JP4364887B2 - Optical pickup device and control method thereof - Google Patents

Description

  The present invention relates to an optical pickup apparatus that performs at least one of reproduction and recording on an optical disc having a plurality of recording layers, and a control method therefor.

  In recent years, the amount of information distributed has increased. Along with this, it is required to increase the recording density of the optical disc and to read information on the optical disc at high speed.

  As means for increasing the recording density of the optical disc, increasing the linear recording density in the information recording layer of the optical disc and narrowing the track pitch have been performed. In recent years, the recording information in the thickness direction of the optical disc has also been increased in density. That is, it is a multilayer optical disc in which information recording layers are laminated, and has already been commercialized.

  On the other hand, as a means for reading information on an optical disk at high speed, increasing the rotation speed of the optical disk is performed.

  However, when the above measures are taken, some new problems arise.

  First, when the rotational speed of the optical disk is increased, the amount of return light from the optical disk decreases accordingly. If a sufficient amount of light cannot be obtained, a high-quality reproduction signal cannot be obtained.

  Further, in order to increase the linear recording density and reduce the track pitch, it is necessary to reduce the beam diameter of the light beam condensed on the information recording layer of the optical disc. As a method of reducing the beam diameter of the light beam, it is conceivable to shorten the wavelength of the light beam and to increase the numerical aperture (NA) of the objective lens that functions as a condensing optical system of the optical pickup device. .

  Regarding the shortening of the wavelength of the light beam, it is possible to replace the light source from a red semiconductor laser having a wavelength of 650 nm generally used in a DVD (Digital Versatile Disc) to a blue-violet semiconductor laser having a wavelength of 405 nm.

  On the other hand, when the numerical aperture (NA) of the objective lens is increased, the influence of the error of spherical aberration increases. As a result, there arises a problem that the reading accuracy of information is reduced. Therefore, in order to achieve high recording density using an objective lens having a high numerical aperture (NA), it is necessary to correct spherical aberration.

  Here, spherical aberration will be described. Generally, in an optical disc, the information recording layer is covered with a cover glass in order to protect the information recording layer from dust and scratches. Therefore, the light beam that has passed through the objective lens of the optical pickup device passes through the cover glass, and is condensed on the information recording layer underneath to focus. When the light beam passes through the cover glass, spherical aberration (SA) occurs. Usually, the objective lens is designed to cancel out this spherical aberration. However, when the thickness of the cover glass deviates from a predetermined value, spherical aberration occurs in the light beam condensed on the information recording layer. That is, the beam diameter becomes large, and information cannot be read and written correctly.

  In particular, in an optical disc on which a plurality of information recording layers are formed, the thickness from the surface of the optical disc (cover glass surface) to each information recording layer is different. For this reason, the spherical aberration that occurs when the light beam passes through the cover glass of the optical disk differs depending on each information recording layer. Therefore, more complicated spherical aberration correction is required.

  In addition, in an optical disc on which a plurality of information recording layers are formed, unnecessary reflected light (stray light) from a layer (non-target layer) different from the layer to be reproduced or recorded (target layer) is reflected from the target layer. There is a concern about the influence on various signals detected from. That is, the stray light is a light beam that is not related to the information being reproduced or recorded. Therefore, noise is generated in the various signals by mixing the stray light with the reflected light from the target layer.

  Here, as a technique for reducing the influence of stray light on the various signals, there is a technique described in Patent Document 1, for example. This is to detect a push-pull signal as a light receiving region of the light separating means in an optical pickup device that guides reflected light from the optical disk to a light receiving element via an objective lens and light separating means and reproduces information on the optical disk. This is a technique in which a region and a region for detecting a focus error signal are provided, and stray light is diffracted toward the region for detecting the focus error signal in the light separation means. By this method, the influence of stray light on the various signals can be reduced. Details will be described below with reference to FIGS.

  First, a schematic configuration of the optical pickup device described in Patent Document 1 will be described.

  FIG. 11 is a cross-sectional view of the optical pickup device.

  As shown in the figure, the optical pickup device 108 includes a semiconductor laser 101, a hologram element 102, a collimator lens 103, an objective lens 104, and a photodetector 107. In addition, the optical disk 106 includes a cover glass 106a, an information recording layer 106c, an information recording layer 106d, and a substrate 106b in order from the objective lens 104. That is, the optical disk 106 is a two-layer disk.

  The hologram element 102, the collimator lens 103, and the objective lens 104 are disposed on the optical axis formed between the light beam emitting surface of the semiconductor laser 101 and the light beam reflecting surface of the optical disk 106. Further, the photodetector 107 is disposed at the focal position of the diffracted light of the hologram element 102. Thereby, the optical pickup device 108 performs the following operation.

  First, the light beam emitted from the semiconductor laser 101 passes through the hologram element 102 as 0th-order diffracted light, is converted into parallel light by the collimator lens 103, passes through the objective lens 104, and passes through the information recording layer of the optical disc 106. The light is focused on 106c or the information recording layer 106d. Then, the light beam reflected by the information recording layer 106c or the information recording layer 106d passes through each member in the order of the objective lens 104 and the collimator lens 103, enters the hologram element 102, and is diffracted by the hologram element 102 to detect light. Condensed on the vessel 107.

  Next, the hologram element 102 will be described in detail.

  FIG. 12 is a plan view of the element. Hereinafter, the direction on the hologram element 102 corresponding to the radial direction of the optical disk 106, that is, the x-axis direction in FIG. Further, a direction on the hologram element 102 corresponding to the circumferential direction of the optical disk 106, that is, the y-axis direction in FIG. 12, is referred to as a circumferential direction. The optical axis center 63 is a position corresponding to the optical axis of the reflected light from the optical disk 106 incident on the element.

  As shown in FIG. 12, the hologram element 102 has three regions 102a, 102b, and 102c. The first region 102a is constituted by a radial dividing line segment D140, D142 passing through the optical axis center 63, a semicircle E130 centered on the optical axis center 63, and a circle E131 centered on the optical axis center 63. It is an enclosed area. The second region 102b is a region surrounded by a semicircle E130, a circle E131, a circumferential segment line D141 passing through the optical axis center 63, and a segment line D140. The third region 102c is a region surrounded by the dividing line segment D141, the dividing line segment D142, the semicircle E130, and the circle E131.

  The light beams diffracted in the second region 102b and the third region 102c are detected by the light receiving elements on the photodetector 107, respectively. Then, a tracking error signal (TES) is detected from the result. The light beam diffracted in the region 102 a is detected by another light receiving element on the photodetector 107. Then, a focus error signal (FES) is detected from the result.

  As described above, when the light beam is condensed on the information recording layer 106 c on the side close to the objective lens 104 and recording or reproduction is performed, the reflected light from the information recording layer 106 d that is not reproduced is reflected on the hologram element 102. Irradiates to the central part. The reflected light does not include a reproduction signal, and when it is incident on the light receiving element, it affects various signals. In particular, it introduces an offset in the tracking error signal (TES). However, in the optical pickup device 108, the reflected light is diffracted in the first region and is incident on a light receiving element that detects a focus error signal (FES). At this time, since the reflected light is uniformly incident, the focus error signal (FES) can be normally detected. Further, since the light does not enter the light receiving element that detects the tracking error signal (TES), it does not affect.

With the above configuration, the optical pickup device 108 can reduce the influence of stray light on various signals.
JP 2004-288227 A (released on October 14, 2004)

  The conventional optical pickup device 108 performs signal detection using only the first-order diffracted light without using the zero-order light. Therefore, in an optical pickup device that performs recording and reproduction at a higher speed, the amount of light returning from the optical disk is insufficient, and a high-quality signal cannot be obtained.

  In order to solve this problem, it is conceivable to improve the conventional optical pickup device 108 so as to detect zero-order light. That is, an optical pickup having a configuration in which unnecessary reflected light from a non-target layer is diffracted and incident on a light receiving element for detecting a focus error signal (FES), and signal detection is performed using zero-order light. Device.

