JP2007122851A - Optical information recording and reproducing device and objective lens for same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical information recording/reproduction device capable of suppressing spherical aberration for each of three types of optical discs and preventing deterioration of focusing performance when a lower recording density optical disc is used. <P>SOLUTION: The optical information recording and reproducing device having compatibility with a plurality of optical discs comprises an objective lens. At least one surface of the objective lens has a step structure which is divided into a plurality of concentric refraction surface and gives an optical path length difference to an incident beam at each step. When the third laser beam passes through the objective lens, the objective lens produces normal diffraction order light and undesired diffraction order light. A distance from a point to which the normal diffraction order light converges to a point to which the undesired diffraction order light converges is larger than or equal to twice a pull-in range of a focus error signal obtained when the third optical disc is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

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. An apparatus for recording or reproducing information on two types of optical discs having different standards is exemplified in Patent Document 1 below.

JP-A-8-240718

  The apparatus described in Patent Document 1 generates two types of diffracted light of 0th order and 1st order using a hologram element. Information is recorded on or reproduced from each optical disc by properly using the 0th-order light and the primary light according to the optical disc to be used. Japanese Patent Laid-Open No. 2004-228867 attempts to suppress the influence of diffracted light that does not contribute to information recording or reproduction by reducing the focal position of each diffracted light in the optical axis direction.

  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. In view of the convenience of users who use a plurality of optical discs with different standards in this way, in recent years, optical information recording / reproducing apparatuses, more strictly, the objective optical system provided in the apparatus have been used for the above three types of optical disks. It is required to have compatibility. 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.

  However, since the apparatus described in Patent Document 1 is configured to be compatible only with two types of optical discs having different standards such as CD and DVD, it cannot meet the above requirement.

  In order for the device to be compatible with three types of optical discs with different standards, first, when switching between optical discs with different standards, the spherical aberration, which changes with the thickness of the protective layer, is corrected while recording or reproducing information. 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 used. Generally, the spot diameter can be made smaller as the wavelength is shorter. Accordingly, it has been proposed that laser light having a plurality of wavelengths can be used properly in accordance with the recording density of the optical disk used. 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 2 proposes an objective lens that is compatible with three types of optical discs such as CD, DVD, and HD DVD.

Japanese Patent Laid-Open No. 2004-247025

  Patent Document 2 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 2, the light use efficiency during recording or reproduction of information with respect to a CD can be secured only about 40%, and unnecessary diffraction order light (in this case, 1%). The following occurs. 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 problems, the optical information recording / reproducing apparatus according to claim 1 sets the first to third wavelengths in order from the short wavelength side to the first to third optical disks in the descending order of recording density. An optical information recording / reproducing apparatus for recording or reproducing information with respect to each optical disk by using any one of three kinds of light beams having an objective lens, and at least one surface of the objective lens is concentric The third wavelength light beam transmitted through the objective lens is divided into a plurality of refracting surfaces and has a step structure having a step that gives an optical path length difference to the incident light beam between adjacent refracting surfaces. Normal diffraction order light that converges on the recording surface of the third optical disc and unnecessary diffraction order light that concentrates at a position away from the recording surface of the third optical disc are generated, and unnecessary diffraction order light is generated from the recording surface of the third optical disc. Where to focus Distance in, characterized in that it is the third least twice pull-in range of the recording or the focus error signal obtained when performing the reproduction of information with respect to the optical disc.

  Here, the normal diffraction order light means a light beam having a diffraction order used for recording or reproducing information, and the unnecessary diffraction order light means a light beam having a diffraction order not used for recording or reproducing information. .

  According to the optical information recording / reproducing apparatus of claim 1, from the position where the normal diffraction order light converges on the recording surface of the third optical disc and the normal diffraction order light converges when the light beam of the third wavelength is used. Even if the objective lens has a step structure that generates unwanted diffraction order light that concentrates at a distant position, the distance from the third optical disk to the position where unwanted diffraction order light is concentrated By setting the step structure to be twice or more of the range, not only can the spherical aberration be suppressed when using each optical disc, but a spot suitable for recording or reproducing information can be formed, and a light beam of the third wavelength can be formed. When recording or playing back information on a third optical disk using a, the focus error signal waveform collapse is suppressed and a highly accurate focusing function is realized. It can be.

  According to the optical information recording / reproducing apparatus of the second aspect, the step structure has a step that gives an optical path length difference of approximately odd number times to the light flux of the first wavelength. The paraxial power component is set so that the position where the unwanted diffraction order light is concentrated away from the recording surface of the third optical disk in the region where the light beam of the third wavelength is converged on the recording surface of the third disk. It is characterized by that.

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（３）、
−２０．００＜（ｆ１×Ｐ_２）／（ｔ３−ｔ１）＜０．００・・・（３）
ただし、ｆ１は、前記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）、
を満たすことを特徴とする。 Furthermore, according to the optical information recording / reproducing apparatus according to claim 3, the step structure has a first wavelength of λ1 (nm) and the difference in optical path length 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.
And 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 luminous flux,
In the following condition (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
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),
It is characterized by satisfying.

According to the optical information recording / reproducing apparatus according to claim 4, the following condition (4):
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
It is desirable to satisfy.

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（３）、
−２０．００＜（ｆ１×Ｐ_２）／（ｔ３−ｔ１）＜０．００・・・（３）
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。 From another point of view, the optical information recording / reproducing apparatus according to claim 5 is any of three types of light beams having first to third wavelengths with respect to 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), 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 and second light fluxes are substantially parallel light fluxes, the third light flux is divergent light incident on the objective lens, and at least one surface of the objective lens has the third wavelength. A first region for converging the light beam on the recording surface of the third optical disk, and the first region is divided into a plurality of concentric refractive surfaces, and the incident light beam is formed between adjacent refractive surfaces. A step structure having a step for providing a difference in optical path length, and in the first region, at least a step in the vicinity of the boundary portion gives the optical path length difference given to the light flux of the first wavelength by ΔOPD (nm ), The following condition (1),
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
Where N is an integer,
And 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 luminous flux,
In the following condition (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
However, f1 satisfies the focal length of the objective lens with respect to the first wavelength.

