JP2003131125A - Objective lens for optical pickup, condensing optical system for optical pickup and optical pickup device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an objective lens, a condensing optical system and an optical pickup device in which the variation in the wavefront aberration due to temperature distribution caused by heat given from a heat source during use is suppressed to a level which is practically free from problems. SOLUTION: The objective lens 20 for the optical pickup is composed of a material of which the absolute value of the temperature coefficient dn/dT of refractive index in the vicinity of a used wavelength is 50×10<-6> or greater, and is used for the optical pickup of which the numerical aperture on the image side is 0.5 or greater. The objective lens 20 has a refraction face which is not a rotating body face having an optical axis as a rotary axis, corresponding to a temperature distribution so that the condition WFE<0.05 λ(λ: used wavelength) is satisfied where WFE stands for the RMS value of a wavefront aberration when the difference between the maximum and the minimum values of the temperature distribution is 1 deg.C, when the objective lens is used in an environment in which an aerotropic temperature distribution, which is not a rotational body having the optical axis as a rotational axis, is generated in the lens. Thus, the wavefront aberration is substantially canceled out by the structure which is not a rotational body having the optical axis of the objective lens as the rotational axis when the temperature difference is 1 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup device, a condensing optical system and an objective lens used therefor, and more particularly, to an optical system capable of effectively correcting the condensing characteristic of the optical system due to a change in temperature distribution. The present invention relates to a pickup device, a condensing optical system, and an objective lens.

[0002]

2. Description of the Related Art In recent years, the numerical aperture of an objective lens used in an optical pickup device has been increased in order to increase the storage capacity. For this reason, if the objective lens is made of plastic, the influence of environmental changes such as temperature and humidity of the plastic lens on the imaging performance of the lens becomes a very important problem. Particularly, in recent years, in order to make the optical pickup device compact, an actuator for focusing and tracking of the objective lens is arranged close to the objective lens. Therefore, the influence of heat generated by the actuator becomes an important problem when using the plastic objective lens.

[0003]

The actuator of the above optical pickup device is not arranged concentrically around the objective lens, but is surrounded by, for example, a rectangle around the objective lens or sandwiched by two members. Is arranged as. As a result, the temperature of the objective lens rises using the actuator as a heat source, but the temperature distribution in the objective lens becomes non-uniform. When the objective lens is made of a material having a large linear expansion coefficient such as plastic, a refractive index distribution due to the temperature distribution occurs. This effect becomes remarkable as the numerical aperture of the objective lens increases.

FIG. 4 is a diagram schematically showing how an asymmetrical temperature distribution is generated in the first lens of the objective lens having a two-lens structure of NA 0.85, and the vertical axis is from the reference temperature. The amount of displacement. Peripheral part φ of the lens in two orthogonal directions
A temperature difference of 1 ° C. occurs at 4.8 mm. Although the temperature difference is small, if the lens material is made of a material with a large linear expansion coefficient such as a plastic lens, 1E-
A refractive index difference of about 05 (= 1 × 10 ⁻⁵ ) occurs, and N
When A is 0.85, wavefront aberration, especially 0.034λRMS, occurs as an astigmatism component. When the temperature difference is large, astigmatism increases proportionally. The temperature distribution around the objective lens in the optical pickup changes due to the heat generated from the actuator according to the tracking frequency,
If the temperature anisotropy in the peripheral part of the objective lens also increases or decreases and the largest temperature anisotropy occurs, the increase in spot due to the astigmatism component cannot be ignored and the recording mark on the optical disk cannot be read properly. . The wavefront aberration due to the refractive index distribution due to such temperature distribution has various forms other than the above-mentioned astigmatism corresponding to the arbitrary arrangement of the heat source.

It is an object of the present invention to provide an objective lens, a condensing optical system and an optical pickup device capable of suppressing a change in wavefront aberration caused by the temperature distribution to a practically satisfactory level.

[0006]

In general, when plastic is used as the material of the objective lens, various factors such as thermal conductivity, the approximate size of the objective lens, and the amount of heat generated by the actuator when used in an optical pickup device are considered. When the case was examined, it was estimated from experiments that the maximum temperature difference that could occur in the outer peripheral portion of the plastic lens was 2 ° C to 3 ° C.

Therefore, in the objective lens for an optical pickup according to claim 1, the temperature coefficient dn / d of the refractive index in the vicinity of the used wavelength is used.
An objective lens used in an optical pickup having an absolute value of T of 50 × 10 ⁻⁶ or more and having an image-side numerical aperture of 0.5 or more is not a rotating body having an optical axis as a rotation axis inside the lens. WFE is the RMS (root mean square) of the wavefront aberration when the difference between the maximum value and the minimum value of the temperature distribution is 1 ° C. when used in an environment where an anisotropic temperature distribution occurs. It is characterized in that it has a refracting surface which is not a rotating body surface having an optical axis corresponding to the temperature distribution as a rotation axis so as to satisfy the following conditional expression (1). Thus, when the temperature difference is 1 ° C., the wavefront aberration is almost canceled by the structure that is not the rotating body having the optical axis of the objective lens as the rotation axis.

