WO2011122275A1

WO2011122275A1 - Optical pickup device and coupling lens for the optical pickup device

Info

Publication number: WO2011122275A1
Application number: PCT/JP2011/055477
Authority: WO
Inventors: 清乃立山
Original assignee: コニカミノルタオプト株式会社
Priority date: 2010-03-30
Filing date: 2011-03-09
Publication date: 2011-10-06
Also published as: JPWO2011122275A1

Abstract

Provided are a compact and low-cost optical pickup device which can read and write information on an optical disc having multi-layered information storage surfaces, and a coupling lens therefor. To this end, the coupling lens is made up of a positive lens having positive refractive power and a negative lens having negative refractive power, and only one of the positive lens and the negative lens can be displaced along the optical axis. The difference in thickness ΔT(mm) between the information storage surfaces that have the smallest and the greatest protecting-substrate thickness between the incidence surface of the optical disc and the information storage surface satisfies that 0.04 ≤ ΔT ≤ 0.05. The amount of displacement L(mm) of the one lens along the optical axis for focusing light beams of wavelength λ1 on the information storage surfaces with the smallest and the greatest protecting-substrate thickness satisfies that 0.5 ≤ L ≤ 2.0. The focal distance f(mm) of the coupling lens achieved when the one lens is displaced to the position at which the coupling lens emits a collimated light beam satisfies that 9 ≤ f ≤ 15.

Description

Optical pickup device and coupling lens of optical pickup device

The present invention relates to an optical pickup device capable of recording and / or reproducing information with respect to an optical disc having three or more information recording surfaces in the thickness direction, and a coupling lens used therefor.

There is known a high-density optical disk system capable of recording and / or reproducing information (hereinafter, “recording and / or reproduction” is referred to as “recording / reproduction”) using a blue-violet semiconductor laser having a wavelength of about 400 nm. As an example, an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4. It is possible to record 25 GB of information per layer on an optical disk having a diameter of 12 cm, which is the same size as 7 GB).

Incidentally, in contrast to a BD having a one-layer information recording surface, a BD having a two-layer information recording surface has recently been developed and is already on the market. Here, in Patent Document 1, the magnification is changed by moving a coupling lens including two lenses arranged between a light source and an objective lens in the optical axis direction, for example, two layers (or four layers, etc.). There has been disclosed an optical pickup device that can select any one of information recording surfaces and collect a light beam with suppressed aberration.

JP 2005-129204 A JP 2002-197712 A

By the way, in order to increase the recording capacity, a BD having an information recording surface of three layers or more has been developed. In an optical pickup device capable of recording / reproducing information with respect to a BD having an information recording surface of three layers or more. Conventionally, a relatively thick type called a so-called half-height mounted on a stationary recorder or the like has no significant problem because a relatively large moving space for the coupling lens can be secured. On the other hand, recently, there is a strong demand to use a BD having an information recording surface of three or more layers in a relatively thin optical pickup device called a so-called slim type mounted on the back of a notebook PC or thin television. However, such a slim type optical pickup device has a problem that a sufficient space for moving the coupling lens cannot be secured.

More specifically, such a problem will be described. For example, when recording / reproducing information with respect to an optical disk having three or more information recording surfaces, a long moving distance of the coupling lens is required. Especially when a plastic objective lens is used, since the refractive index change with respect to the temperature change is relatively large, spherical aberration is likely to increase due to environmental temperature fluctuations, but when this is corrected by movement of the coupling lens, In addition, a longer moving distance is required. When the moving distance of the coupling lens is increased, the optical path length from the light source to the objective lens is increased, and for example, there is a possibility that the standard size of the slim type optical pickup device is exceeded. In addition, there is a problem that a large actuator for driving the coupling lens is required and the cost is increased. That is, in a slim type optical pickup device that is required to be downsized, there is a restriction that the optical path length from the light source to the objective lens cannot be increased, so that it is difficult to cope with a BD having three or more layers of information recording surfaces. The issue is becoming more apparent.

In particular, in the case of the coupling lens disclosed in Patent Document 1, it is suitably used for a half-height type optical pickup device. However, the focal length f exceeds 15 mm, and any of information recording surfaces of three or more layers in a BD is used. However, there is a problem that the lens movement amount becomes too large to be mounted on a slim type optical pickup device.

On the other hand, the coupling lens disclosed in Patent Document 2 can be mounted on a slim type optical pickup device. However, the focal length f of the coupling lens exceeds 15 mm, and is essentially three or more layers. It is not intended to use a BD having an information recording surface. This is because the coupling lens disclosed in Patent Document 2 has a small amount of spherical aberration with respect to the amount of movement, and therefore the amount of lens movement becomes too large when recording or reproducing information recording surfaces of three or more layers on a BD. This is because it is difficult to mount on a slim type optical pickup device.

The present invention has been made in consideration of the above problems, and an optical pickup device capable of recording / reproducing information on / from an optical disc having a multilayer information recording surface while being compact and low in cost. It is an object to provide a coupling lens.

The optical pickup device according to claim 1 is an optical pickup device that selects and records information and / or reproduces information by selecting any information recording surface in an optical disk having three or more information recording surfaces in the thickness direction. There,
A light source that emits a light beam having a wavelength λ1 (390 nm <λ1 <415 nm), an objective lens for condensing the light beam on an information recording surface of an optical disc, and a cup disposed between the light source and the objective lens A ring lens,
The coupling lens includes a positive lens having a positive refractive power and a negative lens having a negative refractive power, and only one of the positive lens and the negative lens is movable in the optical axis direction. ,
The thickness difference ΔT between the thinnest information recording surface and the thickest information recording surface from the incident side surface of the optical disc to the information recording surface satisfies the equation (1),
Further, it is necessary for condensing the light flux having the wavelength λ1 so that information can be recorded and / or reproduced on the information recording surface having the thinnest protective substrate thickness and the information recording surface having the thickest protective substrate thickness. The movement amount L in the optical axis direction of the one lens satisfies the formula (2),
Further, the focal length f of the coupling lens when the one lens is moved to a position where a parallel light beam is emitted from the coupling lens toward the objective lens satisfies the expression (3).
0.04 (mm) ≦ ΔT ≦ 0.05 (mm) (1)
0.5 (mm) ≤ L ≤ 2.0 (mm) (2)
9 (mm) ≤ f ≤ 15 (mm) (3)
It is characterized by that.

