JP2002197713A - Optical head and optical disk device using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head and an optical disk device capable of coping with various optical disks different in disk thickness and recording material and also capable of performing stable and excellent recording/ reproducing to the optical disks different in track structure. SOLUTION: A diffraction grating having a cross type parting line is arranged among a first light source and a second light source which have different wavelengths respectively, an object lens for condensing a luminous flux radiated from the first light source and the second light source onto various optical disks different in disk thickness or the like and recording material, and a photodetector which receives reflected light from the optical disk and detects an electric signal. A reflected luminous flux from the optical disk is quadri-divided by the diffraction grating, diffracted light which is diffracted and separated in respective regions is guided to respective independent light receiving surface on the photodetector, and a tracking error signal by a detecting method in accordance with disk structure and a focus error signal by a knife edge system are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head capable of recording and reproducing information on and from an optical disk and an optical disk apparatus.

[0002]

2. Description of the Related Art An optical disk apparatus is an information recording / reproducing apparatus characterized by a non-contact, large-capacity, high-speed access, and low-cost medium, and as a recording / reproducing apparatus for a digital audio signal and a digital video signal, utilizing these characteristics. Or as an external storage device of a computer.

[0003] With the expansion of use, miniaturization and cost reduction of optical disk devices are being promoted, but miniaturization and simplification of optical heads are indispensable.

[0004] As means effective for miniaturization and simplification of an optical head, many configurations in which a detection optical system is provided with a diffraction grating or a hologram element are disclosed. For example, JP-A-8-77
No. 578 discloses a push-pull system in which a hologram element is arranged immediately below one objective lens and a multi-segmented photodetector is provided in the vicinity of a laser light source, so that a tracking offset accompanying the displacement of the objective lens hardly occurs. A configuration effective to detect a tracking error signal by the above method and to reduce the size and simplify the optical head is disclosed.

[0005] By the way, optical disks widely used at present are various types of optical disks having different substrate thicknesses, recording materials and corresponding wavelengths, and are widely used. For example, a DVD-ROM, a DVD-RAM, or the like has a disk substrate thickness of 0.6 mm and a corresponding wavelength of 650 nm. Alternatively, the substrate thickness of a CD or CD-R is 1.2 mm, and the wavelength of a laser beam most suitable for recording / reproduction is in the 780 nm band. However, it is practically difficult to use an objective lens optimally designed for a DVD disk and to record / reproduce data on / from a CD disk with the same optical system due to aberrations such as spherical aberration caused by differences in disk substrate thickness and the like. is there.

As a means for solving such a problem, for example, Japanese Patent Application Laid-Open No. 2000-81566 discloses a special objective lens having a function of correcting spherical aberration caused by a difference in disk substrate thickness by utilizing a difference in corresponding wavelength. A method of obtaining a good light spot on each optical disc by using the method is disclosed.

Apart from such differences in disk substrate thickness and corresponding wavelengths, currently used optical disks can be broadly classified into two types depending on the structure of recording tracks on which information is recorded. it can. That is, a continuous guide groove is provided in advance on the information recording surface of the disk, and a recordable disk capable of recording or erasing an information signal along the guide groove, and concave and convex pits corresponding to the information signal. The columns are two types of read-only discs formed in advance on the disc. However, the push-pull method, which is an optimal tracking error signal detection method for a recordable disc having a guide groove, is not suitable for a read-only disc without a guide groove, and conversely, a tracking error signal of a read-only disc. Since there is a problem that a general three-spot method or a differential phase detection method (hereinafter abbreviated as DPD method) is not applied to a recordable disc as a detection method, a disc that can be recorded with a single optical head and a read-only disc are used. It was difficult to accommodate both disks.

As an optical pickup capable of solving these problems and capable of compatible reproduction of various optical disks having different disk thicknesses, corresponding wavelengths and track structures, for example, Japanese Patent Application Laid-Open
000-82226 discloses a 650 nm band and 7 band.
A configuration is disclosed in which two light sources in the 80 nm band and a diffraction grating are provided in front of each light source, and reflected light from the disk is received by one photodetector having a plurality of divided light receiving units.

