WO2011099329A1

WO2011099329A1 - Objective lens of optical pickup device and optical pickup device

Info

Publication number: WO2011099329A1
Application number: PCT/JP2011/050704
Authority: WO
Inventors: 野村　英司
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-02-12
Filing date: 2011-01-18
Publication date: 2011-08-18
Also published as: JPWO2011099329A1

Abstract

Disclosed are an objective lens offering great ease in attachment, by facilitating highly precise detection of the attitude of the optical lens, and an optical pickup device employing same. The optical lens comprises a light source-side optical face and an optical disc-side optical face wherethrough light beams that collect upon an information recording face of the optical disc pass; a light source-side end face that is formed upon the exterior of the light source-side optical face and that has surface roughness (Ra) of 10nm or less; and an optical disc-side end face that is formed upon the exterior of the optical disc-side optical face and that has surface roughness (Ra) of 10nm or less. The optical lens satisfies the following formula (1): |α| ≠ |β| (1) Wherein α represents an angle formed by the optical disc-side end face and a face orthogonal to the optical axis of the optical disc-side optical face, and β represents an angle formed by the light source-side end face and a face orthogonal to the optical axis of the light source-side optical face.

Description

Objective lens of optical pickup device and optical pickup device

The present invention relates to an objective lens of an optical pickup device and an optical pickup device, and more particularly to an objective lens having an NA of 0.6 or more and an optical pickup device using the objective lens.

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 is known. As an example, an optical disc that records and reproduces 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, Information of 25 GB per layer can be recorded on an optical disk having a diameter of 12 cm which is the same size as the storage capacity 4.7 GB.

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

JP 2001-324673 A

When assembling a high NA objective lens into an optical pickup device, coma aberration or the like may occur if the orientation of the objective lens is not determined accurately, resulting in deterioration of the performance of the optical pickup device. For this reason, when assembling the objective lens into the optical pickup device, in many cases, the optical disc side is irradiated with the inspection light on the optical disc side end surface which is a smooth surface, and the reflected light is detected. Thus, the posture of the objective lens is adjusted. However, the end face of the objective lens may be provided on both the light source side and the optical disc side, and the objective lens is made of a transparent material. For example, when the inspection light is irradiated from the optical disc side, the end face on the optical disc side In addition to the reflected light from the light source, the reflected light from the light source side end face is also detected at the same time, which makes it difficult to adjust the posture of the objective lens. The problem is particularly noticeable in a BD objective lens having a NA of 0.8 or more, but may also occur in a DVD objective lens having a NA of around 0.65.

The present invention has been made in view of the problems of the prior art, and by making it possible to accurately detect the posture of an objective lens, particularly a high NA objective lens, the ease of assembly can be improved. An object is to provide an objective lens 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 λ (390 nm ≦ λ ≦ 680 nm), and an objective lens that focuses the light beam on an information recording surface of an optical disc, In an objective lens of an optical pickup device that records and / or reproduces information by condensing a light beam emitted from the light source onto an 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 0.6 or more,
The objective lens is formed on the light source side optical surface and the optical disc side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, and outside the light source side optical surface, and has a surface roughness Ra of 10 nm or less. A light source side end surface and an optical disc side end surface formed outside the optical disc side optical surface and having a surface roughness Ra of 10 nm or less;
The following conditional expression (1),
| Α | ≠ | β | (1)
It is characterized by satisfying. Here, α represents an angle formed by the end surface on the optical disc side and a surface orthogonal to the optical axis of the optical surface on the optical disc side, and β is formed on a surface orthogonal to the optical axis of the light source side optical surface. Represents a corner. If the values of α and β vary depending on the position of the end surface of the same objective lens, the average value of α values on the entire optical disk side end surface of the objective lens and the average value of β values on the entire light source side end surface Are α and β, respectively.

According to the present invention, when determining the attitude of the objective lens based on the end face on the optical disc side using the auto collimator installed on the optical disc side, the auto collimator uses the spot image on the optical disc side end face and the spot image on the light source side end face. Appears. When the end face on the optical disk side and the end face on the light source side satisfy the relationship of the conditional expression (1), the directions of the reflected light from the end face on the optical disk side and the reflected light from the end face on the light source side are different. Thereby, in the autocollimator, the size of the spot image by the reflected light from the optical disc side end surface and the size of the spot image by the reflected light from the light source side end surface can be made different. This makes it possible to clearly identify the spot image of the reflected light from the end face of the optical disc and the spot image of the reflected light from the end face of the light source, and determine the posture of the objective lens based on the spot image of only one reflected light. Easy to do.

