JP2003178482A - Photodetector, signal processing circuit, and optical information reproducing device using photodetector and signal processing circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To dramatically reduce influence of disturbance experienced in detecting a defocusing signal by means of an astigmatism system in reproducing a DVD-RAM disk or the like, and to dramatically reduce influence of offset accompanied by object lens displacement experienced in detecting a tracking error signal by means of a push-pull system, and to realize an optical disk device having high general-purpose properties and complying with the reproduc tion of existing optical disks, including CD, CD-ROM, CD-R as well as high- density disks, including DVD-RAM, DVD-ROM disks by using a simple optical head. <P>SOLUTION: Three optical beams separated by diffraction grating are irradiated at the optical disk at its prescribed position. A 12-split photodetector having a prescribed configuration is provided. Thereby a good defocusing signal and a tracking error signal are obtained and the optical disk device is realized, which has the high general-purpose properties and is capable of reproducing a signal in a plurality of optical disks having different recording densities and different disk configurations by using the simple optical head. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus (hereinafter referred to as an optical disk apparatus) used for reproducing a data signal recorded on an optical information recording medium (hereinafter referred to as an optical disk). In particular, the present invention relates to improving the performance of various error signal detection for controlling the light spot position.

[0002]

2. Description of the Related Art Conventionally, there are a knife edge method (Foucault method), a beam size method, an astigmatism method, etc. as a method for detecting a focus position shift signal in an optical disk apparatus, but the optical system is simple and easy to adjust. The astigmatism method is most commonly used from the viewpoint of ease of combination with the tracking error signal detection method. However,
This astigmatism method has a serious problem that a defocus signal is easily disturbed when a light spot irradiated on the optical disk crosses a recording track of the disk. The influence of the disturbance is particularly remarkable in a land-groove type disk represented by a DVD-RAM disk which is planned to be commercialized in the near future. This is because in a land-groove type optical disc, the width of the guide groove (groove) provided in the disc and the width of the space between the guide grooves (lands) are almost equal, and the groove depth of the guide groove is the wavelength of the reproducing laser beam ( Since it is set to about ⅙ to 1/7 with respect to (650 nm), the main cause is that the amplitude of a so-called push-pull signal generated by the diffraction of the guide groove becomes large.

As a conventional means for reducing the disturbance generated in the defocus signal of the astigmatism method, for example, a method of shielding the central portion of the detection light beam (Japanese Patent Application No. 4-31450).
No. 0) and a method of reducing the rotation by adjusting the rotation of the objective lens (Japanese Patent Publication No. 5-68774) and the like are disclosed, but the current situation is that no sufficient reduction effect is obtained. Therefore, conventionally, in the above-mentioned optical disk device for DVD-RAM disk, there is no choice but to adopt the knife edge method or the beam size method in which the configuration and adjustment of the optical system are complicated.

On the other hand, as a method of detecting the tracking error signal in the optical disk device, there are a three spot method and a push pull method as typical methods. The three-spot method is widely used for conventional read-only discs such as CDs and CD-ROMs because of the simplicity of the optical system, the ease of adjustment, and the resistance to disturbance. On the other hand, DVD
In an optical disc device for reproducing a large capacity read-only disc such as a ROM disc, (1) the sensitivity of the tracking error signal cannot be sufficiently obtained due to the influence of the narrowing of the recording track pitch. (2) The relative positional adjustment accuracy of the three light spots radiated on the disk must be made much more severe than that of the CD. Due to such reasons, the 3-spot method is shunned, and the phase difference detection method (differential phase detection method) that detects the tracking error signal by arithmetic processing from the time change of the reflected light intensity distribution of one light spot is widely adopted. Has been done.
On the other hand, in an optical disk device for a read / write type disk represented by a DVD-RAM disk, due to a problem of offset generation due to a difference in disk reflected light amount between the leading sub-spot and the trailing sub-spot during recording operation, Again, the 3-spot method cannot be used, and the push-pull method, which is another typical tracking error signal detection method, is most commonly used.

By the way, this push-pull method has an excellent advantage that a highly sensitive tracking error signal can be obtained by a relatively simple optical system, but on the other hand, when the objective lens is displaced in the tracking direction, it is accompanied by it. It has a serious problem that a large offset occurs in the tracking error signal. Therefore, a means called a differential push-pull method (differential push-pull method) has been disclosed as an effective method for significantly reducing the tracking error signal offset due to such displacement of the objective lens. (Optical Memory Symposium '86 Proceedings (1986) PP.127-132) This method irradiates an optical disk with three optical spots as in the three-spot method, and the tracking error detected by the push-pull method from each optical spot. By performing a predetermined subtraction process on the signal, the offset component due to the displacement of the objective lens is canceled.

[0006]

As described above, in the present situation, the most suitable tracking error signal detection method is completely different depending on the type of the optical disk. However, these optical discs are already in widespread use, or will surely be in widespread use in the near future. Therefore, as an optical disk device, it is naturally desirable that a single device can satisfactorily support all of these plural types of optical disks. However, as described above, under the present circumstances, there is no defocus detecting means having a simple structure and capable of obtaining a good defocus signal without the influence of disturbance, and various tracking error signal detecting means are simply provided in one optical disc. There is an unavoidable problem that the structure of the optical head and the internal structure of the photodetector become extremely large and complicated when they are incorporated in the device. That is, in order to realize a more practical optical disc device, a good defocus signal free from the influence of disturbance can be obtained while using a simple optical head or a photodetector with a simple structure, and the tracking error signals described above can be obtained. There is a need for completely new optical means that can realize all the detection means.

