JP2006040352A - Optical element and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress deformation of an optical element made of resin caused by absorption of light energy without increasing a manufacturing cost. <P>SOLUTION: An optical pickup device PU performs recording and/or reproducing of information using a luminous flux emitted from semiconductor laser oscillators LD1, LD2, LD3. A beam shaper BE, collimate lenses COL1, COL2, or sensor lenses SEN1, SEN2 provided on an optical path of this optical pickup device PU include at least base material resin including C-F coupling in a unit molecule. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical element and an optical pickup device including the optical element.

  In recent years, development of a high-density optical disc having a size comparable to that of a DVD (digital versatile disc) and a capacity larger than that of a DVD has been advanced. A high-density optical disk is a generic term for optical disks that use a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information.

  As such a high-density optical disc, information is recorded / reproduced by an objective optical system having a numerical aperture NA of 0.85, and a protective optical disc having a thickness of about 0.1 mm (Blu-Ray Disk: hereinafter referred to as BD). In addition, there is a standard optical disc (HD DVD: hereinafter referred to as HD) in which information is recorded / reproduced by an objective optical system having a numerical aperture NA of 0.65 and the protective layer has a thickness of about 0.6 mm. Has been developed. Moreover, as a high density optical disc, in addition to the optical disc having the protective layer as described above on its information recording surface, an optical disc having a protective film with a thickness of about several to several tens of nm on the information recording surface, or protection An optical disk having a layer or a protective film with a thickness of 0 is also included. Further, as a high-density optical disk, a magneto-optical disk using a blue-violet semiconductor laser or a blue-violet SHG laser as a light source for recording / reproducing information can be cited.

In such an optical pickup device for recording / reproducing with respect to a high-density optical disc, a blue to blue-violet laser beam having a wavelength (about 380 to 450 nm) shorter than the wavelength of the DVD laser beam (about 650 nm) is used. This makes it possible to reduce the diameter of the focused spot and to record / reproduce high density signals.
In recent optical pickup devices, a resin optical element is preferably used rather than glass from the viewpoint of moldability and manufacturing cost. Further, by using a resin optical element, the apparatus can be reduced in cost and weight.

By the way, the short-wavelength laser light as described above has very large light energy. For this reason, it is preferable that the optical element disposed on the optical path of the laser beam is molded from a resin having excellent light resistance so as not to be deformed by absorption of light energy.
As resins having relatively excellent light resistance, resins having an alicyclic structure such as norbornene-based hydrogenated polymers, norbornene / α-olefin copolymers, and styrene / butadiene block copolymers have been developed. Light resistance is still insufficient as a raw material for optical elements used in an optical pickup device for blue laser light.
In addition, there is a technique for obtaining a resin having high light resistance by providing a C—F bond in a unit molecule (see, for example, Patent Document 1).
Japanese Patent Publication No. 6-5321

However, a resin having a C—F bond in a unit molecule has a lower refractive index than a resin conventionally used for an optical element. For this reason, for example, when applied to an optical element having a relatively short focal length such as a single objective lens that collects light, it is necessary to reduce the radius of curvature of the optical surface, which makes it difficult to manufacture a mold. Further, as shown in FIG. 11, the radius of curvature of the optical surface is reduced while keeping the entire thickness W ₁ of the optical element constant, so that the distance between the optical surface on the light source side and the optical surface on the optical information recording medium side is reduced. W ₂ , that is, the injection flow path width of the resin material when the optical element is injection-molded cannot be secured. Therefore, since injection molding, which is an inexpensive manufacturing method, cannot be used for manufacturing an optical element, the manufacturing cost of the optical element increases.

  An object of the present invention is to provide a resin-made optical element that can improve light resistance without increasing the manufacturing cost, and an optical pickup device including the optical element.

In order to solve the above problems, the invention described in claim 1
In an optical element provided on an optical path of an optical pickup device that records and / or reproduces information using a light beam emitted from a light source,
Containing at least a base resin containing a C—F bond in a unit molecule;
It functions as a beam shaper, collimating lens, coupling lens, or sensor lens.

Here, the beam shaper is for converting the intensity distribution of a light beam into a circular shape in a plane perpendicular to the optical axis, and the collimating lens is for converting divergent light into parallel light. The coupling lens converts the divergence angle of the light beam, and the sensor lens condenses the reflected light from the optical information recording medium on the light receiving element. These beam shapers, collimating lenses, coupling lenses, and sensor lenses, for example, as shown in Table 1 below, have a larger absolute value of the radius of curvature than a single objective lens that collects light.

  According to the first aspect of the present invention, since the unit molecule of the base resin contains a C—F bond, it is less likely to absorb light energy than when no C—F bond is contained. Even if it absorbs, radical reaction is suppressed, so that deformation, discoloration, and alteration are suppressed, that is, light resistance is improved. In addition, since it functions as a beam shaper, collimating lens, coupling lens, and sensor lens, it does not need to reduce the radius of curvature of the optical surface compared to the case of functioning as a single objective lens that collects light. Manufacturing becomes easy. Therefore, light resistance can be improved without increasing the manufacturing cost. In other words, even a material having a low refractive index can obtain a sufficient function as an optical element. In addition, since an optical element having excellent heat resistance and light resistance can be obtained, the life of the optical pickup device can be extended. In particular, these effects are more effective when the optical element functions as a beam shaper that is disposed in the vicinity of the light source and is exposed to light of high heat or high energy.

  In addition, since the intermolecular force of the base resin increases due to the polarity of the fluorine atoms in the C—F bond, the glass transition point Tg is higher than that of the resin not containing fluorine atoms, and the heat resistance is improved. To do. Therefore, deformation of the optical element due to temperature fluctuation can be suppressed.

  Furthermore, since the Abbe number of the base material resin including the C—F bond is about 90, which is larger than the Abbe number of 50 to 60 of the conventional resin, the wavelength of the incident light beam is instantaneously generated by the mode hopping of the semiconductor laser. The amount of axial chromatic aberration generated can be suppressed even when the change occurs. Here, the Abbe number is a refractive index with respect to the He d-line (wavelength 587.6), and indicates a change in refractive index when the wavelength varies.

