JP2001325738A - Optical head, ld module and optical recording/ reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical head, an LD module for the optical head and an optical recording/reproducing device which enable tracking control and focus control capable of easily removing an offset with simple constitution without necessitating complicated signal processing and positional adjustment. SOLUTION: The diameter D3 of the spot 21 of a sub beam whose image is formed on a disk 5 is set so as to become 2.5 times or more the diameter D1 of the spot 20 of a main beam. Thus, a track crossing component which is produced by the beam spot traversing a track is hardly included in an output signal of a detector detecting reflected light by the sub beam, that is, a signal of the difference of the output of a light receiving element which is divided by a dividing line in the radial direction, and the only DC offset which is generated by movement in the radial direction or the like caused by tracking control of an objective lens or the like is substantially included. Then, a tracking error signal and a focus error signal which do not substantially include the DC offset are obtained by reducing the output signal of the detector from the push-pull signal of the main beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an optical recording / reproducing apparatus, an optical head used for the apparatus, and an LD module.

[0002]

2. Description of the Related Art At present, as the types of optical disks are diversified, there is a demand for an optical recording / reproducing apparatus and an optical head capable of achieving stable tracking for disks of a plurality of types. The methods used in this case include (1) a method using an RF signal for generating a tracking error signal (hereinafter abbreviated as a TE signal), such as a phase difference detection method and a heterodyne method, (2) a three-beam method, Like the dynamic push-pull method,
The method is roughly divided into a method using a sub beam divided into TE signals on a disc and (3) a method using only a main beam and not using an RF signal, such as a push-pull method. In the push-pull method, as shown in FIG. 4C, a detector 51, which is a light receiving element that receives reflected light of a main beam spot, is divided into a dividing line 52 in a track direction and a dividing line 53 in a radial direction. The light is divided into the elements, and the arithmetic circuit 54 shown in FIG. 4 (D) calculates TE = (A + D) −
A tracking error signal (B + C) was obtained, and a spot 5
TE = 0 when 0 is at the center of the track (pit)
However, since TE> 0 or TE <0 when the spot is biased to either side, this TE is used for tracking control.

[0003] Among them, the method (1) uses a CD-
It cannot be applied to media such as R and DVD-R that require tracking servo for unregistered portions. In the method (2), it is necessary to incline the divided sub-beams with an accuracy of μm unit with respect to the track direction, and the optimum value of the interval depends on the track pitch of the disk. There is a drawback that it is not possible to handle disks simultaneously. In comparison, the push-pull method (3) does not depend on the presence or absence of an RF signal, and secondly, does not require highly accurate angle adjustment and high positional accuracy with respect to the disk rotation center. Third, since there is an advantage that there is no restriction on the difference in the track pitch of the disk, the optical disk has been widely used from the beginning when it was put to practical use.

On the other hand, there are a knife edge method, a Foucault method, a beam size method, an astigmatism method, and the like as a method for obtaining a focus error signal in a conventional optical head. In an optical head in which a light source and a light receiving element are individually mounted, The knife edge method and the astigmatism method have become widespread, and the hologram Foucault method and the beam size method have become widespread in LD modules in which both are mounted in the same package.

[0005]

However, in this push-pull system, an objective lens is driven by a tracking coil for tracking control and moves relatively to another optical system in the radial direction of the disk. If the disc is inclined with respect to the objective lens, the position and intensity of the spot 50 falling on the detector 51 constituted by the light receiving element changes, and the generated TE signal (TE)
Causes a DC fluctuation, which is called a DC offset.

If the servo is applied while including the DC offset component, especially when a disk with large eccentricity is used, the tracking performance is remarkably deteriorated, and the track is easily deviated. For this reason, the push-pull method is often used in combination with the means for removing the DC offset.

As a conventional method excluding the DC offset, there is known a method in which the amount of occurrence of a DC offset due to the eccentricity of a disk is estimated in advance, learned, and then the offset amount is corrected at the time of tracking servo. As another conventional method, there is known a method of improving the following performance of an optical head in a thread direction and minimizing a lens shift. Further, as another conventional method, there is known a method in which a mirror area is provided on a disk and tracking servo is performed while correcting an offset in the mirror portion.

However, all of these require complicated signal processing, a mechanism part having good response characteristics, or a disk of a special format, so that the configuration and the like are actually simpler and offset-resistant. (1),
There is a situation that the method (2) has more practical examples.

