JP2007294033A - Optical pickup and optical information processing apparatus - Google Patents

Abstract

Kind Code: A1 A favorable spot is formed on the recording surfaces of four types of optical recording media having a plurality of light sources according to operating wavelengths and having different substrate thicknesses with a single objective lens.
A central region 502a corresponds to NA 0.45 of a CD system 137 of an optical recording medium, and a first light beam is divided into one that transmits and diffracts, second and third light beams are diffracted, and HD, DVD , CD aberration is corrected. The second region 502b corresponds to NA 0.45 to 0.65 of the CD system to HD and DVD systems 117 and 127, and divides the first light beam into one that transmits and diffracts the second light beam. The light beam 3 is not condensed on the CD system. The third region 502c is a flat portion corresponding to NA 0.65 to 0.85 of the BD system 107 from the HD and DVD systems, transmits the first to third light beams, and the BD system condenses with the objective lens 106. Don't focus on HD, DVD, CD. The diffractive surface 502 corrects aberrations for the HD, DVD, and CD systems, and switches the aperture to form a spot.
[Selection] Figure 2

Description

  The present invention relates to an optical pickup used in an optical information processing apparatus, and in particular, records information on a plurality of types of optical recording media having different recording densities due to different wavelengths of light sources or transparent substrate thicknesses of optical recording media. , And an optical information processing apparatus having compatibility when reproducing.

  As means for storing video information, audio information, or data on a computer, optical recording media such as a CD with a recording capacity of 0.65 GB and a DVD with a recording capacity of 4.7 GB are becoming widespread. In recent years, there has been an increasing demand for further improvement in recording density and increase in capacity.

  As means for improving the recording density of such an optical recording medium, in an optical pickup for writing or reading information on the optical recording medium, the numerical aperture (hereinafter referred to as NA) of an objective lens is increased, or a light source It is effective to reduce the diameter of the beam spot that is collected by the objective lens and formed on the optical recording medium by shortening the wavelength of the light beam.

  Therefore, for example, in the “CD optical recording medium”, the NA of the objective lens is 0.50 and the wavelength of the light source is 780 nm, whereas the recording density is higher than that of the “CD optical recording medium”. In the “DVD optical recording medium”, the NA of the objective lens is 0.65 and the wavelength of the light source is 660 nm. As described above, the optical recording medium is desired to further improve the recording density and increase the capacity. For this purpose, the NA of the objective lens is set to be larger than 0.65 or the wavelength of the light source is increased. It is desired to make it shorter than 660 nm.

  As such a large-capacity optical recording medium and an optical information processing apparatus, two standards as described in Patent Document 1 have been proposed. One is a “Blu-ray Disc” standard (hereinafter referred to as BD) that uses a blue wavelength region light source and an NA 0.85 objective lens to satisfy 22 GB equivalent capacity. The other is the “HD-DVD” standard (hereinafter referred to as “HD”) that satisfies the same capacity of 20 GB using an objective lens with NA of 0.66, although the blue wavelength is the same.

  The former increases the capacity by shortening the wavelength and increasing the NA, compared to the DVD system, and the latter allows the linear recording density to be improved by improving signal processing instead of increasing the NA. The capacity has been increased by adopting.

  BD and HD are common in that a blue-violet semiconductor laser light source having an oscillation wavelength of about 405 nm is used, but the optical recording media have substrate thicknesses different from 0.1 mm and 0.6 mm, respectively.

  Even for optical pickups that can record and / or reproduce high-density information such as BD and HD, it is necessary to ensure the recording and / or reproduction of information even for CDs and DVDs that have been supplied in large quantities. There is. Furthermore, when the BD and HD standards are spread simultaneously, it is desirable to integrate the BD, HD, DVD, and CD optical systems.

  Then, a light source having an appropriate wavelength is selected according to the type of optical recording medium to be recorded and reproduced, and an appropriate optical process is performed on the selected light flux, and the difference in the substrate thickness of each optical recording medium It is desirable to correct the spherical aberration caused by.

  Then, a light source having an appropriate wavelength is selected according to the type of optical recording medium to be recorded and reproduced, and an appropriate optical process is performed on the selected light flux, and the difference in the substrate thickness of each optical recording medium It is desirable to correct the spherical aberration caused by.

As a method for recording or reproducing four different optical recording media using one optical pickup, a means using two objective lenses has been proposed (see Patent Document 2).
JP 2005-339718 A JP 2005-209299 A

  However, since the means of Patent Document 2 uses two objective lenses, the number of parts increases, and it is not suitable for downsizing and cost reduction. Furthermore, since it is necessary to move the objective lens in accordance with the optical recording medium, there is a problem that the mechanism of the actuator becomes complicated and it takes time to access information.

  In a compatible optical pickup that records and reproduces four types of optical recording media, it is desirable to achieve a common optical system including an objective lens in order to reduce the size and cost.

  The present invention is directed to solving the above-mentioned problems of the prior art, and includes four types of optical recordings having different substrate thicknesses with a single objective lens while having a plurality of light sources according to the wavelength used. It is an object of the present invention to provide an optical pickup and an optical information processing apparatus that converge a light beam with a necessary numerical aperture (NA) on a recording surface of a medium.

  In order to achieve the above object, the optical pickup according to claim 1 of the present invention is an optical pickup that performs one or more of recording, reproduction, and erasing on a plurality of types of optical recording media having different recording densities. As the first, second, third, and fourth optical recording media in descending order of the recording density of the optical recording medium, a first light beam having a first wavelength λ1 corresponding to the first and second optical recording media is used. A first light source that emits light, a second light source that emits a second light beam having a second wavelength λ2 corresponding to the third optical recording medium, and a third wavelength corresponding to the fourth optical recording medium a third light source that emits a third light beam having λ3, a single objective lens that focuses the first to third light beams on the recording surfaces of the first to fourth optical recording media, and an objective lens And aberration correction means provided between the first to third light sources, and the first, second and third light sources. With respect to four types of optical recording media, the wavelength is in the relationship of λ1 <λ2 <λ3, and the aberration correcting means is provided with a diffractive surface having a diffractive structure whose concentric shape is a concentric cross section. It is possible to correct the generated aberrations on the same plane.

  The optical pickup according to claims 2 and 3 is the optical pickup according to claim 1, wherein the diffractive surface is divided into at least three or more concentric regions within the effective beam diameter through which the light beam passes. By forming the diffractive structure in at least two regions and forming the diffractive structure in two regions in order from the center side among the regions divided on the diffraction surface, four types of optical recording media can be used. Thus, the aberration can be corrected and the aperture can be switched over the entire diffractive surface, and the aberration correction and the aperture limitation can be configured with a single element.

  An optical pickup according to a fourth aspect is the optical pickup according to the first, second, or third aspect, wherein each of the diffractive structures formed in two regions among the regions divided on the diffractive surface has an uneven shape. By changing the groove depth, the switching of the aperture can be shared with the aberration correcting means for the four types of optical recording media.

  An optical pickup according to a fifth aspect is the optical pickup according to any one of the first to fourth aspects, wherein the diffractive structure formed in the central region among the regions divided on the diffractive surface has a wavelength. For a light beam with λ1, a 0th-order diffracted light beam that is transmitted without being diffracted and a diffracted diffracted light beam are emitted. By diffracting diffracted light, the aberration can be satisfactorily corrected with respect to four types of optical recording media over the entire diffraction surface.

The optical pickup according to claim 6 is the optical pickup according to any one of claims 1 to 5, wherein a diffractive structure formed in a central region among regions divided on the diffractive surface is: When the orders of diffracted light used in the second, third, and fourth optical recording media are N11, N12, and N13, respectively, the following condition is satisfied: | N12 | <| N11 | <| N13 |
Aberrations can be satisfactorily corrected with respect to four types of optical recording media with a single diffractive surface, and wavefront deterioration due to axial misalignment caused by the movement of the objective lens can be reduced.

  The optical pickup according to claim 7 is the optical pickup according to any one of claims 1 to 6, wherein the diffraction formed in the second region from the center among the regions divided on the diffraction surface. The structure is such that when the orders of diffracted light used in the second and third optical recording media are N21 and N22, respectively, the following condition is satisfied: | N22 | <| N21 | On the other hand, the aberration can be satisfactorily corrected and the aperture can be switched over the entire diffractive surface, and the wavefront deterioration due to the axis deviation when the objective lens is moved can be reduced because the infinite system light beam can be used.

