JP2009037717A - Objective optical element and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low cost optical pickup device which is compatible with four types of optical disks without using a complicated mechanism and to provide an objective optical element. <P>SOLUTION: An optical plane of a first lens is divided into a plurality of zones concentric on the optical axis, and the plurality of zones include at least a first area for optical disk for condensing a light beam with a wavelength λ1 onto an information recording surface of the first optical disk and at least a second area for optical disk for condensing the light beam with the wavelength λ1 onto an information recording surface of the second optical disk. The optical plane of the second lens is divided into a plurality of zones concentric on the optical axis and the central zone including the optical axis for the plurality of zones condenses the light beam with a wavelength λ2 onto an information recording surface of the third optical disk and condenses the light beam with a wavelength λ3 onto an information recording surface of the fourth optical disk. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an objective optical element capable of recording and / or reproducing information interchangeably with different types of optical discs.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. Such an optical disk is called a high density optical disk.

  Also, given the reality that DVDs and CDs (compact discs) on which a wide variety of information is recorded are currently being sold, information can be appropriately recorded on as many different types of optical discs as possible with a single player. It is desired to enable reproduction. Furthermore, considering that the optical pickup device is mounted on a notebook personal computer or the like, it is not only necessary to have compatibility with a plurality of types of optical discs, but it is important to further promote downsizing.

  Here, in the optical pickup device, it is preferable to realize compactness if it is possible to use different optical disks interchangeably using a single objective lens. However, considering the specifications of the high-density optical disk, it is technically difficult to use the objective lens in common, which may increase the cost. In particular, BD and HD use light beams having the same wavelength even though the protective substrate thickness is different, so that aberration correction cannot be performed using a diffractive structure, and it is difficult to share an objective lens. There is.

In an optical pickup device, there is an attempt to use two objective lenses in order to achieve both “compatibility” and “compact” for four different types of optical disks and to obtain more preferable optical performance. In such an attempt, since the numerical aperture is close, it is conceivable to use two objective lenses dedicated for BD and HD / DVD / CD shared objective lenses. However, as described in Patent Document 1, since the wavelength of the light beam used in the BD and the wavelength of the light beam used in the HD are the same, the light beam emitted from the blue-violet semiconductor laser is converted into the objective for the BD. A configuration in which the lens and the objective lens shared by HD / DVD / CD are distributed is necessary.
JP 2007-4875 A Japanese Patent Application Publication No. 2007-18856 JP 2007-73173 A JP 2007-26540 A

  Here, since the optical pickup device described in Patent Document 1 requires a liquid crystal to distribute the light flux, it requires power supply, electrical control, etc., which complicates the mechanism and increases the cost. There is a problem of end. In addition, since the optical pickup devices described in Patent Documents 2 to 4 use a special polarization method for distributing the light flux, there is a problem that the configuration is complicated, adjustment errors are likely to occur, and reproducibility is reduced. .

  The present invention has been made in consideration of the above-described problems, and an object of the present invention is to provide an objective optical element and an optical pickup device that can be compatible with four types of optical disks at low cost without using a complicated mechanism. To do.

The optical element according to claim 1 includes a single or a plurality of light sources, a first objective lens unit, and a second objective lens unit, and the first objective lens unit has a light flux having a wavelength λ1 having a thickness t1. Condensing on the information recording surface of the first optical disc having the protective layer, and condensing the light beam having the wavelength λ1 on the information recording surface of the second optical disc having the protective layer of thickness t2 (t1 <t2). Information is recorded and / or reproduced by the second objective lens unit on the information recording surface of the third optical disc having a protective layer having a thickness of t3 (t3 ≧ t2) with a light beam of wavelength λ2 (λ1 <λ2). Information is recorded and / or reproduced by condensing the light beam having the wavelength λ3 (λ2 ≦ λ3) onto the information recording surface of the fourth optical disc having a protective layer having a thickness t4 (t3 <t4). In an optical element for an optical pickup device that performs
The optical element is a combination of the first objective lens part and the second objective lens part,
The optical surface of the first lens unit has a plurality of concentric annular zones centered on the optical axis, and the plurality of annular zones pass the light beam having the wavelength λ1 passing through the information recording surface of the first optical disc. At least one first optical disk area where the light beam having the wavelength λ1 condensed and passed is not condensed on the information recording surface of the second optical disk, and the light beam having the wavelength λ1 passed through is recorded on the information recording medium on the second optical disk. Including at least one second optical disc area in which the light beam having the wavelength λ1 that is condensed on the surface and that has passed therethrough is not condensed on the information recording surface of the first optical disc,
The optical surface of the second lens unit has a plurality of concentric annular zones around the optical axis.

  According to the present invention, the light beam having the wavelength λ1 that has passed through the first optical disk area can be condensed on the information recording surface of the first optical disk, and has passed through the second optical disk area. By condensing the light beam having the wavelength λ1 on the information recording surface of the second optical disc, the light beam having the same wavelength λ1 can be distributed using the same first objective lens unit. The utilization efficiency of light can be maintained high, and since the ring pitch can be increased, the manufacturability is also improved. The second objective lens unit may focus the light beam having the wavelength λ2 on the information recording surface of the third optical disc, and may focus the light beam having the wavelength λ3 on the information recording surface of the fourth optical disc. Therefore, it is not necessary to provide an optical path switching mechanism, and the apparatus can be reduced in cost and simplified. Furthermore, a part of the optical path of the light beams having the wavelengths λ1 to λ3 can be shared or completely separated, and the degree of freedom in the layout of the optical system is improved. As described above, information can be appropriately recorded / reproduced on any of the four types of optical disks. Further, the optical element of the present invention has a merit that the interval between the lenses can be narrowed since the flange portion can be made common as compared with the case where two lenses molded individually are used. There is also an advantage that assembly adjustment can be simplified and cost can be reduced. The configuration of the second objective lens section may be a type in which the area used for the third optical disk and the area used for the fourth optical disk are divided as in the first objective lens section, but the wavelength λ2 is the wavelength. If it is different from λ3, the diffraction effect can be used effectively, so it is desirable to sort by the diffraction structure.

An optical element according to a second aspect is the optical element according to the first aspect, wherein the light flux having the wavelength λ2 that has passed through the central annular zone including the optical axis of the plurality of annular zones of the second objective lens unit is provided. Condensing on the information recording surface of the third optical disc, and the light beam having the wavelength λ3 that has passed through is condensed on the information recording surface of the fourth optical disc,
Of the plurality of annular zones in the second objective lens section, the annular zone formed outside the central annular zone including the optical axis collects the light flux having the wavelength λ3 on the information recording surface of the third optical disc. Without condensing, the light beam having the wavelength λ4 is condensed on the information recording surface of the fourth optical disc,
Out of the plurality of annular zones in the second objective lens portion, the outer zone formed on the outermost side does not collect the luminous flux having the wavelength λ4 on the information recording surface of the fourth optical disc, but the luminous flux having the wavelength λ3. The light is condensed on the information recording surface of the third optical disc.

  The optical element according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the wavelength λ2 is equal to the wavelength λ3, so that a single light source can be used. Cost reduction and simplification can be achieved.

  The optical element according to claim 4 is the optical element according to claim 1 or 2, wherein the wavelength λ2 is different from the wavelength λ3, and the light source emits a light beam having the wavelength λ2. And a second light-emitting portion that emits a light beam having the wavelength λ3. Therefore, an appropriate condensing spot can be formed using a readily available light source.

  The optical element according to claim 5 is characterized in that, in the invention according to claim 4, the first light emitting part and the second light emitting part are accommodated in the same package. The device can be made compact.

  An optical element according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the number of the plurality of annular zones of the first objective lens portion is an odd number, and the second objective lens portion The number of the plurality of annular zones is an even number.

  The optical element according to claim 7 is the invention according to any one of claims 1 to 5, wherein the number of the plurality of annular zones of the first objective lens unit is an even number, and the optical element of the second objective lens unit is The number of the plurality of annular zones is an odd number.

  An optical element according to an eighth aspect is the invention according to any one of the first to fifth aspects, wherein the number of the plurality of annular zones of the first objective lens section and the plurality of the second objective lens section. The number of annular zones is both an even number.

  An optical element according to a ninth aspect is the invention according to any one of the first to fifth aspects, wherein the number of the plurality of annular zones of the first objective lens portion and the plurality of the second objective lens portions. The number of annular zones is both odd.

