JP4433818B2 - Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device - Google Patents

Description

  The present invention relates to an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device.

  In recent years, DVD (digital versatile disc; abbreviated as DVD) is rapidly spreading as an optical information recording medium for recording video information and the like. A DVD can record information of 4.7 GB per surface by using a red semiconductor laser having a wavelength of 650 nm and an objective lens having a numerical aperture (NA) of 0.6 in an optical pickup device mounted on the player. .

  However, since one DVD can record high-definition image information only for about 30 minutes per side, it is pointed out that the capacity is too small to be used as an optical information recording medium in the coming digital high-definition broadcasting era. . Against this background, in recent years, research and development of a high-density recording optical disk system using a blue-violet semiconductor laser with a wavelength of 405 nm and an objective lens with NA of 0.85 has progressed. (Blu-ray Disc; abbreviated as BD) was announced in February 2002. Since the BD has a recording capacity of about 23.3 to 27 GB per side, if it is used, high-definition image information can be recorded for about 2 hours per side.

  By the way, in order to make use of the DVD software assets that already exist in the world, the BD player is additionally required to have a function capable of recording and / or reproducing compatible with the DVD. Therefore, it is difficult to use a single light source, and therefore it is necessary to mount two types of light sources, a blue-violet semiconductor laser for BD and a red semiconductor laser for DVD. This is because the light beam in the short wavelength region has a characteristic that the reflectivity of the intermediate layer of the double-layer disc is low, so that the double-layer disc of DVD cannot be reproduced using the light beam from the blue-violet semiconductor laser. Is.

The applicant of the present application has previously described a patent document as an objective lens for an optical pickup device that is equipped with two types of light sources, a blue-violet semiconductor laser and a red semiconductor laser, and that is compatible with recording and / or reproducing with respect to BD and DVD. The objective lens described in 1 was proposed.
JP 2002-82280 A

  By the way, in BD, since a protective layer (BD: 0.1 mm, DVD: 0.6 mm) thinner than DVD is formed on the information recording surface, spherical aberration is corrected with respect to the protective layer of 0.1 mm (BD). If the protective layer of the objective lens is 0.6 mm (DVD), the spherical aberration changes greatly, and a good spot cannot be formed on the information recording surface of the DVD. Therefore, in the objective lens for the optical pickup device described in Patent Document 1 described above, the wavelength dependency of the diffractive structure formed on the optical surface is used to depend on the difference in the thickness of the protective layer between BD and DVD. By canceling the change in spherical aberration, it is possible to form a good spot on the information recording surface of each optical disc. However, since the wavelength difference between the blue-violet semiconductor laser and the red semiconductor laser is large, if the same order diffracted light is used as a light beam for recording and / or reproduction like this objective lens, sufficient diffraction efficiency can be obtained. There is a problem that you can not.

  FIG. 1 is a graph showing diffraction efficiency of first-order diffracted light when a diffractive structure is blazed at a manufacturing wavelength of 405 nm, blazed at 500 nm, or blazed at 650 nm. Even when blazed at 500 nm, which is an intermediate wavelength between the blue-violet semiconductor laser and the red semiconductor laser, diffraction efficiency in the vicinity of 400 nm and 650 nm can be obtained only about 80%. If sufficient diffraction efficiency cannot be obtained in this way, the spot intensity on the information recording surface becomes weak, which may adversely affect recording and / or reproducing characteristics. In the present specification, “optimizing the diffractive structure at the manufacturing wavelength λB” and “blazing the diffractive structure at the wavelength λB” have the same meaning.

  The present invention has been made in view of the above-described problems. For example, two types of optical information recording media having a different protective layer thickness and a large difference in operating wavelength, such as BD and DVD, can be recorded and compatible. An object of the present invention is to provide an objective lens for an optical pickup device, an optical pickup device, and an optical information recording / reproducing device that can be reproduced.

  Furthermore, the present invention is capable of forming a good spot on each of two types of optical information recording media having different protective layer thicknesses such as BD and DVD and having a large difference in operating wavelength. It is an object of the present invention to provide an objective lens for an optical pickup device, an optical pickup device, and an optical information recording medium that can obtain sufficient diffraction efficiency at the wavelength used for each optical information recording medium.

An objective lens for the optical pickup device according to claim 1, having a first wavelength λ1 (390nm <λ1 <420nm) first light beams to be condensed Thus the first protective layer to be emitted from the first light source reproducing and / or recording of information for the BD, the information for the DVD having a second second light flux Thus the second protective layer to be condensed with the second wavelength λ2 emitted from the light source (640nm <λ1 <670nm) In an objective lens for an optical pickup device for reproducing and / or recording
The objective lens is a single lens,
The objective lens is the largest of the diffracted light generated when the second light beam is incident, with respect to the order n1 of the diffracted light having the maximum light amount among the diffracted light generated when the first light beam is incident. Having a first diffractive structure composed of a plurality of concentric annular zones set so that the order n2 of the diffracted light having a light amount is lower, on at least one optical surface;
n1 and n2 are each an integer other than 0;
As the RMS value when measuring the wavefront aberration in the first numerical aperture within NA1 is 0.07 lambda 1 or less, the n1-order diffracted light on the information recording surface of the BD through the first protective layer condensed, as its RMS value when measuring the wavefront aberration in the second numerical aperture NA2 (NA2 <NA1) in becomes 0.07 lambda 2 or less, the n2-order diffracted light through the second protective layer Condensing on the information recording surface of the DVD ,
It is characterized by satisfying the following formula .
NA1> 0.8 (14)
0.8 <d / f1 <1.6 (15)
Where d is the thickness of the lens on the optical axis of the objective lens, and f1 is the focal length of the objective lens at the first wavelength λ1.

According to the above configuration, spherical aberration that changes due to the difference in thickness between the first protective layer and the second protective layer due to the action as a refractive lens is canceled using the wavelength dependence of the diffractive structure. It can be corrected. Further, in the objective lens for an optical pickup device according to the present invention, when the first numerical aperture NA1 is larger than 0.8 (the expression (14) is satisfied), the lens thickness d on the optical axis of the objective lens is the first It is preferable that the focal length f1 at the wavelength λ1 is determined so as to satisfy the above formula (15). Equation (15) is a condition for ensuring a good image height characteristic for the first light flux, a sufficient manufacturing tolerance for the first light flux, and a sufficient working distance for the second optical information recording medium. If the value of the lens thickness d is larger than the lower limit of the expression (15), the third-order astigmatism component when the image height characteristic is evaluated by wavefront aberration does not become too large, and the fifth-order or higher-order coma aberration component It doesn't get too big. On the other hand, if the lens thickness d on the optical axis is smaller than the upper limit of equation (15), the third-order spherical aberration component, the fifth-order astigmatism component, and the third-order coma when the image height characteristic is evaluated by wavefront aberration. The aberration component and astigmatic difference do not become too large. Further, since the radius of curvature of the optical surface on the light source side does not become too small, the occurrence of coma aberration due to the optical axis shift between the optical surfaces can be suppressed, and sufficient manufacturing tolerance can be secured. In addition, since the lens thickness does not become excessively large, the lens can be reduced in weight, can be driven by a smaller actuator, and can sufficiently secure a working distance with respect to the second optical information recording medium. it can.

