JPH041933A - Optical head - Google Patents

Abstract

PURPOSE:To reduce the offset of a tracking error signal due to the shift of an objective lens produced in the tracking direction by a splitting/focusing element and a multi-split photodetector to form a tracking error signal detection means. CONSTITUTION:A light source 1 is provided together with an objective lens 3, a 2-split detection means 5, and a focus/tracking servo application means 6. Then a tracking error signal detection means consists of a splitting/focusing element 8 which splits and focuses the reflected light sent from an information recording medium 4 and a multi-split photodetector 5. Thus the lens 3 moves from a neutral position of a movable range set in the tracking direction. As a result, the offset is reduced and the quality is improved for the tracking error signal which is obtained as an output even if an optical spot moves on the photodetector.

Description

[Detailed Description of the Invention] Industrial Application Fields of the Invention The present invention relates to an optical head of an optical disk device that has an information recording medium and performs arrangement, reproduction, erasure, etc. of information by irradiating it with a light beam such as a laser beam. The present invention relates to an optical head constituted by tracking error signal detection means.

BACKGROUND OF THE INVENTION Although many reports have been made regarding technologies related to tracking error signal detection means in conventional optical heads, the conventional optical read will be explained below with reference to the drawings.

An example of a schematic configuration of a conventional optical head is shown in FIG.

In Fig. 6, 1 is light fL, 2 is) 1-fmirror,
3 is an objective lens 2; 4 is an optical disk which is an information recording medium; 5 is a two-split photodetector; 6 is a differential amplifier; 7 is a light spot; and 5a is a dividing line of the two-split photodetector 5. Note that the present invention relates to an optical readout constructed by effective tracking error signal detection means, and other means such as focus error signal detection means are omitted. The operation of the conventional optical head will be described below with reference to the drawings.

The light emitted from the light source 1 is reflected by a half mirror 2, passes through an objective lens 3, and forms a light spot on an optical disk 4. At this time, the direction of the recording track on the optical disk 4 is perpendicular to the paper surface.The reflected light from the optical disk 4 follows the opposite path, passes through the objective lens 3, and passes through the half mirror 2.
A light spot 7 is formed on the two-split photodetector 5. There is a dividing line 5a on the two-split photodetector 5.The tracking error signal is detected by taking the difference between the electric signals reproduced in the two light receiving areas using the differential amplifier 6. This is the so-called push-pull method, and it is a method that has been widely put into practical use. In this conventional example, the reflected light from the optical disc 4 is directly received by the two-split photodetector 5.The reflected light passes through a lens before entering the two-split photodetector 5, and the two-split light is There are many conventional examples in which the detector 5 is made smaller, that is, the optical head is made smaller (
- Problems to be Solved by the Invention The push-pull method of the conventional optical head described above is a tracking error signal detection means with a simple structure. Generally, the target track on the optical disk 4 is followed by driving in the X direction (tracking direction) in FIG. 6 using a driving means (not shown). The light spot 7 moves in the X direction in response to the movement of the objective lens 3.

FIG. 7(A), FIG. 7(B), and FIG. 7(C) are diagrams showing the position of the light spot 7 on the two-split photodetector 5 and the state of the tracking error signal obtained thereby. a 7th
Figure (A) shows the case where the objective lens 3 is at the neutral position of X, and the optical spot 7 is at a position approximately symmetrical with respect to the dividing line 5a.At this time, the optical disk 4 rotates and only the focus servo operates. If the target voltage when the tracking servo operates is 0, a signal that is almost symmetrical with respect to the voltage O can be obtained. Figure 7 (B) shows that the tracking error signal obtained when the objective lens 3 is This shows the case of movement in the 10th direction of the X direction. In this case, the position of the light spot 7 on the two-split photodetector 5 moves and the symmetry with respect to the dividing line 5a is lost. Therefore, the tracking error signal at this time loses its symmetry with respect to the voltage 0, and becomes a signal in which the offset of the voltage +V is superimposed.4 Figure 7 (C) shows the case where the objective lens 3 moves in the negative direction of the X direction. The tracking error signal ζ obtained at this time becomes a signal on which the voltage -■ is superimposed, contrary to the case of FIG. 7(B).