  However, there is a new problem in the optical pickup device having the above configuration. That is, the reflected light from the non-target layer interferes with the tracking error signal (TES) because the zero-order light and the diffracted light interfere with each other.

  Here, FIG. 13 is a plan view showing the state of the light spot on the light detection means 112 in the above configuration. A signal detection method in the optical pickup apparatus having the above configuration will be described with reference to FIG.

  The optical pickup device having the above configuration is different from the conventional optical pickup device 108 in that a three-beam generation grating for three-beam tracking is included in the forward optical path, and the shapes of the hologram element and the photodetector are different. It is. The region 212 a of the hologram element 22 has the same shape as the region 102 a of the hologram element 102 described in Patent Document 1. The photodetector 112 includes light receiving elements 112 a to 112 h for receiving zeroth-order light and light receiving elements 112 m to 112 n for detecting primary light diffracted by the hologram element 22. The light receiving elements 112a to 112d detect a reproduction signal (RF signal). The light receiving elements 112e to 112h detect the ± first-order light generated by the three-beam generation grating placed in the forward path. Based on the result and the signals detected by the light receiving elements 112a to 112d, a tracking error signal (TES) is detected, and three-beam tracking is performed. The light receiving elements 112m and 112n detect the primary light diffracted in the region 212a of the hologram element 22. Based on the result, a focus error signal (FES) is detected and focusing is performed. The signal detection methods are summarized below, assuming that the signals detected by the light receiving elements 112a to 112n are Sa to Sn.

RF = Sa + Sb + Sc + Sd
FES = Sm-Sn
TES = {(Sa + Sb)-(Sc + Sd)}
−α {(Se−Sf) + (Sg−Sh)}
Here, α is set to an optimum coefficient for adjusting offset due to objective lens shift or optical disc tilt.

  Here, as described above, when the light beam is condensed on the information recording layer 106c on the side close to the objective lens 104 and recording or reproduction is performed, the reflected light from the information recording layer 106d that is not reproduced is a hologram. The central portion of the element 22 is irradiated.

  FIG. 14 is a plan view showing a light spot on the photodetector 112 of the reflected light from the information recording layer 106d that has not been reproduced. The light spot 50a represents zero-order light, the light spot 50b represents + 1st-order light diffracted by the hologram element 22, and the light spot 50c represents -1st-order light. At this time, as shown in the figure, the light spots 50a to 50c are greatly spread on the light receiving element and have overlapping regions. In the overlapped portion, the light spots interfere with each other, resulting in interference fringes. Due to the interference fringes, offsets occur in the RF signal and the TES signal, thereby causing problems that the signal quality is degraded and accurate tracking cannot be performed.

  The present invention has been made in view of the above conventional problems. The purpose is to optimize the separation shape of the light beam to detect the 0th-order light and ensure the absolute value (signal quality) of the reproduction signal, and to influence the reflected light from the non-target layer on the tracking control. An object of the present invention is to provide an optical pickup device that can be sufficiently small.

  In order to solve the above problems, an optical pickup device according to the present invention includes a light source that emits a light beam, a condensing unit that focuses the light beam on one recording layer of an optical disc having a plurality of recording layers, A first light separating means for separating the reflected light from the optical disc; and a light detecting means for detecting a light beam that includes all or part of the light beam separated by the first light separating device and includes non-diffracted light. The first optical separation means includes a first region that does not have a light separation function and includes an optical axis center of reflected light from the optical disc.

  According to said structure, the said light detection means detects non-diffracted light (0th-order light) with strong light intensity. Therefore, even in an optical pickup device that performs at least one of reproduction and recording at high speed, the signal quality of the reproduction signal can be ensured.

  Moreover, according to said structure, the said light separation means has a 1st area | region which does not have a light separation function including the optical axis center of the said reflected light. Here, reflection from another recording layer (hereinafter referred to as non-target layer) located farther from the light collecting means than the recording layer (hereinafter referred to as target layer) on which the light beam emitted from the light source is focused. Due to the difference in optical path length, the light is incident on a narrower area on the light separating means than the light beam reflected by the target layer. Therefore, by not separating the light beam in the first region, it is possible to suppress the separation of the light beam from the non-target layer while sufficiently separating the light beam from the target layer. Here, when the light flux from the non-target layer is separated, the non-diffracted light and the diffracted light interfere with each other to form interference fringes on the light collecting means. The interference fringes hinder accurate tracking control. Therefore, accurate tracking control can be performed by suppressing the separation of the light beam from the non-target layer.

  As described above, in an optical pickup device that performs at least one of reproduction and recording on an optical disc having a plurality of recording layers, there is an effect that accurate tracking control can be performed while ensuring the signal quality of the reproduction signal. .

  The first light separation means of the optical pickup device according to the present invention is preferably a hologram element.

  According to said structure, a hologram element is used as said 1st light separation means. Thereby, unlike the case of using a simple (linear) diffraction grating pattern, the condensing position of the light beam diffracted by the first light separating means can be arbitrarily set. As a result, the reflected light beam from the target layer of the optical disk can be diffracted so as to be in a desired condensing state on the light detection means.

  The first region of the optical pickup device according to the present invention preferably transmits the incident light beam without separating it, or blocks the incident light beam.

  With the above configuration, it is possible to realize that the light flux from the non-target layer is not separated.

  In addition, since the first region transmits the incident light beam, the amount of non-diffracted light incident on the light detection means can be increased. As a result, the signal quality of the reproduction signal can be further ensured.

  Alternatively, the first region may shield the incident light beam. Thereby, the non-diffracted light of the light beam from the non-target layer can be prevented from entering the light detection means. Therefore, it is possible to further prevent the influence of the reflected light from the non-target layer on various signals.

  The first region of the optical pickup device according to the present invention is located at a position farther from the one recording layer as viewed from the light condensing means, and the reflected light from the other recording layer of the optical disc is the first light. It is preferable to include all the regions incident on the separating means.

  With the above configuration, it is possible to completely prevent the formation of interference fringes formed by the light flux from the non-target layer. Thereby, there is an effect that more accurate tracking control can be performed.

  The first region of the optical pickup device according to the present invention is preferably a region surrounded by a circle centered on the optical axis center of the reflected light on the first light separating means.

  According to the above configuration, the first region is a region surrounded by a circle. This is a general shape when the light beam is incident on the light separation means in the optical pickup device. Therefore, the first region has an additional effect that it can efficiently include the region where the light flux from the non-target layer is incident.

  In the first optical separation unit of the optical pickup device according to the present invention, a portion other than the first region is divided into second and third regions, and a boundary between the second and third regions. It is preferable that the line exists on a first straight line passing through the center of the optical axis and parallel to the radial direction of the optical disc.

  According to said structure, it has an area | region substantially divided | segmented by the straight line which passes along the said optical-axis center on the said light separation means. Therefore, it is possible to detect the focus error by using the knife edge method.

  In the first optical separation unit of the optical pickup device according to the present invention, the third region is divided into fourth and fifth regions, and a boundary line between the fourth and fifth regions is The first, second, third, fourth, and fifth line segments are connected in this order, and are symmetric with respect to a straight line that passes through the optical axis center and that is perpendicular to the first straight line. The first, third, and fifth line segments and the first straight line are parallel to each other, and the distance between the first and fifth line segments and the first straight line is Are equal to each other, and the distance between the third line segment and the first straight line is longer than the distance between the first line segment and the first straight line, and the first line segment, The minor angle created by the second line segment is preferably greater than a right angle.

  According to said structure, the said light separation means has four area | regions. Various signals can be detected based on the result of the light detection means detecting the light beam diffracted in each of the above regions. For example, the focus error signal can be detected based on the result of detection of the light beam diffracted in the second region or the light beam diffracted in the second region and the fifth region. Further, the spherical aberration error signal can be detected based on the result of detection of the light beam diffracted in the fifth region, or the light beam diffracted in the fourth region and the fifth region. There is an effect that can be done.

  The light detection means of the optical pickup device according to the present invention detects a focal position of a light beam diffracted in the second region, and the optical pickup device detects a focus error based on the detection result. Preferably further means are provided.