According to a tenth aspect of the present invention, in the invention according to the first aspect, the second objective lens unit includes a central region including the optical axis and a peripheral region disposed outside the central region. Divided into at least two regions,
The central region and the plurality of regions each include the plurality of annular zones,
The light beam having the wavelength λ2 that has passed through the central region is condensed on the information recording surface of the third optical disc, and the light beam having the wavelength λ3 that has passed through the central region is collected on the information recording surface of the fourth optical disc. Light
The light beam having the wavelength λ2 that has passed through the peripheral area is collected on the information recording surface of the third optical disc, while the light beam having the wavelength λ3 that has passed through the peripheral region is collected on the information recording surface of the fourth optical disc. It does not shine.

  By configuring the optical element in this way, the effect of improving the mold structure and the adjustment during molding can be obtained.

  An optical element according to an eleventh aspect is the optical element according to the tenth aspect, wherein an optical path difference providing structure for providing an optical path difference according to a wavelength of a light beam passing therethrough is formed in the peripheral region. Therefore, the light flux having the wavelength λ3 that has passed through the peripheral region can be made flare.

  The optical element according to claim 12 is the invention according to any one of claims 1 to 11, wherein the first objective lens part and the second objective lens part are integrally formed by integral molding. Features.

  According to a thirteenth aspect of the present invention, in the invention according to any one of the first to eleventh aspects, the first objective lens portion and the second objective lens portion are engaged and formed integrally. Features.

  The optical element according to claim 14 is characterized in that, in the invention according to claim 13, the first objective lens part is made of glass and the second objective lens part is made of plastic.

  An optical pickup device according to a fifteenth aspect uses the optical element according to any one of the first to fourteenth aspects.

  The optical pickup apparatus of the present invention records and reproduces information in a manner compatible with the first to fourth optical disks. The optical pickup device has at least one light source that emits a light beam having a wavelength λ1 to a wavelength λ3. Further, the optical pickup device condenses the light beam having the wavelength λ1 on the information recording surface of the first optical disc, and collects the light beam having the wavelength λ1 on the information recording surface of the second optical disc; A condensing optical system comprising an optical element having a second objective lens unit that condenses the light beam of λ2 on the information recording surface of the third optical disk and condenses the light beam of wavelength λ4 on the information recording surface of the fourth optical disk Have The optical pickup device also includes a light receiving element that receives each reflected light beam from the information recording surfaces of the first optical disc to the fourth optical disc.

  In addition to the first light source that emits the light beam having the wavelength λ1, the optical pickup device preferably includes a second light source that emits the light beam having the wavelength λ2 and / or a third light source that emits the light beam having the wavelength λ3.

  The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The first optical disc and the second optical disc have the same wavelength of light flux used for recording / reproduction. The first optical disk is preferably a BD and the second optical disk is preferably an HD, but the present invention is not limited to this. When the third optical disk or the fourth optical disk is used, the third optical disk has a protective substrate having a thickness t3 (t2 ≦ t3) and an information recording surface. The fourth optical disc has a protective substrate having a thickness t4 (t3 <t4) and an information recording surface. The third optical disk is preferably a DVD and the fourth optical disk is preferably a CD, but is not limited thereto. The first optical disc, the second optical disc, the third optical disc, or the fourth optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In the BD, information is recorded / reproduced by an objective optical element having an NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm. Furthermore, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like are included. Further, in this specification, a CD is a CD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.45 to 0.51 and the protective substrate has a thickness of about 1.2 mm. It is a generic name and includes CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

  In addition, regarding the thicknesses t1, t2, t3, and t4 of the protective substrate, it is preferable to satisfy the following conditional expressions (1), (2), (3), and (4), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (1)
0.5mm ≦ t2 ≦ 0.7mm (2)
0.5mm ≦ t3 ≦ 0.7mm (3)
1.0mm ≦ t4 ≦ 1.3mm (4)

  In the present specification, the light source such as the first light source, the second light source or the third light source is preferably a laser light source. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used.

  When BD is used as the first optical disk and HD is used as the second optical disk, the wavelength λ1 of the light beam having the wavelength λ1 emitted from the first light source is preferably 380 nm or more and 450 nm or less. When a DVD is used as the third optical disk and a CD is used as the fourth optical disk, the wavelength λ2 of the light beam having the wavelength λ2 emitted from the second light source is preferably 630 nm or more and 670 nm or less, and is emitted from the third light source. The wavelength λ3 of the light beam having the wavelength λ3 is preferably 760 nm or more and 820 nm or less. However, the wavelength λ2 and the wavelength λ3 may be the same wavelength, and recording and / or reproduction of the third optical disc and the fourth optical disc may be performed by a common light source.

  As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the amount of light due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical element for focusing and tracking based on this detection I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving portions corresponding to the respective light sources.

  The condensing optical system has an optical element. The first lens portion of the optical element condenses the light beam having the wavelength λ1 so that information can be recorded / reproduced on the information recording surface of the first optical disk, and the light beam having the wavelength λ1 is formed on the information recording surface of the second optical disk. Light is collected so that information can be recorded / reproduced. The second objective lens portion of the optical element condenses the light beam having the wavelength λ2 so that information can be recorded / reproduced on the information recording surface of the third optical disk, and the light beam of the wavelength λ3 is focused on the information recording surface of the fourth optical disk. The light is collected so that information can be recorded / reproduced. The condensing optical system may include only an optical element, but may include a coupling lens such as a collimator lens or a beam expander in addition to the optical element. The coupling lens is a single lens or a lens group that is disposed between the optical element of the objective lens portion of the optical element and the light source and changes the divergence angle of the light beam. The beam expander is a lens group that is disposed between the objective lens portion of the optical element and the light source and changes the diameter of the light beam without changing the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that changes a light beam incident on the collimating lens into parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be.

  In this specification, the objective lens unit is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. An optical system having The optical element may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like. When the optical element has a plurality of objective lens portions, a glass lens and a plastic lens may be mixed and used. The objective lens portion of the optical element may have an optical path difference providing structure. The objective lens portion of the optical element preferably has an aspheric refractive surface.

In the case where the objective lens portion of the optical element is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.54 to 1.54. The refractive index change rate dN / dT (° C. ⁻¹ ) is −20 × 10 ^{−5 to} −− with respect to the wavelength of 405 nm in accordance with the temperature change in the temperature range of −60 ° C. to 70 ° C. It is more preferable to use a resin material in the range of 5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective lens portion is a plastic lens, the coupling lens is preferably a plastic lens.

  The objective optical element necessary for reproducing and / or recording information on the first optical disk is NA1, and the objective optical necessary for reproducing and / or recording information on the second optical disk is NA1. The image-side numerical aperture of the element is NA2 (NA1> NA2), and the image-side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the third optical disk is NA3 (NA2 ≧ NA3), Let NA4 (NA3> NA4) be the image-side numerical aperture of the objective optical element necessary for reproducing and / or recording information on the fourth optical disk. NA1 is preferably 0.8 or more and 0.9 or less. NA2 and NA3 are preferably 0.55 or more and 0.7 or less. NA4 is preferably 0.4 or more and 0.55 or less.

  The optical surface of the first objective lens portion of the optical element is divided into a first region including at least the optical axis and a second region around the first region. The first region and the second region may have a clear structural difference between the first region and the second region on the optical surface of the objective optical element. On the other hand, the objective optical element may be a convenient area without providing a clear area in terms of configuration. Further, a third region may be further provided around the second region.

  The light beam having the wavelength λ1 that has passed through the first area of the first objective lens unit is used for recording / reproduction of the first optical disk and the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is recorded on the first optical disk. It may be used for / reproduction and not used for recording / reproduction of the second optical disk. In this case, the first area is a so-called shared area (first optical disk area + second optical disk area described later) used for both the first optical disk and the second optical disk, and the second area is the first optical disk. It can be said that this is a so-called dedicated area (first optical disk area to be described later) that is used only for this purpose. The first area is preferably an area of NA2 or less, and the second area is preferably an area larger than NA2 and NA1 or less. For example, when the first optical disk is a BD and the second optical disk is an HD, the first area is preferably an area having an image-side numerical aperture (NA) of 0.65 or less, and the second area is an image. It is preferable that the side numerical aperture is greater than 0.65 and 0.85 or less.