In optical disk devices, when searching for a target track at high speed, it is common practice to operate the tracking servo after moving the optical head at high speed. If we move from the neutral position in the X direction with an acceleration of
B), the situation shown in Figure 7(C) will occur.a If you try to operate the tracking servo in these conditions, there is a very high probability that the servo will fail to pull in, but even if it were to pull in, k In view of the above-mentioned problem, the present invention has the disadvantage that if there is a large eccentricity (approximately 100 μm or more) in the target track, the tracking performance is significantly degraded. An object of the present invention is to provide an optical head that can significantly reduce offset.A Means for Solving the ProblemsTo achieve this object, the optical head of the present invention includes a light source and a recording track that converts the light emitted from the light source into a recording track. an objective lens for converging on an information recording medium having an information recording medium, a detection means for detecting an information signal, a focus error signal, and a tracking error signal by reflected light from the information recording medium; means for detecting a tracking error signal by driving in a tracking direction substantially perpendicular to the recording track and the focus direction; and means for detecting a tracking error signal; In the cross section of the light beam, with the center line approximately parallel to the recording track as the symmetry axis, the light beam is spatially symmetrically divided into two light beams: a central light beam that includes the symmetry axis, and a peripheral light beam that does not include the symmetry axis. a converging element; a multi-segmented photodetector having one straight dividing line into which the transmitted light of the split converging element enters and which substantially coincides with the center line of at least the beam cross section of the reflected light with respect to the beam cross section of the incident light; Q on the beam cross section of the reflected beam The central beam that includes the axis of symmetry does not invert with respect to the axis of symmetry, and the two peripheral beams that do not include the axis of symmetry invert with respect to the axis of symmetry and reach the multi-split photodetector. The incident force\ or the two peripheral beams that do not include the axis of symmetry are not reversed with respect to the axis of symmetry, and the central beam that includes the axis of symmetry is reversed with respect to the axis of symmetry and enters the multi-split photodetector. It is said that

In addition, a split convergence element (friend) is used when the focus servo is applied and the objective lens is at the neutral position in the tracking direction.
This method is characterized in that, in a cross-section of a beam of reflected light from an information recording medium, most of the beam of reflected light is a beam of light in a central portion that includes an axis of symmetry with a center line that is approximately parallel to the recording track. Depending on the configuration, when the objective lens moves from the neutral position of its movable range in the tracking direction, the light spot on the photodetector moves and the center of intensity shifts.
The tracking error signal obtained as an output is a high-quality signal with very little offset.4 Example A first example of the present invention will be explained below with reference to the drawings. In FIG. 1, l is a light source; 2 is a half mirror; 13 is an objective lens; 4 is an optical disk serving as an information recording medium; The split photodetector 6 is a differential amplifier, and 8 is a split convergence element, which transmits the reflected light from the optical disk 4, and in the cross section of the light beam, the axis of symmetry is set at the center line approximately parallel to the recording track. A first lens 8a on which the light beam in the central part including the symmetry axis is incident, and a second lens 8a having the same focal length and having a focus different from the focus of the first lens 8a, on which each of the two light beams in the peripheral part not including the axis of symmetry enters. ．． It is a composite element consisting of the third two lenses 8b and 8c, which spatially symmetrically divides and converges a light beam in the central part including the axis of symmetry and two light beams in the peripheral part not including the axis of symmetry. 9a, 9b.

9C is the three light spots formed on the two-split photodetector 5 by the split convergence element 8; 5a is the dividing line of the two-split photodetector 5, which records the beam cross section of the reflected light from the optical disk 4; This is one straight dividing line that substantially coincides with a center line that is substantially parallel to the track. Here, the two-split photodetector 5 is located after the focal point of the first lens 8a.The present invention relates to tracking error signal detection means, and other means such as focus error signal detection means will be omitted. ing.

The operation of the optical head according to the first embodiment of the present invention will be explained below with reference to the drawings.The emitted light ζ from the light source 1 is reflected by the half mirror 2, passes through the objective lens 3, and is directed onto the optical disk 4. Form a spot. At this time, the direction of the recording track on the optical disk 4 is perpendicular to the plane of the paper.The objective lens 31 is driven in the optical axis direction of the objective lens 3 by an objective lens driving means (not shown) to drive the focus servo in the X direction (tracking direction). Even if the optical disc 4 is driven in the direction of the optical disc 4 and the tracking servo is applied, the reflected light from the optical disc 4 follows the opposite path, passes through the objective lens 3, passes through the half mirror 2, and is spatially divided into three light beams by the dividing converging element 8. Three light spots 9 on split photodetector 5
a, 9b.