  According to said structure, the said light detection means detects the focus position of the light beam diffracted in the said 2nd area | region. Therefore, a focus error can be detected using the knife edge method based on the detection result. Therefore, according to the above configuration, there is an effect that accurate focus control can be performed.

  The light detection means of the optical pickup device according to the present invention detects a focal position of the light beam diffracted in the fifth region and a focal position of the light beam diffracted in the second region, and the optical pickup device It is preferable to further include a focus error detection means for detecting a focus error based on the detection result.

  According to said structure, the said light detection means detects the focus position of the two light beams diffracted in the said 2nd area | region and the 5th area | region in the previous term. Therefore, a focus error can be detected using the double knife edge method based on the detection result. Therefore, according to the above configuration, more accurate focus control can be performed. For this reason, it is possible to suppress the influence of the focus offset due to the positional deviation of the optical system due to a change with time. Thereby, an optical pickup device with high reliability can be provided.

  The light detection means of the optical pickup device according to the present invention detects a focal position of the light beam diffracted in the fourth region and a focal position of the light beam diffracted in the fifth region, and the optical pickup device Preferably, the apparatus further comprises spherical aberration error detecting means for detecting a spherical aberration error based on the detection result.

  According to the above configuration, a spherical aberration error can be detected. This makes it possible to perform spherical aberration correction that is indispensable when reproducing a high-density optical disk with a thin cover glass layer that protects the information recording layer. Therefore, a higher performance optical pickup device can be provided.

  The light detection means of the optical pickup device according to the present invention detects a focal position of a light beam diffracted in the fifth region, and the optical pickup device detects a spherical aberration error based on the detection result. It is preferable to further include error detection means.

  According to the above configuration, a spherical aberration error can be detected. Therefore, there is an effect that accurate spherical aberration correction can be performed.

  In the optical pickup device according to the present invention, the light detection means includes a plurality of light receiving elements, and the fourth region is reflected from the optical disk toward a position where the light receiving elements are not formed in the light detection means. It is preferable to diffract light.

  According to said structure, the light receiving element which light-receives the light beam diffracted in the said 4th area | region becomes unnecessary, and the number of required light receiving elements decreases. Therefore, there is an effect that it is possible to provide a small-scale photodetection means with high reliability and low cost.

  It is preferable that the fourth region of the optical pickup device according to the present invention transmits the incident light beam without separating it.

  According to said structure, since the said 4th area | region transmits the incident light beam, the light quantity of non-diffracted light increases. Therefore, a sufficient amount of light for detecting the reproduction signal can be obtained. Therefore, even in an optical pickup device that reads and writes at high speed, there is an effect that the signal quality of the reproduction signal can be ensured.

  Second light separation that exists between the light source and the light condensing means of the optical pickup device according to the present invention and that partially diffracts the light beam from the light source to form a main light beam and two sub-light beams. Preferably further means are provided.

  According to the above configuration, the second light separation unit separates the light beam emitted from the light source into three beams. Then, each recording layer of the optical disc reflects the light beam that has become three beams. As a result, the tracking error can be detected using the three-beam method, the differential push-pull (DPP) method, the phase shift DPP method, or the like.

  The light detection means of the optical pickup device according to the present invention includes tracking control means for detecting reflected light from the optical disc of the main light beam and the sub light beam, respectively, and performing three-beam tracking control based on the detection result. It is preferable to further provide.

  According to the above configuration, tracking control is performed. That is, even if the objective lens follows the track and the positional deviation occurs in the radial direction of the optical disk, it is possible to perform accurate tracking.

  The second light separation means of the optical pickup device according to the present invention has a polarization characteristic whose diffraction efficiency changes depending on the polarization of the light beam, and the polarization characteristic of the second light separation means is the second light The separating means is preferably set so that the reflected light from the optical disk is not diffracted.

  The purpose of the second light separating means is to separate the light beam emitted from the light source as described above. That is, it is not necessary to separate the reflected light from the optical disk. Therefore, according to the above configuration, useless diffraction can be omitted. Therefore, the light quantity of the light beam incident on the light detection means can be increased. Therefore, even in an optical pickup device that reads and writes at high speed, there is an effect that the signal quality of the reproduction signal can be ensured.

  The first light separation means of the optical pickup device according to the present invention has a polarization characteristic whose diffraction efficiency changes depending on the polarization of the light beam, and the polarization characteristic of the first light separation means is the first light The separating means is preferably set so that the light beam from the light source is not diffracted.

  The purpose of the first light separating means is to separate the light beam reflected from the optical disc as described above. That is, it is not necessary to separate the light beam emitted from the light source. Therefore, according to the above configuration, useless diffraction can be omitted. Therefore, it is possible to increase the amount of light flux irradiated on the optical disc. Therefore, even in an optical pickup device that reads and writes at high speed, there is an effect that the signal quality of the reproduction signal can be ensured.

  An optical pickup device control method according to the present invention includes: a light emitting step for emitting a light beam; a light condensing step for focusing the light beam on one recording layer of an optical disk having a plurality of recording layers; Control of an optical pickup device comprising: a light separation step for separating the reflected light of the light; and a light detection step for detecting a light beam that is all or part of the light beam separated in the light separation step and includes non-diffracted light In the method, it is preferable that the light separation step does not separate a light beam in the vicinity of the optical axis center of the reflected light from the optical disc.

  According to the above configuration, since the non-diffracted light with high light intensity is detected in the light detection step, the signal quality of the reproduction signal is ensured even in the information reproducing method and information recording method of the optical disc that is reproduced or recorded at high speed. it can.

  Further, according to the above configuration, the light separation step does not separate the light beam near the center of the optical axis of the reflected light from the upper optical disk. Here, in the light separation step, the reflected light from the non-target layer is more concentrated near the optical axis than the light beam reflected by the target layer due to the difference in optical path length. Therefore, the separation of the light beam from the non-target layer can be suppressed while sufficiently separating the light beam from the target layer by not separating the light beam near the optical axis center of the reflected light from the optical disk. . Here, when the light beam from the non-target layer is separated, the non-diffracted light and the diffracted light interfere with each other, and an interference fringe is formed on the light collecting means, which hinders accurate tracking control. . Therefore, the tracking operation can be made accurate by suppressing the separation of the light beam from the non-target layer.

  As described above, in the information reproducing method and information recording method of an optical disc for reproducing or recording on an optical disc having a plurality of recording layers, the effect that accurate tracking control can be performed while ensuring the signal quality of the reproduced signal. Play.

  As described above, the optical pickup device according to the present invention has a light separating function in which the light separating means for separating the reflected light from the optical disk having a plurality of recording layers includes the optical axis center of the reflected light from the optical disk. It has a region that does not have. Therefore, diffraction of the reflected light from the non-target layer can be prevented. As a result, the influence of the reflected light from the non-target layer on the tracking control can be suppressed sufficiently small after detecting the 0th-order light and ensuring the signal quality of the reproduction signal.

[First Embodiment]
An embodiment of the present invention will be described with reference to FIGS. In the present embodiment, an example will be described in which the optical pickup apparatus of the present invention is used in an optical recording / reproducing apparatus that optically reproduces and / or records information on / from an optical disk as an optical recording medium.

(Schematic configuration of optical recording / reproducing apparatus)
FIG. 2 is a cross-sectional view showing a schematic configuration and a light path of the optical pickup device 10 according to the present embodiment. The schematic configuration of the optical recording / reproducing apparatus according to the present embodiment will be described below with reference to FIG.

  An optical recording / reproducing apparatus according to this embodiment includes a spindle motor (not shown) that rotates and drives an optical disc (optical recording medium) 6, an optical pickup device 10 that records and reproduces information on the optical disc 6, and the spindle motor and optical pickup device 10 described above. A drive control unit (not shown) for drive control and a control signal generation circuit are provided.

  The optical pickup device 10 includes a semiconductor laser 1 (light source) that irradiates an optical disk 6 with a light beam, a diffraction element 115 (first and second light separation means), a collimator lens 3, an objective lens 4 (condensing means), and A light detector 7 (light detection means) is provided. The semiconductor laser 1, the diffraction element 115, and the photodetector 7 are configured as a part of the optical integrated unit 100.