[0009]

However, as disclosed in the above-mentioned prior art, when an astigmatism method is used to detect a focus error signal on a recordable disk provided with a guide groove, tracking traversal is performed. It is known that a good focus error cannot be obtained because the signal leaks into the focus error signal. In the prior art, three spots are generated by a diffraction grating provided in front of a light source, and the spots are arranged at approximately 1/2 pitch of a disk track. This problem is improved by obtaining focus error signals and performing arithmetic processing on them. However, the track pitch here refers to an interval in which the phase of the push-pull signal is shifted by 360 °.

However, the degree of improvement of the focus error signal by this method is sufficient for a read-only optical pickup, but insufficient for a recording optical head.

[0011] Further, by a diffraction grating disposed in front of the light source, 3
Due to the configuration for generating spots, the ratio of the amount of light for recording to the amount of light emitted from the light source (light use efficiency) is low, and the power required for recording cannot be secured, or a more expensive high-output light source is required. was there.

A DVD-RAM disk and a DVD-
For a disc having a different track pitch, such as an R disc, there is a problem that both discs cannot be recorded simultaneously.

In addition, two diffraction gratings are required because the diffraction gratings are arranged in front of the two light sources in the 650 nm band and the 780 nm band, respectively.

Therefore, according to the present invention, it is possible to reproduce data from a recordable disc or a read-only disc having a different disc thickness, recording material, corresponding wavelength and track structure, track pitch, and a small, stable and excellent recordable disc. An object of the present invention is to provide a simple and low-cost optical head and an optical disk device using the same.

[0015]

According to the present invention, there is provided a first light source having a wavelength of λ1 and a light source having a wavelength of λ2.
A photodetector that includes an objective lens for condensing a light beam emitted from the second light source onto various optical disks having different disk thicknesses and recording materials, receives reflected light from the optical disk, and outputs an electric signal; A diffraction grating having a cross-shaped dividing line is arranged between the objective lenses. The diffraction grating divides the reflected light beam from the optical disk into four parts, and in each area, a photodetector detects the diffracted light that is diffracted and separated into the wavelengths λ1 and λ2 of the first and second light sources and the diffraction angle determined by the pitch and direction of the diffraction grating. It leads to each independent light receiving surface above. Further, the photodetector was set so as to be able to detect a tracking error signal and a focus error signal by a detection method according to a disk structure, and an optical head and an optical disk device were configured.

The first and second light sources are arranged such that their optical axes are orthogonal to each other, and a mirror or a bonding surface provided at the intersection of the optical axes has a substantially 45-degree prism, a light beam heading for the objective lens and an optical disk. And a beam splitter for splitting the reflected light beam to guide the light beam to the photodetector. Further, the diffraction grating is formed by an optical member having a predetermined polarization anisotropy,
The same linearly polarized light as the light beam traveling from the light source to the optical disk is not diffracted, and the linearly polarized light orthogonal to the predetermined direction is set to be diffracted at a predetermined diffraction efficiency. By providing a phase plate that acts as a quarter-wave plate for the wavelengths of the first and second light sources, the outward light irradiated on the optical disk via the objective lens is not diffracted but reflected from the optical disk. It becomes possible to obtain high light use efficiency by selectively diffracting only the returning light.

In such an optical head, when the knife edge method is used as the focus error signal detection method in the focus error signal detection area,
The diffraction grating can be formed as a straight grating groove having a predetermined angle and a grating pitch in each region. If a diffraction grating having a power other than a linear grating is used, focus detection by a spot size method is also possible.

In the focus error signal detection area of the photodetector, the direction of the boundary between the detection surfaces for receiving the reflected light of the first and second light sources is substantially the same as the direction of diffraction by the diffraction grating. The angle is a direct angle,
1 The boundary line between each detection surface receiving the reflected light of the light source and 0
The distance L1 between the next-order diffracted light irradiation position (the center of the photodetector) and the distance between the boundary line between each detection surface that receives the reflected light of the second light source and the 0th-order diffracted light irradiation position (the center of the photodetector) L
2 and the wavelength λ1 of the first light source and the wavelength λ2 of the second light source, the arrangement was such that the ratio of L1 and L2 was approximately λ1 and λ2. Further, the direction of the boundary line between the detection surfaces in the focus error signal detection region may be formed so as to be substantially parallel to the direction diffracted by the diffraction grating.

