WO2012111554A1 - 対物レンズ及び光ピックアップ装置 - Google Patents
対物レンズ及び光ピックアップ装置 Download PDFInfo
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- WO2012111554A1 WO2012111554A1 PCT/JP2012/053092 JP2012053092W WO2012111554A1 WO 2012111554 A1 WO2012111554 A1 WO 2012111554A1 JP 2012053092 W JP2012053092 W JP 2012053092W WO 2012111554 A1 WO2012111554 A1 WO 2012111554A1
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- Prior art keywords
- objective lens
- optical
- optical axis
- light
- lens according
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1372—Lenses
- G11B7/1374—Objective lenses
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B19/00—Condensers, e.g. light collectors or similar non-imaging optics
- G02B19/0033—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use
- G02B19/0076—Condensers, e.g. light collectors or similar non-imaging optics characterised by the use for use with a detector
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
- G11B7/1353—Diffractive elements, e.g. holograms or gratings
Definitions
- the present invention relates to an objective lens and an optical pickup device, and more particularly to an objective lens and an optical pickup device that can make tilt adjustment more optimal when the objective lens is assembled to the 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.
- 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.
- these blue-violet laser light sources are used, it is possible to record 15 to 20 GB of information on an optical disk having a diameter of 12 cm when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used.
- NA of the objective lens is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.
- BD Blu-ray Disc
- the protective substrate is designed to be thinner than in the case of DVD (with respect to 0.6 mm of DVD).
- BD is 0.1 mm), and the amount of coma due to skew is reduced.
- the tilt of the objective lens is adjusted by adjusting the tilt of the actuator that drives the objective lens in order to align the objective lens and the optical disk.
- Patent Document 1 describes that in order to adjust the tilt of the objective lens as described above, it is necessary to measure the tilt when the objective lens is attached to the optical pickup device, and a method therefor is described. Yes.
- FIG. 1 is a diagram showing a specific measurement method when adjusting the tilt of a conventional objective lens.
- an end surface 13 formed as a flat surface perpendicular to the optical axis O is provided around the second optical surface 16, which is a surface facing the optical disk of the objective lens 1, and a parallel light beam 14 is emitted from the autocollimator 12.
- the reflected light is ideally returned to the exit position.
- the objective lens has a flange portion to be attached to the optical pickup device. Conventionally, if the end surface is provided within the range of the size of the flange, a sufficient amount of reflected light can be obtained and the inclination of the objective lens can be reduced. There were no special problems in the measurement.
- the present invention has been made to solve the above-described problems. Even when the objective lens has a high NA, the tilt when attached to the optical pickup device can be measured well, and the optical pickup device can be assembled with high accuracy. It is an object of the present invention to provide a high-NA objective lens capable of performing the above and an optical pickup device including the high-NA objective lens.
- a first light source that emits a first light beam having a first wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 420 nm) and an objective lens, wherein the first light source emitted from the first light source.
- An objective lens used in an optical pickup device that records and / or reproduces information by condensing a first light flux of wavelength ⁇ 1 on an information recording surface of a first optical disk by the objective lens, A first optical surface formed on the first light source side; a second optical surface facing the first optical surface and having a radius of curvature larger than that of the first optical surface; and an optical axis And an end surface that is a plane substantially orthogonal to the optical axis and located outside the second optical surface when viewed from the direction, and the image-side numerical aperture (NA) is 0.7 or more and 0.9 or less.
- NA image-side numerical aperture
- the light beam 14 ′ incident on the second optical surface 16 is the first light beam 14 ′. Most of the light passes through the optical surface 15 and passes through the objective lens.
- FIG. 2 is a diagram showing the case of adjusting the lens tilt of a high NA objective lens.
- the expected angle at the peripheral portion (indicated by reference numeral 25 'in the drawing) of the first optical surface 25 is larger than that of the conventional objective lens 1 shown in FIG. I understand that.
- the light beam 24 ′ incident on the second optical surface 26 out of the light beam emitted from the autocollimator 12 reaches the peripheral portion 25 ′ of the first optical surface 25, and is a conventional objective lens.
- the light beam 24 ′ that should be transmitted is reflected by the peripheral portion 25 ′ of the first optical surface 25 and reaches the peripheral portion 25 ′′ of the first optical surface 25.
- Even the peripheral portion 25 ′′ is reflected and finally returns to the incident surface side. It turned out that this return light becomes unnecessary light other than the reflected light from the end face, and hinders the measurement.
- the present inventor has found a problem unique to a high-NA objective lens that “the amount of reflected light from the end face needs to be larger than the amount of unnecessary light” compared to a conventional objective lens.
- the above problem of increasing the amount of reflected light from the end face can be achieved by increasing the Strehl ratio.
- the end face area is not expanded, but the optical axis and end face are increased.
- a straight line passing through the end surface range (in other words, the length of the width of the end surface formed outside the second optical surface) is A (mm), from the optical axis to the outermost periphery of the end surface
- the distance of the straight line (in other words, the sum of the radius of the second optical surface and the length of the width of the end surface) is A / B (hereinafter referred to as the end surface width ratio) which is a ratio to B (mm) (see FIG. 2). It was found that the value can be judged by the value of (say).
- FIG. 9 is a diagram showing a relationship between A / B (end face width ratio) and reflected light Strehl ratio.
- the Strehl ratio value increases as the A / B value increases. It can be seen that the amount of reflected light from the end face can be increased by increasing the value of. From the above, the inventor says that “the ratio between the length of the end surface width and the sum of the radius of the optical surface and the width of the end surface should be specified” in order to relatively increase the amount of reflected light from the end surface. I found a solution.
- the Strehl ratio is obtained by dividing the maximum strength of the Airy disk at each end face width ratio as shown by a broken line in FIG. 8 by the maximum strength of the Airy disk when there is no aberration (end face width ratio: 1) shown by a solid line. It is a thing. Airy disk is the size of the disk at the condensing point when collimated light is incident on the lens.
- the inventor of the present application has found that unnecessary light is a phenomenon peculiar to a high NA lens due to the shape of a high NA lens as described above. It has been found that the ratio value is at most about 0.05.
- the ratio value is at most about 0.05.
- the inventors measured the inclination when the Strehl ratio of the reflected light at the end face is surely larger than the value of the Strehl ratio of unnecessary light if the value of the end face width ratio A / B is 0.12 or more. It was found that it can be performed well (see FIG. 9).
- the Strehl ratio is good, but the end face portion becomes too large, and the lens is not large enough to be practically used. Therefore, the above range is desirable for increasing the amount of reflected light while maintaining the practicality of the lens.
- a plane substantially orthogonal to the optical axis means that the angle between the optical axis and the plane is in the range of 89 ° to 91 °, more preferably 89.9 ° to 90.1 °. It means the range.
- the objective lens described in claim 2 is the objective lens described in claim 1, wherein X is the shortest distance from the optical axis to the outermost peripheral portion of the first optical surface when viewed from the direction perpendicular to the optical axis. ,
- X is the shortest distance from the optical axis to the outermost peripheral portion of the first optical surface when viewed from the direction perpendicular to the optical axis.
- the inventor can prevent the amount of unnecessary light from becoming large by “a ratio between a value substantially corresponding to the radius of the light beam used for the inspection and the value of the radius of the first optical surface”. I found a solution. By setting the value of B / X within the range of 0.8 to 1.7, the lens can be practically used and the Strehl ratio of unnecessary light can be extremely increased. I found that it can be prevented.
- the objective lens according to claim 3 is the following formula in the invention according to claim 1 or 2, 0.2 ⁇ A / B ⁇ 0.5 (3) It is characterized by satisfying.
- a / B is expressed by Equation (3) from the viewpoint of manufacturing errors. If it is the range shown, it is more preferable.
- the objective lens according to claim 4 is the invention according to any one of claims 1 to 3, wherein the A (mm) is represented by the following formula: 0.1 ⁇ A ⁇ 0.3 (4) It is characterized by satisfying.
- the lens has a shape of an end surface that satisfies the ratio of the length of the end surface to the sum of the radius of the optical surface and the length of the end surface, as shown in claim 1 It is considered that the larger the area of the end face, the larger the absolute amount of reflected light. Since the objective lens for an optical pickup device has a limit on the overall size depending on its application, it is effective to increase the end face width in order to increase the area. Therefore, it is considered that increasing the end face width from a certain value contributes to increasing the amount of light.
- the end face is rarely in an ideal shape, and aberration may occur due to the inclination or waviness of the face. Then, on the contrary, the amount of aberration due to the inclination and waviness increases in proportion to the width of the end face, and thus a phenomenon occurs in which the amount of light when adjusting the inclination is reduced.
- the amount of light can be increased by actually making the end face width smaller than the upper limit of 0.3 mm. If the lower limit is too small, the amount of light cannot be obtained in the first place.
- the value of A is in the range shown in the equation (4).
- the objective lens according to claim 5 is the following formula when the axial thickness of the objective lens is d (mm) in the invention according to any one of claims 1 to 4. 1.3 ⁇ d ⁇ 3.0 (5) It is characterized by satisfying.
- the objective lens according to claim 6 is characterized in that, in the invention according to any one of claims 1 to 5, an outermost diameter of the objective lens is 4 mm or less.
- the axial thickness d satisfies the formula (5).
- the outermost diameter is preferably 4 mm or less.
- the objective lens described in claim 7 is characterized in that, in the invention described in any one of claims 1, 2, 4, 5, or 6, the objective lens is formed of a glass material.
- glass materials are superior to materials such as resins in terms of shrinkage and the like, the shape of the end surface is also favorable, and even a high NA type objective lens can be measured with good inclination, which is preferable.
- the objective lens according to claim 8 is the invention according to any one of claims 1, 2, 4, 5, 6 or 7, wherein the objective lens has the following formula: 0.35 ⁇ A / B ⁇ 0.5 (6) It is characterized by satisfying.
- the objective lens according to claim 9 is the invention according to any one of claims 1 to 3, wherein at least one of the first optical surface and the second optical surface has an annular optical path difference providing structure. It is characterized by having.
- a ring-shaped optical path difference providing structure may be provided on the lens surface for reasons such as measures against temperature characteristics and recording / reproducing for a plurality of types of optical disks having different substrate thicknesses.