Furthermore, according to the optical information recording / reproducing apparatus of claim 6, the following condition (4):
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
It is preferable to satisfy.

Further, according to the optical information recording / reproducing apparatus of claim 7, the objective lens has an Abbe number νd of the following condition (5):
40 ≦ νd ≦ 80 (5)
The step structure of the first region 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.

According to the optical information recording / reproducing apparatus according to claim 8, the objective lens has the following condition (10) where the Abbe number νd is:
20 ≦ νd <40 (10)
The step structure of the first region 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.

Further, according to the optical information recording / reproducing apparatus of the ninth aspect, the objective lens has the following condition (12), where ΔOPDc (nm) is the optical path length difference that the step is given to the light flux having the third wavelength. ),
1.32 <| ΔOPDc / λ3 | <1.62 (12)
Configured to meet.

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、
で表すと、以下の条件（１５）、
−２０．００＜（ｆ１×Ｐ_２１）／（ｔ３−ｔ１）＜０．００・・・（１５）
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。 From another viewpoint, the optical information recording / reproducing apparatus according to claim 10 has three types of substantially parallel 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 that records or reproduces information with respect to each optical disc, and includes an objective lens, the first wavelength is λ1 (nm), and the second wavelength is λ2 ( nm) and 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 the first region has a plurality of concentric refractions. Having at least two types of step structures that provide different optical path length differences between incident light beams between refractive surfaces that are divided into surfaces and adjacent to each other, and in the first region, at least of at least two types of steps When one of the optical path length differences given to the first wavelength light flux is ΔOPD1 (nm), the following condition (13):
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)
However, N satisfies an integer, 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 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,
λ is the wavelength used for the incident luminous flux,
In the following condition (15),
−20.00 <(f1 × P ₂ 1) / (t3−t1) <0.00 (15)
However, f1 satisfies the focal length of the objective lens with respect to the first wavelength.

According to the optical information recording / reproducing apparatus according to claim 11, the following condition (16) is further given regarding the first optical path difference function:
-15.00 <(f1 × P ₂ 1) / (t3-t1) <-2.50 (16)
By satisfying the above, it is possible to obtain a focus error signal having a better waveform.

According to the optical information recording / reproducing apparatus of claim 12, the step structure of the first region is not only the condition (13) but also the following condition (17),
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
It is desirable to satisfy.

According to the optical information recording / reproducing apparatus of claim 13, when the optical path length difference given to the light flux of the third wavelength by the step is ΔOPDc1 (nm), the following condition (18)
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
Configured to meet.

According to the optical information recording / reproducing apparatus of claim 14, the step structure of the first region is not only the condition (13) but also the following condition (19):
4.70 <| ΔOPD1 / λ1 | <5.30 (19)
It is desirable to satisfy.

Further, according to the optical information recording / reproducing apparatus of claim 15, when the optical path length difference given to the light flux of the third wavelength by the step is ΔOPDc1 (nm), the following condition (20)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)
Configured to meet.

According to the optical information recording / reproducing apparatus of claim 16, the step providing the optical path length difference different from the at least one step provides the optical path length difference given to the light flux of the first wavelength by ΔOPD2 (nm). Then, the following condition (21),
2L−0.20 <| ΔOPD2 / λ1 | <2L + 0.20 (21)
It is desirable to satisfy. Note that L in the condition (21) is an integer.

According to the optical information recording / reproducing apparatus according to claim 17, 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 claim 18, the objective lens has a first wavelength light beam and a second wavelength light beam outside the first region, respectively, and the first optical disk and the second light beam, respectively. 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. There is a step that provides at least one type of optical path length difference, and the absolute value of the optical path length difference provided by the step in the second region is the absolute value of the optical path length difference provided by the step in the first region. Can be configured differently.

  Further, according to the optical information recording / reproducing apparatus of claim 19, the first wavelength light beam and the second wavelength light beam are respectively transmitted to the first optical disc and the second wavelength outside the first region. The second region converges on the recording surface of the optical disc and does not contribute to the convergence of the light beam having the third wavelength. On the other hand, the absolute value of the optical path length difference that the step of the second region imparts to the light flux having the first wavelength is | ΔOPD2 / λ1 | Can be configured differently.

According to the optical information recording / reproducing apparatus of claim 20, the objective lens has the following condition (23):
f1 × NA1> f2 × NA2 (23)
If there is a third region outside the second region, the third region has a third region that converges only the light beam of the first wavelength and does not contribute to the convergence of the light beam of the second and third wavelengths. Has a step which 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 It is desirable that the optical path length difference given by the step difference between the two regions is different from the absolute value.

According to the optical information recording / reproducing apparatus of claim 21, the objective lens has the following condition (24):
f1 × NA1 <f2 × NA2 (24)
When satisfying the above, the third region has a third region outside the second region, and has a third region that converges only the light beam of the second wavelength and does not contribute to the convergence of the light beam of the first and third wavelengths. Has a step which 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 It is desirable that the optical path length difference given by the step difference between the two regions is different from the absolute value.

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（３）、
−２０．００＜（ｆ１×Ｐ_２）／（ｔ３−ｔ１）＜０．００・・・（３）
ただし、ｆ１は、前記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。 The objective lens for an optical information recording / reproducing apparatus according to the present invention uses one of three types of light beams having first to third wavelengths for the first to third optical discs having different recording densities. Thus, an objective lens in an optical information recording / reproducing apparatus for recording or reproducing information on each optical disc, wherein the first wavelength is λ1 (nm), the second wavelength is λ2 (nm), and the third wavelength is If 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
And
The thickness of the protective layer 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 t1, and the second is longer than the first wavelength. Information is recorded or reproduced using a light beam having a wavelength of the second optical disk on which information is recorded or reproduced using a light beam having a wavelength t2, and a light beam having the longest third wavelength among the first to third wavelengths. If the thickness of the protective layer of the third optical disc is t3,
t1 ≒ 0.6mm
t2 ≒ 0.6mm
t3 ≒ 1.2mm
And
The first and second wavelength beams are substantially parallel beams, the third wavelength beam is divergent light incident on the objective lens, and at least one surface of the objective lens has a third wavelength beam. A first region that converges on the recording surface of the third optical disk, the first region being divided into a plurality of concentric refracting surfaces; It has a step structure having a step for providing an optical path length difference, and in the first region, the optical path length difference at least in the vicinity of the boundary portion is given to the light flux of the first wavelength by ΔOPD (nm) Then, the following condition (1),
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
Where 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 luminous flux,
In the following condition (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
However, f1 satisfies the focal length of the objective lens for the first wavelength.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 23, the following condition (4):
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
It is desirable to satisfy.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 24, the Abbe number νd satisfies the following condition (5):
40 ≦ νd ≦ 80 (5)
In the case of a single lens that satisfies the following conditions (6), the step structure of the first region is:
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, the imaging magnification in recording or reproducing information on the second optical disc is M2, and the focal length is f2. In the recording or reproduction of information with respect to the third optical disc, 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)
Configured to meet.

