JP2589848B2 - Optical head - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head of an optical disk device having an information recording medium and performing information recording, reproduction, erasure, and the like by irradiating a light beam such as a laser beam, and the like. The present invention relates to an optical head including effective tracking error signal detection means.

2. Description of the Related Art There have been many reports on techniques relating to a tracking error signal detecting means in a conventional optical head.

Hereinafter, a conventional optical head will be described with reference to the drawings.

FIG. 6 shows an example of a schematic configuration of a conventional optical head. In FIG. 6, 1 is a light source, 2 is a half mirror, 9
Denotes an objective lens, 4 denotes an optical disk as an information recording medium, 5
Is a split photodetector, 6 is an operational amplifier, 7 is a light spot,
5a is a dividing line of the two-part photodetector 5. The present invention relates to an optical head constituted by effective tracking error signal detecting means, and omits other means such as a focus error signal detecting means. Hereinafter, the operation of the conventional optical head will be described with reference to the drawings.

The light emitted from the light source 1 is reflected by the half mirror 2 and forms an optical spot on the optical disk 4 via the objective lens 3. At this time, the direction of the recording track on the optical disc 4 is perpendicular to the paper surface. The reflected light from the optical disc 4 follows the reverse path, passes through the half mirror 2 via the objective lens 3, and forms a light spot 7 on the two-segment photodetector 5. 2
Since the division line 5a exists on the divisional photodetector 5, the difference between the electric signals reproduced in the respective light receiving areas is obtained by the differential amplifier 6, so that the tracking error signal is detected. This is a so-called push-pull method that is widely used. In this conventional example, the reflected light from the optical disc 4 is directly received by the two-segment photodetector 5, but the reflected light passes through a lens before entering the two-segment photodetector 5, so that the two-segment light is used. There are many conventional examples in which the detector 5 is downsized, that is, the optical head is downsized.

Problems to be Solved by the Invention The push-pull method of the conventional optical head described above is a tracking error signal detecting means having a simple structure, but has the following drawbacks.

Normally, the tracking servo drives the objective lens 3 in the X direction (tracking direction) in FIG. 6 by an objective lens driving means (not shown) to follow a target track on the optical disc 4. In this case, the light spot 7 on the two-divided photodetector 5 moves in the X direction according to the movement of the objective lens 3.

7 (A), 7 (B) and 7 (C) are views showing the position of the light spot 7 on the two-segment photodetector 5 and the state of the tracking error signal obtained thereby. . FIG. 7A shows a case where the objective lens 3 is at the neutral position of X, and the light spot 7 is located at a position substantially symmetric with respect to the dividing line 5a. At this time, the tracking error signal obtained when the optical disk 4 is rotated and only the focus servo is operating is a signal substantially symmetric with respect to the voltage 0, assuming that the target voltage when the tracking servo is operating is 0. Obtainable.

FIG. 7B shows a case where the objective lens 3 has moved in the + direction of the X direction. In this case, the split photodetector 5
Above, the position of the light spot 7 moves, and the symmetry with respect to the division line 5a is broken. Therefore, the tracking error signal at this time is a signal in which the symmetry with respect to the voltage 0 is broken and the offset of the voltage + V is superimposed.

FIG. 7 (C) shows a case where the objective lens 3 has moved in one direction in the X direction, and the tracking error signal obtained at this time has a voltage −V opposite to the case of FIG. 7 (B). Are superimposed.

In an optical disc device, when a target track is searched at high speed, it is a general method to operate a tracking servo after moving an optical head at high speed.
At this time, if the objective lens 3 is moved from the neutral position in the X direction due to acceleration or the like at the time of moving the optical head, the states shown in FIGS. 7B and 7C occur. If it is attempted to operate the tracking servo in these states, the probability of failing to pull in the servo becomes very high. Further, even if the target track is pulled in, if there is a large eccentricity (about 100 μm or more) in the target track, there is a drawback that the followability is greatly deteriorated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an optical head capable of greatly reducing an offset of a tracking error signal due to movement of an objective lens in a tracking direction.

