JP2005276373A - Pickup for magneto-optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a pickup for magneto-optical recording medium which is adaptive to a plurality of magneto-optical recording medium having different optimum phase difference and which improves quality of a reproduced signal in all media. <P>SOLUTION: A return light beam reflected by a magneto-optical recording medium 53 is separated to ±first order diffraction light by a diffraction element 55 for branching light provided between a light source 52 and an objective lens 54. The ±first order diffraction light are passed through first and second phase compensation elements 60, 61, and polarized and separated by first and second polarization separation elements 56, 57 and made incident on first and second detectors 58, 59. A magneto-optical signal is reproduced using a differential detecting method by combination of a component being vertical to a track direction detected by the first detector 58 and a component being parallel to the track direction detected by the second detector 59, or a component being parallel to the track direction detected by the first detector 58 and a component being vertical to the track direction detected by the second detector 59. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pickup for a magneto-optical recording medium for recording information on and / or reproducing information from a magneto-optical recording medium.

  As a recording medium for recording information by the magneto-optical recording method, a mini disk (abbreviated as MD) having a diameter of 64 mm for recording music information is widely known. In addition to this MD, there are MO disks used for MO (Magneto-Optical) disk drive devices which are a kind of external storage devices for computers. Various types of MO disks with different recording methods and recording film structures are available.

  For such a magneto-optical recording / reproducing system for an MD or MO disk, various super-resolution techniques have been proposed in order to dramatically improve the recording capacity. For example, in order to record a mark smaller than the light beam diameter, there is a method called a magnetic field modulation recording method. In addition, as a method of reproducing a mark smaller than the light beam diameter, a magnetic super-resolution technique called MSR (Magnetic Super Resolution), a magnetic domain expansion reproduction method called MAMMOS (Magnetic AMplifying Magneto Optical System), and DWDD (Domain Wall Displacement Detection). There has been proposed a domain wall motion detection technique called "." A magneto-optical recording medium (disk) that is an object of the DWDD system includes at least a magnetic three-layer film including a domain wall motion layer, a switching layer, and a magnetic recording layer (memory layer). When reproducing information, the domain wall motion of the domain wall motion layer is used in the region where the magnetic film temperature is equal to or higher than the Curie temperature of the switching layer, thereby effectively expanding the size of the recorded magnetic domain and It can be enlarged.

  Various optical system configurations have also been proposed for optical pickups using the magneto-optical recording method. One of the proposed prior arts is an integrated unit and an optical pickup in which a servo signal and a magneto-optical signal detection system are integrated into one package in order to reduce the size of the optical pickup (for example, Patent Documents). 1). FIG. 8 is a side view schematically showing the structure of a conventional optical pickup, and FIG. 9 is a plan view of the photodetector 7 provided in the optical pickup shown in FIG.

  A conventional optical pickup 1 includes a semiconductor laser element 2, a grating 3, a first polarization separation means 4, an objective lens 5, a second polarization separation means 6, and a photodetector 7. Yes. The semiconductor laser element 2, the grating 3, the first polarization separation means 4, the second polarization separation means 6, and the photodetector 7 are integrated into one package 8. The first polarization separation means 4 is formed on the surface of the glass substrate 9 that is the base material, for example, facing the objective lens 5, and the second polarization separation means 6 is the first polarization separation of the glass substrate 9. It is formed on the surface opposite to the surface on which the means 4 is formed, that is, the surface facing the semiconductor laser 2. The first polarization separation means 4 is a polarization hologram having an enhancement function formed on a birefringent substrate, for example, and is set so that its optical axis is perpendicular to the polarization direction of the light beam from the semiconductor laser element 2. , Has the property of transmitting ordinary light and diffracting extraordinary light.

  The light beam emitted from the semiconductor laser element 2 passes through the first polarization separation means 4 and is irradiated on the information recording surface of the MO disk 10 which is a magneto-optical recording medium. A light beam reflected by the MO disk 10 (hereinafter referred to as a return light beam) passes through the objective lens 5 again and enters the first polarization separation means 4. The return light beam incident on the first polarization separation means 4 is diffracted by the first polarization separation means 4 into at least 0 (zero) order diffracted light and ± (plus or minus) first order diffracted light. The first-order diffracted light of the return light beam diffracted by the first polarization separation means 4 is incident on the second polarization separation means 6.

  The second polarization separation means 6 is divided into two parts, and is composed of a second polarization separation means 6a and a second polarization separation means 6b. The second polarized light separating means 6a and the second polarized light separating means 6b are arranged separately on the right and left sides in FIG. Each of the second polarization separation means 6a and the second polarization separation means 6b is a polarization hologram and is configured to diffract abnormal light. The second polarization separation means 6 is disposed so that the optical axis of the substrate is at an angle of 45 degrees with respect to the polarization direction of the light beam from the semiconductor laser element 2, and the ordinary light is transmitted and the abnormal light is diffracted. Set to do.

