JP2010238277A - Optical pickup device and objective lens unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device which can properly record/reproduce information to/from an optical disk having a plurality of information recording layers, and to provide an objective lens unit. <P>SOLUTION: An opening limiting element AP can be moved by a driving mechanism DR in the direction of the optical axis of an objective lens OL. Then, NA1≈NA0≈NA2 can be attained by changing the optical axis direction position of the opening limiting element AP in accordance with magnification m, so that a change in a numerical aperture can be suppressed, when the numerical aperture is defined as NA0 when a parallel luminous flux indicated by a solid line is made incident on the object lens OL (m=0), the numerical aperture as NA1 when diverging light indicated by a dotted line is made incident (m>0), and the numerical aperture as NA2 when converging light indicated by a chain line is made incident (m<0). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an optical pickup device and an objective lens unit capable of recording / reproducing information with respect to an optical disc having a plurality of information recording layers.

  In a DVD (Digital Versatile Disc), a BD (Blu-ray Disc), or the like, one having two information recording layers is known as means for increasing the recording capacity. In response to the recent demand for larger capacity, optical discs (multilayer discs) and optical pickup devices having a plurality of information recording layers of three or more layers have been developed, particularly having eight or more information recording layers. The optical disk is called a super multi-layer disk.

  As an example, Patent Document 1 discloses information on an optical disc including a guide track layer having a concavo-convex portion and a plurality of information recording layers made of an optical recording material provided above and below the guide track layer. An optical pickup device capable of recording / reproducing data is disclosed.

  By the way, the information recording layer for recording / reproducing information is selected by moving the objective lens in the optical axis direction and correcting the spherical aberration caused by the difference in the thickness of the information recording layer. This can be done by moving the coupling lens or the like arranged between and in the optical axis direction and changing the magnification of the objective lens. However, when the magnification of the optical system is changed, the divergence angle or convergence angle of the light beam incident on the objective lens changes, and the numerical aperture (NA) of the objective lens, which should be essentially constant, may change. The change in NA causes a change in spot diameter on the information recording surface, which may cause a reading error or the like. In the conventional optical pickup device, the number of information recording layers is as small as about 1 to 2 layers, and the change in the magnification for accommodating a plurality of layers is 0 or small, so the problem of change in NA does not become obvious. However, when the number of information recording layers is increased, the thickness change is as large as 0.2 mm to 0.6 mm, and the NA is high NA such as 0.7 or more and 0.9 or less, the information A change in magnification when selecting a recording layer is increased. In such an optical pickup device, the present inventor has found that the problem of NA change accompanying change in magnification becomes particularly significant.

JP 2008-21348 A JP 2002-17027 A

  On the other hand, according to Patent Document 2, in the next-generation optical disc system, when an objective lens having a high numerical aperture of NA = 0.85 is used, the spherical aberration is corrected according to the variation in the thickness of the cover layer of the optical disc. It is described that when the magnification is changed by the beam expander, a change in NA occurs. This corrects the spherical aberration caused by the thickness variation of one cover layer, not a plurality of information recording layers, but is the same phenomenon as the magnification change at the time of selecting the information recording layer in the super multi-layer disc. It can be said. However, as a countermeasure against the change in NA, in the prior art of Patent Document 2, the aperture stop is separated from the objective lens by a substantial focal length to the light source side. In this case, the change in NA increases due to the change in magnification. Regardless of the description in Patent Document 2, it can be said that the change in NA cannot be suppressed.

  The present invention has been made in view of the problems of the prior art, and provides an optical pickup device and an objective lens unit capable of appropriately recording / reproducing information with respect to an optical disc having a plurality of information recording layers. With the goal.

The optical pickup device according to claim 1 includes a first light source, a spherical aberration correction element, an aperture limiting element, and an objective lens, and a light beam having a wavelength λ1 emitted from the first light source. It has a plurality of information recording layers that are incident on the objective lens through the spherical aberration correction element and the aperture limiting element and are stacked in the optical axis direction, and the thickness from the surface to the deepest information recording layer is 0. Information is recorded / reproduced by focusing on one of the information recording layers of the first optical disc having a diameter of 2 mm or more and 0.6 mm or less, and the spherical aberration correction element attempts to record / reproduce information. An optical pickup device adapted to correct spherical aberration caused by a difference in information recording layer by changing the magnification of the objective lens,
The objective lens is a single ball, and the numerical aperture of the objective lens is 0.7 or more and 0.9 or less,
It has a drive mechanism which changes the optical axis direction position of the aperture limiting element according to the change of the magnification.

  The principle of the present invention will be described with reference to FIG. FIG. 1A is an optical path diagram of the objective lens OL and the aperture limiting element AP shown as a comparative example, and FIG. 1B is an optical path diagram of the objective lens OL and the aperture limiting element AP shown as an example of the present invention. Yes, the left side is the light source side, and the right side is the optical disc side. In the comparative example of FIG. 1A, the aperture limiting element AP is fixedly arranged on the light source side with respect to the surface vertex P of the objective lens OL. Therefore, when the numerical aperture when the parallel light beam indicated by the solid line is incident on the objective lens OL is NA0, the magnification of the objective lens is changed, and the numerical aperture when the divergent light indicated by the dotted line is incident is NA1 or It can be seen that the numerical aperture NA2 is NA1> NA0> NA2 when the magnification of the objective lens is changed and the convergent light indicated by the alternate long and short dash line is incident, and the numerical aperture is changed.

  On the other hand, according to the present invention, as shown in FIG. 1B, the aperture limiting element AP can be moved in the optical axis direction of the objective lens OL by the drive mechanism DR. When the numerical aperture when the parallel luminous flux indicated by the solid line enters the objective lens OL (m = 0) is NA0, the magnification of the objective lens changes, and the divergent light indicated by the dotted line is incident (m> 0) NA1 or the magnification of the objective lens is changed, and when convergent light indicated by a one-dot chain line is incident (m <0), the numerical aperture NA2 is the optical axis of the aperture limiting element AP according to the magnification m. It can be seen that by changing the direction position, NA1≈NA0≈NA2 can be achieved, thereby suppressing the change in numerical aperture.

