JP5835320B2 - Objective lens for optical pickup device, optical pickup device and optical information recording / reproducing device - Google Patents

Description

  The present invention relates to an optical pickup device, an objective lens, and an optical information recording / reproducing apparatus capable of recording and / or reproducing (recording / reproducing) information interchangeably with an optical disc.

  In recent years, in an optical pickup device, a laser light source used as a light source for reproducing information recorded on an optical disc and recording information on the optical disc has been shortened. For example, a wavelength 390 such as a blue-violet semiconductor laser is used. A laser light source of ˜420 nm has been put into practical use. When these blue-violet laser light sources are used, when an objective lens having the same numerical aperture (NA) as that of a DVD (digital versatile disk) is used, it is possible to record information of 15 to 20 GB on an optical disk having a diameter of 12 cm. When the NA of the objective optical element is increased to 0.85, 23 to 25 GB of information can be recorded on an optical disk having a diameter of 12 cm.

  As an example of an optical disk using the above-described objective lens with NA of 0.85, there is a BD (Blu-ray disk). Since the coma generated due to the tilt (skew) of the optical disk increases, the BD has a thinner protective substrate than the DVD (0.1 mm compared to 0.6 mm for the DVD) and is caused by the skew. The amount of coma is reduced.

  Furthermore, the relatively thick type called so-called half-height, which has been conventionally installed in stationary recorders, etc., has recently become a relatively thin type called so-called slim type, which is mounted on the back of notebook PCs and thin televisions. An optical pickup device has been developed. The objective lens for BD used in such a slim type optical pickup device has a numerical aperture NA as high as 0.8 or more, and since the entire lens is miniaturized, the edge thickness tends to be thin, and the objective lens is molded. However, there is a problem that it is difficult to process the mold, and the moldability is lowered.

JP 2007-294101 A

  Here, Patent Document 1 discloses an objective lens that has a relatively small lens outer diameter of 3.3 mm and can be used for a thin optical pickup device. However, the objective lens of Patent Document 1 has a problem that the edge thickness is small, it is difficult to process a mold for molding the objective lens, and moldability is deteriorated.

  The present invention aims to solve the above-described problems, and can form an objective lens by securing an edge thickness even though it can be used in a thin BD optical pickup device. It is an object of the present invention to provide an objective lens capable of facilitating the processing of a mold to improve moldability, an optical pickup apparatus including the objective lens, and an optical information recording / reproducing apparatus.

The objective lens according to claim 1 is a first light source that emits a first light flux having a wavelength λ1 (nm), and a first light flux emitted from the first light source through a protective substrate having a thickness t1. A condensing optical system including an objective lens for condensing on the information recording surface of the optical disc, and the condensing optical system collects the light beam from the first light source on the information recording surface of the first optical disc. An objective lens used in an optical pickup device that records and / or reproduces information by making it light,
The objective lens is a single lens, the focal length f at the wavelength λ1 is less than 1.5 (mm), the image-side numerical aperture NA is 0.8 or more,
When the maximum normal angle within the effective diameter of the optical surface on the light source side of the objective lens is θ (°), the following equation is satisfied:
66 ≦ θ ≦ 69.5 (1)
When the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface on the light source side of the objective lens (however, the effective diameter is 1) is represented by S (h), the second floor guide When the function S ″ (h) has a maximum value at h = h1, the following expression is satisfied:
0.85 ≦ h1 ≦ 1 (2)
When the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface on the optical disk side of the objective lens (however, the effective diameter is 1) is represented by Z (h), the first floor guide When the function Z ′ (h) has a minimum value at h = h2 and a maximum value at h = h3, the following expression is satisfied.
0.25 ≦ h2 ≦ 0.4 (3)
0.8 ≦ h3 ≦ 0.95 (4)

  The inventor first tried to secure the edge thickness in order to improve the moldability of the objective lens. Specifically, since the curvature of the optical surface on the light source side of the objective lens greatly affects the edge thickness, the expression (1) is satisfied by satisfying the expression (2). That is, if the second-order derivative S ″ (h) on the light source side optical surface of the objective lens has a maximum value of 0.85 or more and 1 or less with an effective diameter of 1, the light source side optical surface of the objective lens An inflection point occurs near the effective diameter, and the curvature near the effective diameter can be relaxed while maintaining the paraxial curvature of the light source side optical surface as much as possible, so that the edge thickness of the objective lens can be secured. .

  However, if the maximum normal angle θ on the light source side optical surface is in the range of the expression (1), the edge thickness can be obtained, but the refractive power in the vicinity of the effective diameter of the light source side optical surface becomes small as it is, NA is not satisfied. Therefore, it is necessary to cover the shortage of power by increasing the refractive power of the optical surface on the optical disk side. That is, the shape of the optical surface on the optical disc side is adjusted so as to satisfy the expressions (3) and (4). More specifically, if the first-order derivative Z ′ (h) on the optical disc side optical surface has a maximum value at a position h3 satisfying the equation (4), the optical surface optical surface is refracted. The power can be increased, and this can compensate for a decrease in the refractive power of the light source side optical surface. Furthermore, spherical aberration occurs with respect to the thickness change of the objective lens, but the first-order derivative Z ′ (h) on the optical surface on the optical disc side is a minimum value so as to satisfy the expressions (3) and (4). By having a maximum value, it is possible to distribute the third-order spherical aberration into higher-order spherical aberrations such as fifth-order spherical aberration and seventh-order spherical aberration, thereby reducing the total wavefront aberration. As a result, an objective lens resistant to manufacturing errors can be provided. Further, by satisfying the expression (4), it is possible to suppress the occurrence of the fifth or higher order coma aberration when the light source side optical surface and the disk side optical surface are shifted in the direction perpendicular to the optical axis. In particular, h3 is more preferably 0.9 or more. Further, if the expression (3) is out of the range, coma aberration generated when off-axis light is incident increases. Therefore, the occurrence of coma aberration can be suppressed by satisfying the expression (3). The surface normal angle in the case of a diffractive surface may be the normal angle of the envelope surface connecting the surface vertices of each annular zone, or the normal angle of each annular surface.

  According to a second aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the objective lens is formed of a plastic material, an optical path difference providing structure is formed on the light source side optical surface, and the first light. It is used for an optical pickup device dedicated to an information recording medium.

  By forming from a plastic material, an inexpensive objective lens can be formed, and a diffraction structure can be easily provided. Plastics, on the other hand, have a lower refractive index than glass. In particular, BD / DVD / CD3-compatible diffractive objective lenses use diffractive power to extend the WD of the CD. As a result, the envelope of the diffractive structure has an increasingly curved surface. Although the surface normal angle θ tends to increase and the surface normal angle θ tends to increase, the present invention improves the workability and moldability of the mold, so that it can be selected as a practical objective lens material. Note that the occurrence of spherical aberration due to a change in refractive index due to a temperature change in a plastic objective lens can be eliminated by using a diffraction structure or the like.