  An optical pickup according to an eighth aspect is the optical pickup according to any one of the first to fifth aspects, wherein the diffractive structure formed in the central region among the regions divided on the diffractive surface is When the orders of diffracted light used in the second, third, and fourth optical recording media are N11, N12, and N13, respectively, the following condition is satisfied: | N12 | ≦ | N11 | <| N13 | Aberrations can be satisfactorily corrected with a single diffractive surface for various types of optical recording media.

  An optical pickup according to a ninth aspect is the optical pickup according to any one of the first to fifth and eighth aspects, wherein the optical pickup is formed in the second region from the center among the regions divided on the diffraction surface. In the diffractive structure, when the orders of the diffracted light most strongly generated by the first and second light beams are N21 and N22, respectively, the following condition is satisfied: | N21 | ≦ | N22 | Aberration can be satisfactorily corrected and the aperture can be switched over the entire diffractive surface with respect to the optical recording medium.

  An optical pickup according to a tenth aspect is the optical pickup according to any one of the first to seventh aspects, wherein all of the light beams having the wavelengths λ1, λ2, and λ3 are parallel light on the diffraction surface. , Even if the objective lens and the diffractive surface are decentered, a spot where no coma aberration occurs can be formed.

  An optical pickup according to an eleventh aspect is the optical pickup according to any one of the first to ninth aspects, wherein the light beams incident on the diffraction surface are first, second, third, and fourth. With respect to at least one of the optical recording media, the finite system allows a greater degree of freedom in designing the diffractive surface, corrects aberrations favorably, and reduces the decrease in diffraction efficiency.

  An optical pickup according to claim 12 is the optical pickup according to any one of claims 1 to 11, wherein the orders N11, N12, N13 and the orders N21, N22 in the diffracted light of the diffraction structure are By reversing the sign of the order, the aberration can be corrected satisfactorily and the aperture can be switched over the diffractive surface with respect to four types of optical recording media.

  An optical pickup according to a thirteenth aspect is the optical pickup according to any one of the first to twelfth aspects, wherein a central region and a second region from the center are divided among regions divided on the diffraction surface. The formed diffractive structure is formed by repeating the staircase shape, and the inclination direction of each staircase shape is reversed between the central region and the second region from the center, thereby diffracting four types of optical recording media. Aberrations can be corrected satisfactorily and the aperture can be switched.

  An optical pickup according to a fourteenth aspect is the optical pickup according to any one of the first to thirteenth aspects, wherein the diffractive structure formed in the central region among the regions divided on the diffractive surface is a staircase. Repetitive shapes are formed, and each staircase shape is formed so that the groove depth in the optical axis direction decreases from the center of the optical axis toward the outer side. On one side, aberrations can be corrected well and the aperture can be switched.

  The optical pickup according to claim 15 is the optical pickup according to any one of claims 1 to 14, wherein the diffraction formed in the second region from the center among the regions divided on the diffraction surface. The structure is formed by repeating staircase shapes, and each staircase shape is formed so that the groove depth in the optical axis direction increases from the center of the optical axis to the outside. Thus, the aberration can be corrected satisfactorily and the aperture can be switched over the entire diffractive surface.

  An optical pickup according to claim 16 is the optical pickup according to any one of claims 1 to 14, wherein the pitch of the diffractive structure formed on the diffractive surface is a single objective lens. By forming the diffractive structure so as to cancel the spherical aberration that occurs when passing through the substrates of the second, third, and fourth optical recording media, the diffraction surface can be completely aligned with respect to the four types of optical recording media. The aberration can be corrected well.

  The optical pickup according to claim 17 is the optical pickup according to any one of claims 1 to 7 and 10 to 16, wherein the diffractive structure of the diffractive surface has a step shape, and the number of steps M is set to “3”. Therefore, it is possible to satisfactorily correct the aberration with respect to the four types of optical recording media over the entire diffractive surface.

  An optical pickup according to claim 18 is the optical pickup according to any one of claims 1 to 17, wherein the diffraction formed in the second region from the center among the regions divided on the diffraction surface. Since the structure is stepped and the groove depth is lower than that of the central region, the aberration can be corrected satisfactorily and the aperture can be switched over the entire diffractive surface, and the efficiency reduction in the peripheral region can be suppressed.

  The optical pickup according to claim 19 is the optical pickup according to any one of claims 1 to 18, wherein the third region from the center among the regions divided on the diffraction surface is defined as a flat portion. As a result, the opening can be switched with high efficiency.

  An optical pickup according to a twentieth aspect is the optical pickup according to any one of the first to twentieth aspects, wherein an optical axis direction is arranged in a third region from the center among regions divided on the diffraction surface. By forming the steps having different thicknesses, the aberration can be corrected well and the aperture can be switched over the entire diffractive surface, and chromatic aberration due to wavelength fluctuation can be corrected.

  An optical pickup according to a twenty-first aspect is the optical pickup according to any one of the first to twentieth aspects, wherein the objective lens is a first optical recording medium having the largest recording density. By designing the aberration to be minimized by the light beam having the wavelength λ1, zero-order diffracted light can be used for one of the four types of optical recording media, and aberration correction on the entire diffractive surface can be performed with high efficiency. be able to.

  An optical pickup according to a twenty-second aspect is the optical pickup according to any one of the first to twenty-first aspects, wherein a diffraction structure of a diffractive surface is formed on the surface of the objective lens, thereby assembling accuracy. Can be relaxed and the number of parts can be reduced.

  An optical pickup according to a twenty-third aspect is the optical pickup according to any one of the first to twenty-first aspects, wherein the wave plate is disposed on a surface opposite to the diffraction surface of the aberration correcting means provided with the diffraction surface. By forming, the number of parts can be reduced.

  An optical pickup according to a twenty-fourth aspect is the optical pickup according to any one of the first to twenty-third aspects, wherein a divergence angle is formed on a surface opposite to the diffraction surface of the aberration correcting means provided with the diffraction surface. By forming the conversion element, at least one type of divergent light can be incident on the diffraction surface for four types of optical recording media, the design conditions of the diffraction surface can be relaxed, aberration can be corrected well, and diffraction efficiency can be improved. Reduction can be reduced.

  An optical pickup according to claim 25 is the optical pickup according to any one of claims 1 to 24, wherein a beam expander is provided in the optical path of the objective lens from the light source, so that four types of optical pickups are provided. At least one kind of divergent light can be incident on the diffractive surface with respect to the optical recording medium, the design conditions of the diffractive surface can be relaxed, aberrations can be corrected well, and reduction in diffraction efficiency can be reduced.

  An optical pickup according to a twenty-sixth aspect is the optical pickup according to any one of the first to twenty-fourth aspects, wherein the diffractive surface can be easily formed by configuring the diffractive surface of the diffractive surface from a resin material. The load on the movable part of the objective lens can be reduced by reducing the weight.

  An optical pickup according to a twenty-seventh aspect is the optical pickup according to any one of the first to twenty-fourth and twenty-sixth aspects, wherein the outer shape of the aberration correcting means having a diffractive surface is a circle concentric with the diffractive surface. By adopting the shape, it is possible to realize a stable element that does not change its shape even when the environmental humidity varies.

  An optical information processing apparatus according to a twenty-eighth aspect is an optical information processing apparatus that performs one or more of recording, reproduction, and erasing with respect to a plurality of types of optical recording media having different recording densities. By providing the optical pickup according to any one of the above, the generated aberrations can be corrected for four types of optical recording media, and a reduction in efficiency can be suppressed.

  According to the present invention, while providing a plurality of light sources according to the wavelength used, a single objective lens can condense well on the recording surfaces of four types of optical recording media having different substrate thicknesses and recording densities, and stable recording. Therefore, it is possible to realize a high-precision optical pickup and optical information processing apparatus that can perform a reproduction operation and can be reduced in size, cost, and efficiency.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an optical pickup according to Embodiment 1 of the present invention. As shown in FIG. 1, four types of optical recording media (BD system, HD system, DVD system, CD system) are recorded or reproduced with different effective pupil radii using a single objective lens 106 using different light source wavelengths. Is a compatible optical pickup.