9C (here, even if the two-split photodetector 5 is located after the focal point of the first lens 8a), the force that forms a center line approximately parallel to the recording track on the beam cross section of the reflected beam from the optical disk 4. The two peripheral light beams that do not include the axis of symmetry pass through the second lens 8b and third lens 8C of the split converging element 8, and become 2 without being reversed with respect to the axis of symmetry.
The central beam including the symmetry axis that enters the split photodetector 5 and forms light spots 9b and 9c is sent to the split convergence element 8.
The light passes through the first lens 8a, is reversed with respect to the axis of symmetry, and enters the two-split photodetector to form a light spot 9a.

There is a dividing line 5a on the two-split photodetector 5, and when the objective lens 3 is at the neutral position in the X direction, a light spot 9a is created.
, 9b, 9c are formed at substantially symmetrical positions with respect to the dividing line 5a. Even in a configuration where the tracking error signal is detected by taking the difference between the electrical signals reproduced by the light receiving areas 5p and 5q using the differential amplifier 6, Fig. 2 (A) and (B) are divided into two. Photodetector 5 and light spot 9
a, 9b, and 9c, and 49X indicates the intensity center position of the light spot 9a. Figure 2 (A
) is the same as in FIG. 1. Even if the objective lens 3 is at the neutral position in the X direction, the intensity center position 9x of the light spot 9a almost coincides with the dividing line 5a, and the differential amplifier Table 3 Tracking error signal which is the output of . The tracking error signal is the same as the conventional example shown in FIG. 7(A) and has no offset.

FIG. 2(B) shows light spots 9a and 9b when the objective lens 3 moves in the X direction in FIG. 1, as in the conventional example shown in FIG. 7(B).

9c on the two-split photodetector. In this state, the central beam including the axis of symmetry passes through the first lens 8a of the split converging element 8, is reversed with respect to the axis of symmetry, and is split into two. A beam that enters the photodetector and forms a light spot 9a
The shape of the light spora) 9a on the two-split photodetector does not change, but the intensity center position 9X moves to the light receiving area 5p, and the amount of light received in the light receiving area 5p increases.
The two peripheral light beams pass through the second lens 8b and third lens 8c of the split convergence element 8 and enter the two-split photodetector 5 without being reversed with respect to the axis of symmetry, forming light spots 9b and 9c. 8. The light spot 9b becomes smaller and the amount of light received by it decreases, and the light spot 9c becomes larger and the amount of light received increases. .

If the divided areas of 8C are properly determined in advance, the increase or decrease in the amount of light in the light receiving areas 5p and 5q can be made almost the same amount. Differential amplifier 6
The tracking error signal obtained by taking
Unlike the case in Fig. 7(B), when the objective lens 3 moves in the - direction of the X direction in Fig. 1, tracking with very small offset is achieved using 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. 4 In FIG. Numeral 5 is a two-split photodetector having light receiving areas 5p and 5q. Numeral 6 is a differential amplifier, and these configurations and operations are exactly the same as those of the first embodiment shown in FIG. 1. Numeral 10 is a split convergence element. There is a first lens 10a that transmits the reflected light from the optical disk 4, and in the cross section of the light beam, has a center line that is substantially parallel to the recording track as an axis of symmetry, and the light beam in the center including the axis of symmetry enters the first lens 10a. Each of the two peripheral light beams not including the axis enters the second lens, which has a focus different from the focus of the first lens. The third lens consists of two lenses 10b and 10c; The focal points ζ of the third two lenses 10b and 10c exist inverted with respect to the axis of symmetry, and are spatially separated into a central beam that includes the axis of symmetry and two beams of light at the periphery that do not include the axis of symmetry. It is a composite element that symmetrically divides and converges % lla, ll
b, Ilc are three light spots formed on the two-split photodetector 5 by the split convergence element lO, and 5a
is the dividing line of the two-split photodetector 5, and may be a straight dividing line that substantially coincides with the center line that is approximately parallel to the recording track in the cross section of the beam of light reflected from the optical disc 4. In this case, the optical disc 4 The direction of the upper recording track is perpendicular to the plane of the paper. Note that the present invention relates to tracking error signal detection means, and other means such as focus error signal detection means are omitted, and hereinafter, with reference to the drawings, an optical head according to a second embodiment of the present invention will be described. To explain the operation, the reflected light from the optical disk 4 passes through the objective lens 3 and passes through the half mirror 2.The split converging element 10 spatially splits the light into three light beams, and the two light spots appear on the two-split photodetector 5. , 11b, llc (here, the focal point of the second and third lenses 10b and 10c exists inverted with respect to the axis of symmetry) 4 This number The beam cross section of the reflected beam from the optical disk 4 Up With the center line approximately parallel to the recording track as the axis of symmetry, the two peripheral light beams that do not include the axis of symmetry pass through the second lens 10b and third lens 10c of the split converging element IO and are directed toward the axis of symmetry. The central beam including the -X symmetry axis passes through the first lens 10a of the split converging element 10 and is directed toward the symmetry axis. There is a dividing line 5a on the 42-split photodetector 5, and the beam enters the 2-split photodetector 5 without being reversed, forming a light spot 11a.
When the light spots 11a, 1b, and 11c are at neutral positions in the direction (tracking direction), the optical spots 11a, 1b, and 11c may be formed at positions approximately symmetrical to the dividing line 5a.
The configuration is such that a tracking error signal is detected by using a differential amplifier 6 to take the difference between the electrical signals reproduced by the light receiving regions 5p and 5q.

