WO2005117001A1 - 対物光学系、光ピックアップ装置、及び光ディスクドライブ装置 - Google Patents
対物光学系、光ピックアップ装置、及び光ディスクドライブ装置 Download PDFInfo
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- WO2005117001A1 WO2005117001A1 PCT/JP2005/008981 JP2005008981W WO2005117001A1 WO 2005117001 A1 WO2005117001 A1 WO 2005117001A1 JP 2005008981 W JP2005008981 W JP 2005008981W WO 2005117001 A1 WO2005117001 A1 WO 2005117001A1
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- optical system
- objective
- optical
- wavelength
- light beam
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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
- G11B7/1353—Diffractive elements, e.g. holograms or gratings
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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
- 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
- G11B7/1392—Means for controlling the beam wavefront, e.g. for correction of aberration
- G11B7/13922—Means for controlling the beam wavefront, e.g. for correction of aberration passive
Definitions
- the present invention relates to an objective optical system, an optical pickup device, and an optical disk drive device.
- Patent Document 1 JP 2004-079146 A
- Patent Document 2 Japanese Patent Application Laid-Open No. 2002-298422
- Patent Document 3 Japanese Patent Application Laid-Open No. 2003-207714
- Patent Document 4 Japanese Patent Application Laid-Open No. 2003-232997
- Patent Literature 1 discloses a numerical example 7 in which a blue-violet laser beam generates second-order diffracted light and a red laser beam and infrared laser beam generate first-order diffracted light on the surface of the objective lens.
- the structure of this diffraction structure is used to correct the spherical aberration caused by the difference in the thickness of the protective layer between the high-density optical disk and the DVD.
- the divergent light beam is applied to the objective lens during Z playback.
- An objective lens has been disclosed that corrects spherical aberration caused by a difference in the thickness of a protective layer between a high-density optical disc and a CD by making the light incident.
- this objective lens can ensure a high diffraction efficiency in any wavelength region, the degree of divergence of the infrared laser beam becomes too strong at the time of recording information on a CD and Z reproduction, and the objective lens is tracked. In this case, the occurrence of coma aberration becomes too large, so that good recording Z reproduction characteristics cannot be obtained for a CD.
- the spherical aberration caused by the difference in the protective layer thickness between the high-density optical disk and the DVD and the spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the CD are corrected by the action of the diffraction structure.
- the diffraction efficiency of the third-order diffracted light of the blue-violet laser beam and the diffraction efficiency of the second-order diffracted light of the infrared laser beam are as low as about 70%.
- the SZN ratio of the detection signal from the photodetector is low, and good recording / reproducing characteristics cannot be obtained, and the voltage applied to the laser light source is high, so that the life of the laser light source is shortened. There is a problem that.
- the objective lens of Numerical Example 7 of Patent Document 1 which corresponds to a case where both the diffraction efficiency of the diffracted light of the blue-violet laser beam and the diffraction efficiency of the diffracted light of the infrared laser beam are ensured, Since the diffraction angle of the diffracted light of the blue-violet laser light beam and the diffraction angle of the diffracted light of the infrared laser light beam almost coincide with each other, the diffraction structure reduces the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and the CD. It cannot be corrected.
- a diffractive structure is usually provided on the surface of a dispersive material.
- a resin resin lens or a lens in which a diffractive structure is formed on a resin layer formed on a glass surface as in Patent Document 4 it is difficult to correct chromatic aberration, even if it can correct chromatic aberration.
- the objective lens of Numerical Example 3 of Patent Document 2 corresponds to a case where the diffraction angle of the diffracted light of the blue-violet laser beam and the diffraction angle of the diffracted light of the infrared laser beam are made different. Diffraction efficiency of violet laser beam and infrared laser beam This is because both the diffraction efficiency and the diffraction efficiency are low.
- a phase corrector (hereinafter referred to as an optical path difference providing structure) described in Patent Documents 1 and 2 and described in Patent Document 3 that uses only a diffraction structure is used.
- the spherical aberration correction effect on the blue-violet laser light beam and the infrared laser light beam by the optical path difference providing structure and the transmittance of the optical path difference providing structure are in a trade-off relationship with each other. It is in.
- the wavefront aberration accuracy required for an optical element becomes more severe as the wavelength becomes shorter and the numerical aperture becomes larger.
- the design of an objective lens for an optical pickup device that is compatible with a plurality of types of optical disks.
- the design performance is, for example, spherical aberration or coma aberration generated when an off-axis light beam enters.
- the transmittance of the phase structure changes.
- the temperature of the optical element having the phase structure changes due to the heat radiation of the actuator and the change in the environmental temperature. If the refractive index change accompanying this temperature change is large, a change in the transmittance of the phase structure becomes large, and stable recording / reproducing characteristics may not be obtained.
- the object of the present invention has been made in view of the above-mentioned problems, and by the action of a phase structure including a diffractive structure, a spherical aberration caused by a difference in the protective layer thickness between a high-density optical disk, a DVD, and a CD; Alternatively, good spherical aberration due to the difference in wavelength used between high-density optical disc, DVD and CD High light utilization efficiency in any of the blue-violet wavelength region near 400 nm, the red wavelength region near 650 nm, and the infrared wavelength region near 780 nm. It is still another object of the present invention to provide an objective optical system having excellent design performance for a high-density optical disk, an optical pickup device using the objective optical system, and an optical disk drive device equipped with the optical pickup device.
- Another object of the present invention is to provide a high-density optical disc and a CD, which have a relationship in which the wavelength ratio of the used luminous flux is substantially an integer ratio, in order to achieve compatibility between these two luminous fluxes.
- An objective optical system that can emit light at different angles by using the objective optical system, and can secure a high transmittance for any light flux of any wavelength; an optical pickup device equipped with the objective optical system;
- An object is to provide an optical disk drive device equipped with an optical pickup device.
- Still another problem of the present invention is that, due to the action of a phase structure including a diffractive structure, a spherical aberration due to a difference in protective layer thickness between a high-density optical disc and a DVD or a CD, or a high-density optical disc.
- Spherical aberration due to the difference in operating wavelength between DVD and CD can be corrected well, and a blue-violet wavelength region around 400 nm, a red wavelength region around 650 nm, and an infrared wavelength region around 780 nm.
- An object of the present invention is to provide an optical disk drive device equipped with the optical pickup device.
- At least for the first optical information recording medium having the protection substrate thickness tl reproduction and Z or recording of information are performed using the first light beam of the first wavelength ⁇ 1 emitted from the first light source, and the protection substrate thickness is obtained.
- the third optical information recording medium of t3 (tl ⁇ t3) reproduction and recording or recording of information using the third light flux of the third wavelength ⁇ 3 ( ⁇ 1 ⁇ 3) emitted from the third light source.
- An objective optical system having at least a first optical element, wherein the first optical element is composed of a first member made of a material ⁇ and a material ⁇ laminated in the optical axis direction.
- the material A and the material B are different from each other in Abbe number at d-line, and an objective optical element in which a first phase structure is formed on a boundary surface between the first member and the second member.
- a wavelength having a relationship that the wavelength ratio is substantially an integer ratio
- each pattern is formed.
- dl is the depth of the step in the optical axis direction
- the refractive index of the air layer is set to, and each step constituting each pattern is set so that the light flux of wavelength ⁇ 1 is transmitted, that is, so that there is substantially no phase difference to the light flux of wavelength ⁇ 1. Equation (1) below holds when the design is made as follows.
- Equation (2) holds.
- the left side of Eq. (1) and the left side of Eq. (2) have almost the same value, and the value to be raised to 785 on the right side of Eq. (2) is 1Z2 of natural number N1, and if N1 is even, the result is As a result, when a light beam with a wavelength of 3 is incident, the optical path difference given by each step constituting each pattern is an integral multiple of the wavelength.
- the luminous flux of wavelength ⁇ 3 has the same phase as the luminous flux of wavelength ⁇ 1 at the wavefront transmitted through the adjacent level surface.
- the luminous flux of any wavelength can obtain 100% transmittance, but it is not possible to give different optical effects to the luminous flux of the two wavelengths.
- the spherical aberration caused by the difference in thickness of t3 cannot be corrected.
- each step constituting each pattern is designed so that N1 is an odd number
- the optical path difference given by each step constituting each pattern is a half integral multiple of the wavelength.
- a diffraction effect can be given to the light beam having a wavelength of 3 so that spherical aberration caused by the difference between the thicknesses of the protective substrate tl and t3 can be corrected. Since the wavefront of the light beam having the wavelength 3 has a greatly shifted phase, a sufficient transmittance (diffraction efficiency) cannot be obtained for the light beam having the wavelength ⁇ 3.
- the first optical element forming the objective optical system includes a first member made of the material ⁇ and a second member made of the material ⁇ laminated in the optical axis direction,
- the material A and the material B have different Abbe numbers at the d-line, and a first phase structure is formed on a boundary surface between the first member and the second member.
- each step constituting each pattern of the first phase structure in the optical axis direction is dl
- Equation (4) can be satisfied.
- BD Blu-ray disc
- An optical disk using a blue-violet laser light source, such as an HD DVD (hereinafter abbreviated as ⁇ HD '') that uses a 0.67-mm objective optical system and has a protective substrate thickness of 0.6 mm (including optical information recording media! ⁇ ⁇ ) is a generic term for “high-density optical disk” t t.
- an optical disc having a protective film with a thickness of several to several tens nm on the information recording surface, a protective substrate thickness or a protective film thickness may be reduced.
- Zero optical disks also include high-density optical disks.
- the "objective lens” is an optical pickup device that is disposed at a position facing an optical disk and emits a light flux emitted from a light source as information on an optical disk.
- a condensing lens that has the function of condensing light on the recording surface.
- the "objective optical system” refers to an optical
- the objective optical system including at least an objective lens (light collecting element) having a function.
- the objective optical system is composed of only the objective lens.
- an optical system composed of the optical element and the light condensing element is called an objective optical system.
- the optical element is composed of one lens group power! / ⁇ is good, and is composed of two or more lens groups!
- phase structure is a general term for a structure having a plurality of steps in the optical axis direction and adding an optical path difference (phase difference) to an incident light beam.
- the optical path difference added to the incident light beam by this step may be an integral multiple of the wavelength of the incident light beam, or may be a non-integer multiple of the wavelength of the incident light beam.
- phase structure a diffraction structure in which the above-mentioned steps are arranged at periodic intervals in the direction perpendicular to the optical axis, or a step in which the above-mentioned steps are optical
- An optical path difference providing structure also referred to as a phase difference providing structure arranged at aperiodic intervals in the direction perpendicular to the axis.
- a pattern in which the cross-sectional shape including the optical axis has a stepped shape including a plurality of level surfaces is arranged concentrically, and for each of a predetermined number of level surfaces (five level surfaces in FIGS. 21 to 23), Schematic diagrams of the phase structure in which the steps are shifted by the height of the number of steps corresponding to the number of level surfaces (four steps in Figs. 21 to 23) are shown in Figs. 21 to 23. ⁇ ⁇ ).
- Figs. 21 (a) and 21 (b) show the force in the case where the cross-sectional shape is a stepped shape including a plurality of level surfaces and the directions of the patterns are the same. As shown in b), it contains the phase inversion portion PR, or the direction is opposite to the phase inversion portion PR or the sawtooth on the side closer to the optical axis than the phase inversion portion PR as shown in FIGS.
- the pattern includes a sawtooth or a pattern whose direction is opposite to that of a pattern closer to the optical axis than the phase inversion portion PR.
- FIGS. 21 (a) to 23 (b) show the case where the present phase structure is formed on a plane, but may be formed on a spherical surface or an aspherical surface. Also, in FIGS. 21 (a) to 23 (b), the number of predetermined level planes is assumed to be 5! /, But not limited thereto.
- the first phase structure in the present specification is a case where the structures shown in FIGS. 21 (a) to 23 (b) are formed on a boundary surface between a material A and a material B having different Abbe numbers on the d-line. Is equivalent to
- the stage is shifted by a height corresponding to the number of level surfaces.
- the pattern is a pattern other than the phase inversion portion PR, and the phase inversion portion PR is not included in this pattern.
- FIGS. 24 (a) and 24 (b) show the case where the direction of each sawtooth is the same.
- the phase inversion part PR is included, or FIG.
- FIGS. 24 (a) to 26 (b) show the case where the structure having a sawtooth cross section including the optical axis is formed on a flat surface. May be formed.
- FIG. 27 (a) is a schematic view of a staircase structure in which the optical path length increases as the cross-sectional shape including the optical axis moves away from the optical axis. The optical path length decreases as the cross-sectional shape including the optical axis moves away from the optical axis.
- Figure 27 (b) shows a schematic diagram of the staircase structure.
- FIG. 27 shows a case where the staircase structure is formed on a plane, it may be formed on a spherical surface or an aspherical surface.
- the structure shown in Fig. 27 (a) is equivalent to the case where the structure shown in Fig.
- the structure in Fig. 27 (b) is equivalent to the case where the structure in Fig. 24 (b) is formed on a convex surface, and the absolute values of the light convergence function by the convex surface and the light divergence by the phase structure are equal to each other .
- Figure 28 (a) shows a schematic diagram of the staircase structure in which the optical path length is shortened, and when the cross-sectional shape including the optical axis is at a predetermined height from the optical axis, the optical path length decreases as the distance from the optical axis increases, and After the height, the optical path length increases as the optical axis force increases, as shown in Figure 28 (b).
- FIGS. 28 (a) and 28 (b) show the case where the staircase structure is formed on a plane, but it may be formed on a spherical surface or on an aspherical surface.
- DVD digital versatile disc
- DVD-ROM DVD-Video DVD-Audio
- DVD-RAM DVD-R DVD-RW DVD.
- + R, DVD + RW, etc. is a general term for DVD-series optical discs.
- CD Compact Disk
- CD-ROM Compact Disk
- CD-Audio CD-Video
- CD-R Compact Disk
- FIG. 1 is a plan view of a main part showing a configuration of an optical pickup device.
- FIG. 2 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 3 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 4 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 5 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 6 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 7 is side views (a) and (b) showing a configuration of an aberration correction element.
- FIG. 8 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 9 is a side view showing an example of the configuration of the objective lens unit.
- Fig. 10 is a graph showing the relationship between the depth of the step of the diffraction structure and the diffraction efficiency.