The invention according to claim 2 is an optical element provided on an optical path of an optical pickup device that records and / or reproduces information using a light beam emitted from a light source.
Containing at least a base resin containing a C—F bond in a unit molecule;
It functions as a lens other than the lens located closest to the optical information recording medium among the plurality of lenses constituting the objective lens unit.

Here, the objective lens unit functions as an objective lens by the whole of a plurality of combined lenses. Among a plurality of lenses constituting such an objective lens unit, lenses other than the lens closest to the optical information recording medium have an absolute value of the radius of curvature as compared with a single objective lens that collects light. It is getting bigger.
The optical information recording medium is a recording medium capable of recording and reproducing information by light, and specifically, a BD, HD DVD, DVD, CD, and the like.

  According to the invention described in claim 2, since the unit molecule of the base material resin contains a C—F bond, it is less likely to absorb light energy than when no C—F bond is contained. Even if it absorbs, radical reaction is suppressed, so that deformation, discoloration, and alteration are suppressed, that is, light resistance is improved. In addition, since the lens functions as a lens other than the lens located closest to the optical information recording medium among the plurality of lenses constituting the objective lens unit, it is compared with a case where it functions as a single objective lens that collects light. Thus, the manufacturing is facilitated because it is not necessary to reduce the curvature radius of the optical surface. Therefore, light resistance can be improved without increasing the manufacturing cost. In other words, even a material having a low refractive index can obtain a sufficient function as an optical element. In addition, since an optical element having excellent heat resistance and light resistance can be obtained, the life of the optical pickup device can be extended.

  In addition, since the intermolecular force of the base resin increases due to the polarity of the fluorine atoms in the C—F bond, the glass transition point Tg is higher than that of the resin not containing fluorine atoms, and the heat resistance is improved. To do. Therefore, deformation of the optical element due to temperature fluctuation can be suppressed.

  Furthermore, since the Abbe number of the base material resin including the C—F bond is about 90, which is larger than the Abbe number of 50 to 60 of the conventional resin, the wavelength of the incident light beam is instantaneously generated by the mode hopping of the semiconductor laser. The amount of axial chromatic aberration generated can be suppressed even when the change occurs.

The invention described in claim 3 is the optical element according to claim 2,
The numerical aperture on the image plane side of the objective lens unit is 0.73 to 0.87.

  Here, the “numerical aperture on the image plane side” refers to the numerical aperture (beam diameter conversion NA) converted from the spot diameter of the focused spot formed on the information recording surface of the optical information recording medium.

  According to the third aspect of the invention, even if the numerical aperture on the image plane side of the objective lens unit is 0.73 to 0.87, the same effect as that of the second aspect of the invention can be obtained.

Invention of Claim 4 is an optical element as described in any one of Claims 1-3,
The base material resin includes a C—F bond in a main chain portion.

  According to invention of Claim 4, the effect similar to the invention as described in any one of Claims 1-3 can be acquired.

Invention of Claim 5 is an optical element as described in any one of Claims 1-3,
The base material resin includes a 2n + 1 member ring (n is an integer of 1 or more) in a unit molecule,
The annular portion includes a C—F bond.

According to the fifth aspect of the present invention, since the annular portion of the base resin is a 2n + 1 member ring, that is, an odd member ring, the polarity of the base resin is higher than that in the case where the annular portion is an even member ring. . Accordingly, the intermolecular force of the base resin increases, and as a result, the glass transition point Tg increases and the heat resistance improves. Therefore, deformation of the optical element due to temperature fluctuation can be more reliably suppressed.
The structure of the annular portion is preferably asymmetric. In this case, the heat resistance of the optical element is further improved.

The invention according to claim 6 is the optical element according to any one of claims 1 to 5,
It contains fine particles having a temperature dependency dn / dt of refractive index opposite to that of the base resin.

According to the sixth aspect of the invention, since the temperature dependence dn / dt of the refractive index contains fine particles having an opposite sign to that of the matrix resin, the resin material is accompanied by a change in temperature while maintaining the moldability of the resin material. The amount of change in refractive index can be reduced. Therefore, a change in spherical aberration due to a change in refractive index can be suppressed.
In this specification, the refractive index changes with temperature changes while maintaining the moldability of the resin material by mixing fine particles in such an optical material, that is, a resin (for example, a plastic material). An optical material with a reduced amount is called “athermal resin”.

The invention according to claim 7 is the optical element according to claim 6,
The fine particles are inorganic fine particles.

  According to the seventh aspect of the invention, since the fine particles are inorganic fine particles, the reactivity with the base material resin which is a high molecular organic compound is low. Accordingly, the reaction between the base resin and the fine particles can be prevented in the optical element, so that the light resistance and the refractive index can be prevented from deteriorating.

The invention according to claim 8 is the optical element according to claim 6 or 7, wherein
The fine particles have an average particle size in the range of 1 to 100 nm.

  According to the eighth aspect of the invention, the same effect as that of the sixth or seventh aspect of the invention can be obtained.

The invention according to claim 9 is the optical element according to claim 8,
The fine particles have an average particle size in the range of 1 to 30 nm.

  According to the ninth aspect of the invention, the same effect as that of the eighth aspect of the invention can be obtained.

The invention according to claim 10 is the optical element according to any one of claims 1 to 9,
In the optical pickup device, the optical pickup device is disposed on an optical path of a light beam having a wavelength of 200 to 420 nm.

  According to the invention described in claim 10, even when the optical element is disposed on the optical path of the light beam having a wavelength of 200 to 420 nm, the same as the invention described in any one of claims 1 to 9 An effect can be obtained.

Invention of Claim 11 is an optical element as described in any one of Claims 1-10,
In the optical pickup device, the optical pickup device is disposed on an optical path of a light beam having a plurality of wavelengths.

  According to the eleventh aspect of the present invention, it is possible to obtain the same effect as that of the first aspect of the present invention.

Invention of Claim 12 is an optical element as described in any one of Claims 1-11,
At least one optical surface is provided with a fine structure.

  According to the twelfth aspect of the present invention, since the fine structure is provided on at least one optical surface, for example, when the phase structure is provided as the fine structure, the semiconductor laser is changed along with the temperature change. Suppresses spherical aberration when the wavelength changes, suppresses spherical aberration when using a semiconductor laser whose oscillation wavelength deviates from the reference wavelength due to manufacturing error, or wavelength of the incident light beam by mode hopping of the semiconductor laser It is possible to suppress changes in recording / reproducing characteristics when the value changes instantaneously. In addition, when an optical element is disposed on the optical path of a light beam having a plurality of wavelengths and information is recorded / reproduced using a plurality of types of optical information recording media, chromatic aberration due to the wavelength difference of the used wavelengths can be corrected. In addition, the spherical aberration due to the difference in the thickness of the protective layer of the optical information recording medium can be corrected.

