WO2005117002A1

WO2005117002A1 - Objective optical system, optical pickup device, and optical disc drive device

Info

Publication number: WO2005117002A1
Application number: PCT/JP2005/008983
Authority: WO
Inventors: Tohru Kimura; Yuichi Atarashi
Original assignee: Konica Minolta Opto, Inc.
Priority date: 2004-05-27
Filing date: 2005-05-17
Publication date: 2005-12-08
Also published as: JP4483864B2; JPWO2005117002A1

Abstract

An objective optical system is used in an optical pickup device for recording and/or reproducing information by using a first light flux emitted from a first light source, a second light flux emitted from a second light source, and a third light flux emitted from a third light source. The objective optical system includes a first and a second aberration correction element and an objective lens for focusing the first to the third light flux which have passed through the first and the second aberration correction element onto the information recording surface of the first to the third optical disc. The first aberration correction element has a fist phase structure formed by a material having the Abbe constant νd1 on the d line satisfying 40 ≤ νd1 ≤ 80 while the second aberration correction element has a second phase structure formed by a material having the Abbe constant νd2 on the d line satisfying 20 ≤ νd2 < 40.

Description

Specification

Objective optical system, optical pickup device, and optical disk drive:

Technical field

TECHNICAL FIELD [0001] The present invention relates to an objective optical system, an optical pickup device, and an optical disk drive device.

[0002] Compatible with high-density optical disks, DVDs (using a red laser light source), and CDs (using an infrared laser light source), whose recording density has been increased by using a blue-violet laser light source. BACKGROUND ART An optical pickup device and an optical element used for such an optical pickup device are known (for example, see Patent Documents:! To 3).

Patent Document 1: JP 2004-079146 A

Patent Document 2: Japanese Patent Application Laid-Open No. 2002-298422

Patent Document 3: JP 2003-207714 A

[0003] 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 an infrared laser beam generate first-order diffracted light on the surface of an 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. Furthermore, when recording information on a CD, the divergent light beam is applied to the objective lens during Z playback. There is disclosed an objective lens that corrects spherical aberration caused by a difference in protective layer thickness between a high-density optical disc and a CD by being incident.

[0004] In this objective lens, although high diffraction efficiency can be ensured 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 objective lens tracks. In this case, there is a problem that good recording / reproducing characteristics cannot be obtained for a CD because the occurrence of coma aberration becomes too large.

[0005] Further, in Numerical Example 3 of Patent Document 2, third-order diffracted light is generated by a blue-violet laser beam on the surface of an objective lens, and second-order diffracted light is generated by a red laser beam and an infrared laser beam. There is disclosed an objective lens which is provided with a diffractive structure for correcting spherical aberration due to a difference in the thickness of a protective layer between a high-density optical disk, a DVD and a CD. [0006] In this objective lens, 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. Although possible, the diffraction efficiency of the third-order diffracted light of the blue-violet laser light beam and the diffraction efficiency of the second-order diffracted light of the infrared laser light beam are as low as about 70%, so that the recording / reproducing speed for optical discs can be increased. It is not possible to obtain good recording / reproducing characteristics due to the low S / N ratio of the detection signal from the photodetector, or to shorten the life of the laser light source due to the high voltage applied to the laser light source. There is a problem.

[0007] In the objective lens described in Patent Document 1, it is impossible to correct the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and the CD due to the diffractive structure. The reason why the diffraction efficiency of the third-order diffracted light of the above and the diffraction efficiency of the second-order diffracted light in the infrared wavelength region is low is that the wavelength of the blue-violet laser light source used for high-density optical discs Since the wavelength of the laser light source is almost twice, the spherical aberration correction effect on 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 with each other. It is mentioned that there is.

[0008] That is, 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 beam and the diffraction angle of the diffracted light of the infrared laser beam almost coincide, the diffraction structure corrects the spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and the CD. You can't.

On the other hand, in the objective lens of Numerical Example 3 of Patent Document 2, which 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, Both the diffraction efficiency of the diffracted light of the blue-violet laser beam and the diffraction efficiency of the infrared laser beam will be low.

[0010] It should be noted that a phase corrector (hereinafter referred to as an optical path difference providing structure) described in Patent Document 3 is used instead of only the diffraction structures described in Patent Documents 1 and 2. In the technology as well, similarly to the diffraction structure, the spherical aberration correction effect on 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 mutually different. There is a trade-off relationship.

Disclosure of the invention

The present invention has been made in view of the above-mentioned problems, and has a spherical aberration due to a difference in protective layer thickness between a high-density optical disc, a DVD, and a CD due to the action of a phase structure including a diffractive structure. Is capable of satisfactorily correcting spherical aberration due to the difference in wavelength used between high-density optical discs, DVDs, and CDs, as well as a blue-violet wavelength region near 400 nm, a red wavelength region near 650 nm, and a blue wavelength region near 780 nm. An objective optical system capable of obtaining high light use efficiency in any wavelength region including the infrared wavelength region, an optical pickup device using the objective optical system, and an optical disk drive device equipped with the optical pickup device The purpose is to provide.

[0012] The configuration according to item 1 is characterized in that the thickness t is determined by using the first wavelength emitted from the first light source;

Performs recording and Z or reproduction of information on the first optical disc having the protective layer of 11 and a second wavelength emitted from the second light source; using a second light flux of I (> λ) to obtain a thickness t ( ≥t) protective layer

2 1 2 1

Recording and / or reproducing information on / from a second optical disk having a thickness t (> t) using a third light beam of a third wavelength λ (> λ) emitted from a third light source. Third with

3 2 3 2

An objective optical system used in an optical pickup device that records and / or reproduces information on an optical disc, wherein the objective optical system includes a first aberration correction element, a second aberration correction element, (1) An objective lens for converging the first to third light beams passing through the aberration correction element and the second aberration correction element on the information recording surfaces of the first to third optical disks, respectively. The first aberration correction element has a first phase structure made of a material having an Abbe number V1 at d-line that satisfies the following equation (1).

The second aberration correction element is made of a material whose Abbe number V 2 at d-line satisfies the following equation (2):

A second phase structure formed from the material.

[0013] 40≤ V 1≤80 (1)

d

20≤ V 2 40 (2)

d

When the first phase structure and the second phase structure are made of a material having an Abbe number that satisfies the equations (1) and (2), the blue-violet laser light flux and the red laser light flux, which are difficult with the related art, are obtained. While maintaining high transmittance for any wavelength of the infrared laser beam, Mutual compatibility between high-density optical discs and DVDs and CDs can be realized.

When the Abbe number of the first phase structure decreases below the lower limit of the equation (1), the transmittance of the first phase structure for the third wavelength λ 3 increases, but the transmittance of the first phase structure for the second wavelength λ 2 increases. (1) It is preferable because the transmittance of the phase structure is reduced. On the other hand, a material whose Abbe number is larger than the upper limit of the equation (1) is not realistic because the production becomes difficult.

When the Abbe number of the first phase structure increases beyond the upper limit of the expression (2), the transmittance of the second phase structure for the second wavelength λ 2 increases, but the transmittance of the second phase structure for the third wavelength λ 3 increases. This is preferable because the transmittance of the two-phase structure is reduced. On the other hand, if the Abbe number is smaller than the lower limit of the equation (2), it is not practical because the material is difficult to manufacture.

In this specification, a 0.85 mm objective lens and a protective layer thickness of 0.1 mm are used for a Blu-ray disc or NA 0.65 to 0.67 objective lens. Optical disks that use a blue-violet laser light source, such as HD DVDs with a diameter of 0.6 mm, are collectively called “high-density optical disks” and abbreviated as “HD”. In addition to the Blu-ray Disc HD DVD mentioned above, a magneto-optical disc, an optical disc having a protective film with a thickness of several to several tens nm on the information recording surface, or an optical disc having a protective layer or a protective film of zero thickness Is included in the high-density optical disk.

[0017] In this specification, a DVD (digital versatile disc) is a DVD-RM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD_RW, DV D + R, DVD + A generic term for DVD-type optical discs such as RW, and CD (compact disc) is a generic term for optical discs in the CD series such as CD-ROM, CD-Audio, CD-Video, CD-R, and CD-RW. It is.

Further, in the present specification, the “objective lens” is a lens disposed at a position facing the optical disk in the optical pickup device, and emits the light flux emitted from the light source to the optical disk. Refers to a condenser lens that has the function of collecting light on the information recording surface.

Further, in this specification, the “objective optical system” refers to the above-described condensing lens, a first aberration correction element that performs tracking and focusing by an actuator integrated with the converging lens, and a second condensing lens. Refers to an optical system composed of an aberration correction element.

[0020] In this specification, the "phase structure" has a plurality of steps in the optical axis direction, This is a general term for a structure that adds an optical path difference (phase difference) to a bundle. 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 a non-integer multiple of the wavelength of the incident light beam. Specific examples of such a phase structure include a diffractive structure in which the steps are arranged at periodic intervals in the direction perpendicular to the optical axis, and a diffraction structure in which the steps are arranged at non-periodic intervals in the direction perpendicular to the optical axis. An optical path difference providing structure (also referred to as a phase difference providing structure) is arranged.

The phase structure can have various cross-sectional shapes as schematically shown in FIGS. 7 (a) to 12 (b).

FIGS. 7 (a) and 7 (b) show the case where the shape is a sawtooth shape, and FIGS. 8 (a) and 8 (b) show the case where the steps are all in the same direction and FIG. Figures a) and 9 (b) show the case where the direction of the step is stepwise, with the direction of the step being reversed in the middle. FIGS. 10 (a) and 10 (b) show a step-shaped pattern 11 including a plurality of level surfaces 12 arranged concentrically, and a predetermined number of level surfaces (FIGS. 10 (a) and 10 (b)). In each case, the steps are shifted by the height corresponding to the number of levels (four steps in FIGS. 10 (a) and 10 (b)) every 5 levels in (b).

[0022] Figs. 7 (a) and 7 (b) show the case where the direction of each saw tooth is the same, and Figs. 10 (a) and 10 (b) show that the direction of each pattern having a stepped cross section is Although the same case is shown, as shown in FIGS. 11 (a) and 11 (b) and FIGS. 12 (a) and 12 (b), the phase inversion portion PR and the closer to the optical axis than the phase inversion portion PR There may be a sawtooth whose direction is opposite to the sawtooth on the side or a pattern whose direction is opposite to the pattern closer to the optical axis than the phase inversion portion PR. FIGS. 7 (a) to 12 (b) show the case where each structure is formed on a plane, but each structure may be formed on a spherical surface or an aspherical surface. In addition, in 010 (a), 10 (b), 12 (a), and 12 (b), the force having a predetermined number of level faces is not limited to five.

Brief Description of Drawings

FIG. 1 is a plan view of a principal 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 cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.

FIG. 8 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.

FIG. 9 is cross-sectional views (a) and (b) showing an example of a configuration of a phase structure.

FIG. 10 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.

FIG. 11 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.

FIG. 12 is cross-sectional views (a) and (b) showing an example of the configuration of a phase structure.

FIG. 13 is a side view showing an example of the configuration of the objective lens unit.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described.

Item 2 is the objective optical system according to Item 1, wherein the first phase structure of the first aberration correction element has a refractive index n 1 at d-line represented by the following expression (3): Filling resin d

And the second phase structure included in the second aberration correction element is formed of a resin whose refractive index n 2 at d-line satisfies the following expression (4).

d

[0026] 1.48≤n 1 1 57 (3)

d

1.57≤n 2≤1.65 (4)

d

Generally, a resin for an optical element has a refractive index n of 1.48 to d at d-line (587.6 nm).

1. Distributed between 65, the higher the n, the greater the variance (the lower the Abbe number) d

Tend. Therefore, when both the first phase structure and the second phase structure are made of resin as in the configuration described in Item 2, the first phase structure and the second phase structure are made of a material having n that satisfies the equations (3) and (4). d

By doing so, it is possible to achieve the same functions and effects as in item 1.

[0027] The configuration according to Item 3 is the objective optical system according to Item 1 or 2, wherein the first phase structure is a spherical aberration caused by a difference between the first and the second wavelengths or the first wavelength λ and the first wavelength λ. 2 wavelength

1 2 1

Correct the spherical aberration caused by the difference of λ.

2

[0028] As described in item 3, the first phase structure formed of the material satisfying the formula (1) or (3) formed in the first aberration correction element makes the high-density optical disc and DVD compatible with each other. In this way, while maintaining high transmittance for both the blue-violet laser beam and the red laser beam, the spherical aberration due to the difference between t and t, or the first wavelength λ and the second wavelength λ In the difference

It becomes possible to correct spherical aberration caused by 1 2 1 2. The first phase structure may be a diffraction structure or an optical path difference providing structure.

[0030] The configuration described in Item 4 is the objective optical system according to Item 3, wherein the first phase structure does not diffract the first light beam and the third light beam but diffracts the second light beam. Structure

[0031] In particular, since the first phase structure is a diffractive structure that selectively diffracts only the second light beam as described in item 4, it is possible to independently control the aberration with respect to the second light beam, and to achieve high density. Good light-collecting characteristics are obtained for both optical disks and DVDs.

[0032] Item 5 is the objective optical system according to Item 4, wherein the first phase structure is a structure in which a pattern having a stepped cross section including an optical axis is arranged on a concentric circle. Therefore, for each predetermined number A of level surfaces, the level is shifted by a height corresponding to the number of levels corresponding to the number of level surfaces.

[0033] Specifically, by adopting the configuration as described in Item 5, it becomes possible to give the first phase structure the diffraction characteristics as described in Item 4.

When a light source deviating from the design wavelength is used as the first light source, the optical path difference added by each step constituting each pattern slightly deviates from an integral multiple of the wavelength. In one pattern, the wavefront having the local spherical aberration is interrupted at the position where the steps are shifted by the height corresponding to the number of power level planes at which local spherical aberration occurs, causing local spherical aberration. The macroscopic wavefront becomes flat. In this manner, by making the first phase structure a structure in which the steps are shifted by a height corresponding to the number of steps corresponding to the number of level surfaces, the tolerance for the individual difference in the oscillation wavelength of the first light source can be reduced.

[0035] In this specification, a diffraction structure having a property of selectively diffracting one of the first to third light beams is hereinafter referred to as a "wavelength selective diffraction structure".

[0036] In the configuration according to Item 6, in the objective optical system according to Item 5, the number A of the predetermined level surfaces is any one of 4, 5, and 6, and The resulting optical path difference is twice the first wavelength I.

1

[0037] More specifically, by adopting the configuration as described in the item 6, it becomes possible to give the first phase structure the diffraction characteristics as described in the item 4, and also to the three light beams High transmittance can be secured. In order to ensure the highest transmittance for the three luminous fluxes, the required level Preferably, the number A is 5.

Here, the principle of generation of diffracted light will be described for a wavelength-selective diffraction structure (first phase structure) that selectively diffracts the second light beam without diffracting the first light beam and the third light beam. In the following description, the first wavelength λ is 405 nm, which is the recording / reproducing wavelength of the high-density optical disc HD, the second wavelength I is 655 nm, which is the recording / reproducing wavelength of the DVD, and the third wavelength λ is the recording / reproducing of the CD.

