JP4205015B2 - Optical pickup apparatus and information recording / reproducing apparatus including the same - Google Patents

Description

  The present invention relates to an optical pickup device that optically records / reproduces information to / from an information recording medium such as an optical disc, and more particularly to an information recording medium having a laminated structure of two or more recording layers. The present invention relates to an optical pickup device.

  FIG. 10 is a front view showing a configuration of a conventional optical pickup device. FIG. 11 is a front view showing details of a conventional hologram pattern. In the conventional optical pickup device, as shown in FIG. 10, the reflected light from the recording medium 16 is received by the light receiving element 17 to detect the positional deviation of the objective lens.

  Specifically, the light from the light source 11 is mainly divided into one main beam 30 and two sub beams 31 and 32 by the grating 12, and then passes through the hologram 13 and the collimating lens 14 to reach the objective lens 15. Led. Then, the main beam 30 and the sub beams 31 and 32 are condensed on the recording medium 16 by the objective lens 15. The main beam 30 and the two sub-beams 31 and 32 reflected from the recording medium 16 pass through the objective lens 15 and then through the collimating lens 14, so that the first region 13 a, the second region 13 b, and The light is guided to the hologram 13 having the hologram pattern composed of the third region 13c.

  At this time, the position of the light incident on the hologram 13 changes depending on the arrangement of the objective lens 15. For example, when the objective lens 15 is in the neutral position, the main beam 30 reflected from the recording medium 16 is incident on the hologram 13 such that its optical axis passes through the center of the hologram pattern. At this time, the main beam 30 and the sub beams 31, 32 are incident on the second region 13b and the third region 13c at the same rate, respectively. On the other hand, when the objective lens 15 is disposed at a position shifted in the radial direction from the neutral position, the main beam 30 reflected from the recording medium 16 and incident on the hologram has an optical axis divided in the x direction shown in FIG. It will be displaced along the line. At this time, the main beam 30 reflected from the recording medium 16 is incident on either the second region 13b or the third region 13c of the hologram 13 in a biased state.

  FIG. 12 is a diagram illustrating the configuration of the light receiving element 17. The light reflected by the recording medium 16 and incident on the first area 13a of the hologram 13 is diffracted by the hologram 13 and guided to light receiving elements 17a and 17b for detecting a focus error signal. A focus error signal is generated based on the light reception results of the light receiving elements 17a and 17b.

  On the other hand, of the light incident on the hologram second region 13b from the recording medium 16, the main beam 30 is guided to the light receiving element 17d, and the sub beams 31 and 32 are guided to the light receiving elements 17h and 17g, respectively. Of the reflected light incident on the third region 13c from the recording medium 16, the main beam 30 is guided to the light receiving element 17c, and the sub beams 31 and 32 are guided to the detection units 7f and 7e, respectively. And by the light receiving signal by each light receiving element (17g-17h) which receives the light beam diffracted by the 2nd area | region 13b, and by each light receiving element (17e-17f) which receives the light beam diffracted by the 3rd area | region 13c. A tracking error signal representing the displacement of the objective lens 15 is detected based on the received light signal. As a result, a displacement from the neutral position of the objective lens 15 in the radial direction is detected.

  Incidentally, when information is recorded / reproduced on a dual-layer disc, there are the following problems. FIG. 13 is a diagram for explaining light beams reflected from the upper first recording layer 16a and the lower second recording layer 16b in the case of a recording medium having two recording layers.

  In the optical pickup device, when the light from the light source 11 is collected on the first recording layer 16a, a part of the light is transmitted through the first recording layer 16a and reflected on the second recording layer 16b. The second recording layer 16b is located farther from the objective lens 15 than the first recording layer 16a. Accordingly, the light beam reflected from the second recording layer 16b is reflected at a position 19 that is farther from the focal position of the objective lens 15, and the first recording layer 16a is reflected by the objective lens 15 and the collimating lens 14. The light beam is incident on the hologram 13 in a state where the beam diameter is smaller than the light beam reflected from the light beam. Further, when the light beam reflected from the second recording layer 16 b is diffracted by the hologram 13, it has a large spot size on the light receiving element 17, and is incident on a plurality of light receiving elements.

  When the objective lens 15 is in the neutral position, the output signal representing the tracking error signal based on the reflected light from the first recording layer 16a is 0, but the tracking based on the reflected light from the second recording layer 16b is performed. For example, as shown in FIG. 14, reflected light from the second recording layer 16b (recording layer other than the recording layer on which information is recorded / reproduced) is incident on the light receiving element 17g. It does not become 0 due to the influence of the above.

  Further, when the objective lens 15 is shifted from the neutral position, the reflected light from the second recording layer 16b is reflected between the second area 13b and the third area 13c of the hologram pattern as shown in FIG. Of these, it may be incident on only one of them. When the reflected light is incident on only one of the second region 13b and the third region 13c, the reflected light from the second recording layer 16b corresponds to the one region. Incident on the light receiving element. In this case, the output value from the light receiving element that receives the sub-beams 31 and 32 is constant even if the objective lens 15 is displaced, so that an offset occurs in the output value represented by the lens position signal.

  As described above, when a hologram 13 as shown in FIG. 11 is used in a dual-layer recording disk such as a DVD, information recording / reproduction is performed when information is recorded / reproduced on one recording layer. Therefore, the neutral position of the objective lens 15 cannot be obtained accurately with respect to the radial direction. That is, accurate tracking adjustment cannot be performed on a recording medium composed of a plurality of layers.

  Therefore, as a result of diligent study on the problem that accurate tracking adjustment cannot be performed in the above-described known technology, the applicant of the present invention has a content that the hologram pattern has a specific shape in order to solve the problem. The prior invention was proposed (Japanese Patent Application No. 2003-092110: unpublished at the time of confirmation prior to the filing of the present application).

  Specifically, in order to solve the above problem, the following hologram patterns have been proposed by the applicants. FIG. 8 shows the configuration of the hologram pattern.

  As shown in FIG. 8, the hologram pattern includes a first dividing unit 21a and a second dividing unit 21b for generating a tracking error signal, and a third dividing unit 21c for generating a focus error signal.

  And the 1st division part 21a and the 2nd division part 21b are the area | regions except the axial vicinity part of the division line vicinity which corresponds with the optical axis of the reflected light guide | induced to the hologram 13 when the objective lens 15 exists in a neutral position. Placed in. The vicinity of the axis is formed in a circular shape centered on the optical axis. The third divided portion 21c is a portion obtained by removing the first divided portion 21a and the second divided portion 21b from the circular region, and includes a circular shape near the axis. Thus, the hologram pattern has three divided parts.

  By using such a hologram pattern, reflected light having a small beam size incident on the vicinity of the optical axis of the hologram pattern from another recording layer other than one recording layer generates a focus error signal. It is possible to prevent the light from entering the first divided portion 21a and the second divided portion 21b, and accurate track position information and deviation information can be acquired.

  However, as a result of further studies, the applicant of the present application has found that the following technical problems remain in the prior invention. This will be described below.

  In the pickup device including the hologram 21 having the hologram pattern as shown in FIG. 8, the light beam incident on the third divided portion 21c out of the light beam reflected from the first recording layer 16a is received by the light receiving element 17a, Detected at 17b and used to generate a focus error signal.

