JP2010129133A - Optical pickup apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup apparatus which improves accuracy of a signal to be used in tracking control to improve accuracy of the tracking control without generating an interference fringe at a spot from a desired recording layer, projected on a light receiving surface of a light receiving section even when tracking adjustment is performed on an optical disk having a plurality of recording layers in a thickness direction. <P>SOLUTION: The optical pickup apparatus has a light source 1 which emits laser light, an objective lens 5 which focuses the laser light onto the optical disk 101 comprising at least a first recording layer 101a and a second recording layer 101b, an OEIC 7 which receives reflected light from the optical disk 101 via the objective lens 5, and an astigmatism adjusting section 5a which is arranged almost in the center of a face of the objective lens 5, facing the optical disk 101 and generates astigmatism at at least a part of the laser light. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup device that performs at least one of recording and reproduction of information on an optical disc.

At present, an increasing number of optical discs have a plurality of recording layers in the thickness direction of the optical disc so that high-density recording can be realized. When recording on an optical disc having a plurality of recording layers in the thickness direction or reproducing an optical disc having a plurality of recording layers in the thickness direction, the reflected light from other recording layers is stray light to the reflected light from the desired recording layer. Join as. At this time, the optical disc apparatus needs to perform tracking control in a state where the reflected light from the desired recording layer and the reflected light from the other recording layer are simultaneously incident on the light receiving unit.
JP 2007-004867 A

  However, if the reflected light from the desired recording layer and the reflected light from the other recording layer are incident on the light receiving unit at the same time, if tracking adjustment is performed using the reflected light incident on the light receiving unit, tracking control is performed. There was a problem that it might cause trouble.

  In particular, when recording on a Blu-ray disc or playing back a Blu-ray disc, the Blu-ray disc has a thin base material and the distance between the recording layers is close. Reflected light from is easily added as stray light.

  FIG. 8 is a diagram illustrating a state in which reflected light from a desired recording layer and reflected light from another recording layer are simultaneously incident on the light receiving unit. FIG. 8A shows a state in which reflected light from a desired recording layer and reflected light from another recording layer are simultaneously incident on the light receiving portion, and FIG. 8B shows interference fringes projected on the light receiving region. It is a figure which shows a mode. In FIG. 8, reference numerals 11 to 13 denote light receiving areas.

  The light receiving portion of the optical pickup is formed of three light receiving regions, a light receiving region 11, a light receiving region 12, and a light receiving region 13.

  The laser beam emitted from the light source is divided into a total of three main laser beams and two sub laser beams by the diffraction element, and is irradiated onto the optical disc. The three laser beams irradiated on the optical disk are reflected by the optical disk.

  Of the reflected light reflected from the optical disk, the reflected light from the desired recording layer is divided into a total of three, one main laser light and two sub laser lights, and the light receiving region 11, the light receiving region 12, The light enters the light receiving region 13. In addition, among the reflected light reflected from the optical disc, the reflected light other than the desired recording layer is also divided into a total of three of one main laser beam and two sub laser beams, and the light receiving unit of the optical pickup. Is incident on. At this time, the reflected light from the other recording layer has a focus position that is not optimal, so that the spot shape of the reflected light projected on the light receiving region is larger than the spot shape of the reflected light from the desired recording layer.

  For this reason, when the reflected light from the desired recording layer and the reflected light from the other recording layer enter the light receiving unit at the same time, the state shown in FIG. Here, the light incident only on the light receiving region 11 is the main laser light from the desired recording layer, and the light incident only on the light receiving region 12 and the light receiving region 13 is the sub laser light from the desired recording layer, the light receiving region 11 and the light receiving region. 12 and the light incident on all of the light receiving region 13 become main laser light from other recording layers.

  In the light receiving region 11, the spot due to the main laser light from the desired recording layer interferes with the spot due to the main laser light from the other recording layer, and interference fringes shown in FIG. 8B are formed on the light receiving surface of the light receiving region 11. appear. Further, in the light receiving region 12, the sub laser light from the desired recording layer interferes with the main laser light from the other recording layer, and interference fringes shown in FIG. 8B are generated on the light receiving surface of the light receiving region 12. Further, in the light receiving region 13, the sub laser light from the desired recording layer interferes with the main laser light from the other recording layer, and interference fringes shown in FIG. 8B are generated on the light receiving surface of the light receiving region 13.