  When the first objective lens unit is viewed from another viewpoint, the optical surface of the objective optical element is divided into a plurality of concentric areas, and the plurality of areas includes at least one first optical disk area and at least one second optical disk. It can be said that it has a use area. The first light flux that has passed through the first optical disk area is condensed so that information can be recorded / reproduced on the information recording surface of the first optical disk, and is not condensed on the information recording surface of the second optical disk. The first light flux that has passed through the second optical disc area is condensed so that information can be recorded / reproduced on the information recording surface of the second optical disc, and is not condensed on the information recording surface of the first optical disc.

  That is, the first light flux that has passed through the first optical disk area has a very small aberration on the information recording surface of the first optical disk, so that information cannot be recorded / reproduced on the information recording surface of the second optical disk. The aberration is large. On the other hand, the first light flux that has passed through the second optical disk area has a large aberration on the information recording surface of the first optical disk so that information cannot be recorded / reproduced. On the information recording surface of the second optical disk, Aberration is very small.

  In addition, the first optical disk area and the second optical disk area are preferably provided alternately, but the present invention is not limited to this. The most central area including the optical axis may be the first optical disk area or the second optical disk area. For example, FIG. 1 shows a first optical disk area BA1 in which the center area including the optical axis is an aspherical refracting surface, and a second optical disk area HA having an optical path difference providing structure therearound. There is a first optical disk area BA2 which is an aspherical refracting surface.

  The first objective lens section preferably has only the first optical disk area and the second optical disk area, but may have at least one shared area. The first light flux that has passed through the common area is focused on the information recording surface of the first optical disc so that information can be recorded / reproduced, and the first light flux that has passed through the common area is the information recording surface of the second optical disc. The light is also collected so that information can be recorded / reproduced. In this case, the shared area is preferably the innermost area including the optical axis.

  In addition, the first objective lens unit may have an optical path difference providing structure for correcting aberration change when temperature changes or wavelength changes. In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

  In this first example, both the first optical disk area and the second optical disk area are preferably refracting surfaces. In this case, the light beam that has passed through the first optical disk area is refracted. The light is condensed on the information recording surface of the first optical disk, and the light beam that has passed through the second optical disk area is condensed on the information recording surface of the second optical disk. Such a configuration is preferable because a loss of light amount can be reduced when reflected light on the information recording surface of the optical disc passes through the correction surface. In this case, a light receiving element having a relatively low sensitivity can be used as the light receiving element, so that the cost of the optical pickup device can be reduced. However, the first objective lens portion is not provided with the first optical disc region and the second optical disc region. Instead, a diffractive structure is provided, and the first light beam passing through the first objective lens portion is diffracted using the diffraction action. Sorting into m-th order diffracted light and n-th order diffracted light, condensing m-th order diffracted light on the information recording surface of the first optical disc, and condensing n-th order diffracted light on the information recording surface of the second optical disc It may be.

  In the first objective lens portion of the objective optical element, a step is provided in the first area of the aspheric surface, thereby dividing it into a plurality of areas (first optical disk area and second optical disk area), and the second area (first optical disk). 1 optical disk area) may be left as a refractive surface. The first optical disk area and the second area (first optical disk area) in the first area are preferably the same aspherical shape, and the second optical disk area is preferably an aspherical shape different from that. .

  Further, from the viewpoint of facilitating the manufacture of the objective optical element, the number of annular zones including the first optical disk area and the second optical disk area of the first objective lens unit may be 3 or more and 10 or less. preferable. When the number of annular zones is 3, for example, the center area including the optical axis is the first optical disk area BA1 as shown in FIG. 1 showing the cross section of the first objective lens portion, and the second optical disk is surrounded by the area. An example in which the area HA and the outermost peripheral area (second area) around the area HA are used as the first optical disk area BA2 can be considered. As a result of diligent research, the present inventor combined the first optical disk area and the second optical disk area from the viewpoint of reducing the side rope of the spot and facilitating the manufacture of the objective optical element. It has been found that the number of ring zones is preferably 5 or more and 10 or less. More preferably, the number of ring zones is 6 or more and 10 or less.

Next, when performing recording / reproduction of the second optical disc, in order to prevent the light flux that has passed through the first optical disc area from falling on the defocus area, the light flux that has passed through the first optical disc area is 2 It is preferable that the first objective lens unit has a flare on the information recording surface of the optical disc. Specifically, “to flare” means that light that has passed through the first optical disk area on the information recording surface of the second optical disk is distributed in the donut-shaped area. In particular, when the first optical disc is a BD and the second optical disc is an HD, it is preferable that the inner diameter of the donut-shaped region be Φ0.030 mm or more. In the case of a plurality of donut-shaped regions, it is preferable that the smallest diameter among the inner diameters of each donut-shaped region is Φ0.030 mm or more. In order to generate a good flare when the first optical disc is a BD and the second optical disc is an HD, the working distance (WD _BD ) of the first objective lens section in the first optical disc (BD). If the value of a difference between a working distance of the first objective lens unit in the second optical disk _{(HD) (WD HD) (} WD BD -WD HD), - 0.36 (mm) or more, 0.17 (mm) The following is preferable. More preferably, it is -0.10 (mm) or more and 0.15 (mm) or less. From another viewpoint, it is preferable that the following conditional expression (5) is satisfied.
2 ・ f1 ・ NA1 '> 2 ・ f2 ・ NA2' (5)
Here, f1 is the focal length of the first optical disk area of the first objective lens section in the light beam of wavelength λ1, f2 is the focal distance of the second optical disk area of the first objective lens section in the light beam of wavelength λ1, and NA1 ′ is the first. The maximum numerical aperture satisfying the sine condition of the first optical disk area of one objective lens unit and the maximum numerical aperture satisfying the sine condition of the second optical disk area of the NA2 ′ object optical element are shown.

  In order to obtain an appropriate spot diameter, the first objective lens unit preferably satisfies the following conditions.

  First, when the region closest to the center including the optical axis is the second optical disc region, it is preferable that the maximum image-side numerical aperture of the first optical disc region is smaller than NA1. The maximum effective diameter of the first optical disk area is preferably smaller than 2 · f1 · NA1. Note that f1 is the focal length of the first optical disk area of the first objective lens portion in the light beam having the wavelength λ1, and NA1 is an image-side aperture defined by the standard that is necessary for recording / reproduction of the first optical disk. Indicates a number. For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the first optical disk area is preferably smaller than 0.85. In addition, it is preferable that the maximum effective diameter of the first optical disk area is smaller than 2 · f1 · 0.85.

  Next, when the area closest to the center including the optical axis is the first optical disk area, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than NA2. Further, it is preferable that the maximum effective diameter of the second optical disk area is smaller than 2 · f2 · NA2. Note that f2 is a focal length of the second optical disk area of the first objective lens unit in the light beam having the wavelength λ1, and NA2 is an image-side aperture defined by the standard necessary for recording / reproducing of the second optical disk. Indicates a number. For example, when the first optical disk is a BD and the second optical disk is an HD, the maximum image-side numerical aperture of the second optical disk area is preferably smaller than 0.65. The maximum effective diameter of the second optical disk area is preferably smaller than 2 · f2 · 0.65.

  Next, as a configuration for improving the off-axis characteristics of the first objective lens portion of the optical element, 1) change the aspherical shape between the first optical disk area and the second optical disk area, or 2) For example, as shown in FIG. 2, a configuration in which an optical path difference providing structure is provided in the second optical disc region is conceivable. Here, to improve the off-axis characteristics means that the wavefront aberration becomes 0.1 RMS or less when the light beam enters the objective optical element at an oblique incidence of 0.5 °.

In the case of the configuration in which the first optical disk area and the second optical disk area have different aspherical shapes in ₁ ), the working distance (WD ₁ ) of the objective optical element during recording / reproduction of the first optical disk and the second optical disk It is preferable that the absolute value (| WD ₁ −WD ₂ |) of the difference from the working distance (WD ₂ ) of the objective optical element at the time of recording / reproducing is 0.1 (mm) or more.

  On the other hand, in order not to cause a large step on the optical surface, it is preferable to provide an off-axis characteristic by providing an optical path difference providing structure in the second optical disc area as in 2). Depending on other design conditions, the above method 1) or 2) may be used properly.