  For example, when generating a focus error signal by the knife edge method using a two-divided detector, a difference in light intensity detected by each detector is detected. When the focused beam is in focus on the recording layer of the recording medium, the intensities detected by each of the two-divided detectors are equal and the difference is zero. If it is not the in-focus point, one detection intensity is increased. Depending on whether it is nearer or farther than the focal position, the strong detector is replaced.

  FIG. 9 shows a focus error signal by the knife edge method with and without spherical aberration in the hologram pattern.

  In general, in the case of a light beam having spherical aberration, when the focused beam is focused on the recording medium, the difference does not become zero when the reflected light from the recording medium is detected by the two-divided detector. The difference between the light receiving elements 17a and 17b is exactly 0, as shown in FIG. 9, at a position slightly deviated from the focus position.

  In the case of the hologram pattern shown in FIG. 8, since the light beam at the center is not cut in half, the intensity difference of the detector due to the contribution of this part is always canceled even when there is a focus shift, In this case, a focus error signal is generated using the light at the outer edge of the beam.

  The influence of spherical aberration is smaller at the center of the beam and is greater at the outer periphery. In the hologram shown in FIG. 8, since the focus signal is generated only in a region having substantially large spherical aberration, the offset of the focus error signal may be noticeable when the hologram is used. .

Thus, in the case of the hologram pattern shown in FIG. 8 , a good tracking error signal can be obtained, but since an offset occurs in the focus error signal, it is difficult to obtain accurate focus position information, and recording is performed. There is a possibility that the characteristics at the time of recording and reproduction on the medium are deteriorated.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to satisfactorily perform tracking adjustment and focus adjustment when recording / reproducing information on a recording medium having a plurality of layers. An object of the present invention is to provide an optical pickup device that can be used.

In order to solve the above problems, an optical pickup device according to the present invention is a method for obtaining a focus error signal from a light beam reflected from an optical recording medium in which a plurality of recording layers are laminated and passed through a condensing unit. An optical pickup device comprising a separating means having a separation region for separating at least a focusing beam and a tracking beam for obtaining a tracking error signal, and a detecting means for receiving the focusing beam and the tracking beam, respectively. The separation means is a division that passes through a point that coincides with the optical axis of the light beam that is reflected from the recording layer on which information is recorded / reproduced in a state where the light collecting means is in the neutral position. The line A is sandwiched between the parting line A and the parting line B parallel to the parting line A that is separated from the parting line A by a distance smaller than the radius of the light beam. A focusing beam from the light beam in the region (A) and a region (B) having a circle smaller than the beam radius of the light beam centered on a point coincident with the optical axis of the light beam. It is characterized by having a focus separation region for separation and a tracking separation region for separating the tracking beam from the light beam at least in the region excluding the region (A) and the region (B).

  The light beam reflected by the recording layer farther from the recording layer (hereinafter referred to as the target layer) on which information is recorded / reproduced when viewed from the condensing means is caused by the difference in the optical path length. When passing, the light beam is condensed in the vicinity of the optical axis of the light beam reflected from the target layer irradiated on the separating means in a state where the radius is smaller than that of the light beam reflected from the target layer. Since the light beam reflected by the recording layer farther than the target layer is a light beam reflected from other than the target layer, it causes an error when obtaining the tracking error signal.

According to the arrangement, in the area which is an area near the optical axis of the light beam reflected from the target layer (A) and realm (B) at least excluding area (tracking isolation region), is applied to the separating means The tracking beam is separated from the light beam. Thereby, the light beam reflected from the recording layer farther than the target layer is not irradiated to the tracking separation region. In other words, the tracking separation region can separate the tracking beam from the light beam applied to the separation means without including the light beam reflected from the recording layer farther than the target layer. As a result, the tracking error signal can be obtained more accurately as compared with the conventional configuration in which the tracking error signal is obtained in a state where the light beam reflected from the recording layer far from the target layer is included.

  Further, according to the above configuration, the optical recording medium passes through the region (B) and a point that coincides with the optical axis of the light beam reflected from the target layer in a state where the light collecting means is in a neutral position. And a region (A) surrounded by the dividing line A and the dividing line B parallel to the dividing line A separated from the dividing line A by a distance smaller than the radius of the light beam. In this region, the focusing beam is separated from the light beam irradiated on the separating means. That is, the focusing beam is separated from the light beam in a state where the light beam at a portion farther from the dividing line (B) as viewed from the point coincident with the optical axis of the light beam is cut. As a result, the focusing beam can be generated in a state in which the portion of the light beam near the outer edge (outer periphery) of the light beam that is strongly influenced by spherical aberration is cut. Accordingly, the focus error signal can be obtained more accurately. The dividing line A extends in a direction orthogonal to the track direction of the optical recording medium.

  In this way, by adopting the above configuration, a more accurate tracking error signal can be obtained as compared with the conventional configuration in which the tracking error signal is obtained in a state including the light beam reflected from the recording layer farther than the target layer. It is possible to obtain a focus error signal that is less affected by spherical aberration.

  The neutral position indicates a state in which the central axis of the light collecting means and the optical axis of the light beam coincide.

  In the optical pickup device according to the present invention, the light beam reflected by the recording layer farther than the recording layer in which the area (B) is recorded / reproduced information as viewed from the condensing means is condensed. A configuration including a region to be processed is more preferable.

  According to said structure, area | region (B) is an area | region where the light beam reflected by the recording layer farther than the said recording layer which is recording / reproducing information seeing from the said condensing means is condensed. Therefore, the tracking separation region can be prevented from being irradiated with the light beam reflected from the recording layer farther than the target layer.

  In the optical pickup device according to the present invention, the detecting means detects only the light beam reflected from the optical recording medium and passing outside the dividing line B when viewed from the optical axis of the light beam. The structure provided with the detection part to perform is more preferable.

  According to said structure, since the detection part which detects only the light beam which passes outside the said dividing line B is provided, the whole light beam irradiated to the said isolation | separation means can be detected. Therefore, for example, the reproduction signal can be detected using the entire light beam.

  In the optical pickup device according to the present invention, the detection means detects a light beam that passes outside the dividing line B, as viewed from the optical axis of the light beam, from the light beam reflected from the optical recording medium. A configuration including a tracking error signal detection unit that detects a tracking error signal is more preferable.

  With the above configuration, the tracking error signal can be used by using a light beam that passes outside the dividing line B. As a result, a more accurate tracking error signal can be generated.

  In the optical pickup device according to the present invention, it is more preferable that the separating unit has a configuration in which the diffraction efficiency of the light beam passing through the separating unit varies depending on the polarization state of the light beam incident on the separating unit.

  In the case where the separation means is one in which the diffraction efficiency of the light beam passing through the separation means changes depending on the polarization state of the light beam incident on the separation means, for example, the light beam irradiated from the light source is transmitted. The light beam reflected from the optical recording medium can be diffracted. Therefore, for example, since the separating means can be disposed between the light source and the optical recording medium, the optical Bicup device can be miniaturized. Further, since the presence or absence of diffraction can be changed depending on the polarization state of the light beam incident on the separating means, it is possible to suppress the loss of the amount of light reaching the optical recording medium. For this reason, since a strong light beam can be irradiated to the optical recording medium, information can be recorded on the optical recording medium at a high speed.