In addition, for example, when a fine structure of a wavelength order called a sub-wavelength diffraction grating is provided as a fine structure, the material surface may have optical anisotropy or refractive index distribution by an arbitrary cross-sectional shape. It becomes possible. Therefore, using this fine structure, the optical element can function as a polarizing element, a λ / 4 wavelength plate, or an antireflection element.
In addition, for example, when an antireflection structure is provided as a fine structure, it is possible to save the trouble of forming a normal antireflection film, so that the manufacturing cost can be reduced.

Note that the chromatic aberration here refers to a fluctuation in the minimum position of wavefront aberration in the optical axis direction caused by a wavelength difference.
The phase structure may be a diffractive structure or an optical path difference providing structure.

The invention according to claim 13 is the optical element according to claim 12,
The phase structure is a diffractive structure.

  According to the thirteenth aspect, the same effect as that of the twelfth aspect can be obtained.

The invention according to claim 14 is the optical pickup device, wherein
An optical element according to any one of claims 1 to 13,
And a light source for emitting a light beam to pass through the optical element.

  According to the invention of claim 14, the same effect as that of any one of claims 1 to 13 can be obtained.

  According to the present invention, it is possible to improve light resistance without increasing the manufacturing cost.

FIG. 1 is a cross-sectional view showing a schematic configuration of the optical pickup device PU.
As shown in this figure, the optical pickup device PU has three types of semiconductor laser oscillators LD1, LD2, and LD3 as light sources.

  The semiconductor laser oscillator LD1 emits a light beam having a specific wavelength (for example, 405 nm, 407 nm) in a wavelength range of 350 to 450 nm when information is recorded / reproduced using a BD (Blu-ray disc) 10 as a recording medium. In the present embodiment, the thickness of the protective layer of the BD 10 is 0.1 mm.

  The semiconductor laser oscillator LD2 emits a light beam having a specific wavelength (for example, 655 nm) in a wavelength of 620 to 680 nm when information is recorded / reproduced using the DVD 20 as a recording medium, and is integrated with the semiconductor laser oscillator LD3. Thus, the light source unit LU is formed. In the present embodiment, the thickness of the protective layer of the DVD 20 is 0.6 mm. In this specification, DVD is a generic term for DVD-series optical information recording media such as DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, and DVD + RW. It is.

  The semiconductor laser oscillator LD3 emits a light beam having a specific wavelength (for example, 785 nm) in 750 to 810 nm when information is recorded / reproduced using the CD 30 as a recording medium. In the present embodiment, the thickness of the protective layer of CD 30 is 1.2 mm. In this specification, the CD is a general term for CD-series optical information recording media such as CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like.

  In the direction of the optical axis of the light beam emitted from the semiconductor laser oscillator LD1, the beam shaper BE1, the beam splitter BS1, the collimator lens COL1, the beam splitter BS2, the quarter-wave plate RE, the stop, from the lower side to the upper side in FIG. STO and objective lens OBJ are arranged in order. The objective lens OBJ is provided with a two-dimensional actuator AC1 that moves the objective lens OBJ in the vertical direction in FIG. A BD 10, DVD 20 or CD 30 as an optical information recording medium is arranged at a position facing the objective lens OBJ.

  In addition, a sensor lens SEN1 and a photodetector PD1 are sequentially arranged on the right side in FIG. 1 with respect to the beam splitter BS1. The sensor lens SEN1 includes a cylindrical lens L11 and a concave lens L12.

  Further, in the optical axis direction of the light beams emitted from the semiconductor laser oscillators LD2 and LD3, a beam splitter BS3, a collimating lens COL2, and a beam splitter BS2 are arranged in order from the right side to the left side in FIG. A sensor lens SEN2 and a photodetector PD2 are arranged in order on the upper side of the beam splitter BS3 in FIG. The sensor lens SEN2 includes a cylindrical lens L21 and a concave lens L22.

  Next, the operation and action of the optical pickup device PU will be briefly described. At the time of recording information on the BD 10 or reproducing information on the BD 10, the semiconductor laser oscillator LD1 emits a light beam. As indicated by the solid line in FIG. 1, this light beam is first shaped by passing through the beam shaper BE1, and after passing through the beam splitter BS1, is converted into parallel light by the collimator lens COL1. Next, this light beam passes through the beam splitter BS2 and the quarter-wave plate RE, is narrowed by the diaphragm member STO, and then condensed by the objective lens OBJ to form a focused spot on the information recording surface 10a of the BD10. Form. At this time, the objective lens OBJ performs focusing and tracking by the two-dimensional actuator AC1 disposed around the objective lens OBJ.

  Next, the light that forms the condensed spot is modulated by the information pits on the information recording surface 10a of the BD 10 and reflected. Next, the reflected light passes through the objective lens OBJ, the quarter-wave plate RE, the beam splitter BS2, and the collimator lens COL1 and is reflected by the beam splitter BS1, and then given astigmatism by the sensor lens SEN1. It reaches the photodetector PD1. The information in the BD 10 is reproduced by using the output signal of the photodetector PD1.

  When recording information on the DVD 20 or reproducing information on the DVD 20, the semiconductor laser oscillator LD2 emits light. As indicated by the dotted line in FIG. 1, this light beam is first transmitted through the beam splitter BS3 and then converted into parallel light by the collimator lens COL2. Next, the light beam is reflected by the beam splitter BS2, passes through the quarter-wave plate RE, is narrowed by the diaphragm member STO, and then condensed by the objective lens OBJ and is applied to the information recording surface 20a of the DVD 20. A focused spot is formed. At this time, the objective lens OBJ performs focusing and tracking by the two-dimensional actuator AC1 disposed around the objective lens OBJ.