23 It is 785 nm, which is the raw wavelength. Here, the first phase structure needs to satisfy the following equations (8) to (13).

[0039] Ll = A l-(n ~ 1) / λ (8)

φ (Ml) = ΙΝΤ (Α1)-(Α1) (11)

-0.4 <4 (Μ1) <0.4 (12)

Ll = 2 (13)

Α = 4, 5, or 6 (14)

ΙΝΤ (Χ): Integer closest to Χ

However,

Δ1: depth in the optical axis direction of each step constituting each pattern of the first phase structure η: refractive index of the material forming the first phase structure with respect to the first wavelength;

11

η: refractive index of the material forming the first phase structure for the second wavelength λ 2

12

η: third wavelength; refractive index of the material forming the first phase structure for 13

13

A: Number of level surfaces formed in each pattern of the first phase structure

Ll, Ml, and N1 are optical path differences in wavelength units added to the first light flux, the second light flux, and the third light flux by each step formed in each pattern of the first phase structure. . When L1 is 2, the optical path difference L1 added to the first light beam due to the step Δ1 is twice the first wavelength; I, so that the first The wavefront of the light beam is exactly

1

The connection is shifted by two wavelengths. Therefore, the first light beam is transmitted as it is at a transmittance of 100% without being subjected to diffraction by the first phase structure. Further, when the first phase structure is formed from a material whose Abbe number V 1 at the d-line satisfies the above equation (1), the step Δ The optical path difference Nl added to the third luminous flux by 1 is very close to one time of the third wavelength; I.

Three

Therefore, the wavefronts of the third luminous flux passing through the level surfaces that are in tangent to each other are connected by being shifted by one wavelength. Therefore, the third light beam is also transmitted as it is with almost 100% transmittance which is not affected by the diffraction effect by the first phase structure. On the other hand, the optical path difference Ml applied to the second luminous flux by the step Δ1 is about 1.2 times the second wavelength; I, so that the adjacent level surfaces

2

The wavefront of the passing second light beam is shifted by 1.2 wavelengths, but the actual wavefront shift is 0.2 wavelength excluding the shift of one wavefront that is optically in phase. . Here, if each pattern is composed of five level planes, the deviation of the wavefront at both ends of each pattern is about 1 wavelength (= 0.2 wavelength X 5), so the second light flux is about 87% high diffraction Efficiency is diffracted in the first order (first order diffraction). The above equation (12) is a conditional equation for increasing the diffraction efficiency of the first-order diffracted light of the second light flux, and the number of level surfaces A formed in each pattern is set so as to satisfy the equation (12). By determining the value, it is possible to sufficiently secure the diffraction efficiency of the first-order diffracted light of the second light flux. The Abbe number V1 at the d-line is the above-mentioned (1)

d

When formed from a material that satisfies the equation, it is possible to satisfy equation (12) with any of A = 4, 5, and 6, but the value of equation (12) is closest to 0 when A = 5 At this time, the diffraction efficiency of the first-order diffracted light of the second light flux becomes highest.

In the above-described wavelength-selective diffraction structure, the diffraction efficiency of the diffracted light of the second light beam depends only on the Abbe number V 1 at the d-line of the material from which the wavelength-selective diffraction structure is formed. To

d

Which does not depend on the refractive index n 1. Therefore, the refractive index n 1 has a relatively high degree of freedom.

d d

However, as the value of the refractive index _n 1 decreases, the depth dl of each step in the optical axis direction increases,

d

Since it is difficult to manufacture the shape with high accuracy, materials having the same Abbe number V1

d

If there are, it is preferable to select the material with the largest n1.

d

[0041] The configuration according to Item 7 is the objective optical system according to Item 3, wherein the first phase structure generates first-order diffracted light when the first light beam enters, and When two light beams are incident, a / 3 1 (1 <1) order diffracted light is generated.When the third light beam is incident, a Ύ 1 ( _Ύ 1 ≤ β 1) order diffracted light is generated. Diffraction structure.

[0042] In order to make the high-density optical disk and DVD compatible with each other by the first phase structure, in addition to the diffraction characteristics described in Item 4, the first phase structure has the diffraction characteristics described in Item 7 Let me good. By providing such diffraction characteristics, a high transmittance can be secured for three light beams. The diffraction structure having such diffraction characteristics has a saw-tooth shape or a step-like shape in cross section including the optical axis. When the cross-sectional shape including the optical axis has a sawtooth shape, the absolute value of the refractive power of the optical surface on which the first phase structure is formed and the absolute value of the diffraction power of the first phase structure are different from each other. The case where the cross-sectional shape includes a step-like shape is a case where the signs of the refractive power of the optical surface on which the first phase structure is formed and the diffraction power of the first phase structure are opposite to each other and the absolute values are the same.

[0043] In the configuration described in Item 8, in the objective optical system described in Item 7, the diffraction order _α1 is an even number.

In particular, in order to ensure the transmittance of the third light beam by the first phase structure, it is preferable that the diffraction order ct 1 of the first light beam be an even number. Specifically, any combination of l, β ΐ, γ 1) = (2, 1, 1) and (8, 5, 4) is used as a combination of the diffraction orders of the luminous flux of each wavelength. Is preferred because of the spherical aberration due to the difference in t tt or the first and second wavelengths.

1 2 1

, It is possible to satisfactorily correct the spherical aberration caused by the difference between. The combination of diffraction orders

2

When using a combination of (<< 1, β ΐ, γ 1) = (2, 1, 1), it is preferable to set the production wavelength of the first phase structure to a wavelength shorter than λ （( α,, 13 1, γ 1) = (8, 5, 4)

Β

When using a combination, the production wavelength λ of the first phase structure should be longer than 1.

Β

Is preferred. Thereby, a high diffraction efficiency of the light beam of each wavelength can be secured.

[0045] The configuration according to Item 9 is the objective optical system according to any one of Items 1 to 8, wherein the second phase structure includes a spherical aberration caused by a difference between t and t, or Wavelength; I and

1 3 1 The spherical aberration caused by the difference of the second wavelength; I is corrected.

2

As described in item 9, the compatibility between the high-density optical disc and the CD is achieved by the second phase structure formed of the material satisfying the formula (2) or (4) formed on the second aberration correction element. By taking this, while maintaining a high transmittance for both the blue-violet laser light beam and the infrared laser light beam, spherical aberration caused by the difference between t and t, or the first wavelength λ and the second wavelength ; Of I

It is possible to correct spherical aberration caused by the difference.

Note that the second phase structure may be a diffraction structure or an optical path difference providing structure.

[0048] The configuration according to Item 10 is the objective optical system according to Item 9, wherein the second phase structure includes The diffraction structure diffracts the third light beam without diffracting the first light beam and the second light beam.

In particular, since the second phase structure is a diffraction structure that selectively diffracts only the third light beam as described in item 10, it is possible to independently control the aberration of the third light beam, Good light-gathering characteristics are obtained for both high-density optical discs and CDs.

[0050] In the configuration according to item 11, in the objective optical system according to item 10, the second phase structure is a structure in which a pattern having a stepped cross section including an optical axis is arranged on a concentric circle. Thus, for each predetermined number B of level surfaces, the level is shifted by a height corresponding to the number of levels corresponding to the number of level surfaces.

[0051] Specifically, by adopting the configuration as described in the item 11, it becomes possible to give the second phase structure the diffraction characteristics as described in the item 10.

[0052] Further, 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 oscillation wavelength of the first light source can be changed in the same manner as the configuration described in Item 5. Tolerances for individual differences can be reduced.

[0053] In the configuration according to Item 12, in the objective optical system according to Item 11, the number B of the predetermined level surfaces is any one of 3 and 4, and an optical path difference caused by one step of the stairs is provided. Is seven times the first wavelength.

1

More specifically, by adopting the configuration as described in item 12, it becomes possible to provide the second phase structure with the diffraction characteristics as described in item 10, and to provide three light beams High transmittance can be secured. In order to ensure the highest transmittance for the three light beams, the second phase structure must be formed from a material whose Abbe number V 2 at d-line satisfies 25 <v 2 <40.

The number B of the predetermined level surfaces is 3, and the second phase structure is the Abbe number V 2 at the d-line.

When forming from a material that satisfies 20≤ V 2≤ 25, the number B of the specified level surface shall be 4 and d

Is preferred.

Here, the principle of diffracted light generation will be described for a wavelength-selective diffraction structure (second phase structure) that selectively diffracts the third light beam without diffracting the first light beam and the second light beam. In the following description, the first wavelength λ is 405 nm, which is the recording / reproducing wavelength of the high-density optical disc HD, the second wavelength is 655 nm, which is the recording / reproducing wavelength of the DVD, and the third wavelength λ is the CD recording / reproducing. The raw wavelength is 785 nm. Here, the first phase structure needs to satisfy the following equations (15) to (21).

L2 = Δ2 (n -1) / λ (15)

21 1

Μ2 = Δ2 (η '-Ι) / λ (16)

22 2

Ν2 = Δ2 (η -1) / λ (17)

23 3

φ (Ν2) = ΙΝΤ (Β2)-(Β2) (18)

-0.4 <φ (Ν2) <0.4 (19)

L2 = 7 (20)

Β = either 3 or 4 (21)

ΙΝΤ (Χ): Integer closest to Χ

However,

Δ2: Depth in the optical axis direction of each step constituting each pattern of the second phase structure η: Refractive index of the material on which the second phase structure is formed with respect to the first wavelength 1

twenty one

η: refractive index of the material on which the second phase structure is formed for the second wavelength 2

twenty two

η: refractive index of the material on which the second phase structure is formed for the third wavelength 3

twenty three

Β: Number of level surfaces formed in each pattern of the second phase structure

L2, M2, and N2 are optical path differences in wavelength units added to the first light flux, the second light flux, and the third light flux by each step formed in each pattern of the second phase structure. If L2 is set to 7, the optical path difference L2 added to the first light beam due to the step Δ2 is seven times the first wavelength I, so that the first light beam passing through adjacent level surfaces The wavefront is exactly 7

1

The connection is shifted by the wavelength. Therefore, the first light beam is transmitted as it is at a transmittance of 100% without being subjected to diffraction by the first phase structure. When the second phase structure is formed of a material having an Abbe number V 2 at d-line that satisfies the above equation (2), the step Δ d

The optical path difference M2 added to the second light beam by 2 is very close to four times the second wavelength; I.

2

Therefore, the wavefronts of the second luminous flux passing through the level surfaces that are in contact with each other are connected by being shifted by four wavelengths. Therefore, the second light flux is also transmitted as it is with almost 100% transmittance, which is not affected by the diffraction effect by the second phase structure. On the other hand, the optical path difference N2 applied to the third luminous flux by the step Δ2 is about 3.3 times the third wavelength, so that the adjacent level surfaces are The wavefront of the third luminous flux passing therethrough is shifted by 3.3 wavelengths, but the actual wavefront shift excluding the wavefront shift of 3 wavelengths that are optically equiphase is 0.3 wavelength. . Here, if each pattern is composed of three or four level planes, the shift of the wavefront at both ends of each pattern is about one wavelength (= 0.3 wavelength X 3 or = 0.3 wavelength X 4 ), The third light beam is diffracted in the first order with a high diffraction efficiency of 70-80% (first order diffraction). The above equation (19) is a conditional equation for increasing the diffraction efficiency of the diffracted light of the third light flux, and the number B of the level surfaces formed in each pattern is determined so as to satisfy the equation (19). By making the determination, it is possible to sufficiently secure the diffraction efficiency of the first-order diffracted light of the third light flux. When the second phase structure is formed from a material whose Abbe number V 2 at the d-line satisfies 25 <v 2 <40, the value of equation (12) is used.

d d

The force closest to SO is when B = 3, and the second phase structure is expressed by the Abbe number V 2 at the d-line.

d

When forming from a material that satisfies 20≤V2≤25, the value of equation (12) is

Is the case where B = 4, and at this time, the diffraction efficiency of the first-order diffracted light of the third light flux becomes highest.

In the above-described wavelength-selective diffraction structure, the diffraction efficiency of the first-order diffracted light of the third light beam depends only on the Abbe number V 2 at the d-line of the material on which the wavelength-selective diffraction structure is formed, and dd

It does not depend on the refractive index n 2 at the line. Therefore, the refractive index n 2 is relatively free

d d

Depth in the optical axis direction of each step increases as the value of the refractive index n2 decreases.

d

Since it is difficult to manufacture stair shapes with high accuracy, materials having the same Abbe number V 2

d

When there are a plurality of materials, it is preferable to select the material having the largest n2.

d

Item 13 is the objective optical system according to Item 9, wherein the second phase structure generates second-order diffracted light when the first light beam enters, and When two light beams are incident, a diffracted light of order / 32 (2 _< hi2) is generated, and when the third light beam is incident, a diffracted light of order Ύ2 ( _Ύ2≤β2 ) is generated. Diffraction structure.

[0059] In order to make the high-density optical disc and CD compatible with each other by the second phase structure, in addition to the diffraction characteristics described in Item 10, the second phase structure has the diffraction characteristics described in Item 13 You can do it. By providing such diffraction characteristics, high transmittance can be secured for three light beams. Note that the diffraction structure having such diffraction characteristics has a saw-tooth shape or a step-like shape in cross section including the optical axis.

[0060] The configuration described in Item 14 is the objective optical system according to Item 13, wherein the diffraction order α2 is odd. Is a number.

[0061] In particular, in order to ensure the transmittance of the third light beam by the second phase structure, it is preferable that the diffraction order 2 of the first light beam be an odd number. Specifically, the combination of the diffraction orders of the luminous flux of each wavelength is (hi 2, β 2, γ 2) = (5, 3, 2), (7, 4, 3), (9, 5, 4). It is preferable to use any one of the two types of force. This makes it possible to correct spherical aberration caused by the difference in t tt.

13

It works. Furthermore, if the magnification of the objective optical system for recording / reproducing information on the third optical disc is in the range of 0.2 to 0, the spherical aberration caused by the difference between t and t will be better.

13

The ability to rectify s can.

[0062] When the above-described combination of diffraction orders is used for a light beam of each wavelength, if the production wavelength λ of the second phase structure is set to a wavelength shorter than 1, the diffraction efficiency of the light beam of each wavelength is reduced. Highly certain

Β

Can be maintained.

[0063] Patent Document 2 which corresponds to a case where the diffraction angle of the blue-violet laser beam and the diffraction angle of the infrared laser beam are made different by setting the diffraction order of the purple laser beam (first light beam) to an odd number. The objective lens of Numerical Example 3 uses a relatively low-dispersion material having an Abbe number of about 55 at the d-line, so that the diffraction efficiency of both wavelengths is low. In the optical system, a material having high dispersibility that satisfies the expression (2) is used as the material of the second phase structure. Therefore, even if the diffraction order of the violet laser light beam (first light beam) is an odd number, High diffraction efficiency for both wavelengths can be ensured.