In view of the above situation, the problem to be solved by the present invention is to use the astigmatism method as the defocus signal detecting means by one system of detection optical system and photodetector of simple structure. Disclosed is a new optical means capable of significantly reducing the influence of such a disturbance, and at the same time, significantly reducing the influence of the offset generated due to the displacement of the objective lens while using the push-pull method as the tracking error signal. To provide a specific photodetector configuration and a signal processing circuit configuration to realize it. Furthermore, while using an optical head consisting of a simple detection optical system and a photodetector with a simple configuration, the optimum defocus signal detection method or tracking error signal detection method can be selectively selected for a plurality of different types of optical disks. An object of the present invention is to provide a practical optical disk device that can be switched to and applied.

[0008]

In order to solve the above problems, according to the present invention, a semiconductor laser light source and an optical branching element for branching a light beam emitted from the semiconductor laser light source into at least three light beams are provided. A condensing optical system for condensing the light beams branched into the three beams and irradiating predetermined light spots on the optical disc with independent light spots; and a photodetector for receiving the respective light beams reflected by the optical disc, The photoelectric conversion signal obtained from the photodetector is subjected to predetermined arithmetic processing to generate a defocus signal and a tracking error signal of the light spot irradiated on the optical disc and recorded on the optical information recording medium. In an optical disc device including at least a signal processing circuit for reproducing a data signal, the three optical beams incident on the photodetector are used as the photodetector. The light receiving surface has a total of 12 divisions, and the light receiving areas of the first, second, and third four divisions, which are divided into a square shape, are arranged at the respective positions where the light is irradiated, and the light reception of the 12 divisions is performed. To transmit the photoelectric conversion signal from the photodetector to the signal processing circuit by connecting a predetermined signal line among the signal lines transmitting the photoelectric conversion signal obtained from each of the surfaces inside the photodetector The photodetector is limited to at most 9 signal lines.

Further, as a signal processing circuit mounted on the optical disk device, each photoelectric conversion signal obtained from the photodetector is subjected to predetermined arithmetic processing to irradiate a predetermined position on the optical information recording medium. At least an arithmetic circuit is provided for outputting a signal obtained by adding or subtracting the defocus signal by the astigmatism method and the tracking error signal by the push-pull method for each of the three generated light spots.

Further, the signal processing circuit records the optical information for each light spot with respect to two predetermined light spots out of the three light spots irradiated to the predetermined position on the optical information recording medium. It has a function of detecting a photoelectric conversion signal corresponding to the total amount of light reflected from the medium and generating a tracking error signal by the three-spot method from the difference signal.

Further, the signal processing circuit is provided with a differential phase detection system (phase difference detection) for at least one light spot among the three light spots irradiated at a predetermined position on the optical information recording medium. method)
Is provided with a tracking error signal.

Furthermore, as an optical disk device, at least the photodetector and the signal processing circuit are provided, and the signals obtained from the photodetector and the signal processing circuit are different depending on the kind of the optical disk applied to the optical disk device. It has a function of selectively switching and outputting a predetermined defocus signal detection method and a tracking error signal detection method.

Further, the optical disk device includes at least two or more semiconductor laser light sources and one or two optical beams for branching at least three optical beams emitted from each semiconductor laser light source. And a function of selectively switching the semiconductor laser light source to be turned on depending on the type of optical disk applied to the optical disk device.

A diffraction grating is used as the light branching element mounted on the optical disk device.

In the photodetector, a light receiving surface and a current-voltage conversion amplifier for converting a signal current photoelectrically converted by the light receiving surface into a signal voltage are provided inside the package.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments will be described below with reference to the drawings.

FIG. 1 is a perspective view schematically showing a first embodiment of the optical system configuration of an optical head which is a main part of the optical disk device of the present invention.

The semiconductor laser light source 1 has, for example, a wavelength of 650n.
It is an element that emits a laser beam of m. The laser light flux emitted from the semiconductor laser light source 1 is incident on the diffraction grating 2, and the 0th-order light that passes through the diffraction grating 2 as it is and the + 1st-order diffracted light and the -1st-order diffracted light that separate and progress from the 0th-order light at a predetermined diffraction angle. Is separated into at least three light beams. And these 3
The light flux of the book enters the collimator lens 4 through the cubic beam splitter 3, and the collimator lens 4
After being converted into a parallel light flux by the laser beam, the light beam passes through the raising mirror 5 and the objective lens 6, and then is condensed on the recording surface of the optical disk 7 such as a DVD-RAM disk or a DVD-ROM disk, and the light spots 100, 101, 10 are formed.
Form 2. Further, the optical disk 7 is reflected to follow the same optical path as the outward light, the objective lens 6, the rising mirror 5, the collimating lens 4, the reflecting surface of the beam splitter 3 to be reflected, and the cylindrical lens 8 to detect light respectively. The light is focused on a predetermined light receiving surface of the container 9.

As shown in FIG. 1, the photodetector 9 has three light receiving regions 200, 201 and 202 which are divided into four in a square shape and are arranged substantially linearly. It has a face. 0 reflected from optical disk 7
The light fluxes of the second-order light, the + 1st-order diffracted light, and the -1st-order diffracted light are approximately at the centers of the light-receiving regions 200, 201, and 202, that is, the vertical and horizontal dividing lines in the light-receiving regions intersect with each other and the intensity of the light beam. The light is focused at a position where the centers are almost the same. At this time, since each light beam is given a predetermined astigmatism by the cylindrical lens 8, a defocus signal is detected from each light receiving region by an astigmatism method as described later. Similarly, a tracking error signal by the push-pull method can be detected for each light receiving area. (Note that the astigmatism method and the push-pull method itself are publicly known contents, and therefore detailed description thereof is omitted.) The two-dimensional actuator 10 is attached to the objective lens 6. The two-dimensional actuator 10 automatically controls the position of the objective lens on the basis of a predetermined defocus signal and a tracking error signal obtained from the photodetector 9 so that the light spots 100, 101 and 102 are always set to a predetermined recording track of a desired recording track. The position is properly illuminated.

