JP2011165288A - Objective lens of optical pickup and optical pickup - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens and an optical pickup mounting the same, capable of making its mounting easier by enabling the precise detection of the position of the high NA objective lens. <P>SOLUTION: Since the light source side diaphragm surface OB11s is provided together with the objective lens OBJ in one body, a diaphragm need not be provided separately. Further, since the light flux not converging on the information recording surface RL1 of a BD is output from the objective lens OBJ when a limited divergent light flux L' is incident to the light source side diaphragm surface OB11s, the surface OB21a of the optical disk need not be extended to be larger than the effective diameter to the outside in a direction orthogonal to an optical axis. Thus, in comparison with the case employing a separate diaphragm S, the inner diameter becomes larger by Δ at the optical disk edge OB21b, and the width can be increased in the direction orthogonal to the optical axis at the optical disk edge OB21b. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an objective lens and an optical pickup device of an optical pickup device, and more particularly to an objective lens having an NA of 0.8 or more and an optical pickup device using the same.

  There is known 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. 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. It is possible to record 25 GB of information per layer on an optical disk having a diameter of 12 cm, which is the same size as 7 GB).

  An objective lens used in an optical pickup device for BD is disclosed in Patent Document 1, for example.

JP 2001-324673 A

  In the optical pickup device disclosed in Patent Document 1, a diaphragm separate from the objective lens is provided. By the way, even in an objective lens that is designed to receive an infinite parallel light beam, a finite divergent light beam may be incident, for example, to correct spherical aberration caused by the difference in substrate thickness of the optical disk. The finite divergent light beam enters the objective lens with a diameter larger than the aperture diameter. Therefore, the optical surface of the objective lens is extended outward in the direction perpendicular to the optical axis from the effective diameter of the design so that appropriate optical characteristics can be obtained even when a finite divergent light beam is incident.

  Further, when an objective lens having a high NA is assembled to the optical pickup device, coma aberration may occur if positioning is not performed with high accuracy. Therefore, at the time of assembly, the position of the objective lens is detected by making the inspection light incident on the end face arranged outside the optical surface of the objective lens and receiving the reflected light. However, there is a demand for further reducing the diameter of the objective lens in response to the trend toward miniaturization of the optical pickup device, but even if the objective lens is made to have a smaller diameter, as long as a separate diaphragm is used, the optical surface is changed as described above. Since it is unavoidable to extend outward, the width of the end face of the objective lens must be narrowed, which makes it difficult to make the inspection light incident on the end face with high accuracy. There is a problem that it becomes difficult.

  Further, in a high NA objective lens such as a BD, there is a demand for ensuring a long working distance, which is the distance between the optical disc and the objective lens. In order to meet the demand, it is desirable to reduce the thickness of the objective lens and to reduce the value of d (thickness on the objective lens axis) / f (focal length). However, if the value of d / f is reduced, the thickness of the flange of the objective lens is reduced accordingly, and the manufacturing difficulty increases. In particular, in a plastic objective lens that has a gate in the flange portion and is manufactured by injecting resin therefrom, the problem of manufacturing difficulty is significant.

  The present invention has been made in view of the problems of the prior art. By making it possible to accurately detect the position of an objective lens having a high NA, it is possible to improve the ease of assembly, and to improve the d / An object of the present invention is to provide an objective lens that can secure a sufficient flange thickness even if f is reduced and is easy to manufacture, and an optical pickup device using the objective lens.

The objective lens according to claim 1 includes a light source that emits a light beam having a wavelength λ1 (390 nm <λ1 <420 nm), and an objective lens that focuses the light beam on an information recording surface of an optical disc, In the objective lens of the optical pickup device adapted to record and / or reproduce information by focusing the light beam emitted from the light source on the information recording surface of the optical disc by the objective lens,
The objective lens is a single lens, and the image side numerical aperture (NA) is 0.8 or more,
The objective lens includes a light source side optical surface and an optical disc side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, a flange provided around the objective lens, the light source side optical surface, A diaphragm surface disposed between one of the optical surfaces on the optical disk side and the flange portion,
The light beam having the wavelength λ1 incident on the light source side optical surface passes through the optical surface and is condensed on the information recording surface of the optical disc, and the light beam having the wavelength λ1 incident on the diaphragm surface is information on the optical disc. Without focusing on the recording surface,
Further, the following expression is satisfied.
0.8 ≦ d / f ≦ 1.3 (1)
However,
d: Thickness on the optical axis of the objective lens (mm)
f: Focal length (mm) of the objective lens in the light flux with wavelength λ1.

