence). Therefore, the polarization characteristic of the beam splitter 92 is such that, for example, the ratio between the transmitted light and the reflected light is P-polarized (an electric field component parallel to the incident surface).
Is 10: 0, and for S-polarized light is 7: 3.

The laser light reflected by the optical disk 84 is converted into parallel light by an objective lens 93, passes through a beam splitter 92, further passes through an analyzer 94, and passes through a photodetector 95.
Irradiated to The output of the photodetector 95 is amplified by the amplifier 96 and reproduced as an information signal. The analyzer 94 allows light to pass selectively depending on the polarization direction.

FIG. 11 shows another example of an optical recording / reproducing apparatus for a magneto-optical disk. This optical recording / reproducing apparatus has the structure shown in FIG.
Similarly to the optical recording / reproducing apparatus shown in FIG. 1, a laser beam emitted from a laser light source 90 is incident on a beam splitter 92 via a collimator lens 91, and the laser beam refracted by the beam splitter 92 passes through an objective lens 93. The light is irradiated onto the optical disc 84 via the optical disc 84. Then, the laser light reflected by the optical disk 84 passes through the beam splitter 92, and
The light enters a polarization beam splitter 97 via a wave plate 89. The half-wave plate 89 changes the polarization direction of the incident light by 45.
Turn only ゜. Also, the polarizing beam splitter 97
P-polarized light transmittance and S-polarized light transmittance are each 100%,
Plays the role of analyzer. Polarizing beam splitter 97
Is transmitted to the photodetector 98a, and the laser beam reflected by the polarization beam splitter 97 is irradiated to the photodetector 98b. The outputs of the detectors 98a and 98b are provided to a differential amplifier 99, and the difference between the outputs of the two photodetectors 98a and 98b is used as a reproduction signal.

On the optical disc 84, as shown in FIG. 12A, information is recorded as information bits 87 on a plurality of mutually parallel information tracks 84a. Each information track
84a are provided at appropriate intervals, and the pitch of each information track 84a is δ. Then, the light spot 88 focused on the optical disk 84 is relatively
By moving in the direction indicated by, each information bit 87 is scanned along the track direction. As a result, in any of the optical recording / reproducing apparatuses, a light detection signal having a waveform as shown in FIG.

[0010]

SUMMARY OF THE INVENTION Such an optical disk
In FIG. 13A, in order to improve the recording density, FIG.
As shown in the figure, the pitch δ of the information track 84a may be reduced. However, in this way, the information track 84
When the pitch of a is reduced, the light spot 88 also overlaps the information bit 87 on the information track 84a adjacent to the information track 84a to be scanned, and in any optical recording / reproducing apparatus, as shown in FIG. As shown, there is a problem that a detection signal with increased crosstalk is obtained. When the crosstalk increases, the jitter increases, so that the error rate of the reproduction signal detection increases, which may make it difficult to detect the reproduction signal. Thus, there is a limit to reducing the arrangement pitch δ of the information tracks 84a in order to improve the information recording density of the optical disc.

An object of the present invention is to solve such a problem, and an object of the present invention is to provide an optical recording / reproducing apparatus capable of reliably reproducing recorded information by suppressing crosstalk even on an optical disk on which information is recorded at a high density. Is to provide.

[0012]

SUMMARY OF THE INVENTION An optical recording / reproducing apparatus according to the present invention provides an optical recording medium in which information is recorded on mutually parallel information tracks, and a single information track on which information is to be reproduced. An optical recording / reproducing apparatus that irradiates one light spot and reproduces information based on reflected light of the light spot, and receives reflected light from the information track in the light spot irradiated on the information track. main light receiving region and, said main light receiving regions so as to receive the reflected light from the direction with adjacent portions in a direction perpendicular to the said information track
And a three-segment type photodetector having sub light receiving areas provided on both sides of the main light receiving area and an output signal from the main light receiving area.
Waveform equalization so that it does not correlate with the output signal from the light receiving area
And a signal processing unit, whereby the above object is achieved.

[0013]

According to the present invention, an information track irradiated with a light spot is provided.
Of the light detector where the light reflected by the
Received by the light receiving area
The reflected light from the information track
It is. The output signal from the main light receiving area is a signal
The processing unit does not correlate with the output signal from the sub-light receiving area.
The waveform is equalized as follows. As a result, the
These output signals are based on the output signal from the sub-light receiving area.
No interference, ensuring crosstalk effects
Can be eliminated.

