JP2004295998A - Objective lens, optical pickup device and optical information recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To facilitate the handling when an objective lens is assembled to a pickup device, concerning the objective lens which is hard to minimize an aberration of the lens. <P>SOLUTION: The optical pickup device, in which the objective lens 10 is assembled taking the astigmatic direction into consideration, is obtained since a chamfer arranged in the objective lens 10 is fixed to a lens holder 50 in the state facing to the specified direction. Thus, the astigmatism as the optical pickup device is reduced, then the performance as the optical pickup device is improvable as the result. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an objective lens for a high recording density optical disc, and particularly to an objective lens having high difficulty in assembling. Further, the present invention relates to an optical pickup device or an optical information recording / reproducing device using such an objective lens.
[0002]
[Prior art]
As one of means for improving the recording density of so-called optical disks such as CDs and DVDs, increasing the numerical aperture (NA) of an objective lens has been performed. CD requires NA of about 0.45 to 0.53, DVD requires NA of 0.60 to 0.65, and next-generation blue laser requires NA of 0.60 to 0.85.
[0003]
As described above, in a lens having a large NA, the amount of aberration generated by shifting or tilting the lens surface or changing the thickness on the lens axis from a design is larger than that of a lens having a small NA. Therefore, the higher the NA lens becomes, the more difficult it is to produce spherical aberration, coma aberration and astigmatism as much as possible. In the optical pickup device, as the demand for mounting errors of the objective lens becomes stricter, the aberration level of the objective lens increases, and the load on the assembling process is further increased. Among them, there is disclosed one in which an objective lens is provided with astigmatism to improve off-axis characteristics in order to widen an allowable error value in an operating environment of an optical pickup device (see Patent Document 1).
[0004]
[Patent Document 1]
Patent No. 3104780
[Problems to be solved by the invention]
The objective lens described in Patent Document 1 has an astigmatism in the objective lens in consideration of off-axis use at the time of tracking, thereby suppressing an aberration generated at the time of tracking as an optical pickup device. However, there is no description on how to attach the objective lens to the pickup. Here, while observing the spot of the optical pickup device, the individual objective lenses can be bonded to the lens holder, but this is not preferable in view of the number of steps.
[0005]
In addition, in the case of a compatible lens or a high NA lens having a high degree of difficulty in manufacturing a lens, it is difficult to suppress the occurrence of aberrations, not only off-axis. Therefore, when such an objective lens is incorporated in an optical pickup device, more consideration is required. That is, it is necessary to assemble such an objective lens such that the aberration does not increase after the production of the interchangeable type or the high NA type objective lens.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to facilitate handling of an objective lens in which it is difficult to minimize aberrations of the lens when assembling it into a pickup device.
[0007]
Another object of the present invention is to provide an optical pickup device and an optical information recording / reproducing device provided with the above-mentioned objective lens.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, a first objective lens according to the present invention is provided with a pair of optical surfaces and at least one side of the pair of optical surfaces to provide an optical function using a phase difference. An objective lens for an optical pickup including a phase difference providing unit and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, wherein the reference mark is oriented in a certain direction. The distribution range of the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, is within 90 degrees. Here, the “reference mark” is not limited to a mark that can be visually recognized by a human, and may be a characteristic portion that can be identified by various sensors using light, electricity, or the like. Note that the reference mark is not limited to a mark formed with a notch, protrusion, printing, or the like in the astigmatism direction, and may be a mark having no mark only in the astigmatism direction. The term “phase difference providing unit” refers to a unit that gives a specific effect by giving a predetermined phase difference to an incident light beam for each incident light beam wavelength. Specifically, a phase shift type in which a part of the same curved surface is moved in parallel in the optical axis direction to form an annular step may be used, or a blaze type annular diffraction structure may be formed. Further, “the distribution range in the astigmatism direction is within 90 degrees” means that when considering a plurality of objective lenses obtained by the method of the present invention, i ( Let i = 1, 2, 3,...) the astigmatism direction of the th lens be θi
α−45 ° ≦ θi ≦ α + 45 ° (α is a constant) (1)
Is satisfied. However, when a plurality of objective lenses are formed using a single or a plurality of molds described later, the value of the constant α may be different for each cavity of the mold, but preferably all the cavities of the mold are used. To make the constant α substantially the same. More preferably, in consideration of a later assembling step, α = 0 is preferably set in all the cavities.
[0009]
In the objective lens, when the reference mark is oriented in a certain direction, the distribution range of the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, is within 90 degrees. This objective lens can be assembled to the optical pickup device while taking into consideration the astigmatism direction of the lens. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, astigmatism as the optical pickup device can be reduced. Further, when astigmatism in a specific direction is allowed in the optical pickup device, if the astigmatism direction of the objective lens is set and attached in that direction, the performance as the optical pickup device can be improved.
[0010]
It should be noted that, although an objective lens provided with the above-described phase difference providing means is required to have high specifications, it is usually not easy to suppress aberrations to such an extent that such requirements are sufficiently satisfied. However, by using the reference mark, a high-performance optical pickup device can be assembled while controlling the astigmatism direction of the objective lens.
[0011]
A second objective lens according to the present invention is an objective lens for an optical pickup, and is formed on a pair of optical surfaces and at least one side of the pair of optical surfaces, and uses an optical difference utilizing a phase difference. A phase difference providing unit for providing a function; and a reference mark for displaying an astigmatism direction, which is a direction of astigmatism existing after forming the pair of optical surfaces, within a predetermined tolerance range. Here, “the astigmatism direction is within a predetermined tolerance range” means that the direction of the reference mark when the astigmatism direction is the reference direction is φ.
β−45 ° ≦ φ ≦ β + 45 ° (β is a constant) (2)
Is satisfied. However, when a plurality of objective lenses are formed using a single or a plurality of molding dies described later, the value of the constant β may be different for each cavity of the molding dies. It is preferable for convenience of assembly.
[0012]
In the objective lens, the reference mark indicates the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, within a predetermined tolerance range. By controlling the astigmatism direction, this objective lens can be assembled to the optical pickup device. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, astigmatism as the optical pickup device can be reduced. Further, when astigmatism in a specific direction is allowed in the optical pickup device, if the astigmatism direction of the objective lens is set and attached in that direction, the performance as the optical pickup device can be improved.
[0013]
In a specific aspect of the objective lens, the phase difference providing means is a diffraction structure. In this case, various functions including correction of chromatic aberration and the like can be imparted to the objective lens by the presence of the diffraction structure.