On the other hand, a signal generated when an optical spot crosses a track (referred to as a track cross signal) is superimposed on the conventional focus error signal due to the eccentricity of the optical disk, and this becomes a disturbance and causes a focus. There was a problem that the servo was hindered. The superposition of the track cross signal is particularly remarkable in the astigmatism method, but has a property that cannot be completely avoided in other methods.

Conventionally, in order to reduce the superposition of the track cross signal, as disclosed in Japanese Patent Application Laid-Open No. H11-296875, a special diffraction grating for shifting the phase of a part of the sub-beam has been used. As disclosed in JP-A-2000-82226, a disturbance in a focus error signal is removed by using a light receiving element with an increased number of divided detectors and a special arithmetic processing.

The present invention has been made in view of the above-mentioned problems of the prior art, and does not require complicated signal processing and position adjustment, and enables tracking control and focus control that can easily remove offset with a simple configuration. It is an object to provide an optical head, an LD module for the optical head, and an optical recording / reproducing apparatus.

[0012]

According to the first aspect of the present invention, there is provided an optical head comprising:
An optical head provided in an optical recording / reproducing apparatus for dividing a laser beam emitted from a light source into a plurality of laser beams by a diffraction element, irradiating the plurality of laser beams onto a disk, and using the sub-beams for tracking control; The spot diameter of the sub beam to be imaged is set to be 2.5 times or more of the main beam.

If the spot diameter of the sub-beam is set to 2.5 times or more of the main beam, the spot of the sub-beam is irradiated over a wide range in the radial direction over several tracks on the disk. Therefore, the reflected light due to the sub-beam hardly contains a track cross component (a component due to a difference in intensity of reflected light between the track groove and the land) caused by the beam spot crossing the track. In other words, the cut-off frequency of the optical transfer coefficient (OTP) in the sub-beam shifts to the lower side due to the increase in the spot diameter of the sub-beam, so that the track cross component having a high spatial frequency (the reciprocal of the track pitch) is not A signal that is removed and contains only a DC offset component caused by a lens shift or the like is obtained. That is, in the present invention, the spatial frequency component corresponding to the track pitch is designed to be removed by a filter effect by increasing the spot diameter of the sub beam to at least 2.5 times the spot diameter of the main beam.

The reflected light of this sub-beam is made incident on, for example, a detector composed of light receiving elements divided along a dividing line in the track direction, and a difference between output signals from the respective light receiving elements is obtained. The signal due to the cross component is hardly included. However, since the objective lens relatively moves in the radial direction with respect to other optical systems such as a light source and a detector, a difference in intensity of reflected light corresponding to the movement occurs in the divided light receiving element, which is caused by the DC. The amount of offset will be displayed.

On the other hand, the spot diameter of the main beam is originally determined uniquely from the track (pit) width, and the reflected light of the main beam naturally contains a track cross component and also has a DC Offset is also included.
The track cross signal including these DC offsets is detected by the detector of the reflected light of the main beam.

Therefore, if an operation for substantially subtracting the DC offset signal obtained from the detector of the reflected light of the sub-beam from the signal containing the DC offset obtained from the detector of the reflected light of the main beam is performed, the DC offset is removed. A TE signal is obtained.

On the other hand, in the detection of a focus error signal, if a sub beam having a large spot diameter is used and the same arithmetic processing as that of the related art is performed, a signal component necessary for focus servo generally called an S-shaped signal is left. As it is, only the track cross signal can be removed by the same filter effect as described above, which is convenient. In this case, if the spot diameter of the sub beam satisfies the above condition, there is an advantage that the detection method of the focus error signal is not particularly limited.

Note that the sub-beam does not necessarily have to be a perfect circle, but may be an ellipse or the like. If the width of the disk in the radial direction is 2.5 or more with respect to the spot diameter of the main beam, the post-calculation Can be maintained at 90% or more of the track cross signal that should be originally obtained.

The upper limit of the spot diameter of the sub beam is limited because it is necessary to set the size such that the sub beam does not overlap the main beam on the disk. In addition, there is a limitation due to the light receiving area of the sub-beam detector. Of these limitations, the limit due to the light receiving area of the detector is more severe, and one side of this detector is usually approximately 150 μm.
m or less, and if the magnification of the optical head on the disk side and the light receiving element side is designed to be 10 times, the spot diameter of the sub-beam is set to 15 μm or less, which is practical. On the other hand, the spot diameter of the main beam on the disk is 1 μm.
Therefore, it is desirable that the spot diameter of the sub beam be 15 times or less the spot diameter of the main beam.