The configuration described in Item 15 is the objective optical system according to any one of Items 1 to 14, wherein the first aberration correction element and the second aberration correction element are joined to each other.

[0065] The configuration described in Item 16 is the objective optical system according to any one of Items 1 to 14, wherein the first aberration correction element and the second aberration correction element are separated from each other.

[0066] The configuration according to Item 17 is the object optical system according to any one of Items 1 to 16, wherein at least one of the first aberration correction element and the second aberration correction element is the second aberration correction element. It has a three-phase structure.

[0067] As described in Item 17, by forming the third phase structure on one of the optical surfaces of the first aberration correction element and the second aberration correction element, light is condensed for each light beam of the objective optical system. The characteristics can be made better. This third phase structure is a diffractive structure. Or an optical path difference providing structure. The aberration corrected by the third phase structure may be, for example, chromatic aberration caused by a minute change in the first wavelength λ1, or spherical aberration caused by a change in the refractive index of the objective lens caused by a change in temperature. May be.

In the optical pickup device, the detection of the focus signal and the tracking signal by the photodetector may be unstable due to the influence of the reflected light from the objective optical system.

[0069] In order to avoid such a problem, in the objective optical system of the present invention, any one of the first to third phase structures is formed on the optical surface closest to the laser light source. It ’s been a good thing,

[0070] Thus, the light reflected by the optical surface closest to the laser light source is diffracted, so that it is diffracted in a direction having a predetermined angle with respect to the optical axis. As a result, reflected light can be prevented from entering the light receiving surface of the photodetector, and stable detection characteristics can be obtained.

[0071] In the configuration according to Item 18, in the objective optical system according to Item 17, the third phase structure includes a near-field generated in the objective optical system when the first wavelength λ changes within ± 5 nm.

1

It has a function of suppressing the movement of the axial image point position.

According to the configuration of Item 18, switching from reproduction to recording is performed by providing the third phase structure with a function of suppressing the movement of the paraxial image point position in the wavelength region of the first wavelength λ ± 5 nm. In this case, even if the wavelength changes (mode hop) instantaneously due to the change in the output of the first light source, the focused spot does not become large and it is possible to always maintain a good focused state .

[0073] The configuration according to Item 19 is the objective optical system according to Item 17 or 18, wherein the third phase structure is used when the first wavelength λ changes within ± 5 nm. It has the function of suppressing the change in generated spherical aberration.

According to the configuration described in Item 19, by giving the third phase structure a function of suppressing a change in spherical aberration in the wavelength region of the first wavelength λ ± 5 nm, the oscillation wavelength of the first light source can be reduced. The tolerance for individual differences can be relaxed, and the selection of the first light source is not required, so that the cost of the optical pickup device can be reduced.

[0075] The configuration of Item 20 is the objective optical system according to any one of Items 17 to 19, wherein the third phase structure suppresses a change in spherical aberration caused by a change in the refractive index of the objective optical system. Has the function of suppressing. As is well known, the increase in spherical aberration due to a change in the refractive index increases in proportion to the fourth power of the NA of the objective lens. Therefore, when the objective lens is made of a resin that has a large change in the refractive index due to a temperature change. It is necessary to take measures against the increase of strong spherical aberration. Also, in the NAO.85 objective lens, even if the refractive index change due to temperature change is smaller than that of resin, the increase in spherical aberration due to temperature change may not be negligible. According to the configuration described in Item 20, 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.

[0077] The configuration according to Item 21 is the objective optical system according to any one of Items 17 to 20, wherein the third phase structure is one of the first aberration correction element and the second aberration correction element. It is formed on either one.

[0078] In the configuration according to Item 22, in the objective optical system according to Item 21, the third phase structure is formed in the first aberration correction element, and the first wavelength λ Of 10

Adds 1x optical path difference.

[0079] As described in Item 22, the third phase structure is formed in the first aberration correction element, and the optical path difference added to the first light beam by the third phase structure is equal to the first wavelength. Designed to be 10 times

1

In this case, the optical path difference added to the second light flux is approximately six times the second wavelength λ,

2

Since the added optical path difference is approximately five times the third wavelength, the diffracted light of

Three

It is possible to ensure a sufficiently high transmittance.

Item 23 is the objective optical system according to any one of Items 1 to 22, wherein the first phase structure and the second phase structure are both formed of resin.

[0080] As a material of the aberration correction element, any optical glass or optical resin can be applied. In order to form a fine phase structure with a small shape error, a material having a low viscosity in a molten state, that is, Resins are suitable. In addition, resin is lower cost and lighter than glass. In particular, if a resin is used for the aberration correction element to reduce the weight, the driving force for performing the focus and tracking control of the optical pickup device during recording / reproducing of the optical disk may be reduced.

[0081] When both the first phase structure and the second phase structure are formed of resin, the first phase structure may be made of Zeonex (registered trademark) manufactured by Zeon Corporation or Abel (registered trademark) manufactured by Mitsui Chemicals, Inc. The second phase structure that is preferably formed from a cyclic oleolefin-based resin represented by a mark) or the like is a fluorene-based polyester represented by an ultraviolet curable resin or a thermosetting resin, or OKP4 manufactured by Osaka Gas Chemical Company, etc. Preferably, a resin is used.

[0082] Item 24 is the objective optical system according to any one of items 1 to 23, wherein one of the first phase structure and the second phase structure is an ultraviolet curable resin. Or formed from a thermosetting resin.

In the case where the second phase structure is formed on the surface of a resin layer formed on a resin substrate or a glass substrate to produce a second aberration correction element having a so-called hybrid structure, the material thereof is described in Item 24. Such an ultraviolet curable resin or a thermosetting resin is suitable for production.

As a method of manufacturing the aberration correction element formed on the surface of the phase structure, a method of forming the phase structure directly on a resin substrate or a glass substrate by repeating a process of photolithography and etching is used. In the meantime, a mold (die) with a phase structure is manufactured, and an aberration correction element with a phase structure formed on the surface is obtained as a replica of the mold. So-called molding is suitable for mass production. ing. In addition, as a method of manufacturing a mold having a phase structure formed thereon, a method of repeating a process of photolithography and etching to form a diffraction structure or a method of machining a diffraction structure with a precision lathe may be used.

Item 25 is the objective optical system according to Item 24, wherein the phase formed from an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure. The structure is the second phase structure.

[0086] For an ultraviolet curable resin or a thermosetting resin, it is relatively easy to control the Abbe number V at the d-line in the production process to obtain an optimal Abbe number V. Therefore, Abbe

d d

A second phase structure having a small tolerance of several v is formed from an ultraviolet-curing resin or a thermosetting resin.

Preferably, it is formed.

[0087] The configuration according to Item 26 is the objective optical system according to Item 24 or 25, wherein the first phase structure and the second phase structure are formed of an ultraviolet curable resin or a thermosetting resin. The phase structure is formed on a glass substrate.

[0088] An ultraviolet curable resin or a thermosetting resin has relatively excellent adhesion to a glass substrate. . Accordingly, the mold and the phase structure are separated from each other by forming the phase structure formed of the ultraviolet curable resin or the thermosetting resin on the glass substrate among the first phase structure and the second phase structure. Deformation of the phase structure during molding can be suppressed, and the occurrence of aberrations and a decrease in diffraction efficiency due to shape errors are reduced.

[0089] The structure according to Item 27 is the objective optical system according to any one of Items 1 to 26, wherein the objective lens corrects spherical aberration for a combination of the t and the first wavelength λ. Is optimized.

It is preferable that the aspherical shape of the objective lens is determined so that spherical aberration correction is minimized with respect to the first wavelength λ and the thickness tl of the protective layer of the first optical disc. In this configuration, the focusing performance of the first wavelength λ is determined by the objective lens. Therefore, as described in Item 27, the objective is set so that spherical aberration correction is minimized with respect to the first wavelength and the thickness tl of the first protective layer.

1

By determining the aspherical shape of the lens, it becomes easier to obtain the light-collecting performance of the first light beam that requires the strictest wavefront accuracy. Here, “the objective lens has been optimized for spherical aberration correction with respect to the combination of the tl and the first wavelength” means that the objective lens and the first optical disc are protected by the first optical disc through the protective layer. It means that the wavefront aberration when the light beam is collected is 0.05 λ RMS or less.

[0091] The configuration described in Item 28 satisfies the following Expressions (5) to (7) in the objective optical system according to any one of Items 1 to 27.

[0092] 380 nm <λ <420 nm (5)

1.5 <λ / λ <1.7 (6)

twenty one

1.8 <λ / λ <2.1 (7)

3 1

Item 29 is the objective optical system according to any one of Items 4 to 6, wherein the first phase structure has an action of diverging the second light flux.

[0093] By diverging the second light beam by the first phase structure, recording is performed on the second optical disc.

作動 It is possible to secure a sufficient working distance when performing regeneration.

[0094] In the configuration according to Item 30, in the objective optical system according to any one of Items 10 to 12, the second phase structure has an action of diverging the third light flux.

[0095] By diverging the third light beam by the second phase structure, recording is performed on the third optical disc. z It is possible to secure a sufficient working distance when performing regeneration.

[0096] In the configurations described in the paragraphs 29 and 30, "diverging the second light beam (or the third light beam) by the first phase structure (or the second phase structure)" means that the incident light beam is generated by these phase structures. The paraxial power of the diffractive structure defined by the diffraction order M and the second-order diffraction surface coefficient B when the optical path difference to be added is expressed by [optical path difference function] described later. The sign of is negative

twenty two

Synonymous with that.

[0097] The configuration according to Item 31 is the objective optical system according to Item 7 or 8, wherein the first phase structure is used in the objective optical system when the first wavelength λ1 changes in wavelength within ± 5 nm. It has a function of suppressing the movement of the paraxial image point position that occurs.

[0098] In a diffraction structure in which the cross-sectional shape including the optical axis has a saw-tooth shape or a step-like shape, the difference in t

1 Correct spherical aberration caused by 2 or the difference between the first wavelength λ and the second wavelength λ.

1 2

In addition to the function, the movement of the paraxial image point in the first wavelength range of ± 5 nm is suppressed.

1

Function can be provided. According to the configuration described in Item 31, even if a mode hop occurs due to a change in the output of the first light source when switching from reproduction to recording, the focused spot does not become large and a good focused state is always maintained. It is possible to do.

[0099] Item 32 is the objective optical system according to any one of Items 1 to 31, wherein at least one of the first aberration correction element and the second aberration correction element is the first wavelength. It has a negative paraxial power with respect to λ.

[0100] As described in Item 32, paraxial power (combined power of diffraction power and refraction power) for at least one of the first aberration correction element and the second aberration correction element with respect to the first wavelength λ.

1

If the value is negative, it is possible to secure a large working distance when recording / reproducing with respect to the optical disk. In this case, it is preferable that the design magnification of the objective lens is negative. Furthermore, spherical aberration correction is minimized with respect to the first wavelength and the thickness ti of the protective layer of the first optical disc.

1

More preferably, the aspherical shape is determined.

[0101] In the configuration according to Item 33, in the objective optical system according to any one of Items 1 to 32, the first to third light beams are all the first aberration correction element and the second aberration light. The light enters the correction element in the form of a parallel light beam.

[0102] According to the configuration described in Item 33, even when the objective optical system performs tracking driving, the object point Since the arrangement does not change, good tracking characteristics can be obtained for light beams of any wavelength.

[0103] In the configuration according to Item 34, in the objective optical system according to Item 1, the first aberration correction element has an Abbe number V1 at d-line satisfying Expression (1) and a first phase structure. The said d

(2) The aberration correction element has the Abbe number V 2 at the d-line satisfying the expression (2) and the second phase structure d

Has structure.

[0104] In the configuration according to Item 35, in the objective optical system according to Item 2, the first aberration correction element has a refractive index n1 at d-line satisfying Expression (3) and a first phase structure. The second d

The aberration correction element has a refractive index n 2 at d-line that satisfies equation (4) and a second phase structure

Have.

[0105] The configuration according to Item 36 is the objective optical system according to any one of Items 1 to 35, wherein the first aberration correction element has a positive paraxial power with respect to the first wavelength λ. The second error correction element has a negative paraxial power with respect to the first wavelength λ.

According to the configuration described in Item 36, in the wavelength region of the first wavelength λ ± 5 nm, the difference in dispersion between the first aberration correction element that is a positive lens and the second aberration correction element that is a negative lens is used. The movement of the paraxial image point position can be suppressed, so even if a mode hop occurs due to a change in the output of the first light source when switching from playback to recording, the focused spot does not increase, and It is possible to maintain a good light-collecting state.

Item 37 is the objective optical system according to Item 36, wherein the first aberration correction element and the second aberration correction element are joined to each other, and the first aberration correction element and the second aberration It is characterized in that the joint surface of the correction element has a convex shape on the side of the second aberration correction element.

[0108] The movement of the paraxial image point position in the wavelength region of the first wavelength; I ± 5 nm is better suppressed.

1

In order to achieve this, it is preferable that the first aberration correction element and the second aberration correction element are joined to each other as described in Item 37.

Item 38 is the objective optical system according to Item 24, wherein the phase structure formed of an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure. A non-heat-reflection anti-reflection coat is formed on the surface of. [0110] According to the configuration described in Item 38, the heat resistance is relatively low, and the antireflection coat can be formed on the surface of the phase structure formed of the ultraviolet curable resin or the thermosetting resin. Thus, the transmittance of the first aberration correction element and the second aberration correction element can be improved.

[0111] The configuration according to Item 39 is the objective optical system according to Item 23, wherein the first phase structure is formed of a cyclic oleolefin resin, and the second phase structure is formed of a fluorene-based polyester resin. ing.

[0112] According to the constitution of Item 39, by forming the resin from the cyclic oleolefin-based resin, low dispersibility can be given to the first phase structure, and by forming the material from the fluorene-based polyester resin, the second phase structure can be formed. On the other hand, high dispersibility can be provided, so that high transmittance (diffraction efficiency) can be ensured for light beams of any wavelength. In addition, ZEONEX (registered trademark) manufactured by Zeon Corporation or Apel (registered trademark) manufactured by Mitsui Chemicals, Inc. is used as the cyclic oleo-refin resin, and OKP4 manufactured by Osaka Gas Chemical Company is used as the fluorene-based polyester resin. This is suitable for mass production because each phase structure can be manufactured by a molding method using a mold.

[0113] The configuration according to Item 40 is the object optical system according to any one of Items 4 to 6, wherein the optical surface on which the first phase structure is formed has a first central region including an optical axis. And a first peripheral region surrounding the first central region, wherein the first phase structure is formed in the first central region.

[0114] According to the configuration described in Item 40, by setting the first central area as an area corresponding to a numerical aperture (NA) required for recording and reproducing information Z on the second optical disc, the difference between t and t

2 1 2 spherical aberration due to the first wavelength or spherical aberration due to the difference between I and the second wavelength λ

1 2 2 Correct only inside (first central area), では Stronger sphere outside area (first peripheral area)

2

It is possible to prevent the surface aberration from being corrected. As a result, the area outside ΝΑ

2

The luminous flux of the second wavelength λ that passes through the

2

Therefore, the objective optical system according to the present invention has an aperture control corresponding to the light beam of the second wavelength λ.

