JP5310918B2 - Optical element for optical pickup device - Google Patents

Abstract

Provided is a method for machining a mold for molding an optical element such as an objective lens with compatibility for three kinds of optical disks such as BD/DVD/CD, said mold capable of minimizing the reduction of the efficiency of the optical element. Also provided are a machined mold and an optical element transcribed from the mold. By cutting a material by a tool provided with a cutting face at least part of which is outlined by a linear first edge and a second edge extending in the direction crossing the first edge, the first edge being set to be inclined with respect to a rotation axis, a first peripheral face cut by the first edge becomes parallel to the rotation axis. Therefore, if an optical element is transcribed using a thus formed mold, the first peripheral face can be made parallel to the optical axis.

Description

The present invention relates to an optical element for the optical pickup device, interchangeably it relates to a recording and / or reproducing (recording / reproducing) optical element for the optical pickup device capable of performing information especially for different types of optical discs.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜420 nm has been put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.

  As an example of an optical disk using the above-described objective lens with NA of 0.85, there is a BD (Blu-ray disk). Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate than the DVD (0.1 mm compared to 0.6 mm for the DVD) and is caused by the skew. The amount of coma is reduced.

  By the way, the value of an optical disc player / recorder (optical information recording / reproducing device) as a product cannot be said to be sufficient simply by being able to record / reproduce information appropriately for a BD. In light of the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, it is not possible to record / reproduce information with respect to BDs. For example, DVDs owned by users, Similarly, it is possible to appropriately record / reproduce information on a CD, which leads to an increase in the commercial value of an optical disc player / recorder for BD. From such a background, the optical pickup device mounted on the BD optical disc player / recorder can record / reproduce information appropriately while maintaining compatibility with any of BD, DVD, and CD. It is desirable to have

  As a method for appropriately recording / reproducing information while maintaining compatibility with both BD and DVD, and further with CD, information between BD optical system and DVD or CD optical system is used. Although a method of selectively switching according to the recording density of the optical disc to be recorded / reproduced is conceivable, it requires a plurality of optical systems, which is disadvantageous for miniaturization and increases the cost.

  Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, even in an optical pickup device having compatibility, the optical system for BD and the optical system for DVD or CD can be shared. It is preferable to reduce the number of optical components constituting the pickup device as much as possible. And, it is most advantageous to simplify the configuration of the optical pickup device and to reduce the cost to make the objective lens arranged facing the optical disc in common. In order to obtain a common objective lens for a plurality of types of optical disks having different recording / reproducing wavelengths, it is necessary to form an optical path difference providing structure such as a diffraction structure having a wavelength dependency of spherical aberration in the objective lens. is there.

  By the way, since such an optical path difference providing structure of the objective lens is generally a fine structure, there is a problem that it is difficult to process the mold. On the other hand, Patent Document 1 discloses a technique of cutting a fine groove corresponding to a so-called blazed diffraction grating having a sawtooth cross section using a diamond tool.

JP 2003-62707 A

  By the way, according to the research by the present inventors, when a fine groove is processed by the technique of Patent Document 1 described above, for example, the processing efficiency is actually increased with respect to the design efficiency in an objective lens for BD / DVD / CD compatibility. It has been found that the actual efficiency of the objective lens transferred and molded by the mold is greatly reduced. In particular, the present inventors have also found that the actual efficiency is remarkably reduced particularly in a structure having peripheral walls extending substantially in the optical axis direction and facing each other, rather than a blazed shape. For example, an objective lens having an optical path difference providing structure is also used in DVDs, CDs, and the like. However, even if fine grooves are processed by the technique of Patent Document 1, the actual efficiency is particularly high with respect to the design efficiency. There is a fact that there is no significant decline.

The present invention is intended to solve the problems described above, for example, a BD / DVD / 3 kinds of optical element such as an objective lens for an optical disk compatible CD, as much as possible to suppress the efficiency degradation An object of the present invention is to provide an optical element for an optical pickup device capable of performing

A preferred mold processing method for molding the optical element is a second mold that extends a material of the mold for molding the optical element in a direction intersecting the first edge and the first edge. In a method of processing a mold for cutting with a tool having a rake face that is at least partially contoured from an edge, the first edge rotates the mold material more than the second edge. Cutting while rotating the material of the mold with the tool set so that the axis of the tool is inclined with respect to the rotation axis so that the tip of the rake face is away from the rotation axis, and the tool is positioned far from the axis. Thus, at least a part of a concave annular zone structure having a first peripheral surface cut by the first edge and a second peripheral surface cut by the second edge is formed. It is characterized by.

  The present inventor has analyzed the reason why the efficiency is lowered in an actual objective lens through intensive research. As a result, the following was found. FIG. 1 is an enlarged view of an optical surface S1 of an objective lens molded from a mold processed by a conventional technique. This objective lens has a diffractive structure D having a plurality of annular projections having an inner wall IW and an outer wall OW, and the inner wall IW and the outer wall OW extend in a direction facing each other. ing. Here, when the parallel light beam L is incident on the objective lens, the light beam incident on the optical surface other than the inner wall IW and the outer wall OW is used for condensing the optical disk, but is incident on the inner wall IW and the outer wall OW. The luminous flux (indicated by hatching) is rarely used for light collection. This is called the shadow effect, and is a factor in reducing efficiency. However, the decrease in efficiency due to the shadow effect is generally negligible with DVD and CD objective lenses, but with a BD / DVD / CD compatible objective lens, etc. It can be said that it is necessary to increase the actual efficiency.

