JP4525051B2 - Lens unit manufacturing method, lens unit, optical head, and optical pickup device - Google Patents

Description

The present invention relates to a lens unit suitable for an objective lens or the like incorporated in an optical head for an optical pickup and a method for manufacturing the same , and further relates to an optical head and an optical pickup device including the lens unit.

Up to now, various optical pickup devices for reproducing and recording information on optical information recording media such as CD (compact disc) and DVD (digital video disc) have been developed and manufactured, and are widely used. Yes. As an optical head device incorporated in such an optical pickup device, there is an optical head device in which an objective lens is fixed to a holder together with a phase control element so as to stably record and reproduce both a CD and a DVD. At this time, positioning marks for center axis alignment are provided on the objective lens and the phase control element, respectively, to prevent decentration and reduce wavefront aberration (see Patent Document 1).
JP 2001-6203 A

  However, in the optical head device as described above, since the objective lens and the phase control element are indirectly fixed via the holder, it is difficult to obtain alignment accuracy with respect to the tilt between the objective lens and the phase control element. In recent years, in the Blu-ray system using an objective lens with a higher NA, higher-precision alignment is required.

  In addition, the phase control element and the positioning mark of the objective lens that are fitted in the holder are generally difficult to observe, and it is not easy to ensure the alignment accuracy of both in such an assembly process.

Therefore, an object of the present invention is to provide a lens unit that can easily improve alignment accuracy between a phase control element and an objective lens and a manufacturing method thereof without complicating an assembly process.

  It is another object of the present invention to provide a high-precision optical head and an optical pickup device incorporating the lens unit as described above.

In order to solve the above-described problem, a method for manufacturing a lens unit according to the present invention is provided by supporting a flange portion that fits the protrusions of the flange portion extending around each of two optical elements, at least one of which is a lens. Performing preliminary alignment in the direction perpendicular to the optical axis by the alignment means, and after preliminary alignment, the two optical elements are observed while observing the optical axis alignment positioning marks respectively formed on at least one optical surface of each of the two optical elements. And a step of performing fine alignment by relatively moving the flange portion of the element in the direction perpendicular to the optical axis.
The lens unit according to the present invention includes (a) two optical elements at least one of which is a lens, and (b) optical axis alignment formed on at least one optical surface of each of the two optical elements. A positioning mark, and (c) extending around each of the two optical elements and having auxiliary alignment means for preliminarily aligning the two optical elements in the direction perpendicular to the optical axis by mutual connection, And a flange portion for fixing the elements to each other.

In the lens unit described above, when the optical axes of the two optical elements are aligned using the positioning mark, the two optical elements are fixed to each other using the flange portions provided on the two optical elements. Can be fixed directly while eliminating waste of the process. That is, not only can the assembly process be simplified by omitting the holder used for fixing in the past, but also a lens unit with high imaging performance can be manufactured by direct connection.
In the case where the flange portion includes auxiliary alignment means for preliminarily aligning the two optical elements, temporary alignment can be performed temporarily before the main alignment using the positioning mark, thereby speeding up the main alignment. be able to. In addition, when performing this alignment using a positioning mark, for example by microscope observation, two positioning marks can be rapidly introduce | transduced into a microscope visual field by utilizing the above-mentioned auxiliary alignment means.

  In a specific aspect of the present invention, each of the two optical elements and each flange portion extending around the two optical elements are plastic members formed by integral molding. In this case, a lens unit composed of two optical elements can be manufactured by joining both plastic members while performing alignment using a positioning mark. In addition, for both plastic members, the positioning mark and the flange portion can be formed at the same time when the optical surface is molded, and each positioning mark and each flange portion are formed with substantially the same accuracy as the molding of the two optical elements. Therefore, it is possible to precisely set the arrangement of the positioning marks, the interval between the optical elements, and the like. Further, since each flange portion is formed of a light transmissive material, the positioning mark can be illuminated from the side perpendicular to the optical axis so as not to hinder observation, and the alignment accuracy can be further improved.

  Moreover, in another specific aspect of the present invention, the auxiliary alignment means fits the uneven shape formed to face each of the flange portions. In this case, the auxiliary alignment means can have a simple structure. When preliminary alignment is performed by the auxiliary alignment means, the distance between the two optical elements in the optical axis direction can be adjusted, or the occurrence of an inclination with respect to the optical axis can be prevented.

