JP2005317120A - Optical pickup and optical recording medium recording/reproducing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compensate spherical aberration generated by the difference in the thickness of a protective substrate in a recording medium and the difference in the layer thickness between recording layers with a simple configuration. <P>SOLUTION: An optical pickup 1 comprises a basic optical system, having a light source, a photodetector for receiving reflection light on a recording surface for reading out a light signal, a light separation element for separating emission light and return light, an element for generating a focus signal or a tracking signal, and the like; an objective lens 13 for condensing a light beam emitted from the light source onto the recording surface of the optical disk; a diffraction grating 14 arranged at the forward passage light incidence side of an objective lens; a liquid crystal element 15 for giving a phase difference for correcting aberration to the light beam; and a liquid crystal control circuit 16 for controlling the liquid crystal element 15. In an optimized optical system for generating primary diffraction light for both BDs and DVDs, primary diffraction light is used also for CDs, the liquid crystal molecule orientation of the liquid crystal element 15 is changed according to the difference in the recording layer of an optical recording medium to be recorded or reproduced and the type of the optical recording medium, and a phase difference is given to the transmitted light beam, thus compensating aberration including spherical aberration by the difference in the thickness of the protective substrate and the difference in the layer thickness between the recording layers. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical system for recording / reproducing an optical recording medium, and relates to an optical pickup and an optical recording medium recording / reproducing apparatus capable of writing to and reading from a plurality of recording media using different recording / reproducing wavelengths.

  In recent years, recording media such as CD (Compact Disc), MD (Mini Disc), and DVD (Digital Versatile Disc) have been required to have a larger capacity, and various technologies have been developed to increase the capacity. Yes. In addition, it is required that various data such as music content data, video content data, and data for computer use can be freely recorded and reproduced on one medium. In particular, a new disc format (hereinafter referred to as a Blu-ray disc; BD) using a laser having a wavelength band of 405 nm has attracted much attention as a next-generation recording technology.

  When developing media for general use, compatibility and consistency between new and old media recording and playback devices are also important. Newly developed recording and playback devices can use legacy assets such as DVDs and CDs. It is preferable that However, it is not easy to design a device having compatibility between media having different disk structures and accompanying laser specifications.

The simplest method is a method in which different optical systems are provided and a dedicated objective lens is switched for each wavelength used, but a switching mechanism for a plurality of types of objective lenses is required, leading to an increase in cost. Further, since the actuator is enlarged, it is disadvantageous for downsizing the apparatus. For this reason, a multi-wavelength compatible optical system in which a part of the optical system such as an objective lens is shared is used, but spherical aberration occurs in proportion to the thickness of the protective substrate that protects the recording surface. Therefore, it is difficult to focus light beams having different wavelengths on a recording surface with almost no aberration through protective substrates having different layer thicknesses.
In view of this, a device has been devised in which an optical element such as a diffractive element is used to cause a specific wavelength to be incident on the objective lens without being diffracted or diffracted.

  In the two-wavelength compatible type, a diffractive element that satisfies the optimum value of the combination of two different disc protective substrate thicknesses and recording / reproducing wavelengths (two degrees of freedom) is designed by a combination of a lens curved surface and a diffractive element (two degrees of freedom). This can solve the above-mentioned proposition.

  However, when realizing three-wavelength compatibility between a DVD and a CD and, for example, the BD of the above-described new format, the thickness of the protective substrate and the wavelength that need to be optimized are three. The technique used lacks the degree of freedom and it is difficult to optimize the diffraction efficiency and diffraction angle at the same time.

  In the case of using a dedicated objective lens that considers the use of a single BD, it is relatively easy to design a lens that achieves a high efficiency of light utilization efficiency of 95% or more. However, there are many problems when trying to achieve compatibility with conventional assets such as DVD (Digital Versatile Disc) and CD (Compact Disc). Here, as an example, a case will be described in which a two-wavelength compatible optical system of BD and DVD that has already achieved a certain degree of compatibility is extended to a CD light beam.

  For example, as a two-wavelength compatible optical system for BD and DVD, an optical system based on a light beam for BD recording / reproducing is used, and a light beam for BD incident on an objective lens is used as an infinite system for recording and reproducing CD and DVD. There is a system that uses a finite system of the light beam. The infinite system indicates that a light beam is irradiated onto the objective lens from infinity, that is, the light beam is incident on the objective lens as parallel light, and the finite system indicates that divergent light is incident on the objective lens. The infinite system and the finite system compatible system do not use diffractive action, so the light utilization efficiency is good, and the focal length can be changed according to the divergence of the light beam incident on the objective lens, so it works properly There is an advantage that a distance can be secured. However, the fact that the light beam is incident on the objective lens as divergent light has a drawback that the tracking resistance is remarkably reduced because there is no margin for the lateral deviation of the objective lens with respect to the optical axis.

  In addition, as a two-wavelength compatible optical system for BD and DVD, an optical system based on a light beam for BD recording and reproduction, and a system using an optical element optimized to generate first-order diffracted light for both BD and DVD, Although about 90% of the first order diffracted light is obtained in the light beam for BD (405 nm), only about 70% of the first order diffracted light is obtained in the light beam for DVD (655 nm), which is advantageous in terms of aberration characteristics. In addition, the diffraction efficiency of the DVD light beam is low and the light utilization efficiency deteriorates, and it is difficult to achieve compatibility with the CD light beam (785 nm).

