JP2006012394A - Optical system, optical pickup device, and optical disk driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical system capable of correcting a spherical aberration caused by a difference in protective layer thickness among a high-density optical disk, a DVD, and a CD and a spherical aberration caused by a difference in used wavelength among these optical disks by the operation of a phase structure including a diffraction structure, and obtaining high light utilization efficiency even in a wavelength area in the vicinity of 400nm, 650nm or 780nm, an optical pickup device, and an optical disk driving device. <P>SOLUTION: This optical system is arranged in an optical path common among the first luminous flux of a first wavelength λ<SB>1</SB>, the second luminous flux of a second wavelength λ<SB>2</SB>(>λ<SB>1</SB>) and the third luminous flux of a third wavelength λ<SB>3</SB>(>λ<SB>2</SB>). It is constructed by laminating two materials having different Abbe numbers on a d line. A phase structure having an annular step is formed on the boundary surface of the two materials. The phase structure has no aberration correction function for the first luminous flux but has an aberration correction function for the second and third luminous fluxes. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical system, an optical pickup device, and an optical disk drive device.

Conventionally, an optical pickup compatible with a high density optical disc, a DVD (using a red laser light source), and a CD (using an infrared laser light source) whose recording density is increased by using a blue-violet laser light source. Devices and optical elements used in such optical pickup devices are known (see, for example, Patent Documents 1 to 3).
JP 2004-079146 A JP 2002-298422 A JP 2003-207714 A

Numerical Example 7 of Patent Document 1 has a diffractive structure on the surface of an objective lens that generates second-order diffracted light with a blue-violet laser beam and first-order diffracted light with a red laser beam and an infrared laser beam. Due to the action of this diffractive structure, spherical aberration due to the difference in the protective layer thickness between the high-density optical disc and the DVD is corrected, and a divergent light beam is incident on the objective lens when recording / reproducing information with respect to the CD. An objective lens that corrects spherical aberration due to the difference in the thickness of the protective layer between a density optical disk and a CD is disclosed.
Although this objective lens can secure 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 / reproducing information on a CD, and the coma when the objective lens is tracking. There is a problem in that good recording / reproducing characteristics cannot be obtained with respect to a CD because the generation of aberration becomes too large.

In Numerical Example 3 of Patent Document 2, diffraction is performed on the surface of the objective lens such that a third-order diffracted light is generated with a blue-violet laser beam and a second-order diffracted light is generated with a red laser beam and an infrared laser beam. An objective lens is disclosed which has a structure and corrects spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and DVD and CD.
Although this objective lens can correct spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the DVD and further spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the CD due to the action of the diffractive structure. Since 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 photodetector cannot cope with the increase in the recording / reproducing speed for the optical disk. There are problems in that good recording / reproduction characteristics cannot be obtained due to the low S / N ratio of the detection signal, and that the life of the laser light source is shortened because the voltage applied to the laser light source is high.

In the objective lens described in Patent Document 1, the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disk and the CD cannot be corrected by the diffractive structure, or in the objective lens described in Patent Document 2, the third time in the blue-violet wavelength region. The reason why the diffraction efficiency of the folded light and the diffraction efficiency of the second-order diffracted light in the infrared wavelength region are low is that the wavelength of the blue-violet laser light source used for the high-density optical disk is different from that of the infrared laser light source used for the CD. Since the wavelength is approximately twice, the spherical aberration correction effect for the blue-violet laser beam and the infrared laser beam of the diffracted light generated by the diffractive structure and the diffraction efficiency of the diffracted light are in a trade-off relationship. Can be mentioned.
That is, in the objective lens of Numerical Example 7 of Patent Document 1 corresponding 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 to be high, the blue-violet laser beam The diffraction angle of the diffracted light and the diffraction angle of the diffracted light of the infrared laser beam substantially coincide with each other, so that the spherical aberration due to the difference in the thickness of the high-density optical disc and the CD protective layer cannot be corrected by the diffractive structure. .

On the other hand, in the objective lens of Numerical Example 3 of Patent Document 2, which corresponds to the case where a difference is made between 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, the blue-violet laser Both the diffraction efficiency of the diffracted light of the light beam and the diffraction efficiency of the infrared laser light beam are lowered.
In addition to the diffraction structures described in Patent Documents 1 and 2, not only in the technology using a phase corrector (referred to as an optical path difference providing structure in this specification) as described in Patent Document 3. Similarly to the diffraction structure, the spherical aberration correction effect for the blue-violet laser beam and the infrared laser beam by the optical path difference providing structure and the transmittance of the optical path difference providing structure are in a trade-off relationship.

  The present invention has been made in view of the above-described problems. Due to the action of a phase structure including a diffractive structure, spherical aberration due to a difference in protective layer thickness between a high-density optical disc and a DVD and a CD, or a high-density optical disc Spherical aberration due to the difference in operating wavelength between DVD and CD can be corrected satisfactorily, and any of a blue-violet wavelength region near 400 nm, a red wavelength region near 650 nm, and an infrared wavelength region near 780 nm It is an object of the present invention to provide an aberration correction element that can obtain high light utilization efficiency even in a wavelength region, an optical pickup device that uses this aberration correction element, and an optical disk drive device that includes this optical pickup device.

In order to solve the above problems, a first aspect of the present invention provides a first optical disc having a protective layer having a thickness t ₁ using a first light flux having a first wavelength λ ₁ emitted from a first light source. Information is recorded and / or reproduced, and a protective layer having a thickness t ₂ (≧ t ₁ ) is provided using a second light flux having a second wavelength λ ₂ (> λ ₁ ) emitted from the second light source. Information is recorded on and / or reproduced from the second optical disk, and a third light beam having a third wavelength λ ₃ (> λ ₂ ) emitted from the third light source is used to obtain a thickness t ₃ (> t ₂ ). An optical system used in an optical pickup device for recording and / or reproducing information with respect to a third optical disc having a protective layer, and having at least one optical element,
The optical element is disposed in an optical path through which the first light beam, the second light beam, and the third light beam pass in common, and is formed by stacking materials A and B having different Abbe numbers in the d-line. A phase structure having a ring-shaped step is formed on the boundary surface between the material A and the material B,
The phase structure does not have an aberration correction function for the first light beam and has an aberration correction function for the second light beam and the third light beam.