  In the optical pickup device according to the present invention, the radius of the area (B) is 30 to the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separation means. A configuration in the range of 60% is more preferable.

  According to the above configuration, by setting the radius of the region (B) within the range of 30 to 60% with respect to the beam radius of the light beam, it is surely reflected from the recording layer farther than the target layer. The focused light beam can be within the region (B), and the focus beam separated in the focus separation region can have a sufficient amount of light to obtain a focus error signal. A signal can be obtained.

  In the optical pickup device according to the present invention, the distance from the dividing line A to the dividing line B is set to be equal to the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separating means. Therefore, a structure larger than 50% is more preferable.

  According to the above configuration, the focus beam separated in the focus separation region is focused by setting the interval from the dividing line A to the dividing line B to be larger than 50% with respect to the beam radius of the light beam. Since a sufficient amount of light can be obtained to obtain an error signal, a good focus error signal can be obtained.

An optical pickup device according to the present invention includes a light beam reflected from an optical recording medium in which a plurality of recording layers are laminated and passed through a focusing means, a focus beam for obtaining a focus error signal, and a tracking error signal. a separation means having a separation region at least separated into a tracking beam for obtaining, an optical pickup device provided with a detecting means for receiving a focusing beam and tracking beams respectively, it said separating means includes a condenser A straight line passing through a point that coincides with the optical axis of the light beam reflected from the recording layer on which information is recorded / reproduced in a state where the means is in the neutral position and applied to the separation means, and is parallel to the straight line Smaller than the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separation means Distance stripe region is sandwiched between the remote Do parallel straight lines from the straight line, and, the light beam centered on the point which is coincident with the optical axis smaller radius than the beam radius of the light beam irradiated onto said separating means A tracking separation region that separates the light beam into a focusing beam, and a separation region that separates the light beam into a tracking beam in a region that excludes the band region and the circular region at least. And a separation region.

To obtain an accurate tracking error signal and a focus error signal, a focusing means to irradiate the light beam to the separating means to match the optical axis of the light beam reflected from the optical recording medium in a state where the neutral position . At this time, the light beam reflected by the recording layer farther than the recording layer (hereinafter referred to as the target layer) where information is recorded / reproduced as viewed from the light collecting means is collected due to the difference in optical path length. When passing through the light means, the light beam is irradiated in the vicinity of a point that has a smaller beam radius than the light beam reflected by the target layer and coincides with the optical axis of the light beam . Since the light beam reflected by the recording layer farther than the target layer is a light beam reflected from other than the target layer, it causes an error when obtaining the tracking error signal.

In the above configuration, the light beam is separated into a tracking beam in a region excluding the vicinity of a point coincident with the optical axis of the light beam. Accordingly, it is possible to obtain a tracking beam in a state where the light beam reflected from the recording layer farther than the target layer is removed. As a result, the tracking error signal can be obtained more accurately as compared with the conventional configuration in which the tracking error signal is obtained in a state where the light beam reflected from the recording layer far from the target layer is included.

Further, according to the above configuration, the focusing beam is separated from the light beam applied to the separating means in the region including the circular region and the belt-like belt region surrounded by the straight line and the parallel straight line. Yes. The distance from the straight line to the parallel straight line is shorter than the beam radius of the light beam reflected from the target layer and applied to the separating means. That is, in a state where the arbitrary one point and the optical axis of the light beam coincide with each other, the light beam in a state where the light beam far from the parallel straight line as viewed from the point coincident with the optical axis of the light beam is cut off. The focusing beam is separated from the lens. Thereby, it is possible to generate a focusing beam in a state in which the light beam in the vicinity of the outer edge (outer periphery) of the light beam is cut in a portion where the influence of spherical aberration is strong. Therefore, by using the focusing beam, the influence of spherical aberration can be reduced, so that a more accurate focus error signal can be obtained.

  In this way, by adopting the above configuration, a more accurate tracking error signal can be obtained as compared with the conventional configuration in which the tracking error signal is obtained in a state including the light beam reflected from the recording layer farther than the target layer. It is possible to obtain a focus error signal that is less affected by spherical aberration.

  In order to solve the above problems, an information recording / reproducing apparatus according to the present invention includes the optical pickup device.

  According to the above configuration, since the optical pickup unit is provided, tracking adjustment and focus adjustment can be satisfactorily performed even with a recording medium having a plurality of information recording layers.

In the optical pickup device according to the present invention, the separating means includes an optical axis of a light beam reflected from the recording layer that is recording / reproducing information in a state where the condensing means is in a neutral position and irradiated to the separating means. A region (A) sandwiched between a dividing line A passing through the coincident point, a dividing line A separated from the dividing line A by a distance smaller than the radius of the light beam, and a dividing line B parallel to the dividing line A; A focus separation region that separates the focus beam from the light beam in a region that includes a circle region (B) smaller than the beam radius of the light beam around a point that coincides with the optical axis of the light beam, and at least a region ( A tracking separation region for separating the tracking beam from the light beam in a region excluding A) and the region (B).

  Therefore, it is possible to obtain a more accurate tracking error signal than the conventional configuration in which a tracking error signal is obtained in a state including a light beam reflected from a recording layer farther from the target layer, and the influence of spherical aberration. There is an effect that a focus error signal with less can be obtained.

  An embodiment of the present invention will be described as follows.

  FIG. 2 is a front view showing a schematic configuration of the optical pickup device according to the embodiment of the present invention. FIG. 1 is a front view showing a hologram pattern of a hologram according to the present embodiment. As shown in FIG. 2, the optical pickup device according to the present embodiment includes a light source 1, a grating 2, a hologram (separating means) 3, a collimating lens 4, an objective lens (condensing means) 5, and a detecting unit (detecting means). 7 is provided.

  The light source 1 irradiates the recording medium 6 with laser light. The light source 1 emits a laser beam (light beam) having a wavelength of 650 nm, for example. Note that the wavelength of the light beam emitted from the light source 1 is not particularly limited, and may be, for example, 405 nm.

  The grating 2 is a diffraction grating and is disposed between the light source 1 and the recording medium 6. The grating 2 generates one main beam (0th order transmitted light) and two sub beams (+ 1st order diffracted light and −1st order diffracted light) from one light beam emitted from the light source 1. . That is, the light beam emitted from the light source 1 becomes three light beams by the grating 2. In the present embodiment, the grating 2 is provided between the light source 1 and the objective lens 5 (more specifically, between the light source 1 and the hologram 3). The grating 2 generates two types of light beams such that the main beam is larger than the light intensity of the sub beam. More specifically, the grating 2 generates the main beam and the sub beam so that the light amount of the main beam is larger than the sum of the light amounts of the + 1st order diffracted light and the −1st order diffracted light that are two sub beams. ing. When the grating 2 is composed of a diffraction grating, the ratio of the 0th order transmitted light and the ± 1st order diffracted light can be controlled by the depth of the groove of the diffraction grating. In the above description, the grating 2 has been described with respect to an example in which two sub beams are generated. However, the number of sub beams to be generated is not particularly limited.