  Further, as a two-wavelength compatible optical system for BD and DVD, an optical system based on a light beam for BD recording / reproduction, and an optical system optimized to generate second-order diffracted light in BD and first-order diffracted light in DVD In the system using the element, a diffraction efficiency of about 90% is obtained in the second-order diffracted light of the BD light beam and the first-order diffracted light of the DVD light beam, which shows good light utilization efficiency, but the wavelength dependence of spherical aberration is high. It was very large and it was still difficult to achieve compatibility with a CD light beam (785 nm).

  The characteristics of the above-mentioned two-wavelength compatible optical system for BD and DVD are schematically shown in FIG. The vertical axis in FIG. 4 indicates the thickness of the protective substrate that protects the recording surface of each optical disk, and the horizontal axis indicates the wavelength band used. Since the amount of generated spherical aberration is proportional to the protective substrate thickness and the diffraction angle is proportional to the wavelength, the relationship between the amount of spherical aberration and the diffraction angle generated at this wavelength is also expressed.

According to FIG. 4, an optical system based on a light beam for BD recording / playback is used, and the first-order diffracted light of a CD is converted into an objective lens using an optical element optimized to generate first-order diffracted light for both BD and DVD. BD / DVD / CD = primary / primary / primary) BD and DVD compatible optical system cannot compensate for the CD light beam SA ₁₁₁ (here, this) (Referred to as residual spherical aberration).

In addition, an optical system based on a light beam for BD recording / reproducing is used, and a first-order diffracted light of a CD is generated in a system using an optical element optimized to generate second-order diffracted light in a BD and first-order diffracted light in a DVD. Even when the light is incident on the objective lens (BD / DVD / CD = 2 order / primary / primary order), the residual spherical aberration SA ₂₁₁ occurs with respect to the light beam for CD. Since the second-order diffracted light is considered to be equivalent to a light beam having a double wavelength, when using the BD second-order diffracted light, the optical system adapts the BD second-order light beam of 810 nm and the DVD (655 nm) light beam. Can think.

  As shown in the straight line of the first order / first order / first order in FIG. 4, the optical system that generates the first order diffracted light of BD, DVD, and CD can reduce the remaining amount of spherical aberration, but the diffraction efficiency is not good.

  In addition, in DVD and BD, a disk standard having a multi-layered recording layer has been formulated for further high-density recording. In an optical disc having a multi-layered recording layer, an aberration due to the recording layer thickness difference is generated, and it is required to correct this aberration together with the spherical aberration due to the protective substrate thickness. For example, in the case of a DVD and CD two-wavelength compatible optical system, different spherical aberrations caused by the difference in protective substrate thickness, wavelength, and NA show aberration characteristics for both DVD and CD by drawing a complicated diffraction element pattern on the objective lens. I was satisfied. In addition, there has been a technique for changing the magnification on the CD side, that is, using an optical beam for CD in a finite system to provide an aperture restriction to achieve compatibility with DVD.

  In addition, as an example of a technique for reducing aberration due to a layer thickness difference of a recording medium having a multilayer recording layer, a phase difference that reduces spherical aberration is given to a light beam by a liquid crystal element in which molecular orientation is deviated by applying a voltage. A method is disclosed (see Patent Document 1).

  However, liquid crystal elements are used to correct aberrations due to the difference in layer thickness of the recording layers, and when trying to correct spherical aberration caused by differences in the protective substrate thickness of DVD and CD, the configuration and control become complicated, and optical characteristics There was a problem that it led to deterioration of the cost and cost increase. In addition, in the liquid crystal element, the change in phase amount can be adjusted in principle by changing the thickness of the liquid crystal layer. However, the thickness of the liquid crystal layer to be biased is proportional to the square of the displaced phase amount. There is. When the phase amount change becomes 10 times, the thickness of the liquid crystal layer becomes 100 times. Since the response speed of the liquid crystal element is in units of seconds, it cannot be used in practice.

  Thus, it has been very difficult to design an optical system that achieves three-wavelength compatibility of BD, DVD, and CD. Further, when the recording layers of BD and / or DVD are multi-layered, it is difficult to design an optical system adapted to the aberration due to the protective substrate thickness difference and the aberration due to the recording layer thickness difference.

JP 2002-373444 A

  The present invention has been made in view of the above-described conventional situation. When recording / reproducing is performed on optical recording media having different protective substrate thicknesses with light beams having different wavelengths, the recording layer has a multilayered recording layer. An optical pickup capable of compensating for spherical aberration caused by a protective substrate thickness difference or a layer thickness difference between recording layers with a simple configuration when recording / reproducing with respect to an optical recording medium, and an optical recording medium recording / reproducing using the pickup An object is to provide an apparatus.