By the way, in the present embodiment, the optical disk 7
Light spots 100 and 101, 102 irradiated on top
The irradiation position interval in the disk radial direction is
-It is set to match approximately half the guide groove pitch of the RAM disk. That is, for example, as shown in FIG. 2B, when the light spot 100 of the 0th order light is located directly above the guide groove 301 of the disc, the light spot 101 of the + 1st order diffracted light and the −1st order diffracted light. Light spot 102
Are located directly above the adjacent guide grooves 300. Even when the light spot irradiation position is relatively displaced with respect to the guide groove, for example, the positional relationship as shown in (a) or (c) of FIG. 2 is always maintained. On the other hand, the disc reflected light flux has a unique intensity distribution pattern that periodically changes according to the change of the relative position of the light spot irradiation position and the disc guide groove due to the influence of diffraction by the guide groove. . The intensity distribution patterns of the reflected light flux of the 0th-order light spot 100 and the reflected light fluxes of the + 1st-order diffracted light spot 101 and the -1st-order diffracted light spot 102 are as shown in FIG.
As shown in the figure, the changes are shown as if the left and right were completely reversed.

By the way, if a defocus signal by the astigmatism method is detected from these reflected light beams, there is a problem that a large disturbance is likely to occur in the defocus signal detected as described above. The main cause is the periodic change of the intensity distribution pattern of the reflected light flux due to the influence of diffraction in the groove and the leakage of the push-pull signal component caused by it. Therefore, FIG.
As shown in (b), when comparing the defocus signal obtained from the reflected light flux of the light spot 100 with the defocus signal obtained from the reflected light flux of the light spot 101 and the light spot 102, the waveform of the defocus signal itself is While the components are almost the same, the phase of the disturbance component generated in the signal is almost completely inverted. Therefore, when the defocus signal obtained from the reflected light beam of the light spot 100 and the defocus signal obtained from the reflected light beam of the light spot 101 or the light spot 102, or the sum signal of both signals are added,
As shown in (c), the defocus signal itself is doubled, while the disturbance component is almost completely canceled, and a good defocus signal can be obtained.

The phenomenon as described above is similarly applied to the tracking error signal detection by the push-pull method. That is, in general, when the tracking error signal is detected by the push-pull method, when the objective lens is displaced in the tracking direction, the light spot irradiated on the light receiving surface is also displaced accordingly, and FIGS.
A large offset occurs in the detected tracking error signal as shown in FIG. This offset is
As in (a) and (b), the tracking signal detected from the reflected light flux of the light spot 100 and the tracking signal detected from the reflected light flux of the light spots 101 and 102 are generated in the same direction and to the same extent. On the other hand, the tracking error signal itself is exactly the same as the reason described in the description of the defocus signal above, and the phase of the signal detected from the reflected light beam of the light spot 100 and the light spots 101 and 10 are the same.
The phase of the signal detected from the reflected light flux of No. 2 is almost completely inverted. From this, by subtracting the tracking error signal detected from the disc reflected light of each spot, only the offset component is canceled and the tracking error signal shown in FIG.
It is possible to obtain a good tracking error signal in which the offset is significantly reduced as shown in (c).

The present invention is to detect good defocus signal and tracking error signal by utilizing the above principle.

FIG. 5 is a plan view and a schematic block diagram showing a first embodiment of the photodetector and the signal processing circuit of the present invention.

As shown in the figure, in the photodetector 9, the light receiving surface is first divided into four in a square shape, and each divided light receiving surface is represented by symbols a, b, c and d.
The light receiving regions 200 represented by the above are arranged, and the divided light receiving surfaces are provided on both sides thereof in the same manner as the light receiving regions 200 by the symbols e, f,
A four-divided light receiving area 201 represented by g and h and a four-divided light receiving area 202 represented by symbols i, j, k, and 1 are arranged. Then, on the light receiving area 200,
The disc reflected light of the on-disc light spot 100 is condensed to form a detection light spot 110. Similarly, the disc reflected light of the on-disc light spot 101 is condensed on the light receiving area 201, and the disc reflected light of the on-disc light spot 102 is condensed on the light receiving area 202 to form detection light spots 111 and 112. There is.

First, the detected currents photoelectrically converted and detected on the light-receiving surfaces a, b, c, d are the current-voltage conversion amplifiers 40, 4 provided inside the package of the photodetector 9.
The voltage is converted by 1, 42, 43 into the output terminals of the photodetector 9, respectively. The output line of the light receiving surface e is connected to the output line of the light receiving surface i and then connected to the current-voltage conversion amplifier 44. Therefore, the detection current detected on the light receiving surface e and the detection current detected on the light receiving surface i are added together, and then converted into a voltage by the current-voltage conversion amplifier 44 and sent to the output terminal. Similarly, the detection current detected on each of the light-receiving surfaces f and j, the detection current detected on each of the light-receiving surfaces g and k, and the detection current detected on each of the light-receiving surfaces h and l are added together to obtain a current-voltage. It is converted into a voltage by the conversion amplifiers 45 to 47 and sent to the output terminal. (Hereinafter, for simplification of description, these voltage-converted detection signals are denoted by the same symbols as the light-receiving surface on which the detection signals are detected.) Eventually, the eight output terminals of the photodetector 9 , A, b, c,
d, e + i, f + j, g + k, h + 1 are output.

