JPWO2005117002A1 - Objective optical system, optical pickup device, and optical disk drive device - Google Patents

Abstract

The objective optical system of the present invention records and / or reproduces information using the first light beam emitted from the first light source, the second light beam emitted from the second light source, and the third light beam emitted from the third light source. Information recording on the first to third optical discs respectively for the first and second aberration correction elements and the first to third light fluxes that have passed through the first and second aberration correction elements. The first aberration correction element has a first phase structure formed of a material in which the Abbe number νd1 in the d-line satisfies 40 ≦ νd1 ≦ 80. The two-aberration correction element has a second phase structure formed from a material in which the Abbe number νd2 in the d-line satisfies 20 ≦ νd2 <40.

Description

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

Optical pickup device compatible with high-density optical discs, DVD (using red laser light source), and CD (using infrared laser light source) that have increased recording density by using a blue-violet laser light source. And the optical element used for such an optical pick-up apparatus is known (for example, refer patent documents 1-3).
JP 2004-079146 A JP 2002-298422 A JP 2003-207714 A

  Numerical Example 7 of Patent Document 1 has a diffractive structure on the surface of an objective lens that generates second-order diffracted light with a blue-violet laser beam and first-order diffracted light with a red laser beam and an infrared laser beam. Due to the action of this diffractive structure, spherical aberration due to the difference in the protective layer thickness between the high-density optical disc and the DVD is corrected, and a divergent light beam is incident on the objective lens when recording / reproducing information with respect to the CD. An objective lens that corrects spherical aberration due to the difference in the thickness of the protective layer between a density optical disk and a CD is disclosed.

  Although this objective lens can secure a high diffraction efficiency in any wavelength region, the degree of divergence of the infrared laser beam becomes too strong at the time of recording / reproducing information on a CD, and the coma when the objective lens is tracking. There is a problem in that good recording / reproducing characteristics cannot be obtained with respect to a CD because the generation of aberration becomes too large.

  In Numerical Example 3 of Patent Document 2, diffraction is performed on the surface of the objective lens such that a third-order diffracted light is generated with a blue-violet laser beam and a second-order diffracted light is generated with a red laser beam and an infrared laser beam. An objective lens is disclosed which has a structure and corrects spherical aberration due to the difference in the thickness of the protective layer between the high-density optical disc and DVD and CD.

  Although this objective lens can correct spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the DVD and further spherical aberration due to the difference in the protective layer thickness between the high-density optical disk and the CD due to the action of the diffractive structure. Since the diffraction efficiency of the third-order diffracted light of the blue-violet laser beam and the diffraction efficiency of the second-order diffracted light of the infrared laser beam are as low as about 70%, the photodetector cannot cope with the increase in the recording / reproducing speed for the optical disk. There are problems in that good recording / reproduction characteristics cannot be obtained due to the low S / N ratio of the detection signal, and that the life of the laser light source is shortened because the voltage applied to the laser light source is high.

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

  That is, in the objective lens of Numerical Example 7 of Patent Document 1 corresponding to a case where both the diffraction efficiency of the diffracted light of the blue-violet laser beam and the diffraction efficiency of the diffracted light of the infrared laser beam are ensured to be high, the blue-violet laser beam The diffraction angle of the diffracted light and the diffraction angle of the diffracted light of the infrared laser beam substantially coincide with each other, so that the spherical aberration due to the difference in the thickness of the high-density optical disc and the CD protective layer cannot be corrected by the diffractive structure. .

  On the other hand, in the objective lens of Numerical Example 3 of Patent Document 2, which corresponds to the case where a difference is made between the diffraction angle of the diffracted light of the blue-violet laser beam and the diffraction angle of the diffracted light of the infrared laser beam, the blue-violet laser Both the diffraction efficiency of the diffracted light of the light beam and the diffraction efficiency of the infrared laser light beam are lowered.

  In addition to the diffraction structures described in Patent Documents 1 and 2, not only in the technology using a phase corrector (referred to as an optical path difference providing structure in this specification) as described in Patent Document 3. Similarly to the diffraction structure, the spherical aberration correction effect for the blue-violet laser beam and the infrared laser beam by the optical path difference providing structure and the transmittance of the optical path difference providing structure are in a trade-off relationship.

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

The configuration according to Item 1 records and / or reproduces information with respect to a first optical disc having a protective layer having a thickness of t ₁ using a first light beam having a first wavelength λ ₁ emitted from a first light source. Recording of information on the second optical disk having a protective layer having a thickness t ₂ (≧ t ₁ ) using the second light flux having the second wavelength λ ₂ (> λ ₁ ) emitted from the second light source and / or Alternatively, information is obtained with respect to the third optical disc having a protective layer having a thickness of t ₃ (> t ₂ ) by using the third light flux having the third wavelength λ ₃ (> λ ₂ ) emitted from the third light source. An objective optical system used in an optical pickup device that records and / or reproduces the first aberration correction element, the first aberration correction element, the second aberration correction element, the first aberration correction element, and the first aberration correction element. 2 The first to third light fluxes that have passed through the aberration correction element are respectively converted into the first light beam. And an objective lens for focusing on the information recording surface of the third optical disk, and the first aberration correction element is a material whose Abbe number ν _d 1 in the d-line satisfies the following expression (1): The second aberration correcting element has a second phase structure formed from a material in which the Abbe number ν _d 2 in the d-line satisfies the following expression (2).

40 ≦ ν _d 1 ≦ 80 (1)
20 ≦ ν _d 2 <40 (2)
When the first phase structure and the second phase structure are formed of a material having an Abbe number satisfying the expressions (1) and (2), the blue-violet laser beam, the red laser beam, and the red, which have been difficult in the prior art, are difficult. It is possible to achieve mutual compatibility between the high-density optical disc, the DVD, and the CD while maintaining a high transmittance for any wavelength of the outer laser beam.

  When the Abbe number of the first phase structure decreases beyond the lower limit of the expression (1), the transmittance of the first phase structure for the third wavelength λ3 increases, but the transmittance of the first phase structure for the second wavelength λ2 increases. Since it becomes low, it is not preferable. On the other hand, a material having an Abbe number exceeding the upper limit of the equation (1) is difficult to manufacture, so it is not realistic.

  Further, if the Abbe number of the first phase structure increases beyond the upper limit of the expression (2), the transmittance of the second phase structure increases with respect to the second wavelength λ2, but the transmission of the second phase structure with respect to the third wavelength λ3 increases. Since the rate is low, it is not preferable. On the other hand, a material whose Abbe number is smaller than the lower limit of the equation (2) is not realistic because it becomes difficult to manufacture.

  In this specification, an objective lens with a NA of 0.85 and a protective layer thickness of 0.1 mm, a Blu-ray disc with an objective lens with an NA of 0.65 to 0.67 and a protective layer thickness of 0 are used. An optical disc using a blue-violet laser light source such as HD DVD of 6 mm is collectively referred to as “high density optical disc” and is abbreviated as “HD”. In addition to the above-described Blu-ray Disc HD DVD, there are magneto-optical discs, optical discs having a protective film with a thickness of several to several tens of nanometers on the information recording surface, and optical discs having a protective layer or protective layer having a zero thickness. Included in high density optical discs.

  In this specification, DVD (Digital Versatile Disc) means DVD series optical discs such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, etc. CD (compact disc) is a generic term for CD-series optical discs such as CD-ROM, CD-Audio, CD-Video, CD-R, and CD-RW.

  In the present specification, the “objective lens” is a condensing element that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. Refers to the lens.

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

  Further, in this specification, the “phase structure” is a general term for a structure having a plurality of steps in the optical axis direction and adding an optical path difference (phase difference) to the incident light flux. The optical path difference added to the incident light flux by this step may be an integer multiple of the wavelength of the incident light flux or a non-integer multiple of the wavelength of the incident light flux. Specific examples of such a phase structure include a diffractive structure in which the above steps are arranged at periodic intervals in the direction perpendicular to the optical axis, and the above steps are arranged at non-periodic intervals in the direction perpendicular to the optical axis. This is an optical path difference providing structure (also referred to as a phase difference providing structure).

  The phase structure can take various cross-sectional shapes as schematically shown in FIGS. 7 (a) to 12 (b). 7 (a) and 7 (b) show a case of a sawtooth shape, and FIGS. 8 (a) and 8 (b) show a case of a step shape in which all steps are in the same direction. a) and 9 (b) are cases where the direction of the step is a stepped shape that is opposite in the middle. 10 (a) and 10 (b), a cross-sectional pattern 11 including a plurality of level surfaces 12 is arranged concentrically, and a predetermined number of level surfaces (FIGS. 10 (a) and 10 (b) are shown. In (b), the level is shifted by a height corresponding to the number of level planes (four levels in FIGS. 10 (a) and 10 (b)) every five level planes).

  7A and 7B show the case where the directions of the saw blades are the same, and in FIGS. 10A and 10B, the directions of the patterns whose cross-sectional shapes are stepped are the same. As shown in FIGS. 11A and 11B and FIGS. 12A and 12B, the phase inversion portion PR and the phase inversion portion PR are closer to the optical axis. There may be included a saw tooth whose direction is opposite to the saw tooth and a pattern whose direction is opposite to the pattern closer to the optical axis than the phase inversion portion PR. FIGS. 7A to 12B 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. 10 (a), 10 (b), 12 (a), and 12 (b), the predetermined number of level faces is 5, but the present invention is not limited to this.

It is a principal part top view which shows the structure of an optical pick-up apparatus. It is a side view which shows an example of a structure of an objective lens unit. It is a side view which shows an example of a structure of an objective lens unit. It is a side view which shows an example of a structure of an objective lens unit. It is a side view which shows an example of a structure of an objective lens unit. It is a side view which shows an example of a structure of an objective lens unit. It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is sectional drawing (a) which shows an example of a structure of a phase structure, (b). It is a side view which shows an example of a structure of an objective lens unit.

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

The configuration according to Item 2 is the objective optical system according to Item 1, wherein the first phase structure included in the first aberration correction element is a resin in which a refractive index n _d 1 at d-line satisfies the following expression (3): It is formed from the second phase structure and the second aberration correcting element has a refractive index n _{d 2} at the d-line is formed of a resin satisfying the following equation (4).

1.48 ≦ n _d 1 <1.57 (3)
1.57 ≦ n _d 2 ≦ 1.65 (4)
Generally, the resin for an optical element, the refractive index _{n d} of d line (587.6 nm) are distributed between 1.48 to 1.65, dispersed enough _{to n d} increases increases ( The Abbe number tends to be small). Therefore, as in the configuration described in claim 2, when together with the resin of the first phase structure and the second phase structure, made of a material having n _d which satisfies the equation (3) and (4) By doing so, the same effect as that of Item 1 can be achieved.

The configuration according to Item 3 is the objective optical system according to Item 1 or 2, wherein the first phase structure includes spherical aberration caused by a difference between the t ₁ and the t ₂ , or the first wavelength λ ₁ and the The spherical aberration due to the difference of the second wavelength λ ₂ is corrected.

As described in item 3, by using the first phase structure made of a material satisfying the formula (1) or (3) formed in the first aberration correction element, the high-density optical disc and the DVD are made compatible with each other. While maintaining high transmittance for both the blue-violet laser beam and the red laser beam, spherical aberration due to the difference between t ₁ and t ₂ , or the first wavelength λ ₁ and the second wavelength λ ₂ It becomes possible to correct the spherical aberration due to the difference.

  The first phase structure may be a diffractive structure or an optical path difference providing structure.

  The configuration described in Item 4 is the objective optical system described in Item 3, wherein the first phase structure is a diffraction structure that does not diffract the first light beam and the third light beam but diffracts the second light beam.

  In particular, by making the first phase structure a diffractive structure that selectively diffracts only the second light flux as in Item 4, it becomes possible to independently control the aberration with respect to the second light flux. Good condensing characteristics can be obtained for both.

  The configuration according to Item 5 is the objective optical system according to Item 4, wherein the first phase structure is a structure in which patterns having a stepped cross-sectional shape including an optical axis are arranged on a concentric circle. For each of the number A of level surfaces, the level is shifted by the height corresponding to the number of levels corresponding to the number of level surfaces.

  Specifically, by adopting the configuration as in item 5, it is possible to give the first phase structure the diffraction characteristics as in item 4.

  When a light source deviated from the design wavelength is used as the first light source, the optical path difference added by each step constituting each pattern is slightly deviated from an integral multiple of the wavelength. Local spherical aberration will occur, but the wavefront with local spherical aberration will be interrupted at the part where the level is shifted by the height corresponding to the number of level surfaces. The wavefront is flat. In this way, by making the first phase structure a structure in which the steps are shifted by the height corresponding to the number of level surfaces, the tolerance for the individual difference of the oscillation wavelength of the first light source can be relaxed.