The objective lens described in claim 3 is characterized in that, in the invention described in claim 2, the following expression is satisfied.
0.30 ≦ dmin / d ≦ 0.50 (5)
However,
dmin: minimum thickness of the objective lens d: axial thickness of the objective lens

  Since the molten resin is poured from the end face when the objective lens is molded, the resin can be smoothly flowed if the value is equal to or more than the lower limit of the value of the expression (5). On the other hand, the image-side numerical aperture NA can be made 0.8 or more if it is less than or equal to the upper limit of the expression (5).

According to a fourth aspect of the present invention, there is provided the objective lens according to the first aspect, wherein the objective lens is formed of a glass material and satisfies the following expression.
0.5 ≦ dmin ≦ 0.8 (6)
However,
dmin: minimum thickness of the objective lens

  When a glass objective lens is molded from a spherical preform, it is not necessary to ensure the fluidity of the material, but when molding by the droplet method, it is necessary to consider that the glass flows to the flange. There is. However, in any molding method, if the edge thickness is too thin, damage or the like may occur at the time of mold release. Therefore, if the value is equal to or greater than the lower limit of the expression (6), the occurrence of breakage or the like can be suppressed. It becomes possible.

The objective lens described in claim 5 is characterized in that, in the invention described in any one of claims 1 to 4, the following expression is satisfied.
1.1 ≤ A2 / B2 ≤ 1.6 (7)
However,
A2: Optical surface diameter on the optical disc side of the objective lens
B2: Effective diameter of the objective lens on the optical disk side

  In the BD, a multi-layer structure is being promoted in order to improve the storage capacity. However, unlike DVD, spherical aberration due to interlayer thickness cannot be ignored due to high NA, and a correction mechanism is required. Normally, correction is performed by moving a collimator, a coupling lens, or the like disposed on the light source side of the objective lens in the optical axis direction and changing the magnification of the objective lens. In the objective lens, when the magnification is changed, the incident height (from the optical axis) and the outgoing height (from the optical axis) of the marginal ray are changed, so that the optical surface needs to be formed up to the maximum height. In equation (7), if A2 / B2 is equal to or greater than the lower limit, the light beam emitted from the surface of the objective lens on the optical disk side is all within the optical plane even if the processing accuracy of the objective lens or the assembly error to the optical pickup device occurs. And the required NA can be satisfied. On the other hand, when A2 / B2 falls below the upper limit of the expression (7), the outer diameter of the objective lens does not become too large, and a lens suitable for a slim type optical pickup device is obtained. Furthermore, if the outer diameter is constant, a space on the end face provided around the optical surface of the objective lens is secured, and the object lens can be confirmed using reflected light from the end face when the objective lens is attached to the optical pickup device.

  In other words, by setting A2 / B2 to be equal to or higher than the lower limit of the expression (7), the information can be accurately collected on the information recording surface of the BD having a high NA so that information can be recorded / reproduced. In other words, the outer diameter of the objective lens can be reduced while suppressing the vignetting of the light beam on the surface on the optical disk side. On the other hand, by setting A2 / B2 to be equal to or less than the upper limit of the expression (7), it is possible to secure the space of the end surface provided around the optical surface of the objective lens. It can be attached with high accuracy.

The objective lens described in claim 6 is characterized in that, in the invention described in claim 5, when the objective lens is made of glass, the following expression is satisfied.
1.15 <A2 / B2 <1.3 (7A)

By making A2 / B2 larger than the lower limit of the expression (7A), it is possible to secure a more sufficient optical surface diameter with respect to the effective diameter in the glass objective lens and to guarantee the performance within the effective diameter.
On the other hand, by making A2 / B2 smaller than the upper limit of the expression (7A), the outer diameter of the objective lens can be reduced while ensuring a wider end face. As described above, the glass objective lens can reduce the amount of movement of the collimator and the coupling lens because it is not necessary to perform magnification correction due to temperature change, so the emission area on the optical surface on the optical disc side is reduced. Since it can suppress, an upper limit is restrained small like (7A) Formula.

  In this specification, the “optical surface” of the objective lens is a surface having an optical function of condensing a light beam, and generally refers to a region inside the end surface. The “end surface” of the objective lens is generally a surface orthogonal to the optical axis. When the objective lens is assembled to the optical pickup device, the light beam is emitted from the inspection device and the reflected light from the end surface is used. Often used for positioning. The optical surface and the end surface may be in contact with each other, but a small boundary portion may be provided between them. The “effective diameter” of an objective lens is an area in an optical surface through which a light beam used for recording / reproduction passes when a parallel light beam is incident on the objective lens. , An area in the optical plane through which the parallel light flux that has passed through the inside of the aperture limiting element passes. Therefore, the “effective diameter on the light source side” is the inner diameter of the stop.

The objective lens described in claim 7 is characterized in that, in the invention described in claim 5, when the objective lens is made of plastic, the following expression is satisfied.
1.2 <A2 / B2 <1.4 (7B)

  By making A2 / B2 larger than the lower limit of the expression (7B), it is possible to secure a further sufficient optical surface diameter with respect to the effective diameter, and to guarantee the performance within the effective diameter. On the other hand, by making A2 / B2 smaller than the upper limit of the expression (7B), the outer diameter of the objective lens can be reduced while ensuring a wider end face. When the objective lens is made of plastic, the refractive index change due to temperature change tends to be large compared to glass, so when the environmental temperature is relatively high, when focusing on the information recording surface with the thickest substrate thickness Therefore, it is necessary to make a divergent light beam having a larger divergence angle incident. Therefore, when the objective lens is made of plastic, it is desirable to satisfy the expression (7B).

The objective lens described in claim 8 is characterized in that, in the invention described in any one of claims 5 to 7, the following expression is satisfied.
1.0 ≤ A1 / B1 ≤ 1.1 (8)
However,
A1: Optical surface diameter on the light source side of the objective lens
B1: Effective diameter of the objective lens on the light source side

  Since the optical surface on the light source side of the objective lens is closer to the stop than the optical surface on the optical disk side, it can be said that the influence of incident convergent light or divergent light is small, and the involvement of A1 / B1 is relatively small. However, a better objective lens can be obtained by designing the optical surface on the light source side together with the design of the optical surface on the optical disc side. More specifically, by setting A1 / B1 to be equal to or greater than the lower limit of the formula (8), it is possible to secure a more sufficient optical surface diameter with respect to the effective diameter and to guarantee the performance within the effective diameter. On the other hand, the outer diameter of the objective lens can be reduced by setting A1 / B1 to be equal to or less than the upper limit of the equation (8). In an objective lens having a high NA, the optical surface on the light source side has a large expected angle of the surface and is often difficult to mold. However, this makes it possible to reduce the expected angle and improve manufacturability.