  As a result of the inventor's investigation, it was found that when the NA is small, such as 0.6, the problem of the present invention that the NA changes with the magnification change does not become large. A certain NA of 0.7 or more was defined as the scope of the present invention. When NA is 0.7 or more, in an optical disc having a plurality of information recording layers, the magnification fluctuation necessary for correcting spherical aberration that occurs when focusing on an information recording layer different from an information recording layer is large. Thus, the problem of the present invention is that the NA change that occurs is increased accordingly. On the other hand, when NA is larger than 0.9, the spherical aberration generated when the light is condensed on an information recording layer different from a certain information recording layer becomes excessive, and it is not at a level that can be corrected by a variation in magnification. Therefore, NA of 0.9 or less was set as the scope of the present invention.

An optical pickup device according to a second aspect is characterized in that, in the invention according to the first aspect, a position in the optical axis direction of the aperture limiting element in accordance with the change in the magnification satisfies the following expression.
−0.020 ≦ m × (D / f) ≦ 0.018 (1)
However, m is the magnification D [mm] of the objective lens, and the distance f [mm] in the optical axis direction from the light source side surface vertex of the objective lens to the aperture limiting position of the aperture limiting element is the objective lens at the wavelength λ1. Focal length

  When the magnification m of the objective lens, the distance D from the light source side surface vertex of the objective lens to the aperture limiting element, and the focal length f of the objective lens are within a range satisfying the expression (1), the change in magnification It can be said that it is preferable for practical use.

According to a third aspect of the present invention, there is provided an optical pickup device according to the first or second aspect of the present invention, wherein when the light flux having the wavelength λ1 is incident at a design magnification, the sine is between 50% and 90% of the effective aperture radius h. The coma aberration correction state is set so that the condition violating amount has a positive maximum value, and the sine condition violating amount is reduced in the peripheral portion, and the following equation is satisfied.
0.015 <SC _max /f<0.045 (2)
However, SC _max is the maximum value of the sine condition violation amount.

According to the present invention, the change in spherical aberration due to the change in magnification of the objective lens of the light beam having the wavelength λ1 is substantially similar to the change in spherical aberration due to the change in position of the information recording layer for recording / reproducing information. It is. More specifically, when the light beam of λ1 is incident on the objective lens at a design magnification, the sine condition violation amount has a positive maximum value between 50% and 90% of the effective aperture radius h. The coma aberration correction state is set so that the amount of violation of the sine condition is reduced at the periphery, and the conditional expression (4) is satisfied, where SC _max is the maximum value of the sine condition violation amount and f is the focal length. It is. As a result, it is possible to appropriately correct the spherical aberration caused by the change in the position of the information recording layer for recording / reproducing information without changing the higher-order aberration, by changing the divergence convergence degree of the incident light. Become. Here, the “substantially similar shape” means a higher order when spherical aberration caused by a change in the position of the information recording layer for recording / reproducing information is corrected by a change in the magnification of the objective lens of the light beam of λ1. It means that the spherical aberration is below the Marechal limit (0.07λrms). “High-order spherical aberration” refers to fifth-order or higher spherical aberration. When the light beam having the wavelength λ1 is incident on the objective lens at the design magnification, it is preferable that the sine condition violation amount monotonously decreases in the peripheral portion from the position where the sine condition violation amount has a positive maximum value. “Monotonically decreasing” means that it continues to decrease, at least means that it decreases once and never increases, and preferably, the reduction rate does not change greatly at a certain position. This also means. Preferably, when the light beam having the wavelength λ1 is incident on the objective lens at the design magnification, the sine condition violation amount has a positive maximum value between 60% and 90% of the effective aperture radius h.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the wavelength λ1 is 390 nm ≦ λ1 ≦ 420 nm.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to third aspects, the wavelength λ1 is 520 nm ≦ λ1 ≦ 540 nm.

  According to a sixth aspect of the present invention, there is provided the optical pickup device according to any one of the first to fifth aspects, wherein a light beam having a wavelength λ1 emitted from the first light source is recorded on a Blu-ray Disc by the objective lens. Since the information is recorded / reproduced by focusing on the surface, the information can be recorded / reproduced to be compatible with the super multi-layer disc and the Blu-ray Disc.

  According to a seventh aspect of the present invention, in the optical pickup device according to any of the first to sixth aspects, in addition to the first light source, a second light source that emits a light beam having a wavelength λ2 (λ1 <λ2). And recording / reproducing information by making a light beam of wavelength λ2 emitted from the second light source incident on the objective lens and condensing it on an information recording layer of a second optical disc. To do.

  An optical pickup device according to an eighth aspect of the present invention is the invention according to any one of the first to sixth aspects, further comprising a second objective lens in addition to the objective lens, and a wavelength in addition to the first light source. an information recording layer of a second optical disc having a second light source that emits a light beam having a wavelength of λ2 (λ1 <λ2), the light beam having a wavelength of λ2 emitted from the second light source being incident on the second objective lens; It is characterized in that information is recorded / reproduced by condensing light on the light.

  The objective lens unit according to claim 9 has an objective lens unit having an aperture limiting element and an objective lens, a first light source, and a spherical aberration correction element, and a wavelength emitted from the first light source. A light beam of λ1 is made incident on the objective lens through the spherical aberration correction element and the aperture limiting element, and has a plurality of information recording layers stacked in the optical axis direction, from the surface to the deepest information recording layer. Information is recorded / reproduced by focusing on any information recording layer of the first optical disc having a thickness of 0.2 mm or more and 0.6 mm or less, and the spherical aberration correction element is configured to record / reproduce information. An objective lens unit used in an optical pickup device adapted to correct spherical aberration caused by a difference in an information recording layer to be reproduced by changing a magnification of the objective lens. The objective lens is a single lens, the numerical aperture of the objective lens is 0.7 or more and 0.9 or less, and a driving mechanism that changes the position of the aperture limiting element in the optical axis direction according to the change of the magnification. It is characterized by having.

  The optical pickup device according to the present invention includes a first light source that emits a light beam having a wavelength λ1, but a second light source that emits a light beam having a wavelength λ2 (λ1 <λ2) and / or a wavelength λ3 (λ2 <λ3). You may have the 3rd light source which radiate | emits this light beam. Furthermore, the optical pickup device of the present invention condenses the light beam having the wavelength λ2 emitted from the second light source on the guide layer of the optical disk, and simultaneously converts the light beam having the wavelength λ1 emitted from the first light source to the optical disk. You may have the condensing optical system for condensing in any layer of an information recording layer. Moreover, the optical pickup device of the present invention may have a light receiving element that receives a reflected light beam from the information recording surface and the guide layer of the optical disc.