  By configuring the optical system as in the first aspect, the spherical aberration correction effect of the blue-violet laser beam (first beam) and the infrared laser beam (third beam), which was difficult in the prior art. And ensuring the transmittance can be realized. The phase structure includes a sawtooth type (diffractive structure DOE) shown in FIG. 1A and a step type (diffractive structure DOE or optical path difference providing structure NPS) shown in FIG. ). In FIG. 1B, the case where the direction of the step is changed in the middle is illustrated as the staircase type, but the direction of the step may be always constant. In the present specification, the two materials laminated with the phase structure as a boundary surface in the optical element (also referred to as an aberration correction element) in the present invention are called “material A” and “material B” including the drawings. .

In this specification, an objective lens with a NA of 0.85 and a protective layer thickness of 0.1 mm, a Blu-ray disc with an objective lens with an NA of 0.65 to 0.67 and a protective layer thickness of 0 are used. An optical disk using a blue-violet laser light source, such as a HD DVD of 6 mm, is collectively referred to as a “high density optical disk”. In addition to the above-mentioned Blu-ray disc and HD DVD, a magneto-optical disc, an optical disc having a protective film with a thickness of several to several tens of nanometers on the information recording surface, an optical disc with a protective layer or a protective film having a zero thickness Are also included in the high density optical disk.
In this specification, DVD (Digital Versatile Disc) means DVD series optical discs such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, etc. CD (compact disc) is a generic term for CD-series optical discs such as CD-ROM, CD-Audio, CD-Video, CD-R, and CD-RW.

As a second aspect of the present invention, information is recorded on and / or recorded on a first optical disc having a protective layer having a thickness t ₁ using a first light flux having a first wavelength λ ₁ emitted from a first light source. Information is recorded on the second optical disk having a protective layer with a thickness t ₂ (≧ t ₁ ) using the second light flux having the second wavelength λ ₂ (> λ ₁ ) emitted from the second light source. Recording and / or reproduction is performed on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using a third light beam having a third wavelength λ ₃ (> λ ₂ ) emitted from the third light source. An optical system that is used in an optical pickup device that records and / or reproduces information with respect to the optical system and has at least one optical element,
Optical element, the the difference [Delta] n ₁ of the refractive index in the first wavelength lambda _1, the difference .DELTA..nu _d Abbe number at the d-line, respectively, material A and material satisfying the following formula (1) and (2) The phase structure is formed by laminating B and having a ring-shaped step at the boundary surface between the material A and the material B.
| Δn ₁ | <0.01 (1)
20 <| Δν _d | <40 (2)

When a material is selected such that the difference in refractive index Δn _{1 at} the first wavelength λ ₁ is substantially zero as in the second aspect, the first light flux is not affected by the phase structure of the boundary surface and remains as it is. To Penetrate. Further, when the materials A and B are selected so that the Abbe number difference Δν _d in the d-line falls within the range of the expression (2), the second light beam and the third light beam have a predetermined optical path due to the phase structure. Since a difference can be added, a spherical aberration correction function can be provided. Thereby, it becomes possible to obtain the same operation effect as the 1st mode.
If Δν _d is larger than the lower limit of the expression (2), a sufficient difference in refractive index can be obtained between the second wavelength λ ₂ and the third wavelength λ ₃ , so that the step d of the phase structure does not become too large and manufacturing is easy. It becomes. On the other hand, when Δν _d is larger than the upper limit of the formula (2), the combination of materials satisfying the formula (1) is extremely reduced. Therefore, if Δν _d is smaller than the upper limit of the expression (2), the number of combinations of materials increases, and it becomes possible to select an optimum material.

  In the above optical system, the phase structure is a diffractive structure (also referred to as a first diffractive structure), and the first diffractive structure does not diffract the first light beam, but diffracts the second light beam and the third light beam. It is a preferable form.

  When the phase structure is a diffractive structure, the first light beam is not diffracted and the second light beam and the third light beam are selectively diffracted by adopting the configuration as described in the first or second aspect. It becomes possible. Thereby, the spherical aberration correction effect and diffraction efficiency (transmittance) securing of the blue-violet laser beam (first beam) and the infrared laser beam (third beam), which were the problems of Patent Documents 1 and 2 described above, are ensured. A balance can be realized.

In the above optical system, it is more preferable to satisfy the following expressions (3) and (4).
0 <| INT (d · Δn ₂ / λ ₂ ) − (d · Δn ₂ / λ ₂ ) | <0.3 (3)
0 <| INT (d · Δn ₃ / λ ₃ ) − (d · Δn ₃ / λ ₃ ) | <0.3 (4)
However,
d: Step difference of the phase structure Δn ₂ : Difference in refractive index between the material A and material B at the λ ₂ Δn ₃ : Difference in refractive index between the material A and the material B at the λ ₃ INT (X): Integer obtained by rounding to the first decimal place

  When the materials A and B are appropriately selected so as to satisfy the expressions (3) and (4), the second light flux and the third light flux can have a spherical aberration correction function and the second light flux. Since the diffraction efficiency of the third light beam can be secured, it is preferable. When the value is larger than the lower limit of the expression (3), a sufficient spherical aberration correction function can be given to the second light beam, and when the value is smaller than the upper limit of the expression (3), the diffraction efficiency of the second light beam can be sufficiently secured. Further, when the value is larger than the lower limit of the expression (4), a sufficient spherical aberration correction function can be given to the third light beam, and when the value is smaller than the upper limit of the expression (4), the diffraction efficiency of the third light beam can be sufficiently secured. .

Further, in the above-described optical system, it is preferable that the following expression (5) is satisfied.
M ₂ = M ₃ (5)
However,
M ₂ = INT (d · Δn ₂ / λ ₂ ) (6)
M ₃ = INT (d · Δn ₃ / λ ₃ ) (7)

In the above-described optical system, it is particularly preferable that the following expression (8) is satisfied.
M ₂ = M ₃ = 1 (8)
As in the above-described optical system, when the material A and the material B are selected so that the diffraction orders of the second light beam and the third light beam are the same, an aberration correction element having excellent design characteristics can be obtained.
In particular, as shown in the equation (8), when the diffraction orders of the second light beam and the third light beam are both 1, the design characteristics are the best.

  In the first aspect or the second aspect described above, a diffractive structure (also referred to as a second diffractive structure) is formed on the boundary surface between the material A and the material B having the larger Abbe number in the d-line and air. Is preferably formed.

When the second diffractive structure is formed on the boundary surface between the material having the larger Abbe number in the d-line and air, the wavelengths λ ₁ , the first light beam, the second light beam, and the third light beam, The diffraction efficiency for λ ₂ and λ ₃ can be further increased.