  According to the present invention, a diaphragm surface is provided between one of the light source side optical surface and the optical disk side optical surface and the flange portion, and the light flux having the wavelength λ1 incident on the diaphragm surface is the optical disk. Since the light is not condensed on the information recording surface, a diaphragm separate from the objective lens can be omitted, so that it is not necessary to extend the optical surface outward from the effective diameter in the direction perpendicular to the optical axis. In a small objective lens satisfying the formula (1), it becomes easier to make the diameter smaller, and the mountability of the optical pickup device is improved. On the other hand, when the diameter is the same as that of the conventional objective lens, the area of the end surface on the side of the optical surface opposite to the optical surface provided with the diaphragm surface is equivalent to that of the diaphragm surface compared to the conventional objective lens. It is no longer necessary to secure an amount corresponding to the light beam that should have passed through the position as an optical surface, so that the area of the end surface can be increased and the degree of freedom in designing the end surface can be ensured, so the value of d / f is small. Even in an objective lens that is easy to secure a working distance, it is possible to secure a thicker flange, and not only an objective lens that is easy to manufacture can be obtained, but also the end surface area can be expanded, so that the objective lens Inspection light can be easily incident on the end face when the lens is positioned, whereby the objective lens can be positioned with high accuracy.

  According to a second aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the diaphragm surface is a light source side diaphragm surface disposed between the light source side optical surface and the flange portion, and the optical disk side. An optical disc-side end surface is disposed between the optical surface and the flange portion.

  According to a third aspect of the present invention, there is provided the objective lens according to the second aspect, wherein the optical disc side end surface is orthogonal to the optical axis of the objective lens.

The objective lens according to claim 4 is the light source side stop disposed between the light source side optical surface and the flange portion in the invention according to any one of claims 1 to 3. The light source side diaphragm surface is displaced so as to approach the light source with respect to a virtual surface that is a surface and extends the light source side optical surface outward in the direction perpendicular to the optical axis.

The objective lens according to claim 5 is characterized in that, in the invention according to any one of claims 1 to 4, the following expression (1 ′) is satisfied.
0.8 ≦ d / f ≦ 1.1 (1 ′)

  According to the above conditional expression, since the value of d / f becomes smaller, the subject of the present invention becomes larger. However, even if it is such a large subject, the present invention can solve the subject. Because it can, it can be said that the effect becomes more remarkable.

  An objective lens according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein the objective lens is formed of a glass material.

  According to a seventh aspect of the present invention, in the invention according to any one of the first to fifth aspects, the objective lens is made of a plastic material.

  An optical pickup device according to an eighth aspect includes the objective lens according to any one of the first to seventh aspects.

  The optical pickup device according to claim 9 is characterized in that it does not have a diaphragm separate from the objective lens.

  The optical pickup device according to the present invention has at least one light source (first light source). Of course, a plurality of types of light sources may be provided so as to support a plurality of types of optical disks. Furthermore, the optical pickup device of the present invention has a condensing optical system for condensing at least the first light flux from the first light source on the information recording surface of the first optical disc. In the optical pickup apparatus that can handle a plurality of types of optical disks, the condensing optical system condenses the second light beam on the information recording surface of the second optical disk, and the third light beam on the information recording surface of the third optical disk. You may make it condense. The optical pickup device of the present invention includes a light receiving element that receives at least a reflected light beam from the information recording surface of the first optical disc. In an optical pickup device that can handle a plurality of types of optical disks, the light receiving element receives a reflected light beam from the information recording surface of the second optical disk and receives a reflected light beam from the information recording surface of the third optical disk. Also good.

  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 BD, the second optical disc is a DVD, and the third optical disc is preferably a CD, but is not limited thereto.

  The first optical disk may have a plurality of information recording surfaces stacked in the thickness direction. The second optical disc and the third optical disc may also have a plurality of information recording surfaces.