Further, according to the objective lens for an optical information recording / reproducing apparatus according to claim 25, the Abbe number νd satisfies the following condition (10):
20 ≦ νd <40 (10)
In the case of a single lens that satisfies the following conditions (6), the step structure of the first region is:
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, the imaging magnification in recording or reproducing information on the second optical disc is M2, and the focal length is f2. In the recording or reproduction of information with respect to the third optical disc, 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)
Configured to meet.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 26, the objective lens has the following condition (ΔOPDc (nm), where ΔOPDc (nm) is an optical path length difference given to a light beam having a third step. 12)
1.32 <| ΔOPDc / λ3 | <1.62 (12)
Configured to meet.

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、
で表すと、第１の光路差関数に関して、以下の条件（１５）、
−２０．００＜（ｆ１×Ｐ_２１）／（ｔ３−ｔ１）＜０．００・・・（１５）
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。 From another viewpoint, the objective lens for an optical information recording / reproducing apparatus according to claim 27 has three types of substantially parallel light beams having first to third wavelengths with respect to first to third optical disks having different recording densities. Is an objective lens for an optical information recording / reproducing apparatus that records or reproduces information with respect to each optical disc by using one of the first wavelength λ1 (nm) and the second wavelength 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 the first region has a plurality of concentric refractions. A step structure having at least two kinds of steps for providing different optical path length differences with respect to an incident light beam between refracting surfaces that are divided into surfaces and adjacent to each other, and at least two kinds of steps in the first region; Assuming that the optical path length difference that at least one of the light beams gives to the light flux having the first wavelength is ΔOPD1 (nm), the following condition (13):
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)
However, N is an integer.
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 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,
λ is the wavelength used for the incident luminous flux,
In terms of the first optical path difference function, the following condition (15):
−20.00 <(f1 × P ₂ 1) / (t3−t1) <0.00 (15)
Where f1 is the focal length of the objective lens with respect to the first wavelength,
It is characterized by satisfying.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 28, with respect to the first optical path difference function, the following condition (16):
-15.00 <(f1 × P ₂ 1) / (t3-t1) <-2.50 (16)
It is desirable to satisfy.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 29, the step structure of the first region has the following condition (17):
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
It is desirable to satisfy.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 30, when the optical path length difference given by the step to the light beam having the third wavelength is ΔOPDc1 (nm), the following condition ( 18)
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
Configured to meet.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 31, the step structure of the first region has the following condition (19):
4.70 <| ΔOPD1 / λ1 | <5.30 (19)
It is desirable to satisfy.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 32, when the optical path length difference given to the light beam having a step by the third wavelength is ΔOPDc1 (nm), the objective lens satisfies the following condition ( 20)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)
Configured to meet.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 33, the optical path length difference that the step providing the optical path length difference different from at least one of the steps provides 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.
Configured to meet.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 34, the following condition (22):
1.80 <| ΔOPD2 / λ1 | <2.20 (22)
It is desirable to satisfy further.

  According to the objective lens for an optical information recording / reproducing device according to claim 35, a first wavelength light beam and a second wavelength light beam are respectively transmitted to the outside of the first region. And a second region that does not contribute to the convergence of the light beam of the third wavelength, and the second region is at least relative to the incident light beam at the boundary between adjacent refractive surfaces. The absolute value of the optical path length difference given by the step of the first region is the absolute value of the optical path length difference given by the step of the first region. Can be configured differently.

  According to the objective lens for an optical information recording / reproducing apparatus according to claim 36, a first wavelength light beam and a second wavelength light beam are respectively transmitted to the first optical disc and the second wavelength outside the first region. The second region converges on the recording surface of the optical disk and does not contribute to the convergence of the light beam having the third wavelength, and the second region is the boundary between the adjacent refractive surfaces with respect to the incident light beam. At least one kind of optical path length difference is provided, and the absolute value of the optical path length difference provided to the light flux of the first wavelength by the step in the second region is different from | ΔOPD2 / λ1 |. It may be configured.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 37, the following condition (23):
f1 × NA1> f2 × NA2 (23)
When satisfying, has a third region outside the second region, to converge only the light beam of the first wavelength, does not contribute 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,
You may comprise so that the absolute value of the optical path length difference provided by the level | step difference of said 3rd area | region may differ from the absolute value of the optical path length difference provided by the level | step difference of said 2nd area | region.

According to the objective lens for an optical information recording / reproducing apparatus according to claim 38, the following condition (24):
f1 × NA1 <f2 × NA2 (24)
When satisfying the above, the third region has a third region outside the second region, which has a third region that converges only the light beam of the second wavelength and does not contribute to the convergence of the light beam of the first and third wavelengths. Has a step which 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 You may comprise so that it may differ from the absolute value of the optical path length difference provided by the level | step difference of two area | regions.

  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 as well as spherical aberration.

  That is, according to the present invention, 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 deteriorating the focusing function, and the objective lens 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. An optical disc having a low recording density (for example, DVD or DVD-R) is referred to as a second optical disc D2, and an optical disc having a lowest recording density (for example, CD or CD-R) is referred to as a third optical disc D3.

