JP2011243268A - Objective lens for optical pickup device, and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens having a thin axial thickness and high NA while securing a working distance, an excellent formability and assemblability; and an optical pickup device using the same.SOLUTION: Using a glass material whose refractive index satisfies an inequality (1) enables securing of not only a working distance but also an area (width) of the end face where an inspection light is entered even if the outer diameter of a lens is reduced, therefore achieving an accurate adjustment of the objective lens attitude. Provided inequalities are (1) 1.55≤n1≤1.75 and (2) 0.8≤d/f≤1.1, where n1 is a refractive index of an objective lens material to a light flux having a wavelength λ1, d is a thickness of an objective lens on the optical axis (mm), and f is a focal distance of an objective lens material to a light flux having a wavelength λ1 (mm).

Description

  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 0.8 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 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) 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 a capacity of 4.7 GB.

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

JP 2001-324673 A

  As shown in Patent Document 1, a high NA objective lens tends to have a thick axial thickness. In recent years, there has been an increasing demand for miniaturization and thinning of optical pickup devices in the market. Compared with the objective lens described in Patent Document 1, an objective lens having a thinner on-axis thickness and a smaller outer diameter. Is desired.

  Since reducing the outer diameter of the objective lens is almost the same as reducing the focal length of the objective lens, simply reducing the outer diameter of the objective lens also shortens the working distance and is mounted on the optical pickup device. When doing so, there is a risk of contact between the optical disk and the objective lens.

  On the other hand, when assembling a high-NA objective lens into an optical pickup device, coma aberration may occur if the posture is not determined accurately, so it must be placed outside the optical surface of the objective lens during assembly. In some cases, the orientation of the objective lens is detected by causing the inspection light to enter the received end face and receiving the reflected light. When the outer diameter of the objective lens is further reduced, the area of the end face of the objective lens becomes smaller (or narrower), and the amount of reflected light decreases, which makes it difficult to detect the posture of the objective lens. There is also. Furthermore, there is a demand for further improving moldability by reducing the axial thickness of the objective lens.

  The present invention has been made in view of the problems of the prior art, and has a high NA objective lens with a thin on-axis thickness while ensuring a working distance and good moldability and assemblability, and An object of the present invention is to provide an optical pickup device used.

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 made of a single glass, and the image-side numerical aperture (NA) is 0.8 or more,
Further, the following expression is satisfied.
1.55 ≦ n1 ≦ 1.75 (1)
0.8 ≦ d / f ≦ 1.1 (2)
However,
n1: Refractive index of the material of the objective lens with respect to the light beam having the wavelength λ1 d: Thickness on the optical axis of the objective lens (mm)
f: Focal length (mm) of the objective lens in the light beam having the wavelength λ1.

  According to the present invention, by using a glass material having a refractive index that satisfies the expression (1), the on-axis thickness can be reduced so as to satisfy the expression (2). This increases the moldability of the objective lens, and even if the outer diameter of the objective lens is made excessively small, a sufficient working distance can be secured and the area (width) of the end surface on which the inspection light is incident can be secured. Highly accurate posture determination can be realized when determining the lens posture.

The objective lens described in claim 2 is characterized in that, in the invention described in claim 1, the following expression (1 ′) is satisfied.
1.65 <n1 ≦ 1.75 (1 ′)

  According to a third aspect of the present invention, there is provided the objective lens according to the first or second aspect, wherein the objective lens has a meniscus shape.

  According to a fourth aspect of the present invention, in the invention according to any one of the first to third aspects, the outer diameter of the objective lens is φ3.5 mm or less.

  An optical pickup device according to a fifth aspect has the objective lens according to any one of the first to fourth 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 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 (3), (4), and (5), 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 (3)
0.5mm ≤ t2 ≤ 0.7mm (4)
1.0 mm ≤ t3 ≤ 1.3 mm (5)

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 (6) and (7).
1.5 · λ1 <λ2 <1.7 · λ1 (6)
1.8 · λ1 <λ3 <2.0 · λ1 (7)

  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.

  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 lens. A single-lens biconvex or meniscus objective lens is preferable. In particular, when the refractive index of glass is high, there is a high possibility that the objective lens has a meniscus shape. 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 has 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, and a flange portion provided around the optical surface. 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. Further, it is preferable that the flange portion has an end surface arranged outside at least one of the light source side optical surface and the optical disc side optical surface.

  The end surface is preferably orthogonal to the optical axis of the objective lens, and the end surface disposed outside the optical surface on the optical disc side is preferably orthogonal to the optical axis of the objective lens. Further, when there are end faces arranged outside the optical surfaces of both the light source side optical surface and the optical disc side optical surface, it is preferable that the respective end surfaces are non-parallel. The end surface and the flange surface may be flush with each other or may be shifted in the optical axis direction.

  The numerical aperture on the image side of the objective lens necessary for recording / reproducing information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for recording / reproducing information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for recording / reproducing information with respect to 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 an objective lens satisfy | fills the following formula | equation (1), (preferably (1 ')), (2).
1.55 ≦ n1 ≦ 1.75 (1)
1.65 <n1 ≦ 1.75 (1 ′)
0.8 ≦ d / f ≦ 1.1 (2)
However,
n1: Refractive index for a light beam having a wavelength λ1 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 objective lens satisfying the expression (2) is often small in diameter, and the range in which the inspection light for determining the posture of the objective lens is irradiated becomes narrow.

