JP2004030725A - Objective optical element of optical pickup device, and optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device capable of attaining compatibility between optical disks whose protective substrates thicknesses are different by using light sources of the same wavelengths. <P>SOLUTION: The objective optical element of an objective optical disk device performs recording and reproduction of information to both of a first optical information recording medium whose protective substrate thickness is t1 and a second optical information recording medium whose protective substrate thickness is t2. The optical function surface of the objective optical element consists of at least three concentric circle-shaped areas centered on an optical axis and the three concentric circle-shaped areas include respectively the optical axis and are respectively a first area which is used to both of the first optical information recording medium and the second optical information recording medium and a second area which exists at an outer peripheral side than the first area and which is used to the first optical information recording medium and a third area which exists at an outer peripheral side than the second area and which is used to the first optical information recording medium and the objective optical element has optical compensation structure for performing temperature compensation and/or chromatic aberration to the light source to be used at least in the third area. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical pickup device and an objective optical element used for the optical pickup device, and more particularly, to an optical pickup device capable of complying with the standards of a plurality of optical information recording media (optical discs) and an optical pickup device. It relates to an objective optical element.
[0002]
[Prior art]
From the past to the present, an optical pickup device (also referred to as an optical head or an optical head device) for reproducing / recording information on / from an optical information recording medium (also referred to as an optical disk or a medium) such as a CD or DVD has been developed.・ Manufactured and widely used.
[0003]
In recent years, research and development have also been carried out on standards for optical information recording media capable of recording information at a higher density.
Such an optical pickup device converts a light beam emitted from a light source (mainly a laser diode) into an optical element such as a beam shaping prism, a collimator, a beam splitter, and an objective lens (also referred to as an objective optical element). The light is condensed on the information recording surface of the optical disk via the optical system to form a spot, and the reflected light from the information recording holes (also called pits) on the recording surface is again collected on the sensor via the optical system. The information is reproduced by illuminating the light and converting it into an electric signal. At this time, since the luminous flux of the reflected light also changes depending on the shape of the information recording hole, the information of "0" and "1" is distinguished by using this. Note that a protective substrate (a protective layer made of plastic; also referred to as a cover glass) is provided on the information recording surface of the optical disc.
[0004]
When recording information on a recordable medium such as a CD-R or CD-RW, a spot is formed by a laser beam on a recording surface, and a thermochemical change occurs on a recording material on the recording surface. Thereby, for example, in the case of CD-R, the shape similar to the information recording hole is formed by irreversible change of the heat diffusible dye. In the case of CD-RW, since a phase change material is used, the information is reversibly changed between a crystalline state and an amorphous state by a thermochemical change, so that information can be rewritten.
[0005]
In an optical pickup device for reproducing information from a CD-standard optical disk, the NA of the objective lens is about 0.45, and the wavelength of the light source used is about 785 nm. For recording, about 0.50 is often used. Note that the thickness of the protection substrate of the optical disc of the CD standard is 1.2 mm.
[0006]
Now, CDs have become widespread as optical information recording media, but DVDs (also called digital versatile disks or digital video disks) have become widespread in recent years. This is to increase the information recording amount by making the protective substrate thinner and making the information recording hole smaller than the CD. The CD is about 600 to 700 MB (megabyte), whereas about 4 to 4 MB. It has a large recording capacity of 0.7 GB (gigabyte) and is often used as a distribution medium that records moving images such as movies.
[0007]
An optical pickup device for reproducing information from a DVD-standard optical disk is in principle the same as that for a CD, but the information recording hole is small as described above. Is around 0.60, and the wavelength of the light source used is around 655 nm. For recording, about 0.65 is often used. The thickness of the protective substrate of the DVD standard optical disk is 0.6 mm.
[0008]
Also, recordable optical discs of the DVD standard have already been put into practical use, and there are various standards such as DVD-R, DVD-RAM, DVD-RW, and DVD + RW. The technical principle regarding these is also the same as in the case of the CD standard.
[0009]
As described above, optical disks with higher density and higher capacity are being proposed. In this method, a so-called blue-violet laser light source having a wavelength of about 405 nm is mainly used as a light source.
[0010]
Regarding such a “high-density optical disk”, even if the wavelength to be used is determined, the thickness of the protective substrate, the storage capacity, the NA, etc. are not uniformly determined.