  In the second polarization separation means 6a, the + 1st order diffracted light diffracted by the first polarization separation means 4 is incident, the 0th order diffracted light of the incident light is transmitted, and the −1st order diffracted light is refracted. In the second polarization separation means 6b, the −1st order diffracted light diffracted by the first polarization separation means 4 is incident, the 0th order diffracted light of the incident light is transmitted, and the + 1st order diffracted light is refracted. Then, the 0th-order light and the ± 1st-order diffracted light by the second polarization separation means 6a and 6b are incident on the portions 7a and 7b of the photodetector 7, respectively. That is, the 0th-order diffracted light and the −1st-order diffracted light by the second polarization separation means 6a are incident on the portion 7a of the photodetector 7, and the 0th-order light and the + 1st-order diffracted light by the second polarization separation means 6b are detected by light. The light enters the portion 7b of the vessel 7.

  As shown in FIG. 9, the photodetector 7 includes a first photodetector 7 a and a second photodetector 7 b that are separated from each other with respect to the semiconductor laser element 2, and the first and second photodetectors are arranged. The devices 7a and 7b include main light receiving units 15 and 12 for receiving and detecting the main beam and sub light receiving units 14, 16, 11, and 13 for receiving and detecting the sub beam, respectively. Each of the main light receiving units 12 and 15 is further divided into left and right. If the left and right outputs of the main light receiving unit 12 are a and b, and the left and right outputs of the main light receiving unit 15 are c and d, MO The read signal MO of the disk 10 is given by the following equation (1). The servo signal detection method is omitted. Patent Document 1 discloses that the optical pickup can be miniaturized by such a configuration.

MO = (a + d)-(b + c) (1)
Patent Document 2 discloses a technique that uses a polarization separation element for reproducing a magneto-optical signal. . In this case, if the optical disk records and reproduces a magneto-optical signal, the magneto-optical signal is reproduced by detecting the difference signal between the p-polarized light and the s-polarized light branched by the polarization separation element. be able to. Further, Patent Document 2 discloses an optical pickup that uses a polarization separation element for reproduction of a magneto-optical signal and replaces a polarizing beam splitter and other optical components with this, thereby enabling the optical pickup to be reduced in size and thickness. doing.

In this specification, in the laser light used for reproducing the magneto-optical recording medium, a component parallel to the track direction is described as s-polarized light, and a component perpendicular to the track direction is described as p-polarized light.
JP-A-8-297875 Japanese Patent Laid-Open No. 2-192031

  In the optical pickup 1 disclosed in Patent Document 1, a polarization hologram is used as the first polarization separation means 4 that diffracts the return light beam from the MO disk 10 toward the photodetector 7. This polarization hologram has an enhancement function for increasing the modulation degree of the magneto-optical reproduction signal and improving the signal quality. That is, the optical axis of the birefringent substrate constituting the polarization hologram is set so as to be perpendicular to the polarization direction of the light beam emitted from the semiconductor laser element 2, and the diffraction efficiency is 0 for ordinary light (p-polarized light), for example. The primary light is 67% and the ± primary light is 27%, and for the extraordinary light (s-polarized light), the zero-order light is 18% and the ± primary light is 76%.

  However, there may be a phase difference between the p-polarized light and the s-polarized light of the ± first-order diffracted light for detecting the magneto-optical reproduction signal. When this phase difference increases, that is, when linearly polarized light becomes elliptically polarized light, reproduction is performed. There is a problem that the quality of the signal is greatly degraded.

  As the magneto-optical recording medium, super-resolution media having various recording film structures have been proposed. In the DWDD system having a magnetic multilayer film structure, even if linearly polarized light is incident on the magneto-optical recording medium, the return light beam itself that is modulated by the Kerr rotation angle may return to elliptically polarized light. In other words, there may be a phase difference between the polarization component of incident light and the component perpendicular thereto. Even in such a case, the quality of the reproduction signal is greatly deteriorated, as in the case where a phase difference is generated between the p-polarized light and the s-polarized light of the ± first-order diffracted light by the polarization hologram. For this reason, in the conventional optical pickup, one optical pickup cannot cope with magneto-optical recording media of different recording / reproducing systems.

  In this case, the phase difference between the p-polarized light and the s-polarized light, which differs depending on the medium, can be reproduced by two optical systems each provided with an optimum amount of phase compensation. Rather, servo signal generation and detection is essential. Naturally, in one detection system, it is necessary to generate a focus error signal and a radial error signal. Therefore, in either one of the photodetectors, it is necessary to divide the photodetector into a large number for the servo error signal. In a photodetector that generates a signal for servo, it is necessary to divide a light receiving element into a large number. Therefore, when a magneto-optical reproduction signal is generated from this, there is a problem that the signal quality is lowered.