- a high NA objective lens as described above, there is a case where it is reflected without transmitting at the periphery of the optical surface.
- the structure is formed at the periphery of the optical surface. May become complicated, and the above phenomenon may become more remarkable. Therefore, the present invention has a particularly remarkable effect with respect to a high NA objective lens having an annular optical path difference providing structure on the optical surface.
- the objective lens according to claim 10 is the invention according to claim 9, wherein the A (mm) is the following formula: 0.1 ⁇ A ⁇ 0.3 (4) It is characterized by satisfying.
- the objective lens according to claim 11 is the following formula when the axial thickness of the objective lens is d (mm) in the invention according to claim 9 or 10: 1.3 ⁇ d ⁇ 3.0 (5) It is characterized by satisfying.
- the objective lens according to claim 12 is characterized in that, in the invention according to any one of claims 9 to 11, an outermost diameter of the objective lens is 4 mm or less.
- An objective lens according to a thirteenth aspect is the invention according to the ninth aspect, wherein an optical path difference providing structure is formed on the first optical surface, and the first optical surface includes a central region and a central region.
- the optical path difference providing structure includes at least a first optical path difference providing structure in the central area, and a second optical path difference providing structure is provided in the central area. It is provided in the middle region.
- the optical pickup device has a second wavelength ⁇ 2 in addition to the first light source that emits the first light flux having the first wavelength ⁇ 1.
- a second light source that emits a second light beam of ( ⁇ 2> ⁇ 1) and a third light source that emits a third light beam of a third wavelength ⁇ 3 ( ⁇ 3> ⁇ 2);
- the second optical disk having a protective substrate with a thickness t2 (t1 ⁇ t2) using the second light flux Is an optical pickup device that records and / or reproduces information on a third optical disk having a protective substrate with a thickness of t3 (t2 ⁇ t3) using the third light flux.
- the objective lens passes through the central region
- the first light flux is condensed on the information recording surface of the first optical disc so that information can be recorded and / or reproduced
- the second light flux passing through the central region is focused on the information recording surface of the second optical disc.
- the third light flux passing through the central area is condensed so that information can be recorded and / or reproduced on the information recording surface of the third optical disc.
- 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 first optical disc
- the second light flux passing through the intermediate area is The third optical flux is focused on the information recording surface of the second optical disc so that information can be recorded and / or reproduced
- the third light flux passing through the intermediate region is recorded and / or recorded on the information recording surface of the third optical disc.
- Two light beams are not condensed on the information recording surface of the second optical disk so that information can be recorded and / or reproduced, and the third light beam passing through the peripheral region is focused on the information recording surface of the third optical disk.
- the light is not condensed so that information can be recorded and / or reproduced.
- the optical path difference providing structure of the objective lens for 3 compatibility as described above has different functions, such as being divided into 3 areas and having different information recording surfaces for focusing on each area.
- the optical path difference providing structure having such a configuration has a complicated structure as compared with, for example, an optical path difference providing structure for correcting temperature characteristics in one region. Therefore, the phenomenon of reflecting without transmitting at the periphery of the optical surface as described above becomes more remarkable. Therefore, the present invention has a particularly remarkable effect on a high NA objective lens having a three-compatible optical path difference providing structure.
- the objective lens according to claim 15 is the invention according to claim 13 or 14, wherein the A (mm) is the following formula: 0.1 ⁇ A ⁇ 0.3 (4) It is characterized by satisfying.
- the objective lens according to claim 16 is the following formula according to the invention according to any one of claims 13 to 15, where the axial thickness of the objective lens is d (mm): 1.3 ⁇ d ⁇ 3.0 (5) It is characterized by satisfying.
- the objective lens according to claim 17 is characterized in that, in the invention according to any one of claims 13 to 16, an outermost diameter of the objective lens is 4 mm or less.
- WD working distance
- an optical path difference providing structure is provided to solve the problem of WD. It is necessary to provide a larger number of ring zones than the three compatible objective lenses of normal size. This is because it is necessary to increase the diffraction power so that light can be collected even with a short focal length. However, even if the diameter is reduced, the ring pitch (width in the direction perpendicular to the optical axis) becomes narrower, and if the number of ring zones is increased, the ring pitch is naturally much larger than that of a normal three-compatible objective lens.
- the present invention has a particularly remarkable effect in a small-diameter high-NA three-compatible objective lens having an annular optical path difference providing structure on the optical surface.
- the objective lens according to claim 18 is characterized in that, in the invention according to any one of claims 1 to 3, the end surface is formed adjacent to the second optical surface.
- the objective lens according to claim 19 is characterized in that, in the invention according to any one of claims 1, 2, 3 or 18, the objective lens has a flange portion on an outer peripheral portion of the end face.
- the objective lens according to claim 20 is the invention according to claim 19, wherein the objective lens is formed of a resin material, and the surface of the flange portion provided on the outer periphery of the end surface as viewed from the optical axis direction is: It is characterized by being formed so as to have substantially the same height as the end face as viewed from the direction perpendicular to the optical axis.
- FIG. 3 is a cross-sectional view showing an example of a high NA objective lens 2 according to the present invention.
- the end face 31 and the flange portion 32 have the same height, thereby improving the fluidity of the resin injected from the gate portion 36, and as a result, the end face shape transferability is also improved and the reflection is improved. It is more preferable because the amount of light is improved.
- the objective lens according to claim 21 is the objective lens according to claim 19, wherein the objective lens is formed of a resin material, and the surface of the flange portion provided on the outer periphery of the end surface as viewed from the optical axis direction is: The optical disc is provided on the optical disc side from the end face as viewed from the direction perpendicular to the optical axis.
- FIG. 4 is a cross-sectional view showing another example of the high NA objective lens 2 according to the present invention.
- the surface of the flange portion 32 can function as a protector for avoiding a collision between the optical surface and the optical disc. become able to.
- the objective lens according to claim 22 is the objective lens according to any one of claims 19 to 21, wherein the objective lens is formed of a resin material, and the first optical element is viewed from a direction perpendicular to the optical axis.
- a connecting surface between the surface and the first optical surface side surface of the flange portion, and the connecting surface is closer to the second optical surface side than the first optical surface side surface of the flange portion. It is formed.
- the objective lens according to a twenty-third aspect is the invention according to the twenty-second aspect, wherein the connecting surface is formed on a surface that is not perpendicular to the optical axis when viewed from the direction perpendicular to the optical axis. .
- the objective lens described in Item 24 is characterized in that, in the invention described in Item 22 or 23, the end surface and the connecting surface are mirror surfaces.
- the end surface 13 is a mirror surface, better reflection can be performed, and the amount of reflected light returning to the autocollimator can be increased. Further, by using the connecting surface 33 as a mirror surface, more accurate attachment can be performed than when the connecting surface 33 is used for attaching a lens (in the case of the shape shown in FIG. 3).
- the objective lens according to claim 25 is the invention according to any one of claims 19 to 24, wherein a part of the outer periphery of the flange portion has a linear portion when viewed from the optical axis direction.
- the objective lens according to claim 26 is characterized in that, in the invention according to claim 25, the linear portion is provided on the outer peripheral side with respect to the end face.
- FIG. 5 is a view of the high NA objective lens according to the present invention as seen from the optical axis direction.
- a resin objective lens includes a step of cutting the gate portion 36 into which resin flows in the manufacturing process.
- the flange part 32 may be cut
- the straight line portion 35 is applied to the end face 13, the loss of the amount of reflected light and the possibility that accurate measurement cannot be performed increase. In particular, the problem becomes remarkable in a small-diameter objective lens.
- the linear portion 35 is provided outside the end surface 13 so as not to be adversely affected by the reduction of the area of the end surface or the distortion of flatness in connection with the cutting of the gate portion. preferable.
- An objective lens according to a twenty-seventh aspect is the objective according to the twenty-sixth aspect, wherein the straight line portion has a gate portion, and the length of a straight line perpendicular to the straight line portion from the optical axis to the straight line portion is set.
- C the following formula: 1.05 ⁇ C / B ⁇ 1.60 (7) It is characterized by satisfying.
- An objective lens according to a twenty-eighth aspect is the objective lens according to any one of the twenty-fifth to twenty-seventh aspects, wherein the straight line portion has a gate portion, and the flange portion has a first shape when viewed from a direction perpendicular to the optical axis.
- the difference h in the optical axis direction between the surface on the optical surface side of 2 and the end surface portion is expressed by the following equation: 0.02 ⁇ h ⁇ 0.1 (8) It is characterized by satisfying.
- the flange width 32 b from the straight part to the end face is larger than the normal flange width 32 a. Becomes shorter.
- FIG. 6 is an enlarged sectional view around the flange portion of the objective lens shown in FIG.
- the surface of the flange portion 32 on the second optical surface 26 side is located closer to the second optical surface 26 than the end surface 13, so that the difference h between these two surfaces is increased.
- the molten resin is injected from the gate portion 36, the molten resin collides with the flange inner side surface portion 34, which is a boundary surface between the end surface 13 and the flange portion 32, as shown by arrows, and the fluidity deteriorates and the end surface 13 is adversely affected. Arise.
- the distance from the gate portion 36 to the mold corresponding to the flange inner side surface portion 34 is not excessively long, and an accurate shape as a product shape can be maintained. Further, by not exceeding the upper limit value, in the case of a D-shaped lens having a linear portion on the outer periphery, it is possible to maintain merits such as ease of gate cutting. Therefore, by performing shape design within the above conditional expression range, a linear portion is provided, and the amount of reflected light is sufficient and good measurement can be performed.
- the objective lens according to a twenty-ninth aspect is characterized in that, in the invention according to any one of the first to the twenty-eighth aspects, the objective lens has a marking at a location other than the end face when viewed from the optical axis direction of the objective lens.
- An objective lens according to a thirty-first aspect has the following formula when the axial thickness of the objective lens is d (mm) in the invention according to any one of the eighteenth to thirtieth aspects: 1.3 ⁇ d ⁇ 3.0 (5) It is characterized by satisfying.
- the objective lens described in Item 32 is characterized in that, in the invention described in any one of Items 18 to 31, the outermost diameter of the object lens is 4 mm or less.