  As described above, when interference fringes are generated in each of the light receiving region 11, the light receiving region 12, and the light receiving region 13, an error occurs in the light amount distribution on the light receiving region, which may cause a problem in tracking control. there were.

  The present invention has been made to solve the above problems, and is projected onto the light receiving surface of the light receiving means even when tracking adjustment is performed on an optical disk having a plurality of recording layers in the thickness direction. It is an object of the present invention to provide an optical pickup device capable of increasing the accuracy of tracking control by increasing the accuracy of a signal used for tracking control without generating interference fringes at a spot from a desired recording layer.

  The present invention has been made to solve the above-described problem, and includes a light source that emits laser light, an objective lens that condenses the laser light on an optical disc composed of at least a first recording layer and a second recording layer, A light receiving means for receiving reflected light from the optical disk via the objective lens, and an astigmatism generating means disposed at substantially the center of the surface of the objective lens facing the optical disk and generating astigmatism in at least a part of the laser light. It is characterized by comprising.

  In the present invention, when the reflected light from the other recording layer is added as the stray light to the reflected light from the desired recording layer, the light having a large light amount per unit area among the reflected light from the other recording layers, That is, astigmatism is generated in the reflected light from the other recording layer that passes through the astigmatism generating means, and light having a large amount of light out of the reflected light from the other recording layer is not incident on the specific light receiving region. Interference fringes are not generated in spots formed on a specific light receiving area by reflected light from the recording layer. As a result, even when tracking adjustment is performed on an optical disc having a plurality of recording layers in the thickness direction, interference fringes are not generated at spots from a desired recording layer projected onto the light receiving surface of the light receiving means. In addition, it is possible to realize an optical pickup device that can improve the accuracy of tracking control by increasing the accuracy of a signal used for tracking control.

  According to a first aspect of the present invention, there is provided a light source for emitting laser light, an objective lens for condensing the laser light on an optical disc composed of at least a first recording layer and a second recording layer, and reflection from the optical disc via the objective lens. A light receiving means for receiving light; and an astigmatism generating means that is arranged at substantially the center of the surface of the objective lens facing the optical disk and generates astigmatism in at least a part of the laser light. To do. Accordingly, when the reflected light from the other recording layer is added as the stray light to the reflected light from the desired recording layer, the light having a large light amount per unit area among the reflected light from the other recording layers, that is, other recordings Astigmatism is generated in the reflected light that passes through the astigmatism generating means out of the reflected light from the layer, and light having a large amount of light from the other recording layers is not incident on the specific light receiving region. Interference fringes are not generated in spots formed on a specific light receiving area by reflected light from the recording layer. As a result, even when tracking adjustment is performed on an optical disc having a plurality of recording layers in the thickness direction, interference fringes are not generated at spots from a desired recording layer projected onto the light receiving surface of the light receiving means. In addition, it is possible to realize an optical pickup device that can improve the accuracy of tracking control by increasing the accuracy of a signal used for tracking control. In addition, since the astigmatism generating means is disposed on the surface of the objective lens facing the optical disk, the astigmatism is not reflected on the reflected light from other recording layers immediately before entering the optical component group, that is, at the position farthest from the light receiving means on the optical path. Aberration can be generated, and interference fringes are not reliably generated for spots formed on a specific light receiving area by reflected light from a desired recording layer.

  The invention according to claim 2 is characterized in that the surface of the astigmatism generating means facing the optical disk is formed of a cylindrical surface. As a result, the astigmatism is generated according to the shape of the astigmatism generating means without changing the refractive index of each part of the astigmatism generating means according to the composition ratio of the material constituting the astigmatism generating means. As a result, it is possible to generate astigmatism with high accuracy with an easy configuration.

  According to the third aspect of the present invention, the reflected light from the optical disk that is formed of at least three light receiving regions in which the light receiving means are arranged in a straight line and has passed through the astigmatism generating means is substantially elliptical. The major axis direction has an inclination of approximately 45 ° with respect to a straight line connecting at least three light receiving regions. As a result, astigmatism is generated in the reflected light that passes through the astigmatism generating means out of the reflected light from the other recording layer, that is, the light having a large light amount per unit area, that is, the reflected light from the other recording layer. Therefore, light with a large amount of light reflected from the other recording layer is not directed to the specific light receiving area so as to be directed to the position farthest from the specific light receiving area, and therefore specified by the reflected light from the desired recording layer. Interference fringes are not reliably generated for spots formed on the light receiving region.