Next, the arithmetic circuit will be described. Of the eight detection signals output from the output terminals of the photodetector 9, the output signals a, b, c, d are first added by the adders 50, 51,
The subtracter 71 outputs the signal (a + c)-(b + d), and the adders 48 and 49 output the signal (a + b),
(C + d) is output. Of these, the signal (a + c)-
(B + d) corresponds to a defocus signal of the optical spot 100 on the disc detected by a so-called astigmatism method. Further, (a + b) and (c + d) are detection light spots 1
10 corresponds to the amount of detected light in each area when divided in the tracking direction (radial direction) of the disk, and the difference signal between these two signals is the tracking of the optical spot 100 on the disk detected by the so-called push-pull method. Corresponds to the error signal.

Further, a phase difference detection circuit 80 is connected to the output signals a, b, c and d, and by this circuit, a light spot 100 on the disc by a so-called phase difference detection method (differential phase detection method) is connected.
The tracking error signal of is also detected. Since this phase difference detection method is already known, a detailed description is omitted.

On the other hand, output signals e + i, f + j, g + k,
From h + 1, the signals (e + i + g + k)-(h + l + f + j) are output by the adders 53 and 54 and the subtractor 70, and further amplified by the amplifier 60 at a predetermined amplification factor K1. The amplification factor K1 of the amplifier 60 is the signal (e
+ I + g + k)-(h + l + f + j) is the signal (a + c)
It is determined that the signal amplitude is almost the same as − (b + d). This signal (e + i + g + k)-(h +
1 + f + j) corresponds to the sum signal of the defocus signals of the optical spots 101 and 102 on the disc detected by the so-called astigmatism method.

The output signals e + i, f + j, g + k,
From h + 1, signals (e + f) are added by adders 52 and 55.
+ I + j) and (h + g + l + k) are output, and further amplifiers 61 and 62 for amplifying the signal with a predetermined amplification factor K2 are connected. This amplifier 61,6
The amplification factor K2 of 2 is equal to the signals (e + f + i + j) and (h +
g + l + k) has a signal amplitude substantially the same as that of the signals (a + b) and (c + d). This signal (e + f + i + j), (h + g + l + k)
Corresponds to the sum of the detected light amount in each area when the detected light spots 111 and 112 are divided into two in the disc tracking direction (radial direction), and the difference signal between these two signals is detected by the so-called push-pull method. Corresponds to the sum of the tracking error signals of the spots 101 and 102 on the disk. And the amplifier 61
After being amplified by and 62, they are added with (a + b) and (c + d) by adders 56 and 57, and finally subtracter 72
Is subtracted. As a result, the signal output from the subtractor 72 is: {(a + b)-(c + d)}-K2 · {(e + f + i + j)-
(h + g + l + k)}. This signal is received by the light receiving area 20.
It corresponds to the signal obtained by subtracting the tracking error signals of the spots 101 and 102 on the disc obtained from the light receiving regions 201 and 202 from the tracking error signal of the spot 100 on the disc obtained from 0.

By the way, changeover switches 90 and 91 are provided at the defocus signal output terminal and the tracking error signal output terminal of this signal processing circuit, respectively.
This is provided in order to appropriately switch the defocus signal and the tracking error signal used for controlling the actuator 10 according to the type of disk as described below.

That is, when reproducing an optical disc such as a DVD-RAM disc having a continuous guide groove on the recording surface of the disc, as shown in FIG. 71
Signal (a + c)-(b + d) output from the amplifier 6
The signal K1 output from 0 {(e + i + g + k)-
The signal {(a + c) − (b + d)} + K1 · {(e + i + g + k) − obtained by adding (h + l + f + j)} through the adder 58.
(h + l + f + j)} is output as a defocus signal. This signal is the defocus signal of the optical spot 100 and the optical spot 10 on the optical disk by the astigmatism method as described above.
The sum signal of the defocus signals 1 and 102 corresponds to a signal obtained by adding together the signal amplitudes. Therefore, this signal becomes a good defocus signal in which the disturbance of the defocus signal due to the diffraction in the guide groove is largely eliminated as described above.

Then, for the tracking error signal, the changeover switch 91 is changed over to change the signal {(a + b)-(c + d)}-K2.multidot. {(E + f + i + j)-.
(h + g + l + k)} is output. This is the spot 10 on the disc obtained from the light receiving area 200 as described above.
On-disk spots 101 and 1 obtained from the light receiving regions 201 and 202 from the tracking error signal of 0.
This corresponds to a signal obtained by subtracting the sum signal of the tracking error signals 02. Therefore, although this signal is detected by the push-pull method, it is a good tracking error signal in which the offset due to the displacement of the objective lens is largely eliminated.

On the other hand, when reproducing a reproduction-only disc such as a DVD-ROM disc or a CD in which phase pits corresponding to a recording signal are provided on the disc, a normal astigmatism method is used as a defocus signal. There is no influence of disturbance even if the signal is used. Further, the tracking error signal output from the phase difference detection circuit 80 by the phase difference detection method can be used as the tracking error signal. Therefore, as shown in FIG. 7, the changeover switches 90 and 91 are changed over so that (a + c)-(b + d) is used as the defocus signal.
As a tracking error signal
By outputting the tracking error signal output from, it is possible to obtain each error signal suitable for the read-only disc.

As described above, the defocus signal and the tracking error signal selectively obtained according to the type of the optical disc are supplied to a predetermined actuator control circuit (not shown) to drive the two-dimensional actuator 10. Thus, the position of the objective lens 6 in the optical axis direction and the position in the tracking direction are automatically controlled.