  An object of the present invention is to provide a pickup for a magneto-optical recording medium that can cope with a plurality of magneto-optical recording media having different optimum phase differences and can improve the quality of a reproduction signal in all the media.

  According to the magneto-optical recording medium pickup according to the present invention, in the magneto-optical recording medium pickup for recording information on the magneto-optical recording medium and / or reproducing information from the magneto-optical recording medium, An objective lens for condensing the light emitted from the light source on the information recording surface of the magneto-optical recording medium, and reflected light that is reflected between the light source and the objective lens and reflected by the magneto-optical recording medium and transmitted through the objective lens. A diffracting light splitting diffraction element, a first polarization splitting element and a second polarization splitting element that split the + 1st order diffracted light and −1st order diffracted light diffracted by the light splitting diffraction element, respectively, and the first polarization splitting element And a first detector and a second photodetector that receive and detect the light separated by the second polarization separation element, respectively. The first detector and the second detector so as to receive the components separated by the first polarization separation element and the second polarization separation element and parallel to the component perpendicular to the track direction of the magneto-optical recording medium, respectively. The component perpendicular to the track direction detected by the first detector and the component parallel to the track direction detected by the second detector, or the component parallel to the track direction detected by the first detector And a magneto-optical signal are reproduced using a differential detection method based on a combination of components perpendicular to the track direction detected by the second detector.

  According to this configuration, for example, a magneto-optical signal in a magneto-optical recording medium having a different configuration, such as a normal magneto-optical recording medium and a magneto-optical recording medium using the DWDD technology, is combined with a light-receiving unit with good signal quality to detect a differential signal. Therefore, the reproduction signal quality can be improved.

  Preferably, in the magneto-optical recording medium pickup, optical phase compensation of a phase difference generated in the optical branching diffraction element is performed for each of the + 1st order diffracted light and the −1st order diffracted light diffracted by the optical branching diffraction element. The first phase compensation element and the second phase compensation element are provided, and the phase compensation amount of the first phase compensation element is different from the phase compensation amount of the second phase compensation element.

  According to this configuration, even when reproducing the first magneto-optical recording medium and the second magneto-optical recording medium having different recording film structures, the first phase compensation element can reproduce the first magneto-optical recording medium. The phase compensation amount corresponding to the signal is set, and the second phase compensation element can perform the optimum phase compensation by setting the phase compensation amount corresponding to the reproduction signal of the second magneto-optical recording medium. Signal quality can be improved. As a result, a magneto-optical recording medium of a different magneto-optical recording system can be obtained with one optical pickup without changing the phase compensation element according to the type of the magneto-optical recording medium, or by ON / OFF switching operation of the liquid crystal compensation element. It becomes possible to cope with.

  In the above-mentioned magneto-optical recording medium pickup, it is more preferable that either one of the first detector and the second detector has a tracking error signal and / or a focus error signal of a disk constituting the magneto-optical recording medium. The light receiving part is divided into four or more so that it can be detected, and the light receiving part can extract the component perpendicular to the track direction and the component parallel to the track direction contained in the reflected light from the magneto-optical recording medium. In the other detector, the component perpendicular to the track direction included in the reflected light from the magneto-optical recording medium separated by the polarization separation element and the track direction included in the reflected light from the magneto-optical recording medium. Divide the light receiving part into two or more and less than the number of divisions of the light receiving part of one detector so that parallel components can be taken out, and detect one of them Obtained from the component parallel to the track direction and the component perpendicular to the track direction obtained from the other detector, or obtained from the component perpendicular to the track direction obtained from one detector and the other detector. A magneto-optical signal is obtained using any of the components parallel to the track direction.

  According to this configuration, for example, a servo signal is detected by the three-beam method, so that the noise component is increased as compared with the case where the signals obtained by the light receiving portions of the detector divided into a large number are added to form a reproduction signal. Can be suppressed, and the quality of the reproduction signal can be improved.

  More preferably, in the above-described pickup for a magneto-optical recording medium, the light branching diffraction element is a polarizing diffraction element having a Kerr rotation angle multiplication function.

  According to this configuration, by using a polarizing diffraction element having a Kerr rotation angle multiplication function as the light branching diffraction element, not only the reflected light from the magneto-optical recording medium is separated from the forward path but also the Kerr rotation angle is increased. It is possible to detect a magneto-optical signal that has been doubled to increase the modulation degree and improve the signal quality.

  In the magneto-optical recording medium pickup, more preferably, the first polarization separation element and the second polarization separation element are polarizing diffraction elements.

  According to this configuration, the angle of polarization separation can be set large by using the first and second polarization separation elements as polarization diffraction elements. In addition, beam separation on the photodetector can be facilitated, and the degree of freedom of arrangement of the photodetector can be increased.

  In the magneto-optical recording medium pickup, more preferably, at least one of the first polarization separation element and the second polarization separation element is divided into a plurality of regions having different groove structures.