Means for Solving the Problems In order to achieve this object, an optical head according to the present invention comprises a light source, an objective lens for causing light emitted from the light source to converge on an information recording medium having a recording track, and an Detecting means for detecting an information signal, a focus error signal, and a tracking error signal based on the reflected light; a focus direction substantially parallel to an optical axis direction of the objective lens;
Means for driving in the tracking direction substantially perpendicular to the recording tracking and focus directions to apply focus servo and tracking servo. The means for detecting the tracking error signal transmits reflected light from the information recording medium, and With the center line substantially parallel to the recording track in the light beam cross section as the axis of symmetry, the light beam at the center including the axis of symmetry and the two light beams at the peripheral portion not including the axis of symmetry are spatially symmetrically divided and converged. The light transmitted through the element and the divided converging element is incident, and at least substantially coincides with at least the center line in the light beam cross section of the reflected light with respect to the light beam cross section of the incident light.
A central light beam including a symmetric axis on the light beam cross section of the reflected light beam is not inverted with respect to the symmetric axis and has two peripheral portions that do not include the symmetric axis. Either the light beam is inverted with respect to the axis of symmetry and enters the multi-segmented photodetector, or two peripheral light beams that do not include the axis of symmetry are not inverted with respect to the axis of symmetry, and the central beam that includes the axis of symmetry is the axis of symmetry. On the other hand, it is characterized by being inverted and incident on the multi-segmented photodetector.

When the focus servo is applied and the objective lens is at the neutral position in the tracking direction,
In the cross section of the light beam of the reflected light from the information recording medium, most of the reflected light beam may be a light beam of a central portion including a center line substantially parallel to the recording track and including the axis of symmetry.

Operation With this configuration, even if the objective lens moves from the neutral position in the movable range in the tracking direction, and the light spot on the photodetector moves to shift the center of intensity, the tracking error signal obtained as an output is offset. Of very high quality signals.

First Embodiment Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an optical head according to a first embodiment of the present invention.

In FIG. 1, 1 is a light source, 2 is a half mirror, 3 is an objective lens, 4 is an optical disk as an information recording medium, 5 is a two-segment photodetector having light receiving areas 5p and 5q, 6 is a differential amplifier, 8 Is a divided converging element, which transmits reflected light from the optical disk 4 and, on a cross section of the light beam, receives a light beam at a central portion including a symmetry axis with a center line substantially parallel to a recording track as a symmetry axis. Each of the lens 8a and two peripheral light fluxes not including the axis of symmetry enters, and the first lens
Second and third of the same focal length with a different focal point than the focal point of 8a
This is a composite element composed of the two lenses 8b and 8c, and spatially symmetrically divided and converged into a central light beam including the symmetry axis and two peripheral light beams not including the symmetry axis. 9a, 9b,
Reference numeral 9c denotes three light spots formed on the split photodetector 5 by the split converging element 8;
Which substantially coincides with the center line substantially parallel to the recording track in the light beam cross section of the reflected light from the optical disk 4.
It is a linear dividing line of a book. Here, the split photodetector 5 is located after the focal point of the first lens 8a. Note that the present invention relates to a tracking error signal detecting means, and omits other means such as a focus error signal detecting means.

Hereinafter, the operation of the optical head according to the first embodiment of the present invention will be described with reference to the drawings.

The light emitted from the light source 1 is reflected by the half mirror 2 and forms an optical spot on the optical disk 4 via the objective lens 3. At this time, the direction of the recording track on the optical disc 4 is perpendicular to the paper surface. The objective lens 3 is driven in the optical axis direction of the objective lens 3 by an objective lens driving means (not shown) to control the focus servo in the X direction (tracking direction).
And a tracking servo can be applied. The reflected light from the optical disk 4 follows the reverse path, passes through the half mirror 2 via the objective lens 3, is spatially divided into three light beams by the divided converging element 8, and is divided into three light beams on the two-part photodetector 5. Spots 9a, 9b and 9c are formed, where the two-segment photodetector 5 is located after the focal point of the first lens 8a.
For this reason, the center line substantially parallel to the recording track on the light beam cross section of the light beam reflected from the optical disk 4 is set as a symmetric axis, and two peripheral light beams not including the symmetric axis are divided and converged by the element 8.
Then, the light passes through the second lens 8b and the third lens 8c and enters the split photodetector 5 without being inverted with respect to the axis of symmetry to form light spots 9b and 9c. On the other hand, the central beam including the axis of symmetry passes through the first lens 8a of the split converging element 8, is inverted with respect to the axis of symmetry, and enters the two-segment photodetector to form a light spot 9a. There is a dividing line 5a on the two-part photodetector 5,
When the objective lens 3 is at the neutral position in the X direction, the light spots 9a, 9b, 9c are formed at positions substantially symmetric with respect to the division line 5a. Therefore, the difference between the electric signals reproduced in the light receiving regions 5p and 5q is obtained by the differential amplifier 6, thereby detecting the tracking error signal.