  The collimating lens 4 changes the light emitted from the light source into parallel light. The collimating lens 4 makes light from the grating 2 substantially parallel. The collimating lens 4 converts light reflected from the recording medium 6 and passed through the objective lens 5 into condensed light.

  The objective lens 5 focuses the three light beams diffracted by the grating 2 on the recording medium 6. The light beam reflected by the recording medium 6 passes through the objective lens 5 and the collimating lens 4 and enters the hologram 3.

  The objective lens 5 can be displaced in the radial direction and the focus direction within a movable range including a neutral position. The neutral position indicates a state in which the objective lens 5 is arranged so that the optical axis of the beam guided to the objective lens 5 and the center position of the objective lens are coaxial. The radial direction indicates the radial direction when the recording medium 6 is an optical disc such as a DVD, for example. The focus direction is a direction parallel to the optical axis of the light beam guided to the objective lens 5. The direction is perpendicular to the recording surfaces of the first and second recording layers described later. The position of the objective lens 5 is displaced in the radial direction and the focus direction by an actuator which is a driving means (not shown).

  The hologram 3 separates the light beam reflected by the recording medium 6 and passed through the objective lens 5 and the collimating lens 4. The hologram 3 is divided into a plurality of regions, and the light beam that has passed through the objective lens 5 is divided into the divided regions and is incident on the detection unit 7. Specifically, the light beam is separated into at least a focusing light beam for obtaining a focus servo signal and a tracking light beam for obtaining a tracking servo signal in the hologram 3. The detailed configuration of the hologram pattern (divided pattern) of the hologram 3 will be described later. The hologram 3 allows the light beam emitted from the light source 1 to pass therethrough.

  The detection unit 7 includes a plurality of light receiving elements, and receives (detects) the light beams (focusing beam and tracking beam) separated by the separating unit and converts them into electrical signals. The detection unit 7 detects the light intensity of the received light beam. The detection unit 7 includes a focusing light receiving unit that receives the focusing light beam and a tracking light receiving unit that receives the tracking light beam. The focus light receiving unit generates a focus servo signal, and the tracking light receiving unit generates a tracking servo signal.

  A recording medium (optical disc) 6 has a plurality of recording layers for recording information. The plurality of recording layers are stacked in a direction parallel to the optical axis of the light irradiated on the recording medium 6. Examples of the recording medium 6 include a DVD. When the recording medium 6 is a DVD, the DVD has a single layer structure in which the CD has a thickness of 1.2 mm, whereas, for example, two discs having a thickness of 0.6 mm are bonded together. A multi-layer structure is formed.

  Although three or more recording layers may be formed on the recording medium 6, in the following description, a case of a two-layer structure including a first recording layer and a second recording layer will be described for convenience. The first recording layer will be described as being disposed at a position closer to the objective lens 5 than the second recording layer.

  Next, the light beam emitted from the light source 1 will be described. The light beam emitted from the light source 1 first enters the grating 2 provided between the light source 1 and the objective lens 5. Periodic irregularities are formed in the grating 2, and the emitted light is diffracted to generate several sub beams in addition to the main beam 30. The main beam 30 is a light beam (main luminous flux) for reading information recorded on the recording medium 6. The sub beam is light used for controlling the condensing position of the main beam 30. When the irregularities formed on the grating 2 have a simple periodic rectangular shape, the main diffracted light generated is + 1st order light and −1st order light. In the following description, the two sub beams will be described as a first sub beam 31 and a second sub beam 32, respectively.

  Then, the light beam (main beam 30, first sub beam 31, second sub beam 32) that has passed through the grating 2 enters the collimating lens 4 via the hologram 3. The collimating lens 4 makes the light beam that has passed through the grating 2 substantially parallel light. Next, the light beam from the collimating lens 4 is condensed on one recording layer of the recording medium 6 by the objective lens 5.

  The main beam 30 and the first and second sub beams 31 and 32 guided to the recording medium 6 are reflected by the recording medium 6. Then, the light beam reflected by the recording medium 6 is guided to the hologram 3 via the objective lens 5 and then the collimating lens 4.

  The light beam applied to the hologram 3 is at least separated by the hologram 3 into a focusing beam for obtaining a focus error signal and a tracking beam for obtaining a tracking error signal.

  Thereafter, the focusing beam is incident on the focusing light receiving unit, and the tracking beam is incident on the tracking light receiving unit. The focus light receiving unit generates a focus servo signal, and the tracking light receiving unit generates a tracking servo signal.

  Here, the hologram 3 according to the present embodiment will be described in detail. The hologram 3 according to the present embodiment is disposed between the light source 1 and the objective lens 5. As shown in FIG. 1, the hologram 3 includes a first division unit (tracking separation region) 3a and a second division for generating a tracking error signal in a region through which the light beam reflected from the recording medium 6 passes. The three divided parts (tracking separation area) 3b and the third division part (focus separation area) 3c for generating a focus error signal, and a substantially D-shaped first adjacent to the third division part 3c. It has a hologram pattern including a quadrant 3d.

  The first dividing unit 3a and the second dividing unit 3b for generating a tracking error signal are divided axial lines (information of the information) that coincide with the optical axis of the light beam guided to the hologram 3 when the objective lens 5 is in the neutral position. A point that coincides with the optical axis of the light beam reflected from the recording layer that is recording / reproducing and applied to the separation means, an arbitrary point) Area near the axis near a (area (B), circular area) It is formed in a region excluding. The vicinity of the axis is formed in a substantially circular shape centered on the dividing axis a.

And the 1st division part 3a and the 2nd division part 3b are formed in the substantially sector shape which lacked near the center. The first dividing portion 3a is formed in a portion excluding a circular region centered on the dividing axis a, and passes through the dividing axis a and is parallel to the radial direction ( tracking direction). ) And the virtual dividing line A and the virtual dividing line C passing through the perpendicular dividing axis a. The second dividing portion 3b is located on the opposite side of the first dividing portion 3a from the virtual dividing line C and in a region surrounded by the virtual dividing line A and the virtual dividing line C, excluding the circular region near the axis. It is formed.

That is, the virtual dividing line A is a straight line that passes through the optical axis (dividing axis a) of the light beam incident on the hologram 3 in a state where the objective lens 5 is in the neutral position and is parallel to the radial direction ( tracking direction ). is there. The virtual dividing line C is a straight line orthogonal to the virtual dividing line A.

On the other hand, the third dividing unit 3c for generating a focus error signal is a virtual dividing line A and a virtual dividing line that is parallel to the virtual dividing line A and separated from the virtual dividing line A by a distance d in the present embodiment. A region (region (A), band region) sandwiched between B (partition line B) and a substantially circular region near the axis centering on the division axis a.
The fourth dividing portion 3d is a region farther from the virtual dividing line B when viewed from the optical axis. Then, the end portion of the main beam 30 is irradiated to the fourth divided portion 3d.

A plurality of grooves are formed in the first and second divided portions 3a, 3b and the third divided portion 3c. The depth and interval of these grooves are set based on the diffraction efficiency of the hologram pattern, the arrangement position of the detection unit 7 and the like.