2

Function can be provided.

[0115] The configuration according to Item 41 is the objective optical system according to Item 40, wherein the first peripheral region has a small size. At least in part, a fourth phase structure for controlling the condensing position of the second light beam passing through this portion is formed, and the fourth phase structure converts the first light beam and the third light beam. This is a diffraction structure that diffracts the second light beam without diffraction.

[0116] According to the configuration described in Item 41, the diffraction power for the second wavelength λ of the first phase structure formed in the first central region and the second wavelength λ of the fourth phase structure formed in the first peripheral region are provided. To

By making the diffraction powers different from each other, it is possible to arbitrarily control the position at which the second light beam passing through the fourth phase structure is collected and the amount of spherical aberration. At this time, by designing the fourth phase structure so that the detection characteristic of the focus error signal of the second light beam by the photodetector is the best, the focusing characteristic of the objective optical system at the time of recording / reproducing information on / from the second optical disc is achieved. Can be improved.

[0117] Note that it is not necessary to control the condensing position of the second light flux and the amount of spherical aberration in the entire first peripheral region, and the fourth phase structure is not necessarily formed in the second peripheral region. It is only necessary to control the condensing position of the second light beam and the amount of spherical aberration only in a portion that adversely affects the detection characteristic of the focus error signal. Therefore, it is not always necessary to form the fourth phase structure over the entire first peripheral region.This prevents the range in which the fourth phase structure is formed from being unnecessarily widened. 3 It is possible to improve the transmittance of the light beam.

[0118] The configuration according to Item 42 is the objective optical system according to any one of Items 10 to 12, wherein the optical surface on which the second phase structure is formed includes: a second central region including an optical axis; Divided into a second peripheral region surrounding the second central region, the second phase structure is formed in the second central region.

[0119] According to the configuration described in Item 42, the second central area is an area corresponding to a numerical aperture (ΝΑ) necessary for recording / reproducing information on / from the third optical disc, the difference between t and t

The spherical aberration caused by 3 13 is corrected only within the NA (second central area), and the area outside the NA (second

3 3

In the (2 peripheral areas), it is possible to prevent such spherical aberration from being corrected. As a result, the luminous flux of the third wavelength λ passing through the area outside the NA does not contribute to spot formation.

3 3

Since it can be a flare component, the third wavelength;

It is possible to provide an aperture limiting function corresponding to the light flux of No. 3.

[0120] The configuration described in Item 43 is the objective optical system according to Item 42, wherein the second peripheral region has a small size. At least in part, a fifth phase structure for controlling the condensing position of the third light beam passing through this portion is formed, and the fifth phase structure converts the first light beam and the second light beam. It is a diffraction structure that diffracts the third light beam without diffraction.

[0121] According to the configuration described in Item 43, similarly to the configuration described in Item 41, it is possible to arbitrarily control the position where the third light flux passing through the fifth phase structure is collected and the amount of spherical aberration. Therefore, it is possible to improve the focusing characteristics of the objective optical system at the time of recording information on the third optical disc and reproducing Z information.

[0122] The configuration described in Item 44 is characterized in that, in the objective optical system according to any one of Items 1 to 43, the back focus fB for the first wavelength and the back focus fB for the second wavelength λ.

1 1 2

The difference between the scum fB and the back focus fB with respect to the first wavelength and the second wavelength λ

The difference from the back focus fB with respect to 2 1 1 3 is 0.2 mm or less.

Three

[0123] According to the configuration described in Item 44, since the difference in the working distance at the time of recording / reproducing information on the first to third optical disks is reduced, the stroke of the focusing actuator of the objective optical system is reduced. As a result, the size of the actuator can be reduced. Here, the “back focus fB with respect to the i-th wavelength λ” is defined as the position on the optical axis of the objective optical system and the i-th optical disc when the i-th light beam is focused on the information recording surface of the i-th optical disc. Refers to the interval.

[0124] The configuration according to Item 45 is characterized in that, in the objective optical system according to Item 11 or 12, the ratio 最小 / λ power S25 of the minimum width の of the pattern of the second phase structure to the first wavelength λ is equal to or more than S25.

Μ 1 M l

is there.

[0125] According to the configuration described in Item 45, the pattern of the second phase structure with respect to the first wavelength;

1

Since the minimum width Λ is sufficiently large, the vector calculation of the diffraction efficiency of the first wavelength; I

M 1

As the value increases, the reduction in diffraction efficiency due to the shape error of the second phase structure decreases.

[0126] The configuration according to Item 46 is the objective optical system according to any one of Items 1 to 45, wherein the first phase structure is formed on a surface of the first aberration correction element, and The phase structure is

Are formed on the surface of the second aberration correction element.

[0127] According to the configuration described in Item 46, since both the first phase structure and the second phase structure are formed at the interface with the air, the wavefront of the first light beam transmitted through the first aberration correction element is , Second aberration compensation The wavefronts of the first light flux transmitted through the positive element are in a state of high transmittance. Therefore, it is possible to evaluate the wavefront aberration of each aberration correction element by the interferometer for the first light beam, and it is easy to obtain the performance when manufacturing each aberration correction element.

[0128] In the configuration according to Item 47, in the objective optical system according to Item 5, both the first phase structure and the second phase structure are formed on a plane.

[0129] In the structure according to Item 48, in the objective optical system according to Item 11, both the first phase structure and the second phase structure are formed on a plane.

[0130] According to the configurations described in the paragraphs 47 and 48, the first phase structure and the second phase structure are easily manufactured.

[0131] The configuration according to Item 49 is the object optical system according to any one of Items 1 to 48, wherein the first aberration correction element and the second aberration correction element are relative to the objective lens. It is held by the holding member so that the general positional relationship is universal.

[0132] According to the configuration described in Item 49, even when the objective optical system performs tracking, the optical axes of the first aberration correction element and the second aberration correction element and the objective lens do not deviate, so that coma occurs. And good tracking characteristics can be obtained.

[0133] The configuration according to item 50 is characterized in that a first light source that emits a first light beam of a first wavelength λ for recording and / or reproducing information on the first optical disc, and a second light source Writing information

1

A second light source that emits a second light beam of a second wavelength λ (> λ) for recording and recording or reproduction

twenty one

And a third wavelength for recording and reading or reproducing information on the third optical disc; I (>

A third light source that emits a third light beam of (3λ), and the objective optical according to any one of claims 1 to 49.

2

And a system,

The first optical disk is used to record and Z or reproduce information on a first optical disk having a protective layer having a thickness of t, and has a protective layer having a thickness of t (≥t) using the second optical beam. No. 2

twenty one

Recording and / or reproducing information on / from the optical disc, and recording / reproducing information on / from the third optical disc having a protective layer having a thickness t (> t) using the third light flux.

3 2

An optical pickup device.

According to Item 50, an optical pickup device having the same effects as in any one of Items 1 to 49 can be obtained. [0135] Item 51 is the optical disk drive device equipped with the optical pickup device according to item 50 and a moving device that moves the optical pickup device in a radial direction of the optical information recording medium.

According to the item 51, an optical disk drive having the same effect as the item 50 can be obtained.

[First Embodiment]

Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, the objective optical system of the present invention and an optical pickup device using this objective optical system will be described with reference to FIG.

FIG. 1 is a diagram schematically showing a configuration of an optical pickup device PU capable of appropriately recording / reproducing information on any of a high-density optical disk HD, a DVD, and a CD. The optical specifications of HD are the first wavelength λ = 408 nm, the thickness t of the protective layer PL1 = 0.1 mm, and the numerical aperture NA = 0.85.The optical specifications of DVD are the second wavelength λ = 658 nm, Protection layer PL2 thickness t

twenty two

= 0.6 mm, numerical aperture NA = 0.65, and the optical specification of the CD is the third wavelength λ = 785η

23 m, protective layer PL3 thickness t = 1.2 mm, numerical aperture NA = 0.50. However, wavelength, protection

3 3

The combination of the layer thickness and the numerical aperture is not limited to this.

[0138] The optical pickup device PU emits information when recording / reproducing information to / from the HD, emits a blue-violet laser beam (first light beam) of 405 nm, and emits information to the blue-violet semiconductor laser LD1 and DVD. The first emission point EP1, which emits a 655 nm red laser beam (second beam) and emits light when recording / reproducing data, and emits 785 nm light when recording / reproducing information on CDs A laser light source unit LU for DVD / CD, a photodetector PD for HDZDVD / CD, and a second light emitting point EP2 that emits an infrared laser beam (third beam) formed on one chip. It has a function of converging the laser beam transmitted through the first and second aberration correction elements L1 and L2 onto the information recording surfaces RL1, RL2 and R L3. Objective lens unit 〇U (objective optical system) composed of an objective lens OL with aspheric surfaces on both sides, 2-axis Actuator AC1, single-axis actuator AC2, first lens EXP1 with negative paraxial refractive power, second lens EXP2 with positive paraxial refractive power, and expander lens EXP, first polarized lens One splitter BS1, 2nd polarizing beam splitter BS2, 1st collimating lens C〇L1, 2nd It is composed of a collimating lens C〇L2, a third collimating lens C〇L3, and a sensor lens SEN for adding astigmatism to the reflected light beams from the information recording surfaces RL1, RL2 and RL3. . As a light source for HD, a blue-violet SHG laser may be used in addition to the above-mentioned blue-violet semiconductor laser LD1.

[0139] In the optical pickup device PU, when performing Z recording and reproducing of information for HD, as shown in Fig. 1, the light path is drawn by a solid line, and first, the blue-violet semiconductor laser LD1 is used. To emit light. 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, and After passing through the 1 lens EXP1 and the 2nd lens EXP2, the beam diameter is regulated by the aperture STO (not shown), and the luminous flux diameter is regulated by the objective lens unit OU on the information recording surface RL1 via the HD protective layer PL1. It is a spot that is formed. The objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.

[0140] The reflected light flux modulated by the information pits on the information recording surface RL1 has passed 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. Later, when the light passes through the third collimating lens COL3, it becomes a convergent light beam, and astigmatism is added by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. Then, it is possible to read information recorded in the HD using the output signal of the photodetector PD.

[0141] In addition, in the case where information is recorded on and reproduced from a DVD in the optical pickup device PU, the light emitting point EP1 emits 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 and then reflected by the second polarizing beam splitter BS2, as indicated by the broken line in FIG. Then, the diameter is increased 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 DVD protective layer PL2. The objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.

[0142] The reflected luminous flux modulated by the information pits on the information recording surface RL2 is returned to the objective lens unit. G OU, the second lens EXP2, the first lens EXP1, the second polarizing beam splitter BS2, and after passing through the first polarizing beam splitter BS1, pass through the third collimating lens COL3 to become a convergent light flux, which is not reflected by the sensor lens SEN. Astigmatism is added and converges on the light receiving surface of the photodetector PD. Then, it is possible to read the information recorded on the DVD using the output signal of the photodetector PD.

[0143] Further, in the case where information recording Z reproduction is performed on a CD in the optical pickup device PU, the interval between the first lens EXP1 and the second lens EXP2 becomes narrower than when recording / reproducing information on the HD. After the first lens EXP1 is driven in the optical axis direction by the uniaxial actuator AC2, the light emitting point EP2 emits light. 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. Become. The objective lens unit OU performs focusing and tracking by a two-axis actuator AC1 arranged around it.

[0144] The reflected light flux modulated by the information pits on the information recording surface RL2 again passes through the objective lens unit OU, the second lens EXP2, the first lens EXP1, the second polarization beam splitter BS2, and the first polarization beam splitter BS1. Later, when the light passes through the third collimating lens COL3, it becomes a convergent light beam, and astigmatism is added by the sensor lens SEN, and converges on the light receiving surface of the photodetector PD. Then, it is possible to read information recorded on the CD using the output signal of the photodetector PD.

As schematically shown in FIG. 2, the objective lens unit OU in the present embodiment has a first phase structure PS1 made of resin and a second phase structure PS2 made of resin, and is joined to each other. And the aspheric shape so that spherical aberration is minimized with respect to the first wavelength λ and the thickness t of the HD protective layer PL1. Design

1

The glass objective lens ΔL is coaxially integrated through a lens frame B. Specifically, the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of the cylindrical lens frame B while the objective lens OL is fitted and fixed to the other end. ,these It is configured to be coaxially integrated along the optical axis X.

[0146] As a method of manufacturing the first aberration correction element L1 and the second aberration correction element L2, the first aberration correction element L1 and the second aberration correction element L2 are manufactured by molding, and thereafter, the respective aberration correction elements are corrected. A method of joining the elements may be used, or an ultraviolet curable resin is applied on one of the aberration correction elements manufactured by molding, and a phase structure is formed on the surface of the ultraviolet curable resin. A method in which a phase structure is transferred by pressing a molded mold and irradiating ultraviolet rays is acceptable. A thermosetting resin may be used instead of the ultraviolet curable resin.

[0147] Further, in the present embodiment, both first phase structure PS1 and second phase structure PS2 are made of resin, but one of the aberration correction elements may be made of glass and the other may be made of resin. . The method of manufacturing the aberration correction element having a glass phase structure may be molding or a method of forming a diffraction structure by repeating photolithography and etching processes. When an aberration correcting element having a phase structure made of glass is manufactured by molding, in order to extend the life of the mold and improve the transferability of the diffractive structure, the viscosity in the molten state is small and the glass is made of glass. It is preferable to use a glass having a transition point Tg of 450 ° C. or less. Examples of such a glass include “K-PG325” and “K-PG375” manufactured by Sumita Optical Glass Co., Ltd. In addition, as a method of joining the aberration correction element having a resin phase structure and the aberration correction element having a glass phase structure, an aberration correction element having a resin phase structure is manufactured by molding, and thereafter, Alternatively, a method of bonding with an aberration correcting element having a glass phase structure may be used, or an ultraviolet curable resin may be applied on the aberration correcting element having a glass phase structure, and the ultraviolet curable resin may be bonded to the glass. A method of transferring the phase structure by pressing a mold having a phase structure formed on the surface and irradiating the mold with ultraviolet light may be used. A thermosetting resin may be used in place of the ultraviolet curable resin.

In the present embodiment, the objective lens OL is made of glass. The present invention is not limited to this, and the objective lens OL may be made of resin. In this case, the resin used for the objective lens ΔL is preferably a oleolefin resin.

[0149] Further, as a material used for the objective lens OL, a resin having an average particle diameter of 3 It is acceptable to use a material in which inorganic particles of Onm or less are dispersed. By mixing inorganic particles with a refractive index change rate opposite to the sign of the refractive index change rate due to the temperature change of the base resin, refraction due to temperature change is achieved while maintaining the moldability of the resin. Since a material having a small absolute value of the rate of change can be obtained, a change in spherical aberration due to a change in temperature of the objective lens ΔL can be reduced.