  The first optical disk used in the optical pickup device of the present invention has a plurality of information recording layers stacked in the thickness direction (optical axis direction). The optical pickup device of the present invention can be more suitably used in an optical disc having eight or more information recording layers. More preferably, it has 8 or more and 20 or less information recording layers. The thickness from the optical disk surface to the information recording surface of the deepest information recording layer is 0.2 mm or more and 0.6 mm or less. Further, the optical disc may have a guide layer in which position information is recorded. There may be only one guide layer or a plurality of guide layers, but it is preferably less than the number of information recording layers, and it is less than half the number of information recording layers. This facilitates the design and is preferable. In addition, when the numerical aperture NA necessary for recording / reproducing information on the optical disc is 0.7 or more and 0.9 or less, the effect of the present invention becomes more remarkable, and the NA is 0.8 or more. When the ratio is 0.9 or less, it becomes more prominent. Further, when NA is 0.8 or more and 0.9 or less, compatibility with BD is facilitated, which is also preferable in this respect. The optical disk preferably has a protective layer on the surface, and the thickness of the protective layer is not particularly limited, but is 0.6 mm or less when the numerical aperture of the objective lens is 0.7 or more. It is preferable that it is 0.2 mm or less. Further, when the information recording layer is 8 layers or more, or when the thickness of the plurality of information recording layers excluding the protective layer is 0.1 mm or more, the effect of the present invention becomes more remarkable, which is preferable. .

  However, the optical pickup device of the present invention may be an optical pickup device that is compatible with at least one or all of BD, DVD, and CD in addition to the optical disc.

  In the BD, information is recorded / reproduced by an objective lens having an NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. DVD is a general term for DVD-series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67, and the thickness of the protective substrate is about 0.6 mm. DVD-ROM, DVD -Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, etc. CD is a general term for CD optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.53, and the thickness of the protective substrate is about 1.2 mm. CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by HD, DVD, and CD in that order.

  In the present specification, the light sources such as the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) preferably satisfies the following conditional expression.

1.5 × λ1 <λ2 <1.7 × λ1
1.9 × λ1 <λ3 <2.1 × λ1

  The first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm or more and 420 nm or less, and the second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, More preferably, the third wavelength λ3 of the third light source is preferably 750 nm or more and 880 nm or less, and more preferably 760 nm or more and 820 nm or less when the third light source is provided. As the first light source, one having a first wavelength λ1 of 520 nm or less and 540 nm or less may be used.

  Further, at least two of the first light source, the second light source, and 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.

  The optical pickup device may include a light receiving element that receives a light beam reflected from the optical disk. 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 light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking 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 elements corresponding to the respective light sources.

  The condensing optical system used for the optical pickup device has an objective lens. The condensing optical system may include only the objective lens, but may include a coupling lens such as a collimator lens in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that emits light incident on the collimating lens as parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing the light beam emitted from the light source onto the information recording surface of the optical disk. Preferably, the objective lens is an optical system which is disposed at a position facing the optical disk 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, and further includes an actuator An optical system that can be integrally displaced at least in the optical axis direction.

  The objective lens is a single objective lens. The objective lens preferably has a refractive surface that is aspheric.

  The objective lens may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like.

  When the objective lens is a glass lens, the influence of temperature change in the optical pickup device can be reduced.

When the objective lens is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.52 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) is −20 × 10 ^{−5 to} −5 × 10 ^{− with} respect to the wavelength of 405 nm accompanying the temperature change within the range of −5 ° C. to 70 ° C. ^It is more preferable to use a resin material within a range of ⁵ (more preferably, −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective lens is a plastic lens, the coupling lens is preferably a plastic lens.

  Moreover, it is preferable that the Abbe number of the material which comprises an objective lens is 50 or more.

  The objective lens may have an optical path difference providing structure for correcting a spherical aberration caused by a change in refractive index with respect to a temperature change or a spherical aberration caused by a change in wavelength of the light source. 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. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference / phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. Preferably, the optical path difference providing structure is a diffractive structure.

  It should be noted that information recording / reproduction of an information recording layer (referred to as layer A) of an optical disc having a plurality of information recording layers is performed, and then information recording / reproduction of another information recording layer (referred to as layer B) is performed. When performing the above, spherical aberration due to the difference between the thickness from the optical disk surface to the layer A and the thickness from the optical disk surface to the surface layer B occurs. Therefore, a spherical aberration correction element that corrects the spherical aberration caused by the difference in thickness from the optical disk surface to the information recording layer in different information recording layers is required.

  Examples of such spherical aberration correction means include a liquid crystal device that corrects spherical aberration of a light beam having a wavelength λ1, and at least one lens that is movable in the optical axis direction. Examples include first magnification conversion means for changing. Examples of the first magnification conversion unit include the above-described single ball coupling lens movable in the optical axis direction, a single ball collimator lens, at least one positive lens and at least one negative lens. Examples include a two-group coupling lens that can move these in the optical axis direction, a beam expander that has at least one positive lens and at least one negative lens, and one of them can move in the optical axis direction.

  Moreover, the optical pickup device may include a second magnification conversion unit that changes the magnification of the objective lens of the light beam having the wavelength λ2 when the light beam having the wavelength λ2 can be used. Examples of the second magnification conversion means include the above-described single coupling lens movable in the optical axis direction, a single collimator lens, at least one positive lens and at least one negative lens, Examples include a two-group coupling lens that can move these in the optical axis direction, a beam expander that has at least one positive lens and at least one negative lens, and one of them can move in the optical axis direction. By including the second magnification conversion means, it is possible to easily cope with an optical disc having a plurality of guide layers.

  Furthermore, it is preferable that the optical pickup device has first focusing means for focusing the light beam having the wavelength λ1 on any one of the information recording layers.

  In addition, the optical pickup device preferably includes second focusing means for focusing the light beam having the wavelength λ2 on the guide layer. For example, it is preferable to have an actuator for moving and adjusting the position of the objective lens in the optical axis direction for this purpose.

  The optical pickup device of the present invention has an aperture limiting element. Examples of the aperture limiting element include a generally used donut-shaped aperture, and the case where the aperture of the pickup bobbin also serves as the aperture.