According to a second aspect of the present invention, in the LD module used in the optical head of the first aspect, as a means for increasing the spot diameter of the sub-beam formed on the disk from the main beam, a diffraction element for splitting the beam is provided. A hologram element designed to give an aberration to a beam other than the zero-order light is used.

As described above, if a sub-beam having an enlarged spot diameter is obtained by a diffraction element for splitting a beam, a component similar to that of a conventional differential push-pull system can be obtained without increasing the number of components. Points and scale are sufficient.

According to a third aspect of the present invention, an optical recording / reproducing apparatus includes the optical head according to the first aspect or the LD module according to the second aspect. It has a dividing line in the track direction, and obtains a tracking error signal by performing arithmetic processing on an output signal of the light receiving element divided by the dividing line of each detector relating to the main beam and the sub beam.

If tracking is obtained by such a method, an arithmetic circuit having the same configuration as the conventional differential push-pull method can be applied as an arithmetic method.
It can be easily implemented.

According to a fourth aspect of the present invention, in the optical recording / reproducing apparatus of the third aspect, a signal obtained by a push-pull method of a sub beam is converted from a tracking error signal obtained by a push-pull method of a main beam. The subtraction removes a DC offset signal component of the tracking error signal.

In the fourth aspect, the implementation is easy as in the third aspect.

According to a fifth aspect of the present invention, there is provided an optical recording / reproducing apparatus including the optical head according to the first aspect, wherein the optical head has at least four or more divided detectors for receiving the sub-beam reflected light from the disk. It is characterized in that a focus error signal is obtained by performing arithmetic processing on an output signal.

As described above, by obtaining the focus error signal by the arithmetic processing using the large-sized sub-beam,
A signal having a small track cross component can be easily obtained.

According to a sixth aspect of the present invention, there is provided an optical recording / reproducing apparatus including the LD module according to the second aspect, wherein the LD module includes a detector, and the detector for receiving the sub-beam reflected light from the disk is divided into at least two or more. A focus error signal is obtained by performing arithmetic processing on an output signal of the detector.

As described above, by arranging the detector at the position where the sub beam returns, and performing arithmetic processing on this signal, it is possible to generate a focus error signal with a small track cross component.

[0030]

FIG. 1 is a block diagram showing an embodiment of an optical head according to the present invention. In FIG. 1, 1
Is a light source composed of a laser unit, 2 is a diffraction element that divides a laser beam from the light source 1 into a plurality of beams, 3 is a collimator lens, 4 is a beam splitter, and the beam splitter 4 converts light from the collimator lens 3 The light is transmitted to the optical disk 5 and the reflected light from the optical disk 5 is reflected to the detector 6. Reference numeral 7 denotes an objective lens, and reference numeral 8 denotes an anamorphic lens that converges reflected light from the beam splitter 4 on the detector 6.

FIG. 2 is a diagram for explaining the structure of the diffraction element 2 used in the optical head. As shown in FIG. 2A, a hologram element 9 is formed in the diffraction element 2 by forming a plurality of grooves 2a on one surface. As shown in FIG. 2B, the pitch P of the groove 2a of a general hologram element is
It is constant in the arrangement direction X of the grooves. When the pitch P is kept constant as described above, as shown in FIG. 3A, the disk 5 (11 is a track groove and 12 is a land) as in the conventional three-beam method and the differential push-pull method. The diameter D1 of the main beam spot 13 due to the zero-order light is equal to the diameter D2 of the sub-beam spot 14 due to the ± first-order light (D1
= D2).

On the other hand, in the present invention, for example, FIG.
As shown in (B), as the distance from the position x1 corresponding to the center of the beam emitted from the light source 1 increases, the solid line 1
The pitch P is gradually expanded as shown by 5 and 16,
Alternatively, the pitch P is reduced as shown by broken lines 17 and 18. As a result, an aberration is given to the beam other than the zero-order light, and as shown in FIG. 3B, the diameter D1 of the main beam spot 20 due to the zero-order light is smaller than the diameter D1 of the sub-beam spot 21 due to ± primary light. D3 is 2.5 times or more (2.5 × D
1 ≦ D3).

As a method of increasing the diameter D3 of the sub beam spot 21, the pitch P is periodically changed as shown in FIG. 2D, or as shown by a solid line or a broken line in FIG. There is a method of forming the shape of the groove 2a in a curved shape.