According to the present invention, the coupling lens includes a positive lens having a positive refractive power and a negative lens having a negative refractive power, and only one of the positive lens and the negative lens is in the optical axis direction. Since the movement distance can be reduced and the load on the actuator can be reduced, for example, a compact optical pickup device suitable for a slim type can be provided. Here, when L is below the lower limit of the expression (2), the moving sensitivity of the one lens to be moved (ratio of the amount of spherical aberration generated with respect to the moving distance) becomes too large, and is limited to the minimum driving unit of the actuator. Therefore, the aberration cannot be corrected appropriately. On the other hand, if L exceeds the upper limit of the expression (2), the moving amount of the one lens to be moved becomes too large, and it is necessary to move other parts away to interfere with this. It cannot be mounted on the optical pickup device. Therefore, L should satisfy the formula (2).

On the other hand, if f is lower than the lower limit of the expression (3), the light spot emitted from the laser must be used up to the periphery where the amount of light has dropped to form a converging spot. There is a problem that the size is increased and an error signal is easily generated. On the other hand, if f exceeds the upper limit of the expression (3), the divergence angle of the light beam incident on the coupling lens from the light source becomes too small, and the light utilization efficiency of the pickup device is lowered. Therefore, f should satisfy the expression (3).

An optical pickup device according to a second aspect of the present invention is the invention according to the first aspect, wherein the following equation (2 ′):
0.5 (mm) ≤ L ≤ 1.5 (mm) (2 ')
It is characterized by satisfying. By setting the value to the upper limit of the expression (2 ′) or less, it is possible to provide a pickup device that is suitable when a space for other members is required.

The optical pickup device according to claim 3 is characterized in that, in the invention according to claim 1 or 2, the light source, the negative lens, and the positive lens are arranged in this order.

When the negative lens is disposed at a position close to the light source side, the effective diameter can be reduced compared to the case where the negative lens is disposed on the optical disk side, so that the weight can be reduced, and the burden on the actuator when moving the negative lens is reduced. Can be reduced.

An optical pickup device according to a fourth aspect of the present invention is the optical pickup device according to any one of the first to third aspects, wherein the negative lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens. Is the equation (4),
−1.3 ≦ P2 / P1 ≦ −0.9 (4)
Where P1: power of the negative lens, P2: power of the positive lens,
It is characterized by satisfying.

Since the negative lens is thinner and lighter than the positive lens, it is possible to reduce the burden on the actuator that moves the negative lens. In such a case, satisfying the expression (4) is preferable because the expression (2) is satisfied.

The optical pickup device according to claim 5 is the optical pickup device according to any one of claims 1 to 3, wherein the positive lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens. Is the equation (5),
-8.0 ≦ P2 / P1 ≦ −1.25 (5)
Where P1: power of the negative lens, P2: power of the positive lens,
It is characterized by satisfying.

In particular, a polarizing beam splitter or the like is generally arranged between the light source and the coupling lens, and the moving space is limited. Therefore, the moving space is reduced by arranging the positive lens on the optical disc side. Can be secured. In such a case, satisfying the expression (5) is preferable because the expression (2) is satisfied.

The coupling lens of the optical pickup device according to claim 6 performs recording and / or reproduction of information by selecting one of the information recording surfaces in an optical disc having three or more information recording surfaces in the thickness direction. An optical pickup device, comprising: a light source that emits a light beam having a wavelength λ1 (390 nm <λ1 <415 nm); an objective lens that collects the light beam on an information recording surface of an optical disc; the light source and the objective lens; In a coupling lens of an optical pickup device having a coupling lens disposed between
The coupling lens includes a positive lens having a positive refractive power and a negative lens having a negative refractive power, and only one of the positive lens and the negative lens is movable in the optical axis direction. ,
The thickness difference ΔT between the thinnest information recording surface and the thickest information recording surface from the incident side surface of the optical disc to the information recording surface satisfies the equation (1),
Further, it is necessary for condensing the light flux having the wavelength λ1 so that information can be recorded and / or reproduced on the information recording surface having the thinnest protective substrate thickness and the information recording surface having the thickest protective substrate thickness. The movement amount L in the optical axis direction of the one lens satisfies the formula (2),
Further, the focal length f of the coupling lens when the one lens is moved to a position where a parallel light beam is emitted from the coupling lens toward the objective lens satisfies the expression (3).
0.04 (mm) ≦ ΔT ≦ 0.05 (mm) (1)
0.5 (mm) ≤ L ≤ 2.0 (mm) (2)
9 (mm) ≤ f ≤ 15 (mm) (3)
It is characterized by that.

A coupling lens of an optical pickup device according to a seventh aspect is the invention according to the sixth aspect, wherein the following expression (2 ′):
0.5 (mm) ≤ L ≤ 1.5 (mm) (2 ')
It is characterized by satisfying.

The coupling lens of the optical pickup device according to claim 8 is characterized in that, in the invention according to claim 6 or 7, the negative lens and the positive lens are arranged in this order from the light source.

The coupling lens of the optical pickup device according to claim 9 is the invention according to any one of claims 6 to 8, wherein the negative lens is movable in an optical axis direction, and the negative lens and the positive lens are movable. The power ratio of the lens is given by equation (4)
−1.3 ≦ P2 / P1 ≦ −0.9 (4)
Where P1: power of the negative lens, P2: power of the positive lens,
It is characterized by satisfying.

A coupling lens of an optical pickup device according to a tenth aspect is the invention according to any one of the sixth to eighth aspects, wherein the positive lens is movable in the optical axis direction, and the negative lens and the positive lens The power ratio of the lens is given by equation (5)
-8.0 ≦ P2 / P1 ≦ −1.25 (5)
Where P1: power of the negative lens, P2: power of the positive lens,
It is characterized by satisfying.