  In the present specification, the diffraction structure having the characteristic of selectively diffracting one light beam among the first light beam to the third light beam is hereinafter referred to as a “wavelength selective diffraction structure”.

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 of 4, 5, and 6, and an optical path difference caused by one step of the steps is the first is twice the wavelength lambda _1.

  More specifically, the configuration as described in item 6 enables the first phase structure to have the diffraction characteristics as described in item 4, and allows high transmission for three light beams. The rate can be secured. In order to ensure the highest transmittance for the three light beams, the number A of predetermined level surfaces is preferably set to 5.

Here, the principle of diffracted light generation 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 ₁ is set to 405 nm which is the recording / reproducing wavelength of the high-density optical disc HD, the second wavelength λ ₂ is set to 655 nm which is the recording / reproducing wavelength of DVD, and the third wavelength λ _{3 is set} to the CD. The recording / reproducing wavelength is 785 nm. Here, the first phase structure needs to satisfy the following formulas (8) to (13).

L1 = Δ1 · (n ₁₁ −1) / λ ₁ (8)
M1 = Δ1 · (n ₁₂ −1) / λ ₂ (9)
N1 = Δ1 · (n ₁₃ −1) / λ ₃ (10)
φ (M1) = INT (A · M1) − (A · M1) (11)
−0.4 <φ (M1) <0.4 (12)
L1 = 2 (13)
Any of A = 4, 5, 6 (14)
INT (X): an integer closest to X, where
Δ1: Depth in the optical axis direction of each step constituting each pattern of the first phase structure n ₁₁ : Refractive index of the material forming the first phase structure with respect to the first wavelength λ 1 n ₁₂ : First with respect to the second wavelength λ 2 Refractive index of material forming one phase structure n ₁₃ : Refractive index of material forming first phase structure with respect to third wavelength λ3 A: Number of level planes formed in each pattern of first phase structure L1, M1 , 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 a and 2, the optical path difference L1 to be added for the first light flux by the step Δ1, since twice the first wavelength lambda _1, the first light flux passing through the level surface between adjacent The wavefront is connected with a shift of exactly two wavelengths. Therefore, the first light flux is transmitted as it is with a transmittance of 100% without being diffracted by the first phase structure. Further, when the first phase structure is formed from a material in which the Abbe number ν _d 1 in the d-line satisfies the above equation (1), the optical path difference N1 added to the third light flux by the step Δ1 is 3 since very close to 1 times the wavelength lambda _3, the wavefront of the third light flux passing through the level surface between adjacent leads shifted by one wavelength. Accordingly, the third light flux is also transmitted as it is with a transmittance of almost 100% without being diffracted by the first phase structure. On the other hand, the optical path difference M1 is added to the second light flux by the step Δ1, so becomes about 1.2 times the second wavelength lambda _2, the wave front of the second light flux passing through the level surface Adjacent 1. The wavefront is shifted by two wavelengths, but the substantial wavefront shift excluding the wavefront shift for one wavelength that is optically in phase is 0.2 wavelength. Here, if each pattern is composed of five level surfaces, the wavefront shift at both ends of each pattern is about one wavelength (= 0.2 wavelength × 5), so the second light flux has a high diffraction of about 87%. Diffracts in the first-order direction with efficiency (first-order diffraction). The above expression (12) is a conditional expression for increasing the diffraction efficiency of the first-order diffracted light of the second light beam, and the number A of level surfaces formed in each pattern is set so as to satisfy the expression (12). By determining, it is possible to sufficiently secure the diffraction efficiency of the first-order diffracted light of the second light beam. In the case where the first phase structure is formed of a material whose Abbe number ν _d 1 in the d-line satisfies the above-described expression (1), any of A = 4, 5, and 6 can satisfy the expression (12). However, the value of the equation (12) is closest to 0 when A = 5, and at this time, the diffraction efficiency of the first-order diffracted light of the second light flux is the highest.

In the above wavelength selective diffraction structure, the diffraction efficiency of the diffracted light of the second light beam depends only on the Abbe number ν _d 1 in the d line of the material on which the wavelength selective diffraction structure is formed, and the refractive index in the d line. It does not depend on n _d 1. Therefore, there is a relatively freedom with respect to the refractive index n _{d 1,} the refractive index n _{d 1} becomes higher depth d1 is the optical axis direction of each step becomes deeper small, that a step shape to accurately manufacture Since it becomes difficult, when there are a plurality of materials having the same Abbe number ν _d 1, it is preferable to select a material having the largest n _d 1.

  The configuration according to Item 7 is the objective optical system according to Item 3, wherein the first phase structure generates α-order diffracted light when the first light beam is incident, and the second light beam is incident. In this case, the diffraction structure generates β1 (β1 <α1) order diffracted light, and generates γ1 (γ1 ≦ β1) order diffracted light when the third light beam is incident.

  In order to achieve mutual compatibility between the high-density optical disc and the DVD by the first phase structure, in addition to the diffraction characteristic described in item 4, the first phase structure may have the diffraction characteristic as described in item 7. good. By providing such diffraction characteristics, high transmittance can be secured for the three light beams. Note that the diffractive structure having such a diffractive characteristic has a sawtooth or stepped cross section including the optical axis. When the cross-sectional shape including the optical axis is a sawtooth shape, the absolute value 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 different from each other. The case where the shape is a staircase type 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.

  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 flux with the first phase structure, it is preferable that the diffraction order α1 of the first light flux is an even number. Specifically, it is preferable to use any combination of (α1, β1, γ1) = (2, 1, 1), (8, 5, 4) as a combination of diffraction orders of light beams of respective wavelengths. This makes it possible to satisfactorily correct spherical aberration due to the difference between t ₁ and t ₂ or spherical aberration due to the difference between the first wavelength λ ₁ and the second wavelength λ ₂ . When the combination of (α1, β1, γ1) = (2,1,1) is used as the combination of diffraction orders, it is preferable that the manufacturing wavelength λ _B of the first phase structure is shorter than λ1. When the combination of (α1, β1, γ1) = (8, 5, 4) is used, it is preferable that the manufacturing wavelength λ _B of the first phase structure is longer than λ1. Thereby, the diffraction efficiency of the light flux of each wavelength can be ensured high.

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 spherical aberration caused by a difference between the t ₁ and the t ₃ , or the first The spherical aberration due to the difference between the wavelength λ ₁ and the second wavelength λ ₂ is corrected.

As described in item 9, by using the second phase structure formed of the material satisfying the formula (2) or (4) formed in the second aberration correction element, the high-density optical disc and the CD are mutually compatible. While maintaining high transmittance for both the blue-violet laser beam and the infrared laser beam, spherical aberration due to the difference between t ₁ and t ₃ , or the first wavelength λ ₁ and the second wavelength it is possible to correct the spherical aberration due to the difference of the lambda _2.

  The second phase structure may be a diffractive structure or an optical path difference providing structure.

  The configuration described in Item 10 is the objective optical system described in Item 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.

  In particular, by making the second phase structure a diffractive structure that selectively diffracts only the third light flux as in Item 10, it becomes possible to independently control the aberration with respect to the third light flux. Good condensing characteristics can be obtained for both.

  The configuration according to Item 11 is the objective optical system according to Item 10, wherein the second phase structure is a structure in which patterns having a stepped cross-sectional shape including an optical axis are arranged on a concentric circle. In this structure, the level is shifted by a height corresponding to the number of levels corresponding to the number of level planes.

  Specifically, with the configuration as in item 11, it is possible to give the second phase structure the diffraction characteristics as in item 10.

  In addition, since the second phase structure has a structure in which the steps are shifted by a height corresponding to the number of level surfaces, the tolerance with respect to the individual difference of the oscillation wavelength of the first light source is obtained as in the configuration of Item 5. Can be relaxed.

The configuration described in item 12 is the objective optical system described in item 11, wherein the number B of the predetermined level surfaces is either 3 or 4, and the optical path difference caused by one step of the steps is the first level. 1, which is 7 times the wavelength λ _1.

More specifically, by adopting the configuration as described in item 12, it is possible to give the second phase structure the diffraction characteristics as described in item 10, and high transmission with respect to three light beams. The rate can be secured. In order to ensure the highest transmittance with respect to the three light beams, the second phase structure is formed from a material in which the Abbe number ν _d 2 in the d-line satisfies 25 <ν _d 2 <40. When the second phase structure is formed of a material in which the Abbe number ν _d 2 in the d-line satisfies 20 ≦ ν _d 2 ≦ 25, the number B of the predetermined level surfaces is set to 4. 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 flux without diffracting the first light flux and the second light flux. In the following description, the first wavelength λ ₁ is set to 405 nm which is the recording / reproducing wavelength of the high-density optical disc HD, the second wavelength λ ₂ is set to 655 nm which is the recording / reproducing wavelength of DVD, and the third wavelength λ _{3 is set} to the CD. The recording / reproducing wavelength is 785 nm. Here, the first phase structure needs to satisfy the following formulas (15) to (21).

L2 = Δ2 · (n ₂₁ −1) / λ ₁ (15)
M2 = Δ2 · (n ₂₂ ^ −1) / λ ₂ (16)
N2 = Δ2 · (n ₂₃ −1) / λ ₃ (17)
φ (N2) = INT (B · N2) − (B · N2) (18)
−0.4 <φ (N2) <0.4 (19)
L2 = 7 (20)
B = 3 or 4 (21)
INT (X): an integer closest to X, where
Δ2: Depth in the optical axis direction of each step constituting each pattern of the second phase structure n ₂₁ : Refractive index of the material on which the second phase structure with respect to the first wavelength λ1 is formed n ₂₂ : With respect to the second wavelength λ2 Refractive index of the material in which the second phase structure is formed n ₂₃ : Refractive index of the material in which the second phase structure is formed with respect to the third wavelength λ3 B: Number of level planes 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, respectively, by the steps formed in the patterns of the second phase structure. When the L2 to 7, the optical path difference L2 to be added for the first light flux by the step Δ2, since the seven times of the first wavelength lambda _1, the first light flux passing through the level surface between adjacent The wavefronts are connected with a shift of exactly 7 wavelengths. Therefore, the first light flux is transmitted as it is with a transmittance of 100% without being diffracted by the first phase structure. Further, when the second phase structure is formed from a material in which the Abbe number ν _d 2 in the d-line satisfies the above-described expression (2), the optical path difference M2 added to the second light flux by the step Δ2 is Since it is very close to four times the two wavelengths λ ₂ , the wavefronts of the second light fluxes passing through adjacent level surfaces are shifted and connected by four wavelengths. Therefore, the second light flux is also transmitted as it is with a transmittance of almost 100% without being diffracted by the second phase structure. On the other hand, the optical path difference N2 being added to the third light flux by the step Δ2 is since about 3.3 times of the third wavelength lambda _3, the wavefront of the third light flux passing through the level surface Adjacent 3. The wavefront shifts by three wavelengths, but the substantial wavefront shift excluding the wavefront shift for three wavelengths that are optically in phase is 0.3 wavelength. Here, when each pattern is constituted by three or four level planes, the deviation of the wave front at both ends of each pattern is about one wavelength (= 0.3 wavelength × 3 or = 0.3 wavelength × 4). Therefore, the third light beam is diffracted in the first-order direction with a high diffraction efficiency of 70 to 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 beam, and the number B of level surfaces formed in each pattern is determined so as to satisfy the equation (19). By doing so, 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 in which the Abbe number ν _d 2 in the d-line satisfies 25 <ν _d 2 <40, the value of the equation (12) is closest to 0 when B = 3. And when the second phase structure is formed of a material in which the Abbe number ν _d 2 in the d-line satisfies 20 ≦ ν _d 2 ≦ 25, the value of the equation (12) is closest to 0 when B = 4 In this case, the diffraction efficiency of the first-order diffracted light of the third light flux is 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 ν _d 2 at the d line of the material from which the wavelength selective diffraction structure is formed, and the refraction at the d line. It does not depend on the rate n _d 2. Therefore, there is a relatively freedom with respect to the refractive index n _{d 2,} the value of the refractive index n _{d 2} is about the depth d2 is the optical axis direction of each step becomes deeper small, that a step shape to accurately manufacture Since it becomes difficult, when there are a plurality of materials having the same Abbe number ν _d 2, it is preferable to select a material having the largest n _d 2.

  The configuration according to Item 13 is the objective optical system according to Item 9, wherein the second phase structure generates α-order diffracted light when the first light beam is incident, and the second light beam is incident. In this case, the diffraction structure generates β2 (β2 <α2) -order diffracted light, and generates γ2 (γ2 ≦ β2) -order diffracted light when the third light beam is incident.