FIGS. 2A and 2B show the two-segment photodetector 5 and the light spots 9a, 9b and 9c. 9x indicates the intensity center position of the light spot 9a. FIG. 2A shows a case where the objective lens 3 exists at the neutral position in the X direction, as in FIG. In this case, the intensity center position 9x of the light spot 9a substantially coincides with the division line 5a, and the tracking error signal output from the differential amplifier 6 is the same as that shown in FIG. The signal has no offset.

FIG. 2 (B) shows a conventional example as in FIG. 7 (B).
FIG. 3 shows the positions of the light spots 9a, 9b, and 9c on the two-segment photodetector when the objective lens 3 moves in the + direction of the X direction in FIG. In this state, the central luminous flux including the axis of symmetry passes through the first lens 8a of the divided converging element 8, is inverted with respect to the axis of symmetry, and is incident on the two-segment photodetector to form the light spot 9a. Light spot 9a on a two-segment photodetector
Does not change, but the intensity center position 9x moves to the light receiving region 5p, and the amount of received light in the light receiving region 5p increases. The two peripheral light beams not including the axis of symmetry pass through the second lens 8b and the third lens 8c of the split converging element 8, and enter the two-segment photodetector 5 without being inverted with respect to the axis of symmetry. , Light spot 9b, 9c
Is formed, the light spot 9b becomes smaller and the amount of received light decreases, and the light spot 9c becomes larger and the amount of received light increases. Therefore, if the divided areas of the lenses 8a, 8b, 8c forming the divided converging element 8 are appropriately determined in advance for the reflected light from the optical disc 4, the light receiving area 5
The amount of increase or decrease in the amount of light at p and 5q can be made substantially the same. As a result, the tracking error signal obtained by taking the difference between the electric signals reproduced in the light receiving areas of the light receiving areas 5p and 5q by the differential amplifier 6 is shown in FIG. 7 (B).
Unlike the above case, the signal has a very small offset. Even when the objective lens 3 moves in the minus direction of the X direction in FIG. 1, a tracking error signal with a very small offset can be obtained by the same principle.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 is a schematic configuration diagram of an optical head according to a second embodiment of the present invention.

In FIG. 3, 1 is a light source, 2 is a half mirror, 3 is an objective lens, 4 is an optical disk as an information recording medium, 5 is a two-segment photodetector having light receiving areas 5p and 5q, and 6 is a differential amplifier. The construction and operation of these are exactly the same as those of the first embodiment shown in FIG.

Reference numeral 10 denotes a divided converging element, which transmits reflected light from the optical disc 4 and, in a cross section of the light beam, has a center line substantially parallel to the recording track as a symmetry axis, and a light beam at a central portion including the symmetry axis is incident thereon. A first lens 10a, and two second and third lenses 10b and 10c, each of which receives two light beams in the peripheral portion not including the axis of symmetry and having a focal point different from the focal point of the first lens, The focal points of the second and third lenses 10b and 10c are inverted with respect to the axis of symmetry, and are located at the central portion including the axis of symmetry and the two beams at the peripheral portion not including the axis of symmetry. Is a composite element that is divided spatially symmetrically and converged. 11a, 11b and 11c are divided by the converging element 10 to 2
The three light spots formed on the split photodetector 5 are denoted by 5a, and the dividing line 5a is a split line of the split photodetector 5, which has a center line substantially parallel to the recording track in the cross section of the light beam of the reflected light from the optical disk 4. This is one linear dividing line that substantially matches. At this time, the direction of the recording track on the optical disc 4 is perpendicular to the paper surface. Note that the present invention relates to a tracking error signal detecting means, and omits other means such as a focus error signal detecting means.

Hereinafter, the operation of the optical head according to the second embodiment of the present invention will be described with reference to the drawings.

