JP2011238316A - Optical pickup device and optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical pickup device which can obtain a stable servo signal because a focus error signal and a tracking error signal are not affected by a stray signal from other layer in recording/regeneration on a multilayer optical disk.SOLUTION: A light beam reflected from a multilayer optical disk is divided by two polarization gratings. A polarization in which a diffraction effect by one of the polarization gratings occurs and a polarization in which a diffraction effect by the other of the polarization gratings occurs are at right angles to each other. A regeneration signal is created with a diffraction light by one of the polarization gratings and a tracking error signal is created with a diffraction light by the other of the polarization gratings.

Description

  The present invention relates to an optical pickup device and an optical disc device.

  As background art in this technical field, for example, there is JP-A-2006-344344 (Patent Document 1). This publication describes that “a desired signal is accurately obtained from an optical disc having a plurality of recording layers” as a problem, and “a P-polarized light beam emitted from the light source unit 51 is transmitted on the optical disc 15 as a solving means. The light is reflected and becomes S-polarized light and enters the lens 61. Then, in the quarter-wave plates 62 and 63, an optical phase difference of +1/4 wavelength of the light beam incident on the + X side of the optical axis is given. An optical phase difference of -1/4 wavelength is given to the light beam incident on the -X side, so that the signal light passing through the 1/4 wavelength plate 63 becomes S-polarized light and the stray light becomes P-polarized light, so that the polarizing optical element 64, only signal light is transmitted. "

JP 2006-344344 A (page 26, FIG. 3, FIG. 5) JP 2009-217916 A

  In general, an optical pickup device irradiates a spot correctly on a predetermined recording track in an optical disc, so that the objective lens is displaced in the focus direction by detection of the focus error signal, and the tracking error signal is adjusted. Is detected and the objective lens is displaced in the radial direction of the disk to perform tracking adjustment. The position of the objective lens is controlled by these servo signals.

  Among the servo signals, the tracking error signal has a big problem because it becomes a multi-layer disc having a plurality of recording layers. In a multilayer disc, in addition to the signal light reflected from the target recording layer, stray light reflected from a plurality of non-target recording layers enters the same light receiving section. When signal light and stray light are incident on the same light receiving portion, the light beams interfere with each other and the fluctuation component is detected in the tracking error signal.

  In order to solve this problem, in Patent Document 1, the light beam reflected by the optical disk is stopped by the condensing lens, and the light spread through the two quarter-wave plates and the polarizing optical element is stopped by the condensing lens. The stray light is not incident on the photodetector. Therefore, there is a problem that the detection optical system is complicated and the size of the optical pickup device is increased.

  In addition, as a recording / reproducing method for an optical disc, there are a 1-beam method and a 3-beam method, but the 3-beam method has lower light utilization efficiency in the forward path and the laser output required for recording is higher than the 1-beam method. Therefore, it is disadvantageous in dealing with multi-layer discs. In the above three-beam method, for example, Patent Literature 2 discloses a technique for reducing the interference with stray light reflected from other layers of the optical disc. “The signal light reflected from the information recording layer 16a of the optical disc 16 is a photodetector. In the optical path to reach 17, the polarization diffraction element 40 having a function of causing the incident light to reach the photodetector 17 so as to overlap the light detector 17 by changing the traveling direction for each orthogonal polarization component is provided. There is a description of “reducing interference fringes on the detector” (see Patent Document 2, Abstract).

  The present invention relates to an optical pickup device that can obtain a stable servo signal and can be miniaturized when recording / reproducing an information recording medium having a plurality of information recording surfaces, for example, in a one-beam system, and the like. An object of the present invention is to provide an optical disk device mounted.

  The above object can be achieved by the invention described in the claims as an example.

  According to the present invention, an optical pickup device that can obtain a stable servo signal and can be miniaturized when recording / reproducing an information recording medium having a plurality of information recording surfaces, for example, in a one-beam system or the like, and An optical disk device equipped with this can be provided.

1 is a diagram illustrating an optical system of the present invention in Example 1. FIG. FIG. 3 is a diagram showing the characteristics of the polarization diffraction grating of the present invention in Example 1. 1 is a diagram showing a polarization diffraction grating of the present invention in Example 1. FIG. It is a figure which shows the light-receiving part of this invention in Example 1. FIG. It is a figure which shows the shape (on a photodetector) of the stray light at the time of recording / reproducing the double layer disk in Example 1. FIG. It is a figure explaining the behavior of the stray light from the other layer of a two-layer disc. It is a figure explaining the behavior of the stray light from the other layer of a two-layer disc. 6 is a diagram showing another polarization diffraction grating of the present invention in Example 1. FIG. 6 is a diagram showing another polarization diffraction grating of the present invention in Example 1. FIG. 6 is a diagram illustrating a light receiving unit according to the present invention in Example 2. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 2. FIG. 6 is a diagram showing a polarization diffraction grating of the present invention in Example 3. FIG. 6 is a view showing a light receiving portion of the present invention in Example 3. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 3. FIG. 6 is a diagram showing another polarization diffraction grating of the present invention in Example 3. FIG. It is a figure which shows the light-receiving part of this invention in Example 4. FIG. FIG. 6 is a diagram showing characteristics of the polarization diffraction grating of the present invention in Example 4. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing the double layer disk in Example 4. FIG. It is a figure which shows the light-receiving part of this invention in Example 5. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 5. FIG. It is a figure which shows the light-receiving part of this invention in Example 6. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 6. FIG. It is a figure which shows the light-receiving part of this invention in Example 7. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 7. FIG. It is a figure which shows the other light-receiving part of this invention in Example 7. FIG. It is a figure which shows the light-receiving part of this invention in Example 8. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 8. FIG. FIG. 10 is a view showing another light receiving part of the present invention in Example 8. It is a figure which shows the light-receiving part of this invention in Example 9. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing the double layer disc in Example 9. FIG. It is a figure which shows the other light-receiving part of this invention in Example 9. FIG. It is a figure which shows the light-receiving part of this invention in Example 10. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disk in Example 10. FIG. It is a figure which shows the light-receiving part of this invention in Example 11. FIG. It is a figure which shows the shape (on a photodetector) of the signal beam | light and stray light at the time of recording / reproducing on the double layer disc in Example 11. FIG. FIG. 20 is a diagram for explaining an optical reproducing device according to a twelfth embodiment. It is a figure explaining the optical recording / reproducing apparatus in Example 13. FIG.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows an optical system of an optical pickup device according to a first embodiment of the present invention. Here, BD (Blu-ray Disc) will be described, but DVD (Digital Versatile Disc) and other recording methods may be used. In the following description, the optical disc layer includes a recording layer in a recordable optical disc and a reproduction layer of a read-only optical disc.