WFE <0.05λ (1) Where λ: wavelength used

Since the wavefront aberration of the objective lens is corrected to 0.05 λrms or less so as to satisfy the above-mentioned conditional expression (1), when the temperature difference becomes as large as 2 ° C. or 3 ° C., or the temperature difference becomes 0. Even if the effect of temperature difference is maximum, such as when the angle becomes °, sufficient wavefront aberration can be obtained, and a low-cost plastic objective lens is used without providing a special heat countermeasure mechanism in the optical pickup device. be able to.

Further, in the objective lens for an optical pickup according to a second aspect, the maximum value and the minimum value of the temperature at the outer peripheral portion of the lens are alternately arranged at every rotation angle of about 90 °, and the maximum value and the minimum value of the temperature are set. When the RMS of the third-order astigmatic wavefront aberration component when the temperature difference is 1 ° C. is WAS1, the following conditional expression (2) is satisfied.

[0011] WAS1 <0.03λ (2) Where λ is the wavelength used

By disposing an actuator or the like serving as a heating element with the objective lens in between while the objective lens is being used, there is a temperature difference between the outer peripheral portion facing the objective lens and the outer peripheral portion facing orthogonally thereto. Although it occurs, if it is configured as in the above-mentioned claim 2, its influence can be reduced. In such a state of use, a saddle-shaped refractive index distribution is generated inside the lens, and as a result, wavefront aberration mainly due to a third-order astigmatism component is generated, but the maximum temperature difference that can occur is 2
Since it is about ℃, if the wavefront aberration when the temperature difference of 1 ° C in the middle is satisfied so as to satisfy the conditional expression (2), the degree of deterioration of the wavefront aberration over the entire temperature range that can change. It doesn't grow too big.

Further, in the objective lens for an optical pickup according to a third aspect, the RMS of the third-order asth wavefront aberration component when the temperature inside the lens is almost uniform, that is, when the temperature difference is 0.1 ° C. or less. As WAS0, the maximum value and the minimum value of the temperature at the outer peripheral portion of the lens are alternately arranged at every rotation angle of about 90 °, and the difference between the maximum value and the minimum value of the temperature is 1 ° C. and 2 ° C. When the RMSs of the third-order asth wavefront aberration components of are WAS1 and WAS2, respectively, the following conditional expressions (3) and (4) are satisfied.

WAS1 <WAS0 (3)

WAS1 <WAS2 (4)

As described above, the conditional expressions (3) and (4) are satisfied, and the RMS of the wavefront aberration when the temperature difference is 1 ° C. is smaller than when the temperature difference is 2 ° C. or when there is no temperature difference. When the objective lens is configured as described above, the wavefront aberration does not become too large when the temperature difference is 2 ° C.

Further, in the objective lens for an optical pickup of claim 4, the RMS of the third-order astigmatic wave aberration component when the temperature inside the lens is almost uniform, that is, when the temperature difference is 0.1 ° C. or less. When WAS is 0 and RMS of the remaining wavefront aberration excluding the third-order astigmatism component is WT, the following conditional expressions (5) and (6) are satisfied.

[0018] 0.02 <WAS0 <0.05λ (5)

WT <0.05λ (6)

When the temperature distribution in the objective lens is uniform, as described above, the RMS of the third-order astigmatism component of the wavefront aberration is made to satisfy the conditional expression (5), and the remaining wavefront excluding the third-order astigmatism component is satisfied. When the aberration is made to satisfy the conditional expression (6), a temperature distribution is generated, and even if astigmatism occurs, the third-order astigmatism component of the wavefront aberration existing in the objective lens is canceled out, and the total wavefront aberration is always Keeps good.

For example, the temperature distribution as described above occurs in a normal rotating lens in which the coefficient A in the objective lens of Table 1 of Example 1 described later is all 0, and about 2 is generated in the outer peripheral portion of the lens. When there is a temperature difference of 0.
A third-order asth wavefront aberration of 067λRMS occurs. However, the wavefront aberration excluding the third-order astigmatism component of the objective lens is 0.
04λ, and the objective lens has, for example, 0.03λ in advance.
When tertiary astigmatic component of the RMS has been granted, killing and by the third-order astigmatism component and the temperature distribution phase, overall wavefront ^{aberration, √ {0.04 2 + (0.067-0} . 0
3) ² } = 0.054λRMS. On the contrary, even if there is no temperature distribution, the total wavefront aberration is √ {0.04
² + 0.03 ² } = 0.05λRMS, and the wavefront aberration is satisfactorily corrected even if the temperature difference in the outer peripheral portion occurs between 0 ° C and 2 ° C. In this example, the wavefront aberration excluding the third-order astigmatism component is estimated to be relatively large at 0.04λRMS, and it goes without saying that a better overall wavefront aberration can be obtained if this is further suppressed.

Further, by arranging so that the distribution of the third-order As wavefront aberration added to the objective lens and the temperature distribution generated in the objective lens coincide with each other, a sufficient effect can be obtained.

Further, in order to add the wavefront aberration component of the third-order astigmatism to the objective lens, as described in claim 6, one of the refracting surfaces of the objective lens is a curved surface which is not a rotating body having the optical axis as the rotation axis. Then, it can be manufactured relatively easily.