Further, a first detection method comprising a push-pull method as a tracking error signal detection means, and a DPD
A second detection method is provided, and the second and second tracking error signal detection means are appropriately switched according to the difference in the structure of the optical disk.

The optical head according to the present invention includes the first and second optical heads.
A forward light monitor detector for receiving a part of light emitted from each light source for maintaining a constant power of the light sources and controlling recording power, wherein the forward light monitor detectors are the first and second light monitor detectors. It is installed in the common optical path of the light beam emitted from the light source and before entering the objective.

Further, an output proportional to the output of each light source of the forward light monitor detector for receiving a part of the light emitted from the first and second light sources is output with respect to a predetermined output of the objective lens. And means for adjusting each to a predetermined value.

Further, the optical disk device includes the above-described optical head and disk determining means for determining the type of the mounted optical disk. The first and second tracking error signal detection methods are appropriately switched depending on whether the loaded optical disk is a recordable disk or a read-only disk.

The first or second light source corresponding to the corresponding wavelength of the disk is turned on in accordance with the determination result of the disk determining means, and the forward direction adjusted to a predetermined value with respect to the predetermined objective lens output. A means for maintaining constant power and controlling recording power using the output of the optical monitor detector is provided.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration and operation of an optical head according to a first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic perspective view of an optical head according to a first embodiment of the present invention.

The laser light sources 1 and 2 having different wavelengths are
The wavelength λ1 corresponding to each of the optical discs 10a and 10b
And λ2. In the case of recording and reproducing of the optical disk 10a (for example, DVD disk),
When the laser light source 1 is turned on, a light beam emitted from the light source passes through the dichroic prism 3, and the laser light source 1 and the laser light source 2
Is arranged so as to be incident on a beam splitter 4 acting as a polarization beam splitter for the wavelength of. The light beam emitted from the beam splitter 4 is converted into a parallel light beam by the collimator lens 6 and reaches the diffraction grating 7.
Further, the beam splitter 4 is arranged so that the polarization directions of the laser light source 1 and the light source 2 are substantially P-polarized light.

The diffraction grating 7 is divided into four crosses by a cross-shaped dividing line, and grating grooves are provided in each of the divided regions so that the diffraction directions of the light beams are different from each other. Further, the diffraction grating 7 is formed of a material having optical anisotropy, and the forward light flux toward the optical disc 10a is hardly diffracted, and the light having linearly polarized light orthogonal to the polarization direction of the forward light is diffracted almost 100%. It has become.

The outgoing luminous flux transmitted through the diffraction grating 7 further passes through a phase plate 8 acting as a quarter wavelength plate with respect to the wavelength of the laser light source 1 and the laser light source 2, reaches the objective lens 9, and reaches the objective lens 9. Light is collected on the information recording surface. The objective lens 9 satisfactorily condenses the light beam of the wavelength λ1 on the information recording surface of the optical disk 10a (for example, a DVD disk having a disk substrate thickness of 0.6 mm), and the objective lens 9 converts the light beam of the wavelength λ2 to the optical disk 10b (for example, the disk substrate thickness). 1.2m
m CD disk) with the function of condensing light well on the information recording surface. And the optical disk 1
The reflected light flux reflected at 0a passes through the objective lens 9 again, and acts as a quarter-wave plate for the wavelength of the laser light source 1 and the laser light source 2;
It is led to. At this time, since the returning light beam is transmitted and reciprocated through the phase plate 8, the light beam becomes linearly polarized light whose polarization direction is orthogonal to the forward light beam.
00% is diffracted.

The ± 1st-order diffracted light of the return light beam diffracted in each area of the diffraction grating 7 is converted into substantially S-polarized light by the beam splitter 4.
Then, the light is reflected from the beam splitter surface to enter a predetermined light receiving surface of a detector 12 having a plurality of independent light receiving surfaces.

On the other hand, in the case of recording and reproduction of the optical disk 10b (for example, a CD disk), the laser light source 2 is turned on, and the light beam emitted from the light source is reflected by the dichroic prism 3 and is the same as in the case of recording and reproducing the DVD disk. The light is incident on a predetermined light receiving surface of the detector 12 through the path. Dichroic prism 3
, The laser light source 1 and the laser light source 2 may be switched and installed. Further, the dichroic prism 3 may be replaced with a dichroic mirror.