The information signal recorded on the optical disc is generated by an adder 59 as a sum signal of the output signals a, b, c and d, and this signal is supplied to a predetermined signal reproducing circuit (not shown). However, since this signal reproducing circuit is already known, detailed description thereof will be omitted. Although not shown in this embodiment, by adding the adder 59 in the package of the photodetector 9 and adding the output terminal of the sum signal (a + b + c + d) to the signal output terminal of the photodetector 9, It is also conceivable that the total number of output terminals output from the detector package is 9 pins.

As described above, in the present embodiment, the internal structure of the photodetector and the signal processing circuit are configured as described above, so that the photodetector has 12 independent light-receiving surfaces even though the photodetector has 12 independent light-receiving surfaces. The number of output signal terminals can be limited to 8 or 9, and a practical photodetector package (for example, 12-pin package) can be used.

The guide groove interval Tp1 of the DVD-RAM disk is the recording track pitch T of the DVD-ROM disk.
It is just twice as large as p2. (The recording track pitch of a DVD-ROM disc is 0.74 μm,
Therefore, the relative distance between the irradiation positions of the light spots 100, 101, 102 irradiated on the DVD-RAM disk is shown in FIG.
If the same optical head is used for DVD-
When the ROM disk is reproduced, the three light spots are inevitably irradiated right above the three recording tracks adjacent to each other as shown in FIG. Moreover, FIG.
In the present invention as shown in FIG.
The disc reflected light of each of 00, 101 and 102 is incident on the independent light receiving regions 200, 201 and 202. Therefore, it is possible to simultaneously and independently reproduce the information signals recorded on the different recording tracks by each of these three light spots. However, in this case, it is necessary to make the internal configuration of the photodetector 9 and the configuration of the signal processing circuit such that at least the reflected light amounts of the light spots 100, 101, and 102 can be independently output. That is, for example, in the embodiment of FIGS. 5 to 7, the sum of the detection signals from the predetermined two light receiving surfaces, that is, the signal (e + i), from the output terminal of the photodetector 9,
Although (f + j), (g + k), and (h + 1) are output, the signals thus added are not output, and the signals e, f, g, h, i, j, k, and l are independently output. By outputting the signals and outputting the signals (e + f + g + h) and (i + j + k + l) from these signals by using a predetermined adder, by combining with the signals (a + b + c + d), the three separate recording tracks as described above. The signals from can be reproduced at the same time.

Also for a DVD-RAM disk, the information signals recorded on a plurality of recording tracks can be reproduced at the same time on the completely same principle. That is, DVD-
Since the RAM disk is so-called land-groove recording, an information signal recorded in a predetermined guide groove (groove) and an information signal recorded between the guide grooves (lands) adjacent to both sides thereof (or, conversely, a predetermined guide). The information signal recorded on the space between the grooves and the information signals recorded on the guide grooves adjacent to both sides thereof can be simultaneously reproduced by the three light spots.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 9 is a front view schematically showing an embodiment of the optical system configuration of an optical head which is a main part of the optical disc device of the present invention. The same parts as those in the embodiment of FIG. 1 are designated by the same reference numerals.

In the first embodiment shown in FIG. 1, a cubic beam splitter 3 is used in order to separate the optical path of the outgoing light beam entering the optical disk from the optical path of the returning light beam reflected from the disk. The cylindrical lens 8 is provided to give a predetermined astigmatism to the light flux. On the other hand, in the second embodiment shown in FIG. 9, instead of the cubic type beam splitter in order to separate the optical paths of the outgoing light flux and the returning light flux, the cubic light splitter has a predetermined plate thickness and is approximately 45 with respect to the optical axis. A flat plate type half mirror 11 arranged at an inclination is used. The laser light flux emitted from the semiconductor laser light source 1 passes through the diffraction grating 2, is reflected by the half mirror 11, and is then converted into a parallel light flux by the collimator lens 4, passes through the rising mirror 5 and the objective lens 6, and is recorded on the recording surface of the optical disk 7. It is supposed to be incident. On the other hand, the return light reflected by the optical disk 7 passes through the objective lens 6, the rising mirror 5, and the collimator lens 4 to be a convergent light beam, which enters the half mirror 11. And this half mirror 1
After passing through 1, the light enters the photodetector 9 through the concave lens 12. At this time, since the backward-path light (detection light) bundle is a convergent light flux and is transmitted through the half mirror 11 arranged at an angle of about 45 ° with respect to the optical axis, a predetermined astigmatism is given. As with the first embodiment, the defocus signal can be detected using the astigmatism method. However, in this case, the direction of the grating groove of the diffraction grating 2 and the mounting direction of the photodetector 9 are rotated about 45 ° around the optical axis with respect to the configuration of the embodiment shown in FIG. It is necessary to rotate the optical disc about 45 ° around the optical axis of the optical disc. Further, the concave lens 12 provided after the half mirror 11 is arranged in a direction opposite to the half mirror 11 and inclined by a predetermined angle. This is intended to correct the coma aberration generated together with the astigmatism when the backward light passes through the half mirror 11. The above-mentioned detection optical system is already known in CD optical heads and the like, and therefore a detailed description thereof will be omitted.

As described above, it is possible to realize the same optical disc apparatus as that of the present invention and the first embodiment shown in FIGS. 1 to 7 even if a simple optical head having a small number of parts is used. it can.

Next, FIG. 10 shows the third embodiment of the present invention.
Will be explained. FIG. 10 shows an optical system configuration 1 of an optical head which is a main part of the optical disk device of the present invention.
It is the front view which showed the Example schematically. The same parts as those in the embodiments of FIGS. 1 and 9 are designated by the same reference numerals.

