JPWO2008146675A1 - Objective optical element for optical pickup device and optical pickup device - Google Patents

Abstract

In order to provide an objective optical element for an optical pickup device capable of appropriately recording and / or reproducing information with respect to different optical information recording media at low cost, the order of diffracted light used in the optical path difference providing structure Is (r, s, t) = (10, 6, 5) or (2, 1, 1), for any of the three types of light beams having the wavelengths (λ1, λ2, λ3) passing through the central region However, the light use efficiency can be maintained high, and a balance between the compatibility function and the function of suppressing the deterioration of the spherical aberration when the environmental temperature changes can be ensured. Further, when the order of the diffracted light to be used is (u, v) = (10, 6), (5, 3) or (2, 1), two types of wavelengths (λ1, λ2) passing through the intermediate region For any of the luminous fluxes, the light utilization efficiency can be maintained high, and a balance between the compatibility function and the function of suppressing the deterioration of the spherical aberration when the environmental temperature changes can be ensured.

Description

  The present invention relates to an objective optical element and an optical pickup device for an optical pickup device, and more particularly to an objective optical element and an optical pickup device for an optical pickup device capable of recording and / or reproducing information on different types of optical disks.

  In recent years, research on a high-density optical disk system capable of recording and / or reproducing 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, 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). ), Which can record information of about 25 GB per layer and record / reproduce 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 about 15 GB per layer can be recorded on an optical disk having a diameter of 12 cm. Hereinafter, in this specification, such an optical disc is referred to as a “high-density optical disc”.

  In addition, considering the reality that DVDs (digital versatile discs) and CDs (compact discs) on which various types of information are recorded are currently being sold, various types of optical discs can be used as much as possible with a single information recording / reproducing device. Therefore, it is desired to appropriately record / reproduce information. 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, as a method for appropriately recording / reproducing information while maintaining compatibility with any of a high-density optical disc, a DVD, and a CD, an optical system for a high-density optical disc and an optical system for a DVD Can be selectively switched according to the recording density of the optical disk for recording / reproducing information, but a plurality of optical systems are required, which is disadvantageous for miniaturization and increases the cost.

Therefore, in order to simplify the configuration of the optical pickup device and reduce the cost, the optical system for the high-density optical disc and the optical system for the DVD / CD are made common in the compatible optical pickup device. It is preferable to reduce the number of optical components constituting the optical pickup device as much as possible. Patent Document 1 discloses an optical pickup device that can realize compatible use of optical disks having different protective substrate thicknesses using a diffraction structure.
JP 2005-158217 A

  However, according to the technique of Patent Document 1, it is possible to provide an optical pickup device that can be used interchangeably with a high-density optical disk and other optical disks. However, as an objective optical element unit, a spherical surface caused by the thickness of the protective substrate of the optical disk. Since a plastic parallel plate on which a diffractive structure for correcting aberration (an optical path difference providing structure for compatibility) is formed and a glass lens are used, there is a problem that the cost is increased. On the other hand, in order to reduce the cost, it is conceivable that the lens is made of plastic, but the characteristic of the plastic becomes a problem. More specifically, since a plastic has a large refractive index change as compared with glass due to a change in temperature, a lens made of plastic may generate a relatively large spherical aberration due to a change in temperature. Such a problem is remarkable particularly in a high-density optical disk used at a high NA.

  On the other hand, apart from the technique of Patent Document 1, an optical pickup device that can be used interchangeably with a high-density optical disc and other optical discs using a single objective lens has also been developed. In this case, the same problem occurs.

  On the other hand, in order to correct the spherical aberration caused by the temperature change, an optical path difference providing structure that corrects the temperature change can be provided separately, but the compatibility performance of sharing different optical disks depending on the position and configuration The present inventor has found that the state is reduced or becomes incompatible.

  The present invention has been made in view of the above-mentioned problems found by the present inventors. Even when a plastic optical element is used, information recording / reproduction is appropriately performed on three different types of optical disks. It is an object of the present invention to provide an objective optical element and an optical pickup device for an optical pickup device capable of performing the above.

The objective optical element for an optical pickup device according to claim 1 includes a first light source that emits a first light beam having a wavelength λ1 (nm) and a second light beam that has a wavelength λ2 (nm) (λ1 <λ2). An objective optical element for an optical pickup device, comprising: a second light source that emits light; a third light source that emits a third light flux having a wavelength λ3 (nm) (λ2 <λ3); and an objective optical element,
The objective optical element has at least one plastic lens;
The optical surface of the objective optical element includes at least three regions: a central region including an optical axis, an intermediate region disposed around the central region, and a peripheral region disposed around the intermediate region,
The objective optical element focuses the first light flux that has passed through the central region, the intermediate region, and the peripheral region on the information recording surface of the first optical disc through a protective substrate having a thickness t1. Information can be recorded / reproduced, and the second light flux that has passed through the central area and the intermediate area is secondly passed through a protective substrate having a thickness t2 (t1 ≦ t2). Information can be recorded / reproduced by condensing it on the information recording surface of the optical disc, and the third light flux that has passed through the central region has a thickness of t3 (t2 <t3). Information can be recorded / reproduced by condensing on the information recording surface of the third optical disc via the protective substrate,
The central region has a first temperature characteristic correction structure having a plurality of concentric annular zone steps,
The intermediate region has a second temperature characteristic correction structure having a plurality of concentric annular zone steps,
The peripheral region has a third temperature characteristic correction structure having a plurality of concentric annular zone steps,
The first temperature characteristic correction structure increases the r-th order diffracted light amount of the first light flux that has passed through the first temperature characteristic correction structure to be larger than any other order diffracted light amount. The s-order diffracted light amount of the second light flux that has passed through the second light beam is made larger than any other order of diffracted light amount, and the t-order diffracted light amount of the third light flux that has passed through the first temperature characteristic correction structure is Is an optical path difference providing structure that is larger than the diffracted light quantity of any order of
The second temperature characteristic correction structure makes the u-order diffracted light amount of the first light flux that has passed through the second temperature characteristic correction structure larger than any other order of diffracted light amount, and the second temperature characteristic correction structure. An optical path difference providing structure that makes the v-th order diffracted light amount of the second light flux that has passed through the light beam larger than any other order diffracted light amount,
The third temperature characteristic correction structure is an optical path difference providing structure that makes the x-order diffracted light quantity of the first light flux that has passed through the third temperature characteristic correction structure larger than any other order diffracted light quantity,
(R, s, t) = (10, 6, 5) or (2, 1, 1)
(U, v) = (10, 6), (5, 3) or (2, 1)
x is an arbitrary integer.

  According to the present invention, when (r, s, t) = (10, 6, 5) or (2, 1, 1), three types of wavelengths (λ1, λ2, λ3) passing through the central region For any of the luminous fluxes, the light utilization efficiency can be maintained high, and a balance between the compatibility function and the function of suppressing the deterioration of the spherical aberration when the environmental temperature changes can be ensured.

  Further, when (u, v) = (10, 6), (5, 3) or (2, 1), for any of two kinds of light beams having wavelengths (λ1, λ2) passing through the intermediate region However, the light use efficiency can be maintained high, and a balance between the compatibility function and the function of suppressing the deterioration of the spherical aberration when the environmental temperature changes can be ensured.

  The peripheral region is a dedicated region for the first wavelength, and therefore does not need to have a compatibility function. As long as the light use efficiency can be maintained high and the mold can be easily manufactured, any one of them can be used. You may make it correspond to an order (however, an integer).

The objective optical element for an optical pickup device according to claim 2 is the invention according to claim 1,
(R, s, t) = (2,1,1)
(U, v) = (5, 3) or (2, 1)
x = 1-5.

  Further, according to the present invention, when (r, s, t) = (2, 1, 1), even when the light source wavelength is changed, the fluctuation of the diffraction efficiency is small, so that reading errors can be suppressed. In addition, since the depth of the annular zone step does not become too deep, there is an advantage that it is easy to manufacture a mold for molding the objective optical element. In addition, when (u, v) = (5, 3) or (2, 1), even when the light source wavelength is changed, the fluctuation in diffraction efficiency is small, so that reading errors can be suppressed. More preferably, (u, v) = (2, 1).

  The objective optical element for an optical pickup device according to claim 3 is the invention according to claim 1 or 2, wherein the first temperature characteristic correction structure and the second temperature characteristic correction structure are used. The composite structure is combined with the height of the optical axis as the height from the optical axis increases, and becomes shallower in the optical axis direction as the height from the optical axis increases at a predetermined height. It is characterized by that.

  The objective optical element for an optical pickup device according to claim 4 is the invention according to claim 1 or 2, wherein the first temperature characteristic correction structure and the second temperature characteristic correction structure are used. And the third temperature characteristic correcting structure, the composite structure is deeper in the optical axis direction as the height from the optical axis is higher, and the height from the optical axis is higher than the predetermined height. It is characterized by becoming shallower in the optical axis direction.