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

  An optical information recording / reproducing apparatus according to a tenth aspect has the optical pickup apparatus according to the ninth aspect.

  The optical pickup device according to the present invention includes the first light source, but may further include a second light source and a third light source. Furthermore, the optical pickup device of the present invention has a condensing optical system for condensing the first light flux on the information recording layer of the first optical disc. The condensing optical system uses the second light flux for information on the second optical disc. It may also be used for condensing on the recording layer and condensing the third light beam on the information recording layer of the third optical disc. In addition, the optical pickup device of the present invention has a light receiving element that receives a reflected light beam from the information recording layer of the first optical disk, but receives a reflected light beam from the information recording layer of the second optical disk or the third optical disk. You may have.

  The first optical disc has a protective substrate having a thickness t1 and an information recording layer. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording layer. The third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording layer. 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 disc, the second optical disc, or the third optical disc may be a multi-layer optical disc having a plurality of information recording layers.

  In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 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 layer, a BD having two or more information recording layers, 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 (9), (10), and (11), 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 surface of the optical disk to the information recording layer closest to the surface.

0.020mm ≦ t1 ≦ 0.125mm (9)
0.5mm ≤ t2 ≤ 0.7mm (10)
1.0 mm ≤ t3 ≤ 1.3 mm (11)

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 (12) and (13).
1.5 · λ1 <λ2 <1.7 · λ1 (12)
1.8 · λ1 <λ3 <2.0 · λ1 (13)

  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 415 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.

  In addition, when using the second light source or the third light source in addition to the first light source, at least two of the light sources 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 layer 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 has an objective lens. The condensing optical system preferably has a coupling lens such as a collimator in addition to the objective lens. The coupling lens is a single lens or a lens group that is disposed between the objective lens and the light source and changes the divergence angle of the light beam. The collimator is a type of coupling lens, and is a lens that emits light incident on the collimator as parallel light. 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 a light source onto an information recording layer of the optical disk. The objective lens may be composed of two or more lenses and / or optical elements, or may be composed of a single lens, but is preferably an objective lens composed of a single convex lens. . The objective lens may be a glass lens or a plastic lens, or an optical path difference providing structure is provided on the glass lens with a photo-curing resin, a UV-curing resin, or a thermosetting resin. A hybrid lens may also be used. When the objective lens has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective lens includes a plurality of lenses, it may be a combination of a flat optical element having an optical path difference providing structure and an aspherical lens (which may or may not have an optical path difference providing structure). 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 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

  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.

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

When the objective lens is a plastic lens, it is preferable to use an alicyclic hydrocarbon polymer material such as a cyclic olefin resin material. Further, the resin material has a refractive index within a range of 1.54 to 1.60 at a temperature of 25 ° C. with respect to a wavelength of 405 nm, and a wavelength of 405 nm associated with a temperature change within a temperature range of −5 ° C. to 70 ° C. The refractive index change rate dN / dT (° C. ⁻¹ ) is −20 × 10 ^{−5 to} −5 × 10 ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ) It is more preferable to use a certain resin material. When the objective lens is a plastic lens, the coupling lens is preferably a plastic lens.

  Some preferred examples of the alicyclic hydrocarbon polymer are shown below.

  A first preferred example includes a polymer block [A] containing a repeating unit [1] represented by the following formula (I), a repeating unit [1] represented by the following formula (1) and the following formula ( II) and / or polymer block [B] containing a repeating unit [3] represented by the following formula (III), and repeating in the block [A] From the block copolymer in which the relationship between the molar fraction a (mol%) of the unit [1] and the molar fraction b (mol%) of the repeating unit [1] in the block [B] is a> b. It is the resin composition which becomes.

(In the formula, R ¹ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms, and R ^{2 to} R ¹² each independently represents a hydrogen atom, an alkyl group having 1 to 20 carbon atoms, a hydroxyl group, or 1 carbon atom. ˜20 alkoxy groups or halogen groups.)

(In the formula, R ¹³ represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

(In the formula, R ¹⁴ and R ¹⁵ each independently represents a hydrogen atom or an alkyl group having 1 to 20 carbon atoms.)

  Next, a second preferred example is obtained by addition polymerization of a monomer composition comprising at least an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (IV). A polymer (B) obtained by addition polymerization of a polymer (A), a monomer composition comprising an α-olefin having 2 to 20 carbon atoms and a cyclic olefin represented by the following general formula (V) ).

[Wherein n is 0 or 1, m is 0 or an integer of 1 or more, q is 0 or 1, and R ^{1 to} R ¹⁸ , R ^a and R ^b are each independently a hydrogen atom, A halogen atom or a hydrocarbon group, R ^{15 to} R ¹⁸ may be bonded to each other to form a monocycle or polycycle, and the monocycle or polycycle in parentheses may have a double bond Alternatively, R ¹⁵ and R ¹⁶ , or R ¹⁷ and R ¹⁸ may form an alkylidene group. ]

[Wherein, R ^{19 to} R ²⁶ each independently represents a hydrogen atom, a halogen atom or a hydrocarbon group. ]

  In order to add further performance to the resin material, the following additives may be added.

(Stabilizer)
It is preferable to add at least one stabilizer selected from a phenol stabilizer, a hindered amine stabilizer, a phosphorus stabilizer, and a sulfur stabilizer. By suitably selecting and adding these stabilizers, for example, it is possible to more highly suppress the white turbidity and the optical characteristic fluctuations such as the refractive index fluctuations when continuously irradiated with light having a short wavelength of 405 nm. .