  FIG. 3 is a diagram showing the relationship between the light beam divided by the hologram 3 and the detection unit 7 that receives the light beam. The light beam incident on the hologram 3 from the recording medium 6 is divided by four division parts, a first division part 3a, a second division part 3b, a third division part 3c, and a fourth division part 3d. Among them, the light beam reflected from at least the first division unit 3 a to the third division unit 3 c is guided to the detection unit 7. The detection unit 7 includes three light receiving units, a first light receiving unit 8A, a second light receiving unit 8B, and a third light receiving unit 8C. The first light receiving unit 8A and the second light receiving unit 8B respectively receive the light beams (tracking beams) separated by the second division unit 3b and the first division unit 3a of the hologram 3, and provide track position information in the radial direction. It is the light-receiving part (tracking light-receiving part) for obtaining. The third light receiving unit 8C is a light receiving unit (focusing light receiving unit) that receives the light beam (focusing beam) separated by the third dividing unit 3c and acquires position information in the optical axis direction. The first light receiving unit 8A, the second light receiving unit 8B, and the third light receiving unit 8C have one or a plurality of light receiving elements.

  The third light receiving unit 8C includes at least two light receiving elements, and the light beam light separated by the third dividing unit 3c is detected by at least one of the light receiving elements 8a and 8b. A focus error signal, which is position information in the optical axis direction, is acquired by the knife edge method. The knife edge method can be obtained by taking the difference in light intensity received by each of the light receiving elements 8a and 8b of the third light receiving portion 8C.

Specifically, assuming that the light intensities detected by 8a and 8b are I8a and I8b, the focus error signal (FES) is expressed by the following equation (1).
FES = I8a-I8b (1)
Is obtained by the following equation. In the case of the arrangement shown in FIG. 2, when focusing is performed before (near side) the recording layer for recording / reproducing information on the recording medium 6, the light beam is in front of the light receiving elements 8a and 8b (hologram 3). And the detection unit 7), the intensity of light incident on the light receiving element 8b side is increased, and FES has a negative sign. Conversely, when focusing is performed behind (far side) the recording layer for recording / reproducing information on the recording medium 6, the light beam is focused at a position farther from the front than the light receiving elements 8a and 8b. Therefore, the intensity of light incident on the light receiving element 8a side is increased, and FES has a positive sign.

  FIG. 4 is a graph showing the relationship between the width d of the virtual dividing line A and the virtual dividing line B in the hologram pattern and the magnitude of the offset appearing in the focus error signal. The horizontal axis represents the ratio of the length d to the radius of the light beam applied to the hologram 3. The vertical axis represents the magnitude of the offset. In FIG. 4, the relationship between the radius r of the circular part near the axis and the spot radius (radius of the light beam) R of the main beam 30 is the case where r / R = 0.3, 0.45, and 0.6. Show.

  The larger the size of the region (B), that is, the larger the radius centered on the optical axis of the light beam, the other layer (recording layer other than the recording layer on which information is recorded / reproduced; The light beam reflected from the outer layer is likely to be taken in, but if it is too large, the area of the portion contributing to the tracking error signal is reduced, and its characteristics are adversely affected. Therefore, the range of r / R is more preferably in the range of 0.3 <r / R <0.6. In other words, in the focus separation region for separating the focus beam, the preferable size of the region (B) is centered on the optical axis of the light beam guided to the hologram 3 when the objective lens 5 is in the neutral position. When the beam radius of the light beam is 100%, the range of 30 to 60% is more preferable.

Note that a point O shown in FIG. 4 indicates an offset when the region (B) is r / R = 0, that is, when a semicircle (r / R = 0) of the light beam is used. Yes. Actually, since the focus servo can be performed even in this case, the offset amount of the range of the line P and the line Q is set within an allowable range (r / R = 0.45, with reference to the position where the offset of the focus error signal is 0 . d / R = 1) is set as 40% of the offset when d / R = 1, and a d / R value is set so that the offset is included in this range.

  In addition to the r / R = 0.45, the graph shows graphs for r / R = 0.3 and 0.6. Thus, since the offset-d / R curve changes depending on the value of r / R, the range d / R included in the allowable range also changes with respect to the change of r, and the width d satisfies the allowable range. Set the value of.

  If d is too small, the amount of light for generating the focus error signal decreases, so the width d is set in the range of d / R> 0.5.

  It can be seen from the respective curves in the figure that the offset of the focus error signal is gradually reduced by reducing the width d compared to when d / R = 1. For this reason, out of the light beam that contributes to the focus error signal, the outer periphery of the light beam reflected from the recording medium 6 is eliminated, and the contribution from the region with large spherical aberration is reduced. It shows that it can be suppressed.

  Further, by reducing the width d, the beam radius of the light beam used for generating the focus error signal is reduced in the track direction. Therefore, in the third light receiving portion 8C, the beam diameter expands in the track direction as compared with the case where the width d is the maximum (the spot radius of the light beam). This leads to a decrease in focus error signal detection sensitivity. Further, by reducing the width d, the light intensity for generating the focus signal is lowered.

  Therefore, the width d of the third dividing portion 3c needs to be set to an appropriate width determined by the balance between the offset correction amount due to spherical aberration and the sensitivity required for the focus error signal required for the system.

  As shown in FIG. 1, the focus separation region according to the present embodiment is a region obtained by combining a region (A) sandwiched between two straight lines A and B and a semicircular partial region (B). When a focus error is detected favorably using the focus separation area, the sizes of the area (A) and the area (B) are affected. As shown in FIG. 4, for example, when r / R = 0.3, it is more preferable that d / R = 0.8 to 0.96. Further, for example, when r / R = 0.45, it is more preferable that d / R = 0.2 to 0.88, but in order to generate a focus error signal satisfactorily, More preferably, d / R is in the range of 0.5 to 0.88. Further, for example, when r / R = 0.6, it is more preferable that d / R = 0.5 to 0.7.

  Here, a case where a tracking error signal is obtained will be described. The first light receiving portion 8A includes three light receiving elements 8c, 8e, and 8f. Of the light beams that have passed through the second division part 3b of the hologram 3, the main beam 30 is received by the light receiving element 8c. The first sub beam 31 and the second sub beam 32 are received by the light receiving elements 8f and 8e, respectively.

  Similarly, the second light receiving unit 8B is also composed of three light receiving elements 8d, 8g, and 8h. Of the light beams that have passed through the first division unit 3a of the hologram 3, the main beam 30, the first sub beam 31, and the second sub beam are included. 32 is received by different light receiving elements 8d, 8h and 8g.

  At this time, the light intensities received by the detectors from the light receiving elements 8c to 8h are set as light intensities I8c to I8h, respectively.

  The track position information is detected based on, for example, a phase difference method (DPD method: Differential Phase Detection) based on each light reception result by the first light receiving unit 8A and the second light receiving unit 8B. In the DPD method, the light intensity I8c by the light receiving element 8c that receives the main beam 30 separated by the second dividing unit 3b in the first light receiving unit 8A, and the first dividing unit 3a in the second light receiving unit 8B. Is detected by the phase difference of the light intensity I8d by the light receiving element 8d that has received the main beam 30 separated by.