  In the present specification, the “objective lens for an optical pickup device” is a collection arranged to face the optical information recording medium at a position closest to the optical information recording medium in a state in which the optical pickup device is loaded. It includes a condensing lens having a light action. In addition, when there is an optical element that is integrated with the above-described condenser lens and can be moved by an actuator, a lens group including the optical element and the above-described condenser lens is referred to as an “optical pickup” in this specification. It becomes an “objective lens for the apparatus”. Therefore, the “objective lens for the optical pickup device” in the present specification may be composed of only the above-described condensing element, or may be composed of a plurality of optical elements including the above-described condensing element. Also good. The “first numerical aperture NA1” is the numerical aperture defined by the standard of the first optical information recording medium, or the recording and / or reproduction of information according to the first wavelength λ1 with respect to the first optical information recording medium. Refers to the numerical aperture of the optical surface closest to the optical information recording medium of the above-described condenser lens, which can obtain a spot diameter necessary for performing the above-described processing, and “second numerical aperture NA2” refers to the second light It is possible to obtain a spot diameter necessary for recording and / or reproducing information according to the numerical aperture defined by the standard of the information recording medium or the second wavelength λ2 with respect to the second optical information recording medium. The numerical aperture of the optical surface located closest to the optical information recording medium of the above-described condenser lens is indicated.

  Further, in this specification, the “optical surface on which a diffractive structure is formed” means an optical surface that has an action of diffracting an incident light beam by providing an amplitude type or phase type Fresnel zone plate on the surface. In the objective lens for an optical pickup device according to the present invention, when there are a region where diffraction occurs and a region where it does not occur on the same optical surface, the region where diffraction occurs. The diffractive structure refers to a region where this diffraction occurs. The shape of the phase type Fresnel zone plate is formed on the surface of the optical surface as a substantially concentric annular zone centered on the optical axis, and each annular zone is sawtooth-shaped (blazed) when the cross section is viewed in a plane including the optical axis. Type) or step-like (binary type) shapes are known, but include such shapes.

  In general, a diffractive structure generates 0th-order diffracted light, ± 1st-order diffracted light, ± 2nd-order diffracted light,..., Innumerable orders of diffracted light. In the case of a blaze type Fresnel zone plate having a diffraction efficiency of a specific order higher than the diffraction efficiency of other orders, or in some cases, a diffraction efficiency of a specific order (eg, + 1st order diffracted light) The shape of the Fresnel zone plate can be set so that is approximately 100%.

  In this specification, “form a good wavefront (or spot) within the first numerical aperture NA1” means that when the wavefront aberration is measured within the first numerical aperture NA1, the RMS value is 0. This is equivalent to being equal to or less than 07λ1, and “forming a good wavefront (or spot) within the second numerical aperture NA2” means that the RMS value is obtained when the wavefront aberration is measured within the second numerical aperture NA2. Is equivalent to 0.07λ2 or less.

If the objective lens for the optical pickup device according to claim 2 is the invention according to claim 1, in said second numerical aperture NA2, the first diffractive structure, the wavelength of the incident light flux becomes longer The spherical aberration has a wavelength dependency such that the spherical aberration changes in the direction of insufficient correction, and satisfies the following expression.
INT ( λ1 · n1 / λ2 ) − ( λ1 · n1 / λ2 )> 0 (4)
However, n1 is an integer of 2 to 10, and INT (λ1 · n1 / λ2) is an integer obtained by rounding off the value of λ1 · n1 / λ2.

  Here, when the first wavelength λ1, the second wavelength λ2, the order n1, and the order n2 satisfy the above-described expression (4), the change in the long wavelength direction of the incident light beam is within the second numerical aperture NA2. By giving the diffractive structure such a dependency that the spherical aberration of the light beam changes in the direction of insufficient correction, a favorable spot can be formed on each optical information recording medium.

An objective lens for an optical pickup device according to a third aspect of the present invention is the objective lens according to the first or second aspect , wherein the first diffractive structure is a blaze structure and the stepped portion is located on the side closer to the optical axis. It preferably has a structure. FIG. 2A shows an example of an objective lens having a blazed structure in which the step portion is located on the side close to the optical axis. As shown in FIG. 2A, the “step portion” refers to a substantially cylindrical surface-shaped portion that is substantially concentric with the optical axis at the boundary between adjacent blazed structures. Also, “the stepped portion is located on the side closer to the optical axis” means that the wavefront transmitting through the outer blazed structure is delayed in phase than the wavefront transmitting through the blazed structure inside the adjacent blazed structure. In addition, it means that a step is formed in the vicinity of the boundary between adjacent blazed structures.

The objective lens for an optical pickup device according to claim 4 is the objective lens according to claim 1 , wherein the first diffractive structure has a long incident light beam wavelength within the second numerical aperture NA2. 2. The objective lens for an optical pickup device according to claim 1 , wherein the spherical aberration has a wavelength dependency such that the spherical aberration changes in an overcorrected direction and satisfies the following expression.
INT ( λ1 · n1 / λ2 ) − ( λ1 · n1 / λ2 ) <0 (8)
However, n1 is an integer of 2 to 10, and INT (λ1 · n1 / λ2) is an integer obtained by rounding off the value of λ1 · n1 / λ2.

  When the first wavelength λ1, the second wavelength λ2, the order n1, and the order n2 satisfy the above equation (8), the spherical aberration within the second numerical aperture NA2 with respect to the change in the long wavelength direction of the incident light beam By providing the diffractive structure with a dependency that changes in the overcorrection direction, a good spot can be formed on each optical information recording medium.

An objective lens for an optical pickup device according to a fifth aspect is the blaze structure according to the third or fourth aspect , wherein the first diffractive structure is a blaze structure and the stepped portion is located on a side far from the optical axis. It has a structure.

  When such a diffractive structure is formed on the optical surface of the objective lens as a blazed structure, it is preferable to have a blazed structure in which the stepped portion is located on the side far from the optical axis as shown in FIG. .

The objective lens for an optical pickup device according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the first diffractive structure is a blaze structure, and the first diffractive structure is formed. The optical surface includes a first region where a blaze structure is formed in which the step portion is located on the side far from the optical axis, and a step portion formed outside the first region is located on the side closer to the optical axis. It is preferable to have two regions.

  A blaze structure in which the step portion is located on the side close to the optical axis is formed in the inner region including the optical axis (“first region” in FIG. 2D), and the outer region (in FIG. 2D) By forming a blazed structure in which the step portion is located on the side far from the optical axis in the “second region”), it is possible to suppress a focus shift due to a wavelength change of the incident light beam.

The objective lens for an optical pickup device according to a seventh aspect is the invention according to any one of the first to sixth aspects, wherein the combination of n1 and n2 is (n1, n2) = (2, 1), (3 , 2), (5,3), it has preferably be either (8,5).