By the way, when performing an operation of changing an information recording surface on which information is to be recorded and / or reproduced from one information recording surface to another information recording surface (hereinafter referred to as “focus jump” in this specification). As a method for reducing the amount of movement of the coupling lens, among the lenses (including the lens group) constituting the coupling lens, the power of the lens moved in the optical axis direction is increased (that is, in the optical axis direction). It is conceivable to shorten the focal length of the lens that is moved to (1). This is because the amount of movement of the lens moved in the optical axis direction decreases as the power of the lens increases (that is, as the focal length of the lens decreases). However, when the coupling lens has a group configuration, if the focal length of the lens moved in the optical axis direction (that is, equal to the focal length of the coupling lens) is shortened, the spot condensed by the objective lens becomes elliptical. Therefore, there is a possibility that the recording and / or reproduction of information on the BD may be hindered. The reason for this will be described below.

Generally, since a light beam emitted from a semiconductor laser used as a light source of an optical pickup device has an elliptical shape, the light quantity distribution in the major axis direction and the minor axis direction of the ellipse is different. If the focal length of the coupling lens becomes too short, the asymmetry of the light amount distribution taken in by the coupling lens becomes remarkable, so that the spot condensed by the objective lens becomes elliptical, and information recording on the BD and / or There is a risk that playback will be hindered. Therefore, when the coupling lens has a one-group configuration, it is difficult to reduce both the amount of movement of the coupling lens required at the time of focus jump and the symmetry of the light amount distribution captured by the coupling lens.

In order to make the above compatible, in the optical pickup device of the present invention, the coupling lens has a two-group configuration including a positive lens and a negative lens, and the positive lens or the negative lens is moved in the optical axis direction.

In order to simplify the description, it is assumed that the coupling lens is a two-group thin lens system composed of a positive lens and a negative lens, and the positive lens is moved along the optical axis direction during focus jump. Assuming that the positive lens power is P2, the positive lens focal length is f _P , the negative lens power is P1, the negative lens focal length is f _N , and the distance between the positive lens and the negative lens is D, the entire coupling lens system The power P _C and the focal length f of the entire coupling lens system are expressed by the following equation (6):
P _C = P2 + P1-D ・ P2 ・ P1
P _C = 1 / f
_{_{_{P C = 1 / f P +}}} 1 / f N -D / (f P · f N) (6)
It is represented by

Here, when the focal length of the objective lens is f 2 _O , the magnification M of the condensing optical system composed of the coupling lens and the objective lens is expressed by the following equation (7):
M = −f 2 _O / f (7)
It becomes.

In order to improve the symmetry of the distribution of the amount of light captured by the coupling lens and make the shape of the spot collected by the objective lens circular, it is optical with respect to the ellipticity of the light beam emitted from the semiconductor laser used as the light source. It is necessary to set the system magnification M to an optimum value. In the BD optical pickup device, the optimum value of the magnification of the condensing optical system is about -0.1. In consideration of a space for arranging an optical element such as a polarization beam splitter arranged between the light source and the coupling lens, the focal length f of the entire coupling lens system cannot be extremely shortened. Furthermore, when recording and / or reproducing information on the BD, the distance between the objective lens and the BD (also referred to as a working distance) is not too short, and in order to reduce the thickness of the optical pickup device, optimal range of the focal length f _O of the lens naturally determined. As described above, from equation (7), as the coupling lens for the optical pickup device for BD, the focal length range of the entire system needs to be a certain predetermined range, and the movement of the coupling lens required at the time of focus jump Considering only the amount, the focal length f of the entire coupling lens system cannot be reduced excessively. Therefore, in the present invention, the focal length f is limited to a range satisfying the expression (3).

Here, in order to keep the movement amount at the time of focus jump small, the power P2 of the positive lens is increased, and the negative lens power P1 is absolute so that the focal length f of the entire coupling lens system does not become too short. It is preferable to increase the value (see formula (6)).

As described above, in the optical pickup device of the present invention, it is possible to reduce both the amount of movement of the lens required at the time of focus jump and the symmetry of the light amount distribution taken in by the coupling lens.

As a result, even in an optical pickup device that has a relatively large amount of movement of the coupling lens, which is an optical disc having three or more layers, the optical path length from the light source to the objective lens is suppressed, and the optical pickup device can be reduced in size and size. Cost can be reduced.

In this specification, among the coupling lenses, a lens that is movable in the optical axis direction may be referred to as a “movable lens”. Further, in this specification, “movement amount of the coupling lens” is used in the same meaning as “movement amount of the movable lens”.

Note that “the state in which a parallel light beam is incident on the objective lens” means that the position of the movable lens of the coupling lens is optimized so that the light beam emitted from the coupling lens and directed to the objective lens becomes a parallel light beam. It is synonymous with that.

The optical pickup device according to the present invention has at least one light source (first light source). Of course, a plurality of types of light sources may be provided so as to support a plurality of types of optical disks. Furthermore, the optical pickup device of the present invention has a condensing optical system for condensing at least the first light flux from the first light source on the information recording surface of the first optical disc. In the optical pickup apparatus that can handle a plurality of types of optical disks, the condensing optical system condenses the second light beam on the information recording surface of the second optical disk, and the third light beam on the information recording surface of the third optical disk. You may make it condense. The optical pickup device of the present invention includes a light receiving element that receives at least a reflected light beam from the information recording surface of the first optical disc. In an optical pickup device that can handle a plurality of types of optical disks, the light receiving element receives a reflected light beam from the information recording surface of the second optical disk and receives a reflected light beam from the information recording surface of the third optical disk. Also good.

The first optical disc has a protective substrate having a thickness t1 and an information recording surface. The second optical disc has a protective substrate having a thickness t2 (t1 <t2) and an information recording surface. The third optical disc has a protective substrate having a thickness t3 (t2 <t3) and an information recording surface. The first optical disc is preferably a BD, the second optical disc is a DVD, and the third optical disc is preferably a CD, but is not limited thereto.

