JP4849979B2 - Objective lens for optical information recording / reproducing apparatus and optical information recording / reproducing apparatus - Google Patents

Description

  The present invention relates to, for example, an optical information recording / reproducing apparatus that records or reproduces information on a plurality of types of optical disks having different recording densities and protective layer thicknesses, and an objective lens mounted on the apparatus.

  Conventionally, there are a plurality of standards for optical disks, such as CD and DVD, which have different recording densities and protective layer thicknesses. In recent years, optical discs of a new standard having a higher recording density than that of DVDs are being put into practical use in order to realize a higher capacity for information recording. Examples of the new standard optical disc include HD DVD and BD (Blu-ray Disc). Such a new standard optical disc has a protective layer thickness equal to or less than the protective layer thickness of DVD. Since there are a plurality of optical discs with different standards in this way, in view of user convenience, in recent years, an optical information recording / reproducing device, more strictly, an objective optical system provided in the device has been used for the above three types of optical discs. And compatibility is required. In the text, the term “optical information recording / reproducing apparatus” includes all of the information recording apparatus, the information reproduction apparatus, and the information recording / reproducing apparatus. “Compatible” means that recording or reproduction of information is guaranteed without changing parts even if the optical disk to be used is switched.

  In order for the device to be compatible with a plurality of optical discs with different standards, first, it is used for recording or reproducing information while correcting the spherical aberration that changes depending on the thickness of the protective layer when switching between optical discs with different standards. It is necessary to obtain a beam spot having a size corresponding to the difference in recording density by changing the numerical aperture (NA) of the light. Generally, the spot diameter can be made smaller as the wavelength is shorter. Therefore, conventionally, laser light having a plurality of wavelengths is used in the optical information recording / reproducing apparatus according to the recording density. For example, when using a DVD, laser light having a wavelength of about 660 nm, which is shorter than about 790 nm used when using a CD, is used. In addition, when the optical disc of the new standard is used, light having a wavelength shorter than that used when recording or reproducing information on a DVD (for example, so-called blue laser light per 408 nm) is used because of its high recording density.

  Further, as one means for converging on the recording surface position of each optical disk in a good state with respect to each optical disk, a ring is formed on an arbitrary surface of one or a plurality of optical elements (for example, an objective lens) constituting the objective optical system. A technology has been put into practical use in which a ring-shaped structure having a band-shaped fine step is provided and light of different wavelengths is converged well on the recording surface of the corresponding optical disk by the action of the ring-shaped structure.

  The optical element preferably has an action of correcting spherical aberration that occurs when the wavelength of the laser beam to be used deviates from the design wavelength due to environmental differences such as individual differences of light sources and temperature changes. The design wavelength means the wavelength of each laser beam that is optimal for recording or reproducing information on each optical disc.

  As described above, for example, the following Patent Document 1 proposes an objective lens that is compatible with three types of optical disks such as CD, DVD, and HD DVD.

Japanese Patent Laid-Open No. 2004-247025

  Patent Document 1 discloses an optical pickup device that is compatible with three types of optical disks having different recording densities. Specifically, the objective lens mounted on the optical pickup device uses third-order diffracted light when recording or reproducing information on a high-density optical disk, and uses second-order diffracted light when recording or reproducing information on a DVD or CD. It has such an annular structure. By mounting such an objective lens, a spot suitable for recording or reproducing information is formed particularly on the recording surface of each optical disc. Thus, an optical pickup device having compatibility with three types of optical disks having different recording densities is provided.

  However, in the optical pickup device disclosed in Patent Document 1, the light use efficiency during recording or reproduction of information with respect to a CD can be secured only about 40%, and an unnecessary diffraction order (in this case, the first order). ) Light is generated. For this reason, the waveform of the focus error signal is broken, and the focusing function is deteriorated, or the spot cannot be narrowed down to a desired value.

  In view of the circumstances described above, the present invention provides a recording surface of each optical disc even when information is recorded or reproduced on any of the three types of optical discs having different standards using a plurality of types of light beams having different wavelengths. In this case, the objective lens is provided with a step structure that suppresses spherical aberration and forms a good spot and generates unwanted diffraction order light when using an optical disk having a relatively low recording density such as a CD. However, the optical information recording / reproducing apparatus capable of suppressing the deterioration of the focusing function, narrowing the spot to a desired value, and maintaining high efficiency when using an optical disk having a high recording density such as HD DVD, and the optical An object of the present invention is to provide an objective lens for an information recording / reproducing apparatus.

In order to solve the above-mentioned problems, the objective lens for an optical information recording / reproducing apparatus according to the present invention has the first to third wavelengths in order from the short wavelength side with respect to the first to third optical discs in the descending order of the recording density. An objective lens used in an optical information recording / reproducing apparatus that records or reproduces information on each optical disc by using any one of three types of light beams having the first wavelength of λ1 (nm), Assuming that the third wavelength is λ3 (nm), λ1≈405 nm and λ3≈790 nm, and at least one surface is a first region for converging a light beam of the third wavelength on the recording surface of the third optical disk. The first region has a step structure that is divided into a plurality of concentric refracting surfaces and has a step that provides an optical path length difference with respect to the incident light flux between adjacent refracting surfaces.

The objective lens for an optical information recording / reproducing apparatus according to the present invention can not only form a spot suitable for recording or reproducing information while suppressing spherical aberration when each optical disk is used, but also a light beam having a third wavelength. When the information is recorded or reproduced on the third optical disk, the collapse of the waveform of the focus error signal can be suppressed, and a highly accurate focusing function can be realized.

The objective lens for an optical information recording / reproducing apparatus according to the present invention has a step structure in which the first wavelength is λ1 (nm), and the optical path length difference that the step imparts to the light flux having the first wavelength is ΔOPD (nm). Then, the following condition (1),
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
( However, N is an integer. )
To meet.

ただし、ｈは、光軸からの高さ、
Ｐ _２ 、Ｐ _４ 、Ｐ _６ 、…は、それぞれ二次、四次、六次、…の係数、
ｍは、入射光束の回折効率が最大となる回折次数、
λは、入射光束の使用波長、
で表すと、以下の条件（４）、
２．５０＜（ｆ１×Ｐ _２ ）／（ｔ３−ｔ１）＜１３．００・・・（４）
（ただし、ｆ１は、第一の波長に対する対物レンズの焦点距離、
ｔ３は、第三の光ディスクのディスク厚、
ｔ１は、第一の光ディスクのディスク厚（ただしｔ１＜ｔ３であり、第一から第三の各光ディスクのディスク厚のうちｔ１は最も薄く、ｔ３は最も厚い））、
を満たす。 The objective lens used in the optical information recording / reproducing apparatus according to the present invention has an optical path difference function φ (h) that defines the step structure as the following equation (2),

Where h is the height from the optical axis,
P ₂ , P ₄ , P ₆ ,... Are secondary, quaternary, sixth order,.
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
λ is the wavelength used for the incident luminous flux,
In the following condition (4),
2.50 <(f1 × P ₂ ) / (t3-t1) <13.00 (4)
(Where f1 is the focal length of the objective lens relative to the first wavelength,
t3 is the disc thickness of the third optical disc,
t1 is the disk thickness of the first optical disk (where t1 <t3, and t1 is the thinnest and t3 is the thickest among the disk thicknesses of the first to third optical disks)),
Meet.

From another point of view, the optical information recording / reproducing apparatus according to the present invention provides any one of three types of light beams having first to third wavelengths for the first to third optical disks having different recording densities. Is an optical information recording / reproducing apparatus for recording or reproducing information with respect to each optical disc, comprising an objective lens, a first wavelength of λ1 (nm), a second wavelength of λ2 (nm), a first wavelength If the third wavelength is λ3 (nm),
λ1 <λ2 <λ3
NA1 for the numerical aperture necessary for recording or reproducing information on the first optical disc, NA2 for the numerical aperture necessary for recording or reproducing information on the second optical disc, and recording or reproducing information on the third optical disc If the required numerical aperture is NA3,
NA1> NA3 and NA2> NA3
The thickness of the protective layer of the first optical disc on which information is recorded or reproduced using the light beam having the shortest first wavelength among the first to third wavelengths is t1, which is longer than the first wavelength. The recording layer of the second optical disc on which information is recorded or reproduced using a light beam having a second wavelength is t2, and the information recording is performed using a light beam having the longest third wavelength among the first to third wavelengths. Or if the protective layer thickness of the third optical disk to be played is t3,
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm
The first wavelength and the second wavelength of the light beam are substantially parallel light beams, the third wavelength of the light beam is divergent light incident on the objective lens, and at least one surface of the objective lens has a third wavelength. Has a first region that converges the light beam on the recording surface of the third optical disc, and is divided into a plurality of concentric refracting surfaces within the first region, and is incident between adjacent refracting surfaces. The optical path length difference that the step has with respect to the light beam having the first wavelength in the first region is ΔOPD (nm). The following condition (1),
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
( However, N is an integer .)
Meet.

ただし、ｈは、光軸からの高さ、
Ｐ _２ 、Ｐ _４ 、Ｐ _６ 、…は、それぞれ二次、四次、六次、…の係数、
ｍは、入射光束の回折効率が最大となる回折次数、
λは、入射光束の使用波長、
で表すと、以下の条件（４）、
２．５０＜（ｆ１×Ｐ _２ ）／（ｔ３−ｔ１）＜１３．００・・・（４）
（ただし、ｆ１は、第一の波長に対する対物レンズの焦点距離）
を満たすことを特徴とする。 In the optical information recording / reproducing apparatus according to the present invention, the optical path difference function φ (h) defining the step structure is expressed by the following equation (2),

Where h is the height from the optical axis,
P ₂ , P ₄ , P ₆ ,... Are secondary, quaternary, sixth order,.
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
λ is the wavelength used for the incident luminous flux,
In the following condition (4),
2.50 <(f1 × P ₂ ) / (t3-t1) <13.00 (4)
(Where f1 is the focal length of the objective lens with respect to the first wavelength)
It is characterized by satisfying.

Further, according to the optical information recording / reproducing apparatus of the present invention , the objective lens has an Abbe number νd of the following condition (5):
40 ≦ νd ≦ 80 (5)
The step structure is a single lens satisfying the following condition (6),
2.70 <| ΔOPD / λ1 | <3.30 (6)
In the recording or reproduction of information on the first optical disc, the imaging magnification is M1, the focal length is f1, and in the recording or reproduction of information on the second optical disc, the imaging magnification is M2, the focal length is f2, In the recording or reproduction of information on the three optical discs, when the imaging magnification is M3 and the focal length is f3, the following conditions (7) to (9)
−0.02 <f1 × M1 <0.02 (7)
−0.02 <f2 × M2 <0.02 (8)
−0.12 <f3 × M3 <−0.04 (9)
It is desirable to satisfy.