FIG. 4A is a diagram showing the structure of the detector 6. As shown in FIG. Reference numeral 6a denotes a detector of the reflected light of the main beam, and a dividing line 2 in the track direction of the image on the detector.
5 and four light receiving elements divided by a radial dividing line 26. Reference numerals 6b and 6c denote detectors of the reflected light of the sub-beams, and the dividing lines 27 in the track direction,
It consists of two light receiving elements divided by 28.

FIG. 4B shows an arithmetic circuit for obtaining a TE signal from output signals of the detectors 6a to 6c. The arithmetic circuit is mounted on the optical head or installed in a region other than the optical head based on a signal obtained by the detector 6 of the optical head. In FIG. 4B, an arithmetic circuit 30 calculates (A + D)-(B + C) from the output of each splitting element of the detector 6a of the reflected light of the main beam.
The arithmetic circuits 31 and 32 respectively calculate (E−F), (E−F) from the outputs of the detectors 6 a and 6 c of the reflected light of the sub-beams.
(GH). Reference numeral 33 denotes a circuit that obtains a value appropriate for removing DC offset by multiplying the output (E−F) + (G−H) of the outputs of the arithmetic circuits 31 and 32 by the coefficient α. Numeral 34 denotes an arithmetic circuit for obtaining the TE signal by subtracting the output of the arithmetic circuit 33 from the output of the arithmetic circuit 30.

Therefore, the output TE of the arithmetic circuit 34 is given by: TE = (A + D)-(B + C) -α {(EF) + (G-
H)}.

Here, the output of the arithmetic circuit 30 (A + D)-
(B + C) includes a DC offset in the track cross signal. On the other hand, since the sub beam spot is irradiated over the plurality of track grooves 11 or lands 12, the outputs of the arithmetic circuits 31 and 32 take the difference between the output signals from the light receiving elements divided by the dividing lines, respectively. The difference hardly includes a signal due to the track cross component. However, since the objective lens 7 has moved in the radial direction relative to the optical system other than the objective lens 7 such as the light source 1 and the detector 6, the outputs of the divided light receiving elements of the detectors 6b and 6c are A difference in the intensity of the reflected light due to the optical axis shift due to the movement is generated, and this indicates the amount of the DC offset. The arithmetic circuit 6a also includes a DC offset in addition to the track cross signal.

In the arithmetic circuit 33, the coefficient α is set so that the signal level of the DC offset included in the output of the arithmetic circuit 30 is substantially equal to the signal level of the DC offset output from the arithmetic circuit 33. Is set. By performing such an operation, a TE signal from which the DC offset has been removed can be obtained. The configuration of the arithmetic circuit used in the conventional differential push-pull method can be applied to the arithmetic circuit of FIG. 4 as it is.

FIG. 5 shows that the wavelength λ of the beam from the light source 1 is 65.
In the case of 0 nm, the waveform of the TE signal obtained by changing the spot diameter of the sub-beam on the disk variously with respect to the spot diameter of the main beam and changing the optical head in the radial direction of the disk is shown. In the case of FIG. 5, the arithmetic circuit 3 of FIG.
Is 0.5, the spot ratio is the spot diameter of the sub beam / the spot diameter of the main beam, and the spot ratios 1.0, 1.8, 2.5, and 3.3 are ± 1 respectively. This is obtained when defocus of 0, 3λ, 4λ, and 5λ is generated with respect to the light source wavelength λ in the light of the next order or more. When the spot ratio was 2.5, the amplitude of the push-pull signal of the sub beam was about 16% as compared with the amplitude of the main beam.

FIG. 6 shows the signal levels obtained at the various spot ratios. As is clear from FIGS. 5 and 6, the larger the spot ratio, the larger the TE signal is obtained. In order to keep the amplitude of the track cross signal of the calculated TE signal at 90% or more, the ratio of the spot diameter is 2 .5 times or more.

In practicing the present invention, the auxiliary beam does not need to detect the contrast of the track or pit at all.
As a result, the sub-beam can be located anywhere on the disc on which the information is engraved. This is advantageous because the optical head does not need to adjust the position of the sub-beam in units of μm, and the optical recording / reproducing apparatus does not need to consider the difference in the track pitch of the disk.

In this embodiment, an example is shown in which two sub beams are provided, but they may be integrated into one including the detector.
When two sub beams are used, the detector 6
Each of b and 6c may be provided with only one light receiving element.

Further, the hologram element may be used alone, or an integrated module may be formed together with the detector 6. Further, the type of the generated aberration and the hologram pattern are not particularly limited as long as the purpose of enlarging the imaging spot can be achieved.