In the first aspect or the second aspect, the optical system includes an objective optical element on the optical disc side of the optical element, and the objective optical element has an Abbe number ν _{d of} d line of the following formula (9 It is preferable that a second diffractive structure is formed on the surface of the objective optical element.
40 ≦ ν _d ≦ 70 (9)

Since the Abbe number ν _d of the d-line in the objective optical element arranged on the disk side satisfies the above equation (9) and the surface of the objective optical element has a diffractive structure, the first light flux, The diffraction efficiency with respect to the wavelengths λ ₁ , λ ₂ , and λ ₃ of the light beam and the third light beam can be further increased.

  In the above optical system, it is preferable that the second diffractive structure is a diffractive structure having a plurality of steps in cross section, and selectively diffracts or transmits light according to the wavelength.

If the second diffractive structure is a diffractive structure having a plurality of steps in cross section (wavelength selective diffractive structure) and selectively diffracts or transmits light according to the wavelength, for example, the first light flux with the first wavelength λ ₁ Can be diffracted by giving a phase difference to the second light flux of the second wavelength λ ₂ and the third light flux of the third wavelength λ ₃ without giving a phase difference to the light beam. . If a phase difference can be given only to a light beam having a predetermined wavelength, a diffraction effect can be imparted only to the DVD light, and the spherical aberration of the DVD that remains in the configuration of the first aspect or the second aspect. Can be corrected.

  In the above-described optical system, it is also a preferred embodiment that the second diffractive structure is a blazed diffractive structure.

  Here, the blazed diffractive structure is a structure in which the cross-sectional shape including the optical axis is formed in a sawtooth shape. If the second diffractive structure is a blazed diffractive structure, it is effective for correcting chromatic aberration. Color correction means that the focal position of the objective lens does not change with respect to wavelength change. The laser used in the pickup device has a mode hop phenomenon, and the actuator of the objective lens does not catch up with the sudden wavelength change, resulting in a defocused state. Therefore, in short-wave Blu-ray and HD DVD, it is necessary to perform color correction that does not change the focal position of the objective lens even if the wavelength changes. Color correction is possible using a wavelength-selective diffractive structure, but the number of zonal zones is larger than that of a blazed diffractive structure, and DVD or CD light is transmitted, so that a color correction function can be simultaneously applied. The blazed diffractive structure is preferably used in that it cannot be used.

In the above optical system, it is preferable that the following expression (10) is satisfied.
0.9 × t ₁ ≦ t ₂ ≦ 1.1 × t ₁ (10)

It defines an preferred range of the thickness t ₂ of the protective layer of the second optical disk. If the thickness t ₂ is within this range, it is only necessary to correct the spherical aberration caused by the difference in wavelength as in the combination of HD DVD and DVD, so that the diffraction pitch can be increased and the workability can be increased. Can be increased.

In the optical system described above, one of the materials A and B is preferably an optical glass and the other is an optical resin.
Since there are many types of optical glass and the range of material selection is widened, it is preferable that one of the two materials is an optical glass. Furthermore, considering that the two materials are laminated with the phase structure, which is a fine structure, as the boundary surface, the other material is preferably an optical resin.

  The optical resin is preferably an ultraviolet curable resin.

Furthermore, the optical glass is preferably manufactured by molding.
As a method of laminating optical resin on optical glass, optical glass having a phase structure formed on its surface is used as a mold, and optical resin is molded on optical glass to form a laminate (so-called insert molding). However, a method in which an ultraviolet curable resin is laminated on an optical glass having a phase structure formed on the surface thereof and then cured by irradiation with ultraviolet rays is suitable for production.

  In addition, as a method for producing an optical glass having a phase structure formed on its surface, a method of directly forming a phase structure on an optical glass substrate by repeating photolithography and etching processes may be used. The so-called mold molding is suitable for mass production, in which a mold (mold) having a surface is formed and optical glass having a phase structure formed on the surface is obtained as a replica of the mold. In addition, as a method of producing the mold in which the phase structure is formed, a method of repeating the photolithography and etching processes to form the phase structure, or a method of machining the phase structure with a precision lathe may be used.

In the above-described optical system, it is preferable that the following expressions (11) and (12) are satisfied.
α × λ ₁ = λ ₃ (11)
K1-0.1 ≦ α ≦ K1 + 0.1 (12)
However,
K1: Natural number The present invention is particularly suitable for an optical system that satisfies the above relationship.

The third aspect of the present invention includes a first light source that emits a first light beam having a first wavelength λ ₁ ; a second light source that emits a second light beam having a second wavelength λ ₂ (> λ ₁ ); ₃ (> λ ₂ ) of a third light source that emits a third light beam; and any one of the optical systems described above,
Information is recorded and / or reproduced with respect to the first optical disc having the protective layer having the thickness t ₁ using the first light beam, and the thickness t ₂ (≧ t ₁ ) is protected using the second light beam. Recording and / or reproducing information on a second optical disc having a layer, and recording and / or reproducing information on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using the third light flux And / or reproduction.

In the third aspect described above, it is one of preferred embodiments that the optical system includes the optical element and an objective optical element disposed on the optical disc side of the optical element.
It is also a preferred embodiment that the optical element is the objective optical element itself.

When the optical element (aberration correction element) in the present invention is mounted on an optical pickup device, it may be arranged on the light source side of an objective optical element (also referred to as an objective lens) (see FIG. 2). Thereby, since the aberration correction element can be formed into a substantially flat plate shape, there is an advantage that the aberration correction element can be easily manufactured. In this case, if the objective optical element that is the aberration correction element and the light condensing element are held so that their relative positional relationship remains unchanged, the occurrence of aberration due to decentering is eliminated during tracking. Therefore, it is preferable.
Alternatively, the objective optical element (objective lens) may have the function of the aberration correction element (integrated) (see FIG. 3). Thereby, the number of parts of the optical pickup device can be reduced and the space can be saved.

In the present specification, the “objective optical element” is a collecting element that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. An optical system including at least an optical element. The objective optical element may be composed of only a light condensing element.
Further, when there is another optical element that is integrated with the above-described condensing element and performs tracking and focusing by an actuator, an optical system composed of these optical element and condensing element is called an objective optical element. There is also.

