JP2009087492A - Objective optical element for optical pickup device and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective optical element for an optical pickup device and the optical pickup device, which inexpensively achieve interchangeable use of optical disks of different kinds while making incident luminous fluxes of the same wavelength on one objective optical element without depending on complex mechanism and which have high efficiency of use of light. <P>SOLUTION: The objective optical element is provided in which a refraction surface for BD and a refraction surface for HD are provided in a divided way, wherein the element is designed beforehand so that the number of aperture of image side becomes small, and a convergence spot is formed on an information recording surface of BD or an information recording surface of HD using the above number of aperture. Concretely, by satisfying expression (1), f<SB>BD</SB>≥(EPD<SB>BD</SB>/2NA<SB>BD</SB>), and expression (2), f<SB>HD</SB>>(EPD<SB>HD</SB>/2NA<SB>HD</SB>), the number of aperture of image side is made small formally, and even when so-called super resolution phenomenon is caused, a convergence spot having an appropriate diameter can be formed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an objective optical element for an optical pickup device and an optical pickup device capable of recording and / or reproducing information interchangeably with respect to different types of optical disks using light beams having the same wavelength.

  In recent years, research and development of high-density optical disc systems that can record and / or reproduce 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. Development is progressing rapidly. As an example, in an optical disc for recording / reproducing information with specifications of NA 0.85 and light source wavelength 405 nm, so-called Blu-ray Disc (hereinafter referred to as BD), DVD (NA 0.6, light source wavelength 650 nm, storage capacity 4.7 GB) Can record information of 23 to 27 GB per layer on an optical disk with a diameter of 12 cm, which is the same size as the above, and an optical disk that records and reproduces information with specifications of NA 0.65 and light source wavelength 405 nm, so-called With HD DVD (hereinafter referred to as HD), information of 15 to 20 GB per layer can be recorded on an optical disk having a diameter of 12 cm. Such an optical disc is referred to as a high density optical disc in this specification.

  By the way, simply saying that information can be appropriately recorded / reproduced with respect to one high-density optical disc cannot be said to have sufficient value as a product of an optical disc player / recorder (optical information recording / reproducing apparatus). Considering the fact that the software recorded on both high-density optical disks is already on the market, it is possible to record / reproduce information on both high-density optical disks in the same way. This leads to an increase in commercial value as an optical disc player / recorder for optical discs.

  However, for BD and HD, which are high-density optical discs, the thickness of each protective substrate is different even though the wavelength of the light beam used is the same. It is difficult to correct spherical aberration generated based on the above. Therefore, it is more difficult to provide compatibility between BD and HD using a single objective optical element, as compared with compatibility with other optical disks.

On the other hand, Patent Document 1 describes an objective optical element and an optical pickup device that use liquid crystals to give different aberrations during recording / reproduction of BD and HD, and enable compatibility with one objective optical element. ing. Patent Document 2 describes a pickup device that enables BD and HD to be used interchangeably with a single objective optical element by sorting light beams of the same wavelength using a diffraction effect.
JP 2007-26540 A JP 2006-147069 A

  However, since the optical pickup device described in Patent Document 1 requires a liquid crystal, power supply and electrical control are necessary, which complicates the mechanism and increases the cost. It was.

  Further, as in the optical pickup device described in Patent Document 2 above, when realizing the compatible use of BD and HD using the diffraction effect, for example, the light from the light source passing through the diffraction structure to one of the optical disks Utilization efficiency (the utilization efficiency here is the ratio of the amount of light that contributes to the spot on the optical disk with respect to the amount of light incident on the optical surface on the light source side of the objective optical element) is 40% (diffractive distribution using a diffraction structure) (Theoretically does not exceed 50%), the utilization efficiency of light passing from the optical disk through the same diffraction structure toward the photodetector (the utilization efficiency here is the optical surface on the optical disk side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the light detector is 40%, so the total utilization efficiency (the utilization efficiency here is the light on the light source side of the objective optical element) The ratio of the amount of light that contributes to the spot on the photodetector with respect to the amount of light incident on the surface is only 40% square, and only 16% of light can be used. It can be said that it is difficult.

  On the other hand, there is an attempt to realize the compatible use of BD and HD by separately providing the optical surface area for BD and the optical surface area for HD on the optical surface of the objective optical element. According to such an attempt, since a liquid crystal element or the like is not used, the structure can be simplified and energy saving can be achieved, and the use of the diffraction structure is not compatible, so that there is an advantage that the light use efficiency can be increased.

  However, according to the study by the present inventors, when an objective optical element in which an optical surface area for BD and an optical surface area for HD are divided is designed, the light use efficiency can be improved. However, it was found that the tolerance range of the tilt error of the objective optical element with respect to the optical disk is narrowed, and the risk of generating an error signal is increased. Furthermore, as a result of examination of the reason by the present inventor, it has been found that the reason is that the focused spot is too narrowed.

  The present invention takes the above-mentioned problems into consideration, and allows different types of optical disks to be used interchangeably while allowing light beams of the same wavelength to be incident on one objective optical element without depending on a complicated mechanism and at low cost. And it aims at providing the objective optical element and optical pick-up apparatus for optical pick-up apparatuses with high light utilization efficiency.