  In order to achieve mutual compatibility between the high-density optical disk and the CD by using the second phase structure, in addition to the diffraction characteristic described in item 10, the second phase structure may have a diffraction characteristic as described in item 13. good. By providing such diffraction characteristics, high transmittance can be secured for the three light beams. Note that the diffractive structure having such a diffractive characteristic has a sawtooth or stepped cross section including the optical axis.

  The configuration described in item 14 is the objective optical system described in item 13, wherein the diffraction order α2 is an odd number.

In particular, in order to ensure the transmittance of the third light beam with the second phase structure, it is preferable to set the diffraction order α2 of the first light beam to an odd number. Specifically, any combination of (α2, β2, γ2) = (5, 3, 2), (7, 4, 3), (9, 5, 4) is used as a combination of diffraction orders of light beams of respective wavelengths. It is preferable to use a combination of the above, which makes it possible to correct spherical aberration due to the difference between t ₁ and t ₃ . Further, when the magnification of the objective optical system when recording / reproducing information with respect to the third optical disk is set within the range of −0.2 to 0, spherical aberration caused by the difference between t ₁ and t ₃ is better. Can be corrected.

When the diffraction order of the above combination is used for the light flux of each wavelength, a high diffraction efficiency of the light flux of each wavelength can be secured if the manufacturing wavelength λ _B of the second phase structure is shorter than λ1.

  Numerical example of Patent Document 2 corresponding to a case where a difference is made between the diffraction angle of the blue-violet laser beam and the diffraction angle of the infrared laser beam by making the diffraction order of the violet laser beam (first beam) odd. The objective lens 3 uses a relatively low dispersion material having an Abbe number of about 55 at the d-line, so that both the diffraction efficiencies of the light beams of both wavelengths are low. However, in the objective optical system according to the present invention, the second Since a material having high dispersibility that satisfies the formula (2) is used as the material of the phase structure, even when the diffraction order of the violet laser beam (first beam) is an odd number, the diffraction efficiency of the beams of both wavelengths is improved. Both can be secured high.

  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.

  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.

  Item 17 is the objective 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 has a third phase structure. .

  According to Item 17, the third phase structure is formed on any one of the optical surfaces of the first aberration correction element and the second aberration correction element, so that the condensing characteristic with respect to each light beam of the objective optical system is further improved. It can be made good. The third phase structure may be a diffractive structure or an optical path difference providing structure. The aberration corrected by the third phase structure may be, for example, chromatic aberration associated with a minute change in the first wavelength λ1, or spherical aberration generated due to a change in the refractive index of the objective lens associated with a temperature change. good.

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

  In order to avoid such a problem, in the objective optical system according to the present invention, any one of the first to third phase structures is formed on the optical surface closest to the laser light source. Is preferred.

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

The configuration according to item 18 is the objective optical system according to item 17, wherein the third phase structure is a paraxial image generated in the objective optical system when the wavelength of the first wavelength λ ₁ changes within ± 5 nm. It has a function to suppress the movement of the point position.

According to the configuration described in item 18, when the third phase structure has a function of suppressing the movement of the paraxial image point position in the wavelength region of the first wavelength λ ₁ ± 5 nm, when switching from reproduction to recording, Even when a wavelength change (mode hop) occurs instantaneously with a change in the output of the first light source, the condensing spot does not become large, and a good condensing state can always be maintained.

Structure of claim 19, wherein, in the objective optical system according to claim 17 or 18, wherein the third phase structure is generated in the objective optical system when the first wavelength lambda ₁ has wavelength change within ± 5 nm spherical It has a function of suppressing changes in aberration.

According to the configuration described in item 19, by providing the third phase structure with a function of suppressing a change in spherical aberration in the wavelength region of the first wavelength λ ₁ ± 5 nm, it is possible to cope with individual differences in the oscillation wavelength of the first light source. The tolerance can be relaxed and the selection of the first light source is not necessary, so that the cost of the optical pickup device can be reduced.

  Item 20 is the objective optical system according to any one of Items 17 to 19, wherein the third phase structure has a function of suppressing a change in spherical aberration due to a change in refractive index of the objective optical system. Have

  As is well known, since the increase in spherical aberration associated with a change in refractive index increases in proportion to the fourth power of the NA of the objective lens, such a spherical surface is required when the objective lens is made of a resin having a large refractive index change associated with a temperature change. Measures against the increase in aberration are essential. In addition, in an objective lens with NA of 0.85, even if the refractive index change due to temperature change is smaller than that of resin, an 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 the increase in spherical aberration accompanying the temperature change by the third phase structure.

  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. Formed.

The structure according to Item 22 is the objective optical system according to Item 21, wherein the third phase structure is formed in the first aberration correction element, and the first wavelength λ ₁ is 10 with respect to the first light flux. Double the optical path difference.

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 flux by the third phase structure is 10 times the first wavelength λ _1. If you leave designed to be, a second substantially 6 times optical path difference of the second wavelength lambda ₂ to be added to the light flux, the optical path difference added to the third light flux and the third wavelength lambda ₃ of substantially Since the magnification is five times, it is possible to ensure a sufficiently high transmittance of the diffracted light of any light flux.
Item 23 is the objective optical system according to any one of Items 1 to 22, wherein both the first phase structure and the second phase structure are made of a resin.

  Any optical glass or optical resin can be used as the material for the aberration correction element. However, in order to form a phase structure that is a fine structure with little shape error, a material with a low viscosity in the molten state, that is, a resin is used. Is suitable. Also, the resin is lighter and lighter than glass. In particular, if the aberration correction element is reduced in weight by using a resin, the driving force for performing focus and tracking control of the optical pickup device at the time of recording / reproducing of the optical disk can be reduced.

  When both the first phase structure and the second phase structure are formed from a resin, the first phase structure is represented by ZEONEX (registered trademark) manufactured by ZEON Corporation or Apel (registered trademark) manufactured by Mitsui Chemicals. Preferably, the second phase structure is made of an ultraviolet curable resin, a thermosetting resin, or a fluorene polyester resin typified by OKP4 manufactured by Osaka Gas Chemical Company. preferable.

  Item 24 is the objective optical system according to any one of Items 1 to 23, wherein either one of the first phase structure and the second phase structure is an ultraviolet curable resin or thermosetting. Formed from a functional resin.

  In the case where a second aberration correction element having a so-called hybrid structure is manufactured by using the second phase structure on the surface of a resin layer formed on a resin substrate or a glass substrate, the material is an ultraviolet ray as described in item 24. A curable resin or a thermosetting resin is suitable for production.

  In addition, as a method for producing an aberration correction element formed on the surface of the phase structure, a method of forming the phase structure directly on the resin substrate or the glass substrate by repeating the photolithography and etching processes may be used. A so-called mold molding is suitable for mass production, in which a mold (mold) having a phase structure is produced, and an aberration correction element having a phase structure formed on the surface is obtained as a replica of the mold. As a method for producing a mold having a phase structure formed thereon, a method of forming a diffractive structure by repeating photolithography and etching processes, or a method of machining the diffractive structure by a precision lathe may be used.

  The configuration according to Item 25 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 is A second phase structure.

UV curable resin, or thermosetting resin, it is easy compared suited to obtain an Abbe number [nu controls _d optimum Abbe number [nu _d in d line in the manufacturing process. Therefore, preferably formed of Abbe number [nu _d of tolerance is small second phase structure an ultraviolet curing resin, or thermosetting resin.

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

  An ultraviolet curable resin or a thermosetting resin is relatively excellent in adhesiveness with a glass substrate. Accordingly, by forming a phase structure formed of an ultraviolet curable resin or a thermosetting resin, out of the first phase structure and the second phase structure, on the glass substrate, the mold and the phase structure are formed. It is possible to suppress the deformation of the phase structure at the time of mold release, and the occurrence of aberration due to the shape error and the reduction in diffraction efficiency are reduced.

In the configuration according to Item 27, in the objective optical system according to any one of Items 1 to 26, the objective lens is optimally corrected for spherical aberration with respect to a combination of the t ₁ and the first wavelength λ _1. It becomes.

Objective lens, as the first wavelength lambda ₁ and spherical aberration correction with respect to the thickness t1 of the protective layer of the first optical disk is minimized, preferably the aspheric shape is determined. In this configuration, the condensing performance of the first wavelength λ ₁ is determined by the objective lens. Therefore, as described in item 27, by determining the aspherical shape of the objective lens so that the spherical aberration correction is minimized with respect to the first wavelength λ ₁ and the thickness t ₁ of the first protective layer, It becomes easy to obtain the condensing performance of the first light flux that requires strict wavefront accuracy. Here, "the objective lens, the spherical aberration correction is optimized for the combination of the t1 and the first wavelength lambda _1" is a first light beam through the protective layer of the objective lens and the first optical disk The wavefront aberration when the light is condensed is 0.05λ ₁ RMS or less.

  The configuration described in item 28 satisfies the following equations (5) to (7) in the objective optical system described in any one of items 1 to 27.

380 nm <λ ₁ <420 nm (5)
1.5 <λ ₂ / λ ₁ <1.7 (6)
1.8 <λ ₃ / λ ₁ <2.1 (7)
Item 29 is the objective optical system according to any one of Items 4 to 6, wherein the first phase structure has a function of diverging the second light flux.

  With the first phase structure, it is possible to ensure a sufficient working distance when recording / reproducing with respect to the second optical disc by diverging the second light flux.

  Item 30 is the objective optical system according to any one of Items 10 to 12, wherein the second phase structure has a function of diverging the third light flux.

  Due to the second phase structure, the third light beam is diverged, thereby making it possible to secure a sufficient working distance when recording / reproducing with respect to the third optical disk.

In the configurations described in Items 29 and 30, when the second light beam (or the third light beam) is diverged by the first phase structure (or the second phase structure), the phase structure is added to the incident light beam. Sign of the paraxial power of the diffractive structure defined as -2 · M · B ₂ by the diffraction order M and the second-order diffractive surface coefficient B ₂ Is synonymous with negative.

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

In a diffractive structure in which the cross-sectional shape including the optical axis is a sawtooth type or a staircase type, spherical aberration due to the difference between t ₁ and t ₂ , or spherical aberration due to the difference between the first wavelength λ ₁ and the second wavelength λ ₂ In addition to the function of correcting the above, it is possible to provide a function of suppressing the movement of the paraxial image point position in the wavelength region of the first wavelength λ ₁ ± 5 nm. According to the configuration described in item 31, even when a mode hop occurs due to a change in the output of the first light source when switching from reproduction to recording, the condensing spot does not increase, and a good condensing state is always maintained. It becomes possible to do.

The configuration according to 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 relative to the first wavelength λ _1. Negative paraxial power.

As described in Item 32, when the paraxial power (the combined power of diffraction power and refraction power) with respect to the first wavelength λ ₁ of at least one of the first aberration correction element and the second aberration correction element is negative, the optical disk It is possible to ensure a large working distance at the time of recording / reproduction with respect to. In this case, it is preferable that the design magnification of the objective lens is negative, and further, as the first wavelength lambda ₁ and spherical aberration correction with respect to the thickness t1 of the protective layer of the first optical disk is minimized, the non More preferably, the spherical shape is determined.

  The configuration according to Item 33 is the objective optical system according to any one of Items 1 to 32, wherein all of the first light flux to the third light flux are relative to the first aberration correction element and the second aberration correction element. Incident in the state of parallel light flux.

  According to the configuration described in Item 33, since the object point position does not change even when the objective optical system is driven for tracking, good tracking characteristics can be obtained for a light beam of any wavelength.

The configuration according to Item 34 is the objective optical system according to Item 1, wherein the first aberration correction element has an Abbe number ν _d 1 in the d-line that satisfies Equation (1) and has a first phase structure, The second aberration correcting element has the second phase structure while the Abbe number ν _d 2 in the d-line satisfies the expression (2).

The configuration according to Item 35 is the objective optical system according to Item 2, wherein the first aberration correction element has a refractive index n _d 1 at the d-line that satisfies Equation (3) and has a first phase structure, The second aberration correction element has a refractive index n _d 2 at the d-line that satisfies the formula (4) and a second phase structure.

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 ₁ . the second aberration correcting element having a negative paraxial power to the first wavelength lambda _1.

According to the configuration described in Item 36, by using 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, near-wavelength in the wavelength region of the first wavelength λ ₁ ± 5 nm is obtained. Since the movement of the axial image point position can be suppressed, even when 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 increase and is always good. It is possible to maintain the light collection state.

  The configuration described in Item 37 is the objective optical system described in 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 correction element are connected to each other. The cemented surface has a convex shape on the second aberration correction element side.

In order to better suppress the movement of the paraxial image point position in the wavelength region of the first wavelength λ ₁ ± 5 nm, as described in Item 37, the first aberration correction element and the second aberration correction element are mutually connected. It is preferable to adopt a structure to join.