The beam splitter 4 reflects a part of the luminous flux of the laser light source 1 and the laser light source 2 toward the collimator lens 6 and makes the luminous flux enter the front monitor detector 5. The front monitor detector 5 maintains a constant output power from the objective lens 9 and a recording power for recording on various optical disks.
Used for control. Further, a function of adjusting the values of the front monitor detectors of the laser light sources 1 and 2 to constant values with respect to a predetermined output from the objective lens as shown in FIG. By arranging the output adjustment circuit 14 having the function of switching the output of the front monitor detector on the optical head, it becomes easy to handle the optical head when the optical disk device is mounted. The output adjustment circuit 14 includes an output adjustment unit 1 (14a) that adjusts the front monitor detector 5 of the laser light source 1 and an output adjustment unit 2 (14b) that adjusts the front monitor detector 5 of the laser light source 2. Further, a switch 14c for switching the output of the front monitor detector 5 when the light source corresponding to the optical disk 10 is turned on is provided.

The objective lens 9 is fixed together with the diffraction grating 7 and the phase plate 8 to a lens holder 13 of an actuator, and is driven integrally by a general lens driving means (not shown). With this configuration, for example, even if the objective lens 9 is displaced in the disk radial direction during tracking control, the relative position between the reflected light beam reflected by the optical disk 10 and the dividing line of the diffraction grating 7 does not change. As shown in (1), when detecting the tracking error signal by the push-pull method, an offset accompanying the displacement of the objective lens hardly occurs, and a good signal can be detected.

FIG. 2, FIG. 3, FIG. 4, and FIG.
FIG. 2 is a schematic perspective view showing an example of the arrangement of a light receiving surface of No. 2 and a positional relationship with a diffraction grating 7. FIG. 2 shows a state where a light spot by the laser light source 1 (wavelength λ1) is focused on the information recording surface on the optical disk 10a. FIG. 3 shows a state in which the light spot by the laser light source 1 (wavelength λ1) is defocused on the positive side.

Similarly, FIG. 4 shows a laser light source 2 (wavelength λ).
The state where the light spot according to 2) is focused on the information recording surface on the optical disk 10b is shown. FIG. 5 shows a state in which the light spot by the laser light source 2 (wavelength λ2) is defocused on the positive side.

The photodetector 12 is, for example, as shown in FIG.
Light receiving surfaces 12a, 12b, 12c, 12d,
12e, 12f, 12g, 12h, 12I, 12j, 12
k, 121, and four rectangular light receiving surfaces 12m, 12n, 12o, 12p having a larger detection area.
The twelve strip-shaped light receiving surfaces are 12a, 12b, 12c, 1
2d, 12e, 12f, 12g, 12h, 12I, 12
j, 12k and 12l are light receiving surfaces for detecting a focus error signal by a so-called knife edge method, and two light receiving surfaces 12a and 12b and 12c and 1c respectively arranged in parallel.
By combining 2d, 12e and 12f, and 12g and 12h, respectively, a total of four laser light sources 1 (wavelength λ1)
Light receiving surfaces 12a and 12i in the same manner as
And 12c and 12j and 12e and 12k and 12
g and 12l respectively, and 4 sets of laser light sources 2
A light receiving area is formed for (wavelength λ2). Said each 2
The boundary line between the light receiving surfaces was arranged so as to be substantially perpendicular to the direction diffracted by the diffraction grating 7. Was. The rectangular light receiving surfaces 12m, 12n, 12o, and 12p are for detecting a tracking error signal by the push-pull method or the DPD method and a recording information signal of the optical disk 10. And a laser light source 1 for detecting a focus error signal.
Each of the four light receiving areas and the four light receiving surfaces for detecting the tracking error signal is arranged on a circle centered on the projection point on the detector of the central optical axis. However, depending on the difference in the grating pitch of each region of the diffraction grating 4,
They are not necessarily arranged on the same circumference. However, the distance L1 between the boundary line between the detection surfaces that receive the reflected light of each of the first and second light sources (for each region of the diffraction grating 4) and the 0th-order diffracted light irradiation position (the center of the photodetector). They are arranged so that L2 is approximately equal to the wavelengths λ1 and λ2 of the first and second light sources.