  The optical disk 6 includes a cover glass 6a, a substrate 6b, and two information recording layers 6c and 6d (recording layers) formed between the cover glass 6a and the substrate 6b. That is, the optical disk 6 is a two-layer disk. The optical pickup device 10 reproduces information on each information recording layer or records information on each information recording layer by condensing a light beam on the information recording layer 6c or the information recording layer 6d.

  Next, a schematic operation of the optical pickup device 10 will be described. 2 shows the light emitted from the semiconductor laser 1 and the reflected light from the information recording layer 6c when the objective lens 6 is focused on the information recording layer 6c. The optical axis 61 is a common optical axis for the emitted light and the reflected light.

  First, the semiconductor laser 1 emits a light beam. The emitted light beam passes through the diffraction element 115 and enters the collimator lens 3. The collimator lens 3 converts the incident light beam into parallel light. The objective lens 4 condenses the light beam that has become parallel light on the information recording layer 6 c or the information recording layer 6 d of the optical disc 6. The information recording layers 6c and 6d reflect the light beam (hereinafter, the reflected light beam is referred to as “return light”). The return light passes through the objective lens 4 and the collimator lens 3 and then enters the diffraction element 115. The diffraction element 115 separates the return light. The photodetector 7 receives the separated return light.

  Here, the control signal generation circuit generates a tracking error signal TES, a focus error signal FES, and a spherical aberration error signal SAES based on the signal obtained from the photodetector 7. Then, the tracking error signal TES is output to the tracking drive circuit. Further, the focus error signal FES is output to the focus drive circuit. Further, the spherical aberration error signal SAES is output to the spherical aberration correction mechanism drive circuit. In response to the above signals, each drive circuit performs drive control of each member based on each error signal.

  A focus drive circuit (not shown) controls an objective lens drive mechanism (not shown) based on the value of the input focus error signal FES. The objective lens driving mechanism moves the objective lens 4 in the optical axis direction. As described above, the focal position shift of the objective lens 4 is corrected.

  A spherical aberration correction mechanism drive circuit (not shown) controls a spherical aberration correction actuator (not shown) based on the value of the input spherical aberration error signal SAES. The spherical aberration correcting actuator moves the collimator lens 3 in the optical axis direction (z direction). As described above, the spherical aberration generated in the optical system of the optical pickup device 10 is corrected.

(Detailed description of optical system)
FIG. 3A is a plan view of the optical integrated unit 100 viewed from the optical axis OZ direction (Z direction) in FIG. In order to avoid complication of the drawing, the polarization beam splitter 114, the diffraction element 115, and the quarter wavelength plate 116 are omitted in FIG. FIG. 3B is a cross-sectional view of the optical integrated unit 100. Hereinafter, an outline of the optical integrated unit 100 will be described with reference to FIGS.

  As shown in FIGS. 3A and 3B, the optical integrated unit 100 includes a semiconductor laser 1, a photodetector 7, a polarization beam splitter 114, a diffraction element 115, a quarter wavelength plate 116, a package, and a package. 117.

  The polarization beam splitter 114 includes a polarization beam splitter (PBS) surface 114a and a reflection mirror (reflection surface) 114b. The polarization beam splitter surface 114 a is disposed on the optical axis 61 of the light beam emitted from the semiconductor laser 1. The reflection mirror 114b is disposed to face the polarization beam splitter surface 114a in parallel. Hereinafter, the surface of the polarizing beam splitter 114 on which the light beam emitted from the semiconductor laser 1 is incident is referred to as the light beam incident surface of the polarizing beam splitter 114. In addition, a surface on which the return light is incident on the polarization beam splitter 114 is a return light incident surface of the polarization beam splitter 114.

  Next, the diffraction element 115 will be described. The diffraction element 115 includes a first polarization hologram element 2 (first light separation means) and a second polarization hologram element 5 (second light separation means). Both the first polarization hologram element 2 and the second polarization hologram element 5 are disposed on the optical axis 61 of the light beam. The first polarization hologram element 2 is disposed at a position closer to the semiconductor laser 1 than the second polarization hologram element 5. This arrangement is not necessarily required. For example, the second polarization hologram element 5 can be arranged at a position closer to the semiconductor laser 1 than the first polarization hologram element 2.

  Hereinafter, a surface on which the light beam emitted from the semiconductor laser 1 in the diffraction element 115 is incident is referred to as a light beam incident surface of the diffraction element 115. Further, the surface of the diffractive element 115 on which the return light is incident is the return light incident surface of the diffractive element 115. The light beam incident surface of the polarization hologram element 2 is installed to face the return light incident surface of the polarization beam splitter 114.

  The first polarization hologram element 2 separates the incident light beam into 0th order diffracted light (non-diffracted light) and ± 1st order diffracted light (diffracted light). The detailed hologram pattern of the first polarization hologram element 2 will be described later. As described above, the first hologram element 2 is used as the first light separating means. Thereby, unlike the case of using a simple (linear) diffraction grating, the condensing position of the light beam diffracted by the first light separating means can be arbitrarily set. For this reason, the light collection state on the photodetector 7 of the reflected light beam from the target layer of the optical disc 6 can be described later.

  The second polarization hologram element 5 separates the incident light beam into three beams (main beam and two sub beams) for detecting a tracking error signal (TES). The hologram pattern of the second polarization hologram element 5 is a regular linear grating suitable for detecting a tracking error signal (TES) using a three-beam method or a differential push-pull method (DPP method).

  These diffractions are caused by a groove structure (grating) formed in each polarization hologram element 2 and 5. The diffraction angle is defined by the pitch of the grating (hereinafter referred to as “grating pitch”).

  The quarter wavelength plate 116 is disposed on the optical axis of the light beam at a position farther from the semiconductor laser 1 than the diffraction element 115. The quarter-wave plate 116 has a function of converting incident linearly polarized light into circularly polarized light and a function of converting incident circularly polarized light into linearly polarized light.

  The semiconductor laser 1 emits a light beam having a wavelength λ = 405 nm. In the present embodiment, the light beam is linearly polarized light (P-polarized light) having a polarization vibration surface in the x direction in FIG. In addition, the z direction in the figure is a direction along the optical axis 61.

  Here, the polarization characteristics of the polarization beam splitter 114 and the diffraction element 115 will be described. The polarization characteristic is a property that the diffraction efficiency changes depending on the polarization of the light beam.

  The polarization beam splitter surface 114a in the present embodiment transmits linearly polarized light (P-polarized light) having a polarization vibration surface in the x direction in FIG. Then, linearly polarized light (S-polarized light) having a polarization vibration surface perpendicular to the polarization vibration surface, that is, having a polarization vibration surface in the y direction in the figure is reflected.

  The first polarization hologram element 2 diffracts S-polarized light. Then, the P-polarized light is transmitted as it is.

  The second polarization hologram element 5 diffracts P-polarized light. Then, the S-polarized light is transmitted as it is.

  With the combination of the above polarization characteristics, the light beam emitted from the semiconductor laser 1 follows the following path.

  First, the light beam emitted from the semiconductor laser 1 enters the polarization beam splitter 114. The polarization beam splitter surface 114a transmits the incident light beam (P-polarized light) as it is. The light beam that has passed through the polarization beam splitter surface 114 a then enters the diffraction element 115.

  Of the polarization hologram elements constituting the diffraction element 115, the first polarization hologram element 2 present at a position close to the semiconductor laser 1 transmits the incident P-polarized light beam. The second polarization hologram element 5 separates the light beam emitted from the first polarization hologram element 2 and detects three beams (main beam and two sub beams) for detecting a tracking error signal (TES). To do.

  The light beam separated by the second polarization hologram element 5 enters the quarter-wave plate 116. The quarter-wave plate 116 converts the P-polarized light beam (linearly polarized light) into a circularly-polarized light beam.