  In the optical surface on the optical disc side of the first objective lens portion of the optical element, a region through which the light beam used for recording / reproduction of the first optical disc passes and a region through which the light beam used for recording / reproduction of the second optical disc passes. It is preferable to use an objective optical element that does not overlap with each other since the loss of light quantity can be reduced. When this viewpoint is emphasized, it is preferable that the number of ring zones is small. For example, it is preferable that the first objective lens unit has three zones. The number of annular zones of the first objective lens portion may be odd or even, and the number of annular zones of the second objective lens portion may be odd or even.

  Further, from the viewpoint of reducing the thickness of the objective optical element, a step is provided on the surface of the optical surface of the first objective lens unit, and the step is closer to the region closer to the optical axis than the region far from the step. Also, it is desirable that the step has a step that shortens the optical path. For example, the example shown in FIG. 3 is an example in which a step for thinning the first objective lens unit is further provided in the first optical disc region, which is the central region, with respect to the first objective lens unit shown in FIG. Even when such a step is provided, it is desirable that the spherical aberration and the sine condition are corrected to a necessary level.

  The step between the first optical disc area and the second optical disc area is not limited to the example shown in FIG. In the case where the first objective lens portion is made of plastic, it may be a step that produces a diffractive action that compensates for a change in spherical aberration caused by a temperature change of the plastic by a change in laser oscillation wavelength accompanying the temperature change. Further, when the first objective lens portion is made of glass, it is easy to obtain a deep step without deteriorating temperature characteristics because the influence of temperature change is small.

The sum Δ of the lengths of coding in the optical axis direction of all the steps provided on the optical surface of the first objective lens part (the sign is a region closer to the optical axis of each step than a region farther from the side. In the case where the optical path is shortened, it is desirable that the following conditional expression (6) is satisfied.
0.1 mm ≦ Δ ≦ 1.0 mm (6)
If it is above the lower limit, the effect of thinning is great, and if it is below the upper limit, the sine condition can be corrected to the required level while reducing the thickness. Note that “the sum of the coding lengths” means that when both a positive length value and a negative length value exist, they are added as they are. For example, if the positive length value is +1 and the negative length value is −0.5, (+1) + (− 0.5) = + 0.5, ie, +0. 5 is “the sum of the lengths of encoding”.

  As shown in FIG. 1, when the first objective lens unit is provided with the first optical disk area and the second optical disk area, a large step (for example, a step of 50 μm or more in the optical axis direction) at the boundary between the areas. May occur. Such a large level difference may interfere with the removal of the first objective lens part from the mold when the first objective lens part is molded using a mold, making it more difficult to manufacture the objective optical element. It will be something. Therefore, when a large step (for example, a step of 50 μm or more in the optical axis direction) occurs at the boundary of each region, the inclined surface is inclined with respect to the optical axis at the step portion so that it can be easily removed from the mold. (Taper) is preferably provided. For example, in the case where the intermediate region has a shape that is recessed in the optical axis direction as shown in FIG. 1, as shown in FIG. 4, only the surface SS1 in which the step surface faces the optical axis is inclined. The surface SS2 in which the step surface faces in the direction opposite to the optical axis is not inclined, so that the influence on the optical performance can be minimized, and the loss of light amount due to the taper can be reduced. It is preferable because it can be easily removed from.

  Furthermore, an optical path difference providing structure for the purpose of correcting the change in aberration that occurs when the temperature or wavelength changes may be superimposed on the structure of the correction surface. One preferred example is a configuration in which an optical path difference providing structure is provided in the first optical disc region of the first objective lens unit for the purpose of correcting a change in aberration that occurs when the temperature or wavelength changes. In the above description, the example in which the optical path difference providing structure is provided on the optical surface on the light source side is described. However, the optical path difference providing structure for the above-described purpose may be provided on the optical surface on the optical disc side. .

  Next, the step amount of the first objective lens portion will be described. Examples of the level difference are roughly divided into three types.

In the first example, the step amount of the step of the first objective lens unit is a step amount that gives an optical path difference of a times the wavelength λ1 to the light beam having the wavelength λ1. Note that a is an arbitrary positive integer other than 0. In this case, the step amount d1 can be expressed by the following equation (7).
d1 = a · λ1 / (n−1) (7)
Here, n is the refractive index of the optical element having a correction surface for the light flux with wavelength λ1.

A second example is a case where the step amount of the first objective lens step is a step amount that gives an optical path difference of b times the wavelength λ1 to the light beam having the wavelength λ1. Note that b is 0 or the sum of any positive integer and x. x is an arbitrary value between 0.4 and 0.6. In this case, the step amount d2 can be expressed by the following equation (8).
d1 = b · λ1 / (n−1) (8)

The third example is a case where the step amount of the step of the first objective lens portion is a step amount that gives an optical path difference c times the wavelength λ1 to the light beam having the wavelength λ1. Note that c is 0 or the sum of any positive integer and y. y is an arbitrary value greater than 0 and less than 0.4 or greater than 0.6 and less than 1. In this case, the step amount d3 can be expressed by the following equation (9).
d1 = c · λ1 / (n−1) (9)

When the first objective lens portion of the optical element of the present invention is applied to a hybrid optical disc in which recording layers of a plurality of types of optical discs including the first optical disc and the second optical disc are laminated on one optical disc, the first optical disc It is preferable that the working distance (WD ₁ ) of the first objective lens portion in the second optical disc is different from the working distance (WD ₂ ) of the first objective lens portion in the second optical disc. When the first optical disc is BD and the second optical disc is HD, that is, when a hybrid optical disc in which BD and HD are laminated is used, it is more preferable to set the value of the difference between these working distances to (WD ₁ −WD ₂ ), preferably 50 μm or more and 250 μm or less. More preferably, it is 100 μm or more and 250 μm or less. An example in which recording layers of a plurality of types of optical disks are stacked on a single optical disk is a hybrid disk in which recording layers of BD / HD / DVDs are stacked on one side as disclosed in JP-A-2007-42254. Can be mentioned.

  The optical surface of the second objective lens unit has a plurality of concentric annular zones around the optical axis. The modes applicable as the second objective lens unit are roughly classified into two types.

  The first aspect is as follows. In the central annular zone including the optical axes of the plurality of annular zones of the second objective lens unit, the light flux having the wavelength λ2 that has passed is condensed on the information recording surface of the third optical disc, and the light flux having the wavelength λ3 that has passed is the fourth. Condensed on the information recording surface of the optical disc. In addition, among the plurality of annular zones in the second objective lens unit, at least one annular zone formed outside the central annular zone including the optical axis transmits a light beam having a wavelength λ3 to the information recording surface of the third optical disc. Without condensing, the light beam of wavelength λ4 is condensed on the information recording surface of the fourth optical disk. Of the plurality of annular zones in the second objective lens section, the outermost annular zone does not collect the light beam having the wavelength λ4 on the information recording surface of the fourth optical disk, and the light beam having the wavelength λ3. Focus on the information recording surface.

  That is, according to the first aspect, the second objective lens unit does not collect the light beam having the wavelength λ3 on the information recording surface of the third optical disk, but condenses the light beam having the wavelength λ4 on the information recording surface of the fourth optical disk. A region for the fourth optical disc, a region for the third optical disc for condensing the light beam of wavelength λ3 on the information recording surface of the third optical disc without condensing the light beam of wavelength λ4 on the information recording surface of the fourth optical disc, and a wavelength of λ3 It can be said that it has a common area for condensing the light beam on the information recording surface of the third optical disk and condensing the light beam of wavelength λ4 on the information recording surface of the fourth optical disk. In this aspect, the third optical disc and the fourth optical disc can be interchanged mainly using the refraction action.

  In the first embodiment, the wavelength λ2 may be equal to the wavelength λ3, and the wavelength λ2 may be different from the wavelength λ3.

    As a second aspect, the second objective lens unit is divided into at least two regions including a central region including the optical axis and a peripheral region disposed outside the central region, the central region and the peripheral region Includes a plurality of ring zones, and the light beam having the wavelength λ2 that has passed through the central region is condensed on the information recording surface of the third optical disc, and the light beam having the wavelength λ3 that has passed through the central region is the information on the fourth optical disc. The light beam having the wavelength λ2 that has been condensed on the recording surface and passed through the peripheral area is condensed on the information recording surface of the third optical disc, while the light beam having the wavelength λ3 that has passed through the peripheral region is focused on the information recording surface of the fourth optical disc. The aspect which does not condense is mentioned. It is preferable that both the central region and the peripheral region of the second objective lens portion have an optical path difference providing structure.