Next, detection of a focus error signal will be described. Although only the light beam of the laser light source 1 is described here, the light beam of the laser light source 2 is the same in principle. The return light beam reflected by the optical disk 10a and having passed through the objective lens 9 and the phase plate 8 travels downward from above in FIGS. 2 and 3 (indicated by arrows in the drawings) and enters the diffraction grating 7. Then, after being divided into substantially quarter-disk shapes in the respective divided regions of the diffraction grating 7 and diffracted in different directions, for example, of the ± 1st-order diffracted light generated in the region 7a, the + 1st-order light is the light receiving surfaces 12a and 12b. , And the -1 order light enters the light receiving surface 12m. The + 1st-order light incident on the light receiving surfaces 12a and 12b is transmitted when the spot on the optical disk 10a is focused on a recording track of the disk.
Focus on the boundary line 2b. When the spot on the optical disk is defocused on the positive or negative side, a 1/4 disc-shaped spot is projected on the light receiving surface 12b in FIG. 3 on the positive side and on the light receiving surface 12 on the negative side. A 1/4 disc-shaped spot is projected. Therefore, by detecting a difference signal between the light intensity signals detected on the light receiving surfaces 12a and 12b, a focus error signal by a so-called knife edge method becomes possible. Similarly, the + 1st-order light is also incident on the light-receiving area for detecting a focus error signal, and the -1st-order light is incident on the light-receiving surface for detecting a tracking error signal. It is arranged to be. Therefore, a good focus error signal can be obtained by detecting the focus error signal from the difference signal of the light intensity signal in the light receiving region for detecting each focus error signal and outputting the sum signal thereof.

With such a configuration, it is possible to detect a focus error signal by a knife edge method (or a spot size method described later) with sufficiently small track crossing signal leakage without depending on the track pitch of the disk. .

In this embodiment, since only one spot is used on the disk, the light utilization factor is higher than in the system using three spots, and the emission power of the laser light source 1 and the light source 2 can be suppressed low. . This allows longer laser life or lower cost laser light sources to be used.

In this embodiment, the laser light source 1
The polarity of the focus error signal at the time of use and the polarity of the focus error signal at the time of use of the laser light source 2 are inverted.

FIG. 6 is a schematic block diagram showing a mechanism for outputting a focus error signal and a tracking error signal from a light intensity signal detected on each light receiving surface of the photodetector 12.

The light spot 100a is connected to the light receiving surfaces 12a and 12a.
b, the light spot 100b is located on the light receiving surface 1
A light spot 100c is placed in the light receiving area composed of 2c and 12d.
Is incident on the light receiving area composed of the light receiving surfaces 12g and 12h, and the light spot 100d is incident on the light receiving area composed of the light receiving surfaces 12e and 12f. Then, the sum of the detection signals from the light receiving surfaces 12a, 12e and 12d, 12h and the light receiving surface 12
The sum of the detection signals from b, 12f and 12c, 12g is input to the operational amplifier 200, and the difference signal is detected to detect the focus error signal by the knife edge method.

On the other hand, the light receiving surfaces 12m, 12n, 12o, 1
The output signal from each of the 2p corresponds to the light intensity modulation signal of each divided area when the reflected light beam from the optical disc 10 is divided into four in a cross shape. Therefore, the output signal from each of the light receiving surfaces is input to a predetermined phase difference detection circuit 202 via a predetermined signal delay circuit 201 and is subjected to a predetermined calculation, thereby detecting a tracking error signal by the so-called DPD method.

The sum signal of the output signals from the light receiving surfaces 12m and 12n and the sum signal of the output signals from the light receiving surfaces 12o and 12p are each obtained when the reflected light beam from the optical disk 10 is divided into two in the radial direction of the disk. Since the signal corresponds to the light intensity modulation signal obtained in the divided area, if the operational amplifier 203 detects a difference signal between these signals, a tracking error signal by a so-called push-pull method can be detected. By performing a predetermined operation on the output signal of each light receiving surface of the detector 12 in this manner, a focus error signal and two types of tracking error signals having different detection methods can be obtained at the same time. It is possible to select a tracking error signal suitable for each of the reproduction-only types.