In the above-described optical pickup device, it is one of preferred embodiments that the objective optical element is optimized for spherical aberration correction with respect to the first wavelength λ ₁ and the t ₁ .
The objective optical element preferably has an aspherical shape determined so that spherical aberration correction is minimized with respect to the first wavelength and the thickness of the protective layer of the first optical disc. In the present invention, the first wavelength is transmitted as it is without being affected by the phase structure of the aberration correction element, so that the condensing performance of the first wavelength is determined by the objective optical element. Therefore, by determining the aspherical shape of the objective optical element so that the spherical aberration correction is minimized with respect to the first wavelength and the thickness of the first protective layer, the strictest wavefront accuracy is required. It becomes easy to obtain the condensing performance of one light beam. Here, “the objective optical element is optimized for spherical aberration correction with respect to the first wavelengths λ ₁ and t ₁ ” means that the first light flux passes through the protective layer of the objective optical element and the first optical disc. It shall be said that the wavefront aberration when condensed is 0.05λ ₁ RMS or less.

A fourth aspect of the present invention is an optical disk drive device on which any one of the optical pickup devices described above is mounted.
According to the fourth aspect, it is possible to obtain an optical disk drive device having the same effects as those of the optical pickup device described above.

  According to the present invention, due to the action of the phase structure including the diffractive structure, spherical aberration due to the difference in the protective layer thickness between the high-density optical disc and the DVD and CD, or due to the difference in use wavelength between the high-density optical disc and the DVD and CD. Spherical aberration can be corrected satisfactorily, and high light utilization efficiency can be obtained in any wavelength region of a blue-violet wavelength region near 400 nm, a red wavelength region near 650 nm, and an infrared wavelength region near 780 nm. An optical system that can be used, an optical pickup device that uses the optical system, and an optical disk drive device that includes the optical pickup device can be obtained.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an optical pickup apparatus PU using an optical element (aberration correction element) used in the optical system according to the embodiment of the present invention will be described with reference to FIG.
FIG. 4 is a diagram schematically showing a configuration of an optical pickup apparatus PU capable of appropriately recording / reproducing information for any of the high density optical disc HD, DVD, and CD. The optical specification of HD is the first wavelength λ ₁ = 405 nm, the thickness t ₁ of the protective layer PL1 is 0.1 mm, and the numerical aperture NA1 = 0.85. The optical specification of the DVD is the second wavelength λ ₂ = 655 nm, protective layer PL2 thickness t ₂ = 0.6 mm, numerical aperture NA2 = 0.65, CD optical specifications are third wavelength λ ₃ = 785 nm, protective layer PL3 thickness t ₃ = 1.2 mm and numerical aperture NA3 = 0.50. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU records / reproduces information to / from the blue-violet semiconductor laser LD1 and DVD that emits a 405 nm blue-violet laser beam (first beam) when recording / reproducing information on the HD. The first emission point EP1 that emits a 655 nm red laser beam (second beam) and the 785 nm infrared laser beam (first beam) that is emitted when information is recorded / reproduced on a CD. DVD / CD laser light source unit LU, HD / DVD / CD shared photodetector PD, aberration correcting element SAC, and aberrations formed thereon, on a single chip, the second light emitting point EP2 that emits three light beams). An objective composed of an objective lens OL having aspherical surfaces on both sides, which has a function of condensing the laser beam transmitted through the correction element SAC on the information recording surfaces RL1, RL2, and RL3. An expander lens EXP including a second lens unit OU, a biaxial actuator AC1, a monoaxial actuator AC2, a first lens EXP1 having a negative refractive power in the paraxial axis, and a second lens EXP2 having a positive refractive power in the paraxial axis, Astigmatism with respect to reflected light beams from the first polarizing beam splitter BS1, the second polarizing beam splitter BS2, the first collimating lens COL1, the second collimating lens COL2, the third collimating lens COL3, the information recording surfaces RL1, RL2, and RL3. And a sensor lens SEN for adding. In addition to the blue-violet semiconductor laser LD1 described above, a blue-violet SHG laser can also be used as the HD light source.

  In the optical pickup device PU, when information is recorded / reproduced with respect to the HD, the blue-violet semiconductor laser LD1 is first caused to emit light, as shown by the solid line in FIG. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is converted into a parallel light beam by the first collimating lens COL1, then reflected by the first polarizing beam splitter BS1, passes through the second polarizing beam splitter BS2, and passes through the first lens. After being expanded by passing through EXP1 and the second lens EXP2, the diameter of the light beam is regulated by a stop STO (not shown) and formed on the information recording surface RL1 by the objective lens unit OU via the HD protective layer PL1. Become a spot. The objective lens unit OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light flux modulated by the information pits on the information recording surface RL1 passes through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1 again, When passing through the three collimating lens COL3, it becomes a convergent light beam, is added with astigmatism by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. And the information recorded on HD can be read using the output signal of photodetector PD.

  In addition, when the optical pickup device PU records / reproduces information with respect to a DVD, 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 by the broken line in FIG. 4, and then reflected by the second polarization beam splitter BS2, The diameter is increased by transmitting through the first lens EXP1 and the second lens EXP2, and becomes a spot formed on the information recording surface RL2 via the protective layer PL2 of the DVD by the objective lens unit OU. The objective lens unit OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL2 passes through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1 again, When passing through the three collimating lens COL3, it becomes a convergent light beam, is added with astigmatism by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. And the information recorded on DVD can be read using the output signal of photodetector PD.

  In the optical pickup device PU, when information is recorded / reproduced with respect to a CD, the interval between the first lens EXP1 and the second lens EXP2 is narrower than that during recording / reproduction of information with respect to HD. After the first lens EXP1 is driven in the optical axis direction by the uniaxial actuator AC2, the light emitting point EP2 is caused to emit light. The divergent light beam emitted from the light emission point EP2 is converted into a parallel light beam by the second collimating lens COL2 as depicted by the alternate long and short dash line in FIG. 4, and then reflected by the second polarization beam splitter BS2, By passing through the first lens EXP1 and the second lens EXP2, the diameter is expanded and converted into a divergent light beam, which becomes a spot formed on the information recording surface RL3 by the objective lens unit OU via the CD protective layer PL3. . The objective lens unit OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL2 passes through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and the first polarizing beam splitter BS1 again, When passing through the three collimating lens COL3, it becomes a convergent light beam, is added with astigmatism by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. And the information recorded on CD can be read using the output signal of photodetector PD.

As schematically shown in FIG. 2, the objective lens unit OU in the present embodiment has the smallest spherical aberration with respect to the aberration correction element SAC, the first wavelength λ ₁ and the thickness t ₁ of the HD protective layer PL _1. The objective lens OL, which is a dedicated HD lens whose aspherical shape is designed so as to have the following configuration, is coaxially integrated via the lens frame B. Specifically, 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. It has a configuration.