4(A) and 4(B) illustrate the two-split photodetector 5 and the light spots 11a, 1lb, and 11c, and 411x indicates the center position of the light spot lla. (A) shows the case where the objective lens 3 is at the neutral position in the X direction, as in FIG. The tracking error signal 1, which is the output of the amplifier 6, is a signal with no offset similar to that shown in the conventional example shown in Fig. 7 (A). Fig. 4 (B) shows the case of the conventional example shown in Fig. 7 (B). Similarly, even if the positions of the optical spots Ila, 11b, and llc on the two-split photodetector are shown when the objective lens 3 moves in the + direction of the X direction in Fig. 3, in this state, the axis of symmetry is The central light beam containing the light passes through the first lens 10a of the split convergence element 10 and enters the two-split photodetector 5 without being reversed with respect to the axis of symmetry, forming a light beam (2).
Although the shape of the light spot lla on the split photodetector 5 does not change, the intensity center position 11x moves to the light receiving area 5q, and the amount of light received in the light receiving area 5q increases, but the two peripheral light beams that do not include the axis of symmetry are not divided and converged. Second lens 1 of element 10
The light beam passes through 0b and the third lens IOC, is reversed with respect to the axis of symmetry, and enters the two-split photodetector 5, where the light spot llb.
The number of light spots llb to form llc becomes smaller and the amount of light received by it decreases, and the light spot llc becomes larger and the amount of light received increases. Therefore, a split converging element 10 is formed for the light reflected from the optical disk 4. If the divided areas of the lenses 10a, 10b, and 10c are properly determined in advance, it is possible to make the amount of light increase or decrease in the light receiving areas 5p and 5q almost the same. A tracking error signal obtained by using a differential amplifier 6 to calculate the difference between electrical signals reproduced in the regions 1. L Figure 7 (B
), a tracking error signal with very little offset is generated. If the objective lens 3 moves in the - direction of the X direction in Fig. In the embodiment shown in Figure 3, the focus servo is applied and the objective lens is moved in the tracking direction (X direction).
When the split converging element C is at the neutral position, in the cross-section of the beam of light reflected from the information recording medium, most of the beam of reflected light is directed to the central part that includes the axis of symmetry, with the center line approximately parallel to the recording track. Although it has been experimentally confirmed that a tracking error signal with the least offset can be obtained in the vicinity of this positional relationship as a luminous flux, it is still possible to obtain a tracking error signal with the smallest offset. It is not a composite element combining the lenses shown above, but includes at least one deflection splitting prism that splits the luminous flux of reflected light from the information recording medium, changes the direction of the split luminous flux, and may have the convergence effect of a lens. It goes without saying that the object of the present invention can be achieved even if the structure is configured as follows. A composite element including at least one deflection splitting prism that splits the luminous flux of reflected light, changes the direction of the divided luminous flux, and may have a lens convergence effect, and at least one The main part of tracking error signal detection in this case is shown in FIG. 5 as a third embodiment of the present invention.

