JPH11161980A - Tracking error signal detector for optical head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To comply with a recordable optical disk and a reproduction exclusive optical disk by the same photodetector and to prevent the occurrence of a large offset in a tracking error signal by a push-pull method due to the positional deviation of optical parts, etc. SOLUTION: This device is provided with a laser beam source, a lens for converging a light beam outputted from the laser beam source on an optical disk, a photodetector for receiving a light beam reflected by the optical disk and a signal processing circuit for generating a tracking error signal from the output of the photodetector. The photodetector 5 receives light beams divided into continuous four areas D, A, B, C in this order by three divided lines being the divided lines in the tracking direction of the optical disk and provided at equal intervals. By representing the output signals from the areas D, A, B, C by D, A, B, C, respectively, the signal processing circuit generates a tracking error signal based on the difference of A+C and B+D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a track error signal detecting device for an optical head which supports different types of optical disks in an optical disk device for recording or reproducing information using light.

[0002]

2. Description of the Related Art An optical head for an optical disk apparatus needs a function of condensing a minute spot on a recording medium and detecting and correcting a position shift of the spot on the recording medium in a focus direction and a direction perpendicular to a track. Become. There are several methods for detecting a track misalignment, that is, a track error signal, and these are used properly according to the type of recording medium.

For example, in a recordable optical disk, a pre-group, which is a track guide groove, is provided on a medium surface. The reflected light from the medium has a symmetrical light amount distribution when the spot is at the center of the groove, but the reflected light distribution in the direction perpendicular to the track becomes asymmetric when the spot is off the center of the groove. This change in distribution is detected by a two-segment photodetector having a dividing line in the track parallel direction, and a track error signal can be obtained by creating a difference between the two detection signals. This method is generally called a push-pull method.

On the other hand, a read-only optical disk in which prepits are formed in advance on a medium such as a compact disk requires a different detection method. As a device for detecting a track error signal from the distribution of the medium reflected light, as shown in FIG. 4, a device using a quadrant photodetector 55 divided into a cross by two dividing lines in the track parallel direction and the orthogonal direction is used. is there. In the two signals (A + D) and (B + C) obtained by adding the diagonals of the four outputs, a time difference corresponding to the track shift occurs in the signal change when the spot moves on the prepit. Using this time difference, a track error signal can be obtained by applying some signal processing methods called a phase difference detection method or a heterodyne method.

[0005] As described above, when one optical head is used for a recordable optical disk and a read-only optical disk, the same optical system needs to support different track error detection systems. For example, in the four-division photodetector 55 shown in FIG. 4, a track error signal is formed by a push-pull method by forming (A + C) and (B + D) as left and right area signals instead of the sum of diagonals. It can be used for both optical discs.

[0006]

However, in such an optical system that receives all the reflected light 6 from the optical disk, as shown in FIG. 5, the light is displaced due to the displacement of the lens or the displacement of the optical parts. When the position of the reflected light 6 on the detector 55 moves, the light receiving area on the photodetector becomes asymmetric, and a large offset occurs in the track error signal by the push-pull method. Such an offset is not preferable because it causes deterioration in spot tracking accuracy.

As a method of suppressing track offset by the push-pull method, it is possible to limit the width of the photodetector 56 as shown in FIG. 6 and reduce the change in the light receiving area with respect to the movement of the position of the reflected light 6. It is. However, if the width of the photodetector is limited as described above, a region in which the amount of received light due to the pre-pit greatly changes cannot be used, and the detection sensitivity in the phase difference detection method or the heterodyne method is reduced.

[0008]

An object of the present invention is to improve the disadvantages of the prior art, and in particular, it is possible to cope with a recordable optical disc and a read-only optical disc with the same photodetector, and to reduce the displacement of optical components. It is an object of the present invention to provide an optical head track error signal detection device that does not cause a large offset in a track error signal by the push-pull method.

[0009]

To achieve the above object, according to the first aspect of the present invention, a laser light source, a lens for condensing light output from the laser light source on an optical disk, and a lens reflected by the optical disk. And a signal processing circuit for generating a track error signal from the output of the photodetector. The photodetector is divided into four areas D, which are divided lines along the track direction of the optical disc and are consecutively arranged by three equally spaced division lines.
The light split into A, B, and C is received. The signal processing circuit converts the output signals from the areas D, A, B, and C to D,
As A, B, and C, a track error signal is generated based on the difference between A + C and B + D.