Next, detection of a focus error signal will be described. FIG. 7A shows a conventional detector division structure and an arithmetic method for detecting a focus error signal by an astigmatism method. 6a is a detector for receiving the return light of the main beam, and 6b and 6b are detectors for receiving the sub-beam. In the conventional astigmatism method, the focus error signal FE receives the return light of the main beam as shown in FIG.
From outputs A to D of each area of the divided detector 6a, FE
= (A + C)-(B + D).

FIG. 7B shows an embodiment of a detector structure and arrangement for calculating a focus error signal according to the present invention. In the present embodiment, the detector 6b for receiving the return light of one of the sub-beams is divided into four parts, and the focus error signal FE is obtained from the outputs A to D of the respective divided areas.
FE = (A + C)-(B + D).

As described above, if the focus error signal is calculated from the return light of the sub beam whose size has been enlarged, a focus error signal having a small track cross component can be obtained.

When the configuration of the focus error signal calculation according to the present invention shown in FIG. 7B is employed, the main beam detector 6a and the other sub beam detector 6c are used for detecting the tracking error signal. As described above. In addition, Japanese Patent Application Laid-Open No. 2000-82226
, Each detector 6a, 6c is connected to 4
It is also possible to adopt a method in which division is performed, a necessary signal is appropriately generated by arithmetic processing, and used.

FIG. 8 is a configuration diagram showing an optical head having an LD module 61 provided with both the light source 1 and the detector 6. Reference numeral 2 denotes a diffraction grating for generating a sub beam having a spot diameter of 2.5 times or more of the main beam as described above. Reference numeral 60 denotes a hologram element that bends return light from the disk 5 toward the detector 6.

FIG. 9A shows that the hologram element 60 is divided into three areas α, β, and γ, and α, β, and γ of the detectors 6d to 6j are respectively assigned to the corresponding detectors.
This indicates that the zero-order light (that is, the return light of the main beam) of each of the 0 regions α, β, and γ falls. Β ′, β ″, γ ′,
γ ″ are the primary and −1 order (or −) of the regions β and γ, respectively.
1st order, 1st order), that is, the return light of the sub beam falls. Conventionally, a sub beam with the same size as the main beam is used,
The focus error signal FE is detected by calculating the difference between the outputs A and B of the two areas divided by the dividing line in the detector 6d (FE = AB).

FIG. 9B shows an example of the relationship between the division pattern of the hologram element 60 and the arrangement of the detectors in the case of employing the structure of FIG. 8 and the arithmetic processing method. In this example, a two-divided detector 6k is provided at a position (α ′) where the sub beam falls from the area α of the hologram element 60, and the difference between the output signals of the divided areas (FE = A−
By calculating B), a focus error signal is obtained. As described above, by calculating the focus error signal from the return light of the sub beam whose size has been enlarged, a focus error signal having a small track cross component can be obtained.
In this case, the detector 6d uses the output I of the RF signal and obtains RF = I + C + D (where C and D are the outputs of the 0th-order light detectors 6e and 6h in the areas β and γ), and the light use efficiency. Is provided to raise

FIG. 9C shows another example of the relation between the division pattern of the hologram element 60 and the arrangement of the detectors and the arithmetic processing method in the case of employing the structure of FIG. 8 according to the present invention. In this example, the detectors 6k and 6k that detect both the ± 1st-order sub beams (α ′, α ″) in the output of the area α.
An example in which m is provided is shown. In this case, the focus error signal F
E is calculated by FE = AB or FE = ab. The sum of these differences may be calculated. The calculation of the RF signal is the same as in the above example.

[0052]

According to the first aspect, the spot diameter of the sub-beam formed on the disk is set to be 2.5 times or more of the main beam, so that complicated signal processing and position adjustment can be performed. It is not necessary, and the DC offset can be easily removed by a simple configuration.

According to the second aspect, as means for making the spot diameter of the sub-beam formed on the disk larger than that of the main beam, the diffractive element for splitting the beam is designed to give an aberration to the beam other than the zero-order light. Since the used hologram element is used, the number of components and the scale are the same as those of the conventional differential push-pull system without increasing the number of components.

According to the third and fourth aspects, the detector receiving the disk reflected light of the main beam and the sub-beam has a dividing line in the track direction in the image incident on the detector, and the detector of each detector relating to the main beam and the sub-beam has Since the tracking error signal is obtained by arithmetically processing the output signal divided by the dividing line, an arithmetic circuit having the same configuration as the conventional differential push-pull method can be applied as the arithmetic method. , Can be easily implemented.