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 numerical apertures required for recording or reproducing information on each of the optical discs D1 to D3 are NA1, NA2, and NA3, respectively, in each embodiment, the following relationships are associated with NA1 to NA3. There is.
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 using the optical discs D1 to D3 having different recording densities as described above, laser beams having different wavelengths are used so as to obtain a beam spot having a size corresponding to each recording density. Specifically, when information is recorded on or reproduced from the first optical disc D1, the beam spot having the smallest diameter is formed on the recording surface of the first optical disc D1. Therefore, laser light (hereinafter referred to as first laser light) having the shortest wavelength (first wavelength) is irradiated from the light source. Further, when information is recorded on or reproduced from the third optical disc D3, a beam spot having the largest diameter is formed on the recording surface of the third optical disc D3. Therefore, a laser beam (hereinafter referred to as a third laser beam) having the longest wavelength (third wavelength) is emitted from the light source. When information is recorded on or reproduced from the second optical disc D2, a spot having a relatively small diameter is formed on the recording surface of the second optical disc D2. Therefore, a laser beam (hereinafter referred to as a second laser beam) having a longer wavelength than the first laser beam and a shorter wavelength (second wavelength) than the third laser beam is irradiated from the 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 as described above. 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 passed through the diffraction gratings 2A to 2C, the coupling lenses 3A to 3C, and the beam splitters 41 and 42, respectively. The light is guided to a common optical path and 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. The phase shift structure here is the same as the above step structure. 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 at least the innermost region including the intersection with the optical axis of the objective lens 10 and the region that contributes to the convergence of all the first to third laser beams (hereinafter referred to as the first). One area). The phase shift structure in the first region has a level difference that gives an optical path length difference of approximately odd number times when the first laser beam is incident.

Specifically, the optical path length difference of approximately the odd number is the following condition 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). It is defined 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 when information is recorded or reproduced 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 in the first region that satisfies the above condition (1) can be expressed by the following optical path difference function φ (h). The optical path difference function φ (h) expresses the function of the objective lens 10 as a diffractive lens in the form of an additional optical path length at a height h from the optical axis. It prescribes. 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 secondary, quaternary, 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 in the first region of the objective lens 10 represented by the above formula (2) is designed to satisfy the following condition (3).

−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (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 a case where information is recorded or reproduced on the third optical disc D3 using an objective lens having a phase shift structure that does not satisfy the condition (3) (more specifically, exceeds the upper limit of the condition (3)). FIG. 6 is a diagram showing a component obtained by normal diffraction order light, a component obtained by unnecessary diffraction order light, and a focus error signal obtained as a total of both components among the focus error signals obtained in FIG. 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 which can be obtained as a total of the component obtained by order light and both components. 4 and 5, the vertical axis indicates the detected focus error signal level, and the horizontal axis indicates the defocus amount (movement amount in the optical axis direction) 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, 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 relatively Close position. For this reason, the waveform of the focus error signal as a whole collapses, and the focus detection function deteriorates, 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 is configured such that the distance from the recording surface of the third optical disc D3 (that is, the position where normal diffraction order light converges) to the position where unnecessary diffraction order light concentrates is increased. Is done. Specifically, the distance is configured to be at least twice as large as a focus error signal pull-in range obtained when information is recorded or reproduced on the optical disc D3. Here, the pull-in range refers to a range in which focusing can be performed by driving the actuator in accordance with the control voltage in the focus error signal. When the detected focus error signal takes a value outside the pull-in range, a correction operation is performed so as to take a value within the pull-in range. Specifically, the pull-in range is defined as the distance in the horizontal axis direction from point A to point B in the total focus error signal shown in FIG.

In order to realize the configuration relating to the above-described pull-in range, the objective lens 10 is unnecessary in the region where the third laser light is converged on the recording surface of the third disk D3 in the phase shift structure provided on the first surface 11. The paraxial power component is set so that the position where the diffraction order light is concentrated is away from the recording surface of the third optical disc D3. The paraxial power component is a component for controlling unwanted diffraction order light and axial chromatic aberration, and specifically corresponds to P ₂ h ^{2 in} the above formula (2).

  Condition (3) is a specific condition for realizing the objective lens 10 having the above-described configuration. By satisfying the condition (3), the zero cross point of the focus error signal component based on the unnecessary diffraction order light can be normalized when the third laser beam is used (that is, when information is recorded or reproduced by the third optical disc D3). The focus error signal component based on light can be greatly separated from the zero cross point. Thereby, the waveform of the focus error signal actually detected by the light receiving unit 6C can be maintained in an S shape necessary for the focus detection function to operate effectively. If the lower limit of the condition (3) is exceeded, the light quantity loss increases due to an increase in the number of annular zones, which is also not preferable.

In order to obtain a focus error signal having a much better waveform, the phase shift structure in the first region should satisfy the following condition (4).
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)

More specifically, the Abbe number νd satisfies the following condition (5):
40 ≦ νd ≦ 80 (5)
When the objective lens 10 satisfying the above is used, the optical path length difference ΔOPD imparted to the first laser light by the step in the phase shift structure in the first region is designed to satisfy the following condition (6). .
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. Accordingly, 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, the objective lens 10 is provided with a lens to suppress various aberrations due to off-axis light. It is desired that a substantially parallel light beam be incident.

For example, the objective lens 10 having the phase shift structure designed to satisfy the condition (6) in the first region 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 phase shift structure that effectively suppresses the aberration when using each of the optical discs D1 and D2 having a narrow tolerance for aberration is set in the first region of the objective lens 10, information on the third optical disc D3. Spherical aberration remains during recording or reproduction. 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 is used, the phase shift structure in the first region is designed so that the optical path length difference ΔOPD given to the first laser light by the step satisfies the above condition (6). The 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. On the other hand, the optical path length difference ΔOPDc to be applied is designed to satisfy the following condition (12).
1.32 <| ΔOPDc / λ3 | <1.62 (12)

  The optical information recording / reproducing apparatus 100 of the first embodiment uses the objective lens 10 configured to satisfy each of the above conditions, thereby suppressing the disturbance of the waveform of the focusing error signal when using the third optical disc D3. Good focusing function can be maintained. 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.