  Here, the inventors focused on the outer wall OW. If the outer wall OW is formed parallel to the optical axis as indicated by the dotted line, it is possible to suppress the parallel light beam from entering the outer wall OW, and accordingly, it is possible to suppress the efficiency reduction of the objective lens. However, according to the prior art, as shown in FIG. 1, the mold is processed so that the outer wall OW is inclined.

  More specifically, it is an example of the prior art in which the tool axis BX is cut parallel to the rotation axis with respect to the mold material WK in FIG. In the prior art, since the axis BX of the diamond tool BT for cutting is set parallel to the rotation axis RO of the material WK, the outer wall OW ′ of the ring-shaped recess PJ is the edge of the rake face of the diamond tool BT. Along the part, it was inclined to approach the axis of rotation as it approached the tool tip. When the objective lens is transfer-molded using a die formed by such cutting, an annular groove having an outer wall OW inclined with respect to the optical axis is formed as shown in FIG.

  Therefore, the present inventors have come up with the idea of improving the diffraction efficiency by rotating the rake face of the tool BT based on the above knowledge. That is, as shown in FIG. 2B, a mold capable of forming an objective lens close to the design state by rotating (θ) the axis BX of the rake face of the tool BT within a plane orthogonal to the rotation axis RO. Can be processed. More specifically, a tool having a rake face BT3 that is at least partially contoured from a first edge BT1 and a second edge BT2 extending in a direction intersecting the first edge BT1. The BT is formed so that the first edge BT1 is farther from the rotation axis RO of the mold material WK than the second edge BT2, and the tip of the rake face BT3 is separated from the rotation axis RO. Since the material WK is set while being inclined with respect to the rotation axis of the mold material WK, the first peripheral surface OW ′ cut by the first edge portion BT1 can be made substantially parallel to the rotation axis. If the optical element is transferred using such a mold, the outer OIW (see FIG. 1) of the annular groove transferred by the first peripheral surface can be made parallel to the optical axis. Thereby, the efficiency of the optical element can be increased.

In the above invention, a preferable die machining method is characterized in that cutting is performed in a state in which the axis of the tool is set to be inclined with respect to the rotation axis from the outer periphery to the center of the workpiece in the workpiece. This saves the labor of setting the tool.

A preferable mold machining method is characterized in that an inclination angle of the axis of the tool with respect to the rotation axis is changed during the cutting of the workpiece portion of the material. With such a configuration, for example, in an area having only a blaze type structure, the tool axis is parallel to the rotation axis, and in an area having recesses having peripheral walls facing each other, the tool axis is inclined with respect to the rotation axis, etc. Depending on the structure, it is preferable because cutting can be performed at the most preferable angle of the axis of the tool, a mold closer to the design shape can be obtained, and the light utilization efficiency can be further improved.

A preferable die machining method is the above invention, in which the cutting is performed in a state where the axis of the tool is set parallel to the rotation axis, from the outer periphery to the intermediate portion of the workpiece to be processed, from the intermediate portion to the center, Cutting is performed in a state where the axis of the tool is set to be inclined with respect to the rotation axis. In particular, since the vicinity of the center of the optical element often has a compatible optical path difference providing structure, the effect of the present invention can be expected.

In a preferred method of processing a mold, in the above invention, at least a part of the peripheral wall of the concave annular zone structure is such that at least the peripheral wall far from the optical axis of the annular zone structure is parallel to the optical axis. Features. Since this structure can reduce the effect of shadows due to the outer wall of the annular groove as described above, it is preferable because the efficiency of the optical element can be increased.

A preferable mold processing method is characterized in that, in the above-described invention, at least a peripheral wall near the optical axis of the annular structure is inclined with respect to the optical axis. In the peripheral wall close to the optical axis, for example, the inner wall IW in FIG. 1, even if the inner wall is made parallel to the optical axis, the effect of shadow is inevitable. Therefore, the necessity of making the inner wall IW parallel to the optical axis is lower than that of the outer wall OW. Therefore, it is preferable that the inner wall IW is kept inclined with respect to the optical axis, so that a greater degree of freedom can be secured for setting the inclination angle of the tool axis with respect to the rotation axis. For example, the tilt angle of the tool axis with respect to the rotation axis is set so that the outer wall is parallel to the optical axis, and it is possible to cut all steps with the tilt angle. Operation becomes easier.

In a preferred die processing method, in the above invention, the rake face of the tool has an arc-shaped third edge portion connecting the first edge portion end portion and the second edge portion end portion. The radius of the third edge is 0.1 to 0.5 μm. Thereby, sagging of processing decreases and a fine structure can be processed with high accuracy.

In a preferred method of processing a mold, in the above invention, an inclination angle of the axis of the tool with respect to the rotation axis is about half of a vertex angle formed by the first edge and the second edge. Features. With this configuration, since the first edge is parallel to the rotation axis, the step cut at the first edge is easily parallel to the rotation axis.

In a preferred method of processing a mold, in the above invention, an apex angle formed by the first edge portion and the second edge portion is 20 to 30 °. As a result, interference with the fine shape is reduced, and processing closer to the design shape becomes possible.

Method for processing a preferred mold angle tilted with respect to the axis of rotation of the axis of the tool, characterized in that it is a 8 to 18 °.

A preferable mold is processed by the above processing method.