The first optical disc has three or more information recording surfaces stacked in the thickness direction. Of course, you may have four or more information recording surfaces. The second optical disc and the third optical disc may also have a plurality of information recording surfaces.

In this specification, BD means that information is recorded / reproduced by a light beam having a wavelength of about 390 to 415 nm and an objective lens having an NA of about 0.8 to 0.9, and the thickness of the protective substrate is 0.05 to 0.00 mm. A general term for a BD series optical disc of about 125 mm, including a BD having only a single information recording surface, a BD having three or more information recording surfaces, etc. The optical pickup device of the present invention has at least three layers. It is possible to deal with a BD having the above information recording surface. Further, in this specification, DVD is a general term for DVD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.60 to 0.67 and the thickness of the protective substrate is about 0.6 mm. Including DVD-ROM, DVD-Video, DVD-Audio, DVD-RAM, DVD-R, DVD-RW, DVD + R, DVD + RW, and the like. In this specification, CD is a general term for CD series optical discs in which information is recorded / reproduced by an objective lens having an NA of about 0.45 to 0.51 and the thickness of the protective substrate is about 1.2 mm. Including CD-ROM, CD-Audio, CD-Video, CD-R, CD-RW and the like. As for the recording density, the recording density of BD is the highest, followed by the order of DVD and CD.

In addition, regarding the thicknesses t1, t2, and t3 of the protective substrate, it is preferable to satisfy the following conditional expressions (8), (9), and (10), but is not limited thereto.

0.050 mm ≦ t1 ≦ 0.125 mm (8)
0.5mm ≦ t2 ≦ 0.7mm (9)
1.0mm ≦ t3 ≦ 1.3mm (10)
The thickness of the protective substrate referred to here is the thickness of the protective substrate provided on the surface of the optical disk. That is, the thickness of the protective substrate from the optical disc surface to the information recording surface closest to the surface.

In the present specification, the first light source, the second light source, and the third light source are preferably laser light sources. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used. The first wavelength λ1 of the first light beam emitted from the first light source, the second wavelength λ2 (λ2> λ1) of the second light beam emitted from the second light source, and the third of the third light beam emitted from the third light source. The wavelength λ3 (λ3> λ2) preferably satisfies the following conditional expressions (11) and (12).

1.5 · λ1 <λ2 <1.7 · λ1 (11)
1.8 · λ1 <λ3 <2.0 · λ1 (12)
When BD, DVD, and CD are used as the first optical disc, the second optical disc, and the third optical disc, respectively, the first wavelength λ1 of the first light source is preferably 350 nm or more and 440 nm or less, more preferably 390 nm. The second wavelength λ2 of the second light source is preferably 570 nm or more and 680 nm or less, more preferably 630 nm or more and 670 nm or less, and the third wavelength λ3 of the third light source is preferably 415 nm or less. It is 750 nm or more and 880 nm or less, More preferably, it is 760 nm or more and 820 nm or less.

Also, at least two of the first light source, the second light source, and the third light source may be unitized. The unitization means that the first light source and the second light source are fixedly housed in one package, for example. In addition to the light source, a light receiving element to be described later may be packaged.

As the light receiving element, a photodetector such as a photodiode is preferably used. Light reflected on the information recording surface of the optical disc enters the light receiving element, and a read signal of information recorded on each optical disc is obtained using the output signal. Furthermore, it detects the change in the light amount due to the spot shape change and position change on the light receiving element, performs focus detection and track detection, and based on this detection, the objective lens can be moved for focusing and tracking I can do it. The light receiving element may comprise a plurality of photodetectors. The light receiving element may have a main photodetector and a sub photodetector. For example, two sub photodetectors are provided on both sides of a photodetector that receives main light used for recording and reproducing information, and the sub light for tracking adjustment is received by the two sub photodetectors. It is good also as a simple light receiving element. The light receiving element may have a plurality of light receiving elements corresponding to the respective light sources.

The condensing optical system has a coupling lens and an objective lens. The coupling lens is a lens that is arranged between the objective lens and the light source and changes the divergence angle of the light beam. The coupling lens has a positive lens and a negative lens. The positive lens has at least one positive lens. The positive lens may be a single positive lens or may have a plurality of lenses. The negative lens has at least one negative lens. The negative lens may be a single negative lens or a plurality of lenses. An example of a preferable coupling lens is a combination of one positive lens and one negative lens.

Further, the positive lens and the negative lens may be arranged in the order of the negative lens and the positive lens from the light source side, or may be arranged in the order of the positive lens and the negative lens from the light source side.

As described above, the optimum example of the coupling lens in the optical pickup device of the present invention is a combination of one positive lens and one negative lens, and is arranged in order of the negative lens and the positive lens from the light source side. .

In order to correct spherical aberration generated on the selected information recording surface of the first optical disc, the negative lens or the positive lens can be moved in the optical axis direction. For example, when recording and / or reproducing an information recording surface of the first optical disk and then recording and / or reproducing another information recording surface of the first optical disk, a negative lens or a positive lens of the coupling lens Moves in the direction of the optical axis, changes the divergence of the light beam, and changes the magnification of the objective lens, thereby correcting the spherical aberration that occurs at the time of focus jump to a different information recording surface of the first optical disc.

FIG. 1 is a diagram showing the results of studies conducted by the present inventors. The inventor has made a plurality of information recordings using an objective lens made of plastic, having a focal length f = 1.18 mm, an optical surface being an aspherical surface or a diffractive surface, and an image-side numerical aperture of 0.85. In an optical disc (BD) having a surface, the maximum spherical aberration difference A that occurs when an optimum focused spot is formed on each information recording surface that is the maximum distance, and the maximum that occurs when the environmental temperature changes by ± 30 ° C. And the maximum spherical aberration C that occurs when the wavelength of the light source changes by ± 5 nm. This is represented by the bar graph of FIG. Such spherical aberration can be corrected by moving the coupling lens in the optical axis direction and changing the magnification of the objective lens. However, if the same coupling lens is used, the total amount of spherical aberration is the amount of movement of the coupling lens. It is equivalent to.