  As described in FIGS. 1 and 2, the objective lens and the aperture limiting element may be separated. Further, as shown in FIGS. 12 and 13, an objective lens unit in which the objective lens OL and the aperture limiting element AP are integrated may be used. FIG. 12 shows an example in which the objective lens OL and the aperture AP which is an aperture limiting element are integrated by a lens barrel LB. (The objective lens unit also has a drive means for driving the aperture limiting element, but it is not shown.) FIG. 13 shows the light source of the flange portion by extending the flange portion FL of the objective lens OL toward the light source side in the optical axis direction. This is an example in which a diaphragm AP, which is an aperture limiting element, is fixed to the side tip and integrated. (The objective lens unit also has driving means for driving the aperture limiting element, but it is not shown.)

  Furthermore, various actuators such as a PLZT, a voice coil motor, and a piezoelectric conversion element can be used as a driving device that drives the aperture limiting element in the optical axis direction. The drive position of the aperture limiting element is converted from the position in the optical axis direction of the spherical surface aberration correction element by obtaining the optimum position for the magnification m of the objective lens in advance and storing it in the form of a table or the like through experiments or simulations. The aperture limiting element can be driven to the target position based on the table or the like according to the current magnification m.

Further, the position of the aperture limiting element in the optical axis direction according to the change in magnification is preferably arranged closer to the optical disc than the light source side surface of the objective lens. More preferably, the following expression is satisfied.
−0.020 ≦ m × (D / f) ≦ 0.018 (1)
However, m is the magnification D [mm] of the objective lens, and the distance f [mm] in the optical axis direction from the light source side surface vertex of the objective lens to the aperture limiting position of the aperture limiting element is the objective lens at the wavelength λ1. Focal length

  The distance in the optical axis direction to the aperture limiting position of the aperture limiting element will be described below. When a very thin stop as shown in FIG. 14 is used as the aperture limiting element, the aperture limiting position is AL, and D is the length shown in FIG. 14 (from the light source side lens surface vertex to the surface of the aperture limiting element). Distance). On the other hand, when an edge-shaped stop as shown in FIG. 15 is used as the aperture limiting element, the aperture limiting position is AL at the edge tip, and D is the length shown in FIG. Distance to the edge tip of the limiting element). In addition, when a thick flat diaphragm as shown in FIG. 16 is used as the aperture limiting element, the aperture limiting position is set as an intermediate point AL of the thickness in the optical axis direction of the diaphragm, and D is a length ( Distance from the vertex of the light source side lens surface to the intermediate point of the aperture limiting element).

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

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

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

  According to the present invention, when information is recorded / reproduced on an optical disc having a plurality of information recording layers and a large required numerical aperture, the numerical aperture is changed even if the spherical aberration is corrected by changing the magnification. It is possible to provide an optical pickup device and an objective lens unit that can suppress and appropriately record / reproduce information.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG. The optical pickup device PU1 according to the present embodiment can be incorporated in an optical disk drive device. FIG. 1 is a diagram showing a schematic configuration of the optical pickup device PU1. The optical pickup device PU1 is capable of recording / reproducing information so as to be compatible with four types of optical discs, that is, a multilayer optical disc (MLD), a Blu-ray disc (BD), a digital versatile disc (DVD), and a compact disc (CD). is there. Here, the multilayer optical disk MLD is a guide track in which a plurality of (eight or more layers) information recording layers RL capable of recording information stacked in the thickness direction and pits as position information for tracking servo control are formed. Layer GL.

The optical pickup device PU1 includes a blue-violet semiconductor laser LD1, an LD2 in which a red semiconductor laser and an infrared semiconductor laser are integrated in one package, a first polarization beam splitter PBS1, a first lens BE1 of a beam expander, and a first lens BE1. A two-lens BE2, a first dichroic prism DBS1, a second dichroic prism DBS2, a λ / 4 wavelength plate QWP, a raising mirror ML, a first objective lens OL1, a second objective lens OL2, and a first sensor. Lens SL1, second sensor lens SL2, pinhole PH, first photodetector PD1, second photodetector PD2, first coupling lens CP1, second coupling lens CP2, biaxial Actuator AC1, first actuator AC2, second actuator AC3, third actuator Having over data AC4. The single objective lens OL1 is used for recording / reproduction of a multilayer optical disc, BD, and DVD, and the second objective lens OL2 is used for recording / reproduction of a CD. The first aperture limiting element AP1 disposed immediately before the first objective lens OL1 having a numerical aperture of 0.7 or more is moved in the optical axis direction by a driving unit (not shown). Further, as shown in FIG. 1B, the first aperture limiting element AP1 is provided on the optical disc side from the surface vertex of the first objective lens OL1, and in the optical axis direction so as to satisfy the following expression (1). Moving. Furthermore, the objective lens satisfies the following formula (2).
−0.020 ≦ m × (D / f) ≦ 0.018 (1)
0.015 <SC _max /f<0.045 (2)
However, when m is the magnification of the objective lens, D [mm] is the distance f [mm] from the light source side surface apex of the objective lens to the aperture limiting element, and the focal length SC _max of the objective lens is the sine condition violation amount. Local maximum

  The red semiconductor laser in the LD 2 emits red laser light having a wavelength of λ2 = 650 nm to 680 nm. The red laser light is used as servo light that is applied to the guide track layer GL to read tracking information when information is recorded / reproduced with respect to the multilayer optical disk MLD, and information is recorded on the information recording layer of the DVD. Is used as recording / reproducing light for performing recording / reproducing, and its numerical aperture is NA 0.65. On the other hand, the blue-violet semiconductor laser LD1 emits blue-violet laser light having a wavelength of λ1 = 390 nm to 420 nm. The blue-violet laser beam is focused on each information recording layer of the multilayer optical disc MLD, used as recording / reproducing light for recording / reproducing information, and also for recording / reproducing information on the BD information recording layer. It is also used as recording / reproducing light for reproducing, and its numerical aperture is NA 0.85. The infrared semiconductor laser in the LD 2 emits infrared laser light having a wavelength of λ3 = 760 nm to 820 nm. Infrared laser light is used as recording / reproducing light for recording / reproducing information on / from a CD.

  The first objective lens OL1 is an objective lens that can be applied to three types of optical disks MLD, BD, and DVD. On the other hand, the second objective lens OL2 is an objective lens that is compatible with CD.