For example, in the case of | α | <| β |, compared with a spot image by reflected light from the end surface far from the autocollimator, that is, the light source side end surface, from the end surface closer to the autocollimator, that is, from the end surface on the optical disc side Since the spot image due to the reflected light is small and the light intensity is high, it becomes easy to determine the posture of the objective lens based on the end face on the optical disc side.

In the case of | α |> | β |, the end face closer to the autocollimator than the end face closer to the autocollimator, that is, the end face far from the autocollimator, that is, the end face on the light source side. Since the spot image due to the reflected light from the light source is small and the light intensity is high, it is easy to determine the posture of the objective lens based on the end surface on the light source side. In many cases, | α | <| β | is preferable because the posture of the objective lens is determined based on the end surface on the optical disc side.

The surface roughness Ra is a parameter defined by JIS and represents the average value of the absolute value deviation from the average line. Both the surface roughness Ra of the light source side end surface and the optical disc side optical surface are preferably 1 nm or more and 5 nm or less.

The objective lens according to claim 2 is the following conditional expression (2) in the invention according to claim 1,
| Α | <| β | (2)
It is characterized by satisfying.

With the above configuration, the spot image due to the reflected light from the end surface on the optical disc side of the inspection light irradiated from the auto collimator installed on the optical disc side is the spot image due to the reflected light from the end surface on the side far from the auto collimator. Therefore, it is easy to determine the posture of the objective lens based on the end face on the optical disc side.

Furthermore, when the autocollimator is installed on the optical disc side, the amount of reflected light from the end surface on the optical disc side of the inspection light is larger than the amount of reflected light from the end surface on the light source side, so the light intensity of the spot image due to the reflected light from the end surface on the optical disc side Becomes higher, and posture determination can be made easier.

The objective lens described in claim 3 is characterized in that, in the invention described in claim 1 or 2, the optical disc side end surface is substantially orthogonal to the optical axis of the optical disc side optical surface.

The state that the optical disc side end surface is substantially orthogonal to the optical axis of the optical disc side optical surface means a state where | α | is less than 3 minutes (3 ′). When | α | is less than 3 minutes, the spot image on the autocollimator is smaller and the light intensity is higher, so that it is easier to determine the posture of the objective lens based on the end face on the optical disc side.

The objective lens according to claim 4 is the objective lens according to any one of claims 1 to 3, wherein the following conditional expression (3):
| Β | ≧ 3 ′ (3)
It is characterized by satisfying.

Preferably, the following conditional expression (3 ′),
| Β | ≧ 5 ′ (3 ′)
Is to satisfy.

In addition, it is preferable that the upper limit of | β | does not exceed 1 degree.

The objective lens according to claim 5 is the objective lens according to any one of claims 1 to 4, wherein the image side numerical aperture (NA) of the objective lens is 0.8 or more, and the following conditional expressions (4), (5) ,
390 nm ≦ λ ≦ 420 nm (4)
0.8 ≦ d / f ≦ 1.3 (5)
It is characterized by satisfying. Here, d represents the thickness (mm) of the objective lens on the optical axis, and f represents the focal length (mm) of the objective lens in the light flux with wavelength λ.

The objective lens satisfying the conditional expression (5) is an objective lens having a relatively small axial thickness as an objective lens having a high NA of 0.8 or more, and therefore, the flange thickness tends to be thin, and as a result, the optical disc. Since the thickness between the side end face and the light source side end face is also reduced, the problem of unnecessary reflected light becomes larger. Even in such a case where the problem becomes large, since the problem can be solved in the present invention, the effect of the invention becomes more remarkable.

The objective lens described in claim 6 is characterized in that, in the invention described in any one of claims 1 to 5, the objective lens is formed of a glass material.

The objective lens according to claim 7 is characterized in that, in the invention according to any one of claims 1 to 5, the objective lens is formed of a plastic material.

An objective lens according to an eighth aspect is the invention according to any one of the first to seventh aspects, wherein the following conditional expression (12),
|| α |-| β ||> 0.3 '(12)
It is characterized by satisfying.

