JP2006244656A - Objective lens, optical pickup device, and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens wherein aberration can be satisfactorily corrected and an actuation distance is secured for products of a plurality of generations whose thicknesses of transparent substrates and an image side numerical apertures are different. <P>SOLUTION: A resin layer 8b is joined to the surface on the light source side of a refractive lens 8a and a diffraction surface of a blaze shape is formed on the surface thereof. The diffraction grating shape of the blaze shape or the so-called kinoform shape advantageously has the highest diffraction efficiency as the shape of the diffraction grating, and when the shape is optimized to a wavelength, diffraction efficiency in the wavelength is made to be 100% according to a scalar diffraction theory and ≥90% diffraction efficiency is expected even in a stepwise approximated shape. A code (d) denotes the depth of the blaze-shaped grating groove and acts on the diffraction efficiency of the diffraction surface. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an objective lens, an optical pickup device, and an optical disk device, and more specifically, an objective lens that focuses an incident light beam from a light source on a recording surface of an information recording medium, and irradiates the recording surface of the information recording medium with light. The present invention relates to an optical pickup device that receives reflected light from a recording surface, and an optical disk device including the optical pickup device.

In recent years, optical discs such as CDs and DVDs have been widely used as information recording media (hereinafter referred to as optical discs), and optical disc apparatuses for recording and reproducing (accessing) these optical discs have been developed. Recently, development of an optical disk having a larger capacity such as a Blu-ray Disc and an HD-DVD and an optical disk apparatus for accessing the optical disk is also in progress. In these optical disk apparatuses, information is recorded by forming a light beam of a small spot of laser light on the recording surface of the optical disk, and information is reproduced based on reflected light from the recording surface. The optical disk device is provided with an optical pickup device as a device for irradiating the recording surface with laser light and receiving reflected light from the recording surface.
In general, an optical pickup device includes an objective lens, and is disposed at a light receiving position and an optical system that guides a light beam emitted from a light source to a recording surface and guides a return light beam reflected by the recording surface to a predetermined light receiving position. It has a photodetector. This photodetector outputs not only the reproduction information of the data recorded on the recording surface but also a signal including information (servo information) necessary for position control of the optical pickup device itself and the objective lens. The optical disc apparatus performs various servo controls based on the output signal from the photodetector so that a light spot having a predetermined shape is formed at a predetermined position on the recording surface.

As described above, there are several types of information recording media such as CDs and DVDs, large-capacity Blu-ray Discs and HD-DVDs, etc. with different standards such as light source wavelength, transparent substrate thickness, and NA (numerical aperture) of the objective lens. An optical disc exists. Although it is desirable that these optical disks can be handled by the same optical disk apparatus, it is not preferable to mount a plurality of optical pickup apparatuses corresponding to the respective optical disks from the viewpoint of miniaturization and cost reduction.
Therefore, as shown in FIG. 12, each light source of a blue (Blu-ray Disc, HD-DVD, etc.) light source 100, a DVD light source 200, and a CD light source 300, and an emitted light beam from each light source are applied to a predetermined optical disc 9. A configuration including one objective lens 8 for condensing light is desirable. That is, it is necessary to correct the aberration to an almost diffraction limit with respect to optical discs of different standards of blue, DVD, or CD with one objective lens.
However, compared with a standard such as HD-DVD where the transparent substrate thickness of DVD and optical disk and the NA of the objective lens are the same, as in Blu-ray Disc, the transparent substrate thickness of DVD and optical disk is the same as that of the objective lens. Standards with different NAs need to correct larger spherical aberrations that occur between different standards.
Note that Patent Document 1 discloses a ring-like shape used in an optical pickup device that records and reproduces a light beam from a corresponding laser light source on the signal recording surfaces of a plurality of optical disks having different transparent substrate thicknesses. A single objective lens having a diffractive structure is described.
JP 2002-236253 A

By the way, in order to secure the working distance (WD) of the objective lens that can prevent the objective lens from colliding with the optical disc, particularly DVD or CD, it is necessary to reduce the thickness of the objective lens, while the objective like the Blu-ray Disc is used. Since a high NA is required for the lens, a high refractive index is required as a material for the objective lens. However, in Patent Document 1, the material of the objective lens is optical plastic, and it is difficult to realize a high refractive index at present.
Therefore, the objective lens must be thick, and the working distance to the DVD is only about 0.2 mm.
The present invention has been made under such circumstances, and an objective lens in which aberrations are satisfactorily corrected for a plurality of generations having different transparent substrate thicknesses and image-side numerical apertures and a working distance is secured is used. A compact optical pickup device capable of forming a good focused spot on the recording surfaces of a plurality of information recording media having different standards, and an optical disk device capable of stably accessing a plurality of information recording media having different standards The purpose is to provide.