The objective optical element for an optical pickup device according to claim 1 includes a light source that emits a light beam having a wavelength λ1 (380 nm <λ1 <450 nm), and an objective optical for condensing the light beam on an information recording surface of an optical disk. A condensing optical system having an element;
The light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the light beam is collected on the information recording surface of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element for an optical pickup device that records and / or reproduces information by light,
On the optical surface of the objective optical element, a circular or ring-shaped first region and a second region are arranged side by side in a direction orthogonal to the optical axis, and the region farthest from the optical axis is the first region. ,
The light beam having the wavelength λ1 that has passed through the first area is used for recording and / or reproduction of the first optical disk, and the light beam having the wavelength λ1 that has passed through the first area is used for recording and / or recording on the second optical disk. Or not used for regeneration,
The light beam having the wavelength λ1 that has passed through the second area is used for recording and / or reproduction of the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is used for recording and / or recording on the first optical disk. Or not used for regeneration,
The following (1) and (2) are satisfied.
f ₁ ≧ (EPD ₁ / 2NA ₁ ) (1)
f ₂ > (EPD ₂ / 2NA ₂ ) (2)
However,
f ₁ : Focal length EPD ₁ for the light flux having the wavelength λ1 that has passed through the first region of the objective optical element: Effective diameter NA ₁ of the objective optical element when the first optical disk is used: Standard of the first optical disk Required numerical aperture f ₂ : focal length EPD ₂ for the light beam having the wavelength λ 1 that has passed through the second region of the objective optical element: effective diameter NA ₂ of the objective optical element when the second optical disk is used: Necessary numerical aperture in the standard of the second optical disk

When the focal length in the objective optical element for the optical pickup device is f, the effective diameter is EPD, and the required numerical aperture for a certain optical disk is NA,
f = (EPD / 2NA) (0)
It is common technical common sense to design an objective optical element so as to satisfy the above. The present inventors satisfy the following formulas (10) and (20) for the objective optical element in which the optical surface area for BD and the optical surface area for HD are separately provided in accordance with such technical common sense. Designed to. As a result, although the light utilization efficiency could be improved compared to the case of using the diffraction effect, the allowable range of the tilt error of the objective optical element with respect to the optical disk is narrowed, and the possibility of generating an error signal may be increased. all right. Furthermore, as a result of studies by the present inventor, it has been found that the reason is that the focused spot is too narrowed. The fact that the inventor found out that the cause of the error signal was in a focused spot that was too narrowed led to the following present invention.
f _BD = (EPD _BD / 2NA _BD ) (10)
f _HD = (EPD _HD / 2NA _HD ) (20)

  The inventors of the present invention do not use the light flux that passes through the BD area for HD, and do not use the light flux that passes through the HD area for BD. This led to the idea that the condensing spot was too narrow because the image-side numerical aperture of the objective optical element of No. 1 increased. This is because when the so-called super-resolution phenomenon occurs, the optical characteristics as designed cannot be obtained even if the relationship of the expressions (10) and (20) is satisfied. Therefore, the present inventors have designed in advance an objective optical element in which the optical surface area for BD and the optical surface area for HD are separately provided so that the image-side numerical aperture is small, and this is used. An attempt was made to form a focused spot on the information recording surface of the BD or the information recording surface of the HD. That is, on the form, the image-side numerical aperture is reduced, so that even when a so-called super-resolution phenomenon occurs, a condensing spot with an appropriate diameter can be formed, and the allowable range of the tilt error of the objective optical element with respect to the optical disc can be maintained, An error signal is not generated.

  Here, there remains a problem of how to reduce the image-side numerical aperture in terms of form. In order to change the image-side numerical aperture, it is necessary to change at least one of the effective diameter and the focal length. However, if the effective diameter is changed, the relationship between the light source of the optical pickup device and the collimating lens must be changed as a whole, which is a major change and is not a preferable change for the pickup manufacturer. Also, it is not easy to change the effective diameter of the objective optical element due to the problem of the space around the objective optical element in the optical pickup device. On the other hand, the focal length can be changed relatively easily only by changing the design of the objective optical element, and it is relatively easy for the pickup manufacturer to cope with it. Therefore, the present inventors have also found that it is preferable to reduce the image-side numerical aperture by changing the focal length and satisfying the expressions (1) and (2).

  In addition, by satisfying the expressions (1) and (2), there is an advantage that the working distance is increased. This merit is particularly advantageous when using HD with a thick transparent substrate.

  As described above, the present invention provides an objective optical element that enables compatibility between BD and HD with a single optical system, and A) obtains high light utilization efficiency, and B) provides an allowable range of tilt error of the objective optical element with respect to the optical disc. In addition, the four effects of eliminating the generation of error signals, C) increasing the design tolerance of the pickup manufacturer by maintaining the effective diameter of the objective optical element, and D) extending the working distance. It is possible to get at once.

The objective optical element for an optical pickup device according to claim 2 satisfies the following expression (1 ′) in the invention according to claim 1, and therefore the information recording surface of the first optical disc: A clearer spot light can be formed above, and a spot light with an appropriate diameter can be formed on the information recording surface of the second optical disk.
f ₁ = (EPD ₁ / 2NA ₁ ) (1 ′)

The objective optical element for an optical pickup device according to claim 3 satisfies the following expression (1 ″) in the invention according to claim 1. Therefore, the first optical disk and the second optical element are satisfied. Spot light with an appropriate diameter can be formed on the information recording surface of the optical disc, and the working distance of the first optical disc can be made longer.
f ₁ > (EPD ₁ / 2NA ₁ ) (1 ″)

An objective optical element for an optical pickup device according to a fourth aspect is characterized in that, in the invention according to any one of the first to third aspects, NA ₁ = 0.85 and NA ₂ = 0.65. . This is the case when the first optical disc is BD and the second optical disc is HD.