Further, according to the optical information recording / reproducing apparatus according to the present invention , the objective lens has an Abbe number νd of the following condition (10):
20 ≦ νd <40 (10)
The step structure is a single lens satisfying the following condition (6),
2.70 <ΔOPD / λ1 <3.30 (6)
In the recording or reproduction of information on the first optical disc, the imaging magnification is M1, the focal length is f1, and in the recording or reproduction of information on the second optical disc, the imaging magnification is M2, the focal length is f2, In the recording or reproduction of information on the three optical discs, when the imaging magnification is M3 and the focal length is f3, the following conditions (7), (8), (11),
−0.02 <f1 × M1 <0.02 (7)
−0.02 <f2 × M2 <0.02 (8)
−0.38 <f3 × M3 <−0.30 (11)
It is desirable to satisfy.

The step structure has the following condition (12), where ΔOPDc (nm) is the optical path length difference that the step gives to the light beam having the third wavelength:
1.32 <| ΔOPDc / λ3 | <1.62 // (12)
Configured to meet.

From another point of view, the optical information recording / reproducing apparatus according to the present invention is an abbreviation of any one of the three types having the first to third wavelengths for the first to third optical disks having different recording densities. An optical information recording / reproducing apparatus that records or reproduces information on each optical disk by using different parallel light beams, and includes an objective lens, a first wavelength is λ1 (nm), and a second wavelength is λ2 (nm) If the third wavelength is λ3 (nm),
λ1 <λ2 <λ3
NA1 for the numerical aperture necessary for recording or reproducing information on the first optical disc, NA2 for the numerical aperture necessary for recording or reproducing information on the second optical disc, and recording or reproducing information on the third optical disc If the required numerical aperture is NA3,
NA1> NA3 and NA2> NA3
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using a light beam of the first wavelength is t1, and the information is recorded or reproduced using a light beam of the second wavelength. If the protective layer thickness of the optical disk is t2, and the protective layer thickness of the third optical disk on which information is recorded or reproduced using a light beam of the third wavelength is t3,
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm
And at least one surface of the objective lens has a first region for converging the light beam of the third wavelength on the recording surface of the third optical disc, and a plurality of concentric shapes are formed in the first region. And having at least two types of step structures that give different optical path length differences to the incident light flux between adjacent refracting surfaces. If at least one of the steps is ΔOPD1 (nm), the following condition (13):
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)
( However, N is an integer .)
To meet.

ただし、ｈは、光軸からの高さ、
Ｐ _２ ｉ、Ｐ _４ ｉ、Ｐ _６ ｉ、…は、それぞれ第ｉの光路差関数における二次、四次、六次、…の係数、
ｍは、入射光束の回折効率が最大となる回折次数、
λは、入射光束の使用波長、
で表すと、第１の光路差関数に関して、以下の条件（１６）、
２．５０＜（ｆ１×Ｐ _２ １）／（ｔ３−ｔ１）＜１３．００・・・（１６）
（ただし、ｆ１は、第一の波長に対する対物レンズの焦点距離）
を満たすことを特徴とする。 According to the optical information recording / reproducing apparatus of the present invention, the step structure is defined by at least the first and second optical path difference functions, and the i-th (i is a natural number) optical path difference function φi (h) is Equation (14),

Where h is the height from the optical axis,
P ₂ i, P ₄ i, P ₆ i,... Are coefficients of second order, fourth order, sixth order,... In the i th optical path difference function,
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
λ is the wavelength used for the incident luminous flux,
In terms of the first optical path difference function, the following condition (16),
2.50 <(f1 × P ₂ 1) / (t3-t1) <13.00 (16)
(Where f1 is the focal length of the objective lens with respect to the first wavelength)
It is characterized by satisfying.

According to the optical information recording / reproducing apparatus of the present invention, it is desirable that the step satisfying the condition (13) in the first region further satisfies the following condition (17).
2.70 <| ΔOPD1 / λ1 | <3.30 (17)

According to the optical information recording / reproducing apparatus of the present invention, when the optical path length difference that the step satisfying the condition (13) imparts to the third wavelength light flux is ΔOPDc1 (nm) in the first region, It is desirable to satisfy the following condition (18).
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)

Alternatively, the step structure may be configured such that the step satisfying the condition (13) further satisfies the following condition (19) in the first region.
4.70 <| ΔOPD1 / λ1 | <5.30 (19)

Further, when the step satisfying the condition (13) in the first region and the difference in optical path length given to the light beam having the third wavelength by the step is ΔOPDc1 (nm), the following condition (20) is satisfied. It is desirable to satisfy.
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)

According to the optical information recording / reproducing apparatus of the present invention, when the step that provides the optical path length difference different from at least one of the steps is ΔOPD2 (nm), the optical path length difference that is applied to the light flux of the first wavelength. The following condition (21),
2L−0.20 <| ΔOPD2 / λ1 | <2L + 0.20 (21)
( However, L is an integer. )
It is desirable to satisfy.

According to the optical information recording / reproducing apparatus of the present invention , the following condition (22):
1.80 <| ΔOPD2 / λ1 | <2.20 (22)
By satisfying the above, it is possible to obtain a high light utilization efficiency particularly when using the first optical disk having a high recording density.

According to the optical information recording / reproducing apparatus of the present invention , the objective lens records the first wavelength light beam and the second wavelength light beam on the first optical disk and the second optical disk, respectively, outside the first region. A second region that converges on the surface and does not contribute to the convergence of the light beam of the third wavelength, and the second region is at least one kind with respect to the incident light beam at a boundary between adjacent refractive surfaces. The absolute value of the optical path length difference provided by the step in the second region is different from the absolute value of the optical path length difference provided by the step in the first region.

Further, according to the optical information recording / reproducing apparatus of the present invention , the objective lens has a first wavelength light beam and a second wavelength light beam outside the first region, respectively, the first optical disk and the second optical disk. The second region is focused on the recording surface of the optical disk and does not contribute to the convergence of the light beam having the third wavelength. At least one kind of optical path length difference is provided, and the absolute value of the optical path length difference provided by the step in the second region is different from | ΔOPD1 / λ1 |.

Further, according to the optical information recording / reproducing apparatus of the present invention , the following condition (23),
f1 × NA1> f2 × NA2 (23)
And the objective lens has a third region outside the second region that converges only the light flux of the first wavelength and does not contribute to the convergence of the light flux of the second and third wavelengths, The third region has a step that gives at least one kind of optical path length difference to the incident light flux at the boundary between adjacent refractive surfaces, and the absolute value of the optical path length difference given by the step in the third region Is different from the absolute value of the optical path length difference given by the step in the second region.

Further, according to the optical information recording / reproducing apparatus of the present invention , the following condition (24):
f1 × NA1 <f2 × NA2 (24)
And the objective lens has a third region outside the second region that converges only the light flux of the second wavelength and does not contribute to the convergence of the light flux of the first and third wavelengths, The third region has a step that gives at least one kind of optical path length difference to the incident light flux at the boundary between adjacent refractive surfaces, and the absolute value of the optical path length difference given by the step in the third region Is different from the absolute value of the optical path length difference given by the step in the second region.

  As described above, according to the present invention, by forming a predetermined step structure on at least one surface of the objective lens in the optical information recording / reproducing apparatus, the aberration generated on the recording surface of each optical disk is satisfactorily suppressed. Even when the third optical disk is used, it is possible to suppress deterioration of the focus error signal due to unnecessary diffraction order light generated as well as spherical aberration. That is, an optical information recording / reproducing objective lens capable of recording or reproducing information with high accuracy on all three types of optical disks having different recording densities without degrading the focusing function, and an optical information recording equipped with the objective lens A playback device is provided.

  Hereinafter, two embodiments of the objective lens for an optical information recording / reproducing apparatus according to the present invention will be described. The objective lens of each embodiment is mounted on an optical information recording / reproducing apparatus, and is compatible with three types of optical discs having different standards such as protective layer thickness and recording density.

  In the following, for convenience of explanation, among the above three types of optical discs, an optical disc having the highest recording density (for example, a new standard optical disc such as HD DVD or BD) is relatively compared to the first optical disc D1 and the first optical disc D1. The second optical disk D2 has a low recording density (for example, DVD or DVD-R), and the third optical disk D3 has the lowest recording density (for example, CD or CD-R).

Assuming that the protective layer thicknesses of the optical disks D1 to D3 are t1 to t3, the protective layer thicknesses have the following relationship.
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm

Further, when recording or reproducing information on each of the optical discs D1 to D3, it is necessary to change the required NA value so that a beam spot having a size corresponding to the difference in recording density can be obtained. There is. Here, assuming that the optimum design numerical apertures required for recording or reproducing information with respect to each of the optical discs D1 to D3 are NA1, NA2, and NA3, each NA has the following relationship.
NA1> NA3 and NA2> NA3

  That is, when recording or reproducing information with respect to the first optical disc D1 and the second optical disc D2 having a high recording density, formation of a spot with a smaller diameter is required, so that the necessary NA is increased. On the other hand, when recording or reproducing information on the third optical disc D3 having the lowest recording density, the required NA is relatively small. All optical disks are placed on a turntable (not shown) and rotated when information is recorded or reproduced.

  When the optical discs D1 to D3 having different recording densities are used as described above, laser beams having different wavelengths are used in the optical information recording / reproducing apparatus so as to obtain a beam spot having a size corresponding to each recording density. Used. Specifically, when information is recorded on or reproduced from the first optical disc D1, in order to form the beam spot having the smallest diameter on the recording surface of the first optical disc D1, the shortest wavelength (the first wavelength) A laser beam (hereinafter, referred to as a first laser beam) that is one wavelength) is irradiated from a light source. Further, when recording or reproducing information on the third optical disc D3, in order to form a beam spot with the largest diameter on the recording surface of the third optical disc D3, A laser beam having a wavelength) (hereinafter referred to as a third laser beam) is irradiated from a light source. When recording or reproducing information on the second optical disc D2, a longer wavelength than that of the first laser beam is formed in order to form a relatively small-diameter spot on the recording surface of the second optical disc D2. In addition, a laser beam (hereinafter referred to as a second laser beam) having a shorter wavelength (second wavelength) than the third laser beam is irradiated from a light source.