  From the semiconductor laser 50, a light beam having a wavelength of about 405 nm is emitted as diverging light. The light beam emitted from the semiconductor laser 50 reflects the beam splitter 52. A part of the light beam passes through the beam splitter 52 and enters the front monitor 53. In general, when recording information on a recordable optical disk, it is necessary to control the light quantity of the semiconductor laser with high accuracy in order to irradiate the information recording surface (recording layer) of the optical disk with a predetermined light quantity. Therefore, the front monitor 53 detects a change in the light amount of the semiconductor laser 50 when recording a signal on the recordable optical disk, and feeds it back to a drive circuit (not shown) of the semiconductor laser 50. As a result, the amount of light on the optical disk can be monitored.

  The light beam reflected from the beam splitter 52 is converted into a substantially parallel light beam by the collimating lens 51. The light beam that has passed through the collimating lens 51 enters the beam expander 54. The beam expander 54 is used to compensate for spherical aberration due to the thickness error of the cover layer of the optical disk by changing the divergence / convergence state of the light beam. The light beam emitted from the beam expander 54 is reflected by the rising mirror 55, transmitted through the quarter-wave plate 56, and then condensed on the optical disk by the objective lens 2 mounted on the actuator 5.

  The light beam reflected from the optical disk passes through the objective lens 2, the quarter wavelength plate 56, the rising mirror 55, the beam expander 54, the collimator lens 51, and the beam splitter 52, and enters the polarization diffraction grating 11 and the polarization diffraction grating 12. Incident. The incident light beam is separated by the polarization diffraction grating 11 into one light beam and two light beams having different polarizations. One of the separated light beams is divided into a plurality of regions by the polarization diffraction grating 12, travels in different directions for each region, and focuses on the photodetector 10. The remaining two light beams are transmitted through the polarization diffraction grating 12 and focused on the photodetector. A plurality of light receiving portions are arranged on the photodetector 10, and each light receiving portion is irradiated with a light beam divided by the diffraction grating 11 and the diffraction grating 12. An electrical signal is output from the photodetector 10 in accordance with the amount of light applied to the light receiving unit, and these outputs are calculated to generate an RF signal, a focus error signal, and a tracking error signal that are reproduction signals.

  Here, the tracking error signal detection will be described. As a general tracking error signal detection method, a three-beam differential push-pull method (DPP: Differential Push Pull method) in which three light beams are irradiated on a disk is known. In this three-beam DPP method, a light beam is separated into a main beam, a sub beam + 1st order diffracted light, and a subbeam-1st order diffracted light by a diffraction grating, and three spots are formed on the disk. At this time, the disc reflected light of the three spots is detected, and the main push-pull (MPP) signal obtained from the main beam and the sub push-pull (SPP) signal obtained from the sub beam + 1st order and the subbeam-1st order are calculated as follows. By doing so, a three-beam DPP signal in which the DC component accompanying the displacement of the objective lens is reduced is detected.

なお、ｋｓはメインビームとサブビームの光量比を補正する係数である。

Note that ks is a coefficient for correcting the light amount ratio between the main beam and the sub beam.

  Here, the 3-beam DPP method has a problem in recording / reproduction of a disc having two layers and more. This will be described with the simplest two-layer disc.

  A two-layer disc is an optical disc having two recording layers, and reflected light is generated in each recording layer. For this reason, in the two-layer disc, the light beam is separated into two by the disc and enters the photodetector along two optical paths. For example, when focusing on one layer, the light beam forms a spot (signal light) on the surface of the light detector, and the light beam reflected from the other layer (stray light) is blurred on the light detector. Incident in the state. At this time, on the photodetector, the signal light reflected from each layer and the stray light overlap on the photodetector surface, and interference occurs. Originally, a beam emitted from a laser having the same frequency does not change with time, but the interval between the layers changes with the rotation of the optical disk, so the phase relationship between the two lights changes with time, and a DPP signal that is a tracking error signal Cause fluctuations. The fluctuation of the three-beam DPP signal is mainly caused by the SPP signal. This is because the light amount ratio of the main beam (0th order diffracted light), sub beam + 1st order diffracted light and sub beam-1st order diffracted light is generally 10: 1: 1 to 20: 1: 1. Therefore, the interference between the sub-beam signal light and the stray light of the main beam is greatly generated with respect to the signal light. As a result, the SPP signal largely fluctuates, and as a result, the three-beam DPP signal that is a tracking error signal fluctuates greatly. When the tracking error signal fluctuates, the spot on the optical disc cannot follow along the track, which mainly causes a problem of deterioration in recording / reproducing performance.

  In order to solve this problem, in Patent Document 1, the light beam reflected by the optical disk is stopped by the condensing lens, and the light spread through the two quarter-wave plates and the polarizing optical element is stopped by the condensing lens. The stray light is not incident on the photodetector. Therefore, there is a problem that the detection optical system is complicated and the size of the optical pickup device is increased.

  On the other hand, since the optical pickup device in the present embodiment is a very simple optical system as shown in FIG. 1, the optical pickup device can be downsized. Hereinafter, the optical pickup device in the present embodiment will be described.