  The objective optical element for an optical pickup device according to claim 5 is the optical element according to claim 4, wherein the height from the optical axis reaches the third temperature characteristic correction structure. The depth in the optical axis direction of the composite structure is returned.

The objective optical element for an optical pickup device according to claim 6 is the invention according to any one of claims 1 to 5, wherein the plastic forming the objective optical element is -5. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change in the temperature range from ℃ to 70 ° C. is in the range of −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ It is characterized by.

  The objective optical element for an optical pickup device according to claim 7 is the invention according to any one of claims 1 to 6, wherein the objective optical element is a flat optical element. And a lens having an aspherical surface.

  The objective optical element for an optical pickup device according to claim 8 is the invention according to claim 7, wherein the plate-like optical element includes the first temperature characteristic correction structure and the second optical element. It has a temperature characteristic correction structure and the third temperature characteristic correction structure.

  The objective optical element for an optical pickup device according to claim 9 is the invention according to claim 7, wherein the lens includes the first temperature characteristic correction structure and the second temperature characteristic correction structure. And the third temperature characteristic correction structure.

  The objective optical element for an optical pickup device according to claim 10 is the invention according to any one of claims 1 to 6, wherein the objective optical element is a single piece of plastic. It consists only of lenses.

  The objective optical element for an optical pickup device according to claim 11 is the interchangeable optical element according to any one of claims 1 to 10 having a plurality of concentric annular zone steps. The structure is characterized in that the structure is superposed on the first to third temperature characteristic correction structures.

  An optical pickup device according to claim 12 has the objective optical element according to any one of claims 1 to 11.

  The optical pickup device of the present invention can have a first light source, a second light source, and a third light source. In the optical pickup device of the present invention, the first light beam from the first light source is condensed on the information recording surface of the first optical disk (also referred to as an optical information recording medium, hereinafter the same), and the second light from the second light source is collected. A condensing optical system including an objective optical element for condensing the light beam on the information recording surface of the second optical disk and condensing the third light beam from the third light source on the information recording surface of the third optical disk; ing. In addition, the optical pickup device of the present invention may include a light receiving element that receives a reflected light beam from the information recording surface of the first optical disc, the second optical disc, and the third optical disc.

  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 third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disc is preferably a high-density optical disc, the second optical disc is preferably a DVD, and the third optical disc is preferably a CD, but is not limited thereto. In addition, when t1 <t2 (for example, when the first optical disk is BD and the second optical disk is DVD), when t1 = t2 (for example, the first optical disk is HD and the second optical disk is DVD). It is more difficult to record and / or reproduce three different optical discs with one objective optical element, but the present invention makes it possible. The first optical disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording surfaces.

  In the present specification, as an example of a high-density optical disc, a standard optical disc (for example, a BD) in which information is recorded / reproduced by an objective optical element having a NA of 0.85 and a protective substrate has a thickness of about 0.1 mm. : Blu-ray Disc). As another example of a high-density optical disk, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and a protective optical disk having a protective substrate thickness of about 0.6 mm (for example, HD DVD: also simply referred to as HD). In addition, the high-density optical disc includes an optical disc having a protective film with a thickness of about several to several tens of nanometers on the information recording surface (in this specification, the protective substrate includes the protective film), and the thickness of the protective substrate. Also included are optical discs with a zero. The high-density optical disk includes a magneto-optical disk in which a blue-violet semiconductor laser or a blue-violet SHG laser is used as a light source for recording / reproducing information. Further, in this specification, a DVD refers to a DVD series optical disc in which information is recorded / reproduced by an objective optical element having an NA of about 0.60 to 0.67 and the protective substrate has a thickness of about 0.6 mm. It is a generic name and includes DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. 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 the high-density optical disk is the highest, and then decreases in the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, the following conditional expressions (1), (2), (3),
0.0750mm ≦ t1 ≦ 0.1125mm or 0.5mm ≦ t1 ≦ 0.7mm
(1)
0.5mm ≦ t2 ≦ 0.7mm (2)
1.0mm ≦ t3 ≦ 1.3mm (3)
However, the present invention is not limited to this.

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

The first light source emits a first light flux having a wavelength λ1. The second light source emits a second light flux having a wavelength λ2 (λ1 <λ2). The third light source emits a third light flux having a wavelength λ3 (λ2 <λ3). In the present specification, the first light source and the second light source are preferably laser light sources. A laser light source may be used when a third light source is used. As the laser light source, a semiconductor laser, silicon laser, SHG laser, or the like can be preferably used. Λ1, λ2, and λ3 are the following conditional expressions (4), (5),
1.5 × λ1 (nm) <λ2 <1.7 × λ1 (nm) (4)
1.9 × λ1 (nm) <λ3 <2.1 × λ1 (nm) (5)
It is preferable to satisfy.

  When BD or HD and DVD are used as the first optical disc and the second optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 380 nm or more and 415 nm or less. In addition, the second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less. Further, when a CD is used as the third optical disk, the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

  Further, the first light source and the second light source may be unitized, and in addition to these, the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. However, the unitization is not limited to this, and the two light sources are fixed so that the aberration cannot be corrected. Is widely included. In addition to the light source, a light receiving element to be described later may be packaged.

  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 (or an objective optical element to be described later) records / reproduces information by condensing the first light flux on the information recording surface of the first optical disc via a protective substrate having a thickness t1. It is possible to record / reproduce information by condensing the second light flux on the information recording surface of the second optical disc via the protective substrate having a thickness t2. Further, the condensing optical system makes it possible to record / reproduce information by condensing the third light flux on the information recording surface of the third optical disc via the protective substrate having a thickness t3.

  The condensing optical system has an objective optical element. The condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens in addition to the objective optical element. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. The collimating lens is a lens that emits an incident light beam as a parallel light beam. 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 optical element 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. Refers to an optical element or a unit of optical elements.

  As an example of the objective optical element of the present invention, each of the objective optical element can have a single flat optical element and a lens. It is preferable that the flat optical elements and the lenses are arranged in the optical axis direction and their positions are relatively fixed. At least one of the flat optical element and the lens has a portion extending in the optical axis direction, the extending portion is in contact with the other, the flat optical element and the lens are bonded to each other, and the objective It is preferable to form an optical element. On the other hand, the objective optical element may be formed by fixing a flat optical element and a lens to a separate frame. Normally, when the objective optical element is disposed in the optical pickup device, the flat optical element is on the light source side, and the lens is on the optical disk side. As another example of the objective optical element, the objective optical element can be constituted by only a single lens.

The objective optical element of the present invention is made of plastic. More specifically, when the objective optical element is composed of a plate-like optical element and a lens, when only the plate-like optical element is made of plastic, when only the lens is made of plastic, the plate-like optical element Sometimes the lens is made of plastic. On the other hand, when the objective optical element is a single lens, it is made of plastic. The plastic may be any plastic that is generally used for optical materials, but is preferably a cyclic olefin resin material. In addition, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is in the range of 1.54 to 1.60, and the refractive index change rate with respect to the wavelength of 405 nm accompanying a temperature change within a temperature range of −5 ° C. to 70 ° C. A resin material having dN / dT (° C. ⁻¹ ) in the range of −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ) is used. More preferably. Further, when the objective optical element is made of plastic, the coupling lens is also preferably a plastic lens. Further, when the objective optical element is formed by fixing the flat optical element and the lens to a separate frame, the frame is preferably made of plastic.

  At least one optical surface of the objective optical element has a central region, an intermediate region around the central region, and a peripheral region around the intermediate region. By providing the intermediate area and the peripheral area, it is possible to more appropriately perform recording / reproduction with respect to an optical disk with a high NA. The central region is preferably a region including the optical axis of the objective optical element, but may be a region not including the optical axis. The central region, the intermediate region, and the peripheral region are preferably provided on the same optical surface. Taking a single lens as an example, as shown in FIG. 11, the central region CN, the intermediate region MD, and the peripheral region OT are provided on the same optical surface in a concentric manner with the optical axis as the center. Preferably it is. In addition, a first temperature characteristic correction structure is provided in the central area of the objective optical element, a second temperature characteristic correction structure is provided in the intermediate area, and a third temperature characteristic correction structure is provided in the peripheral area. Yes. The central region, the intermediate region, and the peripheral region are preferably adjacent to each other, but there may be a slight gap between them.

  The first temperature characteristic correction structure is preferably provided in a region of 70% or more of the area of the central region of the objective optical element, and more preferably 90% or more. More preferably, the first temperature characteristic correction structure is provided on the entire surface of the central region. The second temperature characteristic correction structure is preferably provided in a region of 70% or more of the area of the intermediate region of the objective optical element, and more preferably 90% or more. More preferably, the second temperature characteristic correction structure is provided on the entire surface of the intermediate region. The third temperature characteristic correction structure is preferably provided in a region of 70% or more of the area of the peripheral region of the objective optical element, and more preferably 90% or more. More preferably, the third temperature characteristic correction structure is provided on the entire surface of the peripheral region.