  A drive mechanism for the aperture limiting element will be described. FIG. 3 is a perspective view of the driving mechanism DR that drives the first aperture limiting element AP1, and shows the first objective lens OL1 and the beam expander lens BE1, but the other configurations are omitted. The first objective lens OL1 is held by a lens holder LH1, and the drive mechanism DR is provided on the lens holder LH1. The first aperture limiting element AP1 has a ring shape with a thin inner peripheral edge, and is connected to a connecting portion DH1a that receives a driving force.

  The end portion of the connecting portion DH1a is provided with a square groove DH1b having a shape corresponding to and in contact with the quadrangular columnar drive shaft XDS, and the leaf spring XSG is sandwiched between the square shaft DH1b and the drive shaft XDS. It is attached. A drive shaft XDS, which is a drive member sandwiched between the connecting portion DH1a and the leaf spring XSG, extends in the optical axis direction of the first objective lens OL1, and is appropriately pressed by the urging force of the leaf spring XSG. ing. One end of the drive shaft XDS is a free end, and the other end is connected to a piezoelectric actuator XPZ which is an electromechanical conversion element. The piezoelectric actuator XPZ is attached to the side wall of the lens holder LH1. The piezoelectric actuator XPZ receives a drive signal from a control circuit CPU that receives a signal from the actuator AC3 of the lens BE1 of the beam expander.

  The piezoelectric actuator XPZ is formed by laminating piezoelectric ceramics formed of PZT (zircon / lead titanate) or the like. Piezoelectric ceramics have a property in which the center of gravity of the positive charge and the center of gravity of the negative charge in the crystal lattice do not coincide with each other, are themselves polarized, and extend when a voltage is applied in the polarization direction. However, since the distortion of the piezoelectric ceramics in this direction is very small and it is difficult to drive the driven member by the amount of distortion, a plurality of piezoelectric ceramics PE are stacked between the electrodes as shown in FIG. A laminated piezoelectric actuator having a structure in which C is connected in parallel is provided as a practical one. In the present embodiment, this stacked piezoelectric actuator PZ is used as a drive source.

  Next, a driving method of the first aperture limiting element AP1 will be described. In general, a laminated piezoelectric actuator has a small displacement when a voltage is applied, but has a large generated force and sharp response. Therefore, when a pulse voltage having a substantially sawtooth waveform with a sharp rise and a slow fall as shown in FIG. 5A is applied to the piezoelectric actuator XPZ, the piezoelectric actuator XPZ suddenly extends and rises at the rise of the pulse. It shrinks more slowly when it falls. Therefore, when the piezoelectric actuator XPZ is extended, the driving shaft XDS is pushed out to the near side in FIG. 3 by the impact force, but the connecting portion DH1a of the first opening limiting element AP1 and the leaf spring XSG are driven by the inertia of the driving shaft XDS. Does not move together with the drive shaft XDS, and slips with the drive shaft XDS and stays in that position (may move slightly). On the other hand, when the pulse falls, the drive shaft XDS returns more slowly than when the pulse rises. Therefore, the connecting portion DH1a and the leaf spring XSG do not slide with respect to the drive shaft XDS, and are integrated with the drive shaft XDS as shown in FIG. Move to the side. That is, by applying a pulse whose frequency is set to several hundred to several tens of thousands of hertz, the first aperture limiting element AP1 can be continuously moved at a desired speed in the optical axis direction.

  That is, the control circuit CPU that has received a signal from the actuator AC3 of the lens BE1 of the beam expander applies a predetermined pulse input to the piezoelectric actuator XPZ, thereby causing the first aperture limiting element AP1 to move in the optical axis direction. It can be continuously moved at a desired speed. As is clear from the above, as shown in FIG. 5B, when a pulse with a slow rising voltage and a sharp falling edge is applied, the first aperture limiting element AP1 can be moved in the opposite direction. it can. In the present embodiment, since the drive shaft XDS has a quadrangular prism shape (anti-rotation mechanism), the anti-rotation function of the first aperture limiting element AP1 is exhibited, and the tilt of the first aperture limiting element AP1 is suppressed. There is no need to provide a guide shaft.

  Information recording / reproduction in the multilayer optical disk MLD will be described. In the optical pickup device PU1 shown in FIG. 2, the divergent light beam emitted from the red semiconductor laser of LD2 passes through the second polarization beam splitter PBS2 and the second coupling lens CP2, is reflected by the first dichroic prism DBS1, and λ / 4 wave plate QWP, reflected by the second dichroic prism DBS2, passes through the first aperture limiting element AP1, enters the first objective lens OL1, and then passes through the protective substrate of the multilayer optical disk MLD. It becomes a spot formed on GL.

  In the present embodiment, the coupling lens CP2 can be moved in the optical axis direction by the third actuator AC4, and the magnification of the first objective lens OL1 at the wavelength λ2 can be converted. Even if it has a plurality of guide layers, it is possible to cope with the change in temperature when the first objective lens is a plastic lens, and also for the minute change in the protective layer thickness up to the guide layer. It becomes possible.

  The reflected light beam modulated by the pits in the guide layer GL again passes through the first objective lens OL1 and the first aperture limiting element AP1, is reflected by the second dichroic prism DBS2, passes through the λ / 4 wavelength plate QWP, The light is reflected by the 1 dichroic prism DBS1, passes through the coupling lens CP2, is further reflected by the second polarization beam splitter PBS2, and enters the second photodetector PD2 via the second sensor lens SL2. The tracking position of the multilayer optical disk MLD can be read from the output signal of the second photodetector PD2. Based on such tracking information, the biaxial actuator AC1 and / or the third actuator AC4 can be driven to perform tracking servo control on the track of the guide layer GL, and thereby the information recording layer of the multilayer optical disc MLD. Even if tracking information is not recorded in the RL, information can be recorded / reproduced appropriately. Accordingly, the irradiation of the red semiconductor laser of the LD 2 is continuously performed while information recording / reproduction is being performed on the information recording layer RL.

  Here, when recording / reproducing information with respect to any information recording layer RL of the multilayer optical disc MLD, the second actuator AC3 is driven to move the first lens BE1 of the beam expander in the optical axis direction. Displacement is performed to change the divergence angle of the incident light beam to the first objective lens OL1, and to change the magnification of the first objective lens. Thereby, any of the information recording layers desired to be recorded / reproduced can be arbitrarily selected. At this time, the control circuit CPU (FIG. 3) that has received the drive signal from the second actuator AC3 obtains the magnification m therefrom, obtains the position of the first aperture limiting element AP1 optimum for the magnification m, and inputs a predetermined pulse. Is applied to the piezoelectric actuator XPZ to move the first aperture limiting element AP1 to the optimum position in the optical axis direction. This makes it possible to suppress a change in NA accompanying a change in the magnification of the objective lens.