In order to achieve the above object, the invention described in claim 1 is an objective lens that condenses incident light beams from a plurality of light sources on a recording surface of an information recording medium, and is a glass having a resin layer bonded to at least one surface. And a diffractive surface formed on at least one surface of the resin layer or the refractive lens.
According to a second aspect of the present invention, in the objective lens according to the first aspect, the incident light flux from the plurality of light sources is configured with a wavelength having a relationship of λ ₁ <λ ₂ <λ _3. To do.
According to the first and second aspects, since a glass glass material having a high refractive index can be used for the refractive lens, it is possible to achieve both a working distance and a high NA, while a diffractive surface, a refractive lens, and a resin layer. Therefore, it is possible to obtain an objective lens that has a high degree of freedom in designing an objective lens and that has been favorably corrected for aberrations for a plurality of generations. In addition, since the objective lens is substantially made of glass, it is possible to suppress deterioration of aberration due to a change in refractive index or expansion due to an environmental change such as a temperature change.
According to a third aspect of the present invention, in the objective lens according to the first or second aspect, at least one surface of the objective lens is a spherical lens. If constituted in this way, manufacture becomes easy and cost reduction is realizable.
According to a fourth aspect of the present invention, in the objective lens according to any one of the first to third aspects, the diffraction grating shape on the diffraction surface is a blazed shape. If comprised in this way, the diffraction efficiency in a diffraction surface can be made high, and high diffraction efficiency can be ensured with respect to a several light source.

を満たすことを特徴とする。このように構成すれば、青色／ＤＶＤ／ＣＤの３世代に対して良好に収差補正された光利用効率の高い対物レンズを得ることができる。
また請求項６に記載した発明において、請求項１乃至請求項５のいずれか一項に記載の対物レンズと、情報記録媒体の記録面からの反射光を受光する光検出器と、を備え、波長が異なる複数の光源からの光束を、前記対物レンズにより前記情報記録媒体の記録面に集光して、前記記録面からの反射光を前記光検出器により受光する光ピックアップ装置であることを特徴とする。このように構成すれば、規格の異なる複数の情報記録媒体の記録面に対して良好な集光スポットを形成できる小型の光ピックアップ装置を得ることができる。
また請求項７に記載した発明において、情報記録媒体に対して情報の記録、再生、及び消去のうち少なくともいずれか１以上の処理を行う光ディスク装置において、請求項６記載の光ピックアップ装置と、前記光ピックアップ装置の信号を処理する処理手段と、を備えたことを特徴とする。このように構成すれば規格の異なる複数の情報記録媒体へのアクセスを安定して行う光ディスク装置を得ることができる。 According to a fifth aspect of the present invention, there is provided the objective lens according to any one of the first to fourth aspects, wherein each of the plurality of light sources having the wavelengths λ ₁ , λ ₂ , and λ ₃ is provided on the diffractive surface. When the diffraction orders that maximize the diffraction efficiency among the diffracted light generated with respect to the incident light beam are m ₁ , m ₂ , and m ₃ , the following conditions are satisfied.

It is characterized by satisfying. With this configuration, it is possible to obtain an objective lens with high light utilization efficiency in which aberrations are favorably corrected for the three generations of blue / DVD / CD.
Moreover, in the invention described in claim 6, the objective lens according to any one of claims 1 to 5 and a photodetector that receives reflected light from the recording surface of the information recording medium, The optical pickup device collects light beams from a plurality of light sources having different wavelengths on the recording surface of the information recording medium by the objective lens and receives reflected light from the recording surface by the photodetector. Features. If comprised in this way, the small optical pick-up apparatus which can form a favorable condensing spot with respect to the recording surface of the several information recording medium from which a specification differs can be obtained.
Further, in the invention described in claim 7, in an optical disc apparatus that performs at least one of recording, reproduction, and erasing of information on an information recording medium, the optical pickup device according to claim 6, And processing means for processing a signal of the optical pickup device. With this configuration, it is possible to obtain an optical disc apparatus that stably accesses a plurality of information recording media having different standards.

  As described above, according to the objective lens according to the present invention, it is possible to sufficiently correct aberrations for a plurality of generations having different transparent substrate thicknesses and image-side numerical apertures, and at the same time, it is possible to secure a working distance, and an optical pickup using the same. According to the apparatus and the optical disc apparatus, it is possible to configure a small optical pickup device that can form a good light-converging spot on the recording surfaces of a plurality of information recording media having different standards, and further to a plurality of information recording media having different standards. There is an effect that it is possible to obtain an optical disk apparatus that performs stable access.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing a configuration of an optical pickup device according to an embodiment of the present invention.
As shown in FIG. 1, as a blue optical system, a semiconductor laser 1 in a blue wavelength band, a coupling lens 2, a polarization beam splitter 3, dichroic prisms 23 and 33, a deflection prism 4, a quarter wavelength plate 5, and an opening 6 are used. , Aperture limiting means 7, objective lens 8, detection lens 10, light beam splitting means 11, and photodetector 12.
The DVD optical system includes a hologram unit 21, a coupling lens 22, dichroic prisms 23 and 33, a deflection prism 4, a quarter wavelength plate 5, an opening 6, an aperture limiting unit 7, and an objective lens 8.
The CD optical system includes a hologram unit 31, a coupling lens 32, a dichroic prism 33, a deflection prism 4, a ¼ wavelength plate 5, an opening 6, an aperture limiting unit 7, and an objective lens 8.
As described above, the optical pickup device according to the present embodiment includes the blue optical system, the DVD optical system, and the CD optical system. Among the optical systems, the dichroic prisms 23 and 33, the deflecting prism 4, the quarter wavelength plate 5, the aperture 6, the aperture limiting means 7, and the objective lens 8 are common components of a plurality of optical systems.
The optical disks 9a, 9b and 9c are optical disks having different light source wavelengths, the optical disk 9a is a blue optical disk having a transparent substrate thickness of 0.1 mm, and the optical disk 9b is a DVD optical disk and optical disk having a transparent substrate thickness of 0.6 mm. 9c is a CD-type optical disk having a transparent substrate thickness of 1.2 mm.
The opening 6 can be regulated on a bobbin that holds the objective lens 8 on the actuator that moves the objective lens 8 in the focus direction and the track direction, and it is not necessary to use a specific optical component.