  In another specific aspect of the present invention, each positioning mark is formed at or near the optical axis of each optical element, and is formed in a circular region having a radius of 0.1 mm. In this case, the accuracy of the main alignment using the positioning marks can be improved, and when the main alignment is performed by, for example, microscopic observation, the two positioning marks can be easily placed in the microscope visual field.

  Further, in another specific aspect of the present invention, the positioning marks are formed on the optical surfaces facing each other of the two optical elements, and the distance between the positioning marks in the optical axis direction when the two optical elements are connected. It is within 0.3 mm. In this case, the accuracy of the main alignment using the positioning mark can be improved. That is, when this alignment is performed by, for example, microscopic observation, both of the two positioning marks can be observed relatively clearly simultaneously.

  In another specific aspect of the present invention, each positioning mark has a concave or convex three-dimensional shape. In this case, the formation of the mark is simple, and simple observation using scattering by the mark becomes possible.

In another specific aspect of the present invention, when the width of each positioning mark in the optical axis direction is hM, the following conditional expression 2 μm <hM <50 μm
Satisfied. When the width hM in the optical axis direction of each positioning mark exceeds 2 μm, scattering from both positioning marks increases moderately, and observation of both positioning marks becomes relatively easy. On the other hand, when the width hM is less than 50 μm, it is possible to prevent the scattering from both positioning marks from being excessive and to suppress the generation of noise signals at the time of detection, thereby increasing the detection accuracy of both positioning marks.

Further, in another specific aspect of the present invention, when the inscribed circle radius of the smaller one of the contours of each positioning mark viewed from the optical axis direction is r, and the distance between the positioning marks in the optical axis direction is d In addition,
0.02 <r / d
Satisfied. When the ratio r / d between the inscribed circle and the interval of the mark exceeds 0.02, the interval between the two marks with respect to the inscribed circle is relatively small, so that it is easy to observe the two marks simultaneously. . That is, since the occurrence of out-of-focus blur is small, it is possible to prevent the image of the mark from being enlarged and to improve the contrast, so that the visibility is remarkably improved and alignment can be performed with sufficient accuracy.

  An optical head according to the present invention is an optical head for forming a spot on a recording surface of an optical information recording medium, and is one of the lens units described above as an objective lens unit that converges an incident light beam as a spot. Is provided. In this case, for example, when forming a spot on the recording surface, the NA can be increased with high accuracy, and the spot can be miniaturized, that is, information can be recorded / reproduced at high speed and high density.

  An optical pickup device according to the present invention includes the above-described optical head, and can read information on the recording surface of the optical information recording medium or write information on the optical information recording medium. In this case, when forming a spot on the recording surface, the NA can be increased with high accuracy, for example, 0.85 or more, and information can be recorded or reproduced at high speed and high density by making the spot finer. In this case, astigmatism, spherical aberration, and the like are less likely to occur during spot formation on the recording surface, and high detection accuracy and the like can be ensured even with an optical head composed of a high NA objective lens. Information can be recorded / reproduced at high speed on an optical disc having a recording density.

[First Embodiment]
Hereinafter, a lens unit for an optical head according to a first embodiment of the present invention will be described.

  FIG. 1 is a side sectional view of the lens unit. This lens unit 10 is obtained by joining a condenser objective lens member 20 and a wavefront aberration correcting phase optical element member 30. The former objective lens member 20 is a pair of molded plastic members, and includes a circular lens portion 21 that is an optical element, and an annular flange portion 22 formed around the lens portion 21. The latter phase optical element member 30 is also a pair of molded plastic members, and includes a circular phase element part 31 that is an optical element and an annular flange part 32 formed around the phase element part 31. Prepare. The flange portion 22 of the objective lens member 20 and the flange portion 32 of the phase optical element member 30 are connected to each other at their joint surfaces by means such as laser, and the assembly of the lens unit 10 is completed.

  In the objective lens member 20, the lens unit 21 is designed to minimize wavefront aberration in, for example, a Blu-ray system. Specifically, the light source light having a wavelength of 408 nm is Blu with a numerical aperture NA of 0.85. -Focusing on the recording surface in the ray disc. On the other hand, the flange portion 22 includes an annular protrusion 22a protruding toward the phase optical element member 30, and an annular step 22b that is lowered outward is formed at the tip. As will be described later, the step 22b is used for alignment in the optical axis OA direction and preliminary alignment in the direction perpendicular to the optical axis OA.