  As a preferable phenol-based stabilizer, conventionally known ones can be used, for example, 2-t-butyl-6- (3-t-butyl-2-hydroxy-5-methylbenzyl) -4-methylphenyl acrylate, 2 , 4-di-t-amyl-6- (1- (3,5-di-t-amyl-2-hydroxyphenyl) ethyl) phenyl acrylate and the like, and JP-A Nos. 63-179953 and 1-168643. Acrylate compounds described in Japanese Patent Publication No. 1; octadecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2,2'-methylene-bis (4-methyl-6-tert-butylphenol) ), 1,1,3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 1,3,5-trimethyl-2,4,6-tris (3 5-di-t-butyl-4-hydroxybenzyl) benzene, tetrakis (methylene-3- (3 ′, 5′-di-t-butyl-4′-hydroxyphenylpropionate)) methane [ie pentaerythritol Methyl-tetrakis (3- (3,5-di-tert-butyl-4-hydroxyphenylpropionate))], triethylene glycol bis (3- (3-tert-butyl-4-hydroxy-5-methylphenyl) Alkyl-substituted phenolic compounds such as propionate); 6- (4-hydroxy-3,5-di-t-butylanilino) -2,4-bisoctylthio-1,3,5-triazine, 4-bisoctylthio- 1,3,5-triazine, 2-octylthio-4,6-bis- (3,5-di-t-butyl-4-oxyanilino) -1,3,5-to Triazine group-containing phenol compounds such as azine; and the like.

  Preferred hindered amine stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (2,2,6,6-tetramethyl-4-piperidyl) succinate, bis ( 1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, bis (N-octoxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-benzyloxy-2, 2,6,6-tetramethyl-4-piperidyl) sebacate, bis (N-cyclohexyloxy-2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6) -Pentamethyl-4-piperidyl) 2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1-acryloyl-2,2,6 6-tetramethyl-4-piperidyl) 2,2-bis (3,5-di-t-butyl-4-hydroxybenzyl) -2-butylmalonate, bis (1,2,2,6,6-pentamethyl) -4-piperidyl) decandioate, 2,2,6,6-tetramethyl-4-piperidyl methacrylate, 4- [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy]- 1- [2- (3- (3,5-di-t-butyl-4-hydroxyphenyl) propionyloxy) ethyl] -2,2,6,6-tetramethylpiperidine, 2-methyl-2- (2 , 2,6,6-tetramethyl-4-piperidyl) amino-N- (2,2,6,6-tetramethyl-4-piperidyl) propionamide, tetrakis (2,2,6,6-tetramethyl- 4-pipe Jill) 1,2,3,4-butane tetracarboxylate, tetrakis (1,2,2,6,6-pentamethyl-4-piperidyl) 1,2,3,4-butane tetracarboxylate, and the like.

  Further, the preferable phosphorus stabilizer is not particularly limited as long as it is a substance usually used in the general resin industry. For example, triphenyl phosphite, diphenylisodecyl phosphite, phenyl diisodecyl phosphite, tris (nonyl). Phenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite, 10- (3,5-di-t-butyl-4-hydroxybenzyl) -9 Monophosphite compounds such as 1,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; 4,4′-butylidene-bis (3-methyl-6-tert-butylphenyl-di-tridecyl) Phosphite), 4,4 'isopropylidene-bis (phenyl-di-alkyl (C12-C15) phos Aito) and the like diphosphite compounds such as. Among these, monophosphite compounds are preferable, and tris (nonylphenyl) phosphite, tris (dinonylphenyl) phosphite, tris (2,4-di-t-butylphenyl) phosphite and the like are particularly preferable.

  Preferred sulfur stabilizers include, for example, dilauryl 3,3-thiodipropionate, dimyristyl 3,3′-thiodipropionate, distearyl 3,3-thiodipropionate, lauryl stearyl 3,3- Thiodipropionate, pentaerythritol-tetrakis- (β-lauryl-thio) -propionate, 3,9-bis (2-dodecylthioethyl) -2,4,8,10-tetraoxaspiro [5,5] undecane Etc.

  The blending amount of each of these stabilizers is appropriately selected within a range that does not impair the purpose of the present invention, but is usually 0.01 to 2 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based copolymer, Preferably it is 0.01-1 mass part.

(Surfactant)
A surfactant is a compound having a hydrophilic group and a hydrophobic group in the same molecule. The surfactant can prevent white turbidity of the resin composition by adjusting the rate of moisture adhesion to the resin surface and the rate of moisture evaporation from the surface.

  Specific examples of the hydrophilic group of the surfactant include a hydroxy group, a hydroxyalkyl group having 1 or more carbon atoms, a hydroxyl group, a carbonyl group, an ester group, an amino group, an amide group, an ammonium salt, a thiol, a sulfonate, A phosphate, a polyalkylene glycol group, etc. are mentioned. Here, the amino group may be primary, secondary, or tertiary. Specific examples of the hydrophobic group of the surfactant include an alkyl group having 6 or more carbon atoms, a silyl group having an alkyl group having 6 or more carbon atoms, and a fluoroalkyl group having 6 or more carbon atoms. Here, the alkyl group having 6 or more carbon atoms may have an aromatic ring as a substituent. Specific examples of the alkyl group include hexyl, heptyl, octyl, nonyl, decyl, undecenyl, dodecyl, tridecyl, tetradecyl, myristyl, stearyl, lauryl, palmityl, cyclohexyl and the like. Examples of the aromatic ring include a phenyl group. The surfactant only needs to have at least one hydrophilic group and hydrophobic group as described above in the same molecule, and may have two or more groups.

  More specifically, examples of such surfactants include myristyl diethanolamine, 2-hydroxyethyl-2-hydroxydodecylamine, 2-hydroxyethyl-2-hydroxytridecylamine, 2-hydroxyethyl-2- Hydroxytetradecylamine, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, di-2-hydroxyethyl-2-hydroxydodecylamine, alkyl (8-18 carbon atoms) benzyldimethylammonium chloride, ethylene Examples thereof include bisalkyl (carbon number 8 to 18) amide, stearyl diethanolamide, lauryl diethanolamide, myristyl diethanolamide, palmityl diethanolamide, and the like. Among these, amine compounds or amide compounds having a hydroxyalkyl group are preferably used. In the present invention, two or more of these compounds may be used in combination.

  From the viewpoint of effectively suppressing the white turbidity of the molded product accompanying fluctuations in temperature and humidity and maintaining the light transmittance of the molded product high, the surfactant is added to 100 parts by mass of the alicyclic hydrocarbon-based polymer. It is preferable to add 0.01-10 mass parts with respect to it. The addition amount of the surfactant is more preferably 0.05 to 5 parts by mass, and still more preferably 0.3 to 3 parts by mass with respect to 100 parts by mass of the alicyclic hydrocarbon-based polymer.

(Plasticizer)
The plasticizer is added as necessary to adjust the melt index of the copolymer.