  FIG. 2 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. On the other hand, the polarization diffraction grating 12 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, it is assumed that the diffraction efficiencies of the polarization diffraction grating 11 and the polarization diffraction grating 12 are + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1. Therefore, the light beam including the linearly polarized light X and the linearly polarized light Z is separated into the components of the linearly polarized light X and the linearly polarized light Z by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions. FIG. 3 shows a pattern of the polarization diffraction grating 12. The solid line indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th-order diffracted light and the ± 1st-order diffracted light diffracted by the track of the optical disk. Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed. For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the filled portions between the light receiving portions r, s, t, u, and v are dark line portions for detecting a knife edge type focus error signal. The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the −1st order diffracted light diffracted from the regions Da, Db, Dc, and Dd is incident on the dark line portions of the light receiving portions r, s, t, u, and v for detecting the focus error signal, and the regions De, Df, Dg, The −1st order diffracted light diffracted by Dh is incident on the light receiving parts e2, f2, g2, and h2. Further, the ± first-order diffracted lights diffracted by the polarization diffraction grating 11 are incident on the light receiving parts i1 and i2, respectively.

  A1, B1, C1, D1 obtained from the light receiving parts a1, b1, c1, d1, e1, f1, g1, h1, e2, f2, g2, h2, r, s, t, u, v, i1, i2. , E1, F1, G1, H1, E2, F2, G2, H2, R, S, T, U, V, I1, and I2 signals are subjected to the following calculation to obtain a focus error signal (FES) and a tracking error signal (TES). The RF signal (RF) is generated.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。ここで、フォーカス誤差検出方式はナイフエッジ方式である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced. Here, the focus error detection method is a knife edge method.

  FIG. 5 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  As can be seen from FIG. 5, the signal light and the stray light from other layers do not overlap on the light receiving unit except for the light beams incident on the light receiving units i1 and i2. Thereby, a stable tracking error signal can be detected. Here, since the signals I1 and I2 detected from the light receiving sections i1 and i2 are not used for detection of the tracking error signal but are used only for the reproduction signal, there is no practical problem even if stray light is present.

In addition, the optical pickup device according to the present embodiment has a configuration in which stray light does not easily enter the light receiving unit even when the objective lens is displaced. This will be described below.
In actual signal detection, since the objective lens performs recording / reproduction while following the track on the disc, the objective lens is displaced in the disc radial direction (Rad direction). When the objective lens is Rad displaced, only the stray light component is displaced in the Rad direction on the photodetector. For this reason, if the light receiving portion of a normal photodetector is disposed, stray light from other layers may enter the light receiving portion when the objective lens is displaced. On the other hand, in the optical pickup device according to the present embodiment, the displacement tolerance of the objective lens can be increased by optimizing the photodetector 10 with respect to the pattern of the polarization diffraction grating 12. What should be considered here is how to separate the signal light and stray light with respect to the objective lens displacement direction. This will be described below.

  FIG. 6 shows a light beam diffracted in the region Dh of the polarization diffraction grating 12 and incident on the light receiving unit h1. FIG. 7 shows a light beam diffracted in the region Dd and incident on the light receiving part d1. (A), (b), and (c) are classified according to the state of the light spot on the disc, (b) is in a state of focusing on the disc, and (a) and (c) are the objective lenses. It shows a defocused state. Note that (a) and (c) differ in the direction in which the objective lens is defocused. The relationship between (a), (b), and (c) hardly depends on the position of the light receiving unit. Here, the defocusing will be described because the stray light of the two-layer disc can be interpreted as defocused light reflected at a position other than the focal position.

  Comparing FIG. 6 and FIG. 7, it can be seen that the moving direction of the light beam varies depending on the defocus. The light beam diffracted in the region Dh in FIG. 6 moves in the track direction of the optical disc (hereinafter referred to as the Tan direction) by defocusing. In contrast, the light beam diffracted in the region Dd in FIG. 7 moves in the Rad direction. This is because stray light is blurred in a point-symmetric manner with respect to the light beam center 15 on the diffraction grating, so that the moving direction by defocus differs depending on the region. For this reason, it is important to divide how to avoid stray light according to the region. When the region of the diffraction grating is separated from the light beam center 15 in the Tan direction (regions Dh, De, Df, Dg (region A)), it is desirable to avoid stray light in the Tan direction. By avoiding stray light in this way, even if the objective lens is displaced in the Rad direction, it does not enter the photodetector. For this reason, it is possible to minimize the influence of stray light that is diffracted in other regions by arranging light receiving units that detect light beams diffracted in the diffraction grating regions Dh, De, Df, and Dg in the Rad direction. .

Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. For this reason, it becomes possible to minimize the influence of stray light by arranging the light receiving parts for detecting the light beams diffracted in the areas Da, Db, Dc, and Dd in the Tan direction.
As described above, the signal light and the stray light can be effectively separated by arranging the light receiving section as shown in FIG. 4, so that a stable tracking error signal can be detected even in a multilayer disk.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further noise reduction is possible by connecting the light receiving parts i1 and i2 to an electric signal after connecting them. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.
In this embodiment, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st order diffracted light: 0th order diffracted light: -1st order diffracted light = 1: 0: 0, and the RF signal may be detected only by the light receiving unit i1.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  In the present embodiment, the + 1st order diffracted light and the −1st order diffracted light in the region Di are not specified, but for example, other servo signals such as a spherical aberration error signal and adjustment signals are detected by using them. Alternatively, the light receiving units i1 and i2 may receive light as a reproduction signal. Needless to say, the −1st order light in the diffraction grating regions De, Df, Dg, and Dh may be detected as a focus error signal or other signal instead of the tracking error signal. Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 10 shows a light receiving portion of a photodetector of an optical pickup device according to the second embodiment of the present invention. The difference from the first embodiment is that the arrangement of the light receiving portions of the photodetector 10 is different, and the other configuration is the same as that of the first embodiment.