  For example, when a DVD is used as the third optical disk and a CD is used as the fourth optical disk, the central area is preferably an area of NA4 or less. Further, it is preferable that diffracted light is generated when the light beam having the wavelength λ2 and the light beam having the wavelength λ3 pass through the central region, and the same order of diffracted light is generated most in the light beam having the wavelength λ2 and the light beam having the wavelength λ3 It is preferable. Therefore, in this aspect, it is preferable that the third optical disc and the fourth optical disc can be compatible mainly using the diffraction action.

  As shown in FIG. 5, the optical element of the present invention includes a single objective lens OL1 of the present invention for the first optical disk and the second optical disk, an objective lens OL2 for the third optical disk and the fourth optical disk, Are integrally formed. As shown in FIG. 5, the integrally formed objective optical element includes a case where the first objective lens section OL1 and the second objective lens OL2 are fused (for example, the first objective lens section and the second objective lens section). (When an objective optical element having a second objective lens part is obtained by integral molding by injection molding), the first objective lens part and the second objective lens part are separately molded as shown in FIGS. In addition, the optical element may be integrated by being fitted later, bonded, or engaged.

  FIG. 6 shows an example of a lens unit in which the first objective lens unit and the second objective lens unit are integrally formed. The second objective lens OL2 made of plastic forms an opening HL having a stepped portion ST in the rectangular plate-shaped flange portion FL2, and the flange portion FL1 is held by the stepped portion ST in the opening HOL. Thus, the first objective lens portion OL1 made of glass or plastic of the present invention is assembled from the optical axis direction and integrated by bonding or the like, and the first first objective lens portion OL1 and the second objective lens portion are integrated. A lens unit OE in which the lens portions OL2 are arranged in parallel is formed.

  FIG. 7 shows another example of the objective optical element in which the first objective lens unit and the second objective lens unit are integrally formed. The second objective lens portion OL2 made of plastic forms a cutout CT having a stepped portion ST in the rectangular plate-shaped flange portion FL2 so that the flange portion FL1 is held by the stepped portion ST in the cutout CT. Thus, the first objective lens portion OL1 made of glass or plastic of the present invention is assembled from the direction orthogonal to the optical axis and integrated by bonding or the like, and the first objective lens portion OL1 and the second objective lens portion are integrated. A lens unit OE in which OL2 is arranged in parallel is formed.

  As shown in FIG. 8, the flange portion FL1 of the first first objective lens portion OL1 may be supported on the upper surface of the flange portion FL2 without forming the step ST in the opening HL or the notch CT. . Alternatively, as shown in FIG. 9, the first objective lens portion OL1 made of glass or plastic and the second objective lens portion OL2 made of plastic are provided in separate holding members H in the notches CT1 and CT2, respectively. These may be integrated by assembling via the step portions ST1 and ST2. In any case, it is preferable that the holding member has an opening or a notch, and the objective lens unit is fitted therein.

  FIG. 10 shows still another example of an objective optical element that is integrally formed by engaging the first objective lens portion OL1 and the second objective lens portion OL2. The lower side is the optical disc side. The second objective lens portion OL2 is formed integrally with the holding member H, and the second objective lens portion OL1 is inserted into and fixed to the opening of the holding member H. Here, the optical surface of the first objective lens section OL1 includes the first annular zone R1 including the optical axis, and the second annular zone R2, the third annular zone R3, the fourth annular zone R4, in order toward the outside. A fifth annular zone R5 is formed. The first annular zone R1, the third annular zone R3, and the fifth annular zone R5 are on the same aspherical surface AS as indicated by the dotted line, so that the light flux having the wavelength λ1 is condensed on the information recording surface of the BD. This is a so-called first optical disk area. On the other hand, the second annular zone R2 and the fourth annular zone R4 are shaped so as to be retracted toward the optical disk side with respect to the aspherical surface AS, and so-called second so that the light flux having the wavelength λ1 is condensed on the information recording surface of HD. This is an optical disk area.

  The light beam having the wavelength λ1 may be incident on the first objective lens unit as parallel light, or may be incident on the first objective lens unit as divergent light or convergent light. Preferably, the magnification m1 of the light beam having the wavelength λ1 incident on the first objective lens unit satisfies the following formula (11).

−0.02 <m1 <0.02 (11)

  On the other hand, when the light beam having the wavelength λ1 is incident on the first objective lens unit as diverging light, the magnification m1 of the light beam incident on the first objective lens unit of the light beam having the wavelength λ1 satisfies the following formula (12). preferable.

  -0.10 <m1 <0.00 (12)

In order to make the sine condition compatible during both recording / reproduction of the first optical disk and recording / reproduction of the second optical disk, it is preferable to satisfy the following conditional expression (13).
m11 <m12 (13)
Here, m11 represents the magnification of the light beam incident on the first objective lens portion of the light beam having the wavelength λ1 at the time of recording / reproduction of the first optical disk, and m12 represents the wavelength of λ1 at the time of recording / reproduction of the second optical disk. The magnification of the light beam incident on the first objective lens portion of the light beam is shown.

  For example, when recording / reproducing the first optical disk, a light beam having a wavelength λ1 is incident on the first objective lens unit as infinite parallel light, and when recording / reproducing the second optical disk, the light beam having a wavelength λ1 is finite on the first objective lens unit. A preferred example is an embodiment in which the light is incident as convergent light.

  The optical information recording / reproducing apparatus has an optical disc drive apparatus having the optical pickup device described above.

  Here, the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described. The optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out and a system in which the optical disk drive apparatus main body in which the optical pickup device or the like is stored is taken out.

  An optical information recording / reproducing apparatus using each of the above-described methods is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

  In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

  According to the present invention, with a simple and low-cost configuration, without using a complicated mechanism for BD and HD, it is compatible with one objective optical element of BD and HD that uses the same light beam at low cost. In addition, it is possible to provide an optical pickup device and an objective optical element with high light utilization efficiency.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 11 shows information for all of BD (also referred to as first optical disk), HD (also referred to as second optical disk), DVD (also referred to as third optical disk), and CD (also referred to as fourth optical disk). It is a schematic sectional drawing of the optical pick-up apparatus concerning 1st Embodiment which can perform recording / reproduction | regeneration. In the present embodiment, the second semiconductor laser LD2 and the third semiconductor laser LD3 are a so-called two-laser one package 2L1P housed in the same casing.

  The optical element OE (see FIG. 10) integrally including the first objective lens portion OL1 and the second objective lens portion OL2 is supported by the lens holder HLD. The lens holder HLD is movably supported at least two-dimensionally by the actuator ACT. Actuator ACT has actuator base ACTB attached so that position adjustment was possible to the frame (not shown) of an optical pick-up device. As shown in FIG. 10, the first objective lens unit has first optical disk areas R1, R3, R5 and second optical disk areas R2, R4, and the boundary between R5 and R4 is exactly NA 0.65. It is a corresponding position. In addition, the second objective lens portion has an optical path difference providing structure in both the central region and the peripheral region, and the boundary between the central region and the peripheral region is just a position corresponding to NA 0.45.

A case of recording / reproducing information with respect to a BD will be described. In FIG. 11 , a light beam emitted from a first semiconductor laser LD1 (wavelength λ1 = 380 nm to 450 nm) serving as a first light source passes through a beam shaper BS and the shape of the light beam is corrected, and then a first collimator. The light enters the lens CL1 and becomes a parallel light beam. The light beam emitted from the first collimating lens CL1 passes through the first diffraction grating G1.

  The light beam that has passed through the first diffraction grating G1 passes through the first polarizing beam splitter PBS1, passes through the first λ / 4 wavelength plate QWP1, and then passes through the first optical disc region R1, the first objective lens section OL1. The light is condensed by R3 and R5, and is condensed on the information recording surface through a protective layer (thickness t1 = 0.1 mm) of BD to form a condensing spot. The light beam that has passed through the second optical disk area of the first objective lens section OL1 is not condensed on the information recording surface of the BD.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the first objective lens section OL1 and the first λ / 4 wavelength plate QWP1, is reflected by the first polarizing beam splitter PBS1, and further Since the light enters the light receiving surface of the first photodetector PD1 via the one sensor lens SL1, a read signal of information recorded on the BD is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting changes in the shape of the spot on the first photodetector PD1 and changes in the amount of light due to position changes. Based on this detection, the actuator ACT is driven so that the first objective lens section OL1 is moved together with the lens holder HLD so that the light flux from the first semiconductor laser LD1 is imaged on the information recording surface of the BD.