- FIG. 11 is a drawing showing an optical path for an objective lens unit.
- FIG. 12 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 13 is a side view showing an example of the configuration of the objective lens unit.
- FIG. 14 is a plan view of relevant parts showing the configuration of the optical pickup device.
- FIG. 15 is a side view showing an example of the configuration of the objective optical system.
- FIG. 16 is plan views (a) and (b) of a main part showing the configuration of a first optical element.
- FIG. 17 is a front view showing the configuration of the first optical element.
- FIG. 18 is a plan view of relevant parts showing a [18] diffraction structure.
- FIG. 19 is a graph for explaining a method of selecting material A and material B.
- FIG. 20 is a table showing the diffraction efficiency, the depth of each pattern, and the like for each combination of material A and material B.
- FIG. 21 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 22 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 23 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.
- FIG. 24 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 25 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.
- FIG. 26 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 27 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.
- FIG. 28 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 29 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.
- FIG. 30 is a side view showing an example of the configuration of the objective optical system.
- FIG. 31 is a side view showing an example of the configuration of the objective optical system.
- FIG. 32 is a side view showing an example of the configuration of the objective optical system.
- FIG. 33 is side views (a) to (c) showing an example of a phase structure.
- FIG. 34 is a fragmentary plan view showing the configuration of the optical pickup device.
- FIG. 35 is a side view showing an example of the configuration of the objective optical system. .
- FIG. 36 is a side view showing an example of the configuration of the objective optical system. .
- FIG. 37 is a side view showing an example of the configuration of an objective optical system in an example.
- FIG. 38 is a side view showing an example of the configuration of an objective optical system in an example.
- FIG. 39 is a side view showing an example of the configuration of an objective optical system in an example.
- FIG. 40 is a side view showing an example of the configuration of an objective optical system in an example.
- FIG. 41 is a side view showing an example of the configuration of an objective optical system in an example.
- the base curve which is a macroscopic curve of the first phase structure, is configured to be an aspheric surface or a spherical surface.
- the difference ⁇ V d between the Abbe number at the d-line and the Abbe number at the d-line of the material B satisfies the following expression (11), and the refractive index of the first member at the first wavelength ⁇ 1 and the second member Of the refractive index at the first wavelength ⁇ satisfies the following equation (12).
- the optical pickup device further has a second wavelength ( ⁇ 1 ⁇ 2 ⁇ 3) at which a second light source power is also emitted to a second optical information recording medium having a protective substrate thickness t2 (tl ⁇ t2 ⁇ t3). Use the second light beam to reproduce and / or reproduce information.
- the objective optical system in the configuration described in Item 4, in the objective optical system described in Item 2, the objective optical system has an objective lens on the optical information recording medium side of the first optical element.
- the first optical element is an objective lens.
- the first phase structure is a diffraction structure.
- the first member having the Abbe number difference satisfying the expression (11)
- the second member By providing the second member and forming a phase structure on the boundary surface, the spherical aberration correction effect of the blue-violet laser light beam (first light beam) and the infrared laser light beam (third light beam), which was difficult with the conventional technology, And transmittance can be ensured at the same time.
- the first member and the second member with a refractive index difference satisfying the expression (12) at the first wavelength ⁇ 1
- the step along the optical axis of each annular zone can be reduced. And the manufacture of the phase structure becomes easy.
- the first optical element has The correction of the spherical aberration and the correction of the sine condition for one light beam can both be achieved, and the design performance for the first light beam can be improved.
- the "base curve” here refers to an envelope connecting the vertices of each sawtooth of the phase structure, as indicated by a dotted line in Fig. 2 described later, and this envelope is a macroscopic view of the phase structure. It represents a simple curvature.
- Item 7 is the objective optical system according to Items 2 to 6, wherein the base curve is
- the aspherical surface force which is the distance along the optical axis of the spherical force expressed by the paraxial radius of curvature, is the aspherical surface that increases as the optical axis force increases.
- the amount of aspheric deformation which is the distance along the optical axis from the spherical surface whose base curve is expressed by the paraxial radius of curvature, increases as the distance from the optical axis increases.
- the “aspherical deformation amount” is represented by the following equation (18) when the aspherical shape of the base curve is represented by [aspherical surface expression] described later. Things.
- z is the aspherical shape (mm) representing the distance in the direction along the optical axis between the plane tangent to the surface vertex and the aspherical surface.
- ⁇ Indicates the plane tangent to the surface vertex and the paraxial radius of curvature.
- the expression “the aspherical deformation amount expressed by the above equation (18) increases as the distance from the optical axis increases” means that ⁇ z asymptotically increases as y (distance from the optical axis) increases.
- the optical surface of the second member opposite to the boundary surface is also made to be an aspheric surface having substantially the same shape as the base force, so that the design performance for the first light beam is further improved. Can be improved.
- the “aspherical surface having substantially the same shape as the base curve” here means the aspherical shape zl (mm) of the base curve on the boundary surface side and the optical surface of the second member opposite to the boundary surface.
- the aspherical surface shape z2 (mm) of is expressed by [Aspherical expression formula] described later, it means that the following formula (19) is satisfied at any y (distance of optical axis force) within the effective radius. .
- the convergence (divergence) action due to diffraction in the diffractive structure and the optical surface of the second member on the opposite side to the boundary surface can be achieved.
- the divergent (convergent) action due to refraction can be canceled out, and the first light beam entering the first optical element in a parallel light state can be emitted from the first optical element in a parallel light state.
- the second member sufficiently thin with respect to the axial thickness of the first member, the light beam diameter of the first light beam incident on the first optical element and the first optical element force are emitted. The difference between the first light beam and the light beam diameter can be reduced.
- the “paraxial diffraction power ⁇ ⁇ ⁇ ⁇ at the first wavelength ⁇ 1” here means the first light flux due to the diffraction structure.
- optical path difference function ⁇ is the production wavelength of the diffractive structure
- 2 is the second-order diffraction surface coefficient
- ⁇ -2 ⁇ ⁇ / ⁇ ⁇ ⁇ ⁇ 20 (20)
- the refractive index of the first member at the second wavelength ⁇ 2 and the second wavelength of the second member is as follows (15). While satisfying the expressions (17) to (17), the first phase structure has a negative paraxial diffraction power. 0.22 I ⁇ ⁇ 2 I / I ⁇ ⁇
- Equations (15) to (17) described in Item 10 are conditions for generating diffracted light of the same order for each wavelength and ensuring diffraction efficiency for each wavelength.
- the paraxial diffraction power of the phase structure negative, the longer the wavelength, the greater the degree of divergence and the greater the possibility of incidence on the objective lens. A large working distance to the optical disk can be ensured.
- each wave in the diffraction structure at the boundary surface is obtained.
- the light beam of any wavelength must be used. It is preferable to set the difference in the refractive index between the first member and the second member at each wavelength so that the first-order diffracted light is generated.
- the ⁇ ⁇ order diffracted light is generated in the diffractive structure means that among the diffracted lights of various diffraction orders generated by the diffractive structure, the steps are set so that the diffraction efficiency of the ⁇ order diffracted light is maximized. That is being done.
- the first phase structure corrects a spherical aberration caused by a difference between the tl and the t3.
- the third light beam is weakly incident on the objective optical system as a divergent light beam.
- the step is set so that diffracted light of the same order is generated for the light flux of each wavelength, so the degree of divergence of the third light flux entering the objective optical system is strong. Not too much. Therefore, good tracking characteristics can be maintained in which the amount of coma generated when the objective optical system performs tracking driving is sufficiently small.
- the first phase structure includes a spherical aberration caused by a difference between the tl and the t2, or the first wavelength ⁇ 1 And the second wavelength ⁇ 2 is corrected for spherical aberration.
- a second phase structure is formed on an optical surface of the first member opposite to the boundary surface.
- phase structure As in the configuration described in Item 13, by forming a phase structure on the optical surface of the first member opposite to the boundary surface, the light-collecting characteristics of the objective optical system with respect to each light beam are provided. Can be made better.
- This phase structure may be a diffraction structure or an optical path difference providing structure.
- the aberration corrected by the phase structure may be, for example, chromatic aberration caused by a minute change in the first wavelength ⁇ 1, or spherical aberration caused by a change in the refractive index of the objective lens caused by a change in temperature. Is also good.
- the second phase structure has a characteristic of selectively diffracting the second light beam without diffracting the first light beam and the third light beam, and a difference between the tl and the t2 due to the second phase structure.
- spherical aberration and force correction are performed on two light beams having different wavelengths from each other. Therefore, in the objective optical system shared for three light beams having different wavelengths like the objective optical system of the present invention, the spherical aberration of the three light beams is corrected only by the action of the phase structure. I can't do that. As a result, in the case where the objective optical element has only one phase structure, the magnification of the remaining one light beam is uniquely determined to correct spherical aberration, which cannot be completely corrected by the action of the phase structure. Therefore, the degree of freedom in designing the optical pickup device is lost.
- the second phase structure should have a characteristic of selectively diffracting the second light beam without diffracting the first light beam and the third light beam. Then, spherical aberration caused by the difference between tl and t2 or spherical aberration caused by the difference between the first wavelength ⁇ 1 and the second wavelength ⁇ 2 is corrected, and tl and t3 are corrected by the phase structure formed on the boundary surface.
- spherical aberration caused by the difference between the wavelengths it becomes possible to correct the spherical aberration of the light beam of each wavelength at the same magnification while securing a high diffraction efficiency for the light beam of each wavelength.
- the configuration described in Item 15 is the objective optical system according to Items 2 to 8, wherein, of the first member and the second member, a member made of a material having a larger Abbe number at d-line and air. A second phase structure is formed at the boundary interface with.
- the second phase structure is formed on the boundary surface between the air and the material having the larger Abbe number in the d-line of the first member and the second member. Therefore, it is possible to increase the diffraction efficiency with respect to the wavelengths ⁇ , 2, and 3 of the first light beam, the second light beam, and the third light beam.
- the configuration described in Item 16 is the objective optical system according to Items 2 to 8, wherein the Abbe number Vd of the d-line of the objective lens arranged on the optical information recording medium side is expressed by the following equation (29).
- the second phase structure is formed on the surface of the objective lens.
- the Abbe number Vd of the d-line in the objective lens arranged on the optical information recording medium side satisfies the above expression (29), and the surface of the objective optical lens has the second phase. Since the structure is formed, it is possible to increase the diffraction efficiency with respect to the wavelengths 1, 1, 2, X3 of the first light beam, the second light beam, and the third light beam.
- the second phase structure is cut off.
- the surface has a step-like diffractive structure, and selectively diffracts or transmits light according to the wavelength.
- the second phase structure is a diffraction structure having a stepped cross section, and selectively diffracts or transmits light according to a wavelength.
- the cross section of the second phase structure has a step-shaped diffraction structure.
- the first light beam of the first wavelength ⁇ 1 is transmitted without any phase difference without diffraction.
- the second phase structure is a blaze-type diffraction structure.
- the second phase structure is a blaze-type diffraction structure.
- the blazed diffraction structure is a structure in which the cross-sectional shape including the optical axis is formed in a sawtooth shape.
- the second phase structure is a blazed diffraction structure as in the items 19 and 20, it is effective for chromatic aberration correction.
- Color correction means that the focus position of the objective lens does not change with wavelength.
- the laser used for the pickup device has a mode hop phenomenon, and the actuator of the objective lens does not follow the sudden change in wavelength, and a defocus state occurs. Therefore, it is necessary for short-wavelength Blu-ray and HD DVD to perform color correction in which the focusing position of the objective lens does not change even if the wavelength changes.
- color correction can be performed using a wavelength-selective diffraction structure, the number of zones is greater than that of a blazed diffraction structure, and since DVD or CD light is transmitted, a color correction effect is simultaneously provided. I can't do it!
- Item 21 has a preferable thickness t2 of the protective layer of the second optical disc (second recording information medium). It defines a new range. If this thickness t2 is within this range, only the spherical aberration caused by the difference in wavelength, such as the combination of HD DV D and DVD, can be corrected, so that the diffraction pitch can be increased and the processing can be increased. Can be enhanced.
- the material B is a UV-curable resin.
- the first member is manufactured by molding.
- a method of laminating the optical resin on the first member a method of laminating the optical resin on the first member by using an optical glass having a phase structure formed on the surface thereof as a mold is used.
- a method (so-called insert molding) may be used, as described in Item 22, after the ultraviolet curing resin is laminated on the second member having the phase structure formed on its surface, it is cured by irradiating ultraviolet rays. The method is suitable for manufacturing.
- a method of manufacturing the first member having the phase structure formed on the surface thereof a method of forming the phase structure directly on the first member by repeating photolithography and etching processes may be used.
- a mold (die) having a phase structure is manufactured, and a first member having a phase structure formed on the surface is obtained as a replica of the mold.
- Suitable for The mold having the phase structure formed thereon may be formed by repeating the photolithography and etching processes to form the phase structure, or by machining the phase structure using a precision lathe. .
- the material A is a resin.
- any optical glass or optical resin can be applied as the material of the first member.
- a material having a low viscosity that is, an optical resin is suitable.
- Resin lenses are lower cost and lighter than glass lenses.
- the first optical element is made of resin and lightweight
- the configuration according to Item 25 is the objective optical system according to any one of Items 4 to 24, wherein the objective lens has a spherical aberration with respect to a combination of the tl and the first wavelength ⁇ 1. The correction is optimized.
- the aspherical shape of the objective lens is preferably determined so that spherical aberration correction is minimized with respect to the first wavelength ⁇ 1 and the thickness tl of the protective layer of the first optical information medium. .
- the strictest wavefront accuracy is required. It is easier to obtain the light-gathering performance of one light beam.
- the objective lens has been optimized for spherical aberration correction with respect to the combination of the tl and the first wavelength ⁇ 1 means that the objective lens and the first optical information medium have a protective layer interposed therebetween. It means that the wavefront aberration when the first light beam is condensed is 0.05 ⁇ 1RMS or less.
- K1 is a natural number.
- the first light source that emits the first light beam of the first wavelength ⁇ 1 the third light source that emits the third light beam of the third wavelength ⁇ 3 ( ⁇ 1 ⁇ 3), and any one of items 2 to 26
- the objective optical system described above is mounted, and information is reproduced and Z or recorded using the first light beam on the first optical information recording medium having the protective substrate thickness tl, and the protective substrate thickness t3 (tl ⁇ t3)
- the third optical information recording medium having the protective substrate thickness tl, and the protective substrate thickness t3 (tl ⁇ t3)
- the configuration described in Item 28 includes the optical pickup device described in Item 27 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- the first optical element is disposed in an optical path through which the first light beam and the third light beam pass in common, and the first phase structure diffracts the first light beam to form the third light beam. Does not diffract the bundle.