Next, the configuration of the aberration correction element SAC and the principle of aberration correction will be described. As shown in FIG. 1, the aberration correcting element SAC has a refractive index difference [Delta] n ₁ at the first wavelength lambda _1, the difference .DELTA..nu _d Abbe number at the d-line satisfies the following formula (1) and (2) A diffractive structure DOE as a phase structure having a ring-shaped step is formed on the boundary surface between the two materials, in which a material A that is an ultraviolet curable resin and a material B that is optical glass are laminated. This diffractive structure DOE is a structure for correcting spherical aberration caused by the difference in the protective layer thickness of each optical disc and spherical aberration caused by the difference in the wavelength used for each optical disc. The diffractive structure DOE may have a sawtooth shape as shown in FIG. 1A or a stepped shape as shown in FIG.
| Δn ₁ | <0.01 (1)
20 <| Δν _d | <40 (2)

Now, the diffraction efficiency η (λ) of a diffractive structure sandwiched between two materials having different Abbe numbers (dispersions) is generally the wavelength λ and the refractive indices of the materials A and B at this wavelength λ. As a function of the difference Δn (λ), the step d of the diffractive structure, and the diffraction order M (λ), it is expressed by the following equation (13).
η (λ) = sinc ² [[d · Δn (λ) / λ] −M (λ)] (13)
However, sinc (X) = sin (πX) / (πX), and the value of η (λ) is closer to 1 as the value in [] is closer to an integer.

The difference in refractive index at the first wavelength λ ₁ used for HD is Δn ₁ , the diffraction order of the diffracted light of the first light beam is M ₁ , and the difference in refractive index at the second wavelength λ ₂ used for DVD is Δn ₂ . If the diffraction order of the two-beam diffracted light is M ₂ , the difference in refractive index at the third wavelength λ ₃ used for the CD is Δn ₃ , and the diffraction order of the diffracted light of the third light beam is M ₃ , the diffraction at each wavelength Efficiency η (λ ₁ ), η (λ ₂ ), and η (λ ₃ ) are expressed by the following equations (14) to (16).
η (λ ₁ ) = sinc ² [[d · Δn ₁ / λ ₁ ] −M ₁ ] (14)
η (λ ₂ ) = sinc ² [[d · Δn ₂ / λ ₂ ] −M ₂ ] (15)
η (λ ₃ ) = sinc ² [[d · Δn ₃ / λ ₃ ] −M ₃ ] (16)
In order to ensure high diffraction efficiency at each wavelength, the difference in refractive index Δni (where i is 1, so that the values in [] in Equations (14) to (16) are close to integers). The materials A and B having any one of (2 and 3), the step d, and the diffraction order Mi (i is any one of 1, 2, and 3) may be selected.

Here, in the aberration correction element SAC of the present embodiment, as the materials A and B, materials having the characteristics satisfying the above-described equations (1) and (8) are selected, so the first light flux Does not receive any action by the diffractive structure DOE and passes through as it is (that is, M ₁ = 0 in the equation (14)). In addition, since the materials A and B have characteristics satisfying the above-described expressions (3) and (8), when the second light beam and the third light beam are incident on the diffractive structure DOE, the first-order diffracted light is (That is, M ₂ = M ₃ = 1 in the equations (15) and (16)). Table 1 shows the physical properties of the materials A and B, and FIG. 5 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. 5, by setting the step d of the diffractive structure DOE in the vicinity of 35 μm, a diffraction efficiency (transmittance) as high as 95% can be secured for a light beam of any wavelength.

In this way, by stacking two materials that satisfy the above formulas (1) and (2) and forming a diffractive structure at the boundary surface, the first light flux is not diffracted, and the second light flux The diffractive structure DOE can have a function of selectively diffracting only the third light beam, and the blue-violet laser light beam (first light beam) and the infrared laser light beam (third light beam), which were difficult in the prior art. ) Of the diffracted light can achieve both the effect of correcting the spherical aberration and ensuring the diffraction efficiency (transmittance).
Here, the diffractive power at the paraxial axis of the diffractive structure DOE is negative, and the second and third light beams incident on the diffractive structure DOE are converted into divergent light beams and incident on the objective lens OL. As a result, the back focus of the objective lens unit OU with respect to the second light flux and the third light flux can be extended, so that a sufficient working distance for a DVD or CD with a thick protective layer can be secured. The diffraction power P _D paraxial diffractive structure DOE is a diffractive surface coefficients B ₂ of the second-order optical path difference function φ described below, the diffraction order M of the diffracted light used for recording / reproducing information on an optical disc Thus, P _D = −2 · M · B ₂ is defined.

Note that in the aberration correcting element SAC, diffractive structure DOE is formed only in a region corresponding to the numerical aperture NA2, the spherical aberration due to the difference in thickness of t ₁ and t ₂ is the correction than the numerical aperture NA2 in the outer region Therefore, the second light flux that has passed through the region outside the numerical aperture NA2 becomes a flare component that spreads to a position sufficiently away from the spot formed on the information recording surface RL2 of the DVD by the diffraction structure DOE.
Further, in the aberration correction element SAC, the region corresponding to the numerical aperture NA2 in which the diffractive structure DOE is formed corresponds to the central region corresponding to the numerical aperture NA3 and the numerical aperture NA3 surrounding the central region to the numerical aperture NA2. It is divided into annular zones. Here, the width of the diffraction zone of the diffractive structure formed in the central region is determined so that both the second light beam and the third light beam are condensed on the information recording surface of each optical disk. On the other hand, the diffractive structure formed in the peripheral region focuses only the second light beam on the DVD information recording surface RL2, and the third light beam is sufficiently separated from the spot formed on the information recording surface RL3 of the CD. The width of the diffracting ring zone is determined so as to have a flare component that spreads to a different position.

As described above, the aberration correction element SAC used in the optical pickup device PU according to the present embodiment corresponds to the aperture limiting function corresponding to the numerical aperture NA2 of DVD and the numerical aperture NA3 of CD in addition to the spherical aberration correction function. Since it also has an aperture limiting function, it is possible to simplify the configuration of the optical pickup device and reduce the number of parts.
In this embodiment, the aberration correction element SAC and the objective lens OL are integrated via the lens frame B. However, when the aberration correction element SAC and the objective lens OL are integrated, the aberration correction element SAC and It is only necessary to hold the relative positional relationship with the objective lens OL so as not to change. In addition to the method using the lens frame B as described above, each of the aberration correction element SAC and the objective lens OL is used. A method of fitting and fixing the flange portions may be used.