[0014]

Embodiments of the present invention will be described below. FIG. 1 shows an example of an optical recording / reproducing apparatus for a phase change optical disk as a first embodiment of the present invention. This optical recording / reproducing apparatus has a laser light source 10, and a laser light 11 emitted from the laser light source 10 emits a collimator lens 12.
Is converted into parallel light. The laser light collimated by the collimator lens 12 is refracted at right angles by the half prism 13. The laser light refracted by the half prism 13 is condensed by the objective lens 14 and irradiated on the optical disc 15. The laser light applied to the optical disc 15 is
A light spot 18 is formed on the optical disk 15 by the objective lens 14.

The laser beam 11 reflected from the optical disk 15
Are converted into parallel light by the objective lens 14 and pass through the half prism 13. The laser beam 11 transmitted through the half prism 13 is applied to three light receiving units 22a, 22b, and 22c of the photodetector 22.

The optical disk 15 is rewritable by a phase change. For example, as shown in FIG. 2, information bits 16, 16,... Are formed on mutually parallel information tracks 17.
Information tracks 17 adjacent to each other in each other is in a state where almost no gap is opened, therefore, the pitch [delta] ₂ of the information track 17 is substantially equal to the width of each information track 17.

Light spot 18 condensed on optical disk 15
Is moved in the direction indicated by arrow A relative to the optical disk 15 so that the information bit of each information track 17 is
16 scans. Therefore, the light spot 18
The central portion 18b excluding each side edge in the direction orthogonal to the track direction, which is the scanning direction, scans the information track 17 on which the information bits 16 to be detected are formed, and the central portion 18b of the light spot 18 Each of the side edges 18a and 18c across the information track 17 scans on each information track 17 adjacent to the information track 17 to be scanned.

The photodetector 22 has three light receiving sections 22b, 22a and
3, the central portion 18b of the light spot 18 corresponds to the main light receiving portion 22b, and the side edges 18a and 18c correspond to the sub light receiving portions 22a and 22c, respectively, as shown in FIG. Each light receiving part 22a, 22b, 22c has a light spot 1
The reflected light in each part of 8 is irradiated. Each light receiving section 22a,
The outputs 22b and 22c output output signals corresponding to the amounts of light irradiated to the amplifiers 23a, 23b and 23c, respectively, and the output signals are amplified by the amplifiers 23a, 23b and 23c. The output of each amplifier 23a, 23b, 23c is
Given to 0.

The signal processing section 30 includes amplifiers 23a, 23b,
A / D converter 3 to which the output signals from 23c are respectively input
1a, 31b, 31c, and each A / D converter 31a, 31b,
The analog signal of each amplifier 23a, 23b, 23c is converted into a digital signal by 31c.

Each side edge 18a and 1 in the light spot 18
The output signals of the A / D converters 31a and 31c to which the output signals of the sub-light receiving units 22a and 22c of the photodetector 22 corresponding to 8c are applied are directly input to the adder 36, The output of the A / D converter 31b to which the output signal of the main light receiving section 22b of the photodetector 22 corresponding to the central portion 18b is input to the adder 36 via the transversal filter 35. The adder 36 adds each input signal and outputs the result to the amplifier 18, and the output of the amplifier 18 is used as an information reproduction signal. The output of the adder 36 is provided to a coefficient control circuit 34 that performs feedback control of the adder 36, and the output of the coefficient control circuit 34 is provided to a transversal filter 35.

The transversal filter 35 is provided so as to perform an n-th tap control on the output signal from the A / D converter 31b, and as shown in FIG. 4, a flip-flop for delaying the output in clock units. N delay circuits 40, such as circuits and latch circuits, are connected in series. Then, each delay circuit 40 extracts a digital signal output from the A / D converter 31b as a component for each clock unit. Each delay circuit 40 includes an integrator 41 ...
Are respectively connected, and each integrator 41 is provided with each of the coefficients k ₀ , k ₁ , k ₂ ,..., K _n-1 set by the coefficient control circuit 34.
Is added to the signal component extracted by each delay circuit 40. Then, the output signals of the respective integrators 41 are mixed and input to the adder 36 as the output of the transversal filter 35. The coefficient control circuit 34 calculates, based on the added output signals of all the light receiving sections 22a, 22b, and 22c of the photodetector 22 added by the adder, a coefficient integrated into the signal component extracted from each delay circuit 40. Controlling. This allows
The transversal filter 35 outputs the output of the light receiving unit 22b corresponding to the central portion 18b of the light spot 18 to the light spot 18.
Each light receiving section 22 corresponding to each side edge 18a and 18c in 18
In order not to correlate with the output signals of a and 22c,
That is, the waveform equalization is performed so that the output of the light receiving unit 22b at the center of the photodetector 22 is not interfered by the output signals of the light receiving units 22a and 22c at the respective side edges.