The optical element according to claim 1 emits a first light source that emits a first light beam having a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm) and a second light beam that emits a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm). And a third light source that emits a third light beam having a third wavelength λ3 (760 nm ≦ λ3 ≦ 820 nm), and a protective substrate having a thickness t1 using the first light beam. Recording and / or reproducing information, recording and / or reproducing information of a DVD having a protective substrate with a thickness of t2 (t1 <t2) using the second light beam, and using the third light beam An optical element used in an optical pickup apparatus for recording and / or reproducing information on a CD having a protective substrate having a thickness of t3 (t2 <t3), wherein at least one optical surface of the optical element is a central region And around the central area The optical element has at least an intermediate region and a peripheral region around the intermediate region, and the optical element can record and / or reproduce information on the information recording surface of the BD with the first light flux passing through the central region. The third light beam is condensed so that the second light beam passing through the central region is condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD, and the third light beam passes through the central region. Is recorded on the information recording surface of the CD so that information can be recorded and / or reproduced, and the first light flux passing through the intermediate area is recorded and / or reproduced on the information recording surface of the BD. The second light flux passing through the intermediate area is condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD, and the second light flux passing through the intermediate area is passed through the intermediate area. Three light beams are recorded on the information recording surface of the CD. The first light flux that passes through the peripheral area without being condensed so that it can be reproduced is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD, and the peripheral area is The second light beam passing therethrough is not condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD, and the third light beam passing through the peripheral region is collected on the information recording surface of the CD. The central region has a first optical path difference providing structure, and the first optical path difference providing structure has a blaze-type structure and a blaze type so that light is not collected so that information can be recorded and / or reproduced. A second base structure having a mold structure is superimposed on each other in opposite directions, the step of the first base structure is directed in the direction opposite to the optical axis, and the step of the second base structure is the optical axis And the first optical path difference providing structure is substantially in the direction of the optical axis. It has a annular protrusion having a mutually opposite peripheral walls extending in direction, before the far side of the peripheral wall from the optical axis of Kiwatai convex portion becomes 0 ° or 7 ° less inclination with respect to the optical axis It is characterized by.

  Even if the peripheral wall near the optical axis has an ideal shape, the efficiency loss due to the shadow effect is unavoidable, and therefore the loss of light quantity does not change much even if it is not made the ideal shape. That is, the contribution of efficiency due to the inclination closer to the optical axis is smaller than the contribution of efficiency due to the inclination of the peripheral wall far from the optical axis. Therefore, by tilting the peripheral wall on the side close to the optical axis of the annular convex part, it is not necessary to control the angle of the tool too finely, it is easy to manufacture, and the loss of light utilization efficiency due to the shadow effect is greatly increased. Never do. In addition, by inclining the peripheral wall on the side close to the optical axis of the annular zone convex portion away from the optical axis toward the tip of the annular zone convex portion with respect to the optical axis, at the time of injection molding, from the mold Since the optical element can be released smoothly, the moldability can be improved. Furthermore, by making the peripheral wall far from the optical axis of the annular convex part parallel to the optical axis, the loss of efficiency due to the shadow effect can be greatly reduced, and ideal light utilization efficiency close to the design value can be obtained. Is possible. In other words, it is possible to obtain an optical element that is easy to manufacture and mold and yet has high light utilization efficiency.

  In addition, the first optical path difference providing structure is a structure in which a first basic structure having a blazed structure and a second basic structure having a blazed structure are overlapped in opposite directions, and the first basic structure is The first-order diffracted light amount of the first light beam that has passed through one basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is set to any other order The first order diffracted light amount of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light amount (hereinafter also referred to as “1/1/1”). It is a diffractive structure, and the second basic structure has a second-order diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order of diffracted light amount, and has passed through the second basic structure. Diffracted light of any other order with the first-order diffracted light quantity of the light beam The first order diffracted light amount of the third light flux that has passed through the second basic structure is larger than any other order diffracted light amount (hereinafter also referred to as “2/1/1”). is there. As described above, when the “1/1/1” diffractive structure having the blazed structure and the “2/1/1” diffractive structure having the blazed structure are superimposed in the opposite directions, the first optical path difference is given. The step of the structure can be lowered. If the level difference of the optical path difference providing structure can be reduced, the loss of efficiency due to manufacturing errors can be reduced, so that it is possible to obtain an optical element with even higher light utilization efficiency.

  Further, when the first basic structure having the blazed structure and the second basic structure having the blazed structure are overlapped in the opposite directions, the step difference of the first basic structure having the diffraction structure of “1/1/1” is light. The step of the second basic structure having the diffractive structure of “2/1/1” is directed in the direction opposite to the axis, and is directed in the direction of the optical axis. In this case, the step of the first basic structure having the diffraction structure of “1/1/1” is directed in the direction of the optical axis, and the step of the second basic structure having the diffraction structure of “2/1/1” is The number of peripheral walls on the side farther from the optical axis of the annular zone convex portion of the first optical path difference providing structure is larger than when facing in the direction opposite to the optical axis. Therefore, by making the peripheral wall far from the optical axis of the annular convex part parallel to the optical axis, the loss of efficiency due to the shadow effect is greatly reduced, and ideal light utilization efficiency close to the design value is obtained. The present invention becomes more useful.