Since the aberration correction element SAC and the objective lens OL are held in such a manner that the relative positional relationship between the aberration correction element SAC and the objective lens OL remains unchanged, the occurrence of aberration during focusing and tracking can be suppressed, and excellent focusing can be achieved. Characteristics or tracking characteristics can be obtained.
In the present embodiment, the aberration correction element SAC and the objective lens OL are arranged as separate elements. However, as schematically shown in FIG. 4, the function as the aberration correction element SAC is the objective lens OL. A so-called hybrid type objective lens provided in the above may be used instead of the objective lens unit OU.

  Further, the objective lens unit OU of FIG. 2 may be configured to further improve the light condensing performance of the objective lens unit OU by further adding a phase structure different from the diffraction structure DOE. Such a phase structure may be formed on any optical surface of the aberration correction element SAC and the objective lens OL, but is formed on the optical surface of the aberration correction element SAC on the light source side or the optical surface of the optical disk of the aberration correction element SAC. This is preferable for production. As a function to be provided to the phase structure, for example, compensation of an increase in the condensing spot (so-called chromatic aberration) of the objective lens unit OU with a change in wavelength, or an increase in a condensing spot of the objective lens unit OU with a temperature change (so-called , Temperature aberration) compensation.

  Further, by driving the first lens EXP1 of the expander lens EXP in the optical axis direction by the uniaxial actuator AC2, the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected. The cause of the spherical aberration to be corrected by adjusting the position of the first lens EXP1 is, for example, wavelength variation due to manufacturing error of the blue-violet semiconductor laser LD1, refractive index change or refractive index distribution of the objective lens system due to temperature change, double-layer disk For example, focus jump between information recording layers of a multi-layer disc such as a four-layer disc, thickness variation or thickness distribution due to manufacturing error of an HD protective layer, and the like. Note that the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected even if the second lens EXP2 or the first collimating lens COL1 is driven in the optical axis direction instead of the first lens EXP1.

In the above description, 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, but on the DVD information recording surface RL2. Further, it is possible to correct the spherical aberration of the spot formed on the CD and further the spherical aberration of the spot formed on the information recording surface RL3 of the CD.
Further, in the present embodiment, the DVD / CD laser light source unit LU in which the first light emission point EP1 and the second light emission point EP2 are formed on one chip is used. Further, a single-chip laser light source unit for HD / DVD / CD having a light emitting point for emitting a laser beam having a wavelength of 405 nm for HD formed on the same chip may be used. Alternatively, a one-can laser light source unit for HD / DVD / CD 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.

In the present embodiment, the light source and the photodetector PD are arranged separately. However, the present invention is not limited to this, and a laser light source module in which the light source and the photodetector are integrated may be used.
Although not shown, the optical pickup device PU shown in the above embodiment, the rotational drive device that holds the optical disc rotatably, and the control device that controls the drive of these various devices are mounted, so An optical disk drive device capable of executing at least one of recording information and reproducing information recorded on the optical disk can be obtained.

Further, in the present embodiment, the case where the diffractive structure DOE is formed only at the boundary surface between the material A and the material B has been described as an example. However, as shown in FIG. A diffractive structure may also be formed at the interface between the material having a larger Abbe number in the line and air. As described above, since the diffractive structure is formed on the boundary surface between the material having the larger Abbe number in the d-line and air, the wavelength λ of each of the first light flux, the second light flux, and the third light flux. _The diffraction efficiency for ₁ , λ ₂ and λ ₃ can be increased.

Further, as shown in FIG. 8, the objective lens (objective optical element) disposed on the disk side has an Abbe number ν _{d of} d-line satisfying 40 ≦ ν _d ≦ 70, and the surface of the objective lens A diffractive structure may be formed.
In this way, since the Abbe number ν _d of the d line in the objective lens arranged on the disk side satisfies the above formula and a diffractive structure is formed on the surface of the objective lens, the first light flux and the second light flux The diffraction efficiencies for the wavelengths λ ₁ , λ ₂ , and λ ₃ of the third light flux can be increased.

These diffractive structures may be wavelength selective diffractive structures or blazed diffractive structures.
For example, if the diffractive structure is a wavelength selective diffractive structure, a phase difference can be given only to a light beam of a predetermined wavelength, a diffractive action can be given only to the DVD light, and the remaining DVD spherical surface. Aberration can be corrected.
On the other hand, if the diffractive structure is a blazed diffractive structure, chromatic aberration correction is effective.
Further, when the diffraction structure is provided in addition to the boundary surface between the material A and the material B as described above, the thickness t ₂ of the protective layer PL2 of the DVD is set to 0.9 × t ₁ ≦ t ₂ ≦ 1.1 × t. If it is set to satisfy ₁ , it only corrects the spherical aberration caused by the difference in wavelength as in the combination of HD DVD and DVD, so that the diffraction pitch can be increased and the workability is improved. Can do.

[Example 1]
Next, specific numerical examples of the objective lens unit OU including the aberration correction element SAC and the objective lens OL shown in FIG. 2 will be illustrated. The aberration correction element SAC has an attack of laminating the material A, which is an ultraviolet curable resin, and the material B, which is a glass lens (BACD5 manufactured by HOYA), and a diffraction structure DOE is formed at the boundary between the material A and the material B. ing. The objective lens OL is a glass lens exclusively for HD (BACD5 manufactured by HOYA), but may be a plastic lens.
The lens data of Example 1 is shown in Table 2, the specifications are shown in Table 3, and the optical path diagram is shown in FIG. In this numerical example, the optical path difference added to the incident light beam by the diffractive structure DOE is represented by an optical path difference function. Also, the diffraction structure DOE is not shown in the optical path diagram of FIG.