  The configuration according to Item 38 is the objective optical system according to Item 24, wherein the surface of the phase structure formed of an ultraviolet curable resin or a thermosetting resin out of the first phase structure and the second phase structure is provided on the surface. An unheated antireflection coating is formed.

  According to the configuration described in Item 38, since it is possible to form an antireflection coating on the surface of the phase structure formed from an ultraviolet curable resin or a thermosetting resin having relatively low heat resistance, the first aberration correction It is possible to improve the transmittance of the element and the second aberration correction element.

  In the configuration according to Item 39, in the objective optical system according to Item 23, the first phase structure is formed of a cyclic polyolefin-based resin, and the second phase structure is formed of a fluorene-based polyester resin.

  According to the structure of claim | item 39, low dispersibility can be given with respect to a 1st phase structure by forming from a cyclic polyolefin-type resin, and with respect to a 2nd phase structure by forming from a fluorene-type polyester resin. Since high dispersibility can be imparted, high transmittance (diffraction efficiency) can be ensured for a light flux of any wavelength. In addition, ZEONEX (registered trademark) manufactured by Nippon Zeon Co., Ltd., Appel (registered trademark) manufactured by Mitsui Chemicals, etc. are used as the cyclic polyolefin resin, and OKP4 manufactured by Osaka Gas Chemical Co., Ltd. is used as the fluorene polyester resin. It is preferable that each phase structure can be manufactured by a molding method using a mold, which is suitable for mass production.

  Item 40 is the objective optical system according to any one of Items 4 to 6, wherein the optical surface on which the first phase structure is formed includes a first central region including an optical axis, and the first optical region. The first phase structure is divided into a first peripheral region surrounding the central region, and the first phase structure is formed in the first central region.

According to the configuration of Item 40, the first central region is a region corresponding to the numerical aperture (NA ₂ ) necessary for recording / reproducing information with respect to the second optical disc, whereby t ₁ a spherical aberration due to the difference of t _2, or the first wavelength lambda ₁ and spherical aberration within NA ₂ due to the difference of the second wavelength lambda ₂ (first central region) is corrected only, than NA ₂ outer In the region (first peripheral region), it is possible to prevent such spherical aberration from being corrected. As a result, the light beam having the second wavelength λ ₂ that passes through the region outside the NA ₂ can be a flare component that does not contribute to spot formation, so that the objective optical system according to the present invention has the second wavelength λ ₂ . It is possible to provide an aperture limiting function corresponding to the luminous flux.

  The configuration according to Item 41 is the objective optical system according to Item 40, wherein at least a part of the first peripheral region is a fourth phase for controlling a condensing position of the second light flux passing through this part. A structure is formed, and the fourth phase structure is a diffractive structure that does not diffract the first light flux and the third light flux but diffracts the second light flux.

According to the configuration described in claim 41, the diffractive power for the second wavelength lambda ₂ of the first phase structure formed in the first central region, with respect to the second wavelength lambda ₂ of the fourth phase structure formed in the first peripheral area By making the diffraction powers different, the position where the second light beam passing through the fourth phase structure is condensed and the amount of spherical aberration can be arbitrarily controlled. At this time, the focusing characteristic of the objective optical system at the time of recording / reproducing information with respect to the second optical disc is designed by designing the fourth phase structure so that the detection characteristic of the focus error signal of the second light flux by the photodetector is the best. Can be improved.

  Note that it is not always necessary to control the condensing position of the second light beam and the amount of spherical aberration in the entire first peripheral area, and a focus error occurs when the fourth phase structure is not formed in the second peripheral area. The condensing position of the second light beam and the amount of spherical aberration may be controlled only in the portion that adversely affects the signal detection characteristics. For this reason, it is not always necessary to form the fourth phase structure in the entire first peripheral region, and thus the range in which the fourth phase structure is formed does not need to be unnecessarily widened. It becomes possible to improve the light transmittance.

  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, and the second optical region. The second phase structure is divided into a second peripheral region surrounding the central region, and the second phase structure is formed in the second central region.

According to the configuration described in Item 42, the second central area is an area corresponding to the numerical aperture (NA ₃ ) necessary for recording / reproducing information with respect to the third optical disk, whereby t ₁ It is possible to correct spherical aberration due to the difference between t ₃ and t ₃ only within NA ₃ (second central region) and not to correct such spherical aberration in the region outside NA ₃ (second peripheral region). It becomes. Accordingly, since the light beam having the third wavelength λ ₃ that passes through the region outside NA ₃ can be a flare component that does not contribute to spot formation, the objective optical system according to the present invention has the third wavelength λ ₃ . It is possible to provide an aperture limiting function corresponding to the luminous flux.

  The configuration according to Item 43 is the objective optical system according to Item 42, wherein at least a part of the second peripheral region has a fifth phase for controlling a condensing position of the third light flux passing through this part. A structure is formed, and the fifth phase structure is a diffractive structure that does not diffract the first light flux and the second light flux but diffracts the third light flux.

  According to the configuration described in item 43, similarly to the configuration described in item 41, the position where the third light beam passing through the fifth phase structure is condensed and the amount of spherical aberration can be arbitrarily controlled. It is possible to improve the focusing characteristic of the objective optical system at the time of recording / reproducing information with respect to the optical disc.

The configuration according to Item 44 is the difference between the back focus fB ₁ with respect to the first wavelength λ ₁ and the back focus fB ₂ with respect to the second wavelength λ _{2 in} the objective optical system according to any one of Items 1 to 43. When any difference between the back focus fB ₃ with respect to the back focus fB ₁ and the second wavelength lambda ₃ with respect to the first wavelength lambda ₁ is also 0.2mm or less.

According to the configuration described in Item 44, since the difference in working distance during recording / reproduction of information with respect to the first optical disk to the third optical disk is reduced, the stroke of the focusing actuator of the objective optical system can be reduced, and the actuator Can be miniaturized. Here, the term "back focus fB _i for the i wavelength lambda _i" is the time of the i-th light flux onto the information recording surface of the i optical disk is focused, the objective optical system and the optical axis of the i-th optical disc Refers to the upper spacing.

Structure of claim 45, wherein, in the objective optical system according to claim 11 or 12, the ratio lambda _{M /} lambda ₁ to the minimum width lambda said first wavelength lambda ₁ of _M of the pattern of the second phase structure is 25 or more is there.

According to the configuration in Item 45, the minimum width Λ _{M of the} pattern of the second phase structure is sufficiently large with respect to the first wavelength λ ₁ , so that the vector calculation of the diffraction efficiency of the first wavelength λ ₁ is ensured. As the value increases, the decrease in diffraction efficiency due to the shape error of the second phase structure decreases.

  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 second phase structure is It is formed on the surface of the second aberration correction element.

  According to the configuration in Item 46, since the first phase structure and the second phase structure are both formed at the interface with air, the wavefront of the first light flux that has passed through the first aberration correction element, and the second aberration The wavefronts of the first light flux that has passed through the correction element are each in a high transmittance state. Accordingly, since the wavefront aberration of each aberration correction element can be evaluated by the interferometer for the first light flux, it is easy to obtain performance when manufacturing each aberration correction element.

  In the configuration described in Item 47, in the objective optical system described in Item 5, the first phase structure and the second phase structure are both formed on a plane.

  The structure described in Item 48 is the objective optical system described in Item 11, wherein the first phase structure and the second phase structure are both formed on a plane.

  According to the configurations of items 47 and 48, the first phase structure and the second phase structure can be easily manufactured.

  Item 49 is the objective optical system according to any one of Items 1 to 48, wherein the first aberration correction element, the second aberration correction element, and the objective lens are in a relative positional relationship. Is held by a holding member so as to be universal.

  According to the configuration of Item 49, since the optical axes of the first aberration correction element and the second aberration correction element and the objective lens do not deviate even when the objective optical system tracks, the coma aberration does not occur and good tracking characteristics are obtained. Is obtained.

The configuration described in Item 50 includes a first light source that emits a first light flux having a first wavelength λ ₁ for recording and / or reproducing information on the first optical disc, and recording information on the second optical disc. And / or a second light source that emits a second light beam having a second wavelength λ ₂ (> λ ₁ ) to perform reproduction, and a third wavelength to record and / or reproduce information on the third optical disk. A third light source that emits a third light flux of λ ₃ (> λ ₂ ), and the objective optical system according to any one of claims 1 to 49,
Information is recorded and / or reproduced with respect to the first optical disc having the protective layer having the thickness t ₁ using the first light beam, and the thickness t ₂ (≧ t ₁ ) is protected using the second light beam. Recording and / or reproducing information on a second optical disc having a layer, and recording and / or reproducing information on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using the third light flux An optical pickup device that performs reproduction.

  According to Item 50, an optical pickup device having an effect similar to that of any one of Items 1 to 49 can be obtained.

  Item 51 is an optical disk drive device on which 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 are mounted.

According to item 51, an optical disk drive having the same effect as item 50 can be obtained.
[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, an objective optical system of the present invention and an optical pickup device using the objective optical system will be described with reference to FIG.

FIG. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU capable of appropriately recording / reproducing information on any of a high density optical disc HD, a DVD, and a CD. The optical specification of HD is the first wavelength λ ₁ = 408 nm, the thickness t ₁ of the protective layer PL _{1 is} 0.1 mm, and the numerical aperture NA _{1 is} 0.85. The optical specification of the DVD is the second wavelength λ ₂ = 658 nm, thickness t ₂ of the protective layer PL ₂ = 0.6 mm, numerical aperture NA ₂ = 0.65, and the optical specification of the CD is the third wavelength λ ₃ = 785 nm, the thickness t of the protective layer PL 3 ₃ = 1.2 mm and the numerical aperture NA ₃ = 0.50. However, the combination of the wavelength, the thickness of the protective layer, and the numerical aperture is not limited to this.

  The optical pickup device PU records / reproduces information to / from the blue-violet semiconductor laser LD1 and DVD that emits a 405 nm blue-violet laser beam (first beam) when recording / reproducing information on the HD. The first emission point EP1 that emits a 655 nm red laser beam (second beam) and the 785 nm infrared laser beam (first beam) that is emitted when information is recorded / reproduced on a CD. DVD / CD laser light source unit LU, HD / DVD / CD shared photodetector PD, first aberration correction element L1, second light emitting point EP2 that emits three luminous fluxes) on one chip Two surfaces having a function of condensing the two light aberration correcting elements L2 and the laser light beams transmitted through the first aberration correcting element L1 and the second aberration correcting element L2 on the information recording surfaces RL1, RL2, and RL3 are not provided. An objective lens unit OU (objective optical system) composed of a surface objective lens OL, a biaxial actuator AC1, a monoaxial actuator AC2, a first lens EXP1 whose refractive power in the paraxial is negative, and refraction in the paraxial An expander lens EXP including a second lens EXP2 having a positive force, a first polarizing beam splitter BS1, a second polarizing beam splitter BS2, a first collimating lens COL1, a second collimating lens COL2, a third collimating lens COL3, It comprises a sensor lens SEN for adding astigmatism to the reflected light beam from the information recording surfaces RL1, RL2 and RL3. In addition to the blue-violet semiconductor laser LD1 described above, a blue-violet SHG laser can also be used as the HD light source.

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

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

  In addition, when the optical pickup device PU records / reproduces information with respect to a DVD, the light emitting point EP1 is caused to emit light. The divergent light beam emitted from the light emitting point EP1 is converted into a parallel light beam by the second collimating lens COL2, as shown by the broken line in FIG. 1, and then reflected by the second polarization beam splitter BS2, The diameter is increased by transmitting through the first lens EXP1 and the second lens EXP2, and becomes a spot formed on the information recording surface RL2 via the protective layer PL2 of the DVD by the objective lens unit OU. The objective lens unit OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

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

  In the optical pickup device PU, when information is recorded / reproduced with respect to a CD, the interval between the first lens EXP1 and the second lens EXP2 is narrower than that during recording / reproduction of information with respect to HD. After the first lens EXP1 is driven in the optical axis direction by the uniaxial actuator AC2, the light emitting point EP2 is caused to emit light. The divergent light beam emitted from the light emitting point EP2 is converted into a loose divergent light beam 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. A spot which is enlarged by passing through the first lens EXP1 and the second lens EXP2 and converted into a divergent light beam and formed on the information recording surface RL3 by the objective lens unit OU via the protective layer PL3 of the CD. Become. The objective lens unit OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

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

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, respectively, as schematically shown in FIG. the element L1 and the second aberration correcting element L2 made of resin, the aspherical shape as spherical aberration becomes minimum with respect to the thickness t ₁ of the protective layer PL1 of the first wavelength lambda ₁ and the HD is designed The glass objective lens OL has a configuration in which the glass objective lens OL is coaxially integrated through the lens frame B. 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, and the objective lens OL is fitted and fixed to the other end. These are configured so as to be coaxially integrated along the optical axis X.