  The objective optical element for an optical pickup device according to claim 5 is the invention according to any one of claims 1 to 4, wherein the total number of the first region and the second region is 3 or more and 10 or less. It is characterized by that. By satisfying this range, it is possible to obtain an objective optical element that suppresses the side rope and is easy to manufacture. More preferably, the total number of the first region and the second region is 4 or more and 7 or less.

  An objective optical element for an optical pickup device according to a sixth aspect is the invention according to any one of the first to fifth aspects, wherein a plurality of the first regions are provided, and one of the first regions has an optical axis. It is a circular region including it.

  The objective optical element for an optical pickup device according to a seventh aspect is the invention according to any one of the first to fifth aspects, wherein a plurality of the second regions are provided, one of which includes an optical axis. It is a circular region.

An objective optical element for an optical pickup device according to an eighth aspect of the invention is characterized in that, in the invention according to any one of the first to seventh aspects, the following expression (1A) is satisfied. By satisfying the formula (1A), it is preferable that only one of the first optical disc and the second optical disc is not narrowed down, and a better spot can be obtained in both.
_{0.80 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1A)
More preferably, the following expression (1B) is satisfied. In many cases, BD requires a larger amount of light than HD. However, if the following equation (1B) is satisfied, the amount of BD can be greater than the amount of HD. It is particularly preferable when recording with BD.
_{0.90 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1B)
More preferably, the following expression (1C) is satisfied. When the following expression (1C) is satisfied, the light quantity of BD can be made larger than the light quantity of HD further than the expression (1B), which is preferable. It is particularly preferable when recording with BD.
_{0.95 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1C)

An objective optical element for an optical pickup device according to a ninth aspect satisfies the following expression (2A) in the invention according to any one of the first to eighth aspects. By satisfying the formula (2A), it is preferable that only one of the first optical disc and the second optical disc is not excessively focused, and a better spot can be obtained in both.
_{0.70 <(EPD 2/2 ·} f 2 · NA 2) <1 (2A)

  An objective optical element for an optical pickup device according to a tenth aspect is the invention according to any one of the first to ninth aspects, wherein a spot formed on the information recording surface of the first optical disc has a diameter of 0.38 μm. The spot diameter formed on the information recording surface of the second optical disc is 0.50 μm or more and 0.55 μm or less. When a focused spot is formed using an objective optical element designed so as to satisfy the expressions (10) and (20) according to the prior art, a super-resolution phenomenon occurs. For example, in BD, the spot diameter is 0. Since the spot diameter in HD is less than 0.50 μm, it can be clearly distinguished from the objective optical element of the present invention by actually measuring the spot diameter. The definition of the spot diameter will be described later in the specification.

  An optical pickup device according to an eleventh aspect uses the objective optical element according to any one of the first to tenth aspects.

The objective optical element for an optical pickup device according to claim 12,
A light collecting optical system having a light source that emits a light beam having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the light beam on an information recording surface of an optical disk;
The light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the light beam is collected on the information recording surface of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element for an optical pickup device that records and / or reproduces information by light,
On the optical surface of the objective optical element, a circular or ring-shaped first region and a second region are arranged side by side in a direction orthogonal to the optical axis, and the region farthest from the optical axis is the first region. ,
The light beam having the wavelength λ1 that has passed through the first area is used for recording and / or reproduction of the first optical disk, and the light beam having the wavelength λ1 that has passed through the first area is used for recording and / or recording on the second optical disk. Or not used for regeneration,
The light beam having the wavelength λ1 that has passed through the second area is used for recording and / or reproduction of the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is used for recording and / or recording on the first optical disk. Or not used for regeneration,
The diameter of the spot formed on the information recording surface of the first optical disc is not less than 0.38 μm and not more than 0.43 μm,
The diameter of the spot formed on the information recording surface of the second optical disc is 0.50 μm or more and 0.55 μm or less.

  It is preferable that the first optical disc is a BD and the second optical disc is an HD. In the BD, information is recorded / reproduced by an objective optical element having an NA of 0.85, and the thickness of the protective substrate is about 0.1 mm. In the HD, information is recorded / reproduced by an objective optical element having an NA of 0.65 to 0.67, and the thickness of the protective substrate is about 0.6 mm.

  In addition, regarding the thicknesses t1 and t2 of the protective substrate, it is preferable to satisfy the following conditional expressions (3) and (4), but is not limited thereto.

0.0750 mm ≦ t1 ≦ 0.1125 mm (3)
0.5mm ≦ t2 ≦ 0.7mm (4)

  The optical pickup device includes at least one light source, a condensing optical system, and a light receiving element.

  In this specification, the light source is preferably a laser light source. As the laser light source, a semiconductor laser, a silicon laser, or the like can be preferably used.

  When BD is used as the first optical disk and HD is used as the second optical disk, the wavelength λ1 of the light beam emitted from the light source is preferably larger than 380 nm and smaller than 450 nm. More preferably, λ1 is not less than 390 nm and not more than 415 nm. In addition, when it has two light sources and each wavelength is larger than 380 nm and smaller than 450 nm, and the wavelength difference between the two light sources is 20 nm or less, both are light sources as used in this specification, It shall be considered that it is within the scope of the present invention. Further, in addition to a light source that emits a light beam having a wavelength λ1, a light source for another optical disk such as a DVD or a CD may be included.