  When the first wavelength λ1 is set to 390 nm to 420 nm which is a use wavelength region of BD and the second wavelength λ2 is set to 640 nm to 670 nm which is a use wavelength region of DVD, as a combination of orders n1 and n2, (n1, n2 ) = (2,1), (3,2), (5,3), (8,5), it is possible to secure a larger diffraction efficiency in each wavelength region used. More preferably, the combination of n1 and n2 is (n1, n2) = (2,1) or (3,2).

An objective lens for an optical pickup device according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein the number of annular zones of the first diffractive structure is within the second numerical aperture NA2. It is preferable that it is 10-60.

  When the number of ring zones of the diffractive structure in the second numerical aperture NA2 is in the range of 10 to 60, spherical aberration that changes due to the difference in thickness between the first protective layer and the second protective layer is improved. It can be corrected. If the number of annular zones is greater than 10, the spherical aberration is sufficiently corrected. If the number of annular zones is less than 60, the spherical aberration is not excessively corrected. Good recording / reproducing characteristics for the recording medium are maintained.

An objective lens for an optical pickup device according to a ninth aspect is the objective lens according to any one of the first to eighth aspects, wherein the second aperture is obtained when the first wavelength λ1 changes within a range of ± 10 nm. The change rate Δ SA / Δλ ( λ RMS / nm) of the spherical aberration of the first diffractive structure within several NA2, the focal length f1 (mm) of the entire objective lens system at the first wavelength λ 1, and The second numerical aperture NA2 satisfies the following expression.
0.03 <( ΔSA / Δλ ) / {(NA2) ⁴ · f1} <0.14 (19)
Furthermore, it is more preferable to satisfy the following formula (19 ′).
0.05 <( ΔSA / Δλ ) / {(NA2) ⁴ · f1} <0.12 (19 ′)

When the first wavelength λ1 changes within a range of ± 10 nm, the change rate ΔSA / Δλ of the spherical aberration of the diffractive structure within the second numerical aperture NA2 is expressed as the focal length f1 of the entire objective lens system at the first wavelength λ1 . By determining the wavelength dependency of the diffractive structure so that the value normalized by the second numerical aperture NA2 falls within the range of (19) and (19 ′), the first protective layer and the second protective layer Spherical aberration that changes due to the difference in thickness can be corrected satisfactorily, so it is good for optical information recording media such as BD and DVD that have different protective layer thicknesses and large wavelength differences Recording / reproduction characteristics can be obtained.

An objective lens for an optical pickup device according to a tenth aspect is the information recording surface of the DVD according to any one of the first to ninth aspects, wherein the objective lens passes through a region outside the second numerical aperture NA2. The reached second light beam preferably has a spherical aberration of 0.07λ2 RMS or more within the first numerical aperture NA1.

  For example, in an optical information recording medium having different numerical apertures such as BD and DVD, it is necessary to switch the aperture according to the numerical aperture. On the other hand, a method of preparing diaphragms corresponding to the respective numerical apertures and switching them mechanically, and a wavelength selection coat that transmits the first wavelength λ1 and blocks the second wavelength λ2 are provided on the optical surface. However, in either case, the cost of the optical pickup device is increased, which is not preferable. Therefore, in the objective lens for the optical pickup device according to the present invention, an area outside the second numerical aperture NA2 that is used only for recording and / or reproduction on the first information recording medium in the area of the optical surface, A spherical surface that is optimized to minimize the spherical aberration with respect to the first wavelength according to the thickness of the first protective layer, and that is large with respect to the second wavelength according to the thickness of the second protective layer. It is preferable to have aberration. According to this configuration, the second light flux that has passed through the region outside the second numerical aperture NA2 and reached the information recording surface of the second information recording medium is 0.07λ2 RMS or more within the first numerical aperture NA1. This is equivalent to the fact that the aperture is automatically switched in accordance with the second numerical aperture NA2.

The objective lens for an optical pickup device according to claim 11 is the invention according to any one of claims 1 to 10 , wherein the optical surface of the objective lens is a center corresponding to the inside of the second numerical aperture NA2. And a peripheral region surrounding the central region and outside the second numerical aperture NA2, wherein the first diffractive structure is formed in the central region, and a second diffractive structure is formed in the peripheral region. It is preferable.

  When the second diffractive structure is formed in the peripheral region outside the second numerical aperture NA2, the characteristics of the objective lens with respect to the first wavelength l1 can be improved. In other words, it is possible to suppress a change in spherical aberration when the first wavelength l1 fluctuates, or to suppress a change in spherical aberration that occurs with a change in temperature of the plastic lens. Further, by optimizing the second diffractive structure at the first wavelength l1, it is possible to ensure high diffraction efficiency of the first wavelength l1.

The objective lens for an optical pickup device according to claim 12 is the invention according to any one of claims 1 to 10 , wherein an optical surface of the objective lens corresponds to an inner side of the second numerical aperture NA2. It is preferable that a central region and a peripheral region surrounding the central region and outside the second numerical aperture NA2 are provided, the first diffractive structure is formed only in the central region, and the peripheral region is a continuous surface. .

  According to the above configuration, the central region is optimized to form a good wavefront for each optical information recording medium by combining the function as the refractive lens and the wavelength dependence of the diffractive structure, In addition, by optimizing the continuous surface of the peripheral region so as to minimize the spherical aberration with respect to the first wavelength according to the thickness of the first protective layer, the information recording surface of each optical information recording medium A good spot can be formed.

An optical pickup device according to a thirteenth aspect includes the objective lens according to any one of the first to twelfth aspects.

An optical information recording / reproducing apparatus according to claim 14 is an optical information supporting the BD and the DVD so that the optical pickup apparatus according to claim 13 and the information signal can be recorded and / or reproduced by the optical pickup apparatus. And a recording medium support means.

  In the present specification, the first optical information recording medium is preferably a BD type optical disk using, for example, a blue-violet laser as a light source, and the second optical information recording medium is a DVD-ROM used exclusively for reproduction, In addition to DVD-Video, it is preferable to include various DVD-type optical disks such as DVD-RAM, DVD-R, and DVD-RW that also serve as playback / recording. Further, in the present specification, the first optical information recording medium may include an optical information recording medium having a protective layer thickness t1 = 0, that is, an optical information recording medium having no protective layer.

  According to the present invention, for example, an objective lens for an optical pickup device capable of recording and / or reproducing two types of optical information recording media having different protective layer thicknesses and large differences in use wavelengths, such as BD and DVD. An optical pickup device and an optical information recording / reproducing device can be provided.