The first phase structure has an Abbe number V 1 = 56.4 at the d-line and a refractive index n d d at the d-line

1 = 1.509140, and the second-order grain structure is Abbe number V 2 = 22.8 at the ώ line, and d

The refractive index n 2 is 1.638000.

d

[0151] A first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the light source side, and a second phase structure PS2 is formed on the optical surface of the second aberration correction element L2 on the optical disk side. It is formed.

[0152] The first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).

[0153] Each step Δ1 of the staircase structure has a height that satisfies Δ1 = 2 · λ / (η-1) = 1 · 557 µm

1 1

Is set. Here, n is a wavelength; I (in this embodiment, I = 408 nm)

1 1 1

1 is the refractive index of the aberration correction element L1.

[0154] Since the optical path difference L1 added to the first light beam due to the step Δ1 is 2Xλ, the first light beam

1

1-phase structure Transmitted without any effect by PS1.

[0155] Further, the optical path difference N1 added to the third light beam by the step Δ1 is 1Xλ (in the present embodiment,

Three

λ = 785 nm), the third light beam is also not affected by the first phase structure PS1 at all.

Three

Transmit as it is.

On the other hand, the optical path difference Ml added to the second light beam by the step Δ 1 is 1.20 X λ (this embodiment

2

Λ = 658 nm), and the phase of the second light flux passing through the level surface before and after the step Δ 1

2

The difference (the phase difference obtained by subtracting an integral multiple of 2π that is optically equal in phase) is 2πXO.20. Since one saw tooth is divided into five, the phase difference of the second light beam is exactly 5 for one saw tooth. Χ 2 π X O. 20 = 2 π, and the first-order diffracted light power is generated.

As described above, the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.

[0158] The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%, The diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 100%, and high diffraction efficiency is obtained for any light beam.

[0159] The second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, the number of levels is shifted by the number of levels corresponding to the number of level planes for each predetermined number of level planes (four level planes in this embodiment). Is shifted three steps).

[0160] Each step difference Δ2 of the staircase structure has a height satisfying Δ2 = 7 · λ / (η 1) = 4 · 144 μm.

1 1

Is set. Here, n is the refractive index of the second aberration correction element at the wavelength.

1 1

[0161] Since the optical path difference L2 added to the first light beam by the step Δ2 is 7X, the first light beam is

1

Two-phase structure Transmitted without any effect by PS2.

The optical path difference M2 added to the second light beam by the step Δ 2 is 3 · 97 X λ = 4Χλ.

2 2, the second light beam is also transmitted through the second phase structure PS2 with almost no effect.

On the other hand, the optical path difference Ν2 added to the third light beam by the step Δ 2 is 3.28 X λ = 3.25

Three

X λ, the phase difference of the third light beam passing through the level surface before and after the step Δ 2 (optically equal

Three

The phase difference obtained by subtracting an integral multiple of 2π, which is the phase, is 2πΧ0.25. Since one saw tooth is divided into four, the phase difference of the third light beam is exactly 4 × 2πΧ0.25 = 2π for one saw tooth, and a first-order diffracted light is generated.

As described above, the second phase structure PS2 selectively diffracts only the third luminous flux, thereby correcting spherical aberration caused by the difference between the thickness of the protective layer of ΗD and the thickness of the protective layer of CD.

[0165] The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 94.8. %, The diffraction efficiency of the first-order diffracted light of the third light beam is 78.2%, and high diffraction efficiency is obtained for any light beam. [0166] As described above, the first aberration correction element L1 is made of a material that satisfies the expression (1) or (3), and the HD and the DVD are mutually compatible by the first phase structure PS1. As a result, it is possible to secure a high transmittance for both the blue-violet laser beam and the red laser beam, and furthermore, the second aberration correction element L2 can be expressed by the equation (2) or (4). The second phase structure PS2 ensures high transmissivity for both blue-violet laser light and infrared laser light by making the HD and CD compatible with each other. Become possible

[0167] Also, since the first phase structure PS1 is formed only within the numerical aperture NA2 of the DVD, the light flux passing through the area outside of NA2 becomes a flare component on the information recording surface RL2 of the DVD, Is automatically restricted.

[0168] Also, since the second phase structure PS2 is formed only within the numerical aperture NA3 of the CD, the luminous flux passing through the area outside NA3 becomes a flare component on the information recording surface RL3 of the CD, Is automatically restricted.

By driving the negative lens EXP1 of the beam expander EXP in the optical axis direction by the uniaxial actuator UAC, 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 negative lens EXP1 include, for example, wavelength variations due to manufacturing errors of the first light source LD1, changes in the refractive index and refractive index distribution of the objective lens system due to temperature changes, double-layer disks, This includes focus jumps between the information recording layers of a multi-layer disc such as a four-layer disc, and variations in thickness and thickness distribution due to manufacturing errors of the protective layer of a high-density optical disc.

[0170] Note that, instead of the negative lens EXP1, even if the first collimating lens COL1 is driven in the optical axis direction, the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected.

[0171] In the present embodiment, a DVD / CD laser light source unit LU in which the first light emitting point EP1 and the second light emitting point EP2 are formed on one chip is used. Not limited to this, it is also possible to use a laser light source unit for HD / DVDZCD in which the emission point for emitting a laser beam of wavelength 408 nm for HD is formed on the same chip. Alternatively, use three laser light sources, a blue-violet semiconductor laser, a red semiconductor laser, and an infrared semiconductor laser. A laser light source unit for HD / DVDZCD housed in one housing may be used.

[0172] Further, in the present embodiment, the light source and the photodetector PD are arranged separately, but the present invention is not limited to this, and a laser light source module in which the light source and the photodetector are integrated is used. May be.

In the present embodiment, a force obtained by integrating the first aberration correction element L1 and the second aberration correction element L2 joined to each other and the objective lens ΔL via the lens frame B is joined to each other. In the case where the first aberration correction element L1 and the second aberration correction element L2 and the objective lens ΔL are integrated, the first aberration correction element L1 and the second aberration correction element L2, and the object lens OL The first aberration correction element L1 and the second aberration correction element bonded to each other may be used in addition to the method using the lens frame B as described above, as long as the relative positional relationship between them is kept unchanged. This is a method of fitting and fixing the respective flange portions of L2 and the objective lens OL.

[0174] As a method for correcting the spherical aberration of the spot formed on the HD information recording surface RL1, in addition to the method of driving the lens in the optical axis direction as described above, a phase control using a liquid crystal is performed. An element may be used. Since a method for correcting spherical aberration by using such a phase control element is known, a detailed description thereof is omitted here.

In order to suppress coma generated by tracking drive at the time of spherical aberration correction, it is preferable that the objective lens unit OU and the phase control element are integrated.

[0176] The first aberration correction element L1 and the second aberration correction element L2, which are joined to each other, and the objective lens OL are held so that the relative positional relationship between them does not change. Accordingly, it is possible to suppress the occurrence of aberration at the time of focusing / tracking, and to obtain good focusing characteristics or tracking characteristics.

[Second embodiment]

Hereinafter, a second embodiment of the present invention will be described with reference to the drawings. However, description of portions having the same configuration as that of the first embodiment will be omitted.

[0177] The present embodiment is characterized in that in the objective lens unit OU, the first aberration correction element L1 and the second aberration correction element L2 are separated from each other.

[0178] The objective lens unit OU in the present embodiment is made of resin as schematically shown in FIG. The first aberration correction element LI having the first phase structure PS1 of the first, the second aberration correction element L2 having the second phase structure PS2 made of resin, the first wavelength λ, and the thickness t of the HD protective layer PL1. for

1 1

It has a configuration in which it is coaxially integrated via a glass objective lens OL lens frame B whose aspherical shape is designed so as to minimize spherical aberration. Specifically, the first aberration correction element L1 and the second aberration correction element L2 are fitted and fixed to one end of the cylindrical lens frame B with the first aberration correction element L1 and the second aberration correction element L2 separated from each other, and the objective lens OL is fitted and fixed to the other end. Thus, they are coaxially integrated along the optical axis X.

[0179] The first phase structure has an Abbe number at the d-line V 1 = 56.4, a refractive index at the d-line n 1 = 1 d d

509140 and the second phase structure is the Abbe number at the d-line V 2 = 27.0, d at the d-line

Refractive index n 2 = 1.607000.

d

A first phase structure PS1 is formed on the optical surface on the light source side of the first aberration correction element L1, and a second phase structure PS2 is formed on the optical surface on the optical disk side of the second aberration correction element L2. It is formed.

[0181] The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps), and each step Δ 1 of the staircase structure is set to a height satisfying Δ Δ = 2 · λ / (η — 1) = 1.544 zm. Here, n is the wavelength λ (in the present embodiment,

1 1

This is the refractive index of the first aberration correction element L1 at (fly = 405 nm).

[0182] Since the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2Xλ, the first light beam is transmitted through the first phase structure PS1 without any action.

[0183] The optical path difference N1 added to the third light beam by the step Δ1 is 0.99 X λ = 1 λ λ (actual

33 In the embodiment, I = 785 nm), so that the third light flux is not created by the first phase structure PS1.

Three

Transmitted as it is without being used.

On the other hand, the optical path difference Ml added to the second light beam by the step Δ 1 is 1.19 X λ = 1.20Χλ

twenty two

(I = 655 nm in the present embodiment), and the second pass through the level surface before and after the step Δ1.

2

The phase difference between the two light beams (the phase difference obtained by subtracting an integer multiple of 2π, which is optically equiphase) is 2π X O. 20. Since one saw tooth is divided into five, the phase difference of the second light beam is exactly 5Χ2πΧ0.20 = 2π for one saw tooth, and a first-order diffracted light is generated.

As described above, the first phase structure PS 1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.

[0186] Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%, The diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 99.2%, and a high diffraction efficiency is obtained for any light beam.

[0187] The second phase structure PS2 diffracts the first to third light beams, and has a stepped cross section including the optical axis.

Each step Δ 2 of the staircase structure has a height that satisfies Δ 1 = 7 · λ / (η λ 1) = 4.302 μ ΐη

Β Β

Is set to Here, η is the wavelength (e.g., 400 nm in this embodiment).

B B B

Is the refractive index of the first aberration correction element L1 (n = 1.650875 in the present embodiment).

B

[0189] Passing through the second phase structure PS2, the 7th-order diffracted light of the first light beam, the 4th-order diffracted light of the second light beam, and the 3rd-order diffracted light of the third light beam are generated.

[0190] The optical path difference added to the first light beam when passing through the second phase structure PS2 is 6.89 Xe = 7

One

X λ, and the seventh-order diffracted light of the first light beam has the maximum diffraction efficiency.

1

[0191] The optical path difference added to the second light beam when passing through the second phase structure PS2 is 3.94 Χ λ

^ 4 λ λ, and the fourth-order diffracted light of the second light flux has the maximum diffraction efficiency.

twenty two

[0192] Further, the optical path difference added to the third light beam when passing through the second phase structure PS2 is 3.25 λ λ

^ 3 λλ, and the third-order diffracted light of the third light beam has the maximum diffraction efficiency.

3 3

[0193] Thus, spherical aberration caused by the difference between the thickness of the HD protective layer and the thickness of the CD protective layer is corrected.

[0194] The diffraction efficiency of the 7th-order diffracted light of the first light beam generated by the second phase structure PS2 is 96.0%, the diffraction efficiency of the 4th-order diffracted light of the second light beam is 99.0%, and the diffraction efficiency of the third light beam is 39.0%. The diffraction efficiency of the second-order diffracted light is 81.2%, and high diffraction efficiency is obtained for any light flux.

[0195] Also, the paraxial diffraction power for the first wavelength of the second phase structure PS2 and the paraxial refraction power for the first wavelength of the optical surface on the light source side of the second aberration correction element L2 have opposite signs, and By making the values the same, the first aberration passing through the optical surface on the light source side of the second aberration correction element L2 The beam diameter of the light beam does not change.

[Third embodiment]

Hereinafter, a third embodiment of the present invention will be described with reference to the drawings, but the description of the same components as those in the first embodiment will be omitted.

[0196] In the present embodiment, in the objective lens unit OU, the first aberration correction element L1 and the second aberration correction element L2 are separated from each other, and the third phase structure PS3 is connected to the first aberration correction element. It is characterized in that it is provided on the optical surface of L1 on the optical disk side.

As schematically shown in FIG. 4, the objective lens unit OU in the present embodiment includes a first aberration correction element L1 having a first phase structure PS1 made of resin, and a second phase structure PS2 made of resin. With respect to the second aberration correction element L2 and the first wavelength λ and the thickness t of the HD protective layer PL1.

1 1 A glass objective lens whose aspherical shape is designed to minimize spherical aberration. Specifically, the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed at one end of a cylindrical lens frame B, and the objective lens OL is fitted and fixed at the other end. Therefore, they are coaxially integrated along the optical axis X.

1 = 1.509140, and the second phase structure has an Abbe number V 2 = 27.0 at the d-line and d

Refractive index n 2 = 1.607000.

d

[0199] A first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the light source side, and a second phase structure PS2 is formed on the optical surface of the second aberration correction element L2 on the optical disk side. The third phase structure PS3 is formed on the optical surface of the first aberration correction element L1 on the optical disk side.

[0200] The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).

[0201] The first phase structure PS1 does not diffract the first and third light beams, but diffracts the second light beam. There is a structure in which a pattern in which the cross-sectional shape including the optical axis is stepped is arranged concentrically, and the number of level planes is determined for each predetermined number of level planes (5 level planes in this embodiment). (In this embodiment, a structure in which the steps are shifted by four), and each step Δ1 of the staircase structure is represented by Δ · = 2 · λ / (η _1) = 1.544 zm. Here, n is the wavelength λ (in the present embodiment,

1 1

[0202] Since the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2Xλ, the first light beam is transmitted through the first phase structure PS1 without any effect.

[0203] Also, the optical path difference N1 added to the third light beam due to the step Δ1 is 0.99 X = 1 = 1

(3 = 785 nm in the embodiment), so that the third light beam is not created by the first phase structure PS1.

Three

Transmitted as it is without being used.

[0204] On the other hand, the optical path difference Ml added to the second light beam by the step Δ1 is 1.19 X = 1.20X λ

twenty two

(In the present embodiment, 655 nm), and the first through the level surfaces before and after the step Δ 1

2

The phase difference between the two light beams (the phase difference obtained by subtracting an integer multiple of 2π, which is optically equiphase) is 2ππ0.20. Since one saw tooth is divided into five, the phase difference of the second light beam is exactly 5Χ2πΧ0.20 = 2π for one saw tooth, and a first-order diffracted light is generated.

[0205] As described above, the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration due to a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.

The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%, and the diffraction efficiency of the third light beam is The diffraction efficiency of the zero-order diffracted light (transmitted light) is 99.2%, and a high diffraction efficiency is obtained for any light flux.

[0207] The second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for each predetermined number of level surfaces (three-level surfaces in the present embodiment), the level is shifted by a height corresponding to the number of levels corresponding to the number of the level surfaces (in this embodiment, Is a two-stage shifted structure).