- An objective lens according to a thirty-third aspect is the invention according to any one of the first to thirty-second aspects, wherein the thickness t (mm) of the thinnest portion of the end surface when viewed from a direction perpendicular to the optical axis of the objective lens. Is the following formula: 0.35 ⁇ t ⁇ 1.0 (9) It is characterized by satisfying.
- the thickness t of the end surface 13 shown in FIG. 6 is too thin, the shape accuracy of the end surface 13 near the gate portion 36 is deteriorated due to excessive holding pressure due to injection at the time of molding, or the reflected light on the connecting surface 33
- accurate measurement cannot be performed because the light is combined with the reflected light from the end face 13.
- the fluidity of the resin is also deteriorated, there arises a problem that the transferability of the entire lens including the optical surface is deteriorated.
- the thickness t of the end face 13 is preferably larger than the lower limit value of the above conditional expression, and further, by making the thickness t smaller than the upper limit value, it is possible to prevent the lens outer shape from becoming too large, and to have an appropriate size.
- This objective lens can be used.
- the objective lens according to claim 34 is the invention according to claim 33, wherein the t (mm) is the following formula: 0.5 ⁇ t ⁇ 0.8 (10) It is characterized by satisfying.
- the objective lens according to claim 35 is the invention according to any one of claims 1 to 34, wherein the surface roughness Ry at the end surface is expressed by the following equation: 0.3 ⁇ Ry ⁇ 7.0 (11) It is characterized by satisfying.
- the regular reflectance of the end face be high in order to make the amount of reflected light used for measurement more than a certain value.
- the processing cost is too high to finish with high accuracy, it is desirable to keep it within the range of the conditional expression (11).
- the end surface is donut-shaped, the area of the reflecting surface can be maximized, contributing to an increase in the amount of reflected light.
- the objective lens according to claim 37 is the objective lens according to any one of claims 1 to 36, wherein: 0.9 ⁇ d / f ⁇ 1.8 (12) It is characterized by satisfying.
- d (mm) represents the thickness on the objective lens axis
- f (mm) represents the focal length in the first light flux.
- the conditional expression (12) By satisfying the above, it is possible to suppress the generation of astigmatism and decentration coma.
- the objective lens satisfying the conditional expression (12) becomes a relatively thick objective lens, and is reflected by the peripheral portion of the optical surface of the objective lens, thereby reducing the Airy intensity, using FIG.
- An optical pickup device includes the objective lens according to any one of the first to thirty-seventh aspects.
- the optical pickup device has a first light source that emits at least a first light beam having a first wavelength ⁇ 1 (390 nm ⁇ 1 ⁇ 420 nm), and condenses the first light beam on the information recording surface of the first optical disc.
- the optical pickup device of the present invention includes a light receiving element that receives the reflected light beam of the first optical disk.
- the optical pickup device may be an optical pickup device having a plurality of light sources, and has two light sources of a first light source and a second light source, or three light sources including a third light source. May be.
- the optical pickup device of the present invention having the second light source and the third light source in addition to the first light source condenses the first light beam on the information recording surface of the first optical disk, and the second light beam is the second light beam.
- a condensing optical system for condensing on the information recording surface of the optical disc and condensing the third light beam on the information recording surface of the third optical disc is provided.
- the optical pickup device of the present invention includes a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, or the third optical disc.
- the first optical disc has a protective substrate having a thickness t1 and an information recording surface.
- the second optical disc has a protective substrate having a thickness t2 (t1 ⁇ t2) and an information recording surface.
- the third optical disc has a protective substrate having a thickness t3 (t2 ⁇ t3) and an information recording surface.
- the first optical disc is preferably a BD
- the second optical disc is a DVD
- the third optical disc is preferably a CD, but is not limited thereto.
- the first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.
- BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 420 nm and an objective lens having an NA of about 0.7 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00.
- 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.
- 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.
- 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.
- 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.
- 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.
- the first light source, the second light source, and the third light source are preferably laser light sources.
- the laser light source a semiconductor laser, a silicon laser, or the like can be preferably used.
- the wavelength ⁇ 3 ( ⁇ 3> ⁇ 2) is defined by the following conditional expressions (16), (17), 1.5 ⁇ ⁇ 1 ⁇ 2 ⁇ 1.7 ⁇ ⁇ 1 (16) 1.8 ⁇ ⁇ 1 ⁇ 3 ⁇ 2.0 ⁇ ⁇ 1 (17) It is preferable to satisfy.
- the first wavelength ⁇ 1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm.
- the second wavelength ⁇ 2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength ⁇ 3 of the third light source is preferably 420 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.
- the unitization means that the first light source and the second light source are fixedly housed in one package, for example.
- a light receiving element to be described later may be packaged.
- a photodetector such as a photodiode is preferably used.
- Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it.
- the light receiving element may comprise a plurality of photodetectors.
- the light receiving element may have a main photodetector and a sub photodetector.
- two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors.
- a light receiving element may be used.
- the light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.
- the condensing optical system 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.
- 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 a light beam emitted from the light source onto the information recording surface of the optical disk.
- the objective lens may be composed of two or more plural lenses and / or optical elements, or may be composed of only a single lens, but is preferably an objective lens composed of a single-sided double-sided convex lens. is there.
- the objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin.
- a hybrid lens may also be used.
- the objective lens has a plurality of lenses
- a glass lens and a plastic lens may be mixed and used.
- the objective lens may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure).
- the objective lens preferably has a refractive surface that is aspheric.
- the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.
- the objective lens also has a first optical surface and a second optical surface having a radius of curvature larger than that of the first optical surface and facing the first optical surface.
- the radius of curvature is a radius of a circle that approximates a local bend in the vicinity of the optical axis of the optical surface to a circle.
- the objective lens of the present invention has an end face.
- the end face is a plane substantially orthogonal to the optical axis located outside the second optical surface as seen from the optical axis direction as shown in FIG.
- the end surface is preferably formed adjacent to the second optical surface. In this case, since there is no unnecessary portion between the second optical surface and the end surface, the entire objective lens can be made small, and a small pickup lens can be manufactured. Further, by forming the end face on the optical axis side, the distance from the gate portion can be increased, and the influence of deformation due to the injection pressure of the gate portion can be minimized.
- the gate portion is a resin inflow port of a product when the objective lens is molded by injection molding, and is often introduced from a direction perpendicular to the optical axis.
- the gate portion is provided at a part of the flange portion.
- the end surface portion may have a donut shape when viewed from the optical axis direction. When the end surface has a donut shape, the reflecting surface can be maximized, which contributes to an increase in the amount of reflected light.
- the end surface is a surface other than the optical surface, and is a surface on which the light beam is reflected from the surface after being irradiated from a position perpendicular or substantially perpendicular to the surface and returns to the irradiation position. Preferably there is.
- the end surface is preferably a mirror surface, and the surface roughness Ry of the end surface is expressed by the following formula (11), 0.3 ⁇ Ry ⁇ 7.0 (11) It is preferable to satisfy.
- the surface roughness Ry is the height from the lowest valley bottom to the highest mountain peak on the minute irregularities of the surface.
- a flange portion is provided on the outer side of the end face when viewed from the optical axis direction. It is preferable that the flange portion is not a mirror surface.
- the flange portion may have almost the same height as the end surface when viewed from the direction perpendicular to the optical axis as shown in FIG. 3, or the optical disc side from the end surface when viewed from the direction perpendicular to the optical axis as shown in FIG. (It can also be said that there is a step between the flange portion and the end surface, and the flange portion is higher than the end surface).
- the flange portion is a portion that is provided on the outer peripheral portion of the optical surface, for example, and serves as an attachment location when the objective lens is incorporated into the pickup device.
- the lens In the case of forming the lens by injection molding or the like when the flange portion is formed so as to be almost the same height as the end face as seen from the direction orthogonal to the optical axis as in the objective lens shown in FIG. Since the resin flows along the mold surface, it is possible to eliminate the configuration that prevents the resin from flowing. Therefore, the fluidity of the resin after injection from the gate portion is improved, and the end face accuracy is improved accordingly.
- the fluidity of the resin here refers to the ease with which the molten resin flows and flows into the mold until it solidifies.
- the surface of the flange portion is the optical surface. It can also function as a protector for avoiding a collision with the optical disc.
- the connecting surface 33 may be provided as in the objective lens shown in FIG.
- the connecting surface is a surface existing between the first optical surface side and the flange portion.
- the connecting surface 33 may be a surface whose direction is perpendicular to the optical axis, but may not be a surface perpendicular to the optical axis. For example, a minute angle of about 1 to 20 ° with respect to the direction perpendicular to the optical axis may be provided.
- the light reflected from the connecting surface 33 among the light from the autocollimator is converged or diverged. Since the image in the autocollimator can be blurred by the reflected light from the connecting surface 33, the reflected light from the end surface 13 and the reflected light from the connecting surface 33 can be easily discriminated. become.
- the connecting surface may be a mirror surface. In this case, since the surface is made with high accuracy, more accurate attachment can be achieved. Further, the connecting surface may be formed on the second optical surface side with respect to the surface on the first optical surface side of the flange portion. At this time, by forming the joint of the mold on the first optical surface side on the joint surface, it is possible to prevent the burr generated at the joint from protruding from the surface of the flange portion on the first optical surface side. The lens can be stably installed during the mounting adjustment, and the lens can be accurately adjusted.
- a plane substantially orthogonal to the optical axis continues to the end of the lens outside the second optical surface 26.
- the plane substantially perpendicular to the optical axis is the entire mirror surface and the entire surface is irradiated with light, and the light reflected by the entire surface returns to the irradiation position, the entire plane substantially orthogonal to the optical axis Can be regarded as the end face 13.
- the region close to the optical axis is a mirror surface, and the region away from the optical axis is not a mirror surface but a flange portion 32, and is a plane substantially orthogonal to the optical axis.
- the light beam is irradiated, the light beam reflected by the mirror surface returns to the irradiation position.
- a mirror surface region close to the optical axis is formed. It can be regarded as the end face 13.
- the shape is as shown in FIG. 4, the plane closer to the optical axis than the step can be regarded as the end surface 13 among the planes substantially orthogonal to the optical axis, and the outer side of the step is outside.
- One surface becomes the flange portion 32.
- a coat (enhanced reflection coat) for enhancing the reflection of light used for adjusting the tilt may be formed on the end face 13.