  In the phase optical element member 30, the phase element unit 31 corrects the wavefront aberration at the wavelength of the DVD system while hardly generating a wavefront change at the wavelength of the Blu-ray system, for example. That is, the wavefront aberration is designed to be minimized not only in the Blu-ray system but also in the DVD system. Specifically, the light source light having a wavelength of 408 nm is condensed on the recording surface in the Blu-ray disc with a numerical aperture NA of 0.85, and the light source light having a wavelength of 650 nm for DVD with a numerical aperture NA of 0.65 is used for the DVD disc. Focus on the inside recording surface. On the other hand, the flange portion 32 includes an annular protrusion portion 32a protruding toward the objective lens member 20, and an edge 32b directed inward is formed at the tip. As will be described later, the edge 32b functions as auxiliary alignment means in cooperation with the step 22b provided on the objective lens member 20, and is used for alignment in the optical axis OA direction and preliminary alignment in the direction perpendicular to the optical axis OA. Used for.

  FIG. 2 is an enlarged cross-sectional view of the phase element portion 31 provided in the phase optical element member 30. One optical surface 31a provided in the phase element unit 31 faces the one optical surface 21a of the lens unit 21, and an annular Fresnel lens FL centering on the optical axis OA is formed. The other optical surface 31b provided in the phase element unit 31 is formed on the back surface of the one optical surface 31a, and the planar shape is an annular shape centering on the optical axis OA and has a cross-sectional shape passing through the optical axis OA. A stepped phase structure PH is provided.

  FIG. 3 is an enlarged cross-sectional view of a main part of the lens unit 10 shown in FIG. As shown in the figure, one optical surface 21a provided on the objective lens member 20 side is a smooth convex surface, and has a minute projection 21d as a first positioning mark at the tip on the optical axis OA. The protrusion 21d has a cylindrical outer shape, has a radius r1 of about several tens of μm, and a height hM1 of several μm to several tens of μm. If the radius r1 of the projection 21d is small, the alignment accuracy is easy to improve. However, if the radius r1 of the projection 21d is too small, detection and observation become difficult. . In addition, if the height hM1 of the protrusion 21d is low, the scattering on the upper surface and the side surface of the protrusion 21d is reduced. If the height hM1 of the protrusion 21d is high, the scattering is excessive and the detection accuracy is lowered. Thus, the height hM1 of the protrusion 21d is set as appropriate.

  On the other hand, one optical surface 31a provided in the phase element portion 31 of the phase optical element member 30 is opposed to the optical surface 21a of the objective lens member 20, and a second positioning mark is provided at the center on the optical axis OA. A small protrusion 31d. The protrusion 31d has a cylindrical outer shape, has a radius r2 of about several tens of micrometers, and a height hM2 of several micrometers to several tens of micrometers. That is, the shape and dimensions of the protrusion 31d correspond to the protrusion 21d provided on the optical surface 21a.

  A distance d on the optical axis OA from the optical surface 21a of the lens unit 21 to the optical surface 31a of the phase element unit 31 is set to several μm to several tens of μm. If the distance d between the optical surfaces 21a and 31a is too large, the projections 21d and 31d are too far apart to make it difficult to observe at the same time, and the alignment accuracy for superimposing the images of the projections 21d and 31d decreases. The imaging accuracy of the is reduced. On the contrary, if the distance d between the optical surfaces 21a and 31a is too close, the projections 21d and 31d may come close to each other. Therefore, the distance between the projections 21d and 31d is considered in consideration of imaging accuracy, alignment accuracy, and the like. d is set appropriately.