  The substrate thicknesses of the BD, HD, DVD, and CD optical recording media 107, 117, 127, and 137 are 0.1 mm, 0.6 mm, 0.6 mm, and 1.2 mm, respectively. , DVD and CD optical recording media. The numerical apertures are NA0.85, NA0.65, NA0.65, NA0.45, respectively, and the wavelengths λ1, λ2, and λ3 of the first, second, and third light sources are 405 nm, 660 nm, and 785 nm, respectively. is there.

  The optical pickup shown in FIG. 1 has a semiconductor laser 101, a collimating lens 102, a prism 104, a quarter-wave plate 105, an objective lens 106, a polarizing beam splitter with respect to the BD optical recording medium 107 and the HD optical recording medium 117. 103, a detection lens 108, a light receiving element 110, and an aberration correction unit 501. The center wavelength of the semiconductor laser 101 as the first light source is 405 nm, and the numerical aperture (NA) of the objective lens 106 is 0.85. The numerical aperture (NA) of the objective lens 106 with respect to the HD optical recording medium 117 is 0.65, and switching of the NA is limited by the aberration correction unit 501. The substrate thickness of the BD optical recording medium 107 is 0.1 mm, and the substrate thickness of the HD optical recording medium 117 is 0.6 mm.

  The light emitted from the semiconductor laser 101 is made into substantially parallel light by the collimator lens 102. The light that has passed through the collimating lens 102 enters the polarization beam splitter 103 and is deflected by the prism 104. Information is recorded and reproduced by being condensed through the quarter-wave plate 105, the aberration correction means 501, and the objective lens 106. The reflected light from the BD optical recording medium 107 passes through the objective lens 106 and the quarter-wave plate 105, is separated from the incident light by the polarization beam splitter 103, is deflected, and is guided onto the light receiving element 110 by the detection lens 108. Thus, a reproduction signal, a focus error signal, and a track error signal are detected.

  Further, light emitted from the semiconductor laser 130 a having a center wavelength of 660 nm with respect to the DVD optical recording medium 127 is deflected by the prism 104 through the divergence angle conversion lens 132 and the wavelength selective beam splitter 133. Then, the light is condensed on the DVD optical recording medium 127 through the quarter-wave plate 105, the aberration correction unit 501, and the objective lens 106. The substrate thickness of the DVD optical recording medium 127 is 0.6 mm, and the NA of the objective lens 106 is 0.65. The switching of NA is limited by the aberration correction unit 501. The reflected light from the DVD optical recording medium 127 passes through the objective lens 106 and the quarter-wave plate 105, and is then deflected by the wavelength selective beam splitter 133, separated from the incident light by the hologram element 130b, and separated on the light receiving element 130c. Thus, a reproduction signal, a focus error signal, and a track error signal are detected.

  Further, light emitted from the semiconductor laser 140 a having a central wavelength of 785 nm with respect to the CD optical recording medium 137 is deflected by the prism 104 through the divergence angle conversion lens 142 and the wavelength selective beam splitter 143. Then, the light is condensed on the CD optical recording medium 137 through the quarter-wave plate 105, the aberration correction unit 501, and the objective lens 106. The substrate thickness of the CD optical recording medium 137 is 1.2 mm, and the NA of the objective lens is 0.45. The switching of NA is limited by the aberration correction unit 501. Reflected light from the CD-type optical recording medium 137 passes through the objective lens 106 and the quarter-wave plate 105, and is then deflected by the wavelength selective beam splitter 143, separated from incident light by the hologram element 140b, and separated on the light receiving element 140c. Thus, a reproduction signal, a focus error signal, and a track error signal are detected.

  Here, the objective lens 106 is optimally designed so that a BD optical recording medium 107 having a thickness of 0.1 mm can be recorded and reproduced with high accuracy. The design wavelength is 405 nm, and the wavefront aberration is designed to be sufficiently small at 0.01 λrms or less at 405 nm. The objective lens 106 according to the first embodiment is optimally designed for the BD optical recording medium 107 having a thickness of 0.1 mm, but is not limited thereto. For example, in a two-layer BD optical recording medium having two information recording surfaces, the information recording surface is located at positions 0.075 mm and 0.1 mm from the light incident side. It may be optimally designed for different substrate thicknesses so that 0875 mm is the design median value.

  In the first embodiment, the objective lens 106 has a double-sided aspherical shape, and r is a paraxial radius of curvature in an orthogonal coordinate system in which the vertex of the surface is the origin and the optical axis direction from the light source to the optical recording medium is the X axis. When κ is the number of cones and A, B, C, D, E, F, G, H, J,... are aspherical coefficients, the relationship between the distance x in the optical axis direction of the surface and the radius R The aspherical shape is (Equation 1)

で表される。各面および各領域の面データを（表１）に示す。

It is represented by The surface data of each surface and each region is shown in (Table 1).

ここで、ガラスの硝材は住田光学製のＫＶＣ８１、対物レンズの有効瞳半径は２.１５ｍｍである。なお、対物レンズ１０６の材料としては、ガラスに限らず、樹脂を用いても良い。

Here, the glass material of glass is KVC81 manufactured by Sumita Optical Co., Ltd., and the effective pupil radius of the objective lens is 2.15 mm. The material of the objective lens 106 is not limited to glass, and a resin may be used.

  2 to 4 are diagrams for explaining the aberration correcting means 501, FIGS. 2 and 3 are enlarged sectional views, and FIG. 4 is a view showing each diffraction surface.

  The aberration correction unit 501 has a spherical aberration that occurs when the light emitted from the semiconductor laser 101 with a wavelength of 405 nm is generated by the objective lens 106 due to the difference in the substrate thickness with respect to the HD optical recording medium 117 and the DVD optical recording medium 127. Thus, the light emitted from the semiconductor laser 130a having the center wavelength of 660 nm and the light emitted from the semiconductor laser 140a having the center wavelength of 780 nm with respect to the CD optical recording medium 137 are different in the substrate thickness and in the wavelength. This is a compatible element for correcting the spherical aberration generated by the above. Further, the aberration correction unit 501 has an aperture limiting function for switching the aperture of the objective lens 106 for each optical recording medium.

  FIG. 2 is a cross-sectional view schematically showing the configuration of the aberration correction unit 501 and the objective lens 106 according to the first embodiment. As shown in FIG. 2, the aberration correction unit 501 and the objective lens 106 are coaxially integrated by a lens barrel 121. Specifically, the aberration correcting means 501 is fixed to one end of the cylindrical barrel 121, the objective lens 106 is fixed to the other end, and these are coaxially integrated along the optical axis. Yes. The objective lens 106 has a lens surface that has a convex shape mainly inside the lens barrel 121.

  Now, when recording and reproducing the BD, HD, DVD, and CD optical recording media 107, 117, 127, and 137, the objective lens 106 is ± 0. Move within a range of about 5 mm. However, since the HD, DVD, and CD optical recording media 117, 127, and 137 are diffracted by the aberration correction unit 501, the aberration correction unit 501 does not move and only the objective lens 106 moves. Aberrations occur and the focused spot deteriorates.

  Therefore, the aberration correcting means 501 and the objective lens 106 are integrated and moved together during tracking control, thereby obtaining a good condensing spot. Note that at least one of the aberration correction unit 501 and the objective lens 106 may be provided with a flange and directly integrated via the flange. Further, the objective lens 106 and the lens barrel 121, and further, the objective lens 106, the lens barrel 121, and the aberration correction unit 501 may be integrated.

  In the first embodiment, the first, second, and third light beams are all incident on the aberration correction unit 501 as parallel light. That is, since it is not divergent light or convergent light, even when the objective lens 106 and the aberration correction unit 501 integrated by tracking control are decentered during recording / reproduction of each optical recording medium, there is an advantage that coma aberration does not occur. is there. Note that the light may be incident as diverging light or convergent light. For example, in the first embodiment, when the divergent light is incident on the diffraction surface 502 only to the DVD optical recording medium 127, the aberration can be corrected with higher accuracy.

  FIG. 3 shows a cross-sectional view of the aberration correction unit 501 of the first embodiment. The aberration correction unit 501 has a diffractive surface 502 on which a diffractive structure is formed. The diffractive surface as used herein is a surface on which a diffractive structure having an uneven cross-sectional shape is formed. It is only necessary that the diffractive structure is formed on a part of the flat plate surface or the curved surface, and there may be a region where the diffractive structure is not formed.