  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 then the respective aberration correction elements are joined. Alternatively, an ultraviolet curable resin is applied on one of the aberration correction elements manufactured by molding, and a mold having a phase structure formed on the surface of the ultraviolet curable resin is formed. A method of transferring the phase structure by pressing and irradiating with ultraviolet rays may be used. A thermosetting resin may be used instead of the ultraviolet curable resin.

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

  In the present embodiment, the objective lens OL is made of glass, but is not limited thereto, and may be made of resin. In this case, a polyolefin resin is preferable as the resin used for the objective lens OL.

  Further, as a material used for the objective lens OL, a material in which inorganic particles having an average particle diameter of 30 nm or less are dispersed in a base resin may be used. By mixing inorganic particles with a refractive index change rate opposite to the sign of the refractive index change rate accompanying the temperature change of the base resin, the refractive index change due to temperature change while having resin moldability Since a material with a small absolute value of the rate can be obtained, it is possible to reduce the spherical aberration change accompanying the temperature change of the objective lens OL.

The first phase structure has an Abbe number ν _d 1 = 56.4 in the d line and a refractive index n _d 1 = 1.509140 in the d line, and the second phase structure has an Abbe number ν _d 2 in the d line. = 22.8, and the refractive index n _d 2 at the d-line is 1.638000.

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

  The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Shifted structure).

Each step Δ1 of the staircase structure is set to a height that satisfies Δ1 = 2 · λ ₁ / (n ₁ −1) = 1.557 μm. Here, n ₁ is the refractive index of the first aberration correction element L1 at the wavelength λ ₁ (λ ₁ = 408 nm in the present embodiment).

Since the optical path difference L1 added to the first light flux by the step Δ1 is a 2 × lambda _1, the first light flux is directly transmitted without being any action by the first phase structure PS1.

Further, since the optical path difference N1 added to the third light flux by the step Δ1 is 1 × λ ₃ (λ ₃ = 785 nm in the present embodiment), the third light flux is not affected at all by the first phase structure PS1. It passes through as it is.

On the other hand, the optical path difference M1 added to the second light flux by the step Δ1 is 1.20 × λ ₂ (λ ₂ = 658 nm in the present embodiment), and the second light flux passing through the level surface before and after the step Δ1. The phase difference (a phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the first phase structure PS1 selectively diffracts only the second light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the DVD protective layer thickness.

  Note that the diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated in the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%, and the zero-next time of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 100%, and a high diffraction efficiency is obtained for any light flux.

  The second phase structure PS2 does not diffract the first light beam and the second light beam, but diffracts the third light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (four level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces corresponding to the number of level surfaces (in this embodiment, three levels). Shifted structure).

Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ ₁ / (n ₁ −1) = 4.144 μm. Here, n ₁ is the refractive index of the second aberration correction element at the wavelength λ ₁ .

Since the optical path difference L2 added to the first light flux by the step Δ2 is a 7 × lambda _1, the first light flux is directly transmitted without being any action by the second phase structure PS2.

Further, since the optical path difference M2 to be added to the second light flux by the step Δ2 is a _{3.97 × λ 2 ≒ 4 × λ} 2, transmitted as it is without hardly acted by the second light flux is also a second phase structure PS2 .

On the other hand, the optical path difference N2 added to the third light beam by the step Δ2 is 3.28 × λ ₃ ≈3.25 × λ ₃ , and the phase difference of the third light beam passing through the level surface before and after the step Δ2 ( The phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase is 2π × 0.25. Since one sawtooth is divided into four, the phase difference of the third light flux is exactly 4 × 2π × 0.25 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PS2 selectively diffracts only the third light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness.

  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 100%, the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light beam is 94.8%, and the third The diffraction efficiency of the first-order diffracted light of the light beam is 78.2%, and high diffraction efficiency is obtained for any light beam.

  As described above, the first aberration correction element L1 is made of a material satisfying the expression (1) or (3), and the first phase structure PS1 is used to make the HD and DVD compatible with each other. A high transmittance can be secured for both the laser beam and the red laser beam, and the second aberration correcting element L2 is made of a material satisfying the formula (2) or (4), With the two-phase structure PS2, it is possible to ensure a high transmittance for both the blue-violet laser beam and the infrared laser beam by making the HD and CD mutually compatible.

  In addition, since the first phase structure PS1 is formed only within the numerical aperture NA2 of the DVD, the light beam passing through the area outside the NA2 becomes a flare component on the information recording surface RL2 of the DVD, and the aperture limitation on the DVD is limited. It is configured to be performed automatically.

  Further, since the second phase structure PS2 is formed only within the numerical aperture NA3 of the CD, the light beam that passes through the area outside the NA3 becomes a flare component on the information recording surface RL3 of the CD, and the aperture restriction on the CD is limited. It is configured to be performed automatically.

  Incidentally, the spherical aberration of the spot formed on the HD information recording surface RL1 can be corrected by driving the negative lens EXP1 of the beam expander EXP in the optical axis direction by the uniaxial actuator UAC. The cause of the spherical aberration to be corrected by adjusting the position of the negative lens EXP1 is, for example, wavelength variation due to manufacturing error of the first light source LD1, refractive index change or refractive index distribution of the objective lens system due to temperature change, double-layer disk, For example, focus jump between information recording layers of a multi-layer disc such as a layer disc, thickness variation or thickness distribution due to a manufacturing error of a protective layer of a high-density optical disc, and the like.

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

  In the present embodiment, the DVD / CD laser light source unit LU in which the first light emission point EP1 and the second light emission point EP2 are formed on one chip is used. However, the present invention is not limited to this. Further, an HD / DVD / CD laser light source unit having a light emitting point for emitting a laser beam having a wavelength of 408 nm for HD formed on the same chip may be used. Alternatively, an HD / DVD / CD laser light source unit in which three laser light sources of a blue-violet semiconductor laser, a red semiconductor laser, and an infrared semiconductor laser are housed in one housing may be used.

  In the present embodiment, the light source and the photodetector PD are arranged separately. However, the present invention is not limited to this, and a laser light source module in which the light source and the photodetector are integrated may be used. .

  In the present embodiment, the first aberration correction element L1 and the second aberration correction element L2 that are joined to each other and the objective lens OL are integrated via the lens frame B, but the first aberration that is joined to each other. When the correction element L1, the second aberration correction element L2, and the objective lens OL are integrated, the relative positions of the first aberration correction element L1, the second aberration correction element L2, and the object lens OL are mutually relative. As long as the relationship is maintained so as to remain unchanged, the first aberration correction element L1 and the second aberration correction element L2 joined to each other, the objective lens OL, and the method other than the method using the lens frame B as described above. A method of fitting and fixing the respective flange portions may be used.

  Further, as a method of 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 element using liquid crystal may be used. good. Since a method for correcting spherical aberration by such a phase control element is known, a detailed description is omitted here.

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

Since the relative positional relationship between the first aberration correction element L1 and the second aberration correction element L2 and the objective lens OL that are joined to each other and the objective lens OL is kept unchanged, focusing and Occurrence of aberration during tracking can be suppressed, and good focusing characteristics or tracking characteristics can be obtained.
[Second Embodiment]
Hereinafter, the 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.

  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.

As schematically shown in FIG. 3, 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 PS2 made of resin. the aberration correcting element L2, the first wavelength lambda ₁ and the HD thickness t ₁ and its made aspherical shape is designed glass objective lens OL of the spherical aberration is minimum with respect to the protective layer PL1 of It has a configuration integrated coaxially through a lens frame B. 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 while being separated from each other, and the objective lens OL is fitted and fixed to the other end. Thus, these are integrated along the optical axis X coaxially.

The first phase structure has an Abbe number ν _d 1 = 56.4 in the d-line and a refractive index n _d 1 = 1.509140 in the _d -line, and the second phase structure has an Abbe number ν _d 2 = 27 in the d-line. 0.0, the refractive index n _d 2 at the d-line = 1.607000.

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

The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Each step Δ1 of the staircase structure is set to a height that satisfies Δ1 = 2 · λ ₁ / (n ₁ −1) = 1.544 μm. Here, n ₁ is the refractive index of the first aberration correction element L1 at the wavelength λ ₁ (λ ₁ = 405 nm in the present embodiment).

Since the optical path difference L1 of the first phase structure PS1 is added to the first light flux is a 2 × lambda _1, the first light flux is directly transmitted without being any action by the first phase structure PS1.

In addition, since the optical path difference N1 added to the third light flux by the step Δ1 is 0.99 × λ ₃ ≈1 × λ ₃ (λ ₃ = 785 nm in the present embodiment), the third light flux is also in the first phase structure. It passes through PS1 without any action.

On the other hand, the optical path difference M1 added to the second light flux by the step Δ1 is 1.19 × λ ₂ ≈1.20 × λ ₂ (λ ₂ = 655 nm in the present embodiment), and level surfaces before and after the step Δ1. The phase difference of the second light flux passing through (phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the first phase structure PS1 selectively diffracts only the second light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the DVD protective layer thickness.

  The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated in 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 zero-next time of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 99.2%, and a high diffraction efficiency is obtained for any light flux.

  The second phase structure PS2 diffracts the first to third light beams, and the cross-sectional shape including the optical axis is stepped.

Each step Δ2 staircase structure is set to a height satisfying _{Δ1 = 7 · λ B / (} nλ B -1) = 4.302μm. Here, nλ _B is the refractive index (nλ _B = 1.650875 in the present embodiment) of the first aberration correction element L1 at the wavelength λ _B (λ _B = 400 nm in the present embodiment).

  By passing through the second phase structure PS2, the seventh-order diffracted light of the first light flux, the fourth-order diffracted light of the second light flux, and the third-order diffracted light of the third light flux are generated.

The optical path difference added to the first light flux when passing through the second phase structure PS2 is 6.89 × λ ₁ ≈7 × λ ₁ , and the seventh-order diffracted light of the first light flux has the maximum diffraction efficiency.

Further, the optical path difference added to the second light flux when passing through the second phase structure PS2 is 3.94 × λ ₂ ≈4 × λ ₂ , and the fourth-order diffracted light of the second light flux has the maximum diffraction efficiency. .

Further, the optical path difference added to the third light beam when passing through the second phase structure PS2 is 3.25 × λ ₃ ≈3 × λ ₃ , and the third-order diffracted light of the third light beam has the maximum diffraction efficiency. .

  Thereby, spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness is corrected.

  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 third-order diffracted light of the third light beam The diffraction efficiency is 81.2%, and a high diffraction efficiency is obtained for any luminous flux.

Further, 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 the absolute values thereof are the same. Thus, the beam diameter of the first light beam passing through the optical surface on the light source side of the second aberration correction element L2 is prevented from changing.
[Third Embodiment]
Hereinafter, a third 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.

  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 formed on the optical disc side of the first aberration correction element L1. It is characterized in that it is provided on the optical surface.

As schematically shown in FIG. 4, 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 PS2 made of resin. the aberration correcting element L2, the first wavelength lambda ₁ and the HD thickness t ₁ and its made aspherical shape is designed glass objective lens OL of the spherical aberration is minimum with respect to the protective layer PL1 of It has a configuration integrated coaxially through a lens frame B. 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, and the objective lens OL is fitted and fixed to the other end. These are configured so as to be coaxially integrated along the optical axis X.

The first phase structure has an Abbe number ν _d 1 = 56.4 in the d line and a refractive index n _d 1 = 1.509140 in the d line, and the second phase structure has an Abbe number ν _d 2 in the d line. = 27.0, and the refractive index n _d 2 at the d-line is 1.607000.

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

  The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Shifted structure).

The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Each step Δ1 of the staircase structure is set to a height that satisfies Δ1 = 2 · λ ₁ / (n ₁ −1) = 1.544 μm. Here, n ₁ is the refractive index of the first aberration correction element L1 at the wavelength λ ₁ (λ ₁ = 405 nm in the present embodiment).

Since the optical path difference L1 of the first phase structure PS1 is added to the first light flux is a 2 × lambda _1, the first light flux is directly transmitted without being any action by the first phase structure PS1.

In addition, since the optical path difference N1 added to the third light flux by the step Δ1 is 0.99 × λ ₃ ≈1 × λ ₃ (λ ₃ = 785 nm in the present embodiment), the third light flux is also in the first phase structure. It passes through PS1 without any action.