Further, the information signals recorded on the disk are provided with light receiving surfaces 12m and 12m for tracking error signals.
The respective output signals from n, 12o and 12p are converted into operational amplifiers 204
And detecting the sum signal. Alternatively, it may be detected from the sum signal of the output signals from all the light receiving areas.

The present invention is not limited to the above configuration. In the first embodiment, the spots 100a, 10a, 10a,
0b, 100c, 100d and 101a, 101b,
Which light receiving surface or light receiving area in the photodetector 9 each of the light receiving surfaces 101c and 101d can be freely set. At that time, the direction of the grating groove in each divided region of the diffraction grating 7 is set to a predetermined direction according to the combination of the light receiving surface or the light receiving region to be incident, and each of the focus error signal detection region and the tracking error signal detection region is set. By properly setting the method of calculating the detection signal from the light receiving surface, each signal can be detected based on exactly the same detection principle as described above.

Next, a second embodiment will be described. The components are the same as those in the first embodiment, and the arrangement of the light receiving surface of the photodetector 30 for detecting the focus error signal is different. FIG. 7 shows the light spot 1 on the photodetector 30 when the light spots of the laser light source 1 (wavelength λ1) and the laser light source 2 (wavelength λ2) are focused on the information recording surfaces of the optical disks 10a and 10b, respectively.
The states of 00, 101 and 102, 103 are shown. As shown in FIG. 7, two light receiving surfaces 30a and 30b for detecting a focus error signal by the knife edge method, respectively.
The boundaries between the light receiving surfaces 30c and 30d, the light receiving surfaces 30e and 30f, and the light receiving surfaces 30h and 30g are disposed so as to be substantially parallel to the direction in which the light is diffracted by the diffraction grating 7.
Are received in the same area. As shown in FIG. 7, the method of calculating the detection signal from each light receiving surface in each of the focus error signal detection area and the tracking error signal detection area is exactly the same as the detection principle described in the first embodiment. Can be detected. As a result, in the first embodiment, the polarities of the focus error signals from the first and second light sources are inverted. In the second embodiment, the polarities of the focus error signals from the first and second light sources are made the same. It is possible.
In the first embodiment, the light spots 100 and 102, which are focused on the boundary of the light receiving surface due to the wavelength change, deviate from the boundary and affect the focus error signal. It is possible to eliminate the influence on the focus error signal only by moving the focused light spot on the boundary line.

In the first and second embodiments, the knife edge method has been described as the focus detection method. However, if a diffraction grating having a power other than a linear grating is used, focus detection by the spot size method can be performed. It is possible.

FIG. 8 is a block diagram showing a schematic configuration of the optical disk device of the present invention. The operation will be described for the case of a DVD disk. The type of the loaded optical disc 10 is determined by the disc discriminating circuit 50 in the system control circuit 50.
a, and based on the result, the switch circuit 14a
Selects the output of the output adjusting means 1 (14b) in which the output of the front light monitor detector of the laser light source 1 corresponding to the optical disk 10a is adjusted to a predetermined value, and
Of the laser light source 1 by the output selection switch circuit 51a
select. The laser light source 1 is driven by the APC circuit 51c in the laser drive circuit 51 using the output of the output adjustment means 1 (14b) selected by the switch circuit 14a. In the case of recording, the pulse generated by the recording pulse generation circuit 51b in the laser drive circuit 51 is converted to the APC by the recording information sent from the recording system control circuit 50.
The laser light source 1 is driven by adding to the current from the circuit 51c.

Similarly, in the case of a CD disk, the output of the output adjusting means 1 (14c) for adjusting the output of the forward light monitor detector of the laser light source 2 to a predetermined value is selected based on the disk discriminating circuit 50a. Further, the laser light source 2 is selected by the output selection switch circuit 51a in the laser driving device 51. The laser light source 2 is driven by the APC circuit 51c using the output of the output adjusting means 2 (14c) selected by the switch circuit 14a.

The reflected light from the optical disk 10 is
2 and is converted into an electric signal.
2, where signals such as a focus error signal, a tracking error signal, and an information recording signal are generated based on each detection method. The generated signals are transmitted to the system control circuit 5
0 is supplied. However, since the signal generation circuit 52 generates two types of tracking error signals of the DPD method and the push-pull method, it is once sent to the switch circuit 53,
The tracking error signal selected based on the discrimination result of the disc discrimination circuit 50 is supplied to the system control circuit. The mounted disc is a recordable DVD disc 10
In the case of a, the signal from the photodetector 12 is sent to the signal generation circuit 52, and the focus error signal, the information recording signal, and the tracking error signal by the push-pull method selected by the switch circuit 53 are sent to the system control circuit. Supplied.