In this embodiment, two semiconductor laser light sources having different oscillation wavelengths are mounted in the optical head, and the semiconductor laser light sources to be turned on are switched according to the type of optical disc. That is, the semiconductor laser 1a emits a laser beam having a wavelength of, for example, about 650 nm, and the DVD-RA
It is a light source that is turned on when reproducing a high-density optical disc such as an M or DVD-ROM disc. On the other hand, the semiconductor laser 1b is a light source that emits a laser beam having a wavelength of, for example, about 780 nm and is turned on when reproducing an existing optical disk such as a CD, CD-ROM, or CD-R disk. (Of course, contrary to the above, 1a is a CD with a wavelength of 780 nm.
A combination of a light source for DVD and a light source for DVD having a wavelength of 650 nm can be considered. When reproducing a DVD disc, the laser light flux emitted from the semiconductor laser light source 1a is split into three light fluxes by the diffraction grating 2a and then enters the half mirror 11. The half mirror 11 is an optical element having reflectance and transmittance characteristics such that both the light beam emitted from the semiconductor laser light source 1a and the light beam emitted from the semiconductor laser light source 1b function as a half mirror, or a semiconductor laser light source. It functions as a half mirror for the light beam emitted from the laser light source 1a, and about 10 for the light beam emitted from the semiconductor laser light source 1b.
The optical element has a transmittance characteristic close to 0%.
Therefore, the semiconductor laser light source 1a is emitted and the half mirror 1
About half of the light intensity of the light beam incident on the beam No. 1 is reflected and enters the cubic beam splitter 13. The beam splitter 13 is an optical element having reflectance and transmittance characteristics such that both the light beam emitted from the semiconductor laser light source 1a and the light beam emitted from the semiconductor laser light source 1b function as a half mirror, or a semiconductor. Almost 1 for the luminous flux emitted from the laser light source 1a
It is an optical element having a transmittance characteristic of 00% and having reflectance and transmittance characteristics for a light beam emitted from the semiconductor laser light source 1b to function as a half mirror. Therefore, a part or all of the light beam emitted from the semiconductor laser light source 1a and incident on the beam splitter 13 passes through the beam splitter 13 as it is, and is collected on the recording surface of the optical disk 7 via the collimating lens 4, the raising mirror 5, and the objective lens 6. Be illuminated. At this time, as shown in FIG. 11A, the three light spots irradiated on the recording surface have an irradiation position interval in the tracking direction (disk radial direction) of DVD-, as shown in FIG. 11A. It is almost half the guide groove pitch Tp1 of the RAM disk. This is exactly the same as the first and second embodiments described above. The return light reflected from the optical disk 7 follows the optical path almost the same as the outward path in the reverse direction, and the half mirror 1
After reaching 1, the approximately half of the light intensity passes through the half mirror and enters the photodetector 9 through the concave lens 12.

On the other hand, when reproducing a CD, the semiconductor laser light source 1b is turned on as described above.

The light beam emitted from 1b is split into three light beams by the diffraction grating 2b and then enters the beam splitter 13. Then, approximately half of the light intensity is reflected by the beam splitter 13, passes through the collimator lens 4, the rising mirror 5, and the objective lens 6 and is condensed on the recording surface of the optical disk 7. The objective lens 6 has a function of converging a light beam having a wavelength of 650 nm on a recording surface of a DVD disk having a disk substrate thickness of 0.6 mm, and a wavelength of 780 n.
It also has a function of favorably focusing the light flux of m on the recording surface of a CD disc having a disc substrate thickness of 1.2 mm. However, the objective lens is not limited to the special lens as described above, and for example, an objective lens optimally designed for DVD disc reproduction and an objective lens optimally designed for CD disc reproduction can be provided in the same optical head. It can be installed together with and configured to switch depending on the type of disc to be played. Also, at this time, three light spots 100b, 101b, 102b irradiated on the recording surface of the disc during reproduction of the CD disc.
11B, the irradiation position interval in the tracking direction (disk radial direction) is approximately 1 / the recording track pitch Tp3 (= 1.6 μm) of the CD disk.
It is 4. Then, the backward light reflected from the optical disk 7 follows the almost same optical path as the forward path and reaches the beam splitter 13 in reverse, and then approximately half its light intensity passes through this beam splitter, passes through the half mirror 11 and the concave lens 12, and passes through the semiconductor. The light beam emitted from the laser light source 1a enters the same photodetector 9.

Next, the structure of the photodetector 9 used in this embodiment will be described. FIG. 12 shows a schematic front view thereof.
As described above, the photodetector 9 used in this embodiment is configured to irradiate two types of detection light spots having different wavelengths, and in reality, the light is condensed on the light receiving surface according to the disc to be reproduced. The detected light spots to be switched are switched. The basic structure is exactly the same as that of the first embodiment shown in FIG. 5, but as shown in FIG. 12, the four light receiving surfaces e, f, l, and k are slightly extended in the lateral direction of the figure. It has a curved shape. When reproducing a DVD disc, the points where the vertical and horizontal dividing lines intersect in a cross shape in the light receiving areas 200, 201 and 202 and the intensity centers of the detection light spots 110, 111 and 112 substantially coincide with each other. It is irradiated. On the other hand, when reproducing a CD disc, the outer two of the three detected light spots are used.
The individual or detected light spots 121 and 122 are located outside, that is, on the light receiving surfaces e and f or l from the position where the vertical and horizontal dividing lines of the light receiving regions 201 and 202 intersect.
Part closer to the k side (around the position indicated by the broken line in the figure)
Is irradiated. (The detection light spot in the center is spot 10.
As in the case of 0, the central part of the light receiving surface 200 is irradiated. ) That is, the irradiation position interval of the detection light spots 121 and 122 focused on the light receiving areas 201 and 202 during reproduction of the CD disc is the same as that of the detection light spots 111 and 112 focused on the light receiving areas 201 and 202 during DVD playback. It is wider than the irradiation position interval, and these detection light spots are set so as not to reach the light receiving surfaces h, g or i, j, respectively.