  The optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam. In general, the optical path difference providing structure 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 so-called phase shift structure and the NPS structure are both a kind of optical path difference providing structure and a kind of diffractive structure.

  Hereinafter, the temperature characteristic correction structure will be described in detail. The temperature characteristic correction structure is a structure that corrects a spherical aberration that occurs with a change in environmental temperature with respect to a passing light beam. It is preferable that the structure corrects the spherical aberration caused by the change when the wavelength of the light beam passing through the change in the environmental temperature or when the refractive index of the optical element changes. An example of a preferable structure is a so-called NPS structure. The temperature characteristic correction structure preferably gives different power to the light flux when the wavelength of the light flux deviates from the design wavelength due to a change in temperature, variations in manufacturing the light source, or the like. Since the temperature characteristic correction structure has such a function, it is possible to correct spherical aberration that occurs with a change in temperature. Here, “the wavelength deviates from the design wavelength” is preferably within ± 10 nm.

  The temperature characteristic correction structure can take various cross-sectional shapes as schematically shown in FIGS. (In addition, the example described in FIGS. 1-3 is a case where an objective optical element has a flat-plate-shaped optical element.) FIG. 1 is a case where a sawtooth shape is used, and FIG. This is a case of a staircase shape. In addition, FIG. 3 shows a step shape in which the direction of the step is opposite in the middle, that is, the cross-sectional shape including the optical axis is a predetermined height from the optical axis, the optical path length becomes longer as the distance from the optical axis increases. After a predetermined height from the optical axis, a staircase structure in which the optical path length decreases as the distance from the optical axis decreases, or at a predetermined height from the optical axis, the optical path length decreases as the distance from the optical axis decreases. After the height, a case is shown in which the optical path length is increased as the distance from the optical axis increases. Further, the steps of the temperature characteristic correction structure may be arranged with an aperiodic interval in the direction perpendicular to the optical axis. Here, the temperature characteristic correction structure formed in the central region is the first temperature correction structure, the temperature characteristic correction structure formed in the intermediate region is the second temperature correction structure, and the temperature characteristic correction structure formed in the peripheral region is A third temperature correction structure is adopted. In any case, the first to third temperature characteristic correction structures are preferably ring-shaped step structures separated by concentric steps. When the objective optical element is composed of a flat optical element and a lens, the first to third temperature characteristic correction structures are formed only on the flat optical element, and the first to third only on the lens. 3 may be formed. On the other hand, when the objective optical element is a single lens, first to third temperature characteristic correction structures are formed on the optical surface.

  An example in which a composite structure including the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure is formed on the optical surface of the objective optical element will be described. Assuming that the optical surface on which the temperature correction structure is provided is a plane, the cross-sectional shape including the optical axis of the first temperature characteristic correction structure is a predetermined height from the optical axis as shown in FIG. The optical path length becomes shorter as the distance from the optical axis is within the range of the first temperature characteristic correction structure, and after the predetermined height from the optical axis, the optical path length becomes longer as the distance from the optical axis is within the range of the second temperature characteristic correction structure. It has a staircase structure. The third temperature characteristic correction structure is a sawtooth optical path difference providing structure. In other words, in the composite structure in which the first temperature characteristic correction structure and the second temperature characteristic correction structure are combined, as the height from the optical axis increases, the depth increases in the optical axis direction. It can be said that the structure becomes shallower in the direction of the optical axis when it exceeds a predetermined height. The position where the depth of the step changes (the position where the depth of the step is deepest) may be in the second temperature characteristic correction structure, the first temperature characteristic correction structure, or the first temperature. It may be a boundary between the characteristic correction structure and the second temperature characteristic correction structure. Providing such a structure on the optical surface of an objective optical element composed of a single aspherical lens is a preferred example.

  Next, another example is shown. Assuming that the optical surface on which the composite structure including the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure is provided is a plane, the first temperature characteristic correction structure When the cross-sectional shape including the optical axis is at a predetermined height from the optical axis as shown in FIG. 5B, the optical axis is within the range of the first temperature characteristic correction structure and the second temperature characteristic correction structure. As the distance increases, the optical path length becomes shorter, and after the predetermined height from the optical axis, a staircase structure is formed in which the optical path length becomes longer as the distance from the optical axis is within the range of the third temperature characteristic correction structure. In other words, in the composite structure including the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure, the height from the optical axis increases. It can be said that the structure becomes deeper in the direction of the optical axis and becomes shallower in the direction of the optical axis when it exceeds a predetermined height. The position where the depth of the step changes (the position where the depth of the step is the deepest) may be in the second temperature characteristic correction structure or in the third temperature characteristic correction structure, It may be a boundary between the second temperature characteristic correction structure and the third temperature characteristic correction structure. In this case, it is preferable that the depth of the composite structure in the optical axis direction returns before the height from the optical axis reaches the third temperature characteristic correction structure. Providing such a structure on the optical surface of the flat optical element of the objective optical element composed of a flat optical element and an aspherical lens is a preferred example.

  A particularly preferable first temperature characteristic correction structure is such that the r-order diffracted light quantity of the first light beam that has passed through the first temperature characteristic correction structure is larger than any other order diffracted light quantity, and the s-order diffracted light quantity of the second light beam. Is expressed as an optical path difference providing structure in which the t-order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity, and (r, s, t) = (10,6,5) or (2,1,1). By making the first temperature characteristic correction structure like this, an optical element that is easy to manufacture can be obtained. In particular, the second-order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, the first-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, and the third light beam When the first-order diffracted light quantity is made larger than any other order diffracted light quantity, it is preferable because a decrease in diffraction efficiency at the time of wavelength fluctuation can be suppressed.

  Furthermore, the preferable second temperature characteristic correction structure makes the u-order diffracted light quantity of the first light flux that has passed through the second temperature characteristic correction structure larger than any other order diffracted light quantity, and v-order diffraction of the second light flux. When expressed as an optical path difference providing structure in which the amount of light is larger than any other order of the amount of diffracted light, (u, v) = (10, 6), (5, 3) or (2, 1). It is a structure.

  The third temperature characteristic correction structure only needs to make an arbitrary integer diffracted light quantity of the first light flux that has passed through the third temperature characteristic correction structure larger than any other order diffracted light quantity. However, from the viewpoint of ease of manufacture, it is preferable that the diffraction order of the diffracted light with the maximum light amount is 5th or less.

  In the first to third temperature characteristic correction structures, all the regions corresponding to NA2 or lower may be the same structure, or the structure may be changed with NA3 as a boundary.

  Here, the first to third temperature characteristic correction structures described above, and the composite structure becomes deeper in the optical axis direction as the height from the optical axis increases, and exceeds a predetermined height. Now, the principle of correcting spherical aberration caused by a temperature change due to the structure that becomes shallow in the optical axis direction will be described. The line (A) in FIG. 6 represents the state of the wavefront when the temperature rises from the design reference temperature of an example single lens having two optical surfaces that are made of plastic and are aspherical. The horizontal axis represents the effective radius of the optical surface, and the vertical axis represents the optical path difference. In the single lens, spherical aberration occurs due to the influence of the refractive index change accompanying the temperature rise, and the wavefront changes as shown by the line (A). In particular, when the single lens is made of plastic, the amount of spherical aberration is increased because the refractive index change with temperature change is large.

  Line (B) is an optical path difference added to the transmitted wavefront by the first to third temperature characteristic correction structures, and line (C) is the first difference when the temperature rises from the design reference temperature. It is a figure showing the mode of the wave front which permeate | transmitted the temperature characteristic correction structure and the refractive surface of a lens. From the line (B) and the line (C), the wavefront transmitted through the first to third temperature characteristic correction structures and the wavefront of the single lens when the temperature rises from the design reference temperature cancel each other, thereby The wavefront of the laser light focused on the information recording surface is a good wavefront with no optical path difference when viewed macroscopically, and it is understood that the temperature aberration is corrected by the first to third temperature characteristic correction structures. it can.

  The objective optical element can be provided with a compatible structure which is an optical path difference providing structure. The interchangeable structure is a structure that corrects the spherical aberration that occurs according to the thickness of the protective substrate of the optical disk using the wavelength difference of the light beam. When the objective optical element includes a flat optical element and a lens, the compatible structure may be provided in the flat optical element or may be provided in the lens. When providing a compatible structure for a flat optical element, the first to third temperature characteristic correction structures may be provided on one optical surface, and the compatible structure may be provided on the other optical surface. In FIG. 1, the first to third temperature characteristic correction structures and the compatible structure may be overlapped. On the other hand, when providing a compatible structure for the lens, it is preferable to superimpose the first to third temperature characteristic correction structures and the compatible structure on the optical surface on the light source side, but each may be formed on another optical surface. good. When the objective optical element is composed of only a single lens, it is preferable to superimpose the first to third temperature characteristic correction structures and the compatible structure on the optical surface on the light source side. May be.