[0208] Each step Δ2 of the staircase structure has a height that satisfies Δ2 = 7 · λ / (n_1) = 4.371 zm.

1 1

Is set. Here, n is the refractive index of the second aberration correction element at the wavelength. [0209] Since the optical path difference L2 added to the first light beam by the step Δ2 is 7 X λ, the first light beam is

1

Two-phase structure Transmitted without any effect by PS2.

[0210] Also, the optical path difference Μ2 added to the second light beam by the step Δ2 is 4.01 X λ = 4 Χ λ.

[0211] On the other hand, the optical path difference Ν2 added to the third light beam due to the step Δ2 is 3.30 33 λ = 3.33

Three

The phase difference obtained by subtracting an integral multiple of 2π, which is the phase, is 2π Χ 0.33. One saw blade

Since it is divided into three, the phase difference of the third light beam is exactly 3 歯 2 π Χ 0.33 for one sawtooth.

= 2π, and the first-order diffracted light is generated.

[0212] As described above, the second phase structure PS2 selectively diffracts only the third light beam, and

The spherical aberration caused by the difference between the protective layer thickness of D and the protective layer thickness of CD is corrected.

[0213] The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the second phase structure PS1 is 1

The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 99.8%, and the diffraction efficiency of the first-order diffracted light of the third light flux is 66.6%, which is high for any light flux. Diffraction efficiency is obtained.

[0214] The third phase structure PS3 diffracts the first to third light beams, and has a stepped cross section including the optical axis. This third phase structure PS3 is used in response to small changes in the first wavelength.

1

This is a structure for suppressing the movement of the paraxial image point position and the change in spherical aberration.

[0215] Each step Δ 3 of the staircase structure is set to a height that satisfies Δ 1 = 10 · λ / (η-1) = 7.719 z m

1 1

Is set.

[0216] By passing through the third phase structure PS3, the 10th-order diffracted light of the first light flux, the 6th-order diffracted light of the second light flux, and the 5th-order diffracted light of the third light flux are generated.

[0217] The optical path difference added to the first light beam when passing through the third phase structure PS3 is 10.0 X λ.

The 10th-order diffracted light of the first light beam has the highest diffraction efficiency.

[0218] Further, the optical path difference added to the second light beam when passing through the third phase structure PS3 is 5.97 Χ λ

^ 6 λλ, and the sixth-order diffracted light of the second light beam has the maximum diffraction efficiency.

twenty two

[0219] Further, the optical path difference added to the third light beam when passing through the third phase structure PS3 is 4.95 Χ λ

5Χλ, and the fifth-order diffracted light of the third light beam has the maximum diffraction efficiency. [0220] The diffraction efficiency of the 10th-order diffracted light of the first light beam generated by the third phase structure PS3 is 100%, the diffraction efficiency of the 6th-order diffracted light of the second light beam is 99.7%, and the fifth-order diffracted light of the third light beam is generated. Has a diffraction efficiency of 99.1%, and high diffraction efficiency is obtained for any light flux.

[0221] Also, the paraxial diffraction power for the first wavelength of the third phase structure PS3 and the paraxial refraction power for the first wavelength of the optical surface of the first aberration correction element L1 on the optical disk side have opposite signs, and their absolute values are the same. By making the values the same, the light beam diameter of the first light beam passing through the optical surface of the first aberration correction element L1 on the optical disk side does not change.

[0222] [Fourth embodiment]

Hereinafter, a fourth embodiment of the present invention will be described with reference to the drawings. However, description of portions having the same configuration as in the first embodiment will be omitted.

In the present embodiment, in the objective lens unit OU, the first aberration correction element L1 and the second aberration correction element L2 are configured to be separated from each other, and the second lens made of an ultraviolet curable resin is formed on the glass substrate GL. It is characterized in that the second aberration correcting element L2 is formed by forming the phase structure PS2, and the paraxial power of the first aberration correcting element L1 with respect to the first wavelength is negative.

1

[0224] As schematically shown in Fig. 5, the objective lens unit OU in the present embodiment includes a first aberration correction element L1 having a first phase structure PS1 made of resin, and a first aberration correction element L1 made of resin on a glass substrate GL. The second aspherical correction element L2 having a configuration in which the two-phase structure PS2 is formed, and the aspheric shape thereof is minimized with respect to the first wavelength and the thickness t of the HD protective layer PL1 so that spherical aberration is minimized.

1

The designed glass objective lens ΔL is coaxially integrated via a lens frame B. Specifically, the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of the cylindrical lens frame B, and the objective lens 〇L is fitted and fixed to the other end. Thus, these are coaxially integrated along the optical axis X.

[0225] Further, the first phase structure has an Abbe number V 1 = 56.4 at the d-line, a refractive index n d d at the d-line.

1 = 1.509140, and the second-order grain structure is Abbe number V 2 = 23.0 on the ώ line, d

Refractive index n 2 = 1.60000.

d

[0226] The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. The number of predetermined level planes (5 level planes in this embodiment) It has a structure in which the steps are shifted by a height corresponding to the number of steps corresponding to the number of faces (in this embodiment, a structure shifted by four steps).

[0227] The first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam, and a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps), and each step Δ 1 of the staircase structure is set to a height satisfying Δ Δ = 2 · λ / (η — 1) = 1.557 / im. Here, n is the wavelength λ (in the present embodiment,

1 1

This is the refractive index of the first aberration correction element L1 at (fly = 408 nm).

[0228] Since the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2 X λ, the first light beam is transmitted through the first phase structure PS1 without any action.

[0229] Further, the optical path difference N1 added to the third light flux by the step Δ1 is 1 X λ (in the present embodiment,

Three

Transmit as it is.

[0230] On the other hand, the optical path difference Ml added to the second light beam by the step Δ1 is 1.20 X

2

The difference (the phase difference obtained by subtracting an integral multiple of 2π that is optically equal in phase) is 2πΧ0.20. Since one saw tooth is divided into five, the phase difference of the second light beam is exactly 5 52πΧ0.20 = 2π for one saw tooth, and a first-order diffracted light power is generated.

As described above, the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration due to a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.

The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%, The diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 100%, and high diffraction efficiency is obtained for any light beam.

[0233] The second phase structure PS2 does not diffract the first light beam and the second light beam but diffracts the third light beam. A pattern having a stepped cross section including the optical axis is arranged on a concentric circle. In this structure, for each predetermined number of level surfaces (three-level surfaces in the present embodiment), the level is shifted by a height corresponding to the number of levels corresponding to the number of the level surfaces (in this embodiment, Is 2 (Shifted structure).

[0234] Each step difference Δ2 of the staircase structure has a height satisfying Δ2 = 7 · λ / (η _ 1) = 4.410 z m.

1 1

Is set. Here, n is the refractive index of the second aberration correction element at wavelength; I.

1 1

[0235] Since the optical path difference L2 added to the first light beam by the step Δ2 is 7Xλ, the first light beam is

1

Two-phase structure Transmitted without any effect by PS2.

[0236] The optical path difference Μ2 added to the second light beam by the step Δ2 is 3.97 Χλ = 4Χλ.

On the other hand, the optical path difference Ν2 added to the third light beam due to the step Δ 2 is 3.28 X = 3.25

Three

As described above, the second phase structure PS2 corrects spherical aberration due to the difference between the thickness of the protective layer of D and the thickness of the protective layer of CD by selectively diffracting only the third light beam.

[0239] The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 95.8. %, The diffraction efficiency of the first-order diffracted light of the third light beam is 77.5%, and high diffraction efficiency is obtained for any light beam.

[0240] Further, the objective optical system OU of the present embodiment is arranged such that the first wavelength of the first aberration correction element L1;

It has a configuration in which the paraxial power for one is negative, and the luminous flux of each wavelength enters the objective lens OL in a divergent luminous flux state. This ensures a sufficient working distance when playing back recorded CDs on CDs with a thick protective layer. Note that the design magnification of the objective lens ΔL is negative, and this design magnification corresponds to the divergence of the first light beam incident on the objective lens OL.

[0241] [Fifth Embodiment]

Hereinafter, a fifth embodiment of the present invention will be described with reference to the drawings. However, description of portions having the same configuration as that of the first embodiment will be omitted.

[0242] In the present embodiment, the thickness t of the protective layer PL1 is 0.6 mm and the numerical aperture NA is 0.67.

1 1

Compatible with high-density optical discs HD (eg, HD DVD) and DVDs and CDs The objective lens unit OU is characterized by the fact that the first aberration compensating element L1 and the second aberration compensating element L2 are joined together and the first phase structure PS1 is a diffraction structure with a saw-tooth cross section. Have.

[0243] As schematically shown in Fig. 6, the objective lens units OU in this embodiment are joined to each other, each having a first phase structure PS1 made of resin and a second phase structure SP2 made of resin. In addition, the first aberration correction element L1 and the second aberration correction element L2 and the resin objective lens OL are coaxially integrated by fitting and fixing respective flange portions FL1 and FL2.

The first phase structure PS1 diffracts the first to third light beams, and has a sawtooth cross section including the optical axis. The first phase structure PS1 has the first wavelength and the second wavelength λ.

This is a structure for compensating for the spherical aberration caused by the 1 2 difference and the movement of the paraxial image point position due to the minute change of the first wavelength λ.

Each step Δ 1 of the first phase structure PS 1 is set to a height that satisfies Δ 1 = 8 · λ / (η 1) = 7.042 xm (in the present embodiment, f = 407 nm) Passes through the first phase structure PS1

1

As a result, an eighth-order diffracted light of the first light flux, a fifth-order diffracted light of the second light flux, and a fourth-order diffracted light of the third light flux are generated.

[0246] The optical path difference added to the first light flux when passing through the first phase structure PS1 is 8.0 X λ.

One

The 8th-order diffracted light of the first light beam has the highest diffraction efficiency, and the optical path difference added to the second light beam when passing through the first phase structure PS1 is 4.81 X λ = 5 λ λ (this embodiment). In the form I = 65

2 2 2

5nm), the fifth-order diffracted light of the second light beam has the highest diffraction efficiency, and the optical path difference added to the third light beam when passing through the first phase structure PS1 is 3.99 X λ = 4 λ λ (This embodiment

3 3

Λ = 785 nm), and the fourth-order diffracted light of the third light beam has the maximum diffraction efficiency.

Three

[0247] Note that the diffraction efficiency of the 8th-order diffracted light of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the 5th-order diffracted light of the second light beam is 89.1%, and the fourth-order diffracted light of the third light beam is generated. Has a diffraction efficiency of 100%, and high diffraction efficiency is obtained for any light flux.

[0248] The second phase structure PS2 diffracts the third light beam without diffracting the first light beam and the second light beam, and a pattern in which the cross section including the optical axis is stepped is arranged on a concentric circle. The number of predetermined level planes (four level planes in this embodiment) The structure is such that the steps are shifted by a height corresponding to the number of steps corresponding to the number of surfaces (in the present embodiment, a structure shifted three steps).

[0249] Each step Δ 2 of the staircase structure has a height satisfying Δ 2 = 7 · λ / (n _ 1) = 4.396 z m

1 1

[0250] Since the optical path difference L2 added to the first light beam by the step Δ2 is 7Xλ, the first light beam is

1

Two-phase structure Transmitted without any effect by PS2.

[0251] Further, the optical path difference Μ2 added to the second light beam by the step Δ2 is 3.98 X λ = 4 Χ λ.

[0252] On the other hand, the optical path difference Ν2 added to the third light beam by the step Δ 2 is 3.27 Χ λ = 3.25

Three

2

The phase difference obtained by subtracting an integral multiple of 2π, which is the phase, is 2πΧ0.25. One saw blade

Since it is divided into four, the phase difference of the third light beam is exactly 4 X 2 π Χ 0.25 for one sawtooth.

= 2π, and the first-order diffracted light is generated.

As described above, the second phase structure PS2 selectively diffracts only the third light beam, and

[0254] Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated by the second phase structure PS1 is 1

The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 97.5%, and the diffraction efficiency of the first-order diffracted light of the third light flux is 79.6%, which is high for any light flux. Diffraction efficiency is obtained.

[Sixth embodiment]

Hereinafter, the sixth embodiment of the present invention will be described with reference to the drawings, but the description of the same components as those in the first embodiment will be omitted.

In the present embodiment, in the objective lens unit OU, the first aberration correction element L1 and the second aberration correction element L2 are joined, and the joint surface is convex toward the second aberration correction element L2. It is characterized in that a fifth phase structure PS5 is formed in a peripheral area PA (second peripheral area) of the optical surface on the light source side of the second aberration correction element L2.

As schematically shown in FIG. 13, the objective lens unit OU in the present embodiment has a first aberration correction element L1 having a first phase structure PS1 made of resin and a second phase structure made of resin. The second wavelength correction element L2 and the first wavelength λ and the thickness t of the HD protective layer PL1.

1 1

A glass objective lens OL, the aspherical shape of which is designed to minimize the surface aberration, is coaxially integrated via a lens frame B. Specifically, the first aberration correction element L1 and the second aberration correction element L2 are joined and fixed to one end of a cylindrical lens frame B, and the objective lens 〇L is fitted and fixed to the other end. Therefore, they are coaxially integrated along the optical axis X.

[0257] The first phase structure has an Abbe number V 1 = 56 at the d-line and a refractive index n 1 = d d at the d-line

1. 550000, and the second phase structure is based on the Abbe number at the d-line V 2 = 23.0, d at the d-line

Refractive index n 2 = 1.630000.

d

[0258] Also, a first phase structure PS1 is formed on the optical surface of the first aberration correction element L1 on the optical disk side, and a central area CA (second center area) of the optical surface of the second aberration correction element L2 on the light source side is provided. The second phase structure PS2 is formed in the region (region), and the fifth phase structure PS5 is formed in the peripheral region PA (second peripheral region) surrounding the central region CA.

[0259] The first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps).

[0260] The first phase structure PS1 does not diffract the first light beam and the third light beam but diffracts the second light beam. A pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, for every predetermined number of level surfaces (five level surfaces in this embodiment), the level is shifted by the height corresponding to the number of level surfaces (in this embodiment, Is shifted four steps), and each step Δ 1 of the staircase structure is set to a height satisfying Δ Δ = 2 · λ / (η — 1) = 1.429. Here, η is the refractive index of the first aberration correction element L1 at the wavelength λ (λ = 405 nm in the present embodiment).

Since the optical path difference L1 added to the first light beam by the first phase structure PS1 is 2 × λ, the first light beam is transmitted through the first phase structure PS1 without any action.

[0262] The optical path difference N1 added to the third light beam due to the step Δ1 is 0.99 X = 1 1 (actual (I = 785 nm in the embodiment), so that the third light flux is not created by the first phase structure PS1.

Three

Transmitted as it is without being used.

twenty two

2

The phase difference between the two light beams (the phase difference obtained by subtracting an integer multiple of 2π, which is optically equal in phase), is 2π 200.20. Since one saw tooth is divided into five, the phase difference of the second light beam is exactly 5Χ2πΧ0.20 = 2π for one saw tooth, and a first-order diffracted light is generated.