As described above, similarly to the first embodiment, the phase shift structure of the second embodiment can control spherical aberration generated in the refractive lens portion of the objective lens 10 due to the difference in wavelength between the first and second laser beams. Designed to have That is, the phase shift structure in the first region of the second embodiment also has an optical path length difference of approximately odd times when the first laser light is incident, more specifically, the first wavelength is λ1 (nm ) If the optical path length difference that at least one of the steps gives to the light flux of the first wavelength is ΔOPD1 (nm), it is defined by the following condition (13).
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)

  By satisfying the condition (13), 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 (13), if the optical path length difference | ΔOPD1 / 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.

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 normal diffraction order light related to the third laser light have higher diffraction efficiency than the unnecessary diffraction order light, in the second embodiment, the first type of step in the first region is the above condition (13 ) Is designed so that the optical path length difference ΔOPDc1 applied to the third laser light satisfies the following conditions (18) and (20). More specifically, the first type step configured to satisfy the condition (17) satisfies the condition (18), and the first type step configured to satisfy the condition (19) satisfies the condition (20). Fulfill.
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)

When the first region is configured to satisfy the above condition (13), more specifically, the condition (17) or the condition (19), the optical path length difference ΔOPD1 provided by at least one step is It is approximately (2J + 1) wavelengths with respect to the laser light. Therefore, in particular, the amount of light used for recording or reproducing information on the third optical disc D3 must be reduced. Therefore, the second type of step providing an 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 second type of step providing an optical path length difference different from the optical path length difference ΔOPD1 is the following condition (21), more specifically the condition: Designed to satisfy (22).
2L−0.20 <| ΔOPD2 / λ1 | <2L + 0.20 (21)
1.80 <| ΔOPD2 / λ1 | <2.20 (22)
However, L is an integer.

  By designing the second step of the phase shift structure in the first region so as to satisfy the above condition (21), more specifically, the condition (22), not only the third laser beam but also the first The diffraction efficiency of laser light can be increased. That is, it is possible to secure a large amount of light on the recording surface 22 when using the first optical disc D1 and the third optical disc D3.

  The phase shift structure as described above has at least two types of optical path difference functions, for example, a first optical path difference function and a 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 light beams. 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 phase shift structure of the second embodiment, the i-th (i is a natural number) optical path difference function φi (h) in a plurality of optical path difference functions defining the phase shift structure 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 phase shift structure of the objective lens 10 of the second embodiment is the first optical path difference function φ1 when the first laser beam is used and the height h from the optical axis is within the effective range. The value obtained by (h) (optical path length addition amount) is designed so that the position where unnecessary diffraction order light concentrates is away from the recording surface of the third optical disc. More specifically, the phase shift structure is designed to satisfy the following condition (15) and further satisfy the following condition (16).
−20.00 <(f1 × P ₂ 1) / (t3−t1) <0.00 (15)
-15.00 <(f1 × P ₂ 1) / (t3-t1) <-2.50 (16)

  By satisfying the condition (15) and further the condition (16), a focus error signal component based on unnecessary diffraction order light when the third laser beam is used (that is, when information is recorded or reproduced by the third optical disc D3). This zero cross point can be greatly separated from the zero cross point of the focus error signal component based on the normal diffraction order light. Thereby, the waveform of the focus error signal actually detected by the light receiving unit 6C can be maintained in an S shape necessary for the focus error function to operate effectively.

  By designing the phase shift structure as described 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, the optical discs D1 to D3 are used. It is possible to satisfactorily suppress spherical aberration that occurs during use, 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. In the objective lens 10 according to the first and second embodiments, the outside of the first region depends on the difference in effective light beam diameter for ensuring the NA necessary for recording or reproducing information on the optical discs D1 to D3. A second region having a phase shift structure different from that of the first region, and a third region having a phase shift structure different from that of the first and second regions outside the second region. It is also effective.

  That is, the phase shift structure of the second region is generally the first and second laser beams used when the first and second optical discs D1 and D2 are used, which requires a higher NA than when the third optical disc D3 is used. Has a diffractive action for favorably 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 in the second embodiment in the first region, steps that satisfy the conditions (21) and (22) are steps that exist in the first region. It corresponds to.

  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.

  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 are a total of three examples as Example 1 to Example 3, and the objective lens of the second embodiment. Specific examples of the optical information recording / reproducing apparatus using 10 as the objective optical system are shown in total from Example 4 to Example 6.

  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 6 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 6.

  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).

  The phase shift structure formed on the first surface 11 of the objective lens 10 of Example 1 is specifically shown in Table 10. 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 given by the first laser beam or the third laser beam passing through each annular zone. It is the table | surface which showed the length difference. 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 same applies to the same type of table presented in the examples described below.

  As shown in Table 10, as for the 1st surface 11 of the objective lens 10 of Example 1, the whole area within an effective diameter functions as the 1st area | region mentioned above.

  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. Similarly, as shown in Table 10, the optical path length difference | ΔOPDc / λ3 | to which the third laser light is imparted by the step between the annular zones is 1.47, which also 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 recording surface 22 and the protective layer 21 of the optical disk 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 number 17 , 18 are the coupling lens 3C, surface numbers 19 and 20 are the half mirror 5C, and surface number 21 is the light receiving unit 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 optical information recording / reproducing apparatus of the comparative example. The objective lens provided in the optical information recording / reproducing apparatus of the comparative example is assumed to have the same phase shift structure as that of the first embodiment except that the values of the conditions (3) and (4) are 0.00. To do. As can be seen by comparing FIG. 7 and FIG. 8, the focus error signal detected by the light receiving unit 6C of the first embodiment has a better S-shape with less collapse when the defocus amount is near 0 μm than the comparative example. It has a waveform. 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 −0.08. 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 the spherical aberration diagrams presented in the examples described below.

  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 phase shift 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 value of condition (3) is -15.33. Therefore, the objective lens 10 of Example 2 satisfies the condition (3).

  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 given by the first laser beam or the third laser beam passing through each annular zone. It is the table | surface which showed the length difference.