- This coat is desirably a coat that enhances the reflection of a light beam emitted from the autocollimator, for example, light having a wavelength of 600 to 700 nm, by 30% or more, more preferably 60% or more, compared to the state without the coat.
- the coat for enhancing the reflected light may be formed only on the end surface 13 of FIG. 3, but the flange portion 32 may be formed together. As a result, the range of the end face 13 is reliably coated, so that the reflected light becomes stronger.
- the coat may be formed only on the end face 13 or may be formed including the flange portion 32.
- a part of the flange portion may have a straight portion 35 when viewed from the optical axis direction.
- the linear part 35 is formed in the outer peripheral side rather than the end surface 13.
- the mold is provided with the straight part 35 from the beginning and only the gate part 36 is cut within the circumference, and the mold is not provided with the straight part.
- These methods are suitable for mass production because gate cutting can be performed more easily than the gate cutting method in which finishing or the like is performed along the circumference so that burrs or the like do not jump out on the circumference.
- the gate cut location is very close to the end face near the straight line portion, so when performing the gate cut, the end face may be adversely affected and the surface accuracy may deteriorate. Since the straight line portion is provided on the outer peripheral side of the end face, a sufficient amount of light can be ensured at the time of inclination measurement in attachment even with such a cutting method.
- the straight portion 35 when the straight portion 35 is provided on the outer peripheral side of the end surface of the flange portion as viewed from the optical axis direction and has a gate portion in this straight portion, the straight portion extends from the optical axis.
- the length of a straight line perpendicular to the straight line part up to the part is C, the following formula (7), 1.05 ⁇ C / B ⁇ 1.60 (7) It is preferable to satisfy.
- the surface on the second optical surface 26 side of the flange portion 32 relative to the end surface 13 is located on the optical disc side. Therefore, if the difference h between these two surfaces is increased, the molten resin After the injection, the resin collides with the end face 13 and the flange inner side face 34, which adversely affects the molding of the end face. At this time, if the distance from the gate portion 36 to the mold corresponding to the flange inner side surface portion 34 is too short, the injection pressure increases during injection molding, adversely affecting the molding of the end surface 13, and the end surface is not a good smooth surface. As a result, good reflected light cannot be obtained.
- the B / C value larger than the lower limit value, the influence of the injection pressure can be suppressed. This is the same even when the straight part is provided from the beginning in the molding and the gate part is cut within the circumference. In this case, the flange part cutting affects the end face accuracy. Furthermore, by making it smaller than the upper limit value, the distance from the gate portion 36 to the mold corresponding to the flange inner side surface portion 34 is not excessively long, and an appropriate shape as the product shape can be maintained. Further, by not exceeding the upper limit value, in the case of an objective lens having a D-shaped outer shape as shown in FIG. 5, merits such as ease of gate cutting can be maintained.
- the resin flowable width is narrowed.
- the possibility of resin hitting is increased. Therefore, the influence on the end face 13 can be minimized by making it smaller than the upper limit value of h shown in the conditional expression (8). Further, by setting the value larger than the lower limit value, burrs do not protrude when the lens is placed.
- markings may be provided at locations other than the end face when viewed from the optical axis direction.
- the marking is a mark for identifying a lens, a mark for identifying a mold for manufacturing a lens, or a mark for adjustment when the lens is assembled.
- the marking itself is performed by a method of transferring dimples to the lens by providing dimples on the mold or a method of printing directly on the lens by inkjet or the like.
- the formula (10), 0.5 ⁇ t ⁇ 0.8 (10) Is to satisfy.
- the range of formula (10) is more desirable for stably producing a large amount of products.
- the thickness between the end surface 13 and the connecting surface 33 is t as viewed from the direction perpendicular to the optical axis.
- t the thickness between the end surface 13 and the connecting surface 33 is t as viewed from the direction perpendicular to the optical axis.
- the value of t larger than the lower limit value, it is possible to prevent the shape accuracy of the end face 13 near the gate portion 36 from being deteriorated due to excessive holding pressure due to injection during molding, and the reflection at the connecting face 33. It is possible to prevent the light from being combined with the reflected light at the end face, and more accurate measurement can be performed.
- the fluidity of the resin can be improved, and the transferability of the entire lens including the optical surface can be kept good.
- the value of t from exceeding the upper limit value, it is possible to prevent the lens outer shape from becoming too large, and an objective lens having an appropriate size can be obtained.
- d (mm) represents the axial thickness of the objective lens
- f (mm) represents the focal length in the first light flux
- the objective lens of the present invention is a straight line that passes through at least the optical axis and the end surface when viewed from the optical axis direction, and is a straight line distance (in other words, the second optical surface of the second optical surface).
- the length of the width of the end face formed on the outer side) is A (mm)
- the distance of the straight line from the optical axis to the outermost periphery of the end face (in other words, the radius of the second optical surface and the length of the width of the end face) Sum) is B (mm).
- increasing the amount of reflected light can be achieved by increasing the Strehl ratio.
- the end surface area is not increased, but the ratio of A / B, which is the ratio of A and B described above. It can be judged by (end face width ratio). In order to increase the amount of reflected light, it is possible to increase the value of A / B.
- the Strehl ratio is about 0.05 or less, and the reflected light on the end face for adjusting the lens becomes weak and adjustment is performed. Becomes difficult.
- the A / B value is 0.5 or more, the Strehl ratio is good, but the end face portion becomes too large, and the lens cannot be practically used. Therefore, by setting the value of A / B within the range of the following conditional expression (1), the amount of reflected light can be increased while maintaining the practicality of the lens.
- the Strehl ratio is obtained by dividing the maximum strength of the Airy disk at each end face width ratio by the maximum strength of the Airy disk when there is no aberration (end face width ratio: 1) as shown in FIG.
- Airy disk is the size of the disk at the condensing point when collimated light is incident on the lens.
- the Strehl ratio is about 0.1 for normal product accuracy. Therefore, by setting the lower limit value to 0.2, even if the Strehl ratio becomes low due to a manufacturing error, it is possible to secure a light amount at a level that does not cause a problem in measurement. Therefore, in order to enable the assembly process of the optical pickup device that can perform good measurement even with a high NA type objective lens more reliably, the following conditional expression (3) from the viewpoint of manufacturing error: 0.2 ⁇ A / B ⁇ 0.5 (3) It is more preferable to satisfy.
- an objective lens is made of a glass material, it is excellent in terms of shrinkage and the like as compared with a material such as a resin, so that the shape of the end surface is likely to be good. Therefore, in order to enable an assembly process of an optical pickup that can perform good measurement even with a high NA type objective lens, the above conditional expression (6), 0.35 ⁇ A / B ⁇ 0.5 (6) It is more preferable to satisfy.
- the objective lens has the following conditional expression (2), where X (mm) is the shortest distance from the optical axis to the outermost peripheral portion of the first optical surface when viewed from the direction perpendicular to the optical axis. 0.8 ⁇ B / X ⁇ 1.7 (2) It is more preferable to satisfy.
- the Strehl ratio of unnecessary light increases as the value of X increases. Therefore, if the value of X is made too large, that is, if B / X is made too small, the end face width becomes too small compared to the radius of the first optical surface, and the side surface of the first optical surface becomes too small. As a result, the Strehl ratio of the unnecessary light reflected is also increased. Conversely, when the value of B / X is increased, B is increased with respect to X which is the radius of the first optical surface.
- the value of B / X is increased in a state where X is set to a common sense value to some extent, it means that the size of B increases. As a result, the value of B is substantially equal to the sum of the radius of the second optical surface and the width of the end surface. Therefore, when B is increased, the outer shape of the lens also increases, and the lens cannot be practically used. End up.
- the inventor can prevent the amount of unnecessary light from becoming large by “a ratio between a value substantially corresponding to the radius of the light beam used for the inspection and the value of the radius of the first optical surface”. I found a solution. By setting the value of B / X within the range of 0.8 to 1.7, the lens can be practically used and the Strehl ratio of unnecessary light can be extremely increased. I found that it can be prevented.
- the lens satisfies the ratio between the value of the end face and the radius of the optical surface and has an ideal end face shape, ideally, the larger the end face area, the greater the absolute amount of light. it is conceivable that. Since the objective lens for an optical pickup device has a limit on the overall size depending on its application, it is effective to increase the end face width in order to increase the area. Therefore, it is considered that increasing the end face width from a certain value contributes to increasing the amount of light.
- the end face is rarely in an ideal shape, and aberration may occur due to the inclination or waviness of the surface. Then, on the contrary, since the amount of aberration due to the inclination and waviness increases in proportion to the width of the end face, a phenomenon occurs in which the amount of light when adjusting the inclination is reduced. Therefore, in practice, the light amount can be further increased by making the width of the end face smaller than 0.3 mm. If the lower limit is too small, the amount of light cannot be obtained in the first place. Therefore, the following conditional expression (4), 0.1 ⁇ A ⁇ 0.3 (4) The amount of light can be increased by making the objective lens to satisfy the above.
- the range of 1.3 ⁇ d ⁇ 2.0 is satisfied, where d (mm) is the thickness of the optical axis of the objective lens.
- the outermost diameter of the objective lens is desirably 4 mm or less.
- the lens shape can be reduced with a sufficient amount of reflected light even with a BD objective lens that tends to be large. Thereby, the objective of weight reduction and size reduction of a lens can be achieved.
- the objective lens is a glass lens
- a glass material having a glass transition point Tg of 500 ° C. or lower more preferably 400 ° C. or lower.
- a glass material having a glass transition point Tg of 500 ° C. or lower molding at a relatively low temperature is possible, so that the life of the mold can be extended.
- Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.
- the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the mass is increased and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity.
- the specific gravity is preferably 4.0 or less, more preferably 3.0 or less.
- one of the important physical property values when molding and manufacturing a glass lens is the linear expansion coefficient a. Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still larger than that of a plastic material. When lens molding is performed using a glass material having a large linear expansion coefficient a, cracks are likely to occur when the temperature is lowered.
- the linear expansion coefficient a of the glass material is preferably 200 ( ⁇ 10 ⁇ 7 / K) or less, and more preferably 120 ( ⁇ 10 ⁇ 7 / K) or less.
- the objective lens is a plastic lens
- an alicyclic hydrocarbon polymer material such as a cyclic olefin resin material.