  FIG. 4 is an enlarged view for explaining alignment between the flange portion 22 of the objective lens member 20 and the flange portion 32 of the phase optical element member 30 shown in FIG. The protruding portion 22a having an uneven shape provided on one flange portion 22 has a step 22b, and the retracted end surface ES1 is another unevenness formed on the protruding portion 32a provided on the other flange portion 32. It contacts the end surface ES1 of the edge 32b having a shape. Accordingly, the positioning of the flange portion 22 and the flange portion 32 in the optical axis OA direction, that is, the distance between the lens portion 21 and the phase element portion 31 in the optical axis OA direction can be accurately set. Further, the step 22b formed on the former protrusion 22a has an outer peripheral surface OS, and the edge 32b formed on the latter protrusion 32a has an inner peripheral surface IS. The diameter of the outer peripheral surface OS is slightly smaller than the diameter of the inner peripheral surface IS, and a slight gap of several μm to several tens of μm is formed between the outer peripheral surface OS and the inner peripheral surface IS. Thereby, rough positioning of the flange portion 22 and the flange portion 32 in the direction perpendicular to the optical axis OA can be performed, and as a result, the lens portion 21 and the phase element portion 31 are positioned in a plane perpendicular to the optical axis OA. Preliminary alignment can be performed. By such preliminary alignment, both the protrusions 21d and 31d shown in FIG. 3 can be arranged close to each other within a certain accuracy. In other words, the projections 22a of the flange portion 22 and the projections 32b of the flange portion 32 can be preliminarily aligned with each other by simple operations such as fitting the projections 22a and 31d of the flange portion 32 together. Thus, when the objective lens member 20 and the phase optical element member 30 after preliminary alignment are observed, the images of both the protrusions 21d and 31d can be observed simultaneously in the microscope field of view. Therefore, at the time of this alignment, the lens portion is moved by relatively finely moving both flange portions 22 and 32 in the direction perpendicular to the optical axis OA so that the images of both projections 21d and 31d completely overlap while observing the microscope field of view. 21 and the phase element unit 31 can be precisely aligned in a direction perpendicular to the optical axis OA, and the resultant imaging performance of the lens unit 10 can be set to a desired accuracy for each wavelength used. it can. In this alignment, illumination light for observation can be introduced into the lens unit 10 from the protrusions 22a and 32b constituting the side surface of the lens unit 10. Thereby, both projections 21d and 31d for this alignment can be observed with dark field illumination, and the measurement using scattered light at both projections 21d and 31d becomes more precise.

  FIG. 5 is a diagram for explaining the production of the objective lens member 20. The surface of the objective lens member 20 includes a first optical surface 21a, a second optical surface 21b, and a flange surface 21c. Here, both optical surfaces 21 a and 21 b correspond to the lens portion 21, and the flange surface 21 c corresponds to the flange portion 32. Each of the surfaces 21a, 21b, and 21c corresponds to the inner surfaces of three mold members that form a cavity formed during injection molding of the objective lens member 20, and is between the first optical surface 21a and the flange surface 21c. Is formed with a first parting line L1 which is a boundary between the pair of mold members, and a second parting line L2 which is a boundary between the pair of mold members between the second optical surface 21b and the flange surface 21c. Is formed. As is clear from the above, the flange surface 21c is formed with the same accuracy as the optical surfaces 21a and 21b. In other words, both the projections 21d and 31d for preliminary alignment are formed with the accuracy of the optical surface, and in the preliminary alignment, it is possible to reduce the inclination of the lens unit 21 and the phase element unit 31 with extremely high accuracy.

[Second Embodiment]
Hereinafter, the lens unit according to the second embodiment will be described. This lens unit is a modification of the lens unit 10 according to the first embodiment with respect to preliminary alignment and the like, and the same portions are denoted by the same reference numerals, and redundant description is omitted. FIG. 6 is a side sectional view of the lens unit 110 according to the present embodiment, and FIG. 7 is a front view of the objective lens member 120. In this case, four grooves RG are formed radially at the tip of the protrusion 122a of the flange portion 22 provided on the objective lens member 120. In these grooves RG, four protrusions PL formed radially at the tips of the protrusions 132a of the flange part 32 provided on the phase optical element member 130 are respectively fitted. As a result, both the protrusions 21d and 31d for the main alignment (see FIG. 3) can be obtained by a simple operation of fitting the groove RG of the protrusion 122a of the flange 122 and the protrusion PL of the protrusion 132a of the flange 132 together. Can be pre-aligned with each other. For example, when the objective lens member 120 and the phase optical element member 130 after the pre-alignment are observed with a microscope, the images of both protrusions 21d and 31d can be simultaneously observed in the observation field. . Furthermore, the distance between the lens unit 21 and the phase element unit 31 in the optical axis OA direction can be precisely set by the contact between the end surfaces of the pair of projections 122a and 132b provided on the flanges 122 and 132.