- the optical pickup device further includes a second wavelength ( ⁇ 1 ⁇ 2 ⁇ 3) emitted from a second light source with respect to a second optical information recording medium having a protective substrate thickness t2 (tl ⁇ t2 ⁇ t3).
- the information is reproduced and / or reproduced by using the second light beam of (2).
- the first phase structure diffracts the second light beam.
- the objective optical system has an objective lens on the optical information recording medium side of the first optical element.
- the first optical element is an objective lens.
- the phase structure has a saw-tooth shape (diffraction structure DOE) shown in Fig. 7 (a) and a step-like shape (diffraction structure DOE or optical path difference providing structure NPS) shown in Fig. 7 (b). ) May be used.
- DOE wavelength-sensitive laser light beam
- NPS optical path difference providing structure
- the first light beam is not affected by the phase structure of the boundary surface, and is left as it is.
- the phase structure for the second and third light beams is determined by the phase structure. Since the optical path difference can be added, a spherical aberration correction function can be provided. As a result, it is possible to obtain the same functions and effects as those in the item 29.
- ⁇ vd is larger than the lower limit of the expression (22)
- a sufficient difference in refractive index is obtained between the second wavelength 3 and the third wavelength 3, so that the step d of the phase structure does not become too large. Manufacturing is easier.
- ⁇ vd is larger than the upper limit of the expression (22)
- the number of combinations of materials satisfying the expression (21) is extremely reduced. Therefore, when ⁇ vd is smaller than the upper limit of the expression (22), the number of combinations of materials increases, and it becomes possible to select the most suitable material.
- the second light beam and the third light beam can be selectively diffracted without diffracting the first light beam.
- the spherical aberration correction effect and diffraction efficiency (transmittance) of the blue-violet laser light beam (first light beam) and the infrared laser light beam (third light beam) which were the issues of Patent Documents 1 and 2 mentioned above, were secured. Can be achieved.
- ⁇ n2 difference in refractive index of the material A and the material B at ⁇ 2
- ⁇ ( ⁇ ) Integer obtained by rounding off the first decimal place of ⁇
- the spherical aberration correction function can be provided for the second and third light fluxes. This is preferable because the diffraction efficiency of the second light beam and the third light beam can be secured. Greater than the lower limit of equation (23) And the second light beam can be provided with a sufficient spherical aberration correction function. When the value is smaller than the upper limit of the expression (23), the diffraction efficiency of the second light beam can be sufficiently ensured.
- the design feature is best when both the diffraction orders of the second light beam and the third light beam are 1.
- the configuration according to Item 38 is the object optical system according to any one of Items 29 to 34, wherein, of the first member and the second member, a material having a larger Abbe number at d-line. A second phase structure is formed at the interface between the member and the air.
- the configuration according to Item 39 is the objective optical system according to any one of Items 32 to 34, wherein the objective lens disposed on the optical information recording medium side has an Abbe number Vd of d-line that is Equation (29) is satisfied, and a second phase structure is formed on the surface of the objective lens.
- each of the first light beam, the second light beam, and the third light beam is obtained.
- the diffraction efficiency for these wavelengths ⁇ 1, ⁇ 2, ⁇ 3 can be increased.
- the configuration according to Item 40 is the objective optical system according to Item 38, wherein the second phase structure is a diffraction structure having a stepped cross section, and selectively diffracts or transmits light according to a wavelength. .
- the configuration according to Item 41 is the objective optical system according to Item 39, wherein the second phase structure is a diffractive structure having a stepped cross section, and selectively diffracts or transmits light according to a wavelength. .
- the second phase structure is a diffraction structure having a stepped cross section.
- the first light beam of the first wavelength ⁇ 1 is transmitted without any phase difference without diffraction.
- the configuration described in Item 42 is the objective optical system according to Item 38, wherein the second phase structure is a blazed diffraction structure.
- the structure described in Item 43 is the objective optical system according to Item 39, wherein the second phase structure is a blazed diffraction structure.
- the blazed diffraction structure is a structure in which the cross-sectional shape including the optical axis is formed in a sawtooth shape.
- the second phase structure is a blazed diffraction structure as in terms 42 and 43, it is effective for chromatic aberration correction.
- Color correction means that the focus position of the objective lens does not change with wavelength.
- the laser used for the pickup device has a mode hop phenomenon, and the actuator of the objective lens does not follow the sudden change in wavelength, and a defocus state occurs. Therefore, it is necessary for short-wavelength Blu-ray and HD DVD to perform color correction in which the focusing position of the objective lens does not change even if the wavelength changes.
- the structure described in Item 44 specifies a preferable range of the thickness t2 of the protective layer of the second optical information recording medium. If the thickness t2 is within this range, only the spherical aberration caused by the difference in wavelength, such as the combination of HD DVD and DVD, is simply corrected, so that the diffraction pitch can be increased and the workability can be improved. Can be enhanced.
- the configuration described in Item 45 is the objective optical system according to any one of Items 29 to 44, wherein one of the material A and the material B is glass and the other is resin.
- the material A is glass and the material B is resin.
- the other material is an optical resin as described in Item 45.
- the structure described in Item 47 is the objective optical system according to Item 46, wherein the resin is an ultraviolet-curing resin.
- the first member is manufactured by molding.
- a method of laminating the optical resin on the optical glass a method of laminating by molding the optical resin on the optical glass using the optical glass having the phase structure formed on the surface as a mold is used. (So-called insert molding) may be used, but as in Item 47, a method is used in which ultraviolet curing resin is laminated on optical glass with a phase structure formed on its surface, and then cured by irradiating ultraviolet. Suitable for you! /
- a method for producing an optical glass having a phase structure formed on the surface thereof a method in which the photolithography and etching processes are repeated to form the phase structure directly on the optical glass substrate may be used.
- a mold (mold) with a phase structure is prepared, and the optical glass with the phase structure formed on the surface is used as a replica of the mold. So-called molding is suitable for mass production.
- a method of manufacturing a mold having a phase structure a method of forming a phase structure by repeating photolithography and etching processes or a method of machining the phase structure with a precision lathe may be used.
- the first phase structure corrects a spherical aberration caused by a difference between the tl and the t3. I do.
- the configuration described in Item 50 includes:
- Item 51 is a configuration in which the first light source that emits the first light beam of the first wavelength ⁇ 1, the third light source that emits the third light beam of the third wavelength 3 ( ⁇ 3), and the items 32 to 50
- the objective optical system described in any one of the above items is mounted, and reproduction and Z or recording of information are performed on the first optical information recording medium having the protective substrate thickness tl using the first light flux, thereby protecting the first optical information recording medium.
- An optical pickup device characterized in that information is reproduced and Z or recorded on a third optical information recording medium having a substrate thickness t3 (tl ⁇ t3) by using the third light flux.
- One optical element is disposed in an optical path between the first and second light sources and the objective lens.
- the configuration according to Item 52 includes the first light source that emits the first light beam of the first wavelength ⁇ 1, the third light source that emits the third light beam of the third wavelength ⁇ 3 ( ⁇ 3), and the item
- the objective optical system according to any one of 32 to 50 is mounted, and reproduction and Z or recording of information are performed on the first optical information recording medium having the protective substrate thickness tl using the first light flux.
- An optical pickup device comprising: a third optical information recording medium having a protective substrate thickness of t3 (tl ⁇ t3); and reproducing and Z or recording information using the third light flux.
- the first optical element and the objective lens are integrated.
- the first optical element When the first optical element according to any one of Items 32 to 50 is mounted on an optical pickup device, the first optical element may be arranged on the light source side of the objective lens as in Item 51 (see FIG. 51). 8 See). This allows the first optical element to have a substantially flat plate shape, and thus has an advantage that the first optical element can be easily manufactured. In this case, it is preferable that the first optical element and the objective lens are held so that the relative positional relationship between the first optical element and the objective lens does not change, because the occurrence of aberration due to eccentricity during tracking is eliminated.
- the function of the first optical element may be provided (integrated) in the objective lens (see FIG. 9). This makes it possible to reduce the number of components of the optical pickup device and to save space.
- the objective lens has an aspheric shape such that spherical aberration correction is minimized with respect to the first wavelength and the thickness of the protective layer of the first optical information recording medium. Preferably it has been determined.
- the light-collecting performance of the first light beam is determined by the objective lens. Therefore, by determining the aspherical shape of the objective lens such that the spherical aberration correction is minimized with respect to the first wavelength and the thickness of the first protective layer as described in Item 53 and Item 54, This makes it easier to obtain the light-gathering performance of the first light beam, which requires the strictest wavefront accuracy.
- the objective lens has spherical aberration correction optimized for the first wavelengths ⁇ 1 and tl
- the objective lens and the protective layer of the first optical information recording medium are used for the first lens. It means that the wavefront aberration when the light beam is collected is 0.051 RMS or less.
- the structure described in Item 55 is the optical disk drive device equipped with the optical pickup device described in Item 51 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- the structure described in Item 56 is the optical disk drive device provided with the optical pickup device described in Item 52 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- the configuration according to Item 57 is the objective optical system according to Item 1, wherein the objective optical system includes two or more optical elements including the first optical element and the second optical element.
- the first phase structure is a diffraction structure in which a pattern having a cross-sectional shape including an optical axis and having a stepped shape including a plurality of level surfaces is arranged concentrically.
- the first phase structure HOE (see Figs. 16 (a) and 16 (b)) has a cross section including the optical axis at the interface between the material A and the material B having a plurality of level surfaces.
- the pattern is formed by concentrically arranging the steps in a stepped pattern including a pattern, and each pattern is divided into a predetermined number of level surfaces (five level surfaces in Figs. 16 (a) and (b)). It has a structure in which the steps are shifted by the height corresponding to the number of levels (four steps in FIGS. 16A and 16B).
- the following effects can be achieved by configuring the objective optical system with two or more optical elements and changing the distribution of refractive power of each optical element with respect to the light beam of wavelength ⁇ 1. It becomes.
- each optical element is made of resin, it is possible to reduce the occurrence of spherical aberration due to a temperature change, so that the objective optical system having a high numerical aperture ( ⁇ ) Can be composed only of a resin lens, which is advantageous for low cost and light weight.
- the working distance WD is shorter than when the objective optical system is composed of a single lens.
- the protective substrate is thick, and the WD on the third optical information recording medium side is a problem.However, the diffraction characteristics that convert a light beam of wavelength ⁇ 3 into a divergent light beam with respect to the first phase structure Giving the third light It is possible to secure sufficient WD on the information recording medium side.
- the refractive power of the first optical element on which the first phase structure is formed with respect to the wavelength ⁇ 1 is substantially zero, it is possible to reduce a decrease in transmittance due to the shading effect of the first phase structure. As a result, the formation of the first phase structure can be facilitated.
- the first phase structure concentrically forms a pattern in which a cross-sectional shape including an optical axis is a stepped shape including a plurality of level surfaces. It has a structure in which the stages are arranged and, for each predetermined number of level surfaces, the stages are shifted by a height corresponding to the number of level surfaces.
- the optical path difference added by each step constituting each pattern slightly shifts by an integral power of the wavelength, and therefore, the light path difference in one pattern is different.
- the wavefront having local spherical aberration is interrupted at the position where the step is shifted by the height corresponding to the number of force level surfaces at which local spherical aberration occurs, so that macroscopic The typical wavefront becomes flat.
- the tolerance for the individual difference in the oscillation wavelength of the first light source can be reduced.
- the configuration according to Item 59 is the objective optical system according to Item 57 or 58, wherein the optical pickup device further comprises a second optical information recording medium having a protective substrate thickness t2 (tl ⁇ t2 * t3).
- the information is reproduced and reproduced or reproduced using the second light flux of the second wavelength ( ⁇ 1 ⁇ 2 ⁇ 3) emitted from the second light source.
- FIG. 19 is a graph in which the Abbe number at the d-line is plotted on the horizontal axis and the refractive index at the d-line is plotted on the vertical axis.
- material A Abbe number V dA at d-line, refractive index ndA
- material B Abbe number V dB at d-line, refractive index ndB
- the material B that is preferably combined is not limited to one, but may be any material that exists within a certain range as shown in a region A in the graph. The same applies to the selection of material B when material A is specified.
- the configuration according to Item 61 is the objective optical system according to any one of Items 57 to 60, wherein the Abbe number and the refractive index of the material A at d-line are V dA and ndA, and the d-line Where the Abbe number and the refractive index of the material B are V dB and ndB,
- each pattern in the first phase structure is such that the ratio (also called aspect ratio) between the length (depth) in the optical axis direction and the length (pitch) in the vertical direction of the optical axis approaches 1: 1. It is known that the transmittance (diffraction efficiency) of a passing light beam is reduced. In order to secure the transmittance (diffraction efficiency), it is desirable to reduce the depth with respect to the pitch. , It is desirable to be within the range of the formula shown in Item 61.
- the refractive index difference between the material A and the material B becomes too small, so that the pattern depth becomes deep and the transmittance (diffraction efficiency) decreases. If the upper limit is exceeded, the refractive index difference between material A and material B becomes too large, so it is necessary to make the refractive index of one material extremely small or make the refractive index of one material extremely large. .
- the former material has a problem that it is not suitable for an optical element such as an objective optical system that requires a large refractive power, and the latter material is less than a resin material. There is a problem in that it is not possible to achieve low cost and light weight due to fatification.
- FIG. 1 [0158]
- the diffraction efficiency, the depth of each pattern, the value of (vdA—vdB) Z ⁇ 100X (ndA—ndB) ⁇ in the expression of item 60, and the value of ((vdA—vdB) 2 + in the expression of item 61 10 is a table showing values of 10 4 X (ndA-ndB) 2 ⁇ 1/2 .
- the configuration according to item 62 is the objective optical system according to item 60,
- the configuration according to Item 63 is the objective optical system according to Item 61 or 62,
- the configuration according to item 64 is the objective optical system according to item 60,
- the configuration according to item 65 is the objective optical system according to item 61 or 62,
- Items 62 to 65 define a preferable range of vdA, vdB, ndA, and ndB.