[0264] As described above, the first phase structure PS1 selectively corrects the second light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of D and the thickness of the protective layer of DVD.

The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated by the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.3%, The diffraction efficiency of the zero-order diffracted light (transmitted light) of the light beam is 99.1%, and a high diffraction efficiency is obtained for any light beam.

[0266] The second phase structure PS2 diffracts the third light beam without diffracting the first light beam and the second light beam, and a pattern in which the cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. In this structure, the number of levels is shifted by the number of levels corresponding to the number of level planes for each predetermined number of level planes (four level planes in this embodiment). Is shifted three steps).

[0267] Each step difference Δ2 of the staircase structure has a height satisfying Δ2 = 7 · λ / (n _ 1) = 4.159 z m

1 1

[0268] Since the optical path difference L2 added to the first light beam by the step Δ2 is 7Xλ, the first light beam

1

Two-phase structure Transmitted without any effect by PS2.

[0269] Also, the optical path difference Μ2 added to the second light beam by the step Δ2 is 3.95 λ λ = 4 Χ λ.

On the other hand, the optical path difference Ν2 added to the third light beam by the step Δ 2 is 3.25 X λ,

The phase difference (the phase difference obtained by subtracting an integral multiple of 2π, which is an optically equal phase) of the third light beam passing through the level surface before and after the three steps Δ2 is 2πΧ0.25. Since one saw tooth is divided into four, the phase difference of the third light beam is exactly 4 X 2 π Χ 0.25 = 2 π for one saw tooth. First-order diffracted light is generated.

As described above, the second phase structure PS2 selectively corrects the third light flux to correct spherical aberration caused by a difference between the thickness of the protective layer of HD and the thickness of the protective layer of CD.

The diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light flux generated by the second phase structure PS1 is 100%, and the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light flux is 88.8. %, The diffraction efficiency of the first-order diffracted light of the third light beam is 81.0%, and high diffraction efficiency is obtained for any light beam.

[0273] The central area CA of the optical surface on the light source side of the second aberration correction element L2 is an area corresponding to the inside of the numerical aperture NA3, and the peripheral area PA is an area corresponding to the outside of the numerical aperture NA3. In the side area PA, a fifth phase structure PS5, which is a structure for controlling the condensing position of the third light beam passing through this area, is formed. Fifth phase structure PS5 diffracts the third light beam without diffracting the first light beam and the second light beam, and has a concentric circle-shaped pattern with a stepped cross section including the optical axis. A structure in which, for each predetermined number of level surfaces (fourth level surface in this embodiment), the number of steps is shifted by the height corresponding to the number of level surfaces (in this embodiment, Three-stage shifted structure). The principle of diffracted light generation by the fifth-phase structure PS5 is the same as that of the second-phase structure PS2, and a detailed description is omitted here.

[0274] When the fifth phase structure PS5 is not formed, the third light beam passing through the peripheral area PA becomes a flare component having large spherical aberration, and this flare component is formed by the second phase structure PS2. Since the light is condensed so as to overlap on the condensing spot, there is a possibility that the focusing operation for the third light beam may be adversely affected. The fourth phase structure PS4 has a function of converting the third light beam passing through the peripheral area PA into a flare component that is condensed on the under side (in a direction in which the condensing position approaches the objective lens unit 〇U). Good focus pull-in operation characteristics can be obtained for the third light flux.

[0275] Further, by forming the joint surface between the first aberration correction element L1 and the second aberration correction element L2 to be convex toward the second aberration correction element L2, the first wavelength; in the wavelength region of I ± 5 nm. Move paraxial image point

1

The focus spot does not increase even if a mode hop occurs due to a change in the output of the first light source when switching from playback to recording. It becomes possible. Real example

Next, a specific numerical example (Example 1) of the objective lens unit ΔU shown in FIG. 2 will be described.

The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other, and the objective lens OL is a glass lens (HOYA LAC130) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1. A good resin lens.

Table 1 1 1 2 shows the lens data of this example. In this numerical example, the optical path difference added to the incident light beam by the first phase structure PS1 and the second phase structure PS2 is represented by an optical path difference function.

[0279] [Table 1-1]

[0280] [Table 1-2] [Diffraction surface coefficient]

[0281] The numerical aperture NA of HD is 0.85, and the numerical aperture NA of DVD in Examples 2 to 4, Example 7, and Example 8 described below, including this example. Is 0 · 65 and of the CD

1 2

The numerical aperture NA is 0.51.

Three

In the present embodiment, the paraxial refraction power of the first aberration correction element L1 is set to be negative, and a divergent light beam is incident on the objective lens OL, so that DVDs and CDs having a thick protective layer can be used. The working distance to this is sufficiently secured. The objective optical system having the negative / positive configuration as in the present embodiment is advantageous in that the working distance for DVDs and CDs is ensured even when the focal length is reduced. Therefore, the objective optical system of this embodiment is most suitable for a slim type optical pickup device.

[0283] In Table 1-1_1 1_2,! "(111111) is the radius of curvature, d (mm) is the lens spacing, n n

408 658 n are the first wavelength; I (= 408 nm), the second wavelength; I (= 658 nm), the third wavelength; I

785 1 2 3

(= 785 nm), the refractive index of the lens, v is the Abbe number of the d-line lens, M M

d HD DVD

M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD

CD

This is the diffraction order of the diffracted light used for recording / reproducing, and the diffraction order of the diffracted light used for recording / reproducing for CD. Further, exponent of 10 (for example, 2. 5 X 10- ^3), shall be expressed by using E (for example, 2. 5E- 3).

[0284] The optical surface on the light source side (first surface) of the first aberration correction element L1, the optical surface on the light source side (fourth surface) of the objective lens ΔL, and the optical surface on the optical disk side (fifth surface) are each non-uniform. The aspheric surface is represented by an equation obtained by substituting the coefficients in the table into the following aspherical form equation. [Aspheric expression]

z = (y ² / R) / [l + ^ {l- (K + l) (y / R) ² }] + A y ⁴ + A y ⁶ + A y ⁸ + A y ¹⁰ + A

4 6 8 10 1 y tens A v tens A y tens A y tens A v

2 14 16 18 20

However,

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

R: radius of curvature

K: conic coefficient

,, Α, Α, Α, Α, A, Α, A, Α: Aspheric coefficient

4 6 8 10 12 14 16 18 20

Further, the first phase structure PS1 and the second phase structure PS2 are represented by an optical path difference added to the incident light beam by each phase structure. Such an optical path difference is represented by an optical path difference function Φ (mm) obtained by substituting the coefficients in the table into an equation representing the following optical path difference function.

[Optical path difference function]

φ = ΜΧ λ / λ X (B y ² + By ⁴ + By ⁶ + B v ⁸ + By ¹⁰ )

B 2 4 6 8 10

However,

Φ: optical path difference function

λ: wavelength of the light beam incident on the diffraction structure

λ: production wavelength

Β

Μ: Diffraction order of diffracted light used for recording / reproducing on optical disc

y: distance from optical axis

B, B, B, B, B, B: Diffraction surface coefficient

2 4 6 8 10

In the present specification, the paraxial power of the diffractive structure diffracted in a direction away from the optical axis is negative (a light beam incident as a parallel light beam on the first phase structure PS1 and the second phase structure PS2 diverges). Direction), and the paraxial power of the diffractive structure that diffracts in the direction approaching the optical axis is positive (the light beam entering the first phase structure PS1 and the second phase structure PS2 as a parallel light beam converges).レく方向方向方向.

Next, a specific numerical example (Example 2) of the objective lens unit ΔU shown in FIG. 3 will be described. [0286] The first aberration correction element LI having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other. 〇L is a glass lens (HOYA BACD5) whose aspheric shape is designed to minimize spherical aberration with respect to the first wavelength; I and the thickness t of the HD protective layer PL1. ,

[0287] Lens data of the present example are shown in Table 2--2_2.

[0288] [Table 2-1]

[0289] [Table 2-2] [Diffraction surface coefficient]

[0290] In Tables 2-1 and 2-2, r (mm) is the radius of curvature, d (mm) is the lens spacing, n, n,

405 655 n are the first wavelength; I (= 405 nm), the second wavelength; I (= 655 nm), the third wavelength; I

785 1 2 3

(= 785nm), v is the Abbe number of the d-line lens, M, M,

d HD DVD

CD

It is the diffraction order of the diffracted light used for recording Z reproduction for CD, and the diffraction order of the diffracted light used for recording Z reproduction for CD.

[0291] The optical surface on the light source side (third surface) of the second aberration correction element L2, the optical surface on the light source side (fifth surface) of the objective lens ΔL, and the optical surface on the optical disk side (sixth surface) are each non-uniform. The aspheric surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical surface expression.

[0292] Further, the first phase structure PS1 and the second phase structure PS2 are represented by an optical path difference added to the incident light beam by each phase structure. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients in Tables 2-1 and 2-2 into the expression representing the optical path difference function.

Next, a specific numerical example (Example 3) of the objective lens unit OU shown in FIG. 4 will be described.

[0294] The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other. The lens OL has the smallest spherical aberration with respect to the first wavelength 1 and the thickness t of the HD protective layer PL1.

1

As described above, the glass lens (HOYA BACD5) whose aspherical shape is designed, but may be a resin lens.

[0295] Lens data of the present example are shown in Tables 3-1 and 3-2. [0296] [sf £ _Table. 3-1]

[0297] [Table 3-2]

[Diffraction surface coefficient]

[0298] In Table 3-1 3-2,! Is the radius of curvature, d (mm) is the lens spacing, n n

785 1 2 3

d HD DVD

CD

It is the diffraction order of the diffracted light used for recording / reproducing on CD, and the diffraction order of diffracted light used for recording / reproducing on CD. [0299] The optical surface (second surface) of the first aberration correction element LI on the optical disk side, the optical surface of the objective lens OL on the light source side (fifth surface), and the optical surface of the optical disk side (sixth surface) are each aspherical. This aspherical surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical shape expression.

[0300] The first to third phase structures PS1 to PS3 are represented by optical path differences added to the incident light beam by the respective phase structures. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients in Tables 3-1 and 3_2 into the equation representing the optical path difference function.

Next, a specific numerical example (Example 4) of the objective lens unit ΔU shown in FIG. 5 will be described.

[0302] The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are spaced apart from each other. The lens OL has the smallest spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1.

1 1

[0303] In the present embodiment, the paraxial refraction power of the first aberration correction element L1 is set to be negative, and a divergent light beam is incident on the objective lens OL. The working distance to this is sufficiently secured. The objective optical system having the negative / positive configuration as in the present embodiment is advantageous in that the working distance for DVDs and CDs is ensured even when the focal length is reduced. Therefore, the objective optical system of this embodiment is most suitable for a slim type optical pickup device.

[0304] The lens data of this example are shown in Tables 4-11 and 4-12.

[0305] [Table 4-1]

[Table 4-2]

[Diffraction surface coefficient]

In Table 4—1 4—2, r (mm) is the radius of curvature, d (mm) is the lens spacing, n n

785 1 2

(= 785 nm), v is the Abbe number of the d-line lens, M M d HD DVD

M is the diffraction order of the diffracted light used for recording / reproducing for HD, the diffraction order of the diffracted light used for recording / reproducing for DVD, and the diffraction order of the diffracted light used for recording / reproducing for CD, respectively. [0308] The optical surface on the light source side (the fourth surface) of the first aberration correction element LI, the optical surface on the light source side (the sixth surface) of the objective lens ΔL, and the optical surface (the seventh surface) on the optical disk side are each non-uniform. The aspheric surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical surface expression.

[0309] The first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light beam by the respective phase structures. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients in Table 4-1 2 into the equation representing the optical path difference function.

Next, a specific numerical example (Example 5) of the objective lens unit ΔU shown in FIG. 6 will be described.

[0311] The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure PS2 have a configuration in which they are joined to each other. Is a resin lens.

Incidentally, in Example 6 to be described later, including this Example, the numerical aperture NA of HD is 0.67, the numerical aperture NA of DVD is 0.65, and the numerical aperture NA of CD is 0.51. It is.

twenty three

[0312] The lens data of this example is shown in Table 5-15-2.

[0313] [Table 5-1]

[0314] [Table 5-2]

[0315] In Table 5—1 5—2, r (mm) is the radius of curvature, d (mm) is the lens spacing, n n

407 655 n are the first wavelength (= 407 nm), the second wavelength (= 655 nm), and the third wavelength, respectively.

785 1 2 3

d HD DVD

CD

It is the diffraction order of the diffracted light used for recording / reproducing on CD, and the diffraction order of diffracted light used for recording / reproducing on CD.

[0316] The optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens OL are aspherical, respectively. It is expressed by a formula with the coefficients inside substituted.

[0317] The first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light beam by the respective phase structures. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients in Table 5-15_2 into the expression representing the optical path difference function.

Next, a numerical example (Example 6) which is a modification of the objective lens unit ΔU shown in FIG. 6 will be described. The objective lens unit OU of the present embodiment has the diffraction order of the diffracted light of each wavelength generated by the first phase structure PS1 of the objective lens unit 〇U shown in FIG. It is characterized in that the first-order diffracted light is the second-order diffracted light, the first-order diffracted light is the second light, and the first-order diffracted light is the third light.

[0319] The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other. It is a resin lens.

[0320] The lens data of this example is shown in Table 6-1-6-2.

[0321] [Table 6-1]

[0322] [Table 6-2]

[Diffraction surface coefficient]

[0323] In Table 6-16-2, 111111) is the radius of curvature, (1 (111111) is the lens interval, 11 n

407 655 n are the first wavelength (= 407 nm), the second wavelength (= 655 nm), and the third wavelength λ, respectively.

785 1 2

d HD DVD

CD

It is the diffraction order of the diffracted light used for recording / reproducing for CD, and the diffraction order of the diffracted light used for reproducing Z for recording on CD. [0324] The optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens 〇L are aspherical, respectively. It is represented by an equation with the coefficients in the table substituted.

[0325] Further, the first phase structure PS1 and the second phase structure PS2 are represented by the optical path difference added to the incident light beam by each phase structure. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients in Tables 6-1 and 6_2 into the expression representing the optical path difference function.

Next, a numerical example (Embodiment 7) as a modification of the objective lens unit ΔU shown in FIG. 13 will be described. The objective lens unit OU of the present embodiment is different from the objective lens unit OU shown in FIG. 3 in that the light flux incident surface and the light flux exit surface of the second aberration correction element L2 are replaced with each other. It has a configuration in which the correction element L2 is joined. Further, by passing through the second phase structure PS2, the fifth-order diffracted light of the first light beam, the third-order diffracted light of the second light beam, and the second-order diffracted light of the third light beam are generated.

[0327] Both the first phase structure PS1 and the second phase structure PS2 are made of resin, and the objective lens OL has a minimum spherical aberration with respect to the first wavelength and the thickness t of the HD protective layer PL1. So that non

1 1

It is a glass lens (HOYA BACD5) designed with a spherical shape, but may be a plastic lens.