  Further, the blue-violet semiconductor laser LD1 is caused to emit light when information is recorded on or reproduced from the multilayer optical disk MLD. The divergent light beam emitted from the blue-violet semiconductor laser LD1 passes through the first polarizing beam splitter PBS1, the first lens BE1 and second lens BE2 of the beam expander, the first dichroic prism DBS1, and the λ / 4 wavelength plate QWP. After being reflected by the second dichroic prism DBS2 and entering the first objective lens OL1 via the first aperture limiting element AP1, it is formed on the selected information recording layer RL via the protective substrate of the multilayer optical disk MLD. It becomes a spot. The first objective lens OL1 is driven by a biaxial actuator AC1, and focusing and tracking are performed.

  The reflected light flux modulated by the information pits in the selected information recording layer RL again passes through the first objective lens OL1 and the first aperture limiting element AP1, is reflected by the second dichroic prism DBS2, and is a λ / 4 wavelength plate QWP. , Passes through the second dichroic prism DBS1, the second lens BE2 and the first lens BE1 of the beam expander, is further reflected by the first polarizing beam splitter PBS1, passes through the first sensor lens SL1, and passes through the pinhole PH. Thus, stray light reflected by another information recording layer that is not a desired layer is removed, and is incident on the first photodetector PD1. Information recorded on the selected information recording layer RL can be read by the output signal of the first photodetector PD1.

  Next, recording or reproduction of information on the BD will be described. When the blue-violet semiconductor laser LD1 is caused to emit light, the divergent light beam emitted from the laser beam is a first polarizing beam splitter PBS1, a first lens BE1 and a second lens BE2 of a beam expander, a first dichroic prism DBS1, and a λ / 4 wavelength. The light passes through the plate QWP, is reflected by the second dichroic prism DBS2, passes through the first aperture limiting element AP1, enters the first objective lens OL1, and then is formed on the information recording layer RL via the BD protective substrate. It becomes a spot. The first objective lens OL1 is driven by a biaxial actuator AC1, and focusing and tracking are performed.

  The reflected light beam modulated by the information pits in the information recording layer RL again passes through the first objective lens OL1 and the first aperture limiting element AP1, is reflected by the second dichroic prism DBS2, and is reflected by the λ / 4 wavelength plate QWP and the dichroic prism. DBS1 passes through the second lens BE2 and the first lens BE1 of the beam expander, is further reflected by the first polarizing beam splitter PBS1, passes through the first sensor lens SL1, passes through the pinhole PH, and detects the first light. Is incident on the device PD1. Information recorded on the information recording layer RL of the BD can be read by the output signal of the first photodetector PD1. Note that when the BD is used, when the parallel light is incident on the first objective lens OL1, the first aperture limiting element AP1 may be in any position, but when diverging light or convergent light is incident, the magnification is increased. Accordingly, the drive mechanism DR can move the first aperture limiting element AP1 to an optimal position.

  Next, recording or reproduction of information on the DVD will be described. When the red semiconductor laser of LD2 emits light, the divergent light beam having the wavelength λ2 emitted therefrom passes through the second polarizing beam splitter PBS2 and passes through the coupling lens CP2. In addition, it is also possible to correct the spherical aberration generated in the DVD by moving the coupling lens CP2 to a desired position in the optical axis direction by the third actuator AC4. The light beam that has passed through the coupling lens CP2 is reflected by the dichroic prism DBS1, passes through the λ / 4 wavelength plate QWP, is reflected by the second dichroic prism DBS2, passes through the first aperture limiting element AP1, and passes through the first objective lens. After entering the OL1, it becomes a spot formed on the information recording layer RL via the DVD protective substrate.

  The reflected light beam modulated by the pits in the information recording layer RL again passes through the first objective lens OL1 and the first aperture limiting element AP1, is reflected by the second dichroic prism DBS2, passes through the λ / 4 wavelength plate QWP, The light is reflected by the first dichroic prism DBS1, further reflected by the second polarization beam splitter PBS2, and enters the second photodetector PD2 via the second sensor lens SL2. DVD information can be read by the output signal of the second photodetector PD2.

  Next, recording or reproduction of information with respect to a CD will be described. When the infrared semiconductor laser of LD2 is caused to emit light, a divergent light beam having a wavelength λ3 emitted therefrom passes through the second polarization beam splitter PBS2 and passes through the coupling lens CP2. Note that the spherical aberration occurring in the CD can be corrected by moving the coupling lens CP2 to a desired position in the optical axis direction by the third actuator AC4. The light beam that has passed through the coupling lens CP2 is reflected by the dichroic prism DBS1, passes through the λ / 4 wavelength plate QWP, passes through the second dichroic prism DBS2, is reflected by the rising mirror ML, and is reflected by the second aperture limiting element AP2. After passing through and entering the second objective lens OL2, it becomes a spot formed on the CD information recording layer via the CD protective substrate.

  The reflected light beam modulated by the pits in the information recording layer of the CD again passes through the second objective lens OL2 and the second aperture limiting element AP2, is reflected by the rising mirror ML2, passes through the second dichroic prism DBS2, and λ / 4 wave plate QWP, reflected by the first dichroic prism DBS1, further reflected by the second polarization beam splitter PBS2, and incident on the second photodetector PD2 via the second sensor lens SL2. CD information can be read by the output signal of the second photodetector PD2.

Next, examples that can be used in the above-described embodiment will be described. The objective lens of the present embodiment can be applied to the objective lens OL1. In the following table, ri represents the radius of curvature, di represents the position in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni represents the refractive index of each surface. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E−3). The optical surface of the objective optical element is formed as an aspherical surface that is axisymmetric about the optical axis, each of which is defined by a mathematical formula obtained by substituting the coefficient shown in Table 1 into Formula 1. The design magnification is represented by m in the table.

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A _i is an aspheric coefficient, h is a height from the optical axis, and r is a paraxial curvature. Radius.