An embodiment of an optical pickup device equipped with an objective lens for an optical pickup device according to the present invention will be described with reference to the drawings. An optical information recording / reproducing apparatus is obtained by adding optical information recording medium supporting means to the following optical pickup apparatuses PU1 to PU3. FIG. 3A shows a first optical pickup device PU1 equipped with the first objective lens OBJ1 for the optical pickup device according to the present invention and capable of recording and / or reproducing BD and DVD in a compatible manner. It is a figure which shows a structure schematically. The optical pickup device PU1 is a BD module MD1 in which a blue-violet semiconductor laser LD1 that emits a 405 nm laser beam and emits a light beam when recording and / or reproducing information on a BD is integrated with a photodetector PD1. , A DVD module MD2 in which a red semiconductor laser LD2 that emits a 655-nm laser beam and emits a 655 nm laser beam when recording and / or reproducing information on a DVD and a photodetector PD2, an objective lens OBJ1, and a polarization It is composed of a beam splitter BS, a collimator lens COL, a stop STO corresponding to a numerical aperture of 0.85, and a biaxial actuator AC. As the blue-violet semiconductor laser LD1, either a semiconductor laser made of a gallium nitride material or a semiconductor laser using second harmonic generation can be used.

  On the optical surface of the objective lens OBJ1 on the semiconductor laser side, as shown in a partially enlarged view 3b of the objective lens OBJ1, a diffractive structure composed of a plurality of concentric annular zones is formed. By utilizing the wavelength dependency of this diffractive structure, the spherical aberration that changes due to the difference in thickness between the protective layer of the BD and the protective layer of the DVD is corrected. Can be condensed so that the light flux from the red semiconductor laser LD2 is within the diffraction limit within the numerical aperture 0.65. Further, in this diffractive structure, the light beam from the red semiconductor laser LD2 is incident on the order n1 of the diffracted light having the maximum light amount among the diffracted light generated when the light beam from the blue-violet semiconductor laser LD1 is incident. Since the order n2 of the diffracted light having the maximum light amount among the diffracted light generated in this case is determined to be lower, sufficient diffraction efficiency can be obtained in each wavelength region. Further, on the optical surface of the objective lens OBJ1 on the semiconductor laser side, the peripheral region having a numerical aperture of 0.65 to 0.85 is optimized so as to minimize the spherical aberration with respect to the BD, and the large spherical aberration with respect to the DVD. Have been to have. When recording and / or reproducing information on a DVD, the peripheral area functions in the same manner as an aperture, so that the optical pickup device PU1 equipped with the objective lens OBJ1 corresponds to BD and DVD. It is not necessary to switch the aperture, and when recording and / or reproducing information on a DVD, all the light flux from the red semiconductor laser LD2 can pass through the aperture STO corresponding to BD. In FIG. 3A, only the light beam corresponding to the numerical aperture of 0.65 is drawn out of the light beam emitted from the red semiconductor laser LD2 and passing through the stop STO corresponding to the BD and entering the objective lens OBJ1. This also applies to FIGS. 4 and 5 described later.

  The objective lens OBJ1 has a flange portion FL having a surface extending perpendicularly to the optical axis, and the objective lens OBJ1 can be attached to the optical pickup device PU1 with high accuracy by the flange portion FL.

In the optical pickup device PU1, when recording and / or reproducing information on the BD, the BD module MD1 is operated to emit the blue-violet semiconductor laser LD1. The divergent light beam emitted from the blue-violet semiconductor laser LD1 passes through the polarization beam splitter BS, becomes a parallel light beam through the collimating lens COL, and then the diameter of the light beam is regulated by the stop STO, and the protective layer of the BD is formed by the objective lens OBJ1. It becomes a spot formed on the information recording surface RL1 through PL1. The objective lens OBJ1 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ1. The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OBJ1, the aperture stop STO, and the collimator lens COL, then becomes a convergent light beam, passes through the polarization beam splitter BS, and then the light from the BD module MD1. It converges on the light receiving surface of the detector PD1. And the information recorded on BD can be read using the output signal of photodetector PD1.

Further, in the optical pickup device PU1, when recording and / or reproducing information with respect to a DVD, the DVD module MD2 is operated to cause the red semiconductor laser LD2 to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the polarization beam splitter BS, becomes a parallel light beam through the collimator lens COL, and then the diameter of the light beam is regulated by the stop STO. This is a spot formed on the information recording surface RL2. The objective lens OBJ1 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ1. The reflected light beam modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OBJ1, the stop STO, and the collimator lens COL, becomes a converged light beam, is reflected by the polarization beam splitter BS, and then is reflected on the DVD module MD2. It converges on the light receiving surface of the photodetector PD2. And the information recorded on DVD can be read using the output signal of photodetector PD2.

  FIG. 4 schematically shows the configuration of a second optical pickup device PU2 equipped with the second objective lens OBJ2 for the optical pickup device according to the present invention and capable of recording and / or reproducing BD and DVD in a compatible manner. FIG.

  The configuration of the objective lens OBJ2 is the same as that of the objective lens OBJ1 in the optical pickup device PU1 except that the divergent light beam from the red semiconductor laser LD2 is incident thereon, and thus detailed description thereof is omitted.

  When recording and / or reproducing information on the BD in the optical pickup device PU2, the BD module MD1 is operated to emit the blue-violet semiconductor laser LD1. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is converted into a parallel light beam through the collimator lens COL, and then transmitted through the polarization beam splitter BS. It becomes a spot formed on the information recording surface RL1 through PL1. The objective lens OBJ1 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ1. The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OBJ1, the stop STO, the polarization beam splitter BS, and the collimating lens COL, and then becomes a convergent light beam, which is reflected by the photodetector PD1 of the BD module MD1. It converges on the light receiving surface. And the information recorded on BD can be read using the output signal of photodetector PD1.

  Further, in the optical pickup device PU2, when recording and / or reproducing information with respect to the DVD, the DVD module MD2 is operated to cause the red semiconductor laser LD2 to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the polarization beam splitter BS, the diameter of the light beam is regulated by the stop STO, and formed on the information recording surface RL2 by the objective lens OBJ1 via the protective layer PL2 of the DVD. Become a spot. The objective lens OBJ1 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ1. The reflected light beam modulated by the information pits on the information recording surface RL2 passes through the objective lens OBJ1 and the stop STO again, is reflected by the polarization beam splitter BS, becomes a convergent light beam, and is reflected by the photodetector PD2 of the DVD module MD2. It converges on the light receiving surface. Then, information recorded on the DVD can be read using the output signal of the photodetector PD2.

  FIG. 5A shows a third optical pickup device PU3 equipped with the third objective lens OBJ3 for the optical pickup device according to the present invention and capable of recording and / or reproducing BD and DVD in a compatible manner. It is a figure which shows a structure schematically. The optical pickup device PU3 includes a laser module LM in which the BD module MD1 and the DVD module MD2 in the optical pickup device PU1 are integrated (a front view thereof is shown in FIG. 5B), and apertures of the objective lenses OBJ1 and BD. It comprises a stop STO corresponding to the number 0.85 and a biaxial actuator AC.

  The laser module LM records and / or reproduces information on the first light emitting point EP1 that emits light and emits a 405 nm laser beam when recording and / or reproducing information on the BD. A second light emitting point EP2 that emits a 655 nm laser light beam, a first light receiving unit DS1 that receives a reflected light beam from the information recording surface RL1 of the BD, and a reflected light beam from the information recording surface RL2 of the DVD. The second light receiving part DS2 and the prism PS are configured, and the distance between the light emitting point EP1 and the light emitting point EP2 is about 100 μm.