  FIG. 1 is a schematic diagram showing a schematic configuration of an optical information recording / reproducing apparatus 100 having an objective lens 10 according to the first embodiment. The optical information recording / reproducing apparatus 100 includes a light source 1A for irradiating a first laser beam, a light source 1B for irradiating a second laser beam, a light source 1C for irradiating a third laser beam, diffraction gratings 2A, 2B, 2C, a cup. Ring lenses 3A, 3B, and 3C, beam splitters 41 and 42, half mirrors 5A, 5B, and 5C, and light receiving portions 6A, 6B, and 6C are included. In the optical information recording / reproducing apparatus 100, it is necessary to cope with different NAs required when using each optical disk. Therefore, in the optical information recording / reproducing apparatus 100, although not shown, an aperture limiting element that defines the beam diameter of the third laser beam may be provided.

  As shown in FIG. 1, the first to third laser light beams emitted from the light sources 1A to 1C are guided to a common optical path via the coupling lenses 3A to 3C and the beam splitters 41 and 42, The light enters the objective lens 10. Each light beam transmitted through the objective lens 10 converges in the vicinity of the recording surface of each of the optical discs D1 to D3 to be recorded or reproduced. Each laser beam reflected by the recording surface passes through the half mirrors 5A to 5C and is detected by the light receiving units 6A to 6C.

  FIG. 2A to FIG. 2C are diagrams showing the optical path from each light source to each optical disc when the objective lens 10 and each optical disc D1 to D3 are used for each optical disc. 2A to 2C, the reference axis AX of the optical information recording / reproducing apparatus 100 is indicated by a one-dot chain line in the drawing. In the states shown in FIGS. 2A to 2C, the optical axis of the objective lens coincides with the reference axis AX. However, the optical axis of the objective lens may deviate from the reference axis AX by a tracking operation or the like. The relationship between the reference axis AX and the optical axis is the same in the second embodiment described later (see FIG. 6).

The objective lens 10 has a first surface 11 and a second surface 12 in order from the light source side. As shown in FIGS. 2A to 2C, the objective lens 10 is a biconvex plastic single lens in which the surfaces 11 and 12 are both aspherical. The shape of the aspheric surface is the distance (sag amount) from the tangential plane on the optical axis of the aspherical surface at the coordinate point on the aspherical surface where the height from the optical axis is h, and X (h). The curvature (1 / r) above is C, the conic coefficient is K, the fourth, sixth, eighth, tenth, twelfth, etc. aspheric coefficients are A ₄ , A ₆ , A ₈ , A ₁₀ , A ₁₂ is expressed by the following equation (3).

  Each of the optical disks D1 to D3 has a protective layer 21 and a recording surface 22 respectively. In the actual optical disks D1 to D3, the recording surface 22 is sandwiched between the protective layer 21 and a substrate layer or label layer (not shown).

  As in the optical information recording / reproducing apparatus 100, when laser beams having different wavelengths are used when the optical disks D1 to D3 are used, the refractive index of the objective lens changes and the thickness of the protective layer 21 of each of the optical disks D1 to D3 varies. Due to this, the spherical aberration changes. In order to make the optical information recording / reproducing apparatus 100 compatible with each of the optical discs D1 to D3, it is necessary to satisfactorily correct spherical aberration that occurs when any of the optical discs is used. Therefore, a plurality of refraction surfaces formed concentrically on the reference axis AX and a boundary between the refraction surfaces on at least one surface of the objective lens 10 (the first surface 11 in the present embodiment). A step structure consisting of a minute step is provided. This level | step difference is comprised so that a predetermined | prescribed optical path length difference may be provided with respect to an incident light beam.

  FIG. 3 is an enlarged view of the phase shift structure provided on the first surface 11. In the text, the phase shift structure is synonymous with the step structure described above. Further, as shown in FIG. 3, the optical path length difference is a boundary position of a virtual extended surface (AA ′ surface) obtained by extending the shape of the (j−1) th refracting surface in a direction away from the optical axis. An optical path length when evaluated up to the image plane obtained when refracting at (hj), and a virtual extended surface (BB ′ surface) obtained by extending the shape of the jth refractive surface in the direction toward the optical axis Means the difference in optical path length when evaluated up to the image plane obtained when refracting at the boundary position (hj).

  The phase shift structure shown in FIG. 3 is designed to have such characteristics that the spherical aberration generated in the refractive lens portion of the objective lens 10 can be controlled by the difference in wavelength between the first and second laser beams. In the present embodiment, the phase shift structure is the innermost region including the optical axis of the objective lens 10 and contributes to the convergence of the third laser beam, that is, any of the first to third laser beams. In a region that also contributes to convergence (hereinafter referred to as the first region), there is a level difference that gives an optical path length difference that is approximately odd times when the first laser beam is incident.

Specifically, the optical path length difference of approximately odd multiples is as follows when the first wavelength is λ1 (nm) and the optical path length difference that the step is given to the light flux having the first wavelength is ΔOPD (nm): Stipulated in 1).
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
However, N is an integer. The same applies to N used in the following conditions.

  By satisfying the condition (1), it is possible to suitably realize information recording or reproduction by the first and second laser beams at the time of recording and reproducing information on the optical disks D1 and D2 having a relatively high recording density. In the condition (1), if the optical path length difference | ΔOPD / λ1 | exceeds the upper limit, the diffraction efficiency of the first laser light is particularly lowered, and if it is less than the lower limit, the diffraction efficiency of the second laser light is particularly lowered.

  The phase shift structure that satisfies the condition (1) can be expressed by the following optical path difference function φ (h). The optical path difference function φ (h) represents the function of the objective lens 10 as a diffraction lens in the form of an additional optical path length at a height h from the optical axis. The optical path difference function φ (h) is expressed by the following equation (2).

In the optical path difference function φ (h), P ₂ , P ₄ , P ₆ are coefficients of second order, fourth order, sixth order,. m represents the diffraction order at which the diffraction efficiency of the laser beam to be used is maximized, and λ represents the design wavelength of the laser beam to be used (incident).

  The phase shift structure of the objective lens 10 according to the present embodiment has a differential value of the optical path difference function φ (h) when the height h from the optical axis is not less than 30% and not more than 70% of the effective radius of the first region. Is designed to change from positive to negative, in other words, across zero. More specifically, the phase shift structure is designed to satisfy the following condition (3).

0.00 <(f1 × P ₂ ) / (t3−t1) <18.00 (3)
Here, f1 represents the focal length of the objective lens 10 when the first laser beam is used.

  The effect of the condition (3) will be verified with reference to FIGS. FIG. 4 shows information recording or reproduction among focus error signals obtained when information is recorded or reproduced on the third optical disk D3 using an objective lens having a phase shift structure that does not satisfy the condition (3). Obtained by a light beam of a diffraction order (hereinafter referred to as normal diffraction order light for convenience) used in the above, and a light beam of a diffraction order not used for recording or reproduction of information (hereinafter referred to as unnecessary diffraction order light for convenience). It is a figure which shows the focus error signal obtained as a component and total which added both components. FIG. 5 shows components obtained by normal diffraction order light, unnecessary diffraction among focus error signals obtained when information is recorded on or reproduced from the third optical disc D3 using the objective lens of the present embodiment. It is a figure which shows the focus error signal obtained as a component obtained by order light, and total which added both components. 4 and 5, the vertical axis represents the detected focus error signal level, and the horizontal axis represents the defocus amount of the objective lens. The same applies to the drawings relating to the focus error signal described later.

  As shown in FIG. 4, when the value of the condition (3) exceeds the upper limit and lower limit, the zero cross point of the focus error signal component based on the normal diffraction order light and the zero cross point of the focus error signal component based on the unnecessary diffraction order light are I will leave. For this reason, the waveform of the focus error signal as a total collapses, and the focus error function is deteriorated, which may affect the recording or reproduction of information, particularly when the third optical disc D3 is used.

  On the other hand, the objective lens 10 of the present embodiment satisfies the condition (3), so that the zero-cross point of the focus error signal component obtained by the normal diffraction order light and the focus error signal component obtained by the unnecessary diffraction order light are satisfied. The zero cross point can be brought closer. Therefore, it can be seen that the waveform of the focus error signal as a total also has an S-shape necessary for effectively operating the focus error function.

In order to obtain a focus error signal having a much better waveform, the following condition (4) may be satisfied.
2.50 <(f1 × P ₂ ) / (t3-t1) <13.00 (4)

More specifically, the Abbe number νd satisfies the following condition (5):
40 ≦ νd ≦ 80 (5)
When the objective lens 10 satisfying the above condition is used, the phase shift structure is designed so that the optical path length difference ΔOPD imparted to the first laser light by the steps constituting the phase shift structure satisfies the following condition (6) Is done.
2.70 <| ΔOPD / λ1 | <3.30 (6)

  If the upper limit of condition (6) is exceeded, the amount of light of the first wavelength is undesirably reduced. On the other hand, if the lower limit is exceeded, the amount of unwanted diffraction order light in the third wavelength light beam increases and the focusing function deteriorates, which is not preferable.

  Usually, the objective lens 10 is disposed on the reference axis AX of the optical information recording / reproducing apparatus 100. However, in the process of recording or reproducing information, the position of the objective lens 10 may deviate from the reference axis AX due to tracking shift. In this case, no aberration is generated if a parallel light beam is incident on the objective lens 10, but off-axis such as coma and astigmatism is generated when non-parallel light such as diverging light or convergent light is incident. Will occur. In general, an optical disc that requires a high NA for recording or reproducing information has a narrower tolerance for aberration. Therefore, when using an optical disc that requires a high NA for recording or reproducing information, even if the objective lens 10 is subjected to tracking shift or the like, the objective lens 10 is provided with the objective lens 10 in order to suppress the occurrence of various aberrations due to off-axis light. It is desirable that a substantially parallel light beam be incident.

For example, the objective lens 10 having a phase shift structure designed to satisfy the above condition (6) is designed to satisfy the following condition (7) and condition (8).
−0.02 <f1 × M1 <0.02 (7)
−0.02 <f2 × M2 <0.02 (8)
However, M1 and f1 respectively represent the imaging magnification and focal length of the objective lens 10 when the first optical disk D1 is used.
M2 and f2 respectively represent the imaging magnification and the focal length of the objective lens 10 when the second optical disc D2 is used.

  By designing the objective lens 10 so as to satisfy the conditions (7) and (8), the light used is a substantially parallel light beam when the first optical disk D1 and the second optical disk D2 are used. Therefore, it is possible to satisfactorily reduce the coma and astigmatism generation amounts during the tracking shift to a level that can be ignored.

  In the first embodiment, the first light source 1A and the second light source 1B are arranged at positions where the laser beams emitted from the light sources 1A and 1B are converted into parallel light beams by the coupling lenses 3A and 3B. Thus, the imaging magnification M1 or M2 of the objective lens 10 is set to zero. That is, each coupling lens 3A, 3B of the first embodiment functions as a collimating lens for the first laser light and the second laser light.