(Embodiment 1)
Embodiment 1 of the present invention will be described below with reference to the drawings.

  In the first embodiment, an optical disc having a plurality of recording layers in the thickness direction will be described as an optical disc having two recording layers. Also, a recording layer that records or reproduces information is a recording layer 101a, a recording layer that does not record or reproduce information is a recording layer 101b, the recording layer 101a is a desired recording layer, and the recording layer 101b is another recording layer. explain.

  FIG. 1 is a configuration diagram of an optical pickup device according to Embodiment 1 of the present invention. In FIG. 1, 1 is a light source, 2 is a diffraction grating, 3 is a collimator lens, 4 is a splitting element, 5 is an objective lens, 5a is an astigmatism modulation unit, 6 is a detection lens, and 7 is an OEIC (Opto-Electronic Integrated Circuit). , Hereinafter referred to simply as OEIC), 101 is an optical disc, 101a is a recording layer, and 101b is a recording layer. In the first embodiment, the light source corresponds to the light source 1, the objective lens corresponds to the objective lens 5, the light receiving means corresponds to the OEIC 7, and the astigmatism generation means corresponds to the astigmatism modulation unit 5a.

  The light source 1 includes a semiconductor laser for BD (Blu-ray Disc, hereinafter simply referred to as BD) that emits laser light having a wavelength of 405 nm, and a DVD (Digital Versatile Disc, hereinafter simply referred to as DVD) that emits laser light having a wavelength of about 650 nm. And a semiconductor laser for CD (Compact Disc, hereinafter simply referred to as CD) that emits laser light having a wavelength of about 780 nm. The optical disk device emits laser light corresponding to the mounted optical disk 101.

  The laser light emitted from the light source 1 is incident on the diffraction grating 2 and then divided into a total of three, one main laser light and two sub laser lights. The three divided laser beams enter the collimator lens 3 and are converted from divergent light into parallel light. Thereafter, the three divided laser beams are reflected by the dividing element 4 and guided to the objective lens 5. The three laser beams guided to the objective lens 5 are focused on the recording surface 101a of the optical disc 101, that is, a desired recording layer. Thereafter, the three laser beams reflected by the recording surface 101 a of the optical disc 101 are guided to the dividing element 4 via the objective lens 5.

  Since the splitting element 4 has characteristics of reflecting light incident from the light source 1 in the direction of the objective lens 5 and transmitting light incident from the objective lens 5, the splitting element 4 is guided to the splitting element 4 via the objective lens 5. The three laser beams pass through the dividing element 4 and enter the detection lens 6. Here, the three laser beams incident on the detection lens 6 are each focused and reach the light receiving surface of the OEIC 7.

  Here, the characteristic part of this invention is demonstrated.

  Between the optical disk 101 and the objective lens 5, there is provided astigmatism generating means for generating astigmatism in at least a part of the laser light emitted from the light source 1. In the case of the first embodiment, this astigmatism generation means corresponds to the astigmatism modulation unit 5a.

  Next, details of the objective lens 5 provided with the astigmatism modulation unit 5a will be described.

  FIG. 2 is a diagram showing an upper surface and a side surface of the objective lens according to the first embodiment of the present invention. 2A shows a top view of the objective lens, and FIG. 2B shows a cross-sectional view of the objective lens. In FIG. 2, 5 is an objective lens, 5a is an astigmatism modulation section, 5e is a lens edge section, 5d is a focusing section, 101 is an optical disk, 101a is a recording layer, and 101b is a recording layer. In FIG. 2B, the main laser light reflected from the recording layer 101a is indicated by a solid line, and the main laser light reflected from the recording layer 101b is indicated by a broken line.