  Plasticizers include bis (2-ethylhexyl) adipate, bis (2-butoxyethyl) adipate, bis (2-ethylhexyl) azelate, dipropylene glycol dibenzoate, tri-n-butyl citrate, tri-citrate -N-butylacetyl, epoxidized soybean oil, 2-ethylhexyl epoxidized tall oil, chlorinated paraffin, tri-2-ethylhexyl phosphate, tricresyl phosphate, t-butylphenyl phosphate, tri-2-ethylhexyl phosphate Diphenyl, dibutyl phthalate, diisohexyl phthalate, diheptyl phthalate, dinonyl phthalate, diundecyl phthalate, di-2-ethylhexyl phthalate, diisononyl phthalate, diisodecyl phthalate, ditridecyl phthalate, butylbenzyl phthalate, dicyclophthalate Xylyl, di-2-ethylhexyl sebacate, tri-2-ethylhexyl trimellitic acid, Santizer 278, Paraplex G40, Drapex 334F, Plastolein 9720, Mesamoll, DNODP-610, HB-40, etc. are applicable. . The selection of the plasticizer and the addition amount are appropriately performed under the condition that the permeability of the copolymer and the resistance to environmental changes are not impaired.

  As these resins, cycloolefin resins are preferably used, and specifically, ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS manufactured by TOPAS ADVANCED POLYMERS, ARTON manufactured by JSR, and the like are preferable. Take as an example.

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

  The shape of the objective lens will be described below. Referring to FIG. 1, the objective lens OBJ of the present invention has a light source side optical surface S1 and an optical disc side optical surface S2 facing each other in the optical axis direction. The objective lens preferably has a flange portion FL.

As shown in FIG. 1, when the maximum normal angle within the effective diameter of the light source side optical surface S1 of the objective lens OBJ is θ (°), the following equation is satisfied.
66 ≦ θ ≦ 69.5 (1)

Further, when the sag amount with respect to the height h from the optical axis within the effective diameter of the light source side optical surface S1 of the objective lens OBJ (however, the effective diameter is 1) is represented by S (h), 2 When the derivative S ″ (h) of the floor has a maximum value at h = h1, the following equation is satisfied.
0.85 ≦ h1 ≦ 1 (2)

Furthermore, when the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface S2 on the optical disk side of the objective lens OBJ (however, the effective diameter is 1) is expressed as Z (h), 1 The following equation is satisfied when the derivative Z ′ (h) of the floor has a minimum value at h = h2 and a maximum value at h = h3.
0.25 ≦ h2 ≦ 0.4 (3)
0.8 ≦ h3 ≦ 0.9 (4)

  The objective lens may have an optical path difference providing structure. The optical path difference providing structure referred to in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. A diffractive surface is a surface having a diffractive structure. The optical path difference providing structure of the present invention is preferably a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. When the objective lens provided with the optical path difference providing structure is a single aspherical lens, the incident angle of the light flux to the objective lens differs depending on the height from the optical axis. Each will be slightly different. For example, when the objective lens is a single-lens aspherical convex lens, even if it is an optical path difference providing structure that provides the same optical path difference, generally the distance from the optical axis tends to increase.

  In addition, the diffractive structure referred to in this specification is a general term for structures that have a step and have an action of converging or diverging a light beam by diffraction. For example, a plurality of unit shapes are arranged around the optical axis, and a light beam is incident on each unit shape, and the wavefront of the transmitted light is shifted between adjacent annular zones, resulting in new It includes a structure that converges or diverges light by forming a simple wavefront. The diffractive structure preferably has a plurality of steps, and the steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis. In addition, when the objective lens provided with the diffractive structure is a single aspherical lens, the incident angle of the light beam to the objective lens differs depending on the height from the optical axis, so the step amount of the diffractive structure is slightly different for each annular zone. It will be. For example, when the objective lens is a single aspherical convex lens, even if it is a diffractive structure that generates diffracted light of the same diffraction order, generally, the distance from the optical axis tends to increase.

  By the way, it is preferable that the optical path difference providing structure has a plurality of concentric annular zones centered on the optical axis. The optical path difference providing structure can generally have various cross-sectional shapes (cross-sectional shapes on the plane including the optical axis), and the cross-sectional shapes including the optical axis are roughly classified into a blazed structure and a staircase structure.

  As shown in FIGS. 2A and 2B, the blazed structure means that the cross-sectional shape including the optical axis of an optical element having an optical path difference providing structure is a sawtooth shape. In the example of FIG. 2, it is assumed that the upper side is the light source side and the lower side is the optical disk side, and the optical path difference providing structure is formed on a plane as a mother aspherical surface. In the blazed structure, the length in the direction perpendicular to the optical axis of one blaze unit is called a pitch P. (See FIGS. 2A and 2B.) The length of the step in the direction parallel to the optical axis of the blaze is referred to as a step amount B. (See Fig. 2 (a))

  In addition, as shown in FIGS. 2C and 2D, the staircase structure has a small staircase shape in cross section including the optical axis of an optical element having an optical path difference providing structure (referred to as a staircase unit). ). In the present specification, “V level” means a ring-shaped surface (hereinafter also referred to as a terrace surface) corresponding to (or facing) the vertical direction of the optical axis in one step unit of the step structure. In other words, it is divided by V steps and divided into V ring zones. Particularly, a three-level or higher staircase structure has a small step and a large step.

  For example, the optical path difference providing structure illustrated in FIG. 2C is referred to as a five-level step structure, and the optical path difference providing structure illustrated in FIG. 2D is referred to as a two-level step structure (also referred to as a binary structure). . A two-level staircase structure is described below. A plurality of annular zones including a plurality of concentric annular zones around the optical axis, and a plurality of annular zones including the optical axis of the objective lens have a plurality of stepped surfaces Pa and Pb extending in parallel to the optical axis, The light source side terrace surface Pc for connecting the light source side ends of the adjacent step surfaces Pa and Pb and the optical disk side terrace surface Pd for connecting the optical disk side ends of the adjacent step surfaces Pa and Pb are formed. The surface Pc and the optical disc side terrace surface Pd are alternately arranged along the direction intersecting the optical axis.

In the staircase structure, the length in the direction perpendicular to the optical axis of one step unit is referred to as a pitch P.
(See FIGS. 2C and 2D) The length of the step in the direction parallel to the optical axis of the staircase is referred to as step amounts B1 and B2. In the case of a three-level or higher staircase structure, a large step amount B1 and a small step amount B2 exist. (See FIG. 2 (c))

  The optical path difference providing structure is preferably a structure in which a certain unit shape is periodically repeated. As used herein, “unit shape is periodically repeated” naturally includes shapes in which the same shape is repeated in the same cycle. In addition, the unit shape that is one unit of the cycle has regularity, and the shape in which the cycle gradually increases or decreases gradually is also included in the “unit shape is periodically repeated”. Suppose that

  When the optical path difference providing structure has a blazed structure, the sawtooth shape as a unit shape is repeated. As shown in FIG. 2 (a), the same serrated shape may be repeated, or as shown in FIG. 2 (b), the serrated shape gradually increases as it moves away from the optical axis. A shape in which the pitch becomes longer or a shape in which the pitch becomes shorter may be used. In addition, in some areas, the blazed structure has a step opposite to the optical axis (center) side, and in other areas, the blazed structure has a step toward the optical axis (center). It is good also as a shape in which the transition area | region required in order to switch the direction of the level | step difference of a blaze | braze type | mold structure is provided in the meantime. In addition, when it is set as the structure which switches the direction of the level | step difference of a blaze | braze type | mold in this way, it becomes possible to widen an annular zone pitch and it can suppress the transmittance | permeability fall by the manufacturing error of an optical path difference providing structure.