  Next, the light that forms the focused spot is modulated by the information pits on the information recording surface 20a of the DVD 20 and reflected. Next, this reflected light is transmitted through the objective lens OBJ and the quarter-wave plate RE, reflected by the beam splitters BS2 and BS3, respectively, and then given astigmatism by the sensor lens SEN2, so that the photodetector PD2 To reach. Then, information in the DVD 20 is reproduced by using the output signal of the photodetector PD2.

  The semiconductor laser oscillator LD3 emits light when information is recorded on the CD 30 or when information on the CD 30 is reproduced. As indicated by a two-dot chain line in FIG. 1, this light beam is first transmitted through the beam splitter BS3 and then converted into parallel light by the collimator lens COL2. Next, this light beam is reflected by the beam splitter BS2, passes through the quarter-wave plate RE, is narrowed by the diaphragm member STO, and then condensed by the objective lens OBJ and is applied to the information recording surface 30a of the CD 30. A focused spot is formed. At this time, the objective lens OBJ performs focusing and tracking by the two-dimensional actuator AC1 disposed around the objective lens OBJ.

  Next, the light that forms the focused spot is modulated by the information pits on the information recording surface 20a of the CD 30 and reflected. Next, this reflected light is transmitted through the objective lens OBJ and the quarter-wave plate RE, reflected by the beam splitters BS2 and BS3, respectively, and then given astigmatism by the sensor lens SEN2, so that the photodetector PD2 To reach. Then, the information in the CD 30 is reproduced by using the output signal of the photodetector PD2.

Next, the configuration of the objective lens OBJ will be described in detail.
The objective lens OBJ has a function of condensing the light beams emitted from the respective semiconductor laser oscillators LD1, LD2, and LD3 on the information recording surfaces 10a, 20a, and 30a of the BD10, DVD20, or CD30. The overall numerical aperture NA of the objective lens OBJ is 0.85 for the light beam emitted from the semiconductor laser oscillators LD1 and LD2, and 0.45 to 0.51 for the light beam emitted from the semiconductor laser oscillator LD3. It has become. The objective lens OBJ is a lens unit having a plurality of lenses. In the present embodiment, as shown in FIG. 2, the objective lens OBJ is composed of two lenses, a light source side lens OBJ1 and a disk side lens OBJ2. The optical surfaces of the light source side lens OBJ1 and the disk side lens OBJ2 are aspherical surfaces.

  Of these light source side lens OBJ1 and disk side lens OBJ2, the lens other than the disk side lens OBJ2 located closest to the optical information recording medium, that is, the light source side lens OBJ1 is an optical element according to the present invention.

  Specifically, of the two optical surfaces of the light source side lens OBJ1, at least the optical surface on the light source side is divided into a first area AREA1 and a second area AREA2, as shown in FIG. The first area AREA1 is an area through which the light beams emitted from the semiconductor laser oscillators LD1, LD2, and LD3 are transmitted, and the second area AREA2 is an area through which the light beams emitted from the semiconductor laser oscillators LD1, LD2 are transmitted. The second area ALER2 may be further divided into an area where the two light beams of the semiconductor laser oscillators LD1 and LD2 are transmitted and an area where only the light beam emitted from the semiconductor laser oscillator LD2 is transmitted. In the first area AREA1, as shown in FIG. 4A or 4B, a diffractive structure as a phase structure is formed.

  This diffractive structure condenses the light beams from the semiconductor laser oscillators LD1, LD2, and LD3 on the information recording surfaces 10a, 20a, and 30a of the corresponding optical information recording media by generating an optical path difference. As the shape of such a diffraction structure, a conventionally known shape can be used. The diffractive structure in the present embodiment is composed of a plurality of annular zones 100 centered on the optical axis, and the cross-sectional shape including the optical axis is a sawtooth shape.

Note that the diffractive structure may have other shapes, for example, as shown in FIGS. Here, the diffractive structure of FIG. 5 is composed of a plurality of annular zones 102 in which the direction of the step 101 is the same within the effective diameter, and the cross-sectional shape including the optical axis is a staircase shape. Further, the diffractive structure in FIG. 6 is composed of a plurality of annular zones 103 in which a staircase structure is formed.
Here, FIGS. 4 to 6 schematically show the case where each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface.

  The light source side lens OBJ1 is formed by injection molding a so-called athermal resin. This athermal resin contains a base material resin and fine particles. Hereinafter, these will be described.

  The light source side lens OBJ1 can be formed by injection molding a mixed material of a base material resin and fine particles. Hereinafter, these will be described.

(Base material resin)
The base material resin is a thermoplastic resin and contains a C—F bond in a unit molecule. Therefore, the light source side lens OBJ1 hardly absorbs light energy, and even if it absorbs light energy, radical reaction can be suppressed. Further, since the intermolecular force of the base material resin is increased due to the polarity of fluorine atoms in the C—F bond, the glass transition point Tg is higher than that of a resin not containing fluorine atoms. Furthermore, since the Abbe number of the base material resin including the C—F bond is about 90, which is larger than the Abbe numbers of 50 to 60 which are the conventional resins, the Abbe number of the entire light source side lens OBJ1 becomes high.
However, this base material resin has a feature that its refractive index is lower than that of resins conventionally used for optical elements.

  As such a base resin, for example, “Cytop” (registered trademark) manufactured by Asahi Glass Co., Ltd. represented by the following chemical formulas 1 and 2 and “Teflon AF” (registered trademark) manufactured by DuPont are used. Can do.

  Moreover, as a base material resin, what is shown to the following Chemical formulas 3-22 can also be used. However, other resins may be used as long as they contain a C—F bond in the unit molecule. In addition, the base material resin of Chemical formulas 6-22 can be manufactured with the manufacturing method disclosed by the said patent document 1. FIG.

  In addition, the C—F bond may be included in the main chain portion or may be included in the annular portion. When the C—F bond is included in the cyclic part, the cyclic part is preferably an odd-membered ring. In this case, since the polarity of the base material resin is higher than that in the case where the annular portion is an even-numbered ring, the intermolecular force of the base material resin is increased, resulting in a higher glass transition point Tg.

(Fine particles)
The fine particles have a refractive index temperature dependency dn / dt having the opposite sign to that of the base material resin. Therefore, even if the so-called athermal property is imparted to the light source side lens OBJ1 and the temperature rises, the amount of change in the refractive index of the light source side lens OBJ1 is reduced.