Further, the non-rotating surface having the optical axis as the rotation axis is an anamorphic surface as described in claim 7, whereby the astigmatism component of the wavefront aberration can be effectively generated. That is, in the above-mentioned objective lens, at least one of the refracting surfaces is a non-rotating body surface which is not a rotating body surface having the optical axis as a rotation axis, and a point on the effective diameter on the non-rotating body surface is an effective radius ρ and an angular coordinate. Denote by θ, the displacement amount of the non-rotating body surface in the optical axis direction at the position of (ρ, θ) is X (ρ, θ)
Xav is the average value of the amount of displacement in one rotation on the effective diameter.
(Ρ) and the refractive indexes before and after the non-rotational surface are n and n ′, respectively, a region θ of θ that satisfies the conditional expression (7).
It is preferable that + and regions θ− of θ that satisfy the conditional expression (8) are alternately arranged at every 90 ° on the effective diameter.

[0025]   (N−n ′) {X (ρ, θ) −Xav (ρ)}> 0 (7)

[0026]   (N−n ′) {X (ρ, θ) −Xav (ρ)} <0 (8)

Further, as described in claim 8, by arranging so as to match the distribution of the astigmatic wave aberration added to the objective lens and the temperature distribution generated in the objective lens, a sufficient effect can be obtained.

Further, as described in claim 9, by arranging the angular region satisfying the conditional expression (7) and the angular region satisfying the conditional expression (8) according to the temperature distribution in the optical pickup. As a result, it is possible to satisfactorily cancel out the asbestos components generated in the temperature distribution.

As another method of adding a third-order astigmatism component to the objective lens in a state where the temperature distribution is uniform, the objective lens is provided with an anisotropic refractive index distribution. Can be easily obtained with.

Furthermore, as described in claim 11, the refractive index distribution is of a radial type in which the refractive index changes according to the distance from the optical axis, and the coefficient of the refractive index distribution is in one direction and orthogonal to it. The astigmatism component can be added to the objective lens by giving conditional expression (9) so as to satisfy the condition. That is, a certain direction in which a lens having a non-rotary anisotropic refractive index distribution with the optical axis as the axis of rotation is orthogonal to the optical axis is called the x axis, and from the optical axis along the x axis Is x, the refractive index of the lens medium at that position is n (x), the direction orthogonal to the optical axis and orthogonal to the x axis is the y axis, and the optical axis along the y axis is When y is the displacement from and the refractive index of the lens medium at that position is n (y), it is preferable to satisfy the following conditional expression (9).

D ² n (x) / dx ² > d ² n (y) / dy ² (9)

Further, in each of the above-mentioned objective lenses, the objective lens itself has a structure for correcting the astigmatism component generated by the temperature. The objective lens itself has such a structure. As described above, by providing an optical element different from the objective lens and forming a condensing optical system including the same, the above-described operation of the objective lens can be similarly obtained, and the optical system based on the change of the temperature distribution can be obtained. It is possible to effectively correct the light condensing characteristic of.

That is, in the condensing optical system for an optical pickup according to claim 12, the temperature coefficient dn / d of the refractive index in the vicinity of the used wavelength.
An anisotropic refractive index that is made of a material having an absolute value of T of 50 × 10 ⁻⁶ or more, has an image-side numerical aperture of 0.5 or more, and is not a rotating body having an optical axis as a rotation axis inside the objective lens. A condensing optical system for an optical pickup, which is provided with an objective lens used in an environment in which a distribution is generated and condenses a light flux from a light source onto an optical information recording medium, and has a maximum value of a temperature distribution of the objective lens. If the RMS of the wavefront aberration when the difference between the minimum value and the minimum value is 1 ° C. is WFE, a structure that is not a rotating body having the optical axis corresponding to the temperature distribution as the rotation axis is satisfied so as to satisfy the above-mentioned conditional expression (1). It is characterized by including an optical element having.

Further, in the condensing optical system for an optical pickup according to a thirteenth aspect, the maximum value and the minimum value of the temperature at the outer peripheral portion of the objective lens are alternately arranged at every rotation angle of about 90 °, and the maximum value of the temperature is obtained. When the RMS of the third-order astigmatism component of the wavefront aberration in the entire optical system when the temperature difference between the minimum value and the minimum value is 1 ° C is WAS1, the optical axis corresponding to the temperature distribution is satisfied so as to satisfy the above conditional expression (2). It is characterized in that it includes an optical element having a structure which is not a rotating body having a rotation axis of.

According to a fourteenth aspect of the present invention, there is provided a converging optical system for an optical pickup, wherein the wavefront in the entire optical system when the temperature inside the objective lens is almost uniform, that is, when the temperature difference is 0.1 ° C. or less. RMS of third-order astigmatism component of aberration is WAS
0, the maximum value and the minimum value of the temperature at the outer peripheral portion of the objective lens are alternately arranged at every rotation angle of about 90 °, and the difference between the maximum value and the minimum value of the temperature is 1 ° C. and 2 ° C. When the RMS of the third-order astigmatism component of the wavefront aberration in a given optical system is WAS1 and WAS2, respectively, the optical axis corresponding to the temperature distribution is rotated so as to satisfy the above conditional expressions (3) and (4). It is characterized in that it includes an optical element having a structure which is not a rotating body having an axis.