On the other hand, the optical path difference M1 added to the second light flux by the step Δ1 is 1.19 × λ ₂ ≈1.20 × λ ₂ (λ ₂ = 655 nm in the present embodiment), and level surfaces before and after the step Δ1. The phase difference of the second light flux passing through (phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the first phase structure PS1 selectively diffracts only the second light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the DVD protective layer thickness.

  The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated in 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 zero-next time of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 99.2%, and a high diffraction efficiency is obtained for any light flux.

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

Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ ₁ / (n ₁ −1) = 4.371 μm. Here, n ₁ is the refractive index of the second aberration correction element at the wavelength λ ₁ .

Since the optical path difference L2 added to the first light flux by the step Δ2 is a 7 × lambda _1, the first light flux is directly transmitted without being any action by the second phase structure PS2.

Further, since the optical path difference M2 to be added to the second light flux by the step Δ2 is a _{4.01 × λ 2 ≒ 4 × λ} 2, which is transmitted through the little acted by the second light flux is also a second phase structure PS2 .

On the other hand, the optical path difference N2 added to the third light flux by the step Δ2 is 3.30 × λ ₃ ≈3.33 × λ ₃ , and the phase difference of the third light flux passing through the level surface before and after the step Δ2 ( The phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase is 2π × 0.33. Since one sawtooth is divided into three, the phase difference of the third light beam is exactly 3 × 2π × 0.33 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PS2 selectively diffracts only the third light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness.

  Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated in the second phase structure PS1 is 100%, the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light beam is 99.8%, and the third The diffraction efficiency of the first-order diffracted light of the light beam is 66.6%, and high diffraction efficiency is obtained for any light beam.

The third phase structure PS3 diffracts the first to third light beams, and the cross-sectional shape including the optical axis is stepped. The third phase structure PS3 is the movement of a paraxial image point position caused by the minute change of the first wavelength lambda _1, a structure for suppressing a change in spherical aberration.

Each step Δ3 of the staircase structure is set to a height that satisfies Δ1 = 10 · λ ₁ / (n ₁ −1) = 7.719 μm.

  By passing through the third phase structure PS3, the 10th-order diffracted light of the first light beam, the 6th-order diffracted light of the second light beam, and the fifth-order diffracted light of the third light beam are generated.

Optical path difference added to the first light flux when passing through the third phase structure PS3 is 10.0 × lambda _1, 10-order diffracted light of the first light flux having the maximum diffraction efficiency.

The optical path difference added to the second light flux when passing through the third phase structure PS3 is 5.97 × λ ₂ ≈6 × λ ₂ , and the sixth-order diffracted light of the second light flux has the maximum diffraction efficiency. .

The optical path difference added to the third light flux when passing through the third phase structure PS3 is 4.95 × λ ₃ ≈5 × λ ₃ , and the fifth-order diffracted light of the third light flux has the maximum diffraction efficiency. .

  Note that the diffraction efficiency of the 10th-order diffracted light of the first light beam generated in 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 diffraction efficiency of the 5th-order diffracted light of the third light beam. Is 99.1%, and a high diffraction efficiency is obtained for any luminous flux.

  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 on the optical disc side of the first aberration correction element L1 have opposite signs, and the absolute values thereof are the same. Thus, the beam diameter of the first light beam passing through the optical surface on the optical disk side of the first aberration correction element L1 is kept unchanged.

[Fourth Embodiment]
Hereinafter, the fourth 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.

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 second phase structure PS2 made of an ultraviolet curable resin is formed on the glass substrate GL. forming constitutes the second aberration correcting element L2 by further has a feature in that a negative paraxial power for the first wavelength lambda ₁ of the first aberration correcting element L1.

As schematically shown in FIG. 5, the objective lens unit OU in the present embodiment includes a first aberration correction element L1 having a resin-made first phase structure PS1, and a resin-made second phase structure on a glass substrate GL. a second aberration correcting element L2 having PS2 is formed configuration, the aspherical shape as spherical aberration with respect to the thickness t ₁ of the protective layer PL1 of the first wavelength lambda ₁ and the HD is minimum design The made glass objective lens OL is integrated coaxially through the lens frame B. 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, and the objective lens OL is fitted and fixed to the other end. These are configured so as to be coaxially integrated along the optical axis X.

The first phase structure has an Abbe number ν _d 1 = 56.4 in the d line and a refractive index n _d 1 = 1.509140 in the d line, and the second phase structure has an Abbe number ν _d 2 in the d line. = 23.0, refractive index n _d 2 at d-line = 1.60000.

  The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Shifted structure).

The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Each step Δ1 of the staircase structure is set to a height satisfying Δ1 = 2 · λ ₁ / (n ₁ −1) = 1.557 μm. Here, n ₁ is the refractive index of the first aberration correction element L1 at the wavelength λ ₁ (λ ₁ = 408 nm in the present embodiment).

Since the optical path difference L1 of the first phase structure PS1 is added to the first light flux is a 2 × lambda _1, the first light flux is directly transmitted without being any action by the first phase structure PS1.

Further, since the optical path difference N1 added to the third light flux by the step Δ1 is 1 × λ ₃ (λ ₃ = 785 nm in the present embodiment), the third light flux is not affected at all by the first phase structure PS1. It passes through as it is.

On the other hand, the optical path difference M1 added to the second light flux by the step Δ1 is 1.20 × λ ₂ (λ ₂ = 658 nm in the present embodiment), and the second light flux passing through the level surface before and after the step Δ1. The phase difference (a phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the first phase structure PS1 selectively diffracts only the second light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the DVD protective layer thickness.

  Note that the diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated in the first phase structure PS1 is 100%, the diffraction efficiency of the first-order diffracted light of the second light beam is 87.5%, and the zero-next time of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 100%, and a high diffraction efficiency is obtained for any light flux.

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

Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ ₁ / (n ₁ −1) = 4.410 μm. Here, n ₁ is the refractive index of the second aberration correction element at the wavelength λ ₁ .

Since the optical path difference L2 added to the first light flux by the step Δ2 is a 7 × lambda _1, the first light flux is directly transmitted without being any action by the second phase structure PS2.

Further, since the optical path difference M2 to be added to the second light flux by the step Δ2 is a _{3.97 × λ 2 ≒ 4 × λ} 2, transmitted as it is without hardly acted by the second light flux is also a second phase structure PS2 .

On the other hand, the optical path difference N2 added to the third light beam by the step Δ2 is 3.28 × λ ₃ ≈3.25 × λ ₃ , and the phase difference of the third light beam passing through the level surface before and after the step Δ2 ( The phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase is 2π × 0.25. Since one sawtooth is divided into four, the phase difference of the third light flux is exactly 4 × 2π × 0.25 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PS2 selectively diffracts only the third light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness.

  Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated in the second phase structure PS1 is 100%, the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light beam is 95.8%, and the third The diffraction efficiency of the first-order diffracted light of the light beam is 77.5%, and a high diffraction efficiency is obtained for any light beam.

Further, the objective optical system OU of the present embodiment, has a negative paraxial power for the first wavelength lambda ₁ of the first aberration correcting element L1, the light flux of each wavelength to the objective lens OL is divergent light flux It has the structure which injects in a state. This ensures a sufficient working distance during recording / reproduction for a CD having a thick protective layer. The design magnification of the objective lens OL is negative, and this design magnification corresponds to the divergence of the first light beam incident on the objective lens OL.

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

This embodiment is compatible with a high-density optical disc HD (for example, HD DVD), DVD, and CD of a standard having a thickness t ₁ = 0.6 mm of the protective layer PL1 and a numerical aperture NA ₁ = 0.67. The objective lens unit OU includes a first aberration correction element L1 and a second aberration correction element L2, and is characterized in that the first phase structure PS1 has a diffractive structure having a sawtooth cross section. Have

  As shown schematically in FIG. 6, the objective lens unit OU in the present embodiment has a first aberration correction element joined to each other, each having a first phase structure PS1 made of resin and a second phase structure SP2 made of resin. The L1 and the second aberration correction element L2 and the resin objective lens OL have a configuration in which the flange portions FL1 and FL2 are fitted and fixed to be coaxially integrated.

The first phase structure PS1 diffracts the first to third light beams, and the cross-sectional shape including the optical axis is a sawtooth shape. The first phase structure PS1 is used to correct spherical aberration caused by the difference between the first wavelength λ ₁ and the second wavelength λ ₂ and the movement of the paraxial image point position due to the minute change of the first wavelength λ ₁ . Structure.

Each step Δ1 of the first phase structure PS1 is set to a height satisfying Δ1 = 8 · λ ₁ / (n ₁ −1) = 7.042 μm (λ ₁ = 407 nm in the present embodiment). By passing through the one-phase structure PS1, the eighth-order diffracted light of the first light beam, the fifth-order diffracted light of the second light beam, and the fourth-order diffracted light of the third light beam are generated.

The optical path difference added to the first light flux when passing through the first phase structure PS1 is 8.0 × λ ₁ , the eighth-order diffracted light of the first light flux has the maximum diffraction efficiency, and the first phase structure PS1 The optical path difference added to the second light beam when passing through the beam is 4.81 × λ ₂ ≈5 × λ ₂ (λ ₂ = 655 nm in the present embodiment), and the fifth-order diffracted light of the second light beam is the largest The optical path difference added to the third light flux when having the diffraction efficiency and passing through the first phase structure PS1 is 3.99 × λ ₃ ≈4 × λ ₃ (in this embodiment, λ ₃ = 785 nm). The fourth-order diffracted light of the third light beam has the maximum diffraction efficiency.

  The diffraction efficiency of the 8th order diffracted light of the first light beam generated in 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 diffraction efficiency of the 4th order diffracted light of the third light beam. Is 100%, and high diffraction efficiency is obtained for any luminous flux.

  The second phase structure PS2 does not diffract the first light beam and the second light beam, but diffracts the third light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (four level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces corresponding to the number of level surfaces (in this embodiment, three levels). Shifted structure).

Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ ₁ / (n ₁ −1) = 4.396 μm. Here, n ₁ is the refractive index of the second aberration correction element at the wavelength λ ₁ .

Since the optical path difference L2 added to the first light flux by the step Δ2 is a 7 × lambda _1, the first light flux is directly transmitted without being any action by the second phase structure PS2.

Further, since the optical path difference M2 to be added to the second light flux by the step Δ2 is a _{3.98 × λ 2 ≒ 4 × λ} 2, transmitted as it is without hardly acted by the second light flux is also a second phase structure PS2 .

On the other hand, the optical path difference N2 added to the third light flux by the step Δ2 is 3.27 × λ ₃ ≈3.25 × λ ₂ , and the phase difference of the third light flux passing through the level surface before and after the step Δ2 ( The phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase is 2π × 0.25. Since one sawtooth is divided into four, the phase difference of the third light flux is exactly 4 × 2π × 0.25 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PS2 selectively diffracts only the third light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness.

Note that the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the first light beam generated in the second phase structure PS1 is 100%, the diffraction efficiency of the 0th-order diffracted light (transmitted light) of the second light beam is 97.5%, and the third The diffraction efficiency of the first-order diffracted light of the light beam is 79.6%, and high diffraction efficiency is obtained for any light beam.
[Sixth Embodiment]
Hereinafter, the sixth 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.

  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, and further A feature is that a fifth phase structure PS5 is formed in the peripheral area PA (second peripheral area) of the optical surface on the light source side of the second aberration correcting 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 aberration having a second phase structure made of resin. a correcting element L2, the first wavelength lambda ₁ and the HD thickness t ₁ and the relative spherical aberration its aspheric shape designed glass objective lens OL to minimize the protective layer PL1 of the mirror It has the structure integrated coaxially through the frame B. 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, and the objective lens OL is fitted and fixed to the other end. These are configured so as to be coaxially integrated along the optical axis X.

The first phase structure has an Abbe number ν _d 1 = 56 for the d line and a refractive index n _d 1 = 1.550000 for the d line, and the second phase structure has an Abbe number ν _d 2 = 23 for the d line. 0.0, the refractive index n _d 2 at the d-line = 1.630000.

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

  The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shape including the optical axis is stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Shifted structure).

The first phase structure PS1 does not diffract the first light beam and the third light beam, but diffracts the second light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (5 level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces (4 levels in the present embodiment). Each step Δ1 of the staircase structure is set to a height that satisfies Δ1 = 2 · λ ₁ / (n ₁ −1) = 1.429. Here, n ₁ is the refractive index of the first aberration correction element L1 at the wavelength λ ₁ (λ ₁ = 405 nm in the present embodiment).

Since the optical path difference L1 of the first phase structure PS1 is added to the first light flux is a 2 × lambda _1, the first light flux is directly transmitted without being any action by the first phase structure PS1.