In the optical element according to claim 2, in the invention according to claim 1, the peripheral wall on the side farther from the optical axis of the annular projection has an inclination of 0 ° or more and 2 ° or less with respect to the optical axis. It is characterized by being.
The optical element according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the peripheral wall on the side farther from the optical axis of the annular projection is parallel to the optical axis.
According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the peripheral wall on the side close to the optical axis of the annular zone convex portion is a portion of the annular zone convex portion with respect to the optical axis. It is characterized by tilting away from the optical axis toward the tip.
The optical element according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the diameter of the optical element in the direction perpendicular to the optical axis is 1.45 mm or more and 4.05 mm or less. To do.
The optical element according to claim 6 is characterized in that, in the invention according to claim 5, the diameter of the optical element in the direction perpendicular to the optical axis is 2.95 mm or more and 4.05 mm or less.
The optical element according to claim 7 is the optical element according to any one of claims 1 to 6, wherein the first-order diffracted light amount of the first light flux that has passed through the first basic structure is less than any other order of diffracted light amount. The first-order diffracted light amount of the second light beam that has passed through the first basic structure is larger than any other order of diffracted light amount, and the first-order of the third light beam that has passed through the first basic structure. The diffracted light quantity of any other order is greater than the diffracted light quantity of any other order, the second-order diffracted light quantity of the first light beam that has passed through the second basic structure is greater than any other order of diffracted light quantity, The first-order diffracted light amount of the second light beam that has passed through the basic structure is larger than any other order of diffracted light amount, and the first-order diffracted light amount of the third light beam that has passed through the first basic structure is any other Greater than the amount of diffracted light of the order It is characterized in.
An optical element according to an eighth aspect is characterized in that, in the invention according to any one of the first to seventh aspects, the annular groove has an optical path difference providing structure.

An optical element according to a ninth aspect is the invention according to any one of the first to eighth aspects, wherein the optical element is an objective lens.
An optical element according to a tenth aspect is the invention according to any one of the first to ninth aspects, wherein the optical element has a surface that extends in the substantially optical axis direction and connects the facing peripheral walls between the peripheral walls facing each other. And

  An optical pickup device in which the optical element according to the present invention is used has at least three light sources: a first light source, a second light source, and a third light source. Furthermore, the optical pickup device of the present invention condenses the first light beam on the information recording surface of the BD, condenses the second light beam on the information recording surface of the DVD, and focuses the third light beam on the information recording surface of the CD. A condensing optical system for condensing the light. The optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from an information recording surface of a BD, DVD, or CD.

  The BD has a protective substrate having a thickness t1 and an information recording surface. The DVD has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The CD has a protective substrate having a thickness of t3 (t2 <t3) and an information recording surface. The BD, DVD, or CD may be a multi-layer optical disc having a plurality of information recording surfaces.

  In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording layer, a BD having two or more information recording layers, and the like. Furthermore, in this specification, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. Including DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (1), (2), and (3), but is not limited thereto. The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.
0.050 mm ≤ t1 ≤ 0.125 mm (1)
0.5mm ≤ t2 ≤ 0.7mm (2)
1.0mm ≤ t3 ≤ 1.3mm (3)

In this specification, a first light source for BD that emits a light beam with a first wavelength λ1, a second light source for DVD that emits a light beam with a second wavelength λ2, and a first light source for CD that emits a light beam with a third wavelength λ3. The three light sources are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) preferably satisfies the following conditional expressions (4) and (5).
1.5 · λ1 <λ2 <1.7 · λ1 (4)
1.8 · λ1 <λ3 <2.0 · λ1 (5)

  The first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm or more and 415 nm or less, and the second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably. Is 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

  The condensing optical system of the optical pickup device has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. These are all optical elements. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens is preferably a single lens or a plurality of plastic or glass lenses. A convex lens is preferable. The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

  When a resin is used as the material of the optical element, a cycloolefin resin is preferably used. Specifically, ZEONEX manufactured by Nippon Zeon Co., Ltd., APEL manufactured by Mitsui Chemicals, Inc. TOPAS manufactured by TOPAS ADVANCED POLYMERS, manufactured by JSR Corporation A preferred example is ARTON.

  Moreover, it is preferable that the Abbe number of the material which comprises an objective lens is 50 or more.

  The 3 compatible objective lens is described below. At least one optical surface of the three-compatible objective lens has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. The central region is preferably a region including the optical axis of the three-compatible objective lens. However, a minute region including the optical axis is used as an unused region or a special purpose region, and the surrounding region is a central region (also referred to as a central region). Say). The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG. 3, it is preferable that the central region CN, the intermediate region MD, and the peripheral region OT are provided concentrically around the optical axis on the same optical surface. In addition, a three-wavelength shared first optical path difference providing structure is provided in the central area of the 3-compatible objective lens, and a two-wavelength shared second optical path difference providing structure is provided in the intermediate area. The peripheral region may be a refracting surface, or a third optical path difference providing structure may be provided in the peripheral region. The central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

  The central area of the 3 compatible objective lens can be said to be a preferred BD / DVD / CD shared area when used for recording / reproduction of BD, DVD and CD. That is, the 3-compatible objective lens condenses the first light flux that passes through the central area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux that passes through the central area becomes the DVD. It is preferable that the light is condensed on the information recording surface so that information can be recorded / reproduced, and the third light flux passing through the central region is condensed so that information can be recorded / reproduced on the information recording surface of the CD. In addition, the first optical path difference providing structure provided in the central region has the BD protective substrate thickness t1 and the DVD protective substrate thickness with respect to the first and second light fluxes passing through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference in thickness t2 / spherical aberration generated due to the difference in wavelength between the first light beam and the second light beam. Further, the first optical path difference providing structure is different from the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate with respect to the first and third light fluxes that have passed through the first optical path difference providing structure. It is preferable to correct the spherical aberration caused by the difference in the wavelength of the first light beam and the third light beam.