  The interchangeable structure also preferably has a plurality of concentric annular zones around the optical axis. The interchangeable structure can also have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis) as shown in FIGS. In addition, as shown in FIG. 4, a pattern whose cross-sectional shape including the optical axis is stepped is arranged concentrically, for each predetermined number of level surfaces (in the example shown in FIG. 4, the number of level surfaces is 5). ) May have a shape in which the steps are shifted by the height corresponding to each level surface (four steps in the example shown in FIG. 4). There can also be a binary structure as shown as D2 in FIG.

  Hereinafter, an example of a preferable interchangeable structure in the case where the objective optical element is a single plastic aspheric lens will be described.

  In the central region of the objective optical element, it is preferable that the first temperature characteristic correction structure and the first compatibility structure are overlapped and provided. The first interchangeable structure here is preferably a structure in which the first basic structure and the second basic structure are overlapped.

  In the first basic structure, the second-order diffracted light amount of the first light beam that has passed through the first basic structure is made larger than any other order of diffracted light amount, and the first-order diffracted light amount of the second light beam is set to any other order. In this optical path difference providing structure, the first order diffracted light amount of the third light flux is made larger than the diffracted light amount and larger than any other order diffracted light amount. Moreover, it is preferable that a 1st basic structure is an optical path difference providing structure which makes the diffraction angle of the 2nd light beam which passed the 1st basic structure differ from the diffraction angle of a 1st light beam and a 3rd light beam.

  In addition, the second basic structure makes the 0th-order (transmitted light) diffracted light amount of the first light beam that has passed through the second basic structure larger than any other order diffracted light amount, and the 0th-order (transmitted light) of the second light beam. ) Is made larger than any other order diffracted light quantity, and the ± 1st order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. Moreover, it is preferable that a 2nd basic structure is an optical path difference providing structure which makes the diffraction angle of the 3rd light beam which passed the 2nd basic structure differ from the diffraction angle of a 1st light beam and a 2nd light beam. A preferable example of the shape of the second basic structure is a binary structure as shown as D2 in FIG.

  In the intermediate region of the objective optical element, it is preferable that the second compatibility structure is overlapped with the second temperature characteristic correction structure. The second interchangeable structure is preferably any one of the first basic structure, the third basic structure, and the fourth basic structure.

  In the third basic structure, the first-order diffracted light quantity of the first light beam that has passed through the third basic structure is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light beam is set to any other order. In this optical path difference providing structure, the first order diffracted light amount of the third light flux is made larger than the diffracted light amount and larger than any other order diffracted light amount.

  In the fourth basic structure, the third-order diffracted light amount of the first light beam that has passed through the fourth basic structure is made larger than any other order diffracted light amount, and the second-order diffracted light amount of the second light beam is set to any other order. In this optical path difference providing structure, the second order diffracted light amount of the third light beam is made larger than the diffracted light amount, and the diffracted light amount of any other order is made larger.

  The peripheral region of the objective optical element preferably has only the third temperature characteristic correction structure and does not have a compatible structure.

  Next, an example of a preferable compatible structure when the objective optical element has a flat optical element and an aspheric lens, and the flat optical element is provided with a temperature characteristic correcting structure and a compatible structure. Indicates.

  The flat optical element has a first optical surface and a second optical surface that face each other, the first optical surface being the light source side, and the second optical surface being the optical disk side and the aspheric lens side. In the central region of the second optical surface of the flat optical element, no temperature characteristic correction structure is provided, and only the first compatibility structure is provided. It is preferable that the structure for 1st compatibility here consists only of a 2nd foundation structure. It is preferable that neither an interchangeable structure nor a temperature characteristic correction structure is provided in the intermediate region and the peripheral region of the second optical surface of the flat optical element.

  On the other hand, a first temperature characteristic correcting structure and a second compatible structure are provided to overlap each other in the central region of the first optical surface of the flat optical element. The second compatible structure consists only of the fifth basic structure.

  In the fifth basic structure, the first-order diffracted light quantity of the first light beam that has passed through the fifth basic structure is made larger than the diffracted light quantity of any other order, and the first-order diffracted light quantity of the second light beam This is an optical path difference providing structure in which the diffracted light amount of the third light beam is larger than any other order of diffracted light amount. The fifth basic structure is preferably an optical path difference providing structure that makes the diffraction angle of the second light flux that has passed through the fifth basic structure different from the diffraction angles of the first light flux and the third light flux. In addition, as a preferable example of the shape of the fifth basic structure, as shown in FIG. 4, a pattern in which the cross-sectional shape including the optical axis is stepped is arranged concentrically, for each predetermined number of level surfaces (see FIG. In the example shown in FIG. 4, the number of level surfaces is 5), and the shape is shifted by the height corresponding to each level surface (4 steps in the example shown in FIG. 4).

  In addition, it is preferable that the second temperature characteristic correction structure and the third compatibility structure are provided to overlap each other in an intermediate region of the first optical surface of the flat optical element. It is preferable that the third compatible structure is composed of only the fifth basic structure.

  It is preferable that only the third temperature characteristic correction structure is provided in the peripheral region of the first optical surface of the flat optical element.

In addition, by having the temperature characteristic correction structure of the present invention, the temperature characteristic has the following conditional expressions (6) and (7),
+ 0.00045 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0027
(6)
−0.045 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0045
(7)
It is preferable to satisfy.

  However, δSAT1 represents δSA3 / δT of the objective optical element at the time of recording and / or reproduction of the first optical disk at the wavelength used (in this case, there is no wavelength variation accompanying temperature change). The used wavelength refers to the wavelength of a light source used in an optical pickup device having an objective optical element. Preferably, the wavelength used is a wavelength in the range of 400 nm or more and 415 nm or less, and is a wavelength at which recording and / or reproduction of the first optical disc can be performed via the objective optical element. When the use wavelength cannot be set as described above, δSAT1 of the objective optical element and δSAT2 and δSAT3 described later may be obtained using 405 nm as the use wavelength. In other words, δSAT1 indicates the temperature change rate (temperature characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength (no wavelength variation). Note that WFE indicates that the third-order spherical aberration is expressed by wavefront aberration. Further, δSAλ represents δSA3 / δλ when recording and / or reproducing the first optical disk at the used wavelength under a condition where the environmental temperature is constant. That is, δSAλ indicates the wavelength change rate (wavelength characteristic) of the third-order spherical aberration of the objective optical element when recording and / or reproducing the first optical disk at the used wavelength under the condition where the environmental temperature is constant. The ambient temperature is preferably room temperature. The room temperature is 10 ° C. or more and 40 ° C. or less, and preferably 25 ° C. f indicates the focal length of the objective optical element at the used wavelength (preferably 405 nm) of the first light flux.

More preferably, the following conditional expression (6) ′,
+ 0.00091 ≦ δSAT1 / f (WFEλrms / (° C. mm)) ≦ + 0.0018
(6) '
Is to satisfy.

Preferably, the following conditional expression (7) ′,
−0.032 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.0091
(7) '
More preferably, the following conditional expression (7) '',
−0.015 ≦ δSAλ / f (WFEλrms / (nm · mm)) ≦ −0.011
(7) ''
Is to satisfy.

Furthermore, the objective optical element has the wavelength dependency of the spherical aberration so that the change of the spherical aberration due to the refractive index change accompanying the temperature change of the objective optical element is corrected by the wavelength change of the first wavelength accompanying the temperature change. Is preferred. Preferably, the following conditional expression (8),
0 ≦ δSAT2 / f (WFEλrms / (° C. mm)) ≦ + 0.00136
(8)
Is to satisfy.

  However, δSAT2 is δSA3 / δT of the objective optical element at the time of recording and / or reproducing the first optical disc at a use wavelength of 405 nm (wavelength variation with temperature change is 0.05 nm / ° C.) (preferably 405 nm). Represents. That is, δSAT2 is a temperature change rate (temperature characteristic of the third-order spherical aberration of the objective optical element at the time of recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation with temperature change is 0.05 nm / ° C.). ).

Further, when the condensing optical system of the optical pickup device has a coupling lens such as a collimator lens, and the coupling lens is a plastic lens, the following conditional expression (9),
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.00091
(9)
It is preferable to satisfy.