  FIG. 2 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. On the other hand, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, it is assumed that the diffraction efficiencies of the polarization diffraction grating 11 and the polarization diffraction grating 12 are + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  3 includes regions De, Df, Dg, and Dh (region A) where only the 0th-order diffracted light diffracted from the track on the disk is incident, and the 0th-order diffracted light of the diffracted light, ± 1 It is formed of regions Da, Db, Dc, Dd (region B) where the next diffracted light is incident and region Di (region C).

  With respect to such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the filled portions between the light receiving portions r, s, t, u, and v are dark line portions for detecting a knife edge type focus error signal. The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the −1st order diffracted light diffracted from the regions Da, Db, Dc, and Dd is incident on the dark line portions of the light receiving portions r, s, t, u, and v for detecting the focus error signal, and the regions De, Df, Dg, The −1st order diffracted light diffracted by Dh is incident on the light receiving parts e2, f2, g2, and h2. Further, the ± first-order diffracted lights diffracted by the polarization diffraction grating 11 are incident on the light receiving parts i1 and i2, respectively.

  A1, B1, C1, D1 obtained from the light receiving parts a1, b1, c1, d1, e1, f1, g1, h1, e2, f2, g2, h2, r, s, t, u, v, i1, i2. , E1, F1, G1, H1, E2, F2, G2, H2, R, S, T, U, V, I1, and I2 signals are subjected to the following calculation to obtain a focus error signal (FES) and a tracking error signal (TES). The RF signal (RF) is generated.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。ここで、フォーカス誤差検出方式はナイフエッジ方式である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced. Here, the focus error detection method is a knife edge method.

  FIG. 11 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

From FIG. 11, it can be seen that the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts i 1 and i 2. Thereby, a stable tracking error signal can be detected. Here, since the signals I1 and I2 detected from the light receiving sections i1 and i2 are not used for detection of the tracking error signal but are used only for the reproduction signal, there is no practical problem even if stray light is present.
As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction and avoiding stray light in the Tan direction as in the light receiving portions e1, f1, g1, and h1 in FIG. It does not enter the part.
Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. For this reason, it is possible to minimize the influence of stray light by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction as in the light receiving parts a1, b1, c1, and d1 in FIG.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 10, it is possible to detect a stable tracking error signal.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further noise reduction is possible by connecting the light receiving parts i1 and i2 to an electric signal after connecting them. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In this embodiment, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st order diffracted light: 0th order diffracted light: -1st order diffracted light = 1: 0: 0, and the RF signal may be detected only by the light receiving unit i1.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  In the present embodiment, the + 1st order diffracted light and the −1st order diffracted light in the region Di are not specified, but for example, other servo signals such as a spherical aberration error signal and adjustment signals are detected by using them. Alternatively, the light receiving units i1 and i2 may receive light as a reproduction signal. Needless to say, the −1st order light in the diffraction grating regions De, Df, Dg, and Dh may be detected as a focus error signal or other signal instead of the tracking error signal. Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

FIG. 13 shows a light receiving portion of a photodetector of an optical pickup device according to the third embodiment of the present invention. The difference from the first embodiment is that the pattern of the polarization diffraction grating 12 and the arrangement of the light receiving portions of the photodetector 10 are different, and the other configuration is the same as that of the first embodiment.
FIG. 2 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. On the other hand, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, it is assumed that the diffraction efficiencies of the polarization diffraction grating 11 and the polarization diffraction grating 12 are + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions. FIG. 12 shows a pattern of the polarization diffraction grating 12. The solid line indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th-order diffracted light and the ± 1st-order diffracted light diffracted by the track of the optical disk. Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. Region Dab, Dcd (region B) and region Di (region C).

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. The black dots in the figure indicate signal light, and the filled portions between the light receiving portions re, se, tg, ug, tf, uf, rh, and sh are dark line portions for detecting a knife edge type focus error signal. It has become.

  The light beam of 0th-order diffracted light from the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted lights diffracted by the diffraction grating regions Dab, Dcd, De, Df, Dg, and Dh are incident on the light receiving portions ab1, cd1, e1, f1, g1, and h1, respectively. The −1st order diffracted light diffracted in the regions Dab and Dcd is incident on the light receiving portions ab2 and cd2, and the −1st order diffracted light diffracted in the regions De, Df, Dg, and Dh is received in the light receiving portions re, se, tf, and uf, respectively. , Tg, ug, rh, sh is incident on the dark line part. Further, the ± first-order diffracted lights diffracted by the polarization diffraction grating 11 are incident on the light receiving parts i1 and i2, respectively.

  AB1, CD1, E1, F1, G1 obtained from the light receiving parts ab1, cd1, e1, f1, g1, h1, ab2, cd2, re, se, tg, ug, tf, uf, rh, sh, i1, i2 , H1, AB2, CD2, RE, SE, TG, UG, TF, UF, RH, SH, I1, and I2 signals are subjected to a focus error signal (FES), a tracking error signal (TES), and an RF signal ( RF).

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。ここで、フォーカス誤差検出方式はナイフエッジ方式である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced. Here, the focus error detection method is a knife edge method.

FIG. 14 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the dual layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.
As can be seen from FIG. 14, the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts i1 and i2. Thereby, a stable tracking error signal can be detected. Here, since the signals I1 and I2 detected from the light receiving sections i1 and i2 are not used for detection of the tracking error signal but are used only for the reproduction signal, there is no practical problem even if stray light is present.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction to avoid stray light in the Tan direction as in the light receiving portions e1, g1, f1, and h1 in FIG. Does not enter the part.

  Further, when the diffraction grating region is separated in the Rad direction with respect to the light beam center 15 (regions Dab, Dcd (region B)), stray light is desirably avoided in the Rad direction. For this reason, it is possible to minimize the influence of stray light by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction as in the light receiving parts ab1 and cd1 in FIG.