By satisfying the conditional expression (12), the difference in the spot image in the autocollimator between the end surface on the light source side and the end surface on the optical disk side is more clearly shown. It becomes easy.

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

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. 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. Further, 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 (6), (7), and (8), but is not limited thereto.

0.050 mm ≦ t1 ≦ 0.125 mm (6)
0.5mm ≦ t2 ≦ 0.7mm (7)
1.0mm ≦ t3 ≦ 1.3mm (8)
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.

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 flux emitted from the first light source, the second wavelength λ2 of the second light flux emitted from the second light source (λ2> λ1), and the third of the third light flux emitted from the third light source. The wavelength λ3 (λ3> λ2) is defined by the following conditional expressions (9), (10),
1.5 × λ1 <λ2 <1.7 × λ1 (9)
1.8 × λ1 <λ3 <2.0 × λ1 (10)
It is preferable to satisfy.

Further, 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 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 preferable. Is 750 nm or more and 880 nm or less, more preferably 760 nm or more and 820 nm or less.

Also, 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 a light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens is a single glass lens or a single plastic 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.

When the objective lens is a glass lens, it is preferable to use a glass material having a glass transition point Tg of 500 ° C. or lower, more preferably 400 ° C. or lower. 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 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

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 (× 10 ⁻⁷ / K) or less, and more preferably 120 (× 10 ⁻⁷ / K) or less.

By the way, since the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the mass is increased 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.

Further, the Abbe number of the material constituting the objective lens is preferably 50 or more.

The objective lens includes a light source side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, an optical disc side optical surface, a light source side end surface disposed outside the light source side optical surface, and an optical disc side optical surface. It has at least an optical disc side end surface arranged outside. Moreover, what has a flange part around the objective lens may be used. 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 light source side end surface and the optical disc side end surface are not parallel to each other. The light source side end surface and the flange portion may be flush with each other, or the light source side end surface may be shifted in the optical axis direction with respect to the flange portion as shown in FIG.

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.

Moreover, it is preferable that the objective lens satisfies the following conditional expression (5). The objective lens satisfying the formula (5) is often small in diameter, and the range in which the inspection light for positioning is irradiated becomes narrow and the thickness between the end faces becomes thin, so that the problem of unnecessary light reflection becomes larger. In particular, the present invention is effective.

0.8 ≦ d / f ≦ 1.3 (5)
However, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length (mm) of the objective lens in the first light flux. In addition, it is preferable that f is 1.0 mm or more and 1.8 mm or less.

The following conditional expression (5 ′),
0.8 ≦ d / f <1.1 (5 ′)
In this case, the problem becomes more serious because the thickness between the end faces becomes thinner. Therefore, there is a further effect of the present invention.

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 some cases, astigmatism easily occurs, and a working distance (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 (5), it is possible to suppress the generation of astigmatism and the surface shift sensitivity.

Also, 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.

Further, the objective lens has a flange portion around the optical surface, and when the minimum thickness of the flange portion is t (mm), the following conditional expression (11),
5.0 <d / t ≦ 8.0 (11)
If the objective lens posture is determined based on the optical disc side end surface, the flange is relatively thin so that the light beam incident on the optical disc side end surface is transmitted and reflected by the light source side end surface. The negative effect is likely to increase. Therefore, the problem of the present invention becomes larger, but even in such a case, the objective lens of the present invention can solve the problem.

Further, even in an objective lens suitable for a slim type optical pickup device in which the effective diameter Φ of the light source side optical surface is 2.7 mm or less, the same problem as described above arises because the flange is relatively thin. However, even in such a case, the objective lens of the present invention can solve the problem.

Moreover, in the objective lens in which the end surface on the light source side exists up to the outer peripheral portion of the flange and the objective lens in which the area of the end surface on the light source side is larger than the area of the end surface on the optical disk side, the above-mentioned problem is still caused. It will be big. Even in such a case, the objective lens of the present invention can solve the problem.

An optical information recording / reproducing apparatus according to the present invention includes an optical disc drive apparatus having the above-described optical pickup apparatus.

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.

The optical information recording / reproducing apparatus using each method described above 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, it is possible to provide an objective lens capable of improving the ease of assembly and an optical pickup device using the objective lens by making it possible to accurately detect the posture of the objective lens.