  Such fine particles are preferably inorganic fine particles, 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. Specifically, for example, titanium oxide, zinc oxide, aluminum oxide, zirconium oxide, hafnium oxide, niobium oxide, tantalum oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, yttrium oxide, lanthanum oxide, cerium oxide, oxide Phosphate and sulfate formed in combination with these oxides such as indium, tin oxide, lead oxide, and double oxides composed of these oxides such as lithium niobate, potassium niobate, and lithium tantalate And niobium oxide and lithium niobate are particularly preferably used.

  When inorganic fine particles are used as fine particles in this way, the reactivity between the matrix resin, which is a high molecular organic compound, and the fine particles is low, so that the reaction between the matrix resin and the fine particles in the light source side lens OBJ1 occurs. As a result, deterioration of light resistance and refractive index is prevented.

  Further, when an oxide is used as the fine particles, even if the blue laser is transmitted through the light source side lens OBJ1 for a long time, the transmittance deterioration and the wavefront aberration deterioration can be prevented. Further, even under high temperature conditions, deterioration of transmittance and wavefront aberration due to oxidation can be prevented.

As fine particles, fine particles having a semiconductor crystal composition can also be preferably used. Although there is no restriction | limiting in particular in this semiconductor crystal composition, The thing which does not produce absorption, light emission, fluorescence, etc. in the wavelength range used as an optical element is desirable. Specific examples of the composition include simple elements of Group 14 elements of the periodic table such as carbon, silicon, germanium and tin, simple elements of Group 15 elements of the periodic table such as phosphorus (black phosphorus), and periodic tables such as selenium and tellurium. A group 16 element simple substance, a compound comprising a plurality of Group 14 elements such as silicon carbide (SiC), tin oxide (IV) (SiO ₂ ), tin sulfide (II, IV) (Sn (II) Sn (IV ) S ₃ ), tin sulfide (IV) (SnS ₂ ), tin sulfide (II) (SnS), tin selenide (II) (SnSe), tin telluride (II) (SnTe), lead sulfide (II) ( PbS), lead selenide (II) (PbSe), lead telluride (II) (PbTe) periodic table group 14 element and periodic table group 16 element compound, boron nitride (BN), boron phosphide (BP), boron arsenide (BAs), aluminum nitride (AlN), Aluminum phosphide (AlP), aluminum arsenide (AlAs), aluminum antimonide (AlSb), gallium nitride (GaN), gallium phosphide (GaP), gallium arsenide (GaAs), gallium antimonide (GaSb), indium nitride (InN) ), Indium phosphide (InP), indium arsenide (InAs), indium antimonide (InSb), etc., a compound of a periodic table group 13 element and a periodic table group 15 element (or III-V compound semiconductor), sulfide Aluminum (Al ₂ S ₃ ), Aluminum selenide (Al ₂ Se ₃ ), Gallium sulfide (Ga ₂ S ₃ ), Gallium selenide (Ga ₂ Se ₃ ), Gallium telluride (Ga ₂ Te ₃ ), Indium oxide ( In ₂ O _3), indium sulfide (In ₂ S _3), indium selenide (In ₂ e _3), compounds of tellurium indium (In ₂ Te ₃₎ periodic table group 13 elements and the periodic table group 16 elements such as zinc oxide (ZnO), zinc sulfide (ZnS), zinc selenide (ZnSe) Zinc telluride (ZnTe), cadmium oxide (CdO), cadmium sulfide (CdS), cadmium selenide (CdSe), cadmium telluride (CdTe), mercury sulfide (HgS), mercury selenide (HgSe), mercury telluride (HgTe) and other compounds of the periodic table group 12 element and periodic table group 16 element (or II-VI group compound semiconductor), arsenic sulfide (III) (As ₂ S ₃ ), arsenic selenide (III) ( As2Se3), telluride arsenic (III) (As2Te3), antimony sulfide _{(III) (Sb 2 S 3} ), selenium antimony _{(III) (Sb 2 Se 3} ), Lulu antimony _{(III) (Sb 2 Te 3} ), bismuth sulfide _{(III) (Bi 2 S 3} ), bismuth selenide _{(III) (Bi 2 Se 3} ), bismuth telluride _{(III) (Bi 2 Te 3} ) Periodic table group 11 element and periodic table group 16 element compound, copper oxide (I) (Cu ₂ O), selenide copper (I) (Cu ₂ Se), etc. Compounds with Group 16 elements, copper chloride (I) (CuCl), copper bromide (I) (CuBr), copper iodide (I) (CuI), silver chloride (AgCl), silver bromide (AgBr) A compound of a periodic table group 11 element and a periodic table group 17 element such as nickel oxide (II) (NiO), a periodic table group 10 element and a periodic table group 16 element, cobalt oxide (II ) (CoO), cobalt sulfide (II) (CoS), etc. A compound of an element and a group 16 element of the periodic table, a compound of a group 8 element of the periodic table and a group 16 element of the periodic table, such as triiron tetrachloride (Fe ₃ O ₄ ), iron (II) sulfide (FeS), Periodic table such as manganese (II) (MnO) and other periodic table group 7 elements and periodic table group 16 elements, molybdenum sulfide (IV) (MoS2), tungsten oxide (IV) (Wo ₂ ), etc. Periodic table 5 such as compounds of Group 6 elements and Group 16 elements, vanadium oxide (II) (VO), vanadium oxide (IV) (VO ₂ ), tantalum oxide (V) (Ta ₂ O ₅ ), etc. Compounds of group elements and group 16 elements of the periodic table, Group 4 elements of the periodic table and group 16 elements of the periodic table such as titanium oxide (TiO ₂ , Ti ₂ O ₅ , Ti ₂ O ₃ , Ti ₅ O ₉ etc.) Compounds, magnesium sulfide (MgS), magnesium selenide (MgSe), etc. Periodic table The compounds of the second group elements and Periodic Table Group 16 element, cadmium oxide (II) chromium (III) (CdCr2O4), cadmium selenide (II) chromium _{(III) (CdCr 2 Se 4} ), copper sulfide ( II) Chalcogen spinels such as chromium (III) (CuCr ₂ S ₄ ), mercury selenide (II) chromium (III) (HgCr ₂ Se ₄ ), barium titanate (BaTiO ₃ ), and the like. In addition, G. Schmid et al .; Adv. Mater. , Vol. 4, p. 494 (1991), a semiconductor cluster having a fixed structure such as Cu ₁₄₆ Se ₇₃ (triethylphosphine) ₂₂ reported in the same manner is also exemplified.