According to a fifteenth aspect of the present invention, there is provided a converging optical system for an optical pickup, wherein the wavefront in the entire optical system when the temperature inside the objective lens is almost uniform, that is, when the temperature difference is 0.1 ° C. or less. RMS of third-order astigmatism component of aberration is WAS
RMS of the remaining wavefront aberration which is set to 0 and the third-order astigmatism component is removed
Is represented by WT, an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis so as to satisfy the above conditional expressions (5) and (6) is included.

In addition, since the optical pickup device includes each of the above-mentioned objective lenses or each of the above-mentioned condensing optical systems, the first actuator for focusing and the second actuator for tracking are provided. Even if a temperature distribution occurs in the objective lens or the optical element due to the above reasons, the change in the wavefront aberration caused by the temperature distribution can be suppressed to a level at which there is no practical problem.

Further, according to a twenty-sixth aspect, a refractive index distribution variable element for producing a rotationally asymmetric refractive index distribution with respect to the optical axis is included, and the aforesaid non-rotationally symmetrical temperature distribution is generated in the objective lens. By using an optical pickup device in which the wavefront aberration is corrected by the refractive index distribution variable element, the refractive index distribution generated in the objective lens is corrected even in a usage state where a large temperature difference occurs, and an optical information recording medium is obtained. It is possible to obtain an optical pickup device which always connects good spots and has good signal characteristics.

The above-mentioned "non-rotary anisotropic temperature distribution with the optical axis as the axis of rotation" means a cross section when the lens is cut along the optical axis so as to include the optical axis. It means that the temperature distribution at is different in the cutting direction. Further, "a non-rotating body surface that is not a rotating body surface having the optical axis as a rotation axis" means that a surface shape in a cross section when an optical element such as a lens is cut along the optical axis direction so as to include the optical axis is cut. It means different in direction.

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view showing an objective lens and an actuator of an optical pickup device according to an embodiment of the present invention.

The actuator shown in FIG. 1 is the most common moving coil type actuator among the two-axis electromagnetic objective lens actuators. The upward direction of the drawing is the optical disk side, and the lower part is from the light source to the objective lens 20. Laser light is incident. The objective lens 20 is composed of a first lens 21 and a second lens 22. The focusing coil 31 is attached to the support 38 so as to surround the first lens 21, and the tracking coils 32 and 33 are attached to both sides of the support 38 so as to sandwich the outer periphery of the first lens 21. Are arranged. In addition, the support 3 of the actuator is arranged so as to face the tracking coils 32 and 33.
The first yoke 35 through the magnets 34 and 36 on the 9 side.
a and 37a are arranged respectively, and the tracking coil 3
The second yokes 35b and 37b are arranged between the second and third portions 33 and 33 and the outer peripheral portion of the first lens 21, respectively.

The objective lens 20, together with the focusing coil 31 and the tracking coils 32 and 33 attached to the support 38, is displaced in the direction F of the drawing by the operation by energizing the focusing coil 31, and the tracking coils 32 and 33 are provided. By the actuation by energizing, the pair of upper and lower springs 40 in the drawing are displaced in the direction T in the drawing along the longitudinal direction.

As described above, since the tracking coils 32 and 33 are eccentrically arranged with respect to the objective lens 20, the portion of the first lens 21 close to the tracking coils 32 and 33 particularly rises in temperature when the actuator operates. , A saddle-shaped refractive index gradient occurs inside the lens (see FIG. 4). Also, in the case of a moving magnet type actuator in which the coil is fixed and the magnet is attached to the objective lens side, a similar refractive index gradient occurs. The objective lens and the condensing optical system for correcting the refractive index distribution generated in the objective lens when using such an actuator will be specifically described below with reference to examples.

[0044]

EXAMPLE A refracting surface such as an objective lens of the condensing optical system in this example can be expressed by the following formula 1.

[0045]

[Equation 1]

<Example 1>

The first embodiment is an N lens composed of two lenses.
This is a condensing optical system including an A0.85 objective lens, but this objective lens has a linear expansion coefficient of 7 × 10 ⁻⁵ depending on temperature.
/ Degree, the coefficient of change in refractive index with temperature change is dn / dT
It is made of a plastic material of -12 × 10 ^-5 / degree. Therefore, when there is a temperature difference of 1 ° C. in the lens, a refractive index difference of 12 × 10 ⁻⁵ occurs. In the optical pickup device, an actuator for focusing and tracking of the objective lens is arranged around the objective lens as shown in FIG. 1, but due to the structure of the actuator,
It is difficult to form a ring shape that uniformly surrounds the periphery of the objective lens, and non-uniform heat is generated when the actuator is continuously driven. For this reason, a temperature distribution also occurs in the objective lens, and a refractive index gradient-like refractive index distribution occurs.

Lens data of the objective lens of Example 1 are shown in Table 1 below, and its optical path diagram is shown in FIG. As shown in FIG. 2, the first lens and the second lens are arranged in this order from the light source side. Is shown.

[0049]

[Table 1]

The refracting surface of the objective lens according to the first embodiment has the above-mentioned numerical formula 1.
And the first surface thereof is composed of an anamorphic surface whose coefficient A is not zero.
When there is no temperature difference inside the lens, the wavefront aberration is WAS0.
= 0.033λRMS, and the remaining wavefront aberration excluding the third-order astigmatism component is Wr = 0.007λRMS. In addition, the x-axis direction is installed so that it is substantially aligned with the direction toward the tracking coil.