As described above, when the objective lens 10 is set with a phase shift structure that effectively suppresses aberrations when using the optical disks D1 and D2 that have a narrow tolerance range for aberrations, when information is recorded or reproduced on the third optical disk D3. Spherical aberration remains. Therefore, the spherical aberration generated when the third optical disk D3 is used is corrected by making the light beam incident on the objective lens 10 into divergent light as shown in FIG. Specifically, when the imaging magnification of the objective lens 10 when the third optical disc D3 is used is M3 and the focal length is f3, the objective lens 10 is designed to satisfy the following condition (9).
−0.12 <f3 × M3 <−0.04 (9)

  Exceeding the upper limit of the condition (9) is not preferable because excessive spherical aberration remains when the third optical disk D3 is used. On the other hand, if the lower limit of the condition (9) is not reached, under spherical aberration occurs when the third optical disc D3 is used, which is not preferable. By designing the objective lens 10 so as to satisfy the condition (9), it is possible to satisfactorily suppress spherical aberration that occurs when the third optical disc D3 is used.

  When a phase shift structure is used in which the optical path length difference given by the step is about three wavelengths for the first laser beam, the disc thickness of the first optical disc D1 and the third optical disc D3 is Relative spherical aberration due to differences can be corrected to some extent. Therefore, the divergence angle of the third laser light incident on the objective lens 10 is compared with the case where the optical path length difference given by the step is approximately 2J wavelengths (J is an integer, the same shall apply hereinafter) for the first laser beam. Can be made smaller.

The Abbe number νd is the following condition (10):
20 ≦ νd <40 (10)
Even when the objective lens 10 satisfying the above condition is used, the phase shift structure is set so that the optical path length difference ΔOPD given to the first laser light by the steps constituting the phase shift structure satisfies the above condition (6). It is preferable to design. Further, as described above, when using an optical disc that requires a high NA for recording or reproducing information, it is desirable that a substantially parallel light beam be incident on the objective lens 10. Therefore, the objective lens 10 is configured to satisfy the above conditions (7) and (8).

However, the objective lens 10 that satisfies the above condition (10) is designed to satisfy the following condition (11) in order to satisfactorily correct spherical aberration that occurs during recording or reproduction of information with respect to the third optical disc D3. .
−0.38 <f3 × M3 <−0.30 (11)

In addition, in order for the regular diffraction order light related to the third laser light to have higher diffraction efficiency than the unnecessary diffraction order light, a phase shift structure having a step satisfying the above condition (6) is used for the third laser light. In contrast, the optical path length difference ΔOPDc to be applied is designed to satisfy the following condition (12).
1.32 <| ΔOPDc / λ3 | <1.62 (12)

  As described above, the optical information recording / reproducing apparatus 100 of the first embodiment is defined by the optical path difference function such that the differential value crosses zero at a height of 30% to 70% of the effective radius of the first region. By using the phase shift structure, the focusing function can be kept good by suppressing the disturbance of the waveform of the focusing error signal when the third optical disc D3 is used. Further, by adopting the above-described configuration according to the value of the Abbe number νd of the objective lens 10, as shown in FIGS. 2A to 2C, information is recorded or reproduced on each of the optical discs D1 to D3. The laser light emitted from the light source corresponding to the optical disk to be used is converged in the vicinity of the recording surface of the optical disk via the coupling lenses 3A to 3C, the beam splitters 41 and 42, and the objective lens 10 to record or record information. A spot suitable for reproduction is formed.

  Next, the optical information recording / reproducing apparatus 100 of 2nd embodiment is demonstrated. 6A to 6C are diagrams showing the objective lens 10 and the optical discs D1 to D3 mounted on the optical information recording / reproducing apparatus 100 of the second embodiment separately for each optical path when each optical disc is used. is there. 2A to 2C, the reference axis AX of the optical information recording / reproducing apparatus 100 is indicated by a one-dot chain line in the drawing. In addition, in 2nd embodiment, the same code | symbol is attached | subjected to the member same as 1st embodiment, and detailed description here is abbreviate | omitted.

  In the second embodiment, the light sources 1A to 1C are disposed at positions where the laser beams emitted from the light sources 1A to 1C are converted into parallel light beams by the coupling lenses 3A to 3C. The imaging magnification of the lens 10 is set to approximately zero. That is, the coupling lenses 3A to 3C of the second embodiment function as collimating lenses for the first to third laser beams.

  In the phase shift structure of this embodiment, the refractive index change of the objective lens 10 due to the difference in wavelength between the first to third laser beams and the spherical aberration due to the difference of the protective layer 21 of each of the optical discs D1 to D3 are substantially omitted. It is designed to have a characteristic that can be controlled to be zero. Specifically, it has at least two types of steps different in the optical path length difference applied to the incident light flux.

  The step structure as described above has at least two kinds of optical path difference functions, for example, the first optical path difference function and the second optical path difference function, which are different from each other in the ratio of the diffraction orders at which the diffraction efficiency becomes maximum in the first to third laser beams. It is defined by the optical path difference function.

ただし、ｈは、光軸からの高さ、Ｐ_２ｉ、Ｐ_４ｉ、Ｐ_６ｉ、…は、それぞれ第ｉの光路差関数における二次、四次、六次、…の係数、ｍは、入射光束の回折効率が最大となる回折次数、λは、入射光束の使用波長、をそれぞれ表す。 For convenience of describing the second embodiment, in a plurality of optical path difference functions, the i-th (i is a natural number) optical path difference function φi (h) is expressed by the following formula (14).

Where h is the height from the optical axis, P ₂ i, P ₄ i, P ₆ i,... Are the coefficients of the second, fourth, sixth,. , The diffraction order that maximizes the diffraction efficiency of the incident light beam, and λ represents the wavelength used for the incident light beam.

Here, the step structure of the objective lens 10 of the second embodiment is the first when the first laser beam is used and the height h from the optical axis is within the effective range in the first region. The differential value of the value obtained by the optical path difference function φ1 (h) (optical path length addition amount) changes from positive to negative, in other words, it is designed to cross zero. More specifically, the step structure is designed to satisfy the following condition (15) and further satisfy the following condition (16).
0.00 <(f1 × P ₂ 1) / (t3-t1) <18.00 (15)
2.50 <(f1 × P ₂ 1) / (t3-t1) <13.00 (16)

  Since the effect obtained by satisfying the condition (15) and the condition (16) is the same as that verified for the condition (3), description thereof will be omitted with reference to FIGS.

  As described above, the step structure of the second embodiment can control the spherical aberration generated in the refractive lens portion of the objective lens 10 by the difference in wavelength between the first and second laser beams as in the first embodiment. Designed to have properties. That is, the step structure of the second embodiment also has a step that gives an optical path length difference of approximately odd number times when the first laser beam is incident.

Specifically, when the optical path length difference is approximately odd times, the first wavelength is λ1 (nm), and the optical path length difference that the first type of step imparts to the first wavelength light flux is ΔOPD1 (nm). It is defined by the following condition (13).
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)

More specifically, the optical path length difference is defined by the condition (17) when N is set to 1 in the condition (13), and the condition (19) when N is set to 2.
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
4.70 <| ΔOPD1 / λ1 | <5.30 (19)

In addition, in order to make the regular diffraction order light related to the third laser light have a higher diffraction efficiency than the unnecessary diffraction order light, in the phase shift structure of the second embodiment, the step satisfying the condition (13) is The optical path length difference ΔOPDc1 applied to the third laser beam is designed to satisfy the following condition (18) or condition (20). Furthermore, the step satisfying the condition (17) is designed to satisfy the following condition (18). Similarly, the first step satisfying the condition (19) is designed such that the optical path length difference ΔOPDc1 satisfies the following condition (20).
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)

When configured to satisfy the above condition (13), more specifically, the condition (17) and the condition (19), the optical path length difference ΔOPD1 provided by at least one step is Approximately (2J + 1) wavelengths. For this reason, the amount of light especially when the third optical disc D3 is used must be reduced. Therefore, the step for providing the optical path length difference different from the optical path length difference ΔOPD1 is designed to increase the amount of light particularly when the third optical disc D3 is used. Specifically, the optical path length difference ΔOPD2 provided to the first laser beam by the step providing the optical path length difference different from the optical path length difference ΔOPD1 satisfies the following condition (21), more specifically, the condition (22). Designed to satisfy.
2L−0.20 <| ΔOPD2 / λ1 | <2L + 0.20 (21)
1.80 <| ΔOPD2 / λ1 | <2.20 (22)

  By designing the step structure so that the optical path length difference ΔOPD2 satisfies the condition (21) and the condition (22), the diffraction efficiency related to the first laser beam and the second laser beam is maintained at a high level. The amount of light on the recording surface 22 when using the optical disc D3 can be increased.

  By designing the step structure as shown above, even when each of the optical discs D1 to D3 is used, even if the corresponding first to third laser beams are converted into a substantially parallel light beam, each of the optical discs D1 to D3 is used. It is possible to satisfactorily suppress spherical aberration that sometimes occurs and to satisfactorily suppress coma and astigmatism that occur during tracking operation. Further, when the third optical disc D3 is used, generation of unnecessary diffraction order light can be suppressed, and the focusing function can be kept good.

  Two embodiments have been described above. Further, in the objective lens 10 of the first and second embodiments, the outside of the first region according to the difference in effective beam diameter for ensuring the NA necessary for recording or reproducing information on each of the optical discs D1 to D3. A second region having a phase shift structure different from the first region, and a third region having a phase shift structure different from the first and second regions outside the second region. Sometimes.

  The phase shift structure of the second region generally includes the first and second laser beams used when using the first and second optical discs D1 and D2, which require a higher NA than when using the third optical disc D3. It has a diffractive action for satisfactorily converging on the recording surface 22 of the corresponding optical disk D1, D2.

  Further, the phase shift structure of the second region has a level difference that does not contribute to the convergence of the third laser beam. That is, when the first laser beam is used as a reference (in other words, when the first laser beam is incident), at least one absolute value of the optical path length difference provided at the step of the second region is: This is different from the absolute value of the optical path length difference given at the step existing in the first region. Here, when there are a plurality of types of steps in the first region, the step that gives an even optical path length difference to the first laser light corresponds to the step existing in the first region. . For example, when there are two types of steps as described above in the first region, the steps satisfying the above conditions (21) and (22) correspond to the steps existing in the first region.

  The phase shift structure in the third region is provided when the incident light beam diameter of the first laser light on the first surface 11 of the objective lens 10 is different from the effective light beam diameter of the second laser light.