  In order to achieve the above-described object, an optical pickup according to the present invention performs recording / reproduction with respect to an optical recording medium in which a plurality of recording layers are laminated, or a plurality of optical recording media having different protective substrate thicknesses for protecting the recording surface. In an optical pickup that performs recording / reproduction with respect to a light beam having a different wavelength and numerical aperture, a first light source that emits a first light beam having a first wavelength, and a second light beam having a second wavelength are provided. A second light source that emits light, a third light source that emits a third light beam having a third wavelength, and the first, second, and third light beams are collected on individual optical recording media. The first light beam is disposed on the objective lens and immediately before the light source side of the objective lens, and the first light beam is condensed on the first optical recording medium having the first protective substrate thickness via the objective lens. A second having a protective substrate thickness of 2 A diffractive means for condensing the third light beam on the optical recording medium and condensing the third light beam on the third optical recording medium having the third protective substrate thickness, and being disposed immediately before the light source side of the diffractive means. A liquid crystal diffractive means having a variable refractive index distribution in a cross section perpendicular to the traveling direction of the light beam, a light receiving means for receiving a reflected beam reflected by each optical recording medium and converting it into an electrical signal; An optical recording medium in which a plurality of recording layers are laminated, or an optical recording medium detecting means for detecting the type of an optical recording medium having a different protective substrate thickness for protecting the recording surface, and a recording layer or optical detected by the optical recording medium detecting means Liquid crystal control means for controlling the liquid crystal alignment pattern of the liquid crystal diffraction means according to the type of the recording medium, and the liquid crystal diffraction means according to the difference in the recording layer of the optical recording medium to be recorded or reproduced, or according to the type of the optical recording medium Liquid crystal alignment pattern Changing the down giving a phase difference to the light beam that enters, the spherical aberration due to the protective substrate thickness difference, to compensate for aberrations including spherical aberration caused by thickness difference of recording layers.

  At this time, the objective lens, the diffractive means, and the liquid crystal diffractive means are fixed to each other, and the first light beam, the second light beam, and the third light beam are incident on the liquid crystal diffractive means in an infinite system. It is characterized by that.

  When the first optical recording medium has a plurality of stacked recording layers, the liquid crystal diffracting means has an aberration caused by the recording layer thickness difference of the first optical recording medium with respect to the first light beam. The position of correcting the aberration caused by the difference in thickness of the protective substrate with respect to the third optical beam focused on the third optical recording medium via the objective lens by the diffraction means and the electrode pattern causing the phase difference to be corrected. And an electrode pattern for generating a phase difference.

  Further, when the second optical recording medium has a plurality of stacked recording layers, the liquid crystal diffracting means is generated due to the recording layer thickness difference of the second optical recording medium with respect to the second light beam. Corrects the aberration caused by the difference in thickness of the protective substrate with respect to the third optical beam focused on the third optical recording medium via the objective lens by the diffraction means and the electrode pattern that generates the phase difference for correcting the aberration. And an electrode pattern for generating a phase difference.

  The liquid crystal diffractive means also functions as an aperture limiting function, and the liquid crystal control means sets the numerical aperture of the light beam having the smallest numerical aperture among the first light beam, the second light beam, and the third light beam. The liquid crystal diffracting means is controlled so as to match, and the light beam is regulated.

  To achieve the above object, an optical recording medium recording / reproducing apparatus according to the present invention includes a first light source that emits a first light beam having a first wavelength, and a second light source having a second wavelength. A second light source that emits a light beam, a third light source that emits a third light beam having a third wavelength, and the first, second, and third light beams on individual optical recording media. An objective lens that condenses, and a second light that is disposed immediately before the light source side of the objective lens and condenses the first light beam onto the first optical recording medium having the first protective substrate thickness via the objective lens. Diffractive means for condensing the beam onto a second optical recording medium having a second protective substrate thickness and condensing a third light beam onto a third optical recording medium having a third protective substrate thickness; Refractive index component in the cross section perpendicular to the traveling direction of the light beam that is placed and transmitted just before the light source side of the diffraction means A liquid crystal diffractive means having a variable thickness; a light receiving means for receiving a reflected beam reflected by each optical recording medium and converting it into an electrical signal; and an optical recording medium or recording surface on which a plurality of recording layers are laminated. An optical recording medium detecting means for detecting the type of the optical recording medium having a different protective substrate thickness to be protected, and a liquid crystal alignment pattern of the liquid crystal diffracting means according to the type of the recording layer or the optical recording medium detected by the optical recording medium detecting means. And an optical pickup having a liquid crystal control means for controlling. In this optical pickup, the objective lens, the diffracting means, and the liquid crystal diffracting means are fixed to each other so that the first light beam, the second light beam, and the third light beam are infinite with respect to the liquid crystal diffracting means. Is incident.

  Thereby, the optical recording medium recording / reproducing apparatus according to the present invention changes the liquid crystal alignment pattern of the liquid crystal diffracting means according to the difference in the recording layer of the optical recording medium to be recorded / reproduced or the type of the optical recording medium. A phase difference is given to the light beam to compensate for aberrations including spherical aberration due to protective substrate thickness difference and spherical aberration due to layer thickness difference between recording layers.