  The objective lens 5 is formed of a substantially spherical condensing part 5d for condensing laser light and a lens edge part 5e for fixing the objective lens 5 to a holder (not shown) so that tracking control or focus control can be performed. ing. The light condensing unit 5d is arranged so that the optical axes of the three laser beams passing through the substantially spherical surface are substantially perpendicular to the recording surface 101a and the recording surface 101b of the optical disc 101. And the astigmatism modulation part 5a is provided in the surface which opposes the optical disk 101 of this condensing part 5d. Since the astigmatism modulation unit 5a has a function of generating astigmatism in the light passing through the astigmatism modulation unit 5a, at least part of the light passing through the objective lens 5 is astigmatism. Aberration will occur.

  When recording on an optical disc 101 having a plurality of recording layers in the thickness direction or reproducing an optical disc having a plurality of recording layers in the thickness direction, reflected light from the optical disc 101 is reflected from the recording layer 101a which is a desired recording layer. In addition to the reflected light, reflected light from the recording layer 101b, which is another recording layer, is also included. The reflected light from the recording layer 101a and the reflected light from the recording layer 101b are incident on the optical path of the optical component group including at least the dividing element 4 and the detection lens 6 via the objective lens 5. .

  Here, since the astigmatism modulation unit 5a is provided at substantially the center of the objective lens 5, the reflected light from the recording layer 101a and the reflected light from the recording layer 101b are respectively transmitted by the astigmatism modulation unit 5a. Astigmatism occurs in a region in which the amount of light per unit area is large in the reflected light. Then, the reflected light from the recording layer 101a and the reflected light from the recording layer 101b travel toward the dividing element 4 while maintaining the astigmatism component when passing through the objective lens 5.

  FIG. 3 is a diagram showing a top surface and a cross section of the objective lens according to Embodiment 1 of the present invention. 3A is a top view of the objective lens, FIG. 3B is a cross-sectional view taken along the line II ′ of the objective lens shown in FIG. 3A, and FIG. 3C is FIG. 3A. JJ 'sectional drawing of an objective lens, FIG.3 (d) is KK' sectional drawing of the objective lens shown to Fig.3 (a). In FIG. 3, 5 is an objective lens, 5a is an astigmatism modulation unit, 5d is a condensing unit, and 5e is a lens edge unit.

  The astigmatism modulation unit 5 a is disposed at approximately the center of the surface of the objective lens 5 facing the optical disc 101, and generates astigmatism in at least a part of the reflected light from the optical disc 101. Thereby, when the reflected light from the recording layer 101b is added as stray light to the reflected light from the recording layer 101a and enters the objective lens 5, a region where the light amount per unit area is large in the reflected light of the recording layer 101b, that is, astigmatism. Astigmatism is generated in the reflected light from the other recording layer that passes through the aberration modulator 5a. At the same time, astigmatism is generated in the reflected light from the desired recording layer that passes through the astigmatism modulation section 5a, that is, the region having a large amount of light per unit area in the reflected light of the recording layer 101a.

  Further, the astigmatism modulation unit 5a has a so-called cylindrical shape in which a column is divided into two in the axial direction, and a surface facing the optical disc 101 is a cylindrical surface. As a result, when astigmatism is generated in the astigmatism modulation unit 5a, astigmatism is obtained by changing the refractive index of each part of the astigmatism modulation unit 5a according to the composition ratio of the material constituting the astigmatism modulation unit 5a. Astigmatism is generated by the shape of the astigmatism modulation unit 5a without generating the astigmatism, so that it is possible to generate astigmatism with high accuracy with an easy configuration.

  Furthermore, since the astigmatism modulation unit 5a is integrally formed with the objective lens 5 using a material such as resin or glass, the position of the astigmatism modulation unit 5a with respect to the objective lens 5 can be stabilized.

  FIG. 4 is a diagram showing a state in which reflected light from a desired recording layer and reflected light from other recording layers are simultaneously incident on the dividing element in Embodiment 1 of the present invention. It is the figure seen from the direction which reflected light and the reflected light from another recording layer inject, ie, the L direction shown in FIG. In FIG. 4, 4 is a dividing element, and 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b are regions.