When the saddle type refractive index gradient is expressed by the following model of Equation 2, the PV value of the refractive index change at the outer peripheral portion (diameter φ4.8) of the first lens is 12 × corresponding to a temperature difference of 1 ° C. ^10-5
, The coefficient of the refractive index distribution is n2 = 1.04.
2E-05, the astigmatism component due to the refractive index distribution cancels out the astigmatism component due to the rotationally asymmetric surface, and the wavefront aberration generated in the objective lens is the minimum value, WAS1 = 0.007λRMS.
(Λ: wavelength used). Further, when the temperature difference is 2 ° C. and 0 ° C., the astigmatism component of the wavefront aberration cannot be offset and remains, but the wavefront aberration is WAS0 = WAS2 = 0.
It becomes 033λRMS and can be used sufficiently.
As described above, in Example 1, the wavefront aberration can be suppressed to 0.033λRMS or less when the temperature difference of the outer peripheral portion of the objective lens is between 0 ° C and 2 ° C.

[0052]

[Equation 2]

In the first embodiment, in order to cancel the third-order AS component due to the temperature distribution, the coefficient A is 0 on the first surface of the objective lens.
Although it is not an anamorphic surface, the same effect can be obtained by using a rotating body surface with A = 0 and providing the first lens with a refractive index distribution that cancels the refractive index distribution generated by the temperature distribution in advance. be able to. Also in this case, the coefficient of the refractive index distribution when there is no temperature difference is set to n2 = -1.042E-05 so as to cancel out the refractive index distribution when the temperature difference in the first lens outer shape φ4.8 is 1 ° C. Should be

<Example 2>

In the second embodiment, a correction plate having an anamorphic surface, which is separate from the two-element objective lens, is arranged at a position on the optical axis of the optical system that is not affected by the heat of the actuator of the objective lens. It is an optical system. Table 2 shows lens data of the correction plate and the objective lens of the condensing optical system applicable to the optical pickup device, and its optical path diagram is shown in FIG.
Shown in. As shown in FIG. 3, the correction plate, the first lens, and the second lens are arranged in this order from the light source side.
No. 8 of the surface No. Is shown.

[0056]

[Table 2]

The objective lens of Example 2 has a coefficient of linear expansion with temperature of 7 × 10 ⁻⁵ / degree and a coefficient of change of refractive index with temperature change of dn / dT = −12 ×, similarly to Example 1. 1
0 ^- is formed by ^{5 /} of the plastic material. The first surface of the correction plate is a saddle-shaped anamorphic surface that is determined by the equation 1 and the coefficient of Table 2.

In the second embodiment, when the temperature difference does not occur in the objective lens, the wavefront aberration when the correction plate and the objective lens are combined is mainly the third-order astigmatism component, and WAS0 = 0.03.
3λRMS, and the wavefront aberration excluding the third-order astigmatism is WT =
It is 0.007λ RMS. When a temperature difference of 1 ° C. occurs at the outer peripheral portion (diameter φ4.8) of the objective lens, the coefficient n2 of the refractive index distribution is n2 = 1.04E-05, which is expressed by the above mathematical expression 2 as in Example 1. A saddle-shaped refractive index distribution is generated, and the third-order astigmatic component generated thereby cancels out the third-order astigmatic wavefront aberration possessed by the correction plate, and approximately WAS1 = 0.00.
It becomes 7λRMS. WAS even when the temperature difference is 0 ° C or 2 ° C
0 = WAS2 = 0.033λRMS, and 0 ° C to 2
A good spot can be obtained even if a temperature difference of ° C occurs.

In Example 2 as well, the refracting surface is an anamorphic surface in which A is not 0 in the above mathematical expression 1 so that the correcting plate has a third-order astigmatic component, but it is also possible to give the correcting plate a refractive index distribution. The same effect can be obtained.

The refractive index distribution due to the above-mentioned temperature difference is formed by a variable refractive index distribution element such as a liquid crystal element, and the refractive index distribution is electrically controlled while monitoring the shape of the spot, thereby making it complicated. The changing temperature distribution and refractive index distribution may be appropriately corrected.

Further, in the present specification, E (or e) is used to express the power of 10, and for example, E-02 (= 10
^-2 ).

[0062]

According to the objective lens, the condensing optical system, and the optical pickup device of the present invention, the wavefront aberration change caused by the temperature distribution generated by the heat from the heat source during use can be suppressed to a practically satisfactory level. be able to.

[Brief description of drawings]

FIG. 1 is a perspective view showing an objective lens and an actuator of an optical pickup device according to an embodiment of the present invention,
FIG. 6 is a diagram showing a configuration example of an actuator of an optical pickup device that can use the condensing optical system shown in Examples 1 and 2.

2 is an optical path diagram of the condensing optical system of Example 1. FIG.

FIG. 3 is an optical path diagram of a condensing optical system of Example 2.

FIG. 4 is a diagram showing an example of temperature distribution generated in a lens by heat of an actuator.