As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 13, a stable tracking error signal can be detected.
Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further noise reduction is possible by connecting the light receiving parts i1 and i2 to an electric signal after connecting them. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the diffraction grating 12 has been described with reference to FIG. 12. However, the present invention is not limited to this. For example, the same effect can be obtained even with a pattern as shown in FIGS. Needless to say. In addition, the diffraction grating 12 can of course obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Yes. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In this embodiment, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st-order diffracted light: 0th-order diffracted light: -1st-order diffracted light = 1: 0: 0, and a light receiving unit corresponding thereto may be arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  It goes without saying that the −1st order light in the diffraction grating regions Dab and Dcd of the polarization diffraction grating 12 may be detected as other signals instead of the tracking error signal. Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 16 shows a light receiving portion of a photodetector of an optical pickup device according to the fourth embodiment of the present invention. The difference from the first embodiment is that the characteristics of the polarization diffraction grating 11 and the arrangement of the light receiving portions of the photodetector 10 are different, and the other configuration is the same as that of the first embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, it is assumed that the diffraction efficiencies of the polarization diffraction grating 11 and the polarization diffraction grating 12 are + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the first embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed.

  With respect to such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the −1st order diffracted light diffracted from the diffraction grating areas Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving parts a2, b2, c2, d2, e2, f2, g2, and h2, respectively. . Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  A1 obtained from the light receiving parts a1, b1, c1, d1, e1, f1, g1, h1, a2, b2, c2, d2, e2, f2, g2, h2, ia1, ib1, ic1, ia2, ib2, ic2 , B1, C1, D1, E1, F1, G1, H1, A2, B2, C2, D2, E2, F2, G2, H2, IA1, IB1, IC1, IA2, IB2, and IC2 signals by the following arithmetic expression A focus error signal (FES), a tracking error signal (TES), and an RF signal (RF) are generated.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 18 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  As can be seen from FIG. 18, the signal light and the stray light from the other layers do not overlap on the light receiving unit except for the light beams incident on the light receiving units ia1, ib1, ic1 and ia2, ib2, and ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction and avoiding stray light in the Tan direction like the light receiving portions e1, g1, f1, and h1 in FIG. It does not enter the part.
Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. Therefore, by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction like the light receiving parts a1, b1, c1, and d1 in FIG. 18, the influence of stray light can be minimized.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 16, it is possible to detect a stable tracking error signal.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In this embodiment, the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st-order diffracted light: 0th-order diffracted light: -1st-order diffracted light = 1: 0: 0, and a light receiving unit corresponding thereto may be arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  In the present embodiment, the + 1st order diffracted light and the −1st order diffracted light in the region Di are not specified, but for example, other servo signals such as a spherical aberration error signal and adjustment signals are detected by using them. Alternatively, it may be detected as a reproduction signal. Needless to say, the −1st order light of the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh may be detected as a focus error signal or other signal instead of a tracking error signal. . Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 19 shows a light receiving portion of a photodetector of an optical pickup device according to the fifth embodiment of the present invention. The difference from the fourth embodiment is that the arrangement of the light receiving portions of the photodetector 10 is different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, it is assumed that the diffraction efficiencies of the polarization diffraction grating 11 and the polarization diffraction grating 12 are + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the first embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed.

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the −1st order diffracted light diffracted from the diffraction grating areas Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving parts a2, b2, c2, d2, e2, f2, g2, and h2, respectively. . Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  A1 obtained from the light receiving parts a1, b1, c1, d1, e1, f1, g1, h1, a2, b2, c2, d2, e2, f2, g2, h2, ia1, ib1, ic1, ia2, ib2, ic2 , B1, C1, D1, E1, F1, G1, H1, A2, B2, C2, D2, E2, F2, G2, H2, IA1, IB1, IC1, IA2, IB2, and IC2 signals by the following arithmetic expression A focus error signal (FES), a tracking error signal (TES), and an RF signal (RF) are generated.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 20 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  As can be seen from FIG. 20, the signal light and the stray light from other layers do not overlap on the light receiving unit except for the light beams incident on the light receiving units ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction and avoiding stray light in the Tan direction like the light receiving portions e1, f1, g1, and h1 in FIG. Does not enter the part.

  Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. For this reason, it is possible to minimize the influence of stray light by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction like the light receiving parts a1, c1, b1, and d1 in FIG.

As described above, the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 19, and thus a stable tracking error signal can be detected.
Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In this embodiment, the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st-order diffracted light: 0th-order diffracted light: -1st-order diffracted light = 1: 0: 0, and a light receiving unit corresponding thereto may be arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  In the present embodiment, the + 1st order diffracted light and the −1st order diffracted light in the region Di are not specified, but for example, other servo signals such as a spherical aberration error signal and adjustment signals are detected by using them. Alternatively, it may be detected as a reproduction signal. Needless to say, the −1st order light of the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh may be detected as a focus error signal or other signal instead of a tracking error signal. . Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

FIG. 21 shows a light receiving portion of a photodetector of an optical pickup device according to the sixth embodiment of the present invention. The difference from the fourth embodiment is that the pattern of the polarization diffraction grating 12 and the arrangement of the light receiving portions of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.
FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 1. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes ± first order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the third embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. Region Dab, Dcd (region B) and region Di (region C).

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted by the areas Da, Db, Dc, Dd, De, Df, Dg, Dh of the polarization diffraction grating 12 is incident on the light receiving parts ab1, cd1, e1, f1, g1, h1, respectively. Further, the −1st order diffracted light diffracted from the diffraction grating areas Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions ab2, cd2, e2, f2, g2, and h2, respectively. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  AB1, CD1, E1, F1, G1 obtained from the light receiving portions ab1, cd1, e1, f1, g1, h1, ab2, cd2, e2, f2, g2, h2, ia1, ib1, ic1, ia2, ib2, ic2 , H1, AB2, CD2, E2, F2, G2, H2, IA1, IB1, IC1, IA2, IB2, and IC2 are expressed by a focus error signal (FES), tracking error signal (TES), and RF by the following arithmetic expressions. A signal (RF) is generated.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 22 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the dual layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  FIG. 22 shows that the signal light and the stray light from other layers do not overlap on the light receiving unit except for the light beams incident on the light receiving units ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, the stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction and avoiding stray light in the Tan direction like the light receiving portions e1, g1, f1, and h1 in FIG. Does not enter the part.