[0014]
Further, a third objective lens according to the present invention includes a pair of optical surfaces, and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and at least two types of optical disks. An objective lens for an optical pickup that can be used, wherein when the reference mark is oriented in a certain direction, of the astigmatism present after the formation of the pair of optical surfaces, the astigmatism at the time of use of an optical disc having the highest recording density. The distribution range of the astigmatism direction which is the direction of the astigmatism is within 90 degrees.
[0015]
In the objective lens, when the reference mark is oriented in a certain direction, among the astigmatisms existing after the formation of the pair of optical surfaces, the astigmatism direction is the direction of the astigmatism when the optical disc having the highest recording density is used. Since the distribution range of the astigmatism direction is within 90 degrees, the objective lens can be assembled to the optical pickup device while considering the astigmatism direction of the objective lens when using an optical disc having the highest recording density. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, the astigmatism as a compatible optical pickup device can be reduced. . In addition, when astigmatism in a specific direction is allowed in the optical pickup device, setting the astigmatism direction of the objective lens in that direction and mounting the objective lens can improve the performance as a compatible optical pickup device. it can.
[0016]
The objective lens that can be used for two or more types of optical disks as described above requires a high specification especially when the optical disk with the highest recording density is used. Although it is usually not easy to suppress aberrations, it is possible to assemble a high-performance optical pickup device while controlling the astigmatism direction of the objective lens by using the above-described reference marks.
[0017]
Further, a fourth objective lens according to the present invention includes a pair of optical surfaces, and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and includes at least two types of optical discs. An objective lens for an optical pickup that can be used, wherein, among the astigmatisms present after the formation of the pair of optical surfaces, the astigmatism direction that is the direction of the astigmatism when the optical disc with the highest recording density is used is determined. A reference mark to be displayed within the tolerance range.
[0018]
In the above-mentioned objective lens, this objective lens can be assembled to the optical pickup device while taking into consideration the astigmatism direction of the objective lens when using an optical disc having the highest recording density. The aberration can be reduced, or the performance as a compatible optical pickup device can be improved.
[0019]
A fifth objective lens according to the present invention includes a pair of optical surfaces and a reference mark provided on a part of the entire surface including the periphery of the pair of optical surfaces, and has a numerical aperture of 0.65 or more. Wherein the distribution range of the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, is 90 degrees when the reference mark is oriented in a certain direction. It is characterized by being within.
[0020]
In the objective lens, when the reference mark is oriented in a certain direction, the distribution range of the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, is within 90 degrees. This objective lens can be assembled to the optical pickup device while taking into consideration the astigmatism direction of the lens. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, astigmatism as the optical pickup device can be reduced. Further, when astigmatism in a specific direction is allowed in the optical pickup device, if the astigmatism direction of the objective lens is set and attached in that direction, the performance as the optical pickup device can be improved.
[0021]
It should be noted that the objective lens for an optical pickup having a numerical aperture of 0.65 or more, as described above, is required to suppress aberrations to such an extent that the requirements are sufficiently satisfied, although high specifications are required. Is usually not easy, but by using the above-described reference mark, a high-performance optical pickup device can be assembled while controlling the astigmatism direction of the objective lens.
[0022]
A sixth objective lens according to the present invention includes a pair of optical surfaces and a reference mark provided on a part of the entire surface including the periphery of the pair of optical surfaces, and has a numerical aperture of 0.65 or more. An objective lens for an optical pickup, comprising: a reference mark for displaying an astigmatism direction, which is a direction of astigmatism existing after the formation of the pair of optical surfaces, within a predetermined tolerance range. I do.
[0023]
In the above-mentioned objective lens, the objective lens can be assembled to the optical pickup device while taking into consideration the astigmatism direction of the objective lens, so that the astigmatism of the optical pickup device can be reduced, or Performance can be improved.
[0024]
In a specific mode of the first to sixth objective lenses, an angle between the astigmatism direction and the azimuth of the reference mark is 45 degrees or less. In this case, it means that α = 0 and β = 0 in the above equation (1).
[0025]
In another specific mode of the objective lens, the objective lens is formed by molding using a molding die, and is provided with astigmatism forming means for giving astigmatism to the molding die. In this case, since the mold is used, the objective lens can be stably supplied. Further, since the direction of astigmatism can be determined at the time of molding, it is easy to form the reference mark. When the astigmatism forming means is provided in the molding die, the astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens can be obtained by appropriately mounting the objective lens in an appropriate position in the optical pickup device. Aberration can be positively controlled to cancel.
[0026]
In another specific mode of the objective lens, the molding die has a fixed-side fixed die and a movable-side movable die that are separable from each other, and the astigmatism forming unit has a fixed die. Is provided. In this case, a relatively precise astigmatism can be stably given to the objective lens by the fixed type.
[0027]
The movable mold is usually composed of two parts, that is, a member that determines the outer peripheral portion of the objective lens and a member that forms the optical surface. Here, since each member has a clearance of several microns, it is possible to control the coma as a lens by finely adjusting the surface shift and the surface tilt of the several microns by a spacer or the like. Therefore, the astigmatism amount and the direction of the astigmatism of the objective lens are controlled by providing the astigmatism in the fixed type, and the astigmatism is not provided in the movable type. It is more advantageous to control coma aberration and spherical aberration as a lens in view of production stability.
[0028]
In another specific aspect of the objective lens, the astigmatism forming means is a positional shift of a molding surface formed by applying a mechanical pressure when holding the molding die. In this case, the astigmatism forming means can be provided without performing special processing on the mold, and adjustment for achieving the target amount of astigmatism is easy.
[0029]
In another specific embodiment of the objective lens, the objective lens is formed by molding using a mold, and astigmatism is formed by applying at least one of pressure and heat after molding.
[0030]
In another specific aspect of the objective lens, the reference mark is correlated with a gate used for injection molding. In this case, a projection or notch corresponding to the gate portion can be used as a reference mark. The gate portion used for injection molding serves as a resin inflow port, and retains some shape characteristic after molding, and can be used as it is as a reference mark for determination. Further, in injection molding, the direction of the gate portion is an important one which serves as a reference in various senses, and it is convenient for handling to display optical characteristics with reference to the gate portion. That is, since the gate portion has a relationship with the occurrence of astigmatism, it is relatively easy to match or orthogonal to the astigmatism direction, or it is easy to intentionally form astigmatism in the gate direction. In such a case, a projection or notch formed due to the presence of the gate portion can be automatically used as a reference mark.
[0031]
In another specific aspect of the objective lens, astigmatism existing after the formation of the pair of optical surfaces is a surface astigmatism caused by a surface shape of the pair of optical surfaces. In this case, astigmatism due to the external shape can be managed. In the case where astigmatism existing after the formation of the pair of optical surfaces is assumed to be astigmatism, it is convenient to control the amount of astigmatism intentionally.