  As shown in Table 21, the first surface 11 of the objective lens 10 of Example 2 also functions as the first region described above in the entire effective diameter area, as in Example 1.

  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. Similarly, as shown in Table 21, the optical path length difference | ΔOPDc / λ3 | to which the third laser light is imparted by the step between the annular zones is 1.47, which also 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, the surface numbers 11 and 12 are the recording surface and the protective layer 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. 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 can be seen from a comparison between FIG. 8 showing the comparative example and FIG. 10, the focus error signal detected by the light receiving unit 6C of the second embodiment is better than that of the comparative example when the defocus amount is near 0 μm. S-shaped waveform. That is, the optical information recording / reproducing apparatus 100 according to the second embodiment also can satisfy the condition (3) as in the first embodiment, thereby suppressing the collapse of the focus error signal and preventing the focusing function from being lowered.

  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, and f3 × M3 is −0.11, 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. In the first area. 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 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 1.95 and f2 × NA2 is 1.81. That is, the optical information recording / reproducing apparatus 100 of Example 3 satisfies the condition (23). Therefore, as described above, the first surface 11 of the objective lens 10 of Example 3 has the phase shift structure having the first region contributing to the convergence of each laser beam and the 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 second laser beam and 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 <= 1.490,
Second region: 1.490 <h ≦ 1.860,
Third region: 1.860 <h ≦ 1.950.

  Similar to the first and second 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.

The coefficient P ₂ in the optical path difference function for defining the phase shift structure to be formed on the first surface 11 of the objective lens 10 of Example 3 (in the second region defined by a plurality of optical path difference functions) Table 30 shows coefficients P ₂ i... In the i-th optical path difference function. In addition, in each optical path difference function, the diffraction order m that maximizes the diffraction efficiency of each laser beam is shown in Table 31.

  From Tables 23 and 30, the values of Condition (3) and Condition (4) are −13.50. Therefore, the objective lens 10 of Example 3 satisfies 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 shows the range of each annular zone formed on the first surface 11 of the objective lens 10 of Example 3, and the optical path provided when the first laser beam or the third laser beam passes through each annular zone. It is the table | surface which showed the length difference.

  In Table 32, no. The 18 steps are special steps having a property of giving an optical path length change amount obtained by a sum of optical path length change amounts given by the first and second types of steps.

  The objective lens 10 of the optical information recording / reproducing apparatus of Example 3 satisfies the condition (5) with an Abbe number νd of 58. Further, as shown in Table 32, the optical path length difference | ΔOPD / λ1 | to which the first laser beam is imparted by the step in the first region is 3.12, which satisfies the conditions (1) and (6) . Similarly, as shown in Table 32, the optical path length difference | ΔOPDc / λ3 | to which the third laser light is imparted by the step in the first region is 1.54, 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 recording surface and protective layer 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 can be seen from a comparison between FIG. 12 and FIG. 8 showing the comparative example, the focus error signal detected by the light receiving unit 6C of Example 3 is better than that of the comparative example when the defocus amount is near 0 μm. S-shaped waveform. That is, the optical information recording / reproducing apparatus 100 according to the second embodiment can suppress the collapse of the focus error signal by satisfying the condition (3) and the condition (4) as in the first embodiment, thereby reducing the focusing function. It is preventing.

  Further, as can be seen from Table 23, 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 −0.09. 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. In other words, the objective lens 10 of Example 4 has a phase shift structure formed of steps that give two different optical path length differences in the first region of the first surface 11. 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 phase shift structure to be formed on the first surface 11 of the objective lens 10 of Example 4. 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 -12.50. 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.

  As shown in Table 43, the objective lens 10 of the optical information recording / reproducing apparatus of Example 4 has optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | They 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 applied by the first type of step is 1.47. 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 information is recorded or reproduced on the third optical disc D3 in the optical information recording / reproducing apparatus 100 having the objective lens 10 according to the fourth embodiment. As shown in FIG. 14, 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 satisfies the conditions (15) and (16), so that the collapse of the focus error signal can be suppressed, and the focusing function is prevented from being lowered.

  Furthermore, as can be seen from FIGS. 6A to 6C and Table 34, in the optical information recording / reproducing apparatus 100 of Example 4, 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. 15A to 15C 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 fourth 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 composed of steps providing two different optical path length differences in the first region of the first surface 11. Have. 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 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 order.

Table 52 shows coefficients P ₂ i... In the i-th optical path difference function for defining the phase shift structure to be formed in the first region of the first surface 11 of the objective lens 10 of Example 5. . 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 −5.75. 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.

  As shown in Table 54, the objective lens 10 of the optical information recording / reproducing apparatus of Example 5 has optical path length differences | ΔOPD1 / λ1 | and | ΔOPD2 / λ1 | They are 5.21 and 2.00, respectively. That is, in Example 5, 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 2.56. 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.

  Furthermore, as can be seen from FIGS. 6A to 6C and Table 45, in the optical information recording / reproducing apparatus 100 of Example 5, f1 × M1, f2 × M2, and f3 × M3 are all 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 of Example 6 has a phase shift structure composed of steps that give 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 6 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 1.95 and f2 × NA2 is 2.01. That is, the optical information recording / reproducing apparatus 100 of Example 6 satisfies the condition (24). Therefore, the first surface 11 of the objective lens 10 of Example 6 has a phase shift structure having a first region contributing to convergence of each laser beam and an aperture limiting function for the third laser beam as described above. And a third region having a phase shift structure having an aperture limiting function with respect to the first laser beam and 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 <= 1.580,
2nd area | region ... 1.580 <h <= 1.950,
Third region: 1.950 <h ≦ 2.010.

  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 a phase shift structure to be formed in each area of the first surface 11 of the objective lens 10 of Example 6 (first area defined by a plurality of optical path difference functions) Table 63 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 64.

  From Tables 56 and 63, the values of the conditions (15) and (16) are −13.50. 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, | 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 imparted by each step are 3.00 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. Further, the optical path length difference | ΔOPDc1 / λ3 | to which the third laser beam is applied by the first type of step is 1.47. Therefore, the conditions (13), (17), (18), (21), and (22) are satisfied.