Further, the average particle diameter di of the fine particles is within the range represented by the following formula (1), and preferably within the range represented by the following formula (2). If the average particle diameter di of the fine particles is less than 1 nm, it is difficult to disperse the particles, so that desired performance may not be obtained. On the other hand, if the average particle diameter exceeds 30 nm, the resulting thermoplastic material composition may become turbid, resulting in a decrease in transparency and a light transmittance of less than 70%. Furthermore, if the average particle diameter exceeds 100 nm, the light transmittance may further decrease. Here, the average particle diameter means a diameter when converted to a sphere having the same volume as the particle.
1 nm ≦ di ≦ 100 nm (1)
1nm ≦ di ≦ 30nm (2)

  The shape of the fine particles used in the present invention is not particularly limited, but spherical particles are preferably used. Further, the particle size distribution is not particularly limited, but in order to achieve the effect of the present invention more efficiently, a particle having a relatively narrow distribution is preferably used rather than a particle having a wide distribution. Used.

  As these fine particles, one type of fine particles may be used, or a plurality of types of fine particles may be used in combination.

  The amount of the fine particles added to the base material resin can be appropriately adjusted in view of the required performance, and is not particularly limited, but the amount of the fine particles added is 5% by weight or more and 80% by weight based on the total weight. The following is preferable.

  In the present invention, an optical element can be obtained by injection molding after adding nano-level fine particles to a matrix resin. However, if the amount of fine particles added is less than 5%, performance improvement (athermal Improvement) may not be sufficiently obtained.

  On the other hand, when the addition amount exceeds 80%, the moldability may be deteriorated or the weight as an optical element may be increased, and the performance as a resin material (molding material) may be deteriorated. Furthermore, problems such as “burning” may occur around the particles during molding.

Further, although the athermal effect varies depending on the value of dn / dt possessed by the fine particles, the effect of improving the athermal property can be obtained by adding 5% by weight or more of fine particles. When using fine particles such as PLZT or LiNbO _{3, the} addition of 5% by weight or more can reduce the dn / dt of the resin by about 10% or more, so that it is necessary to correct the aberration change due to the temperature change. Sex is reduced. For this reason, the freedom degree of optical design can be increased.

  On the other hand, the increase in specific gravity can be suppressed by making the addition amount of fine particles 80% by weight or less. In particular, when the optical element is the light source side lens OBJ1 constituting the objective lens OBJ, an increase in power consumption of the driving member (actuator) AC due to an increase in weight can be suppressed, and generation of a high temperature due to an increase in power consumption can be suppressed. it can.

In addition, it is also possible to reverse dn / dt of resin by adjusting the addition amount of a fine particle. That is, it is possible to make the refractive index increase as the temperature of the optical element increases. For example, when fine particles made of LiNbO ₃ are dispersed in the base resin, the sign of dn / dt of the base resin can be reversed by setting the addition amount of the fine particles to 40% by weight or more. Since the optical element having such a configuration is excessively corrected with respect to the temperature change, it is possible to cancel the refractive index change due to the temperature change by combining with an optical element made of a normal resin. In this way, by overcorrecting some of the optical elements, it is possible to cancel the refractive index change due to temperature change in the entire system without athermalizing all the optical elements in the optical system.

  The method for producing such fine particles is not particularly limited, and any known method can be used. For example, desired fine particles can be obtained by using a metal halide or alkoxy metal as a raw material and hydrolyzing in a reaction system containing water. At this time, a method of using an organic acid, an organic amine, or the like in combination is also used for stabilizing the particles.

  More specifically, for example, in the case of titanium dioxide particles, a known method described in Journal of Chemical Engineering of Japan Vol. 1, No. 1, pages 21-28 (1998) can be used. In the case of zinc, a known method described in Journal of Physical Chemistry, Vol. 100, pages 468-471 (1996) can be used.

  According to these methods, for example, titanium oxide having an average particle diameter of 5 nm can be easily obtained by using titanium tetraisopropoxide or titanium tetrachloride as a raw material and coexisting appropriate additives when hydrolyzed in an appropriate solvent. Can be manufactured. Zinc sulfide having an average particle diameter of 40 nm can be produced by adding a surface modifier when dimethylzinc or zinc chloride is used as a raw material and sulfurized with hydrogen sulfide or sodium sulfide.

  In addition, it is preferable that surface modification is given to said fine particle. The method for surface modification is not particularly limited, and any known method can be used. For example, a method of modifying the surface of fine particles by hydrolysis under conditions where water is present can be mentioned. In this method, a catalyst such as acid or alkali is preferably used, and it is generally considered that a hydroxyl group on the particle surface and a hydroxyl group generated by hydrolysis of the surface modifier dehydrate to form a bond.

  Preferred surface modifiers used in the present invention include, for example, tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, tetraphenoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, methyltriethoxysilane. , Methyltriphenoxysilane, ethyltriethoxysilane, phenyltrimethoxysilane, 3-methylphenyltrimethoxysilane, dimethyldimethoxysilane, diethyldiethoxysilane, diphenyldimethoxysilane, diphenyldiphenoxysilane, trimethylmethoxysilane, triethylethoxysilane, Examples include triphenylmethoxysilane and triphenylphenoxysilane. These compounds have different characteristics such as reaction rate, and compounds suitable for surface modification conditions can be used. Further, only one type may be used or a plurality of types may be used in combination.

  It is also possible to achieve affinity with the base material resin by selecting a compound used for surface modification. The ratio of the surface modification is not particularly limited, but the ratio of the surface modifier is preferably 10 to 99% by weight, and preferably 30 to 98% by weight with respect to the fine particles after the surface modification. More preferred.

  An antireflection film (not shown) is provided on at least one optical surface of the light source side lens OBJ1. This antireflection film is formed by alternately stacking silicon oxide layers and zirconium oxide layers from the inner side toward the outer side, and has a seven-layer structure in this embodiment. The light source side lens OBJ2 provided with the antireflection film preferably exhibits the optical characteristics shown in FIGS. 7 (a) and 7 (b). This antireflection film is preferably formed after surface treatment such as surface modification with UV light is applied to the optical surface of the light source side lens OBJ1. Thereby, even when the adhesion and adhesion of the antireflection film are low due to fluorine atoms in the base material resin, it is possible to form an antireflection film that is difficult to peel off.