  In the case where the optical path difference providing structure has a staircase structure, there may be a shape such that a 5-level stair unit as shown in FIG. 2C is repeated. Furthermore, it may be a shape in which the pitch of the staircase unit gradually increases as it moves away from the optical axis, or a shape in which the pitch of the staircase unit gradually decreases.

  The optical path difference providing structure is preferably provided on the light source side surface of the objective lens rather than the surface of the objective lens on the optical disc side. In other words, the optical path difference providing structure is preferably provided on the optical surface with the smaller absolute value of the radius of curvature of the 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.

Moreover, it is preferable that an objective lens satisfy | fills the following conditional expression (14).
0.9 ≦ d / f ≦ 1.5 (14)
Here, d represents the thickness (mm) on the optical axis of the objective lens, and f represents the focal length of the objective lens in the first light flux. Note that f is preferably 1.0 mm or more and 1.5 mm or less.

  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 (14), it is possible to suppress astigmatism and surface shift sensitivity.

  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.

  According to the present invention, although it can be used for a thin optical pickup device for BD, by securing the edge thickness, the processing of the mold for molding the objective lens is facilitated and the moldability is improved. It is possible to provide an objective lens that can be used, an optical pickup device including the objective lens, and an optical information recording / reproducing device.

It is an optical axis direction sectional view of objective lens OBJ of the present invention. It is an axial direction sectional view showing an example of an optical path difference grant structure, (a) and (b) show an example of a blaze type structure, and (c) and (d) show an example of a step type structure. It is a figure which shows roughly the structure of optical pick-up apparatus PU1 of this Embodiment which can record and / or reproduce | regenerate information appropriately with respect to BD. When the sag amount with respect to the height h from the optical axis within the effective diameter of the light source side optical surface S1 of the objective lens corresponding to each embodiment is represented by S (h), the second-order derivative S ″ (h ). When the sag amount with respect to the height h from the optical axis within the effective diameter of the optical disk side optical surface S2 of the objective lens corresponding to each embodiment is expressed by Z (h), the first-order derivative Z ′ (h ).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows a case where information is appropriately recorded on a BD that is an optical disc having three information recording layers RL1 to RL3 (referred to as RL1, RL2, and RL3 in ascending order of distance from the light incident surface of the optical disc) in the thickness direction. It is a figure which shows schematically the structure of optical pick-up apparatus PU1 of this Embodiment which can perform recording / reproduction | regeneration. The optical pickup device PU1 is a slim type optical pickup device (the outline is schematically shown by a dotted line). The present invention is not limited to this embodiment, and for example, the information recording surface may be a single layer. FIG. 3 shows a BD-dedicated optical pickup device. However, the objective lens OBJ is used for BD / DVD / CD compatibility, or the objective lens for DVD / CD is separately arranged, so that the BD / DVD is used. / An optical pickup device compatible with CD can be used.

  The optical pickup device PU1 includes a single objective lens OBJ, a triaxial actuator AC2 that moves the objective lens OBJ in the focusing direction and the tracking direction, and tilts in the radial direction and / or tangential direction of the optical disc, and a λ / 4 wavelength plate QWP, rising mirror MR, coupling lens CL having a positive lens L2 having a positive refractive power and a negative lens L3 having a negative refractive power, a uniaxial actuator AC1 for moving only the positive lens L2 in the optical axis direction, polarization A prism PBS, a semiconductor laser LD that emits a laser beam (beam) of 405 nm, a sensor lens SL, and a light receiving element PD that receives reflected beams from the information recording layers RL1 to RL3 of the BD.

  In the present embodiment, the coupling lens CL is disposed between the polarizing prism PBS and the λ / 4 wavelength plate QWP. The semiconductor laser LD is arranged in the order of the negative lens L3 and the positive lens L2. However, the semiconductor laser LD may be arranged in the order of the positive lens L2 and the negative lens L3. The negative lens L3 is movable in the optical axis direction, and the positive lens L2 is fixed to the optical pickup device.

The objective lens OBJ is a single lens, the focal length f at the wavelength λ1 is less than 1.5 (mm), the image-side numerical aperture NA is 0.8 or more, and the light source side optical surface S1 of the objective lens OBJ. When the maximum normal angle within the effective diameter is θ (°), the following expression is satisfied.
66 ≦ θ ≦ 69.5 (1)

Further, when the sag amount with respect to the height h from the optical axis within the effective diameter of the light source side optical surface S1 of the objective lens OBJ (however, the effective diameter is 1) is represented by S (h), 2 When the derivative S ″ (h) of the floor has a maximum value at h = h1, the following equation is satisfied.
0.85 ≦ h1 ≦ 1 (2)

Furthermore, when the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface S2 on the optical disk side of the objective lens OBJ (however, the effective diameter is 1) is expressed as Z (h), 1 The following equation is satisfied when the derivative Z ′ (h) of the floor has a minimum value at h = h2 and a maximum value at h = h3.
0.25 ≦ h2 ≦ 0.4 (3)
0.8 ≦ h3 ≦ 0.95 (4)

  First, a case where recording / reproduction is performed on the first information recording layer RL1 of the BD will be described. In such a case, the positive lens L2 of the coupling lens CL is moved to the position of the solid line by the uniaxial actuator AC1. Here, the divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) is transmitted through the polarizing prism PBS, passes through the negative lens L3 of the coupling lens CL, and the divergence angle is increased. After passing through the lens L2 to be a weakly convergent light beam, it is reflected by the rising mirror MR, converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, and its light beam diameter is regulated by a diaphragm (not shown). It becomes a spot formed on the first information recording layer RL1 by the lens OBJ through the transparent substrate PL1 having the first thickness as shown by a solid line.