The operation of each blue / DVD / CD optical system will be described below with reference to FIG.
First, the operation of the blue optical system will be described. The linearly polarized divergent light emitted from the semiconductor laser 1 having a wavelength of 405 nm is converted into substantially parallel light by the coupling lens 2, passes through the polarizing beam splitter 3 and the dichroic prisms 23 and 33, and deflects the optical path by 90 degrees. Then, it passes through the quarter-wave plate 5 and becomes circularly polarized light, is limited to NA 0.85 at the opening 6, passes through the aperture limiting means 7, enters the objective lens 8, and is a fine spot on the recording surface of the optical disk 9 a. It is condensed as. Information is recorded, reproduced, or erased by this spot. Further, the light reflected from the optical disk 9a becomes circularly polarized light in the opposite direction to the outward path, is again made substantially parallel light by the objective lens 8, passes through the quarter-wave plate 5 and becomes linearly polarized light orthogonal to the outward path, The light is reflected by the polarization beam splitter 3, is converged by the detection lens 10, is deflected and divided into a plurality of optical paths by the light beam splitting means 11, and reaches the photodetector 12. An information signal and a servo signal are detected from the photodetector 12.

Next, the operation of the DVD optical system will be described.
In FIG. 1, a hologram unit 21 is a unit configured by integrating a semiconductor laser 21a, a hologram 21b, and a photodetector 21c. The linearly polarized divergent light emitted from the chip of the semiconductor laser 21a having a wavelength of 660 nm mounted in the hologram unit 21 is transmitted through the hologram 21b and is made substantially parallel light or predetermined divergent light by the coupling lens 22, and is dichroic. Reflected in the direction of the deflecting prism 4 by the prism 23, the optical path is deflected by 90 degrees by the deflecting prism 4, passes through the quarter-wave plate 5, becomes circularly polarized, passes through the opening 6, and is NA0 in the aperture limiting means 7. .65, the light is incident on the objective lens 8 and is condensed as a minute spot on the recording surface of the optical disk 9b. Information is recorded, reproduced, or erased by this spot. The light reflected from the optical disk 9b is deflected by the polarizing prism 4, reflected by the dichroic prism 23, converged by the coupling lens 22, and divided and diffracted into a plurality of optical paths by the hologram 21b to be light in the hologram unit 21. It reaches the detector 21c. An information signal and a servo signal are detected from the photodetector 21c.
Next, the operation of the CD optical system will be described.
In FIG. 1, a hologram unit 31 is a unit configured by integrating a semiconductor laser 31a, a hologram 31b, and a photodetector 31c. The linearly polarized divergent light emitted from the chip of the semiconductor laser 31 a having a wavelength of 785 nm mounted in the hologram unit 31 is transmitted through the hologram 31 b, converted into predetermined divergent light by the coupling lens 32, and deflected by the dichroic prism 33. Reflected in the direction of the prism 4, the optical path is deflected by 90 degrees by the deflecting prism 4, passes through the quarter-wave plate 5, becomes elliptically polarized light or circularly polarized light, passes through the opening 6, and NA0. It is limited to 50, enters the objective lens 8, and is condensed as a minute spot on the recording surface of the optical disk 9c. Information is recorded, reproduced, or erased by this spot. Further, the light reflected from the optical disk 9c is deflected by the polarization prism 4, reflected by the dichroic prism 33, and converged by the coupling lens 32, and divided and diffracted into a plurality of optical paths by the hologram 31b, and is reflected in the hologram unit 31. To the photodetector 31c. An information signal and a servo signal are detected from the photodetector 31c.

Here, the opening limiting means 7 shown in FIG. 1 will be described in detail with reference to FIG.
The blue optical system, DVD optical system, and CD optical system have different optical system magnifications and restricted NA, so that the entrance pupil diameters φ1, φ2, and φ3 incident on the objective lens 8 are not necessarily equal.
Therefore, an opening limiting means 7 as shown in FIGS. 2A to 2C is necessary.
As an example, the aperture limiting means 7 has a configuration having first and second wavelength selective films 13a and 13b. That is, the first wavelength selective film 13a is a film that transmits blue light flux in the light source wavelength band of DVD and reflects light flux in the light source wavelength band of CD, and restricts the NA of the CD.
The second wavelength selective film 13b is a film that transmits a light beam in a blue light source wavelength band and reflects a light beam in a light source wavelength band of DVD and CD, and restricts the NA of the DVD.
Further, it is desirable that the aperture limiting means 7 be movable integrally with the objective lens 8 in order to limit the entrance pupil diameter incident on the objective lens 8, and is mounted on an actuator that moves the objective lens 8 as shown in FIG. It is desirable.
In view of reducing the weight of the movable part in the actuator and reducing the number of assembling steps, it is more preferable to configure the first and second wavelength selective films 13a and 13b described above on the lens surface of the objective lens 8. As another configuration of the aperture limiting means 7, a wavelength-selective diffraction grating may be configured to diffract rather than reflect selectively.