According to the fifth and sixth aspects, the focus error signal is obtained by using the sub-beam whose size is enlarged, so that a focus error signal with a small track cross component can be obtained. Therefore, good focus control without disturbance due to the track cross component is performed.

[Brief description of the drawings]

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

2A is a perspective view illustrating a diffraction element, FIG. 2B is a graph illustrating a pitch configuration of grooves of a general diffraction element,
(C) and (D) are graphs showing examples of the pitch configuration of the diffraction element used in the present invention, and (E) is an example of a groove pattern showing the pitch configuration of the diffraction element used in the present invention.

3A is a diagram for explaining the arrangement and size of a main beam and a sub-beam on a conventional differential push-pull disk, and FIG. 3B is a diagram illustrating the arrangement and size of a main beam and a sub-beam according to the present invention; It is a figure explaining a size.

4A is a diagram showing a configuration example of a detector when the present invention is implemented, FIG. 4B is a diagram showing a configuration example of an arithmetic circuit when the present invention is implemented, and FIG. FIG. 3D is a diagram illustrating a configuration of a pull-type detector, and FIG. 4D is a diagram illustrating a conventional arithmetic circuit.

FIG. 5 is a waveform diagram of a TE signal when the optical head is moved in the radial direction by setting various ratios of spot diameters of the sub beam and the main beam on the disk.

FIG. 6 is a graph showing a change in the output level of the TE signal when the ratio of the spot diameter of the sub beam to the spot of the main beam on the disk is variously set.

FIGS. 7A and 7B are diagrams respectively showing a conventional detector and a detector according to the present invention, and a calculation method for detecting a focus error signal by an astigmatism method.

FIG. 8 is a configuration diagram illustrating an optical head having an LD module including both a light source and a detector.

9A is a diagram showing a conventional hologram element division pattern and an example of detector arrangement when an LD module is provided with a light source and a detector as shown in FIG. 8;
(B) and (C) are diagrams showing two examples of the case of the present invention.

[Explanation of symbols]

1: light source, 2: diffraction element, 3: collimator lens, 4:
Beam splitter, 5: optical disk, 6, 6a-6m:
Detector, 7: objective lens, 8: anamorphic lens, 9: hologram element, 11: track groove, 12: land, 13, 20: main beam spot, 14, 21:
Sub beam spot, 25 to 28: division line, 30 to 3
4: arithmetic circuit, 60: hologram element, 61: LD module

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 5D118 AA21 CA22 CA23 CD02 CD03 CD11 CF03 CF05 CG04 CG14 CG24 CG36 CG44 DA02 DA20 DA33 DA35 DA43 DB02 DB04 DB08 DB16 5D119 AA13 AA29 EA02 EA03 EB08 EB15 EC05 FA30 JA24 JA23 JA23 JA23 LB05 LB07

Claims (6)

[Claims] An optical head provided in an optical recording / reproducing apparatus for dividing a laser beam emitted from a light source into a plurality of laser beams by a diffraction element, irradiating the plurality of laser beams onto a disk, and using the sub-beams for tracking control. An optical head, wherein the spot diameter of the sub-beam formed on the disk is set to be 2.5 times or more the main beam. 2. An LD module for use in an optical head according to claim 1, wherein the means for making the spot diameter of the sub-beam formed on the disk larger than that of the main beam includes: Module using a hologram element designed to give aberration to the laser 3. An optical head according to claim 1, or an LD according to claim 2.
A detector for receiving the reflected light of the main beam and the sub-beam on the disk, the detector having a dividing line in a track direction in an image incident on the detector, and receiving light divided by the dividing line of each detector regarding the main beam and the sub-beam. An optical recording / reproducing apparatus, wherein a tracking error signal is obtained by arithmetically processing an element output signal. 4. An optical recording / reproducing apparatus according to claim 3, wherein a signal obtained by a sub-beam push-pull method is subtracted from a tracking error signal obtained by a main beam push-pull method to obtain a tracking error signal. An optical recording / reproducing apparatus, which removes a DC offset signal component. 5. An optical head according to claim 1, wherein a detector receiving the sub-beam reflected light of the sub-beam is divided into at least four or more divisions, and an output signal of the detector is processed by arithmetic processing. An optical recording / reproducing apparatus for obtaining a focus error signal. 6. The LD module according to claim 2, wherein the LD module includes a detector, and the detector that receives the disk reflected light of the sub-beam is divided into at least two or more parts, and an output signal of the detector is calculated. An optical recording / reproducing apparatus, wherein a focus error signal is obtained by processing.