JP2007035240A - Objective optical system for optical pickup apparatus and optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective optical system for an optical pickup apparatus that can suppress occurrence of a ghost and can secure a working distance while temperature characteristics are improved and to provide the optical pickup apparatus using the same. <P>SOLUTION: The objective optical system for the optical pickup apparatus is constituted of a first lens and a second lens made of plastic. Each lens has a refractive power. Thereby the curvature of each optical surface is relaxed to improve temperature characteristics. Since the refractive power P1 of the first lens and the power P of the whole system of the first and the second lenses satisfy the predetermined condition, the refractive power of the first lens is not made too high and an improvement effect of the temperature characteristics and securing of the working distance can be attained. Since opposite optical surfaces of the first lens are convex surfaces, adverse influence on a detector by reflection light can be suppressed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an objective optical system for an optical pickup device and an optical pickup device, and more particularly to an objective optical system for an optical pickup device using a plurality of plastic lenses and an optical pickup device using the same.

  In recent years, research and development of a high-density optical disk system capable of recording / reproducing information using a blue-violet semiconductor laser having a wavelength of about 400 nm is rapidly progressing. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4, 7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. In the BD, since coma aberration generated due to the tilt (skew) of the optical disk increases, the protective layer is designed to be thinner than in the DVD (0.1 mm with respect to 0.6 mm of the DVD) The amount of coma due to skew is reduced. Hereinafter, in this specification, such an optical disc is referred to as a “high-density optical disc”.

  By the way, a plastic lens can be injection-molded at a low temperature (about 120 ° C.), can ensure a long mold life, and has a low material cost compared to a glass lens. There is an advantage that mass production is possible while maintaining stable accuracy at low cost. Therefore, Patent Document 1 proposes an objective optical system for an optical pickup device composed of a plastic single lens capable of realizing a numerical aperture NA of 0.85.

However, the single lens made of plastic has the advantages as described above, but on the other hand, there is a problem that the spherical aberration generated due to the refractive index change accompanying the temperature change becomes large. This is because the change in spherical aberration that occurs in a plastic single lens with a change in refractive index increases in proportion to the fourth power of the numerical aperture (NA ⁴ ), and in particular, in order to achieve a high numerical aperture, When an optical surface having a large curvature is formed, the refractive index change with temperature change tends to become more prominent. In the following description, the characteristics of the optical element when the temperature changes may be referred to as “temperature characteristics”.

  As a technique for correcting temperature characteristics of a single lens made of plastic, correction of chromatic aberration is achieved by providing a single lens optical surface with a diffraction structure and a plurality of step structures (NPS: non-periodic phase structure) extending in the optical axis direction. Patent Document 2 discloses a technique for correcting temperature characteristics. By providing such a step structure on the optical surface, the temperature characteristics can be improved.

However, in the laser light source used in the optical pickup device, there is a case where the center wavelength instantaneously causes a few nm, so-called mode hopping may occur. There is a problem of increasing so-called wavelength characteristics. Further, when a minute step structure such as NPS is provided on the optical surface of a single lens having a high numerical aperture, there is a problem that light vignetting occurs and the light transmittance is lowered.
JP 2001-324673 A International Publication No. 02/41307 Pamphlet

  On the other hand, there is an attempt to configure the objective optical system from two lenses in order to improve the temperature characteristics. More specifically, by providing each lens with refractive power, the curvature at the optical surface is relaxed to improve the temperature characteristics. However, if any one of the optical surfaces of the two lenses is a flat surface, the light beam from the light source is reflected by the flat surface, and the reflected light may be detected by the photodetector to cause a ghost. On the other hand, if a lens having a flat optical surface is tilted with respect to the optical axis, the occurrence of ghosts can be suppressed, but there is a risk that coma will occur instead.

  Further, when the objective optical system is composed of two lenses, a problem relating to working distance occurs. More specifically, if the refractive power of the lens on the light source side is increased, the temperature characteristic of the objective optical system is improved, but the working distance is shortened, which causes a problem in mounting in the optical pickup device. On the other hand, if the refractive power of the lens on the light source side is reduced, the working distance is ensured, but there is a problem that the effect of improving the temperature characteristics becomes thin.

  The present invention has been made in view of the problems of the prior art, and uses the objective optical system for an optical pickup device that can suppress the occurrence of ghost and can ensure the working distance while improving the temperature characteristics and the same. An object is to provide an optical pickup device.

The objective optical system for an optical pickup device according to claim 1 is an information recording surface of a first optical information recording medium having a protective layer having a thickness t1 using a first light beam having a wavelength λ1 emitted from a first light source. In an objective optical system for an optical pickup device that can be used for an optical pickup device that records and / or reproduces information,
A plastic first lens having a positive refractive power disposed on the light source side, and a plastic second lens having a positive refractive power disposed on the optical information recording medium side than the first lens. And
The optical surfaces of the first lens are both convex surfaces, and satisfy the following expression, where P1 is the refractive power of the first lens and P is the power of the entire objective optical system.
0.04 <P1 / P <0.24 (1)

  This objective optical system is composed of the first lens and the second lens made of plastic, and by giving each lens refractive power, the curvature on the optical surface is relaxed and the temperature characteristics are improved. Furthermore, since both optical surfaces of the first lens are convex surfaces, it is possible to suppress an adverse effect on the detector due to the reflected light. In addition, since the distribution of the refractive power P1 of the first lens and the power P of the entire system composed of the first lens and the second lens is within the range of the expression (1), the refractive power of the first lens is Therefore, the temperature characteristic does not become too large, and therefore both the effect of improving the temperature characteristics and the securing of the working distance can be achieved.