If the direction in which the recording density is significantly improved is selected, the thickness of the protective substrate of the optical disk is reduced, and accordingly, the NA is increased. Conversely, the thickness and NA of the protective substrate can be the same as the standard of a conventional optical disk such as a DVD. In this case, the physical recording density does not increase significantly, but the performance required as an optical system becomes relatively moderate.
[0011]
Specifically, the thickness of the protective substrate has been proposed to be 0.1 mm or thinner, or 0.6 mm which is the same as that of DVD.
The plurality of standards for such a “high-density optical disk” are, of course, the same in principle as CDs and DVDs, but if the thickness of the protective substrate is different, the size of the information recording hole will also be different. Even if a light source of the same wavelength is used, it is not possible to simply reproduce / record information using the same optical pickup device.
[0012]
In order to achieve "compatibility" of reproducing and recording information with respect to multiple standards of "high-density optical disc" using the same optical pickup device including the objective optical element, several problems were solved. There must be.
[0013]
(1) When trying to achieve “compatibility” between optical disc standards having the same wavelength and different protective substrate thicknesses / NAs (for example, when using a light source with a wavelength of 405 nm), spherical aberration (= Although spherical aberration (chromatic aberration corresponding to chromatic aberration) does not occur, occurrence of spherical aberration due to a difference in substrate thickness is inevitable, and it is necessary to eliminate this. For example, when the protective substrate thickness is set to 0.1 mm and when the protective substrate thickness is set to 0.6 mm, very remarkable spherical aberration occurs.
[0014]
(2) Since the NAs are different from each other, a “aperture” function for selectively using each NA according to the medium is required.
[0015]
[Problems to be solved by the invention]
Conventionally, as for "interchangeability" between different optical disks, a method of using a dichroic filter having wavelength selectivity and a method of providing wavelength selectivity by providing a diffractive structure in an objective optical element have been proposed and realized. In the case of "using the same wavelength" which is to be solved this time, a method depending on wavelength selectivity cannot be adopted.
[0016]
The inventors of the present application have found a method of solving the above-described problem and achieving compatibility by applying a conventionally known method of dividing an objective optical element into a special annular zone structure.
[0017]
It was found that this was not enough, the wavelength used was relatively short, and it was necessary to take measures to reduce the effects of temperature fluctuations and wavelength fluctuations caused by using a high-energy light source.
[0018]
In addition, since the optical pickup device itself is required to be reduced in size and weight, and particularly reduced in thickness, extremely strict performance is required for element parts, particularly optical elements.
[0019]
In particular, making the objective optical element have various optical functions is suitable for reducing the number of parts, reducing cost, and miniaturizing the optical element, but may not achieve optical performance.
[0020]
Accordingly, an object of the present invention is to provide a suitable objective optical element or optical pickup device that satisfies required performance and specifications.
[0021]
[Means for Solving the Problems]
(1) Light for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). In the objective optical element of the pickup device, the optical functional surface of the objective optical element is composed of at least three concentric regions centered on the optical axis, and each of the three concentric regions includes the optical axis. A first area used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first area used for the second optical information recording medium; A second area, a third area on the outer edge side with respect to the second area, used for the first optical information recording medium, and at least the third area has a temperature compensation for a light source used and / or Optical correction structure for chromatic aberration compensation Objective optical element of an optical pickup device characterized in that it has.
[0022]
(2) The objective optical element of the optical pickup device according to (1), wherein the wavelength of the light source used is 390 nm to 420 nm.
(3) The objective optical element of the optical pickup device according to (1) or (2), wherein NA of the first region and the second region is 0.58 to 0.68.
[0023]
(4) The objective optics of the optical pickup device according to any one of (1) to (3), wherein NA from the first region to the third region is 0.83 to 0.87. element.
[0024]
(5) The objective optical element of the optical pickup device according to any one of (1) to (4), wherein the t1 is 0.1 mm.
(6) The objective optical element of the optical pickup device according to any one of (1) to (5), wherein t2 is 0.6 mm.
[0025]
(7) Any of (1) to (6), wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. The objective optical element of the optical pickup device according to any one of the above.
[0026]
(8) The first region and / or the second region has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. 4. The objective optical element of the optical pickup device according to any one of the above.
[0027]
(9) An optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. An objective optical element of the optical pickup device described in the above.