In the optical recording / reproducing apparatus having such a configuration, the light spot of the laser light 11 emitted from the laser light source 10 is
When the 18 scans the information bits 16 of the optical disk 15 as shown in FIG. 2A, light intensity signals as shown in FIGS. 2B to 2E are obtained. As shown in FIG. 2B, the light receiving unit 22b that captures the reflected light from the central portion 18b of the light spot 18
A signal corresponding to the information bit 16 on the information track 17b to be scanned is output. Each side edge 18a and 1 of the light spot 18
Each of the light receiving sections 22a and 22c capturing the reflected light of 8c is shown in FIG.
As shown in (c) and (d), each information track 17a adjacent to the information track 17b to be scanned
And outputs a signal corresponding to the information bit 18 on 17c. All the light receiving sections 22a to 22c of the photodetector 22 are shown in FIG.
As shown in (1), the output signals of the respective light receiving sections 22a to 22c are superimposed, and therefore, the crosstalk is increased.

In this embodiment, each light receiving section 22a of the photodetector 22
After being amplified to an appropriate level by amplifiers 23a to 23c, the signals output from
/ D converters 31a to 31c. The light spot 18 is output from the main light receiving portion 22b that receives the reflected light from the central portion 18b located on the information track to be scanned,
The signal digitally converted by the A / D converter 31b is input to the transversal filter 35, and the transversal filter 35 causes the other sub-light receiving section 22a
And 22c are waveform-equalized so as not to be correlated with the signals output from the A / D converters 31a and 31c. The output of the transversal filter 35 whose waveform has been equalized is output to each of the A / D converters 31a and 31c.
Is input to the adder 36, and all the input signals are added by the adder 36. At this time, the output of the light receiving unit 22b that receives the reflected light from the central portion 18b located on the information track 17b to be scanned in the light spot 18 is:
Although the waveform is equalized, the coefficient of the transversal filter 35 and the adder 36 are set so that the correlation between the output signal added by the adder 36 and the output signals of the sub-light receiving units 22a and 22c becomes zero. Are controlled by a coefficient control circuit. As a result, crosstalk is suppressed. Therefore, the output of the adder 36 removes the crosstalk component of the information bit 16 on the information track 17b on which the light spot 18 is to be scanned. This signal is amplified to an appropriate level by the amplifier 33 to be a reproduced signal.

As described above, according to the optical recording / reproducing apparatus of this embodiment, even if the optical disc has a significantly improved recording density by reducing the pitch of the information tracks, the recorded information can be transferred without crosstalk. To play.

FIG. 5 shows an optical recording / reproducing apparatus according to a second embodiment of the present invention. The present embodiment relates to an optical recording / reproducing apparatus for a magneto-optical disk, and a laser beam 51 emitted from a laser light source 50 is incident on a beam splitter 52 via a collimator lens 12. The laser light source 50 emits linearly polarized light 51 having a plane of polarization in a direction perpendicular to the optical axis. Further, the beam splitter 52 has a polarization characteristic in which the transmission reflectance differs depending on the polarization direction of the incident light,
For P-polarized light (electric field component parallel to the plane of incidence), the ratio of transmittance to reflectance is 10: 0, and for S-polarized light (electric field component perpendicular to the plane of incidence), the transmittance and reflectance are The ratio with the reflectance is 7: 3. The laser light 51 of the laser light source 50 corresponds to S-polarized light with respect to the beam splitter 52. In the direction in which the laser light 51 incident on the beam splitter 52 is reflected, an objective lens 14 and an optical disc 15 are arranged in this order, and the laser light 11 condensed by the objective lens 14 forms a light spot 18 on the optical disc 15. I do.

The laser light 51 reflected from the optical disk 15
Is converted into parallel light by the objective lens 14, passes through the beam splitter 52, and further passes through the analyzer 53 to the photodetector 22.
Is irradiated. The configurations of the photodetector 22 and the signal processing unit 30 for the detection signal by the photodetector 22 are the same as those in the first embodiment, and thus the description is omitted.