  More specifically, by making P1 / P larger than the lower limit of the above equation (1), spherical aberration can be reduced even when the objective optical system changes in temperature or when the oscillation wavelength of the light source deviates from the reference wavelength. It is possible to satisfactorily suppress, and information can be appropriately recorded and / or reproduced in an optical pickup device using the same. Also, when the refractive power of the first lens is increased with respect to the power of the entire objective optical system, the amount of wavefront aberration that changes when the temperature changes and the wavelength changes can be reduced, while the working distance (working distance) is reduced. As described above, the tendency to decrease is as described above, but the necessary working distance can be ensured by making it smaller than the upper limit of the above equation (1).

  An objective optical system for an optical pickup device according to a second aspect is the optical system according to the first aspect, wherein the optical surface on the light source side of the first lens, the optical surface on the optical information recording medium side of the first lens, and the optical surface Of the optical surfaces on the light source side of the second lens, at least one optical surface has a first phase structure.

  By providing the first phase structure, the temperature characteristics can be further improved by utilizing the function. In particular, since the first lens is a biconvex surface, it is preferable to provide a phase structure on any one of these optical surfaces from the viewpoint of molding transferability and light utilization efficiency such as diffraction efficiency. For example, assuming that the first lens has a meniscus shape, if an optical path difference providing structure is provided on the optical surface, a decrease in diffraction efficiency in a phase structure provided in a deep part of the optical surface, a deterioration in molding transferability, etc. However, if it is provided on either of the two convex surfaces as in the present invention, such a problem can be suppressed.

  Further, in this specification, the “phase structure” is a general term for a structure having a plurality of steps in the optical axis direction and adding an optical path difference (phase difference) to the incident light flux. The optical path difference added to the incident light flux by this step may be an integer multiple of the wavelength of the incident light flux or a non-integer multiple of the wavelength of the incident light flux. Specific examples of such a phase structure include a diffractive structure in which the above steps are arranged at periodic intervals in the direction perpendicular to the optical axis, and the above steps are arranged at non-periodic intervals in the direction perpendicular to the optical axis. This is an optical path difference providing structure (also referred to as a phase difference providing structure).

  Further, in the present specification, the “first phase structure” is a structure composed of a central region including the optical axis and a plurality of annular zones divided with a fine step outside the central region, At a predetermined temperature, an optical path difference that is an integral multiple of the wavelength of the incident light beam is generated between wavefronts that pass through adjacent annular zones, and when the temperature changes from the predetermined temperature, along with a change in refractive index, This refers to a structure having such a characteristic that an optical path difference generated between wavefronts passing through adjacent annular zones deviates from an integral multiple of the wavelength of an incident light beam.

  The objective optical system for an optical pickup device according to a third aspect is the invention according to the second aspect, wherein the first phase structure has a function of suppressing deterioration of wavefront aberration that occurs when the environmental temperature changes. It is characterized by.

  The first phase structure may be an optical path difference providing structure including a diffractive structure, and is a concept including the NPS described above. In general, it is desirable to provide the phase structure on an optical surface with a small curvature from the viewpoint of workability and moldability. However, when the focal length of the first lens is fixed, it is most preferable if the biconvex shape is used. The curvature can be reduced.

  The objective optical system for an optical pickup device according to a fourth aspect is the optical system according to the second aspect, wherein the optical pickup device emits a second light flux having a wavelength λ2 (λ1 <λ2) emitted from a second light source. Information can be recorded and / or reproduced by focusing on the information recording surface of the second optical information recording medium having a protective layer having a thickness of t2 through the objective optical system for the optical pickup device. Therefore, for example, information can be recorded and / or reproduced in a compatible manner with a high-density optical disc and a DVD or CD.

The objective optical system for an optical pickup device according to claim 5 is the optical system according to claim 7, wherein the refractive power of the first lens is P1, and the combined power of the first lens and the second lens is P. Sometimes, the following formula is satisfied.
0.04 <P1 / P <0.15 (2)

  By making P1 / P larger than the lower limit of the above equation (2), spherical aberration can be satisfactorily suppressed even when the objective optical system changes in temperature or when the oscillation wavelength of the light source deviates from the reference wavelength. In the optical pickup device using this, information can be recorded and / or reproduced appropriately. In addition, when the refractive power of the first lens is increased with respect to the power of the entire objective optical system, the amount of wavefront aberration that changes when the temperature changes and the wavelength changes can be reduced, while the working distance tends to decrease. As described above, the necessary working distance can be ensured by considering the second light flux having the wavelength λ2 by making it smaller than the upper limit of the above equation (2).

  The objective optical system for an optical pickup device according to a sixth aspect is the optical system according to the fourth or fifth aspect, wherein when the first light flux having the wavelength λ1 passes, the light amount of the 0th-order diffracted light becomes the highest, An optical surface having a second phase structure in which the amount of the first-order diffracted light is the highest when the second light flux having the wavelength λ2 passes is provided.

  By providing the second phase structure, it is possible to provide a diffraction effect only when the second light flux having the wavelength λ2 passes, thereby the thickness t1 of the protective layer of the first optical information recording medium, Spherical aberration that occurs due to the difference from the thickness t2 of the protective layer of the second optical information recording medium can be corrected.