Next, the objective lens according to the present invention, which is a common component for a plurality of optical systems in the optical system of the optical pickup apparatus as described above, will be described in detail.
FIG. 3 is a diagram showing an outline of the objective lens.
As shown in FIG. 3, a resin layer 8b is bonded to the surface of the refractive lens 8a on the light source side, and a blazed diffractive surface is formed on the surface.
A diffraction grating shape called a blazed shape or kinoform has the highest diffraction efficiency and is advantageous as a diffraction grating shape. When optimized for a certain wavelength, the diffraction efficiency at that wavelength is 100% according to the scalar diffraction theory, and a diffraction efficiency of 90% or more can be expected even with a shape approximating this step. The symbol d shown in FIG. 3 is the depth of the blazed grating groove, which affects the diffraction efficiency on the diffraction surface. Since the objective lens 8 is required to have a high transmittance, it is desirable that the diffraction efficiency on the diffraction surface is high.
FIG. 4 is a diagram showing the calculation result of the analysis efficiency based on the scalar diffraction theory.
4 shows a blue color with respect to the grating groove depth d when a glass material (511.396) having a d-line refractive index nd1.511 and an Abbe number νd39.6 is used as the material of the resin layer 8b of the objective lens 8. It is the figure which showed the result of having calculated | required the diffraction efficiency with respect to wavelength (405 nm), DVD (wavelength 660 nm), and CD (wavelength 785 nm) using the scalar diffraction theory.
By setting the grating groove depth d to various depths, primary light and secondary light are generated for each wavelength, and the diffraction efficiency for each diffracted light varies. They are different from each other. Therefore, according to the results shown in FIG. 4, the grating groove depth is such that secondary light is generated for a wavelength of 405 nm, primary light is generated for a wavelength of 660 nm, and primary light is generated for a wavelength of 785 nm. This shows that high diffraction efficiency can be secured for three wavelengths. Specifically, as shown in FIG. 4, the grating groove depth d is preferably about 1.3 to 1.4 μm.
Further, since the material of the refractive lens 8a is glass, a glass material having a higher refractive index can be selected as compared with the case where the material is a resin, and the refractive index changes or expands with respect to environmental changes such as temperature changes. It is possible to suppress the deterioration of aberration due to.
Further, if the surface shape is a spherical lens, it is easy to manufacture. The material used for the resin layer 8b may be a photo-curing resin or a thermosetting resin, and a diffraction surface is formed by forming a diffraction grating shape to be formed on the surface of the resin layer in a mold. Can be obtained.

・・・（数１）
また、回折面による光路差の付加量は、光軸と垂直方向の軸（光軸からの高さ）Ｙ、回折面係数Ｃ１，Ｃ２，Ｃ３，Ｃ４，Ｃ５・・・を用いて次式の光路差関数Φは（数２）で表される。

・・・（数２）
なお、これに用いる回折次数がｍ次であった場合は、ｍ倍する必要がある。 Hereinafter, a specific example of the objective lens used in the optical pickup device of this embodiment will be described.
The objective lens of the present embodiment includes a light source wavelength of 405 nm, a transparent substrate thickness of 0.1 mm, a blue optical disc having a NA of 0.85, a light source wavelength of 660 nm, a transparent substrate thickness of 0.6 mm, and a NA 0.65 DVD optical disc, It is an objective lens used in an optical pickup device for recording and reproducing on three types of optical discs of a CD type optical disc having a light source wavelength of 785 nm, a transparent substrate thickness of 1.2 mm, and an NA of 0.50. Hereinafter, Examples 1-4 of the objective lens will be described in detail.
FIG. 6 is a graph showing the lens data of the objective lens of Example 1 and the third generation on-axis wavefront aberration characteristics.
The lens data of the objective lens of Example 1 is as shown in FIG.
First, the case where it is used for a blue optical disk having a light source wavelength of 405 nm will be described.
FIG. 5 is a schematic diagram of the objective lens.
In the objective lens shown in FIG. 5, the refractive lens 8a is made of HOYA M-NbFD13, and the resin layers 8b and 8b 'bonded to the refractive lens 8a are d-line refractive index nd1.511 and Abbe number. A glass material (511.396) of νd39.6 is used. Further, the aspherical shape of the lens surface includes an axis X in the optical axis direction, an axis Y perpendicular to the optical axis (height from the optical axis), a paraxial radius of curvature R, a conical coefficient K, and aspherical coefficients A and B. , C, D,..., Represented by the following (Equation 1).