  The reflected light beam modulated by the information pits on the first information recording layer RL1 is again transmitted through the objective lens OBJ and the stop, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and the rising mirror MR , And passes through the positive lens L2 and the negative lens L3 of the coupling lens CL to form a convergent light beam. 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. Then, using the output signal of the light receiving element PD, the information recorded in the first information recording layer RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

  Next, a case where recording / reproduction is performed on the second information recording layer RL2 of the BD will be described. In such a case, the positive lens L2 of the coupling lens CL is moved to the position of the alternate long and short dash line by the uniaxial actuator AC1. Here, the divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) is transmitted through the polarizing prism PBS, passes through the negative lens L3 of the coupling lens CL, and the divergence angle is increased. After passing through the lens L2 and made into a substantially parallel light beam, it is reflected by the rising mirror MR, converted from linearly polarized light to circularly polarized light by the λ / 4 wave plate QWP, and the light beam diameter is regulated by a diaphragm (not shown). It becomes a spot formed on the second information recording layer RL2 by the lens OBJ through the transparent substrate PL2 having the second thickness (thicker than the first thickness) as shown by a one-dot chain line.

  The reflected light beam modulated by the information pits on the second information recording layer RL2 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and is raised to the rising mirror MR. , And passes through the positive lens L2 and the negative lens L3 of the coupling lens CL to form a convergent light beam. 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. Then, using the output signal of the light receiving element PD, the information recorded in the second information recording layer RL2 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

  Next, a case where recording / reproduction is performed on the third information recording layer RL3 of the BD will be described. In such a case, the positive lens L2 of the coupling lens CL is moved to the dotted line position by the uniaxial actuator AC1. Here, the divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) is transmitted through the polarizing prism PBS, passes through the negative lens L3 of the coupling lens CL, and the divergence angle is increased. After passing through the lens L2 to be a weak divergent light beam, it is reflected by the rising mirror MR, converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, and its light beam diameter is regulated by a diaphragm (not shown). It becomes a spot formed on the third information recording layer RL3 by the lens OBJ via the transparent substrate PL3 having a third thickness (thicker than the second thickness) as indicated by a dotted line.

  The reflected light beam modulated by the information pits on the third information recording layer RL3 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and is raised to the rising mirror MR. , And passes through the positive lens L2 and the negative lens L3 of the coupling lens CL to form a convergent light beam. 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. Then, using the output signal of the light receiving element PD, the information recorded in the third information recording layer RL3 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

(Example)
Examples that can be used in the above-described embodiment will be described below. In the following (including lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) may be expressed using E (for example, 2.5 × E−3). The optical surface of the objective lens is formed as an aspherical surface that is symmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in Table 1 are substituted into Formula 1.

  Here, X (h) is an axis in the optical axis direction (with the light traveling direction being positive), κ is a conical coefficient, Ai is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial radius of curvature. It is.

  Further, in the case of the embodiment using the diffractive structure, the optical path difference given to the light flux of each wavelength by the diffractive structure is defined by an equation in which the coefficient shown in the table is substituted into the optical path difference function of Formula 2. .

(Equation 2)
Φ (h) = Σ (C _i h ²ⁱ × λ × m / λB)
Here, λ: wavelength used, m: diffraction order, λB: manufacturing wavelength, h: distance in the direction perpendicular to the optical axis from the optical axis.
Further, the pitch P (h) = λB / (Σ (2i × C _i × h ^2i-1 )).

Example 1
The objective lens of Example 1 is a single glass lens. Table 1 shows lens data. In this embodiment, the focal length f = 1.41 mm, the maximum normal angle θ = 67.5 ° of the light source side optical surface, the minimum thickness dmin = 0.61 mm, and the axial thickness d = 1. The wavefront aberration is 0.046λrms when .65 mm, dmin / d = 0.37, and the axial thickness is +0.01 mm.

(Example 2)
The objective lens of Example 2 is a glass single lens. Table 2 shows lens data. In this embodiment, the focal length f = 1.41 mm, the maximum normal angle θ = 67.9 ° of the light source side optical surface, the minimum thickness dmin = 0.60 mm, and the axial thickness d = 1. The wavefront aberration is as good as 0.044 λrms when .65 mm, dmin / d = 0.37, and the axial thickness is +0.01 mm.

(Example 3)
The objective lens of Example 3 is a single glass lens. Table 3 shows lens data. In this embodiment, the focal length f = 1.41 mm, the maximum normal angle θ = 66.7 ° of the light source side optical surface, the minimum thickness dmin = 0.61 mm, and the axial thickness d = 1. The wavefront aberration is 0.032λrms when .65 mm, dmin / d = 0.37, and the axial thickness is +0.01 mm.

Example 4
The objective lens of Example 4 is a glass single lens. Table 4 shows the lens data. In this example, the focal length f = 1.18 mm, the maximum normal angle θ = 67.3 ° of the light source side optical surface, the minimum thickness dmin = 0.50 mm, and the axial thickness d = 1. .37 mm, dmin / d = 0.37, and when the axial thickness is +0.01 mm, the wavefront aberration is as good as 0.045 λrms.

(Example 5)
The objective lens of Example 5 is a plastic single lens with a diffractive structure, and can be used in an optical pickup device capable of recording / reproducing information so as to be compatible with BD, DVD, and CD.
Table 5 shows lens data. The light source side optical surface of the objective lens of Example 5 has a central region, an intermediate region around the central region, and a peripheral region around the intermediate region, and the central region has the first optical path difference providing structure. The intermediate region has a second optical path difference providing structure.

  The first optical path difference providing structure is a structure in which a first basic structure and a second basic structure are overlapped, and the first basic structure is a first light beam (here, a light beam having a wavelength of 405 nm) that has passed through the first basic structure. The first-order diffracted light amount of the second light beam is made larger than any other order diffracted light amount, and the first-order diffracted light amount of the second light beam (here, the light beam having a wavelength of 658 nm) that has passed through the first basic structure is diffracted in any other order. The first order diffracted light amount of the third light beam (here, a light beam having a wavelength of 785 nm) that has passed through the first basic structure is made larger than any other order diffracted light amount. In addition, the second foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the second foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the second foundation structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light flux that has passed through the second basic structure is made larger than any other order of diffracted light quantity.

  On the other hand, the second optical path difference providing structure is a structure in which the third basic structure and the fourth basic structure are overlapped, and the third basic structure is the first light flux (here, having a wavelength of 405 nm) that has passed through the third basic structure. The first order diffracted light amount of the light beam) is made larger than any other order diffracted light amount, and the first order diffracted light amount of the second light beam (here, the light beam having a wavelength of 658 nm) that has passed through the third basic structure is changed to any other order. The first order diffracted light amount of the third light beam (here, the light beam having a wavelength of 785 nm) that has passed through the third basic structure is made larger than any other order diffracted light amount. In addition, the fourth foundation structure makes the second-order diffracted light amount of the first light beam that has passed through the fourth foundation structure larger than any other order of diffracted light amount, and the first-order of the second light beam that has passed through the fourth foundation structure. Is made larger than any other order of the diffracted light quantity, and the first order diffracted light quantity of the third light beam that has passed through the fourth basic structure is made larger than any other order of diffracted light quantity.