  In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 420 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. It is a generic term for a BD series optical disc of about 125 mm, and includes a BD having only a single information recording surface, a BD having two or more information recording surfaces, and the like. Furthermore, in this specification, 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. Including DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW, and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

  In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (2), (3), and (4), but is not limited thereto. The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.

0.050 mm ≤ t1 ≤ 0.125 mm (2)
0.5mm ≤ t2 ≤ 0.7mm (3)
1.0mm ≤ t3 ≤ 1.3mm (4)

In the present specification, 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 expressions (5) and (6).
1.5 · λ1 <λ2 <1.7 · λ1 (5)
1.8 · λ1 <λ3 <2.0 · λ1 (6)

  When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third 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 390 nm. 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, and the third wavelength λ3 of the third light source is preferably 420 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

  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. 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 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 of the optical pickup device may have a coupling lens and an objective lens. The coupling lens is a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam.

  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. The objective lens is a single glass or plastic lens. Preferably, the objective lens is a single convex lens. The objective lens may be composed of only a refractive surface or may have an optical path difference providing structure. In addition, the hybrid lens which provided the optical path difference providing structure with the photocurable resin, UV curable resin, or thermosetting resin etc. on the glass lens may be sufficient. The objective lens preferably has a refractive surface that is aspheric. In the objective lens, the base surface on which the optical path difference providing structure is provided is preferably an aspherical surface.

  Moreover, when using an objective lens as a glass lens, it is preferable to use the glass material whose glass transition point Tg is 500 degrees C or less, More preferably, it is 400 degrees C or less. By using a glass material having a glass transition point Tg of 500 ° C. or lower, molding at a relatively low temperature is possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 manufactured by Sumita Optical Glass Co., Ltd. and K-PG375 (both are product names).

  In addition, a physical property value that is important when a glass lens is molded and manufactured is a linear expansion coefficient α. Even if a material having a Tg of 400 ° C. or lower is selected, the temperature difference from room temperature is still large compared to the resin material. When lens molding is performed using a glass material having a large linear expansion coefficient α, cracks are likely to occur when the temperature is lowered. The linear expansion coefficient α of the glass material is preferably 200 (10E-7 / K) or less, and more preferably 120 or less.

  By the way, since the specific gravity of a glass lens is generally larger than that of a resin lens, if the objective lens is a glass lens, the weight increases and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.

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

  The objective lens includes a light source side optical surface and an optical disc side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, a flange provided around the objective lens, a light source side optical surface and an optical disc side optical surface. A diaphragm surface is disposed between one of the flange portions. Furthermore, it is preferable to have an end surface disposed between the other of the light source side optical surface and the optical disc side optical surface and the flange portion. The flange portion is a portion that is disposed around the optical surface and is used for attaching an objective lens to the optical pickup device. The diaphragm surface is preferably a light source side diaphragm surface disposed between the light source side optical surface and the flange portion, but is an optical disk side diaphragm surface disposed between the optical disk side optical surface and the flange portion. Also good. Preferably, the end surface has at least one of a light source side end surface disposed between the light source side optical surface and the flange portion and an optical disc side end surface disposed between the optical disc side optical surface and the flange portion. However, it is preferable that the diaphragm surface and the end surface are provided on opposite sides of the objective lens in the optical axis direction. The light beam having the wavelength λ1 that has passed through the light source side optical surface and the optical disk side optical surface is condensed on the information recording surface of the optical disk, and the light beam having the wavelength λ1 incident on the light source side diaphragm surface or the optical disk side diaphragm surface is the information on the optical disk. Does not concentrate on the recording surface. The light source side optical surface and the light source side diaphragm surface are preferably in contact with each other, and the optical disk side optical surface and the optical disk side diaphragm surface are preferably in contact with each other.

  The optical disc side end surface is preferably orthogonal to the optical axis of the objective lens. The light source side end surface is preferably non-parallel to the optical disc side end surface. Furthermore, it is preferable that the light source side diaphragm surface is displaced so as to approach the light source with respect to a virtual surface obtained by extending the light source side optical surface outward in the direction perpendicular to the optical axis. The light source side end surface and the light source side surface of the flange portion may be flush with each other or may be shifted in the optical axis direction. Further, the end face on the optical disc side and the optical disc side surface of the flange portion may be flush with each other or may be shifted in the optical axis direction. It is preferable that the optical pickup device does not have a diaphragm separate from the objective lens. A diaphragm means an aperture limiting function for a light beam emitted from a light source and incident on an objective lens.