... (Equation 1)
Further, the additional amount of the optical path difference due to the diffractive surface is expressed by the following equation using an axis Y (height from the optical axis) Y perpendicular to the optical axis, and diffractive surface coefficients C1, C2, C3, C4, C5. The optical path difference function Φ is expressed by (Expression 2).

... (Equation 2)
In addition, when the diffraction order used for this is m order, it is necessary to multiply by m.

Further, symbols in FIG. 6A will be described.
OBJ means an object point (light source position), which is an infinite system for the blue optical system, and has a radius of curvature RDY and a thickness THI of INFINITY (infinite).
STO is an entrance pupil plane, the radius of curvature is INFINITY, and the thickness THI is set to 0 in design. S2 is a light source side surface of the objective lens, and S5 is a surface of the objective lens on the optical disk side. Specifically, as shown in FIG. 5, the objective lens is composed of four surfaces S2 to S5, and the diffraction surface (S2) formed on the surface of the resin layer 8b, the resin layer 8b, and the refractive surface from the light source side surface, respectively. These are the joint surface (S3) of the lens 8a, the joint surface (S4) of the refractive lens 8a and the resin layer 8b ′, and the surface (S5) of the resin layer 8b ′.
The total thickness of the objective lens is 1.82 mm, and the thickness THI of S5: 1.13965 mm represents the distance on the optical axis from the objective lens to the blue optical disk surface. S6 is the light incident surface of the optical disk, and IMG is the recording surface of the optical disk. The distance between these surfaces, that is, the thickness of the transparent substrate is 0.1 mm. EPD represents the entrance pupil diameter and is 4.14 mm. Note that secondary light is used as diffracted light on the diffraction surface.

Next, a case where the above-described objective lens is used for a DVD optical disk having a light source wavelength of 660 nm will be described with reference to FIG.
The DVD optical system is also an infinite system, and the distance from the object point OBJ to the entrance pupil plane STO is INFINITY. The distance on the optical axis from the objective lens to the DVD optical disk surface is 0.97336 mm. Note that primary light is used as diffracted light on the diffraction surface.
A case where the above-described objective lens is used for a CD optical disk having a light source wavelength of 785 nm will be described with reference to FIG.
The CD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 23 mm. The distance on the optical axis from the objective lens to the CD optical disk surface is 0.871623 mm. Note that primary light is used as diffracted light on the diffraction surface.
FIG. 6B is a graph showing on-axis wavefront aberration characteristics for the blue optical disc, DVD optical disc, and CD optical disc when the objective lens of Example 1 is used.
The wavefront aberration for each optical disk is 0.01λ rms or less, and the lens has good aberration characteristics. Further, a sufficient distance on the optical axis from the objective lens to the surface of each blue / DVD / CD optical disk can be secured.

FIG. 7 is a graph showing the lens data of the objective lens of Example 2 and the third generation on-axis wavefront aberration characteristics.
The lens data of the objective lens of Example 2 is as shown in FIG.
First, the case where it is used for a blue optical disk having a light source wavelength of 405 nm will be described. The schematic diagram of the objective lens is as shown in FIG.
In the objective lens shown in FIG. 5, the refractive lens 8a is made of HOYA M-NbFD13, and the resin layers 8b and 8b 'bonded to the refractive lens 8a are d-line refractive index nd1.511, Abbe number νd39. .6 glass material (511.396) is used.
Further, the added amount of the optical path difference due to the aspherical shape of the lens surface and the diffractive surface is expressed by (Equation 1) and (Equation 2) as in the first embodiment.
Furthermore, symbols in FIG. 7A will be described.
OBJ means an object point (light source position), which is an infinite system for the blue optical system, and has a radius of curvature RDY and a thickness THI of INFINITY (infinite).
STO is the entrance pupil plane, the radius of curvature is INFINITY, and the thickness THI is set to 0 in design. S2 is a light source side surface of the objective lens, and S5 is a surface of the objective lens on the optical disk side. Specifically, as shown in FIG. 5, the objective lens is composed of four surfaces S2 to S5, and the diffraction surface (S2) formed on the surface of the resin layer 8b, the resin layer 8b, and the refractive surface from the light source side surface, respectively. These are the joint surface (S3) of the lens 8a, the joint surface (S4) of the refractive lens 8a and the resin layer 8b ′, and the surface (S5) of the resin layer 8b ′. The total thickness of the objective lens is 1.82 mm, and the thickness THI of S5: 1.07712 mm represents the distance on the optical axis from the objective lens to the blue optical disk surface. S6 is the light incident surface of the optical disk, and IMG is the recording surface of the optical disk. The distance between these surfaces, that is, the thickness of the transparent substrate is 0.1 mm. EPD represents the entrance pupil diameter and is 4.08 mm. Note that secondary light is used as diffracted light on the diffraction surface.