According to the second aspect of the present invention, the photodetector comprises four regions D, A, and B which are successively divided by three division lines provided at equal intervals along the track direction of the optical disk. , C.

According to the third aspect of the present invention, a diffractive element is provided between the optical disk and the photodetector for transmitting the lights of the regions D, A, B, and C individually to predetermined positions.

According to the fourth aspect of the invention, between the optical disk and the photodetector, the light in the areas A and C is diffracted in the same direction, and the light in the areas B and D is diffracted in the other same direction. A diffraction element is provided. The photodetector is configured to receive light in the region A and the region C by one light receiving element and receive light in the region B and the region D by the other light receiving element.

According to the present invention, the track error signal is detected by the push-pull method, and corresponds to the tracking control of the recordable optical disk.

According to the fifth aspect of the present invention, the reflected light from the optical disk is further divided into upper and lower regions by dividing lines in a direction perpendicular to the track direction. The upper four regions of the eight regions configured in this manner are sequentially defined as regions D, A, B, and C, and the lower four
The areas are assumed to be areas B, C, D and A in the same order. The signal processing circuit sets the output signals of the photodetector by receiving light in the regions A, B, C, and D to A, B, C, and D, respectively, and A +
A track error signal can be detected by a phase difference detection method or a heterodyne method from the output difference between D and B + C.

According to the present invention, a track error signal can be detected by a phase difference detection method or a heterodyne method, and tracking control of a read-only optical disk on which prepits are formed can be performed.

According to the sixth aspect of the present invention, the reflected light from the optical disk is further divided into upper and lower regions by a dividing line perpendicular to the track direction. The upper four regions of the eight regions configured as described above are sequentially referred to as regions D, A, B, and C. The lower four areas are assumed to be areas B, C, D, and A in the same order. The signal processing circuit sets the output signals of the photodetector by receiving light in the regions A, B, C, and D to A, B, C, and D, respectively, and uses the astigmatism method based on the signal difference between A + D and B + C. It is configured so that a focus position shift signal of the lens can be detected.

According to the seventh aspect of the invention, the reflected light from the optical disk is further divided into upper and lower regions by a dividing line in a direction orthogonal to the track direction. The upper four regions of the eight regions configured as described above are sequentially referred to as regions D, A, B, and C. The lower four areas are assumed to be areas B, C, D, and A in the same order. Further, an astigmatic optical element is provided between the optical disk and the photodetector. Then, the direction in which the astigmatism is generated by the astigmatism optical element is set so as to be 45 degrees with respect to the track direction of the optical disc. The photodetector is arranged between two focal points generated in the ± 45 degrees direction with respect to the track direction by the astigmatism optical element. The signal processing circuit
Assuming that the output signals of the photodetector by receiving the light in the areas A, B, C, and D are A, B, C, and D, respectively, the focus position shift of the lens by the astigmatism method from the signal difference between A + D and B + C It was configured to be able to detect signals.

According to the invention described in claim 6 or 7, the tracking control of both the recordable optical disk and the read-only optical disk can be performed, and at the same time, the same photodetector detects the focus position shift signal.

With these, the above-mentioned object is to be achieved.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIGS. 1 and 2.

In FIG. 1, light emitted from a laser light source 3 is reflected by a beam splitter 4, passes through a lens 2, and is condensed on the optical disk 1 as a minute spot.
The reflected light from the optical disk 1 passes through the lens 2 and the beam splitter 4 and is received by the split-type photodetector 5. As shown in FIG. 2, the photodetector 5
Three division lines formed at substantially equal intervals in a direction substantially parallel to the track direction, and one division line substantially orthogonal to the track direction.
It is divided into eight regions by one dividing line. Then, as shown in FIG. 2, a signal processing circuit is configured to electrically connect outputs of two regions that are not adjacent to each other and obtain four signal outputs A, B, C, and D. In other words, the photodetector 5 has four areas newly added to the outside in addition to the conventional four-part division of the cross, and as shown in FIG.
It is divided. The four outer regions are electrically connected to the four inner predetermined regions (regions having the same reference numerals A, B, C, and D).