[Explanation of symbols]

20 Objective lens 21 First lens 22 Second lens 31 Focusing coil 32,33 tracking coil

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H087 KA13 NA01 NA08 PA02 PA17                       PB02 QA02 QA12 QA41 RA05                       RA07 RA12 RA42 UA01                 5D119 AA32 BA01 EC01 JA09 JA43                       JB03                 5D789 AA32 BA01 EC01 JA09 JA43                       JB03

Claims (26)

[Claims] 1. A temperature coefficient dn of a refractive index near a wavelength used.
In an objective lens used in an optical pickup with an image-side numerical aperture of 0.5 or more, the objective lens is made of a material with an absolute value of / dT of 50 × 10 ⁻⁶ or more, and is a rotating body with the optical axis as the axis of rotation. If the RMS of the wavefront aberration when the difference between the maximum value and the minimum value of the temperature distribution is 1 ° C. is WFE when used in an environment where a non-isotropic temperature distribution occurs, the following conditions An objective lens for an optical pickup, which has a refracting surface which is not a rotating body surface having an optical axis corresponding to the temperature distribution as a rotation axis so as to satisfy the expression. WFE <0.05λ where λ: wavelength used 2. The temperature coefficient dn of the refractive index near the wavelength used.
In an objective lens used in an optical pickup with an absolute value of / dT of 50 × 10 ⁻⁶ or more and an image-side numerical aperture of 0.5 or more, the maximum and minimum values of the temperature at the outer periphery of the lens Rotation angle is about 9
RMS of third-order astigmatic wavefront aberration component when the difference between the maximum value and the minimum value of the temperature is 1 ° C. arranged alternately every 0 °.
Where WAS1 is satisfied, an objective lens for an optical pickup which satisfies the following conditional expression. WAS1 <0.03λ where λ is the wavelength used 3. A temperature coefficient dn of the refractive index near the wavelength used.
In an objective lens used in an optical pickup with an absolute value of / dT of 50 × 10 ⁻⁶ or more and an image-side numerical aperture of 0.5 or more, the temperature inside the lens is almost uniform and the temperature difference is 0.
WA of the RMS of the third-order astigmatic wavefront aberration component at 1 ° C or less
S0, the maximum value and the minimum value of the temperature at the outer peripheral portion of the lens are alternately arranged at every rotation angle of about 90 °, and the difference between the maximum value and the minimum value of the temperature is 1 ° C. and 2 ° C. RMS of the third-order ass wavefront aberration component of WAS1, WAS
An objective lens for an optical pickup which satisfies the following conditional expression when the number is 2. WAS1 <WAS0 WAS1 <WAS2 4. The temperature coefficient dn of the refractive index near the wavelength used.
In an objective lens used in an optical pickup with an absolute value of / dT of 50 × 10 ⁻⁶ or more and an image-side numerical aperture of 0.5 or more, the temperature inside the lens is almost uniform and the temperature difference is 0.
WA of the RMS of the third-order astigmatic wavefront aberration component at 1 ° C or less
RM of the remaining wavefront aberration with S0 excluded
An objective lens for an optical pickup, characterized in that the following conditional expression is satisfied, where S is WT. 0.02 <WAS0 <0.05λ WT <0.05λ 5. The objective lens according to claim 4, wherein the maximum value and the minimum value of the temperature are alternately arranged on the outer peripheral portion of the objective lens at every rotation angle of about 90 ° under the environment of use, and the wavefront aberration is reduced. When the reference surface is advanced with respect to the wave front, if it is defined as positive, it is arranged so that the angular range in which the wave aberration of the third-order astigmatism component is positive and the direction in which the maximum value of the temperature is substantially coincide. An objective lens characterized by being used. 6. The objective lens according to any one of claims 1 to 5, wherein at least one of the refracting surfaces is a curved surface which is not a rotating body surface having an optical axis as a rotation axis. 7. The objective lens according to any one of claims 2 to 6, wherein at least one of the refracting surfaces is a non-rotating body surface that is not a rotating body surface having an optical axis as a rotation axis, and is on the non-rotating body surface. The point on the effective radius of is the effective radius ρ and the angle coordinate θ
The displacement amount of the non-rotating body surface in the optical axis direction at the position (ρ, θ) is represented by X (ρ, θ), and the average displacement amount per rotation on the effective diameter is Xav (ρ ), And the refractive indexes before and after the non-rotational surface are n and n ′, respectively, a region of θ that satisfies the conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)}> 0. θ + and a region θ− of θ satisfying the conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)} <0 are alternately arranged at every 90 ° on the effective diameter. Objective lens characterized by. 8. The objective lens according to claim 7, wherein
Under the environment of use, the maximum value and the minimum value of the temperature are alternately arranged on the outer peripheral portion of the objective lens at every rotation angle of about 90 °, and the direction in which the maximum value of the temperature is and the direction of the angle region θ + are substantially An objective lens characterized by being used so as to be aligned. 9. The objective lens according to claim 1, wherein at least one of the refracting surfaces is a non-rotating body surface which is not a rotating body surface having an optical axis as a rotation axis, and a point on an effective diameter on the non-rotating body surface is effective. The displacement amount in the optical axis direction of the non-rotating body surface at the position (ρ, θ) is represented by a radius ρ and an angular coordinate θ, and x (ρ,
θ), and the average value of the amount of displacement in one rotation on the effective diameter is X