  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 amount of light due to the change in the shape and position of the spot on the light receiving element, performs focus detection and track detection, and moves the objective optical element for focusing and tracking based on this detection 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. Moreover, when it has a some light source, the light receiving element may have the some light-receiving part corresponding to each light source.

  The condensing optical system has an objective optical element. The objective optical element condenses the light beam so that information can be recorded / reproduced on the information recording surface of the first optical disk, and collects the light beam so that information can be recorded / reproduced on the information recording surface of the second optical disk. Shine. The condensing optical system may include only the objective optical element, but may include a coupling lens such as a collimator lens and a beam expander in addition to the objective optical element. The coupling lens is a single lens or a lens group that is disposed between the objective optical element and the light source and changes the divergence angle of the light beam. The beam expander is a lens group that is disposed between the objective optical element and the light source and changes the diameter of the light beam without changing the divergence angle of the light beam. The collimating lens is a kind of coupling lens, and is a lens that changes a light beam incident on the collimating lens into parallel light. Further, the condensing optical system has an optical element such as a diffractive optical element that divides the light beam emitted from the light source into a main light beam used for recording and reproducing information and two sub light beams used for tracking and the like. May be. In addition to the objective optical elements for the first optical disk and the second optical disk, the condensing optical system may have objective optical elements for other optical disks.

  In this specification, the objective optical element is disposed at a position facing the optical disk in a state where the optical disk is loaded in the optical pickup device, and has a function of condensing the light beam emitted from the light source on the information recording surface of the optical disk. An optical system having Preferably, the objective optical element is an optical system that is disposed at a position facing the optical disc in the optical pickup device and has a function of condensing a light beam emitted from the light source on the information recording surface of the optical disc, An optical system that can be integrally displaced at least in the optical axis direction by an actuator. The objective optical element may be composed of two or more lenses and optical elements, or may be only a single lens. The objective optical element may be a glass lens, a plastic lens, or a hybrid lens in which an optical path difference providing structure or the like is provided on a glass lens with a photocurable resin or the like. When the objective optical element has a plurality of lenses, a glass lens and a plastic lens may be mixed and used. When the objective optical element has a plurality of lenses, a combination of a flat optical element having an optical path difference providing structure and an aspherical lens may be used. The objective optical element may have an optical path difference providing structure. The objective optical element preferably has an aspheric refractive surface.

When the objective optical element is a plastic lens, it is preferable to use a cyclic olefin-based resin material. Among the cyclic olefin-based materials, the refractive index at a temperature of 25 ° C. with respect to a wavelength of 405 nm is 1.54 to 1.60. The refractive index change rate dN / dT (° C. ⁻¹ ) with respect to the wavelength of 405 nm accompanying the temperature change within the temperature range of −5 ° C. to 70 ° C. is −20 × 10 ^{−5 to} −5 × 10 ^It is more preferable to use a resin material in the range of ⁻⁵ (more preferably −10 × 10 ^{−5 to} −8 × 10 ⁻⁵ ). When the objective optical element is a plastic lens, the coupling lens is preferably a plastic lens.

    On the optical surface of the objective optical element, a circular or ring-shaped first region and a second region are arranged side by side in the direction perpendicular to the optical axis. The most central region including the optical axis is a circular region, and the surrounding region is a concentric ring-shaped region centering on the optical axis. The first region and the second region may have a clear structural difference between the first region and the second region on the optical surface of the objective optical element. On the other hand, the objective optical element may be a convenient area without providing a clear area in terms of configuration. The first region and the second region are preferably arranged alternately in the direction perpendicular to the optical axis, but other regions may be included between the first region and the second region, or the first region may be included in the first region. The structure may include other regions.

  The light beam having the wavelength λ1 that has passed through the first region of the objective optical element is used for recording / reproduction of the first optical disc, and the light beam having the wavelength of λ1 that has passed through the first region is used for recording and / or reproduction of the second optical disc. I can't. The light beam having the wavelength λ1 that has passed through the second area is used for recording / reproduction of the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is not used for recording and / or reproduction of the first optical disk. . The region farthest from the optical axis is the first region. The most central area (area including the optical axis) may be the first area or the second area.

  The objective optical element may have a compatible area or an optical path difference providing structure that enables use of a third optical disk and / or a fourth optical disk different from the high-density optical disk. The compatible optical path difference providing structure may be provided in the first region or the second region, or another region different from the first region and the second region may be provided and provided there. Further, the objective optical element may have an optical path difference providing structure for correcting the aberration change at the time of temperature change or wavelength change. In addition, the first region or the second region of the objective optical element may have an optical path difference providing structure for reducing the step amount of the step with the adjacent region. In addition, the optical path difference providing structure in this specification is a general term for structures that add an optical path difference to an incident light beam. The optical path difference providing structure also includes a phase difference providing structure for providing a phase difference. The phase difference providing structure includes a diffractive structure. The optical path difference providing structure has a step, preferably a plurality of steps. This step adds an optical path difference and / or phase difference to the incident light flux. The optical path difference added by the optical path difference providing structure may be an integer multiple of the wavelength of the incident light beam or a non-integer multiple of the wavelength of the incident light beam. The steps may be arranged with a periodic interval in the direction perpendicular to the optical axis, or may be arranged with a non-periodic interval in the direction perpendicular to the optical axis.