The objective optical system for an optical pickup device according to claim 7 is the invention according to any one of claims 4 to 6, wherein the first phase structure is centered on an optical axis on an optical surface on which the first phase structure is formed. Divided into a plurality of annular zones, each adjacent annular zone is separated by a step of a predetermined depth d parallel to the optical axis,
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (3)
640 nm <λ2 <680 nm (4)
The depth d satisfies the following conditional expression.
1.7 × λ1 / {n (λ1) −1} ≦ d ≦ 2.3 × λ1 / {n (λ1) −1} (5)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.

  If the step difference of the first phase structure is set such that two adjacent optical zones have an optical path difference corresponding to two wavelengths for the wavelength λ1 in the reference state, the temperature is changed from the design reference temperature, or the wavelength is changed from the reference wavelength. It is possible to reduce the fitting error when the wavefront aberration with respect to the light beam having the wavelength λ1 generated by the change is fitted up to 36 terms of the fringe Zernike polynomial.

The objective optical system for an optical pickup device according to claim 8 is the invention according to any one of claims 4 to 6,
The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (6)
640 nm <λ2 <680 nm (7)
The depth d satisfies the following conditional expression.
4.7 × λ1 / {n (λ1) −1} ≦ d ≦ 5.3 × λ1 / {n (λ1) −1} (8)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.

  When the step difference of the first phase structure is set to give an optical path difference of 5 wavelengths with respect to the wavelength λ1 in the reference state between adjacent annular zones, the wavefront aberration with respect to the light flux having the wavelength λ2 at the design reference temperature and the reference wavelength state Fit error when fitting up to 36 terms of fringe Zernike polynomial can be reduced.

  An objective optical system for an optical pickup device according to a ninth aspect is the invention according to the fourth aspect, wherein the optical pickup device emits a third light flux having a wavelength λ3 (λ2 <λ3) emitted from a third light source. Information can be recorded and / or reproduced by focusing on the information recording surface of the third optical information recording medium having a protective layer having a thickness of t3 through the objective optical system for the optical pickup device. Therefore, information can be recorded and / or reproduced in a compatible manner with, for example, a high-density optical disc, a DVD, and a CD.

The objective optical system for an optical pickup device according to claim 10 is the optical system according to claim 9, wherein the refractive power of the first lens is P1, and the combined power of the first lens and the second lens is P. Sometimes, the following formula is satisfied.
0.04 <P1 / P <0.11 (9)

  By making P1 / P larger than the lower limit of the above equation (9), spherical aberration is reduced even when the objective optical system changes by +30 degrees from the reference temperature or when the oscillation wavelength of the light source changes by +5 nm from the reference wavelength. It is possible to satisfactorily suppress, and information can be appropriately recorded and / or reproduced in an optical pickup device using the same. In addition, when the refractive power of the first lens is increased with respect to the power of the entire objective optical system, the amount of wavefront aberration that changes when the temperature changes and the wavelength changes can be reduced, while the working distance tends to decrease. As described above, the necessary working distance can be ensured by considering the third light flux having the wavelength λ3 by making it smaller than the upper limit of the above equation (9).

The objective optical system for an optical pickup device according to claim 11 is the invention according to claim 9 or 10, wherein the thicknesses t1, t2, and t3 satisfy t1 ≦ t2 <t3,
When the first light beam having the wavelength λ1 passes, the light amount of the 0th-order diffracted light becomes the highest, and when the second light beam having the wavelength λ2 passes, the light amount of the first-order diffracted light becomes the highest, An optical surface having a second phase structure in which the amount of zero-order diffracted light is highest when the third light beam passes;
When the first light beam having the wavelength λ1 passes, the light amount of the 0th-order diffracted light becomes the highest, and when the second light beam having the wavelength λ2 passes, the light amount of the 0th-order diffracted light becomes the highest, And an optical surface having a third phase structure in which the amount of the first-order diffracted light becomes the highest when the third light beam passes.

  By providing the third phase structure in addition to the second phase structure, it is possible to provide a diffraction effect only when the third light flux having the wavelength λ3 passes, thereby protecting the first optical information recording medium. Spherical aberration caused by the difference between the layer thickness t1 and the thickness t3 of the protective layer of the third optical information recording medium can be corrected.

The objective optical system for an optical pickup device according to claim 12 is the invention according to any one of claims 9 to 11,
The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (10)
640 nm <λ2 <680 nm (11)
760 nm <λ3 <805 nm (12)
The depth d satisfies the following conditional expression.
1.7 × λ1 / {n (λ1) −1} ≦ d ≦ 2.3 × λ1 / {n (λ1) −1} (13)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.

  If the step difference of the first phase structure is set such that two adjacent optical zones have an optical path difference corresponding to two wavelengths for the wavelength λ1 in the reference state, the temperature is changed from the design reference temperature, or the wavelength is changed from the reference wavelength. It is possible to reduce the fitting error when the wavefront aberration with respect to the light beam having the wavelength λ1 generated by the change is fitted up to 36 terms of the fringe Zernike polynomial.

The objective optical system for an optical pickup device according to claim 13 is the invention according to any one of claims 9 to 11,
The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (14)
640 nm <λ2 <680 nm (15)
760 nm <λ3 <805 nm (16)
The depth d satisfies the following conditional expression.
9.7 × λ1 / {n (λ1) −1} ≦ d ≦ 10.3 × λ1 / {n (λ1) −1} (17)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.