av (ρ) and the refractive indices before and after the non-rotating body surface are n and n ′, respectively, the following conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)}> 0 is satisfied. There is a region θ + of θ and a region θ− of θ that satisfies the conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)} <0, and the direction of the maximum value of the temperature distribution An objective lens, which is used such that the region θ + substantially coincides with the region θ +. 10. The objective lens according to claim 1, wherein at least one lens component forming the objective lens is not a non-rotary anisotropic body having an optical axis as a rotation axis. An objective lens having a refractive index distribution. 11. The objective lens according to claim 10, wherein a lens having an anisotropic refractive index distribution which is not a rotary body having the optical axis as a rotation axis is a direction perpendicular to the optical axis in an x-axis direction. That is, x is the displacement from the optical axis along the x-axis, and the refractive index of the lens medium at that position is n (x).
Let y be the direction orthogonal to the optical axis and orthogonal to the x axis, and let y be the displacement from the optical axis along the y axis, and let the refractive index of the lens medium at that position be n (y ), An objective lens characterized by satisfying the following conditional expression. d ² n (x) / dx ² > d ² n (y) / dy ² 12. The temperature coefficient d of the refractive index near the wavelength used.
It is made of a material having an absolute value of n / dT of 50 × 10 ⁻⁶ or more, has an image-side numerical aperture of 0.5 or more, and is a non-isotropic non-rotary body having an optical axis as a rotation axis inside the objective lens. Equipped with an objective lens used in an environment where a refractive index distribution occurs,
A condensing optical system for an optical pickup that condenses a light flux from a light source onto an optical information recording medium, wherein the difference between the maximum value and the minimum value of the temperature distribution of the objective lens is 1 ° C.
When the RMS of the wavefront aberration at that time is WFE, an optical element including an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis so as to satisfy the following conditional expression: Condensing optical system for pickup. WFE <0.05λ where λ is the wavelength used 13. The temperature coefficient d of the refractive index near the wavelength used.
An optical pickup which is made of a material having an absolute value of n / dT of 50 × 10 ⁻⁶ or more, and has an objective lens having an image-side numerical aperture of 0.5 or more, and focuses a light flux from a light source on an optical information recording medium. And a maximum value and a minimum value of the temperature at the outer peripheral portion of the objective lens are alternately arranged at every rotation angle of about 90 °, and a difference between the maximum value and the minimum value of the temperature is 1 Assuming that the RMS of the third-order astigmatism component of the wavefront aberration in the all optical system at a temperature of ℃ is WAS1, the optical structure has a structure that is not a rotating body whose rotation axis is the optical axis corresponding to the temperature distribution so as to satisfy the following conditional expression A condensing optical system for an optical pickup, which includes an element. WAS1 <0.03λ where λ is the wavelength used 14. A temperature coefficient d of a refractive index in the vicinity of a used wavelength.
An optical pickup which is made of a material having an absolute value of n / dT of 50 × 10 ⁻⁶ or more, and has an objective lens having an image-side numerical aperture of 0.5 or more, and focuses a light flux from a light source on an optical information recording medium. RMS of the third-order astigmatism component of the wavefront aberration in the entire optical system when the temperature inside the objective lens is almost uniform and the temperature difference is 0.1 ° C. or less is WAS0, The maximum value and the minimum value of the temperature at the outer peripheral portion of the objective lens are alternately arranged at every rotation angle of about 90 °, and the difference between the maximum value and the minimum value of the temperature is 1 ° C and 2 ° C. When the RMS of the third-order astigmatism component of the wavefront aberration in the optical system is WAS1 and WAS2, respectively, an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis so as to satisfy the following conditional expression: Optical pick, characterized by including Up for the converging optical system. WAS1 <WAS0 WAS1 <WAS2 15. The temperature coefficient d of the refractive index near the wavelength used.
An optical pickup which is made of a material having an absolute value of n / dT of 50 × 10 ⁻⁶ or more, and has an objective lens having an image-side numerical aperture of 0.5 or more, and focuses a light flux from a light source on an optical information recording medium. Is a condensing optical system for use, wherein the RMS of the third-order astigmatism component of the wavefront aberration in the entire optical system when the temperature inside the objective lens is almost uniform and the temperature difference is 0.1 ° C. or less is WAS0, 3 Letting WT be the RMS of the remaining wavefront aberration excluding the secondary astigmatism component, it is possible to include an optical element having a structure that is not a rotating body whose rotation axis is the optical axis corresponding to the temperature distribution so as to satisfy the following conditional expression. Characterizing optical system for optical pickup. 0.02λ <WAS0 <0.05λ WT <0.05λ where λ is the wavelength used. 16. The condensing optical system for an optical pickup according to claim 15, wherein the maximum value and the minimum value of the temperature are alternately arranged at rotation angles of about 90 ° on the outer peripheral portion of the objective lens under the environment of use. When the wavefront aberration is defined as positive when the reference surface is advanced with respect to the wavefront, the directions substantially coincide with each other when the angular range in which the wavefront aberration of the tertiary astigmatism component is positive and the maximum value of the temperature are present. Thus, the condensing optical system for an optical pickup is characterized in that an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis is arranged. 17. The converging optical system for an optical pickup according to claim 12, wherein an optical element having a structure which is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis is refracted. A condensing optical system for an optical pickup, wherein at least one of the surfaces has a curved surface that is not a rotating body surface with respect to the optical axis. 18. The condensing optical system for an optical pickup according to claim 13, wherein the refraction of an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis. At least one of the surfaces is a non-rotating body surface that is not a rotating body surface having the optical axis as a rotation axis, and a point on the effective diameter on the non-rotating body surface is represented by an effective radius ρ and an angular coordinate θ, (ρ, θ) The displacement amount of the non-rotating body surface in the optical axis direction at the position of is represented by x (ρ, θ), and is 1 on the effective diameter.