  A case where information is recorded / reproduced with respect to the HD will be described. The light beam emitted from the first semiconductor laser LD1 (wavelength λ1 = 380 nm to 450 nm) as the first light source is incident on the first collimating lens CL1 after passing through the beam shaper BS and correcting the shape of the light beam. And becomes a parallel light flux. The light beam emitted from the first collimating lens CL1 passes through the first diffraction grating G1.

  The light beam that has passed through the first diffraction grating G1 passes through the first polarization beam splitter PBS1, passes through the first λ / 4 wavelength plate QWP1, and then passes through the second optical disc region R2, of the first objective lens section OL1. The light is condensed by R4 and condensed on the information recording surface through an HD protective layer (thickness t2 = 0.6 mm) to form a condensing spot. The light beam that has passed through the first optical disk area of the first objective lens section OL1 is not condensed on the HD information recording surface.

  The light beam modulated and reflected by the information pits on the information recording surface again passes through the first objective lens section OL1 and the first λ / 4 wave plate QWP1, is reflected by the first polarization beam splitter PBS1, and further Since the light is incident on the light receiving surface of the first photodetector PD1 via the one sensor lens SL1, a read signal of information recorded in the HD is obtained using the output signal.

  In addition, focus detection and track detection are performed by detecting changes in the shape of the spot on the first photodetector PD1 and changes in the amount of light due to position changes. Based on this detection, the actuator ACT is driven so that the first objective lens section OL1 is moved together with the lens holder HLD so that the light flux from the first semiconductor laser LD1 is imaged on the information recording surface of HD.

  A case of recording / reproducing information on a DVD will be described. The light beam emitted from the second semiconductor laser LD2 (wavelength λ2 = 600 nm to 700 nm) exits from the two laser 1 package 2L1P, passes through the diffraction correction element DE, and further enters the second collimating lens CL2. Becomes parallel light flux. The light beam emitted from the second collimating lens CL2 passes through the second diffraction grating G2, passes through the second polarizing beam splitter PBS2, passes through the second λ / 4 wavelength plate QWP2, and passes through the second objective. The light is condensed by the lens portion OL2 and is condensed on the information recording surface via the protective layer (thickness t3 = 0.6 mm) of the DVD to form a condensing spot. When the light beam passes through the optical path difference providing structure of the second objective lens unit, the most primary diffracted light is generated in both the central region and the peripheral region, and the primary diffracted light is generated on the information recording surface of the DVD. Condensate.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the second objective lens section OL2 and the second λ / 4 wavelength plate QWP2, is reflected by the second polarizing beam splitter PBS2, and further the second Since the light enters the light receiving surface of the second photodetector PD2 through the sensor lens SL2 and the optical axis correction element SE, a read signal of information recorded on the DVD can be obtained using the output signal.

  Further, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the second photodetector PD2. Based on this detection, the actuator ACT is driven so that the second objective lens section OL2 is moved together with the lens holder HLD so that the light beam from the second semiconductor laser LD2 forms an image on the information recording surface of the DVD.

  A case where information is recorded / reproduced on a CD will be described. A light beam emitted from the third semiconductor laser LD3 (wavelength λ3 = 700 nm to 800 nm) exits from the two laser 1 package 2L1P, passes through the diffraction correction element DE, and further enters the second collimating lens CL2. Becomes parallel light flux. The light beam emitted from the second collimating lens CL2 passes through the second diffraction grating G2, and further passes through the second polarizing beam splitter PBS2.

  The light beam that has passed through the second polarizing beam splitter PBS2 passes through the second λ / 4 wavelength plate QWP2, is condensed by the second objective lens unit OL2, and is protected by a CD protective layer (thickness t4 = 1.2 mm). ) To be focused on the information recording surface through which a condensing spot is formed. When the light beam passes through the optical path difference providing structure of the second objective lens unit, the first-order diffracted light is generated most in the central region, and the first-order diffracted light is condensed on the information recording surface of the CD. On the other hand, the first-order diffracted light is generated most in the peripheral region, but the first-order diffracted light is not condensed on the information recording surface of the CD, but becomes flare.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the second objective lens section OL2 and the second λ / 4 wavelength plate QWP2, is reflected by the second polarizing beam splitter PBS2, and further the second Since the light enters the light receiving surface of the second photodetector PD2 via the sensor lens SL2 and the optical axis correction element SE, a read signal of information recorded on the CD is obtained using the output signal.

  Further, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the second photodetector PD2. Based on this detection, the actuator ACT is driven so that the second objective lens section OL2 is moved together with the lens holder HLD so that the light beam from the third semiconductor laser LD3 forms an image on the information recording surface of the CD.

  FIG. 12 shows information for all of BD (also referred to as first optical disk), HD (also referred to as second optical disk), DVD (also referred to as third optical disk) and CD (also referred to as fourth optical disk). It is a schematic sectional drawing of the optical pick-up apparatus concerning 2nd Embodiment which can perform recording / reproduction | regeneration.

  As shown in FIG. 12, the lens holder HLD that supports the objective optical element OE (see FIG. 10) integrally including the first objective lens portion OL1 and the second objective lens portion OL2 is at least two-dimensionally formed by the actuator ACT. Is movably supported. The actuator ACT is attached to the frame (not shown) of the optical pickup device via the actuator base ACTB.

  A case where information is recorded and / or reproduced on a BD will be described. In FIG. 12, the light beam emitted from the first semiconductor laser LD1 (wavelength λ1 = 380 nm to 450 nm) as the first light source passes through the beam shaper BS, and the shape of the light beam is corrected, and then the first collimator. The light enters the lens CL1 and becomes a parallel light beam. The light beam emitted from the first collimator lens CL1 passes through a diffraction grating G, which is an optical means for separating the light beam emitted from the light source into a main beam for recording / reproducing and a sub beam for detecting a tracking error signal. The light passes through the splitter PBS, the expander lens EXP, the first dichroic prism DP1, and the λ / 4 wavelength plate QWP, and is reflected by the second dichroic prism DP2.

  The light beam reflected by the second dichroic prism DP2 is condensed by the first optical disk area of the first objective lens section OL1, and the information recording is performed via the protective layer (thickness t1 = 0.1 mm) of the BD. The light is focused on the surface and a focused spot is formed here. The light beam that has passed through the second optical disk area of the first objective lens section OL1 is not condensed on the information recording surface of the BD.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the first objective lens section OL1, is reflected by the second dichroic prism DP2, and is reflected by the λ / 4 wavelength plate QWP1 and the first dichroic prism DP1. Then, the light passes through the expander lens EXP, is reflected by the polarization beam splitter PBS, passes through the sensor lens SL, passes through the optical axis correction element SE, and enters the light receiving surface of the photodetector PD. By using this, a read signal of information recorded on the BD is obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT is driven so that the first objective lens section OL1 is moved together with the lens holder HLD so that the light flux from the first semiconductor laser LD1 is imaged on the information recording surface of the BD.

  A case where information is recorded and / or reproduced on the HD will be described. The light beam emitted from the first semiconductor laser LD1 (wavelength λ1 = 380 nm to 450 nm) as the first light source is incident on the first collimating lens CL1 after passing through the beam shaper BS and correcting the shape of the light beam. And becomes a parallel light flux. The light beam emitted from the first collimator lens CL1 passes through a diffraction grating G, which is an optical means for separating the light beam emitted from the light source into a main beam for recording / reproducing and a sub beam for detecting a tracking error signal. The light passes through the splitter PBS, the expander lens EXP, the first dichroic prism DP1, and the λ / 4 wavelength plate QWP, and is reflected by the second dichroic prism DP2.

  The light beam reflected by the second dichroic prism DP2 is condensed by the second optical disk area of the first objective lens section OL1, and the information is recorded through the HD protective layer (thickness t2 = 0.6 mm). The light is focused on the surface and a focused spot is formed here. The light beam that has passed through the first optical disk area of the first objective lens section OL1 is not condensed on the HD information recording surface.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the first objective lens section OL1, is reflected by the second dichroic prism DP2, and is reflected by the λ / 4 wavelength plate QWP1 and the first dichroic prism DP1. Then, the light passes through the expander lens EXP, is reflected by the polarization beam splitter PBS, passes through the sensor lens SL, passes through the optical axis correction element SE, and enters the light receiving surface of the photodetector PD. By using this, a read signal of information recorded in the HD can be obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT is driven so that the first objective lens section OL1 is moved together with the lens holder HLD so that the light flux from the first semiconductor laser LD1 is imaged on the information recording surface of HD.