  According to this configuration, not only polarization separation but also wavefront division can be easily realized by using a polarization separation element that is divided into a plurality of regions having different groove structures. Thereby, the function of the servo signal generating hologram can be added at the same time.

  More preferably, the pickup for a magneto-optical recording medium includes a three-beam generating diffraction grating that separates light emitted from the light source into three beams, and the first polarization separation element and one of the surfaces of the transparent substrate, A second polarization separation element is provided, and a three-beam generation diffraction grating is provided on the other surface of the transparent substrate.

  Since the grating that generates the tracking servo signal and the polarization separation element that generates and separates the magneto-optical signal can be configured as one component, the apparatus can be miniaturized.

  FIG. 1 is a side view showing a simplified structure of a magneto-optical recording medium pickup according to an embodiment of the present invention. A magneto-optical recording medium pickup 51 (hereinafter simply referred to as a pickup) records information on a light source 52 composed of a semiconductor laser that emits light, and information emitted from the light source 52 on a magneto-optical recording medium 53 such as a magneto-optical disk. An objective lens 54 that collects light on the surface; a light branching diffraction element 55 that is provided between the light source 52 and the objective lens 54 and that diffracts the return light beam reflected by the magneto-optical recording medium 53 and transmitted through the objective lens; A first polarization separation element 56 and a second polarization separation element 57 that respectively separate the + 1st order diffracted light 64 and the −1st order diffracted light 65 diffracted by the light branching diffraction element 55, and the first polarization separation element 56 and the second polarization The first detector 58 and the second detector 59 that receive and detect the light separated by the separation element 57, the light branching diffraction element 55, and the first polarization component, respectively. Between the element 56 and the first phase compensation element 60 provided on the optical path of the + 1st order diffracted light 64, between the light branching diffractive element 55 and the second polarization separation element 57, and to the −1st order diffracted light 65 And a collimator lens 62 provided between the light branching diffraction element 55 and the objective lens 54. The pickup 51 is for recording information on the magneto-optical recording medium 53 and / or reproducing information from the magneto-optical recording medium 53.

  The three-dimensional azimuth axis shown in FIG. 1 indicates the radial direction of the magneto-optical recording medium 53 and the Y axis of the magneto-optical recording medium 53 when the magneto-optical recording medium 53 is mounted on the pickup 51. A tangential direction of a track formed on the information recording surface is shown, and a Z axis is a direction perpendicular to the X axis and the Y axis. In the pickup 51 of the present embodiment, the Z axis coincides with the axial direction of the light emitted from the light source 52. The notation of the X, Y, and Z axes is used throughout this specification.

  As the light source 52, a semiconductor laser is used. The magneto-optical recording medium 53 is, for example, a mini disk (MD). In FIG. 1, only one magneto-optical recording medium 53 mounted on the pickup 51 is shown. In place of the magneto-optical recording medium 53, another magneto-optical recording medium having a different magneto-optical recording system, for example, a high-density MD using a magnetic super-resolution technique or a domain wall motion detection technique is mounted. Can be recorded and reproduced.

  FIG. 2 is a cross-sectional view showing the configuration of the optical branching diffraction element of the present embodiment. In the present embodiment, the light branching diffraction element 55 is composed of a polarization hologram in which a groove is formed in a birefringent crystal layer. As the polarization hologram, for example, a film in which an anisotropic polymer layer 72 is formed on a glass substrate 71 as shown in FIG. 2 can be used. The anisotropic polymer layer 72 can be formed by polymerizing a liquid crystal monomer aligned on the glass substrate 71 by ultraviolet irradiation or the like. This polarization hologram has optical anisotropy (birefringence characteristics). Forming an isotropic photopolymer layer 73 by forming a groove 74 having a specific width and depth in the anisotropic polymer layer 72 and filling the groove 74 with a photopolymer of an isotropic material. A polarization hologram can be obtained.

  The optical axis of the light branching diffraction element 55 is set to coincide with or orthogonal to the polarization direction (X-axis direction) of the light beam emitted from the light source 52, and parameters such as the groove depth are appropriately set. By selecting, it is possible to obtain a characteristic of transmitting part of ordinary light and diffracting part of extraordinary light. The optical branching diffraction element 55 has a Kerr rotation angle multiplication function (enhancement function) necessary for magneto-optical signal detection.

  Polarizing holograms can also be used for the first polarization separation element 56 and the second polarization separation element 57. The polarization hologram used as the first polarization separation element 56 and the second polarization separation element 57 is different from the polarization hologram having the enhancement function used as the light branching diffraction element 55 described above. Set to diffract all light. The first polarization separation element 56 and the second polarization separation element 57 in the present embodiment emit the optical axis of the optical anisotropy (birefringence characteristic) polymer layer from the light source 52 in order to differentially detect the magneto-optical signal. The light beam is disposed at an angle of 45 degrees with respect to the polarization direction (X-axis direction) of the light beam.