  Resin is used as the material of the aberration correction means 501. Resin is lighter than glass and easy to mold, so mass production is easy. Since the aberration correction unit 501 of the first embodiment is mounted on the movable portion 120 of the objective lens 106 and is driven integrally with the objective lens 106, it is desirable that the aberration correction unit 501 be light. For example, PMMA (polymethyl methacrylate) is used as the resin. PMMA is one of the most widely used resins for optical parts because it has high transparency and weather resistance, and particularly has strengths suitable for injection molding. Further, ZEONEX (ZEONEX: registered trademark), which is an optical resin manufactured by Nippon Zeon Co., Ltd., which has low moisture absorption may be used. Furthermore, the material of the aberration correction unit 501 can be applied to any optical resin and optical glass including ultraviolet curable resin.

  As shown in FIG. 4, the first diffractive surface 502 has three regions concentrically divided within a range through which the light beam passes, a first central region 502a, and a second region from the second center. 502b has a third region 502c from the center which is the third outermost periphery.

  The center area 502a corresponds to an area of NA 0.45 with respect to the CD optical recording medium 137, and is set to a radius of 1.25 mm in the first embodiment. The central region 502a has a diffractive structure so that the first light beam having a wavelength of 405 nm is transmitted and diffracted as it is, and the second and third light beams having wavelengths of 660 nm and 785 nm are diffracted. Is formed. The diffractive structure is formed so as to correct the spherical aberration caused by the difference in substrate thickness and the difference in wavelength between the HD, DVD, and CD optical recording media 117, 127, and 137.

  The second area 502b corresponds to an area of NA 0.65 for the HD and DVD optical recording media 117 and 127 from the area of NA 0.45 for the CD optical recording medium 137. In the first embodiment, the radius is 1.25 mm. To 1.715 mm. In the second region 502b, the third light beam having a wavelength of 785 nm is diffracted so that the second light beam having a wavelength of 660 nm is diffracted so that the first light beam having a wavelength of 405 nm is transmitted as it is and diffracted. Is formed with a diffractive structure so as not to be focused on the recording surface of the CD optical recording medium 137.

  The third region 502c corresponds to a region from NA 0.65 to HD type and DVD type optical recording media 117 and 127 to NA 0.85 to BD type optical recording medium 107. In the first embodiment, the radius is from 1.715 mm to 2 Set to 15 mm. The third region 502c is a flat portion where a diffractive structure is not formed, and passes through the first, second, and third light beams as they are, so that the BD optical recording medium 107 is condensed by the objective lens 106, The HD, DVD, and CD optical recording media 117, 127, and 137 are not condensed.

  Accordingly, the diffractive surface 502 is configured to correct the generated aberration and switch the aperture with respect to the HD system, DVD system, and CD system optical recording media 117, 127, and 137. Can form a good spot.

  The aberration correction unit 501 corrects the aberration by diffracting the light beam incident as parallel light in the diverging direction. That is, the correction is made by making the aberration generated when diverging light enters the objective lens 106 and the aberration generated due to the difference in the substrate thickness and wavelength to be opposite in polarity. When diverging light is incident on the objective lens 106, the working distance, which is the distance between the objective lens 106 and the optical recording medium, is widened. Therefore, it is convenient to focus the light on a thick substrate with the high NA objective lens 106. It will be a good configuration.

  Further, the cross section of the central region 502a of the aberration correction means 501 is composed of a plurality of annular concavo-convex portions formed concentrically as shown in FIG. Each ring-shaped uneven portion has a step shape and has three steps. Here, the number of stages is counted including the lowest stage. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

  The pitch of the ring-shaped concavo-convex portions is -2nd order diffracted light for the HD optical recording medium 117, -first order diffracted light for the DVD optical recording medium 127, and In this case, the third-order diffracted light is used to correct aberrations generated in each.

  Here, the −1st order diffracted light will be described with reference to FIG. FIG. 5 shows the state of the wavefront when the incident light 201a passes through the four-step staircase-shaped diffraction structure. When the wavefront of the incident light 201a passes through the four-step staircase-shaped diffraction structure, a phase difference is generated according to each staircase shape. As a result, the wavefront of the incident light 201a is diffracted as −1st order diffracted light like the output light 201b. The height of each step of the staircase shape is set to give a phase difference of 0.75λ.

  Further, the -second order diffracted light will be described with reference to FIG. FIG. 6 shows the state of the wave front when the incident light 202a passes through the four-step stair-shaped diffraction structure. When the wavefront of the incident light 202a passes through the four-step staircase-shaped diffraction structure, a phase difference is generated in accordance with each staircase shape. As a result, as the outgoing light 202b and 202c, -2nd order diffracted light and + 2nd order diffracted light are generated. Diffracted. At this time, the height of each step of the staircase shape is set so as to give a phase difference of 0.5λ.

  The -2nd order diffracted light generated as described above is condensed by the objective lens 106 and is collected on the HD optical recording medium 117, and the -1st order diffracted light is collected by the objective lens 106 and is applied on the DVD optical recording medium 127. The pitch is set so that the folded light is well focused on the CD optical recording medium 137.

  The optical path difference function of the diffractive surface 502 is (Equation 2)

と定義される。

Is defined.

  However, in an orthogonal coordinate system in which the point intersecting the optical axis of the optical axis vertical plane is the origin and the optical axis direction from the light source toward the optical recording medium is the X axis, φ is the optical path difference function, R is the radius (from the optical axis) Distance), C1, C2,... Are optical path difference coefficients. The optical path difference coefficient on the surface of the central region 502a is shown in (Table 2).

図５，図６を比較すると分かるように、同じピッチであれば、回折光の次数の絶対値が大きいほど、回折する角度が大きい。

As can be seen from a comparison between FIGS. 5 and 6, if the pitch is the same, the greater the absolute value of the order of the diffracted light, the greater the angle of diffraction.

  FIGS. 7A, 7B, and 7C show wavefronts in HD, DVD, and CD optical recording media. The horizontal axis is the pupil diameter, and the vertical axis is the phase (λ). It is a figure which shows a mode when a working distance is ensured 0.3 mm or more with respect to CD type | system | group optical recording medium. The amount of spherical aberration is larger in the optical recording medium of the HD system than the DVD system and in the CD system of the HD system. This is because the difference in substrate thickness and wavelength is large. Accordingly, when the order of the diffracted light used for the optical recording medium having a large aberration correction amount is increased and the order of the diffracted light used for the optical recording medium having a small spherical aberration generation amount is decreased, the HD system, DVD system, CD Aberrations can be corrected simultaneously for the optical recording medium. That is, when the orders of the diffracted light used in the light beams having wavelengths λ1, λ2, and λ3 are N11, N12, and N13, respectively, the relationship | N12 | <| N11 | <| N13 |

  In the first embodiment, N11 = -2, N12 = -1, and N13 = -3. This is because the smaller the order used, the higher the diffraction efficiency. When the order as described above is used, as shown in FIGS. 8A, 8B, and 8C, the wavefront aberration is reduced, and HD, DVD, and CD optical recording media can be corrected simultaneously. I understand that

  Further, the cross section of the second region 502b of the aberration correction means 501 is composed of a plurality of ring-shaped uneven portions formed concentrically as shown in FIG. Each ring-shaped uneven portion has a staircase shape and has three steps. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

  The pitch of the ring-shaped concavo-convex portions is set so as to correct the generated aberration for HD and DVD optical recording media. Therefore, when the orders of the diffracted light used at the wavelengths λ1 and λ2 are N21 and N22, respectively, it is set so that | N22 | <| N21 | In the first embodiment, N21 = -2 and N22 = -1 are used.

  The optical path difference coefficient of the second region 502b is the same as that of the central region 501a shown in (Table 2). Note that different optical path difference coefficients may be used.

  The second region 502b has a step-like groove depth at which the -3rd order diffracted light is not generated so as to have a function of restricting the opening of the CD optical recording medium 137. The minimum value of the pitch of the center region 502a and the second region 502b in the first embodiment is 52 μm, and the number of ring zones is 21.

  The above-described diffractive structure transmits the light beam having the wavelength λ1 as it is, condenses it on the BD optical recording medium, and diffracts it to correct the spherical aberration caused by the difference in the substrate thickness of the HD optical recording medium. It is formed to do. That is, since a part of the incident light is emitted as 0th order diffracted light and a part is emitted as diffracted light of ± 1st order or more, a configuration of a bifocal lens combined with the objective lens 106 is obtained. Spots that converge to the diffraction limit are formed on BD and HD optical recording media having the same wavelength and different substrate thicknesses. Due to this diffractive surface, the diffracted light beam and the undiffracted light beam are condensed at different focal positions on the optical axis to form spots on the respective optical recording media. However, when information is recorded / reproduced at one focal point, the light flux having the other focal point as the condensing point is greatly spread and the light intensity is small, and recording / reproduction is not affected.