  By providing such an optical path difference providing structure, the objective lens of the present embodiment condenses the first light flux passing through the central region so that information can be recorded and / or reproduced on the information recording surface of the BD. Then, the second light beam passing through the central region is condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD, and the third light beam passing through the central region is condensed into the information recording surface of the CD. The light is condensed so that information can be recorded and / or reproduced, and the first light flux passing through the intermediate region is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD. The second light flux passing through the intermediate area is condensed so that information can be recorded and / or reproduced on the information recording surface of the DVD, and the third light flux passing through the intermediate area is focused on the information recording surface of the CD. It is not concentrated so that information can be recorded and / or reproduced. The first light beam passing through the optical disk is condensed so that information can be recorded and / or reproduced on the information recording surface of the BD, and the second light beam passing through the peripheral area is recorded on the information recording surface of the DVD. In addition, the third light flux that passes through the peripheral area is not condensed so that it can be reproduced, and is not condensed so that information can be recorded and / or reproduced on the information recording surface of the CD.

  In this embodiment, the focal length f = 1.41 mm, the maximum normal angle θ = 67.8 ° of the light source side optical surface, the minimum thickness dmin = 0.52 mm, and the axial thickness d = 1. The wavefront aberration is as good as 0.059 λrms when .62 mm, dmin / d = 0.32, and the axial thickness is +0.01 mm.

  Table 6 summarizes the numerical values of the formulas defined in the claims corresponding to the respective embodiments.

  When the sag amount with respect to the height h from the optical axis within the effective diameter of the light source side optical surface S1 of the objective lens corresponding to each embodiment is represented by S (h) in FIG. FIG. 4 is a graph of S ″ (h). As shown in FIG. 4, Example 1 has a maximum value at h1 = 0.95, Example 2 has a maximum value at h1 = 0.96, and Example 3 Has a maximum value at h1 = 0.94, Example 4 has a maximum value at h1 = 0.94, and Example 5 has a maximum value at h1 = 0.92.

  In FIG. 5, when the sag amount with respect to the height h from the optical axis within the effective diameter of the optical disk side optical surface S2 of the objective lens corresponding to each embodiment is represented by Z (h), the derivative of the first floor It is a graph of Z '(h). As shown in FIG. 5, Example 1 has a minimum value at h2 = 0.31, has a maximum value at h3 = 0.90, Example 2 has a minimum value at h2 = 0.31, and h3 = 0.94 has a local maximum, Example 3 has a local minimum at h2 = 0.32, h3 = 0.91 has a local maximum, Example 4 has a local minimum at h2 = 0.31, h3 = 0.90 has a maximum value, Example 5 has a minimum value at h2 = 0.31, and h3 = 0.88 has a maximum value.

  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.

AC1 3-axis actuator AC2 1-axis actuator CL Coupling lens L2 Positive lens L3 Negative lens LD Blue-violet semiconductor laser MR Rising mirror OBJ Objective lens PBS Polarizing prism PD Light receiving element PL1 Transparent substrate PL2 Transparent substrate PL3 Transparent substrate PU1 Optical pickup device QWP λ / 4 wavelength plate RL1 Information recording layer RL2 Information recording layer RL3 Information recording layer S1 Light source side optical surface S2 Optical disc side optical surface SL Sensor lens

Claims (10)

A first light source that emits a first light beam having a wavelength λ1 (nm) and a first light beam emitted from the first light source are condensed on the information recording surface of the first optical disc via a protective substrate having a thickness t1. A condensing optical system including the objective lens, and the condensing optical system condenses the light beam from the first light source on the information recording surface of the first optical disc, thereby recording and / or recording information. Or an objective lens used in an optical pickup device for reproducing,
The objective lens is a single lens, the focal length f at the wavelength λ1 is less than 1.5 (mm), the image-side numerical aperture NA is 0.8 or more,
When the maximum normal angle within the effective diameter of the optical surface on the light source side of the objective lens is θ (°), the following equation is satisfied:
66 ≦ θ ≦ 69.5 (1)
When the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface on the light source side of the objective lens (however, the effective diameter is 1) is represented by S (h), the second floor guide When the function S ″ (h) has a maximum value at h = h1, the following expression is satisfied:
0.85 ≦ h1 ≦ 1 (2)
When the sag amount with respect to the height h from the optical axis within the effective diameter of the optical surface on the optical disk side of the objective lens (however, the effective diameter is 1) is represented by Z (h), the first floor guide An objective lens characterized by satisfying the following expression when the function Z ′ (h) has a minimum value at h = h2 and a maximum value at h = h3.
0.25 ≦ h2 ≦ 0.4 (3)
0.8 ≦ h3 ≦ 0.95 (4)   2. The objective lens according to claim 1, wherein the objective lens is made of a plastic material, and an optical path difference providing structure is formed on the light source side optical surface, and is used for an optical pickup device dedicated to the first optical information recording medium. Objective lens described in 1. The objective lens according to claim 2, wherein the following expression is satisfied.
0.30 ≦ dmin / d ≦ 0.50 (5)
However,
dmin: minimum thickness of the objective lens d: axial thickness of the objective lens The objective lens according to claim 1, wherein the objective lens is made of a glass material and satisfies the following expression.
0.5 ≦ dmin ≦ 0.8 (6)
However,
dmin: minimum thickness of the objective lens The objective lens according to claim 1, wherein the following expression is satisfied.
1.1 ≤ A2 / B2 ≤ 1.6 (7)
However,
A2: Optical surface diameter on the optical disc side of the objective lens
B2: Effective diameter of the objective lens on the optical disk side The objective lens according to claim 5, wherein when the objective lens is made of glass, the following expression is satisfied.
1.15 <A2 / B2 <1.3 (7A) The objective lens according to claim 5, wherein when the objective lens is made of plastic, the following expression is satisfied.
1.2 <A2 / B2 <1.4 (7B) The objective lens according to claim 5, wherein the following expression is satisfied.
1.0 ≤ A1 / B1 ≤ 1.1 (8)
However,
A1: Optical surface diameter on the light source side of the objective lens
B1: Effective diameter of the objective lens on the light source side   An optical pickup device comprising the objective lens according to claim 1.   An optical information recording / reproducing apparatus comprising the optical pickup apparatus according to claim 9.