- the same effect as that of the item 60 or 61 can be obtained.
- the technique of the present invention is effective in achieving compatibility between optical information recording media in which the ratio of the used wavelengths is substantially an integral multiple as described in Item 66. Specifically, as described in Item 67, it is effective when achieving compatibility between a high-density optical disk (BD or HD) whose use wavelength ratio is approximately twice and a CD.
- BD or HD high-density optical disk
- the structure described in Item 68 is the objective optical system according to Item 66 or 67, wherein the first light beam incident on the first phase structure is not diffracted, and the third light beam is diffracted. I do.
- the third light flux is provided.
- the direction of diffraction of the light beam can be set freely. That is, the diffraction direction of the third light beam can be controlled so that the aberration of the third light beam without affecting the aberration of the first light beam is the best.
- the manufacturing of an optical element becomes more difficult as the wavelength becomes shorter. Therefore, the aspherical shapes of the first optical element and the second optical element are adjusted so that the light condensing property for the first light beam is the best. It is preferable to determine it.
- the configuration according to item 69 is the objective optical system according to item 68, and satisfies the following expression.
- dl Depth in the optical axis direction of each step constituting each pattern of the first phase structure
- nAl Refractive index of the material A with respect to the first light flux
- nBl refractive index of the material B for the first light flux
- nA3 refractive index of the material A for the third light flux
- nB3 refractive index of the material B with respect to the third light flux
- L and M are added to the first and third light beams, respectively, according to the optical axis depth of each step formed in each pattern of the first phase structure. This is the optical path difference in wavelength units.
- the optimal combination of material A and material B by selecting a material having a refractive index that satisfies equation (37), a diffraction effect can be given to the third light flux.
- the number of level planes formed in each pattern so as to satisfy the expression (39), it is possible to ensure a sufficiently high diffraction efficiency of the third light flux.
- L is preferably 2 or 3.
- the depth dl of each step in the optical axis direction increases, making it difficult to manufacture staircase shapes with high accuracy. This increases the depth dl in the direction, which is not preferable.
- the value of L is 1, the diffraction efficiency of the third light beam cannot be secured.
- the configuration according to Item 70 is the objective optical system according to Item 58, wherein the depth dl in the optical axis direction of each step constituting each pattern is:
- nAl refractive index of the material A with respect to the first light flux
- nBl refractive index of the material B with respect to the first light beam
- each pattern of the first phase structure is configured to be substantially an integral multiple of the optical path difference wavelength ⁇ ⁇ ⁇ ⁇ given to the first light flux, as in the configuration described in Item 72. It is preferable to design the depth dl of each step in the direction of the optical axis, thereby making it possible to ensure a sufficiently high transmittance of the first light flux.
- the configuration according to Item 72 is the objective optical system according to any one of Items 58 to 71, wherein the number of level surfaces constituting each pattern is five.
- the number of level surfaces refers to the number of annular optical surfaces within one period of the first phase structure.
- the number of level planes constituting each pattern is five.
- the optical path difference added to the third light beam by each pattern of the first phase structure can be made substantially an integral multiple of the wavelength ⁇ 3.
- the design value of the diffraction efficiency of the third light beam can be maximized.
- the configuration according to Item 73 is the objective optical system according to any one of Items 57 to 72, wherein the first phase structure has a spherical aberration caused by a difference between the tl and the t3. It has a correction function.
- the first phase structure has a spherical aberration characteristic such that when the wavelength of the incident light beam becomes longer, the spherical aberration changes in the direction of undercorrection.
- the number of level surfaces constituting each pattern is designed so that the optical path difference giving the depth dl in the optical axis direction of each step to the first light flux is substantially an integral multiple of the wavelength ⁇ 1. Is appropriately selected according to the ratio of the difference between the refractive indices of the materials ⁇ and ⁇ , In addition, it is possible to secure a high transmittance (diffraction efficiency) for a light beam having a shifted wavelength (particularly, a light beam having a longer or shorter wavelength).
- the configuration according to item 75 is the objective optical system according to item 59,
- L dl-( ⁇ 1 - ⁇ 1) / ⁇ 1 (35)
- N dl-( ⁇ 2- ⁇ 2) / ⁇ 2 (41)
- ⁇ (N) INT (D-N) (D-N) (43)
- dl Depth in the optical axis direction of each step constituting each pattern of the first phase structure
- nAl Refractive index of the material A with respect to the first light flux
- nBl refractive index of the material B for the first light flux
- nA2 refractive index of the material A for the second light flux
- nB2 refractive index of the material B for the second light flux
- L and N are respectively added to the first and second light fluxes according to the optical axis depth of each step formed in each pattern of the first phase structure. This is the optical path difference in wavelength units.
- a refraction satisfying the expression (42) in addition to the expression (37) is used. Since it is preferable to select a material having a refractive index, the phase difference added to the second light beam by the depth of each step in the optical axis direction becomes substantially zero. Can be transmitted as it is.
- L is preferably 2. If L takes a value other than 2, it is difficult to simultaneously transmit the second light flux with a high transmittance because it is impossible to satisfy Expressions (42) and (44) at the same time.
- Item 77 is the objective optical system according to any one of Items 59, 75, and 76, wherein the objective optical system is configured by a plurality of concentric annular zone forces centered on an optical axis. It has a second phase structure.
- the configuration according to Item 78 is the objective optical system according to Item 77, wherein the second phase structure includes the first member and the second member of the optical surface of the first optical element. Formed on optical surfaces other than the boundary surface.
- the configuration according to Item 79 is the objective optical system according to Item 77, wherein the second phase structure is made of the material A and the material B, each of which has a larger Abbe number at d-line. It is formed on the interface with.
- the configuration according to Item 80 is the objective optical system according to Item 77, wherein the second phase structure is formed on an optical surface of the second optical element.
- the first phase structure formed on the lens surface is the same as that of the prior art. It is possible to give different optical effects to the light flux and the second light flux.
- the configurations described in the paragraphs 78 to 80 define a preferable portion for forming a second phase structure for providing compatibility between a high-density optical disc and a DVD in the objective optical system of the present invention.
- the configuration according to Item 81 is the objective optical system according to Items 77 to 80, wherein the second phase structure is such that the first and third light beams incident on the second phase structure are different from each other.
- the second light flux is a diffractive structure having a property of diffracting without diffracting.
- the second phase structure can be designed while controlling the diffraction direction of the second light beam so that the aberration with respect to the second light beam becomes the best.
- the configuration according to Item 82 is the objective optical system according to Item 81, wherein the second phase structure is a concentric circle pattern having a stepped shape including a plurality of level surfaces in a cross section including an optical axis.
- the number of level surfaces is shifted by a height corresponding to the number of level surfaces for each predetermined number of level surfaces.
- the optical path difference added by each step constituting each pattern of the second phase structure is an integer of the wavelength. Since the boost is slightly shifted, local spherical aberration occurs in one pattern. However, the wavefront having local spherical aberration is interrupted in the portion where the steps are shifted by the height corresponding to the number of level surfaces, so that the macroscopic wavefront becomes flat. In this way, by making the second phase structure a structure in which the steps are shifted by a height corresponding to the number of levels corresponding to the number of level surfaces, the tolerance for the individual difference in the oscillation wavelength between the first light source and the third light source can be reduced.
- the configuration according to Item 83 is the objective optical system according to Item 82, wherein the depth d2 in the optical axis direction of each step constituting the pattern of the second-layer structure is:
- nC a refractive index of a member having a surface on which the second phase structure is formed for a light beam of wavelength ⁇ 1, of the first member and the second member,
- the second phase structure when the second phase structure is given a diffraction characteristic that gives a diffracting effect only to the second light flux, the second phase structure has the following structure. It is preferable to design the depth d2 in the optical axis direction of each step constituting each pattern of the second phase structure so that the optical path difference given to one light flux is substantially even multiple of the wavelength ⁇ 1. As a result, it is possible to ensure a sufficiently high transmittance of the first light flux. At the same time, the optical path difference added to the third light beam due to the step designed in this way is almost an odd multiple of the wavelength ⁇ 3, so that the transmittance of the third light beam can be ensured sufficiently high. It is possible.
- the depth dl of each step in the optical axis direction is designed so that an optical path difference of approximately twice the wavelength ⁇ 1 is given to the first light flux. This makes it possible to increase the design value of the diffraction efficiency of the second light beam that is diffracted by the second phase structure.
- the configuration according to Item 85 is the objective optical system according to Items 82 to 84, wherein the number of level surfaces constituting each of the patterns is five.
- the number of level surfaces indicates the number of orbicular optical surfaces within one period of the second phase structure.
- the second phase structure having the characteristic or configuration according to any one of Items 82 to 84 is It is preferable that the number of level planes constituting each pattern be 5, U,. This makes it possible to make the optical path difference added to the second light flux by each pattern (for one period of the diffraction ring zone) of the second phase structure substantially equal to the wavelength ⁇ 2, The design value of the diffraction efficiency of the second light beam can be maximized.
- the structure according to Item 86 is the objective optical system according to any one of Items 77 to 80, wherein a cross-sectional shape including an optical axis of the second phase structure is a saw-tooth shape.
- the configuration according to Item 87 is the objective optical system according to any one of Items 77 to 80, wherein a cross-sectional shape of the second phase structure including an optical axis has an optical path length as the distance from the optical axis increases. Is a staircase structure in which the optical path length becomes longer, or a staircase structure in which the optical path length becomes shorter as the optical axis force increases.
- the configuration according to Item 88 is the objective optical system according to any one of Items 77 to 80, wherein a cross-sectional shape of the second phase structure including the optical axis is at a predetermined height from the optical axis. Then, the optical path length increases as the distance from the optical axis increases, and after a predetermined height from the optical axis, the optical path length decreases as the distance from the optical axis decreases, or at a predetermined height from the optical axis, the optical path length increases. The optical path length becomes shorter as the distance from the optical axis increases, and after a predetermined height from the optical axis, the optical path length increases as the distance from the optical axis increases.
- phase structure besides the diffraction structure described in Items 81 to 85, a phase structure described in Items 86 to 88 can also be used.
- These phase structures can have an aberration correction function not only for the second light beam but also for the first light beam and the third light beam.
- chromatic aberration correction functions in the wavelength region of wavelength ⁇ 1 are provided to improve the light-collecting characteristics of the objective optical system. Can be improved.
- Item 89 The configuration described in Item 89 is the objective optical system according to Items 77 to 88, wherein an optical path difference added to the first light beam by the second phase structure is an even multiple of ⁇ 1. It is.
- the second phase structure is added to the first light beam. It is preferable that the optical path difference is designed to be substantially an even multiple of the wavelength ⁇ 1, whereby the transmittance of the first light beam can be secured sufficiently high. At the same time, the optical path difference added to the third luminous flux by the second phase structure designed in this way is almost an odd multiple of the wavelength ⁇ 3. It is also possible to ensure a sufficiently high transmittance of the light beam.
- the configuration according to Item 90 is the objective optical system according to Item 77, wherein a distance d3 [ ⁇ m] of a step in the optical axis direction of each of the annular zones constituting the second phase structure is:
- step d3 in the optical axis direction of each annular zone constituting the second phase structure so as to satisfy the expression of the term 90, reduction in transmittance due to the shading effect of the second phase structure is prevented. It is possible to reduce the number and facilitate the formation of the second phase structure.
- the configuration according to Item 92 is the objective optical system according to any one of Items 77 to 90, wherein tl ⁇ t2 is satisfied, and the second phase structure is defined by the relationship between the tl and the t2. It has the function of correcting spherical aberration caused by the difference.
- the configuration according to Item 93 is the objective optical system according to any one of Items 59 to 92, wherein the optical system magnification ml, m2 of the objective optical system with respect to the first, second, and third light fluxes And m3 are
- the object point position does not change even when the objective optical system performs tracking driving, so that good tracking characteristics can be obtained even for a light beam having a shifted wavelength. It is.
- the objective optical system that is compatible with high-density optical discs and CDs can also be made compatible with DVDs.
- the configuration according to Item 94 is the objective optical system according to any one of Items 77 to 93, wherein the second phase structure has a function of correcting chromatic aberration with respect to the first light flux.
- the convergence characteristics of the objective optical system can be further improved by providing a function of correcting chromatic aberration in the wavelength region of the wavelength ⁇ 1.
- the regenerative power instantaneously changes in wavelength (mode hop) due to a change in the output of the first light source when switching to recording, the focused spot does not increase and a good focusing state is always maintained. It can be maintained.
- the configuration according to Item 95 is the objective optical system according to any one of Items 77 to 93, wherein the second phase structure is at least one of the first optical element and the second optical element. It has a function of correcting an increase in spherical aberration caused by a change in the refractive index.
- the increase in spherical aberration due to a change in the refractive index increases in proportion to the fourth power of ⁇ ⁇ of the objective optical system. If it is manufactured, measures must be taken against the increase in strong spherical aberration. Also, in the object optical system of ⁇ .85, even if the refractive index change with temperature change is smaller than that of resin, the increase in spherical aberration with temperature change may not be negligible. According to the configuration of Item 95, it is possible to provide an objective optical system having a wide usable temperature range by correcting an increase in spherical aberration due to a strong temperature change by the third phase structure.
- the configuration according to Item 96 is the objective optical system according to any one of Items 57 to 95, wherein the boundary surface has a central region including an optical axis and a peripheral region surrounding the central region.
- the central area includes a light beam used for reproducing and / or recording information on the first optical information recording medium, and the third light beam among the first light beams.
- Out of the luminous flux an area through which the luminous flux used for reproducing and / or recording information with respect to the third optical information recording medium is both passed, wherein the first phase structure is: It is formed in the central region and is not formed in the peripheral region.
- the spherical aberration caused by the difference in the protective substrate thickness between the high-density optical disc and the CD causes the numerical aperture (NA3 ) Since the correction is performed only within the region and is not corrected in the region outside NA3, the second light flux passing through the region outside NA3 can be a flare component that does not contribute to spot formation.
- NA3 numerical aperture
- the configuration according to Item 97 is the objective optical system according to any one of Items 57 to 95, wherein the boundary surface includes a central region including an optical axis, and a peripheral region surrounding the central region.