  The collimator lens 3 converts the circularly polarized light beam emitted from the quarter-wave plate 116 into parallel light. The objective lens 4 condenses the light beam on the optical disc 6. Then, the light beam reflected by the recording layers 6 c and 6 d of the optical disk 6, that is, the return light, passes through the objective lens 4 and the collimator lens 3 again and enters the quarter wavelength plate 116 of the optical integrated unit 100 again. To do.

  The quarter-wave plate 116 of the optical integrated unit 100 converts the incident circularly polarized return light into linearly polarized light (S-polarized light) having a polarization oscillation plane in the y direction with respect to the illustrated optical axis direction (z direction). Convert.

  The second polarization hologram element 5 transmits the incident S-polarized return light as it is and makes it incident on the first polarization hologram element 2. The first polarization hologram element 2 diffracts the incident S-polarized return light into 0-order diffracted light (non-diffracted light) and ± 1st-order diffracted light (diffracted light) and emits it. The polarization beam splitter 114 reflects the incident S-polarized return light by the polarization beam splitter (PBS) surface 114 a, further reflects by the reflection mirror 114 b, and exits from the polarization beam splitter 114. The photodetector 7 receives the S-polarized return light emitted from the polarization beam splitter 114.

  As described above, in the second polarization hologram element 5, the light emitted from the semiconductor laser 1 is not diffracted in the first polarization hologram element 2 by appropriately setting the polarization characteristics of the two hologram elements. The reflected light from the optical disk 6 can be prevented from being diffracted. Thereby, useless diffraction can be avoided and the intensity of the light beam can be maintained.

(Description of the first polarization hologram element 2)
Next, the first polarization hologram element 2 will be described in detail. FIG. 4 is a plan view of the first polarization hologram element 2. As shown in the figure, the first polarization hologram element 2 has four regions 2a, 2b, 2c, and 2d. Light beams diffracted in the respective regions are incident on different positions on the photodetector 7. Each region is called a first region 2d, a second region 2c, a fourth region 2a, and a fifth region 2b. For convenience of explanation, the fourth region and the fifth region are combined. Is referred to as a third region.

  Further, the direction on the first polarization hologram element 2 corresponding to the radial direction of the optical disk 6, that is, the x-axis direction in FIG. In addition, a direction corresponding to the circumferential direction of the optical disc 6 on the first polarization hologram element 2, that is, the y-axis direction in FIG. 4 is referred to as a circumferential direction. The position corresponding to the optical axis 61 of the reflected light from the optical disk 6 on the first polarization hologram element 2 is defined as the optical axis center 62.

  First, the first region 2d is a region surrounded by a circle E5 having a radius r3 with the optical axis center 62 as the center.

  Next, the area other than the first area 2d is divided into a second area 2c and a third area by dividing lines D1 and D7 on a straight line in the radial direction passing through the optical axis center 62. That is, the second region 2c is a region outside the circle E5 surrounded by the circle E5, the semicircle E4 having the radius r2 centered on the optical axis center 62, and the dividing line segments D1 and D7.

  Furthermore, the third region is divided into a fourth region 2a and a fifth region 2b. The boundary line is obtained by connecting the dividing line segments D2, D3, D4, D5, and D6 in this order. Hereinafter, this boundary line will be described. First, the boundary line is a figure that is line-symmetric with respect to a straight line in the circumferential direction that passes through the optical axis center 62. The dividing line segments D2, D4, and D6 are line segments that are parallel to the dividing line segment D1, respectively. The length of the dividing line segment D4 is w1. Further, the distance h1 between the dividing line segments D2 and D6 and the dividing line segment D1 is equal, and the distance h2 between the dividing line segment D4 and the dividing line segment D1 is longer than that. Further, the minor angle θ formed by the dividing line segment D2 and the dividing line segment D3 is larger than the right angle. As described above, since the boundary line is a line-symmetric figure, the minor angle formed by the dividing line segment D5 and the dividing line segment D6 is also equal to θ.

  That is, the fourth region 2a is a region outside the circle E5 surrounded by the dividing line segments D1 to D7, arcs E1 and E2 having a radius r2 centered on the optical axis center 62, and the circle E5. . The fifth region 2b is a region surrounded by the dividing lines D2 to D6 and an arc E3 having a radius r2 with the optical axis center 62 as the center.

  Note that all the above-described divided straight lines and arcs are figures on a plane that is orthogonal to the optical axis 61 of the reflected light from the optical disc 6.

  Here, the effective diameter of the reflected light from the optical disk 6 on the first polarization hologram element 2 is assumed to be r. r is defined by the numerical aperture of the objective lens 4. At this time, in this embodiment, the distance h1 = 0.3r between the dividing line segment D1 and the dividing line segment D2, the distance h2 = 0.6r between the dividing line segment D1 and the dividing line segment D4, θ = 135 deg, The length w1 of the line segment D4 is set to 0.6r. The radius r2 is set to be sufficiently larger than r in consideration of objective lens shift and adjustment error. The radius r3 is set to be equal to or larger than the radius of the region through which the reflected light 60 from the non-target layer described later passes. In the present embodiment, the radius r3 = 0.1r.

  Hologram patterns are formed in the second region 2c, the fourth region 2a, and the fifth region 2b, and the reflected light from the incident optical disk 6 is separated. A hologram pattern is not formed in the first region 2d, and the reflected light from the optical disc 6 is transmitted.

(Various signal detection methods)
FIG. 5 is a plan view showing a light spot on the photodetector 7. As shown in the figure, the photodetector 7 is composed of 14 light receiving elements 7a to 7n. The figure further shows the correspondence relationship on which light receiving element on the photodetector 7 the light beams diffracted in the three regions 2a, 2b and 2c of the first polarization hologram element 2 are incident. Yes.

  A spot where the light beam diffracted in the fifth region 2b is incident on the photodetector 7 is referred to as a light spot SP1. Similarly, a spot where the light beam diffracted in the fourth region 2a is incident on the photodetector is referred to as a light spot SP2. A spot where the light beam diffracted in the second region 2c is incident on the photodetector is referred to as a light spot SP3. As described above, no diffraction occurs in the first region 2d.

  Actually, the center position of the first polarization hologram element 2 is installed at a position corresponding to the center position of the light receiving elements 7a to 7d of the photodetector 7, but for the sake of explanation, the optical axis direction (z direction). Is shifted in the y direction. Further, the minus first-order light is also incident on the photodetector 7, but it is not shown.

  The three light beams (main beam and two sub beams) formed by the second polarization hologram element 5 are reflected by the optical disc 6 and are diffracted by the first polarization hologram element 2 with non-diffracted light (0th order diffracted light). It is separated into light (+ 1st order diffracted light). As a result, a total of twelve light beams of three non-diffracted lights and nine diffracted lights are formed.

  The photodetector 7 includes a light receiving element for receiving a light beam necessary for detection of an RF signal and a servo signal among the above light beams. In particular, in order to detect the tracking error signal TES using the push-pull method, the non-diffracted light is designed to be received as a light beam having a certain beam diameter. In the present embodiment, the photodetector 7 is installed at a position slightly shifted to the near side with respect to the condensing point of the non-diffracted light so that the beam diameter of the non-diffracted light has a certain size. ing. In addition, this invention is not limited to this, You may install the photodetector 7 in the position shifted to the back | inner side with respect to the condensing point of non-diffracted light.

  Hereinafter, the servo signal generation operation will be described with reference to FIGS. Here, the output signals of the light receiving elements 7a to 7n are represented as Sa to Sn.

First, the reproduction signal RF is detected using non-diffracted light (0th order diffracted light). That is, the reproduction signal RF is
RF = Sa + Sb + Sc + Sd
Obtained by.

Next, as a TES detection method using three beams, a three-beam method, a working push-pull (DPP) method, a phase shift DPP method, or the like can be used. In the present embodiment, the tracking error signal TES is
TES = {(Sa + Sb)-(Sc + Sd)}
−α {(Se−Sf) + (Sg−Sh)}
Obtained by. Α is set to an optimum coefficient for canceling an offset caused by objective lens shift or optical disc tilt.