  Further, at this time, when the first optical recording medium has a plurality of stacked recording layers, the liquid crystal diffracting means is caused by the difference in recording layer thickness of the first optical recording medium with respect to the first light beam. An aberration caused by the difference in thickness of the protective substrate with respect to the third light beam focused on the third optical recording medium via the objective lens by the diffraction means and the electrode pattern for correcting the generated aberration And an electrode pattern for generating a phase difference for correcting.

  Further, when the second optical recording medium has a plurality of stacked recording layers, the liquid crystal diffracting means is generated due to the recording layer thickness difference of the second optical recording medium with respect to the second light beam. Corrects the aberration caused by the difference in thickness of the protective substrate with respect to the third optical beam focused on the third optical recording medium via the objective lens by the diffraction means and the electrode pattern that generates the phase difference for correcting the aberration. And an electrode pattern for generating a phase difference.

  According to the present invention, when recording / reproducing with respect to optical recording media having different protective substrate thicknesses is performed with light beams having different wavelengths, and when recording / reproducing with respect to an optical recording medium having multilayered recording layers is performed, the protective substrate is used. It is possible to compensate for spherical aberration caused by the thickness difference or the layer thickness difference between the recording layers, and to simplify the optical system configuration. Manufacturing costs can be reduced by simplifying the optical system configuration of the optical pickup.

  In addition, the optical pickup according to the present invention uses the first light beam, the second light beam, and the third light as an infinite optical system in the first light beam, the second light beam, and the third light beam. By making the beam incident on the recording surface of the optical recording medium, it is possible to ensure the visual field characteristics of the third light beam, which is the light beam having the smallest numerical aperture and the longest wavelength. Thereby, the tracking characteristic of the longest wavelength beam can be stabilized.

  Hereinafter, specific examples of the optical pickup according to the present invention will be described in detail with reference to the drawings. First, an optical system of an optical pickup shown as a specific example of the present invention will be described with reference to FIG. In this specific example, the first optical disk 31 is a Blu-ray disk (hereinafter referred to as BD) that uses a light beam having a protective substrate thickness of 0.1 mm and a wavelength of 405 nm as recording / reproducing light, and the second optical disk 32. Is a DVD (Digital Versatile Disc) that uses a protective substrate thickness of 0.6 mm and a light beam with a wavelength of 655 nm as recording / reproducing light, and the third optical disc 33 records and reproduces a light beam with a protective substrate thickness of 1.2 mm and a wavelength of 785 nm. CD (Compact Disc) used as light.

  This optical pick-up 1 corrects the residual spherical aberration of the CD and the multilayer, which are problems when using the first-order diffracted light of the CD in the optical system optimized to generate the first-order diffracted light for both BD and DVD shown in FIG. Aberration correction due to the layer thickness difference between the recorded recording layers is achieved.

  The optical pickup 1 is a basic optical system having a light detection element that receives reflected light from a light source and a recording surface and reads an optical signal, a spectroscopic element that branches outgoing light and return light, an element that generates a focus signal or a tracking signal, and the like. An objective lens 13 for condensing the light beam emitted from the light source on the recording surface of the optical disc, a diffraction grating 14 disposed on the outward light incident side of the objective lens, and a phase difference for correcting aberrations in the light beam. A liquid crystal element 15 and a liquid crystal control circuit 16 for controlling the liquid crystal element 15 are provided. In the optical pickup 1, the objective lens 13, the diffractive element 14, and the liquid crystal element 15 are fixed to each other as an imaging unit 17 and driven by one actuator.

  In this specific example, as the basic optical system described above, a first light source that generates a BD light beam 41 having a wavelength of 405 nm, a photodetector that detects reflected light from the first optical disk 31, and a BD standard Is provided with a first basic optical system 11 including an element that generates a focus signal or a tracking signal. In addition, a second light source that generates a DVD light beam 42 having a wavelength of 655 nm, a photodetector that detects reflected light from the second optical disk 32, and a CD light beam 43 having a wavelength of 785 nm are generated. 3 and a photodetector that detects reflected light from the third optical disc 33, and an element that generates a focus signal or a tracking signal based on the DVD or CD standard, and is compatible with DVD and CD. The second basic optical system 12 is provided.

  A first light source included in the first basic optical system 11 (not shown) emits a light beam 41 having a wavelength of 405 nm for BD recording / reproduction as a first wavelength. A second light source included in the second basic optical system 12 (not shown) emits a light beam 42 having a wavelength of 655 nm for DVD recording / reproduction as the second wavelength. A third light source is also included in the second basic optical system 12 and emits a light beam 43 having a wavelength of 785 nm for CD recording / reproducing as the third wavelength.

  The objective lens 13 can collect the light beam 41 having the first wavelength with respect to the BD as the first optical disk having the first protective substrate thickness 31a. Further, the light beam 42 having the second wavelength is applied to the DVD as the second disk having the second protective substrate thickness 32a, and the CD as the third optical disk having the third protective substrate thickness 33a is applied. Thus, the light beam 43 having the third wavelength can be collected.