  When the step difference of the first phase structure is such that an optical path difference corresponding to 10 wavelengths with respect to the wavelength λ1 in the reference state between adjacent annular zones is given, the wavefront aberration with respect to the light flux having the wavelength λ2 in the design reference temperature and the reference wavelength state Fit error when fitting up to 36 terms of fringe Zernike polynomial can be reduced.

  An objective optical system for an optical pickup device according to a fourteenth aspect is the invention according to any one of the first to thirteenth aspects, wherein the single first lens is irradiated with a light beam at a magnification of m1 = 0 and transmitted therethrough. When measuring light, the wavefront aberration is 0.070λ1 rms or less, and the magnification m2 = P1 / P (where P1: refractive power of the first lens, P: the first lens) with respect to the single second lens. And the combined power of the second lens), the wavefront aberration is 0.070λ1 rms or less when the transmitted light is measured.

  By suppressing the aberration in a single state for each of the first lens and the second lens, it is possible to provide the objective optical system having a low spherical aberration regardless of the individual difference of the lenses even in any combination.

The objective optical system for an optical pickup device according to claim 15 is the invention according to any one of claims 1 to 14,
The second lens has a general chemical formula (I);

（式中、R1は、炭素数２〜20の炭化水素基群から選ばれる1種ないし2種以上の二価の基、R2は、水素および炭素数１〜5の炭化水素基からなる群から選ばれる1種ないし2種以上の一価の基、ｘおよびｙは共重合比を示し、x/yが5/95以上、95/5以下となる実数である。）
で表現される環状オレフィン系共重合体にヒンダードアミン系耐光安定剤と耐熱安定剤が添加された材料で構成されることを特徴とするので、耐光性、耐熱安定性に優れた光ピックアップ装置用対物光学系を提供できる。

(In the formula, R1 is one or more divalent groups selected from a hydrocarbon group having 2 to 20 carbon atoms, and R2 is a group consisting of hydrogen and a hydrocarbon group having 1 to 5 carbon atoms. (One or more selected monovalent groups, x and y are copolymerization ratios, and x / y is a real number of 5/95 or more and 95/5 or less.)
It is composed of a material in which a hindered amine light-resistant stabilizer and a heat-resistant stabilizer are added to the cyclic olefin-based copolymer expressed by the objective for an optical pickup device having excellent light resistance and heat-resistant stability. An optical system can be provided.

  In the general chemical formula (I), R1 is preferably one or more divalent groups selected from the group of hydrocarbon groups having 2 to 12 carbon atoms, and more preferably the general chemical formula (II);

（式中、ｐは、0乃至2の整数である。）
で表される二価の基であり、最も好ましくは、前記一般化学式(II)においてｐが0または１である二価の基である。R1の構造は1種のみを用いても、2種以上を併用しても構わない。また、前記化学式（Ｉ）において、R2の例としては水素、メチル基、エチル基、n-プロピル基、I-プロビル基、n-ブチル基、2-メチルプロビル基等が挙げられるが、好ましくは、水素及び／または−ＣＨ3であり、最も好ましくは水素である。

(In the formula, p is an integer of 0 to 2.)
Most preferably, it is a divalent group in which p is 0 or 1 in the general chemical formula (II). The structure of R1 may be used alone or in combination of two or more. In the chemical formula (I), examples of R2 include hydrogen, methyl group, ethyl group, n-propyl group, I-propyl group, n-butyl group, 2-methylpropyl group, etc. Is hydrogen and / or —CH 3, most preferably hydrogen.

  In addition, the type of copolymerization is not limited at all in the present invention, and various known copolymerization types such as random copolymer, block copolymer, alternating copolymerization and the like can be applied, but random copolymer is preferable. .

(Hindered amine light resistance stabilizer)
Specific examples of the hindered amine light-resistant stabilizer (D) include N, N ′, N ″, N ′ ″-tetrakis- (4,6-bis (butyl- (N-methyl-2,2,6, 6-tetramethylpiperidin-4-yl) amino) -triazin-2-yl) -4,7-diazadecane-1,10-amine, dibutylamine and 1,3,5-triazine and N, N′-bis ( 2,2,6,6-tetramethyl-4-piperidyl) butylamine polycondensate, poly [{(1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2, 4-diyl} {(2,2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}], 1,6- Hexanediamine-N, N′-bis (2,2,6,6-tetramethyl (Lu-4-piperidyl) and morpholine-2,4,6-trichloro-1,3,5-triazine, poly [(6-morpholino-s-triazine-2,4-diyl) [( 2,2,6,6-tetramethyl-4-piperidyl) imino] -hexamethylene [(2,2,6,6-tetramethyl-4-piperidyl) imino], etc., and the piperidine ring via the triazine skeleton Multiple-bonded high molecular weight hindered amine light stabilizers; polymer of dimethyl succinate and 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, 1,2,3,4-butanetetracarboxylic Acid, 1,2,2,6,6-pentamethyl-4-piperidinol and 3,9-bis (2-hydroxy-1,1-dimethylethyl) -2,4,8,10-tetraoxaspiro High molecular weight hindered amine light stabilizers in which piperidine rings are bonded via an ester bond, such as a mixed esterified product with [5,5] undecane.