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 a figure which shows the state at the time of attaching the objective lens OBJ to optical pick-up apparatus PU1. It is sectional drawing which shows the objective lens OBJ concerning the modification of this Embodiment. It is a figure which shows the spot image in the autocollimator used when detecting the attitude | position of an objective lens.

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. In addition, the objective lens OBJ has the following formula:
0.8 ≦ d / f ≦ 1.3 (5)
Meet. Here, d represents the thickness (mm) of the objective lens on the optical axis, and f represents the focal length (mm) of the objective lens in the light flux with wavelength λ.

First, 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 (for example, λ = 405 nm) is transmitted through the polarization prism PBS and passed through the coupling lens CL to be a substantially parallel light beam. The linearly polarized light is converted into circularly polarized light by QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and becomes a spot formed on the information recording surface RL1 through the protective substrate PL1 by the objective lens OBJ.

The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective lens OBJ and the diaphragm again, and then is converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and passes 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.

FIG. 2 is a cross-sectional view showing the objective lens OBJ of the present embodiment, and the alternate long and short dash line indicates the light beam L that passes through the outermost edge of the effective diameter. That is, the positions where the light beam L intersects the light source side optical surface OB11a and the optical disc side optical surface OB21a are effective diameters. Note that the light source side optical surface OB11a and the optical disc side optical surface OB21a are extended to the outside of the effective diameter (range indicated by hatching) in consideration of a case where a misalignment between an aperture (not shown) and the objective lens OBJ occurs.

In FIG. 2, the objective lens OBJ has a circular light source side optical surface OB11a including the optical axis X11 around the optical axis X11 of the light source side optical surface, followed by an annular light source side end surface region (also referred to as a light source side end surface). ) OB11b, a ring-shaped light source side transition region OB11c following it, a light source side flange end surface OB11d of the annular flange portion OBF, a circumferential surface OB11e of the flange portion OBF orthogonal thereto, and a disk side optical surface A circular optical disc-side optical surface OB21a including the optical axis X21, an annular optical disc-side end surface region (also referred to as an optical disc-side end surface) OB21b, and a subsequent annular optical disc-side transition region OB21c centered on the optical axis X21. And an optical disc side flange end surface OB21d of the flange portion that follows. 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 optical disc side end surface region OB21b has an inclination α of less than 3 minutes with respect to the surface T21 orthogonal to the optical axis X21 of the optical disc side optical surface OB21a, whereas the light source side end surface region OB11b has the light source side optical surface. The inclination β of the OB11a with respect to the plane T11 orthogonal to the optical axis X11 is inclined to be 3 minutes (0.05 degrees) or more. The optical axes X21 and X11 are not necessarily coaxial. The optical disc side end surface region OB21b and the light source side end surface region OB11b are mirror surfaces like the optical surface, and the surface roughness is Ra 10 nm or less.

FIG. 4 is a cross-sectional view showing an objective lens OBJ according to a modification of the present embodiment. In the modification shown in FIG. 4, the objective lens has no light source side transition region OB11c, light source side flange end surface OB11d, optical disc side transition region OB21c, and optical disc side flange end surface OB21d as in the embodiment shown in FIG. Various types of lenses are also included in the present invention.

FIG. 3 is a diagram showing a state when the objective lens OBJ is assembled to the optical pickup device PU1. When the inspection light DL is emitted from an autocollimator DET that is arranged on the optical disk side of the objective lens OBJ and is set to match the optical axis of the optical pickup device PU1, the inspection light DL is irradiated onto the optical disk side end face region OB21b. A part of the irradiated inspection light DL is reflected by the optical disc side end face region OB21b as indicated by a solid line and detected by the autocollimator DET. The remaining inspection light DL incident on the optical disc side end surface region OB21b is transmitted through the objective lens OBJ as indicated by a dotted line, and partially reflected by the light source side end surface region OB11b. The reflected light is also detected by the autocollimator DET. The