Next, the case where the above-described objective lens is used for a DVD optical disk having a light source wavelength of 660 nm will be described with reference to FIG.
The DVD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 39 mm. The distance on the optical axis from the objective lens to the DVD optical disk surface is 1.08903 mm. Note that primary light is used as diffracted light on the diffraction surface.
A case where the above-described objective lens is used for a CD optical disk having a light source wavelength of 785 nm will be described with reference to FIG.
The CD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 25 mm. The distance on the optical axis from the objective lens to the surface of the CD optical disk is 0.780597 mm. Note that primary light is used as diffracted light on the diffraction surface.
FIG. 7B is a graph showing the on-axis wavefront aberration characteristics for the blue optical disc, DVD optical disc, and CD optical disc when the objective lens of Example 2 is used.
The wavefront aberration for each optical disk is 0.01λ rms or less, and the lens has good aberration characteristics. Further, a sufficient distance on the optical axis from the objective lens to the surface of each blue / DVD / CD optical disc is sufficiently secured.
Further, the objective lens of Example 2 has a wavefront at the best focus position with respect to the center wavelength (405 nm) when the wavelength variation (so-called mode hop) associated with the output change at the time of recording and reproduction at the blue light source is +1 nm. Aberration is suppressed to a very small amount of about 0.001 λrms as a deterioration amount and 0.0025 · m / nm as a variation of the best focus position, and has a sufficient chromatic aberration correction function. As a result, even when this objective lens is used in an optical disc apparatus capable of recording / reproducing, when the recording / reproducing is switched, the light spot on the recording surface of the optical disc becomes defocused and information recording becomes insufficient. There is no problem of being unable to play back.
Furthermore, the objective lens of Example 2 has a wavefront at the best focus position with respect to the wavelength of the center wavelength +5 nm, for example, with respect to the wavelength change of the blue light source due to the temperature change in the light source part and the solid variation of the oscillation wavelength of the light source. Aberration is suppressed to about 0.017λrms and has sufficient aberration characteristics. As a result, there is no problem that the light collection spot on the recording surface of the optical disk deteriorates due to the aberration caused by the wavelength fluctuation, and the information reproduction performance or the like deteriorates.
As described above, in Example 1 and Example 2, the resin layer is bonded to both surfaces of the refractive lens. By adopting a configuration in which the resin layer is bonded to only one surface of the refractive lens, it becomes easier to manufacture the objective lens than to bond the resin layer to both surfaces.

Hereinafter, Example 3 and Example 4 have a configuration in which the resin layer is bonded only to one surface of the refractive lens.
FIG. 9 is a graph showing the lens data of the objective lens of Example 3 and the third generation on-axis wavefront aberration characteristics.
The lens data of the objective lens of Example 3 is as shown in FIG.
First, the case where it is used for a blue optical disk having a light source wavelength of 405 nm will be described. A schematic diagram of the objective lens is shown in FIG.
In the objective lens 8 shown in FIG. 8, the refractive lens 8a is made of HOYA M-NbFD13, and the resin layer 8b bonded to the refractive lens 8a is made of a d-line refractive index nd1.511 and an Abbe number νd39.6. Glass material (511.396).
Further, the added amount of the optical path difference due to the aspherical shape of the lens surface and the diffractive surface is expressed by (Equation 1) and (Equation 2) as in the first embodiment.

Further, symbols in FIG. 9A will be described.
OBJ means an object point (light source position), which is an infinite system for the blue optical system, and has a radius of curvature RDY and a thickness THI of INFINITY (infinite).
STO is the entrance pupil plane, the radius of curvature is INFINITY, and the thickness THI is set to 0 in design. S2 is a surface on the light source side of the objective lens, and S4 is a surface on the optical disc side of the objective lens. Specifically, as shown in FIG. 8, the objective lens is composed of three surfaces S2 to S4, and the diffraction surface (S2) formed on the surface of the resin layer 8b, the resin layer 8b, and the refractive surface from the light source side surface, respectively. These are the cemented surface (S3) of the lens 8a and the surface (S4) of the refractive lens 8a.
As shown in FIG. 9A, in the objective lens 8 of Example 3, the resin layer 8b ′ in the objective lens 8 of Examples 1 and 2 is eliminated, and the surface (S4) of the refractive lens 8a is aspheric. It has a configuration.
The total thickness of the objective lens is 1.81 mm, and the thickness THI of S4: 1.242828 mm represents the distance on the optical axis from the objective lens to the blue optical disk surface. S5 is a light beam incident surface of the optical disk, and IMG is a recording surface of the optical disk, and the distance between these surfaces, that is, the thickness of the transparent substrate is 0.1 mm. EPD represents the entrance pupil diameter and is 4.08 mm. Note that secondary light is used as diffracted light on the diffraction surface.

Next, a case where the above-described objective lens is used for a DVD optical disk having a light source wavelength of 660 nm will be described with reference to FIG.
The DVD optical system is also an infinite system, and the distance from the object point OBJ to the entrance pupil plane STO is INFINITY. The distance on the optical axis from the objective lens to the DVD optical disk surface is 1.03304 mm. Note that primary light is used as diffracted light on the diffraction surface.
A case where the above-described objective lens is used for a CD-type optical disk having a light source wavelength of 785 nm will be described with reference to FIG.
The CD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 23 mm. The distance on the optical axis from the objective lens to the surface of the CD optical disk is 0.948916 mm. Note that primary light is used as diffracted light on the diffraction surface.
FIG. 9B is a graph showing on-axis wavefront aberration characteristics with respect to a blue optical disc, a DVD optical disc, and a CD optical disc when the objective lens of Example 3 is used.
The wavefront aberration for each optical disk is 0.01λ rms or less, and the lens has good aberration characteristics. Further, a sufficient distance on the optical axis from the objective lens to the surface of each blue / DVD / CD optical disc is sufficiently secured.