  In addition, the optical path length difference | ΔOPDd1 / λ2 | shown in Table 65 differs between the second region and the third region. Furthermore, the optical path length difference | ΔOPDd1 / λ2 | given in the third region is 1.00. From this, the third region has a phase shift structure defined by an optical path difference function different from that of the second region, and the phase shift structure is effective for the convergence of the second laser beam. It can be seen that it is configured to contribute only.

  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.

  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. For example, the number of optical elements such as lenses constituting the objective optical system of the optical information recording / reproducing apparatus may be plural. 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 arranged 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 and configured to satisfy the above conditions (7) and (8) so that the imaging magnification is as small as possible, it is the same as in the above embodiments. The effect of can be produced.

It is a schematic diagram showing schematic structure of the optical information recording / reproducing apparatus of embodiment of this invention. 1 is a diagram showing an optical information recording / reproducing apparatus according to a first embodiment of the present invention divided 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 using each optical disc. 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. 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 (38)

Recording information on each optical disc by using any one of the three types of light beams 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 optical information recording / reproducing apparatus for performing reproduction,
With an objective lens,
At least one surface of the objective lens is divided into a plurality of concentric refracting surfaces, and has a step structure having a step that gives an optical path length difference between incident refracting surfaces to an incident light beam,
The light beam having the third wavelength that has passed through the objective lens does not need to be concentrated at a normal diffraction order light that converges on the recording surface of the third optical disc and at a position away from the recording surface of the third optical disc. Produces diffraction order light,
The distance from the position where the normal diffraction order light converges to the position where the unnecessary diffraction order light concentrates is twice the pull-in range of the focus error signal obtained when information is recorded or reproduced on the third optical disc. What is described above is an optical information recording / reproducing apparatus. The optical information recording / reproducing apparatus according to claim 1.
The step structure has a step that gives an optical path length difference of approximately an odd multiple to the light flux of the first wavelength,
In the step structure, in a region where the light beam of the third wavelength is converged on the recording surface of the third disk, the position where the unnecessary diffraction order light is concentrated is separated from the recording surface of the third optical disk. In addition, an optical information recording / reproducing apparatus characterized in that a paraxial power component is set. The optical information recording / reproducing apparatus according to claim 2.
In the step structure, when the first wavelength is λ1 (nm) and the optical path length difference that the step imparts to the light beam having the first wavelength is ΔOPD (nm), the following condition (1):
2N + 0.70 <| ΔOPD / λ1 | <2N + 1.30 (1)
Where 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 (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
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),
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 3.
Furthermore, the following condition (4),
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
An optical information recording / reproducing apparatus characterized by satisfying the above. Optical information recording / reproduction for recording / reproducing information on / from each optical disc by using one of three kinds of light beams having first to third wavelengths for the first to third optical discs having different recording densities A 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 of two wavelengths is t2, and the information is obtained using the longest light beam of the third wavelength from 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,
The first region is divided into a plurality of concentric refracting surfaces, and has a step structure having a step that gives an optical path length difference between incident refracting surfaces to an incident light beam,
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)
Where 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 (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
However, f1 satisfies the focal length of the objective lens with respect to the first wavelength. The optical information recording / reproducing apparatus according to claim 5.
Furthermore, the following condition (4),
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 5 or 6,
The objective lens has an Abbe number νd of the following condition (5):
40 ≦ νd ≦ 80 (5)
Single lens satisfying
The step structure of the first region 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 5 or 6,
The objective lens has an Abbe number νd of the following condition (10):
20 ≦ νd <40 (10)
Single lens satisfying
The step structure of the first region 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. In the optical information recording / reproducing apparatus according to claim 7 or 8,
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. Light that records or reproduces information on each optical disc by using any one of three types of substantially parallel light beams having first to third wavelengths for the first to third optical discs having different recording densities. An information recording / reproducing apparatus,
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,
The first region is divided into a plurality of concentric refracting surfaces, and has a step structure having at least two types of steps that provide different optical path length differences with respect to the incident light flux between adjacent refracting surfaces. And
In the first region, when the optical path length difference that at least one of the at least two kinds of steps gives to the light flux having the first wavelength is ΔOPD1 (nm), the following condition (13):
2N + 0.70 <| ΔOPD1 / λ1 | <2N + 1.30 (13)
Where 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,
λ is the wavelength used for the incident light flux,
In terms of the first optical path difference function, the following condition (15):
−20.00 <(f1 × P ₂ 1) / (t3−t1) <0.00 (15)
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 10,
Regarding the first optical path difference function, the following condition (16):
-15.00 <(f1 × P ₂ 1) / (t3-t1) <-2.50 (16)
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 10 or 11,
The step structure of the first region has the following condition (17):
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
An optical recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 12,
When the optical path length difference given by the step to the light flux of the third wavelength is ΔOPDc1 (nm), the following condition (18)
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
An optical recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 10 or 11,
The step structure of the first region has the following condition (19):
4.70 <| ΔOPD1 / λ1 | <5.30 (19)
An optical recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 14.
Assuming that the optical path length difference given to the light flux of the third wavelength by the step is ΔOPDc1 (nm), the following condition (20)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)
An optical recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to any one of claims 10 to 15,
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)
Where L is an integer.
An optical information recording / reproducing apparatus characterized by satisfying the above. The optical information recording / reproducing apparatus according to claim 16,
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 5 to 9,
Outside the first region, the light flux of the first wavelength and the light flux of the second wavelength are converged on the recording surfaces of the first optical disc and the second optical disc, respectively, and the third Having a second region that does not contribute to the convergence of the light flux of 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 10 to 17,