- the central region includes a light beam used for reproducing and Z or recording information on the first optical information recording medium, and Among the three light beams, a region through which both light beams used for information reproduction and Z or recording with respect to the third optical information recording medium pass, and the peripheral region is one of the first light beams
- An area through which light beams not used for recording pass together, wherein the first phase structure includes the central area and the peripheral area. Also formed in any of the area! Puru.
- the first phase structure formed in the opening number (NA3) necessary for recording and reproducing information Z on the CD and the first phase structure formed in an area outside the NA3
- the second light beam passing through the area outside of NA3 can be a flare component that does not contribute to spot formation, It is possible to arbitrarily control the position where the second light flux passing through the outer region is collected. This allows the objective optical system according to the present invention to have an aperture limiting function corresponding to the second light flux.
- the configuration according to Item 98 is the objective optical system according to Item 96, wherein, among the third light beams, the light beam that has passed through the region that has passed through the peripheral region is the light beam that has passed through the central region. Focus on the over side.
- the configuration according to item 99 is the objective optical system according to item 97, wherein, among the third light beams, the light beam that has passed through the peripheral region and the light beam that has passed through the central region Focus on the over side.
- the third light beam Is incident the spherical aberration remains on the over side. Therefore, as in the configuration described in paragraphs 98 and 99, the third light flux passing through the area outside the numerical aperture (NA3) necessary for recording and reproducing information Z on CD is If spherical aberration is corrected by the first phase structure formed in the area inside NA3 so that the light beam that has passed through the area is focused on the over side, diffraction of the first phase structure formed in the area inside NA3 will occur.
- the pitch is not unnecessarily too fine, and the transmittance of the incident light beam can be improved.
- the configuration described in [100] is the objective optical system according to any one of [57] to [99], wherein the boundary surface is a plane having no refracting power for an incident light beam.
- each level surface forming each pattern of the first phase structure is perpendicular to the optical axis, a mold for forming the first phase structure is added. Improve the performance.
- the structure described in Item 101 is the objective optical system according to any one of Items 57 to 100, wherein one of the material A and the material B is an ultraviolet curable resin.
- ultraviolet curable resin makes it easy to control the Abbe number at d-line. Therefore, as described in Item 101, one of material A and material B is UV curable resin. As a result, the optimal combination of materials can be obtained, and the transmittance (diffraction efficiency) of the first phase structure with respect to the incident light beam can be immediately increased.
- the method of manufacturing the first optical element is as follows. An ultraviolet curable resin is laminated on the optical element having the first phase structure formed on its surface, and then cured by irradiating ultraviolet light. The method of making is suitable for manufacturing.
- a method of manufacturing an optical element having the first phase structure formed on the surface a method of forming the first phase structure directly on the substrate by repeating a photolithography and etching process
- So-called molding is suitable for mass production by producing a mold (mold) having a phase structure and obtaining an optical element that works as a replica of the mold.
- a method of manufacturing a mold having a phase structure formed thereon a method of forming a phase structure by repeating a photolithography and etching process or a method of machining the phase structure with a precision lathe may be used. .
- the configuration described in Item 102 is the objective optical system according to any one of Items 57 to 101.
- the material A and the material B are also resin.
- the configuration described in Item 103 is the objective optical system according to any one of Items 57 to 102, wherein at least one of the optical surfaces of the first optical element is an aspheric surface.
- the design characteristics of the objective optical system can be improved by forming at least one aspheric surface on the first optical element.
- Item 104 The configuration described in Item 104 is the objective optical system according to any one of Items 77 to 103.
- the second optical element is disposed on the optical information recording medium side with respect to the first optical element.
- the configuration according to item 105 is the objective optical system according to any one of items 57 to 104, wherein the first phase structure corrects spherical aberration caused by a difference between the tl and the t3. I do.
- the configuration described in Item 106 is the objective optical system according to any one of Items 57 to 105, wherein the material constituting the second optical element has an Abbe number in a d-line range of 50 to 70. Within.
- the configuration according to item 107 is characterized in that the first light source that emits the first light beam of the first wavelength ⁇ 1, the third wavelength ⁇ 3 ( ⁇ ⁇ ⁇ 3) A third light source that emits a third light beam and the objective optical system according to any one of Items 57 to 106 are mounted on the first optical information recording medium having a protective substrate thickness tl.
- the information reproduction and Z or recording are performed using the first light flux, and the information reproduction and Z are performed using the third light flux on a third optical information recording medium having a protective substrate thickness t3 (tl ⁇ t3).
- the configuration described in Item 108 is the optical disk drive device provided with the optical pickup device described in Item 107 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- the configuration according to Item 109 is the objective optical system according to Item 1, wherein a difference ⁇ Vd between the Abbe number of the material A at the d-line and the Abbe number of the material B at the d-line is as follows: ), The refractive index change rate (dnZdT) of the material A with temperature change, and the material B
- the first phase structure has a ring-shaped step.
- the configuration described in Item 110 is the objective optical system described in Item 109, and satisfies the following expression (53).
- Item 111 is the objective optical system according to Item 109 or 110, wherein the optical pickup device further includes a second optical information recording medium having a protective substrate thickness t2 (tl ⁇ t2 * t3). Then, information is reproduced and reproduced or reproduced using the second light flux of the second wavelength ( ⁇ 1 ⁇ 2 ⁇ 3) emitted from the second light source.
- the configuration described in Item 112 is the objective optical system according to any one of Items 109 to 111, wherein both the material ⁇ and the material ⁇ are resin.
- the configuration according to Item 113 is the objective optical system according to Item 1, wherein the difference ⁇ Vd between the Abbe number of the material A at the d-line and the Abbe number of the material B at the d-line is as follows:
- the material A is glass
- the material B is a material in which inorganic particles having an average particle diameter of 30 nm or less are dispersed in a matrix resin.
- the first phase structure has a ring-shaped step.
- Item 114 is the objective optical system according to Item 113, wherein the material B
- the rate of change of the refractive index of the resin as a matrix with a temperature change and the rate of change of the refractive index of the inorganic particles with a temperature change have opposite signs.
- the structure described in Item 115 is the objective optical system according to Item 113 or 114, wherein the material A has a glass transition point Tg of 400 ° C or less.
- the configuration described in Item 116 is the objective optical system according to any one of Items 113 to 115, wherein the Abbe number at d-line of the material A is V dA, and the d-line of the second material is V dA.
- the Abbe number in is set to V dB, the following equations (54) and (55) are satisfied.
- the structure described in Item 117 is the objective optical system according to any one of Items 113 to 116, wherein the first wavelength ⁇ 1 and the third wavelength ⁇ 3 satisfy the following expression (56).
- ⁇ ⁇ 3 ⁇ ⁇ 1 and j8 are natural numbers.
- the structure described in Item 119 is the objective optical system according to any one of Items 109 to 118, wherein the annular step is 5 ⁇ m or more.
- the configuration described in Item 120 is the objective optical system according to any one of Items 113 to 119, wherein the annular step is 5 ⁇ m or more.
- the configuration described in Item 121 is the objective optical system according to Item 119, wherein the annular step is 10 m or more.
- the configuration described in Item 122 is the objective optical system according to Item 120, wherein the annular step is 10 m or more.
- the structure described in Item 123 is the objective optical system according to any one of Items 109 to 122, wherein the first phase structure is a diffraction structure.
- the configuration described in Item 124 is the objective optical system described in any one of Items 109 to 123.
- the configuration described in Item 125 is the objective optical system according to any one of Items 109 to 124, wherein the first optical element is an objective lens.
- the configuration according to paragraph 126 is the objective optical system according to any one of paragraphs 109 to 124, wherein the objective optical system includes an objective lens on the optical information recording medium side of the first optical element. Yes.
- the configuration according to Item 127 is the objective optical system according to Item 111, wherein t2> tl, and the objective optical system includes a spherical aberration caused by a difference between the tl and the t3; The spherical aberration caused by the difference between tl and t2 is corrected.
- the configuration described in Item 129 is the objective optical system according to any one of Items 126 to 128, wherein the objective lens has spherical aberration correction for the first wavelength ⁇ 1 and the tl. Optimized.
- the configuration according to paragraph 130 is the objective optical system according to any one of paragraphs 109 to 129, wherein the first phase structure corrects a spherical aberration caused by a difference between the tl and the t3. It is characterized by
- Item 131 The configuration described in Item 131 is the objective optical system according to any one of Items 109 to 130,
- the configuration according to Item 132 includes a first light source that emits a first light beam of a first wavelength ⁇ 1, a third light source that emits a third light beam of a third wavelength 3 ( ⁇ 1 ⁇ 3), and Items 109 to 112 equipped with the objective optical system according to any one of the above, with respect to a first optical information recording medium having a protective substrate thickness tl, Reproduction, Z or recording of information is performed using the first light beam, and reproduction, Z or recording of information is performed on the third optical information recording medium having the protective substrate thickness t3 (tl ⁇ t3) using the third light beam.
- the configuration according to Item 133 includes: a first light source that emits a first light beam of a first wavelength ⁇ 1, a third light source that emits a third light beam of a third wavelength 3 ( ⁇ 1 ⁇ 3), and Item 113.
- the objective optical system according to any one of Items 113 to 131 is mounted, and reproduction and Z or recording of information are performed on the first optical information recording medium having the protective substrate thickness tl using the first light flux.
- the configuration described in Item 134 is the optical disk drive device equipped with the optical pickup device described in Item 132 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- the configuration described in Item 135 is an optical disk drive device provided with the optical pickup device described in Item 133 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.
- phase structure sandwiched between two materials when the refractive index difference between the two materials changes from the design value, the phase structure of the phase structure is changed.
- the transmittance may fluctuate, and stable recording and reproduction may not be performed.
- one of the two materials is glass and the other is resin
- the rate of change of the refractive index due to the temperature change of the glass and resin is different by more than an order of magnitude.
- the difference in the refractive index due to the temperature change varies greatly. As a result, the transmittance greatly fluctuates with the temperature change, which hinders recording Z playback.
- resin is most suitable!
- the viscosity of the resin is low in a molten state, it is possible to form a fine structure such as a phase structure on the surface thereof with a small shape error.
- resin lenses are lower cost and lighter than glass lenses.
- the diffractive optical element is made of resin and lightweight, the driving force for performing the focusing / tracking control at the time of recording / reproducing information on / from the optical disk can be reduced.
- two resin lenses each having a phase structure formed on each surface are produced by molding using a mold, and then the phase of the two resin lenses is formed.
- a resin lens with a phase structure formed on its surface was fabricated by molding using a mold, and an ultraviolet-cured resin was laminated on the surface of the resin lens phase structure. Thereafter, a method of curing by irradiating ultraviolet rays is suitable for manufacturing.
- the refractive index rises as the temperature rises, and the refractive index rises as the temperature rises.
- Inorganic particles with an average particle diameter of 30 nm or less are homogeneously mixed, so that the refractive index of the two depends on the temperature. It is possible to negate the nature.
- an optical material having a small refractive index change due to a temperature change while maintaining the moldability of the resin hereinafter, such an optical material is referred to as “Asa-mal resin”.
- the rate of change of the refractive index with respect to temperature change is represented by the following A by differentiating the refractive index n with the temperature t based on the Lorentz-Lorenz formula.
- n is the refractive index of the optical element with respect to the wavelength of the laser light source
- a is the linear expansion coefficient of the optical element
- [R] is the molecular refractive power of the optical element.
- the contribution of the second term in the above equation is substantially increased, and To counteract the changes due to the line expansion.
- the refractive index change rate with respect to conventional temperature change was approximately 12 X 10_ 5
- X 10_ 5 Preferably, to suppress an absolute value less than 10 X 10_ 5. More preferably, 8 X 10_ less than 5, more preferably, it is held to less than 6 X 10- 5, preferably in order to reduce the spherical aberration change following the temperature change of the optical element ⁇ .
- the resin used as the base material has a volume ratio of 80, and the iodide niobium has a ratio of about 20, and these are uniformly mixed.
- a technique of giving a charge to the particle surface to disperse the fine particles is also known, and a required dispersion state can be generated.
- the strength of the inorganic resin in the asamal resin is further increased by the fact that the resin is an oxidized product. Is preferred. It is preferable that the iris state is saturated and the iris state is not further oxidized.
- the shape of the inorganic particles used in the present invention is not particularly limited, but spherical particles are preferably used. Although there is no particular limitation on the particle size distribution, in order to more effectively exhibit the effects of the present invention, those having a relatively narrow distribution than those having a wide distribution are required. It is preferably used.
- Examples of the inorganic particles used in the present invention include inorganic oxide particles.
- the composition of the semiconductor crystal is not particularly limited, but it is preferable that the composition does not cause absorption, light emission, fluorescence or the like in a wavelength region used as an optical element.
- Specific examples of the composition include a simple substance of group 14 element of the periodic table such as carbon, silicon, germanium, and tin, a simple substance of group 15 element of the periodic table such as phosphorus (black phosphorus), and a periodic substance such as selenium and tellurium.
- a simple substance of group 16 elements a compound that also has a plurality of group 14 elements such as silicon carbide (SiC), oxidized tin (IV) (SiO 2), tin sulfide (SiC), oxidized tin (IV) (SiO 2), tin sulfide (SiC), oxidized tin (IV) (SiO 2), tin sulfide (SiC), oxidized tin (IV) (SiO 2), tin s
- Periodic group 13 elements such as indium (In Se) and indium telluride (In Te) and their periods
- Table 16 Compounds with Group 16 elements, zinc oxide (ZnO), zinc zinc oxide (ZnS), zinc zinc selenide (Zn Se), zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfate (CdS), Cadmium Selenide (CdSe), Cadmium Telluride (CdTe), Mercury Sulfide (HgS), Selenyi Mercury (HgSe), Mercury Telluride (HgTe), etc.
- Group elements or II-VI compound semiconductors
- Periodic table of periodic table such as compounds of Group 15 elements and Group 16 elements, copper oxide (I) (Cu20), copper selenide (I) (Cu Se), etc.
- a compound of a Group 11 element and a Group 16 element of the periodic table
- titanium oxide Tio, TiO, TiO, TiO, etc.
- Periodic table group 2 element and periodic table such as compounds of group 4 element and periodic table group 16 element, magnesium sulfate (MgS), magnesium selenide (MgSe), etc.