  The configuration of the objective lens OBJ3 is the same as that of the objective lens OBJ1 in the optical pickup device PU1 except that divergent light beams from the light emission point EP1 and the light emission point EP2 are incident, and thus detailed description thereof is omitted.

  In the optical pickup device PU3, when recording and / or reproducing information on the BD, the light emitting point EP1 is caused to emit light. The divergent light beam emitted from the light emitting point EP1 is reflected by the prism PS, and the diameter of the light beam is regulated by the stop STO, and then the spot formed on the information recording surface RL1 via the protective layer PL1 of the BD by the objective lens OBJ3. Become. The objective lens OBJ3 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ3. The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective lens OBJ3 and the stop STO, then reflected twice inside the prism PS and condensed on the light receiving unit DS1. And the information recorded on BD can be read using the output signal of light receiving part DS1.

  In the optical pickup device PU3, when information is recorded and / or reproduced on a DVD, the light emitting point EP2 is caused to emit light. The divergent light beam emitted from the light emitting point EP2 is reflected by the prism PS, the diameter of the light beam is regulated by the stop STO, and then the spot formed on the information recording surface RL2 via the protective layer PL2 of the DVD by the objective lens OBJ3. Become. The objective lens OBJ3 is subjected to focus control and tracking control by a biaxial actuator AC arranged around the objective lens OBJ3. The reflected light flux modulated by the information pits on the information recording surface RL2 is transmitted again through the objective lens OBJ3 and the stop STO, then reflected twice inside the prism PS and condensed on the light receiving unit DS2. And the information recorded on DVD can be read using the output signal of light-receiving part DS2.

  In the optical pickup devices PU1 to PU3 described above, each of the objective lenses OBJ1 to OBJ3 has a single lens configuration. However, the refractive lens has a single lens configuration having a positive power, and is disposed on the semiconductor laser side of the refractive lens. A compound type lens having a diffractive structure on the optical surface of this optical element may be used as the objective lenses OBJ1 to OBJ3. When such a compound lens is used as the objective lenses OBJ1 to OBJ3, in order to obtain good tracking characteristics, an optical element in which a refractive lens and a diffractive structure are formed is integrated by bonding a lens frame or a flange portion, and the like. It is preferable that the actuator AC is integrally driven for tracking.

  FIG. 24 shows an example in which a refractive lens L1 and an optical element L2 on which a diffractive structure is formed are integrated by a lens frame B. Further, in FIG. 25, the refractive lens L1, the optical element L2 having a diffractive structure, and a part of the flange portions FL1 and FL2 formed integrally with the optical surface are brought into contact and / or fitted together. An example is shown. In the case of FIG. 24, there is an advantage that the outer diameter of the objective lens can be reduced, and in the case of FIG. B, the number of parts can be reduced, which is advantageous for cost reduction.

(Example)
Next, six examples suitable for the objective lenses OBJ1 to OBJ3 described above are presented. In any of the examples, a BD that has a protective layer with a thickness of 0.1 mm and records and / or reproduces information by a blue-violet semiconductor laser, and a red semiconductor laser that has a protective layer with a thickness of 0.6 mm. It is an objective lens for an optical pickup device that is also used as a DVD for recording and / or reproducing information.

The aspherical surface in each embodiment has a deformation amount from a plane in contact with the apex of the surface as X (mm), a height perpendicular to the optical axis as h (mm), and a radius of curvature as r (mm). And expressed by the following formula 1. Here, κ is a conic coefficient, and A2i is an aspheric coefficient.

Moreover, the diffractive structure in each embodiment is represented by an optical path difference added to the transmitted wavefront by this diffractive structure. This optical path difference occurs when the incident light beam has a wavelength of λ (nm), the height in the direction perpendicular to the optical axis is h (mm), B _2j is an optical path difference function coefficient, and n is a light beam of wavelength λ. When the diffraction order having the maximum amount of light, λB, is the manufacturing wavelength of the diffraction structure, it is expressed by an optical path difference function Φb (mm) defined by

In the lens data table of each example, f1 is the focal length of the entire system at the first wavelength λ1 when BD is used, NA1 is the first numerical aperture when BD is used, and λ1 is the design wavelength when BD is used. 1 wavelength, m1 is the first imaging magnification when using the BD, n1 is the order of the diffracted light having the maximum light amount generated when the first wavelength λ1 is incident, and f2 is the total at the second wavelength λ2 when using the DVD. Focal length of the system, NA2 is the second numerical aperture when using DVD, λ2 is the second wavelength that is the design wavelength when using DVD, m2 is the second imaging magnification when using DVD, and n2 is incident at the second wavelength λ2 In this case, the order of the diffracted light having the maximum light amount, r (mm) is the radius of curvature, d (mm) is the surface separation, Nλ1 is the refractive index at the first wavelength λ1, and Nλ2 is the refractive index at the second wavelength λ2. , Νd represents the Abbe number in the d-line. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).

[Example 1]
FIG. 6A is a lens cross-sectional view showing the objective lens and the BD according to the first embodiment, and FIG. 6B is a lens cross-sectional view showing the objective lens and the DVD according to the first embodiment. The objective lens of Example 1 is a plastic lens suitable as the objective lens OBJ1 described above, and specific lens data is shown in Table 1.

  In the objective lens of Example 1, a diffractive structure having an optical path difference function shown in Table 1 is formed on the entire first surface, and is located on the inner side of the second numerical aperture 0.65 (the height from the optical axis is 0). Is optimized at a wavelength of 410 nm in the central region (region up to 1.165 mm), and at a wavelength of 405 nm in the peripheral region outside the second numerical aperture of 0.65 (region outside the optical axis from 1.165 mm). Optimized with. According to the above configuration, the diffraction efficiency of the third-order diffracted light with respect to the first wavelength in the central region is 99.6%, the diffraction efficiency of the second-order diffracted light with respect to the second wavelength is 95.2%, and 3 for the first wavelength in the peripheral region. The diffraction efficiency of the next-order diffracted light is 100.0%, and all can secure high diffraction efficiency.

  FIG. 7 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 1. FIG. 7A is a spherical aberration at 410 nm, 405 nm, and 400 nm, and FIG. The values of spherical aberration at 660 nm, 655 nm, and 650 nm corresponding to the time of use are shown. As understood from these spherical aberration graphs, in the objective lens of Example 1, the spherical aberration is well corrected within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.65. Further, since the above equation (4) is satisfied, the spherical aberration at 410 nm and 660 nm when the wavelength incident on the design wavelengths of 405 nm and 655 nm is long is undercorrected within the second numerical aperture of 0.65. It has become.

  FIG. 8 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.65 when the DVD is used. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a small light density scattered at a position separated by 20 μm or more from the spot formed by the central area. Thus, even if the light beam from the red semiconductor laser LD2 passes through the stop STO corresponding to BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the photodetector PD2.