  Among these, preferred hindered amine light stabilizers are poly [{6- (1,1,3,3-tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl} {(2, 2,6,6-tetramethyl-4-piperidyl) imino} hexamethylene {(2,2,6,6-tetramethyl-4-piperidyl) imino}].

  The amount of the hindered amine light resistance stabilizer (D) is usually 0.01 to 1.5 parts by weight, preferably 0.03 to 1.0 parts by weight, more preferably 100 parts by weight of the polymer (A). 0.05 to 0.5 parts by weight.

(Heat stabilizer)
Further, as a heat stabilizer to be blended as an optional component, tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate) methane, β- (3,5-di-t Phenol-type antioxidants such as 2-butyl-4-hydroxyphenyl) propionic acid alkyl ester, 2,2'-oxamide bis [ethyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, stearin Fatty acid metal salts such as zinc acid, calcium stearate, calcium 1,2-hydroxystearate, polyvalent such as glycerin monostearate, glycerin distearate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate Alcohol fatty acid esters and the like, and distearyl pentaerythritol diphor Phyto, phenyl-4,4'-isopropylidenediphenol-pentaerythritol diphosphite, bis (2,6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite, tris (2,4-di Phosphorus stabilizers such as -t-butylphenyl) phosphite may be used. These may be blended alone or in combination. For example, a combination of tetrakis [methylene-3- (3.5-di-t-butyl-4-hydroxyphenyl) propionate) methane, zinc stearate and glycerin monostearate can be exemplified. These stabilizers can be used alone or in combination of two or more.

  The objective optical system for an optical pickup device according to claim 16 is the invention according to any one of claims 1 to 15, wherein at least one of the first lens and the second lens is made of a resin serving as a base material. It is formed of a material in which particles of 30 nanometers or less are dispersed. Such a resin material has a feature that a change in refractive index with respect to a temperature change is smaller than that of a resin for ordinary optical use. Therefore, in order to improve temperature characteristics, a lens design such as providing a lens with a phase structure and a lens. The load on molding can be reduced. In addition, since the effect of improving the temperature characteristics by the first phase structure can be moderated, the deterioration of the wavelength characteristics can be suppressed correspondingly. Alternatively, if the effect of improving the temperature characteristics by the first phase structure is maintained as it is, the power of the first lens can be reduced, so that a long working distance can be ensured.

  An objective optical system for an optical pickup device according to a seventeenth aspect is the invention according to the sixteenth aspect, wherein the fine particles are inorganic particles.

  The objective optical system for an optical pickup device according to an eighteenth aspect is the invention according to the sixteenth aspect, wherein the fine particles are inorganic oxide particles.

The objective optical system for an optical pickup device according to claim 19 is characterized in that, in the invention according to any one of claims 16 to 18, the amount of change in refractive index when the temperature of the at least one lens rises by 1 ° C. When |, the following expression is satisfied.
| A | <8 × 10 ^-5 (18)

  An athermal resin is known as a material in which particles of 30 nanometers or less are dispersed in a resin as a base material. Since the athermal resin has a feature that the refractive index change with respect to the temperature change is small compared to a normal optical resin, the effect of improving the temperature characteristics by the first phase structure can be moderated. , Deterioration of wavelength characteristics can be suppressed. Alternatively, if the effect of improving the temperature characteristics by the first phase structure is maintained as it is, the power of the first lens can be reduced, so that a long working distance can be ensured.

  In general, when powder is mixed with a transparent resin material, light scattering occurs and the transmittance decreases, so that it has been difficult to use as an optical material. It has been found that by using fine particles having a diameter of 30 nm or less, scattering can be virtually prevented. Here, such a resin material is a resin material in which fine particles having a refractive index change rate larger than a refractive index change rate accompanying a temperature change of a resin serving as a base material and having an average particle size of 30 nm or less are dispersed. It is preferable. In addition, when the sign of the refractive index change rate of the resin that is the base material is negative, the refractive index change rate is large, the negative refractive index change rate that is closer to zero than that, and the sign is It includes everything that is a positive refractive index change rate.

The refractive index of the resin material is lowered when the temperature rises, but it is also known that the refractive index change can be reduced by dispersing and mixing inorganic particles. Specifically, the conventionally -1.2 × 10 ^-4 about a a refractive index change A, it is preferable to suppress to less than 8 × 10 ^-5 in an absolute value, more preferably the absolute value 6 × 10 ^- It should be less than ⁵ . More preferably, the absolute value is less than 4 × 10 ⁻⁵ . By using a material in which fine particles of 30 nanometers or less, preferably 20 nanometers or less, more preferably 10 to 15 nanometers are dispersed in the base resin as the material of the lens, the temperature dependence of the refractive index is obtained. It is possible to provide a lens having no temperature dependence or reduced temperature dependency.

For example, niobium oxide (Nb ₂ O ₅ ) fine particles are dispersed in an acrylic resin. The base resin is 80 by volume and niobium oxide is about 20 and these are uniformly mixed. Although the fine particles tend to aggregate, a necessary dispersion state can be generated by a technique such as applying a charge to the particle surface to disperse the particles. Instead of niobium oxide, fine particles of silicon oxide (SiO ₂ ) may be used.

  As will be described later, it is preferable to mix and disperse the base resin and particles in-line during the injection molding of the lens. In other words, after mixing and dispersing, it is preferable that the material is not cooled and solidified until it is molded into a lens.