[0032]
Further, in another specific mode of the objective lens, when the wavelength used of the objective lens is λ (nm), the difference in the aspheric displacement amount corresponding to the surface astigmatism is 0.03λ (nm) or more. .49λ (nm) or less. Here, if the difference in the amount of displacement of the aspherical surface is too large, the amount of astigmatism of the objective lens itself tends to increase. If this is too small, it will be difficult to control the direction of astigmatism. That is, under the above conditions, astigmatism generated by other optical elements can be canceled while suppressing generation of astigmatism, so that a high-performance optical pickup device can be provided.
[0033]
In another specific aspect of the objective lens, the difference in the amount of displacement of the aspheric surface is 0.03λ (nm) or more and 0.25λ (nm) or less. In this case, a higher performance optical pickup device can be provided.
[0034]
Further, an optical pickup device according to the present invention includes the above-described objective lens and a lens holder that fixes the objective lens with the reference mark directed in a certain direction.
[0035]
In the above optical pickup device, since the reference mark provided on the objective lens is fixed to the lens holder in a state where the reference mark is oriented in a certain direction, the device can incorporate the objective lens while considering the astigmatism direction. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, astigmatism as the optical pickup device can be reduced. Further, when astigmatism in a specific direction is allowed in the optical pickup device, if the astigmatism direction of the objective lens is set and attached in that direction, the performance as the optical pickup device can be improved.
[0036]
In a specific aspect of the optical pickup device, the lens holder includes a direction recognition unit for aligning the reference mark provided on the objective lens. In this case, a high-precision optical pickup device can be assembled by simple alignment using the reference mark and the direction recognition means.
[0037]
In another specific aspect of the optical pickup device, optical pickups of at least two types of optical disks are performed. In this case, the optical pickup device can be adapted to various standards, and a highly accurate and multifunctional optical information recording / reproducing device can be provided.
[0038]
Further, another optical pickup device according to the present invention includes a first objective lens according to the present invention used for an optical pickup of a specific type of optical disk and a second objective lens used for an optical pickup of another type of optical disk. An objective lens; and a lens holder for fixing the first and second objective lenses, respectively. Also in this case, the optical pickup device can be adapted to various standards, and in particular, in the optical pickup using the objective lens of the present invention, highly accurate optical information recording and reproduction can be performed.
[0039]
Still another optical pickup device according to the present invention includes a first objective lens of the present invention used for an optical pickup of a specific type of optical disk, and an optical pickup device of the present invention used for an optical pickup of another type of optical disk. A second objective lens; and a lens holder for fixing the first and second objective lenses, respectively. Also in this case, the optical pickup device can be adapted to various standards, and a highly accurate and multifunctional optical information recording / reproducing device can be provided.
[0040]
Note that two objective lenses can be provided in the optical pickup device. In such a case, a two-lens-one-actuator type and a two-lens-two-actuator type are considered. The two-lens, one-actuator type is preferable because the entire apparatus is simplified. However, in one actuator type, it is preferable that the lens tilt direction for coma aberration correction is constant regardless of the objective lens. In this case, the astigmatism amount, the astigmatism direction, The amount of coma aberration and the direction of coma aberration may be attached in consideration of the lens arrangement, the astigmatism generation direction of the light source, or the like, or the attaching direction may be determined and separately set on the objective lens side. After the type of the disc is determined on the optical pickup device side, an optimal lens tilt servo may be applied to the corresponding objective lens.
[0041]
Further, an optical information recording / reproducing device according to the present invention includes the above-described optical pickup device according to the present invention.
[0042]
The above optical information recording / reproducing device incorporates an optical pickup device incorporating an objective lens while taking into account the direction of astigmatism, so that high-density optical information recorded on various disks can be recorded / reproduced with high precision. Can be. The "optical information recording / reproducing device" means a video deck, a personal computer, an external device, or the like on which the above-described optical pickup device is mounted.
[0043]
BEST MODE FOR CARRYING OUT THE INVENTION
[First Embodiment]
FIG. 1A is a front view illustrating the structure of an objective lens according to an embodiment of the present invention, and FIG. 1B is a rear view thereof. The objective lens 10 is an objective lens for an optical pickup, and includes a lens body 12 having a diffraction pattern and a flange portion 14 for supporting the lens body 12 from the periphery. The objective lens 10 can have an NA of 0.65 or more for 650 nm pickup light, for example, and can be used as a compatible type objective lens that can be used for optical pickups of both CD and DVD optical disks. The lens 10 itself has a high error sensitivity and is difficult to create.
[0044]
The lens body 12 has a convex lens-like outer shape as a whole, and a plurality of orbicular divided surfaces 12c are formed concentrically on an upper surface 12a constituting one optical surface. Each divided surface 12c is formed of an aspherical surface or a spherical surface, and a stepped diffraction groove 12d is formed as a phase difference providing means between a pair of adjacent divided surfaces 12c. The radius of curvature of each divided surface 12c, the width and radius of the annular zone, and the like are appropriately set according to the purpose of use of the objective lens 10.
[0045]
Further, the lower surface 12b constituting the other optical surface in the lens body 12 is a smooth convex surface on the entire surface formed of an aspherical surface or a spherical surface, and does not form a diffraction pattern as in the case of the upper surface 12a.
[0046]
The flange portion 14 is a portion used when fixing the objective lens 10 to a holder or the like, and is an annular body extending around the lens body 12. A cutout 16 is formed in a part of the flange portion 14 as a reference mark serving as an index of the spherical aberration direction of the objective lens 10. This arc-shaped notch 16 has a cylindrical surface that is depressed by appropriately cutting the gate portion formed corresponding to the position of the injection gate when the objective lens 10 is injection-molded by using an end mill or the like after molding. It was done.
[0047]
FIG. 2A is a diagram illustrating the relationship between the astigmatism direction indicating the direction of astigmatism of the objective lens 10 and the azimuth of the notch 16 that is a reference mark. In the illustrated objective lens 10, the notch 16 is set in the upper part of the drawing. Therefore, ideally, it is desirable to make the astigmatic direction ASD coincide with the direction of the notch 16 as shown by a solid line. However, it is not always easy to make the astigmatism direction ASD exactly coincide with the direction of the notch 16. That is, unless the spot shape of the objective lens 10 is actually measured or its wavefront aberration is not measured by an interferometer, it is difficult to specify the astigmatism direction ASD accurately. If the notch 16 is formed in the lens 10, the burden of the inspection becomes excessive, and the cost of the objective lens 10 increases. For this reason, in the present embodiment, by modifying the manufacturing method of the objective lens 10 or the like, a certain degree of astigmatism, though not excessive, appears in the direction of the injection gate when the objective lens 10 is formed. If the astigmatism direction ASD is controlled by the manufacturing method as described above, the astigmatism direction ASD may not always be able to be accurately controlled. , Within a certain distribution range (90 °) corresponding to the error as shown by the dashed line. This means that the notch 16 is formed within a certain allowable range (± 45 ° in the illustrated case) around the astigmatism direction ASD. The notch 16 at the position of the dashed line is the most deviated within the allowable range (see FIG. 2B).