The system control circuit 50 drives an actuator driving means (not shown) through the actuator driving circuit 54 based on each error signal, and outputs a quarter of the wavelength of the objective lens 9 and the laser light sources 1 and 2. 1
Focus control and tracking control are performed by displacing the phase plate 8 acting as a wavelength plate and the diffraction grating 7 integrally.

[0052]

As described above, according to the present invention, a recordable disc and a read-only disc having different disc thicknesses, recording materials, track structures and track pitches can be used.
In addition to being able to detect the tracking error signal and the focus error signal by the respective optimum detection methods, the disk thickness, the recording material and the track structure are further reduced by using a small, simple and low-cost optical head having a small number of parts. It is possible to provide an optical disk device that performs stable and good recording and reproduction on different optical disks with a single device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical head according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view showing a light receiving surface arrangement of a photodetector and a positional relationship with a diffraction grating according to the first embodiment of the present invention, wherein a light spot of a light source 1 is focused on a disk recording track. The state is shown.

FIG. 3 is a schematic perspective view showing a light receiving surface arrangement of a photodetector and a positional relationship with a diffraction grating according to the first embodiment of the present invention, in which a light spot of a light source 1 is out of focus on a positive side. The state is shown.

FIG. 4 is a schematic perspective view showing a light receiving surface arrangement of a photodetector and a positional relationship with a diffraction grating according to the first embodiment of the present invention, wherein a light spot of a light source 2 is focused on a disk recording track. The state is shown.

FIG. 5 is a schematic perspective view showing a light receiving surface arrangement of a photodetector and a positional relationship with a diffraction grating according to the first embodiment of the present invention, in which a light spot of a light source 2 is defocused on a positive side. The state is shown.

FIG. 6 is a block diagram illustrating an example of a schematic shape of a detector light receiving unit and a signal generation unit of a focus error signal and a tracking error signal according to the first embodiment of the present invention.

FIG. 7 is a block diagram illustrating a schematic configuration of a detector light receiving unit and an example of a signal generation unit for a focus error signal and a tracking error signal according to a second embodiment of the present invention.

FIG. 8 is a block diagram showing an embodiment of the optical disc device according to the first embodiment of the present invention.

[Explanation of symbols]

1 laser light source 1, 2 laser light source 2, 3 dichroic prism 4 beam splitter, 5 forward light monitor detector, 6 collimating lens, 7 diffraction grating, 8 phase plate, 9 objective lens, 10 optical disk, 11 detection lens, 12 light detection vessel

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) G11B 7/09 G11B 7/09 C 7/125 7/125 C 7/13 7/13 (72) Inventor Shinji Fujita 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Digital Media Product Division, Hitachi, Ltd. (72) Inventor Shinta Ikuo 1410 Inada, Hitachinaka-shi, Hitachi, Ltd. Shinro Inui 1410 Inada, Hitachinaka-shi, Ibaraki Pref. Digital Media Product Division, Hitachi, Ltd. (72) Inventor Yasuyuki Sugi 1410 Inada, Hitachinaka-shi, Ibaraki Digital Media Product Division, Hitachi, Ltd. 1 Yasuhiro Ishigaki, Kitano, Majo, Mizusawa City, Iwate Prefecture Hitachi Media Electronics, Ltd. Within Kutronix (72) Inventor Kuniichi Onishi 292 Yoshida-cho, Totsuka-ku, Yokohama City, Kanagawa Prefecture F-term (reference) 2H049 AA02 AA50 AA57 AA65 2H099 AA05 BA17 CA02 CA07 DA01 5D090 AA01 BB02 BB03 BB04 CC01 CC04 CC18 DD03 FF02 FF05 HH01 JJ11 KK03 LL02 LL05 5D118 AA01 AA26 BA01 BB01 BB05 BF02 BF03 CD02 CD03 CD08 CF02 CF03 CF04 CG07 DA20 DA35 DC03 5D119 AA01 AA04 AA41 BA03 EC03 FA03 BB01 CA03 EA01 JA11 JA12 JA14 JA32 KA02 KA16 KA17 KA18 LB07