The analyzer 53 is, for example, as shown in FIG.
For example, the analyzer has an analyzer polarization plane with an analyzer angle α of 5 ° with respect to the P polarization direction, and transmits transmitted light A _{R + in the} analyzer polarization plane direction with respect to incident lights R ₊ and R ₋ having different polarization directions. And A
It has a characteristic of selectively transmitting incident light depending on the polarization direction of the incident light so as to transmit _R- . This analyzer 53
The change in the polarization direction of the laser light 51 reflected by the optical disk 15 is converted into a change in the light intensity, and the change is incident on the light receiving unit of the photodetector 22.

In the optical recording / reproducing apparatus having such a configuration, similarly to the first embodiment, the laser light 51 emitted from the laser light source 50 is irradiated on the optical disc 15 in a condensed state so as to form the light spot 18. You. The reflected light from the optical disk 15 is transmitted through the objective lens 14 and the beam splitter 52 and is incident on the analyzer 53. The analyzer 53 changes the polarization direction of the laser light reflected by the optical disk 15 to light intensity. And irradiates the light receiving units 22a to 22c of the photodetector 22. As in the first embodiment, each of the light receiving units 22a to 22c outputs a signal corresponding to the intensity of irradiated light, and a crosstalk component in a reproduction signal of an information bit of an information track on which the light spot 18 is scanned is The signal is removed by the signal processing unit 30.

As described above, even in the case of a magneto-optical type optical disk, even when the pitch of information tracks is reduced and the recording information density is remarkably improved, a good reproduction signal with suppressed crosstalk can be obtained.

FIG. 7 shows still another embodiment of the optical recording apparatus for a magneto-optical disk. The optical recording / reproducing apparatus of this embodiment is similar to the optical recording / reproducing apparatus shown in FIG.
The laser light 51 emitted from the optical disc 15 enters the beam splitter 52 via the collimator lens 12, and the laser light reflected by the beam splitter 52 is applied to the optical disc 15 via the objective lens 14.

In this embodiment, the laser beam reflected by the optical disk 15 is transmitted through the beam splitter 52 and is incident on the polarization beam splitter 61 via the half-wave plate 60. The half-wave plate 60 rotates the polarization direction of incident light by 45 °. Further, as shown in FIG. 8, the polarization beam splitter 61 forms incident lights R ₊ and R _{− having} different polarization directions.
On the other hand, the transmitted light P _{R +} and P
_R- is transmitted, and reflected light S _{R +} and S _R- are reflected in the S polarization direction, respectively.

The laser beam transmitted through the polarization beam splitter 61 is applied to the photodetector 25, and the laser beam reflected by the polarization beam splitter 61 is applied to the photodetector 26. Each of the photodetectors 25 and 26 has three light receiving portions 25a to 25c and 26a to 26c, respectively, similarly to the photodetector 22 of each of the above embodiments, and the sub light receiving portions 25a and 26a The reflected light of one side edge 18a in the direction orthogonal to the track direction in the 15 light spots 18 is received, and the sub light receiving portions 25c and 26c are connected to the other side edge 18c.
The reflected light is received. Each of the main light receiving portions 25b and 26b is connected to each side edge portion 18a and 18c of the light spot 18.
And receives the reflected light of the central portion 18b excluding the above.

The outputs of the light receiving sections 25a to 25c of each photodetector 25 are as follows:
The signals are respectively supplied to the + terminals of the differential amplifiers 37a to 37c of the signal processing unit 30 via the amplifiers 27a to 27c.
The outputs of the light receiving units 26a to 26c of the photodetectors 26 are respectively supplied to the minus terminals of the differential amplifiers 37a to 37c of the signal processing unit 30 via the amplifiers 28a to 28c.

The output of each operational amplifier 37a and 37c is A /
The signal is input to the adder 36 via the D converters 38a and 38c, and the output of the operational amplifier 37b is supplied to the transversal filter 35 via the A / D converter 38b. The output of the transversal filter 35 is provided to an adder 36, and the adder 36 adds all inputs and outputs the result. The output of the adder 36 is supplied to a coefficient control circuit 34 as in the above embodiments, and the output of the coefficient control circuit 34 is supplied to a transversal filter 35. The functions of the transversal filter 35, the adder 36 and the coefficient control circuit 34 are as follows.
This is the same as each of the above embodiments.

In the present embodiment, the laser beams applied to the photodetectors 25 and 26 are the transmitted light and the reflected light of the polarization beam splitter 61, respectively, and have opposite phases. On the other hand, since the noise due to the light quantity fluctuation is in phase, the noise can be reduced by calculating the output difference between the detectors 25 and 26 by the differential amplifiers 37a to 37b.

As described above, also in the optical recording / reproducing apparatus of this embodiment, information recorded on a magneto-optical disk having a reduced information track pitch can be reproduced with high accuracy.