  Further, when the diffraction grating region is separated in the Rad direction with respect to the light beam center 15 (regions Dab, Dcd (region B)), stray light is desirably avoided in the Rad direction. Therefore, by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction like the light receiving parts ab1 and cd1 in FIG. 22, the influence of stray light can be minimized.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 21, a stable tracking error signal can be detected.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 12, but the present invention is not limited to this, and the same effect can be obtained even with patterns such as those shown in FIGS. 15 (a) and 15 (b). Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In this embodiment, the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, but is not limited to this. + 1st-order diffracted light: 0th-order diffracted light: -1st-order diffracted light = 1: 0: 0, and a light receiving unit corresponding thereto may be arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other.

  In the present embodiment, the + 1st order diffracted light and the −1st order diffracted light in the region Di are not specified, but for example, other servo signals such as a spherical aberration error signal and adjustment signals are detected by using them. Alternatively, it may be detected as a reproduction signal. Needless to say, the −1st order light of the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh may be detected as a focus error signal or other signal instead of a tracking error signal. . Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 23 shows a light receiving portion of a photodetector of an optical pickup device according to the seventh embodiment of the present invention. The difference from the fourth embodiment is that the diffraction efficiency of the polarization diffraction grating 12 and the arrangement of the light receiving section of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 0. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes + 1st order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the first embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed.

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  A1, B1, C1, D1, E1, F1, G1, H1, and IA1 obtained from the light receiving portions a1, b1, c1, d1, e1, f1, g1, h1, ia1, ib1, ic1, ia2, ib2, and ic2. , IB1, IC1, IA2, IB2, and IC2 are used to generate a focus error signal (FES), a tracking error signal (TES), and an RF signal (RF) by the following arithmetic expression.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 24 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  From FIG. 24, it can be seen that the signal light and the stray light from other layers do not overlap on the light receiving unit except for the light beams incident on the light receiving units ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, even if the objective lens is displaced in the Rad direction by arranging the light receiving units in the Rad direction and avoiding stray light in the Tan direction like the light receiving units e1 and h1 and the light receiving units g1 and f1 in FIG. Does not enter the light receiving section.
Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. Therefore, by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction like the light receiving parts a1, b1, c1, and d1 in FIG. 24, it is possible to minimize the influence of the stray light.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 23, a stable tracking error signal can be detected.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. In this case, it goes without saying that the same effect can be obtained, and it is needless to say that, for example, the arrangement of the light receiving portions as shown in FIGS. Furthermore, the light receiving portions do not need to be in contact with each other. When unnecessary diffracted light such as −1st order diffracted light is generated, the light receiving portions may be separated from each other so that the unnecessary diffracted light does not enter.

  In the present embodiment, the + diffracted light in the region Di is not specified, but other servo signals such as a spherical aberration error signal and adjustment signals may be detected and reproduced, for example. It may be detected as a signal. Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 26 shows a light receiving portion of a photodetector of an optical pickup device according to the eighth embodiment of the present invention. The difference from the fourth embodiment is that the diffraction efficiency of the polarization diffraction grating 12 and the arrangement of the light receiving parts of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 0. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes + 1st order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the first embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed.

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted from the diffraction grating regions Da, Db, Dc, Dd, De, Df, Dg, and Dh is incident on the light receiving portions a1, b1, c1, d1, e1, f1, g1, and h1, respectively. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  A1, B1, C1, D1, E1, F1, G1, H1, and IA1 obtained from the light receiving portions a1, b1, c1, d1, e1, f1, g1, h1, ia1, ib1, ic1, ia2, ib2, and ic2. , IB1, IC1, IA2, IB2, and IC2 are used to generate a focus error signal (FES), a tracking error signal (TES), and an RF signal (RF) by the following arithmetic expression.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 27 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  From FIG. 27, it can be seen that the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, the stray light is received even when the objective lens is displaced in the Rad direction by arranging the light receiving portions in the Rad direction to avoid stray light in the Tan direction as shown in the light receiving portions e1, f1, g1, and h1 in FIG. Does not enter the part.

  Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. Therefore, by arranging the light receiving units in the Tan direction and avoiding stray light in the Rad direction like the light receiving units a1 and b1 and the light receiving units c1 and d1 in FIG. 27, it is possible to minimize the influence of stray light.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 26, a stable tracking error signal can be detected.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. In this case, it goes without saying that the same effect can be obtained, and it is needless to say that the arrangement of the light receiving parts as shown in FIGS. 28 (a), 28 (b) and 28 (c) may be used. Furthermore, the light receiving portions do not need to be in contact with each other. When unnecessary diffracted light such as −1st order diffracted light is generated, the light receiving portions may be separated from each other so that the unnecessary diffracted light does not enter.
In this embodiment, the diffracted light in the region Di is not specified, but other servo signals such as spherical aberration error signals and adjustment signals may be detected using the diffracted light. May be detected as Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 29 shows a light receiving portion of a photodetector of an optical pickup device according to the ninth embodiment of the present invention. The difference from the fourth embodiment is that the pattern and diffraction efficiency of the polarization diffraction grating 12 and the arrangement of the light receiving section of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 0. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes + 1st order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the third embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. Region Dab, Dcd (region B) and region Di (region C).