  In the second embodiment described above, the side edges of the four grooves RG provided in the flange portion 22 of the objective lens member 120 spread radially around the optical axis OA. That is, these grooves RG extend linearly toward the outside and gradually increase in width toward the outside. Although not shown, the four protrusions PL provided on the flange portion 32 of the phase optical element member 130 also extend linearly toward the outside and gradually increase in width toward the outside. By forming the grooves RG and the protrusions PL in such a shape, even when the flange portions 22 and 32 are similarly deformed due to thermal contraction during cooling when forming the objective lens member 120 and the phase optical element member 130, both members Secure fitting of 120 and 130 can be ensured, and the accuracy of preliminary alignment is also maintained.

[Third Embodiment]
FIG. 8 is a diagram schematically showing a configuration of an optical pickup device in which the lens units 10 and 110 according to the first and second embodiments are incorporated in an optical head.

  This optical pickup device has a semiconductor laser 62 for information reproduction of the first optical disc 61 and a semiconductor laser 66 for information reproduction of the second optical disc 65, that is, laser beams having different wavelengths from each other. Can be injected. Laser light from both the semiconductor lasers 62 and 66 is applied to the optical discs 61 and 65 using the objective lens unit (specifically, the lens units 10 and 110 of the first and second embodiments) incorporated in the optical head 200. Irradiated and reflected light from the optical discs 61 and 65 is collected using lens units 10 and 110 as objective lens units.

  First, when reproducing the first optical disc 61, a beam is emitted from the first semiconductor laser 62, and the emitted light beam is transmitted through the beam splitter 71, and the polarized beam splitter 72, the collimator 73, and the quarter wavelength plate 74 are passed through. The light passes through and becomes a circularly polarized parallel light beam. This light beam is focused by the diaphragm 76 and is condensed by the lens units 10 and 110 onto the information recording surface 61b via the transparent substrate 61a of the first optical disk 61.

  The light beam modulated and reflected by the information bit on the information recording surface 61b is transmitted again through the lens units 10 and 110, the stop 76, the quarter wavelength plate 74, and the collimator 73 and enters the polarization beam splitter 72, where Reflected and given astigmatism by the cylindrical lens 78, is incident on the photodetector 79, and a read signal of information recorded on the first optical disc 61 is obtained using the output signal.

  Further, a change in the amount of light due to a change in the shape of the spot and a change in position on the photodetector 79 is detected to perform focus detection and track detection. Based on this detection, the two-dimensional actuator 81 incorporated in the optical head 200 forms the light beam from the first semiconductor laser 62 on the information recording surface 61b of the first optical disc 61 so that the lens units 10 and 100 are optical axes. The lens units 10 and 100 are moved in a direction perpendicular to the optical axis so that the light flux from the semiconductor laser 62 is imaged on a predetermined track.

  On the other hand, when reproducing the second optical disk 65, a beam is emitted from the second semiconductor laser 66, and the emitted light beam is reflected by the beam splitter 71, which is a light synthesizing unit, and is combined with the light beam from the first semiconductor laser 62. Similarly, the light passes through the polarization beam splitter 72, the collimator 73, the quarter wavelength plate 74, the diaphragm 76, and the lens units 10 and 110, and is condensed on the information recording surface 65b via the transparent substrate 65a of the second optical disk 65. .

  The light beam modulated and reflected by the information bit on the information recording surface 65 b is detected again through the lens units 10 and 110, the stop 76, the quarter wavelength plate 74, the collimator 73, the polarization beam splitter 72, and the cylindrical lens 78. A signal for reading information recorded on the second optical disk 65 is obtained using the output information.

  Further, as in the case of the first optical disc 61, a two-dimensional image incorporated in the optical head 200 is detected by detecting a change in the amount of light due to a change in the shape of the spot on the photodetector 79 and a change in position, and detecting a focus. An actuator 81 moves the lens units 10 and 100 for focusing and tracking.

  In the optical pickup device of the third embodiment, since the lens units 10 and 110 including a pair of precisely aligned optical elements are used, spot light from the pair of semiconductor lasers 62 and 66 by the lens units 10 and 110 is used. The imaging accuracy can be improved together. That is, the lens units 10 and 110 provided in the optical head 200 can be operated as an objective lens unit having a high NA, and high detection accuracy and recording accuracy can be ensured while increasing the recording density.

  Although the present invention has been described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications are possible. For example, in the above-described embodiment, the pair of positioning marks for the alignment is formed by the pair of columnar protrusions 21d and 31d. However, these positioning marks are not limited to convex portions, and can be concave portions. The shape is not limited to a cylinder, and various three-dimensional shapes such as a prismatic shape, a pyramid shape, an annular projection shape, and an annular recess shape can be used. Further, these positioning marks are not limited to a single three-dimensional shape, but may be a plurality of three-dimensional shapes, or a fine scattering structure may be formed on an appropriate surface of the three-dimensional shape.