[0048]
FIG. 3 is a perspective view illustrating astigmatism intentionally generated in the objective lens 10. When the objective lens 10 has astigmatism, the astigmatism is caused by the birefringence of the material forming the objective lens 10 and by the surface shape of the objective lens 10 (so-called astigmatism). Conceivable. Hereinafter, it is assumed that astigmatism is imparted by adjusting the shape of the molding surface of the mold, and the astigmatism imparted to the objective lens 10 is a surface astigmatism caused by the surface shape. Note that, in recent resin materials and glass materials, the birefringence component has become smaller, and the above-described astigmatism is considered to be substantially the upper surface astigmatism. There are many. However, when astigmatism due to birefringence cannot be ignored, the astigmatism direction ASD is set in consideration of such birefringence astigmatism, and the notch 16 is formed.
[0049]
When astigmatism is caused by surface astigmatism, considering a circle CI with a radius r around the optical axis OA, the upper surface 12a and the lower surface 12 are determined from two points on the circle CI corresponding to the two orthogonal directions X and Y. A line segment parallel to the optical axis OA is dropped on 12b. The lengths ΔX and ΔY of these line segments are equal to each other if the upper surface 12a is completely symmetric about the optical axis OA. However, if the upper surface 12a is asymmetric about the optical axis OA, Will be different values. Here, assuming that the direction X and the direction Y match the astigmatism direction due to surface astigmatism,
ΔX ≠ ΔY,
The aspheric displacement difference AD is
AD = | ΔX−ΔY |
Given by As is clear from the above description, the surface astigmatism is caused by the asymmetry of the upper surface 12a and the lower surface 12b of the objective lens 10.
[0050]
FIG. 4 is a view for explaining the direction of astigmatism given to the objective lens 10, that is, the direction of astigmatism. When the objective lens 10 has a plane deviation in a specific direction, the condensed spot SP of the objective lens 10 near the best defocus position BDP and near (in focus) and far from the objective lens 10 (out focus). Are narrowed down in two orthogonal directions. Here, the direction in which the focused spot SP of the objective lens 10 is narrowed and extended on the far side (out focus) of the objective lens 10 (the direction in which the wavefront advances) is referred to as the astigmatism direction ASD. In this case, the astigmatism direction ASD has an angle θ with reference to the X-axis direction having the notch 16. In the objective lens 10 of the present embodiment, this angle is
−45 ° ≦ θ ≦ 45 °
The objective lens 10 is provided with a surface astigmatism as follows.
[0051]
FIG. 5 is a diagram conceptually illustrating a case where surface astigmatism is measured as a wavefront aberration, and shows an example in which the wavefront aberration at each position of the objective lens 10 is measured by an interferometer. In this case, the wavefront advances in the direction in which the notch 16 exists, and the sign “+” is added. That is, the direction with the sign “+” is the astigmatism direction ASD in which the wavefront advances due to astigmatism.
[0052]
FIG. 6 is a side sectional view for explaining the shape and structure of a molding die for manufacturing the objective lens 10 shown in FIG. 1 and the like. The molding die 30 includes a fixed die 32 and a movable die 34. As shown, the movable mold 34 is abutted against the fixed mold 32 to form a cavity CA between the two molds 32 and 34, and a gate GA communicating with the cavity CA is formed in a part around the cavity CA. You. The cavity CA is supplied with molten plastic resin through a gate GA to fill the inside.
[0053]
The fixed mold 32 has a smooth concave molding surface 32a facing the movable mold 34, and an annular groove molding surface 32b disposed around the molding surface 32a. The former molding surface 32a corresponds to one optical surface, that is, the lower surface 12b, of the objective lens 10 (see FIG. 1) which is a molded product, and the latter molding surface 32b corresponds to the flange portion 14 provided around the objective lens 10. Corresponding.
[0054]
The movable mold 34 includes a projecting portion 41 that is a mold member on the center side, and a mold body 43 that supports the projecting portion 41 from the periphery. Of these, the central molding surface 41a formed in the protruding portion 41 corresponds to the other optical surface of the objective lens 10, that is, the upper surface 12a, and has a concave surface as a whole, and has an annular diffraction pattern. have. This diffraction pattern usually has a depth of several μm. On the other hand, the peripheral molding surface 43 a formed by the mold body 43 corresponds to the flange 14 around the objective lens 10.
[0055]
The protruding portion 41 is slidable in the axis AX direction while being fitted in a hole 43b provided in the mold body 43. After the mold is opened to separate the two molds 32 and 34, the protrusion 41 is moved toward the fixed mold 32 with respect to the mold body 43, so that the objective lens 10 remaining on the movable mold 34 can be easily separated from the mold. Can be. The objective lens 10 thus formed is intentionally provided with a surface astigmatism in which the astigmatism direction is set in the direction of the gate GA.
[0056]
FIG. 7 is a view for explaining an example of astigmatism forming means formed on the molding die 30 of FIG. If, for example, the fixed mold 32 of the molding dies 30 is originally spherical, by giving a slight aberration to the fixed mold 32, the lower surface 12b of the objective lens 10 can be given a surface astigmatism. In FIG. 7, the curvature of the molding surface 32a of the fixed mold 32 in the gate direction G1 where the gate GA is located is slightly larger than the curvature in the direction G2 orthogonal to the gate direction G1. That is, astigmatism is given to the molding surface of the fixed mold 32 itself. Thus, the aspherical surface displacement amount difference AD described in FIG. 3 can be given to the molding surface 32a, that is, the lower surface 12b, to a desired degree, and the surface astigmatism along the gate direction G1 can be accurately formed. Such processing can be realized relatively easily by program control of a die processing apparatus for manufacturing the molding die 30.
[0057]
In a specific example, when the wavelength used of the objective lens 10 is λ ≒ 650 nm, the aspherical displacement amount difference AD given to the objective lens 10 is 0.03λ (nm) or more and 0.49λ at the outer peripheral portion of the effective diameter. (Nm) or less. Since the aspheric displacement difference AD, that is, the astigmatism amount, has the purpose of controlling the astigmatism direction, the direction cannot be controlled even if the astigmatism amount given to the molding die 30 is too small, and the molding cannot be performed. If the amount of astigmatism given to the mold 30 is too large, the amount of astigmatism of the lens itself becomes large, which is not preferable. That is, the range is set such that astigmatism generated by, for example, other optical elements can be easily canceled while preventing the surface astigmatism from becoming extremely large and deteriorating the characteristics of the objective lens. Further, in this case, by setting the aspherical surface displacement difference AD between 0.03λ (nm) and 0.25λ (nm), astigmatism occurring in each part can be reduced, and a high-performance optical pickup An apparatus or the like can be provided.