[Example 2]
FIG. 9A is a lens cross-sectional view showing the objective lens and the BD according to the second embodiment, and FIG. 9B is a lens cross-sectional view showing the objective lens and the DVD according to the second embodiment. The objective lens of Example 2 is a plastic lens suitable as the objective lens OBJ1 described above, and specific lens data is shown in Table 2.

  In the objective lens of Example 2, a diffractive structure having an optical path difference function shown in Table 2 is formed on the entire first surface, and is located inside the second numerical aperture 0.65 (the height from the optical axis is 0). Is optimized at a wavelength of 380 nm in the central region (region up to 1.355 mm), and a wavelength of 405 nm in the peripheral region outside the second numerical aperture 0.65 (region from the optical axis is 1.355 mm outside). Optimized with. According to the above configuration, the diffraction efficiency of the second-order diffracted light with respect to the first wavelength in the central region is 95.1%, and the diffraction efficiency of the first-order diffracted light with respect to the second wavelength is 90.9%, which corresponds to the first wavelength λ1 in the peripheral region. The diffraction efficiency of the second-order diffracted light is 100.0%, and both can secure high diffraction efficiency.

  FIG. 10 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 2. FIG. 10A is a spherical aberration at 410 nm, 405 nm, and 400 nm, and FIG. 10B is a DVD. The values of spherical aberration at 655 nm, 650 nm, and 645 nm corresponding to the time of use are shown. As understood from the graphs of these spherical aberrations, in the objective lens of Example 2, the spherical aberration is well corrected within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.65. Further, since the above equation (8) is satisfied, the spherical aberration at 410 nm and 655 nm when the wavelength incident on the design wavelengths 405 nm and 650 nm is long is overcorrected within the second numerical aperture 0.65. It has become.

  In the objective lens of Example 2, the focal length of the diffractive structure formed in the central region is set to 12.755 mm so as to satisfy the above formula (9) with respect to the focal length of the entire system at the first wavelength. Set. As a result, the defocus component generated with respect to the wavelength change of the incident light beam from 405 nm to 406 nm is suppressed to 0.001λ RMS, and the blue-violet semiconductor laser exhibits the mode hopping phenomenon when switching from reproduction to recording for BD. Even if it happens, the light condensing performance can be maintained.

  FIG. 11 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.65 when the DVD is used. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a small light density scattered at a position 30 μm or more away from the spot formed by the central area. Thus, even if the light beam from the red semiconductor laser LD2 passes through the stop STO corresponding to BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the photodetector PD2.

[Example 3]
FIG. 12A is a lens cross-sectional view showing the objective lens and BD according to Example 3, and FIG. 12B is a lens cross-sectional view showing the objective lens according to Example 3 and a DVD. The objective lens of Example 3 is a glass lens suitable as the objective lens OBJ1 described above, and specific lens data is shown in Table 3. In the objective lens of Example 3, PG325 (trade name, manufactured by Sumita Optical Co., Ltd.), which is a glass having a transition point lower than that of general molding glass, was used.

  In the objective lens of Example 3, a diffractive structure having an optical path difference function shown in Table 3 is formed on the entire first surface, and is located on the inner side of the second numerical aperture 0.65 (the height from the optical axis is 0). Is optimized at a wavelength of 410 nm in the central region (region up to 1.165 mm), and at a wavelength of 405 nm in the peripheral region outside the second numerical aperture of 0.65 (region outside the optical axis from 1.165 mm). Optimized with. According to the above configuration, the diffraction efficiency of the third-order diffracted light with respect to the first wavelength in the central region is 99.6%, and the diffraction efficiency of the second-order diffracted light with respect to the second wavelength is 95.2%. .

  FIG. 13 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 3. FIG. 13A is a spherical aberration at 410 nm, 405 nm, and 400 nm corresponding to BD use, and FIG. The values of spherical aberration at 660 nm, 655 nm, and 650 nm corresponding to the time of use are shown. As can be understood from these spherical aberration graphs, in the objective lens of Example 3, the spherical aberration is well corrected within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.60. Further, since the above expression (4) is satisfied, the spherical aberration at 410 nm and 660 nm when the wavelength incident on the design wavelengths of 405 nm and 655 nm is long is undercorrected within the second numerical aperture of 0.60. It has become.

  In the objective lens of Example 3, the focal length of the diffractive structure formed in the central region is set to −19.380 mm so as to satisfy the above formula (7) with respect to the focal length of the entire system at the first wavelength. Set to. As a result, the defocus component generated with respect to the wavelength change of the incident light beam from 405 nm to 406 nm is suppressed to 0.002λ RMS, and the blue-violet semiconductor laser causes mode hopping when switching from reproduction to recording for BD. Even in the case of light collection, the light collecting performance can be maintained.

  FIG. 14 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.60 when using a DVD. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a small light density scattered at a position separated by 20 μm or more from the spot formed by the central area. Thus, even if the light beam from the red semiconductor laser LD2 passes through the stop STO corresponding to BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the photodetector PD2.

[Example 4]
FIG. 15A is a lens cross-sectional view showing the objective lens and BD according to the third embodiment, and FIG. 15B is a lens cross-sectional view showing the objective lens and DVD according to the third embodiment. The objective lens of Example 3 is a plastic lens suitable as the objective lens OBJ2 described above, and specific lens data is shown in Table 4.

  In the objective lens of Example 4, the diffractive structure having the optical path difference function shown in Table 4 is inside the second numerical aperture 0.65 of the first surface (a region where the height from the optical axis is 0 to 1.112 mm). ), And this diffractive structure is optimized at a wavelength of 410 nm. According to the above configuration, the diffraction efficiency of the third-order diffracted light with respect to the first wavelength in the central region is 99.6%, and the diffraction efficiency of the second-order diffracted light with respect to the second wavelength is 95.2%. . A peripheral region outside the second numerical aperture of 0.65 (region outside the height from the optical axis of 1.112 mm) is a continuous aspheric surface where no diffractive structure is formed.

  FIG. 16 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 4. FIG. 16A is a spherical aberration at 410 nm, 405 nm, and 400 nm, and FIG. 16B is a DVD. The values of spherical aberration at 660 nm, 655 nm, and 650 nm corresponding to the time of use are shown. As understood from the graphs of these spherical aberrations, in the objective lens of Example 4, the spherical aberration is well corrected within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.60. Further, since the above expression (4) is satisfied, the spherical aberration at 410 nm and 660 nm when the wavelength incident on the design wavelengths of 405 nm and 655 nm is long is undercorrected within the second numerical aperture of 0.60. It has become.

  FIG. 17 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.60 when the DVD is used. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a small light density scattered at a position 30 μm or more away from the spot formed by the central area. Thus, even if the light beam from the red semiconductor laser LD2 passes through the stop STO corresponding to BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the photodetector PD2.

[Example 5]
FIG. 18A is a lens cross-sectional view showing the objective lens and BD according to Example 4, and FIG. 18B is a lens cross-sectional view showing the objective lens according to Example 4 and the DVD. The objective lens of Example 4 is a plastic lens suitable as the objective lens OBJ3 described above, and specific lens data is shown in Table 5.