  With this arrangement, in the magneto-optical recording medium, information recorded by the magnetization direction (laser irradiation surface is N pole or S pole) is reflected at a Kerr rotation angle of ± θk. When the optical axis of the polarization hologram is arranged at 45 degrees with respect to the polarization direction of the light source 52 made of a semiconductor laser, when the Kerr rotation angle ± θk is given, the zero-order light and the ± first-order light depending on the rotation direction (+ or −). Since the light intensity changes, the magneto-optical signal can be detected.

  As the first phase compensation element 60 and the second phase compensation element 61, known ones generally used as wave plates, such as biaxial birefringent crystal plates such as quartz and resin sheets having high birefringence, are used. Can be used.

  In the pickup 51 of the present embodiment, the light branching diffraction element 55 is provided on one surface of the transparent substrate 68 facing the collimator lens 62, and the first polarization separation element 56 and the second polarization separation element 57 are provided on the transparent substrate. It is provided on the other surface facing the 68 light sources 52. That is, the light branching diffraction element 55, the first polarization separation element 56, and the second polarization separation element 57 are formed to constitute an integral member.

  The + 1st order diffracted light 64 and the −1st order diffracted light 65 of the return light beam diffracted by the polarization hologram which is the light branching diffraction element 55 have a p-polarized component and an s-polarized component. Since the diffraction efficiencies of the p-polarized component and the s-polarized component are different, a phase difference occurs between them. The light beam incident on the magneto-optical recording medium 53 with linearly polarized light becomes a return light beam whose polarization direction is slightly rotated by the Kerr effect of the magneto-optical recording medium 53. In general, when linearly polarized light becomes elliptically polarized light due to a phase difference added by an optical component or the like, the modulation degree of the magneto-optical reproduction signal is lowered, and the reproduction signal quality is deteriorated.

  The first phase compensation element 60 and the second phase compensation element 61 are optical elements provided to cancel such a phase difference. Actually, an optical phase difference is also generated in an optical component other than the light branching diffraction element 55, a transparent substrate used in a magneto-optical recording medium, or the like. However, since the phase difference generated in the optical branching diffraction element 55 is larger than the optical phase difference generated by them, the first phase compensation element 60 is changed into the + 1st order diffracted light 64 by the optical branching diffraction element 55. A phase compensation amount that cancels the added phase difference is provided.

  The second phase compensation element 61 adds a phase compensation amount different from that of the first phase compensation element 60. In the photodetector in which the second phase compensation element is arranged, a high-density MD based on, for example, DWDD is reproduced in addition to a normal MD. In this case, in addition to the phase difference added to the −1st order diffracted light 65 by the polarization hologram of the light branching diffraction element 55, the phase difference caused by different recording film structures is constantly added to the return light beam. The phase compensation amount is given so as to cancel the phase difference including this.

  In the pickup 51, the light beam emitted from the light source 52 is divided into three beams of a main beam and two sub beams by the grating 63, then passes through the light branching diffraction element 55, and is made into substantially parallel light by the collimator lens 62. Then, the information recording surface of the magneto-optical recording medium 53 is condensed and irradiated by the objective lens 54. The return light beam reflected by the magneto-optical recording medium 53 passes through the objective lens 54 and the collimator lens 62 again and is guided to the light branching diffraction element 55.

  The + 1st order diffracted light 64 of the return light beam diffracted by the light branching diffraction element 55 is compensated for the phase difference by the first phase compensation element 60 and then enters the first polarization separation element 56. The −1st order diffracted light 65 of the return light beam diffracted by the light branching diffraction element 55 is compensated for the phase difference by the second phase compensation element 61 and then enters the second polarization separation element 57.

  The + 1st-order diffracted light 64 of the return light beam is further separated into zero-order diffracted light 66a and ± 1st-order diffracted lights 66b and 66c, which are polarization components orthogonal to each other, by the first polarization separation element 56, and then to the first detector 58. Incident. The −1st-order diffracted light 65 of the return light beam is separated into zero-order diffracted light 67a and ± 1st-order diffracted lights 67b and 67c, which are polarized components orthogonal to each other, by the second polarization separation element 57, and then to the second detector 59. Incident.

  As described above, in the pickup 51 of the present embodiment, the + 1st order diffracted light 64 and the −1st order diffracted light 65 of the return light beam diffracted by the light branching diffraction element 55 are converted into the first polarization separation element 56 and the second polarization separation element. Before the polarization separation by 57, the phase difference is compensated by the first phase compensation element 60 and the second phase compensation element 61. As described above, the phase compensation amount that the first phase compensation element 60 gives to the + 1st order diffracted light 64 of the return light beam is different from the phase compensation amount that the second phase compensation element 61 gives to the −1st order diffracted light 65 of the return light beam. .