The objective optical element satisfies the following expressions (1) and (2).
f ₁ ≧ (EPD ₁ / 2NA ₁ ) (1)
f ₂ > (EPD ₂ / 2NA ₂ ) (2)
Note that f ₁ represents the focal length of the light beam having the wavelength λ1 that has passed through the first region of the objective optical element. EPD ₁ represents the effective diameter of the objective optical element when the first optical disk is used. NA ₁ represents a necessary numerical aperture in the standard of the first optical disc. (When the first optical disc is a BD, this value is 0.85.) F ₂ represents the focal length of the light beam having the wavelength λ1 that has passed through the second region of the objective optical element. EPD ₂ represents the effective diameter of the objective optical element when the second optical disk is used. NA ₂ represents a required numerical aperture in the standard of the second optical disc. (If the second optical disc is HD, this value is 0.65.)

In addition, the effective diameter as used in this specification means the following things. EPD ₁ is twice the outer edge diameter of the light beam incident on the optical surface on the light source side or the distance between the outermost peripheral portion of the first region farthest from the optical axis and the optical axis. EPD ₂ This is twice the distance between the outermost peripheral portion of the second region farthest from the axis and the optical axis.

NA ₁ and NA ₂ may be regarded as the numerical aperture in terms of spot diameter. In this case, NA ₁ and NA ₂ can be expressed by the following equations.
NA ₁ = 0.824 × λ1 / SD ₁
NA ₂ = 0.824 × λ1 / SD ₂
However, SD ₁ represents the spot diameter formed on the information recording surface of the first optical disk, and SD ₂ represents the spot diameter formed on the information recording surface of the second optical disk. The definition of the spot diameter will be described later.

  Further, the total number of the first region and the second region is preferably 3 or more and 10 or less, and more preferably 4 or more and 7 or less. When a region other than the first region and the second region is included, it is preferable that the total number of all regions including the first region satisfies the above range.

Moreover, it is preferable to satisfy | fill the following (1A) Formula.
_{0.80 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1A)
More preferably, the following expression (1B) is satisfied.
_{0.90 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1B)
More preferably, the following expression (1C) is satisfied.
_{0.95 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1C)

Moreover, it is preferable to satisfy | fill the following (2A) Formula.
_{0.70 <(EPD 2/2 ·} f 2 · NA 2) <1 (2A)

The spot diameter formed on the information recording surface of the first optical disc is preferably 0.38 μm or more and 0.43 μm or less. The spot diameter formed on the information recording surface of the second optical disc is preferably 0.50 μm or more and 0.55 μm or less. The spot diameter here refers to the diameter of a spot at a position where the intensity is 1 / e ^{2 of the} central intensity in a focused spot that is actually formed by making a light beam of wavelength λ1 incident on the objective optical element. The spot diameter formed on the information recording surface of the first optical disk is preferably smaller than (2 · f ₁ · 0.824 · λ1) / EPD ₁ . The spot diameter formed on the information recording surface of the second optical disk is preferably smaller than (2 · f ₂ · 0.824 · λ1) / EPD ₂ .

Next, when performing recording and / or reproduction of the second optical disk, the light beam that has passed through the first area is prevented from obscuring the second optical disk in order to prevent the light beam that has passed through the first area from getting over the defocus area. It is preferable that the objective optical element has a flare on the information recording surface. Specifically, “to make flare” means a spot formed by the light passing through the first area on the information recording surface of the second optical disc distributed in the donut-shaped area or formed by the light passing through the second area. Distribution in a thin circular region at the center. When the first optical disc is a BD and the second optical disc is an HD, the working distance (WD _BD ) of the objective optical element in the first optical disc ( _BD ) is 0.55 or more and 0.64 (mm). It is preferable that Moreover, the working distance of the objective optical element in the second optical disk _(HD) (WD HD) is 0.40 or more and 0.46 (mm) or less. In order to generate a good flare when the first optical disc is a BD and the second optical disc is an HD, the working distance (WD _BD ) of the objective optical element in the first optical disc (BD); the value of the difference between the working distance of the objective optical element (WD _HD) in the second optical disk _{(HD) (WD BD -WD HD} ), - 0.36 (mm) or more, to 0.17 (mm) or less Is preferred. More preferably, it is -0.10 (mm) or more and 0.15 (mm) or less.

  As a configuration for improving the off-axis characteristics of the objective optical element, 1) change the aspherical shape of the first region and the second region, or 2) provide an optical path difference providing structure in the second region, etc. The configuration of can be considered. Here, to improve the off-axis characteristics means that the wavefront aberration becomes 0.1 RMS or less when the light beam enters the objective optical element at an oblique incidence of 0.5 °.

  In the case of the configuration in which the aspherical shapes of the first area and the second area in 1) are different, the working distance (WD1) of the objective optical element at the time of recording and / or reproduction of the first optical disk, the recording of the second optical disk, and It is preferable that the absolute value (| WD1-WD2 |) of the difference from the working distance (WD2) of the objective optical element during reproduction is designed to be 0.1 (mm) or more.

  On the other hand, in order not to cause a large step on the optical surface, it is preferable to provide an off-axis characteristic by providing an optical path difference providing structure in the second optical disc dedicated area as in 2). Depending on other design conditions, the above method 1) or 2) may be used properly.

  The light beam having the wavelength λ1 may be incident on the objective optical element as parallel light, or may be incident on the objective optical element as divergent light or convergent light. Preferably, the magnification m1 of the light beam having the wavelength λ1 incident on the objective optical element satisfies the following formula (5).