  The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for reproducing / recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

The objective lens satisfies the following conditional expression (1).
0.8 ≦ d / f ≦ 1.3 (1)
However,
d: Thickness on the optical axis of the objective lens (mm)
f: Focal length (mm) of the objective lens in the light flux with wavelength λ1
An objective lens that satisfies the formula (1) is often small in diameter, and has an advantage that it is easy to secure a working distance (working distance). On the other hand, the range in which the inspection light for positioning is irradiated becomes narrow, and the flange Since the thickness tends to be thin, the present invention is particularly effective.

In the case of an objective lens corresponding to an optical disk with a short wavelength and high NA such as BD, if the ratio of the thickness on the optical axis to the focal length of the objective lens becomes too large, an off-axis light beam enters the objective lens. In this case, astigmatism tends to occur, and a working distance cannot be secured. On the other hand, if the ratio of the thickness on the optical axis to the focal length of the objective lens becomes too small, there arises a problem that the surface shift sensitivity increases. By satisfying conditional expression (1), astigmatism and surface shift sensitivity can be suppressed. Furthermore, it is more preferable when the following formula is satisfied.
0.8 ≦ d / f ≦ 1.1 (1 ′)

  Further, the working distance of the objective lens when using the first optical disk is preferably 0.15 mm or more and 1.0 mm or less.

  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 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.

  ADVANTAGE OF THE INVENTION According to this invention, the objective lens which can improve the assembly ease by enabling it to detect the position of a high NA objective lens accurately, and an optical pick-up apparatus using the same can be provided.

It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can record / reproduce information appropriately with respect to BD which is an optical disk. It is sectional drawing which shows the objective lens OBJ of this Embodiment. It is an expanded sectional view showing objective lens OBJ of this embodiment. It is a figure which shows the state at the time of attaching the objective lens OBJ to optical pick-up apparatus PU1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a configuration of an optical pickup apparatus PU1 of the present embodiment that can appropriately record / reproduce information with respect to a BD that is an optical disk. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

The optical pickup device PU1 emits an objective lens OBJ, an actuator AC that moves the objective lens OBJ in a focusing direction and a tracking direction, a λ / 4 wavelength plate QWP, a coupling CL, a polarizing prism PBS, and a laser beam (light beam) of 405 nm. It has a light receiving element PD that receives a reflected light beam from the information recording surface RL1 of the semiconductor laser LD, sensor lenses SL, and BD. In the present embodiment, the objective lens OBJ is a single ball made of glass or plastic. The objective lens OBJ satisfies the following expression.
0.8 ≦ d / f ≦ 1.3 (1)
However,
d: Thickness on the optical axis of the objective lens OBJ (mm)
f: Focal length (mm) of the objective lens OBJ in the light flux with wavelength λ1

  A case where recording / reproduction is performed on the first information recording surface RL1 of the BD will be described. A divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) passes through the polarization prism PBS, passes through the coupling lens CL, and becomes a substantially parallel light beam, and then is emitted by the λ / 4 wavelength plate QWP. A spot formed on the information recording surface RL1 through the protective substrate PL1 by the objective lens OBJ, which is converted from linearly polarized light into circularly polarized light, and whose beam diameter is restricted by the optical diaphragm surface OB11s (see FIGS. 2 and 3). It becomes.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective lens OBJ, converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and converged through the coupling lens CL. After being reflected by the polarizing prism PBS, it is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. The information recorded on the information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the actuator AC using the output signal of the light receiving element PD.

  FIGS. 2 and 3 are cross-sectional views showing the objective lens OBJ of the present embodiment, and show the outer edge L of the light beam passing through the closest inward side of the effective diameter with a solid line. That is, the positions where the outer edge L of the light beam intersects the light source side optical surface OB11a and the optical disc side optical surface OB21a are effective diameters.