[0058]
The method of forming astigmatism by the molding die 30 is not limited to the above. For example, an aspherical displacement amount difference AD corresponding to astigmatism can be given to the movable mold 34 side of the molding die 30. With respect to the molding die 30, particularly the movable die 34, it is sufficiently possible to provide astigmatism to a diffraction pattern for imparting a phase difference by controlling a processing program.
[0059]
Further, the cooling of the mold 30 can be asymmetric about the axis AX. For example, by rapidly cooling a pair of end portions of the cavity CA formed by the two molds 32 and 34 in a direction perpendicular to the gate GA, the astigmatism direction corresponding to the direction of the gate GA, that is, the notch 16 can be obtained. Can be provided.
[0060]
8A and 8B are a side sectional view and a plan view for explaining a method of attaching the objective lens 10 shown in FIG. 1 and the like to a lens holder of an optical pickup. The lens holder 50 has an opening 52 for fitting the objective lens 10, and a step 54 for supporting the flange portion 14 of the objective lens 10 is formed around the opening 52. Further, a circular depression 56 serving as a direction recognizing means is formed at one position around the opening 52.
[0061]
The objective lens 10 is fitted into the opening 52 of the lens holder 50, and the notch 16 of the objective lens 10 and the depression 56 of the lens holder 50 are matched with the naked eye, for example, or the notch is automatically recognized by an imaging device or the like provided in the assembly device. 16 and the depression 56 are aligned. Thereafter, the step 54 is irradiated with UV light having an appropriate intensity from below the lens holder 50. Since the lens holder 50 substantially transmits the UV light and heats the flange portion 14 of the objective lens 10, the flange portion 14 and the step 54 can be permanently bonded. As described above, the objective lens 10 can be fixed to the lens holder 50 with high precision, and the rotational position of the objective lens 10 can be aligned with the lens holder 50. That is, since the objective lens 10 has astigmatism in a specific direction with respect to the lens holder 50, the light incorporating the lens holder 50 can be measured without measuring the shape of the condensed spot of the objective lens 10. The astigmatism of the pickup device can be controlled. The case where the single objective lens 10 is incorporated in the single lens holder 50 has been described above. However, in a production line or the like, a large number of objective lenses 10 are incorporated in the lens holder 50 that is continuously conveyed. At this time, if the objective lens 10 is attached to any of the lens holders 50 using the notch 16 of the objective lens 10 as a mark, the workability of the assembling process is greatly improved.
[0062]
Note that the notch 16 and the depression 56 do not necessarily have to match. For example, the objective lens 10 can be fixed to the lens holder 50 in a state where the notch 16 is aligned in a direction rotated clockwise by 90 ° with respect to the depression 56. In short, it is only necessary that an index for arranging the objective lens 10 in the lens holder 50 exists in a predetermined positional relationship.
[0063]
FIG. 9 is a diagram schematically showing a configuration of an optical pickup device including the objective lens 10 shown in FIG. 1 and the like.
[0064]
This optical pickup device has a semiconductor laser 62 for reproducing information on a first optical disk 61 as an information recording medium and a semiconductor laser 66 for reproducing information on a second optical disk 65 as an information recording medium. That is, laser beams having different wavelengths can be emitted. The laser beams from the two semiconductor lasers 62 and 66 are applied to the optical disks 61 and 65 using the above-described objective lens 10, and the reflected lights from the optical disks 61 and 65 are collected using the objective lens 10. . The thickness of one substrate of the optical disk is 0.6 ± 0.1 mm, and the thickness of the other substrate is 1.2 ± 0.1 mm, which are different from each other.
[0065]
First, when reproducing the first optical disk 61, a beam is emitted from the first semiconductor laser 62, and the emitted light beam passes through the coupling lens 62a and the beam splitter 71, and is polarized, and the polarization beam splitter 72, the collimator 73, and the 1 / The light passes through the four-wavelength plate 74 to become a circularly polarized parallel light beam. This light beam is stopped down by the stop 76, and is converged by the objective lens 10 on the information recording surface 61b via the transparent substrate 61a of the first optical disk 61.
[0066]
The light flux modulated and reflected by the information bit on the information recording surface 61b again passes through the objective lens 10, the stop 76, the quarter-wave plate 74, and the collimator 73, enters the polarization beam splitter 72, and is reflected there. Astigmatism is given by the cylindrical lens 78, and the light is incident on the photodetector 79 through the concave lens 78a, and a read signal of information recorded on the first optical disk 61 is obtained using the output signal.
[0067]
Further, a change in the light amount due to a change in the shape and position of the spot on the photodetector 79 is detected, and focus detection and track detection are performed. Based on this detection, the two-dimensional actuator 81 moves the objective lens 10 on the lens holder 50 in the direction of the optical axis so that the light beam from the first semiconductor laser 62 is focused on the recording surface 61b of the first optical disc 61. At the same time, the objective lens 10 on the lens holder 50 is moved in a direction perpendicular to the optical axis so that the light beam from the semiconductor laser 62 is focused on a predetermined track.
[0068]
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 flux is reflected by the beam splitter 71 via the coupling lens 66a, and is emitted from the first semiconductor laser 62. Similarly to the light beam, the light passes through the polarization beam splitter 72, the collimator 73, the quarter-wave plate 74, the stop 76, and the objective lens 10, 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 65b is again passed through the objective lens 10, the stop 76, the quarter-wave plate 74, the collimator 73, the polarization beam splitter 72, the cylindrical lens 78 and the like. The signal is incident on the photodetector 79, and a read signal of information recorded on the second optical disk 65 is obtained using the output information.
[0070]
Further, as in the case of the first optical disk 61, a change in the light amount due to a change in the shape and position of the spot on the photodetector 79 is detected, and focus detection and track detection are performed. Then, the objective lens 10 on the lens holder 50 is moved for tracking.
[0071]
In the optical pickup device described above, the notch 16 provided in the objective lens 10 is fixed to the lens holder 50 in a state where the notch 16 is oriented in a fixed direction. Therefore, the optical pickup incorporating the objective lens 10 while taking into account the direction of astigmatism. Device. Therefore, astigmatism as the optical pickup device can be reduced, and the performance as the optical pickup device can be improved. It should be noted that aberrations other than astigmatism, such as spherical aberration and coma, can be controlled by tilt servo and focus servo in the optical pickup device. It is easy to assemble the device with high accuracy.