  In the objective lens of Example 5, a diffractive structure having an optical path difference function shown in Table 4 is formed on the entire first surface, and is located inside the second numerical aperture 0.65 (the height from the optical axis is 0). Is optimized at a wavelength of 410 nm in the central region (region up to 1.221 mm), and at a wavelength of 405 nm in the peripheral region outside the second numerical aperture of 0.65 (region outside the optical axis from 1.221 mm). Optimized with. According to the above configuration, the diffraction efficiency of the third-order diffracted light with respect to the first wavelength in the central region inside the second numerical aperture 0.60 is 99.6%, and the diffraction efficiency of the second-order diffracted light with respect to the second wavelength is 95.2%. In any case, high diffraction efficiency can be secured.

  FIG. 19 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 4. FIG. 19A is a spherical aberration at 410 nm, 405 nm, and 400 nm corresponding to BD use, and FIG. 19B is a DVD. The values of spherical aberration at 660 nm, 655 nm, and 650 nm corresponding to the time of use are shown. As understood from these spherical aberration graphs, in the objective lens of Example 5, the spherical aberration is corrected well within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.65. Further, since the above equation (4) is satisfied, the spherical aberration at 410 nm and 660 nm when the wavelength incident on the design wavelengths of 405 nm and 655 nm is long is undercorrected within the second numerical aperture of 0.65. It has become.

  FIG. 20 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.65 when the DVD is used. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a low light density scattered at a position 25 μm or more away from the spot formed by the central area. Thus, even if the light beam from the light emitting point EP2 passes through the stop STO corresponding to the BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the light receiving unit DS2.

[Example 6]
FIG. 21A is a lens cross-sectional view showing an objective lens and a BD according to Example 6 , and FIG. 21B is a lens cross-sectional view showing an objective lens according to Example 6 and a DVD. The objective lens of Example 6 is a composite lens suitable as the objective lens OBJ1 described above, and specific lens data is shown in Table 6. The objective lens of Example 6 is composed of a glass lens with spherical aberration corrected for BD and a plastic optical element having no power, and an optical surface on the light beam incident surface side of the plastic optical element having no power ( A diffractive structure is formed on the first surface.

  In the objective lens of Example 6, the diffractive structure having an optical path difference function shown in Table 6 is inside the second numerical aperture 0.65 of the first surface (a region where the height from the optical axis is 0 to 1.182 mm). ), And this diffractive structure is optimized at a wavelength of 410 nm. According to the above configuration, the diffraction efficiency of the third-order diffracted light with respect to the first wavelength in the central region is 99.6%, and the diffraction efficiency of the second-order diffracted light with respect to the second wavelength is 95.2%. . The peripheral region outside the second numerical aperture 0.65 (region outside the height from the optical axis from 1.182 mm) is a flat surface on which no diffractive structure is formed.

  FIG. 22 is a graph of chromatic aberration represented by the spherical aberration of the objective lens of Example 6. FIG. 22A is a spherical aberration at 410 nm, 405 nm, and 400 nm, and FIG. 22B is a DVD. The values of spherical aberration at 660 nm, 655 nm, and 650 nm corresponding to the time of use are shown. As understood from these spherical aberration graphs, in the objective lens of Example 5, the spherical aberration is corrected well within the first numerical aperture of 0.85 when the BD is used due to the action of the diffractive structure formed in the central region. When the DVD is used, the spherical aberration is well corrected within the second numerical aperture of 0.65. Further, since the above equation (4) is satisfied, the spherical aberration at 410 nm and 660 nm when the wavelength incident on the design wavelengths of 405 nm and 655 nm is long is undercorrected within the second numerical aperture of 0.65. It has become.

  FIG. 23 is a diagram showing a spot diagram at the best image plane position within the second numerical aperture 0.65 when the DVD is used. The light beam that has passed through the peripheral area when using the DVD has a large spherical aberration, and becomes a flare component with a small light density scattered at a position separated by 50 μm or more from the spot formed by the central area. Thus, even if the light beam from the red semiconductor laser LD2 passes through the stop STO corresponding to BD, the light beam that has passed through the peripheral region does not adversely affect the light detection characteristics of the photodetector PD2.

Further, λ1 is the wavelength of the first light beam for BD, λ2 is the wavelength of the second light beam for DVD, and λ2 / λ1 is the value of the above embodiment, and f1 is the wavelength λ1 of the first light beam for BD. Table 7 shows the values of f1 / f _{D in} the above example when f is the focal length (mm) of the objective lens system and f _D is the focal length (mm) of the first diffractive structure . Further, Table 7 shows values of the above-described embodiment corresponding to the expressions (4) and ( 15 ).

It is a graph which shows the diffraction efficiency of the 1st-order diffracted light at the time of blazing at a diffraction wavelength of 405 nm, blazing at 500 nm, and blazing at 650 nm. It is an example of a sectional view of an objective lens, and the diffraction structure is exaggerated. FIG. 3A shows a first optical pickup device PU1 equipped with the first objective lens OBJ1 for the optical pickup device according to the present invention and capable of recording and / or reproducing BD and DVD in a compatible manner. FIG. 3B is a diagram schematically showing the configuration, and FIG. 3B is a partially enlarged cross-sectional view of the objective lens OBJ1. The figure which shows schematically the structure of 2nd optical pick-up apparatus PU2 which mounts 2nd objective lens OBJ2 for optical pick-up apparatuses by this invention, and can record and / or reproduce BD and DVD compatible. It is. FIG. 5A shows a third optical pickup device PU3 equipped with the third objective lens OBJ3 for the optical pickup device according to the present invention and capable of recording and / or reproducing BD and DVD in a compatible manner. FIG. 5 is a diagram schematically showing the configuration, and FIG. 5B is a front view of the laser module LM. FIG. 6A is a lens cross-sectional view showing the objective lens and the BD according to the first embodiment, and FIG. 6B is a lens cross-sectional view showing the objective lens and the DVD according to the first embodiment. 3 is a graph of chromatic aberration represented by spherical aberration of the objective lens of Example 1. It is a figure which shows the spot diagram in the best image plane position in 2nd numerical aperture 0.65 at the time of DVD use. FIG. 9A is a lens cross-sectional view showing the objective lens and the BD according to the second embodiment, and FIG. 9B is a lens cross-sectional view showing the objective lens and the DVD according to the second embodiment. 6 is a graph of chromatic aberration represented by spherical aberration of the objective lens of Example 2. It is a figure which shows the spot diagram in the best image plane position in 2nd numerical aperture 0.65 at the time of DVD use. FIG. 12A is a lens cross-sectional view showing the objective lens and BD according to Example 3, and FIG. 12B is a lens cross-sectional view showing the objective lens according to Example 3 and a DVD. 6 is a graph of chromatic aberration represented by spherical aberration of the objective lens of Example 3. It is a figure which shows the spot diagram in the best image-plane position within 2nd numerical aperture 0.60 at the time of DVD use. FIG. 15A is a lens cross-sectional view showing the objective lens and BD according to the third embodiment, and FIG. 15B is a lens cross-sectional view showing the objective lens and DVD according to the third embodiment. 10 is a graph of chromatic aberration represented by spherical aberration of the objective lens in Example 4. It is a figure which shows the spot diagram in the best image-plane position within 2nd numerical aperture 0.60 at the time of DVD use. FIG. 18A is a lens cross-sectional view showing the objective lens and BD according to Example 4, and FIG. 18B is a lens cross-sectional view showing the objective lens according to Example 4 and the DVD. 10 is a graph of chromatic aberration represented by spherical aberration of the objective lens in Example 4. It is a figure which shows the spot diagram in the best image plane position in 2nd numerical aperture 0.65 at the time of DVD use. FIG. 21A is a lens cross-sectional view showing an objective lens and a BD according to Example 5, and FIG. 21B is a lens cross-sectional view showing an objective lens according to Example 5 and a DVD. 10 is a graph of chromatic aberration represented by spherical aberration of the objective lens in Example 6. It is a figure which shows the spot diagram in the best image plane position in 2nd numerical aperture 0.65 at the time of DVD use. 3 is a cross-sectional view showing a lens in which a refractive lens L1 and an optical element L2 having a diffractive structure are integrated by a lens frame B. FIG. A refractive lens L1, an optical element L2 having a diffractive structure, and a lens integrated with the optical surface by abutting and / or fitting a part of the disturbance portion FL1, FL2 formed integrally with the optical surface. It is sectional drawing shown. It is a figure which shows an example of the spherical aberration figure of the objective lens of this invention.