  The numerical aperture of the objective lens 13 is 0.85 for the first wavelength, 0.60 for the second wavelength, and 0.45 for the third wavelength. However, the first protective substrate thickness of the first optical disc that is BD is 0.1 mm, the second protective substrate thickness of the second optical disc that is DVD is 0.6 mm, and the third protective substrate is CD. The third protective substrate thickness of the optical disc is 1.2 mm.

  The diffraction grating 14, together with the objective lens 13, exhibits spherical aberration due to the difference in the protective substrate thickness between the BD and the DVD with respect to the light beam 41 with a wavelength of 405 nm for BD recording and reproduction and the light beam 42 with a wavelength of 655 nm for DVD recording and reproduction. It has an optical characteristic to be corrected.

  The objective lens 13 is a lens designed to be compatible with BD and DVD, and the incident cross section of the outward light is curved and has a sawtooth shape (blazed shape). The objective lens 13 condenses the light beam 41 having the first wavelength with respect to the BD as the first optical disc 31 having the first protective substrate thickness 31a and the second protective substrate thickness 32a. The light beam 42 having the second wavelength is condensed with respect to the DVD as the disk 32, and the third wavelength with respect to the CD as the third optical disk 33 having the third protective substrate thickness 33a. The light beam 43 can be condensed.

  Although not shown, the liquid crystal element 15 is configured by sandwiching liquid crystal molecules between two glass substrates, and a concentric electrode pattern is formed by a transparent electrode on one of the two glass substrates. ing. On the other glass substrate, an electrode is formed at a position facing the electrode pattern of the one glass substrate. Since the liquid crystal element 15 has a finely divided electrode pattern, the liquid crystal alignment distribution that generates a phase difference for correcting the residual spherical aberration of the light beam for CD and the recording layer 2 of the BD multilayered are provided. It is possible to obtain a liquid crystal alignment distribution that causes a phase difference for correcting spherical aberration caused by a layer thickness difference when recording / reproducing with respect to the recording layer of the layer. When a driving voltage is applied to each transparent electrode, the alignment of liquid crystal molecules is biased according to an electric field corresponding to the applied voltage. Thereby, the refractive index distribution in the cross section perpendicular to the traveling direction of the light beam transmitted through the liquid crystal element can be arbitrarily set, and the phase of the wavefront of the light beam can be controlled for each electrode pattern region. it can. The liquid crystal element 15 also serves as an aperture limiting element for obtaining the above-described CD light beam having a numerical aperture of 0.45.

  The transparent glass substrate is used for recording / reproducing with respect to the second recording layer of the BD multilayered recording layer and the electrode pattern for generating the phase difference for correcting the residual spherical aberration of the light beam for CD. And an electrode pattern for generating a phase difference for correcting spherical aberration caused by a layer thickness difference. Each electrode pattern will be described with reference to FIG.

  FIG. 2 shows the relationship between the optical phase difference OPD (Optical Path Difference) actually generated in the liquid crystal element 15 and the numerical aperture NA. A curve a0 shown in FIG. 2A indicates the amount of phase change that occurs when the light beam 43 for CD is transmitted through the combination of the objective lens 13 and the diffraction grating 14 used in this specific example. In the case of the light beam 43 for CD, an electrode pattern that causes liquid crystal molecule alignment that gives an opposite phase to the phase amount indicated by the dotted line a1 with respect to the transmitted light beam 43 is used. That is, the electrode pattern divided into about 10 regions whose voltage is controlled so as to produce a molecular alignment in which the liquid crystal molecular alignment changes stepwise and the phase amount change of the light beam 43 becomes the largest in the vicinity of NA 0.30. Form on top. When the light beam 43 is transmitted through the liquid crystal element 15, the phase amount changes as indicated by a2, and the spherical aberration a0 is suppressed.

  A curve b0 shown in FIG. 2B indicates the amount of phase change caused by the layer thickness difference from the first layer when the second recording layer of the BD is read by the BD light beam 41. In the case of the beam 41 for BD, it is set as the electrode pattern which produces the liquid crystal molecular orientation which gives the reverse phase of the phase amount shown with the dotted line b1 with respect to the light beam 41 which permeate | transmits. That is, an electrode pattern different from the above-mentioned pattern that is voltage controlled so as to produce a molecular orientation in which the liquid crystal molecular orientation changes stepwise and the phase amount change of the light beam 41 becomes the largest in the vicinity of NA 0.45 is formed on the glass substrate. Form. When the light beam 41 passes through the liquid crystal element 15, the phase amount changes as indicated by b2, and the spherical aberration b0 is suppressed.

  The objective lens 13, the diffraction grating 14, and the liquid crystal element 15 described above are fixedly disposed on the same actuator. The diffraction grating 14 may be integrated on the objective lens 13. Further, the light beam 41, the light beam 42, and the light beam 43 are incident on the liquid crystal element 15 as infinite light.

  The objective lens 13, the diffraction grating 14, and the liquid crystal element 15 configured as described above receive the first-order diffracted light of the light beam 41 via the objective lens 15 when the light beam 41 having a wavelength of 405 nm is incident from the surface. When the light beam 42 of the DVD recording / reproducing light beam 42 is incident, the first-order diffracted light of the light beam 42 is condensed on the DVD recording surface or the CD recording surface. To do.