The reflected light from the optical disk 4 passes through the half mirror 2 via the objective lens 3 and is
The three light spots 11a, 11b, and 11c are formed on the two-divided photodetector 5 by being spatially divided into two light fluxes.
The focal points of the two lenses 10b and 10c are inverted with respect to the axis of symmetry. For this reason, on the light beam cross section of the light beam reflected from the optical disk 4, the center line substantially parallel to the recording track is set as the symmetry axis, and the two peripheral light beams not including the symmetry axis are separated by the second lens 10 b of the divided converging element 10. The light passes through the third lens 10c, is inverted with respect to the axis of symmetry, and is incident on the two-segment photodetector 5 to form light spots 11b and 11c, respectively. On the other hand, the central beam including the axis of symmetry is the first lens of the split converging element 10.
The light passes through 10a and enters the two-segment photodetector 5 without being inverted with respect to the axis of symmetry to form a light spot 11a. A division line 5a exists on the two-part photodetector 5, and when the objective lens 3 is at a neutral position in the Y direction (tracking direction), the light spots 11a, 11b, and 11c are substantially symmetric with respect to the division line 5a. Formed in position. For this reason, the configuration is such that the difference between the electric signals reproduced in the light receiving regions 5p and 5q is obtained by the differential amplifier 6 to detect the tracking error signal.

FIGS. 4A and 4B show the two-segment photodetector 5 and the light spots 11a, 11b and 11c. 11x is a light spot
This shows the center position of 11a. FIG. 2 () shows a case where the objective lens 3 is located at the neutral position in the X direction, as in FIG. In this case, the intensity center position 11x of the light spot 11a substantially coincides with the division line 5a, and the tracking error signal output from the differential amplifier 6 is the same as that shown in FIG. The signal has no offset.

FIG. 4 (B) is similar to the conventional example in FIG. 7 (B).
3 shows the positions of the light spots 11a, 11b, and 11c on the two-segment photodetector when the objective lens 3 moves in the + direction of the X direction in FIG. In this state, the central beam including the axis of symmetry passes through the first lens 10a of the split converging element 10 and is incident on the two-segment photodetector 5 without being inverted with respect to the axis of symmetry to form a light spot 11a. Therefore, the split photodetector 5
The shape of the upper light spot 11a does not change, but the intensity center position 1
1x moves to the light receiving region 5q, and the amount of received light in the light receiving region 5q increases. Further, two peripheral light fluxes not including the axis of symmetry pass through the second lens 10b and the third lens 10c of the split converging element 10, are inverted with respect to the axis of symmetry, and enter the split photodetector 5, To form the light spots 11b and 11c, the light spot 11b
Becomes smaller, the amount of received light decreases, and the light spot 11c
Increases, and the amount of received light increases. Therefore,
If the divided areas of the lenses 10a, 10b, and 10c forming the divided converging element 10 are appropriately determined in advance with respect to the reflected light from the optical disk 4, the amount of increase or decrease in the amount of light in the light receiving areas 5p and 5q is substantially the same. be able to. This allows
The tracking error signal obtained by taking the difference between the electric signals reproduced in the light receiving areas of the light receiving areas 5p and 5q by the differential amplifier 6, unlike the case of FIG. 7 (B), has a very small offset. Signal. Even when the objective lens moves in the minus direction of the X direction in FIG. 3, a tracking error signal with very little offset can be obtained by the same principle.

In the embodiment shown in FIGS. 1 and 3, when the focus servo is applied and the objective lens is located in a neutral city in the tracking direction (X direction), the divided converging element is a light beam cross section of the reflected light from the information recording medium. In (2), most of the reflected light may be a light flux in a central portion including a center line substantially parallel to the recording track and including the axis of symmetry. It has been experimentally confirmed that a tracking error signal with the least offset can be obtained in the vicinity of this positional relationship.

The divided converging element is not a composite element in which the lenses are combined as shown in the embodiment of FIGS. 1 and 3, but divides the luminous flux of the reflected light from the information recording medium and changes the direction of the divided luminous flux. It is needless to say that the object of the present invention can be achieved even by including at least one or more deflection splitting prisms which may have a lens converging effect.

Further, the divided converging element is not one optical element combining the lenses shown in the embodiments of FIGS.
A composite element including at least one deflection splitting prism that splits a light beam of reflected light from the information recording medium, changes the direction of the split light beam, and may have a lens converging effect; Are independently present, at least one
It may be composed of more than two lenses.

FIG. 5 shows only the main part of the tracking error signal detection in this case as a third embodiment of the present invention. In FIG. 5, reference numeral 12 denotes a composite element, which transmits reflected light from an optical disk, and in a light beam cross section, a light beam at a central portion including a center line substantially parallel to a recording track as a symmetric axis. Each of the incident parallel prism 12a and the two peripheral luminous fluxes not including the axis of symmetry are incident and split.
It comprises deflection splitting prisms 12b and 12c for changing the directions of two light beams to directions opposite to each other with respect to the axis of symmetry. 13
Is a lens on which the light beams split by the composite optical element 12 enter and converge, respectively, and 5 is a split photodetector.