[0072]
In the above-described first embodiment, the diffraction pattern is formed on one surface of the lens body 12 of the objective lens 10. However, the present invention is also applied to a case where no diffraction pattern is formed on both optical surfaces of the lens body 12. be able to. In addition, the optical surface 12b on the fixed mold side is adjusted for surface astigmatism, and the optical surface 12a on the movable mold side is corrected for other aberrations such as coma, so that the aberration can be controlled independently. Becomes possible.
[0073]
Further, in the above-described first embodiment, the astigmatism is formed on the objective lens 10 by giving a slight aberration to the fixed mold 32, that is, by changing the processing surface in the orthogonal direction. It is also possible to give the mold astigmatism as a result by taking into account predetermined factors such as the bolt tightening direction when incorporating the molding die into the die set.
[0074]
In the first embodiment, the direction of the plane asymmetry is specified using the notch 16 as a reference mark. However, the protrusion corresponding to the gate GA may be left in the flange portion 14 of the objective lens 10 to form the objective lens 10. The astigmatism direction can be displayed. Further, a reference mark independent of the gate GA can be formed on the molding surface 32b of the movable mold 34. In this case, it is assumed that astigmatism can be formed in the processing of the molding die 30 in conformity with the orientation of the reference mark. Further, the reference mark may be formed with ink after the objective lens 10 is formed. In this case, since the degree of freedom of the position where the reference mark is provided increases, the reference mark may be provided after forming the lens after recognizing the astigmatism direction.
[0075]
In the first embodiment, the objective lens 10 has been described as having an NA of 0.65 or more. However, even if the objective lens 10 has an NA of 0.65 or less, it is necessary to control astigmatism if the objective lens is of a compatible type. In this case, the direction of astigmatism can be indicated by the notch 16 or the like even for the objective lens 10 having an NA of 0.65 or less.
[0076]
In the first embodiment, the case where the objective lens 10 is formed of a plastic material has been described. However, the material of the objective lens 10 is not limited to resin, but may be glass. In addition, astigmatism can be controlled within a certain range for a hybrid lens obtained by combining glass and a plastic material by the same method.
[0077]
[Second embodiment]
Hereinafter, the objective lens according to the second embodiment will be described. The objective lens of the second embodiment is manufactured by modifying the first embodiment, and the assembly after the manufacture is the same as that of the first embodiment. I do.
[0078]
FIG. 10 is a diagram illustrating the manufacture or processing of the objective lens 110 according to the second embodiment. The objective lens 110 according to the second embodiment is manufactured using the molding die 30 shown in FIG. 6, but the fixed die 32 and the like have no aberration. Is not in a controlled state. For this reason, in the present embodiment, astigmatism is given in a desired direction by performing appropriate processing on the objective lens 110 after the molding of the objective lens 110.
[0079]
As is clear from the figure, the objective lens 110 is held between a pair of processing jigs 182, and a constant compression pressure is applied from both sides. Further, a heater 183 is arranged to face the lower surface 112b of the lens body 112 of the objective lens 110. Thus, a compressive stress can be applied to the lens body 112 while the lens body 112 is overheated from the lower surface 112b side, so that the lower surface 112b can be deformed by heat and pressure to have a desired surface roughness. Also in this case, the direction of the compression pressure by the processing jig 182, the shape of the radiation surface of the heater 183, or the like is adjusted, or the direction of the surface asperity is made to match the direction of the notch 16 by adjusting the cooling method after heating. it can.
[0080]
[Third embodiment]
FIGS. 11 and 12 are views showing the configuration of the optical pickup device of the third embodiment. This optical pickup device is a modification of the device shown in FIG.
[0081]
The illustrated optical pickup device includes two objective lenses 210 and 310, and switches between these objective lenses 210 and 310 for use. One objective lens 210 is a compatible lens that is also used for a pair of different types of recording media such as a CD and a DVD, and emits red light from the first semiconductor laser 262 to a NA of about 0.45 to 0.53 in the case of a CD. In the case of a DVD, the light is condensed by switching the NA to about 0.60 to 0.65. The other objective lens 310 is used for a high-density recording medium using a blue laser, and focuses blue light from the second semiconductor laser 266 at NA of about 0.60 to 0.85.
[0082]
The two objective lenses 210 and 310 are both attached and fixed to the lens holder 250. Here, the two objective lenses 210 and 310 are both manufactured by the same method as in the first embodiment, and a notch serving as a reference mark is formed in the direction of the plane of the objective lens 310. In the case of the objective lens 210, a notch is formed based on the astigmatism direction in the state of NA of 0.60 to 0.65 for DVD having a higher recording density. Corresponding to this, around the opening in which the objective lenses 210 and 310 are fitted in the lens holder 250, direction recognition means similar to the depression 56 shown in FIG.
[0083]
The lens holder 250 and the actuator 81 are held by the lens switching device 285 and are slidable in a direction perpendicular to the optical axis direction. Depending on which of the first and second semiconductor lasers 262 and 266 is used. A corresponding one of the two objective lenses 210 and 310 is arranged on the optical path. More specifically, when the first semiconductor laser 262 is used, the objective lens 210 for red and having a small NA is arranged above the 波長 wavelength plate 74 or the like, and the second semiconductor laser 266 is used. , An objective lens 310 for blue having a large NA is disposed above the 波長 wavelength plate 74 or the like.
[0084]
In this case, since the two objective lenses 210 and 310 requiring high-precision mounting are provided with notches and aligned and fixed to the lens holder 250, astigmatism as an optical pickup device can be reduced, and the optical pickup device can be reduced. Performance can be improved. At this time, since the pair of objective lenses 210 and 310 are driven by one actuator 81, the tilt direction for reducing the coma aberration of both objective lenses 210 and 310 is one when viewed from the optical pickup device. It is desirable to ensure the operation with high accuracy.
[0085]
[Fourth embodiment]
FIG. 13 is a diagram illustrating an objective lens for an optical pickup according to the fourth embodiment. The objective lens 410 is a two-piece lens composed of two lens portions 410A and 410B, has a structure in which both lens portions 410A and 410B are arranged in series, and is joined to each other by flange portions 414A and 414B. . In this case, astigmatism is formed in the lens bodies 412A and 412B of the two lens portions 410A and 410B, respectively, and the direction thereof substantially matches the direction of the notches 416A and 416B. Even with such an objective lens 410, the optical pickup device can be assembled by controlling the astigmatism direction. In this case, the objective lens 410 is composed of two lenses, but the astigmatism can be similarly managed and controlled when three or more lenses are used.