  Next, the configuration of the beam shaper BE, the collimating lenses COL1 and COL2, and the sensor lenses SEN1 and SEN2 will be described in detail.

  The beam shaper BE, the collimating lenses COL1 and COL2, and the sensor lenses SEN1 and SEN2 are optical elements according to the present invention. Here, the beam shaper BE has a function of converting the intensity distribution of the light beam from the semiconductor laser oscillator LD1 into a circular shape in a plane perpendicular to the optical axis. The collimator lens COL1 has a function of converting divergent light emitted from the semiconductor laser oscillator LD1 into parallel light. The collimating lens COL2 has a function of converting divergent light emitted from the semiconductor laser oscillators LD2 and LD2 into parallel light. The sensor lens SEN1 has a function of condensing the reflected light from the BD 10 on the photodetector PD1. The sensor lens SEN2 has a function of condensing the reflected light from the DVD 20 and CD 30 onto the photodetector PD2. The refractive index of these optical elements is 1.33.

  The beam shaper BE, the collimating lenses COL1 and COL2, and the sensor lenses SEN1 and SEN2 are formed by injection molding the same mixed material as that of the light source side lens OBJ1.

  According to the above optical element according to the present invention, that is, the light source side lens OBJ1, the beam shaper BE, the collimator lenses COL1, COL2, or the sensor lenses SEN1, SEN2, the radicals in the optical element are formed by C—F bonds in the base resin. Since the reaction can be suppressed, deformation due to absorption of light energy can be suppressed, that is, light resistance can be improved. In addition, since it functions as the light source side lens OBJ1, beam shaper BE, collimating lenses COL1, COL2 or sensor lenses SEN1, SEN2, the curvature of the optical surface is compared with the case of functioning as a single objective lens for performing condensing. Since it is not necessary to reduce the radius, the manufacturing is facilitated. Therefore, deformation due to absorption of light energy can be suppressed without increasing the manufacturing cost.

  In addition, since the glass transition point of the optical element can be increased by fluorine atoms in the C—F bond, deformation of the optical element due to temperature fluctuation can be suppressed.

  Further, since the Abbe number of the optical element can be increased by the base material resin, even when the wavelength of the incident light beam is instantaneously changed by the mode hopping of the semiconductor laser oscillators LD1, LD2, LD3, the amount of axial chromatic aberration generated Can be suppressed.

  Furthermore, since the amount of change in the refractive index of the objective lens OBJ can be reduced by the second fine particles, the change in spherical aberration due to the change in refractive index can be suppressed.

  In the above embodiment, the optical element according to the present invention has been described as the light source side lens OBJ1, the beam shaper BE, the collimator lenses COL1, COL2, and the sensor lenses SEN1, SEN2, but the coupling lens CU shown in FIG. And so on. Here, the coupling lens CU includes a collimator lens COL1 and a two-dimensional actuator AC2, and converts the divergence angle of the light beam from the semiconductor laser oscillator LD1 by driving the two-dimensional actuator AC2.

  Moreover, although it demonstrated as a diffraction structure being provided in the optical surface of light source side lens OBJ1, it is good also as an optical path difference providing structure being provided. As shown in FIG. 9, the optical path difference providing structure includes a plurality of annular zones 105 in which the direction of the step 104 is changed in the middle of the effective diameter, and the cross-sectional shape including the optical axis is a step shape. This optical path difference providing structure may be a diffractive structure. Here, FIG. 9 schematically shows a case where each phase structure is formed on a plane, but each phase structure may be formed on a spherical surface or an aspherical surface.

  Further, although the optical pickup apparatus PU has been described as performing recording / reproduction of information using the optical information recording medium of the BD 10, DVD 20 and CD 30, it is also possible to perform recording / reproduction using only one of them. . Here, when the optical pickup device PU records / reproduces information using only the BD 10, the antireflection films provided on the optical surface of the light source side lens OBJ1 are alternately stacked from the inside toward the outside. It is preferable that the silicon oxide layer and the zirconium oxide layer have a total of three layers. Furthermore, it is preferable that the light source side lens OBJ1 when the antireflection film is provided exhibits the optical characteristics shown in FIGS. 10 (a) and 10 (b).

  In addition, as an optical information recording medium, the BD 10 having a protective layer thickness of 0.1 mm has been described, but an HD DVD having a protective layer thickness of about 0.6 mm may be used. An optical information recording medium having a thickness of several to several tens of nm, or an optical information recording medium without a protective layer may be used.

Next, examples of the optical element shown in the above embodiment will be described.
In Example 1, as an example, a collimate lens having “Teflon AF” (registered trademark) manufactured by DuPont as a base resin and zinc sulfide as fine particles was injection molded. The content of zinc sulfide was 30 parts by weight with respect to 100 parts by weight of the base resin. The refractive index of zinc sulfide was 2.37 and the average particle size was 40 nm.
As a comparative example, a collimate lens using a cycloolefin copolymer as a base resin was injection molded.

Table 2 shows lens data of these collimating lenses.

  This collimating lens has a focal length f of 20.0 mm and a numerical aperture NA of 0.13 at a wavelength of 407 nm.

The optical surface on the light source side of the collimating lens, that is, the “first surface” in the table, and the optical surface on the optical information recording medium side, ie, the “second surface” in the table, are non-axisymmetric about the optical axis. Specifically, it is formed in a spherical shape, and specifically, has a shape defined by a mathematical formula in which the coefficients in Table 2 are substituted into the following formula.

Here, x is an axis in the optical axis direction (the light traveling direction is positive), κ is a conic coefficient, and A _2i is an aspheric coefficient.

  Spectral transmittance was measured for the collimating lenses of these examples and comparative examples. Specifically, the measurement was performed within a wavelength range of 400 to 850 nm using a “Hitachi autograph spectrophotometer” manufactured by Hitachi, Ltd. as a visible ultraviolet spectrophotometer. The measurement results are shown in Table 3 below. In Table 3, only the spectral transmittance with respect to the wavelength of 405 nm is shown.