In Table 2, r (mm) is a radius of curvature, d (mm) is a lens interval, and n ₄₀₅ , n ₆₅₅ , and n ₇₈₅ are a first wavelength λ ₁ (= 405 nm) and a second wavelength λ ₂ (= 655 nm, respectively. ), The refractive index of the lens for the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , and M _CD are the diffracted light used for recording / reproducing with respect to HD The diffraction order of diffracted light used for recording / reproduction with respect to a DVD, and the diffraction order of diffracted light used for recording / reproduction with respect to a CD. Further, a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E-3).
In Table 3, the numerical aperture NA1 of the objective lens unit OU when using HD is 0.85, the effective diameter of the first surface (S1) is 3.74 mm, the magnification is 0, and the objective lens unit when using DVD Has a numerical aperture NA2 of 0.65, an effective diameter of the first surface (S1) of 2.94 mm, and a magnification of 0. The numerical aperture NA3 of the objective lens unit when using a CD is 0.50, and the first surface (S1) ) Has an effective diameter of 2.32 mm and an optical system magnification of -1 / 22.28. In this embodiment, 0, 1, and 1 were selected as M _HD , M _DVD, and M _CD , respectively. Therefore, the magnification when using the CD when the spherical aberration due to the difference in the protective layer thickness of HD and CD was corrected. Can be set small, and even when the objective lens unit OU is shifted 0.5 mm in the direction perpendicular to the optical axis, the wavefront aberration is as good as about 0.05λ ₃ RMS. In the optical pickup device, since the tracking amount of the objective lens unit OU is about ± 0.5 mm, it can be said that the objective lens unit OU of the present embodiment has a good tracking characteristic with respect to the CD.

The optical surface on the light source side (fourth surface) and the optical surface on the optical disc side (fifth surface) of the objective lens OL are aspherical, and these aspherical surfaces are shown in the following aspherical shape formulas in Tables 2 and 3. It is expressed by a mathematical formula with the coefficient inside.
[Aspherical expression]
z = (y ² / R) / [1 + √ {1- (Κ + 1) (y / R) ² }] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + A ₁₂ y ¹² + A ₁₄ y ¹⁴ + A ₁₆ y ¹⁶ + A ₁₈ y ¹⁸ + A ₂₀ y ²⁰
However,
z: Aspherical shape (distance in the direction along the optical axis from the apex of the aspherical surface)
y: Distance from optical axis R: Radius of curvature Κ: Conic coefficient A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , A ₁₆ , A ₁₈ , A ₂₀ : Aspheric coefficient

Further, the diffractive structure DOE formed on the boundary surface 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 φ (mm) obtained by substituting the coefficients shown in Tables 2 and 3 into an expression representing the following optical path difference function.
[Optical path difference function]
φ = λ × M × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
However,
φ: optical path difference function λ: wavelength of light beam incident on the diffractive structure M: diffraction order of diffracted light used for recording / reproducing with respect to the optical disk y: distances B ₂ , B ₄ , B ₆ , B ₈ , B from the optical axis ₁₀ : Diffraction surface coefficient

[Example 2]
Next, as Example 2, Table 4 shows lens data in the case where a diffractive structure is also provided on the interface between the material having a larger Abbe number on the d-line shown in FIG.

As shown in Table 4, the focal length f ₁ = 2.60 mm when the wavelength λ ₁ = 407 nm and the magnification m 1 = 0 are set in this embodiment, and the focal length f ₂ when the wavelength λ ₂ = 655 nm. = 2.65 mm, magnification m2 = 0, focal length f ₃ = 2.70 mm when wavelength λ ₃ = 785 nm, magnification m3 = 0.
Further, the refractive index nd of the material A at the d-line = 1.5891, the Abbe number ν _d = 61.3 at the d-line, the refractive index nd = 1.5737 at the d-line of the material B, and the Abbe number ν _{d at the d} -line = The refractive index nd of the lens material of the objective lens OL is set to nd = 1.5891, and the Abbe number ν _d of the d line is set to 61.3.

The optical surface on the light source side (fifth surface) and the optical surface on the optical disc side (sixth surface) of the objective lens OL are aspherical, and this aspherical surface is expressed by the following aspherical shape formula with the coefficients in Table 4 It is expressed by a mathematical formula that substitutes.
[Aspherical expression]
z = (y ² / R) / [1 + √ {1- (Κ + 1) (y / R) ² }] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + A ₁₂ y ¹² + A ₁₄ y ¹⁴

Further, the diffraction structure DOE formed on the boundary surface (third surface) between the material A and the material B, and the diffraction structure DOE2 formed on the boundary surface (second surface) between the material A and the air are respectively the diffraction structure DOE. , DOE2 is represented by the optical path difference added to the incident light beam. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficient in Table 4 into an expression representing the next optical path difference function.
[Optical path difference function]
Diffraction structure DOE
φ = λ × M × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
Diffraction structure DOE2
φ = λ × M × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ )
Since M is the diffraction order here, in the case of the diffractive structure DOE on the third surface, 0 is substituted for HD DVD, 1 for DVD, 0 for CD, and diffractive structure DOE2 on the second surface. Is substituted for HD DVD, 1 for DVD, and 0 for CD.

[Example 3]
Next, as Example 3, Table 5 shows lens data when a diffractive structure is also provided on the surface of the objective lens shown in FIG.

As shown in Table 5, in this embodiment, the focal length f ₁ = 2.60 mm when the wavelength λ ₁ = 407 nm and the magnification m 1 = 0 are set, and the focal length f when the wavelength λ ₂ = 655 nm. ₂ = 2.65 mm, the magnification m2 = 0, the focal length f ₃ = 2.70 mm when the wavelength λ ₃ = 785 nm, and the magnification m3 = 0.
Further, the refractive index nd of the material A at the d-line = 1.5891, the Abbe number ν _d = 61.3 at the d-line, the refractive index nd = 1.5737 at the d-line of the material B, and the Abbe number ν _{d at the d} -line = The refractive index nd of the lens material of the objective lens OL is set to nd = 1.5891, and the Abbe number ν _d of the d line is set to 61.3.

The optical surface on the light source side (fifth surface) and the optical surface on the optical disc side (sixth surface) of the objective lens OL are aspherical, and this aspherical surface is a coefficient in Table 5 given by It is expressed by a mathematical formula that substitutes.
[Aspherical expression]
z = (y ² / R) / [1 + √ {1- (Κ + 1) (y / R) ² }] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + A ₁₂ y ¹² + A ₁₄ y ¹⁴

Further, the diffractive structure DOE formed on the boundary surface (third surface) between the material A and the material B and the diffractive structure DOE3 formed on the surface (fifth surface) of the objective lens OL are respectively determined by the diffractive structures DOE and DOE3. It is represented by the optical path difference added to the incident light beam. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficient in Table 5 into an expression representing the following optical path difference function.
[Optical path difference function]
Diffraction structure DOE
φ = λ × M × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
Diffraction structure DOE3
φ = λ × M × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ )
Since M is the diffraction order here, in the case of the diffractive structure DOE on the third surface, 0 is substituted for HD DVD, 1 for DVD, 1 for CD, and diffractive structure DOE3 on the fifth surface. Is substituted for HD DVD, 1 for DVD, and 0 for CD.