Here, as shown in FIGS. 1A and 1B, when an optical disk having two information recording surfaces is used, the amount of spherical aberration is obtained regardless of whether the optical surface is an aspherical refractive surface or a diffractive surface. Is about 410 to 430 mλrms, and it can be said that the amount of movement of the coupling lens is relatively small. On the other hand, as shown in FIG. 1C, when an optical disk having four information recording surfaces is used, the total amount of spherical aberration is 680 mλrms in an objective lens having an aspherical refractive surface. The amount of movement is required to be about 1.5 times that required when an optical disc having two information recording surfaces is used. Furthermore, as shown in FIG. 1D, when an optical disk having four information recording surfaces is used in an objective lens having a diffractive optical surface, spherical aberration that occurs as a result of the temperature change is caused by the diffractive surface. However, as a result, the spherical aberration generated with the change in wavelength increases, and as a result, the total amount of spherical aberration becomes 660 mλrms, and the amount of movement of the coupling lens is 2 on the information recording surface. Similarly, about 1.5 times as much is required as compared with the case of using one optical disk.

However, if the objective lens is made of glass and the optical surface is an aspherical refracting surface, the spherical aberration B (= 140 mλrms) due to a change in environmental temperature is almost zero, and therefore the amount of movement of the coupling lens is smaller (FIG. 1 ( c), the spherical aberration is 540 mλrms. Furthermore, if the objective lens is made of glass and the optical surface is a diffractive surface that corrects spherical aberration that occurs when the wavelength varies, in addition to spherical aberration B caused by environmental temperature changes, spherical aberration C caused by wavelength fluctuations of the light source due to the function of the diffractive surface. Therefore, the amount of movement of the coupling lens is smaller (corresponding to the correction amount of the spherical aberration of 500 mλrms in FIG. 1C). However, even if the objective lens is improved in this way, the amount of movement of the coupling lens when the optical disk having two information recording surfaces is used is smaller than that of the coupling lens when the optical disk having four information recording surfaces is used. Since the amount of movement is still about twice, further ingenuity is required to suppress the amount of movement of the coupling lens. The same applies to the amount of movement of the coupling lens when using an optical disc having three information recording surfaces or five or more information recording surfaces.

In the above examination, as an optical disc having two information recording surfaces (an information recording surface having a smaller distance from the light beam incident surface of the optical disc is RL1, an information recording surface having a larger distance from the light beam incident surface of the optical disc is RL2), an optical disc in which the distance from the light incident surface of the optical disc to RL1 is 75 μm and the distance from the light incident surface of the optical disc to RL2 is 100 μm. Further, as an optical disk having four information recording surfaces (assuming that the information recording surface having the smallest distance from the light beam incident surface of the optical disk is RL1, and the information recording surface having the largest distance from the light beam incident surface of the optical disk is RL4), An optical disk was assumed in which the distance from the light beam incident surface of the optical disk to RL1 was 50 μm and the distance from the light beam incident surface of the optical disk to RL4 was 100 μm.

The following describes the relationship between the configuration of the coupling lens and the amount of movement. 2 is a cross-sectional view of a coupling lens CL1 including only a positive lens (one in the figure) L1, and a coupling lens CL2 including a positive lens (one in the figure) L2 and a negative lens (one in the figure) L3. It is. Here, the focal length of the coupling lens CL1 is equal to the combined focal length of the coupling lens CL2, which is f. Therefore, the focal length f2 of the positive lens L2 of the coupling lens CL2 is shorter than the focal length f of the positive lens L1 of the coupling lens CL1.

Here, the amount of movement of the coupling lens when giving the same magnification change is inversely proportional to the power of the moving lens (= 1 / focal length). Therefore, when the positive lens L1 of the coupling lens CL1 and the positive lens L2 of the coupling lens CL2 are moved to give the same change in magnification, (1 / f) <(1 / f2). The amount of movement of the coupling lens CL1)> (the amount of movement of the coupling lens CL2). That is, the amount of movement required is smaller when the positive lens L2 of the coupling lens CL2 of the positive lens and the negative lens is moved than when the coupling lens CL1 of the single lens is moved.

In this specification, the objective lens refers to an optical system that is disposed at a position facing the optical disk in the optical pickup device and has a function of condensing a light beam emitted from the light source onto the information recording surface of the optical disk. The objective lens is preferably a single lens, but may be formed of a plurality of optical elements. The objective optical element may be a glass lens, a plastic lens, or a hybrid lens in which a diffractive structure or the like is provided on a glass lens with a photocurable resin or the like. The objective optical element preferably has a refractive surface that is aspheric. Further, when the objective lens is provided with an optical path difference providing structure, the base surface is preferably an aspherical surface.

When the objective lens is a glass lens, as described with reference to FIG. 1, it is not necessary to move the coupling lens in order to correct the spherical aberration caused by the temperature change. This is preferable because it can be reduced and the optical pickup device can be downsized.

When the objective lens is a glass lens, it is preferable to use a glass material having a glass transition point Tg of 500 ° C. or lower, more preferably 400 ° C. or lower. By using a glass material having a glass transition point Tg of 500 ° C. or lower, molding at a relatively low temperature is possible, so that the life of the mold can be extended. Examples of such a glass material having a low glass transition point Tg include K-PG325 and K-PG375 (both product names) manufactured by Sumita Optical Glass Co., Ltd.

By the way, since the specific gravity of the glass lens is generally larger than that of the resin lens, if the objective lens is a glass lens, the mass is increased and a load is imposed on the actuator that drives the objective lens. Therefore, when the objective lens is a glass lens, it is preferable to use a glass material having a small specific gravity. Specifically, the specific gravity is preferably 4.0 or less, more preferably the specific gravity is 3.0 or less.

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

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

As the plastic, cycloolefin resin is preferably used. Specifically, ZEONEX manufactured by Nippon Zeon, APEL manufactured by Mitsui Chemicals, TOPAS ADVANCED, TOPAS manufactured by POLYMERS, ARTON manufactured by JSR, etc. are preferable examples. Can be mentioned.