In each of the above embodiments, the photodetector is configured such that the light receiving section is divided into three parts. However, the reflected light from the portion of the light spot adjacent to the information track is divided into two or more parts. Alternatively, a photodetector having a sub-light receiving unit for receiving light may be used.

In each of the above embodiments, the optical disk
When the moving speed of the light spot 15 changes and the scanning speed of the light spot 18 fluctuates, a coefficient that can cancel the speed fluctuation is set, and the coefficient is calculated by each integrator 41 of the transversal filter 35. The integration may be performed.

[0039]

According to the present invention, information to be irradiated with a light spot is obtained.
Photodetector whose light receiving area is divided into three parts
This information track is received by the main light receiving area of
The reflected light from the information track adjacent to the
Received. And the output signal from the main light receiving area
Is output signal from the sub-light receiving area by the signal processing unit.
Waveform equalization is performed so that there is no correlation. As a result, the main
The output signal from the light area is the output signal from the sub light receiving area.
Is not interfered with by the shadow of crosstalk
The sound can be reliably eliminated. Therefore, according to the present invention,
The effect of crosstalk from adjacent information tracks
Information tracks can be reliably eliminated.
Even if the optical recording medium is
Can be achieved. In addition, the present invention
According to the above, only one light beam is required for reading information.
Thus, power consumption can be reduced. In addition, the semiconductor that is the light source
Only one laser is required, and the number of light sources for the optical system such as the objective lens
The number of devices can be reduced to a small size and simple.
Can be Therefore, according to the present invention, low power consumption and small
Optical recording / reproducing device with simple and simple device configuration can be realized.
Can also be achieved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an optical recording / reproducing apparatus for a phase change optical disc according to a first embodiment of the present invention.

FIG. 2A is a schematic diagram showing the relationship between an information track and an optical spot on an optical disk, and FIGS. 2B to 2E show reflected light from the information track and output from each light receiving unit of a photodetector, respectively. It is a graph shown.

FIG. 3 is an enlarged view of a main part of the optical recording / reproducing apparatus.

FIG. 4 is a configuration diagram illustrating an example of a transversal filter used in a signal processing unit.

FIG. 5 is a configuration diagram of an optical recording / reproducing apparatus for a magneto-optical disc according to a second embodiment of the present invention.

FIG. 6 is a graph showing polarization characteristics of a beam splitter used in the optical recording / reproducing apparatus.

FIG. 7 is a configuration diagram of an optical recording / reproducing apparatus for a magneto-optical disk according to a third embodiment of the present invention.

FIG. 8 is a graph showing polarization characteristics of a polarization beam splitter used in the optical recording / reproducing apparatus.

FIG. 9 is a configuration diagram showing a conventional optical recording / reproducing apparatus for a phase change optical disk.

FIG. 10 is a configuration diagram showing a conventional optical recording / reproducing apparatus for a magneto-optical disk.

FIG. 11 is a block diagram showing another example of a conventional optical recording / reproducing apparatus for a magneto-optical disk.

FIG. 12A is a plan view showing an example of an information track on an optical disc, and FIG. 12B shows a detection signal thereof.

FIG. 13A is a plan view showing another example of an information track on an optical disc, and FIG. 13B shows a reproduction signal of a conventional optical recording / reproducing apparatus.

[Explanation of symbols]

 10 Laser light source 11 Laser light 15 Optical disk 16 Information bit 18 Light spot 22 Photodetector 22a, 22c Sub-light receiving part 22b Main light receiving part 30 Signal processing part 34 Coefficient control circuit 35 Transversal filter 36 Adder

Claims (3)

(57) [Claims] 1. Information is recorded on mutually parallel information tracks.
1 for reproducing information from the recorded optical recording medium
Irradiate a single light spot on two information tracks and
Recording that reproduces information based on the reflected light of an optical spot
A playback device, wherein the light spot illuminated on the information track is
Main receiver to receive the reflected light from the information trackregion
And the direction of the information track is adjacent to the
Receives reflected light from partsBoth sides of the main light receiving area
And a sub-light receiving area provided inLight detection
Vessels,The output signal from the main light receiving area is output from the sub light receiving area
Waveform equalization so that it does not correlate with the output signal of Signal processing section
An optical recording / reproducing apparatus comprising: 2. The optical recording / reproducing apparatus according to claim 1, wherein the optical disk is of a phase change type. 3. The optical recording / reproducing apparatus according to claim 1, wherein the optical disk is of a magneto-optical type.