[0086]
[Fifth Embodiment]
FIG. 14 is a diagram illustrating an objective lens for an optical pickup according to the fifth embodiment. In this case, four objective lenses 510 are manufactured simultaneously as one molded product 90. That is, the four runners 92 and the gate 93 extend radially from the central sprue 91 of the molded product 90, and the objective lens 510 is formed at each end. Each objective lens 510 has substantially the same astigmatism set in the direction of the gate 93 due to astigmatism provided in the fixed mold itself with reference to the direction of the gate 93. When such an objective lens 510 is used, an objective lens having uniform characteristics with respect to astigmatism and the like can be provided, and a high-performance optical pickup device can be assembled by controlling the direction of astigmatism. When a large number of cavities are formed in a small number of molds to form a large number of objective lenses, it is possible to stably supply a large amount of objective lenses with little variation among lots and uniform characteristics.
[0087]
As described above, the present invention has been described with reference to the embodiments. However, the present invention is not limited to the above embodiments. For example, in the third embodiment, the objective lens 210 is also used as a pair of recording media such as a CD and a DVD, but a pair of objective lenses are provided corresponding to each recording medium such as a CD and a DVD. You can also. In this case, the pair of objective lenses individually correspond to CDs and DVDs. However, since each objective lens does not have a high NA and does not necessarily need to be provided with a diffractive structure, the astigmatism direction is managed or controlled. It is not necessary to provide a reference mark such as a notch.
[0088]
In the third embodiment, the objective lens 210 may be a CD lens, and the objective lens 310 may be a compatible lens for DVD and blue laser. In this case, since the CD objective lens 210 does not have a high NA and does not necessarily need to be provided with a diffractive structure, it is not necessary to provide a reference mark such as a notch for managing or controlling the astigmatism direction. On the other hand, in the objective lens 310 for DVD and blue laser, a reference mark such as a notch is provided. Further, in the objective lens 310 in this case, it is preferable that the tilt directions for correcting both coma are the same. Therefore, such a compatible lens may reduce high-order coma aberration so that the amount of coma generated by the numerical aperture does not fluctuate.
[0089]
The use of the objective lens 10 described in the first embodiment and the like is also used when performing triple compatibility that enables optical pickup of three types of optical discs of CD, DVD, and blue laser with a single single objective lens. Needless to say, is effective. At this time, when the numerical aperture is limited to the NA corresponding to each optical disc, it is preferable from the viewpoint of improving the performance of the optical pickup that the directions of the lens tilts for reducing the coma aberration of the objective lens are substantially the same.
[0090]
【The invention's effect】
As is apparent from the above description, according to the first objective lens of the present invention, when the reference mark is oriented in a certain direction, in the direction of astigmatism existing after the formation of the pair of optical surfaces. Since the distribution range of a certain astigmatism direction is within 90 degrees, the objective lens can be assembled to the optical pickup device while taking the astigmatism direction of the objective lens into consideration. Therefore, if the objective lens is attached so as to cancel astigmatism generated by other optical system parts in the optical pickup device excluding the objective lens, astigmatism as the optical pickup device can be reduced. Further, when astigmatism in a specific direction is allowed in the optical pickup device, if the astigmatism direction of the objective lens is set and attached in that direction, the performance as the optical pickup device can be improved.
[0091]
According to the second objective lens of the present invention, the reference mark indicates the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, within the predetermined tolerance range. By controlling the astigmatism direction of the objective lens with reference to the fiducial mark, the objective lens can be assembled to the optical pickup device. Therefore, astigmatism as the optical pickup device can be reduced, or performance as the optical pickup device can be improved.
[0092]
Further, according to the third objective lens of the present invention, when the reference mark is oriented in a certain direction, an optical disc having the highest recording density among astigmatism existing after the formation of the pair of optical surfaces is used. Since the distribution range of the astigmatism direction, which is the direction of the astigmatism at the time, is within 90 degrees, this objective lens is used in an optical pickup while taking into consideration the astigmatism direction of the objective lens when using an optical disc having the highest recording density. Can be assembled to the device. Therefore, astigmatism as a compatible optical pickup device can be reduced, or performance as an optical pickup device can be improved.
[0093]
According to the fourth objective lens of the present invention, the reference mark is the direction of the astigmatism when using the optical disc having the highest recording density among the astigmatisms existing after the formation of the pair of optical surfaces. Since the astigmatism direction is displayed within the predetermined tolerance range, the astigmatism direction of the objective lens can be managed with reference to the reference mark, and the objective lens can be assembled to the optical pickup device. Therefore, astigmatism as a compatible optical pickup device can be reduced, or performance as a compatible optical pickup device can be improved.
[0094]
According to the fifth objective lens of the present invention, when the reference mark is oriented in a certain direction, the distribution of the astigmatism direction which is the direction of astigmatism existing after the formation of the pair of optical surfaces is provided. Since the range is within 90 degrees, the objective lens can be assembled to the optical pickup device while considering the astigmatism direction of the objective lens. Therefore, astigmatism as the optical pickup device can be reduced, or performance as the optical pickup device can be improved.
[0095]
Further, according to the sixth objective lens of the present invention, since the reference mark indicates the astigmatism direction, which is the direction of astigmatism existing after the formation of the pair of optical surfaces, within the predetermined tolerance range, By controlling the astigmatism direction of the objective lens with reference to the fiducial mark, the objective lens can be assembled to the optical pickup device. Therefore, astigmatism as the optical pickup device can be reduced, or performance as the optical pickup device can be improved.
[0096]
Further, according to the optical pickup device of the present invention, since the reference mark provided on the objective lens is fixed to the lens holder in a state where the reference mark is oriented in a certain direction, it is possible to use a device incorporating the objective lens while considering the astigmatism direction. can do. Therefore, astigmatism as the optical pickup device can be reduced, or performance as the optical pickup device can be improved.
[0097]
Further, according to another optical pickup device according to the present invention, the optical pickup device can be adapted to various standards, and particularly, in the optical pickup using the objective lens of the present invention, highly accurate optical information recording and reproduction can be performed. become.
[0098]
According to still another optical pickup device of the present invention, the optical pickup device can be adapted to various standards, and a highly accurate and multifunctional optical information recording / reproducing device can be provided.
[0099]
Further, according to the optical information recording / reproducing device according to the present invention, since the optical pickup device incorporating the objective lens is incorporated while taking into account the direction of astigmatism, high-density optical information recorded on various disks or the like can be obtained. Recording and reproduction can be performed with high accuracy.
[Brief description of the drawings]
FIG. 1A is a front view illustrating a structure of an objective lens according to an embodiment of the present invention, and FIG. 1B is a rear view thereof.
FIG. 2 is a diagram illustrating a relationship between an astigmatism direction indicating a direction of astigmatism of an objective lens and a azimuth of a notch serving as a reference mark.