  The volume ratio can be appropriately increased or decreased in order to control the rate of change of the refractive index with respect to the temperature, and a plurality of types of fine particles can be blended and dispersed.

  In the above example, the ratio is 80:20, that is, 4: 1, but can be appropriately adjusted between 90:10 (9: 1) and 60:40 (3: 2). By increasing the ratio more than 9: 1, the effect of suppressing the temperature change is increased, and conversely, by decreasing the ratio to less than 3: 2, there is no problem in resin moldability, which is preferable.

  The fine particles are preferably inorganic and more preferably oxides. And it is preferable that it is an oxide which the oxidation state is saturated and does not oxidize any more.

  The inorganic substance is preferable because the reaction with the resin serving as a base material, which is a high molecular organic compound, can be suppressed to a low level, and the use of the oxide can prevent deterioration due to use. In particular, oxidation of the resin is easily promoted under severe conditions such as high temperature and irradiation with laser light. However, such inorganic oxide fine particles can prevent deterioration due to oxidation.

  Of course, it is possible to add an antioxidant in order to prevent oxidation of the resin due to other factors.

  Incidentally, as the base resin, resins such as those described in Japanese Patent Application Laid-Open Nos. 2004-144951, 2004-144953, and 2004-144554 can be preferably used as appropriate.

  An optical pickup device according to a twentieth aspect includes the objective optical system for an optical pickup device according to the first to nineteenth aspects.

  In this specification, the objective optical system is a lens having a light condensing function that is arranged to face the optical information recording medium at the position closest to the optical information recording medium in a state where the optical information recording medium is loaded in the optical pickup device. And a lens group that can be operated at least in the optical axis direction by an actuator together with the lens.

  According to the present invention, it is possible to provide an objective optical system for an optical pickup device excellent in temperature characteristics while being low in cost, and an optical pickup device using the same.

  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 device PU1 of the present embodiment that can appropriately record / reproduce information with respect to BD, DVD, and CD, which are different optical information recording media (also referred to as optical disks). It is. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. Here, the first optical information recording medium is BD, the second optical information recording medium is DVD, and the third optical information recording medium is CD, but the first optical information recording medium may be HD.

  The optical pickup device PU1 records / reproduces information to / from the blue-violet semiconductor laser LD1 and DVD that emits a 405 nm blue-violet laser beam (first beam) when recording / reproducing information on the BD. The first emission point EP1 that emits a 658 nm red laser beam (second beam) and the 783 nm infrared laser beam (first beam) that is emitted when information is recorded / reproduced with respect to a CD. The second light emitting point EP2 that emits (three luminous fluxes) is integrally fixed by a laser light source unit LU for DVD / CD formed on one chip, a photodetector PD for BD / DVD / CD, and a lens frame. An objective optical system OU comprising a first lens L1 and a second lens L2 and having a function of condensing a laser beam on the information recording surfaces RL1, RL2, RL3, a biaxial actuator AC1, Sensor lens SEN for adding astigmatism to the reflected light beam from the pulling lens CUL, the first polarizing beam splitter BS1, the second polarizing beam splitter BS2, the λ / 4 wavelength plate QWP, the information recording surfaces RL1, RL2, and RL3. It consists of and. In addition to the blue-violet semiconductor laser LD1 described above, a blue-violet SHG laser can also be used as a light source for BD.

  In the optical pickup device PU1, when recording / reproducing information with respect to the BD, the blue-violet semiconductor laser LD1 is caused to emit light. The divergent light beam emitted from the blue-violet semiconductor laser LD1 is reflected by the first polarization beam splitter BS1, passes through the second polarization beam splitter BS2, and then coupled as depicted by the solid line in FIG. The light beam is converted into a parallel light beam by the lens CUL, passes through the λ / 4 wavelength plate QWP, the light beam diameter is regulated by the stop STO (not shown), and formed on the information recording surface RL1 by the objective optical system OU via the protective layer PL1 of the BD Become a spot. The objective optical system OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL1 is transmitted again through the objective optical system OU and the λ / 4 wave plate QWP, and then becomes a convergent light beam when passing through the coupling lens CUL. After passing through BS2 and the first polarizing beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. And the information recorded on BD can be read using the output signal of photodetector PD.

  Further, when recording / reproducing information with respect to the DVD in the optical pickup device PU1, the first light emitting point EP1 is caused to emit light. The divergent light beam emitted from the first light emitting point EP1 is reflected by the second polarization beam splitter BS2 and converted into a parallel light beam by the coupling lens CUL, as shown by the broken line in FIG. , And passes through the λ / 4 wavelength plate QWP and becomes a spot formed on the information recording surface RL2 by the objective optical system OU via the protective layer PL2 of the DVD. The objective optical system OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL2 again passes through the objective optical system OU and the λ / 4 wavelength plate QWP, and then becomes a convergent light beam when passing through the coupling lens CUL. After passing through BS2 and the first polarizing beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. And the information recorded on DVD can be read using the output signal of photodetector PD.

  Further, when recording / reproducing information with respect to a CD in the optical pickup device PU1, the second light emitting point EP2 is caused to emit light. The divergent light beam emitted from the second light emitting point EP2 is reflected by the second polarization beam splitter BS2 and converted into a parallel light beam by the coupling lens CUL, as depicted in the dashed line in FIG. Thereafter, the spot passes through the λ / 4 wavelength plate QWP and becomes a spot formed on the information recording surface RL3 by the objective optical system OU via the CD protective layer PL3. The objective optical system OU performs focusing and tracking by a biaxial actuator AC1 disposed in the periphery thereof.