- the resin material has a refractive index of 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm according to a temperature change within a temperature range of ⁇ 5 ° C. to 70 ° C.
- the coupling lens is preferably a plastic lens.
- a first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (1) and the following formula ( II) and / or polymer block [B] containing a repeating unit [3] represented by the following formula (III), and repeating in the block [A] From the block copolymer in which the relationship between the molar fraction a (mol%) of the unit [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is the resin composition which becomes.
- R 1 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms
- R 2 to R 12 each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or 1 to 20 alkoxy groups or halogen groups.
- R 13 represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
- R 14 and R 15 each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.
- the second preferred example is obtained by addition polymerization of a monomer composition comprising at least an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (IV).
- Polymer (B) obtained by addition polymerization of polymer (A) and a monomer composition comprising an ⁇ -olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (V) ).
- n is 0 or 1
- m is 0 or an integer of 1 or more
- q is 0 or 1
- R 1 to R 18 , R a and R b are each independently a hydrogen atom, halogen An atom or a hydrocarbon group
- R 15 to R 18 may be bonded to each other to form a monocyclic or polycyclic ring, and the monocyclic or polycyclic ring in the parentheses may have a double bond R 15 and R 16 , or R 17 and R 18 may form an alkylidene group.
- R 19 to R 26 each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group.
- the following additives may be added.
- Stabilizer It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .
- phenol-based stabilizer As a preferred phenol-based stabilizer, conventionally known ones can be used. For example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No.
- Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2, , 6-Tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-but
- the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry.
- triphenyl phosphite diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl).
- Phenyl) phosphite tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15)) Fight) and the like diphosphite compounds such as.
- monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.
- Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- ( ⁇ -lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.
- each of these stabilizers is appropriately selected within a range not to impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, The amount is preferably 0.01 to 1 part by mass.
- a surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule.
- the surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.
- hydrophilic group of the surfactant examples include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned.
- the amino group may be primary, secondary, or tertiary.
- the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms.
- the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent.
- Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like.
- the aromatic ring include a phenyl group.
- the surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.
- examples of such a surfactant include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene
- examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like.
- amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.
- the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
- the addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.
- Plasticizer The plasticizer is added as necessary to adjust the melt index of the copolymer.
- Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tricitrate citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisode
- cycloolefin resins are preferably used. Specifically, ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS ADVANCED POLYMERS, TOPAS, JSR manufactured by ARTON, etc. are preferable. Take as an example.
- the Abbe number of the material constituting the objective lens is preferably 50 or more.
- the objective lens may have an optical path difference providing structure.
- the optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam.
- 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.
- 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.
- 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.
- the diffractive structure referred to in this specification is a general term for structures that have a step and have a function of converging or diverging a light beam by diffraction.
- 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.
- 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.
- 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.
- the optical path difference providing structure has a plurality of concentric annular zones with the optical axis as the center.
- 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.
- the blaze type structure means that the cross-sectional shape including the optical axis of the optical element having the optical path difference providing structure is a sawtooth shape.
- the upper side is the light source side and the lower side is the optical disc side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface.
- the length in the direction perpendicular to the optical axis of one blaze unit is referred to as a pitch P (see FIGS. 7A and 7B).
- 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. 7A).
- 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).
- 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.
- a three-level or higher staircase structure has a small step and a large step.
- the optical path difference providing structure illustrated in FIG. 7C is referred to as a five-level staircase structure
- the optical path difference providing structure illustrated in FIG. 7D is referred to as a two-level staircase structure (also referred to as a binary structure).
- a two-level staircase structure is described below.
- a plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis,
- the light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed.
- the surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.
- the length in the direction perpendicular to the optical axis of one staircase unit is referred to as a pitch P (see FIGS. 7C and 7D).
- the length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2.
- a large step amount B1 and a small step amount B2 exist (see FIG. 7C).
- the optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated.
- unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle.
- 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”.
- the sawtooth shape as a unit shape is repeated.
- the same serrated shape may be repeated, and as shown in FIG. 7 (b), the serrated shape gradually increases as it moves away from the optical axis.
- a shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used.
- the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area
- mold structure is provided in the meantime.
- the optical path difference providing structure has a staircase structure
- the inspection light incident from the second optical surface may be reflected without being transmitted on the surface of the peripheral region of the first optical surface.
- the optical path difference providing structure is provided, the structure is complicated on the side surface of the lens, and the above phenomenon may become more remarkable. Therefore, the present invention has a particularly remarkable effect on an objective lens having a high NA having an annular optical path difference providing structure on the optical surface.
- the case where the objective lens has an optical path difference providing structure is divided into several cases, and each is described.
- the optical path difference providing structure is: It is an optical path difference providing structure for correcting temperature characteristics that corrects spherical aberration that occurs when the temperature changes, or an optical path difference providing structure that corrects spherical aberration that occurs when the wavelength changes. Alternatively, it is preferable that the optical path difference providing structure for correcting chromatic aberration for correcting defocus and axial chromatic aberration when the wavelength is changed.
- the optical path difference providing structure for correcting the temperature characteristics is particularly effective when the objective lens is made of plastic.
- a (mm) is the following formula (4), 0.1 ⁇ A ⁇ 0.3 (4) It is desirable to satisfy.
- the objective lens having the optical path difference providing structure has the following formula (5), where the axial thickness is d (mm): 1.3 ⁇ d ⁇ 3.0 (5) It is desirable to satisfy.
- the objective lens having the optical path difference providing structure prefferably has an outermost diameter of 4 mm or less.
- the surface 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 objective lens.
- a minute region including the optical axis may be an unused region or a special purpose region, and the periphery thereof may be a central region.
- the central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. As shown in FIG.
- the central region CN, the intermediate region MD, and the peripheral region OT are preferably provided concentrically around the optical axis on the same optical surface. Moreover, it is preferable that a first optical path difference providing structure is provided in the central region of the objective lens, and a second optical path difference providing structure is provided in the intermediate region.
- 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 objective lens can be said to be a shared area of the first, second, and third optical disks used for recording / reproduction of the first optical disk, the second optical disk, and the third optical disk.
- the 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 first optical disc, and the second light flux that passes through the central area becomes the second light flux.
- Information is recorded and / or reproduced on the information recording surface of the optical disc so that information can be recorded and / or reproduced, and the third light beam passing through the central area can be recorded / reproduced on the information recording surface of the third optical disc.
- the first optical path difference providing structure provided in the central region has the thickness t1 of the protective substrate of the first optical disc and the second optical disc with respect to the first and second light fluxes passing through the first optical path difference providing structure.
- the first optical path difference providing structure has a thickness t1 of the protective substrate of the first optical disc and a thickness of the protective substrate of the third optical disc with respect to the first light beam and the third light beam that have passed through the first optical path difference providing structure. It is preferable to correct spherical aberration generated due to the difference between t3 and spherical aberration generated due to the difference between the wavelengths of the first and third light beams.
- the intermediate area of the objective lens is used for recording / reproduction of the first optical disk and the second optical disk, and can be said to be the first and second optical disk shared areas not used for recording / reproduction of the third optical disk.
- the objective lens condenses the first light flux that passes through the intermediate area so that information can be recorded / reproduced on the information recording surface of the first optical disc, and the second light flux that passes through the intermediate area becomes the second light flux.
- the light is condensed on the information recording surface of the optical disc so that information can be recorded / reproduced.
- 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 third optical disc.
- the third light flux passing through the intermediate region of the objective lens preferably forms a flare on the information recording surface of the third optical disc.
- the peripheral area of the objective lens is used for recording / reproduction of the first optical disk, and can be said to be an area dedicated to the first optical disk that is not used for recording / reproduction of the second optical disk and the third optical disk. That is, the objective lens condenses the first light flux passing through the peripheral region so that information can be recorded / reproduced on the information recording surface of the first optical disc.
- the second light flux passing through the peripheral region is not condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc.
- the third light flux passing through the peripheral region is not condensed so that information can be recorded / reproduced on the information recording surface of the third optical disc.
- the second light flux and the third light flux that pass through the peripheral area of the objective lens preferably form a flare on the information recording surfaces of the second optical disc and the third optical disc.
- a (mm) is expressed by the following formula (4): 0.1 ⁇ A ⁇ 0.3 (4) It is desirable to satisfy.
- the objective lens compatible with the first optical disc, the second optical disc, and the third optical disc has an optical path difference providing structure
- the axial thickness of the objective lens is d (mm)
- the outermost diameter of the objective lens is 4 mm or less.
- the present invention even if it is a high NA type objective lens, it is possible to satisfactorily measure the inclination when attached to the optical pickup device, and to assemble the optical pickup device with high accuracy, and It is possible to provide an optical pickup apparatus including the high NA objective lens.
- FIG. 3 is a cross-sectional view of the objective lens of Example 1.
- 6 is a cross-sectional view of an objective lens according to Example 2.
- FIG. 6 is a cross-sectional view of an objective lens according to Example 3.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 4.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 5.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 6.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 7.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 8.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 9.
- FIG. 10 is a cross-sectional view of an objective lens according to Example 10.
- FIG. It is a figure which shows roughly the structural example of the optical pick-up apparatus only for BD. It is a figure which shows roughly the structural example of a 3 compatible optical pick-up apparatus. It is a block diagram of a 3 compatible optical pick-up lens.
- FIG. 21 is a diagram schematically showing a configuration example of the optical pickup device PU1 capable of appropriately recording and / or reproducing information with respect to the BD.
- Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device.
- the optical pickup device PU1 records and / or reproduces information (hereinafter referred to as recording / reproducing) with respect to the objective lens OBJ, the ⁇ / 4 wavelength plate QWP, the collimating lens CL movable in the optical axis direction, and the polarization beam splitter BS, BD.
- the single objective lens OBJ according to the present embodiment is a plastic lens.
- the linearly polarized light is converted into circularly polarized light by the four-wavelength plate QWP, the diameter of the light flux is regulated by the stop AP, and the light enters the objective lens OBJ.
- the light beam condensed by the objective lens OBJ becomes a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.1 mm.
- the reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OBJ and the aperture AP, and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and converged by the collimating lens CL. And reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. Then, by using the output signal of the light receiving element PD to focus or track the objective lens OBJ by the biaxial actuator AC1, information recorded on the BD can be read.