  A case where information is recorded and / or reproduced on a DVD will be described. The light beam emitted from the second semiconductor laser LD2 (wavelength λ2 = 600 nm to 700 nm) passes through the beam shaper BS, the shape of the light beam is corrected, and then enters the first collimator lens CL1 to become a parallel light beam. . The light beam emitted from the first collimating lens CL1 passes through the diffraction grating G, and further passes through the polarizing beam splitter PBS, the expander lens EXP, the first dichroic prism DP1, and the λ / 4 wavelength plate QWP, and the second dichroic prism DP2. And reflected by the rising mirror M.

  The light beam reflected by the rising mirror M is collected by the second objective lens section OL2 and collected on the information recording surface via the DVD protective layer (thickness t3 = 0.6 mm) and collected here. A light spot is formed. When the light beam passes through the optical path difference providing structure of the second objective lens unit, the most primary diffracted light is generated in both the central region and the peripheral region, and the primary diffracted light is generated on the information recording surface of the DVD. Condensate.

  Then, the light beam modulated and reflected by the information pits on the information recording surface again passes through the second objective lens portion OL2, is reflected by the rising mirror M, and is reflected by the second dichroic prism DP2, the λ / 4 wavelength plate QWP, 1 passes through the dichroic prism DP1 and the expander lens EXP, is reflected by the polarization beam splitter PBS, further passes through the sensor lens SL, passes through the optical axis correction element SE, and enters the light receiving surface of the photodetector PD. Using the output signal, a read signal of information recorded on the DVD can be obtained.

  In addition, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the photodetector PD. Based on this detection, the actuator ACT is driven so that the second objective lens section OL2 is moved together with the lens holder HLD so that the light beam from the second semiconductor laser LD2 forms an image on the information recording surface of the DVD.

  The third semiconductor laser LD3 is a hologram laser, and a laser chip LC as a light source and a photodetector PD3 are packaged. A case where information is recorded and / or reproduced on a CD will be described.

  The light beam emitted from the laser chip LC of the third semiconductor laser LD3 (wavelength λ3 = 700 nm to 800 nm) is reflected by the first dichroic prism DP1 after passing through the second collimating lens CL2 and changing the divergence angle. After that, the light passes through the λ / 4 wavelength plate QWP and the second dichroic prism DP2, is reflected by the rising mirror M, is condensed by the second objective lens section OL2, and is a CD protective layer (thickness t4 = 1) .2 mm) to be focused on the information recording surface to form a focused spot. When the light beam passes through the optical path difference providing structure of the second objective lens unit, the first-order diffracted light is generated most in the central region, and the first-order diffracted light is condensed on the information recording surface of the CD. On the other hand, the first-order diffracted light is generated most in the peripheral region, but the first-order diffracted light is not condensed on the information recording surface of the CD, but becomes flare.

  The light beam modulated and reflected by the information pits on the information recording surface again passes through the second objective lens section OL2, is reflected by the rising mirror M, and passes through the second dichroic prism DP2 and the λ / 4 wavelength plate QWP. Then, the light is reflected by the first dichroic prism DP1, further condensed by the second collimating lens CL2, and incident on the light receiving surface of the photodetector PD3 in the third semiconductor laser LD3. A read signal of information recorded in the information is obtained.

  Further, focus detection and track detection are performed by detecting a change in the amount of light due to a change in the shape and position of the spot on the third photodetector PD3. Based on this detection, the actuator ACT is driven so that the second objective lens section OL2 is moved together with the lens holder HLD so that the light beam from the third semiconductor laser LD3 is imaged on the information recording surface of the CD.

(Example)
Next, examples that can be used in the above-described embodiment will be described. Examples 1 to 5 are lens data of the first objective lens portion having a single lens shape. The lens data of the second objective lens portion to be combined with this can be used in any manner as long as it is a lens compatible with DVD and CD. Here, Examples 1 to 4 are examples in which the working distance of BD is equal to the working distance of HD, and Example 5 is an example in which the working distance of BD is different from the working distance of HD. Among Examples 1 to 5, Examples 1 and 5 are examples of a three-wheel zone, Example 2 is an example of a four-wheel zone, and Example 3 is an example and example of a five-zone. Reference numeral 4 is an example of a six-wheel zone.

In the following tables, ri is the radius of curvature, di is the position in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni is the refractive index of each surface. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E−3). In addition, the optical surface of the objective optical element is formed as an aspherical surface that is symmetric about the optical axis and is defined by mathematical formulas obtained by substituting the coefficients shown in Table 1 into Formula 1.

  Here, X (h) is an axis in the optical axis direction (with the light traveling direction being positive), κ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.

Example 1
In the first embodiment, the center area including the optical axis is the first optical disk area, and from there toward the outside in the optical axis orthogonal direction, the second optical disk area and the second area are sequentially arranged. It is a structure of a three-ring zone in which a region is provided. All the areas have an aspheric shape, and the two first optical disk areas have the same aspheric shape. In addition, the design is easy to manufacture by reducing the amount of step between the central first optical disk area and the outer second optical disk area as much as possible. FIG. 13 shows the lens shape and the light collection state for each of BD and HD. FIG. 13A shows a condensing state for BD, and FIG. 13B shows a condensing state for HD.

  Table 1 shows lens data of Example 1.

(Example 2)
In Example 2, the center area including the optical axis is the second optical disk area, and from there toward the outside in the optical axis orthogonal direction, the first optical disk area, the second optical disk area, This is a four-band structure in which a first optical disk area, which is two areas, is provided. All the regions have an aspheric shape, the two first optical disc regions have the same aspheric shape, and the two second optical disc regions also have the same aspheric shape, The first optical disk area and the second optical disk area have different aspherical shapes. FIG. 14 shows the lens shape and the light collection state for each of BD and HD. FIG. 14A shows a condensing state for BD, and FIG. 14B shows a condensing state for HD. Since the design is based on the first embodiment, the level difference in the optical axis direction is also suppressed.

  Table 2 shows lens data of Example 2.

(Example 3)
In the third embodiment, the center area including the optical axis is the first optical disk area, and from there, the second optical disk area, the first optical disk area, and the second optical disk in this order toward the outside in the optical axis orthogonal direction. This is a five-ring zone structure in which a first optical disk area, which is a second area, is provided. All the regions have an aspheric shape, the three first optical disc regions have the same aspheric shape, and the two second optical disc regions also have the same aspheric shape, The first optical disk area and the second optical disk area have different aspherical shapes. FIG. 15 shows the lens shape and the light collection state for each of BD and HD. FIG. 15A shows a condensing state for BD, and FIG. 15B shows a condensing state for HD. Since the design is based on the first embodiment, the level difference in the optical axis direction is also suppressed.

  Table 3 shows lens data of Example 3.

Example 4
In the fourth embodiment, the center area including the optical axis is the second optical disk area, and from there toward the outside in the optical axis orthogonal direction, the first optical disk area, the second optical disk area, and the first optical disk in order. This is a six-band structure in which an area for the first optical disk, an area for the second optical disk, and an area for the first optical disk as the second area are provided. All the regions have an aspheric shape, the three first optical disc regions have the same aspheric shape, and the three second optical disc regions also have the same aspheric shape, The first optical disk area and the second optical disk area have different aspherical shapes. FIG. 16 shows the lens shape and the light collection state for each of BD and HD. FIG. 16A shows a light collection state for BD, and FIG. 16B shows a light collection state for HD. Since the design is based on the first embodiment, the level difference in the optical axis direction is also suppressed.

  Table 4 shows lens data of Example 4.

(Example 5)
In the fifth embodiment, the center area including the optical axis is the first optical disk area, and from there toward the outside in the optical axis orthogonal direction, the second optical disk area and the second area are sequentially arranged. It is a structure of a three-ring zone in which a region is provided. All the areas have an aspheric shape, and the two first optical disk areas have the same aspheric shape. In addition, the working distance in BD is different from the working distance in HD. FIG. 17 shows the lens shape and the light collection state for each of BD and HD. FIG. 17A shows a condensing state for BD, and FIG. 17B shows a condensing state for HD.