  Next, the height of each step of the diffraction surface 502 will be described with reference to FIG. In a diffractive optical system, not all energy of incident light is converted into emitted light, but is converted only with an efficiency called diffraction efficiency. When the serrated kinoform shape as shown by the broken line in FIG. 9 is blazed at a certain wavelength, the diffraction efficiency at that wavelength is theoretically 100% in the case of thin approximation. Of the three wavelengths, the diffractive surface 502 is used as 0th-order diffracted light for the first light beam of 405 nm, and as diffracted light of ± 1st order or more for the second and third light beams of 660 nm and 785 nm, The shape approximates the stairs as shown in FIG.

  The staircase shape is a shape that approximates a sawtooth kinoform shape, and the staircase shape inclination direction is a sawtooth inclination direction. Also, the staircase shape is easier than making an ideal kinoform shape. Furthermore, 0th-order diffracted light is transmitted light that maintains the traveling direction when incident light is incident.

  The central region 502a of the diffractive surface 502 is an incident parallel light beam, which is a diffraction beam used for light beams of wavelengths λ1, λ2, and λ3 to simultaneously correct aberrations for HD, DVD, and CD optical recording media. The order of the light is | N12 | <| N11 | <| N13 |, and the 0th-order diffracted light is used for the first light flux. Therefore, the height of the diffractive structure must be set so that the efficiency of the diffracted light in each light flux is increased.

  In FIG. 9, assuming that the step-like groove depth is D, the sawtooth-like groove depth is H, and the number of steps of the step shape is M, for example, in the case of four steps, the zero-order diffracted light, ± first-order diffracted light and ± second-order diffracted light The phase difference of the groove depth that gives the maximum diffraction efficiency is as shown in Table 3. Table 4 shows the phase difference per stage when generalized to the M stage. If the height of one step is set to the conditions shown in (Table 4), the desired diffraction order can be obtained most efficiently.

また、各光束で所望の回折次数の効率が大きくなるように、材料と高さを選定する。本実施形態１では、段数を３段にして、第２の光束に対しては−１次回折光、第３の光束に対しては−２次回折光を用いる。材料にＰＭＭＡを用いる場合、全段の溝深さＤを９．９μｍとすると、どの波長に対しても所望の効率を得ることができる。

In addition, the material and height are selected so that the efficiency of a desired diffraction order is increased for each light beam. In the first embodiment, the number of stages is three, and −1st order diffracted light is used for the second light flux, and −2nd order diffracted light is used for the third light flux. When PMMA is used as the material, the desired efficiency can be obtained for any wavelength when the groove depth D of all the stages is 9.9 μm.

  Next, the second region 502b of the diffractive surface 502 diffracts and corrects aberrations for the first and second light fluxes, and collects the third light flux on the CD optical recording medium. Avoid light. In the first embodiment, the groove depth D is set to 1.9 μm in three steps, and the groove depth is set such that the diffracted light of the third-order light of the third light beam is not generated.

  FIG. 10A shows the third light flux when the light is condensed on the CD optical recording medium 137, and FIG. 10B shows the spot on the CD optical recording medium 137. The light beam passing through the central region 502a is condensed on the CD-based optical recording medium 137 as the third-order light. On the other hand, since the light beam passing through the second region 502b is transmitted as it is as the 0th-order diffracted light, it is not condensed on the CD-type optical recording medium 137 and spreads as flare light in the periphery, and does not affect recording / reproduction.

  The third region 502c of the diffractive surface 502 is a flat portion without a diffractive structure. The height of the flat portion of the third region 502b in FIG. 3 is set so as to be an integral multiple of the wavelength of the first light flux with respect to the lowest stage of the diffractive structure. In the first embodiment, the thickness is set to 4.0 μm corresponding to a phase difference of 5 times the wavelength.

  Since the light beam transmitted through the flat portion of the third region 502c is out of the effective diameter for HD, DVD, and CD optical recording media, it becomes unnecessary light for spot formation. It spreads greatly as flare light as shown in). On the other hand, the height of the first light flux is set so that the phase difference is an integral multiple of the wavelength with respect to the lowermost stage of the center region 502a and the second region 502b. In the first embodiment, the wavelength is 4 μm, which is five times the wavelength, but is not limited to this.

  The diffraction efficiency of the staircase-shaped diffraction element becomes closer to a sawtooth kinoform shape as shown by the broken line in FIG. However, if the number of stages is large, the pitch per stage becomes narrow, making it difficult to manufacture, and a reduction in efficiency occurs due to the influence of anyone due to manufacturing errors.

  Further, when the pitch is the same, the efficiency is better when the groove depth D is lower. In addition, it is not easily affected by efficiency reduction due to wavelength and temperature fluctuations. For this reason, it is known that the diffractive structure preferably has a lower groove depth D and a larger number of steps.

  As in the first embodiment, the efficiency is reduced in the peripheral portion where the pitch is narrowed. This is shown in FIG. With respect to the intensity distribution 203 of the light source, it can be seen that the amount of light decreases significantly as the central region 502a goes to the periphery. Further, the pitch of the second region 502b is further narrower than that of the central region 502a. However, in the first embodiment, since the second region 502b has a groove depth lower than that of the central region 502a, the reduction in efficiency is reduced. Can increase the light utilization efficiency. Note that the number and height of the diffractive structure and the material are not limited to those described above.

  As described above, it is possible to realize an aperture restriction that does not easily generate unnecessary light by simply changing the groove depth.

  Next, the outer shape of the aberration correction unit of the first embodiment will be described in detail. As shown in FIG. 4, the outer shape of the aberration correcting means 501 is the same circular shape as the boundary between the diffractive portion (center region 502a and second region 502b) and the flat portion (third region 502c). To do. The circular shape includes a polygon, and the same effect can be obtained even in an octagon as shown in FIG.

  The resin such as PMMA used in the first embodiment has the advantage that it can be injection-molded, so that it is most widely used for optical parts and is easily mass-produced. However, the hygroscopicity is a weak point. Can be mentioned. This not only fluctuates optical characteristics such as refractive index and transmittance, but also appears as deformation.

  FIGS. 13A to 13D show wavefront shapes of transmitted light having a wavelength of 405 nm when the outer shape of the aberration correcting means is a square shape. FIG. 13A shows the result of transmission wavefront measurement in the central region 502a, the second region 502b, and the third region 502c within the effective beam diameter, and shows the wavefront shape. FIGS. 13B and 13C show the results of wavefront measurement by dividing the result of FIG. 13A into regions (diffractive portions and flat portions). FIG. 13B shows the transmitted wavefront shape 502g only in the diffractive portion (the central region 502a and the second region 502b where the diffractive structure is formed), and FIG. 13C shows only the flat portion (third region 502c). The transmitted wavefront shape 502f is shown.

  When calculating the wavefront aberration based on the wavefront shape, the wavefront shape within the effective beam diameter in FIG. 13A has a PV (Peak to Valley) value of 0.5λ and a wavefront aberration of 0.1λrms, and the wavefront accuracy is very high. bad. Usually, it is desirable that the wavefront aberration of the optical component is 0.02λrms or less. The wavefront aberration in the region of the diffractive portion in FIG. 13B is 0.02λrms, which is good wavefront accuracy, whereas the wavefront aberration in the flat portion (third region 502c) in FIG. It can be seen that the cause of poor wavefront accuracy within the effective beam diameter is 0.13λrms in the flat portion. FIG. 13D is a plot of the wavefront shape of the flat portion along the circumferential direction. It is considered that the flat portion is wavy along the square shape of the aberration correction means 501 and causes wavefront deterioration.

  The cause of this swell is that there are 502d and far 502e near the edge of the outer quadrangle at the boundary between the diffraction part and the flat part, and there is a difference in PMMA moisture absorption near 502d and far 502e. This difference in moisture absorption becomes a difference in deformation, and undulation occurs.