  However, δSAT3 is an optical including a coupling lens and an objective optical element when recording and / or reproducing the first optical disk at a wavelength used (wavelength variation with temperature change is 0.05 nm / ° C. (preferably 405 nm)). Represents δSA3 / δT of the entire system, that is, δSAT3 is the third order of the entire optical system when performing recording and / or reproduction of the first optical disc at the wavelength used (wavelength variation accompanying temperature change is 0.05 nm / ° C.). Refers to the temperature change rate (temperature characteristic) of spherical aberration.

More preferably, the following conditional expression (9) ′,
0 ≦ δSAT3 / f (WFEλrms / (° C. mm)) ≦ + 0.00045
(9) '
Is to satisfy.

More preferably, the following conditional expression (9) '',
+ 0.00005 ≦ δSAT3 / f (WFEλrms / (° C./mm))≦+0.0003
(9) ''
Is to satisfy.

  An optical information recording / reproducing apparatus according to the present invention includes 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 disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.

  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 for guiding toward the head, a spindle motor for rotating 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, it is possible to provide an objective optical element and an optical pickup device for an optical pickup device that can appropriately record and / or reproduce information on three different types of optical disks at low cost.

It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure which shows the example of an optical path difference providing structure. It is a figure for demonstrating the 1st optical path difference providing structure. It is a figure for demonstrating the principle which correct | amends the aberration degradation resulting from the temperature change by a temperature characteristic correction structure. It is a schematic block diagram of the optical pick-up apparatus concerning this Embodiment. It is sectional drawing of the objective optical element OBU concerning this Embodiment. It is sectional drawing which expands and shows a part of objective optical element OBU. It is a schematic block diagram of the optical pick-up apparatus concerning another embodiment. It is sectional drawing which shows typically an example of the objective optical element OBJ which concerns on this invention. FIG. 6 is a longitudinal spherical aberration diagram regarding BD, DVD, and CD of Example 2. The first temperature characteristic correction structure and the second temperature characteristic correction structure (the shape shown in FIG. 13B) and the second and third interchangeable structures having a plurality of four-step small staircase structures (FIG. 13A It is a figure which shows the example which piled up the shape shown in ()).

Explanation of symbols

AC1 2-axis actuator AC2 1-axis actuator C1 region C2 region C3 region C4 region CL collimating optical system D1 first optical path difference providing structure D2 second optical path difference providing structure HL lens frame L1 first optical element L2 second optical Element LD1 Blue-violet semiconductor laser LD2 Red semiconductor laser LD3 Infrared semiconductor laser LL Laser light LM Laser module M1 Marker M2 Marker ML Standing mirror NA1 Numerical aperture NA2 Numerical aperture NA3 Numerical aperture OA1 Optical axis OA2 Optical axis OBU Objective optical element OBJ Objective Optical element P1 1st prism P2 2nd prism P3 3rd prism PD photodetector PL1 protective substrate PL2 protective substrate PL3 protective substrate PPS dichroic prism PU optical pickup device PU1 optical pickup device RL1 information recording surface RL 2 Information recording surface RL3 Information recording surface S1 Optical surface on the light source side S2 Optical surface on the optical disk side SE Sensor optical system STO Aperture

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an optical pickup device using the objective optical element according to the present invention will be described with reference to FIG. FIG. 7 shows a configuration of an optical pickup device PU that can appropriately record and reproduce information on any of a high-density optical disc BD (first optical disc), DVD (second optical disc), and CD (third optical disc). It is a figure shown roughly. The specifications of the BD are the first wavelength (design wavelength) λ1 = 405 nm, the thickness t1 = 0.0875 mm of the protective substrate PL1, the numerical aperture NA1 = 0.85 (hereinafter, this numerical aperture is referred to as NA1), DVD The specifications of the second wavelength (design wavelength) λ2 = 658 nm, the thickness t2 of the protective substrate PL2 = 0.6 mm, and the numerical aperture NA2 = 0.60 (hereinafter, this numerical aperture is referred to as NA2). The specifications are the third wavelength (design wavelength) λ3 = 785 nm, the thickness t3 of the protective substrate PL3 = 1.2 mm, and the numerical aperture NA3 = 0.45 (hereinafter, this numerical aperture is referred to as NA3). However, the combination of the wavelength, the thickness of the protective substrate, and the numerical aperture is not limited to this.

  The optical pickup device PU includes a blue-violet semiconductor laser LD1 (first light source) that emits a first light flux with a wavelength λ1 for BD, and a red semiconductor laser LD2 (second light source) for DVD that emits a second light flux with a wavelength λ2. , An infrared semiconductor laser LD3 (third light source) for CD that emits a third light beam of wavelength λ3, a light receiving element PD for BD / DVD / CD, an objective optical element unit OBU, a collimator lens CL, a biaxial actuator AC1, Sensor optical system SE for adding astigmatism to the reflected light beam from the information recording surface of each optical disk, the uniaxial actuator AC2, the first prism P1, the second prism P2, the third prism P3, the rising mirror ML, and the optical disk It consists of and.

  FIG. 8 is a cross-sectional view of the objective optical element OBU according to the present embodiment. The objective optical element unit OBU has a configuration in which a plastic flat first optical element L1 and a second optical element L2 which is a plastic aspherical lens are connected by a plastic lens frame HL. . Although not shown, the optical axis of the first optical element L1 is inclined by 2.5 degrees with respect to the optical axis of the second optical element L2.

  The first optical element L1 has a refractive index of 1.56 in the first light flux having the wavelength λ1, is made of a polyolefin-based plastic having an Abbe number of 50 or more and 60 or less, and the first optical surface S1 on the light source side is: For convenience, it is divided into a region C2 including the optical axis and a surrounding region C3, and the second optical surface S2 on the optical disc side is divided into a region C1 including the optical axis and a surrounding region C4. ing. The central region is a range inside the region C1, the intermediate region is outside the region C1 and inside the region C2, and the peripheral region is outside the region C2 and inside the region C3. is there. Here, the outer edge of the region C1 corresponds to the numerical aperture NA3, the outer edge of the region C2 corresponds to the numerical aperture NA2, and the outer edge of the region C3 corresponds to the numerical aperture NA1.

  A first optical path difference providing structure D1 is formed in a region C2 of the first optical surface S1 of the first optical element L1. When the first optical path difference providing structure D1 has a cross-sectional shape in the optical axis direction, as the height from the optical axis increases, the first temperature characteristic correcting structure and the second temperature structure increase in depth in the optical axis direction. The temperature characteristic correction structure (shape shown in FIG. 13 (b)) is superimposed on the second and third compatible structures (shape shown in FIG. 13 (a)) having a plurality of four-step small staircase structures. It has a shape as shown in FIG.

  The first temperature characteristic correction structure and the second temperature characteristic correction structure increase the second-order diffracted light quantity of the first light flux that has passed through the first temperature characteristic correction structure to be larger than any other order diffracted light quantity. In this optical path difference providing structure, the first-order diffracted light quantity of the two light beams is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity.

  The second and third compatible structures use the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ2 of the second light beam, and the thickness t1 of the BD protective substrate and the thickness t2 of the DVD protective substrate. This structure corrects spherical aberration that occurs based on the difference between the two. In the first compatibility structure, the 0th-order diffracted light quantity of the first light beam that has passed through the first compatible structure is made larger than any other order diffracted light quantity, and the first-order diffracted light quantity of the second light beam is changed to other values. Is an optical path difference providing structure that makes the diffracted light quantity of any order greater than the diffracted light quantity of the third light beam and the diffracted light quantity of the third light beam larger than any other diffracted light quantity of the third light beam. It is a difference giving structure.

  By superimposing the first temperature characteristic correction structure and the second compatibility structure, the light beam that has passed through the center of the first temperature characteristic correction structure can always pass through the center of the second compatibility structure. Therefore, information can be recorded / reproduced appropriately without generating coma due to wavelength change or temperature change.

  In the peripheral region around the region C3 of the first optical surface S1, a third optical path difference providing structure including only the third temperature characteristic correction structure is provided. In the third optical path difference providing structure, the fifth-order diffracted light quantity of the first light flux that has passed through the third optical path difference providing structure is made larger than any other order diffracted light quantity.

  The first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure have a cross-sectional shape including the optical axis at a predetermined height from the optical axis when captured in the entire regions C2 and C3. Then, the depth increases as the distance from the optical axis increases, and after a predetermined height from the optical axis, the depth decreases as the distance from the optical axis decreases.

  Further, a second optical path difference providing structure D2 that is a binary structure is formed in the region C1 of the second optical surface S2 of the first optical element L1. The second optical path difference providing structure D2 utilizes the wavelength difference between the wavelength λ1 of the first light beam and the wavelength λ3 of the third light beam, and the difference between the thickness t1 of the BD protective substrate and the thickness t3 of the CD protective substrate. Only the first compatible structure for correcting the spherical aberration generated based on the above.