  The light beam 42 and the light beam 43 emitted from the basic optical system 12 for DVD and CD are aligned with the optical axis of the light beam 41 emitted from the basic optical system 11 for BD by the wavelength selective combining prism 19. It has become. The respective light beams having the same optical axis are converted into parallel light, that is, infinite light by the collimating lens 18 and then incident on the liquid crystal element 15.

  The liquid crystal control circuit 16 corrects the residual spherical aberration generated by the CD light beam 43 in the liquid crystal element 15 when recording / reproducing the CD in accordance with a detection signal from a disk type discriminating unit 115 described later. When the second recording layer of the BD is read by controlling the voltage applied to the electrode pattern, spherical aberration caused by the layer thickness difference of the recording layer is corrected by the DVD light beam 42 in the liquid crystal element 15. The voltage applied to the electrode pattern is controlled.

  As described above, according to the optical pickup 1 shown as the above-described specific example, in the case of the BD / DVD / CD = primary / primary / primary optical system described with reference to FIG. The light beam 43 is used as infinite light with respect to the liquid crystal element 15 so that the remaining spherical aberration correction of the CD and the aberration correction due to the layer thickness difference between the multilayered recording layers can be made compatible without impairing the tracking characteristics. Can do. This also ensures good visual field characteristics when the CD light beam 43 is used.

  Next, an optical disc recording / reproducing apparatus 101 to which an optical pickup shown as a specific example of the present invention is applied is shown in FIG.

  The optical disk recording / reproducing apparatus 101 includes a spindle motor 103 as a driving means for rotating an optical disk 102 as an optical recording medium, an optical pickup 104 according to the present invention, and a feed motor 105 as the driving means. The optical disc recording / reproducing apparatus 101 is a recording / reproducing apparatus that realizes compatibility among three standards capable of recording / reproducing on three types of optical discs 102 having different formats and an optical disc in which recording layers are laminated.

  As an optical disk that can be used in this specific example, a BD that uses a light beam having a wavelength of 405 nm as recording / reproducing light, a DVD that uses a light beam having a wavelength of 655 nm as recording / reproducing light, and a light beam having a wavelength of 785 nm are used as recording / reproducing light. CD to play. In addition, an optical disc having a recording layer laminated using the same recording / reproducing wavelength is also included. The optical disc 31, the optical disc 32, and the optical disc 33 described in the upper part correspond to the optical disc 102 shown in FIG.

  Here, the spindle motor 103 and the feed motor 105 are driven and controlled in accordance with the disk type by a servo control unit 109 that is controlled based on a command from the system controller 107 that also serves as a disk type discriminating unit. The optical disc 32 and the optical disc 33 are driven at a predetermined rotational speed.

  The optical pickup 104 is an optical pickup having the three-wavelength compatible optical system described with reference to FIGS. 1 and 2, and irradiates a recording layer of an optical disc having a different standard with a light beam having a different wavelength. The reflected light in the recording layer is detected. The optical pickup 104 supplies a signal corresponding to each light beam from the detected reflected light to the preamplifier unit 120.

  The output of the preamplifier unit 120 is sent to a signal modulator / demodulator and error correction code block (hereinafter referred to as a signal modulation / demodulation & ECC block) 108. The signal modulation / demodulation unit and ECC block 108 performs signal modulation, demodulation, and addition of an ECC (error correction code). The optical pickup 104 irradiates a recording layer of the optical disk 102 that rotates in accordance with instructions from the signal modulation / demodulation unit and the ECC block 108, and records or reproduces a signal on the optical disk 102.

  The preamplifier unit 120 is configured to generate a focus error signal, a tracking error signal, an RF signal, and the like based on a signal corresponding to a light beam detected differently for each format. Depending on the type of optical recording medium to be recorded or reproduced, a predetermined control such as demodulation and error correction processing based on the BD, DVD, or CD standard is performed by the servo control circuit 109, the signal modulation / demodulation unit, the ECC block 108, and the like. Is performed.

  Here, for example, if the recording signal demodulated by the signal modulation / demodulation & ECC block 108 is for computer data storage, it is sent to the external computer 130 via the interface 111. Thereby, the external computer 130 or the like can receive a signal recorded on the optical disc 102 as a reproduction signal.

  In addition, if the recording signal demodulated by the signal modulation / demodulation & ECC block 108 is for audio visual, it is digital / analog converted by the D / A conversion unit of the D / A and A / D converter 112 and supplied to the audio visual processing unit 113. Is done. Audio visual processing is performed by the audio visual processing unit 113 and transmitted to an external imaging / projection device (not shown) or the like via the audio visual signal input / output unit 114.

  In the optical pickup 104, for example, control of a feed motor 105 for moving to a predetermined recording track on the optical disk 102, control of a spindle motor 103, and two axes for holding an objective lens serving as a light condensing means in the optical pickup 104 The servo control circuit 109 controls driving of the actuator in the focusing direction and driving in the tracking direction.