- Compounds with Group 16 elements cadmium oxide ( ⁇ ) chromium (III) (CdCr204), cadmium selenide ( ⁇ ) chromium (III) (CdCrSe), copper sulfide ( ⁇ ) chromium ( ⁇ ) (CuCr S) , Mercury selenide (II) chromium (III) (HgCr Se
- These fine particles may use one kind of inorganic particles, or may use plural kinds of inorganic particles in combination.
- the method for producing the inorganic particles used in the present invention is not particularly limited, and any known method can be used.
- a metal halide or an alkoxy metal as a raw material and performing hydrolysis in a reaction system containing water, desired oxide particles can be obtained.
- a method in which an organic acid or an organic amine is used in combination for stabilizing the particles is also used. More specifically, for example, in the case of titanium dioxide particles, a known method described in Journal of Chemical Engineering of Japan, Vol. 1, No. 1, pp. 21-28 (1998) In the case of zinc sulfide, a known method described in Journal of Physical Chemistry, Vol. 100, pp. 468-471 (1996) can be used.
- titanium oxide having an average particle diameter of 5 nm is obtained by using titanium tetraisopropoxide or titanium tetrachloride as a raw material, and coexisting with an appropriate additive when hydrolyzing in an appropriate solvent. In this way, it can be easily manufactured.
- the inorganic particles of the present invention are preferably subjected to surface modification.
- the method for surface modification is not particularly limited, and any known method can be used. For example, a method of modifying the surface of the inorganic particles by hydrolysis under the condition that water is present may be mentioned.
- a catalyst such as an acid or an alkali is suitably used, and the hydroxyl group on the particle surface and the hydroxyl group generated by hydrolysis of the surface modifier are dehydrated and bonded.
- the surface modifier used in the present invention include, for example, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraphenoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, Propyltrimethoxysilane, methyltriethoxysilane, methyltriphenoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, 3-methylphenyltrimethoxysilane, dimethinoresimethoxysilane, ethino reethoxyxysilane, diphen Ninoresimethoxysilane, diphenyldiphen
- a glass having a low melting point has a low viscosity in a molten state, so that the phase structure can be transferred with a small shape error.
- low melting point glass there are "K-PG325" and “K-pG375" manufactured by Sumita Optical Glass Co., Ltd.
- a method of manufacturing a mold having a phase structure a method of forming a diffraction structure by repeating a process of photolithography and etching or a method of machining a phase structure with a precision lathe may be used. But ⁇ .
- a material having an Abbe number (dispersion) that satisfies the formulas (54) and (55) as the first material and the second material. This makes it possible to favorably balance the spherical aberration correction effect of the blue-violet laser light beam (first light beam) and the infrared laser light beam (third light beam) and ensure the transmittance.
- the wavelength ratio is close to an integral multiple as shown in item 8. This is effective for controlling the phase of the light beam, especially for the blue-violet wavelength (near 405 nm), which is the recording Z reproduction wavelength for high-density optical disks, and the infrared wavelength (785 nm), which is the recording Z reproduction wavelength for CDs. This is an effective structure.
- the step of the phase structure formed at the boundary surface between the two materials becomes deeper as the difference in the refractive index becomes smaller, and the transmittance variation of the phase structure accompanying the temperature change becomes remarkable.
- resin is the most suitable.
- the difference in refractive index cannot be sufficiently obtained and the step tends to be deep. It is.
- the diffractive optical element according to the present invention satisfies the expression (52), and thus the transmittance variation due to the temperature change is small.
- the laminated phase structure may be a diffractive structure! / A light path difference providing structure may be used.
- a structure is preferred.
- the specific shape of the stacked phase structure is a sawtooth shape (diffraction structure DOE) shown in FIG. 33 (a) or a step shape (diffraction structure DOE or an optical path difference providing device shown in FIG. 33 (b)).
- a first optical element according to the present invention and a light beam for condensing a light beam transmitted through the first optical element on an information recording surface of an optical first optical information recording medium.
- Objective lens By configuring the objective optical system from the above, an objective optical system compatible with at least three types of optical first optical information recording media can be provided.
- the spherical aberration caused by the difference between tl and t3 and the spherical aberration caused by the difference between tl and t2 By providing the function of correcting the aberration in the first optical element, it is possible to provide an objective optical system compatible with each optical first optical information recording medium.
- the thicknesses of the protective layers of the first optical information recording medium and the second optical information recording medium are the same, spherical aberration caused by the difference between tl and t3, the first wavelength ⁇ 1 and the second wavelength ⁇ 1
- an objective optical system compatible with each optical information recording medium can be provided.
- the objective lens has an aspherical shape such that spherical aberration correction is minimized with respect to the first wavelength ⁇ 1 and the thickness tl of the protective layer of the first optical information recording medium. Preferably it has been determined.
- the strictest wavefront accuracy is required. It becomes easier to obtain the light-collecting performance.
- the first optical element and the objective lens are held such that their relative positional relationship does not change. As a result, it is possible to suppress the occurrence of aberration at the time of focusing / tracking, and to obtain good focusing characteristics or tracking characteristics.
- the first optical element and the objective lens are connected via a lens frame. It is preferable to adopt a method of performing integral shaping or a method of fitting and fixing the respective flange portions of the first optical element and the objective lens.
- the configuration according to Item 136 is the objective optical system according to Item 1, wherein the Abbe number V dA of the material ⁇ with respect to the d-line is 20 ⁇ V dA ⁇ 40, and the d value of the material B is Abbe number for the line vd B is 40 ⁇ v dB ⁇ 70, and a second phase structure is formed at the interface between the first member and the air layer.
- the wavelength ratio is approximately 1: 2
- correction of spherical aberration and transmittance can be ensured.
- the diffractive structure HOE as an example of the phase structure is a concentric circular array of patterns with a stepped cross section including the optical axis at the interface between material A and material B. Each pattern is composed of a plurality of steps (five in FIG. 35).
- A407 B407 A785 B785 Due to the different variances, they are far enough apart from 1, so the left side of equation (3) and the left side of equation (4) have different values. Therefore, the value N3 raised to 785 on the right side of Equation (4) does not become 1Z2 of the natural number N2, and as a result, by freely selecting the combination of dispersion, the light of wavelength ⁇ 1 and the wavelength ⁇ 3 It is possible to give a desired difference in diffraction angle to light.
- a similar effect can be obtained by using a material having anomalous dispersibility in place of the high dispersion material.
- the objective optical system when the objective optical system is composed only of a high-dispersion material, spherical aberration occurs due to an oscillation wavelength change due to individual differences of a laser as a light source.
- the first optical information recording medium and the third optical information recording medium but also a DVD as a second optical information recording medium to be described later can be used as a triple compatible objective optical system.
- the objective optical system of the present invention is formed by laminating at least two layers having different Abbe numbers.
- the number of boundary surfaces (refractive surfaces) is larger than that of a single lens consisting of only one type of optical material. Become. Therefore, by providing a diffractive structure or the like at these boundary surfaces, for example, spherical aberration at the time of temperature change can be corrected.
- the resin may be poured directly onto the low dispersion material or may be a liquid resin. It can be easily manufactured by irradiating light while holding a molded lens of low dispersion material force on the surface. If the low-dispersion material is a resin, a diffractive structure can be provided at the interface between the low-dispersion material and the high-dispersion material.
- the wavelength ⁇ 1 since the light of wavelength ⁇ 1 is transmitted, the decrease in the amount of light due to the effect of the diffraction shadow can be reduced, and by giving the diffraction effect only to the light of wavelength ⁇ 3, the wavelength ⁇ 1 can be obtained.
- the diffraction direction of the light can be set completely individually for the light of (3).
- the configuration according to item 139 is the objective optical system according to item 137, wherein the diffractive structure is configured by a plurality of concentric annular zones centered on the optical axis, and the cross-sectional shape including the optical axis has a sawtooth shape. Shape.
- the configuration according to item 140 is the objective optical system according to item 137, wherein the diffractive structure has a function of correcting chromatic aberration with respect to the first light beam.
- the boundary surface on which the first phase structure is formed and the second phase structure are different. At least one of the formed boundary surfaces is a plane having no refracting power for the passing light beam.
- the configuration according to the item 145 is configured such that the first phase structure includes the third optical information recording portion of the third light beam. It is formed only in the area through which the light beam used for reproducing and Z or recording information on the medium passes.
- a phase structure is provided in an unnecessary area to unnecessarily reduce the amount of light.
- the optical pickup device further includes a protective substrate thickness t2 (0.9tl ⁇ t2 ⁇ t3).
- the second optical information recording medium is used to reproduce and / or record information by using the second light flux of wavelength ⁇ 2 ( ⁇ 1 ⁇ 2 ⁇ 3) emitted from the second light source.
- the optical system magnifications m2 and m3 of the objective optical system with respect to the second and third light fluxes are respectively l / 10 ⁇ m
- the configuration described in Item 149 is the objective optical system according to Item 136, wherein the boundary surface between the second member and the air layer includes a plurality of concentric annular zones centered on an optical axis, A diffraction structure having a sawtooth cross section including the optical axis is formed.
- the configuration according to item 150 is the object optical system according to any one of items 136 to 149, wherein the first phase structure corrects a spherical aberration caused by a difference between the tl and the t3. I do.
- Kl is a natural number
- the configuration according to Item 152 includes the first light source that emits the first light beam of the first wavelength ⁇ 1, the third light source that emits the third light beam of the third wavelength 3 ( ⁇ 1 ⁇ 3), and Items 136 to 136. 151, the reproduction and Z or recording of information using the first light beam on the first optical information recording medium having a protective substrate thickness of tl.
- the optical pickup device PU emits a blue-violet laser light beam (first light beam) of 405 nm and emits a blue-violet laser light beam (first light beam) at the time of recording and reproducing Z information on the HD.
- first light beam blue-violet laser light beam
- second light beam red laser beam
- Objective lens OL and objective lens OU objective optical system composed of an aspheric surface on both sides with the function of condensing light on RL3, 2-axis actuator AC1, 1-axis actuator AC2, and refractive power in the paraxial axis
- the optical pickup device PU has a 1Z4 wavelength plate RE in the optical path between the expander lens EXP and the objective lens unit OU.
- the light path is drawn by a solid line in FIG. 1 as shown in FIG. Flash.
- the divergent light beam emitted from the blue-violet semiconductor laser LD1 is converted into a parallel light beam by the first collimator lens COL1, then reflected by the first polarizing beam splitter BS1, passes through the second polarizing beam splitter BS2, After being expanded by passing through the first lens EXP1 and the second lens EXP2, the beam diameter is regulated by the aperture STO (not shown), and information is recorded via the HD protective layer PL1 by the objective lens unit OU. It becomes a spot formed on the surface RL1.
- the objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
- the reflected light flux modulated by the information pits on the information recording surface RL1 again passes through the objective lens cut OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1. After passing through, it passes through the third collimating lens COL3 to become a convergent light beam, astigmatism is added by the sensor lens SEN, and the light receiving surface of the photodetector PD Converges on. Then, information recorded in the HD can be read using the output signal of the photodetector PD.
- the light emitting point EP1 is caused to emit light.
- the divergent light beam emitted from the light emitting point EP1 is converted into a parallel light beam by the second collimating lens COL2 as shown in FIG.
- the beam is expanded by passing through the first lens EXP1 and the second lens EXP2, and becomes a spot formed on the information recording surface RL2 by the objective lens unit OU via the protective layer PL2 of the DVD.
- the objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
- the reflected light flux modulated by the information pits on the information recording surface RL2 again passes through the objective lens cut OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1. After passing through, it passes through the third collimating lens COL3 to become a convergent light beam, which is added astigmatism by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. Then, information recorded on the DVD can be read using the output signal of the photodetector PD.
- the distance between the first lens EXP1 and the second lens EXP2 may vary depending on the time of information recording and playback on the HD.
- the first lens EXP1 is driven in the optical axis direction by the single-axis actuator AC2 so that the light emission point EP2 emits light so that the light emission point EP2 becomes narrower.
- the divergent luminous flux emitted from the light emitting point EP2 is converted into a loose divergent luminous flux by the second collimating lens COL2 as shown by the dashed line in FIG. 1, and then reflected by the second polarizing beam splitter BS2.
- the spot formed on the information recording surface RL3 by the objective lens unit OU via the protective layer PL3 of the CD through the first lens EXP1 and the second lens EXP2 is expanded in diameter and converted into a divergent light beam by the objective lens unit OU.
- the objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.
- the reflected light flux modulated by the information pits on the information recording surface RL2 is returned to the objective lens cut OU, the second lens EXP2, the first lens EXP1, the second polarization beam splitter BS2, and the first polarization.
- the information recorded on the CD can be read using the output signal of the photodetector PD.
- the objective lens unit (objective optical system) OU in the present embodiment includes an aberration correction element (first optical element) SAC, a first wavelength ⁇ 1, and a protective layer for HD.
- the objective lens OL whose aspherical shape is designed so as to minimize spherical aberration with respect to the thickness tl of the PL1, has a configuration in which the objective lens OL is coaxially integrated via a lens frame B.
- the aberration correction element SAC is fitted and fixed to one end of the cylindrical lens frame B, and the objective lens OL is fitted and fixed to the other end, and these are coaxially integrated along the optical axis X.
- the configuration is as follows.
- the aberration correction element SAC has a base lens (first member) BL, which is a glass lens, and a resin layer (second member), UV, which is an ultraviolet curable resin, laminated on the surface of the base lens BL.
- a diffractive structure (first phase structure) DOE 1 having an annular step is formed on the boundary surface between the base lens BL and the resin layer UV.
- the diffraction efficiency 7? ( ⁇ ) of the diffractive structure DOE1 formed at the boundary between the base lens BL and the resin layer UV having different Abbe numbers (dispersion) is represented by the wavelength ⁇ and the wavelength ⁇ . It is expressed by the following equation (61) as a function of the refractive index difference ⁇ ( ⁇ ) between the base lens BL and the resin layer UV, the step d of the diffractive structure DOE1, and the diffraction order ⁇ ( ⁇ ).
- the base curve BC which is a macroscopic curve of the diffractive structure DOE1, is formed as an aspheric surface, and as described above, the Abbe number at the d-line of the base lens BL and the d-line of the resin layer UV at the d-line
- the Abbe number difference ⁇ vd satisfies the above equation (11), and the difference ⁇ between the refractive index of the base lens BL at the first wavelength ⁇ 1 and the refractive index of the resin layer UV at the first wavelength ⁇ 1 is (1) 2)
- the formula is now satisfied!