In FIG. 5, reference numeral 12 denotes a composite element that transmits the reflected light from the optical disk, and in the cross section of the light beam, the center line that is approximately parallel to the recording track is the axis of symmetry, and the light beam in the center including the axis of symmetry is incident. a parallel prism 12a,
Deflection splitting prisms 12b and 12c into which each of the two peripheral light beams that do not include the axis of symmetry enter and change the directions of the two divided light beams into directions opposite to each other with respect to the axis of symmetry.
L13 is a lens X where each of the light beams divided by the composite optical element 12 enters and is converged.
Reference numeral 5 denotes a two-split photodetector. In the third embodiment of the present invention shown in FIG. 5, the light spot between the path and the second embodiment of the invention shown in FIG. It is also possible to realize the same effect by the same operation that is formed on the detector 5. Second. It goes without saying that the composite element C constituting the split convergence element described in the third embodiment may be an integral element manufactured by jobless molding, etc., and is also effective from the point of view of element transmittance. . As mentioned above, the first to third aspects of the present invention
According to the embodiments described above, it is possible to significantly reduce the offset of the tracking error signal that conventionally occurs due to the positional deviation of the objective lens 3 in the tracking direction. As a result, in an optical disk device, when the objective lens 3 moves from the neutral position in the tracking direction due to acceleration etc. when moving the optical head, the retraction ability of the tracking servo can be greatly improved. L when there is eccentricity (approximately 100 μm or more)
The ability to follow the target track is greatly improved, making it possible to realize stable tracking servo.4 Effects of the Invention 1 Friend of the Invention A light source and the light emitted from the light source are recorded on an information recording medium having a recording track. an objective lens for convergence;
a detection means for detecting an information signal, a focus error signal, and a tracking error signal by reflected light from an information recording medium; A means for detecting a tracking error signal by driving in both directions to apply a focus servo and a tracking servo L A means for detecting a tracking error signal Transmits the reflected light from the information recording medium and is symmetrical about a center line substantially parallel to the recording track in the cross section of the light beam a dividing convergence element that spatially symmetrically divides and converges a light beam in a central part that includes an axis of symmetry and a light flux in a peripheral part that does not include an axis of symmetry;
A multi-segmented photodetector is configured with a multi-segmented photodetector into which the transmitted light of the split convergent element enters, and has one straight dividing line that substantially coincides with the center line of at least the reflected light's beam cross-section with respect to the beam cross-section of the incident light. On the optical east cross-section of the light beam, the central beam that includes the axis of symmetry does not invert with respect to the axis of symmetry, and the two peripheral beams that do not include the axis of symmetry invert with respect to the axis of symmetry and enter the multi-split photodetector. ＼ Or, even if the two peripheral beams that do not include the axis of symmetry are not reversed with respect to the axis of symmetry, and the central beam that includes the axis of symmetry is reversed with respect to the axis of symmetry and enters the multi-split photodetector. Depending on the configuration, when the objective lens moves from the neutral position of its movable range in the tracking direction and the light spot on the photodetector moves accordingly, the tracking error signal obtained as the output is a high-quality signal with very little offset. Become.

Furthermore, when the focus servo is applied and the objective lens is at a neutral position in the tracking direction, the split convergence element directs most of the reflected light from the information recording medium to a center line that is approximately parallel to the recording track. In addition, the split convergence element can be used to divide the beam at the center including the axis of symmetry, with the center line approximately parallel to the recording track as the axis of symmetry, in the cross section of the beam reflected from the information recording medium. The second lens has a focus different from the focus of the first lens, and each of the two light fluxes in the peripheral area that does not include the axis of symmetry enters the first lens. It is a composite element consisting of two third lenses,
The multi-segment photodetector may be located after the focal point of the first lens.In addition, the multi-segment converging element (optional) may be located after the focal point of the first lens. A first lens has a central light beam that includes the symmetry axis, and a second lens has a focus that is different from the focus of the first lens. It is a composite element consisting of two lenses, and the focal points of the two lenses may be inverted with respect to the axis of symmetry (t or
The splitting and converging element may be a composite element including at least one polarizing splitting prism that splits the beam of reflected light from the information recording medium, changes the direction of the split beam, and may have the converging effect of a lens. Okay. Furthermore, the split convergence element is not a single optical element, but rather at least one element that splits the beam of reflected light from the information recording medium, changes the direction of the split beam, and may have the convergence effect of a lens. A composite element including a deflection splitting prism,
The composite element may be composed of at least one or more lenses that exist independently of the composite element. These methods have an extremely simple configuration and can significantly reduce the offset of the tracking error signal that conventionally occurs due to positional deviation of the objective lens in the tracking direction. The retraction ability of the tracking servo is greatly improved when the objective lens moves from the neutral position in the tracking direction due to acceleration during optical head movement after moving at high speed. (above), it is possible to create an excellent optical head that can significantly improve the followability to the target track and realize stable tracking servo.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the optical head in the first embodiment of the present invention. FIG. 2 is a schematic diagram of the main part of the embodiment. Schematic configuration of the optical head Fig. 4 is a schematic diagram of the main parts of this embodiment @ Fig. 5 is a schematic diagram of the main parts of the optical head according to the third embodiment of the present invention Fig. 6 is a conventional diagram Figure 7 is a schematic diagram of the main parts of a conventional example of the optical head.・Two-split photodetector
5a... Division 11L5p, 5q... Light receiving area 6.
・Differential amplifier, 8.10 ・Division convergence element, 1 a, 1 l b, 11 c2 ・Composite element, 8 10b, 10c, 13 ・Parallel prism 12 Prism