As a case where the third region is provided, first, when the focal length when using the first optical disc D1 is f1, and the focal length when using the second optical disc D2 is f2, the following condition (23):
f1 × NA1> f2 × NA2 (23)
That is, that is, when the first laser beam is incident, the effective beam diameter on the incident surface of the objective lens 10 is equal to the effective beam on the incident surface of the objective lens 10 when the second laser beam is incident. The case where it is larger than the diameter is mentioned. In this case, a third region having a phase shift structure is formed on the first surface 11 so that the first laser beam converges satisfactorily with almost no aberration on the recording surface of the first optical disc D1.

  Unlike the second region, the third region formed when the condition (23) is satisfied does not contribute to the convergence of the second laser beam. That is, the third region formed when the condition (23) is satisfied has an aperture limiting function for the second laser beam. Therefore, the structure is designed so that the optical path length difference given at the boundary between adjacent refractive surfaces for the first laser light is different from the optical path length difference for the first laser light in the second region. The At the time of the design, the third region is blazed so that the diffraction efficiency for the first laser beam is maximized.

As a case where the third region is provided, next, the following condition (24),
f1 × NA1 <f2 × NA2 (24)
That is, that is, the effective light beam diameter on the incident surface of the objective lens 10 when the second laser light is incident is the effective light beam on the incident surface of the objective lens 10 when the first laser light is incident. The case where it is larger than the diameter is mentioned. In this case, a third region having a phase shift structure is formed on the first surface 11 so that the second laser beam converges satisfactorily with almost no aberration on the recording surface of the second optical disc D2. Unlike the second region, the third region formed when the condition (24) is satisfied does not contribute to the convergence of the first laser beam. That is, the third region formed when the condition (24) is satisfied has an aperture limiting function for the first laser beam. Therefore, in the phase shift structure, the optical path length difference given at the boundary between the refractive surfaces adjacent to each other for the second laser light is different from the optical path length difference for the second laser light in the second region. Designed. At the time of the design, the third region is blazed so that the diffraction efficiency for the second laser beam is maximized.

  Three specific examples of the optical information recording / reproducing apparatus 100 using the objective lens 10 of the first embodiment described above as an objective optical system, and light using the objective lens 10 of the second embodiment as an objective optical system Four specific examples of the information recording / reproducing apparatus 100 are shown, for a total of seven examples.

  An optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of each of the first to third embodiments is shown in FIGS. 1 and 2A to 2C. An optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of each of Examples 4 to 7 is shown in FIGS. In each example, when the third optical disc D3 is used, the beam diameter is defined using an aperture limiting element (not shown) in order to obtain a numerical aperture suitable for recording or reproducing information. Therefore, as shown in FIGS. 2A to 2C and FIGS. 6A to 6C, the use of the third optical disk D3 is more effective than the use of the first and second optical disks D1 and D2. The beam diameter is reduced.

  The optical disk used in each example is the first optical disk D1 having the highest recording density with the protective layer thickness t1 = 0.6 mm, and the protective layer thickness t2 = 0.6 mm, which is higher in recording density than the first optical disk D1. Assume a low second optical disk D2 and a third optical disk D3 having the lowest recording density with a protective layer thickness t3 = 1.2 mm.

  The objective lens 10 of the optical information recording / reproducing apparatus 100 according to the first embodiment has a phase shift structure on the first surface 11 that is configured by only a step that gives one type of optical path length difference. Specific specifications of the objective lens 10 of Example 1 are shown in Table 1.

  As shown in Table 1, the magnification value indicates that in Example 1, the laser light is incident on the objective lens 10 as a parallel light beam when the optical disks D1 to D2 are used, and the laser light as a divergent light beam when the optical disk D3 is used. Tables 2 to 4 show specific numerical configurations when the optical discs D1 to D3 of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 1 are used.

  As shown in the remarks in Tables 2 to 4, the surface number 0 is the light sources 1A to 1C, the surface numbers 1 and 2 are the diffraction gratings 2A to 2C, the surface numbers 3 and 4 are the coupling lenses 3A to 3C, Surface numbers 5 and 6 in Tables 2 to 3 are beam splitters 41, surface numbers 7 and 8 in Tables 2 to 3, and surface numbers 5 and 6 in Table 4 are beam splitters 42, and surface numbers 9 and 10 in Tables 2 to 3. The surface numbers 7 and 8 in Table 4 are the objective lens 10, the surface numbers 11 and 12 in Tables 2 and 3, and the surface numbers 9 and 10 in Table 4 are the media. The protective layer 21 and the recording surface 22 of each optical disk D1 to D3. Is shown. In Tables 2 to 4, r is a radius of curvature (unit: mm) of each lens surface, d is a lens thickness or lens interval (unit: mm) at the time of recording or reproducing information, and n (Xnm) is a wavelength Xnm. Refractive index. The same applies to the following Examples 2 to 4.

  Further, the second surfaces of the coupling lenses 3A to 3C and the both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 5 to 7 show conical coefficients and aspheric coefficients that define the shape of each aspheric surface when information is recorded or reproduced on the first optical disc D1, the second optical disc D2, and the third optical disc D3. In addition, the notation E in each table | surface represents the power which uses 10 as the radix and the number on the right of E is an exponent.

Table 8 shows coefficients P ₂ in the optical path difference function for defining the annular structure to be formed on the first surface 11 of the objective lens 10 of the first embodiment. Table 9 shows the diffraction order m at which the diffraction efficiency of each laser beam is maximized. As shown in Table 9, the diffraction order m is set to a different value depending on the laser beam used.

  From Tables 1 and 8, the values of conditions (3) and (4) are 5.00. Therefore, the objective lens 10 of Example 1 satisfies both the conditions (3) and (4).

  Table 10 specifically shows an annular structure formed on the first surface 11 of the objective lens 10 according to the first embodiment. Table 10 shows the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 1 and the optical path length difference given when the first and third laser beams pass through each annular zone. It is the table shown. The numbers of the annular zones are assigned in order from the optical axis side, and the range of each annular zone is represented by the heights hmin to hmax from the optical axis.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 1 satisfies the condition (5) because the Abbe number νd is 58. Further, as shown in Table 10, the optical path length difference | ΔOPD / λ1 | to which the first laser light is imparted by the step between the annular zones is 3.00 (that is, N = 1), and the condition (1 ) And condition (6) are satisfied. Further, the optical path length difference | ΔOPD / λ3 | to which the third laser light is imparted by the step between the annular zones is 1.49, which satisfies the condition (12).

  Here, Table 11 shows specific numerical configurations of the optical system for detecting the focus error signal when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 of the first embodiment.

  As shown in the remarks in Table 11, the surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, the surface numbers 13 and 14 are the objective lens 10, the surface numbers 15 and 16 are the beam splitter 42, and the surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 7 shows a focus error signal detected by the light receiving unit 6C when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 of the first embodiment. FIG. 8 shows a focus error signal in the comparative example. As the objective lens of the comparative example, a lens having a phase shift structure configured in the same manner as in Example 1 is assumed except that the values of the conditions (3) and (4) are 0.00. As can be seen by comparing FIG. 7 and FIG. 8, the focus error signal detected by the light receiving unit 6 </ b> C of the first embodiment has a good S-shaped waveform with less collapse than the comparative example. That is, the optical information recording / reproducing apparatus 100 according to the first embodiment satisfies the conditions (3) and (4), thereby suppressing the collapse of the focus error signal and favorably preventing the focusing function from being deteriorated.

  Further, as can be seen from Table 1, in the optical information recording / reproducing apparatus 100 of Example 1, f1 × M1 is 0.000, f2 × M2 is 0.000, and f3 × M3 is −0.081. The conditions (9) are satisfied from 7).

  FIGS. 9A to 9C are aberration diagrams illustrating spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the first embodiment. 9A shows the spherical aberration generated when the first laser beam is used, FIG. 9B shows the spherical aberration generated when the second laser beam is used, and FIG. 9C shows the third laser beam used. Each of the spherical aberrations that sometimes occurs is represented. The same applies to aberration diagrams in the following examples.

  As shown in FIGS. 9A to 9C, the optical information recording / reproducing apparatus 100 on which the objective lens 10 of Example 1 is mounted is at the time of recording or reproducing information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the first embodiment.

  Similarly to the first embodiment, the objective lens 10 of the optical information recording / reproducing apparatus 100 according to the second embodiment also has a phase shift structure on the first surface 11 that includes only a step that provides one type of optical path length difference. . Specific specifications of the objective lens 10 of Example 2 are shown in Table 12. Specific numerical configurations of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 12 when the optical discs D1 to D3 are used are shown in Tables 13 to 15.

  Similar to the first embodiment, the second surfaces of the coupling lenses 3A to 3C and both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 16 to 18 show the conical coefficient and the aspheric coefficient that define the shape of each aspheric surface when information is recorded or reproduced on the first optical disc D1, the second optical disc D2, and the third optical disc D3, respectively.

Table 19 shows coefficients P ₂ in the optical path difference function for defining the annular zone structure to be formed on the first surface 11 of the objective lens 10 of Example 2. Table 20 shows the diffraction order m at which the diffraction efficiency of each laser beam is maximized.

  From Tables 12 and 19, the values of the conditions (3) and (4) are 10.00. Therefore, the objective lens 10 of Example 2 satisfies both the conditions (3) and (4).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 2 is specifically shown in Table 21. Table 21 shows the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 2 and the optical path length difference given when the first and third laser beams pass through each annular zone. It is the table shown.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 2 satisfies the condition (5) with an Abbe number νd of 58. Further, as shown in Table 21, the optical path length difference | ΔOPD / λ1 | to which the first laser light is applied by the step between the annular zones is 3.00 (that is, N = 1), and the condition (1) And Condition (6) is satisfied. Further, the optical path length difference | ΔOPDc / λ3 | to which the third laser beam is imparted by the step between the annular zones is 1.49, which satisfies the condition (12).

  Here, in the optical information recording / reproducing apparatus 100 of Example 2, the specific numerical configuration of the optical system for detecting the focus error signal at the time of recording or reproducing information on the third optical disc D3 is shown in Table 22.

  As shown in the remarks in Table 22, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 10 shows a focus error signal detected by the light receiving unit 6C when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the second embodiment. As shown in FIG. 10, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the second embodiment also can satisfy the conditions (3) and (4) as in the first embodiment, so that the collapse of the focus error signal can be suppressed and the focusing function can be prevented from being lowered. It is out.

  Further, as can be seen from Table 12, in the optical information recording / reproducing apparatus 100 of Example 2, f1 × M1 is 0.000, f2 × M2 is 0.000, f3 × M3 is −0.081, and the condition ( The conditions (9) are satisfied from 7).

  FIGS. 11A to 11C are aberration diagrams showing spherical aberrations that occur when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the second embodiment.

  As shown in FIGS. 11A to 11C, the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 according to the second embodiment can record or reproduce information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the second embodiment.