Outside the first region, the light flux of the first wavelength and the light flux of the second wavelength are converged on the recording surfaces of the first optical disc and the second optical disc, respectively, and the third Having a second region that does not contribute to the convergence of the light flux of 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 a difference in optical path length given to the light flux having the first wavelength by the step in the second region is different from the above | ΔOPD2 / λ1 |. The optical information recording / reproducing apparatus according to claim 18 or 19,
The following conditions (23),
f1 × NA1> f2 × NA2 (23)
The filling,
Outside the second region, has a third 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 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 18 or 19,
The following conditions (24),
f1 × NA1 <f2 × NA2 (24)
The filling,
Outside the second region, has a third 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. Optical information recording for recording or reproducing information on each optical disc by using any one of three types of light beams having first to third wavelengths for the first to third optical discs having different recording densities. An objective lens in a playback device,
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 of two wavelengths is t2, and the information is obtained using the longest light beam of the third wavelength from 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,
The objective lens has at least one surface having a first region for converging a light beam having a third wavelength on a recording surface of a third optical disc,
The first region is divided into a plurality of concentric refracting surfaces, and has a step structure having a step that gives an optical path length difference between incident refracting surfaces to an incident light beam,
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)
Where 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 (3),
−20.00 <(f1 × P ₂ ) / (t3−t1) <0.00 (3)
Here, f1 satisfies the focal length of the objective lens with respect to the first wavelength, the objective lens for an optical information recording / reproducing apparatus, The objective lens for an optical information recording / reproducing apparatus according to claim 22,
Furthermore, the following condition (4),
-15.00 <(f1 × P ₂ ) / (t3−t1) <− 2.50 (4)
An objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to claim 22 or 23,
Abbe number νd is the following condition (5),
40 ≦ νd ≦ 80 (5)
Single lens satisfying
The step structure of the first region 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 objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to claim 22 or 23,
Abbe number νd is the following condition (10):
20 ≦ νd <40 (10)
Single lens satisfying
The step structure of the first region 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 objective lens for optical information recording / reproducing apparatus characterized by satisfying the above. In the objective lens for optical information recording / reproducing apparatus according to claim 24 or claim 25,
Assuming that the optical path length difference given to the light flux of the third wavelength by the step is ΔOPDc (nm), the following condition (12)
1.32 <| ΔOPDc / λ3 | <1.62 (12)
An objective lens for an optical information recording / reproducing apparatus, characterized in that: Optical information that records or reproduces information on each optical disc by using any one of three types of substantially parallel light beams having the first to third wavelengths for the first to third optical discs having different recording densities. An objective lens for a recording / reproducing apparatus,
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,
The first region is divided into a plurality of concentric refracting surfaces, and has a step structure having at least two types of steps that provide different optical path length differences with respect to the incident light flux between adjacent refracting surfaces. And
In the first region, when the optical path length difference that at least one of the at least two kinds of steps gives to the light flux having the first wavelength is ΔOPD1 (nm), the following condition (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,
λ is the wavelength used for the incident light flux,
In terms of the first optical path difference function, the following condition (15):
−20.00 <(f1 × P ₂ 1) / (t3−t1) <0.00 (15)
Where f1 is the focal length of the objective lens with respect to the first wavelength,
An objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to claim 27,
Regarding the first optical path difference function, the following condition (16):
-15.00 <(f1 × P ₂ 1) / (t3-t1) <-2.50 (16)
An objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to claim 27 or claim 28,
The step structure of the first region has the following condition (17):
2.70 <| ΔOPD1 / λ1 | <3.30 (17)
Objective lens for optical recording / reproducing apparatus characterized by satisfying the above. The objective lens for an optical information recording / reproducing apparatus according to claim 29,
When the optical path length difference given by the step to the light flux of the third wavelength is ΔOPDc1 (nm), the following condition (18)
1.32 <| ΔOPDc1 / λ3 | <1.62 (18)
Objective lens for optical recording / reproducing apparatus characterized by satisfying the above. The objective lens for an optical information recording / reproducing apparatus according to claim 27 or claim 28,
The step structure of the first region has the following condition (19):
4.70 <| ΔOPD1 / λ1 | <5.30 (19)
Objective lens for optical recording / reproducing apparatus characterized by satisfying the above. The objective lens for an optical information recording / reproducing apparatus according to claim 31,
Assuming that the optical path length difference given to the light flux of the third wavelength by the step is ΔOPDc1 (nm), the following condition (20)
2.30 <| ΔOPDc1 / λ3 | <2.60 (20)
Objective lens for optical recording / reproducing apparatus characterized by satisfying the above. The objective lens for an optical information recording / reproducing apparatus according to claim 27 or claim 28,
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)
Where L is an integer.
An objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to claim 33,
The following condition (22),
1.80 <| ΔOPD2 / λ1 | <2.20 (22)
An objective lens for an optical information recording / reproducing apparatus, characterized in that: The objective lens for an optical information recording / reproducing apparatus according to any one of claims 22 to 26,
Outside the first region, the light flux of the first wavelength and the light flux of the second wavelength are converged on the recording surfaces of the first optical disc and the second optical disc, respectively, and the third Having a second region that does not contribute to the convergence of the light flux of 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,
For an optical information recording / reproducing apparatus, wherein the absolute value of the optical path length difference given by the step in the second region is different from the absolute value of the optical path length difference given by the step in the first region Objective lens. The objective lens for an optical information recording / reproducing apparatus according to any one of claims 27 to 34,
Outside the first region, the light flux of the first wavelength and the light flux of the second wavelength are converged on the recording surfaces of the first optical disc and the second optical disc, respectively, and the third Having a second region that does not contribute to the convergence of the light flux of 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 objective lens for an optical information recording / reproducing apparatus, characterized in that an absolute value of a difference in optical path length given to the light flux of the first wavelength by the step in the second region is different from the above | . The objective lens for an optical information recording / reproducing apparatus according to claim 35 or claim 36,
The following conditions (23),
f1 × NA1> f2 × NA2 (23)
The filling,
Outside the second region, has a third 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 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 absolute value of the optical path length difference provided by the step in the third region is different from the absolute value of the optical path length difference provided by the step in the second region. Objective lens. The objective lens for an optical information recording / reproducing apparatus according to claim 35 or claim 36,
The following conditions (24),
f1 × NA1 <f2 × NA2 (24)
The filling,
Outside the second region, has a third 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 absolute value of the optical path length difference provided by the step in the third region is different from the absolute value of the optical path length difference provided by the step in the second region. Objective lens.

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