-0.01 <m1 <0.01 (5)

  On the other hand, when the light beam having the wavelength λ1 is incident on the objective optical element as diverging light, the magnification m1 of the light beam incident on the objective optical element of the light beam having the wavelength λ1 preferably satisfies the following formula (6).

  -0.10 <m1 <0.00 (6)

In order to make the sine condition compatible during both recording and / or reproduction of the first optical disk and recording and / or reproduction of the second optical disk, it is preferable to satisfy the following conditional expression (7).
m11 <m12 (7)
Here, m11 represents the magnification of the incident light beam on the objective optical element of the light beam having the wavelength λ1 at the time of recording and / or reproduction of the first optical disk, and m12 is the wavelength at the time of recording and / or reproduction of the second optical disk. The magnification of the light beam incident on the objective optical element of the light beam of λ1 is shown.

  For example, when recording and / or reproducing the first optical disk, the light beam having the wavelength λ1 is incident on the objective optical element as infinite parallel light, and when recording and / or reproducing the second optical disk, the light beam having the wavelength λ1 is finite on the objective optical element. A preferred example is an embodiment in which the light is incident as convergent light.

  The optical information recording / reproducing apparatus has an optical disc drive apparatus having the optical pickup device described above.

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

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

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

  According to the present invention, an objective for an optical pickup device that enables compatible use of different types of optical disks while allowing a light beam of the same wavelength to be incident on one objective optical element without depending on a complicated mechanism and at a low cost. An optical element and an optical pickup device can be provided. Moreover, the present invention provides a high light utilization efficiency, maintains an allowable range of tilt error of the objective optical element with respect to the optical disc, eliminates the generation of an error signal, and maintains the effective diameter of the objective optical element. It is possible to provide an objective optical element for an optical pickup device and an optical pickup device that can increase design tolerance and extend a working distance.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a configuration of an optical pickup apparatus PU1 of the present embodiment that can appropriately record and / or reproduce information on a BD that is a first optical disc and an HD that is a second optical disc. FIG. Such an optical pickup device PU1 can be mounted on an optical information recording / reproducing device. The present invention is not limited to the present embodiment.

  The optical pickup device PU1 includes information recording surfaces of an objective optical element OBJ, a λ / 4 wavelength plate QWP, a collimating lens CL, a polarizing prism PPS, a semiconductor laser LD that emits a 405 nm laser beam (beam), and sensor lenses SL and BD. It has a light receiving element PD that receives a reflected light beam from the information recording surface RL2 of RL1 and HD. In the present embodiment, the objective optical element OBJ is a single ball, but two or more optical elements may be used in combination.

  The optical surface on the light source side, which is a refractive surface of the objective optical element OBJ, has a first area AR1 for a circular BD including the optical axis, a second area AR2 for an HD in a ring shape around it, and further Surrounding ring-shaped first areas AR3 for BD are alternately formed.

  A case of recording / reproducing BD will be described. First, the divergent light beam of the light beam (λ1 = 405 nm) emitted from the blue-violet semiconductor laser LD is transmitted through the polarization prism PBS and converted into a parallel light beam by the collimator lens CL, as indicated by the solid line, and then the λ / 4 wavelength. Linearly polarized light is converted to circularly polarized light by the plate QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and formed on the information recording surface RL1 of the BD via the protective substrate PL1 having a thickness of 0.0875 mm by the objective optical element OBJ. Become a spot.

  At this time, the light beam that has passed through the first areas AR1 and AR3 of the objective optical element OBJ is condensed on the information recording surface of the BD to form a spot, but the light beam that has passed through the second area AR2 becomes flare light. , No focused spot is formed on the information recording surface of the BD.

  The reflected light beam modulated by the information pits on the information recording surface RL1 passes through the objective optical element OBJ and the aperture again, and then is converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, by using the output signal of the light receiving element PD to focus or track the objective optical element OBJ by the biaxial actuator AC, it is possible to read information recorded on the BD.

  Next, a case where HD recording / reproduction is performed will be described. The divergent light beam emitted from the blue-violet semiconductor laser LD (λ1 = 405 nm) passes through the polarizing prism PBS and is converted into a parallel light beam by the collimator lens CL, as indicated by a one-dot chain line, and then a λ / 4 wavelength plate The linearly polarized light is converted into circularly polarized light by QWP, the diameter of the light beam is regulated by a diaphragm (not shown), and formed on the information recording surface RL2 of HD via the protective substrate PL2 having a thickness of 0.6 mm by the objective optical element OBJ. Become a spot.

  At this time, the light beam that has passed through the second area AR2 of the objective optical element OBJ is condensed on the HD information recording surface to form a spot, but the light beam that has passed through the first areas AR1 and AR3 becomes flare light. , No condensing spot is formed on the information recording surface of HD. (In FIG. 1, during HD recording / reproduction, the light beam does not appear to enter the first area AR3, but actually enters the first area AR3.)

  The reflected light beam modulated by the information pits on the information recording surface RL2 again passes through the objective optical element OBJ and the aperture, and then converted from circularly polarized light to linearly polarized light by the λ / 4 wavelength plate QWP, and converged by the collimating lens CL. After being reflected by the polarizing prism PBS, the light is converged on the light receiving surface of the light receiving element PD by the sensor lens SL. Then, by using the output signal of the light receiving element PD to focus or track the objective optical element OBJ by the biaxial actuator AC, the information recorded on the HD can be read.