Further, the Abbe number of the material constituting the objective lens is preferably 50 or more.

The numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the first optical disc is NA1, and the numerical aperture on the image side of the objective lens necessary for reproducing / recording information on the second optical disc. Is NA2 (NA1> NA2), and the image-side numerical aperture of the objective lens necessary for reproducing / recording information on the third optical disk is NA3 (NA2> NA3). NA1 is preferably 0.75 or more and 0.9 or less, and more preferably 0.8 or more and 0.9 or less. In particular, NA1 is preferably 0.85. NA2 is preferably 0.55 or more and 0.7 or less. In particular, NA2 is preferably 0.60 or 0.65. NA3 is preferably 0.4 or more and 0.55 or less. In particular, NA3 is preferably 0.45 or 0.53.

Moreover, it is preferable that the objective lens satisfies the following conditional expression (13).

0.9 ≦ d / f 2 _O ≦ 1.5 (13)
However, d represents the thickness (mm) on the optical axis of the objective lens, and f _O represents the focal length of the objective lens in the first light flux. Incidentally, _{f O} is, 1.0 mm or more, it is preferable that a 1.8mm or less.

In the case of an objective lens corresponding to an optical disk with a short wavelength and high NA such as BD, if the ratio of the thickness on the optical axis to the focal length of the objective lens becomes too large, an off-axis light beam enters the objective lens. In this case, astigmatism tends to occur, and a working distance cannot be secured. On the other hand, if the ratio of the thickness on the optical axis to the focal length of the objective lens becomes too small, there arises a problem that the surface shift sensitivity increases. By satisfying conditional expression (13), it is possible to suppress astigmatism and surface shift sensitivity.

Also, the working distance of the objective lens when using the first optical disk is preferably 0.15 mm or more and 1.0 mm or less.

An optical information recording / reproducing apparatus according to the present invention includes an optical disc drive apparatus having the above-described optical pickup apparatus.

Here, the optical disk drive apparatus provided in the optical information recording / reproducing apparatus will be described. The optical disk drive apparatus can hold an optical disk mounted from the optical information recording / reproducing apparatus main body containing the optical pickup apparatus or the like. There are a system in which only the tray is taken out, and a system in which the optical disc drive apparatus main body in which the optical pickup device is stored is taken out to the outside.

The optical information recording / reproducing apparatus using each method described above is generally equipped with the following components, but is not limited thereto. An optical pickup device housed in a housing or the like, a drive source of an optical pickup device such as a seek motor that moves the optical pickup device together with the housing toward the inner periphery or outer periphery of the optical disc, and the optical pickup device housing the inner periphery or outer periphery of the optical disc These include a transfer means of an optical pickup device having a guide rail or the like that guides toward the head, a spindle motor that rotates the optical disk, and the like.

In addition to these components, the former method is provided with a tray that can be held in a state in which an optical disk is mounted and a loading mechanism for sliding the tray, and the latter method has no tray and loading mechanism. It is preferable that each component is provided in a drawer corresponding to a chassis that can be pulled out to the outside.

According to the present invention, it is possible to provide an optical pickup device and a coupling lens that are capable of recording / reproducing information with respect to an optical disc having a multilayer information recording surface while being compact and low in cost.

It is a figure which compares and shows each spherical aberration based on the examination result which this inventor performed. It is sectional drawing of coupling lens CL1 of a comparative example, and coupling lens CL2 concerning an example of this invention. It is a figure which shows schematically the structure of optical pick-up apparatus PU1. It is a figure which shows schematically the structure of optical pick-up apparatus PU2.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows that information is appropriately recorded on a BD that is an optical disc having three information recording surfaces RL1 to RL3 (referred to as RL1, RL2, and RL3 in ascending order of the distance from the light incident surface of the optical disc) in the thickness direction. FIG. 2 is a diagram schematically showing a configuration of an optical pickup device PU1 of the present embodiment that can perform reproduction. The optical pickup device PU1 is a slim type optical pickup device having a height H = 8 mm or less (outline is schematically shown by a dotted line). The present invention is not limited to the present embodiment. For example, FIG. 3 shows a BD-dedicated optical pickup device. However, the objective lens OBJ is used for BD / DVD / CD compatibility, or a DVD / CD objective lens is separately provided, so that the BD / DVD is used. / An optical pickup device compatible with CD can be used.

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

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

Here, the thickness difference ΔT between the information recording surface with the smallest protective substrate thickness from the incident side surface of the BD to the information recording surface satisfies the formula (1), and the thickness of the protective substrate is The amount of movement L in the optical axis direction of the negative lens for converging the light flux having the wavelength λ1 with respect to the thinnest information recording surface and the thickest information recording surface satisfies the equation (2). The focal length f of the coupling lens CL when the negative lens is moved to a position where the parallel light beam is emitted from the coupling lens CL satisfies the expression (3).

0.04 (mm) ≦ ΔT ≦ 0.05 (mm) (1)
0.5 (mm) ≤ L ≤ 2.0 (mm) (2)
9 (mm) ≤ f ≤ 15 (mm) (3)
First, a case where recording / reproduction is performed on the first information recording surface RL1 of the BD will be described. In such a case, the positive lens L2 of the coupling lens CL is moved to the position of the solid line by the uniaxial actuator AC1. Here, the divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) is transmitted through the polarizing prism PBS, passes through the negative lens L3 of the coupling lens CL, and the divergence angle is increased. After passing through the lens L2 to be a weakly convergent light beam, it is reflected by the rising mirror MR, converted from linearly polarized light to circularly polarized light by the λ / 4 wavelength plate QWP, and its light beam diameter is regulated by a diaphragm (not shown). It becomes a spot formed on the first information recording surface RL1 by the lens OBJ through the transparent substrate PL1 having the first thickness as shown by the solid line.