The focus error signal FES is detected using a double knife edge method. That is, the focus error signal FES is
FES = (Si−Sj) −β (Sk−Sl)
Obtained by. Note that β is set to an optimum coefficient for canceling the offset due to the difference in the amount of light between the two spots.

  Here, the detection operation of the focus error signal FES will be described in detail.

  FIG. 5A is a plan view showing a light spot on the photodetector 7 when neither a focus error nor a spherical aberration error exists. That is, the objective lens 4 is accurately focused on the information recording layer 6c, and the position of the collimator lens 3 in the optical axis direction is appropriately adjusted with respect to the thickness of the cover glass 6a.

  When the focal point is coincident with either the information recording layer 6c or the information recording layer 6d of the optical disc 6, as shown in FIG. 5A, the light spot SP1 is on the boundary line between the light receiving element 7k and the light receiving element 7l. Exists. Therefore, the first output signal (Sk-Sl) becomes zero. On the other hand, the light spot SP3 also exists on the boundary line between the light receiving element 7i and the light receiving element 7j. Therefore, the third output signal (Si-Sj) is also zero. From the above, the focus error signal FES is 0 when no defocus has occurred.

  FIG. 5B is a plan view showing a light spot on the photodetector 7 in a state where the objective lens 4 in FIG. 2 approaches the optical disk 6 from the state of FIG. That is, it shows a state where a focus error has occurred. As the objective lens 4 approaches the optical disc 6, the beam diameter of the light beam increases. However, no light beam protrudes from the light receiving elements 7a to 7d.

  When the optical disc 6 approaches or moves away from the objective lens 4 and the focal position shifts from the information recording layer 6c or the information recording layer 6d, the shapes of the light spot SP1 and the light spot SP3 are as shown in FIG. Each changes. Therefore, the first output signal (Sk-Sl) and the third output signal (Si-Sj) each output a value corresponding to the defocus. From the above, the focus error signal FES indicates a value other than 0 corresponding to defocus.

  That is, the focus error can be detected based on the first output signal (Sk-Sl) and the third output signal (Si-Sj). As shown in FIG. 5, the first output signal (Sk-Sl) is the output of the light receiving elements 7k and 7l that receive the light beam diffracted in the fifth region 2b of the first polarization hologram element 2. It is a signal based on the signal. The third output signal (Si-Sj) is a signal based on the output signals of the light receiving elements 7i and 7j that receive the light beam diffracted in the second region 2c of the first polarization hologram element 2. .

  In order to always make the focal point coincide with either the information recording layer 6c or the information recording layer 6d, the objective lens 4 may be moved in the optical axis direction so that the output of the focus error signal FES is always 0. . Thereby, it is possible to suppress the influence of the focus offset due to the positional deviation of the optical system of the optical pickup device 10 due to a change with time or the like, and it is possible to provide a highly reliable optical pickup device.

The focus error signal FES may be detected using a knife edge method. In that case, the focus error signal FES is
FES = (Si-Sj)
Obtained by. That is, the focus error signal is detected based on the third output signal (Si-Sj). As described above, the third output signal (Si-Sj) is based on the output signals of the light receiving elements 7i and 7j that receive the light beam diffracted in the second region 2c of the first polarization hologram element 2. Signal.

  However, more accurate tracking control is possible using the double knife edge method.

  The spherical aberration error signal SAES is obtained by the following calculation.

SAES = (Sm−Sn) −γ × (Sk−Sl)
Note that γ will be described later.

  Here, the detection operation of the spherical aberration error signal SAES will be described.

  The spherical aberration is generated not only when the thickness of the cover glass 6a of the optical disc 6 is changed, but also when an interlayer jump is performed between the information recording layer 6c and the information recording layer 6d.

  For example, assume that the thickness of the cover glass 6a changes and spherical aberration occurs. In that case, in the same single light beam, the light beam near the optical axis and the light beam in the outer peripheral portion have different focal positions (positions at which the beam diameter is minimized). This is detected from the value of the second output result (Sm-Sn) and the first output signal (Sk-Sl).

  That is, the second output result detects a light beam diffracted in the fourth region 2 a of the first polarization hologram element 2. This corresponds to the defocus of the light beam near the optical axis. The first output result detects a light beam diffracted in the fifth region 2b of the first polarization hologram element 2. This corresponds to the defocus of the light beam on the outer periphery. When the spherical aberration occurs, the second signal and the first signal are not zero, and a value corresponding to the amount of spherical aberration is output. The direction of the focal position shift due to the occurrence of spherical aberration is opposite in the beam inner periphery and the beam outer periphery. Therefore, a spherical aberration error signal SAES having higher sensitivity is obtained by calculating a difference signal between the value of the first output signal (Sk-Sl) and the value of the second output signal (Sm-Sn). Can do. As described above, when the optical disk 6 is a high-density optical disk and the cover glass 6a for protecting the information recording layers 6c and 6d is thin, spherical aberration correction that is essential can be performed, and a higher-performance optical pickup device is provided. be able to.

  The above will be described from a specific light spot state.

  First, when there is no spherical aberration, the light spot SP1 exists on the boundary line between the light receiving element 7k and the light receiving element 71 as shown in FIG. Therefore, the first output signal (Sk-Sl) becomes zero. On the other hand, the light spot SP2 also exists on the boundary line between the light receiving element 7m and the light receiving element 7n. Therefore, the second output signal (Sm-Sn) is also zero. From the above, the spherical aberration error signal SAES becomes zero.

  Next, FIG.5 (c) is a top view which shows the light spot on the photodetector 7 in the state from which the thickness of the cover glass 6a changed from the state of Fig.5 (a). That is, it shows a state where spherical aberration has occurred. However, no focus error has occurred.

  When spherical aberration occurs, as shown in FIG. 5C, the light spot SP1 and the light spot SP2 are not focused on the light receiving element (defocused), although there is no focus error. Status). Therefore, as shown in the figure, the first output signal (Sk-Sl) and the second output signal (Sm-Sn) each show a value other than 0. Furthermore, as shown in the figure, the light spot SP1 and the light spot SP2 are opposite in defocusing direction (defocus direction). Therefore, by using a difference signal between these signals, a highly sensitive spherical aberration error signal SAES can be detected.

  Further, consider a case where spherical aberration occurs in the optical system of the optical pickup device 10 with a slight focus error remaining. In this case, even if there is no spherical aberration, the light spot SP1 and the light spot SP2 are not focused on the light receiving element (defocused state) due to the influence of the focus error. Accordingly, the first output signal (Sk-Sl) and the second output signal (Sm-Sn) each show a value other than zero.

  However, in a range where the focus error is small, changes in the first output signal (Sk-Sl) and the second output signal (Sm-Sn) can be regarded as almost straight lines. Therefore, by optimizing the coefficient γ, the influence of the focus error on the spherical aberration error signal SAES can be removed. Here, the ways of defocusing in the light spot SP1 and the light spot SP2 due to spherical aberration are reversed. That is, one is out of focus and the other is out of focus. Therefore, the spherical aberration error signal SAES is not stopped even if the coefficient γ is optimized.

  FIG. 6 is a graph showing the relationship between the spherical aberration error signal SAES and the thickness change of the cover glass 6a of the optical disk 6 when the first polarization hologram element 2 of the present embodiment is used. As shown in the figure, the spherical aberration error signal SAES can accurately detect that the thickness of the cover glass 6a has changed and spherical aberration has occurred.

The spherical aberration signal SAES uses only the light spot SP1 and SAES = (Sk−Sl)
Can also be obtained. However, a more accurate spherical aberration error can be detected by performing the above calculation.

(Reflected light from non-target layer)
Here, the unnecessary reflected light 60 from the non-target layer in the present embodiment will be described.