  Similarly to the first and second embodiments, the objective lens 10 of the optical information recording / reproducing apparatus 100 according to the third embodiment also has a phase shift structure including only a step that gives one type of optical path length difference on the first surface 11. Have. Specific specifications of the objective lens 10 of Example 3 are shown in Table 23. Specific numerical configurations of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 23 when the optical discs D1 to D3 are used are shown in Tables 24 to 26.

According to Table 23, f1 × NA1 is 1.46 and f2 × NA2 is 1.51. That is, the optical information recording / reproducing apparatus 100 of Example 3 satisfies the condition (24). Therefore, on the first surface 11 of the objective lens 10 of Example 3, a first region contributing to the convergence of each laser beam, and a second region having a phase shift structure having an aperture limiting function for the third laser beam, And a third region having a phase shift structure having an aperture limiting function with respect to the first laser beam or the third laser beam. When the range of each region on the first surface is represented by a height h from the optical axis AX,
1st area | region ... h <= 1.100,
2nd area | region ... 1.100 <h <= 1.460,
Third region: 1.460 <h ≦ 1.510.

  Similar to the above embodiments, the second surfaces of the coupling lenses 3A to 3C and the both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 27 to 29 show conical coefficients and aspheric coefficients in order to define the shape of each aspheric surface when recording or reproducing information on the first optical disc D1, the second optical disc D2, and the third optical disc D3.

Table 30 shows coefficients P ₂ in the optical path difference function for defining the annular zone structure to be formed in each region of the first surface 11 of the objective lens 10 of Example 3. Further, the diffraction order m at which the diffraction efficiency of each laser beam is maximized is different for each region, and is shown in Table 31, respectively.

  From Tables 23 and 30, the values of conditions (3) and (4) are 11.22. Therefore, the objective lens 10 of Example 3 satisfies both the conditions (3) and (4).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 3 is specifically shown in Table 32. Table 32 is a table showing the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 3 and the optical path length difference given by each laser beam passing through each annular zone. . In Table 32, | ΔOPDd / λ2 | represents an optical path length difference in which the second laser light is provided by a step between the annular zones.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 3 satisfies the condition (5) because the Abbe number νd is 58. Further, as shown in Table 32, the optical path length difference | ΔOPD / λ1 | to which the first laser beam is applied by the step between the annular zones is 3.00 (that is, N = 1), and the condition (1) And Condition (6) is satisfied. Further, the optical path length difference | ΔOPD / λ3 | to which the third laser light is applied by the step between the annular zones is 1.58, which satisfies the condition (12).

  Table 33 shows specific numerical configurations of an optical system for detecting a focus error signal when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 according to the third embodiment.

  As shown in the remarks in Table 33, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 12 shows a focus error signal detected by the light receiving unit 6C at the time of recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the third embodiment. As shown in FIG. 12, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the third embodiment can also suppress the collapse of the focus error signal by satisfying the conditions (3) and (4) in the same manner as each of the above-described embodiments, thereby reducing the focusing function. It is preventing.

  Further, as can be seen from Table 12, in the optical information recording / reproducing apparatus 100 of Example 3, f1 × M1 is 0.000, f2 × M2 is 0.000, and f3 × M3 is −0.113. The conditions (9) are satisfied from 7).

  FIGS. 13A to 13C are aberration diagrams illustrating spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the third embodiment. As shown in FIGS. 13A to 13C, the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of Example 3 is used for recording or reproducing information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the third embodiment.

  The objective lens 10 of the optical information recording / reproducing apparatus 100 of Example 4 is a specific example of the second embodiment. That is, the objective lens 10 of Example 4 has a phase shift structure on the first surface 11 that is configured by steps that give two different optical path length differences. Specific specifications of the objective lens 10 of Example 4 are shown in Table 34. Specific numerical configurations of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 34 when the optical disks D1 to D3 are used are shown in Tables 35 to 37.

  Similar to the above embodiments, the second surfaces of the coupling lenses 3A to 3C and the both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 38 to 40 show the conical coefficient and the aspheric coefficient that define the shape of each aspheric surface at the time of recording or reproducing information with respect to the first optical disc D1, the second optical disc D2, and the third optical disc D3.

Table 41 shows coefficients P ₂ i... In the i-th optical path difference function for defining the annular structure to be formed on the first surface 11 of the objective lens 10 of the fourth embodiment. Further, in each optical path difference function, the diffraction order m at which the diffraction efficiency of each laser beam is maximized is shown in Table 42.

  From Tables 34 and 41, the values of the conditions (15) and (16) are 4.00. Therefore, the objective lens 10 of Example 4 satisfies both the conditions (15) and (16).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 4 is specifically shown in Table 43. Table 43 shows the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 4 and the optical path length difference given when the first and third laser beams pass through each annular zone. It is the table shown.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 4 satisfies the condition (5) with an Abbe number νd of 58. Further, as shown in Table 43, the optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | to which the first laser light is applied by the respective steps are 3.00 and 2.00, respectively. That is, in Example 4, N in the condition (13) is set to 1, and L in the condition (21) is set to 1. Further, the optical path length difference | ΔOPDc1 / λ3 | to which the third laser beam is given by the first type of step is 1.49. Therefore, the conditions (13), (17), (18), (21) and (22) are satisfied.

  Here, in Table 44, specific numerical configurations of the optical system for detecting the focus error signal at the time of recording or reproducing information with respect to the third optical disc D3 in the optical information recording / reproducing apparatus 100 of Example 4 are shown.

  As shown in the remarks in Table 44, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 14 shows a focus error signal detected by the light receiving unit 6C when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the third embodiment. As shown in FIG. 12, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the third embodiment satisfies the conditions (15) and (16), thereby suppressing the collapse of the focus error signal and preventing the focusing function from being lowered.

  Furthermore, as can be seen from FIGS. 6A to 6C and Table 34, the optical information recording / reproducing apparatus 100 of Example 4 has f1 × M1 of 0.000, f2 × M2 of 0.000, and f3 × M3. Is 0.000. Therefore, it is possible to satisfactorily suppress the occurrence of aberration at the time of tracking even when information is recorded or reproduced on any optical disk.

  FIGS. 15A to 15C are aberration diagrams illustrating spherical aberrations that occur when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the third embodiment. As shown in (C) to (C), the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of Example 4 exhibits spherical aberration even when information is recorded or reproduced on any of the optical disks D1 to D3. It can be seen that the spots were corrected well and spots suitable for recording or reproducing information were formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the fourth embodiment.

  Similarly to the fourth embodiment, the objective lens 10 of the optical information recording / reproducing apparatus 100 according to the fifth embodiment also has a phase shift structure on the first surface 11 that is configured with steps that give two different optical path length differences. Specific specifications of the objective lens 10 of Example 5 are shown in Table 45. Specific numerical configurations of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 34 when the optical discs D1 to D3 are used are shown in Tables 46 to 48.

  Similar to the other embodiments described above, the second surfaces of the coupling lenses 3A to 3C and the both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 49 to 51 show the conical coefficient and the aspheric coefficient that define the shape of each aspheric surface when information is recorded or reproduced on the first optical disc D1, the second optical disc D2, and the third optical disc D3, respectively.

Table 52 shows coefficients P ₂ i... In the i-th optical path difference function for defining the annular structure to be formed on the first surface 11 of the objective lens 10 of the fifth embodiment. Further, in each optical path difference function, the diffraction order m at which the diffraction efficiency of each laser beam is maximized is shown in Table 53.

  From Tables 45 and 52, the values of the conditions (15) and (16) are 9.50. Therefore, the objective lens 10 of Example 5 satisfies both the conditions (15) and (16).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 5 is specifically shown in Table 54. Table 54 shows the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 5 and the optical path length difference given when the first and third laser beams pass through each annular zone. It is the table shown.

  There is an objective lens 10 of the optical information recording / reproducing apparatus of the fifth embodiment. As shown in Table 54, the optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | to which the first laser beam is applied by each step are 3.00 and 2.00, respectively. That is, in Example 5, N in the condition (13) is set to 1, and L in the condition (21) is set to 1. Further, the optical path length difference | ΔOPDc1 / λ3 | to which the third laser beam is given by the first type of step is 1.49. Therefore, the conditions (13), (17), (18), (21), and (22) are satisfied.

  Table 55 shows the specific numerical configuration of the optical system for detecting the focus error signal at the time of recording or reproducing information with respect to the third optical disc D3 in the optical information recording / reproducing apparatus 100 of the fifth embodiment.

  As shown in the remarks in Table 55, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 16 shows a focus error signal detected by the light receiving unit 6C at the time of recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the fifth embodiment. As shown in FIG. 16, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the fifth embodiment can also suppress the collapse of the focus error signal by satisfying the conditions (15) and (16) as in the fourth embodiment, thereby reducing the focusing function. It is preventing.

  Further, as can be seen from FIGS. 6A to 6C and Table 45, the optical information recording / reproducing apparatus 100 of Example 5 has f1 × M1 of 0.000, f2 × M2 of 0.000, and f3 × M3. Is 0.000. Therefore, it is possible to satisfactorily suppress the occurrence of aberration at the time of tracking even when information is recorded or reproduced on any optical disk.

  FIGS. 17A to 17C are aberration diagrams showing spherical aberrations that occur when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the fifth embodiment. As shown in FIGS. 17A to 17C, the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of Example 5 is used for recording or reproducing information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the fifth embodiment.

  The objective lens 10 of the optical information recording / reproducing apparatus 100 according to the sixth embodiment has a phase shift structure formed of steps providing two different optical path length differences in the first region of the first surface 11. Moreover, it has the 2nd, 3rd area | region which has an aperture limiting function with respect to a specific laser beam on the outer side of a 1st area | region. Specific specifications of the objective lens 10 of Example 5 are shown in Table 56. Specific numerical configurations of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 56 when the optical discs D1 to D3 are used are shown in Tables 57 to 59.

According to Table 56, f1 × NA1 is 1.46 and f2 × NA2 is 1.51. That is, the optical information recording / reproducing apparatus 100 in Example 6 satisfies the condition (24). Therefore, as described above, the first surface 11 of the objective lens 10 of Example 6 has a first region that contributes to the convergence of each laser beam and a phase shift structure that has an aperture limiting function for the third laser beam. A second region and a third region having a phase shift structure having an aperture limiting function for the first laser beam and the third laser beam are formed. When the range of each region on the first surface is represented by a height h from the optical axis AX,
1st area | region ... h <= 1.100,
2nd area | region ... 1.100 <h <= 1.460,
Third region: 1.460 <h ≦ 1.510.

  As in the other embodiments, the second surfaces of the coupling lenses 3A to 3C and the both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 60 to 62 show the conical coefficient and the aspheric coefficient that define the shape of each aspheric surface when information is recorded or reproduced on the first optical disc D1, the second optical disc D2, and the third optical disc D3, respectively.