[0028]
(10) The optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided on both sides of the optical function surface, according to any one of (1) to (8). Objective optical element of the optical pickup device.
[0029]
(11) Light for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). In the pickup device, the optical functional surface of the objective optical element included in the optical pickup device is composed of at least three concentric regions centered on the optical axis, and each of the three concentric regions includes the optical axis. A first area used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first area used for the second optical information recording medium. A second region to be used, a third region used for the first optical information recording medium on the outer edge side of the second region, and at least a temperature compensation for a light source used in the third region. // To perform chromatic aberration compensation The optical pickup apparatus characterized by having an optical compensation structure.
[0030]
(12) The optical pickup device according to (11), wherein the wavelength of the light source used is 390 nm to 420 nm.
(13) The optical pickup device according to (11) or (12), wherein the NA of the first region and the second region is 0.58 to 0.68.
[0031]
(14) The optical pickup device according to any one of (11) to (13), wherein the NA from the first region to the third region is 0.83 to 0.87.
[0032]
(15) The optical pickup device according to any one of (11) to (14), wherein the t1 is 0.1 mm.
(16) The optical pickup device according to any one of (11) to (15), wherein the t2 is 0.6 mm.
[0033]
(17) Any of (11) to (16), wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. The optical pickup device according to any one of the above.
[0034]
(18) Any one of (11) to (17), wherein the first region and / or the second region has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. An optical pickup device according to any one of the above.
[0035]
(19) In any one of the constitutions (11) to (18), an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. An optical pickup device as described in the above.
[0036]
(20) The optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided on both sides of an optical function surface, according to any one of (11) to (18). Optical pickup device.
[0037]
(21) Light for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). In the pickup device, the optical functional surface of the objective optical element included in the optical pickup device is composed of at least three concentric regions centered on the optical axis, and each of the three concentric regions includes the optical axis. A first area used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first area used for the second optical information recording medium. A second area to be used, a third area used on the first optical information recording medium on an outer edge side of the second area, and the objective optical element and an optical path in the optical pickup device. Is a correction optical element provided separately. An optical pickup device, wherein the optical element has an optical correction structure that performs temperature compensation and / or chromatic aberration compensation for a light source to be used for at least the light beam incident on the third region of the objective optical element. .
[0038]
(22) The optical pickup device according to (21), wherein the wavelength of the light source used is 390 nm to 420 nm.
(23) The optical pickup device according to (21) or (22), wherein the NA of the first region and the second region is 0.58 to 0.68.
[0039]
(24) The optical pickup device according to any one of (21) to (23), wherein the NA from the first region to the third region is 0.83 to 0.87.
[0040]
(25) The optical pickup device according to any one of (21) to (24), wherein the t1 is 0.1 mm.
(26) The optical pickup device according to any one of (21) to (25), wherein the t2 is 0.6 mm.
[0041]
(27) Any of (21) to (26), wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. The optical pickup device according to any one of the above.
[0042]
(28) Any one of (21) to (27), wherein the first region and / or the second region has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. An optical pickup device according to any one of the above.
[0043]
(29) In any one of the constitutions (21) to (28), an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. An optical pickup device as described in the above.
[0044]
(30) The optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided on both sides of an optical function surface, according to any one of (21) to (28). Optical pickup device.
[0045]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the contents of the present invention will be described in detail with reference to the drawings, but embodiments of the present invention are not limited thereto.
[0046]
(First Embodiment)
In this embodiment, the target is a "high-density optical disk" using a so-called blue-violet laser light source having a wavelength of 405 nm. It is also assumed that the first optical information recording medium has a protective substrate thickness t1 of 0.1 mm and the second optical information recording medium has a protective substrate thickness t2 of 0.6 mm.
[0047]
FIG. 1 is a diagram showing an objective optical element (objective lens) of the optical pickup device according to the present invention. This is formed of a plastic resin, but may be formed of a glass mold.
[0048]
S1 is the optical function surface on the light source side, and S2 is the optical function surface on the optical disk side.
S1 is divided into three optical function areas centered on the optical axis, 1 is a first area, 2 is a second area, and 3 is a third area.
[0049]
Each has a different aspherical shape, and has a discontinuous step between the first region and the second region (boundary) and between the second region and the third region (boundary). .