  FIG. 7 is a cross-sectional view showing the path of the reflected light 60 from the non-target layer. As shown by comparison with the path of reflected light from the target layer in FIG. 2, the reflected light 60 from the non-target layer is narrower on the first polarization hologram element 2 than the reflected light from the target layer. Incident into the area. This is also shown in FIG. 4, which is a plan view of the first polarization hologram element 2. The region SP5 is a region where the reflected light 60 from the non-target layer is incident, and the region SP6 is a region where the reflected light from the target layer is incident. The region SP6 is a region surrounded by a circle with a radius r centered on the optical axis center 62. The region SP5 is a region surrounded by a circle having a radius r4 with the optical axis center 62 as the center.

  FIG. 1 is an enlarged plan view of a central portion of the first polarization hologram element 2. The relationship between the area SP5 and the first area 2d will be described with reference to FIG.

As shown in the figure, the region SP5 is all included in the first region 2d. That is, as shown in the figure, the first region 2d is a region surrounded by a circle E5 having a radius r3 with the optical axis center 62 as the center. here,
r> r3 ≧ r4
Set so that the above relationship holds. Thereby, all the reflected light 60 from the non-target layer is incident on the first region 2d.

  Here, as described above, no hologram pattern is formed in the first region 2d, and the incident light beam is not separated. Therefore, the reflected light 60 from the non-target layer is not diffracted by the first polarization hologram element 2 and does not form diffracted light. As in the prior art shown in FIG. 14, the interference fringes that hinder tracking control are formed by interference between non-diffracted light and diffracted light of reflected light 60 from the non-target layer. Accordingly, since the first polarization hologram element 2 does not separate the reflected light 60 from the non-target layer, the formation of interference fringes can be avoided.

  FIG. 8 is a plan view showing a state in which the reflected light 60 from the non-target layer spreads on the photodetector 7. As shown in the figure, the reflected light 60 from the non-target layer spreads uniformly on the photodetector 7. And the interference fringe is not formed. Therefore, the influence on the tracking error signal is small.

  In the above description, the case where the first region 2d where the hologram pattern is not formed transmits incident light as it is is described, but the present invention is not limited to this. The first region 2d where the light shielding mask is formed can also block incident light.

  FIG. 5D is a plan view showing a hologram pattern and a light spot on the light receiving element when a light shielding mask is formed in the first region 2d. When a light shielding mask is formed in the first region 2d, light incident on the first region 2d is not transmitted. Therefore, as shown in the figure, on the photodetector 7, the incident non-diffracted light forms a spot lacking light at the center. The ± first-order diffracted light forms a spot similar to the case where the hologram pattern is not formed in the first region 2d described above. Therefore, similar error signal detection can be performed.

  In addition, when a light shielding mask is formed in the first region 2d, the zero-order light of the reflected light 60 from the non-target layer does not generate the light spot 40a on the photodetector 7. That is, the 0th-order light of the reflected light 60 from the non-target layer does not enter the light receiving elements 7a to 7h. For this reason, it is possible to completely eliminate the influence of the reflected light 60 on the tracking error signal (TES).

  However, when the incident light is transmitted as it is without forming a hologram pattern in the first region 2d as in the present embodiment, the amount of light beam detected is increased. Therefore, the signal quality of the reproduction signal can be further improved.

  In the present embodiment, the first polarization hologram element 2 is used as a means for guiding the light beam 120 reflected from the information recording layer of the optical disc 6 to the photodetector 7, but the present invention is not limited to this. For example, a combination of a beam splitter and a wedge prism may be used. However, it is preferable to use a hologram element from the viewpoint of downsizing the apparatus.

  In the present embodiment, an example of a hologram element laser in which a light source and a photodetector are integrated has been described. However, the present invention is not limited to this, and a single semiconductor laser is used as a light source and an optical path is obtained by a polarization beam splitter. Can be divided so that the photodetector 7 receives the reflected light. In this case, the light beam separating means may be arranged in the return optical system. However, in order to reduce the size of the apparatus, it is preferable to use an integrated hologram element laser.

  In the present embodiment, the collimator lens 3 is driven as a spherical aberration correction mechanism, but the interval between two lenses constituting a beam expander (not shown) disposed between the collimator lens 3 and the objective lens 4 is adjusted. You may use the mechanism to do.

[Second Embodiment]
The following will describe another embodiment of the present invention with reference to FIG. 2, FIG. 9, and FIG. The configuration other than that described in the present embodiment is the same as that of the above-described one embodiment. For convenience of explanation, members having the same functions as those shown in the drawings according to the above-described embodiment are given the same reference numerals, and descriptions thereof are omitted.

  As shown in FIG. 2, the optical recording / reproducing apparatus according to the present embodiment includes a spindle motor (not shown) that rotates and drives an optical disc (optical recording medium) 6, an optical pickup device 30 that records and reproduces information on the optical disc 6, A drive control unit (not shown) for driving and controlling the spindle motor and the optical pickup device 30 and a control signal generation circuit are provided.

  The optical pickup device 30 includes a semiconductor laser 1 for irradiating the optical disk 6 with a light beam, a first polarization hologram element 12, a collimating lens 3, an objective lens 4, and a photodetector 113.

  The light beam reflected from the information recording layer 6c or the information recording layer 6d of the optical disc 6 passes through each member in the order of the objective lens 4 and the collimating lens 3 and enters the first polarization hologram element 12, and then enters the first polarization hologram element 12. The light is diffracted by the polarization hologram element 12 and collected on the photodetector 113.

  The difference from the first embodiment is that the first polarization hologram element 12 and the photodetector 113 are provided in place of the first polarization hologram element 2 and the photodetector 7.

  FIG. 8 is a plan view of the first polarization hologram element 12 in the present embodiment.

  As shown in the figure, the first polarization hologram element 12 has a fourth region 12a, a fifth region 12b, a second region 12c, and a first region 12d. Each has the same shape as the 4th field 2a, the 5th field 2b, the 2nd field 2c, and the 1st field 2d in the 1st polarization hologram element 2 of the above-mentioned one embodiment.

  FIG. 10 is a plan view showing a light spot on the photodetector 113. The light spot that the light beam that has passed through the first hologram element 12 joins on the photodetector 113 will be described with reference to FIG. A spot where the light beam that has passed through the second region 12b is incident on the photodetector 113 is referred to as a light spot SP1. Similarly, a spot where the light beam that has passed through the first region 12a is incident on the photodetector 113 is referred to as a light spot SP2. A spot where the light beam that has passed through the third region 12c is incident on the photodetector 113 is referred to as a light spot SP3. Here, the light spot SP2 is different from the above-described one embodiment in that it does not exist on the light receiving element.

  As shown in FIG. 10, the photodetector 113 is composed of twelve light receiving elements 113a to 113l. The photodetector 113 includes a light receiving element for receiving a light beam necessary for detecting an RF signal or a servo signal among non-diffracted light (0th order diffracted light) and diffracted light (+ 1st order diffracted light). Among them, the non-diffracted light (0th order diffracted light) is designed to be a light beam having a certain size so that the tracking error signal TES can be detected by the push-pull method.

  FIG. 10A is a plan view showing a light spot on the photodetector 113 when a hologram pattern is not formed in the region 12 d on the first polarization hologram element 12.

  FIG. 10B is a plan view showing a light spot on the photodetector 113 when a light shielding mask is formed in the region 12 d on the first polarization hologram element 12.

  In both cases, similarly, the non-diffracted light, the light beam diffracted in the region 12c and the region 12b, is received by the light receiving element. With this configuration, the spots of the reflected light 60 do not interfere with each other, and no interference fringes are generated on the light receiving elements 113a to 113h. For this reason, the influence which the reflected light 60 has on the tracking error signal (TES) can be reduced.

In the present embodiment, the spherical aberration signal SAES is obtained by using only the light spot SP1. SAES = (Sk−Sl)
Detect by. That is, it is not necessary to detect the light spot SP2 by the light receiving element. Therefore, the region 12a of the first hologram element 12 diffracts the passing light beam toward a place not on the light receiving element. Therefore, the number of light receiving elements of the photodetector 113 is smaller than that of the above-described one embodiment. Therefore, a simpler and lower cost optical pickup device can be provided.

  FIG. 10C is a plan view showing a light spot on the photodetector 113 when a hologram pattern is not formed in the region 12 a on the first polarization hologram element 12.