  Regions projected onto the dividing element 4 by the main laser light from the recording layer 101a are a region 41a and a region 41b. Since the main laser light from the recording layer 101a reaches the region 41a through the astigmatism modulation unit 5a located substantially at the center of the objective lens 5, the area 41a per unit area of the main laser light from the recording layer 101a. This is an area where a large amount of light reaches. In the region 41b, the main laser light from the recording layer 101a arrives after passing through other than the astigmatism modulation unit 5a of the objective lens 5, so that the amount of light per unit area of the main laser light from the recording layer 101a is small. An area where small light can reach.

  In addition, regions projected onto the dividing element 4 by the sub laser light from the recording layer 101a are a region 42a, a region 42b, a region 43a, and a region 43b. Since the main laser light from the recording layer 101a reaches the region 42a and the region 43a through the astigmatism modulation unit 5a located at the approximate center of the objective lens 5, the unit 42a is a unit of the main laser light from the recording layer 101a. This is a region where light having a large amount of light per area can reach. Further, since the main laser light from the recording layer 101a reaches the region 42b and the region 43b through other than the astigmatism modulation unit 5a of the objective lens 5, the main laser light from the recording layer 101a per unit area is reached. The amount of light is an area where small light can reach.

  The region projected onto the dividing element 4 by the main laser light from the recording layer 101b is a region 44a. Since the main laser light from the recording layer 101b reaches the region 44a through the astigmatism modulation unit 5a located substantially at the center of the objective lens 5, the area 44a per unit area of the main laser light from the recording layer 101a. This is an area where a large amount of light reaches. Further, the region 44b is a region where light having a small light amount per unit area of the main laser light from the recording layer 101b reaches.

  FIG. 5 is a diagram showing a state in which reflected light from a desired recording layer and reflected light from another recording layer are simultaneously incident on the detection lens in Embodiment 1 of the present invention. It is the figure seen from the direction which reflected light and the reflected light from another recording layer inject, ie, the M direction. In FIG. 5, 6 is a detection lens, and 61a, 61b, 61c, 62a, 62b, 62c, 63a, 63b, 63c, 64a, 64b are areas.

  Regions projected onto the detection lens 6 by the main laser light from the recording layer 101a are a region 61a and a region 61b. Since the main laser light from the recording layer 101a reaches the region 61a through the astigmatism modulation unit 5a located substantially at the center of the objective lens 5, the area 61a per unit area of the main laser light from the recording layer 101a. This is an area where a large amount of light reaches. In the region 61b, the main laser light from the recording layer 101a arrives after passing through other than the astigmatism modulation unit 5a of the objective lens 5, so that the amount of light per unit area of the main laser light from the recording layer 101a is small. An area where small light can reach.

  The areas projected onto the detection lens 6 by the sub laser light from the recording layer 101a are the area 62a, the area 62b, the area 63a, and the area 63b. Since the main laser light from the recording layer 101a reaches the region 62a and the region 63a through the astigmatism modulation unit 5a located substantially at the center of the objective lens 5, the unit 62a is included in the main laser light from the recording layer 101a. This is a region where light having a large amount of light per area can reach. Further, since the main laser light from the recording layer 101a reaches the region 62b and the region 63b by passing through other than the astigmatism modulation unit 5a of the objective lens 5, the main laser light from the recording layer 101a per unit area. The amount of light is an area where small light can reach.

  An area projected onto the detection lens 6 by the main laser light from the recording layer 101b is an area 64a. Since the main laser light from the recording layer 101b reaches the region 64a through the astigmatism modulation unit 5a located substantially at the center of the objective lens 5, the region 64a per unit area of the main laser light from the recording layer 101a is reached. This is an area where a large amount of light reaches. The region 64b is a region where light having a small light amount per unit area reaches the main laser light from the recording layer 101b.

  FIG. 6 is a diagram illustrating a state in which reflected light from a desired recording layer and reflected light from other recording layers are simultaneously incident on the light receiving unit in the first embodiment of the present invention. FIG. 6A shows a state in which reflected light from a desired recording layer and reflected light from another recording layer enter the light receiving region at the same time, and FIG. 6B shows the reflected light from the desired recording layer. It is a figure which shows a mode that an interference fringe does not generate | occur | produce in the spot formed in a specific light reception area | region. In FIG. 6, reference numerals 11 to 13 denote light receiving areas, and reference numerals 14 to 19 denote areas.

  The light receiving portion of the OEIC 7 is formed of three light receiving regions, a light receiving region 11, a light receiving region 12, and a light receiving region 13.