- spherical aberration that occurs due to a temperature change or due to a different information recording layer is generated by using a collimator lens CL as a magnification changing means by means of an actuator AC2. It can be corrected by changing in the axial direction and changing the divergence angle or convergence angle of the light beam incident on the objective optical element OBJ. Further, when wavelength variation occurs in the first light flux, the collimating lens CL may be moved in the optical axis direction.
- FIG. 22 is a diagram schematically illustrating a configuration example of an optical pickup device PU2 that can appropriately record and / or reproduce information on BD, DVD, and CD, which are different optical disks.
- the optical pickup device PU2 is a slim type and can be mounted on a thin optical information recording / reproducing device.
- the first optical disc is a BD
- the second optical disc is a DVD
- the third optical disc is a CD.
- the light beam condensed by the central region, the intermediate region, and the peripheral region of the objective lens OBJ becomes a spot formed on the information recording surface RL1 of the BD through the protective substrate PL1 having a thickness of 0.1 mm. .
- the reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OBJ and the diaphragm (not shown), and then converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wavelength plate QWP, and by the collimating lens CL.
- a converged light beam is reflected by the polarization beam splitter BS, and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN. Then, by using the output signal of the light receiving element PD to focus or track the objective lens OBJ by the biaxial actuator AC1, information recorded on the BD can be read.
- the spherical aberration generated due to the wavelength fluctuation or different information recording layers is changed in magnification. Correction can be made by changing the divergence angle or convergence angle of the light beam incident on the objective optical element OBJ by changing the collimator lens CL as means in the optical axis direction.
- the ⁇ / 4 wavelength plate QWP converts the linearly polarized light into circularly polarized light, and enters the objective lens OBJ.
- the light beam condensed by the central region and the intermediate region of the objective lens OBJ (the light beam that has passed through the peripheral region is flared and forms a spot peripheral portion) is passed through the protective substrate PL2 having a thickness of 0.6 mm.
- the spot is formed on the information recording surface RL2 of the DVD and forms the center of the spot.
- the reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective lens OBJ, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens CL.
- the light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
- the information recorded on DVD can be read using the output signal of light receiving element PD.
- the light beam condensed by the central region of the objective lens OBJ (the light beam that has passed through the intermediate region and the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL3 having a thickness of 1.2 mm.
- the spot is formed on the information recording surface RL3 of the CD.
- the reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective lens OL, converted from circularly polarized light to linearly polarized light by the ⁇ / 4 wave plate QWP, and converted into a convergent light beam by the collimating lens CL.
- the light is reflected by the polarization beam splitter BS and converges on the light receiving surface of the light receiving element PD via the sensor lens SEN.
- the information recorded on CD can be read using the output signal of light receiving element PD.
- the end surfaces of the objective lenses of Examples 1 to 10 are all mirror surfaces, and the surface roughness Ry at the end surfaces satisfies 0.3 ⁇ Ry ⁇ 7.0.
- the objective lens OBJ constituting the optical pickup device PU1 in FIG. 21 corresponds to an objective lens dedicated to BD shown in FIGS. 11 to 14 and FIGS. 19 and 20 described later, and the objective lens constituting the optical pickup device PU2 in FIG. OBJ corresponds to a BD, DVD, and CD compatible objective lens shown in FIGS.
- FIG. 11 is a cross-sectional view of the objective lens 2a of the first embodiment.
- the objective lens 2a of Example 1 shown in FIG. 11 is a plastic single lens, and has a first optical surface 25 arranged toward the light source and a larger curvature than the first optical surface, and the first optical surface has Opposing second optical surface 26 is provided.
- An optical disk is disposed on the second optical surface 26 side.
- optical path difference providing structure is formed on the first optical surface 25.
- This optical path difference providing structure is a zonal diffractive structure, and has a function of correcting spherical aberration that occurs with changes in temperature.
- This objective lens 2a is a dedicated objective lens for BD having a numerical aperture of 0.85 and corresponding to laser light having a wavelength of 405 nm.
- the A / B value of the objective lens 2a is 0.26, and the A value is 0.23 mm.
- the value of B / X described above is 0.93.
- the value of d is 1.57 mm and the outermost diameter is 3.3 mm.
- the objective lens 2a of the first embodiment has a Strehl ratio of 0.2 as shown in Table 1, it can be reflected light at the end face with a light amount sufficiently larger than unnecessary light. Therefore, even with a high NA objective lens for BD, sufficient tilt adjustment can be performed with respect to the pickup device.
- the shape of the objective lens 2 a in FIG. 11 is such that the end surface 13 is formed adjacent to the second optical surface 26 and the direction is perpendicular to the optical axis O.
- a flange portion 32 is provided on the outer peripheral portion of the end face 13. Further, the surface of the flange portion 32 provided on the outer periphery of the end surface 13 when viewed from the optical axis O direction is provided on the optical disc side from the end surface 13 when viewed from the direction perpendicular to the optical axis.
- the connecting surface 33 is a mirror surface and is formed on a surface that is not perpendicular to the optical axis when viewed from the direction perpendicular to the optical axis.
- the surface on the optical disc side of the flange portion 32 can also function as a protector for avoiding the collision between the second optical surface 26 and the optical disc. If the joint of the side mold is formed on the joint surface, burrs generated at the joint can be prevented from projecting from the surface of the flange portion on the first optical surface 25 side. Since the lens can be installed, the lens can be accurately adjusted.
- the shape of the objective lens 2 a of Example 1 in FIG. 11 is not shown, but a part of the outer periphery of the flange portion 32 is seen from the optical axis O direction. A straight portion is provided on the outer peripheral side of the end face 13, and the value of C / B is 1.46.
- the objective lens 2a of the first embodiment has a straight portion, but can adjust the inclination of the optical pickup suitable for mass production.
- the objective lens 2a of Example 1 is 0.06. It is. Further, the thickness t of the thinnest portion of the end face is 0.43.
- the objective lens 2a of Example 1 is a lens that can suppress the influence of the resin pressure on the end face shape to the minimum, and can adjust the inclination of the optical pickup suitable for mass production.
- the objective lens 2a of the first embodiment has a marking 38 on a part of the flange portion 32. Since the marking is provided at a place other than the end face 13, the identification / tilt adjustment can be performed without adversely affecting the reflection at the end face.
- the value of d / f obtained by dividing the axial thickness d by the focal length f (not shown) of the first light flux is 1.34.
- FIG. 12 is a cross-sectional view of the objective lens 2b according to the second embodiment.
- the objective lens 2b shown in FIG. 12 is a plastic single lens having an optical path difference providing structure having substantially the same shape as that of the first embodiment, and the value of A / B is changed.
- FIG. 13 is a cross-sectional view of the objective lens 2c according to the third embodiment.
- the objective lens of Example 3 shown in FIG. 13 is a plastic single lens.
- the first optical surface 25 of the objective lens 2c of Example 3 has an aspherical shape that does not have an optical path difference providing structure.
- FIG. 14 is a cross-sectional view of the objective lens 2d according to the fourth embodiment.
- the first optical surface 25 has an aspherical shape without an optical path difference providing structure, like the objective lens 2c of Example 3.
- the objective lenses in Examples 1 to 4 are objective lenses dedicated to BD.
- FIG. 15 is a cross-sectional view of the objective lens 2e according to the fifth embodiment.
- the objective lens 2e of Example 5 shown in FIG. 15 is a plastic single lens.
- the first optical surface 25 of the objective lens 2e of Example 5 has an optical path difference providing structure, and the second optical surface 26 has an aspherical shape without the optical path difference providing structure.
- This optical path difference providing structure is a ring-shaped diffractive structure, and is a disc having a different thickness. It has a function that can read three discs of BD, DVD, and CD.
- the objective lens 2e of Example 5 has a numerical aperture of 0.85, and is a three-compatible objective lens for a pickup device that supports a laser with a wavelength of 405 nm.
- the objective lens 2 e of Example 5 is a plastic material, and the surface of the flange portion 32 provided on the outer periphery of the end surface 13 when viewed from the optical axis O direction is the optical axis O. It is formed so as to have substantially the same height as the end face 13 when viewed from the vertical direction.
- the objective lens 2 e of Example 5 has improved flowability of the resin by forming the end face 13 and the flange portion 32 at the same height. As a result, the shape of the end face 13 is improved. Transferability is improved, the amount of reflected light is improved, and the tilt of the objective lens can be adjusted satisfactorily.
- FIG. 16 is a cross-sectional view of the objective lens 2 f according to the sixth embodiment.
- the objective lens 2f of Example 6 shown in FIG. 16 is a plastic single lens. Similar to Example 5, the disc has a ring-shaped optical path difference providing structure and has a different thickness. It has a function that can read three discs of BD, DVD, and CD. Unlike the fifth embodiment, there is a difference h in the optical axis direction between the surface on the second optical surface 26 side of the flange portion 32 and the end surface 13 when viewed from the direction perpendicular to the optical axis O. The value of h is 0. 06.
- FIG. 17 is a cross-sectional view of the objective lens 2g according to the seventh embodiment.
- the objective lens 2g of Example 7 shown in FIG. 17 is a plastic single lens, and has substantially the same shape as Example 6 having an annular optical path difference providing structure capable of reading three disks of BD, DVD, and CD. It is an objective lens.
- FIG. 18 is a cross-sectional view of the objective lens 2h according to the eighth embodiment.
- the objective lens 2h of Example 8 shown in FIG. 18 is a plastic single lens, and has almost the same shape as Example 6 having an annular optical path difference providing structure capable of reading three disks of BD, DVD, and CD. It is an objective lens, and the value of A / B is changed.
- FIG. 19 is a cross-sectional view of the objective lens 2i according to the ninth embodiment.
- the objective lens 2i of Example 9 shown in FIG. 19 is a single lens made of glass exclusively for BD.
- the first optical surface 25 does not have an optical path difference providing structure and has an aspherical shape, and the value of A / B of the objective lens 2i of Example 9 is 0.43.
- FIG. 20 is a cross-sectional view of the objective lens 2j according to the tenth embodiment.
- the objective lens 2j of Example 10 shown in FIG. 20 is a single lens made of glass exclusively for BD.
- the first optical surface 25 does not have an optical path difference providing structure and has an aspherical shape.