In addition, since the optical path difference N1 added to the third light flux by the step Δ1 is 0.99 × λ ₃ ≈1 × λ ₃ (λ ₃ = 785 nm in the present embodiment), the third light flux is also in the first phase structure. It passes through PS1 without any action.

On the other hand, the optical path difference M1 added to the second light flux by the step Δ1 is 1.19 × λ ₂ ≈1.20 × λ ₂ (λ ₂ = 655 nm in the present embodiment), and level surfaces before and after the step Δ1. The phase difference of the second light flux passing through (phase difference obtained by subtracting an integral multiple of 2π that is optically equiphase) is 2π × 0.20. Since one sawtooth is divided into five, the phase difference of the second light flux is exactly 5 × 2π × 0.20 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the first phase structure PS1 selectively diffracts only the second light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the DVD protective layer thickness.

  The diffraction efficiency of the first-order diffracted light (transmitted light) of the first light beam generated in 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 zero-next time of the third light beam. The diffraction efficiency of the folded light (transmitted light) is 99.1%, and a high diffraction efficiency is obtained for any light flux.

  The second phase structure PS2 does not diffract the first light beam and the second light beam, but diffracts the third light beam, and has a structure in which patterns whose cross-sectional shapes including the optical axis are stepped are arranged concentrically. Thus, for each predetermined number of level surfaces (four level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces corresponding to the number of level surfaces (in this embodiment, three levels). Shifted structure).

Each step Δ2 of the staircase structure is set to a height that satisfies Δ2 = 7 · λ ₁ / (n ₁ −1) = 4.159 μm. Here, n ₁ is the refractive index of the second aberration correction element at the wavelength λ ₁ .

Since the optical path difference L2 added to the first light flux by the step Δ2 is a 7 × lambda _1, the first light flux is directly transmitted without being any action by the second phase structure PS2.

Further, since the optical path difference M2 to be added to the second light flux by the step Δ2 is a _{3.95 × λ 2 ≒ 4 × λ} 2, transmitted as it is without hardly acted by the second light flux is also a second phase structure PS2 .

On the other hand, the optical path difference N2 to be added to the third light flux by the stepped Δ2 is 3.25 × lambda _3, a third phase difference of the light beam (optically equiphase passing level surface before and after the step Δ2 The phase difference obtained by subtracting the integral multiple of 2π) is 2π × 0.25. Since one sawtooth is divided into four, the phase difference of the third light flux is exactly 4 × 2π × 0.25 = 2π for one sawtooth, and first-order diffracted light is generated.

  As described above, the second phase structure PS2 selectively diffracts only the third light beam, thereby correcting the spherical aberration due to the difference between the HD protective layer thickness and the CD protective layer thickness.

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

  The central area CA of the optical surface on the light source side of the second aberration correcting element L2 is an area corresponding to the numerical aperture NA3, and the peripheral area PA is an area corresponding to the outside of the numerical aperture NA3. Is formed with a fifth phase structure PS5 which is a structure for controlling the condensing position of the third light flux passing through this region. The fifth phase structure PS5 does not diffract the first light beam and the second light beam, but diffracts the third light beam, and has a structure in which a pattern whose cross-sectional shape including the optical axis is stepped is arranged on a concentric circle. Thus, for each predetermined number of level surfaces (four level surfaces in the present embodiment), the structure is shifted by a height corresponding to the number of level surfaces corresponding to the number of level surfaces (in this embodiment, three levels). Shifted structure). Since the principle of diffracted light generation by the fifth phase structure PS5 is the same as that of the second phase structure PS2, a detailed description is omitted here.

  When the fifth phase structure PS5 is not formed, the third light flux that passes through the peripheral area PA becomes a flare component having a large spherical aberration, but this flare component is on the focused spot formed by the second phase structure PS2. Since the light is condensed so as to overlap with the light flux, there is a possibility of adversely affecting the focus pull-in operation with respect to the third light flux. The fourth phase structure PS4 has a function of causing the third light flux that passes through the peripheral area PA to be a flare component that condenses in the underside (the direction in which the condensing position approaches the objective lens unit OU). It is possible to obtain good focus pull-in operation characteristics for three light beams.

Further, the joint surface of the first aberration correction element L1 and the second aberration correction element L2 has a convex shape toward the second aberration correction element L2, so that the paraxial image point in the wavelength region of the first wavelength λ ₁ ± 5 nm is obtained. Since the movement of the position is suppressed, even when a mode hop occurs due to a change in the output of the first light source when switching from reproduction to recording, the condensing spot does not become large, and a good condensing state is always obtained. Can be maintained.

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

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are joined to each other, and the objective lens OL has a first wavelength. Although it is a glass lens (LAC130 manufactured by HOYA) whose aspheric shape is designed so that spherical aberration is minimized with respect to λ ₁ and the thickness t ₁ of the HD protective layer PL1, it may be a resin lens. .

  Tables 1-1 and 1-2 show 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.

In addition, the numerical aperture NA _{1 of} HD is 0.85 and the numerical aperture NA _{2 of} DVD is 0. 5 in the _{second to} fourth embodiments, the seventh embodiment, and the eighth embodiment described later including this embodiment. is 65, the numerical aperture NA ₃ of CD is 0.51.

  In the present embodiment, the paraxial refractive power of the first aberration correction element L1 is negative and the divergent light beam is incident on the objective lens OL, so that the working distance for a DVD or CD with a thick protective layer is sufficient. To ensure. The objective optical system having a negative / positive configuration as in this embodiment is advantageous in terms of securing a working distance for a DVD or CD even when the focal length is reduced. Therefore, the objective optical system of the present embodiment is optimal for a slim type optical pickup device.

In Tables 1-1 and 1-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₈ , n ₆₅₈ , and n ₇₈₅ are the first wavelength λ ₁ (= 408 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 658 nm) and the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the CD. Further, a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E-3).

The optical surface (first surface) on the light source side of the first aberration correction element L1, the optical surface (fourth surface) on the light source side of the objective lens OL, and the optical surface (fifth surface) on the optical disc side are each aspherical. This aspherical surface is expressed by a mathematical formula obtained by substituting the coefficient in the table into the following aspherical shape formula.
[Aspherical expression]
z = (y ² / R) / [1 + √ {1- (Κ + 1) (y / R) ² }] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ + A ₁₂ y ¹² + A ₁₄ y ¹⁴ + A ₁₆ y ¹⁶ + A ₁₈ y ¹⁸ + A ₂₀ y ²⁰
However,
z: Aspherical shape (distance in the direction along the optical axis from the plane that contacts the apex of the aspherical surface)
y: Distance from optical axis R: Radius of curvature Κ: Conic coefficient A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ , A ₁₄ , A ₁₆ , A ₁₈ , A ₂₀ : Aspherical coefficient In addition, the first phase The 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 coefficient in the table into an expression representing the next optical path difference function.
[Optical path difference function]
φ = M × λ / λ _B × (B ₂ y ² + B ₄ y ⁴ + B ₆ y ⁶ + B ₈ y ⁸ + B ₁₀ y ¹⁰ )
However,
φ: optical path difference function λ: wavelength λ of light beam incident on the diffractive structure _B : manufacturing wavelength M: diffraction order of diffracted light used for recording / reproducing on optical disc y: distance from optical axis B ₂ , B ₄ , B ₆ , B ₈ , B ₁₀ : Diffraction surface coefficient In this specification, the paraxial power of the diffraction structure that diffracts in a direction away from the optical axis is negative (parallel to the first phase structure PS1 and the second phase structure PS2). The incident beam in the state of the beam is diverging), and the paraxial power of the diffractive structure that diffracts in a direction approaching the optical axis is positive (parallel to the first phase structure PS1 and the second phase structure PS2). Direction in which the incident light beam converges).

  Next, a specific numerical example (Example 2) of the objective lens unit OU shown in FIG. 3 will be exemplified.

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are arranged apart from each other. A glass lens (BACD5 manufactured by HOYA) whose aspherical shape is designed to minimize the spherical aberration with respect to one wavelength λ ₁ and the thickness t ₁ of the HD protective layer PL ₁ is a plastic lens. Also good.

  Tables 2-1 and 2-2 show lens data of this example.

In Tables 2-1 and 2-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₅ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 405 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the CD.

  The optical surface (third surface) on the light source side of the second aberration correction element L2, the optical surface on the light source side (fifth surface), and the optical surface on the optical disc side (sixth surface) of the objective lens OL are each aspherical. This aspherical surface is represented by a mathematical formula in which the coefficients in the table are substituted into the aspherical surface shape formula.

  Further, the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light flux 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 formula 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 exemplified.

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are arranged apart from each other, and the objective lens OL is Although the spherical aberration with respect to the thickness t ₁ of the protective layer PL1 of the first wavelength λ1 and the HD is smallest as the glass lenses aspherical shape is designed (HOYA Co. BACD5), as a resin lens Also good.

  Tables 3-1 and 3-2 show lens data of this example.

In Tables 3-1 and 3-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₅ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 405 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the CD.

  The optical surface on the optical disc side (second surface) of the first aberration correction element L1, the optical surface on the light source side (fifth surface) of the objective lens OL, and the optical surface on the optical disc side (sixth surface) are each aspherical. This aspherical surface is represented by a mathematical formula in which the coefficients in the table are substituted into the aspherical surface shape formula.

  Further, the first phase structure PS1 to the third phase structure PS3 are represented by optical path differences added to the incident light flux 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 3-1 and 3-2 into the formula representing the optical path difference function.

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

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are arranged apart from each other, and the objective lens OL is Although it is a glass lens (BACD5 manufactured by HOYA) whose aspherical shape is designed so that the spherical aberration is minimized with respect to the first wavelength λ ₁ and the thickness t ₁ of the protective layer PL1 of HD, a resin lens It is also good.

  In the present embodiment, the paraxial refractive power of the first aberration correction element L1 is negative and the divergent light beam is incident on the objective lens OL, so that the working distance for a DVD or CD with a thick protective layer is sufficient. To ensure. The objective optical system having a negative / positive configuration as in this embodiment is advantageous in terms of securing a working distance for a DVD or CD even when the focal length is reduced. Therefore, the objective optical system of the present embodiment is optimal for a slim type optical pickup device.

  Lens data of this example are shown in Tables 4-1 and 4-2.

In Tables 4-1, 4-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₈ , n ₆₅₈ , and n ₇₈₅ are the first wavelength λ ₁ (= 408 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 658 nm) and the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the CD.

  The optical surface on the light source side (fourth surface) of the first aberration correction element L1, the optical surface on the light source side (sixth surface) of the objective lens OL, and the optical surface on the optical disc side (seventh surface) are each aspherical. This aspherical surface is represented by a mathematical formula in which the coefficients in the table are substituted into the aspherical surface shape formula.

  Further, the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light flux 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 4-1 and 4-2 into the formula representing the optical path difference function.

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

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure PS2 made of resin are joined together, and the objective lens OL is a resin lens. is there.
In addition, including the present embodiment, the numerical aperture NA _{1 of} HD is 0.67, the numerical aperture NA _{2 of} DVD is 0.65, and the numerical aperture NA _{3 of} CD is 0 in Example 6 described later. .51.

  Lens data of this example are shown in Tables 5-1 and 5-2.

In Tables 5-1, 5-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₇ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 407 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the 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 OL are each aspherical, and for the aspherical surface, the coefficients in the table are substituted into the aspherical shape formula. It is expressed by the formula.

  Further, the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light flux 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 5-1 and 5-2 into the formula representing the optical path difference function.

    Next, a numerical example (Example 6) which is a modification of the objective lens unit OU shown in FIG. 6 will be exemplified. The objective lens unit OU of the present embodiment has the diffraction orders of the diffracted light beams of the respective wavelengths generated by the first phase structure PS1 of the objective lens unit OU shown in FIG. The second light beam is characterized by first-order diffracted light and the third light beam is first-order diffracted light.

  The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are joined to each other, and the objective lens OL is a resin lens. .

  Lens data of this example are shown in Tables 6-1 and 6-2.

In Tables 6-1 and 6-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₇ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 407 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the 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 OL are each aspherical, and for the aspherical surface, the coefficients in the table are substituted into the aspherical shape formula. It is expressed by the formula.

  Further, the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light flux 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 formula representing the optical path difference function.

  Next, a numerical example (Example 7) which is a modification of the objective lens unit OU shown in FIG. 13 will be exemplified. The objective lens unit OU of the present embodiment replaces the light incident surface and the light exit surface of the second aberration correcting element L2 of the objective lens unit OU shown in FIG. The element L2 is joined. Further, by passing through the second phase structure PS2, the fifth-order diffracted light of the first light flux, the third-order diffracted light of the second light flux, and the second-order diffracted light of the third light flux are generated.