  Thus, for example, for an MD that is a first magneto-optical recording medium, the phase difference of the return light beam is compensated by the first phase compensation element 60 and the magneto-optical signal of the MD is reproduced by the first detector 58. However, for the high-density MD that is the second magneto-optical recording medium, the second phase compensation element 61 compensates for the phase difference of the returned light beam, and the second detector 59 reproduces the magneto-optical signal. it can. Thus, depending on the type of magneto-optical recording medium, a single optical pickup can be used for a magneto-optical recording medium of a different magneto-optical recording system without depending on the attachment / detachment of the phase compensation element or the ON / OFF switching operation of the liquid crystal compensation element. It becomes possible to respond.

  FIG. 3 is a plan view showing the configuration of the light splitting diffraction element, FIG. 4 is a plan view showing the configuration of the first polarization separation element, and FIG. 5 is a plan view showing the configuration of the second polarization separation element. FIG. 6 is a plan view showing the configuration and arrangement of the first photodetector and the second photodetector. A method for detecting a magneto-optical reproduction signal in the pickup 51 will be described below with reference to FIGS.

  As shown in FIG. 3, the light branching diffraction element 55, which is a polarization hologram, is configured to be non-divided. The return light beam passing through the light branching diffraction element 55 is diffracted as it is to become the + 1st order diffracted light 64 and the −1st order diffracted light 65, and enters the first polarization separation element 56 and the second polarization separation element 57, respectively. .

  As shown in FIG. 4, the first polarization separation element 56 is divided into two parts, that is, a first divided region 56 a and a remaining part 56 r by a dividing line 56 s parallel to the X-axis direction. The remaining portion 56r is further divided into two divided into a second divided region 56b and a third divided region 56c by a dividing line 56t parallel to the Y-axis direction. Since the first to third divided regions 56a, 56b, and 56c are configured so that the groove structures such as the pitch and the groove direction are different from each other, the first polarization separation element 56 is the + 1st order diffracted light by the light branching diffraction element 55. 64 has a function of splitting polarized light, and also has a function of dividing a wavefront to diffract 64 in different directions.

  As shown in FIG. 6, the first detector 58 includes a pair of two-divided light receiving regions 58-1 and 58-2, and other light receiving regions 58-3, 58-4, 58-configured as a single unit. 5, 58-6, 58-7, 58-8, 58-9, 58-10, 58-11, 58-12.

  Of the reflected light of the main beam and the reflected light of the two sub beams included in the return light beam, the reflected light of the main beam is zero-order diffracted light 66a (ordinary light component by the first polarization separation element 56, with respect to the X-axis direction). (Corresponding to the polarization component in the 45 degree direction) is transmitted as it is and enters the light receiving region 58-9. Further, the + 1st order diffracted light 66b by the first polarized light separating element 56 is divided into two divided light receiving areas 58-1 and 58- when the light diffracted by the first divided area 56a of the first polarized light separating element 56 is in a focused state. 2 converged on the dividing line 58s extending in the X-axis direction and diffracted by the second and third divided regions 56b and 56c are condensed on the light receiving regions 58-3 and 58-4, respectively. Further, in the reflected light of the two sub beams, the + 1st order diffracted light 66b diffracted by the second divided region 56b of the first polarization separation element 56 is condensed on the light receiving regions 58-5 and 58-6, and is divided into the third divided portions. The + 1st order diffracted light 66b diffracted in the region 56c is collected on the light receiving regions 58-7 and 58-8.

  As for the −1st order diffracted light 66c of the main beam by the first polarization separation element 56, the light diffracted by the first divided region 56a is condensed on the light receiving region 58-10, and the second and third divided regions 56b and 56c. -1st order diffracted light 66c diffracted in (5) is collected on the light receiving regions 58-11 and 58-12, respectively.

  As described above, the first polarization separation element 56 can simultaneously perform polarization separation of the 0th-order diffracted light and the ± 1st-order diffracted light and the beam splitting by the first to third divided regions 56a, 56b, and 56c. .

  As shown in FIG. 5, the second polarization separation element 57 is configured in a non-divided manner, and the −1st order diffracted light 65 diffracted by the light branching diffraction element 55 is in the same shape as the 0th order diffracted light 67a and ± 1. Polarized light is separated into the next diffracted beams 67b and 67c.

  As shown in FIG. 6, the second detector 59 includes light receiving areas 59-1, 59-2, 59-3. As the main beam of the return light beam, the 0th-order diffracted light 67a (ordinary light component, corresponding to the polarization component in the direction of 45 degrees with respect to the X-axis direction) by the second polarization separation element 57 is transmitted as it is, and the light receiving region 59-2. Is incident on. The + 1st order diffracted light 67b and the −1st order diffracted light 67c by the second polarization separation element 57 are condensed on the light receiving regions 59-1 and 59-3, respectively.