FIG. 3 is a perspective view illustrating astigmatism intentionally generated in an objective lens.
FIG. 4 is a diagram illustrating a direction of astigmatism given to an objective lens, that is, a direction of astigmatism.
FIG. 5 is a diagram conceptually illustrating a case where surface astigmatism is measured as a wavefront aberration, and shows an example in which the wavefront aberration at each position of the objective lens is measured by an interferometer.
FIG. 6 is a cross-sectional view illustrating a shape and a structure of a mold for manufacturing an objective lens.
FIG. 7 is a view for explaining an example of astigmatism forming means formed on the mold of FIG. 6;
FIGS. 8A and 8B are diagrams schematically illustrating a configuration of an optical pickup device including the objective lens according to the first embodiment.
9 is a diagram showing a configuration of an optical pickup device incorporating the objective lens of FIG.
FIG. 10 is a diagram for explaining manufacturing or processing of the objective lens according to the second embodiment.
FIG. 11 is a diagram illustrating a configuration of an optical pickup device according to a third embodiment.
FIG. 12 is a diagram illustrating a configuration of an optical pickup device according to a third embodiment.
FIG. 13 is a diagram illustrating an objective lens for an optical pickup according to a fourth embodiment.
FIG. 14 is a diagram illustrating an objective lens for an optical pickup according to a fifth embodiment.
[Explanation of symbols]
10, 210, 310 ... objective lens
12 Lens body
12a ... upper surface
12b ... lower surface
12d ... diffraction groove
14 ... Flange part
16 ... Notch
30 ... Mold
32 ... Fixed type
34 movable type
41 ... Projection
43 ... Mold body
50 ... Lens holder
52 ... Opening
56 ... hollow
61, 65 ... Optical disk
62, 262... First semiconductor laser
66,266 ... second semiconductor laser
72 ... Polarizing beam splitter
73… Collimator
74 ... wave plate
79 ... Photodetector
81 ... Actuator
285: Lens switching device

Claims (22)

A pair of optical surfaces, a phase difference providing unit formed on at least one side of the pair of optical surfaces to provide an optical function using a phase difference, and a part of the whole including the periphery of the pair of optical surfaces An objective lens for an optical pickup comprising a reference mark provided in
When the reference mark is oriented in a certain direction, a distribution range of an astigmatism direction which is a direction of astigmatism existing after formation of the pair of optical surfaces is within 90 degrees. A pair of optical surfaces,
A phase difference providing unit formed on at least one side of the pair of optical surfaces and providing an optical function using a phase difference,
An objective lens for an optical pickup, comprising: a reference mark for displaying an astigmatism direction, which is a direction of astigmatism existing after the formation of the pair of optical surfaces, within a predetermined tolerance range. The objective lens according to claim 1, wherein the phase difference applying unit is a diffractive structure. An objective lens for an optical pickup that includes a pair of optical surfaces and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and can be used for at least two types of optical disks,
When the reference mark is oriented in a certain direction, of the astigmatism existing after the formation of the pair of optical surfaces, the distribution of the astigmatism direction which is the direction of the astigmatism when the optical disc having the highest recording density is used. An objective lens having a range of 90 degrees or less. An objective lens for an optical pickup that includes a pair of optical surfaces and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and can be used for at least two types of optical disks,
And a reference mark for displaying, within a predetermined tolerance, an astigmatism direction which is a direction of astigmatism when the optical disc having the highest recording density is used among the astigmatisms existing after the formation of the pair of optical surfaces. An objective lens, characterized in that: An objective lens for an optical pickup having a pair of optical surfaces and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and having a numerical aperture of 0.65 or more,
When the reference mark is oriented in a certain direction, a distribution range of an astigmatism direction which is a direction of astigmatism existing after formation of the pair of optical surfaces is within 90 degrees. An objective lens for an optical pickup having a pair of optical surfaces and a reference mark provided on a part of the whole including the periphery of the pair of optical surfaces, and having a numerical aperture of 0.65 or more,
An objective lens, comprising: a reference mark for displaying an astigmatism direction, which is a direction of astigmatism existing after the formation of the pair of optical surfaces, within a predetermined tolerance range. The objective lens according to any one of claims 1 to 7, wherein an angle between the astigmatism direction and the azimuth of the reference mark is 45 degrees or less. The objective lens according to any one of claims 1 to 8, further comprising astigmatism forming means formed by molding using a molding die and providing astigmatism to the molding die. . 10. The mold according to claim 9, wherein the mold includes a fixed mold on a fixed side and a movable mold on a movable side, which are separable from each other, and the fixed mold is provided with the astigmatism forming unit. The objective lens as described. 11. The method according to claim 9, wherein the astigmatism forming means is a positional shift of a molding surface formed by applying a mechanical pressure when holding the molding die. Objective lens. 9. The method according to claim 1, wherein the astigmatism is formed by molding using a molding die, and at least one of pressure and heat is applied after molding. Objective lens. The objective lens according to claim 1, wherein the reference mark has a correlation with a gate used for injection molding. The objective according to any one of claims 1 to 13, wherein the astigmatism existing after the formation of the pair of optical surfaces is a surface astigmatism caused by a surface shape of the pair of optical surfaces. lens. When the wavelength used by the objective lens is λ (nm), the difference in the amount of aspherical displacement corresponding to the surface astigmatism is not less than 0.03 λ (nm) and not more than 0.49 λ (nm). The objective lens according to claim 14. The objective lens according to claim 15, wherein the difference in the amount of displacement of the aspherical surface is 0.03λ (nm) or more and 0.25λ (nm) or less. An objective lens according to any one of claims 1 to 16,
An optical pickup device comprising: a lens holder for fixing the objective lens with the reference mark oriented in a certain direction. 18. The optical pickup device according to claim 17, wherein the lens holder has a direction recognition unit for aligning the reference mark provided on the objective lens. 19. The optical pickup device according to claim 17, wherein an optical pickup of at least two types of optical disks is performed. The first objective lens according to any one of claims 1 to 16, wherein the first objective lens is used for an optical pickup of a specific type of optical disc;
A second objective lens used for an optical pickup of another type of optical disc;
An optical pickup device comprising: a lens holder that fixes the first and second objective lenses. The first objective lens according to any one of claims 1 to 16, wherein the first objective lens is used for an optical pickup of a specific type of optical disc;
The second objective lens according to any one of claims 1 to 16, which is used for an optical pickup of another type of optical disc;
An optical pickup device comprising: a lens holder that fixes the first and second objective lenses. An optical information recording / reproducing apparatus comprising the optical pickup device according to any one of claims 17 to 21.

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