(Example)
Next, examples that can be used in the above-described embodiment will be described. In the first to fourth embodiments, the center is the second region, and the first region, the second region, the first region, the second region, and the first region are sequentially arranged around the second region in the direction orthogonal to the optical axis. This is a single lens objective optical element having a total of six regions. In the following embodiments, the first optical disc is BD and the second optical disc is HD. NA in Tables 1 to 4 represents the numerical aperture in terms of the spot diameter, but NA of BD 0.85 and NA of HD 0.65 defined as the required numerical aperture in the BD and HD standards. Match.

In the following tables, ri 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. In the following (including the lens data in the table), a power of 10 (for example, 2.5 × 10 ⁻³ ) is represented using E (for example, 2.5 × E−3). In addition, the optical surface of the objective optical element is formed as an aspherical surface that is symmetric about the optical axis and is defined by mathematical formulas obtained by substituting the coefficients shown in Table 1 into Formula 1.

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

Example 1
Table 1 shows lens data of Example 1. 2A and 2B are cross-sectional views of the objective optical element of Example 1. FIG. 2A shows a light condensing state when using BD, and FIG. 2B shows a light condensing state when using HD. In Example 1, f ₁ = 1.765, f ₂ = 1.866, EPD ₁ = 3.000 mm, EPD ₂ = 1.800 mm, NA ₁ = 0.85, NA ₂ = 0.65, spot at BD The diameter = 0.390 μm and the spot diameter in HD = 0.510 μm. At this time, (EPD ₁ / 2NA ₁ ) = 1.765 (= f ₁ ) and (EPD ₂ / 2NA ₂ ) = 1.385 (<f ₂ ). _{Further, (EPD 1/2 · f} BD · NA 1) = 1.000, which is _{(EPD 2/2 · f HD} · NA 2) = 0.742. In this embodiment, the ratio of the area of the optical surface is 94% for BD and 6% for HD. Accordingly, since a large amount of light is distributed to the BD, this embodiment is advantageous in the case of performing BD recording.

(Example 2)
Table 2 shows lens data of Example 2. FIGS. 3A and 3B are cross-sectional views of the objective optical element of Example 2. FIG. 3A shows a condensing state when using BD, and FIG. 3B shows a condensing state when using HD. In Example 2, spots at f ₁ = 1.812, f ₂ = 1.911, EPD ₁ = 3.000 mm, EPD ₂ = 2.080 mm, NA ₁ = 0.85, NA ₂ = 0.65, BD The diameter = 0.393 μm and the spot diameter in HD = 0.511 μm. At this time, (EPD ₁ / 2NA ₂ ) = 1.765 (<f ₁ ) and (EPD ₂ / 2NA ₂ ) = 1.600 (<f ₂ ). _{Further, (EPD 1/2 · f} 1 · NA 1) = 0.974, which is _{(EPD 2/2 · f 2} · NA 2) = 0.837. In this embodiment, the ratio of the area of the optical surface is 77% for BD and 23% for HD. Accordingly, since a large amount of light is distributed to the BD, this embodiment is advantageous in the case of performing BD recording.

(Example 3)
Table 3 shows lens data of Example 3. 4A and 4B are cross-sectional views of the objective optical element of Example 3. FIG. 4A shows a light condensing state when using BD, and FIG. 4B shows a light converging state when using HD. In Example 3, spots at f ₁ = 1.941, f ₂ = 2.031, EPD ₁ = 3.000 mm, EPD ₂ = 2.538 mm, NA ₁ = 0.85, NA ₂ = 0.65, BD The diameter = 0.391 μm, and the spot diameter in HD = 0.510 μm. At this time, (EPD ₁ / 2NA ₁ ) = 1.765 (<f ₁ ) and (EPD ₂ / 2NA ₂ ) = 1.952 (<f ₂ ). _{Further, (EPD 1/2 · f} 1 · NA 1) = 0.909, which is _{(EPD 2/2 · f 2} · NA 2) = 0.960. In this embodiment, the ratio of the area of the optical surface is 53% for BD and 47% for HD. Accordingly, since the light amount is distributed substantially equally between the BD and the HD, this embodiment is advantageous when applying substantially the same function between the BD and the HD.

Example 4
Table 4 shows lens data of Example 4. 5A and 5B are cross-sectional views of the objective optical element of Example 4. FIG. 5A shows a light condensing state when using BD, and FIG. 5B shows a light converging state when using HD. In Example 4, spots at f ₁ = 2.059, f ₂ = 2.148, EPD ₁ = 3.000 mm, EPD ₂ = 2.740 mm, NA ₁ = 0.85, NA ₂ = 0.65, BD The diameter = 0.393 μm, and the spot diameter in HD = 0.516 μm. At this time, (EPD ₁ / 2NA ₁ ) = 1.765 (<f ₁ ) and (EPD ₂ / 2NA ₂ ) = 2.108 (<f ₂ ). _{Further, (EPD 1/2 · f} 1 · NA 1) = 0.857, which is _{(EPD 2/2 · f 2} · NA 2) = 0.981. In this embodiment, the ratio of the area of the optical surface is 27% for BD and 73% for HD. Accordingly, since a large amount of light is distributed to the HD, this embodiment is advantageous in the case of HD recording.

  The main values of each example are summarized in Table 5.