Claims (10)

[Claims] A first light source and a second light source having different wavelengths; an objective lens for condensing a light beam emitted from the first light source and the second light source on an information recording surface of an optical disc; A photodetector that receives reflected light of the light beam from the optical disc by the first and second light sources and detects an electric signal, and a cross-shaped splitter disposed between the photodetector and the objective lens A diffraction grating having a line, wherein the diffraction grating divides a reflected light beam from the optical disc into four light beams with respect to the wavelengths of the first and second light sources, and diffracts and separates the diffracted light in each region with a photodetector. An optical head capable of detecting a tracking error signal and a focus error signal by a detection method according to a disk structure by guiding the light beam to each of the light receiving surfaces. 2. A focus error signal detecting means in a focus error signal detecting area of the photodetector for receiving the reflected light from the optical disk of a light beam from the first and second light sources having different wavelengths is a knife edge type. The optical head according to claim 1, wherein: 3. A focus error signal detecting means in a focus error signal detecting area of the photodetector for receiving the reflected light from the optical disk of a light beam from the first and second light sources having different wavelengths is formed by a spot size method. The optical head according to claim 1, wherein: 4. At least a focus error signal detection area of the photodetector has a direction of a boundary between respective detection surfaces for receiving the reflected light of the first and second light sources, which is diffracted by the diffraction grating. L1, L2, [lambda] 1, defined as described below.
4. The optical head according to claim 1, wherein at λ2, the ratio between L1 and L2 is substantially equal to the ratio between λ1 and λ2. L1 = distance between a boundary line between each detection surface of the photodetector that receives the reflected light of the first light source and the 0th-order diffracted light irradiation position (center of the photodetector) L2 = of the photodetector Distance between the boundary between each detection surface of the second light source that receives the reflected light and the zero-order diffracted light irradiation position (center of the photodetector) λ1 = wavelength of light emitted from the first light source λ2 = wavelength of light emitted from the second light source 5. The direction of a boundary line between each detection surface in at least a focus error signal detection area of the photodetector is determined by the fact that the light reflected from the disk of the light beam from the first or second light source is diffracted by the diffraction. 3. An angle substantially parallel to a direction diffracted by the grating.
An optical head according to item 1. 6. A light beam diffracted from each of said first and second light sources having different wavelengths from said optical disc in respective four-divided regions of said diffraction grating, respectively, and independently receives a tracking error. As a signal detecting means, both a first detection method comprising a push-pull method and a second detection method comprising a differential phase detection method are provided, and the first and second detection methods are provided in accordance with a difference in the structure of the optical disk. 6. The optical head according to claim 1, wherein a tracking error signal detection method is appropriately switched. 7. The polarization anisotropy in which the diffraction grating does not diffract a light beam having a predetermined linear polarization, but diffracts a light beam having a linear polarization whose polarization direction is orthogonal to the linear polarization at a predetermined diffraction efficiency. And a phase plate is provided between the diffraction grating and the objective lens, the phase plate acting as a quarter-wave plate with respect to the wavelengths of the first and second light sources having different wavelengths. The optical head according to any one of claims 1 to 6, wherein: 8. A forward light monitor detector for receiving a part of light emitted from each light source for maintaining constant power and controlling recording power of the first and second light sources having different wavelengths. 8. The apparatus according to claim 1, wherein a forward light monitor detector is provided in a common optical path of light beams emitted from the first and second light sources and before the light beam enters the objective. An optical head according to any of the claims. 9. A means for adjusting a corresponding output of each light source of the forward light monitor detector for receiving a part of light emitted from the first light source and the second light source to a predetermined value. The optical head according to claim 1, wherein the optical head is provided. 10. An optical head according to claim 1, further comprising: a discriminating means for discriminating a difference due to a structure of a mounted optical disc; and the first means according to a discrimination result.
Means for appropriately switching between a second tracking error signal detection method and a second tracking error signal detection method, and using the output adjusted to a predetermined value from the forward light monitor detector of claim 9, the first light source and the second light source. 2. An optical disk device comprising: means for maintaining constant power of the light source reproduction power and controlling recording power.