  The laser beam emitted from the light source 1 is divided into a total of three laser beams, one laser beam and two laser beams, by the diffraction element 2 and is applied to the optical disc 101. Then, the three laser beams irradiated on the optical disc 101 are reflected by the optical disc 101.

  Of the reflected light reflected from the optical disc 101, the reflected light from the recording layer 101a, which is a desired recording layer, is divided into a total of three, one main laser beam and two sub laser beams. It goes to the OEIC 7 via the detection lens 6. Thereafter, in the OEIC 7, one main laser light is incident on the light receiving area 11 that is the light receiving area of the OEIC 7, and the two sub-laser lights are incident on the light receiving area 12 and the light receiving area 13 that are the light receiving areas of the OEIC 7.

  On the other hand, of the reflected light reflected from the optical disc 101, the reflected light from the recording layer 101b, which is another recording layer, is also divided into a total of three of one main laser beam and two sub laser beams. Incident in the light receiving area. At this time, since the position of the objective lens 5 in the focus direction is adjusted so as to be optimal with respect to the recording layer 101a, the reflected light from the recording layer 101b is in a state where the focus is not optimal. For this reason, the reflected light from the recording layer 101b projected onto the light receiving area of the OEIC 7 has a spot shape larger than the spot shape of the reflected light from the recording layer 101a.

  In the present invention, an astigmatism modulation unit 5b is provided in the approximate center of the surface of the objective lens 5 facing the optical disc 101. Therefore, when the reflected light from the recording layer 101a and the reflected light from the recording layer 101b are projected onto the OEIC 7 via the objective lens 5, there is astigmatism depending on the projected position. Reach OEIC7. The reflected light from the recording layer 101a is projected with light having astigmatism on the central areas on the light receiving areas 11, 12, 13; that is, the areas 14, 15, 16; Light without astigmatism is projected so as to surround the periphery.

  Here, since the position of the objective lens 5 in the focus direction is adjusted so as to be optimal with respect to the recording layer 101a, the spot shape of the reflected light from the recording layer 101b projected onto the light receiving region is the recording layer 101a. It becomes larger than the spot shape of the reflected light from. Further, light reflected from the recording layer 101b having a large amount of light per unit area, that is, reflected light from another recording passing through the astigmatism modulation unit 5a has an astigmatism component. Therefore, the reflected light from the recording layer 101a and the reflected light that has passed through the astigmatism modulation unit 5a among the reflected light from the recording layer 101b are projected onto the light receiving region 11.

  The light receiving areas 12 and 13 project the reflected light from the recording layer 101a and the light that has passed through other than the astigmatism modulation unit 5a out of the reflected light from the recording layer 101b. Of the reflected light from the recording layer 101b, the light that has passed through other than the astigmatism modulation unit 5a is reduced due to the focus error between the recording layer 101b and the objective lens 5, and the amount of light is reduced. Since the large area is removed, the light has almost no light quantity. Thereby, the light projected on the light receiving regions 12 and 13 is substantially only the reflected light from the recording layer 101a.

  Thus, in the present invention, when the reflected light from the recording layer 101b is added as the stray light to the reflected light from the recording layer 101a, the reflected light of the recording layer 101b is incident on the light receiving areas 12 and 13 which are specific light receiving areas. Therefore, no interference fringes are generated in the spots formed on the light receiving regions 12 and 13 which are important for generating the tracking control signal of the objective lens 5.

  In addition, the spot shape of the reflected light from the recording layer 101a projected onto the light receiving regions 11, 12, and 13 is substantially elliptical in the central region, that is, the regions 14, 15, and 16 due to the influence of astigmatism. Tracking control that does not affect the focus control by adding an offset to the focus error signal so that the focus control signal in the elliptical shape is set to the reference value, that is, the focus error in the elliptical shape is zero. Can be realized.