[0328] Tables 7-1 and 7-2 show the lens data of this example.

[0329] [Table 7-1]

[0330] [Table 7-2]

[Diffraction surface coefficient]

[0331] In Table 7—1 7—2, r (mm) is the radius of curvature, d (mm) is the lens spacing, n n

405 655 n are the first wavelength (= 405 nm), the second wavelength (= 655 nm), and the third wavelength, respectively.

(= 785 nm), the refractive index of the lens, v is the Abbe number of the d-line lens, M

HD DVD

M is the diffraction order of the diffracted light used for recording / reproducing to HD, DVD This is the diffraction order of the diffracted light used for recording / reproducing, and the diffraction order of the diffracted light used for recording / reproducing for CD.

[0332] The optical surface of the second aberration correction element L2 on the optical disk side (third surface), the optical surface of the objective lens OL on the light source side (fourth surface), and the optical surface of the optical disk side (fifth surface) are each aspherical. This aspherical surface is represented by a mathematical expression obtained by substituting the coefficients in the table into the aspherical shape expression.

[0333] Further, the first phase structure PS1 and the second phase structure PS2 are represented by the optical path difference added to the incident light beam by each phase structure. Such an optical path difference is expressed by the above equation representing the optical path difference function as shown in Table 7-

It is represented by the optical path difference function φ (mm) with the coefficients in 1, 7-2 substituted.

Next, a specific numerical example (Example 8) of the objective lens unit OU shown in FIG. 13 will be described.

The first aberration correction element L1 having the first resin phase structure PS1 and the second aberration correction element L2 having the second resin phase structure have a configuration in which they are joined to each other. And the first wavelength and the thickness t of the HD protective layer PL1 so that spherical aberration is minimized.

1 1

Although the glass lens (HOYA LAC130) is designed with the aspherical shape, it is also good as a resin lens.

[0336] Lens data of the present example are shown in Tables 8-1 and 8-2.

[0337] [Table 8-1]

[I§]

[0338] [Table 8-2]

[0339] In Table 8-· 8-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n n

n is the first wavelength (= 405 nm), the second wavelength (= 655 nm), and the third wavelength, respectively.

785 1 2 3

(= 785nm), the refractive index of the lens, v is the Abbe number of the d-line lens, MM, d HD DVD

CD

This is the diffraction order of the diffracted light used for recording / reproducing, and the diffraction order of the diffracted light used for recording / reproducing for CD.

The optical surface (fourth surface) on the light source side and the optical surface (fifth surface) on the optical disk side of the objective lens ΔL are aspherical, respectively. It is represented by an equation with the coefficients in the table substituted.

[0341] Also, the first phase structure PS1, the second phase structure PS2, and the fourth phase structure PS4 are each a phase structure. It is represented by the optical path difference added to the incident light beam by the structure. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficients shown in Table 7 into the equation representing the optical path difference function.

In the optical surface (first surface) on the light source side of the second aberration correction element L2, the central area CA (the area where the second phase structure PS2 is formed) is an area within φ2.33 mm, The peripheral area PA (the area where the fifth phase structure PS5 is formed) is an area outside φ2.33 mm.

[0343] Table 9 shows a list of numerical data in each of the above Examples. Λ in the table is HD, D

VD, CD design wavelength (nm), f is the focal length of the whole objective lens unit system of HD, DVD, CD (mm), NA is the numerical aperture of HD, DVD, CD, STO is the entrance pupil diameter of HD (mm) ).

[0344] [Table 9]

Industrial applicability

According to the present invention, a high-density optical disc and a DV The spherical aberration due to the difference in the protective layer thickness between D and CD, or the spherical aberration due to the difference in the wavelength used between the high-density optical disk and the DVD and CD can be corrected well, and the blue-violet wavelength region around 400 nm can be corrected. An objective optical system capable of obtaining high light use efficiency in any of a red wavelength region near 650 nm and an infrared wavelength region near 780 nm, an optical pickup device using this objective optical system, and Thus, an optical disk drive device equipped with this optical pickup device can be obtained.

Claims

The scope of the claims

[1] Using a first light beam of a first wavelength emitted from a first light source and having a protective layer having a thickness t

1 1

Recording and / or reproducing information from / to an optical disc, and using a second light flux of a second wavelength (> λ) emitted from a second light source, a second light beam having a protective layer having a thickness t (≥t). 2 optical disc

2 1 2 1

Record and / or reproduce information with respect to the third wavelength emitted from the third light source (

Three

> λ) for a third optical disc having a protective layer of thickness t (> t) using a third light flux

2 3 2

Objective optical system used in an optical pickup device for recording and / or reproducing information,

The objective optical system includes a first aberration correction element, a second aberration correction element, and the first to third light beams that have passed through the first and second aberration correction elements. An objective lens for converging light on the information recording surfaces of the first to third optical disks;

The first aberration correction element is made of a material having an Abbe number V 1 at d-line that satisfies the following equation (1):

An objective having a second phase structure formed of a material having an Abbe number V 2 at d-line that satisfies the following expression (2): Light d

Academic.

40≤ V 1≤80 (1)

d

20≤ V 2 <40 (2)

d

[2] The first phase structure included in the first aberration correction element is formed of a resin that satisfies the following formula (3), wherein a refractive index n 1 at d-line is d or less, and the first phase structure included in the second aberration correction element is The two-phase structure is formed from a resin whose refractive index n 2 at d-line satisfies the following formula (4).

2. The objective optical system according to claim 1, wherein

1.48≤n 1 <1.57 (3)

d

1.57≤n 2≤1.65 (4)

d

[3] The first phase structure may have a spherical aberration due to a difference between the and t, or the first wave.

1 2

Claim 1 to correct spherical aberration caused by the difference between the length and the second wavelength λ.

1 2

Objective optical system.

[4] The first phase structure does not diffract the first light beam and the third light beam, and does not diffract the second light beam. 4. The objective optical system according to claim 3, wherein the objective optical system is a diffraction structure that diffracts light.

[5] The first phase structure is a structure in which a pattern having a stepped cross section including an optical axis is arranged concentrically, and for each predetermined number A of level surfaces, the number of level surfaces is reduced. 5. The objective optical system according to claim 4, wherein the objective optical system has a structure in which the steps are shifted by a height corresponding to the number of steps.

[6] The number A of the predetermined level surfaces is any one of 4, 5, and 6, and an optical path difference caused by one step of the stairs is twice the first wavelength λ. An object optical system according to item 5.

[7] The first phase structure generates α 1 -order diffracted light when the first light beam enters, and β 1 (β 1 <α 1) order when the second light beam enters. The objective optical system according to claim 3, wherein the objective optical system is a diffractive structure that generates a diffracted light of the order γ1 (γ1 ≤ iS1) when the third light flux is incident. .

[8] The objective optical system according to claim 7, wherein the diffraction order a1 is an even number.

[9] The second phase structure may include a spherical aberration due to a difference between the and t, or the first wave.

13

Objective optical system.

10. The objective optical system according to claim 9, wherein the second phase structure is a diffraction structure that does not diffract the first light beam and the second light beam but diffracts the third light beam.

[11] The second phase structure is a structure in which a pattern in which the cross-sectional shape including the optical axis is stepped is arranged concentrically. 11. The objective optical system according to claim 10, wherein the objective optical system has a structure in which the steps are shifted by a height corresponding to the number of steps.

[12] The number of the predetermined level surfaces is any one of 3 and 4, and an optical path difference caused by one step of the stairs is 7 times the first wavelength λ. The object optical system described in the item.

[13] The second phase structure generates _α 2nd-order diffracted light when the first light beam enters, and outputs / 32 (/ 3/2) when the second light beam enters. ) A diffractive structure that generates the next diffracted light and, when the third light beam enters, generates the γ 2 (γ 2 ≤ β 2) order diffracted light. Item 10. The objective optical system according to Item 9.

14. The objective optical system according to claim 13, wherein the diffraction order _α 2 is an odd number.

15. The objective optical system according to claim 1, wherein the first aberration correction element and the second aberration correction element are joined to each other.

16. The objective optical system according to claim 1, wherein the first aberration correction element and the second aberration correction element are separated from each other.

17. The objective optical system according to claim 1, wherein at least one of the first aberration correction element and the second aberration correction element has a third phase structure.

[18] The third phase structure is configured such that, when the first wavelength is changed within ± 5 nm, the third phase structure is not used.

1

18. The objective optical system according to claim 17, having a function of suppressing movement of a paraxial image point position generated in the object optical system.

[19] The third phase structure is configured such that when the wavelength of the first wavelength changes within ± 5 nm, the third phase structure changes the pair.

1

18. The objective optical system according to claim 17, having a function of suppressing a change in spherical aberration generated in the object optical system.

20. The objective optical system according to claim 17, wherein the third phase structure has a function of suppressing a change in spherical aberration caused by a change in a refractive index of the objective optical system.

21. The objective optical system according to claim 17, wherein the third phase structure is formed on one of the first aberration correction element and the second aberration correction element.

22. The method according to claim 21, wherein the third phase structure is formed in the first aberration correction element, and adds an optical path difference of 10 times the first wavelength λ to the first light flux. Stated objective

1

Optical system.

[23] The first phase structure and the second phase structure are both formed of resin.

2. The objective optical system according to item 1.

24. The objective optical system according to claim 1, wherein one of the first phase structure and the second phase structure is formed of an ultraviolet curable resin or a thermosetting resin.

25. The phase structure according to claim 24, wherein, of the first phase structure and the second phase structure, a phase structure formed of an ultraviolet curable resin or a thermosetting resin is the second phase structure. Objective optical system.

26. The phase structure according to claim 24, wherein, of the first phase structure and the second phase structure, a phase structure formed of an ultraviolet curable resin or a thermosetting resin is formed on a glass substrate. Objective optics.

[27] The objective lens has spherical aberration correction for a combination of the t and the first wavelength; I.

1 1

The objective optical system according to claim 1, which is optimized.

[28] The objective optical system according to claim 1, wherein the following formulas (5) to (7) are satisfied.

380 Happy λ Ku 420 Belly (5)

1.δ <λ / λ <1.7 (6)

twenty one

1.8 <λ / λ <2.1 (7)

3 1

29. The objective optical system according to claim 4, wherein the first phase structure has a function of diverging the second light flux.

30. The objective optical system according to claim 10, wherein the second phase structure has a function of diverging the third light flux.

[31] The first phase structure has a function of suppressing a movement of a paraxial image point position generated in the objective optical system when the first wavelength 1 changes in wavelength within ± 5 nm. Item 7. The objective optical system according to Item 7.

32. The objective optical system according to claim 1, wherein at least one of the first aberration correction element and the second aberration correction element has a negative paraxial power with respect to the first wavelength λ.

1

33. The objective optical system according to claim 1, wherein all of the first to third light beams are incident on the first and second aberration correction elements as parallel light beams.

[34] The first aberration correction element is configured such that the Abbe number V1 at the d-line satisfies Expression (1) and the first d

The second aberration correction element has a phase structure, and the Abbe number V 2 at d-line satisfies Expression (2).

2. The objective optical system according to claim 1, further comprising a second phase structure.

[35] The first aberration-correcting element has a refractive index n1 at d-line satisfying the expression (3), and

The second aberration correction element has a phase structure, and the refractive index n 2 at d-line satisfies the expression (4).

3. The objective optical system according to claim 2, further comprising a second phase structure.

[36] The first aberration correction element has a positive paraxial power with respect to the first wavelength λ, and the second aberration correction element has a negative paraxial power with respect to the first wavelength λ. Range of 2. The objective optical system according to item 1.

[37] The first aberration correction element and the second aberration correction element are joined to each other,

37. The objective optical system according to claim 36, wherein a joint surface between the first aberration correction element and the second aberration correction element has a shape that is convex toward the second aberration correction element.

38. Among the first phase structure and the second phase structure, a non-heat-reflection preventing coat is formed on a surface of a phase structure formed of an ultraviolet curable resin or a thermosetting resin. Item 25. The objective optical system according to Item 24.

39. The objective optical system according to claim 23, wherein the first phase structure is formed of a cyclic oleolefin-based resin, and the second phase structure is formed of a fluorene-based polyester resin.

[40] The optical surface on which the first phase structure is formed is divided into a first central region including an optical axis and a first peripheral region surrounding the first central region. The objective optical system according to claim 4, wherein the objective optical system is formed in the first central region.

[41] In at least a part of the first peripheral region, a fourth phase structure for controlling a condensing position of the second light beam passing through this part is formed, and the fourth phase structure is formed by the fourth phase structure. 41. The objective optical system according to claim 40, wherein the objective optical system is a diffractive structure that diffracts the second light beam without diffracting the first light beam and the third light beam.

[42] The optical surface on which the second phase structure is formed is divided into a second central region including an optical axis and a second peripheral region surrounding the second central region. The objective optical system according to claim 10, wherein the objective optical system is formed in the second central region.

[43] In at least a part of the second peripheral region, a fifth phase structure for controlling a condensing position of the third light flux passing through this part is formed, and the fifth phase structure is formed by the fifth phase structure. 43. The objective optical system according to claim 42, wherein the objective optical system has a diffraction structure that diffracts the third light beam without diffracting the first light beam and the second light beam.

[44] The back focus fB for the first wavelength; I and the back focus for the second wavelength; I

1 1 2

The difference between the cascade fB and the back focus fB with respect to the first wavelength λ and the second wavelength

2 1 1

Claim 1 wherein any difference between the back focus fB and λ is 0.2 mm or less.

3 3

Item 4. The objective optical system according to Item 1.

[45] The ratio of the minimum width の of the pattern of the second phase structure to the first wavelength; I

Μ 1 Μ

12. The objective optical system according to claim 11, wherein the / λ power is 25 or more.

1

46. The objective according to claim 1, wherein the first phase structure is formed on a surface of the first aberration correction element, and the second phase structure is formed on a surface of the second aberration correction element. Optical system.

47. The objective optical system according to claim 5, wherein both the first phase structure and the second phase structure are formed on a plane.

48. The objective optical system according to claim 11, wherein both the first phase structure and the second phase structure are formed on a plane.

49. The method according to claim 1, wherein the first aberration correction element and the second aberration correction element, and the objective lens are held by a holding member such that a relative positional relationship is universal. Objective optics.

[50] Recording and / or reproducing information on / from the first optical disk having a thick protective layer

1

A first light source that emits a first light beam of a first wavelength λ

In order to record and / or reproduce information on the second optical disc, a second wavelength (> λ

Two

A second light source that emits a second light beam of

1

In order to record and / or reproduce information on the third optical disc, the third wavelength (> λ

Three

A third light source that emits a third light beam of

2

And the objective optical system according to claim 1,

twenty one

3 2

Optical pickup device.

[51] An optical disc drive device comprising the optical pickup device according to claim 50, and a moving device for moving the optical pickup device in a radial direction of the optical information recording medium.