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted lights diffracted by the diffraction grating regions Dab, Dcd, De, Df, Dg, and Dh are incident on the light receiving portions ab1, cd1, e1, f1, g1, and h1, respectively. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  AB1, CD1, E1, F1, G1, H1, IA1, IB1, IC1, IA2, IB2 obtained from the light receiving parts ab1, cd1, e1, f1, g1, h1, ia1, ib1, ic1, ia2, ib2, ic2. The focus error signal (FES), tracking error signal (TES), and RF signal (RF) are generated from the IC2 signal by the following arithmetic expression.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 30 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  From FIG. 30, it can be seen that the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, even if the objective lens is displaced in the Rad direction by arranging the light receiving units in the Rad direction and avoiding stray light in the Tan direction like the light receiving units e1 and h1 and the light receiving units f1 and g1 in FIG. Does not enter the light receiving section.

  Further, when the diffraction grating region is separated in the Rad direction with respect to the light beam center 15 (regions Dab, Dcd (region B)), stray light is desirably avoided in the Rad direction. Therefore, by arranging the light receiving units in the Tan direction and avoiding stray light in the Rad direction like the light receiving units ab1 and cd1 in FIG. 30, it is possible to minimize the influence of stray light.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 29, a stable tracking error signal can be detected.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 12, but the present invention is not limited to this, and the same effect can be obtained even with patterns such as those shown in FIGS. 15 (a) and 15 (b). Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. In this case, it goes without saying that the same effect can be obtained, and it is needless to say that the arrangement of the light receiving parts as shown in FIGS. 31 (a), 31 (b), and 31 (c) may be used. Furthermore, the light receiving portions do not need to be in contact with each other. When unnecessary diffracted light such as −1st order diffracted light is generated, the light receiving portions may be separated from each other so that the unnecessary diffracted light does not enter.
In this embodiment, the diffracted light in the region Di is not specified, but other servo signals such as spherical aberration error signals and adjustment signals may be detected using the diffracted light. You may detect as. Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 32 shows a light receiving portion of a photodetector of an optical pickup device according to the tenth embodiment of the present invention. The difference from the fourth embodiment is that the diffraction efficiency of the polarization diffraction grating 12 and the arrangement of the light receiving portions of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 0. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes + 1st order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the first embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. The regions Da, Db, Dc, Dd (region B) and the region Di (region C) are formed.

  For such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted by the diffraction grating regions Da, Db, Dc, and Dd is incident on the light receiving portions a1, b1, c1, and d1, respectively. The + 1st order diffracted light diffracted by the diffraction grating areas De and Df is incident on the light receiving part ef1, and the + 1st order diffracted light diffracted by the diffraction grating areas Dg and Dh is incident on the light receiving part gh1. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  A1, B1, C1, D1, EF1, GH1, IA1, IB1, IC1, IA2, IB2 obtained from the light receiving parts a1, b1, c1, d1, ef1, gh1, ia1, ib1, ic1, ia2, ib2, ic2 The focus error signal (FES), tracking error signal (TES), and RF signal (RF) are generated from the IC2 signal by the following arithmetic expression.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 33 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  It can be seen from FIG. 33 that the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, the stray light does not enter the light receiving unit even when the objective lens is displaced in the Rad direction by arranging the light receiving units in the Rad direction and avoiding stray light in the Tan direction like the light receiving units ef1 and gh1 in FIG. .

  Further, when the diffraction grating region is separated from the light beam center 15 in the Rad direction (regions Da, Db, Dc, Dd (region B)), it is desirable to avoid stray light in the Rad direction. Therefore, by arranging the light receiving units in the Tan direction and avoiding stray light in the Rad direction like the light receiving units a1 and b1 and the light receiving units c1 and d1 in FIG. 33, it is possible to minimize the influence of stray light.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 32, a stable tracking error signal can be detected.

Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.
In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 3, but the present invention is not limited to this. For example, the same effect can be obtained even with patterns such as those shown in FIGS. Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. Furthermore, the light receiving portions do not need to be in contact with each other. When unnecessary diffracted light such as −1st order diffracted light is generated, the light receiving portions may be separated from each other so that the unnecessary diffracted light does not enter.

  In this embodiment, the diffracted light in the region Di is not specified, but other servo signals such as spherical aberration error signals and adjustment signals may be detected using the diffracted light. May be detected as Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  FIG. 34 shows a light receiving portion of the photodetector of the optical pickup device according to the eleventh embodiment of the present invention. The difference from the fourth embodiment is that the pattern and diffraction efficiency of the polarization diffraction grating 12 and the arrangement of the light receiving section of the photodetector 10 are different, and the other configuration is the same as that of the fourth embodiment.

  FIG. 17 is a diagram showing the characteristics of the polarization diffraction grating 11 and the polarization diffraction grating 12. (A) shows the polarization diffraction grating 11, and (b) shows the polarization diffraction grating 12. First, the polarization diffraction grating 11 has a property of diffracting only to a light beam of a predetermined linearly polarized light (linearly polarized light X), and a property of transmitting a light beam orthogonal to the linearly polarized light X (linearly polarized light Z). It has become. The polarization diffraction grating 11 is a hologram element, and a predetermined defocus is added to the diffracted light. Further, the polarization diffraction grating 11 has a characteristic of diffracting only to a light beam of linearly polarized light Z, and has a characteristic of transmitting a light beam of linearly polarized light X. Here, the diffraction efficiency of the polarization diffraction grating 11 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light = 1: 0: 1, and the diffraction efficiency of the polarization diffraction grating 12 is + 1st order diffracted light: 0th order diffracted light: −1st order diffracted light. = 1: 0: 0. Therefore, the light beam transmitted through the beam splitter 52 is separated into linearly polarized light X and linearly polarized light Z components by the polarization diffraction grating 11. The component of the linearly polarized light X is diffracted and becomes ± first-order diffracted light. The component of the linearly polarized light Z is transmitted through the polarization diffraction grating 11. Then, the light beam of the linearly polarized light Z transmitted through the polarization diffraction grating 11 is diffracted by the polarization diffraction grating 12 and becomes + 1st order diffracted light. On the other hand, the light beam of linearly polarized light X diffracted by the polarization diffraction grating 11 is configured to pass through the polarization diffraction grating 12. For example, when the polarization component of the light beam transmitted through the beam splitter 52 is separated into the linearly polarized light X and the linearly polarized light Z component, the ratio of the light amount of the linearly polarized light X and the light amount of the linearly polarized light Z is 8: 2. And