  The first compatible structure makes the 0th-order diffracted light quantity of the first light beam that has passed through the first compatible structure larger than any other order of diffracted light quantity, and the second-order diffracted light quantity of the second light flux In this structure, the diffracted light amount of the third light beam is made larger than the diffracted light amount of any other order.

  The second optical element L2 is an aspheric lens made of polyolefin plastic having a refractive index of 1.56. The second optical element L2 is designed to be capable of condensing the first light beam on the information recording surface of the BD without using the first optical element L1.

  FIG. 9 is an enlarged sectional view showing a part of the objective optical element unit OBU. In the objective optical element unit OBU, the optical axis OA1 of the first optical element L1 is inclined at an angle θ = 2.5 ° with respect to the optical axis OA2 of the second optical element L2. Thereby, the possibility that the reflected light from the first optical element L1 is received by the light receiving element can be reduced. 9, the center of the first optical surface on the light source side of the first optical element L1 (that is, the optical surface on which the first optical path difference providing structure and the third optical path difference providing structure are provided). A marker M1 is provided at (optical axis position), and a marker M2 is provided at the center (optical axis position) of the second optical element L2. These markers M1 and M2 are used for alignment of the first optical element L1 and the second optical element L2. The marker may be provided by a paint, or may be provided as a concave portion or a convex portion.

  In order not to deteriorate the imaging characteristics of the objective optical element OBU even when the first optical element L1 is inclined, for example, the laser light LL incident in parallel to the optical axis OA2 of the second optical element L2 from the light source side is used. It is desirable to perform alignment so that the marker M1 that is the center of the first optical element L1 passes through the marker M2 that is the center of the second optical element L2 and travels along the optical axis OA2. As described above, by using the markers M1 and M2 to place the center of the second optical element L2 and the first optical element L1 on the same optical path in the optical axis OA2 direction, the tilt angle of the first optical element L1. Regardless of the value of θ, coma generated at least as the objective optical element OBU (especially for the first light flux and the second light flux) can be reduced.

  When the first optical path difference providing structure and the third optical path difference providing structure are provided not on the light source side surface of the first optical element but on the surface on the optical disk side, It is preferable that the marker is also provided on the surface on the optical disc side and aligned so that the marker and the marker of the second optical element have the same optical path.

  As a method of arranging the marker M1 of the first optical element L1 on the optical axis OA2 of the second optical element L2, the second optical element L2 attached to the lens frame HL is placed on the optical axis OA2 from the left side of the drawing. While observing, the first optical element L1 is arranged in front of the second optical element L2, and the first optical element L1 is moved within the lens frame HL so that both the markers M1 and M2 coincide. Thereby, the state shown in FIG. 9 is achieved, and the imaging characteristics of the objective optical element OBU can be ensured.

  In the optical pickup device PU, when information is recorded / reproduced with respect to the BD, a blue-violet laser beam (first beam) having a wavelength λ1 is emitted in a state of a parallel beam from the collimating optical system CL. After the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first prism P1 and then sequentially passes through the second prism P2 and the third prism P3, as shown by the solid line in FIG. Then, it is converted into a parallel light beam by the collimating optical system CL. After that, after being reflected by the rising mirror ML, the light beam diameter is regulated by the stop STO, and becomes a condensed spot formed on the information recording surface RL1 by the objective optical element OBU via the BD protective substrate PL1. The objective optical element OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof. The first light beam passes through the first optical surface S1 of the first optical element L1, passes through the second optical surface S2, and enters the second optical element L2 in the state of a parallel light beam. All the first light fluxes within the range (that is, the region where C2 and C3 are combined or the region where C1 and C4 are combined) are collected on the information recording surface of the BD by the second optical element L2. Further, when the environmental temperature changes, the spherical aberration can be suppressed by the mechanism described above.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is again transmitted through the objective optical element OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after sequentially passing through the third prism P3, the second prism P2, and the first prism P1, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD. Information recorded on the BD can be read using the output signal of the light receiving element PD.

  Further, when information is recorded / reproduced with respect to the DVD in the optical pickup device PU, the red laser beam (second beam) having the wavelength λ2 is emitted from the collimating optical system CL in a parallel beam state. After the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the red semiconductor laser LD2 is caused to emit light. The divergent light beam emitted from the red semiconductor laser LD2 is reflected by the second prism P2 and then transmitted through the third prism P3 and parallel by the collimating optical system CL as shown by the broken line in FIG. Converted into luminous flux. After that, after being reflected by the rising mirror ML, it becomes a condensing spot formed on the information recording surface RL2 via the protective substrate PL2 of the DVD by the objective optical unit OBU. The objective optical element OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof. The second light flux is converted into divergent light in the region C2 of the first optical surface S1 of the first optical element L1, and is transmitted in the region C3. The second light flux that has passed through the region C2 and converted into divergent light passes through the second optical surface S2, enters the second optical element as divergent light, and is collected on the information recording surface of the DVD. . On the other hand, the second light beam transmitted through the region C3 is incident on the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the DVD. Therefore, the second light flux in the range within NA2 (namely, the C2 region) is condensed on the information recording surface of the DVD, and the second light flux in the range larger than NA2 (namely, the C3 region) becomes flare.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after sequentially passing through the third prism P3, the second prism P2, and the first prism P1, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD. Information recorded on the DVD can be read using the output signal of the light receiving element PD.

  Further, when information is recorded / reproduced with respect to the CD in the optical pickup device PU, an infrared laser beam (third beam) having a wavelength λ3 is emitted from the collimating optical system CL in a state of a parallel beam. In addition, after the position of the collimating optical system CL is adjusted in the optical axis direction by the uniaxial actuator AC2, the infrared semiconductor laser LD3 is caused to emit light. The divergent light beam emitted from the infrared semiconductor laser LD3 is reflected by the third prism P3 and then converted into a parallel light beam by the collimating optical system CL, as depicted by the alternate long and short dash line in FIG. After that, after being reflected by the rising mirror ML, it becomes a focused spot formed on the information recording surface RL3 by the objective optical element OBU via the CD protective substrate PL3. The objective optical unit OBU performs focusing and tracking by a biaxial actuator AC1 arranged in the periphery thereof. The third light flux passes through the first optical surface S1 of the first optical element L1. The third light flux is converted into divergent light in the region C1 of the second optical surface S2 of the first optical element L1, and is transmitted through the region C4. The third light beam that has passed through the region C1 and converted into divergent light is incident on the second optical element as divergent light, and is condensed on the information recording surface of the CD. On the other hand, the third light beam transmitted through the region C4 enters the second optical element as a parallel light beam, and does not form a condensing spot by the second optical element, and becomes a flare on the information recording surface of the CD. Accordingly, the third light flux in the range within NA3 (namely, the C1 region) is collected on the information recording surface of the CD, and the third light flux in the range larger than NA3 (namely, the C4 region) is flare.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective optical unit OBU, then reflected by the rising mirror ML, and becomes a converged light beam when passing through the collimating optical system CL. After that, after sequentially passing through the third prism P3, the second prism P2, and the first prism P1, astigmatism is added by the sensor optical system SE and converges on the light receiving surface of the light receiving element PD. Information recorded on the CD can be read using the output signal of the light receiving element PD.

  In the optical pickup device PU, the spherical aberration when using the BD can be corrected by driving the collimating optical system CL in the optical axis direction by the uniaxial actuator AC2. With such a spherical aberration correction mechanism, wavelength variations due to manufacturing errors of the blue-violet semiconductor laser LD1, refractive index change and refractive index distribution of the objective optical system with temperature change, focus jump between information recording eyebrows of multilayer disks, manufacturing of the protective substrate PL1 It is possible to correct spherical aberration due to thickness variation and thickness distribution due to error. The spherical aberration correction mechanism may correct spherical aberration when using a DVD or CD.

  FIG. 10 is a diagram schematically showing a configuration of an optical pickup device PU1 of another embodiment capable of appropriately recording / reproducing information with respect to BD, DVD and CD which are different optical disks. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical disc is a BD, the second optical disc is a DVD, and the third optical disc is a CD. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 emits a laser beam (first beam) of 405 nm that is emitted when recording / reproducing information with respect to the objective optical element OBJ, aperture stop ST, collimator lens CL, dichroic prism PPS, BD. One semiconductor laser LD1 (first light source), a first light receiving element PD1 that receives a reflected light beam from the information recording surface RL1 of the BD, a laser module LM, and the like.

  The laser module LM also emits a 658 nm laser beam (second beam) and emits a laser beam (second beam) of 658 nm when information is recorded / reproduced on a DVD, and a CD. A third semiconductor laser EP2 (third light source) that emits a 785 nm laser beam (third beam) when recording / reproducing information and a second beam that receives a reflected beam from the information recording surface RL2 of the DVD. Light receiving element DS1, a third light receiving element DS2 that receives a reflected light beam from the information recording surface RL3 of the CD, and a prism PS.