The NA of the first region and the second region is 0.65, while the NA of the first to third regions is 0.85.
[0050]
For each surface, the first area is used for both the first optical information recording medium and the second optical information recording medium, the second area is used only for the second optical information recording medium, and the third area is used for the third optical information recording medium. It is designed to be used only for one optical information recording medium.
[0051]
FIG. 2 is a longitudinal spherical aberration diagram showing this state. The left side shows the case of the first optical information recording medium, and the right side shows the case of the second optical information recording medium.
In the case of the first optical information recording medium, although the portion corresponding to the second area is not stigmatized, it can be generally regarded as stigmatized, which is in a practical range. In the case of the second optical information recording medium, although the aberration at the portion corresponding to the first region is large, the aberration at the portion corresponding to the second region is small, which is also in a practically usable range as a whole. ing. In any case, the configuration is such that the aberration is reduced in the peripheral region.
[0052]
In this example, the area is divided into three areas so as to correspond to two different standards. However, the area can be divided into more ring zones as needed.
The third area has a diffraction structure. It has a blazed wavelength that is optimized to provide temperature and / or chromatic aberration compensation for the light source used.
[0053]
For this reason, it is possible to avoid a situation in which the focal length fluctuates due to a high temperature of the light source and a long wavelength, or a decrease in the refractive index of the glass material forming the objective lens.
[0054]
Here, the temperature compensation and / or the chromatic aberration compensation are achieved by the diffraction structure, but this can be achieved by another optical correction structure, for example, a phase difference providing structure (also referred to as a phase shift structure, NPS). .
[0055]
Further, in this example, a diffraction structure for performing temperature compensation and / or chromatic aberration compensation is provided only in the third region of the S1 surface, but it may be provided in another region.
In particular, for each standard, it is important to keep the aberration on the peripheral side small, but in order to improve the converging spot on the second information recording medium, temperature compensation and / or chromatic aberration compensation are performed on the second area. It is preferable to provide an optical correction structure. In addition, in order to contribute to an increase in the overall amount of light, it is also preferable to provide an optical correction structure in the first area used for optical discs of both standards.
[0056]
In this example, the optical correction structure is provided only on the S1 surface, but such a correction structure may be provided on the S2 surface. Here, a diffractive structure is used as the optical correction structure. However, in consideration of the degree of freedom of design and the transferability during actual molding, a diffractive structure may be preferable, In some cases, a shift structure is preferred. Furthermore, it may be preferable to provide separate optical correction structures on the S1 surface and the S2 surface rather than performing temperature compensation and chromatic aberration compensation using only a single structure.
[0057]
Therefore, in the present invention, the optical correction structure may be provided on either the S1 surface or the S2 surface, or may be provided on both surfaces.
With this configuration, it is possible to achieve “compatibility” between standards having different protective substrate thicknesses using the same wavelength.
[0058]
(Second embodiment)
In this embodiment, a correction optical element is provided in the optical path between the light source and the objective lens in the optical pickup device, and this element is provided with an optical correction structure for performing temperature compensation and / or chromatic aberration compensation.
[0059]
For this reason, the optical action and the effect obtained are the same as those of the first embodiment, but have the advantage that the load on the design and manufacture of the objective lens is reduced.
[0060]
【The invention's effect】
As described above, according to the design method according to the present invention, a plurality of format compatible optical pickup devices can be achieved by using light sources of the same wavelength.
[Brief description of the drawings]
FIG. 1 is a view showing an objective lens having a diffractive structure in a third region according to the present invention.