  The servo control circuit 109 operates the optical coupling efficiency variable element disposed in the optical pickup 104, and the optical coupling efficiency in the optical pickup 104, that is, the total light amount of light emitted from a laser light source such as a semiconductor laser element and the optical disk. Control is performed so that the ratio of the amount of light collected on 102 is changed in the recording mode, in the reproduction mode, or in accordance with the type of the optical disk 102.

  The laser control unit 121 controls the laser light source of the optical pickup 104. In particular, in this specific example, the laser control unit 121 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode. Also, control is performed to vary the output power of the laser light source depending on the type of the optical disk 102. The laser control unit 121 switches the laser light source of the optical pickup 104 in accordance with the type of the optical disc 102 detected by the disc type discrimination unit 115.

  The disc type discriminating unit 115 can detect different formats of the optical disc 102 based on the surface reflectivity, the shape and the external shape among BD, DVD, and CD.

  Each block constituting the optical disc recording / reproducing apparatus 101 is configured to be able to perform signal processing based on the specification of the optical disc to be mounted in accordance with the detection result in the disc type discriminating unit 115.

  The system controller 107 determines the type of the optical disk 102 based on the detection result sent from the disk type determination unit 115. As a method for discriminating the type of the optical recording medium, if the optical recording medium is of a type that is housed in a cartridge, a detection hole is provided in the cartridge and detection is performed using a contact detection sensor or a push switch. In addition, the recording layer in the same optical disc is discriminated with respect to which recording layer is recorded / reproduced based on information by table information (TOC) recorded in premastered pits and grooves in the innermost circumference of the optical disc. Can be used.

  A servo control circuit 109 functioning as an optical coupling efficiency control unit is controlled by the system controller 107 and controls the optical coupling efficiency in the optical pickup 104 according to the determination result of the disk type determination unit 115. The servo control circuit 109 performs recording and / or reproduction by, for example, detecting the relative position between the optical pickup 104 and the optical disk 102 (including the case of detecting the position based on the address signal recorded on the disk 102). The area can be determined. Then, the servo control circuit 109 controls the optical coupling efficiency in the optical pickup 104 according to the determination result of the recording area to be recorded and / or reproduced.

  According to the optical disc recording / reproducing apparatus 101 described above, by using the optical pickup 1 shown in FIG. 1, in the three-wavelength compatible optical system using the respective light beams with wavelengths of 405 nm, 655 nm, and 785 nm, the residual spherical aberration correction of the CD is performed. And correction of aberrations due to the difference in layer thickness between the multilayered recording layers can be achieved.

  The present invention relates to an optical pickup that performs recording and reproduction on optical recording media having different protective substrate thicknesses by using light beams of different wavelengths, and an optical pickup that performs recording and reproduction on an optical recording medium in which a plurality of recording layers are laminated. For example, the present invention can be applied to disc formats other than those described in the specific examples. For example, optical discs include various types of recording / reproducing discs using optical modulation recording, optical discs including so-called “magneto-optical recording”, “phase change recording”, “dye recording”, etc., specifically “CD-R / RW "," DVD-RAM "," DVD-R / RW "," DVD + RW ", etc., or various magneto-optical recording media. The optical disk may be an optical disk in which the recording layer is divided into at least two or more recording areas having different optimum recording and / or reproducing light power on the recording layer.

It is a block diagram explaining the optical system of the optical pick-up shown as a specific example of this invention. It is a figure explaining the relationship between optical phase difference OPD and NA which are actually generated with the liquid crystal element in the said optical pick-up. 1 is a configuration diagram illustrating an optical disc recording / reproducing apparatus to which an optical pickup shown as a specific example of the present invention is applied. FIG. It is a figure explaining the protective substrate thickness which protects the recording surface of an optical disc, a use wavelength band, and the amount of spherical aberration to generate | occur | produce.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Optical pick-up, 11 1st basic optical system, 12 2nd basic optical system, 13 Objective lens, 14 Diffraction element, 15 Liquid crystal element, 16 Liquid crystal control circuit, 17 Imaging unit, 18 Collimating lens, 19 Wavelength selection synthesis Prism 31 First optical disk, 32 Second optical disk, 33 Third optical disk, 41 Light beam (405 nm), 42 Light beam (655 nm), 43 Light beam (785 nm)

Claims (8)