- the spherical aberration due to the difference in the protective layer thickness between HD and DVD, and the difference between HD and CD Both spherical aberrations due to differences in the thickness of the protective layer are now corrected!
- the first diffraction surface has a negative paraxial diffraction power (the effect of diverging the light beam), and the first, second, and third light beams that pass through the first diffraction surface are All are subject to diffraction (divergence).
- the boundary surface and the optical surface of the resin layer UV on the opposite side to the boundary surface have positive paraxial refraction power (the effect of converging the light flux).
- the second light beam incident on the aberration correction element SAC as a parallel light beam is subjected to a diverging operation on the first diffraction surface and is converged by a refraction effect.
- the diffraction power increases in proportion to the wavelength, as described above, the first light flux travels straight as it is, with the paraxial diffraction power and the paraxial refraction canceling out.
- the paraxial diffraction power is larger than the paraxial refraction power, so that the second light beam becomes a divergent light beam and the aberration is corrected.
- Positive element SAC force Emitted Emitted.
- spherical aberration due to the difference in the protective layer thickness between HD and DVD is corrected.
- the third luminous flux incident on the aberration correction element SAC with a gentle divergent luminous flux also undergoes a diverging action on the first diffraction surface, but for the same reason as the second luminous flux, the third luminous flux becomes a divergent luminous flux and becomes Correction element SAC force Injected.
- the degree of divergence of the third light beam becomes larger than that of the second light beam. This is because the diffraction power for the third light beam is larger than the paraxial diffraction power for the second light beam due to the relationship of ⁇ 3> ⁇ 2, and the third light beam is slower than the aberration correction element SAC. This is caused by the incidence of the divergent light beam.
- spherical aberration due to the difference in the protective layer thickness between HD and CD is corrected.
- the conventional technology it is possible to achieve both the spherical aberration correction effect of the blue-violet laser light beam (first light beam) and the infrared laser light beam (third light beam), which have been difficult, and to ensure the transmittance.
- the difference in refractive index between the base lens BL and the resin layer UV at the first wavelength ⁇ 1 satisfying the expression (12) can be reduced to reduce the steps along the optical axis of each annular zone. And the production of the diffractive structure DOE1 becomes easy.
- each primary diffraction light is One light flux is 95.3%, the second light flux is 100%, and the third light flux is 94.4%, and a high diffraction efficiency can be ensured for a light flux of any wavelength.
- spherical aberration of a spot formed on the HD information recording surface RL1 can be corrected.
- the causes of spherical aberration that are corrected by adjusting the position of the first lens EXP 1 include, for example, wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, changes in the refractive index and refractive index of the objective optical system due to changes in temperature, and the like. This includes focus jumps between information recording layers of multi-layer discs such as multi-layer discs and quadruple-layer discs, and thickness variations and thickness distributions due to manufacturing errors of HD protective layers.
- the second lens EXP2 or the first collimating lens COL1 may be driven in the optical axis direction instead of the first lens EXP1, and the spherical aberration of the spot formed on the HD information recording surface RL1 may be reduced. Can be corrected.
- the first lens EXP1 is driven in the optical axis direction to correct the spherical aberration of the spot formed on the HD information recording surface RL1.
- the configuration may be such that the spherical aberration of the spot formed on the recording surface RL2 and the spherical aberration of the spot formed on the information recording surface RL3 of the CD are corrected.
- the laser light source unit LU for DVDZCD in which the first light emitting point EP1 and the second light emitting point EP2 are formed on one chip is used.
- a one-chip laser light source unit for HDZDVDZCD may be used, in which a light emitting point for emitting a laser beam having a wavelength of 405 nm for HD is formed on the same chip.
- a one-can laser light source unit for HDZDVDZCD in which three laser light sources of a blue-violet semiconductor laser, a red semiconductor laser, and an infrared semiconductor laser are housed in one housing may be used.
- the optical pickup device PU described in the above embodiment a rotation drive device that rotatably holds the optical disk, and a control device that controls the driving of these various devices are mounted.
- a rotation drive device that rotatably holds the optical disk
- a control device that controls the driving of these various devices are mounted.
- base lens BL is made of resin, and resin layer UV, which is an ultraviolet curable resin, is laminated on the surface of base lens BL.
- the present embodiment is characterized in that a phase structure different from the diffraction structure DOE 1 is further added to the objective lens unit OU.
- the aberration correction element (first optical element) SAC has a configuration in which a base lens (first member) BL and a resin layer (second member) UV are laminated on the surface of the base lens BL.
- a diffractive structure (first phase structure) DOE1 having an annular step is formed and the optical surface of the base lens BL is different from the interface.
- the other side A diffractive structure (second phase structure) DOE2 is formed as a phase structure on the optical surface of.
- the first diffraction surface corrects the spherical aberration due to the difference in the thickness of the protective layer between HD and CD, and the surface on which the diffraction structure DOE2 of the base lens BL is formed (hereinafter, referred to as "second diffraction surface"). Corrects spherical aberration caused by the difference in protective layer thickness between HD and DVD! / ⁇ ⁇ .
- the second diffraction surface has a positive paraxial diffraction power (the effect of converging the light beam), and only the second light beam passing through the second diffraction surface is subjected to the diffraction effect. (1st time)
- ⁇ 1 is the refractive index of the base lens BL at the first wavelength ⁇ 1, and ⁇ 2 is the second wavelength ⁇ 2.
- L is the refractive index
- the optical path difference caused by this step ⁇ is twice the first wavelength ⁇ 1 and one time the third wavelength 3, the first light beam and the third light beam have no effect due to the diffraction structure DOE2. It is transmitted as it is without receiving it.
- the first light beam incident on the aberration correction element SAC as a parallel light beam passes through the second diffraction surface as it is and undergoes divergence at the first diffraction surface, but at the same time, the boundary surface and the opposite side of the boundary surface
- the resin layer receives a converging effect due to the refraction of the optical surface of UV, so that the light beam goes straight without bending. That is, the above equations (13) and (14) are satisfied.
- the second light beam incident on the aberration correction element SAC as a parallel light beam is converged by the diffraction operation on the second diffraction surface, but is diverged by the divergence operation on the first diffraction surface.
- the light is emitted from the aberration correction element SAC as a light beam.
- each of the objective lens units OU can be formed. It is possible to improve the light-collecting characteristics for the light beam.
- This phase structure may be a diffraction structure or an optical path difference providing structure.
- the aberration corrected by the phase structure may be, for example, chromatic aberration caused by a minute change in the first wavelength ⁇ 1, or spherical aberration caused by a change in the refractive index of the objective lens OL caused by a change in temperature. May be.
- the diffraction structure DOE2 only the second light beam is selectively diffracted as described above. However, the diffraction efficiency of each wavelength light beam is 100.0% for the first light beam (non-diffracted light).
- the second luminous flux (first-order folded light) is 87.5% and the third luminous flux (undiffracted light) is 100%, so that high diffraction efficiency can be secured for luminous flux of any wavelength.
- the base lens BL is made of resin, and a resin layer UV that is an ultraviolet curable resin is laminated on the surface of the base lens BL. Has been done.
- the present embodiment is characterized in that a phase structure different from the diffraction structure DOE1 is further added to the objective lens unit OU.
- the objective lens unit (objective optical element) OU in the present embodiment includes an aberration correction element SAC, a first wavelength ⁇ 1, and an HD protective layer PL 1.
- the objective lens OL whose aspherical shape is designed so that the spherical aberration is minimized with respect to the thickness tl is integrally formed coaxially via a lens frame B.
- the aberration correction element (first optical element) SAC has a configuration in which a base lens (first member) BL and a resin layer (second member) UV are laminated on the surface of the base lens BL.
- a diffractive structure (first phase structure) DOE1 having an annular step is formed and the optical surface of the base lens BL is different from the interface.
- a diffractive structure (second phase structure) DOE2 is formed as a phase structure on the opposite optical surface.
- the first diffraction surface has a positive diffraction power (the effect of converging the light beam), and only the first light beam passing through the first diffraction surface has the diffraction effect (the converging effect). (First-order diffraction).
- the second diffraction surface has a positive diffraction power (the effect of converging the light beam), and only the second light beam passing through the second diffraction surface is subjected to the diffraction effect ( 1st order diffraction).
- boundary surface and the optical surface of the resin layer UV on the opposite side to the boundary surface have negative refracting power (the effect of diverging the luminous flux).
- the first light beam incident on the aberration correction element SAC as a parallel light beam passes through the second diffraction surface as it is and undergoes a convergence effect on the first diffraction surface, but at the same time undergoes a divergence effect due to a refraction effect, so The rays go straight without bending. That is, the above equations (13) and (14) are satisfied. Then, the chromatic aberration of the first light beam is corrected by the function of the first diffraction surface.
- the third light beam incident on the aberration correction element SAC as a parallel light beam passes through the second diffraction surface and the first diffraction surface as it is, and passes through the boundary surface and the resin layer UV on the opposite side of the boundary surface.
- the third light beam is diverged by the refraction effect of the optical surface of the third lens, and is emitted as a divergent light beam, which is emitted from the aberration correction element SAC.
- spherical aberration due to the difference in the protective layer thickness between HD and CD is corrected.
- the second light beam incident on the aberration correction element SAC as a parallel light beam is subjected to a diffractive operation on the second diffraction surface, and thus undergoes a convergence action.
- the refraction effect of the optical surface of the oily layer UV produces a divergent light beam, which is emitted as a divergent light beam.
- the degree of divergence of the second light beam is smaller than the degree of divergence of the third light beam. This is because the second light beam is once converged by the second diffraction surface. As a result, spherical aberration due to the difference in the protective layer thickness between HD and DVD is corrected.
- I ⁇ vd I 33.7,
- 0.0458, I ⁇ ⁇ 2
- 0.271,
- 0.167,
- the diffraction efficiency of the light flux of each wavelength is 100% for the first light flux (first-order diffraction), 91.2% for the second light flux (undiffracted light), and 97.6% for the third light flux (undiffracted light).
- high diffraction efficiency can be ensured for light beams of any wavelength.
- the diffractive structure DOE2 only the second light beam is selectively diffracted as described above. However, the diffraction efficiency of the light beam of each wavelength is 100.0% for the first light beam (non-diffracted light), The second luminous flux (first-order folded light) is 87.5% and the third luminous flux (undiffracted light) is 100%, so that high diffraction efficiency can be secured for luminous flux of any wavelength.
- the diffractive structure DOE2 is a wavelength-selective diffractive structure
- a phase difference can be given only to a light beam of a predetermined wavelength
- a diffractive effect can be given only to DVD light
- diffraction structure DOE2 is a blazed diffraction structure
- chromatic aberration correction is effective.
- the diffractive structure DOE1 is formed at the interface between the base lens BL and the resin layer UV, and the diffractive structure DOE2 is formed of a material having a larger Abbe number at d-line, air, and As shown in Fig. 8, the objective lens OL arranged on the disk side has the Abbe number of the d-line Vd force 0 ⁇ Vd ⁇ 70 as shown in Fig. 8.
- the diffractive structure DOE3 may be formed on the surface of the objective lens OL.
- the thickness t2 of the protective layer DVD L2 of the DVD is set so as to satisfy 0.9 X tl ⁇ t2 ⁇ l. 1 X tl. If so, only the spherical aberration caused by the difference in wavelength, such as the combination of HD DVD and DVD, is simply corrected, so that the diffraction pitch can be increased and the workability can be improved.
- the aberration correction element SAC has a configuration in which a resin layer made of UV-cured resin and a base lens made of glass lens (BACD5 manufactured by HOYA) are laminated, and the boundary surface between the base lens and the resin layer is Has a diffractive structure DOE 1 formed.
- the objective lens OL is a glass lens (HOYA BACD5) whose aspherical shape is designed so that spherical aberration is minimized with respect to the first wavelength ⁇ 1 and the thickness tl of the HD protective layer PL1. ), But also good as a plastic lens!
- Tables 11 and 12 show lens data of this example.
- the optical path difference added to the incident light beam by the diffraction structure DOE1 is represented by an optical path difference function.
- the numerical aperture of the optical density optical disc HD NA1 is 0.85
- DVD numerical aperture NA2 is 0.65
- CD numerical aperture NA3 is 0.50.
- r (mm) is the radius of curvature
- d (mm) is the lens spacing
- V d is the Abbe number of the d-line lens
- M, M, and M are HD, respectively.
- a power of 10 (for example, 2.5X10-3) is represented by using E (for example, 2.5E-3).
- Boundary surface between base lens and resin layer (second surface), optical surface of resin layer on optical disk side (third surface), optical surface of objective lens OL on light source side (fourth surface), optical surface on optical disk side (Fifth surface) each has an aspherical shape, and this aspherical surface is represented by an equation obtained by substituting the coefficients in the table into the following aspherical shape equation.
- z Aspherical shape (distance along the optical axis from the plane tangent to the apex of the aspheric surface)
- y Distance from the optical axis
- ⁇ wavelength of the light beam incident on the diffraction structure
- ⁇ ⁇ Production wavelength ⁇ : Recording on optical disk ⁇ Diffraction order of diffracted light used for reproduction y: Distance from optical axis
- the aberration correction element SAC has a configuration in which a resin layer made of UV-cured resin and a resin base lens are laminated, and a diffraction structure DOE 1 is formed at the interface between the base lens and the resin layer.
- a diffractive structure DOE2 is formed as a phase structure.
- the objective lens OL is a glass lens (HOYA BACD5 (HOYA Corporation) whose aspheric shape is designed so that spherical aberration is minimized with respect to the first wavelength ⁇ 1 and the thickness tl of the HD protective layer PL1. Product name)) is also good as a plastic lens.
- Lens data of the present example are shown in Tables 2-1 and 2-2.
- the optical path difference added to the incident light beam by the diffraction structures DOE1 and DOE2 is represented by an optical path difference function.
- Boundary surface between base lens and resin layer (second surface), optical surface of resin layer on optical disk side (third surface), optical surface of objective lens OL on light source side (fourth surface), optical disk side
- Each of the optical surfaces (fifth surface) has an aspherical shape, and this aspherical surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical shape expression.
- Each of the diffraction structures DOE1 and DOE2 is represented by an optical path difference added to the incident light beam by each diffraction structure.
- Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Tables 2-1 and 2-2 into the equation representing the optical path difference function.