In the third embodiment of the present invention shown in FIG. 5, substantially the same light spot as that of the second embodiment of the present invention shown in FIG. Can achieve the same effect.

Needless to say, the composite element that achieves the split converging element described in the first, second, and third embodiments may be an integrated element manufactured by press molding or the like. It is effective from the point of view. As mentioned above,
According to the first to third embodiments of the present invention, the tracking error signal which has conventionally been generated due to the positional deviation of the objective lens 3 in the tracking direction can be obtained with a very simple configuration of the split converging element and the split photodetector. Can be greatly reduced. Accordingly, in the optical disk device, even when the objective lens 3 moves from the neutral position in the tracking direction due to acceleration or the like at the time of moving the optical head,
The pull-in capability of the tracking servo is greatly improved.
Moreover, even when the target track has a large eccentricity (about 100 μm or more), the followability to the target track is greatly improved, and a stable tracking servo can be realized.

Advantageous Effects of the Invention The present invention provides a light source, and an objective lens for causing light emitted from the light source to converge on an information recording medium having a recording track,
Detecting means for detecting an information signal, a focus error signal, and a tracking error signal by reflected light from the information recording medium; a focus direction substantially parallel to the optical axis direction of the objective lens; Means for applying focus servo and tracking servo by driving in a suitable tracking direction. The means for detecting the tracking error signal transmits the reflected light from the information recording medium and is substantially parallel to the recording track in the light beam cross section. A split converging element that splits and converges a light flux at the center including the symmetry axis and two light fluxes on the periphery that do not include the symmetry axis and converges with the center line as a symmetry axis, and transmission of the split converging element Light is incident, and at least one straight line that substantially coincides with the center line of the light beam cross section of the reflected light with respect to the light beam cross section of the incident light. A central light beam including a symmetric axis on the cross section of the reflected light beam is not inverted with respect to the symmetric axis, and two peripheral light beams not including the symmetric axis are symmetric. Either inverts the axis and enters the multi-segmented photodetector, or two peripheral beams that do not include the axis of symmetry do not invert the axis of symmetry, and the central beam that includes the axis of symmetry inverts the axis of symmetry And enters the multi-segment photodetector. With this configuration, even when the objective lens moves from the neutral position of the operating range in the tracking direction and the light spot on the photodetector moves accordingly, the tracking error signal obtained as an output has a very high quality with very little offset. Signal.

When the focus servo is applied and the objective lens is at the neutral position in the tracking direction,
In the cross section of the light beam of the reflected light from the information recording medium, most of the reflected light beam may be a light beam at the center including the center line substantially parallel to the recording track and the axis of symmetry. Further, the divided converging element has a center line substantially parallel to the recording track as a symmetry axis in a light beam cross section of the reflected light from the information recording medium,
A first lens into which a light beam at the center including the axis of symmetry enters;
Each of two peripheral light beams not including the axis of symmetry is incident, and the second and the second light beams having a focal point different from the focal point of the first lens.
A multi-element photodetector may be located after the focus of the first lens. Further, the divided converging element has a first lens in which a light beam at a central portion including a symmetric axis is incident on a center line substantially parallel to a recording track in a light beam cross section of the reflected light from the information recording medium; Each of the two peripheral light beams not including the axis of symmetry is incident, and is a composite element including the second and third lenses having a focal point different from the focal point of the first lens. May be inverted with respect to the axis of symmetry. The split-converging element splits the light beam of the reflected light from the information recording medium, changes the direction of the split light beam, and includes at least one or more deflection split prisms that may have a lens converging effect. It may be an element. Further, the divided converging element is not one optical element, but at least one element that divides the light beam of the reflected light from the information recording medium, changes the direction of the divided light beam, and has a lens converging effect. The composite element including the above-described deflection splitting prism and at least one or more lenses that exist independently of the composite element may be used. Further, the composite element constituting the divided converging element described above may be an integrated element manufactured by press molding or the like.