FIG. 2 is a diagram showing a longitudinal spherical aberration diagram relating to a first optical information recording medium and a longitudinal spherical aberration diagram relating to a second optical information recording medium according to the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st area | region 2 2nd area | region 3 3rd area | region S1 Optical function surface S2 at the light source side Optical function surface at the optical disk side

Claims (30)

An optical pickup device for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). In the objective optical element,
The optical functional surface of the objective optical element is composed of at least three concentric regions centered on the optical axis,
Each of the three concentric regions includes an optical axis, and is a first region used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first region. A second area used for the second optical information recording medium, an outer edge side of the second area, and a third area used for the first optical information recording medium,
An objective optical element of an optical pickup device, characterized in that at least the third region has an optical correction structure for performing temperature compensation and / or chromatic aberration compensation for a light source to be used. The objective optical element of the optical pickup device according to claim 1, wherein the wavelength of the light source used is 390 nm to 420 nm. The objective optical element of the optical pickup device according to claim 1, wherein NA of the first area and the second area is 0.58 to 0.68. 4. The objective optical element of the optical pickup device according to claim 1, wherein NA of the first region to the third region is 0.83 to 0.87. 5. The objective optical element of the optical pickup device according to claim 1, wherein the t1 is 0.1 mm. The objective optical element of the optical pickup device according to any one of claims 1 to 5, wherein the t2 is 0.6 mm. 7. The device according to claim 1, wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. 8. Objective optical element of the optical pickup device. The light according to any one of claims 1 to 7, wherein the first area and / or the second area has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. Objective optical element of the pickup device. 9. The optical pickup device according to claim 1, wherein an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. Objective optical element. 9. The optical pickup device according to claim 1, wherein optical compensation structures for performing the temperature compensation and / or the chromatic aberration compensation are provided on both sides of the optical function surface. Objective optical element. An optical pickup device for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). ,
The optical functional surface of the objective optical element included in the optical pickup device is composed of at least three concentric regions centered on the optical axis,
Each of the three concentric regions includes an optical axis, and is a first region used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first region. A second area used for the second optical information recording medium, an outer edge side of the second area, and a third area used for the first optical information recording medium,
An optical pickup device having an optical correction structure for performing temperature compensation and / or chromatic aberration compensation on a light source to be used at least in the third region. The optical pickup device according to claim 11, wherein the wavelength of the light source used is 390 nm to 420 nm. 13. The optical pickup device according to claim 11, wherein NA of the first region and the second region is 0.58 to 0.68. 14. The optical pickup device according to claim 11, wherein an NA of the first region to the third region is 0.83 to 0.87. 15. The optical pickup device according to any one of claims 11 to 14, wherein the t1 is 0.1 mm. 16. The optical pickup device according to claim 11, wherein the t2 is 0.6 mm. 17. The device according to claim 11, wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. Optical pickup device. 18. The light according to claim 11, wherein the first region and / or the second region has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. Pickup device. 19. The optical pickup device according to claim 11, wherein an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. . 19. The optical pickup device according to claim 11, wherein optical compensation structures for performing the temperature compensation and / or the chromatic aberration compensation are provided on both sides of the optical function surface. An optical pickup device for reproducing / recording information on both the first optical information recording medium having a protective substrate thickness of t1 and the second optical information recording medium having a protective substrate thickness of t2 (t1 <t2). ,
The optical functional surface of the objective optical element included in the optical pickup device is composed of at least three concentric regions centered on the optical axis,
Each of the three concentric regions includes an optical axis, and is a first region used for both the first optical information recording medium and the second optical information recording medium, and an outer edge side of the first region. A second area used for the second optical information recording medium, an outer edge side of the second area, and a third area used for the first optical information recording medium,
A correction optical element provided separately from the objective optical element in an optical path in the optical pickup device, wherein the optical element is used for a light beam incident on at least the third region of the objective optical element; An optical pickup device comprising: an optical correction structure for performing temperature compensation and / or chromatic aberration compensation for a light source that emits light. 22. The optical pickup device according to claim 21, wherein the wavelength of the light source used is 390 nm to 420 nm. 23. The optical pickup device according to claim 21, wherein NA of the first region and the second region is 0.58 to 0.68. The optical pickup device according to any one of claims 21 to 23, wherein an NA of the first region to the third region is 0.83 to 0.87. The optical pickup device according to any one of claims 21 to 24, wherein the t1 is 0.1 mm. 26. The optical pickup device according to claim 21, wherein the t2 is 0.6 mm. 27. The device according to claim 21, wherein a discontinuous step is formed between the first region and the second region and between the second region and the third region. Optical pickup device. The light according to any one of claims 21 to 27, wherein the first region and / or the second region has an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation. Pickup device. The optical pickup device according to any one of claims 21 to 28, wherein an optical correction structure for performing the temperature compensation and / or the chromatic aberration compensation is provided only on one surface of the optical function surface. . The optical pickup device according to any one of claims 21 to 28, wherein optical correction structures for performing the temperature compensation and / or the chromatic aberration compensation are provided on both sides of an optical function surface.

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