- the aberration correction element SAC has a configuration in which a resin layer made of UV-cured resin and a resin base lens are laminated, and a diffraction structure DOE 1 is formed at the interface between the base lens and the resin layer.
- a diffractive structure DOE2 is formed as a phase structure.
- the objective lens OL is a glass lens (HOYA BACD5) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength ⁇ 1 and the thickness tl of the HD protective layer PL1. However, it may be used as a plastic lens.
- Table 3-1 shows lens data of this example.
- the optical path difference added to the incident light beam by the diffraction structure DOE is represented by an optical path difference function.
- Each of the diffraction structures DOE1 and DOE2 is represented by an optical path difference added to the incident light beam by each diffraction structure.
- Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in the table into the expression representing the optical path difference function.
- Table 4 shows lens data in the case where a diffractive structure is also provided on the boundary surface between the material having a larger Abbe number and air at the d-line shown in FIG.
- * 3 ′ represents the displacement from the 3 ′ plane to the 3rd plane.
- optical surface (fifth surface) on the light source side and the optical surface (sixth surface) on the optical disk side of the objective lens OL are aspherical shapes. It is expressed by a formula with the coefficients inside.
- Each is represented by an optical path difference added to the incident light beam by the diffraction structures DOE and DOE2.
- Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Table 4 into the following expression representing the optical path difference function.
- M is the diffraction order
- 1 is assigned to HD DVD
- 1 is assigned to DVD
- 1 is assigned to CD in the case of the diffractive structure DOE on the third surface. Is set to 2 for HD DVD, 1 for DVD, and 1 for CD.
- Table 5 shows lens data in the case where a diffraction structure is also provided on the surface of the objective lens (objective optical system) shown in FIG.
- Image-side numerical aperture NA1 0.65 NA2: 0.65 NA3: 0.51
- * 3 ′ represents the displacement from the 3 ′ plane to the 3rd plane.
- optical surface (fifth surface) on the light source side and the optical surface (sixth surface) on the optical disk side of the objective lens OL are aspherical shapes. It is expressed by a formula with the coefficients inside.
- the diffractive structure DOE 1 formed on the boundary surface (third surface) between the base lens BL and the resin layer UV (the third surface) and the diffractive structure DOE3 formed on the surface (fifth surface) of the objective lens OL are diffracted. It is represented by the optical path difference added to the incident light beam by the structures DOE and DOE3. Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Table 5 into the following expression representing the optical path difference function.
- M is the diffraction order
- 1 is assigned to HD DVD, 1 to DVD, and 1 to CD in the case of the diffractive structure DOE on the third surface. Is set to 2 for HD DVD, 1 for DVD, and 1 for CD.
- the objective lens unit OU in this embodiment has a spherical surface with respect to the aberration correction element SAC, the first wavelength ⁇ 1, and the thickness tl of the HD protective layer PL1.
- Objective lens OL a dedicated HD lens, whose aspheric shape is designed to minimize aberrations It has a configuration coaxially integrated through a lens frame B. Specifically, an aberration correction element SAC is fitted and fixed to one end of a cylindrical lens frame B, and an objective lens OL is fitted and fixed to the other end, and these are coaxially integrated along the optical axis X.
- the configuration is as follows.
- the aberration correction element (first optical element) SAC has a refractive index difference ⁇ at a first wavelength ⁇ 1 and a difference ⁇ vd of Abbe number at d-line. It has a configuration in which a material A that is an ultraviolet curable resin (first member) and a material B that is an optical glass (second member) that satisfy the following expressions (21) and (22) are laminated.
- a diffractive structure (first phase structure) DOE is formed on the material interface as a phase structure having an annular step. This diffractive structure DOE is a structure for correcting the spherical aberration caused by the difference in the protective layer thickness of each optical disc and the spherical aberration caused by the difference in the used wavelength of each optical disc.
- the diffraction structure DOE may have a saw-tooth shape as shown in FIG. 7A or a step-like shape as shown in FIG. 7B, including the optical axis.
- the diffraction efficiency r? ( ⁇ ) of a diffractive structure sandwiched between two materials having different Abbe numbers (dispersion) is generally represented by the wavelength ⁇ and the refraction of the materials ⁇ and ⁇ ⁇ ⁇ ⁇ at this wavelength ⁇ .
- ⁇ (l) sinc 2 [[d- ⁇ ( ⁇ ) / ⁇ ] - ⁇ ( ⁇ )] (61)
- the difference in refractive index at the first wavelength ⁇ 1 used for HD is ⁇ 1
- the diffraction order of the diffracted light of the first light flux is Ml
- the difference in refractive index at the second wavelength 2 used for DVD is ⁇ 2
- the difference in refractive index at the third wavelength 3 used for CD is ⁇ 3
- the diffraction order of the diffracted light of the third light flux is ⁇ 3
- the diffraction efficiency at each wavelength is 7? ( ⁇ 1), r? ( ⁇ 2), ( ⁇ 3) are expressed by the following equations (62) to (64).
- the difference in the refractive index A ni ( i can be selected from materials A and B having 1, 2, or 3), a step d, and a diffraction order Mi (i is 1, 2, or 3)! / .
- the materials A and B are used as the materials described above.
- Table 6 shows the physical properties of the materials A and B
- Fig. 10 shows the relationship between the step d and the diffraction efficiency of the diffracted light of each light beam. As can be seen from Fig. 10, by setting the step d of the diffractive structure DOE near 35 m, the diffraction efficiency (transmittance) can be as high as 95% for any luminous flux.
- the diffractive structure DOE can have a function of selectively diffracting only the second and third light beams, and the blue-violet laser light beam (first light beam) and infrared light, which were difficult with the conventional technology. It is possible to achieve both the effect of correcting the spherical aberration of the diffracted light of the laser light beam (third light beam) and ensuring the diffraction efficiency (transmittance).
- the diffraction power in the paraxial direction of the diffractive structure DOE is negative, and the second light beam and the third light beam incident on the diffractive structure DOE are converted into divergent light beams and incident on the objective lens OL. .
- the back focus of the objective lens unit OU with respect to the second light beam and the third light beam can be extended, so that the working distance for a DVD or CD having a thick protective layer can be sufficiently ensured.
- the diffractive power P on the paraxial axis of the diffractive structure DOE is described later.
- the diffractive structure DOE corresponds to the area corresponding to the numerical aperture NA.
- the spherical aberration due to the difference in thickness between tl and t2 is outside the numerical aperture NA.
- the numerical aperture NA within the diffraction structure DOE was formed.
- the corresponding areas are the central area corresponding to the numerical aperture NA and the numerical aperture NA surrounding the central area.
- the width of the diffraction ring zone is determined so that both the second light beam and the third light beam are condensed on the information recording surface of each optical disc.
- the diffractive structure formed in the peripheral region focuses only the second light beam on the information recording surface RL2 of the DVD, and the third light beam is sufficiently emitted from the spot formed on the information recording surface RL3 of the CD.
- the width of the diffraction zone is determined so that the flare component spreads far away.
- the aberration correction element SAC used in the optical pickup device PU of the present embodiment includes, in addition to the spherical aberration correction function, an aperture limiting function corresponding to the numerical aperture NA of DVD and a CD.
- the aberration correction element SAC and the objective lens OL are integrated via the lens frame B.
- the aberration correction element SAC and the objective lens OL are integrated.
- a method of fitting and fixing the respective flange portions of the aberration correction element SA C and the objective lens OL may be used.
- the aberration correction element SAC and the objective lens OL are held so that the relative positional relationship between them remains unchanged, thereby suppressing the occurrence of aberration during focusing / tracking. As a result, good focusing characteristics or tracking characteristics can be obtained.
- the aberration correction element SAC and the objective lens OL are configured as separate elements.
- the aberration correction element SAC A so-called hybrid type objective lens with the function of the objective lens OL may be used instead of the objective lens unit OU! / ⁇ .
- a configuration in which the light-collecting performance of the objective lens unit OU may be further improved by further adding a phase structure different from the diffraction structure DOE.
- the strong phase structure may be formed on either the optical surface of the aberration correction element SAC or the objective lens OL, but may be formed on the optical surface on the light source side of the aberration correction element SAC or the optical surface of the optical disk of the aberration correction element SAC. It is preferable in manufacturing to form.
- the functions provided to the phase structure include, for example, compensation for an increase in the focal spot (so-called chromatic aberration) of the objective lens unit OU due to a wavelength change, and an increase in the focal spot of the objective lens unit OU due to a temperature change. (So-called temperature aberration).
- the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected.
- the causes of spherical aberration that are corrected by adjusting the position of the first lens EXP 1 include, for example, wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, changes in the refractive index and refractive index of the objective lens system due to changes in temperature, and the like. Focus jumps between information recording layers of multi-layer discs such as multi-layer discs and four-layer discs, thickness variations and thickness distributions due to manufacturing errors of HD protective layers, etc.
- the second lens EXP2 or the first collimating lens COL1 may be driven in the optical axis direction instead of the first lens EXP1 to reduce the spherical aberration of the spot formed on the HD information recording surface RL1. Can be corrected.
- the first lens EXP1 is driven in the optical axis direction to correct the spherical aberration of the spot formed on the HD information recording surface RL1.
- the configuration may be such that the spherical aberration of the spot formed on the recording surface RL2 and the spherical aberration of the spot formed on the information recording surface RL3 of the CD are corrected.
- the laser light source unit LU for DVDZCD in which the first light emitting point EP1 and the second light emitting point EP2 are formed on one chip is used.
- a one-chip laser light source unit for HDZDVDZCD may be used, in which a light emitting point for emitting a laser beam having a wavelength of 405 nm for HD is formed on the same chip.
- a one-can laser light source unit for HDZDVDZCD in which three laser light sources of a blue-violet semiconductor laser, a red semiconductor laser, and an infrared semiconductor laser are housed in one housing may be used.
- the light source and the photodetector PD are configured separately.
- the power is not limited to this.
- a laser light source module in which the light source and the photodetector are integrated is provided. May be used.
- the optical pickup device PU described in the above embodiment a rotation drive device that rotatably holds the optical disk, and a control device that controls the drive of these various devices are mounted.
- a rotation drive device that rotatably holds the optical disk
- a control device that controls the drive of these various devices are mounted.
- the diffractive structure DOE is formed only on the interface between the material A and the material B has been described as an example.
- a diffractive structure phase structure
- the wavelength ⁇ of each of the first light flux, the second light flux, and the third light flux is obtained. Diffraction efficiency for ⁇ , 1 2, ⁇ 3, can be increased.
- the objective lens (objective optical system) arranged on the disk side satisfies the condition that the Abbe number Vd of d-line satisfies 40 ⁇ Vd ⁇ 70, A diffractive structure is formed on the surface of the.
- the Abbe number Vd of the d-line in the objective lens arranged on the disk side satisfies the above expression and the surface of the objective lens has a diffractive structure
- the first light beam It is possible to increase the diffraction efficiency with respect to the wavelengths ⁇ ⁇ , 2, and 3 of the first, second, and third light beams, respectively.
- These diffraction structures may be either wavelength-selective diffraction structures or blazed diffraction structures.
- the diffraction structure is a wavelength-selective diffraction structure
- a phase difference can be given only to a light beam of a predetermined wavelength
- a diffraction effect can be given only to DVD light
- the diffraction It can correct spherical aberration of DVD.
- chromatic aberration correction is effective.
- the thickness t2 of the protective layer PL2 of the DV D is set to 0.9 X tl ⁇ t2 ⁇ l. If tl is set, only the spherical aberration caused by the difference in wavelength, such as the combination of HD DVD and DVD, can be corrected, so the diffraction pitch can be increased and the workability can be improved. I can do it.
- the aberration correction element SAC has a configuration in which a material A that is an ultraviolet curing resin and a material B that is a glass lens (BACD5 manufactured by HOYA) are laminated, and a diffraction structure DOE is provided at the boundary between the material A and the material B. Is formed.
- the objective lens OL is a glass lens exclusively for HD (HOCD BACD5), but may be a plastic lens.
- Lens data of Example 6 is shown in Table 7, specifications are shown in Table 8, and an optical path diagram is shown in FIG.
- the optical path difference added to the incident light beam by the diffraction structure DOE is represented by an optical path difference function. Further, the diffraction structure DOE is not shown in the optical path diagram of FIG.
- vd is the Abbe number of the d-line lens
- MMM is
- a power of 10 (for example, 2.5 ⁇ 10 _3 ) is represented by using E (for example, 2.5E-3).
- the numerical aperture NA of the objective lens unit is 0.50
- the effective diameter of the first surface (S1) is 0.50
- optical system magnification is set to 1Z22.28.
- the magnification when using a CD when correcting the spherical aberration due to the difference between the two can be set small, and even if the objective lens unit OU is shifted by 0.5 mm in the vertical direction of the optical axis, the wavefront aberration is 0.05 ⁇ 3RMS Degree and good.
- the tracking amount of the objective lens cut OU is about ⁇ 0.5 mm, it is considered that the objective lens cut OU of this embodiment has good tracking characteristics for CD. I can say.
- optical surface (fourth surface) on the light source side of the objective lens OL and the optical surface (fifth surface) on the optical disk side are aspherical shapes. And the equation with the coefficients in Table 8 substituted.
- the diffractive structure DOE formed at the interface between the material A and the material B is represented by an optical path difference added to the incident light beam by the diffractive structure DOE.
- Such an optical path difference is represented by an optical path difference function ⁇ (mm) obtained by substituting the coefficients in Tables 7 and 8 into an equation representing the following optical path difference function.
- ⁇ wavelength of the light beam incident on the diffraction structure
- Table 9 shows lens data in the case where a diffractive structure is also provided on the boundary surface between the material having a larger Abbe number and air at the d-line shown in FIG.
- Image-side numerical aperture NA1 0.65 NA2: 0.65 NA3: 0.51
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- Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Optical Head (AREA)
- Lenses (AREA)
Abstract
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JP2006513848A JPWO2005117001A1 (ja) | 2004-05-27 | 2005-05-17 | 対物光学系、光ピックアップ装置、及び光ディスクドライブ装置 |
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JP2004203417 | 2004-07-09 | ||
JP2004-203417 | 2004-07-09 | ||
JP2004-230967 | 2004-08-06 | ||
JP2004230967 | 2004-08-06 | ||
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US20050265151A1 (en) | 2005-12-01 |
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