That is, the tracking error signal I (DPD) by the DPD method is expressed by the following equation (2),
I (DPD) = ph (I8c−I8d) (2)
Obtained by. In the above formula, ph means that the phase difference of each intensity is taken. Then, the phase difference generated varies depending on which position of the light beam the pit formed on the recording medium 6 passes. When the light beam passes through the center of the pit, the phase difference is zero.

  The tracking error signal indicating the track position information may be obtained by using a differential push pull method (DPP method: Differential push pull) instead of the DPD method. In the DPP method, the tracking error signal is detected by each light reception result by the light receiving elements of the first light receiving unit 8A and the second light receiving unit 8B.

Specifically, when the DPP method is used, the tracking error signal I (DPP) is expressed by the following equation (3),
I (DPP) = (I8c−I8d) −k × [(I8f−I8h) + (I8e−I8g)] (3)
Sought by. In the above equation, the coefficient k is used to correct the difference in light intensity between the main beam 30 that is 0th-order light, the subbeam 31 that is + 1st-order light, and the subbeam 32 that is −1st-order light. Is 0th order light: + 1st order light: -1st order light = a: b: b, the coefficient k = a / (2b).

  Here, (I8c-I8d) of the tracking error signal (TES) is a push-pull signal of the main beam 30, and (I8f-I8h) and (I8e-I8g) are sub-beams 31 and 32 of ± primary light, respectively. This is a push-pull signal. The phase of the push-pull of (I8f-I8h) and (I8e-I8g) is 180 degrees different from the phase of (I8c-I8d) so as to cancel the offset due to the objective lens shift appearing in the tracking error signal. The positions of the beams (the main beam 30, the + 1st order light subbeam 31 and the −1st order light subbeam 32) are arranged so as to be formed on the track of the recording medium 6.

  As described above, the optical pickup device according to the present embodiment uses the light beam reflected from the recording medium 6 on which a plurality of recording layers are laminated and passed through the objective lens 5 for focusing to obtain a focus error signal. An optical pickup device comprising a hologram 3 having a separation region at least separated into a beam and a tracking beam for obtaining a tracking error signal, and a detection unit 7 for detecting the focusing beam and the tracking beam, respectively. The hologram 3 is reflected from the straight line A passing through one arbitrary point on the hologram 3 and the recording layer which is parallel to the straight line A and is recording / reproducing information and is irradiated onto the hologram 3. It is sandwiched between a straight line B separated from the straight line A by a distance smaller than the beam radius of the beam 30. A focus separation region that separates the focusing beam from the light beam in a region A and a region B of a circle having a radius smaller than the beam radius of the light beam irradiated on the hologram 3 from the arbitrary point. (First division unit 3a) and a tracking separation region (first division unit 3a and second division unit 3b) that separates the tracking beam from the light beam in a region excluding at least the region B.

  In other words, in the optical pickup device according to the present embodiment, the light beam reflected from the recording medium 6 on which a plurality of recording layers are laminated and passed through the objective lens 5 is used as a focusing beam for obtaining a focus error signal. An optical pickup device comprising a hologram 3 having a separation region at least separated into a tracking beam for obtaining a tracking error signal, and a detection unit 7 for detecting the focusing beam and the tracking beam, respectively. The hologram 3 is divided through the optical axis of the light beam reflected from the recording layer on which information is recorded / reproduced with the objective lens 5 in the neutral position and orthogonal to the track direction of the recording medium 6. The line A (virtual dividing line A) is separated from the dividing line A by a distance smaller than the radius of the light beam. The region (A) sandwiched between the dividing line A and the dividing line B (virtual dividing line B) parallel to the dividing line A, and the optical axis of the light beam reflected from the recording layer for recording / reproducing the information A focus separation region (first dividing portion 3a) that separates the focusing beam from the light beam in a region including a circular region (B) smaller than the beam radius of the light beam as a center, and the region (B) This is a configuration having tracking separation regions (first divided portion 3a and second divided portion 3b) for separating the tracking beam from the light beam in at least the excluded region.

  A light beam reflected by a recording layer farther than a recording layer (hereinafter referred to as a target layer) where information is recorded / reproduced as viewed from the objective lens 5 is caused to pass through the objective lens 5 due to the difference in optical path length. When passing, the light beam is condensed in the vicinity of the optical axis of the light beam reflected from the target layer irradiated on the hologram 3 with a radius smaller than that of the light beam reflected from the target layer. Since the light beam reflected by the recording layer farther than the target layer is a light beam reflected from other than the target layer, it causes an error when obtaining the tracking error signal.

  According to the above configuration, tracking is performed from the light beam applied to the hologram 3 in a region (tracking separation region) excluding at least the region (B) that is a region near the optical axis of the light beam reflected from the target layer. The beam is separated. Thereby, the light beam reflected from the recording layer farther than the target layer is not irradiated to the tracking separation region. In other words, the tracking separation region can separate the tracking beam from the light beam applied to the hologram 3 in a state in which the light beam reflected from the recording layer farther than the target layer is not included. As a result, the tracking error signal can be obtained more accurately as compared with the conventional configuration in which the tracking error signal is obtained in a state where the light beam reflected from the recording layer far from the target layer is included.

  Further, according to the above configuration, the region (B) passes through the optical axis of the light beam reflected from the objective in a state where the hologram 3 is in the neutral position, and is orthogonal to the track direction of the recording medium 6. The hologram 3 is a region combining the dividing line A and the region (A) surrounded by the dividing line A and the dividing line B parallel to the dividing line A separated from the dividing line A by a distance smaller than the radius of the light beam. The focusing beam is separated from the light beam applied to the beam. That is, the focusing beam is separated from the light beam in a state where the light beam at a portion farther from the dividing line (B) as viewed from the optical axis of the light beam is cut. As a result, the focusing beam can be generated in a state in which the portion of the light beam near the outer edge (outer periphery) of the light beam that is strongly influenced by spherical aberration is cut. Accordingly, the focus error signal can be obtained more accurately.

  Thus, with the above configuration, a more accurate focus error signal and tracking error than the conventional configuration in which the tracking error signal is obtained in a state including the light beam reflected from the recording layer farther from the target layer. Signal.

  In other words, for example, in the case of a dual-layer disc such as a DVD, the tracking error signal offset caused by stray light from the recording layer farther from the target layer when viewed from the objective lens 5 is eliminated, and the focus error The offset of the focus error signal can be reduced because the third dividing unit 3c for acquiring the signal for use has a shape including a circular region of the optical axis of the light beam. Therefore, good tracking servo and focus servo can be realized by using the optical pickup device on which the hologram 3 is mounted.

  The neutral position indicates a state in which the optical axis (center axis) of the objective lens 5 is coincident with the optical axis of the light beam.

  Here, the 4th division part 3d of the hologram 3 is demonstrated. A plurality of grooves similar to those of the first divided portion 3a to the third divided portion 3c may be formed in the fourth divided portion 3d. In this case, the shape of the groove is such that the light beam incident on the fourth dividing portion 3d is guided to a position where it is not received by the first to third light receiving portions provided in the detecting portion 7. An interval may be set.

  Further, the fourth divided portion 3d may be shielded by a mask or the like so that the reflected light from the recording medium 6 does not reach the detection portion 7.