  The intermediate area of the 3 compatible objective lens is used for BD and DVD recording / reproduction, and can be said to be a preferable BD / DVD common area when not used for CD recording / reproduction. That is, the 3-compatible objective lens condenses the first light flux passing through the intermediate area so that information can be recorded / reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is converted into the DVD. It is preferable to collect light so that information can be recorded / reproduced on the information recording surface. On the other hand, it is preferable that the third light flux passing through the intermediate region is not condensed so that information can be recorded / reproduced on the information recording surface of the CD. The third light flux that passes through the intermediate region of the three-compatible objective lens preferably forms a flare on the information recording surface of the CD. As shown in FIG. 4, in the spot formed on the information recording surface of the CD by the third light flux that has passed through the 3-compatible objective lens, the light amount density is changed in the order from the optical axis side (or the center of the spot) to the outside. It is preferable to have a high spot central portion SCN, a spot intermediate portion SMD whose light intensity density is lower than that of the spot central portion, and a spot peripheral portion SOT whose light intensity density is higher than that of the spot intermediate portion and lower than that of the spot central portion. The center portion of the spot is used for recording / reproducing information on the optical disc, and the middle portion of the spot and the peripheral portion of the spot are not used for recording / reproducing information on the optical disc. In the above, this spot peripheral part is called flare. However, there is no spot middle part around the center part of the spot and there is a spot peripheral part, that is, even when a light spot is formed thinly around the condensing spot, the spot peripheral part may be called a flare. Good. In other words, it can be said that the third light flux that has passed through the intermediate region of the three-compatible objective lens preferably forms a spot peripheral portion on the information recording surface of the CD.

  The peripheral area of the 3-compatible objective lens is used for BD recording / reproduction, and can be said to be a preferable BD-dedicated area when not used for DVD / CD recording / reproduction. That is, it is preferable that the three-compatible objective lens condenses the first light beam passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the BD. On the other hand, the second light flux that passes through the peripheral area is not condensed so that information can be recorded / reproduced on the information recording surface of the DVD, and the third light flux that passes through the peripheral area does not converge. It is preferable not to collect light so that information can be recorded / reproduced. The second light flux and the third light flux that pass through the peripheral area of the 3-compatible objective lens preferably form a flare on the information recording surface of DVD and CD. That is, it is preferable that the second light flux and the third light flux that have passed through the peripheral area of the three-compatible objective lens form a spot peripheral portion on the information recording surface of the DVD and CD.

  The first optical path difference providing structure is preferably provided in an area of 70% or more of the area of the central area of the three-compatible objective lens, and more preferably 90% or more. More preferably, the first optical path difference providing structure is provided on the entire surface of the central region. The second optical path difference providing structure is preferably provided in a region of 70% or more of the area of the intermediate region of the three-compatible objective lens, and more preferably 90% or more. More preferably, the second optical path difference providing structure is provided on the entire surface of the intermediate region. When the peripheral region has the third optical path difference providing structure, the third optical path difference providing structure is preferably provided in an area of 70% or more of the area of the peripheral area of the 3-compatible objective lens, and 90% or more is provided. More preferred. More preferably, the third optical path difference providing structure is provided on the entire surface of the peripheral region.

  In addition, the optical path difference providing structure referred to in this specification is a general term for a structure that adds an optical path difference to an incident light beam, and has an annular groove. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure of the present invention is preferably a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. When the objective lens provided with the optical path difference providing structure is a single aspherical lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis. Each will be slightly different. For example, when the objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.

  In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have an action of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, when the objective lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be. For example, when the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

  By the way, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. The optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.

  As shown in FIGS. 5A and 5B, the blazed structure is that the cross-sectional shape including the optical axis of an optical element having an optical path difference providing structure is a sawtooth shape. In the example of FIG. 5, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface. In the blazed structure, the length in the direction perpendicular to the optical axis of one blaze unit is called a pitch P. (See FIGS. 5A and 5B) The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See FIG. 5A) In such a single blazed structure, there are no peripheral walls facing each other.

  Further, as shown in FIGS. 5C and 5D, the staircase structure has a cross-sectional shape including an optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ). In the present specification, “V level” means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step. For example, the optical path difference providing structure illustrated in FIG. 5C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 5D is referred to as a two-level step structure (also referred to as a binary structure). .

  The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

  When the first optical path difference providing structure and the second optical path difference providing structure are provided, they may be provided on different optical surfaces of the objective lens, but are preferably provided on the same optical surface. Furthermore, also when providing a 3rd optical path difference providing structure, it is preferable to provide in the same optical surface as a 1st optical path difference providing structure and a 2nd optical path difference providing structure. Providing them on the same optical surface is preferable because it makes it possible to reduce eccentricity errors during manufacturing. In addition, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disk side. In other words, the first optical path difference providing structure, the second optical path difference providing structure, and the third optical path difference providing structure are preferably provided on the optical surface having the smaller absolute value of the radius of curvature of the objective lens. It is also conceivable to provide the first basic structure and the second basic structure on different optical surfaces without overlapping. Similarly, the third basic structure and the fourth basic structure may be provided on different optical surfaces without overlapping.

  The optical path difference providing structure may be a structure in which a plurality of basic structures (for example, the first basic structure and the second basic structure in FIG. 6D) are overlapped.