  As described above, the astigmatism modulation section 5a for generating astigmatism in at least a part of the laser light is provided at the approximate center of the surface of the objective lens 5 facing the optical disc 101, thereby providing a desired recording layer. When the reflected light from the recording layer 101b, which is another recording layer, is added to the reflected light from the recording layer 101a as stray light, the reflected light from the recording layer 101b has a large amount of light per unit area, that is, astigmatism. Astigmatism is generated in the reflected light from the recording layer 101b that passes through the aberration modulating unit 5a, and light having a large amount of light out of the reflected light from the recording layer 101b is applied to the light receiving regions 12 and 16 that are specific light receiving regions. Since no incidence occurs, interference fringes of spots formed on the light receiving regions 12 and 13 are not generated by the reflected light from the recording layer 101a. As a result, even when tracking adjustment is performed on the optical disc 101 having a plurality of recording layers in the thickness direction, interference fringes are formed on the spots from the recording layer 101a projected on the light receiving surfaces of the light receiving regions 12 and 13. Since it is not generated, it is possible to realize an optical pickup device that can improve the accuracy of tracking control by increasing the accuracy of a signal used for tracking control. Further, since the astigmatism modulation unit 5a is disposed on the surface of the objective lens 5 facing the optical disc 101, it passes through the astigmatism modulation means 5a immediately before entering the optical component group, that is, at a position farthest from the OEIC 7 on the optical path. Astigmatism can be generated in the reflected light from the recording layer 101b, and interference fringes are not reliably generated for the spots formed on the specific light receiving regions 12 and 13 by the reflected light from the recording layer 101a.

  In the present invention, as shown in FIG. 6, the reflected light from the optical disk 101, which is formed of three light receiving regions 11, 12, and 13 in which the OEIC 7 is linearly arranged and passes through the astigmatism modulation unit 5a, is substantially. The major axis direction of the substantially elliptical shape has an inclination of approximately 45 ° with respect to a straight line connecting the three light receiving regions 11, 12, and 13. As a result, when reflected light from the recording layer 101b, which is the other recording layer, is added as stray light to reflected light from the recording layer 101a, which is the desired recording layer, per unit area of the reflected light from the recording layer 101b. Astigmatism is generated in the light that has a large amount of light, that is, the reflected light from the recording layer 101b that passes through the astigmatism modulation unit 5a, and the light that has a large amount of light out of the reflected light from the recording layer 101b. This is important in generating a tracking control signal formed on the light receiving region by the reflected light from the recording layer 101a, since it does not enter the specific light receiving regions 12 and 13 that receive the laser beam that is the basis of the signal used for tracking control. Thus, interference fringes are not reliably generated with respect to spots formed on the specific light receiving regions 12 and 13. As a result, even when tracking adjustment is performed on an optical disc having a plurality of recording layers in the thickness direction, interference fringes are generated at spots from the recording layer 101a projected on the light receiving surfaces of the light receiving regions 12 and 13. Therefore, it is possible to realize an optical pickup device that can improve the accuracy of tracking control by increasing the accuracy of a signal used for tracking control.

  In the first embodiment, the optical disc 101 has two recording layers in the thickness direction as an example. However, the present invention is not limited to this, and the optical disc 101 has three or more recording layers. It is also applicable to what you have.

  FIG. 7 is a diagram showing an optical disk device using the optical pickup device according to Embodiment 1 of the present invention. In FIG. 7, 200 is a housing, 200a is an upper housing portion, 200b is a lower housing portion, 201 is a tray, 202 is a spindle motor, 203 is an optical pickup, 204 is a bezel, 205 is an entrance / exit, 206 is a rail, Reference numeral 207 denotes a rail, 208 denotes an eject switch, and 209 denotes a carriage. In the first embodiment, the rotation driving means is a spindle motor 202, and the moving means is a carriage 209.

  The housing 200 is configured by combining an upper housing portion 200a and a lower housing portion 200b. The upper housing part 200a and the lower housing part 200b are fixed to each other using a spiral or the like. The tray 201 is provided so as to freely move in and out of the housing 200, and a spindle motor 202 is provided near the center of the tray 201.

  The optical pickup 203 performs at least one of recording and reproduction of information on the optical disc 101. The optical pickup 203 is mounted on a carriage 209 that is held so as to be movable in the radial direction of the optical disc. The carriage 209 moves the optical pickup 203 closer to or away from the spindle motor 202.

  The bezel 204 is provided on the front end surface of the tray 201, and is configured to close the entrance / exit 205 of the tray 201 when the tray 201 is stored in the housing 200.