  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 (2), astigmatism and surface shift sensitivity can be suppressed.

  The present invention is particularly preferably applied when the outer diameter of the objective lens is φ3.5 mm or less. The outer diameter here refers to the maximum value of the diameter in the direction perpendicular to the optical axis of the entire objective lens including the flange portion.

  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 an assembly ease by enabling it to detect the attitude | 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 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 which concerns on the modification of this Embodiment. It is a figure which shows the spot image in the autocollimator DET by the reflected light from light source side end surface area | region OB11b and optical disk side end surface area | region OB21b.

  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. The objective lens OBJ satisfies the following expression.
1.55 ≦ n1 ≦ 1.75 (1)
0.8 ≦ d / f ≦ 1.1 (2)
However,
n1: Refractive index of the material of the objective lens with respect to the light flux with wavelength λ1 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.

  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. It is converted from linearly polarized light into circularly polarized light, its light beam diameter is regulated by a stop (not shown), and becomes a spot formed on the information recording surface RL1 via 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.

  In the present embodiment, the on-axis thickness d is made thin so as to satisfy the expression (2) with a glass material having a refractive index satisfying the expression (1). Therefore, the ratio (so-called deviation) of the thickness t of the portion of the objective lens OBJ having the smallest thickness in the optical axis direction (between the light source side end surface region OB11b and the optical disc side end surface region OB21b in FIG. 4) and the axial thickness d. Since a large meat ratio (t / d) can be secured, moldability is improved. Further, the light source side optical surface OB11a of the objective lens OBJ is convex, and the optical disc side optical surface OB21a is concave. That is, the objective lens OBJ has a meniscus shape, so that a long working distance can be secured, and see FIG. Thus, the area (width) of the optical disc side end face OB21b that irradiates the inspection light DL described later can be increased.

  FIG. 2 is a cross-sectional view showing the objective lens OBJ of the present embodiment, and shows the outer edge L of the light beam passing through the closest inward side of the effective diameter by a one-dot chain 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. 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 OEF, a circumferential surface OB11e of the flange portion OBF orthogonal thereto, and a disc side optical surface A circular optical disc side optical surface OB21a including the optical axis X21, the subsequent annular optical disc side end surface region (also referred to as an optical disc side end surface) OB21b, and the subsequent annular optical disc side transition region OB21c around 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 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. FIG. 4 shows an objective lens that does not have the light source side transition region OB11c, the light source side flange end surface OB11d, the optical disc side transition region OB21c, and the optical disc side flange end surface OB21d as compared with the portable device shown in FIG. Are also included in the present invention.

  FIG. 3 is a diagram illustrating 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 so as to match the optical axis of the optical pickup device PU1, the inspection light DL enters the optical disk side end surface region OB21b. A part of the inspection light DL is reflected as indicated by a solid line and detected by the autocollimator DET. The remainder of the inspection light DL that has entered 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 as indicated by a dotted line, and the reflected light is also detected by the autocollimator DET.

  FIG. 5 shows a spot image on the autocollimator DET by the reflected light from the light source side end surface region OB11b and the optical disc side end surface region OB21b. 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. Is large and has low light intensity. Further, according to the present invention, the intensity of the reflected light at the OB 11b can be reduced from the viewpoint that the thickness t of the portion of the objective lens having the smallest thickness in the optical axis direction can be set to a relatively large value. 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 position of the objective lens where 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 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. There is also a method for adjusting the posture of the objective lens.

  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 the examples are for illustrative purposes only, and the scope of the present invention is indicated by the following claims. For example, in the above-described embodiment, the optical disc side optical surface 21a is concave, but may be flat or convex as long as the expressions (1) and (2) are satisfied.

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 OEF Flange portion X11 Light source side optical surface Optical axis X21 Optical axis T11 of the optical surface on the disk side Surface T21 orthogonal to the optical axis of the optical surface on the light source side Surface α orthogonal to the optical axis of the optical surface on the optical disk side OB21 Between 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 The autocollimator DET by the light source side end surface region OB11b Spot S2 at the spot S in the autocollimator DET by the optical disc side end surface region OB21b Attitude position t of the objective lens that coincides with the optical axis of the optical pickup device PU1 Distance between the light source side end surface region OB11b and the optical disc side end surface region OB21b

Claims (5)

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 made of a single glass, and the image-side numerical aperture (NA) is 0.8 or more,
Furthermore, the objective lens characterized by satisfy | filling the following formula | equation.
1.55 ≦ n1 ≦ 1.75 (1)
0.8 ≦ d / f ≦ 1.1 (2)
However,
n1: Refractive index of the material of the objective lens with respect to the light beam having the wavelength λ1 d: Thickness on the optical axis of the objective lens (mm)
f: Focal length (mm) of the objective lens in the light beam having the wavelength λ1. The objective lens according to claim 1, wherein the following expression (1 ′) is satisfied.
1.65 <n1 ≦ 1.75 (1 ′)   The objective lens according to claim 1, wherein the objective lens has a meniscus shape.   The objective lens according to claim 1, wherein an outer diameter of the objective lens is φ3.5 mm or less.   An optical pickup device comprising the objective lens according to claim 1.