Optical path difference function P ₂ for defining an annular structure to be formed in each region of the first surface 11 of the objective lens 10 of Example 6 (in the first region defined by a plurality of optical path difference functions) In this case, the coefficient P ₂ i... In the i th optical path difference function is shown in Table 63. Further, in each optical path difference function, the diffraction order m at which the diffraction efficiency of each laser beam is maximized is shown in Table 64.

  From Tables 56 and 63, the values of the conditions (15) and (16) are 12.11. Therefore, the objective lens 10 of Example 6 satisfies both the conditions (15) and (16).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 6 is specifically shown in Table 65. Table 65 is a table showing the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 6 and the optical path length difference given by each laser beam passing through each annular zone. . In Table 65 and the following tables, | ΔOPDd1 / λ2 | represents the optical path length difference to which the second laser beam is applied by the first step.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 6 has an Abbe number νd of 58. Further, as shown in Table 65, the optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | to which the first laser light is applied by each step are 3.10 and 2.00, respectively. That is, in Example 6, N in the condition (13) is set to 1, and L in the condition (21) is set to 1. Also, the optical path length difference | ΔOPDc1 / λ3 | to which the third laser beam is applied by the first type of step is 1.54. Therefore, the conditions (13), (17), (18), (21), and (22) are satisfied.

  Table 66 shows the specific numerical configuration of the optical system for detecting the focus error signal when recording or reproducing information with respect to the third optical disc D3 in the optical information recording / reproducing apparatus 100 of the sixth embodiment.

  As shown in the remarks in Table 66, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 18 shows a focus error signal detected by the light receiving unit 6C when recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the sixth embodiment. As shown in FIG. 18, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the fourth embodiment also can satisfy the conditions (14) and (15) as in the above-described embodiments, thereby suppressing the collapse of the focus error signal and reducing the focusing function. It is preventing.

  Furthermore, as can be seen from FIGS. 6A to 6C and Table 56, in the optical information recording / reproducing apparatus 100 of Example 6, all of f1 × M1, f2 × M2, and f3 × M3 are 0.000. . Therefore, it is possible to satisfactorily suppress the occurrence of aberration at the time of tracking even when information is recorded or reproduced on any optical disk.

  FIGS. 19A to 19C are aberration diagrams illustrating spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the sixth embodiment. As shown in FIGS. 19A to 19C, the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of Example 6 is used for recording or reproducing information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the sixth embodiment.

  Specific specifications of the objective lens 10 of Example 4 are shown in Table 67. Tables 68 to 70 show specific numerical configurations when the optical discs D1 to D3 of the optical information recording / reproducing apparatus 100 including the objective lens 10 shown in Table 67 are used.

According to Table 67, f1 × NA1 is 1.46 and f2 × NA2 is 1.51. That is, the optical information recording / reproducing apparatus 100 of Example 7 also satisfies the condition (24). Therefore, on the first surface 11 of the objective lens 10 of Example 6, a first region contributing to the convergence of each laser beam, and a second region having a phase shift structure having an aperture limiting function for the third laser beam, And a third region having a phase shift structure having an aperture limiting function with respect to the first laser light. When the range of each region on the first surface is represented by a height h from the optical axis AX,
1st area | region ... h <= 1.100,
2nd area | region ... 1.100 <h <= 1.460,
Third region: 1.460 <h ≦ 1.510.

  Similar to the other embodiments, the second surface of each of the coupling lenses 3A to 3C and both surfaces 11 and 12 of the objective lens 10 are aspherical surfaces. Tables 71 to 73 show conical coefficients and aspheric coefficients that define the shape of each aspheric surface at the time of recording or reproducing information with respect to the first optical disc D1, the second optical disc D2, and the third optical disc D3.

Optical path difference function P ₂ for defining an annular structure to be formed in each region of the first surface 11 of the objective lens 10 of Example 7 (in the first region defined by a plurality of optical path difference functions) Table 74 shows the coefficients P ₂ i... In the i-th optical path difference function. Further, in each optical path difference function, the diffraction order m at which the diffraction efficiency of each laser beam is maximized is shown in Table 75.

  From Table 67 and Table 74, the values of the conditions (15) and (16) are 7.56. Therefore, the objective lens 10 of Example 7 satisfies both the conditions (15) and (16).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 7 is specifically shown in Table 76. Table 76 is a table showing the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 7 and the optical path length difference given when the first laser beam passes through each annular zone. It is.

  The objective lens 10 of the optical information recording / reproducing apparatus in Example 7 has an Abbe number νd of 58. Further, as shown in Table 76, the optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | to which the first laser light is applied by the respective steps are 5.23 and 2.00, respectively. That is, in Example 7, N in the condition (13) is set to 2, and L in the condition (21) is set to 1. Therefore, Example 7 satisfies the conditions (13), (19), (21), and (22). Further, as shown in Table 76, the optical path length difference | ΔOPDc1 / λ3 | to which the third laser beam is applied by the first type of step is 2.59. Therefore, Example 7 also satisfies the condition (20).

  Table 77 shows the specific numerical configuration of the optical system for detecting the focus error signal when recording or reproducing information with respect to the third optical disc D3 in the optical information recording / reproducing apparatus 100 of the seventh embodiment.

  As shown in the remarks in Table 77, surface numbers 11 and 12 are the protective layer and recording surface of the optical disc D3, surface numbers 13 and 14 are the objective lens 10, surface numbers 15 and 16 are the beam splitter 42, and surface numbers 17 and 18 are used. Indicates the coupling lens 3C, the surface numbers 19 and 20, the half mirror 5C, and the surface number 21 indicate the light receiving portion 6C.

  FIG. 20 shows a focus error signal detected by the light receiving unit 6C at the time of recording or reproducing information on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the seventh embodiment. As shown in FIG. 20, the focus error signal detected by the light receiving unit 6C has a good S-shaped waveform with little collapse. That is, the optical information recording / reproducing apparatus 100 according to the seventh embodiment can also suppress the collapse of the focus error signal by satisfying the conditions (15) and (16) as in the above embodiments, and the focusing function is lowered. Is preventing.

  Furthermore, as can be seen from FIGS. 6A to 6C and Table 67, in the optical information recording / reproducing apparatus 100 of Example 7, all of f1 × M1, f2 × M2, and f3 × M3 are 0.000. . Therefore, it is possible to satisfactorily suppress the occurrence of aberration at the time of tracking even when information is recorded or reproduced on any optical disk.

  FIGS. 21A to 21C are aberration diagrams illustrating spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus 100 of the seventh embodiment. As shown in FIGS. 21A to 21C, the optical information recording / reproducing apparatus 100 equipped with the objective lens 10 of Example 7 is used for recording or reproducing information on any of the optical disks D1 to D3. It can be seen that the spherical aberration is satisfactorily corrected and spots suitable for recording or reproducing information are formed on the recording surface. The above is the description of the optical information recording / reproducing apparatus 100 according to the seventh embodiment.

  The above is the embodiment of the present invention. The present invention is not limited to these embodiments, and can be modified in various ranges as exemplified below.

  The objective lens for an optical information recording / reproducing apparatus according to the present invention is not limited to the specific numerical configuration of each embodiment. There may be a plurality of optical elements such as lenses constituting the objective optical system of the optical information recording / reproducing apparatus. When the objective optical system is composed of a plurality of optical elements, the optical element designed by the designing method according to the present invention can be provided with phase shift structures on both sides as well as on one side.

  Further, as shown in the above embodiments, the focal lengths of the coupling lenses 3A to 3C disposed between the light sources 1A to 1C and the optical discs D1 to D3 differ depending on the refractive index due to the wavelength difference. Here, in the optical information recording / reproducing apparatus according to the present invention, the laser light emitted from each of the light sources 1A to 1C may be guided to the recording surface through a common coupling lens. When this configuration is adopted, the light source 1A for irradiating the first laser light and the light source 1B for irradiating the second laser light are on the same substrate, that is, each light source is at the same distance from the coupling lens. In some cases, at least one of the first laser light and the second laser light must be convergent light or divergent light due to a difference in focal length. Even in this case, if the objective lens is arranged so as to satisfy the above conditions (7) and (8) so that the imaging magnification becomes as small as possible, it is the same as in the above embodiments. There is an effect.

It is a schematic diagram showing schematic structure of the optical information recording / reproducing apparatus of 1st embodiment of this invention. FIG. 2 is a diagram showing the optical information recording / reproducing apparatus according to the first embodiment of the present invention separately for each optical path when each optical disk is used. It is an enlarged view of the phase shift structure provided in the 1st surface of the objective lens of 1st and 2nd embodiment of this invention. It is a figure showing a focus error signal obtained when information is recorded on or reproduced from a third optical disk using an objective lens having a phase shift structure that does not satisfy the condition (3). It is a figure showing the focus error signal obtained when information is recorded on or reproduced from the third optical disk using the objective lens of the embodiment of the present invention. FIG. 5 is a diagram showing the optical information recording / reproducing apparatus according to the second embodiment of the present invention separately for each optical path when each optical disk is used. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 1 is used. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of a comparative example is used. FIG. 6 is an aberration diagram showing spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus of Example 1. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 2 is used. FIG. 10 is an aberration diagram showing spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus in Example 2. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 3 is used. FIG. 11 is an aberration diagram showing spherical aberration that occurs when the first to third laser lights are used in the optical information recording / reproducing apparatus in Example 3. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 4 is used. FIG. 11 is an aberration diagram showing spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus in Example 4. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 5 is used. FIG. 10 is an aberration diagram showing spherical aberration that occurs when the first to third laser beams are used in the optical information recording / reproducing apparatus in Example 5. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 6 is used. FIG. 11 is an aberration diagram showing spherical aberration that occurs when the first to third laser lights are used in the optical information recording / reproducing apparatus in Example 6. It is a figure showing the focus error signal detected when the 3rd laser beam of the optical information recording / reproducing apparatus of Example 7 is used. FIG. 10 is an aberration diagram showing spherical aberration that occurs when the first to third laser lights are used in the optical information recording / reproducing apparatus in Example 7.