The reflected light beam modulated by the information pits on the first information recording surface RL1 is again transmitted through the objective lens OBJ and the diaphragm, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wave plate QWP, and is raised to the rising mirror MR. , And passes through the positive lens L2 and the negative lens L3 of the coupling lens CL to form a convergent light beam. After being reflected by the polarizing prism PBS, it is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, using the output signal of the light receiving element PD, the information recorded on the first information recording surface RL1 can be read by focusing or tracking the objective lens OBJ by the triaxial actuator AC2.

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

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

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

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

According to the present embodiment, the polarization prism PBS is disposed close to the coupling lens CL on the side of the semiconductor laser LD, whereas it is launched relatively far from the objective lens OBJ side. Since the mirror MR is arranged, the maximum distance for moving the coupling lens CL arranged at the origin to the semiconductor laser LD side is made smaller than the maximum distance for moving to the objective lens OBJ side, so that different information recording surfaces can be obtained. A compact optical pickup device can be obtained while ensuring a total movement distance for condensing the spots. Further, in order to correct coma generated by warping or tilting of the optical disk when information is recorded and / or reproduced on the optical disk, the objective lens OBJ is moved in the radial direction of the optical disk and / or by the triaxial actuator AC2. Tilt along the tangential direction. As a result, it is possible to stably record and / or reproduce information on the warped optical disc, and to maintain a good spot quality on the information recording surface even when the optical disc is tilted during rotation.

(Second Embodiment)
FIG. 4 shows that information is appropriately recorded on a BD that is an optical disk having three information recording surfaces RL1 to RL3 (referred to as RL1, RL2, and RL3 in order of increasing distance from the light beam incident surface of the optical disk) in the thickness direction. FIG. 6 is a diagram schematically showing a configuration of an optical pickup device PU2 of a second embodiment capable of performing reproduction. This embodiment has the same configuration as the above-described embodiment except that the negative lens L3 is moved and the positive lens L2 is fixed to the optical pickup device.

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

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

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

In the above embodiment, in order to correct coma caused by warping or tilting of the optical disc when information is recorded and / or reproduced on the optical disc, the objective lens OBJ is attached by the triaxial actuator AC2. It can also be tilted along the radial direction and / or the tangential direction of the optical disc. As a result, it is possible to stably record and / or reproduce information on the warped optical disc, and to maintain a good spot quality on the information recording surface even when the optical disc is tilted during rotation.

Furthermore, in the above embodiment, the focal length of the objective lens OBJ is preferably in the range of 1.0 mm to 1.8 mm. Thereby, an optical pickup device suitable for a thin optical pickup device that is required to be downsized can be obtained.

Next, examples of coupling lenses and objective lenses that can be used in the above-described embodiment will be described below. Here, the design wavelength is 405 nm, ri in the following table is the radius of curvature, di is the position in the optical axis direction from the i-th surface to the (i + 1) -th surface, and ni is the refractive index of each surface at the design wavelength 405 nm. . In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented by using E (for example, 2.5 × E−3). The optical surface of the objective lens is formed as an aspherical surface that is axisymmetric about the optical axis, each of which is defined by an equation in which the coefficient shown in Table 1 is substituted into Equation (1).

Here, X (h) is an axis in the optical axis direction (the light traveling direction is positive), κ is a conical coefficient, A _i is an aspherical coefficient, h is a height from the optical axis, and r is a paraxial curvature. Radius.

Example 1
Table 1 shows lens data of Example 1. The condensing optical system of this example is suitable for the second embodiment, and includes a two-group coupling lens having a negative lens (movable lens) and a positive lens (fixed lens), and an objective lens. The The coupling lens of this example has an aspheric surface obtained by substituting the aspheric coefficients of the second and fifth surfaces in Table 1 into Equation 1, and the objective lens of this example is shown in Table 1. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

(Example 2)
Table 2 shows lens data of Example 2. The condensing optical system of this example is suitable for the second embodiment, and includes a two-group coupling lens having a negative lens (movable lens) and a positive lens (fixed lens), and an objective lens. The The coupling lens of this example has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 2 into Equation 1, and the objective lens of this example is shown in Table 2. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

(Example 3)
Table 3 shows lens data of Example 3. The condensing optical system of this example is suitable for the second embodiment, and includes a two-group coupling lens having a negative lens (movable lens) and a positive lens (fixed lens), and an objective lens. The The coupling lens of this embodiment has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 3 into Equation 1, and the objective lens of this embodiment is shown in Table 3. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

Example 4
Table 4 shows lens data of Example 4. The condensing optical system of this example is suitable for the second embodiment, and includes a two-group coupling lens having a negative lens (movable lens) and a positive lens (fixed lens), and an objective lens. The The coupling lens of the present embodiment has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 4 into Equation 1, and the objective lens of the present embodiment is shown in Table 4. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

(Example 5)
Table 5 shows lens data of Example 5. The condensing optical system of this example is suitable for the first embodiment, and includes a two-group coupling lens having a negative lens (fixed lens) and a positive lens (movable lens), and an objective lens. The The coupling lens of this embodiment has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 5 into Equation 1, and the objective lens of this embodiment is shown in Table 5. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

(Example 6)
Table 6 shows lens data of Example 6. The condensing optical system of this example is suitable for the first embodiment, and includes a two-group coupling lens having a negative lens (fixed lens) and a positive lens (movable lens), and an objective lens. The The coupling lens of this example has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 6 into Equation 1, and the objective lens of this example is shown in Table 6. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

(Example 7)
Table 7 shows lens data of Example 7. The condensing optical system of this example is suitable for the first embodiment, and includes a two-group coupling lens having a negative lens (fixed lens) and a positive lens (movable lens), and an objective lens. The The coupling lens of this example has an aspheric surface obtained by substituting the aspheric coefficients of the second surface and the fifth surface in Table 7 into Equation 1, and the objective lens of this example is shown in Table 7. It has an aspheric surface obtained by substituting the aspheric coefficients of the seventh surface and the eighth surface into Equation (1).