  As shown in FIG. 11, the objective optical element OBJ of the present embodiment is a single plastic aspheric lens. In the objective optical element OBJ of the present embodiment, a central region CN including the optical axis on the aspheric optical surface on the light source side, an intermediate region MD disposed around the central region CN, and a peripheral region OT disposed further around the central region CN Are formed concentrically around the optical axis. In FIG. 11, the ratio of the area of the central region, the intermediate region, and the peripheral region is not accurately represented. In the central region CN, a first optical path difference providing structure in which the first temperature characteristic correction structure, which is a ring-shaped step as described above, and the first compatible structure are superimposed is formed, and the intermediate region MD is formed in the above-described manner. A second optical path difference providing structure is formed by superimposing the second temperature characteristic correction structure that is an annular step and the second compatible structure, and the third temperature characteristic correction that is an annular step is formed in the peripheral region OT. A structure is formed. The first temperature characteristic correction structure makes the 10th-order diffracted light amount of the first light beam larger than any other order diffracted light amount, and the 6th-order diffracted light amount of the second light beam becomes larger than any other order diffracted light amount. The fifth order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. In the second temperature characteristic correction structure, the fifth-order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the third-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount. The second order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity. The third temperature characteristic correction structure makes the fifth-order diffracted light amount of the first light beam larger than any other order diffracted light amount, and makes the third-order diffracted light amount of the second light beam larger than any other order diffracted light amount. The second order diffracted light quantity of the third light beam is made larger than any other order diffracted light quantity.

  The first interchangeable structure is a structure in which the first basic structure and the second basic structure are overlapped. In the first basic structure, the second-order diffracted light amount of the first light beam is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount. The first-order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. In the second basic structure, the 0th-order diffracted light quantity of the first light beam is made larger than any other order diffracted light quantity, and the 0th-order diffracted light quantity of the second light beam is made larger than any other order diffracted light quantity. The ± 1st-order diffracted light quantity of the third light flux is made larger than any other order diffracted light quantity. The second interchangeable structure consists only of the first basic structure.

  The divergent light beam of the first light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD1 is transmitted through the dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and then linearly polarized by a λ / 4 wavelength plate (not shown). Is converted into circularly polarized light, its beam diameter is regulated by the stop ST, and becomes a spot formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.0875 mm by the objective optical element OBJ.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical element OBJ and the aperture stop ST, and then converted from circularly polarized light to linearly polarized light by a λ / 4 wavelength plate (not shown). After being transmitted through the dichroic prism PPS, it is converged on the light receiving surface of the first light receiving element PD1. Then, by using the output signal of the first light receiving element PD1 to focus or track the objective optical element OBJ by the biaxial actuator AC, information recorded on the BD can be read.

  The divergent light beam of the second light beam (λ2 = 658 nm) emitted from the red semiconductor laser EP1 is reflected by the prism PS, then reflected by the dichroic prism PPS, and converted into a parallel light beam by the collimator lens CL, and then λ (not shown). The light is converted from linearly polarized light to circularly polarized light by the / 4 wavelength plate and enters the objective optical element OJT. Here, the light beam condensed by the central region and the intermediate region of the objective optical element OBJ (the light beam that has passed through the peripheral region is flared and forms a spot peripheral portion) is passed through the protective substrate PL2 having a thickness of 0.6 mm. Thus, the spot is formed on the information recording surface RL2 of the DVD, and the center of the spot is formed.

  The reflected light beam modulated by the information pits on the information recording surface RL2 is again transmitted through the objective optical element OBJ and the aperture stop ST, and then converted from circularly polarized light to linearly polarized light by a λ / 4 wavelength plate (not shown). After being reflected by the dichroic prism PPS and then reflected twice in the prism, it is converged on the second light receiving element DS1. The information recorded on the DVD can be read using the output signal of the second light receiving element DS1.

  The divergent light beam of the third light beam (λ3 = 785 nm) emitted from the infrared semiconductor laser EP2 is reflected by the prism PS, then reflected by the dichroic prism PPS, converted into a parallel light beam by the collimator lens CL, and is not shown. The light is converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate and enters the objective optical element OJT. Here, the light beam condensed by the central region of the objective optical element OBJ (the light beam that has passed through the intermediate region and the peripheral region is flared and forms a spot peripheral part) is passed through the protective substrate PL3 having a thickness of 1.2 mm. Thus, the spot is formed on the information recording surface RL3 of the CD.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective optical element OBJ and the aperture stop ST, and then converted from circularly polarized light to linearly polarized light by a λ / 4 wavelength plate (not shown). After being reflected by the dichroic prism PPS and then reflected twice in the prism, it is converged on the third light receiving element DS2. The information recorded on the CD can be read using the output signal of the third light receiving element DS2.

When the first light beam emitted from the blue-violet semiconductor laser LD1 enters the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region, the second optical path difference providing structure in the intermediate region, and the second optical path difference providing structure in the peripheral region. The three optical path difference providing structure can appropriately correct the spherical aberration of the first light flux and appropriately record and / or reproduce information with respect to the BD having the thickness t1 of the protective substrate. When the second light beam emitted from the red semiconductor laser EP1 enters the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region and the second optical path difference providing structure in the intermediate region are BD and Corrects the spherical aberration of the second light beam caused by the difference in thickness of the protective substrate of the DVD and the wavelength difference between the first light beam and the second light beam, and records the second light beam in the peripheral area as a DVD information record. Since the flare is formed on the surface, information can be appropriately recorded and / or reproduced with respect to the DVD having the thickness t2 of the protective substrate. Further, when the third light beam emitted from the infrared semiconductor laser EP2 is incident on the objective optical element OBJ as a parallel light beam, the first optical path difference providing structure in the central region is different in the thickness of the protective substrate of BD and CD. In addition, the spherical aberration of the third light beam generated due to the difference in wavelength between the first light beam and the third light beam is appropriately corrected, and the second optical path difference providing structure in the intermediate region and the peripheral region are converted into the CD information. Since flare is formed on the recording surface, information can be appropriately recorded and / or reproduced with respect to the CD having the thickness t3 of the protective substrate. In addition, the first optical path difference providing structure in the central area separates the condensing spot of the necessary light of the third light beam used for recording and reproduction from the condensing spot of the unnecessary light of the third light beam by an appropriate distance, thereby The tracking characteristics when using a CD are also improved. In addition, the second optical path difference providing structure in the peripheral region has a spherochromatism (color spherical surface) when the wavelength of the first light flux and the second light flux deviates from the reference wavelength due to a manufacturing error of the laser. Aberration) can be corrected.
<Example 1>
Next, examples that can be used in the above-described embodiment will be described. The first embodiment is applied to the optical pickup device shown in FIG. 7, and the objective optical elements are, as described above, a polyolefin-based plastic flat optical element and a polyolefin-based plastic aspheric lens. It consists of.

Tables 1 and 2 show lens data of Example 1. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is expressed using E (for example, 2.5E−3).

  The optical surface of the objective optical element is formed as an aspherical surface that is axisymmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Equation (1).

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A _2i is an aspherical coefficient, and h is a height from the optical axis.

  Further, the optical path length given to the light flux of each wavelength by the optical path difference providing structure is defined by a mathematical formula obtained by substituting the coefficient shown in Table 1 into the optical path difference function of Formula 2.

λ is the wavelength of the incident light beam, λB is the manufacturing wavelength (blazed wavelength), dor is the diffraction order, and B _2i is the coefficient of the optical path difference function.

Regarding the temperature characteristics of the objective optical element of Example 1, δSAT1 is +0.0037 WFEλrms / ° C., and δSAT2 is +0.0022 WFEλrms / ° C. Further, since f of the objective optical element at the first wavelength is 2.2 mm, δSAT1 / f is +0.0017 WFEλrms / (° C. · mm). δSAT2 / f is +0.001 WFEλrms / (° C. mm). As for the wavelength characteristics of the objective optical element of Example 1, δSAλ is −0.0284 λrms / nm, and δSAλ / f is −0.0129 λrms / (nm · mm). When a collimator similar to the collimator used in Example 2 is used, δSAT3 is +0.0005 WFEλrms / ° C.
<Example 2>
Example 2 below can be applied to the optical pickup device of FIG. 10, and the objective optical element is a single-lens polyolefin-based plastic lens. A first optical path difference providing structure is formed on the entire surface of the central region CN of the optical surface of the objective optical element. A second optical path difference providing structure is formed on the entire surface of the intermediate region MD of the optical surface. A third optical path difference providing structure is provided on the entire surface of the peripheral area OT of the optical surface.