Example 1
Table 1 shows lens data of Example 1. In FIG. 6, the horizontal axis represents the magnification of the objective lens in Example 1, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 350 mm, the position where the numerical aperture is substantially constant is plotted. 6 and FIGS. 7 to 11 described later, when the position of the stop is zero, the aperture limiting element is located at the same position as the light source side optical surface vertex of the objective lens in the optical axis direction. The amount of movement to is expressed as positive. When the magnification m = 0, theoretically, the aperture limiting element may be located at any position in the optical axis direction.

In the case of Example 1, as shown in FIG. 3, when m = −0.064, the position of the aperture limiting element is set to a position of D = 0.315 mm from the light source side surface apex of the objective lens (m × D /F=0.001), when m = −0.048, the position of the aperture limiting element is D = 0.400 mm from the light source side surface vertex of the objective lens (m × D / f = 0.111). , M = 0.032, the position of the aperture limiting element is D = 0.660 mm from the light source side surface apex of the objective lens (m × D / f = −0.012). In Example 1, the effective diameter of the objective lens is φ = 3.0 mm, and SC _max /f=0.022.

(Example 2)
Table 2 shows lens data of Example 2. In FIG. 7, the horizontal axis represents the magnification of the objective lens in Example 2, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 350 mm, the position where the numerical aperture is substantially constant is plotted. In the case of Example 2, as shown in FIG. 7, when m = −0.093, the position of the aperture limiting element is set to a position of D = 0.290 mm from the light source side surface apex of the objective lens (m × D /F=0.015) and m = −0.073, the position of the aperture limiting element is D = 0.425 mm from the light source side surface apex of the objective lens (m × D / f = 0.018). , M = 0.041, the position of the aperture limiting element is D = 0.870 mm from the light source side surface vertex of the objective lens (m × D / f = −0.020). In Example 2, the effective diameter of the objective lens is φ = 3.0 mm, and SC _max /f=0.043.

Example 3
Table 3 shows lens data of Example 3. In FIG. 8, the horizontal axis represents the magnification of the objective lens in Example 3, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 250 mm, the position where the numerical aperture is substantially constant is plotted. In the case of Example 3, as shown in FIG. 8, when m = −0.041, the position of the aperture limiting element is set to a position of D = 0.450 mm from the light source side surface vertex of the objective lens (m × D /F=0.010) and m = −0.029, the position of the aperture limiting element is set to D = 0.500 mm from the light source side surface vertex of the objective lens (m × D / f = 0.008). When m = 0.022, the position of the aperture limiting element is D = 0.660 mm from the light source side surface apex of the objective lens (m × D / f = −0.008). In Example 3, the effective diameter of the objective lens is φ = 3.0 mm and SC _max /f=0.016.

Example 4
Table 4 shows lens data of Example 4. In FIG. 9, the horizontal axis represents the magnification of the objective lens in Example 4, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 350 mm, the position where the numerical aperture is substantially constant is plotted. In the case of Example 4, as shown in FIG. 9, when m = −0.066, the position of the aperture limiting element is set to a position of D = 0.300 mm from the light source side surface apex of the objective lens (m × D /F=0.011) and m = −0.049, the position of the aperture limiting element is D = 0.390 mm from the light source side surface apex of the objective lens (m × D / f = 0.011). , M = 0.032, the position of the aperture limiting element is D = 0.665 mm from the light source side surface vertex of the objective lens (m × D / f = −0.012). In Example 4, the effective diameter of the objective lens is φ = 3.0 mm and SC _max /f=0.024.

(Example 5)
Table 5 shows lens data of Example 5. In FIG. 10, the horizontal axis represents the magnification of the objective lens in Example 5, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 350 mm, the position where the numerical aperture is substantially constant is plotted. In the case of Example 5, as shown in FIG. 10, when m = −0.065, the position of the aperture limiting element is D = 0.320 mm from the light source side surface apex of the objective lens (m × D /F=0.012), when m = −0.048, the position of the aperture limiting element is D = 0.400 mm from the light source side surface vertex of the objective lens (m × D / f = 0.111). , M = 0.031, the position of the aperture limiting element is D = 0.690 mm from the light source side surface apex of the objective lens (m × D / f = −0.012). In Example 5, the effective diameter of the objective lens is φ = 3.0 mm and SC _max /f=0.024, but the wavelength λ1 used is 530 nm.

(Example 6)
Table 6 shows lens data of Example 6. In FIG. 11, the horizontal axis represents the magnification of the objective lens in Example 6, and the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, 0 In the case where the focused spot is formed at a position of 350 mm, the position where the numerical aperture is substantially constant is plotted. In the case of Example 6, as shown in FIG. 11, when m = −0.053, the position of the aperture limiting element is D = 0.300 mm from the light source side surface apex of the objective lens (m × D /F=0.011) and m = −0.037, the position of the aperture limiting element is D = 0.380 mm from the light source side surface vertex of the objective lens (m × D / f = 0.010) , M = 0.026, the position of the aperture limiting element is D = 0.565 mm from the light source side surface apex of the objective lens (m × D / f = −0.011). In Example 6, the effective diameter of the objective lens is φ = 2.4 mm, and SC _max /f=0.022.

  The values of each example are summarized in Tables 7 and 8. However, the symbols in Tables 7 and 8 correspond to the symbols described in the claims.

It is a figure which shows the principle of this invention. It is a figure which shows schematically the structure of optical pick-up apparatus PU1. It is a perspective view of drive mechanism DR which drives 1st aperture restriction element AP1. FIG. 3 is a perspective view showing a multilayer piezoelectric actuator PZ having a structure in which a plurality of piezoelectric ceramics PE are stacked and electrodes C are connected in parallel therebetween. It is a figure which shows the waveform of the voltage pulse applied to the piezoelectric actuator PZ. The horizontal axis represents the magnification of the objective lens in Example 1, the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction, and the thickness of the protective substrate is 0.020 mm, 0.050 mm, 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in The horizontal axis indicates the magnification of the objective lens in Example 2, and the vertical axis indicates the position of the aperture limiting element (aperture) in the optical axis direction. The thickness of the protective substrate is 0.020 mm, 0.050 mm, and 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in The horizontal axis represents the magnification of the objective lens in Example 3, the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction, and the thickness of the protective substrate is 0.020 mm, 0.050 mm, and 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in The horizontal axis represents the magnification of the objective lens in Example 4, the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction, and the thickness of the protective substrate is 0.020 mm, 0.050 mm, 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in The horizontal axis represents the magnification of the objective lens in Example 5, the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction, and the thickness of the protective substrate is 0.020 mm, 0.050 mm, 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in The horizontal axis represents the magnification of the objective lens in Example 6, the vertical axis represents the position of the aperture limiting element (aperture) in the optical axis direction, and the thickness of the protective substrate is 0.020 mm, 0.050 mm, 0.350 mm. FIG. 6 is a diagram in which positions where numerical apertures are substantially constant are plotted in the case where a condensing spot is formed in It is a figure which shows the relationship between an objective lens and the type with an aperture limiting element. It is a figure which shows the relationship between another type of an objective lens and an aperture limiting element. It is a figure which shows the relationship between another type of an objective lens and an aperture limiting element. It is a figure which shows the relationship between another type of an objective lens and an aperture limiting element. It is a figure which shows the relationship between another type of an objective lens and an aperture limiting element.