Table 8 summarizes numerical values corresponding to conditional expressions (2) to (5) for each example. As shown in Table 8, ΔT = 0.1−0.0535 = 0.0465 (mm) in any of the examples. In the embodiment, the movement sensitivity (λ / 0.01 mm) is 0.0020 to 0.0061, and the lens drive control at the time of focus jump is easy. Here, the distance between the lenses of the coupling lens, the distance between the positive lens and the negative lens through which the parallel light beam enters the objective lens is indicated by A in Table 8, and is the thinnest protective substrate thickness of 0.0535 mm. When a certain information recording surface is selected, the distance between the positive lens and the negative lens of the coupling lens that emits a convergent light beam in which the third-order spherical aberration of the spot of the objective lens is 0 is B in Table 8. The positive lens of the coupling lens that emits a divergent light beam such that the third-order spherical aberration of the spot of the objective lens is zero when the information recording surface having the thickest protective substrate thickness of 0.1 mm is selected. The distance between the negative lens and the negative lens is indicated by C in Table 8. Further, δ in Table 8 is the distance between the surfaces on the optical axes when a parallel light beam is emitted from the coupling lens to the objective lens (see FIGS. 3 and 4).

The present invention is not limited to the embodiments described in the specification, and other embodiments and modifications are apparent to those skilled in the art from the embodiments and ideas described in the present specification. It is. The description and examples are for illustrative purposes only, and the scope of the invention is indicated by the following claims.

OBJ Objective lens PU1, PU2 Optical pickup device LD Blue-violet semiconductor laser AC1 Single-axis actuator AC2 Three-axis actuator PBS Polarizing prism CL Coupling lens L2 Positive lens L3 Negative lens MR Rising mirror PL1 First transparent substrate PL2 Second transparent Substrate PL3 Third transparent substrate RL1 First information recording surface RL2 Second information recording surface RL3 Third information recording surface QWP λ / 4 wavelength plate

Claims

An optical pickup device that selects and records information and / or reproduces information by selecting any information recording surface in an optical disc having three or more information recording surfaces in the thickness direction,
A light source that emits a light beam having a wavelength λ1 (390 nm <λ1 <415 nm), an objective lens for condensing the light beam on an information recording surface of an optical disc, and a cup disposed between the light source and the objective lens A ring lens,
The coupling lens includes a positive lens having a positive refractive power and a negative lens having a negative refractive power, and only one of the positive lens and the negative lens is movable in the optical axis direction. ,
The thickness difference ΔT between the thinnest information recording surface and the thickest information recording surface from the incident side surface of the optical disc to the information recording surface satisfies the equation (1),
Further, it is necessary for condensing the light flux having the wavelength λ1 so that information can be recorded and / or reproduced on the information recording surface having the thinnest protective substrate thickness and the information recording surface having the thickest protective substrate thickness. The movement amount L in the optical axis direction of the one lens satisfies the formula (2),
Further, the focal length f of the coupling lens when the one lens is moved to a position where a parallel light beam is emitted from the coupling lens toward the objective lens satisfies the expression (3). An optical pickup device.
0.04 (mm) ≦ ΔT ≦ 0.05 (mm) (1)
0.5 (mm) ≤ L ≤ 2.0 (mm) (2)
9 (mm) ≤ f ≤ 15 (mm) (3)
The optical pickup device according to claim 1, wherein the following expression (2 ′) is satisfied.
0.5 (mm) ≤ L ≤ 1.5 (mm) (2 ')
3. The optical pickup device according to claim 1, wherein the negative lens and the positive lens are arranged in this order from the light source.
The light according to any one of claims 1 to 3, wherein the negative lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens satisfies the expression (4). Pickup device.
−1.3 ≦ P2 / P1 ≦ −0.9 (4)
Where P1: power of the negative lens, P2: power of the positive lens
The light according to any one of claims 1 to 3, wherein the positive lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens satisfies the expression (5). Pickup device.
-8.0 ≦ P2 / P1 ≦ −1.25 (5)
Where P1: power of the negative lens, P2: power of the positive lens
An optical pickup device that records and / or reproduces information by selecting any information recording surface in an optical disc having three or more information recording surfaces in the thickness direction, and has a wavelength λ1 (390 nm <λ1 <415 nm). ), A light source that emits a light beam, an objective lens for condensing the light beam on an information recording surface of an optical disk, and a coupling lens disposed between the light source and the objective lens. In the coupling lens of
The coupling lens includes a positive lens having a positive refractive power and a negative lens having a negative refractive power, and only one of the positive lens and the negative lens is movable in the optical axis direction. ,
The thickness difference ΔT between the thinnest information recording surface and the thickest information recording surface from the incident side surface of the optical disc to the information recording surface satisfies the equation (1),
Further, it is necessary for condensing the light flux having the wavelength λ1 so that information can be recorded and / or reproduced on the information recording surface having the thinnest protective substrate thickness and the information recording surface having the thickest protective substrate thickness. The movement amount L in the optical axis direction of the one lens satisfies the formula (2),
Further, the focal length f of the coupling lens when the one lens is moved to a position where a parallel light beam is emitted from the coupling lens toward the objective lens satisfies the expression (3). Coupling lens for optical pickup device.
0.04 (mm) ≦ ΔT ≦ 0.05 (mm) (1)
0.5 (mm) ≤ L ≤ 2.0 (mm) (2)
9 (mm) ≤ f ≤ 15 (mm) (3)
The coupling lens of the optical pickup device according to claim 6, wherein the following expression (2 ′) is satisfied.
0.5 (mm) ≤ L ≤ 1.5 (mm) (2 ')
The coupling lens of the optical pickup device according to claim 6 or 7, wherein the negative lens and the positive lens are arranged in this order from the light source.
The light according to any one of claims 6 to 8, wherein the negative lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens satisfies the expression (4). The coupling lens of the pickup device.
−1.3 ≦ P2 / P1 ≦ −0.9 (4)
Where P1: power of the negative lens, P2: power of the positive lens
The light according to any one of claims 6 to 8, wherein the positive lens is movable in an optical axis direction, and a power ratio between the negative lens and the positive lens satisfies the expression (5). The coupling lens of the pickup device.
-8.0 ≦ P2 / P1 ≦ −1.25 (5)
Where P1: power of the negative lens, P2: power of the positive lens