Further, a combination of four signal outputs,
The track error signal of the pre-group medium is changed by the difference signal between (A + C) and (B + D) to (A + D) and (B + C).
Thus, a track error signal of the pre-pit medium is formed. When the phase difference detection method or the heterodyne method is used for a read-only disk or the like, if (A + D) and (B + C) are formed, a signal of the diagonal sum exactly the same as that of the conventional FIG. 4 can be formed. When a push-pull signal is used for a recording disk, a track error signal can be formed from a difference signal between (A + C) and (B + D). In this case, it can be seen that the signals in the four outer regions are added to signals opposite to each other as compared with the conventional push-pull method two-segment photodetector. If the width of the divided area is appropriately set in such a connection, the focus offset due to the displacement of the reflected light 6 can be considerably reduced as in the case of limiting the width of the photodetector 5 as shown in FIG. I can do it.

Here, as one proposal, if a preamplifier is provided for each of the outputs of the eight photodetection areas in FIG. 2 and the output signals of only the inner four divided areas are used, the same detection as in FIG. Will be possible. However, in such a configuration, a decrease in S / N due to an increase in the number of preamplifiers required to detect an information signal becomes a problem, and the reproduction characteristics deteriorate. On the other hand, when the push-pull method is used in FIG. 2, the detection sensitivity is slightly reduced as compared with the conventional case where the width of the photodetector is limited as shown in FIG. Can be obtained, and at the same time, good reproduction characteristics can be secured.

Next, another embodiment of the present invention will be described with reference to FIG.

In this embodiment, in the optical head track error signal detecting device, the light emitted from the laser light source 3 is condensed on the optical disk 1 as a minute spot. Light reflected from the optical disk 1 is received by a split-type photodetector 5. Astigmatism is generated between the photodetector 5 and the optical disk 1 in the direction of the track of the optical disk 1 and approximately 45 degrees with respect to the reflected light from the optical disk 1, and the two focal line forming positions are In the axial direction, an astigmatic optical element 7 is provided which is arranged before and after the photodetector 5.
As in the previous embodiment, the photodetector 5 is divided into eight parts by three parting lines provided at substantially equal intervals in a direction substantially parallel to the track direction of the optical disk 1 and one parting line substantially perpendicular to the track direction. It is divided into regions. Also, as in the previous embodiment, four signal outputs are formed by electrically connecting outputs of two areas that are not adjacent to each other as shown in FIG.

The astigmatism optical element 7 is, for example, a cylindrical lens. As described above, the direction in which astigmatism is generated is set at 45 degrees with respect to the track direction, and the two astigmatisms generated in the ± 45 degree directions are set. The photodetector 5 is installed in the middle of the line.
Then, the signal processing circuit calculates (A + D) and (B
By forming the difference signal of (+ C), a focus position shift signal by the astigmatism method can be obtained (not shown).
In this case, the same operation and effect as those of the previous embodiment can be obtained, and in addition, there is an advantage that all the position shift signals including the focus position shift signal can be detected by one photodetector 5. Here, astigmatism generated as it passes through the parallel-plate beam splitter 4 as convergent light can be used.

Here, in each of the above embodiments, the divided shape of the photodetector is specified. However, the reflected light from the optical disk is divided into the same pattern shape as described above by a hologram element or a prism, and each of them is independent. The same effect can be realized by receiving light at the same time. Further, two regions belonging to the respective signals A to D are diffracted in the same direction by a hologram or the like and detected by one light receiving portion, and the number of light receiving portions is reduced from eight to four.
This is also effective for simplifying the photodetector configuration.

[0028]

According to the present invention, the light reflected from the optical disc is divided into four areas by the dividing line in the track direction of the optical disc. D, A, B, C, etc., which are received by a photodetector, and a signal detection circuit detects A + C and B +
Since the track error signal is detected by the push-pull method from the difference D, it is possible to significantly suppress the occurrence of the offset due to the deviation of the light spot.

According to the fifth aspect of the present invention, the signal processing circuit compares the D + A and B + C signals, thereby enabling detection of the track error signal by the phase difference detection method or the heterodyne method, thereby maintaining the effect of the first aspect. However, both a recordable optical disk and a read-only optical disk can be supported.