  In FIG. 2, the objective lens OBJ has a circular light source side optical surface OB11a including the optical axis X around the optical axis X, a subsequent annular light source side diaphragm surface OB11s, and a subsequent annular light source side end surface. A region OB11b (also referred to as a light source side end surface), a ring-shaped light source side transition region OB11c that follows, a light source side flange end surface OB11d of the annular flange portion OEF that follows, and a circumferential surface OB11e of the flange portion OEF orthogonal thereto Further, a circular optical disk side optical surface OB21a concentrically facing the light source side optical surface OB11a, an annular optical disk side end surface area (also referred to as an optical disk side end surface) OB21b, and a subsequent annular optical disk side transition area OB21c. And an optical disc side flange end surface OB21d of the flange portion subsequent thereto. When assembled in an optical pickup device (not shown), the light source side optical surface OB11a is on the light source side, and the optical disc side optical surface OB21a is on the optical disc side.

  According to the present embodiment, the light source side diaphragm surface OB11s is, as shown in detail in FIG. 3, a virtual surface VP (dotted line) obtained by extending the light source side optical surface OB11a beyond the effective diameter outward in the direction perpendicular to the optical axis. On the other hand, it has a tapered shape displaced to the light source side (left side in FIG. 3). With such a shape, it is possible to secure a relatively large thickness (space between the light source side end surface OB11b and the optical disc side end surface OB21b) δ of the portion where the thickness in the optical axis direction is the thinnest in the objective lens OBJ. The axial thickness d of the objective lens OBJ can be reduced so as to satisfy the above formula (1), while ensuring the injection moldability of the resin objective lens and the support rigidity when the resin objective lens is supported by the flange portion OBF.

  In the prior art, since the diaphragm S (indicated by a dotted line in FIG. 3) is provided separately from the objective lens OBJ, in order to ensure a margin in case the finite divergent light beam L ′ is incident on the objective lens OBJ, The light source side optical surface OB11a is extended from the effective diameter to the outside in the direction orthogonal to the optical axis. Therefore, in order to properly focus the finite divergent light beam L ′ incident from the light source side optical surface OB11a on the information recording surface of the optical disc, the optical disc side optical surface OB21a also extends from the effective diameter to the outside in the direction perpendicular to the optical axis. Accordingly, the inner diameter of the optical disc side end surface OB21b is enlarged correspondingly, and the width of the optical disc side end surface OB21b in the direction perpendicular to the optical axis is narrowed.

  On the other hand, according to the present embodiment, since the light source side diaphragm surface OB11s is provided integrally with the objective lens OBJ, it is not necessary to provide a separate diaphragm. When the finite divergent light beam L ′ is incident on the light source side diaphragm surface OB11s, the light beam that is not condensed on the information recording surface RL1 of the BD is emitted from the objective lens OBJ. The inner diameter of the optical disc side end surface OB21b is increased by Δ, compared with the case where a separate diaphragm S is provided, thereby increasing the width of the optical disc side end surface OB21b in the direction perpendicular to the optical axis. Can be spread. Therefore, it becomes easy to irradiate the optical disc side end surface OB21b with the inspection light DL when positioning an objective lens, which will be described later with reference to FIG. Furthermore, since the width of the optical disk side end surface OB21b in the direction perpendicular to the optical axis can be increased, the degree of freedom in designing the end surface is increased, and a design that can contribute to further increasing δ on the side surface of the optical disk becomes possible.

  The optical disc side end surface region OB21b is orthogonal to the optical axis X, whereas the light source side end surface region OB11b is inclined with respect to the surface orthogonal to the optical axis X, that is, 3 to the optical disc side end surface region OB21b. It is inclined at an angle θ of at least 5 minutes, preferably at least 5 minutes. At least the optical disc side end surface region OB21b and the light source side end surface region OB11b are mirror-transferred by molding with a mold, and the roughness is Ra 10 nm or less, preferably 1 nm or more and 5 nm or less.

  FIG. 4 is a diagram illustrating a state when the objective lens OBJ is assembled to the optical pickup device PU1. The inspection apparatus DET can detect the tilt of the reflection surface optically with high accuracy by emitting inspection light DL and entering the reflected light.

  In FIG. 4, when the inspection light DL is emitted in parallel to the optical axis of the optical pickup device PU1 from the inspection device DET arranged on the optical disk side of the objective lens OBJ, the inspection light DL enters the optical disk side end surface region OB21b. To do. Here, a part of the inspection light DL is reflected as indicated by a solid line and is incident on the inspection apparatus DET to detect whether the optical axis of the objective lens OBJ is inclined with respect to the optical axis of the optical pickup apparatus PU1. can do.