FIG. 10 is a graph showing the lens data of the objective lens of Example 4 and the third generation on-axis wavefront aberration characteristics.
The lens data of the objective lens of Example 4 is as shown in FIG.
First, the case where it is used for a blue optical disk having a light source wavelength of 405 nm will be described. The schematic diagram of the objective lens is as shown in FIG.
In the objective lens 8 shown in FIG. 8, the refractive lens 8a is made of HOYA M-NbFD13, and the resin layer 8b bonded to the refractive lens 8a is made of a d-line refractive index nd1.511 and an Abbe number νd39.6. Glass material (511.396). Further, the added amount of the optical path difference due to the aspherical shape of the lens surface and the diffractive surface is expressed by (Equation 1) and (Equation 2) as in the first embodiment.
Further, symbols in FIG. 10A will be described.
OBJ means an object point (light source position), which is an infinite system for the blue optical system, and has a radius of curvature RDY and a thickness THI of INFINITY (infinite).
STO is the entrance pupil plane, the radius of curvature is INFINITY, and the thickness THI is set to 0 in design. S2 is a surface on the light source side of the objective lens, and S4 is a surface on the optical disc side of the objective lens. Specifically, as shown in FIG. 10, the objective lens is composed of three surfaces S2 to S4, and the diffraction surface (S2) formed on the surface of the resin layer 8b, the resin layer 8b, and the refraction from the light source side surface, respectively. These are the cemented surface (S3) of the lens 8a and the surface (S4) of the refractive lens 8a.
As shown in FIG. 10A, in the objective lens 8 of Example 4, the resin layer 8b ′ in the objective lens 8 of Examples 1 and 2 is eliminated, and the surface (S4) of the refractive lens 8a is aspherical. It has a configuration. The total thickness of the objective lens is 1.81 mm, and the thickness THI of S4: 1.14736 mm represents the distance on the optical axis from the objective lens to the blue optical disc surface.
S5 is a light beam incident surface of the optical disk, and IMG is a recording surface of the optical disk, and the distance between these surfaces, that is, the thickness of the transparent substrate is 0.1 mm. EPD represents the entrance pupil diameter and is 4.12 mm. Note that secondary light is used as diffracted light on the diffraction surface.

Next, the case where the above-described objective lens is used for a DVD optical disk having a light source wavelength of 660 nm will be described with reference to FIG.
The DVD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 38 mm. The distance on the optical axis from the objective lens to the DVD optical disc surface is 1.16408 mm. Note that primary light is used as diffracted light on the diffraction surface.
Further, the case where the above-described objective lens is used for a CD optical disk having a light source wavelength of 785 nm will be described with reference to FIG.
The CD optical system is a finite system, and the distance from the object point OBJ to the entrance pupil plane STO is about 25 mm. The distance on the optical axis from the objective lens to the surface of the CD optical disk is 0.854384 mm. Note that primary light is used as diffracted light on the diffraction surface.
FIG. 10B is a graph showing on-axis wavefront aberration characteristics with respect to a blue optical disc, a DVD optical disc, and a CD optical disc when the objective lens of Example 4 is used.
The wavefront aberration for each optical disk is 0.01λ rms or less, and the lens has good aberration characteristics. Further, a sufficient distance on the optical axis from the objective lens to the surface of each blue / DVD / CD optical disc is sufficiently secured.
Further, the objective lens of Example 4 has a wavefront at the best focus position with respect to the center wavelength (405 nm) when the wavelength variation (so-called mode hop) associated with the output change at the time of recording and reproduction at the blue light source is +1 nm. The aberration is suppressed to about 0.001λrms as a deterioration amount and −0.0005 · m / nm as a variation of the best focus position, and has a sufficient chromatic aberration correction function.
As a result, even when this objective lens is used in an optical disc apparatus capable of recording / reproducing, when the recording / reproducing is switched, the light spot on the recording surface of the optical disc becomes defocused and information recording becomes insufficient. There is no problem that you can not play.

Furthermore, the objective lens of Example 4 has a wavefront at the best focus position with respect to the wavelength of the center wavelength +5 nm, for example, with respect to the wavelength change of the blue light source due to the temperature change in the light source part and the solid variation of the oscillation wavelength of the light source. Aberration is suppressed to about 0.026λrms and has sufficient aberration characteristics. As a result, there is no problem that the light collection spot on the recording surface of the optical disk deteriorates due to the aberration caused by the wavelength fluctuation, and the information reproduction performance or the like deteriorates.
As described above, by attaching a resin layer to at least one surface of a refractive lens and providing a diffractive surface on its surface, an objective lens that is favorably corrected for aberrations for multiple generations can be realized. It is possible to realize a small optical pickup device that can form a good light-condensing spot on the recording surfaces of different optical disks (information recording media).
Although the embodiments have been described so far with respect to blue / DVD / CD having different transparent substrate thicknesses and image-side numerical apertures, the effects of the present invention are not impaired even if the CD optical system is omitted. Since the function required for the lens is reduced, higher performance can be exhibited for the blue / DVD optical system.