  Several examples of superposition of the optical path difference providing structure are shown in FIGS. 6 (a), 6 (b), and 6 (c). These are examples in which two types of blaze structures are superimposed. Although FIG. 6 shows the first optical path difference providing structure ODS1 as a flat plate for convenience, it may be provided on a single aspherical convex lens. The second-order diffracted light quantity of the first light beam that has passed through the second basic structure is made larger than any other order of diffracted light quantity, and the first-order diffracted light quantity of the second light beam that has passed through the second basic structure is set to any other order. And the first-order diffracted light amount of the third light beam that has passed through the second basic structure is larger than any other order diffracted light amount (“2/1/1”). The first-order diffracted light quantity of the first light beam that has passed through the first basic structure is made larger than the diffracted light quantity of any other order in the two basic structure BS2, and the first-order diffraction of the second light beam that has passed through the first basic structure. The light quantity is made larger than any other order diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the first basic structure is made larger than any other order diffracted light quantity (“1/1/1”). ) An example in which the first basic structure BS1 that is a diffractive structure is overlaid. . In FIG. 6A, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 faces the direction opposite to the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG. 6B, the step of the second foundation structure BS2 faces the direction of the optical axis OA, and the step of the first foundation structure BS1 also faces the direction of the optical axis OA. Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1. Next, in FIG.6 (c), the level | step difference of 1st foundation structure BS1 has faced the direction opposite to optical axis OA, and the level | step difference of 2nd foundation structure BS2 has also faced the direction opposite to optical axis OA. . Furthermore, it can be seen that the positions of all the steps of the second foundation structure BS2 are aligned with the positions of the steps of the first foundation structure BS1.

  Various examples of the optical path difference providing structure have been described. In the present specification, when referring to the “optical path difference providing structure having an annular groove with opposed peripheral walls”, in particular, FIGS. 5 (c), (d), This refers to the structure shown in FIG.

  The NA on the image side of the objective lens necessary for reproducing / recording information on the BD is NA1, and the NA on the image side of the objective lens necessary for reproducing / recording information on the DVD is NA2 (NA1 > NA2), and the image side numerical aperture of the objective lens necessary for reproducing / recording information on the CD is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

  The boundary between the central region and the intermediate region of the objective lens is 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more, 1.15 · NA 3) when the third light beam is used. It is preferably formed in a portion corresponding to the following range. More preferably, the boundary between the central region and the intermediate region of the objective lens is formed in a portion corresponding to NA3. Further, the boundary between the intermediate region and the peripheral region of the objective lens is 0.9 · NA 2 or more and 1.2 · NA 2 or less (more preferably 0.95 · NA 2 or more, 1.15) when the second light flux is used. -It is preferably formed in a portion corresponding to the range of NA2 or less. More preferably, the boundary between the intermediate region and the peripheral region of the objective lens is formed in a portion corresponding to NA2.

  When the third light beam that has passed through the objective lens is condensed on the information recording surface of the CD, it is preferable that the spherical aberration has at least one discontinuous portion. In that case, the discontinuous portion has a range of 0.9 · NA 3 or more and 1.2 · NA 3 or less (more preferably 0.95 · NA 3 or more and 1.15 · NA 3 or less) when the third light flux is used. It is preferable that it exists in.

  The present invention is particularly suitable for an objective lens used in a thin slim type optical pickup device. Since the objective lens used in the slim type optical pickup device inevitably has a small diameter, the pitch of the annular zone is also reduced, making it difficult to process. For this reason, the effects of the present invention are more conspicuous, and the effect of the present invention with less loss of light utilization efficiency becomes more remarkable.

  The objective lens used in the slim type optical pickup device preferably has a diameter in the direction perpendicular to the optical axis of the entire objective lens including the flange and the optical surface in the range of 1.45 mm to 4.05 mm. More preferably, it is 2.95 mm or more and 4.05 mm or less. Moreover, it is preferable that the minimum value of the pitch of the optical path difference providing structure in the direction perpendicular to the optical axis is 2.5 μm or more and 10 μm or less. The maximum pitch value is preferably 110 μm or less. Furthermore, it is preferable that the total number of zones of the optical path difference providing structure in the entire objective lens is 150 or more and 250 or less.

  The tool used in the present invention includes a rake face that is at least partially contoured from a first edge and a second edge extending in a direction intersecting the first edge. In the attached state, the first edge is farther from the rotation axis of the mold material than the second edge. The first edge and the second edge may be directly connected with the tool axis as a boundary, or may be connected via a third edge that crosses the tool axis. The first edge and the second edge are each preferably straight, but a part of the first edge may be arcuate.

According to the present invention, for example, a BD / DVD / 3 kinds of optical element such as an objective lens for an optical disk compatible CD, to provide an optical element for the optical pickup device capable of suppressing reduction in efficiency as much as possible Can do.

It is an enlarged view of optical surface S1 of the objective lens shape | molded from the metal mold | die processed by the prior art. It is a schematic diagram for demonstrating the difference of the cutting of this invention, and the cutting of a prior art, (a) shows the example of a prior art, (b) shows the example of this invention, and the locus | trajectory of a tool with an arrow Is shown. It is the figure (a) which looked at the single objective lens OL in the optical axis direction, and the figure (b) which looked at the optical axis orthogonal direction. It is a figure which shows the state which forms the spot which the 3rd light beam which passed the objective lens forms on the information recording surface of a 3rd optical disk. It is an axial direction sectional view which shows the example of an optical path difference providing structure, (a), (b) shows an example of a blazed type structure, (c), (d) shows an example of a step type structure. It is a conceptual diagram of the 1st optical path difference providing structure on which the basic structure was superimposed, (a), (b), (c) shows the example of superimposition of the optical path difference providing structure, (d) is the 1st basic structure and the 2nd basic structure An example of superposition with the structure is shown. It is a figure which shows a diamond tool, (a) is a perspective view which shows the cutting edge of the diamond tool used with the processing method of the metal mold | die concerning this Embodiment, (b) is an enlarged view which shows the front-end | tip part shape of the rake face 3a. is there. It is a perspective view of the XZB axis superprecision lathe concerning an embodiment. It is a figure which shows the setting position relationship of a metal mold | die and a tool. It is a figure which shows the expanded cross-sectional shape concerning a part of metal mold | die to process. It is a figure which shows the expanded cross-sectional shape concerning a part of metal mold | die to process.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a BD / DVD / CD compatible objective lens is designed using optical design software such as codeV. Then, the mold is processed based on the design result. Fig.7 (a) is a perspective view which shows the cutting edge of the diamond tool used with the processing method of the metal mold | die concerning this Embodiment, FIG.7 (b) is an enlarged view which shows the front-end | tip part shape of the rake face 3a. It is. The cutting edge 3 of the diamond tool is brazed to the shank S as shown in the figure, and has a rake face 3a that faces the rotational direction of the mold to be cut. The tip of the rake face 3a connects the edge 3b as the first edge and the edge 3c as the second edge with the end A of the edge 3b and the end B of the edge 3c. It is contoured from the arc part 3d which is the third edge.