A spot image on the autocollimator DET by reflected light from the light source side end surface region OB11b and the optical disc side end surface region OB21b is as shown in FIG. The optical disc side end surface region OB21b has an inclination α of less than 3 minutes with respect to the optical axis X21 of the optical surface on the optical disc side, that is, substantially orthogonal, and therefore enters the autocollimator DET with substantially parallel light. The spot image S2 on the collimator DET is small and the light intensity is high. On the other hand, in the light source side end face region OB11b, since the inclination β of the light source side optical surface with respect to the optical axis X11 is inclined by 3 minutes or more, it enters the autocollimator DET with divergent light, and as a result, the spot image S1 in the autocollimator DET. Becomes larger and the light intensity is lower. Therefore, the spot image S2 and the spot image S1 can be clearly identified on the autocollimator DET. The posture of the objective lens OBJ is adjusted based on the optical disc side end surface region OB21b. As a specific method, the posture of the objective lens in which the spot image S2 by the optical disc side end surface region OB21b coincides with the optical axis of the optical pickup device PU1. The posture of the objective lens is adjusted so as to be at the position S. At this time, since the spot image S1 by the light source side end surface region OB11b is large and the light intensity is low, it does not affect the posture adjustment of the objective lens. After adjusting the inclination of the objective lens OBJ, the objective lens OBJ is bonded to the holder HL of the actuator AC.

Although FIG. 3 shows a method of adjusting the posture of the objective lens using a part of the optical disc side end surface region OB21b, the present invention is not limited to this. For example, the entire optical disc side end surface region OB21b is used. A method of adjusting the posture of the objective lens may be used.

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 light source side end surface region OB11b and the optical disc side end surface region OB21b are inclined outward, but may be inclined inward.

AC actuator CL coupling lens DET autocollimator DL inspection light HL holder LD semiconductor laser 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 OB11a light source side optical surface OB11b Light source side end surface region OB11c Light source side transition region OB11d Light source side flange portion OB11e Flange portion side 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 portion OBJ Objective lens OBF Flange portion X11 Light source side optical surface Optical axis X21 Optical axis of disc optical surface T11 Surface orthogonal to optical axis of light source optical surface T21 Surface orthogonal to optical axis of optical disc side α disc Angle formed by the side end surface region OB21b and a surface T21 orthogonal to the optical axis of the optical disc side optical surface β Angle formed by the light source side end surface region OB11b and the surface T11 orthogonal to the optical axis of the light source side optical surface S1 Light source side end surface region OB11b Spot image on autocollimator DET by S2 Spot image on autocollimator DET by optical disk side end surface region OB21b S Attitude position of objective lens coincident with optical axis of optical pickup device PU1

Claims

A light source that emits a light beam having a wavelength λ (390 nm ≦ λ ≦ 680 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 an objective lens of an optical pickup device that records and / or reproduces information by condensing on an information recording surface of the optical disc by a lens,
The objective lens is a single lens, and the image side numerical aperture (NA) is 0.6 or more,
The objective lens is formed on the light source side optical surface and the optical disc side optical surface through which a light beam condensed on the information recording surface of the optical disc passes, and outside the light source side optical surface, and has a surface roughness Ra of 10 nm or less. A light source side end surface and an optical disc side end surface formed on the outer side of the optical disc side optical surface and having a surface roughness Ra of 10 nm or less,
An objective lens that satisfies the following conditional expression (1):
| Α | ≠ | β | (1)
Here, α represents an angle formed by the end surface on the optical disc side and a surface orthogonal to the optical axis of the optical surface on the optical disc side, and β is formed on a surface orthogonal to the optical axis of the light source side optical surface. Represents a corner.
The objective lens according to claim 1, wherein the following conditional expression (2) is satisfied.
| Α | <| β | (2)
3. The objective lens according to claim 1, wherein the optical disc side end surface is substantially orthogonal to the optical axis of the optical disc side optical surface.
The objective lens according to any one of claims 1 to 3, wherein the following conditional expression (3) is satisfied.
| Β | ≧ 3 ′ (3)
The objective according to any one of claims 1 to 4, wherein an image-side numerical aperture (NA) of the objective lens is 0.8 or more and satisfies the following conditional expressions (4) and (5): lens.
390 nm ≦ λ ≦ 420 nm (4)
0.8 ≦ d / f ≦ 1.3 (5)
Here, d represents the thickness (mm) of the objective lens on the optical axis, and f represents the focal length (mm) of the objective lens in the light flux with wavelength λ.
6. The objective lens according to claim 1, wherein the objective lens is made of a glass material.
6. The objective lens according to claim 1, wherein the objective lens is made of a plastic material.
The objective lens according to claim 1, wherein the following conditional expression (12) is satisfied.
|| α |-| β ||> 0.3 '(12)
An optical pickup device comprising the objective lens according to any one of claims 1 to 8.