  Here, the following light receiving areas or light receiving area sums 58-1, 58-2, 58-3, 58-4, {(58-5) + (58-6)}, {(58-7) + (58 -8)}, 58-9, {(58-10) + (58-11) + (58-12)}, {(59-1) + (59-3)}, 59-2, If the outputs are a, b, c, d, e, f, g, h, i, and j, respectively, the focus error signal (FES) can be detected by the calculation of Expression (2) using the single knife edge method.

FES = a−b (2)
Further, the tracking error signal (TES) can be detected by the calculation of Expression (3) using, for example, a differential push-pull method. In equation (3), the coefficient k is the light quantity ratio between the main beam and the sub beam.

TES = (cd) -k (ef) (3)
The reproduction signal MO1 of the first magneto-optical recording medium is given by equation (4), and the reproduction signal MO2 of the second magneto-optical recording medium having a standard different from that of the first magneto-optical recording medium is given by equation (4). 5).

MO1 = (a + b + c + d + h) −g (4)
MO2 = i−j (5)
Thus, in the pickup 51 of the present embodiment, the first detector 58 reproduces the magneto-optical signal for the first magneto-optical recording medium by compensating the phase difference with the first phase compensation element 60. For a second magneto-optical recording medium that is different from the first magneto-optical recording medium and has a different standard that causes a stationary phase difference in the return light, By compensating for the phase difference with the two-phase compensation element 61, the magneto-optical signal can be reproduced by the second detector 59.

  In this case, the problem is the signal of MO1. As described in the equation (4), (a + b + c + d + h) and the signals of the five photodetectors are added together for differential signal detection. Here, the electrical signal is added directly. In this case, the noise of each photoelectrically converted signal increases by the number of photoelectrically converted elements. That is, the noise component is included five times as compared with the case where the light receiving unit is configured by only one light receiving unit. The reason why the photoelectric conversion is performed by each of the divided detectors is that a single signal is required in order to obtain the FES and TES signals. This circuit is added. Since this amount of noise is included in the reproduction signal of MO1, it is necessary to cope with whether the signal quality in the elements a to h is greatly improved or the noise is reduced. However, as shown in the equation (6), if the signal obtained by i on the MO2 side can be used at the time of reproduction, it becomes a substitute for (a + b + c + d + h), but the optimum optical phase amount is different. Become.

MO1 = ig (6)
FIG. 7 is a diagram showing the relationship between the signal level and the optical phase amount when 0.83 microns and 0.21 microns, which are the shortest marks in normal MD and DWDD, are recorded and reproduced. Both signals are reproduced using the detector (i, j) corresponding to the equation (5), and the reproduction signal level is examined by changing the phase compensation amount. From the figure, when a normal MD is reproduced with a phase compensation amount optimum for DWDD reproduction (when a phase difference of 40 ° is forcibly added to the optimum phase compensation amount of normal MD), the reproduction signal level is ½ ( 3 dB down). Since this is a case corresponding to Equation (5), in the case of the reproduction method of the present invention and Equation (6), the phase amount of one detector (g) is optimal, and the signal quality is predicted in FIG. Expected to be better than what is done. The signal quality is generally evaluated by the ratio of the signal level (C) to the noise (N), C / N. Actually, when the normal MD is reproduced by the same method, the signal quality C / N at the shortest mark is the above equation (6) compared with the case where the signal is reproduced from a plurality of detectors represented by the equation (4). It was confirmed that the signal detection corresponding to is better by 1.7 dB, and that the signal quality is higher when i on the MO2 side is used than when the five light receiving parts are added together. Therefore, in this embodiment, the signal calculated by the equation (6) is used as the magneto-optical reproduction signal MO1 of the first magneto-optical recording medium.

  As described above, the detection method of the present embodiment is effective because the reproduction quality of the magneto-optical signal cannot be sufficiently ensured particularly when the servo detection light-receiving unit needs to be divided into multiple parts using the three-beam method. I understand that.

  As described above, in this embodiment, the signal detection unit is separated on the basis of the difference in density, storage capacity, and optimum optical phase amount associated with the two types of magneto-optical recording media. , It may be separated according to the reproduction frequency band. In this case, it is necessary to reduce the area of the light receiving portion on the side that handles the reproduction signal having a high frequency.

  Here, as a method corresponding to two types of magneto-optical recording media, a configuration in which polarization holograms are used in two stages has been shown. However, the present invention is not limited to this, and reflected light from the magneto-optical recording media. Can be applied to a configuration in which a magneto-optical signal is reproduced from each of the two beams. For example, the same effect can be obtained when the reflected light from the magneto-optical recording medium is separated into transmitted light and reflected light by a microprism and then polarized using a polarization hologram or the like to reproduce a magneto-optical signal. That is, when the reflected light from the magneto-optical medium is divided into a plurality of parts and each light is used to perform magneto-optical signal reproduction, this method can be used.