  As shown in FIG. 10C, even in an optical disc apparatus that increases the detection amount of non-diffracted light and reads / writes at high speed by adopting a configuration in which a hologram pattern is not formed in the region 12a and incident light is not diffracted. It is possible to ensure the signal quality of the reproduction signal.

  The present invention can be suitably applied to an optical recording / reproducing apparatus that performs at least one of reproduction and recording on an optical disk having a plurality of information recording layers.

It is an enlarged plan view of the center part of the 1st polarization hologram element concerning a 1st embodiment. It is sectional drawing which shows schematic structure of the optical pick-up apparatus which concerns on 1st Embodiment. (A) is a top view of the optical integrated unit which concerns on 1st Embodiment, (b) is sectional drawing of the optical integrated unit which concerns on 1st Embodiment. It is a top view of the 1st polarization hologram element concerning a 1st embodiment. (A) is a plan view showing a light spot on the photodetector according to the first embodiment when neither a focus error nor a spherical aberration error exists, and (b) is a focus error. It is a top view which shows the light spot on the photodetector based on 1st Embodiment when a spherical aberration error does not exist, (c) is a case where a focus error does not exist and a spherical aberration error exists. FIG. 3D is a plan view showing a light spot on the photodetector according to the first embodiment, and FIG. 4D is a diagram showing a first case where the first region on the first polarization hologram element blocks the light beam. It is a top view which shows the light spot on the photodetector which concerns on embodiment. 5 is a graph showing a relationship between a change in the thickness of a cover glass of an optical disc and a spherical aberration error signal in the first embodiment. It is sectional drawing which shows the path | route of the reflected light from the non-target layer in the optical pick-up apparatus which concerns on 1st Embodiment. It is a top view which shows the spot which the reflected light from a non-target layer makes on the photodetector which concerns on 1st Embodiment. It is a top view which shows the structure of the 1st polarization hologram element which concerns on 2nd Embodiment. (A) is a top view which shows the light spot on the photodetector which concerns on 2nd Embodiment in case the 1st area | region on a 1st polarization hologram element permeate | transmits a light beam, (b) FIG. 10 is a plan view showing a light spot on the photodetector according to the second embodiment when the first region on the first polarization hologram element blocks the light flux, and FIG. It is a top view which shows the light spot on the photodetector which concerns on 2nd Embodiment in case the 1st and 4th area | region on a polarization hologram element transmits a light beam. It is sectional drawing which shows a prior art and shows schematic structure of an optical pick-up apparatus. It is a top view which shows a prior art and shows the detailed structure of a polarization hologram element. It is a top view which shows a prior art and shows the light spot on a photodetector. It is a top view which shows the prior art and shows the spot which the reflected light from a non-target layer produces on a photodetector.

Explanation of symbols

1 Semiconductor laser (light source)
2, 12 First polarization hologram element (first light separating means)
2a to 2d Area 3 on the first polarization hologram element 3 Collimator lens 4 Objective lens (condensing means)
6 Optical disc 6a Cover glass 6c, 6d Information recording layer (recording layer)
7, 113 Detector (light detection means)
7a to 7l Light receiving elements 10, 30 Optical pickup device 60 Reflected light from non-target layer 61 Optical axis 62 Optical axis center 100 Optical integrated unit 114 Polarizing beam splitter 115 Diffraction element 116 1/4 wavelength plate D1 to D7 Dividing line segment E1 E5 Circle or arc (partition line)
SP1 to SP5 light spot

Claims (16)

A light source that emits a light beam, a condensing unit that focuses the light beam on one recording layer of an optical disc having a plurality of recording layers, and a first light separating unit that separates reflected light from the one recording layer And an optical detection device that detects a light beam that is at least a part of the light beam separated by the first light separation device and includes non-diffracted light.
It said first beam splitting means comprises an optical axis center of the reflected light from the optical disc, have a first region that transmits without separating an incident beam of light,
The first area is an area where reflected light from another recording layer of the optical disc is incident on the first light separating means, which is located farther from the one recording layer as viewed from the light collecting means. Including all
The optical pick-up apparatus , wherein the light detection means detects a reproduction signal using light transmitted through at least the first region .   The optical pickup device according to claim 1, wherein the first light separation unit is a hologram element. The first region is on said first beam splitting means, it in claim 1 or 2, characterized in a region surrounded by a circle around the center of the optical axis of the light reflected from the optical disk The optical pickup device described. In the first light separating means, a portion other than the first region is divided into a second region and a third region,
4. The optical pickup according to claim 3 , wherein a boundary line between the second and third regions exists on a first straight line that passes through the center of the optical axis and is parallel to the radial direction of the optical disc. apparatus. In the first light separating means, the third region is divided into fourth and fifth regions,
The boundary line of the fourth and fifth regions is configured by connecting the first, second, third, fourth, and fifth line segments in this order, and passes through the optical axis center. Axisymmetric with respect to a straight line orthogonal to the first straight line;
The first, third, and fifth line segments and the first straight line are parallel to each other,
The distances between the first and fifth line segments and the first straight line are equal,
The distance between the third line segment and the first straight line is longer than the distance between the first line segment and the first straight line,
The optical pickup device according to claim 4 , wherein an inferior angle formed by the first line segment and the second line segment is larger than a right angle. The light detecting means detects a focal position of a light beam diffracted in the second region;
The optical pickup device according to claim 4 , further comprising a focus error detection unit that detects a focus error based on the detection result. The light detecting means detects a focal position of the light beam diffracted in the fifth area and a focal position of the light beam diffracted in the second area;
6. The optical pickup device according to claim 5 , further comprising focus error detection means for detecting a focus error based on the detection result. The light detecting means detects a focal position of the light beam diffracted in the fourth area and a focal position of the light beam diffracted in the fifth area;
6. The optical pickup device according to claim 5 , further comprising spherical aberration error detecting means for detecting a spherical aberration error based on the detection result. The light detection means detects a focal position of the light beam diffracted in the fifth region;
6. The optical pickup device according to claim 5 , further comprising spherical aberration error detecting means for detecting a spherical aberration error based on the detection result. The light detection means comprises a plurality of light receiving elements,
The optical pickup device according to claim 9 , wherein the fourth region diffracts the reflected light from the optical disc toward a position where the light receiving element is not formed in the light detection unit. The optical pickup device according to claim 9 , wherein the fourth region transmits an incident light beam without being separated. And a second light separation unit that is present between the light source and the light condensing unit and that partially diffracts the light beam from the light source to form a main light beam and two sub light beams. The optical pickup device according to any one of claims 1 to 11 . The light detecting means detects reflected light from the optical disk of the main light beam and the sub light beam, respectively.
13. The optical pickup device according to claim 12 , further comprising tracking control means for performing three-beam tracking control based on the detection result. The second light separation means has a polarization characteristic that the diffraction efficiency changes depending on the polarization of the light beam,
The light according to claim 12 or 13 , wherein the polarization characteristic of the second light separating means is set so that the reflected light from the optical disk is not diffracted by the second light separating means. Pickup device. The first light separation means has a polarization characteristic that the diffraction efficiency changes depending on the polarization of the light beam,
Polarization characteristics of the first optical separating means, wherein the first optical separating means, any one of claims 1 to 14 in which the light beam from the light source is characterized in that it is set not to diffraction The optical pickup device described in 1. A light emitting step for emitting a light beam, a light condensing step for focusing the light beam on one recording layer of an optical disc having a plurality of recording layers, and a light separating step for separating reflected light from the one recording layer And a light detection step of detecting a light beam that is all or a part of the light beam separated in the light separation step and includes non-diffracted light, and a method for controlling the optical pickup device,
In the light separation step , a light beam in the vicinity of the optical axis center of the reflected light from the optical disc, which is at a position farther from the one recording layer as viewed from the light collecting means for focusing in the light light collecting step, The light beam including all the reflected light from the other recording layer of the optical disc is transmitted without being separated ,
In the light detection step, a reproduction signal is detected by using a light beam transmitted without being separated in at least the light separation step .

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