According to the sixth and seventh aspects of the present invention, it is possible to detect the focus position shift signal using the same photodetector by the astigmatism method while maintaining the above-mentioned effect. An excellent optical head track error signal detecting device can be provided.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical system showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a light receiving unit of the photodetector shown in FIG.

FIG. 3 is a configuration diagram of an optical system showing another embodiment of the present invention.

FIG. 4 is a diagram illustrating a positional relationship between a photodetector and a light spot for explaining a conventional example.

FIG. 5 is a diagram illustrating a positional relationship between a photodetector and a light spot in an offset generation state for explaining a conventional example.

FIG. 6 is a configuration diagram of a photodetector showing another conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Lens 3 Laser light source 4 Beam splitter 5 Photodetector 6 Reflected light 7 Astigmatism optical element

Claims (7)

[Claims] 1. A laser light source, a lens for condensing light output from the laser light source on an optical disc, a photodetector for receiving light reflected on the optical disc, and a track error detected from the output of the photodetector. A signal processing circuit for generating a signal, the track error signal detecting device for an optical head, wherein the photodetector is a dividing line along a track direction of the optical disc and three dividing lines provided at equal intervals Receives the light divided into four regions D, A, B, and C which are sequentially continuous according to the following. The signal processing circuit outputs the output signals from the regions D, A, B, and C to D, A, B, and C, respectively. As C, A + C and B +
A track error signal detection device for an optical head, wherein a track error signal is generated based on a difference between the track error signal and a track error signal. 2. The photodetector comprises four regions D, A, B, and C, which are dividing lines along a track direction of the optical disk and are consecutively arranged by three dividing lines provided at equal intervals.
2. The optical head track error signal detecting device according to claim 1, wherein the track error signal detecting device is divided into: 3. A diffractive element is provided between the optical disk and the photodetector, the diffractive element transmitting the light of the regions D, A, B, and C individually to predetermined positions. 2. The track error signal detection device for an optical head according to claim 1. 4. A diffractive element between the optical disc and the photodetector, which diffracts the light in the areas A and C in the same direction and diffracts the lights in the areas B and D in the other same direction. Wherein the photodetector is configured to receive the light of the area A and the area C by one light receiving element and receive the light of the area B and the area D by the other light receiving element. Item 2. A track error signal detection device for an optical head according to Item 1. 5. The reflected light from the optical disk is further divided into upper and lower regions by dividing lines in a direction orthogonal to the track direction, and the upper four regions among the eight regions constituted by the divided lines are sequentially divided into regions D, A, and D. B, C, and the lower four regions are regions B, C, D, and A in the same order, and the signal processing circuit receives the light of the regions A, B, C, and D, and the output signal of the photodetector. To A,
2. A method as claimed in claim 1, wherein a track error signal can be detected by a phase difference detection method or a heterodyne method from the output difference between A + D and B + C.
4. An optical head track error signal detection device according to claim 2. 6. The reflected light from the optical disk is further divided into upper and lower regions by a dividing line in a direction orthogonal to the track direction, and the upper four regions among the eight regions formed by the division lines are sequentially divided into regions D, A, and D. B, C, and the lower four regions are regions B, C, D, and A in the same order. The signal processing circuit outputs an output signal of the photodetector by receiving light in the regions A, B, C, and D. To A,
2. A method according to claim 1, wherein the focus position shift signal of the lens is detected by the astigmatism method from the signal difference between A + D and B + C as B, C, and D.
6. The optical head track error signal detecting device according to 2, 3, or 5. 7. The reflected light from the optical disk is further divided into upper and lower regions by a dividing line in a direction perpendicular to the track direction, and the upper four regions of the eight regions formed by the division lines are sequentially divided into regions D, A, and D. B and C, and the lower four areas are areas B, C, D, and A in the same order. An astigmatism optical element is provided between the optical disc and the photodetector. The direction in which the astigmatism is generated is set so as to be 45 degrees with respect to the track direction of the optical disc. The photodetector includes two astigmatism optical elements that generate in the ± 45 degrees direction with respect to the track direction. The signal processing circuit is arranged in the middle of the focal point, and outputs the output signals of the photodetector by receiving the light in the areas A, B, C, and D to A,
2. A method according to claim 1, wherein the focus position shift signal of the lens is detected by the astigmatism method from the signal difference between A + D and B + C as B, C, and D.
6. The optical head track error signal detecting device according to 2, 3, or 5.