Explanation of symbols

MD1 BD module (first light source)
MD2 DVD module (second light source)
LM Laser module BS Beam splitter COL Collimating lens STO Aperture OBJ1 to OBJ3 Objective lens AC Actuator

Claims (14)

Reproducing and / or recording of information for the BD having a first wavelength λ1 (390nm <λ1 <420nm) first light beams to be condensed Thus the first protective layer that is emitted from the first light source, second light source the second wavelength emitted from λ2 (640nm <λ1 <670nm) the second objective lens for the optical pickup device for reproducing and / or recording of information for DVD having a light beam to be condensed Thus the second protective layer In
The objective lens is a single lens,
The objective lens is the largest of the diffracted light generated when the second light beam is incident, with respect to the order n1 of the diffracted light having the maximum light amount among the diffracted light generated when the first light beam is incident. Having a first diffractive structure composed of a plurality of concentric annular zones set so that the order n2 of the diffracted light having a light amount is lower, on at least one optical surface;
n1 and n2 are each an integer other than 0;
As the RMS value when measuring the wavefront aberration in the first numerical aperture within NA1 is 0.07 lambda 1 or less, the n1-order diffracted light on the information recording surface of the BD through the first protective layer condensed, as its RMS value when measuring the wavefront aberration in the second numerical aperture NA2 (NA2 <NA1) in becomes 0.07 lambda 2 or less, the n2-order diffracted light through the second protective layer Condensing on the information recording surface of the DVD ,
An objective lens for an optical pickup device that satisfies the following formula .
NA1> 0.8 (14)
0.8 <d / f1 <1.6 (15)
Where d is the thickness of the lens on the optical axis of the objective lens, and f1 is the focal length of the objective lens at the first wavelength λ1. Within the second numerical aperture NA2, the first diffractive structure has the wavelength dependence of spherical aberration such that the spherical aberration changes in the direction of insufficient correction when the wavelength of the incident light beam becomes long. The objective lens for an optical pickup device according to claim 1 , wherein:
INT ( λ1 · n1 / λ2 ) − ( λ1 · n1 / λ2 )> 0 (4)
However, n1 is an integer of 2 to 10, and INT (λ1 · n1 / λ2) is an integer obtained by rounding off the value of λ1 · n1 / λ2. 3. The objective lens for an optical pickup device according to claim 1, wherein the first diffractive structure is a blazed structure, and has a blazed structure in which a step portion is located on a side close to the optical axis. Within the second numerical aperture NA2, the first diffractive structure has a wavelength dependency of the spherical aberration such that the spherical aberration changes in the overcorrection direction when the wavelength of the incident light beam becomes long. The objective lens for an optical pickup device according to claim 1 , wherein:
INT ( λ1 · n1 / λ2 ) − ( λ1 · n1 / λ2 ) <0 (8)
However, n1 is an integer of 2 to 10, and INT (λ1 · n1 / λ2) is an integer obtained by rounding off the value of λ1 · n1 / λ2. 5. The objective lens for an optical pickup device according to claim 3, wherein the first diffractive structure is a blazed structure and has a blazed structure in which a step portion is located on a side far from the optical axis. The first diffractive structure is a blazed structure, and the optical surface on which the first diffractive structure is formed includes a first region in which a blazed structure in which a step portion is located on a side far from the optical axis is formed, and 6. The optical pickup device according to claim 1, wherein the step portion formed outside the first region has a second region located on a side close to the optical axis. Objective lens. The combination of n1 and n2, (n1, n2) = ( 2,1), (3,2), (5,3), 1~ claims, characterized in that either (8,5) 7. The objective lens for an optical pickup device according to claim 6 . 8. The optical pickup device according to claim 1 , wherein the number of annular zones of the first diffractive structure is in a range of 10 to 60 in the second numerical aperture NA2. Objective lens. The change rate Δ SA / Δλ ( λ RMS / nm) of the spherical aberration of the first diffractive structure within the second numerical aperture NA2 when the first wavelength λ1 changes within a range of ± 10 nm, the objective lens focal length of the entire system f1 at the first wavelength lambda 1 (mm), and the second numerical aperture NA2 is according to any one of claims 1-8, characterized in that the following expression is satisfied Objective lens for optical pickup device.
0.03 <( ΔSA / Δλ ) / {(NA2) ⁴ · f1} <0.14 (19) The second the second light flux from the numerical aperture NA2 passes through the outer region reaches the information recording surface of the DVD is to have a 0.07 lambda 2RMS more spherical aberration in the first numerical aperture NA1 The objective lens for an optical pickup device according to claim 1 , wherein the objective lens is an optical pickup device. The optical surface of the objective lens has a central region corresponding to the inside of the second numerical aperture NA2, and a peripheral region surrounding the central region and outside of the second numerical aperture NA2, and the first diffractive structure is The objective lens for an optical pickup device according to claim 1 , wherein the objective lens is formed in a central region and a second diffractive structure is formed in the peripheral region . The optical surface of the objective lens has a central region corresponding to the inside of the second numerical aperture NA2, and a peripheral region surrounding the central region and outside the second numerical aperture NA2, and the first diffractive structure is the only formed in the central region, the objective lens for the optical pickup device written in any one of claims 1 to 10, wherein the peripheral region is a continuous surface.   An optical pickup device comprising the objective lens according to claim 1. 14. An optical pickup device according to claim 13, and an optical information recording medium support means for supporting the BD and the DVD so that an information signal can be recorded and / or reproduced by the optical pickup device. Optical information recording / reproducing apparatus.

Images