  The alignment mark for alignment is not limited to the three-dimensional shape as described above, but can be a micromirror formed in an appropriate region, or a microregion formed with a mask or a dye.

  In the above embodiment, the lens units 10 and 110 including two optical elements have been described. However, in the case of a lens unit including three or more optical elements, for example, any two adjacent optical elements are used in the above embodiment. Alignment can be performed using the same positioning mark as in FIG. Also in this case, not only preliminary alignment is possible by the flanges formed around the optical elements, but also the assembly of the lens unit is simplified and the positioning accuracy between the optical elements is improved.

It is side sectional drawing of the lens unit of 1st Embodiment. It is an expanded sectional view of the phase element part provided in the phase optical element member. It is an expanded sectional view of the principal part of the lens unit shown in FIG. It is an enlarged view for demonstrating preliminary alignment with the flange part of an objective lens member, and the flange part of a phase optical element member. It is a figure explaining manufacture of an objective-lens member. It is side sectional drawing of the lens unit which concerns on 2nd Embodiment. It is a front view of an objective lens member among the lens units of FIG. It is a block diagram explaining the structure of the optical pick-up apparatus of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Lens unit, 20 ... Objective lens member, 21 ... Lens part, 21a, 21b ... Optical surface, 21d ... Projection, 22 ... Flange part, 22a ... Projection part, 22b ... Step, 30 ... Phase optical element member, 31 ... Phase element section 31a, 31b ... Optical surface, 31d ... Projection, 32 ... Flange section, 61, 65 ... Optical disk, 62 ... First semiconductor laser, 66 ... Second semiconductor laser, 71 ... Beam splitter, 72 ... Polarizing beam splitter 79 ... Photodetector, FL ... Fresnel lens, OA ... Optical axis, PH ... Phase structure

Claims (11)

Preliminarily aligning in the direction perpendicular to the optical axis by the auxiliary alignment means of the flange portion for fitting the protrusions of the flange portion extending around each of the two optical elements, at least one of which is a lens;
After preliminary alignment, the flange portions of the two optical elements are relatively positioned in the direction perpendicular to the optical axis while observing positioning marks for optical axis alignment formed on at least one optical surface of each of the two optical elements. A step of performing the main alignment by slightly moving
A method of manufacturing a lens unit comprising: Two optical elements, at least one of which is a lens,
A positioning mark for optical axis alignment formed on at least one optical surface of each of the two optical elements;
Auxiliary alignment means extending around each of the two optical elements and preliminarily aligning the two optical elements with respect to a direction perpendicular to the optical axis by mutual connection is provided. A lens unit including a flange portion fixed to the lens. 3. The lens unit according to claim 2, wherein each of the two optical elements and each flange extending around the two optical elements are plastic members formed by integral molding. 4. The auxiliary alignment means according to claim 2, wherein the concave and convex shapes formed to face each of the flange portions are fitted with a gap in a direction perpendicular to the optical axis . The lens unit according to one item . Wherein the positioning mark, the is formed on the optical axis or its vicinity of the respective optical elements, either of claims 2 4, radius, characterized in that it is formed in a circular region of 0.1mm The lens unit according to claim 1. The positioning mark is formed on each of the opposing optical surfaces of the two optical elements, and the distance between the positioning marks in the optical axis direction when the two optical elements are connected is within 0.3 mm. The lens unit according to any one of claims 2 to 5, wherein the lens unit is characterized. The lens unit according to any one of claims 2 to 6, wherein each of the positioning marks has a concave or convex three-dimensional shape. When the width in the optical axis direction of each positioning mark is hM, the following conditional expression 2 μm <hM <50 μm
The lens unit according to claim 7, wherein: Of the contours seen from the optical axis direction of each positioning mark, the smaller inscribed circle radius is r, and the optical axis direction interval between the positioning marks is d,
0.02 <r / d
The lens unit according to claim 7, wherein the lens unit is satisfied. An optical head for forming spots on a recording surface of an optical information recording medium,
An optical head comprising the lens unit according to claim 2 as an objective lens unit that converges an incident light beam as a spot.   An optical pickup device comprising the optical head according to claim 10 and capable of reading information on an optical information recording medium or writing information on the optical information recording medium.

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