In an optical pickup that performs recording / reproduction with respect to an optical recording medium in which a plurality of recording layers are laminated, or performs recording / reproduction with respect to a plurality of optical recording media having different protective substrate thicknesses for protecting the recording surface, using light beams having different wavelengths and numerical apertures. ,
A first light source that emits a first light beam having a first wavelength;
A second light source that emits a second light beam having a second wavelength;
A third light source that emits a third light beam having a third wavelength;
An objective lens for condensing the first, second and third light beams on the individual optical recording media;
The first light beam is disposed immediately before the objective lens on the light source side, and the first light beam is condensed on a first optical recording medium having a first protective substrate thickness via the objective lens, and the second light beam is focused on the second optical beam. Diffraction means for condensing on a second optical recording medium having a protective substrate thickness of 2 and condensing the third light beam on a third optical recording medium having a third protective substrate thickness;
A liquid crystal diffractive means in which the refractive index distribution in the cross section perpendicular to the traveling direction of the light beam disposed and transmitted immediately before the light source side of the diffractive means is variable;
A light receiving means for receiving a reflected beam reflected by each individual optical recording medium and converting it into an electric signal, and an optical recording medium in which the plurality of recording layers are laminated or an optical recording having a different protective substrate thickness for protecting the recording surface Optical recording medium detection means for detecting the type of medium;
Liquid crystal control means for controlling the liquid crystal alignment pattern of the liquid crystal diffraction means according to the type of the recording layer or optical recording medium detected by the optical recording medium detection means,
The objective lens, the diffracting means, and the liquid crystal diffracting means are fixed to each other, and the first light beam, the second light beam, and the third light beam are incident on the liquid crystal diffracting means in an infinite system. An optical pickup characterized by The first optical recording medium has a plurality of recording layers laminated,
The liquid crystal diffracting means includes an electrode pattern that generates a phase difference for correcting an aberration caused by a recording layer thickness difference of the first optical recording medium with respect to the first light beam;
An electrode pattern for generating a phase difference that corrects an aberration caused by a difference in thickness of the protective substrate with respect to the third light beam condensed on the third optical recording medium via the objective lens by the diffracting means; The optical pickup according to claim 1, further comprising: The second optical recording medium that can be recorded and reproduced by the second light beam has a plurality of recording layers laminated,
The liquid crystal diffracting means includes an electrode pattern that generates a phase difference that corrects an aberration caused by a recording layer thickness difference of the second optical recording medium with respect to the second light beam;
An electrode pattern for generating a phase difference that corrects an aberration caused by a difference in thickness of the protective substrate with respect to the third light beam condensed on the third optical recording medium via the objective lens by the diffracting means; The optical pickup according to claim 1, further comprising:   The liquid crystal control means controls the liquid crystal diffraction means so as to match the numerical aperture of the light beam having the smallest numerical aperture among the first light beam, the second light beam, and the third light beam. The optical pickup according to claim 1, wherein the optical pickup is regulated. Individual optical recording media having different protective substrate thicknesses are rotationally driven and moved in the radial direction of the optical recording media by a feeding means, and recording and reproduction are performed by light beams having different wavelengths and numerical apertures according to the types of optical recording media. In an optical recording medium recording / reproducing apparatus that has an optical pickup that performs the control and controls the rotation of the optical recording medium and the movement of the optical pickup in accordance with the recording and / or reproducing operation,
The above optical pickup
A first light source that emits a first light beam having a first wavelength;
A second light source that emits a second light beam having a second wavelength;
A third light source that emits a third light beam having a third wavelength;
An objective lens for condensing the first, second and third light beams on the individual optical recording media;
The first light beam is disposed immediately before the objective lens on the light source side, and the first light beam is condensed on a first optical recording medium having a first protective substrate thickness via the objective lens, and the second light beam is focused on the second optical beam. Diffraction means for condensing on a second optical recording medium having a protective substrate thickness of 2 and condensing the third light beam on a third optical recording medium having a third protective substrate thickness;
A liquid crystal diffractive means in which the refractive index distribution in the cross section perpendicular to the traveling direction of the light beam disposed and transmitted immediately before the light source side of the diffractive means is variable;
A light receiving means for receiving a reflected beam reflected by each individual optical recording medium and converting it into an electric signal, and an optical recording medium in which the plurality of recording layers are laminated or an optical recording having a different protective substrate thickness for protecting the recording surface Optical recording medium detection means for detecting the type of medium;
Liquid crystal control means for controlling the liquid crystal alignment pattern of the liquid crystal diffraction means according to the type of the recording layer or optical recording medium detected by the optical recording medium detection means,
The objective lens, the diffracting means, and the liquid crystal diffracting means are fixed to each other, and the first light beam, the second light beam, and the third light beam are incident on the liquid crystal diffracting means in an infinite system. An optical recording medium recording / reproducing apparatus. The first optical recording medium has a plurality of recording layers laminated,
The liquid crystal diffracting means includes an electrode pattern that generates a phase difference for correcting an aberration caused by a recording layer thickness difference of the first optical recording medium with respect to the first light beam;
An electrode pattern for generating a phase difference that corrects an aberration caused by a difference in thickness of the protective substrate with respect to the third light beam condensed on the third optical recording medium via the objective lens by the diffracting means; 6. The optical recording medium recording / reproducing apparatus according to claim 5, further comprising: The second optical recording medium that can be recorded and reproduced by the second light beam has a plurality of recording layers laminated,
The liquid crystal diffracting means includes an electrode pattern that generates a phase difference that corrects an aberration caused by a recording layer thickness difference of the second optical recording medium with respect to the second light beam;
An electrode pattern for generating a phase difference that corrects an aberration caused by a difference in thickness of the protective substrate with respect to the third light beam condensed on the third optical recording medium via the objective lens by the diffracting means; 6. The optical recording medium recording / reproducing apparatus according to claim 5, further comprising:   The liquid crystal control means controls the liquid crystal diffraction means so as to match the numerical aperture of the light beam having the smallest numerical aperture among the first light beam, the second light beam, and the third light beam. The optical recording medium recording / reproducing apparatus according to claim 5, wherein

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