Although these have a very simple configuration, the offset of the tracking error signal, which has conventionally occurred due to the displacement of the objective lens in the tracking direction, can be greatly reduced, and the optical head is moved at a high speed in the optical disk apparatus. Later, even if the objective lens moves from the neutral position in the tracking direction due to acceleration or the like during the movement of the optical head, the pull-in capability of the tracking servo is greatly improved. In addition, large eccentricity (100μ
(approximately m or more), the followability to the target track is greatly improved, and an excellent optical head capable of realizing stable tracking servo can be realized.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical head according to a first embodiment of the present invention, FIG. 2 is a schematic diagram of a main part of the embodiment, and FIG. 3 is a schematic diagram of an optical head according to a second embodiment of the present invention. FIG. 4 is a schematic view of a main part of the embodiment, FIG. 5 is a schematic view of a main part of an optical head according to a third embodiment of the present invention, and FIG.
FIG. 1 is a schematic configuration diagram of a conventional optical head, and FIG. 7 is a schematic diagram of a main part of the conventional example. 1 light source 2 half mirror 3 objective lens
4 optical disk, 5 split photodetector, 5a split line, 5p, 5q light receiving area, 6 differential amplifier, 8,10
Divided converging element, 7, 9a, 9b, 9c, 11a, 11b, 11c ... light spot, 12 ... composite element, 8a, 8b, 8c, 10a, 10b, 10c, 13 ... lens, 12a ... parallel prism , 12b, 12c ... deflection splitting prism.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-275044 (JP, A) JP-A-2-73531 (JP, A) JP-A-1-59643 (JP, A)

Claims (7)

(57) [Claims] A light source; an objective lens for causing light emitted from the light source to converge on an information recording medium having a recording track; and an information signal by reflected light from the information recording medium.
Detecting means for detecting a focus error signal and a tracking error signal; driving the objective lens in a focus direction substantially parallel to the optical axis direction of the objective lens; and a tracking direction substantially perpendicular to the recording track and the focus direction. Means for applying focus servo and tracking servo, wherein the means for detecting the tracking error signal transmits a reflected light from the situation recording medium and sets a center line substantially parallel to the recording track in a light beam cross section. As a symmetry axis, a divided converging element that spatially symmetrically divides and converges a light flux in a central part including the symmetry axis and two light fluxes in a peripheral part not including the symmetry axis, and transmitted light of the divided convergent element. Is incident, and at least substantially coincides with the center line in the light beam cross section of the reflected light with respect to the light beam cross section of the incident light. A central light beam including the symmetric axis on the light beam cross section of the reflected light beam is not spatially inverted with respect to the symmetric axis, and the symmetric axis The two peripheral light beams not including the symmetric axis are spatially inverted with respect to the symmetry axis and are incident on the multi-segmented photodetector, or the two peripheral light beams not including the symmetry axis are spatially inverted with respect to the symmetry axis. An optical head, wherein a central light beam including the symmetry axis is spatially inverted with respect to the symmetry axis and is incident on the multi-segment detector without being inverted. 2. The split converging element, when a focus servo is applied and an objective lens is at a neutral position in a tracking direction, in a light beam cross section of reflected light from an information recording medium,
2. The optical head according to claim 1, wherein most of the total reflected light is a light flux in a central portion including a center line substantially parallel to the recording track and including a symmetry axis. 3. The split-converging element has a first section on which a light beam at a central portion including the symmetric axis is incident with a center line substantially parallel to a recording track as a symmetric axis in a light beam cross section of the reflected light from the information recording medium. A composite element comprising a lens, and two second and third lenses, each of which receives two light beams in a peripheral portion not including the axis of symmetry and having a focal point different from the focal point of the first lens. 3. The optical head according to claim 1, wherein the multi-segment photodetector is located after the focal point of the first lens. 4. A split-converging element, wherein a light beam at a central portion including a symmetric axis is incident on a cross section of a light beam of reflected light from an information recording medium, with a center line substantially parallel to a recording track as a symmetric axis. A composite element comprising a lens, and two second and third lenses, each of which receives two light beams in a peripheral portion not including the axis of symmetry and having a focal point different from the focal point of the first lens. 3. The optical head according to claim 1, wherein the focal points of the second and third lenses are spatially inverted with respect to the axis of symmetry. 5. A split-converging element splits a light beam of reflected light from an information recording medium, changes the direction of the split light beam, and has at least one deflection splitting lens which may have a lens converging effect. The optical head according to claim 3, wherein the optical head is a composite element including a prism. 6. The divided converging element is not one optical element, but at least may split a light beam of reflected light from an information recording medium, change the direction of the split light beam, and have a lens converging effect. 5. The composite device according to claim 3, wherein the composite device includes one or more deflection splitting prisms and at least one or more lenses independently of the composite device. The optical head according to the item. 7. The composite device according to claim 3, wherein the composite device is an integrated device manufactured by press forming or the like.
Item 7. The optical head according to Item 4, Item 5, Item 5 or Item 6.