  By setting the radius r of the arc portion 3d of the rake face 3a to 0.1 to 0.5 μm (preferably 0.1 to 0.3 μm), it is possible to cut a fine shape with a sharp cutting edge. The scissor angle (vertical angle) between the first edge 3b and the second edge 3c is preferably 20 to 30 ° (preferably 29 ° or less). The bisector of the first edge 3b and the second edge 3c is defined as the axis BX of the tool 3.

  FIG. 8 is a perspective view of an XZB-axis super-precision lathe used for mold machining. FIG. 9 is an enlarged cross-sectional view when cutting a mold using a diamond tool. In FIG. 8, a rotation drive mechanism 9 is provided on a Z-axis stage 5 that is movable in the Z-axis direction with respect to the surface plate 10, and the rotation drive mechanism 9 rotates the mold material 1 to be cut. It is designed to rotate around the axis AX. On the other hand, a B-axis stage 11 that can rotate about the B-axis is provided on the surface plate 10, and an X-axis stage 6 that is movable in the X direction is provided on the B-axis stage 11. Is provided with a tool mounting portion 7 to hold the diamond tool 3. While maintaining the tool axis of the diamond tool 3 in an inclined state by the B-axis stage 11 and rotating the mold material 1 by the rotation drive mechanism 9, the diamond tool 3 is molded by the Z-axis stage 5 and the X-axis stage 6. The optical transfer surface can be processed by moving it relative to the material 1.

  In the present embodiment, the mold material 1 uses an iron-based base material, and after roughing the required shape with respect to the cutting surface, electroless nickel plating is applied as a processing layer to a thickness of about 50 μm. .

  The shape required for the optical surface (surface to be processed) 1a of the mold material 1 is the diffractive optical surface shape of the BD / DVD / CD compatible plastic objective lens.

  The mold material 1 is rotated at, for example, 1000 revolutions per minute, and the X-axis stage 6 and the Z-axis stage 5 are controlled by program control so that the tip of the diamond tool 3 is indicated by the arrow in FIG. The translational movement is performed from the outer peripheral side toward the central portion at a moving speed of 0.1 mm per minute so as to obtain a desired diffractive optical surface shape.

  Here, according to the first processing mode, the bisector BX (see FIG. 7B) of the apex angle of the diamond tool 3 is tilted with respect to the rotation axis AX of the mold material 1 and the outer periphery. Cutting from center to center. At this time, it is preferable that the inclination angle of the bisector BX of the apex angle with respect to the rotation axis is about half of the apex angle. In this case, the angle is 8 ° to 18 °. In such a case, in FIG. 9, the first edge 3b (however, depending on the tilt angle, cutting may be performed at the third edge 3d, but in this case, cutting is performed on the side far from the rotation axis across the tool axis. The peripheral surface (first peripheral surface) closer to the optical axis in the ring-shaped convex portion 1d (first peripheral surface) (in the concave portion, the peripheral surface away from the optical axis) 1b can be formed parallel to the rotation axis AX. In other words, when the objective lens is molded using a die cut by such processing, the objective lens whose peripheral wall (corresponding to the outer wall OW in FIG. 1) on the side far from the optical axis of the annular convex portion is parallel to the optical axis. Can be formed. On the other hand, the second edge 3c forms a circumferential surface (second circumferential surface) 1c far from the optical axis in the annular projection 1d (a circumferential surface closer to the optical axis in the concave portion) 1c. it can. That is, when the objective lens is formed using a die cut by such processing, the peripheral wall (corresponding to the inner wall IW in FIG. 1) on the side closer to the optical axis of the annular convex portion is annular convex with respect to the optical axis It is possible to form an objective lens that is inclined away from the optical axis toward the tip of the part. The first edge 3b does not have to be strictly parallel to the rotation axis AX. If the tip of the rake face is not tilted in a direction approaching the rotation axis AX from a position where the first edge 3b is parallel to the rotation axis AX, the diamond tool 3 is closer to the optical axis by relative movement in the Z direction. This is because the peripheral surface 1b on the side can be formed parallel to the rotation axis AX.

  Furthermore, according to the second machining mode, the bisector BX of the apex angle of the diamond tool 3 is set to the rotational axis AX of the mold material 1 from the outer periphery to the middle part of the machining surface 1a of the mold material 1. Cutting is performed in a parallel state, and then the diamond tool 3 is rotated about the B axis in FIG. 8. From the middle part to the center, the bisector BX of the apex angle of the diamond tool 3 is set as a mold. Cutting can also be performed by changing the angle to a state in which the material 1 is tilted with respect to the rotation axis AX. In such a case, the first edge 3b can form the circumferential surface 1b on the side close to the optical axis of the ring-shaped convex portion 1d in a range from the intermediate portion to the center in parallel to the rotation axis AX. That is, when an objective lens is molded using a die cut by such processing, an objective lens in which the peripheral wall near the optical axis of the annular groove is parallel to the optical axis in the range from the intermediate portion to the center can be formed. .