  In Examples 1 to 4 above, no error signal was generated even when the objective optical element was slightly tilted with respect to the optical disk.

It is a figure which shows schematically the structure of the optical pick-up apparatus which concerns on this invention. 1 is a cross-sectional view of an objective optical element of Example 1. FIG. 6 is a cross-sectional view of an objective optical element according to Example 2. FIG. 7 is a cross-sectional view of an objective optical element according to Example 3. FIG. 6 is a cross-sectional view of an objective optical element according to Example 4. FIG.

Explanation of symbols

AR1, AR3 First area AR2 Second area OBJE Objective optical element PU1 Optical pickup device LD Blue-violet semiconductor laser AC Biaxial actuator PBS Polarizing prism CL Collimating lens PL1 Protection substrate PL2 Protection substrate RL1 Information recording surface RL2 Information recording surface QWP λ / 4 wavelength plate

Claims (12)

A light collecting optical system having a light source that emits a light beam having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the light beam on an information recording surface of an optical disk;
The light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the light beam is collected on the information recording surface of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element for an optical pickup device that records and / or reproduces information by light,
On the optical surface of the objective optical element, a circular or ring-shaped first region and a second region are arranged side by side in a direction orthogonal to the optical axis, and the region farthest from the optical axis is the first region. ,
The light beam having the wavelength λ1 that has passed through the first area is used for recording and / or reproduction of the first optical disk, and the light beam having the wavelength λ1 that has passed through the first area is used for recording and / or recording on the second optical disk. Or not used for regeneration,
The light beam having the wavelength λ1 that has passed through the second area is used for recording and / or reproduction of the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is used for recording and / or recording on the first optical disk. Or not used for regeneration,
An objective optical element for an optical pickup device characterized by satisfying the following expressions (1) and (2):
f ₁ ≧ (EPD ₁ / 2NA ₁ ) (1)
f ₂ > (EPD ₂ / 2NA ₂ ) (2)
However,
f ₁ : Focal length EPD ₁ for the light flux having the wavelength λ1 that has passed through the first region of the objective optical element: Effective diameter NA ₁ of the objective optical element when the first optical disk is used: Standard of the first optical disk Required numerical aperture f ₂ : focal length EPD ₂ for the light beam having the wavelength λ 1 that has passed through the second region of the objective optical element: effective diameter NA ₂ of the objective optical element when the second optical disk is used: Necessary numerical aperture in the standard of the second optical disk The objective optical element for an optical pickup device according to claim 1, wherein the following expression (1 ′) is satisfied.
f ₁ = (EPD ₁ / 2NA ₁ ) (1 ′) The objective optical element for an optical pickup device according to claim 1, wherein the following expression (1 ″) is satisfied.
f ₁ > (EPD ₁ / 2NA ₁ ) (1 ″) The objective optical element for an optical pickup device according to any one of claims 1 to 3, wherein NA ₁ = 0.85 and NA ₂ = 0.65.   5. The objective optical element for an optical pickup device according to claim 1, wherein a total number of the first region and the second region is 3 or more and 10 or less.   6. The objective optical for an optical pickup device according to claim 1, wherein a plurality of the first regions are provided, and one of them is a circular region including the optical axis. element.   6. The objective optical for an optical pickup device according to claim 1, wherein a plurality of the second regions are provided, and one of them is a circular region including the optical axis. element. The objective optical element for an optical pickup device according to claim 1, wherein the following expression (1A) is satisfied.
_{0.80 <(EPD 1/2 ·} f 1 · NA 1) ≦ 1 (1A) The objective optical element for an optical pickup device according to claim 1, wherein the following expression (2A) is satisfied.
_{0.70 <(EPD 2/2 ·} f 2 · NA 2) <1 (2A)   The diameter of the spot formed on the information recording surface of the first optical disc is 0.38 μm or more and 0.43 μm or less, and the diameter of the spot formed on the information recording surface of the second optical disc is 0.50 μm or more and 0. The objective optical element for an optical pickup device according to claim 1, wherein the objective optical element is .55 μm or less.   An optical pickup device using the objective optical element according to claim 1. A light collecting optical system having a light source that emits a light beam having a wavelength of λ1 (380 nm <λ1 <450 nm) and an objective optical element for condensing the light beam on an information recording surface of an optical disk;
The light beam is condensed on the information recording surface of the first optical disk having the protective layer having the thickness t1, and the light beam is collected on the information recording surface of the second optical disk having the protective layer having the thickness t2 (t1 <t2). In an objective optical element for an optical pickup device that records and / or reproduces information by light,
On the optical surface of the objective optical element, a circular or ring-shaped first region and a second region are arranged side by side in a direction orthogonal to the optical axis, and the region farthest from the optical axis is the first region. ,
The light beam having the wavelength λ1 that has passed through the first area is used for recording and / or reproduction of the first optical disk, and the light beam having the wavelength λ1 that has passed through the first area is used for recording and / or recording on the second optical disk. Or not used for regeneration,
The light beam having the wavelength λ1 that has passed through the second area is used for recording and / or reproduction of the second optical disk, and the light beam having the wavelength λ1 that has passed through the second area is used for recording and / or recording on the first optical disk. Or not used for regeneration,
The diameter of the spot formed on the information recording surface of the first optical disc is not less than 0.38 μm and not more than 0.43 μm,
An objective optical element for an optical pickup device, wherein a diameter of a spot formed on the information recording surface of the second optical disc is 0.50 μm or more and 0.55 μm or less.

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