  The rails 206 and 207 are slidably attached to both the tray 201 and the casing 200, and the rails 206 and 207 are provided on both sides of the tray 201. The tray 201 is attached to the casing 200 so that it can freely appear and disappear.

  An eject switch 208 is provided on the bezel 204 provided on the front end surface of the tray 201. By pressing the eject switch 208, an engagement portion (not shown) provided on the housing 200 and the tray 201 are provided. The engagement with the provided engaging portion (not shown) is released.

  By mounting the optical pickup device of the present invention on the optical disc apparatus shown in FIG. 7, when reflected light from another recording layer is added as stray light to reflected light from a desired recording layer, Of the reflected light, the light having a large amount of light per unit area, that is, the reflected light from the other recording layer is caused to generate astigmatism in the reflected light passing through the astigmatism generating means. Since light having a large light quantity is not incident on the specific light receiving area, interference fringes are not generated in spots formed on the specific light receiving area by reflected light from a desired recording layer. As a result, even when tracking adjustment is performed on an optical disc having a plurality of recording layers in the thickness direction, interference fringes are not generated at spots from a desired recording layer projected onto the light receiving surface of the light receiving means. In addition, it is possible to realize an optical disc apparatus capable of increasing the accuracy of tracking control by increasing the accuracy of a signal used for tracking control.

  Even when tracking adjustment is performed on an optical disc having a plurality of recording layers in the thickness direction, the present invention reduces astigmatism to light having a large light amount per unit area among reflected light from other recording layers. An optical pickup device that can increase the accuracy of the tracking control by increasing the accuracy of the signal used for tracking control because light generated from other recording layers is not incident on a specific light receiving region. The purpose is to provide.

1 is a configuration diagram of an optical pickup device according to Embodiment 1 of the present invention. The figure which shows the upper surface and side surface of the objective lens in Embodiment 1 of this invention The figure which shows the upper surface and cross section of the objective lens in Embodiment 1 of this invention The figure which shows a mode that the reflected light from the desired recording layer in Embodiment 1 of this invention and the reflected light from another recording layer enter into a division | segmentation element simultaneously. The figure which shows a mode that the reflected light from the desired recording layer in Embodiment 1 of this invention and the reflected light from another recording layer enter into a detection lens simultaneously. The figure which shows a mode that the reflected light from the desired recording layer in Embodiment 1 of this invention and the reflected light from another recording layer enter into a light-receiving part simultaneously. 1 is a diagram showing an optical disk device using an optical pickup device in Embodiment 1 of the present invention. The figure which shows a mode that the reflected light from a desired recording layer and the reflected light from another recording layer enter into a light-receiving part simultaneously.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Diffraction grating 3 Collimator lens 4 Dividing element 5 Objective lens 5a Astigmatism modulation part 5d Condensing part 5e Lens edge part 6 Detection lens 7 OEIC
11, 12, 13 Light receiving region 14, 15, 16, 17, 18, 19 region 41a, 41b, 42a, 42b, 43a, 43b, 44a, 44b region 61a, 61b, 62a, 62b, 63a, 63b, 64a, 64b Area 101 Optical disc 101a Recording layer 101b Recording layer 200 Housing 200a Upper housing portion 200b Lower housing portion 201 Tray 202 Spindle motor 203 Optical pickup 204 Bezel 205 Recession opening 206 Rail 207 Rail 208 Eject switch 209 Carriage

Claims (3)

A light source that emits laser light;
An objective lens for condensing the laser beam on an optical disc composed of at least a first recording layer and a second recording layer;
A light receiving means for receiving reflected light from the optical disk through the objective lens;
And an astigmatism generating means disposed at substantially the center of the surface of the objective lens facing the optical disc and generating astigmatism in at least a part of the laser beam.   2. The optical pickup device according to claim 1, wherein the astigmatism generating means is configured such that a surface facing the optical disc is a cylindrical surface. The light receiving means is formed of at least three light receiving regions arranged in a straight line,
The reflected light from the optical disk that has passed through the astigmatism generating means is substantially elliptical,
3. The optical pickup device according to claim 2, wherein the major axis direction of the substantially elliptical shape has an inclination of approximately 45 degrees with respect to a straight line connecting the at least three light receiving regions.

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