FIG. 11 is a block diagram showing a schematic configuration of an optical disc apparatus which is an optical information processing apparatus in an embodiment of the present invention.
The optical disk apparatus shown in this figure is an apparatus that performs at least one of information recording, reproduction, and erasing using the optical pickup device 50 described above.
As shown in FIG. 11, the signal processing circuit 51, which is a processing means for processing the output of the photodetector for signal detection from the optical pickup device 50, receives the information signal and generates the servo signal. Feedback control to the focus controller 52, the track controller 53, and the actuator driver 54 performs focusing control and tracking control of the objective lens. Similarly, when tilt control of the objective lens is performed, the tilt signal is fed back to the objective lens tilt controller 55 and the objective lens tilt driver 56 to perform tilt control of the objective lens. The output of the light source is also controlled by signals fed back to the laser controller 57 and the laser driver 58.
The optical disk 9 is rotationally controlled using a spindle motor 61 by a signal fed back to the spindle controller 59 and the spindle driver 60.
According to the optical disk apparatus shown in FIG. 11, the optical pickup apparatus and objective lens described above can be used as appropriate, and at least one of information recording, reproduction, and erasing is performed by a signal from the optical pickup apparatus. Therefore, it is possible to stably access a plurality of information recording media having different standards.

Schematic which shows the structure of the optical pick-up apparatus which concerns on embodiment of this invention. The figure explaining an opening restriction | limiting means. The figure which shows schematic structure of an objective lens. The figure which showed the analysis efficiency calculation result by the scalar diffraction theory. The figure which showed the schematic structure of the objective lens, and the relationship of an optical disk. FIG. 4 is a lens data of the objective lens of Example 1 and a third generation on-axis wavefront aberration characteristic diagram. FIG. 6 is a lens data of the objective lens of Example 2 and a third generation on-axis wavefront aberration characteristic diagram. The figure which showed the schematic structure of the objective lens, and the relationship of an optical disk. FIG. 6 is a lens data of the objective lens of Example 3 and a third generation on-axis wavefront aberration characteristic diagram. FIG. 10 is a lens data of the objective lens of Example 4 and a third generation on-axis wavefront aberration characteristic diagram. 1 is a block diagram showing a schematic configuration of an optical disc apparatus that is an optical information processing apparatus in the present embodiment. Schematic which shows the structure of the conventional optical pick-up apparatus.

Explanation of symbols

1, 21a, 31a Semiconductor laser, 2 coupling lens, 3 polarizing beam splitter, 4 deflection prism, 5 1/4 wavelength plate, 6 aperture, 7 aperture limiting means, 8 objective lens, 9a, 9b, 9c optical disc, 10 Detection lens, 11 beam splitting means, 12, 13a, 13b wavelength selective film, 21c, 31c photodetector, 21 hologram unit, 21b, 31b hologram, 22 coupling lens, 23, 33 dichroic prism, 50 optical pickup device, 51 Signal Processing Circuit, 52 Focus Controller, 53 Track Controller, 54 Actuator Driver, 55 Objective Lens Tilt Controller, 56 Objective Lens Tilt Driver, 57 Laser Controller, 58 Laser Driver, 59 Spindle Controller, 60 S Pindle driver, 61 spindle motor

Claims (7)

  An objective lens for condensing incident light beams from a plurality of light sources on a recording surface of an information recording medium, wherein the refractive lens is made of a glass material having a resin layer bonded to at least one surface, and at least one of the resin layer or the refractive lens. An objective lens comprising a diffractive surface formed on two surfaces. _2. The objective lens according to claim 1, wherein incident light beams from the plurality of light sources are configured with wavelengths having a relationship of λ ₁ <λ ₂ <λ ₃ .   The objective lens according to claim 1, wherein the refractive lens has a spherical lens surface shape on at least one side.   The objective lens according to claim 1, wherein a diffraction grating shape on the diffraction surface is a blaze shape. On the diffraction surface, the diffraction orders having the maximum diffraction efficiency among the diffracted lights generated for the respective incident light beams from the plurality of light sources having the wavelengths λ ₁ , λ ₂ , and λ ₃ are m ₁ , m ₂ , and m ₃ . The following conditions

The objective lens according to any one of claims 1 to 4, wherein:   The objective lens according to any one of claims 1 to 5 and a photodetector that receives reflected light from the recording surface of the information recording medium, and emits light beams from a plurality of light sources having different wavelengths. An optical pickup device characterized in that the light is condensed on the recording surface of the information recording medium by the objective lens and the reflected light from the recording surface is received by the photodetector. 7. An optical pickup apparatus that performs at least one of recording, reproduction, and erasing of information with respect to an information recording medium, and an optical pickup apparatus according to claim 6 and processing means for processing a signal of the optical pickup apparatus An optical disc apparatus comprising:

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