The first phase structure PS1 and the second phase structure PS2 are both made of resin, the objective lens OL is such that the spherical aberration is minimum with respect to the thickness t ₁ of the protective layer PL1 of the first wavelength lambda ₁ and HD Further, the glass lens (BACD5 manufactured by HOYA) whose aspheric shape is designed may be a plastic lens.

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

In Tables 7-1 and 7-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₅ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 405 nm) and second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the CD.

  The optical surface on the optical disc side (third surface) of the second aberration correction element L2, the optical surface on the light source side (fourth surface), and the optical surface on the optical disc side (fifth surface) of the objective lens OL are each aspherical. This aspherical surface is represented by a mathematical formula in which the coefficients in the table are substituted into the aspherical surface shape formula.

  Further, the first phase structure PS1 and the second phase structure PS2 are represented by optical path differences added to the incident light flux 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 7-1 and 7-2 into the formula representing the optical path difference function.

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

The first aberration correction element L1 having the first phase structure PS1 made of resin and the second aberration correction element L2 having the second phase structure made of resin are joined to each other, and the objective lens OL has a first wavelength. Although it is a glass lens (LAC130 manufactured by HOYA) whose aspheric shape is designed so that spherical aberration is minimized with respect to λ ₁ and the thickness t ₁ of the HD protective layer PL1, it may be a resin lens. .

  Tables 8-1 and 8-2 show lens data of this example.

In Tables 8-1 and 8-2, r (mm) is the radius of curvature, d (mm) is the lens interval, n ₄₀₅ , n ₆₅₅ , and n ₇₈₅ are the first wavelength λ ₁ (= 405 nm) and the second, respectively. The refractive index of the lens for the wavelength λ ₂ (= 655 nm), the third wavelength λ ₃ (= 785 nm), ν _d is the Abbe number of the d-line lens, and M _HD , M _DVD , M _CD are the The diffraction order of the diffracted light used for reproduction, the diffraction order of the diffracted light used for recording / reproduction with respect to the DVD, and the diffraction order of the diffracted light used for recording / reproduction with respect to the 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 OL are each aspherical, and for the aspherical surface, the coefficients in the table are substituted into the aspherical shape formula. It is expressed by the formula.

  Further, the first phase structure PS1, the second phase structure PS2, and the fourth phase structure PS4 are represented by optical path differences added to the incident light flux by each phase structure. Such an optical path difference is represented by an optical path difference function φ (mm) obtained by substituting the coefficient in Table 7 into the formula 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 (range in which the second phase structure PS2 is formed) is an area within φ2.33 mm, and the peripheral area PA ( The range in which the fifth phase structure PS5 is formed) is an area outside φ2.33 mm.

Table 9 shows a list of numerical data in each of the above embodiments. In the table, λ _i is the design wavelength (nm) of HD, DVD, and CD, f _i is the focal length (mm) of the entire objective lens unit system of HD, DVD, and CD, and NA _i is HD, DVD, and CD. The numerical aperture, STO, indicates the entrance pupil diameter (mm) of HD.

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

Claims (51)

Performs recording and / or reproducing information for the first optical disk having a protective layer with a thickness of t ₁ using a first first light flux with wavelength lambda ₁ emitted from the first light source is emitted from the second light source Information is recorded and / or reproduced on a second optical disc having a protective layer having a thickness t ₂ (≧ t ₁ ) using a second light beam having a second wavelength λ ₂ (> λ ₁ ). Information recording and / or reproduction is performed on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using a third light beam having a third wavelength λ ₃ (> λ ₂ ) emitted from the light source. An objective optical system used in an optical pickup device to perform,
The objective optical system includes a first aberration correction element, a second aberration correction element, and the first to third light fluxes that have passed through the first aberration correction element and the second aberration correction element, respectively. An objective lens for focusing on the information recording surface of the first optical disc to the third optical disc,
The first aberration correction element has a first phase structure formed of a material having an Abbe number ν _d 1 at the d-line satisfying the following expression (1), and the second aberration correction element is an Abbe number at the d-line: An objective optical system having a second phase structure formed of a material having a number ν _d 2 satisfying the following expression (2).
40 ≦ ν _d 1 ≦ 80 (1)
20 ≦ ν _d 2 <40 (2) The first phase structure included in the first aberration correction element is formed of a resin having a refractive index n _d 1 of d line satisfying the following expression (3), and the second phase structure included in the second aberration correction element: 2. The objective optical system according to claim 1, wherein the objective optical system is formed of a resin having a refractive index n _d2 of d line satisfying the following expression (4).
1.48 ≦ n _d 1 <1.57 (3)
1.57 ≦ n _d 2 ≦ 1.65 (4) The first phase structure corrects a spherical aberration caused by a difference between the t ₁ and the t ₂ or a spherical aberration caused by a difference between the first wavelength λ ₁ and the second wavelength λ ₂ . The objective optical system according to item 1.   The objective optical system according to claim 3, wherein the first phase structure is a diffractive structure that does not diffract the first light flux and the third light flux but diffracts the second light flux.   The first phase structure is a structure in which a pattern whose cross-sectional shape including an optical axis is stepped is arranged on a concentric circle, and the number of steps corresponding to the number of level surfaces for each predetermined number A of the number of level surfaces. The objective optical system according to claim 4, wherein the step is shifted by a height of minutes. 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 steps is twice the first wavelength λ _1. The objective optical system described in 1.   The first phase structure generates α1-order diffracted light when the first light beam is incident, and generates β1 (β1 <α1) -order diffracted light when the second light beam is incident; 4. The objective optical system according to claim 3, wherein the objective optical system has a diffractive structure that generates diffracted light of γ1 (γ1 ≦ β1) order when the third light flux is incident.   The objective optical system according to claim 7, wherein the diffraction order α1 is an even number. The second phase structure corrects a spherical aberration caused by a difference between the t ₁ and the t ₃ or a spherical aberration caused by a difference between the first wavelength λ ₁ and the second wavelength λ ₃ . The objective optical system according to item 1.   The objective optical system according to claim 9, wherein the second phase structure is a diffractive structure that does not diffract the first light flux and the second light flux but diffracts the third light flux.   The second phase structure is a structure in which a pattern whose cross-sectional shape including the optical axis is stepped is arranged on a concentric circle, and the number of steps corresponding to the number of level surfaces for each predetermined number of level surfaces B The objective optical system according to claim 10, which has a structure in which a step is shifted by a height of minutes. 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 steps is 7 times the first wavelength λ _1. Objective optical system.   The second phase structure generates α-order diffracted light when the first light beam is incident, and generates β2 (β2 <α2) -order diffracted light when the second light beam is incident; The objective optical system according to claim 9, wherein the objective optical system has a diffractive structure that generates γ2 (γ2 ≦ β2) order diffracted light when the third light beam is incident.   The objective optical system according to claim 13, wherein the diffraction order α2 is an odd number.   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.   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.   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. The third phase structure is in the range Section 17 claims having a function of suppressing movement of the paraxial image point position in which the first wavelength lambda ₁ is generated in the objective optical system upon wavelength change within ± 5 nm The objective optical system described. The third phase structure, the objective described in the scope paragraph 17 claims having a function of suppressing variation of the spherical aberration of the first wavelength lambda ₁ is generated in the objective optical system upon wavelength change within ± 5 nm Optical system.   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 refractive index of the objective optical system.   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. The said 3rd phase structure is formed in the said 1st aberration correction element, The optical path difference 10 times the said 1st wavelength (lambda) ₁ is added with respect to a said 1st light beam, The range of Claim 21 Objective optical system.   The objective optical system according to claim 1, wherein both the first phase structure and the second phase structure are formed of a resin.   2. 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.   The objective optical according to claim 24, wherein a phase structure formed of an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure is the second phase structure. system.   25. The objective optical system according to claim 24, wherein a phase structure formed of an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure is formed on a glass substrate. . 2. The objective optical system according to claim ₁ , wherein spherical aberration correction is optimized for the combination of the t ₁ and the first wavelength λ ₁ . The objective optical system according to claim 1, wherein the following expressions (5) to (7) are satisfied.
380 nm <λ ₁ <420 nm (5)
1.5 <λ ₂ / λ ₁ <1.7 (6)
1.8 <λ ₃ / λ ₁ <2.1 (7)   The objective optical system according to claim 4, wherein the first phase structure has an action of diverging the second light flux.   The objective optical system according to claim 10, wherein the second phase structure has an action of diverging the third light flux.   8. The first phase structure according to claim 7, wherein the first phase structure has a function of suppressing movement of a paraxial image point position generated in the objective optical system when the wavelength of the first wavelength λ1 changes within ± 5 nm. Objective optical system. 2. 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 .   2. The objective optical system according to claim 1, wherein all of the first to third light beams are incident on the first aberration correction element and the second aberration correction element in a parallel light beam state. The first aberration correction element has an Abbe number ν _d 1 in the d line satisfying the expression (1) and has a first phase structure, and the second aberration correction element has an Abbe number ν _d 2 in the d line ( 2. The objective optical system according to claim 1, wherein the objective optical system satisfies the expression (2) and has a second phase structure. The first aberration correction element has a refractive index n _d 1 at the d line satisfying the expression (3) and has a first phase structure, and the second aberration correction element has a refractive index n _d 2 at the d line ( 4. The objective optical system according to claim 2, wherein the objective optical system satisfies the formula (4) and has a second phase structure. The first aberration correction element has a positive paraxial power with respect to the first wavelength λ ₁ , and the second aberration correction element has a negative paraxial power with respect to the first wavelength λ ₁ . The objective optical system according to the first item in the range.   The first aberration correction element and the second aberration correction element are joined to each other, and a joint surface of the first aberration correction element and the second aberration correction element has a convex shape toward the second aberration correction element. 37. The objective optical system according to claim 36, wherein the objective optical system is provided.   25. An unheated antireflection coating is formed on a surface of a phase structure formed of an ultraviolet curable resin or a thermosetting resin among the first phase structure and the second phase structure. The objective optical system according to item.   The objective optical system according to Claim 23, wherein the first phase structure is formed of a cyclic polyolefin-based resin, and the second phase structure is formed of a fluorene-based polyester resin.   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, and the first phase structure is divided into the first central region. The objective optical system according to claim 4, wherein the objective optical system is formed in a region.   At least a part of the first peripheral region is formed with a fourth phase structure for controlling a condensing position of the second light flux passing through this part, and the fourth phase structure includes the first light flux and the first light flux. 41. The objective optical system according to claim 40, wherein the objective optical system has a diffractive structure that diffracts the second light beam without diffracting the third light beam.   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, and the second phase structure is divided into the second central region. The objective optical system according to claim 10, wherein the objective optical system is formed in a region.   At least a part of the second peripheral region is formed with a fifth phase structure for controlling a condensing position of the third light flux passing through this part, and the fifth phase structure includes the first light flux and the first light flux. 43. The objective optical system according to claim 42, wherein the objective optical system has a diffractive structure that diffracts the third light beam without diffracting the second light beam. Wherein the difference between the back focus fB ₂ with respect to the back focus fB ₁ and the second wavelength lambda ₂ first with respect to the wavelength lambda _1, the first wavelength lambda back focus fB for back focus fB ₁ and the second wavelength lambda ₃ with respect to _{1 2.} The objective optical system according to claim 1, wherein a difference from ₃ is 0.2 mm or less. The objective optical system according to claim 11, wherein according to the minimum width lambda ratio lambda _{M /} lambda ₁ for the first wavelength lambda ₁ of _M is 25 or more of the pattern of the second phase structure.   2. The objective optical system 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.   The objective optical system according to claim 5, wherein each of the first phase structure and the second phase structure is formed on a plane.   The objective optical system according to claim 11, wherein each of the first phase structure and the second phase structure is formed on a plane.   The objective optical according to claim 1, wherein the first aberration correction element, the second aberration correction element, and the objective lens are held by a holding member so that a relative positional relationship is universal. system. A first light source that emits a first light flux of a first wavelength λ ₁ for recording and / or reproducing information with respect to a first optical disc having a protective layer having a thickness of t ₁ ;
A second light source that emits a second light beam having a second wavelength λ ₂ (> λ ₁ ) for recording and / or reproducing information with respect to the second optical disc;
A third light source that emits a third light beam having a third wavelength λ ₃ (> λ ₂ ) for recording and / or reproducing information with respect to the third optical disc;
An objective optical system according to claim 1,
Information is recorded and / or reproduced with respect to the first optical disc having the protective layer having the thickness t ₁ using the first light beam, and the thickness t ₂ (≧ t ₁ ) is protected using the second light beam. Recording and / or reproducing information on a second optical disc having a layer, and recording and / or reproducing information on a third optical disc having a protective layer having a thickness t ₃ (> t ₂ ) using the third light flux An optical pickup device that performs reproduction.   51. An optical disc drive apparatus 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.