When the light from the fourth dividing unit 3d is not received by the detector (light receiving element) as described above, the reproduction signal RF signal I (RF) is expressed by the following equation (4),
I (RF) = I8c + I8d + I8a + I8b (4)
Generated by. That is, the RF signal I (RF) is generated based on the light intensity of the main beam 30.

A fourth light receiving unit (not shown) that receives the light beam divided by the fourth dividing unit 3d may be provided. Specifically, even if the direction and interval of the groove of the fourth divided portion 3d are set so that the fourth light receiving portion can detect the light beam divided (separated) by the fourth divided portion 3d. Good. The RF signal at this time further adds the intensity I8D detected by the fourth light receiving unit, and the following equation (5)
I (RF) = I8c + I8d + I8a + I8b + I8D (5)
Since the information recorded on the recording medium 6 can be detected by the entire light beam, the degree of modulation of the RF signal does not decrease and better information reproduction is possible.
In the case where the fourth light receiving portion is provided, it is desirable that the position of the fourth light receiving portion is provided where there is no influence of a light beam (stray light) from another layer (recording layer other than the target layer).

Further, for example, as shown in FIG. 5, the fourth division part 3d of the hologram 3 is further divided into two divided regions (region 3f, region 3g) by the virtual dividing line b , and passes through each divided region. The direction and interval of the grooves may be set so that the received light beams can be detected by the light receiving elements included in the fourth light receiving unit. This will be described below. FIG. 5 is a front view showing another hologram pattern of the hologram 3.

  FIG. 6 is a diagram showing the relationship between a light beam divided by another hologram pattern of the hologram 3 and a detection unit 7 that receives the light beam. As shown in FIG. 6, when the tracking error signal is generated using the light beam separated by the fourth dividing unit 3d, the light beams separated by the region 3f and the region 3g of the fourth dividing unit 3d are respectively received. Receiving light receiving portions 8E and 8F. The light receiving unit 8E includes a light receiving element 8i that receives the main beam 30 separated by the region 3f, and light receiving elements 8l and 8k that receive the first sub beam 31 and the second sub beam 32, respectively. On the other hand, the light receiving unit 8F includes a light receiving element 8j that receives the main beam 30 separated by the region 3g, and light receiving elements 8n and 8m that receive the first sub beam 31 and the second sub beam 32, respectively.

When the light beams separated by the regions 3f and 3g shown in FIG. 6 are detected by the light receiving units 8E and 8F each composed of three detectors, I (RF), I (DPD), I (DPP) represents the following formulas (6) to (8)
I (RF) = I8c + I8d + I8a + I8b + I8i + I8j (6)
I (DPD) = ph [(I8c + I8i) − (I8d + I8j)] (7)
I (DPP) = [(I8c + I8j)-(I8d + I8i)]
−k × [(I8f−I8h) + (I8e−I8g)
+ (I8n-I8l) + (I8m-I8k)] (8)
Can be generated by the following calculation. In the above formula, I8i to I8n indicate the light intensities detected by the light receiving elements 8i to 8n, respectively.

  With the above configuration, the RF signal can be obtained with the entire light beam reflected from the recording medium 6, and the fourth dividing unit 3d is also used when generating a tracking error signal such as the DPD method or the DPP method. Therefore, the light beam generated when the tracking error signal is generated is increased, and a better tracking servo can be performed. Even when the tracking error signal is generated using the fourth dividing unit 3d, or the light beam separated by the fourth dividing unit 3d is used to obtain a reproduction signal. The fourth divided portion 3d is more preferably arranged at a place where there is no influence of the stray light component reflected from the recording layer other than the target layer.

  Further, the hologram 3 can have a polarization characteristic such that the diffraction efficiency changes depending on the polarization state of the incident light beam. For example, a λ / 4 plate is disposed between the hologram 3 and the recording medium 6, the polarization direction of the light beam (emitted light) emitted from the light source and the polarization of the light beam (reflected light) reflected from the recording medium 6. By rotating the direction by 90 degrees, the emitted light is almost transmitted through the hologram 3, and diffracted light can be generated only with respect to the reflected light. By providing such polarization characteristics, the light use efficiency is increased, so that high-speed recording on the recording medium 6 is also possible.

  Further, the optical pickup device according to the present embodiment receives the light source 1 that irradiates the light beam, the objective lens 5 that focuses the light beam on the recording medium 6, and the reflected light from the recording medium 6. A plurality of recording units each including a detection unit 7 having a plurality of light receiving elements and a hologram 3 that is disposed between the detection unit 7 and the objective lens 5 and has a plurality of division units that divide the reflected light from the recording medium 6. In the optical pickup device that records / reproduces information to / from the recording medium 6 in which the layers are stacked, the hologram 3 includes (1) the reflected light guided to the hologram 3 when the objective lens 5 is in the neutral position. A dividing line A that passes through the optical axis and is orthogonal to the track direction of the recording medium 6, and a radius of reflected light from the recording medium 6 that is parallel to the dividing line A and condensed on the hologram 3 from the dividing line A Shorter distance than a region (A) surrounded by a dividing line B separated by d, and (2) a light beam that is in contact with the region (A) and is irradiated on the hologram 3 around the optical axis of the reflected light. It has a region (C) that is a combination of two regions, a semicircular region (B) having a radius smaller than the radius, and the light beam separated in the region (C) is received by a two-divided detector Thus, the focus signal may be generated.

  Further, the hologram 3 is more than a circle separated by a predetermined distance from the one point a as a center, in one of the regions divided by the straight line A passing through an arbitrary point a on the hologram 3. It has a tracking separation region that is a region far from the point a. Further, the hologram 3 is parallel to the straight line A and the straight line A, and is separated from the straight line A by a predetermined distance d from a circular area inside the circle separated from the straight line A by a predetermined distance with the one point a as the center. It has a focus separation region composed of a region combined with a band-like region sandwiched between parallel straight lines B. The hologram 3 is arranged so that the straight line A is parallel to the radial direction of the recording medium 6. Here, the predetermined distance d is a distance smaller than the beam radius of the main beam 30 irradiated to the hologram 3, and specifically, the distance d is the main beam 30 irradiated to the hologram 3. It is more preferable that the distance d is larger than 50% of the beam radius. When the distance d is 50% or less of the beam radius of the main beam 30 irradiated on the hologram 3, the main beam 30 incident on the light receiving unit for focusing is used. In some cases, it is difficult to obtain an accurate focus error signal.

  The radius of the “circle separated by a predetermined distance” is smaller than the beam diameter (radius) of the main beam 30 irradiated on the hologram 3 and smaller than the distance d. Specifically, the radius of the circle is more preferably in the range of 30 to 60% of the radius of the main beam 30 irradiated on the hologram 3. When the radius of the circle is smaller than 30% of the radius of the main beam 30 irradiated on the hologram 3, the light beam reflected by the recording layer farther than the recording layer on which information is recorded / reproduced. May enter the tracking light receiving unit. On the other hand, when the radius of the circle is larger than 60% of the beam radius of the main beam 30 irradiated on the hologram 3, the amount of light of the main beam 30 incident on the tracking light receiving unit is reduced, and accurate tracking is performed. It may be difficult to obtain an error signal.