Claims (7)

[Claims] (1) A light source, an objective lens that converges the light emitted from the light source onto an information recording medium having a recording track, and detecting an information signal, a focus error signal, and a tracking error signal by the reflected light from the information recording medium. a detection means, and a means for applying focus servo and tracking servo by driving the objective lens in a focus direction substantially parallel to the optical axis direction of the objective lens and in a tracking direction substantially perpendicular to the recording track and the focus direction; The means for detecting the tracking error signal transmits the reflected light from the information recording medium, and in the cross section of the light beam, a center line that is substantially parallel to the recording track is set as an axis of symmetry, and a center line that includes the axis of symmetry is provided. A dividing converging element that spatially symmetrically divides and converges a luminous flux in the area and two luminous fluxes in the peripheral area that do not include the axis of symmetry; and a multi-segment photodetector having at least one straight dividing line that substantially coincides with the center line in the cross section of the beam of the reflected light, and includes the axis of symmetry on the cross section of the beam of the reflected beam. The central beam is not inverted with respect to the symmetry axis, and two peripheral beams that do not include the symmetry axis are inverted with respect to the symmetry axis and enter the multi-segment photodetector, or include the symmetry axis. An optical head characterized in that the two peripheral light beams that are not included are not inverted with respect to the symmetry axis, and the central light beam that includes the symmetry axis is inverted with respect to the symmetry axis and enters the multi-segment photodetector. (2) When the focus servo is applied and the objective lens is at the neutral position in the tracking direction, the split converging element
In a cross-section of a beam of reflected light from an information recording medium, most of the beam of the reflected light is a beam of light in a central portion that includes an axis of symmetry with a center line that is substantially parallel to the recording track. The optical head according to item 1. (3) The split convergence element has a first lens on which, in a cross-section of the beam of reflected light from the information recording medium, a center line that is approximately parallel to the recording track is an axis of symmetry, and a central beam that includes the axis of symmetry is incident thereon. , a composite element consisting of two lenses, a second and a third lens, into which each of the two peripheral light beams not including the axis of symmetry enters, and whose focus is different from the focus of the first lens; Claim 1, wherein the split photodetector is located after the focus of the first lens.
The optical head according to item 1 or 2. (4) The split converging element has a first lens on which, in a cross-section of the beam of reflected light from the information recording medium, a center line including the axis of symmetry is incident, with a center line approximately parallel to the recording track as an axis of symmetry. , a composite element comprising two lenses, a second and a third lens, into which each of the two light beams in the peripheral part not including the axis of symmetry enters, and has a focus different from the focus of the first lens; 3. The optical head according to claim 1, wherein the focal points of the second and third lenses are inverted with respect to the axis of symmetry. (5) The splitting and converging element splits the reflected light beam from the information recording medium, changes the direction of the split light beam, and includes at least one polarizing splitting prism that may have the converging effect of a lens. 5. The optical head according to claim 3, wherein the optical head is a composite element including: (6) The split converging element is not a single optical element, but at least one element that splits the luminous flux of reflected light from the information recording medium, changes the direction of the divided luminous flux, and may have the converging effect of a lens. A composite element including the above-described deflection splitting prism and at least one composite element that exists independently of the composite element.
The optical head according to claim 3 or 4, characterized in that the optical head is composed of at least one lens. (7) The optical head according to claim 3, 4, 5, or 6, wherein the composite element is an integral element manufactured by press molding or the like.