  14A to 14D are diagrams showing wavefront shapes of transmitted light having a wavelength of 405 nm of the aberration correction unit 501 of the first embodiment. The shape is a circle. FIG. 14A shows the result of transmission wavefront measurement of the central region 502a, the second region 502b, and the third region 502c within the effective beam diameter, and shows the wavefront shape. FIGS. 14B and 14C show results of wavefront measurement by dividing the result of FIG. 13A into regions (diffractive portions and flat portions). FIG. 14B shows the transmitted wavefront shape 502g only in the diffractive portion (the central region 502a and the second region 502b where the diffractive structure is formed), and FIG. 14C shows only the flat portion (third region 502c). The transmitted wavefront shape 502f is shown.

  FIG. 14D is a plot of the wavefront shape of the flat portion along the circumferential direction. When the wavefront aberration is calculated from the wavefront shape within the effective ray diameter in FIG. 14A, the PV value is 0.1λ, the wavefront aberration is 0.02λrms, and the wavefront aberration in the region of the diffractive portion in FIG. The wavefront aberration of the flat portion (the third region 502c) in FIG. 14C is 0.017λrms, and there is no waviness in the peripheral portion, and the wavefront accuracy is good.

  Thus, by making the outer shape of the aberration correction means 501 the same circular shape as the boundary between the diffractive portion and the flat portion, the change in shape due to moisture absorption of PMMA can be made uniform, and the swell can be reduced. A high-precision optical pickup can be realized.

  FIG. 15 is a diagram showing a schematic configuration of an optical pickup according to Embodiment 2 of the present invention. The optical pickup according to the second embodiment is different from the optical pickup shown in FIG. 1 according to the first embodiment in that a beam expander 109 and an aberration correction unit 601 are provided. FIG. 16 is an enlarged cross-sectional view of the aberration correction unit 601.

  In contrast to the first embodiment where all of the first embodiment described above is incident parallel light, in the second embodiment, divergent light is incident on the aberration correction means 601 with respect to the HD optical recording medium 1147. For this purpose, the beam expander 109 is moved into divergent light. In addition, parallel light and divergent light may be switched using a liquid crystal element.

  As shown in FIG. 16, the diffractive surface 602 of the aberration correction unit 601 has a central region 602a, a second region 602b, and a third region 602c as three regions that are concentrically divided within the range through which the light beam passes. Have

  As in the first embodiment, the central area 602a and the second area 602b are divided by NA 0.45 for the CD optical recording medium 137 and NA 0.65 for the DVD optical recording medium 127, respectively, and each has a radius of 1.25 mm. Set to 1.715 mm.

  In the second embodiment, the sign of the order of the diffracted light is inverted between the center region 602a and the second region 602b, thereby obtaining the relationship between the diffraction efficiency, the uneven shape, and the height of the first, second, and third light beams. It can be changed greatly. Therefore, it is possible to provide a function as an efficient aberration correction unit and an aperture limiting element that does not affect recording and reproduction.

  In addition, for any one of the BD, HD, DVD, and CD optical recording media, the order of the diffracted light can be reduced by making divergent light incident on the aberration correction means 601. Can provide an efficient optical pickup.

  The cross section of the central region 602a of the aberration correction means 601 is composed of a plurality of annular concavo-convex portions formed concentrically as shown in FIG. Each ring-shaped uneven portion has a staircase shape and has three steps. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

  The pitch of the ring-shaped concavo-convex portions is −1st order diffracted light for the HD optical recording medium 117, −1st order diffracted light for the DVD optical recording medium 127, and for the CD optical recording medium 137. The second-order diffracted light is used to correct aberrations occurring in each.

  The number of steps, the groove depth, and the order of the diffracted light are the same as those of the central region 502a of Embodiment 1, and the diffractive structure is gradually narrowed from the inside toward the outside so as to have a lens effect. The pitch of the ring-shaped uneven portions is set so as to correct the generated aberration by using −1st order diffracted light for the DVD optical recording medium 127 and −2nd order diffracted light for the CD optical recording medium 137. Is done. For the HD optical recording medium 117, the light beam converted into the divergent light by the beam expander 109 is incident on the aberration correcting means 601, and the aberration generated by the −1st order diffracted light is corrected.

  Further, the cross section of the second region 602b of the aberration correcting means 601 is also composed of a plurality of annular concavo-convex portions formed concentrically as shown in FIG. Each ring-shaped uneven portion has a staircase shape and has four steps. The pitch of the ring-shaped uneven portions is gradually narrowed from the inside to the outside so that the diffractive structure has a lens effect.

  In addition, the pitch of the zonal uneven portions is set so as to correct the generated aberration by using + 1st order diffracted light for the HD and DVD optical recording media 117 and 127.

  In the second region 602b, a step-shaped groove depth at which + 2nd order diffracted light is not generated is set so as to have a function of limiting the opening of the CD optical recording medium 137.

  FIGS. 17A, 17B, and 17C show wavefronts in the HD, DVD, and CD optical recording media. The horizontal axis is the pupil diameter, and the vertical axis is the phase (λ). As shown in FIGS. 17A, 17B, and 17C, the wavefront aberration is reduced, and it can be seen that HD, DVD, and CD optical recording media can be corrected simultaneously.

  FIG. 18 is a cross-sectional view showing the configuration of the aberration correction means in Embodiment 3 of the present invention. The aberration correction unit 701 of the third embodiment is provided with a step 704 in any one of the third regions 502c and 602c forming the flat portion of the aberration correction units 501 and 601 shown in the first and second embodiments. It is. This step 704 corrects chromatic aberration that occurs with respect to the BD optical recording medium 107 having a short wavelength and a large NA.

  An optical information processing apparatus that records and reproduces information on an optical recording medium uses a semiconductor laser as a light source, and the oscillation wavelength of the semiconductor laser varies individually or fluctuates with changes in temperature. In particular, since the refractive index of the optical material has a property (dispersion) that varies depending on the wavelength, third-order spherical aberration occurs when the wavelength of the light source varies. Therefore, this spherical aberration becomes one of optical problems when recording and reproducing information. The amount of spherical aberration generated when this wavelength is changed becomes larger due to the shorter wavelength and higher NA of the light source.

  This is because when the wavelength is shortened, the refractive index change of the optical material increases, and the amount of change in spherical aberration when the wavelength changes increases, and the change in spherical aberration increases in proportion to the fourth power of NA. . Therefore, the influence on the deterioration of optical information in recording and reproduction when the wavelength is changed is further increased.

  FIG. 19 shows changes in wavefront aberration due to wavelength fluctuations when an objective lens with NA of 0.65 and NA of 0.85 is used at a wavelength of 405 nm. As shown in FIG. 19, even when the wavelength of the objective lens design wavelength is changed from 405 nm to 10 nm with NA 0.65, the desired performance of the objective lens is 0.03λ rms or less, whereas with NA 0.85 it is 3 nm. If the wavelength fluctuates, it will exceed 0.03λrms, and information may not be recorded or reproduced.

  In general, assuming that the temperature is from 10 ° C. to 80 ° C. as the operating environment of the optical information processing apparatus, the wavelength of the semiconductor laser varies by about 3 nm. Further, it is necessary to assume that the center wavelength variation is about ± 5 nm. Therefore, in an optical system using an objective lens with NA of 0.85, it is necessary to correct spherical aberration due to such a wavelength change.

  Further, the step structure in the step 704 of the aberration correction unit 701 is divided into regions concentrically around the optical axis in the optical axis direction, and is formed so that the thickness increases as the distance from the optical axis increases. Yes. The thickness difference in each region is formed so as to produce an optical path difference that is an integral multiple of the objective lens design wavelength of 405 nm.

  FIG. 20 shows a phase step of the step 704 formed. The horizontal axis represents the radial position, and the vertical axis represents the number of phase steps N. In the third embodiment, a step is provided in the third region 803c using N = 8,14. Therefore, the step is affected when a spot is formed on the BD optical recording medium.

  When the diffractive surface 702 has no step 704, the amount of spherical aberration due to wavelength change is as shown by the broken line in FIG. 21, whereas when the above-described step 704 is formed, a third-order spherical surface as shown by the solid line in FIG. Aberration can be corrected. Here, for example, FIG. 22 shows the state of the wavefront phase when the wavelength changes by 6 nm. It can be seen that the phase of the wavefront is discontinuous when the phase step is applied. In this way, the wavefront is changed discontinuously to correct third-order spherical aberration.