Explanation of symbols

1A, 1B, 1C Light source 2A, 2B, 2C Diffraction grating 3A, 3B, 3C Coupling lens 41, 42 Beam splitter 5A, 5B, 5C Half mirror 6A, 6B, 6C Light receiving unit 10 Objective lens D1-D3 Optical disc 100 Optical information Recording / playback device

Claims (16)

Recording information on each optical disc by using one of the three light fluxes having the first to third wavelengths in order from the short wavelength side to the first to third optical discs in the descending order of recording density. Or an objective lens used in an optical information recording / reproducing apparatus for performing reproduction,
When the first wavelength is λ1 (nm) and the third wavelength is λ3 (nm),
λ1 ≒ 405nm, λ3 ≒ 790nm
And
At least one surface has a first region for converging a light beam of the third wavelength on the recording surface of the third optical disk, and is divided into a plurality of concentric refractive surfaces in the first region. , Having a step structure having a step for providing an optical path length difference with respect to an incident light beam between adjacent refractive surfaces,
In the step structure, when the optical path length difference given to the light flux of the first wavelength by the step is ΔOPD (nm), the following condition (1):
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
(However, N is an integer.)
The filling,
The optical path difference function φ (h) that defines the step structure is expressed by the following equation (2),

Where h is the height from the optical axis,
P ₂ , P ₄ , P ₆ ,... Are secondary, quaternary, sixth order,.
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
λ is the wavelength used for the incident light flux,
In the following condition (4),
2.50 <(f1 × P ₂ ) / (t3-t1) <13.00 (4)
(Where f1 is the focal length of the objective lens with respect to the first wavelength,
t3 is the disc thickness of the third optical disc,
t1 is the disc thickness of the first optical disc (where t1 <t3, and t1 is the thinnest and t3 is the thickest among the disc thicknesses of the first to third optical discs)),
An objective lens for an optical information recording / reproducing apparatus, characterized in that: Optical information recording for recording or reproducing information on each optical disc by using any one of three kinds of light beams having the first to third wavelengths for the first to third optical discs having different recording densities. A playback device,
With an objective lens,
When the first wavelength is λ1 (nm), the second wavelength is λ2 (nm), and the third wavelength is λ3 (nm),
λ1 <λ2 <λ3
And
The numerical aperture required for recording or reproducing information on the first optical disc is NA1, the numerical aperture required for recording or reproducing information on the second optical disc is NA2, and the information is recorded or reproduced on the third optical disc. If the required numerical aperture is NA3,
NA1> NA3 and NA2> NA3
And
The protective layer thickness of the first optical disk on which information is recorded or reproduced using the light beam having the shortest first wavelength among the first to third wavelengths is set to t1, which is longer than the first wavelength. The thickness of the protective layer of the second optical disc on which information is recorded or reproduced using a light beam having a second wavelength is t2, and information is obtained using a light beam having the longest third wavelength among the first to third wavelengths. When the protective layer thickness of the third optical disc on which recording or reproduction is performed is t3,
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm
And
The luminous flux of the first wavelength and the second wavelength is a substantially parallel luminous flux, the luminous flux of the third wavelength makes divergent light incident on the objective lens,
At least one surface of the objective lens has a first region for converging a light beam having a third wavelength on a recording surface of a third optical disc, and a plurality of concentric shapes are formed in the first region. Divided into refractive surfaces,
Between the refracting surfaces adjacent to each other , having a step structure having a step that gives a difference in optical path length to the incident light flux,
In the first region, when the optical path length difference that the step at least near the boundary portion imparts to the light flux having the first wavelength is ΔOPD (nm), the following condition (1):
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
( However, N is an integer .)
The filling,
The optical path difference function φ (h) that defines the step structure is expressed by the following equation (2),

Where h is the height from the optical axis,
P ₂ , P ₄ , P ₆ ,... Are secondary, quaternary, sixth order,.
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
λ is the wavelength used for the incident light flux,
In the following condition (4),
2.50 <(f1 × P ₂ ) / (t3-t1) <13.00 (4)
( Where f1 is the focal length of the objective lens with respect to the first wavelength )
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 2 .
The objective lens has an Abbe number νd of the following condition (5):
40 ≦ νd ≦ 80 (5)
Single lens satisfying
The step structure has the following condition (6):
2.70 <| ΔOPD / λ1 | <3.30 (6)
The filling,
In recording or reproducing information on the first optical disc, the imaging magnification is M1, the focal length is f1, and in recording or reproducing information on the second optical disc, the imaging magnification is M2, and the focal length is f2. In the recording or reproduction of information on the three optical discs, when the imaging magnification is M3 and the focal length is f3, the following conditions (7) to (9)
−0.02 <f1 × M1 <0.02 (7)
−0.02 <f2 × M2 <0.02 (8)
−0.12 <f3 × M3 <−0.04 (9)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 2 .
The objective lens has an Abbe number νd of the following condition (10):
20 ≦ νd <40 (10)
Single lens satisfying
The step structure has the following condition (6):
2.70 <| ΔOPD / λ1 | <3.30 (6)
The filling,
In recording or reproducing information on the first optical disc, the imaging magnification is M1, the focal length is f1, and in recording or reproducing information on the second optical disc, the imaging magnification is M2, and the focal length is f2. In the recording or reproduction of information on the three optical discs, when the imaging magnification is M3 and the focal length is f3, the following conditions (7), (8), (11),
−0.02 <f1 × M1 <0.02 (7)
−0.02 <f2 × M2 <0.02 (8)
−0.38 <f3 × M3 <−0.30 (11)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 3 or 4 ,
When the optical path length difference that the step gives to the light flux of the third wavelength is ΔOPDc (nm), the following condition (12):
1.32 <| ΔOPDc / λ3 | <1.62 (12)
An optical information recording / reproducing apparatus characterized by satisfying the above. Optical information recording for recording or reproducing information on each optical disc by using any one of three kinds of light beams having the first to third wavelengths for the first to third optical discs having different recording densities. A playback device,
With an objective lens,
When the first wavelength is λ1 (nm), the second wavelength is λ2 (nm), and the third wavelength is λ3 (nm),
λ1 <λ2 <λ3
And
The numerical aperture required for recording or reproducing information on the first optical disc is NA1, the numerical aperture required for recording or reproducing information on the second optical disc is NA2, and the information is recorded or reproduced on the third optical disc. If the required numerical aperture is NA3,
NA1> NA3 and NA2> NA3
And
The thickness of the protective layer of the first optical disk on which information is recorded or reproduced using the light beam of the first wavelength is t1, and the information recording or reproduction is performed on the light beam of the second wavelength. When the protective layer thickness of the optical disk is t2, and the protective layer thickness of the third optical disk on which information is recorded or reproduced using the light beam of the third wavelength is t3,
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm
And
At least one surface of the objective lens has a first region for converging a light beam having a third wavelength on a recording surface of a third optical disc, and a plurality of concentric shapes are formed in the first region. A step structure having at least two types of steps that are divided into refracting surfaces and that give different optical path length differences between incident light beams between refracting surfaces adjacent to each other,
In the first region, at least one of the at least two types of steps has the following condition when a difference in optical path length given to the light flux having the first wavelength is ΔOPD1 (nm) at the steps. (13),
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)
( However, N is an integer. )
The filling,
The step structure is defined by at least first and second optical path difference functions, and an i-th (i is a natural number) optical path difference function φi (h) is expressed by the following equation (14):

Where h is the height from the optical axis,
P ₂ i, P ₄ i, P ₆ i,... Are coefficients of second order, fourth order, sixth order,... In the i th optical path difference function,
m is the diffraction order that maximizes the diffraction efficiency of the incident light beam,
When λ is expressed in terms of the used wavelength of the incident light beam, the following condition (16) with respect to the first optical path difference function:
2.50 <(f1 × P ₂ 1) / (t3-t1) <13.00 (16)
( Where f1 is the focal length of the objective lens with respect to the first wavelength )
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 6 .
In the first region, the level difference satisfying the condition (13) is further reduced by the following condition (17):
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 7 .
When the optical path length difference that the step satisfying the condition (17) gives to the light beam having the third wavelength in the first region is ΔOPDc1 (nm), the following condition (18):
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 6 .
In the first region, the level difference satisfying the condition (13) further satisfies the following condition (19),
4.70 <| ΔOPD1 / λ1 | <5.30 (19)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 9 .
When the optical path length difference that the step satisfying the condition (19) imparts to the light beam having the third wavelength in the first region is ΔOPDc1 (nm), the following condition (20):
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to any one of claims 6 to 10 ,
When the optical path length difference that the optical path length difference that gives the optical path length difference different from the at least one step is applied to the light flux of the first wavelength is ΔOPD2 (nm), the following condition (21):
2L−0.20 <| ΔOPD2 / λ1 | <2L + 0.20 (21)
( However, L is an integer. )
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 11 ,
The following condition (22),
1.80 <| ΔOPD2 / λ1 | <2.20 (22)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to any one of claims 2 to 5 ,
The objective lens converges the light flux of the first wavelength and the light flux of the second wavelength on the recording surfaces of the first optical disc and the second optical disc, respectively, outside the first region; and Having a second region that does not contribute to the convergence of the light flux of the third wavelength;
The second region has a step that provides at least one kind of optical path length difference with respect to an incident light beam at a boundary between adjacent refracting surfaces,
An optical information recording / reproducing apparatus, wherein an absolute value of an optical path length difference given by the step of the second region is different from an absolute value of an optical path length difference given by the step of the first region. The optical information recording / reproducing apparatus according to any one of claims 6 to 12 ,
The objective lens, outside the first region, converges the light flux of the first wavelength and the light flux of the second wavelength on the recording surfaces of the first optical disc and the second optical disc, respectively. And having a second region that does not contribute to the convergence of the light flux of the third wavelength,
The second region has a step that provides at least one kind of optical path length difference with respect to an incident light beam at a boundary between adjacent refracting surfaces,
An optical information recording / reproducing apparatus, wherein an absolute value of an optical path length difference given by a step of the second region is different from the | ΔOPD1 / λ1 |. The optical information recording / reproducing apparatus according to claim 13 or 14 ,
The following conditions (23),
f1 × NA1> f2 × NA2 (23)
The filling,
The objective lens has a third region outside the second region for converging only the light beam of the first wavelength and not contributing to the convergence of the light beam of the second and third wavelengths,
The third region has a step that provides at least one kind of optical path length difference with respect to the incident light flux at a boundary between adjacent refracting surfaces,
The optical information recording / reproducing apparatus, wherein the absolute value of the optical path length difference given by the step in the third region is different from the absolute value of the optical path length difference given by the step in the second region. The optical information recording / reproducing apparatus according to claim 13 or 14 ,
The following conditions (24),
f1 × NA1 <f2 × NA2 (24)
The filling,
The objective lens has a third region outside the second region that converges only the light flux of the second wavelength and does not contribute to the convergence of the light flux of the first and third wavelengths,
The third region has a step that provides at least one kind of optical path length difference with respect to the incident light flux at a boundary between adjacent refracting surfaces,
The optical information recording / reproducing apparatus, wherein the absolute value of the optical path length difference given by the step in the third region is different from the absolute value of the optical path length difference given by the step in the second region.

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