  On the other hand, the remainder of the inspection light DL incident on the optical disc side end surface region OB21b is transmitted through the objective lens OBJ and reflected by the light source side end surface region OB11b or the light source side diaphragm surface OB11s as shown by the dotted line, but the light source side end surface region Since the OB 11b and the light source side diaphragm surface OB11s are inclined at an angle θ of 5 minutes or more with respect to the optical disc side end surface region OB21b, the reflected light is suppressed from returning to the inspection apparatus DET. Accordingly, since only a single reflected light is incident on the inspection apparatus DET, the inclination of the optical disk side end face region OB21b, that is, the inclination of the objective lens OBJ can be obtained with high accuracy. After adjusting the inclination of the objective lens OBJ, the objective lens OBJ is bonded to the holder HL of the actuator AC.

  The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims. For example, in the above-described embodiment, the aperture limiting effect is given by the shape of the light source side diaphragm surface. However, the light source side diaphragm surface may be provided by providing a light shielding film on the light source side optical surface extended to the outside of the effective diameter. . Further, a diaphragm surface may be provided on the optical disc side. Further, the light source side end face region OB11b may be omitted and replaced with the light source side stop face OB22s.

AC actuator CL coupling lens DET inspection device DL inspection light HL holder LD semiconductor laser OB11a light source side optical surface OB11b light source side end surface region OB11c light source side transition region OB11d light source side flange end surface OB11e peripheral surface OB11s light source side diaphragm surface OB21a optical disc side optical surface OB21b Optical disc side end surface region OB21c Optical disc side transition region OB21d Optical disc side flange end surface OBJ Objective lens OEF Flange portion PBS Polarizing prism PD Light receiving element PL1 Protective substrate PU1 Optical pickup device QWP λ / 4 wavelength plate RL1 Information recording surface SL Sensor lens X Light axis

Claims (9)

A light source that emits a light beam having a wavelength λ1 (390 nm <λ1 <420 nm), and an objective lens that focuses the light beam on an information recording surface of an optical disc, and the light beam emitted from the light source is In the objective lens of the optical pickup device adapted to record and / or reproduce information by condensing on the information recording surface of the optical disc by the lens,
The objective lens is a single lens, and the image side numerical aperture (NA) is 0.8 or more,
The objective lens includes a light source side optical surface and an optical disc side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, a flange provided around the objective lens, the light source side optical surface, A diaphragm surface disposed between one of the optical surfaces on the optical disk side and the flange portion,
The light beam having the wavelength λ1 incident on the light source side optical surface passes through the optical surface and is condensed on the information recording surface of the optical disc, and the light beam having the wavelength λ1 incident on the diaphragm surface is information on the optical disc. Without focusing on the recording surface,
Furthermore, the objective lens characterized by satisfy | filling the following formula | equation.
0.8 ≦ d / f ≦ 1.3 (1)
However,
d: Thickness on the optical axis of the objective lens (mm)
f: Focal length (mm) of the objective lens in the light flux with wavelength λ1.   The stop surface is a light source side stop surface disposed between the light source side optical surface and the flange portion, and has an optical disc side end surface between the optical disc side optical surface and the flange portion. The objective lens according to claim 1.   The objective lens according to claim 2, wherein the optical disc side end surface is orthogonal to the optical axis of the objective lens.   The diaphragm surface is a light source side diaphragm surface disposed between the light source side optical surface and the flange portion, and the light source with respect to a virtual surface obtained by extending the light source side optical surface outward in the direction perpendicular to the optical axis. The objective lens according to claim 1, wherein the side diaphragm surface is displaced so as to approach the light source. The objective lens according to claim 1, wherein the following expression (1 ′) is satisfied.
0.8 ≦ d / f ≦ 1.1 (1 ′)   The objective lens according to claim 1, wherein the objective lens is made of a glass material.   The objective lens according to claim 1, wherein the objective lens is made of a plastic material.   An optical pickup device comprising the objective lens according to claim 1.   The optical pickup device according to claim 8, wherein the optical pickup device does not have a diaphragm separate from the objective lens.

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