  In addition, the said embodiment disclosed this time is an illustration in all the points, Comprising: It does not become the basis of limited interpretation. Therefore, the technical scope of the present invention is not interpreted only by the above-described embodiments, but is defined based on the description of the claims. Further, all modifications within the meaning and scope equivalent to the scope of the claims are included.

It is a side view which simplifies and shows the structure of the pickup for magneto-optical recording media in embodiment based on this invention. It is sectional drawing which shows the structure of the diffraction element for light branching in embodiment based on this invention. It is a top view which shows the structure of the diffraction element for light branching in embodiment based on this invention. It is a top view which shows the structure of the 1st polarization separation element in embodiment based on this invention. It is a top view which shows the structure of the 2nd polarization splitting element in embodiment based on this invention. It is a top view which shows the structure and arrangement | positioning of the 1st photodetector in the embodiment based on this invention, and a 2nd photodetector. It is a figure which shows the relationship between the signal level and optical phase amount when recording and reproducing | regenerating the shortest marks 0.83 micron and 0.21 micron in normal MD and DWDD, respectively. It is a side view which simplifies and shows the structure of the conventional optical pick-up. It is a top view of the photodetector 7 with which the optical pick-up shown in FIG. 8 is equipped.

Explanation of symbols

  51 Pickup, 52 Light Source, 53 Magneto-optical Recording Medium, 54 Objective Lens, 55 Diffraction Element for Splitting Light, 56, 57 Polarization Separation Element, 58 First Detector, 59 Second Detector, 60 First Phase Compensation Element, 61 Second phase compensation element, 62 collimator lens, 63 grating, 68 transparent substrate.

Claims (7)

In a magneto-optical recording medium pickup for recording information on and / or reproducing information from a magneto-optical recording medium,
A light source that emits light;
An objective lens for condensing the light emitted from the light source on the information recording surface of the magneto-optical recording medium;
A light branching diffractive element that is provided between the light source and the objective lens and diffracts the reflected light reflected by the magneto-optical recording medium and transmitted through the objective lens;
A first polarized light separating element and a second polarized light separating element for polarizing and separating + 1st order diffracted light and −1st order diffracted light diffracted by the light branching diffraction element,
A first detector and a second photodetector for receiving and detecting the light polarized and separated by the first polarization separation element and the second polarization separation element, respectively;
The first detector and the second detector receive each of the components that are separated by the first polarization separation element and the second polarization separation element and that are parallel to the component perpendicular to the track direction of the magneto-optical recording medium. To configure
The component perpendicular to the track direction detected by the first detector and the component parallel to the track direction detected by the second detector, or the component parallel to the track direction detected by the first detector and the second A magneto-optical recording medium pickup that reproduces a magneto-optical signal using a differential detection method based on a combination of components perpendicular to the track direction detected by a detector.   A first phase compensation element and a second phase compensation that perform optical phase compensation of a phase difference generated in the light branching diffraction element for each of the + 1st order diffracted light and the −1st order diffracted light diffracted by the light branching diffraction element. The pickup for a magneto-optical recording medium according to claim 1, further comprising: an element, wherein a phase compensation amount of the first phase compensation element is different from a phase compensation amount of the second phase compensation element. In either one of the first detector and the second detector, the number of light receiving units is four or more so that the tracking error signal and / or focus error signal of the disk constituting the magneto-optical recording medium can be detected. Further, the light receiving unit can extract a component perpendicular to the track direction and a component parallel to the track direction included in the reflected light from the magneto-optical recording medium,
In the other detector, the component perpendicular to the track direction included in the reflected light from the magneto-optical recording medium separated by the polarization separation element and parallel to the track direction included in the reflected light from the magneto-optical recording medium. Two or more light receiving parts and less than the number of divisions of the light receiving parts of one of the detectors.
The component parallel to the track direction obtained from one detector and the component perpendicular to the track direction obtained from the other detector, or the component perpendicular to the track direction obtained from one detector and the other detection 3. The pickup for a magneto-optical recording medium according to claim 1, wherein a magneto-optical signal is obtained by using any of the components parallel to the track direction obtained from the device.   The pickup for a magneto-optical recording medium according to any one of claims 1 to 3, wherein the light branching diffraction element is a polarizing diffraction element having a Kerr rotation angle multiplication function.   5. The pickup for a magneto-optical recording medium according to claim 1, wherein the first polarization separation element and the second polarization separation element are polarization diffractive elements. 6.   The pickup for a magneto-optical recording medium according to claim 5, wherein at least one of the first polarization separation element and the second polarization separation element is divided into a plurality of regions having different groove structures. A three-beam generating diffraction grating for separating light emitted from the light source into three beams;
The first polarization separation element and the second polarization separation element are provided on one surface of the transparent substrate, and a three-beam generating diffraction grating is provided on the other surface of the transparent substrate. A pickup for a magneto-optical recording medium according to any one of the above.

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