  As shown in this table, in the collimating lens of the example, the spectral transmittance with respect to the laser beam having a wavelength of 405 nm was 90% or higher, which was higher than that of the collimating lens of the comparative example.

Moreover, the light resistance test | inspection was performed with respect to these collimating lenses. Specifically, an appearance inspection was performed after irradiating a laser beam having a wavelength of 405 nm with a peak intensity of 120 mW / mm ² for 700 hours in a constant temperature bath at a temperature of 85 ° C. and a relative humidity of 5%. The inspection results are shown in Table 3 above.

  As shown in this table, yellowing was confirmed throughout the collimating lens of the comparative example, indicating that the light resistance was poor. On the other hand, no change was observed in the collimating lens of the example, indicating that the light resistance was excellent.

  Moreover, the weather resistance test | inspection was performed with respect to these collimating lenses. Specifically, a xenon long life weather meter “WEL-6X-HC-EC” manufactured by Suga Test Instruments Co., Ltd. was used as a weather resistance tester, and an appearance inspection was performed after 30 days at room temperature. The inspection results are shown in Table 3 above.

  As shown in this table, the collimating lens of the comparative example was confirmed to have white turbidity and surface deterioration, indicating poor weather resistance. On the other hand, no change was seen in the collimating lens of the example, indicating that the weather resistance was excellent.

Next, examples of the fine particles shown in the above embodiment will be described.
<Preparation of fine particle dispersion (1)>
Under a nitrogen atmosphere, a solution was prepared by adding 2.5 g of pentaethoxyniobium to 32.31 g of 2-methoxyethanol. To this solution, a mixed solution of 0.35 g of water and 34.45 g of 2-methoxyethanol was added dropwise with stirring. After stirring at room temperature for 16 hours, the solution was concentrated to an oxide concentration of 5% by weight to obtain a dispersion of Nb ₂ O ₅ as fine particles. When the particle size distribution of the obtained Nb ₂ O ₅ dispersion was measured by a dynamic confusion method, the average particle size was 6 nm.

<Preparation of fine particle dispersion (2)>
A solution in which 2.0 g of pentaethoxyniobium was added to 16.59 g of 2-methoxyethanol under a nitrogen atmosphere was prepared. To this solution, a mixed solution of 0.26 g of lithium hydroxide-hydrate and 18.32 g of 2-methoxyethanol was added dropwise with stirring. After stirring at room temperature for 16 hours, the mixture was concentrated to an oxide concentration of 5% by weight to obtain a dispersion liquid of LiNbO ₃ as fine particles. When the particle size distribution of the obtained LiNbO ₃ dispersion was measured by a dynamic confusion method, the average particle size was 5 nm.
To 100 g of this dispersion, 300 g of methanol and a 1 mol% nitric acid aqueous solution were added, and a mixture of 100 g of methanol and 6 g of cyclopentyltrimethoxysilane was further added over 60 minutes while stirring at 50 ° C., followed by stirring for 2 hours. The obtained transparent dispersion was suspended in ethyl acetate and centrifuged to obtain a white fine powder. According to TEM observation, this powder had an average particle size of about 6 nm.

It is a top view which shows schematic structure of an optical pick-up apparatus. It is a figure which shows an objective lens unit. It is a figure which shows the optical surface of a light source side lens. It is a figure which shows a phase structure. It is a figure which shows a phase structure. It is a figure which shows a phase structure. It is a figure which shows the optical characteristic of the light source side lens which provided the antireflection film, (a) is a reflectance, (b) is a figure which shows the transmittance | permeability. It is a top view which shows schematic structure in other embodiment of an optical pick-up apparatus. It is a figure which shows a phase structure. It is a figure which shows the optical characteristic of the light source side lens which provided the antireflection film, (a) is a reflectance, (b) is a figure which shows the transmittance | permeability. It is a figure for demonstrating the injection flow path width.

Explanation of symbols

LD1, LD2, LD3 Semiconductor laser oscillator (light source)
BE beam shaper (optical element)
COL1, COL2 Collimating lens (optical element)
CU coupling lens (optical element)
DOE diffractive structure OBJ2 disk side lens (optical element)
PU optical pickup device SEN1, SEN2 Sensor lens (optical element)

Claims (14)

In an optical element provided on an optical path of an optical pickup device that records and / or reproduces information using a light beam emitted from a light source,
Containing at least a base resin containing a C—F bond in a unit molecule;
An optical element that functions as a beam shaper, a collimating lens, a coupling lens, or a sensor lens. In an optical element provided on an optical path of an optical pickup device that records and / or reproduces information using a light beam emitted from a light source,
Containing at least a base resin containing a C—F bond in a unit molecule;
An optical element that functions as a lens other than the lens positioned closest to the optical information recording medium among a plurality of lenses constituting the objective lens unit. The optical element according to claim 2, wherein
An optical element having a numerical aperture on the image plane side of the objective lens unit of 0.73 to 0.87. In the optical element as described in any one of Claims 1-3,
The base material resin includes a C—F bond in a main chain portion. In the optical element as described in any one of Claims 1-3,
The base material resin includes a 2n + 1 member ring (n is an integer of 1 or more) in a unit molecule,
An optical element comprising a C—F bond in the annular portion. In the optical element as described in any one of Claims 1-5,
An optical element comprising fine particles having a temperature dependence dn / dt of refractive index opposite to that of the base resin. The optical element according to claim 6.
The optical element, wherein the fine particles are inorganic fine particles. The optical element according to claim 6 or 7,
The optical element, wherein the fine particles have an average particle diameter in the range of 1 to 100 nm. The optical element according to claim 8.
The optical element, wherein the average particle diameter of the fine particles is in the range of 1 to 30 nm. In the optical element according to any one of claims 1 to 9,
In the optical pickup device, the optical element is disposed on an optical path of a light beam having a wavelength of at least 200 to 420 nm. In the optical element according to any one of claims 1 to 10,
An optical element arranged in an optical path of a light beam having a plurality of wavelengths in the optical pickup device. In the optical element according to any one of claims 1 to 11,
An optical element, wherein at least one optical surface is provided with a fine structure. The optical element according to claim 12, wherein
The optical element, wherein the phase structure is a diffractive structure. An optical element according to any one of claims 1 to 13,
An optical pickup device comprising: a light source that emits a light beam and passes the light through the optical element.

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