- A is 0.68 mm, which is the length of the end face 13 in Examples 1 to 10. Is the longest objective lens.
Abstract
Description
前記第1光源側に形成された第1の光学面と、前記第1の光学面に対向し、前記第1の光学面よりも曲率半径が大きく形成された第2の光学面と、光軸方向から見て前記第2の光学面の外側に位置し、光軸に略直交する平面である端面と、を有し、像側開口数(NA)は、0.7以上、0.9以下であり、光軸方向から見て、光軸と前記端面を通る直線であって、前記端面範囲内の前記直線の距離をA(mm)、光軸から前記端面の最外周部までの前記直線の距離をB(mm)としたときに、以下の式、
0.12<A/B<0.5 (1)
を満たすことを特徴とする。
0.8<B/X<1.7 (2)
を満たすことを特徴とする。
0.2<A/B<0.5 (3)
を満たすことを特徴とする。
0.1<A<0.3 (4)
を満たすことを特徴とする。
1.3<d<3.0 (5)
を満たすことを特徴とする。
0.35<A/B<0.5 (6)
を満たすことを特徴とする。
0.1<A<0.3 (4)
を満たすことを特徴とする。
1.3<d<3.0 (5)
を満たすことを特徴とする。
0.1<A<0.3 (4)
を満たすことを特徴とする。
1.3<d<3.0 (5)
を満たすことを特徴とする。
1.05<C/B<1.60 (7)
を満たすことを特徴とする。
0.02<h<0.1 (8)
を満たすことを特徴とする。
0.1<A<0.3 (4)
を満たすことを特徴とする。
1.3<d<3.0 (5)
を満たすことを特徴とする。
0.35<t<1.0 (9)
を満たすことを特徴とする。
0.5<t<0.8 (10)
を満たすことを特徴とする。
0.3<Ry<7.0 (11)
を満たすことを特徴とする。
0.9≦d/f≦1.8 (12)
を満たすことを特徴とする。ただし、d(mm)は対物レンズ軸上厚を表し、f(mm)は前記第1光束における焦点距離を表す。
0.050mm≦t1≦0.125mm (13)
0.5mm≦t2≦0.7mm (14)
1.0mm≦t3≦1.3mm (15)
尚、ここで言う、保護基板の厚さとは、光ディスク表面に設けられた保護基板の厚さのことである。即ち、光ディスク表面から、表面に最も近い情報記録面までの保護基板の厚さのことをいう。
レーザ光源としては、好ましくは半導体レーザ、シリコンレーザ等を用いることが出来る。第1光源から出射される第1光束の第1波長λ1、第2光源から出射される第2光束の第2波長λ2(λ2>λ1)、第3光源から出射される第3光束の第3波長λ3(λ3>λ2)は以下の条件式(16)、(17)、
1.5・λ1<λ2<1.7・λ1 (16)
1.8・λ1<λ3<2.0・λ1 (17)
を満たすことが好ましい。
0.3<Ry<7.0 (11)
を満たすことが好ましい。なお表面粗さRyとは、当該面の微小凹凸における最低谷底から最大山頂までの高さのことである。
1.05<C/B<1.60 (7)
を満たすことが好ましい。
0.02<h<0.1 (8)
を満たすことが好ましい。
0.35<t<1.0 (9)
を満たすことが望ましい。
0.5<t<0.8 (10)
を満たすことである。製品を大量に安定して生産するには式(10)の範囲がより望ましい。
0.9≦d/f≦1.8 (12)
を満たすことが望ましい。
0.12<A/B<0.5 (1)
なおストレール比とは、図8に示すように各端面幅比でのエアリーディスクの最大強度を無収差時(端面幅比:1)のエアリーディスクの最大強度で割ったものである。またエアリーディスクとはレンズに平行光を入射し、集光したときの集光点の円盤の大きさを言う。
0.2<A/B<0.5 (3)
を満たすことがより好ましい。
0.35<A/B<0.5 (6)
を満たすことがより好ましい。
0.8<B/X<1.7 (2)
を満たすことがより好ましい。
0.1<A<0.3 (4)
を満たすように対物レンズを作製することにより光量を大きくする事ができる。
キル基を表す。
フェノール系安定剤、ヒンダードアミン系安定剤、リン系安定剤及びイオウ系安定剤から選ばれた少なくとも1種の安定剤を添加することが好ましい。これらの安定剤を適宜選択し添加することで、例えば、405nmといった短波長の光を継続的に照射した場合の白濁や、屈折率の変動等の光学特性変動をより高度に抑制することができる。
界面活性剤は、同一分子中に親水基と疎水基とを有する化合物である。界面活性剤は樹脂表面への水分の付着や上記表面からの水分の蒸発の速度を調節することで、樹脂組成物の白濁を防止することが可能となる。
可塑剤は共重合体のメルトインデックスを調節するため、必要に応じて添加される。
対物レンズが、第1光ディスクに対してのみ用いられるものであって、光路差付与構造を有する場合、当該光路差付与構造は、温度が変化した際に発生する球面収差を補正する温度特性補正用の光路差付与構造であるか、波長が変化した際に発生する球面収差を補正する波長特性補正用の光路差付与構造であるか、波長が変化した際のフォーカスずれや軸上色収差を補正する色収差補正用の光路差付与構造であることが好ましい。温度特性補正用の光路差付与構造は、対物レンズがプラスチック製である際に特に効果を有する。
0.1<A<0.3 (4)
を満たすことが望ましい。
1.3<d<3.0 (5)
を満たすことが望ましい。
第1、第2、第3光ディスク互換用の対物レンズにおいては、対物レンズの少なくとも一つの光学面が、中央領域と、中央領域の周りの中間領域と、中間領域の周りの周辺領域とを少なくとも有することが好ましい。中央領域は、対物レンズの光軸を含む領域であることが好ましいが、光軸を含む微小な領域を未使用領域や特殊な用途の領域とし、その周りを中央領域としてもよい。中央領域、中間領域、及び周辺領域は同一の光学面上に設けられていることが好ましい。図23に示したように、中央領域CN、中間領域MD、周辺領域OTは、同一の光学面上に、光軸を中心とする同心円状に設けられていることが好ましい。また、対物レンズの中央領域には第一光路差付与構造が設けられ、中間領域には第二光路差付与構造が設けられていることが好ましい。周辺領域は屈折面であってもよいし、周辺領域に第三光路差付与構造が設けられていてもよい。中央領域、中間領域、周辺領域はそれぞれ隣接していることが好ましいが、間に僅かに隙間があっても良い。
0.1<A<0.3 (4)
を満たすことが望ましい。
1.3<d<3.0 (5)
を満たすことが望ましい。
図11は、実施例1の対物レンズ2aの断面図である。図11に示す実施例1の対物レンズ2aはプラスチック単玉レンズであり、光源に向けて配置される第1の光学面25と、第1の光学面より曲率が大きく、第1の光学面に対向する第2の光学面26を有している。第2の光学面26側に、光ディスクが配置されるものである。
図12は、実施例2の対物レンズ2bの断面図である。図12に示す対物レンズ2bは、実施例1とほぼ同形状の光路差付与構造を有するプラスチック単玉レンズであり、A/Bの値を変えている。
図13は、実施例3の対物レンズ2cの断面図である。図13に示す実施例3の対物レンズはプラスチック単玉レンズである。実施例3の対物レンズ2cの第1の光学面25は光路差付与構造を有していない非球面形状である。
図14は、実施例4の対物レンズ2dの断面図である。図14に示す実施例4の対物レンズ2dは、実施例3の対物レンズ2cと同じく、第1の光学面25は光路差付与構造を有していない非球面形状である。
図15は、実施例5の対物レンズ2eの断面図である。図15に示す実施例5の対物レンズ2eはプラスチック単玉レンズである。
図16は、実施例6の対物レンズ2fの断面図である。図16に示す実施例6の対物レンズ2fはプラスチック単玉レンズである。実施例5と同じく輪帯状の光路差付与構造を有し、異なる厚みのディスクである。BD、DVD、CDの三つのディスクを読み取ることができる機能を有している。実施例5と異なり、光軸Oと垂直な方向から見てフランジ部32の第2の光学面26側の面と端面13の光軸方向の差hを有し、hの値は、0.06である。
図17は、実施例7の対物レンズ2gの断面図である。図17に示す実施例7の対物レンズ2gはプラスチック単玉レンズであって、BD、DVD、CDの三つのディスクを読み取り可能な輪帯状の光路差付与構造を有する実施例6とほぼ同形状の対物レンズである。
図18は、実施例8の対物レンズ2hの断面図である。図18に示す実施例8の対物レンズ2hはプラスチック単玉レンズであって、BD、DVD、CDの三つのディスクを読み取り可能な輪帯状の光路差付与構造を有する実施例6とほぼ同形状の対物レンズであり、A/Bの値を変えている。
図19は、実施例9の対物レンズ2iの断面図である。図19に示す実施例9の対物レンズ2iはBD専用のガラス製の単玉レンズである。第1の光学面25は光路差付与構造を有さず非球面形状であり、実施例9の対物レンズ2iのA/Bの値は0.43である。
図20は、実施例10の対物レンズ2jの断面図である。図20に示す実施例10の対物レンズ2jはBD専用のガラス製の単玉レンズである。第1の光学面25は光路差付与構造を有さず非球面形状であり、実施例9の対物レンズと比べ、Aが0.68mmと実施例1~10のうちで端面13の幅の長さが最も長い対物レンズである。
12 オートコリメータ
13 端面
25 第1の光学面
26 第2の光学面
32 フランジ部
32 フランジ幅
33 つなぎ面
34 フランジ内側面部
35 直線部
36 ゲート部
38 マーキング
O 光軸
PU1、PU2 光ピックアップ装置
OBJ 対物レンズ
AC1 2軸アクチュエータ
CL コリメートレンズ
QWP λ/4波長板
BS 偏光ビームスプリッタ
DP ダイクロイックプリズム
SEN センサレンズ
PD 受光素子
LD1 第1半導体レーザ
LD2 第2半導体レーザ
LD3 第3半導体レーザ
LDP レーザユニット
CN 中央領域
MD 中間領域
OT 周辺領域
PL1、PL2、PL3 保護基板
RL1、RL2、RL3 情報記録面
Claims (38)
- 少なくとも第1波長λ1(390nm<λ1<420nm)の第1光束を出射する第1光源と対物レンズとを有し、前記第1光源から出射された前記第1波長λ1の第1光束を前記対物レンズにより第1光ディスクの情報記録面に集光することによって、情報の記録及び/又は再生を行う光ピックアップ装置に使用される対物レンズであって、
前記第1光源側に形成された第1の光学面と、