By thus defining the two types of spot arrangements of the detection light, it is possible to select the defocus signal detection method and the tracking error signal detection method that are suitable for the DVD disc reproduction and the CD disc reproduction, respectively. That is, when reproducing a DVD-RAM disc and a DVD-ROM disc, the same detection method as that of the first embodiment of the present invention described in FIGS. 5 to 7 is used.
(Detailed description is omitted because it overlaps with the above contents.)
On the other hand, during CD reproduction, the changeover switches 90 and 91 are switched as shown in FIG. 13, the defocus signal is detected by the normal astigmatism method, and the tracking error signal is detected by the three-spot method as described below. . That is, the output signal from the adder 52 is the sum of the signals (e + i) and (f + j) of the output signals of the photodetector 9, that is, the signal (e
+ F + i + j). However, during reproduction of the CD, the detection light spot 122 is not irradiated on the light receiving surfaces i and j as described above, so that the substantial output signal is (e + f). This corresponds to the total detected light amount of the detection light spot 121. Similarly, the substantial output signal from the adder 55 corresponds to (l + k), that is, the total detected light amount of the detected light spot 122. On the other hand, the detection light spots 121 and 12
2 spots on the optical disc 101b, 102b
Is the central light spot 100b as described in FIG.
On the other hand, it is shifted in the tracking direction by about 1/4 of the recording track pitch Tp3 of the disc. Therefore, FIG.
As shown in FIG. 3, when the signals output from the adders 52 and 55 are subtracted by the subtractor 73, (e + f)-(l + k) is obtained as the output signal. It is nothing but a tracking error signal by the spot method. This three-spot method is a very stable and high-performance tracking error signal detection method in the conventional read-only disc.

As described above, when the photodetector and the signal processing circuit of the present invention are used, an optical system having a simple structure equipped with two semiconductor laser light sources, one or two objective lenses and one photodetector. Using the head, DVD-RAM, DV
Starting with high density discs such as D-ROM discs, C
It is possible to realize an optical disc device with high versatility that is compatible with reproduction of existing optical discs such as D, CD-ROM, and CD-R.

FIG. 14 is a schematic block diagram of an optical information reproducing apparatus equipped with the optical head of the present invention. Various detection signals detected by the optical head 608 are sent to the servo signal generation circuit 604 and the information signal reproduction circuit 60 in the signal processing circuit.
Sent to 5. The servo signal generation circuit 604 generates a focus error signal and a tracking error signal suitable for each disc from these detection signals, and drives the objective lens actuator in the optical head 608 via the actuator drive circuit 603 based on this. Controls the position of the objective lens. The information signal reproducing circuit reproduces the information signal recorded on the disc from the detection signal. A part of the signals obtained by the servo signal generation circuit 604 and the information signal reproduction circuit 605 is a control circuit 600.
Sent to. The control circuit 600 discriminates the type of the optical disc 7 to be reproduced at that time by using these signals, and the DVD LD lighting circuit 6 is discriminated according to the discrimination result.
07 or CD LD lighting circuit 606 is driven, and the function of switching the circuit configuration of the servo signal generation circuit is selected so as to select the servo signal detection method according to the type of each disk as described above. Have.
An access control circuit 602 and a spindle motor drive circuit 601 are connected to the control circuit 600, and the access direction position control of the optical head 608 and the rotation of the disk spindle motor are performed respectively.

[0051]

As described above, according to the present invention, it is possible to obtain a good defocus signal in which disturbance is greatly reduced and a good tracking error signal in which offset due to displacement of the objective lens is greatly reduced, and in addition, Starting with high-density discs such as DVD-RAM and DVD-ROM discs, CDs, CD-ROs, etc.
It is possible to realize an optical disc device with high versatility that is compatible with reproduction of existing optical discs such as M and CD-R.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an optical head used in a first embodiment of the present invention.

FIG. 2 is a diagram schematically showing a positional relationship of a light spot irradiated on a DVD-RAM disc and a state of a reflected light flux in the present invention.

FIG. 3 is a diagram for explaining a disturbance reduction effect of a defocus signal according to the present invention.

FIG. 4 is a diagram for explaining an offset reduction effect of a tracking error signal according to the present invention.

FIG. 5 is a first diagram of a photodetector and a signal processing circuit of the present invention.
3 is a schematic plan view and a block diagram showing an embodiment of FIG.

FIG. 6 is a first diagram of a photodetector and a signal processing circuit of the present invention.
3 is a schematic plan view and a block diagram shown for explaining the first function of the embodiment of FIG.

FIG. 7 is a first diagram of a photodetector and a signal processing circuit of the present invention.
3 is a schematic plan view and a block diagram shown for explaining the second function of the embodiment of FIG.

FIG. 8 is a schematic plan view showing the positional relationship of light spots applied to a DVD-ROM disc according to the present invention.

FIG. 9 is a schematic front view showing the configuration of an optical head used in a second embodiment of the present invention.

FIG. 10 is a schematic front view showing the configuration of an optical head used in a third embodiment of the present invention.

FIG. 11 is a schematic plan view showing a positional relationship between light spots irradiated on a DVD-RAM disk and a light spot irradiated on a CD disk according to the present invention.

FIG. 12 is a schematic plan view and a block diagram showing a configuration of a photodetector and a signal processing circuit used in a third embodiment of the present invention.