LD1: Blue-violet semiconductor laser (Multi-layer type optical disc and BD recording / reproducing light)
LD2: Red semiconductor laser (servo light for multilayer optical disk, DVD recording / reproducing light)
PBS1: first polarizing beam splitter PBS2: second polarizing beam splitter BE1: first lens of beam expander (focusing lens for recording / reproducing light of multilayer optical disk)
BE2: the second lens of the beam expander (spherical aberration correction lens for multilayer optical disk and BD recording / reproducing light)
DBS1: Dichroic prism (transmits blue-violet laser light and reflects red laser light)
QWP: λ / 4 wavelength plate ML: Raising mirror OL1: First objective lens OL2: Second objective lens SL1: First sensor lens (for recording / reproducing light of multilayer type optical disc and BD)
SL2: Second sensor lens (for servo light of multilayer optical disk, DVD recording / reproducing light)
PH: Pinhole (for removing stray light from other layers of multilayer optical disks)
PD1: First optical detector (for recording / reproducing light reading of a multilayer optical disk and a BD)
PD2: Second photodetector (for servo light of multilayer optical disk, for reading / recording light of DVD)
AC1: Biaxial actuator (for focusing / tracking of servo light of multilayer optical disk and recording / reproducing light of BD / DVD)
AC2: First actuator (for correcting spherical aberration of multilayer optical disk and BD)
AC3: Second actuator (for focusing servo light on multilayer optical disks)
AP1: first aperture limiting element AP2: second aperture limiting element CPU: control circuit DH1a: connecting portion DH1b: square groove DR: drive mechanism PE: piezoelectric ceramic XDS: drive shaft XPZ: piezoelectric actuator

Claims (9)

A first light source, a spherical aberration correction element, an aperture limiting element, and an objective lens. A light beam having a wavelength λ1 emitted from the first light source is converted into the spherical aberration correction element and the aperture limiting element. A plurality of information recording layers stacked in the optical axis direction and having a thickness from the surface to the deepest information recording layer of 0.2 mm or more and 0.6 mm or less. Information is recorded / reproduced by focusing on one of the information recording layers of the optical disc, and the spherical aberration correction element is adapted to cause spherical aberration caused by a difference in the recording layer to record / reproduce information. An optical pickup device adapted to correct by changing the magnification of the objective lens,
The objective lens is a single ball, and the numerical aperture of the objective lens is 0.7 or more and 0.9 or less,
An optical pickup device comprising: a drive mechanism that changes the position of the aperture limiting element in the optical axis direction in accordance with the change in magnification. The optical pickup device according to claim 1, wherein a position in the optical axis direction of the aperture limiting element according to the change in the magnification satisfies the following expression.
−0.020 ≦ m × (D / f) ≦ 0.018 (1)
However, m is the magnification D [mm] of the objective lens, and the distance f [mm] in the optical axis direction from the light source side surface vertex of the objective lens to the aperture limiting position of the aperture limiting element is the objective lens at the wavelength λ1. Focal length When the light beam having the wavelength λ1 is incident at the design magnification, the sine condition violation amount has a positive maximum value between 50% and 90% of the effective aperture radius h, and the sine condition violation amount decreases in the peripheral portion. The optical pickup device according to claim 1, wherein the coma aberration correction state is set so as to satisfy the following expression.
0.015 <SC _max /f<0.045 (2)
However, SC _max is the maximum value of the sine condition violation amount.   The optical pickup device according to claim 1, wherein the wavelength λ1 is 390 nm ≦ λ1 ≦ 420 nm.   The optical pickup device according to claim 1, wherein the wavelength λ1 satisfies 520 nm ≦ λ1 ≦ 540 nm.   6. Information recording / reproduction is performed by condensing a light beam having a wavelength λ1 emitted from the first light source onto an information recording surface of a Blu-ray Disc by the objective lens. The optical pickup device according to any one of the above.   In addition to the first light source, a second light source that emits a light beam having a wavelength λ2 (λ1 <λ2) is provided, and the light beam having a wavelength λ2 emitted from the second light source is incident on the objective lens. The optical pickup device according to claim 1, wherein information is recorded / reproduced by focusing on an information recording layer of the second optical disc. A second objective lens in addition to the objective lens;
In addition to the first light source, a second light source that emits a light beam having a wavelength λ2 (λ1 <λ2) is provided, and the light beam having a wavelength λ2 emitted from the second light source is supplied to the second objective lens. 7. The optical pickup device according to claim 1, wherein the information is recorded / reproduced by being incident and condensed on an information recording layer of the second optical disc. An objective lens unit having an aperture limiting element and an objective lens, a first light source, and a spherical aberration correction element, and a light beam having a wavelength λ1 emitted from the first light source is converted into the spherical aberration correction element, A plurality of information recording layers that are incident on the objective lens through the aperture limiting element and are stacked in the optical axis direction have a thickness from the surface to the deepest information recording layer of 0.2 mm or more and 0.6 mm. Information is recorded / reproduced by focusing on one of the following information recording layers of the first optical disc, and the spherical aberration correction element is caused by the difference in the information recording layer to record / reproduce information. An objective lens unit used in an optical pickup device adapted to correct the generated spherical aberration by changing the magnification of the objective lens,
The objective lens is a single ball, and the numerical aperture of the objective lens is 0.7 or more and 0.9 or less,
An objective lens unit comprising: a drive mechanism that changes the position of the aperture limiting element in the optical axis direction in accordance with the change in magnification.

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