  Further, the optical pickup device according to the present embodiment includes a focusing beam for obtaining a focus error signal, a light beam reflected from the recording medium 6 in which a plurality of recording layers are laminated and passed through the objective lens 5; An optical pickup device comprising a hologram 3 having a separation region at least separated into a tracking beam for obtaining a tracking error signal, and a detection unit 7 for detecting a focusing beam and a tracking beam, respectively. 3 is a dividing line that passes through the optical axis of the light beam reflected from the recording layer on which information is recorded / reproduced with the objective lens 5 in the neutral position and is orthogonal to the track direction of the recording medium 6. A and a part parallel to the parting line A separated from the parting line A by a distance smaller than the radius of the light beam. The light beam reflected by the recording layer farther than the recording layer where information is recorded / reproduced as viewed from the region (A) between the line B and the light collecting means is collected. A configuration having a focus separation region that separates the focusing beam in a condensing region including the region and a tracking separation region that separates the focusing beam in a region excluding the condensing region may be employed.

  Here, an information recording / reproducing apparatus including the optical pickup device according to the present embodiment will be described.

  As shown in FIG. 7, the information recording / reproducing apparatus 50 according to the present embodiment includes a spindle motor 51 that rotationally drives the recording medium 6, an optical pickup apparatus 20 that records and reproduces information on the recording medium 6, and the spindle motor 51. And a drive control unit 52 for driving and controlling the optical pickup device 20.

  The drive control unit 52 includes a spindle motor drive circuit that performs drive control of the spindle motor 51, a focus drive circuit that performs drive control of a focus actuator that moves the objective lens 5 in the focus direction, and the objective lens 5 in the radial direction. A control signal generation circuit for generating a control signal from the signal obtained from the optical pickup device 20 to each of the control circuits, and a tracking drive circuit for controlling the movement of the tracking actuator to be moved; An information reproducing circuit for reproducing information recorded on the recording medium 6 from a signal obtained from the device 7 and generating a reproduction signal is provided. The information recording / reproducing apparatus 50 is an apparatus that can perform at least one of information recording and reproduction.

  The optical pickup device according to the present invention can be suitably applied particularly to a recordable information recording / reproducing device for recording information on a multilayer optical disk.

It is drawing which shows the hologram pattern of the hologram which is embodiment of this invention. It is a front view which shows the structure of the optical pick-up apparatus which is embodiment of this invention. It is drawing which showed the relationship between the light beam divided | segmented by the hologram, and the detection part which receives the said light beam. It is a graph showing the relationship between the width d of the virtual dividing line A and the virtual dividing line B in the hologram pattern and the magnitude of the offset appearing in the focus error signal. It is a front view which shows the other hologram pattern concerning this Embodiment. It is drawing which showed the relationship between the light beam divided | segmented by the said other hologram pattern, and the detection part which receives those light beams. It is a block diagram which shows the structure of the outline of an information recording / reproducing apparatus. It is a front view which shows the hologram pattern proposed by the present applicant in an unpublished application at the time of confirmation before filing of the present application. In the hologram pattern of the above-mentioned unpublished application, the focus error signal by the knife edge method is expressed with and without spherical aberration. It is a front view which shows the structure of the conventional optical pick-up apparatus. The front view which shows the detail of the conventional hologram pattern is shown. It is drawing explaining the structure of the conventional light-receiving means. 5 is a diagram for explaining a light beam reflected from an upper first recording layer and a lower second recording layer in the case of a recording medium having two recording layers. It is a figure explaining that the reflected light from recording layers other than the recording layer which is recording / reproducing information is irradiated to a light receiving element. It is drawing explaining the light beam which injects into a hologram in the state in which the objective lens 15 has shifted | deviated from the neutral position.

Explanation of symbols

1 Light source 2 Grating 3 Hologram (separation means)
3a First division (tracking separation area)
3b Second division (tracking separation region)
3c Third division (focus separation area)
3d Fourth division part 4 Collimating lens 5 Objective lens 6 Recording medium 7 Detection part (detection means)
8E Light receiver (detector, tracking error signal detector)
8F Light receiver (detector, tracking error signal detector)

Claims (9)

A light beam reflected from an optical recording medium in which a plurality of recording layers are laminated and passed through a condensing means is at least a focusing beam for obtaining a focus error signal and a tracking beam for obtaining a tracking error signal. Separation means having a separation region for separation;
An optical pickup device comprising a detecting means for receiving a focusing beam and a tracking beam,
The separating means includes a dividing line A that passes through a point that coincides with the optical axis of the light beam reflected from the recording layer on which information is recorded / reproduced while the light collecting means is in a neutral position. And a region (A) sandwiched between the dividing line A and the dividing line B parallel to the dividing line A and a distance smaller than the radius of the light beam, and the optical axis of the light beam. A focus separation region that separates the focus beam from the light beam in a region combined with a circular region (B) smaller than the beam radius of the light beam around the point;
An optical pickup device comprising: a tracking separation region for separating a tracking beam from the light beam in a region excluding the region (A) and the region (B).   The region (B) includes a region where a light beam reflected by a recording layer farther than the recording layer on which information is recorded / reproduced as viewed from the condensing means is collected. The optical pickup device according to claim 1. The detection means includes a detection unit that detects only the light beam reflected from the optical recording medium and passing outside the dividing line B when viewed from the optical axis of the light beam. The optical pickup device according to claim 1 or 2, characterized in that The detecting means detects a tracking error signal by detecting a light beam reflected from the optical recording medium and passing outside the dividing line B when viewed from the optical axis of the light beam. The optical pickup device according to claim 1, further comprising a tracking error signal detection unit.   The separation means according to any one of claims 1 to 4, wherein the diffraction efficiency of the light beam passing through the separation means changes depending on the polarization state of the light beam incident on the separation means. The optical pickup device described.   The radius of the region (B) is within the range of 30 to 60% with respect to the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separation means. 2. The optical pickup device according to claim 1, wherein   The interval from the dividing line A to the dividing line B is larger than 50% with respect to the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separating means. 2. The optical pickup device according to claim 1, wherein A light beam reflected from an optical recording medium in which a plurality of recording layers are laminated and passed through a condensing means is at least a focusing beam for obtaining a focus error signal and a tracking beam for obtaining a tracking error signal. Separation means having a separation region for separation;
An optical pickup device comprising a detecting means for receiving a focusing beam and a tracking beam,
The separating means includes a straight line passing through a point that coincides with the optical axis of the light beam reflected from the recording layer on which information is recorded / reproduced in a state where the light collecting means is in a neutral position and irradiated to the separating means ; It is parallel to the straight line and is sandwiched between parallel straight lines separated from the straight line by a distance smaller than the beam radius of the light beam reflected from the recording layer on which information is recorded / reproduced and applied to the separation means. The light beam is a region that is a combination of a belt-like region and a circular region of a circle having a radius smaller than the beam radius of the light beam irradiated to the separation means centered on a point coincident with the optical axis of the light beam. A focus separation region that separates into a focus beam;
An optical pickup device comprising: a tracking separation region for separating the light beam into a tracking beam in a region excluding at least the band region and the circular region.   An information recording / reproducing apparatus comprising the optical pickup device according to claim 1.

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