  Table 5 shows lens data of Example 5.

  In Example 1 where the working distance when using BD is the same as the working distance when using HD, a simulation was performed with an incident angle of the light beam of 0.5 when using HD, and the value of wavefront aberration was 0.1622 λrms. It has become. On the other hand, in Example 5 where the working distance when using BD is different from the working distance when using HD, a simulation was performed with an incident angle of the light beam of 0.5 when using HD. It has become. Therefore, it can be seen that the wavefront aberration value of the obliquely incident light beam becomes smaller and the off-axis characteristics become better when the working distance when using BD is different from the working distance when using HD.

  FIG. 18 is a graph showing the relationship between the number of annular zones and the side lobe values in Examples 1 to 4. Table 6 below lists the number of ring zones and side lobe values. As can be seen from FIG. 18 and Table 6, the value of the side lobe decreases as the number of ring zones increases, and it is particularly preferable when the number of ring zones is 5 or 6. Increasing the number of rings more than this has little effect on the side lobe value, but increases the number of rings, making manufacturing difficult, so from the viewpoint of balance between ease of manufacturing and good side lobe Indicates that the number of ring zones is preferably 5 or 6.

  Table 7 shows a summary of spec data such as focal length, spot diameter, Strehl ratio, side lobe, etc. in Examples 1 to 5.

It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the objective optical element which concerns on this invention. It is sectional drawing of an example of the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the objective optical element which concerns on this invention. It is a part of sectional drawing of an example of the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the objective optical element which concerns on this invention. It is a schematic perspective view of an example of the objective optical element which concerns on this invention. It is a schematic sectional drawing of the optical pick-up apparatus concerning 1st Embodiment. It is a schematic sectional drawing of the optical pick-up apparatus concerning 2nd Embodiment. It is sectional drawing of an example of the objective optical element which concerns on a 1st Example. It is sectional drawing of an example of the objective optical element which concerns on a 2nd Example. It is sectional drawing of an example of the objective optical element which concerns on a 3rd Example. It is sectional drawing of an example of the objective optical element which concerns on a 4th Example. It is sectional drawing of an example of the objective optical element which concerns on a 5th Example. It is a graph which shows the relationship between the value of a side lobe and the number of area divisions.

Explanation of symbols

A1 1st area A2 2nd area BA1, BA2 BD exclusive area HA HD exclusive area OA Optical axis CL Collimating lens CL1 1st collimating lens CL2 2nd collimating lens CS Correction surface CT Notch CT1, CT2 Notch DE Diffraction correction element DP1 1st Dichroic prism DP2 Second dichroic prism EXP Expander lens FL1 Flange part FL2 Flange part G Diffraction grating G1 First diffraction grating G2 Second diffraction grating H Holding member HA First optical disk area HD Second optical disk area HE Frame HL Opening HLD Lens holder HOL Aperture LC Laser chip LD Semiconductor laser LD Blue-violet semiconductor laser LD1 First semiconductor laser LD2 Second semiconductor laser LD3 Third semiconductor laser M Raising mirror OE Objective optical element OL1 First objective lens OL2 Second objective lens PBS Polarization beam splitter PBS1 First polarization beam splitter PBS2 Second polarization beam splitter PD Photodetector or light receiving element PD1 First photodetector PD2 Second photodetector PD3 Third photodetector QWP λ / Four-wave plate QWP1 First λ / 4 wave plate QWP2 Second λ / 4 wave plate R1 Ring zone R2 Ring zone R3 Ring zone R4 Ring zone R5 Ring zone RL1 Information recording surface RL2 Information recording surface SE Optical axis correction element SL Sensor lens SL1 Sensor lens SL2 Sensor lens ST Step ST1, ST2 Step

Claims (15)

Information of the first optical disc having a single or a plurality of light sources, a first objective lens unit, and a second objective lens unit, wherein the first objective lens unit has a protective layer having a thickness t1 for a light beam having a wavelength λ1. Information is recorded and / or reproduced by condensing on the recording surface and condensing the light beam having the wavelength λ1 on the information recording surface of the second optical disc having the protective layer with thickness t2 (t1 <t2). The second objective lens unit focuses the light beam having the wavelength λ2 (λ1 <λ2) on the information recording surface of the third optical disc having the protective layer having the thickness t3 (t3 ≧ t2), and the wavelength λ3 (λ2 In an optical element for an optical pickup device that records and / or reproduces information by condensing a light beam of ≦ λ3) onto an information recording surface of a fourth optical disk having a protective layer having a thickness t4 (t3 <t4) ,
The optical element is a combination of the first objective lens part and the second objective lens part,
The optical surface of the first objective lens unit has a plurality of concentric annular zones centered on the optical axis, and the plurality of annular zones have the light flux of the wavelength λ1 passed through the information recording of the first optical disc. At least one first optical disk area where the light beam having the wavelength λ1 that is condensed and passed on the surface does not converge on the information recording surface of the second optical disk, and the light beam that has passed the wavelength λ1 is reflected on the second optical disk. Including at least one second optical disc region in which the light beam having the wavelength λ1 that is condensed on the information recording surface and passed therethrough is not condensed on the information recording surface of the first optical disc,
The optical element of the second objective lens section has a plurality of concentric annular zones centered on the optical axis. In the central annular zone including the optical axis of the plurality of annular zones of the second objective lens unit, the light flux having the wavelength λ2 that has passed is condensed on the information recording surface of the third optical disc and the wavelength λ3 that has passed therethrough. Is condensed on the information recording surface of the fourth optical disc,
Of the plurality of annular zones in the second objective lens section, the annular zone formed outside the central annular zone including the optical axis collects the light flux having the wavelength λ3 on the information recording surface of the third optical disc. Without condensing, the light beam having the wavelength λ4 is condensed on the information recording surface of the fourth optical disc,
Out of the plurality of annular zones in the second objective lens portion, the outer zone formed on the outermost side does not collect the luminous flux having the wavelength λ4 on the information recording surface of the fourth optical disc, but the luminous flux having the wavelength λ3. The optical element according to claim 1, wherein the optical element is focused on an information recording surface of the third optical disc.   The optical element according to claim 1, wherein the wavelength λ2 is equal to the wavelength λ3. The wavelength λ2 is different from the wavelength λ3,
3. The optical element according to claim 1, wherein the light source includes a first light emitting unit that emits a light beam having the wavelength λ <b> 2 and a second light emitting unit that emits the light beam having the wavelength λ <b> 3. .   The optical element according to claim 4, wherein the first light emitting unit and the second light emitting unit are housed in the same package.   The number of the plurality of annular zones of the first objective lens unit is an odd number, and the number of the plurality of annular zones of the second objective lens unit is an even number. An optical element according to 1.   The number of the plurality of annular zones of the first objective lens unit is an even number, and the number of the plurality of annular zones of the second objective lens unit is an odd number. An optical element according to 1.   The number of the plurality of annular zones of the first objective lens unit and the number of the plurality of annular zones of the second objective lens unit are both even numbers. The optical element described.   The number of the plurality of annular zones of the first objective lens unit and the number of the plurality of annular zones of the second objective lens unit are both odd numbers. The optical element described. The second objective lens unit is divided into at least two regions including a central region including the optical axis and a peripheral region disposed outside the central region.
The central region and the peripheral region each include the plurality of annular zones,
The light beam having the wavelength λ2 that has passed through the central region is condensed on the information recording surface of the third optical disc, and the light beam having the wavelength λ3 that has passed through the central region is collected on the information recording surface of the fourth optical disc. Light
The light beam having the wavelength λ2 that has passed through the peripheral area is collected on the information recording surface of the third optical disc, while the light beam having the wavelength λ3 that has passed through the peripheral region is collected on the information recording surface of the fourth optical disc. The optical element according to claim 1, wherein the optical element does not emit light.   The optical element according to claim 10, wherein an optical path difference providing structure that provides an optical path difference according to a wavelength of a light beam passing therethrough is formed in the peripheral region of the second objective lens unit.   The optical element according to claim 1, wherein the first objective lens part and the second objective lens part are integrally formed by integral molding.   The optical element according to claim 1, wherein the first objective lens portion and the second objective lens portion are integrally formed by engagement.   The optical element according to claim 13, wherein the first objective lens portion is made of glass, and the second objective lens portion is made of plastic.   An optical pickup device using the optical element according to claim 1.