  In Example 2, the first optical path difference providing structure is a structure in which a first temperature characteristic correction structure (a structure in which the first basic structure and the second basic structure are overlapped) and a first compatibility structure are overlapped. Thus, two types of sawtooth diffraction structures and binary structures are superimposed. The cross-sectional shape is shown as a portion indicated as CN in FIG. The first temperature characteristic correction structure, which is a sawtooth diffractive structure, makes the light amount of the 10th-order diffracted light of the first light beam larger than the light amount of diffracted light of any other order (including 0th order, that is, transmitted light), The light quantity of the 6th-order diffracted light of the second light flux is made larger than the light quantity of the diffracted light of any other order (including 0th order, that is, transmitted light), and the light quantity of the 5th-order diffracted light of the third light flux It is designed to be larger than the diffracted light amount of the order (including the 0th order, that is, including the transmitted light).

  In Example 2, the second optical path difference providing structure is a structure in which the second temperature characteristic correcting structure and the second compatible structure are overlapped as shown in MD of FIG. The sawtooth diffraction structure is superimposed. The second temperature characteristic correction structure makes the light amount of the fifth-order diffracted light of the first light beam larger than the light amount of diffracted light of any other order (including the 0th order, that is, the transmitted light), and the third-order of the second light beam. The amount of diffracted light is made larger than the amount of diffracted light of any other order (including 0th order, that is, transmitted light), and the amount of light of the third and second order diffracted light of the third light flux is changed to any other order (0th order). That is, it is designed to be larger than the amount of diffracted light (including transmitted light).

  In Example 2, the third optical path difference providing structure is a structure having only the third temperature characteristic correction structure as shown as OT in FIG. 11, and only one type of sawtooth diffraction structure is used. It has a shape to have. The third temperature characteristic correction structure makes the light amount of the fifth-order diffracted light of the first light beam larger than the light amount of diffracted light of any other order (including 0th order, that is, transmitted light), and The amount of diffracted light is made larger than the amount of diffracted light of any other order (including 0th order, that is, transmitted light), and the amount of light of the third and second order diffracted light of the third light flux is changed to any other order (0th order). That is, it is designed to be larger than the amount of diffracted light (including transmitted light).

  Tables 3 to 5 below show lens data of Example 2. FIG. 12 is a longitudinal spherical aberration diagram according to Example 2. 12A is a longitudinal spherical aberration diagram for BD, FIG. 12B is a longitudinal spherical aberration diagram for DVD, and FIG. 12C is a longitudinal spherical aberration diagram for CD. In the longitudinal spherical aberration diagram, 1.0 on the vertical axis represents NA 0.85 or φ3.74 mm in the BD shown in FIG. 12A, and slightly smaller than NA 0.6 in the DVD shown in FIG. 12B. Or a value slightly larger than φ2.70 mm, and the CD shown in FIG. 12C represents a value slightly larger than NA0.45 or slightly larger than φ2.37 mm. In Example 2, L = 0.60 mm. Therefore, L / f = 0.60 / 2.53 = 0.237. However, f [mm] refers to the focal length of the third light flux that passes through the first optical path difference providing structure and forms the first best focus, and L [mm] is between the first best focus and the second best focus. Refers to distance. The first best focus is the position of the spot formed by the most diffracted light of the third light beam, and the second best focus is the second most diffracted light of the third light beam. This is the position of the spot formed by light. In this embodiment, the first best focus is used for CD recording / reproduction.

  Regarding the temperature characteristics of the objective optical element of Example 2, δSAT1 is +0.0033 WFEλrms / ° C., and δSAT2 is +0.0019 WFEλrms / ° C. Further, since f of the objective optical element at the first wavelength is 2.2 mm, δSAT1 / f is +0.0015 WFEλrms / (° C. mm). δSAT2 / f is +0.0009 WFEλrms / (° C. mm). As for the wavelength characteristics of the objective optical element of Example 2, δSAλ is −0.03λrms / nm, and δSAλ / f is −0.0136λrms / (nm · mm).

  Further, when a single collimator lens CL made of the same material (polyolefin plastic) as the objective optical element is used as the collimator lens CL, and the objective optical element of Example 2 is used in combination, δSAT3 is + 0.0004WFEλrms / ° C., and δSAT3 / f is + 0.0002WFEλrms / (° C. mm). The lens data of the collimator lens is shown in Table 6 below.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

Claims (12)

A first light source that emits a first light flux with a wavelength λ1 (nm), a second light source that emits a second light flux with a wavelength λ2 (nm) (λ1 <λ2), and a wavelength λ3 (nm) (λ2 <λ3) An objective optical element for an optical pickup device having a third light source that emits a third light beam and an objective optical element,
The objective optical element has at least one plastic lens;
The optical surface of the objective optical element includes at least three regions: a central region including an optical axis, an intermediate region disposed around the central region, and a peripheral region disposed around the intermediate region,
The objective optical element focuses the first light flux that has passed through the central region, the intermediate region, and the peripheral region on the information recording surface of the first optical disc through a protective substrate having a thickness t1. It is possible to record and / or reproduce information, and the second light flux that has passed through the central area and the intermediate area is passed through a protective substrate having a thickness t2 (t1 ≦ t2). Information can be recorded and / or reproduced by condensing on the information recording surface of the second optical disc, and the third light flux that has passed through the central region has a thickness t3 (t2). It is possible to record and / or reproduce information by focusing on the information recording surface of the third optical disc via the protective substrate of <t3),
The central region has a first temperature characteristic correction structure having a plurality of concentric annular zone steps,
The intermediate region has a second temperature characteristic correction structure having a plurality of concentric annular zone steps,
The peripheral region has a third temperature characteristic correction structure having a plurality of concentric annular zone steps,
The first temperature characteristic correction structure increases the r-th order diffracted light amount of the first light flux that has passed through the first temperature characteristic correction structure to be larger than any other order diffracted light amount. The s-order diffracted light amount of the second light flux that has passed through the second light beam is made larger than any other order of diffracted light amount, and the t-order diffracted light amount of the third light flux that has passed through the first temperature characteristic correction structure is Is an optical path difference providing structure that is larger than the diffracted light quantity of any order of
The second temperature characteristic correction structure makes the u-order diffracted light amount of the first light flux that has passed through the second temperature characteristic correction structure larger than any other order of diffracted light amount, and the second temperature characteristic correction structure. An optical path difference providing structure that makes the v-th order diffracted light amount of the second light flux that has passed through the light beam larger than any other order diffracted light amount,
The third temperature characteristic correction structure is an optical path difference providing structure that makes the x-order diffracted light quantity of the first light flux that has passed through the third temperature characteristic correction structure larger than any other order diffracted light quantity,
(R, s, t) = (10, 6, 5) or (2, 1, 1)
(U, v) = (10, 6), (5, 3) or (2, 1)
An objective optical element for an optical pickup device, wherein x is an arbitrary integer. (R, s, t) = (2,1,1)
(U, v) = (5, 3) or (2, 1)
2. The objective optical element for an optical pickup device according to claim 1, wherein x = 1 to 5.   The composite structure formed by combining the first temperature characteristic correction structure and the second temperature characteristic correction structure becomes deeper in the optical axis direction as the height from the optical axis increases, 3. The objective optical element for an optical pickup device according to claim 1, wherein the objective optical element is shallow in the optical axis direction as the height from the axis increases.   The composite structure formed by combining the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure becomes deeper in the optical axis direction as the height from the optical axis becomes higher. 3. The objective optical element for an optical pickup device according to claim 1, wherein the objective optical element becomes shallower in the optical axis direction as the height from the optical axis becomes higher.   5. The optical pickup device according to claim 4, wherein the depth of the composite structure returns before the height from the optical axis reaches the third temperature characteristic correction structure. 6. Objective optical element. The plastic forming the objective optical element has a refractive index change rate dN / dT (° C. ⁻¹ ) with respect to a wavelength of 405 nm accompanying a temperature change within a temperature range of −5 ° C. to 70 ° C., from −20 × 10 ^{−5 to} objective optical element for the optical pickup device according to any one of claims paragraphs 1 through fifth term, which is a range of -5 × 10 ^-5.   The objective optical element for an optical pickup device according to any one of claims 1 to 6, wherein the objective optical element includes a flat optical element and a lens having an aspherical surface. .   8. The optical pickup according to claim 7, wherein the flat optical element includes the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure. Objective optical element for equipment.   8. The objective for an optical pickup device according to claim 7, wherein the lens includes the first temperature characteristic correction structure, the second temperature characteristic correction structure, and the third temperature characteristic correction structure. Optical element.   The objective optical element for an optical pickup device according to any one of claims 1 to 6, wherein the objective optical element comprises only a single lens made of plastic.   11. The structure according to claim 1, further comprising a structure in which an interchangeable structure having a plurality of concentric annular zone steps is superimposed on the first to third temperature characteristic correction structures. Objective optical element for the optical pickup device described in 1.   An optical pickup device comprising the objective optical element according to any one of claims 1 to 11.