  Note that the height of the step 704 and the radial position of the step boundary vary depending on the shape of the objective lens, the design wavelength of the objective lens, the material constituting the aberration correction means, and the numerical aperture (NA), and are limited to the third embodiment. It is not something.

  The aberration correction unit according to the fourth embodiment of the present invention has a configuration in which the diffractive surface described in the first to third embodiments is integrated with an objective lens. In the fourth embodiment, as shown in FIG. 23, for example, the aberration correction unit 601 and the objective lens 106 according to the second embodiment are integrated. If the diffractive surface 602 is formed on the surface of the objective lens 106 as shown in FIG. 23, not only the wavefront deterioration due to the axial deviation between the objective lens 106 and the aberration correction element 601 can be reduced, but also the assembly process can be reduced and reduced. Cost reduction can be realized.

  The diffractive surface 602 formed on the surface of the objective lens 106 may be formed integrally with the objective lens 106. A diffractive structure may be separately formed on the surface of the objective lens 106. In that case, as the material of the diffractive structure, an ultraviolet coin resin is suitable for manufacturing.

  24 (a) and 24 (b) are enlarged sectional views showing the aberration correcting means in Embodiment 5 of the present invention. The configuration of the optical pickup and the objective lens in the fifth embodiment are the same as those in the first embodiment. In the aberration correction unit 801 shown in FIGS. 24A and 24B, a wave plate 805 is formed on the back surface of the aberration correction unit 501 of the first embodiment instead of the quarter wave plate 106 shown in FIG. ing.

  Since the wave plate 805 is provided in the optical path where the optical system is shared, the wave plate 805 has a wide range of wavelengths 405, 660 nm, and 785 nm and is 0.25 ± 0. It is necessary to give a phase difference of 05. A general wave plate has a fine structure such as the wave plate 803a (see FIG. 24A), and an expensive material such as quartz or a retardation film made of a resin film is used like the wave plate 805b. (See FIG. 24B). In particular, those having a fine structure such as the wave plate 803a can stably give a phase difference in a wide wavelength range. This fine structure may be the same material as the aberration correction means 801 or a different material.

  If the wave plate 805 and the diffractive surface 802 are formed on both surfaces of the aberration correction unit 801 as in the fifth embodiment, the number of parts can be reduced, and downsizing can be realized. In addition, when the wave plate 805 is formed with a fine structure, the aberration correction means 801 can be integrally molded, and the manufacturing process can be reduced and the cost can be reduced. Further, it may be an aberration correcting means in which a liquid crystal element for making a finite system and a diffractive surface are formed on both sides.

  FIG. 25 is a diagram showing a schematic configuration of an optical information processing apparatus according to Embodiment 6 of the present invention. The sixth embodiment is an embodiment of an optical information processing apparatus, and at least one of reproducing, recording, and erasing information on an optical recording medium using the optical pickup of any of the first to fifth embodiments described above. It is a device that performs one.

  As shown in FIG. 25, the optical information processing apparatus includes an optical pickup 91, a feed motor 92, a spindle motor 98, and the like, which are controlled by a system controller 96 that controls the entire optical information processing apparatus. Then, the movement of the optical pickup 91 in the tracking direction is performed by a control driving means composed of a feed motor 92 and a servo control circuit 93. For example, when reproducing the optical recording medium 100, a control signal from the system controller 96 is supplied to the servo control circuit 93 and the modem circuit 94.

  In the servo control circuit 93, the spindle motor 98 is rotated at a set number of revolutions and the feed motor 92 is driven.

  The modulation / demodulation circuit 94 is supplied with the focusing error signal detected by the photodetector of the optical pickup 91, the tracking error signal, the position information of where the optical recording medium 100 is read, and the like. The focusing error signal and tracking error signal are supplied to the servo control circuit 93 via the system controller 96.

  The servo control circuit 93 drives the focusing coil of the actuator by the focusing control signal, and drives the tracking coil of the actuator by the tracking control signal. The low frequency component of the tracking control signal is supplied to the servo control circuit 93 via the system controller 96 and drives the feed motor 92. As a result, feedback servo of focusing servo, tracking servo, and feed servo is performed.

  Further, the position information of where the optical recording medium 100 is read is processed by the modulation / demodulation circuit 94 and is supplied to the spindle motor 98 as a spindle control signal, and is controlled to a predetermined rotational speed corresponding to the reproduction position of the optical recording medium 100. It is driven and actual reproduction is started from here. The reproduction data processed and demodulated by the modem circuit 94 is transmitted to the outside via the external circuit 95.

  When data is recorded, the same process as the reproduction is performed until the feedback servo of the focusing servo, tracking servo, and feed servo is applied.

  A control signal indicating where the input data input via the external circuit 95 is recorded on the optical recording medium 100 is supplied from the system controller 96 to the servo control circuit 93 and the modulation / demodulation circuit 94.

  The servo control circuit 93 controls the spindle motor 98 to a predetermined number of revolutions and drives the feed motor 92 to move the optical pickup 91 to the information recording position.

  An input signal input to the modulation / demodulation circuit 94 via the external circuit 95 is modulated based on the recording format and supplied to the optical pickup 91. In the optical pickup 91, the modulation of the emitted light and the emitted light power are controlled, and recording on the optical recording medium 100 is started.

  The type of the optical recording medium 100 is determined by the reproduction data signal. As a method for determining the type of the optical recording medium 100, a tracking servo signal or a focus servo signal may be used.

  If the optical pickup included in the optical information processing apparatus dedicated to reproduction and the optical information processing apparatus capable of processing both recording and reproduction includes the optical pickup using the aberration correction means of the present invention, The accuracy of recording and reproducing quality of information on different optical recording media can be improved.

  As described above, according to the optical information processing apparatus in Embodiment 6, the recording surface of four types of optical recording media (BD, HD, DVD, CD) having different substrate thicknesses by the single objective lens 106 is used. By using an optical pickup capable of forming a good spot, it is possible to perform optimum processing for recording, reproducing or erasing information signals on the optical recording medium 100.

  The optical pickup and the optical information processing apparatus according to the present invention are excellent in recording surfaces of four types of optical recording media having different substrate thicknesses and recording densities by a single objective lens, while having a plurality of light sources corresponding to the wavelengths used. The light can be collected and stably recorded and reproduced, and is useful as a compatible device when recording and reproducing information on four or more different optical recording media.

The figure which shows schematic structure of the optical pick-up in Embodiment 1 of this invention. Sectional view enlarging the vicinity of the aberration correction means Cross-sectional view enlarging aberration correction means The figure which shows the diffraction surface of an aberration correction means The figure which shows the mode of the wave front of the -1st order diffracted light in which incident light passes through the diffraction structure of 4 steps | paragraphs shape The figure which shows the mode of the wave front of ± 2nd order diffracted light in which incident light passes through the four-step staircase-shaped diffraction structure (A) is an HD system, (b) is a DVD system, and (c) is a diagram showing a wavefront in each optical recording medium of a CD system. (A) is an HD system, (b) is a DVD system, and (c) is a diagram showing a corrected wavefront in each optical recording medium of a CD system. Diagram explaining the height (groove depth) of the diffraction surface (A) is a light beam condensed on a CD optical recording medium, and (b) is a diagram showing spots formed on the CD optical recording medium. Diagram showing the relationship between the diffraction surface and the intensity distribution of diffracted light The figure which shows the external shape of an aberration correction means (A)-(d) is a figure which shows the wavefront shape of the transmitted light with a wavelength of 405 nm in which the aberration correction means is rectangular. (A)-(d) is a figure which shows the wavefront shape of the transmitted light with a wavelength of 405 nm when the aberration correction means is circular. The figure which shows schematic structure of the optical pick-up in Embodiment 2 of this invention. Sectional view enlarging the vicinity of the aberration correction means (A) is an HD system, (b) is a DVD system, and (c) is a diagram showing a wavefront in each optical recording medium of a CD system. Sectional drawing which expanded the aberration correction means in Embodiment 3 of this invention The figure which shows the change of the wavefront aberration by a wavelength variation when using the objective lens of NA0.65 and NA0.85 in wavelength 405nm The figure which shows the phase level difference formed in the aberration correction means The figure which shows the amount of spherical aberration of the wavelength change by the presence or absence of a level difference The figure which shows the mode of the wave front phase when wavelength changes 6nm The block diagram which integrated the aberration correction means in Embodiment 4 of this invention on the surface of an objective lens (A), (b) in Embodiment 5 of the present invention is a cross-sectional view of an aberration correction means provided with a wave plate on the back surface. The figure which shows schematic structure of the optical information processing apparatus in Embodiment 6 of this invention.