  The reflected light beam modulated by the information pits on the information recording surface RL3 is transmitted again through the objective optical system OU and the λ / 4 wave plate QWP, and then becomes a convergent light beam when passing through the coupling lens CUL. After passing through BS2 and the first polarizing beam splitter BS1, astigmatism is added by the sensor lens SEN and converges on the light receiving surface of the photodetector PD. And the information recorded on CD can be read using the output signal of photodetector PD.

  In the first lens L1 of the objective optical system OU, both optical surfaces are convex aspheric surfaces (convex surfaces). In the present embodiment, the first phase structure and the third phase structure are superimposed on the light source side of the first lens L1, and the second phase structure is provided on the optical disk side of the first lens L1. As shown in FIG. 2 schematically showing a cross section of the first lens, “superimposition” means that the first phase structure (a) having a fine step structure and the third phase structure (b) having a fine annular structure Is added to form the structure (c) having both functions. Note that the third phase structure is a diffractive structure for CD compatibility (the intensity of the 0th-order diffracted light is the highest for the light beams of wavelengths λ1 and λ2 and the intensity of the 0th-order diffracted light is the highest for the wavelength λ3). Further, by providing the third phase structure on the light source side of the first lens L1, the working distance of the CD can be made longer than that provided on the other surface.

(Example)
Hereinafter, examples suitable for the present embodiment will be described. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5E-3).

  The optical surfaces of the objective optical system are each formed as an aspherical surface that is axisymmetric about the optical axis and is defined by a mathematical formula in which the coefficients shown in the table are substituted into Equation (1).

  Further, the optical path difference given to the light flux of each wavelength by the diffractive structure (phase structure) is defined by a mathematical formula obtained by substituting the coefficient shown in the table into the optical path difference function of Formula 2.

Example 1
Table 2 shows lens data (including design wavelength, focal length, image plane side numerical aperture, and magnification) of Example 2. A cross section of the objective optical system of Example 2 is shown in FIG. In Example 2, the optical surfaces on both sides are convex aspheric surfaces. In the second embodiment, only the optical path difference given in each annular zone is described, and the step to which this optical path difference is given is given to the optical surface on the light source side of the first lens. In this embodiment, P1 / P is 0.07. In the table, in the column of the first phase structure, i is the zone number, hi-1 is the height from the optical axis in the optical axis vertical direction where the annular zone starts, and hi is the light in the optical axis vertical direction at which the annular zone ends. The height from the axis and the step in the optical axis direction are positive in the direction from the light source to the protective layer.

  The present invention is not limited to the above embodiments and examples. The first phase structure may be provided on any one of an optical surface on the light source side of the first lens, an optical surface on the optical information recording medium side of the first lens, and an optical surface on the light source side of the second lens. Also, an optical pickup device capable of recording and / or reproducing information only on a high-density optical disc, or an optical pickup device capable of recording and / or reproducing information compatible with a high-density optical disc and DVD or CD. The objective optical system of the present invention can be applied.

It is a figure which shows schematically the structure of the optical pick-up apparatus of this Embodiment. It is a figure which shows the superimposition of a phase structure. Although it is sectional drawing of the objective optical system of Example 1, the lens frame which fixes a 1st lens and a 2nd lens is abbreviate | omitted. Although it is sectional drawing of the objective optical system of Example 2, the lens frame which fixes a 1st lens and a 2nd lens is abbreviate | omitted.

Explanation of symbols

AC1 Biaxial actuator BS1 Polarization beam splitter BS2 Polarization beam splitter CUL Coupling lens EP1 Light emission point EP2 Light emission point L1 First lens L2 Second lens LD1 Blue-violet semiconductor laser LU Laser light source unit OU Objective optical system PD Photodetector PU1 Optical pickup Device QWP λ / 4 wave plate SEN Sensor lens STO Aperture

Claims (20)