前記第1の光学面に対向し、前記第1の光学面よりも曲率半径が大きく形成された第2の光学面と、
光軸方向から見て前記第2の光学面の外側に位置し、光軸に略直交する平面である端面と、を有し、
像側開口数(NA)は、0.7以上、0.9以下であり、
光軸方向から見て、光軸と前記端面を通る直線であって、前記端面範囲内の前記直線の距離をA(mm)、光軸から前記端面の最外周部までの前記直線の距離をB(mm)としたときに、以下の式を満たすことを特徴とする対物レンズ。
0.12<A/B<0.5 (1) - 前記対物レンズは、光軸と垂直な方向からみて、光軸から前記第1の光学面の最外周部までの最短距離をXとしたとき、以下の式を満たすことを特徴とする請求項1に記載の対物レンズ。
0.8<B/X<1.7 (2) - 以下の式を満たすことを特徴とする請求項1又は2に記載の対物レンズ。
0.2<A/B<0.5 (3) - 前記A(mm)が、以下の式を満たすことを特徴とする請求項1から3のいずれか一項に記載の対物レンズ。
0.1<A<0.3 (4) - 前記対物レンズの軸上厚をd(mm)としたとき、以下の式を満たすことを特徴とする請求項1から4のいずれか一項に記載の対物レンズ。
1.3<d<3.0 (5) - 前記対物レンズの最外径が4mm以下であることを特徴とする請求項1から5のいずれか一項に記載の対物レンズ。
- 前記対物レンズは、ガラス材料によって成形されていることを特徴とする請求項1、2、4、5、又は6のいずれか一項に記載の対物レンズ。
- 前記対物レンズが、以下の式を満たすことを特徴とする請求項1、2、4、5、6又は7のいずれか一項に記載の対物レンズ。
0.35<A/B<0.5 (6) - 前記第1の光学面及び前記第2の光学面のうち、少なくとも一方は輪帯状の光路差付与構造を有していることを特徴とする請求項1から3のいずれか一項に記載の対物レンズ。
- 前記A(mm)が以下の式を満たすことを特徴とする請求項9に記載の対物レンズ。
0.1<A<0.3 (4) - 前記対物レンズの軸上厚をd(mm)としたとき、以下の式を満たすことを特徴とする請求項9又は10に記載の対物レンズ。
1.3<d<3.0 (5) - 前記対物レンズの最外径が4mm以下であることを特徴とする請求項9から11のいずれか一項に記載の対物レンズ。
- 前記第1の光学面に光路差付与構造が形成され、
前記第1の光学面は、中央領域と、前記中央領域の周りの中間領域と、前記中間領域の周りの周辺領域とを少なくとも有し、
前記光路差付与構造は、少なくとも第1光路差付与構造が前記中央領域に設けられ、第2光路差付与構造が前記中間領域に設けられていることを特徴とする請求項9に記載の対物レンズ。 - 前記光ピックアップ装置は、
前記第1波長λ1の前記第1光束を射出する前記第1光源に加えて、第2波長λ2(λ2>λ1)の第2光束を射出する第2光源と、第3波長λ3(λ3>λ2)の第3光束を射出する第3光源とを有し、
前記第1光束を用いて厚さがt1の保護基板を有する前記第1光ディスクの情報の記録及び/又は再生を行うことに加えて、前記第2光束を用いて厚さがt2(t1<t2)の保護基板を有する第2光ディスクの情報の記録及び/又は再生を行い、前記第3光束を用いて厚さがt3(t2<t3)の保護基板を有する第3光ディスクの情報の記録及び/又は再生を行う光ピックアップ装置であり、
前記対物レンズは、
前記中央領域を通過する前記第1光束を前記第1光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、前記中央領域を通過する前記第2光束を前記第2光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、前記中央領域を通過する前記第3光束を前記第3光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、
前記中間領域を通過する前記第1光束を前記第1光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、前記中間領域を通過する前記第2光束を前記第2光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、前記中間領域を通過する前記第3光束を前記第3光ディスクの情報記録面上に情報の記録及び/又は再生ができるようには集光させず、
前記周辺領域を通過する前記第1光束を前記第1光ディスクの情報記録面上に情報の記録及び/又は再生ができるように集光し、前記周辺領域を通過する前記第2光束を前記第2光ディスクの情報記録面上に情報の記録及び/又は再生ができるようには集光させず、前記周辺領域を通過する前記第3光束を前記第3光ディスクの情報記録面上に情報の記録及び/又は再生ができるようには集光させないことを特徴とする請求項13に記載の対物レンズ。 - 前記A(mm)が以下の式を満たすことを特徴とする請求項13又は14に記載の対物レンズ。
0.1<A<0.3 (4) - 前記対物レンズの軸上厚をd(mm)としたとき、以下の式を満たすことを特徴とする請求項13から15のいずれか一項に記載の対物レンズ。
1.3<d<3.0 (5) - 前記対物レンズの最外径が4mm以下であることを特徴とする請求項13から16のいずれか一項に記載の対物レンズ。
- 前記端面は前記第2の光学面に隣接して形成されていることを特徴とする請求項1から3のいずれか一項に記載の対物レンズ。
- 前記対物レンズは、前記端面の外周部にフランジ部を有することを特徴とする請求項1、2、3又は18のいずれか一項に記載の対物レンズ。
- 前記対物レンズは、樹脂材料で形成され、光軸方向から見て前記端面の外周に設けられる前記フランジ部の面は、光軸と垂直な方向からみて前記端面とほぼ同一の高さになるように形成されていることを特徴とする請求項19に記載の対物レンズ。
- 前記対物レンズは、樹脂材料で形成され、光軸方向から見て前記端面の外周に設けられる前記フランジ部の面は、光軸と垂直な方向からみて前記端面より光ディスク側に設けられていることを特徴とする請求項19に記載の対物レンズ。
- 前記対物レンズは、樹脂材料で形成され、光軸と垂直な方向から見て、前記第1の光学面と前記フランジ部の第1の光学面側の面との間につなぎ面を有し、
前記つなぎ面は前記フランジ部の第1の光学面側の面よりも前記第2の光学面側に形成されていることを特徴とする請求項19から21のいずれか一項に記載の対物レンズ。 - 前記つなぎ面は、光軸と垂直方向から見て、光軸に対し垂直でない面に形成されていることを特徴とする請求項22に記載の対物レンズ。
- 前記端面と、前記つなぎ面は鏡面であることを特徴とする請求項22又は23に記載の対物レンズ。
- 前記フランジ部の外周の一部が、光軸方向から見て直線部を有していることを特徴とする請求項19から24のいずれか一項に記載の対物レンズ。
- 前記直線部は、前記端面よりも外周側に設けられていることを特徴とする請求項25に記載の対物レンズ。
- 前記直線部はゲート部を有しており、光軸から前記直線部までの前記直線部に垂直な直線の長さをCとしたとき、以下の式を満たすことを特徴とする請求項26に記載の対物レンズ。
1.05<C/B<1.60 (7) - 前記直線部はゲート部を有しており、光軸と垂直な方向から見て前記フランジ部の第2の光学面側の面と前記端面部の光軸方向の差hは、以下の式を満たすことを特徴とする請求項25から27のいずれか一項に記載の対物レンズ。
0.02<h<0.1 (8) - 前記対物レンズの光軸方向から見て前記端面以外の箇所にマーキングを有することを特徴とする請求項1から28のいずれか一項に記載の対物レンズ。
- 前記A(mm)が以下の式を満たすことを特徴とする請求項18から29のいずれか一項に記載の対物レンズ。
0.1<A<0.3 (4) - 前記対物レンズの軸上厚をd(mm)としたとき、以下の式を満たすことを特徴とする請求項18から30のいずれか一項に記載の対物レンズ。
1.3<d<3.0 (5) - 前記対物レンズの最外径が4mm以下であることを特徴とする請求項18から31のいずれか一項に記載の対物レンズ。
- 前記対物レンズの光軸に垂直な方向から見て、前記端面の最薄部の厚みt(mm)が以下の式を満たすことを特徴とする請求項1から32のいずれか一項に記載の対物レンズ。
0.35<t<1.0 (9) - 前記t(mm)が以下の式を満たすことを特徴とする請求項33に記載の対物レンズ。
0.5<t<0.8 (10) - 前記端面における表面粗さRyは、以下の式を満たすことを特徴とする請求項1から34のいずれか一項に記載の対物レンズ。
0.3<Ry<7.0 (11) - 前記端面部は、光軸方向から見てドーナツ状であることを特徴とする請求項1から35のいずれか一項に記載の対物レンズ。
- 以下の式を満たすことを特徴とする請求項1から36のいずれか一項に記載の対物レンズ。
0.9≦d/f≦1.8 (12)
ただし、d(mm)は対物レンズの軸上厚を表し、f(mm)は前記第1光束における焦点距離を表す。 - 請求項1から37のいずれか一項に記載の対物レンズを有することを特徴とする光ピックアップ装置。
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WO2007069612A1 (ja) * | 2005-12-14 | 2007-06-21 | Matsushita Electric Industrial Co., Ltd. | 光ヘッドおよび光情報装置 |
JP2008065883A (ja) * | 2006-09-05 | 2008-03-21 | Sony Corp | レンズ、光ピックアップ、光ディスク装置及び転写不良判別方法 |
WO2009145103A1 (ja) * | 2008-05-27 | 2009-12-03 | コニカミノルタオプト株式会社 | 対物レンズ及び光ピックアップ装置 |
WO2010087068A1 (ja) * | 2009-01-30 | 2010-08-05 | コニカミノルタオプト株式会社 | レンズ及び成形金型 |
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CN103443857A (zh) | 2013-12-11 |
CN103443857B (zh) | 2016-07-06 |
JPWO2012111554A1 (ja) | 2014-07-07 |
JP5429412B2 (ja) | 2014-02-26 |
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