Explanation of symbols

91 Optical pickup 92 Feed motor 93 Servo control circuit 94 Modulation / demodulation circuit 95 External circuit 96 System controller 98 Spindle motor 100 Optical recording medium 101, 130a, 140a Semiconductor laser 102 Collimator lens 103 Polarizing beam splitter 104 Prism 105 1/4 wavelength plate 106 Objective Lens 107 BD optical recording medium 108 Detection lens 110, 130c, 140c, 150 Light receiving element 117 HD optical recording medium 120 Movable part 121 Lens tube 127 DVD optical recording medium 130b, 140b Hologram elements 132, 142, 152 Divergence angle conversion Lenses 133 and 143 Wavelength selective beam splitter 137 CD-based optical recording medium 200 Pitch 201a, 202a Incident light 201b, 202b Emitted light 203 Light source intensity distribution 501, 601 01, 801 Aberration correction means 502, 602, 702, 802 Diffractive surfaces 502a, 602a, 702a Central regions 502b, 602b, 702b Second region 502c, 602c, 702c Third region 502d Nearer 502e Distant 502f Flat portion Transmitted wavefront shape 502g Transmitted wavefront shape 704 of diffraction part Step 805, 805a, 805b Wave plate

Claims (28)

In an optical pickup that performs one or more of recording, reproduction, and erasing on a plurality of types of optical recording media having different recording densities.
As the first, second, third, and fourth optical recording media in descending order of the recording density of the optical recording medium, a first wavelength λ1 corresponding to the first and second optical recording media is provided. Corresponding to a first light source for emitting a light beam, a second light source for emitting a second light beam having a second wavelength λ2 corresponding to the third optical recording medium, and the fourth optical recording medium A third light source that emits a third light beam having a third wavelength λ3, and a single light source that focuses the first to third light beams on the recording surfaces of the first to fourth optical recording media. An objective lens, and an aberration correction means provided between the objective lens and the first to third light sources,
The first, second, and third wavelengths of the light source have a relationship of λ1 <λ2 <λ3, and the aberration correction unit is provided with a diffractive surface having a diffractive structure having a concentric uneven shape in cross section. Features an optical pickup. The optical pickup according to claim 1,
The optical pickup is characterized in that the diffractive surface is divided into at least three or more concentric regions within the effective beam diameter through which the light beam passes to form a diffractive structure in at least two regions. The optical pickup according to claim 1 or 2,
2. An optical pickup comprising a diffraction structure formed in two regions in order from the center side among regions divided on the diffraction surface. The optical pickup according to claim 1, 2, or 3,
An optical pickup characterized in that the groove depths of the concavo-convex shape are different in each diffractive structure formed in two regions among the regions divided on the diffractive surface. The optical pickup according to any one of claims 1 to 4,
Of the regions divided on the diffractive surface, the diffractive structure formed in the central region emits 0th-order diffracted light that is transmitted without being diffracted with respect to the light beam with wavelength λ1 and the light beam with wavelength λ2 that is diffracted. The optical pickup emits diffracted light that diffracts, and emits diffracted light that diffracts the light beam having the wavelength λ3. The optical pickup according to any one of claims 1 to 5,
Of the regions divided on the diffraction surface, the diffractive structure formed in the central region has the following when the orders of diffracted light used for the second, third, and fourth optical recording media are N11, N12, and N13, respectively. Conditions | N12 | <| N11 | <| N13 |
An optical pickup characterized by The optical pickup according to any one of claims 1 to 6,
The diffraction structure formed in the second region from the center among the regions divided on the diffraction surface has the following when the orders of diffracted light used for the second and third optical recording media are N21 and N22, respectively. Condition | N22 | <| N21 |
An optical pickup characterized by The optical pickup according to any one of claims 1 to 5,
Of the regions divided on the diffraction surface, the diffractive structure formed in the central region has the following when the orders of diffracted light used for the second, third, and fourth optical recording media are N11, N12, and N13, respectively. Conditions | N12 | ≦ | N11 | <| N13 |
An optical pickup characterized by The optical pickup according to any one of claims 1 to 5, wherein
The diffraction structure formed in the second region from the center among the regions divided on the diffraction surface has the following when the orders of the diffracted light most strongly generated by the first and second light beams are N21 and N22, respectively. Conditions | N21 | ≦ | N22 |
An optical pickup characterized by The optical pickup according to any one of claims 1 to 7,
An optical pickup characterized in that all light beams having wavelengths λ1, λ2, and λ3 are incident on the diffraction surface as parallel light. The optical pickup according to any one of claims 1 to 9,
An optical pickup characterized in that a light beam incident on the diffraction surface is a finite system with respect to at least one of the first, second, third and fourth optical recording media. The optical pickup according to any one of claims 1 to 11,
An optical pickup characterized in that the orders N11, N12, N13 and the orders N21, N22 in the diffracted light of the diffractive structure have opposite signs. The optical pickup according to any one of claims 1 to 12,
Of the regions divided on the diffraction surface, the diffractive structure formed in the center region and the second region from the center is formed by repeating the staircase shape, and the inclination direction of each step shape is the second from the center region and the center. An optical pickup characterized by being reversed in the area of The optical pickup according to any one of claims 1 to 13,
Of the regions divided on the diffraction surface, the diffractive structure formed in the central region is formed by repeating a staircase shape, and each staircase shape has a groove depth in the optical axis direction outward from the center of the optical axis. An optical pickup characterized by being formed to be low. The optical pickup according to any one of claims 1 to 14,
The diffraction structure formed in the second region from the center among the regions divided on the diffraction surface is formed by repeating a staircase shape, and each staircase shape extends in the optical axis direction from the center of the optical axis toward the outside. An optical pickup characterized in that the groove depth is increased. The optical pickup according to any one of claims 1 to 14,
The diffraction structure is formed so that the pitch of the diffractive structure formed on the diffractive surface cancels out the spherical aberration that occurs when transmitting through the substrates of the second, third, and fourth optical recording media using a single objective lens. An optical pickup characterized by being formed in a structure. The optical pickup according to any one of claims 1 to 7, and 10 to 16,
An optical pickup characterized in that the diffractive structure of the diffractive surface is stepped and the number of steps M is "3". The optical pickup according to any one of claims 1 to 17,
The optical pickup characterized in that the diffraction structure formed in the second region from the center among the regions divided on the diffraction surface has a step shape and has a groove depth lower than that of the center region. The optical pickup according to claim 1,
An optical pickup characterized in that a third region from the center of the regions divided on the diffraction surface is a flat portion. The optical pickup according to claim 1,
An optical pickup characterized in that a step having a different thickness in the optical axis direction is formed in the third region from the center among the regions divided on the diffraction surface. The optical pickup according to any one of claims 1 to 20,
An optical pickup characterized in that the objective lens is designed so that aberration is minimized by a light beam having a wavelength λ1 with respect to a first optical recording medium having the highest recording density. The optical pickup according to any one of claims 1 to 21,
An optical pickup comprising a diffractive structure of the diffractive surface formed on a surface of an objective lens. The optical pickup according to any one of claims 1 to 21,
An optical pickup comprising a wave plate formed on a surface opposite to the diffraction surface of the aberration correcting means provided with the diffraction surface. The optical pickup according to claim 1,
An optical pickup characterized in that a divergence angle conversion element is formed on a surface opposite to the diffraction surface of the aberration correction means provided with the diffraction surface. 25. The optical pickup according to any one of claims 1 to 24, wherein:
An optical pickup comprising a beam expander in a light path from a light source to an objective lens. 25. The optical pickup according to any one of claims 1 to 24, wherein:
An optical pickup comprising a diffractive structure of the diffractive surface made of a resin material. The optical pickup according to any one of claims 1 to 24, 26,
An optical pickup characterized in that the outer shape of the aberration correcting means having the diffractive surface is a circular shape concentric with the diffractive surface. An optical information processing apparatus that performs one or more of recording, reproduction, and erasing on a plurality of types of optical recording media having different recording densities,
An optical information processing apparatus comprising the optical pickup according to claim 1.

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