FIG. 13 is a schematic plan view and a block diagram shown for explaining the second function of the photodetector and the signal processing circuit used in the third embodiment of the present invention.

FIG. 14 is a block diagram of an embodiment of the optical information reproducing apparatus of the present invention.

[Explanation of symbols]

1, 1a, 1b ... Semiconductor laser light source, 2, 2a, 2b
...... Semiconductor laser light source, 4 ... Collimating lens, 6 ...
… Objective lens, 7 …… Optical disk, 9 …… Photodetector.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ken Shimano             1-280, Higashikoigakubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Shigeru Nakamura             1-280, Higashikoigakubo, Kokubunji, Tokyo             Central Research Laboratory, Hitachi, Ltd. (72) Inventor Masayuki Inoue             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Ceremony Hitachi Digital Media Development Book             Department (72) Inventor Yukio Fukui             No. 1 Kitano, Majo, Mizushiro City, Iwate Prefecture             Within Hitachi Media Electronics (72) Inventor Yasuyuki Sugi             No. 1 Kitano, Majo, Mizushiro City, Iwate Prefecture             Within Hitachi Media Electronics (72) Inventor Shinji Fujita             No. 1 Kitano, Majo, Mizushiro City, Iwate Prefecture             Within Hitachi Media Electronics (72) Inventor Mitsuhiko Ota             No. 1 Kitano, Majo, Mizushiro City, Iwate Prefecture             Within Hitachi Media Electronics F term (reference) 5D118 AA13 AA18 AA21 AA26 CA11                       CA13 CA16 CA23 CB06 CC01                       CD02 CD03 CD11 CF06 CF16                       CG04 CG44 DA03 DA06 DA35                 5D119 AA06 AA41 KA20 KA28 KA43

Claims (9)

[Claims] 1. A photodetector which receives a light beam emitted from a semiconductor laser beam and branched into at least three beams reflected from an optical information recording medium to detect data recorded on the optical recording medium. And the photodetector has first, second, and third light-receiving portions that are divided into four in a square shape at a position where each of the three light beams incident on the photodetector is irradiated. The photodetector has a total of 12 divided light receiving surfaces in which regions are arranged, and a predetermined signal line among the signal lines for transmitting photoelectric conversion signals obtained from each of the 12 divided light receiving surfaces is connected inside the photodetector. A photodetector characterized in that the number of signal lines output to the signal processing circuit is 9 or less. 2. The photodetector according to claim 1, wherein a light receiving surface and a current-voltage conversion amplifier for converting a signal current photoelectrically converted on the light receiving surface into a signal voltage are provided in the same package. The photodetector according to claim 1, wherein the photodetector is an element. 3. An optical information recording medium is irradiated with a signal output from a photodetector which receives a light beam emitted from a semiconductor laser beam and reflected into at least three beams reflected from the optical information recording medium. A signal processing circuit for generating a defocus signal and a tracking error signal of the generated light spot and reproducing a data signal recorded on the optical information recording medium, the signal processing circuit predetermined for a signal output from the photodetector. By performing the arithmetic processing of (1), a signal obtained by adding or subtracting the defocus signal by the astigmatism method and the tracking error signal by the push-pull method for each of the three light spots irradiated on the optical information recording medium is obtained. A signal processing circuit characterized by outputting. 4. A tracking according to a three-spot method from a difference signal of signals that are substantially proportional to a total light amount of predetermined two detected light beams among at least three light beams received by the photodetector. The signal processing circuit according to claim 3, wherein the signal processing circuit generates an error signal. 5. A function of generating a tracking error signal by a differential phase detection method with respect to at least one light spot among the three light spots irradiated to a predetermined position on the optical information recording medium. The signal processing circuit according to claim 3, further comprising: 6. A semiconductor laser light source, an optical branching element for branching a light beam emitted from the semiconductor laser light source into at least three light beams, and optical information recording by condensing the three light beams. An optical system for irradiating each light spot to a predetermined position on the medium, a photodetector for receiving each light beam reflected by the optical information recording medium and outputting a signal, and a signal obtained from the photodetector To generate a defocus signal and a tracking error signal of the light spot irradiated on the optical information recording medium by reproducing the data signal recorded on the optical information recording medium. An optical information reproducing device comprising a signal processing circuit and a control circuit for determining the type of the optical information recording medium, wherein the signal processing circuit is the type of the optical information recording medium of the control circuit. Based on the determination result, the detection method of the predetermined defocus signal and the tracking error signal is selectively switched, and the defocus signal and the tracking signal are tracked using the signal obtained from the photodetector corresponding to the selected detection method. An optical information reproducing device characterized by outputting a signal. 7. A plurality of the semiconductor lasers are provided, and the control circuit selectively switches one of the plurality of semiconductor lasers based on a determination result of the type of the optical information recording medium. The optical information reproducing apparatus according to claim 6, which is characterized in that. 8. One of the plurality of semiconductor lasers is a semiconductor laser for DVD and the other one is a semiconductor laser for CD, and the signal processing circuit has a determination result of the control circuit as a DVD-RA.
When the disc is an M disc, the astigmatism method using the detection light of the three light beams is selected as the defocus signal detection method, and the differential push-pull method is selected as the tracking error signal detection method. Is a DVD-ROM disc, the astigmatism method using the detection light of one of the three light beams is selected as the detection method of the tracking error signal as the detection method of the defocus signal. Select the phase difference detection method and the judgment result is CD or CD-ROM or CD-R
Is selected, the astigmatism method using the detection light of one of the three light beams is selected as the defocus signal detection method, and the three-spot method is selected as the tracking error signal. The optical information reproducing device according to claim 7. 9. The optical information reproducing apparatus according to claim 6, wherein the light branching element is a diffraction grating.