When the average value of the displacement amount during rotation is represented as Xav (ρ) and the refractive indices before and after the non-rotating body surface are n and n ′, respectively, the conditional expression (n−n ′) {X (ρ, θ) −Xav The region θ + of θ satisfying (ρ)}> 0 and the region θ− of θ satisfying the conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)} <0 are effective. A condensing optical system for an optical pickup, characterized in that they are arranged alternately every approximately 90 ° on the diameter. 19. The converging optical system for an optical pickup according to claim 18, wherein the maximum value and the minimum value of the temperature at the outer peripheral portion of the objective lens are about 90 ° of rotation angle under the environment when the optical element is used. 2. The condensing optical system for an optical pickup, wherein the condensing optical system is arranged alternately so that the direction in which the maximum value of the temperature is present and the direction in the angular region θ + are substantially aligned and used. 20. The converging optical system for an optical pickup according to claim 12, wherein at least one of refraction surfaces of an optical element having a structure which is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis is an optical element. It is a non-rotating body surface that is not a rotating body having an axis as a rotation axis, and points on the effective diameter on the non-rotating body surface are represented by an effective radius ρ and angular coordinates θ, and the non-rotation at the position (ρ, θ) The amount of displacement of the body surface in the optical axis direction is expressed as X (ρ, θ), and is 1 on the effective diameter.
When the average value of the displacement amount during rotation is represented as Xav (ρ) and the refractive indices before and after the non-rotating body surface are n and n ′, respectively, the conditional expression (n−n ′) {X (ρ, θ) −Xav There is a region θ + of θ that satisfies (ρ)}> 0, and a region θ− of θ that satisfies the conditional expression (n−n ′) {X (ρ, θ) −Xav (ρ)} <0, A condensing optical system for an optical pickup, wherein the optical element is used such that the direction of the maximum value of the temperature distribution and the region θ + are substantially coincident with each other. 21. The converging optical system for an optical pickup according to claim 12, wherein an optical element having a structure that is not a rotating body having an optical axis corresponding to the temperature distribution as a rotation axis is configured. A condensing optical system for an optical pickup, wherein at least one of the constituent elements has a non-rotary anisotropic refractive index distribution having an optical axis as a rotation axis. 22. The condensing optical system for an optical pickup according to claim 21, wherein the constituent element having an anisotropic refractive index distribution that is not in the form of a rotating body and has the optical axis as a rotation axis is orthogonal to the optical axis. X in a direction
The axis is called, and the displacement along the x-axis from the optical axis is x, the refractive index of the lens medium at that position is n (x), and is orthogonal to the optical axis and orthogonal to the x-axis. The direction is the y-axis, and the displacement from the optical axis along the y-axis is y,
A condensing optical system for an optical pickup, characterized in that the following conditional expression is satisfied, where n (y) is the refractive index of the lens medium at that position. d ² n (x) / dx ² > d ² n (y) / dy ² 23. A light source, a condensing optical system including an objective lens for condensing a light beam from the light source onto the optical information recording medium, and a light beam from the light source to be focused on the optical information recording medium. An optical pickup device comprising: a first actuator for driving the objective lens, a second actuator for tracking, and a detection unit for detecting reflected light from the optical information recording medium. As any one of claims 1 to 11.
An optical pickup device using the objective lens described in the item 1. 24. A light source, a condensing optical system including an objective lens for condensing a light beam from the light source on the optical information recording medium, and a light beam from the light source is focused on the optical information recording medium. An optical pickup device including a first actuator for driving the objective lens, a second actuator for tracking, and a detection unit for detecting reflected light from the optical information recording medium. An optical pickup device comprising the condensing optical system according to any one of claims 12 to 22 as an optical system. 25. A light source, a condensing optical system including an objective lens for condensing a light beam from the light source on the optical information recording medium, and a light beam from the light source is focused on the optical information recording medium. An optical pickup device including a first actuator for driving the objective lens for tracking, a second actuator for tracking, and a detection unit for detecting reflected light from the optical information recording medium. An optical pickup device, wherein an optical system uses the objective lens according to any one of claims 1 to 11. 26. A light source, a condensing optical system including an objective lens for condensing a light flux from the light source onto an optical information recording medium, and rotation around the objective lens with an optical axis as a rotation axis. In an optical pickup device including a heating element arranged differently from the body shape, and a detection means for detecting reflected light from the optical information recording medium, the objective lens has a temperature coefficient of a refractive index in the vicinity of a used wavelength. d
A rotating body made of a material having an absolute value of n / dT of 50 × 10 ⁻⁶ or more, having an image-side numerical aperture of 0.5 or more, and the condensing optical system having an optical axis as a rotation axis. An optical pickup including a refractive index distribution variable element that produces a non-isotropic anisotropic refractive index distribution, and the wavefront aberration generated by the temperature distribution generated in the objective lens is corrected by the refractive index distribution variable element. apparatus.