An optical pickup device that records and / or reproduces information on an information recording surface of a first optical information recording medium having a protective layer having a thickness t1, using a first light flux having a wavelength λ1 emitted from a first light source In the objective optical system for an optical pickup device that can be used for
A plastic first lens having a positive refractive power disposed on the light source side, and a plastic second lens having a positive refractive power disposed on the optical information recording medium side than the first lens. And
The optical surface of the first lens is convex on both sides, and the light satisfies the following formula, where P1 is the refractive power of the first lens and P is the power of the entire objective optical system. Objective optical system for pickup devices.
0.04 <P1 / P <0.24 (1)   At least one optical surface has a first phase structure among an optical surface on the light source side of the first lens, an optical surface on the optical information recording medium side of the first lens, and an optical surface on the light source side of the second lens. The objective optical system for an optical pickup device according to claim 1.   The objective optical system for an optical pickup device according to claim 2, wherein the first phase structure has a function of suppressing deterioration of wavefront aberration that occurs when an environmental temperature changes.   The optical pickup device has a second optical information recording having a protective layer having a thickness of t2 through the objective optical system for the optical pickup device for the second light flux having the wavelength λ2 (λ1 <λ2) emitted from the second light source. The objective optical system for an optical pickup device according to any one of claims 1 to 3, wherein information can be recorded and / or reproduced by focusing on an information recording surface of the medium. 5. The objective optical system for an optical pickup device according to claim 4, wherein when the refractive power of the first lens is P1, and the combined power of the first lens and the second lens is P, the following expression is satisfied. system.
0.04 <P1 / P <0.15 (2)   A second phase structure in which the light amount of the 0th-order diffracted light becomes the highest when the first light beam having the wavelength λ1 passes and the light amount of the first-order diffracted light becomes the highest when the second light beam having the wavelength λ2 passes. 6. The objective optical system for an optical pickup device according to claim 4, further comprising an optical surface having the optical surface. The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (3)
640 nm <λ2 <680 nm (4)
The objective optical system for an optical pickup device according to any one of claims 4 to 6, wherein the depth d satisfies the following conditional expression.
1.7 × λ1 / {n (λ1) −1} ≦ d ≦ 2.3 × λ1 / {n (λ1) −1} (5)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure. The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (6)
640 nm <λ2 <680 nm (7)
The objective optical system for an optical pickup device according to any one of claims 4 to 6, wherein the depth d satisfies the following conditional expression.
4.7 × λ1 / {n (λ1) −1} ≦ d ≦ 5.3 × λ1 / {n (λ1) −1} (8)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.   The optical pickup device has a third optical information recording having a protective layer having a thickness of t3 through which a third light beam having a wavelength λ3 (λ2 <λ3) emitted from a third light source is passed through the objective optical system for the optical pickup device. 5. The objective optical system for an optical pickup device according to claim 4, wherein information can be recorded and / or reproduced by condensing light onto the information recording surface of the medium. 10. The objective optical system for an optical pickup device according to claim 9, wherein when the refractive power of the first lens is P1 and the combined power of the first lens and the second lens is P, the following expression is satisfied: system.
0.04 <P1 / P <0.11 (9) The thicknesses t1, t2, and t3 satisfy t1 ≦ t2 <t3,
When the first light beam having the wavelength λ1 passes, the light amount of the 0th-order diffracted light becomes the highest, and when the second light beam having the wavelength λ2 passes, the light amount of the first-order diffracted light becomes the highest, An optical surface having a second phase structure in which the amount of zero-order diffracted light is highest when the third light beam passes;
When the first light beam having the wavelength λ1 passes, the light amount of the 0th-order diffracted light becomes the highest, and when the second light beam having the wavelength λ2 passes, the light amount of the 0th-order diffracted light becomes the highest, 11. The objective optical for an optical pickup device according to claim 9, further comprising: an optical surface having a third phase structure in which the amount of the first-order diffracted light is highest when the third light beam passes. system. The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (10)
640 nm <λ2 <680 nm (11)
760 nm <λ3 <805 nm (12)
The objective optical system for an optical pickup device according to claim 9, wherein the depth d satisfies the following conditional expression.
1.7 × λ1 / {n (λ1) −1} ≦ d ≦ 2.3 × λ1 / {n (λ1) −1} (13)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure. The first phase structure is divided into a plurality of annular zones centering on the optical axis on the optical surface on which the first phase structure is formed, and each adjacent annular zone is separated by a step having a predetermined depth d parallel to the optical axis. And
When the wavelengths λ1 and λ2 satisfy the following conditions:
390 nm <λ1 <420 nm (14)
640 nm <λ2 <680 nm (15)
760 nm <λ3 <805 nm (16)
The objective optical system for an optical pickup device according to claim 9, wherein the depth d satisfies the following conditional expression.
9.7 × λ1 / {n (λ1) −1} ≦ d ≦ 10.3 × λ1 / {n (λ1) −1} (17)
Here, n (λ1) is the refractive index at the wavelength λ1 of the material constituting the first phase structure.   When the single first lens is irradiated with a light beam at a magnification m1 = 0 and the transmitted light is measured, the wavefront aberration is 0.070λ1 rms or less, and the single lens 2 has a magnification m2 = When the light beam is irradiated with P1 / P (where P1: refractive power of the first lens, P: combined power of the first lens and the second lens) and the transmitted light is measured, the wavefront aberration is 0. The objective optical system for an optical pickup device according to claim 1, wherein the objective optical system is 070λ1 rms or less. The second lens has a general chemical formula (I);

(In the formula, R1 is one or more divalent groups selected from a hydrocarbon group having 2 to 20 carbon atoms, and R2 is a group consisting of hydrogen and a hydrocarbon group having 1 to 5 carbon atoms. (One or more selected monovalent groups, x and y are copolymerization ratios, and x / y is a real number of 5/95 or more and 95/5 or less.)
The objective for an optical pickup device according to any one of claims 1 to 14, comprising a material obtained by adding a hindered amine light-resistant stabilizer and a heat-resistant stabilizer to a cyclic olefin copolymer represented by Optical system.   15. At least one of the first lens and the second lens is formed of a material in which particles of 30 nanometers or less are dispersed in a resin as a base material. Objective optical system for optical pickup device as described in 1.   The objective optical system for an optical pickup device according to claim 16, wherein the fine particles are inorganic particles.   The objective optical system for an optical pickup device according to claim 16, wherein the fine particles are inorganic oxide particles. 19. The optical pickup device according to claim 16, wherein the following expression is satisfied, where | A | is a refractive index change amount when the temperature of the at least one lens is increased by 1 ° C. Objective optical system.
| A | <8 × 10 ^-5 (18) An optical pickup device comprising the objective optical system for an optical pickup device according to claim 1.

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