  10 and 11 show an enlarged cross-sectional shape of a part of a mold to be processed, and the shape of the mold is indicated by hatching.

  The inventors divided the bisector of the apex angle of the diamond tool 3 into the bisector of the apex angle of the diamond tool 3 and the comparative mold that does not incline with respect to the rotation axis AX of the mold material 1. Each of the molds of the example in which the line BX was inclined with respect to the rotation axis AX of the mold material 1 was manufactured, and an objective lens having a compatible diffraction structure was molded by both molds. When the diffraction efficiency of the objective lens molded from the comparative mold was measured, diffraction efficiency when using BD: 74.1%, diffraction efficiency when using DVD: 56.4%, diffraction efficiency when using CD: 52 It was 1%. On the other hand, when the diffraction efficiency of the objective lens molded from the mold of the example was measured, diffraction efficiency when using BD: 76.2% (+ 2.1%), diffraction efficiency when using DVD: 62.8% ( + 6.4%) and diffraction efficiency when using CD: 58.3% (+ 6.2%). The diffraction efficiency increased in any wavelength region, and the effect of the present invention was confirmed.

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims. For example, the optical element is not limited to an objective lens.

DESCRIPTION OF SYMBOLS 1 Mold raw material 1a Work surface 1b Peripheral surface 3 Diamond tool 3a Rake face 3b 1st edge 3c 2nd edge 3d Arc part (3rd edge)
4 Optical surface 5 Z-axis stage 6 X-axis stage 7 Tool mounting part 9 Rotation drive mechanism 10 Surface plate 11 B-axis stage A End part AX Rotation axis B End part BX Two equal lines

Claims (10)

A first light source that emits a first light beam with a first wavelength λ1 (390 nm ≦ λ1 ≦ 415 nm), a second light source that emits a second light beam with a second wavelength λ2 (630 nm ≦ λ2 ≦ 670 nm), and a third wavelength λ3 A third light source that emits a third light beam (760 nm ≦ λ3 ≦ 820 nm), and recording and / or reproducing information of a BD having a protective substrate with a thickness of t1 using the first light beam, Recording and / or reproducing information of a DVD having a protective substrate having a thickness of t2 (t1 <t2) using the second light flux, and having a thickness of t3 (t2 <t3) using the third light flux. An optical element used in an optical pickup device for recording and / or reproducing information of a CD having a protective substrate,
At least one optical surface of the optical element has at least a central region, an intermediate region around the central region, and a peripheral region around the intermediate region;
The optical element condenses the first light flux passing through the central area so that information can be recorded and / or reproduced on an information recording surface of a BD, and the second light flux passing through the central area is collected. The third light flux that is condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD and passes through the central area is recorded and / or reproduced on the information recording surface of the CD. Concentrate as much as you can,
The first light flux passing through the intermediate area is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passing through the intermediate area is recorded as information recording on a DVD. The light is condensed so that information can be recorded and / or reproduced on the surface, and the third light flux passing through the intermediate region is condensed so that information can be recorded and / or reproduced on the information recording surface of the CD. Without
The first light flux passing through the peripheral area is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light flux passing through the peripheral area is recorded as information recording on a DVD. The third light flux passing through the peripheral area is collected so that information can be recorded and / or reproduced on the information recording surface of the CD without being condensed so that information can be recorded and / or reproduced on the surface. Without light,
The central region includes a first optical path difference providing structure,
The first optical path difference providing structure is a structure in which a first basic structure having a blazed structure and a second basic structure having a blazed structure are stacked in opposite directions,
The step of the first foundation structure faces in the direction opposite to the optical axis, the step of the second foundation structure faces the direction of the optical axis,
Wherein the first optical path difference providing structure has a zonal convex portion with a mutually opposing peripheral wall extending substantially in the direction of the optical axis, the far side of the peripheral wall from the optical axis of the front Kiwatai projections, the optical axis An optical element having an inclination of 0 ° or more and 7 ° or less . 2. The optical element according to claim 1, wherein the peripheral wall on the side farther from the optical axis of the annular convex portion has an inclination of 0 ° or more and 2 ° or less with respect to the optical axis. 3. The optical element according to claim 1, wherein the peripheral wall of the annular zone convex portion on the side far from the optical axis is parallel to the optical axis. The peripheral wall on the side close to the optical axis of the annular convex portion is inclined so as to be separated from the optical axis toward the tip of the annular convex portion with respect to the optical axis. The optical element according to any one of the above. 5. The optical element according to claim 1, wherein a diameter of the optical element in a direction orthogonal to the optical axis is 1.45 mm or more and 4.05 mm or less. The optical element according to claim 5, wherein a diameter of the optical element in a direction perpendicular to the optical axis is 2.95 mm or more and 4.05 mm or less. The first-order diffracted light amount of the first light beam that has passed through the first basic structure is larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the first basic structure is The first order diffracted light quantity of the third light flux that has passed through the first basic structure is greater than any other order diffracted light quantity,
The second-order diffracted light amount of the first light beam that has passed through the second basic structure is larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam that has passed through the second basic structure is 2. The diffracted light quantity of any other order is greater, and the first-order diffracted light quantity of the third light flux that has passed through the first basic structure is greater than any other order of diffracted light quantity. The optical element of any one of -6. The optical element according to claim 1, wherein the annular zone convex portion has an optical path difference providing structure. The optical element according to claim 1, wherein the optical element is an objective lens. The optical element according to any one of claims 1 to 9, further comprising a surface that connects the facing peripheral walls between the peripheral walls that extend substantially in the optical axis direction and face each other.

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