It is side view (a) and (b) which show the structure of an aberration correction element. It is a side view which shows an example of a structure of an objective lens unit (optical system). It is a side view which shows an example of a structure of an objective lens unit (optical system). It is a principal part top view which shows the structure of an optical pick-up apparatus. It is a graph which shows the relationship between the depth of the level | step difference of a diffraction structure, and diffraction efficiency. It is drawing which shows the optical path with respect to an objective lens unit (optical system). It is a side view which shows an example of a structure of an objective lens unit (optical system). It is a side view which shows an example of a structure of an objective lens unit (optical system).

Explanation of symbols

DOE diffraction structure OL objective lens (objective optical element)
OU Objective lens unit (optical system)
PU optical pickup device SAC Aberration correction element (optical element)

Claims (21)

Performs recording and / or reproducing information for the first optical disk having a protective layer with a thickness of t ₁ using a first first light flux with wavelength lambda ₁ emitted from the first light source is emitted from the second light source Information is recorded and / or reproduced on a second optical disc having a protective layer having a thickness t ₂ (≧ t ₁ ) using a second light beam having a second wavelength λ ₂ (> λ ₁ ). Information recording and / or reproduction is performed on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using a third light beam having a third wavelength λ ₃ (> λ ₂ ) emitted from the light source. An optical system that is used in an optical pickup device to perform and has at least one optical element,
The optical element is disposed in an optical path through which the first light beam, the second light beam, and the third light beam pass in common, and is formed by stacking materials A and B having different Abbe numbers in the d-line. A phase structure having a ring-shaped step is formed on the boundary surface between the material A and the material B,
The optical system is characterized in that the phase structure does not have an aberration correction function for the first light beam and has an aberration correction function for the second light beam and the third light beam. Performs recording and / or reproducing information for the first optical disk having a protective layer with a thickness of t ₁ using a first first light flux with wavelength lambda ₁ emitted from the first light source is emitted from the second light source Information is recorded and / or reproduced on a second optical disc having a protective layer having a thickness t ₂ (≧ t ₁ ) using a second light beam having a second wavelength λ ₂ (> λ ₁ ). Information recording and / or reproduction is performed on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using a third light beam having a third wavelength λ ₃ (> λ ₂ ) emitted from the light source. An optical system that is used in an optical pickup device to perform and has at least one optical element,
Optical element, the the difference [Delta] n ₁ of the refractive index in the first wavelength lambda _1, the difference .DELTA..nu _d Abbe number at the d-line, respectively, material A and material satisfying the following formula (1) and (2) An optical system characterized in that a phase structure having a ring-shaped step is formed on the boundary surface between the material A and the material B.
| Δn ₁ | <0.01 (1)
20 <| Δν _d | <40 (2)   The phase structure is a first diffractive structure, and the first diffractive structure does not diffract the first light beam, but diffracts the second light beam and the third light beam. The optical system described. The optical system according to claim 3, wherein the following expressions (3) and (4) are satisfied.
0 <| INT (d · Δn ₂ / λ ₂ ) − (d · Δn ₂ / λ ₂ ) | <0.3 (3)
0 <| INT (d · Δn ₃ / λ ₃ ) − (d · Δn ₃ / λ ₃ ) | <0.3 (4)
However,
d: Step difference of the phase structure Δn ₂ : Difference in refractive index between the material A and material B at the λ ₂ Δn ₃ : Difference in refractive index between the material A and the material B at the λ ₃ INT (X): Integer obtained by rounding to the first decimal place The optical system according to claim 4, wherein the following expression (5) is satisfied.
M ₂ = M ₃ (5)
However,
M ₂ = INT (d · Δn ₂ / λ ₂ ) (6)
M ₃ = INT (d · Δn ₃ / λ ₃ ) (7) The optical system according to claim 5, wherein the following expression (8) is satisfied.
M ₂ = M ₃ = 1 (8)   4. The second diffractive structure is formed on a boundary surface between the material A and the material B having a larger Abbe number in the d-line and air. The optical system according to item. The optical system has an objective optical element on the optical disc side of the optical element, and the objective optical element has an Abbe number ν _{d of} d-line satisfying the following formula (9), and the surface of the objective optical element is The optical system according to claim 1, wherein a second diffractive structure is formed.
40 ≦ ν _d ≦ 70 (9)   9. The optical system according to claim 7, wherein at least one of the second diffractive structures is a diffractive structure having a plurality of step shapes in cross section, and selectively diffracts or transmits light according to a wavelength.   9. The optical system according to claim 7, wherein the second diffractive structure is a blazed diffractive structure. The optical system according to claim 7, wherein the following expression (10) is satisfied.
0.9 × t ₁ ≦ t ₂ ≦ 1.1 × t ₁ (10)   The optical system according to any one of claims 1 to 11, wherein one of the material A and the material B is an optical glass and the other is an optical resin.   The optical system according to claim 12, wherein the optical resin is an ultraviolet curable resin.   The optical system according to claim 12 or 13, wherein the optical glass is manufactured by molding. The optical system according to any one of claims 1 to 14, wherein the following expressions (11) and (12) are satisfied.
α × λ ₁ = λ ₃ (11)
K1-0.1 ≦ α ≦ K1 + 0.1 (12)
However,
K1: Natural number   The optical system according to any one of claims 1 to 3, wherein the optical element is an objective optical element. A first light source that emits a first light flux having a first wavelength λ ₁ ;
A second light source that emits a second light flux having a second wavelength λ ₂ (> λ ₁ );
A third light source that emits a third light flux having a third wavelength λ ₃ (> λ ₂ );
And an optical system according to any one of claims 1 to 14,
And
Information is recorded and / or reproduced with respect to the first optical disc having the protective layer having the thickness t ₁ using the first light beam, and the thickness t ₂ (≧ t ₁ ) is protected using the second light beam. Recording and / or reproducing information on a second optical disc having a layer, and recording and / or reproducing information on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using the third light flux An optical pickup device that performs reproduction.   The optical pickup device according to claim 17, wherein the optical system includes the optical element and an objective optical element disposed on the optical disk side of the optical element.   The optical pickup device according to claim 17, wherein the optical element is an objective optical element. The optical pickup device according to claim 19, wherein the objective optical element is optimized for spherical aberration correction with respect to the first wavelength λ ₁ and the t ₁ .   21. An optical disc drive apparatus comprising the optical pickup device according to any one of claims 17 to 20.

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