  The polarization diffraction grating 11 is a normal polarization diffraction grating, and is a polarization diffraction grating with one grating groove pitch and one grating groove direction. On the other hand, the polarization diffraction grating 12 has a plurality of regions having different grating groove pitches and grating groove directions, and has a pattern similar to that of the third embodiment as shown in FIG. The solid line in the figure indicates the boundary line of the region, the two-dot chain line indicates the effective diameter of the light beam, and the hatched portion indicates the interference region between the 0th order diffracted light and the ± 1st order diffracted light diffracted by the track of the optical disk. . Polarization diffraction grating 12 receives regions De, Df, Dg, and Dh (region A) where only the 0th order diffracted light diffracted from the track on the disk is incident, and the 0th order diffracted light and ± 1st order diffracted light enter. Region Dab, Dcd (region B) and region Di (region C).

  With respect to such a diffraction grating, the photodetector 10 has a light receiving portion arrangement as shown in FIG. Black dots in the figure indicate signal light, and the light receiving portions ia1, ib1, ic1, ia2, ib2, and ic2 are focus error signal detection light receiving portions by a spot size method.

  The light beam of linearly polarized light Z transmitted through the polarization diffraction grating 11 diffracts the polarization diffraction grating 12. The + 1st order diffracted light diffracted by the diffraction grating regions Dab and Dcd is incident on the light receiving portions ab1 and cd1, respectively. The + 1st order diffracted light diffracted by the diffraction grating areas De and Df is incident on the light receiving part ef1, and the + 1st order diffracted light diffracted by the diffraction grating areas Dg and Dh is incident on the light receiving part gh1. Further, the ± first-order diffracted light diffracted by the polarization diffraction grating 11 is subjected to predetermined defocusing by the diffraction grating, and enters the light receiving portions ia1, ib1, ic1 and ia2, ib2, ic2 in a defocused state. Here, since the defocus directions of the light beams incident on the light receiving portions ia1, ib1, and ic1 and the light beams incident on ia2, ib2, and ic2 are different, the focus error signal can be detected. Since the spot size method is publicly known, the description is omitted.

  The following calculation is performed on the signals of AB1, CD1, EF1, GH1, IA1, IB1, IC1, IA2, IB2, and IC2 obtained from the light receiving units ab1, cd1, ef1, gh1, ia1, ib1, ic1, ia2, ib2, and ic2. A focus error signal (FES), a tracking error signal (TES), and an RF signal (RF) are generated by the equation.

なお、ｋは対物レンズが変位した際にトラッキング誤差信号でＤＣ成分を発生させないようにする係数である。

Note that k is a coefficient that prevents a DC component from being generated in the tracking error signal when the objective lens is displaced.

  FIG. 35 shows the relationship between the signal light and the stray light from the other layers at the time of recording / reproducing the double-layer disc. In the figure, black dots indicate signal light, and hatched portions indicate stray light from other layers, (a) indicates L0 recording / reproduction, and (b) indicates L1 recording / reproduction.

  From FIG. 35, it can be seen that the signal light and the stray light from other layers do not overlap on the light receiving part except for the light beams incident on the light receiving parts ia1, ib1, ic1 and ia2, ib2, ic2. Thereby, a stable tracking error signal can be detected. Here, the signals IA1, IB1, IC1 and IA2, IB2, and IC2 detected from the light receiving portions ia1, ib1, ic1 and ia2, ib2, and ic2 are not used for the detection of the tracking error signal, but the focus error signal and the reproduction signal. Even if there is stray light, it is not a problem for practical use.

  As described in the first embodiment, when the region of the diffraction grating is separated in the Tan direction with respect to the light beam center 15 (regions Dh, De, Df, Dg (region A)), the stray light is in the Tan direction. It is desirable to avoid it. Therefore, the stray light does not enter the light receiving unit even when the objective lens is displaced in the Rad direction by arranging the light receiving units in the Rad direction and avoiding stray light in the Tan direction like the light receiving units ef1 and gh1 in FIG. .

  Further, when the diffraction grating region is separated in the Rad direction with respect to the light beam center 15 (regions Dab, Dcd (region B)), stray light is desirably avoided in the Rad direction. For this reason, it is possible to minimize the influence of stray light by arranging the light receiving parts in the Tan direction and avoiding stray light in the Rad direction as in the light receiving parts ab1 and cd1 in FIG.

  As described above, since the signal light and the stray light can be effectively separated by arranging the light receiving unit as shown in FIG. 34, a stable tracking error signal can be detected.

  Next, the effect of the polarization diffraction grating 11 will be described. For example, in the case where the polarization diffraction grating 11 is not disposed, it is necessary to add signals obtained from a plurality of light receiving units for detecting a tracking error signal in order to detect an RF signal. On the other hand, since the polarization diffraction grating 11 separates the RF signal and the tracking error signal light beam as in this embodiment, the tracking error signal detection unit and the light receiving unit of the RF signal detection unit can be separated. It is possible to reduce the number of light receiving portions of the signal. Thereby, noise generated when the light beam is converted into an electric signal can be reduced. Further, the light receiving parts ia1, ib2, and ic2 are connected, and the light receiving parts ia2, ib1, and ic1 are connected and then converted into an electrical signal, so that further noise reduction is possible. Noise reduction is very advantageous from the viewpoint of S / N in a multilayer disk. Thus, by arranging two polarization diffraction gratings as in the present invention, it becomes possible to detect a stable RF signal and tracking error signal.

  In the present embodiment, the polarization diffraction grating 12 has been described with reference to FIG. 12, but the present invention is not limited to this, and the same effect can be obtained even with patterns such as those shown in FIGS. 15 (a) and 15 (b). Needless to say. Further, the polarization diffraction grating 12 can obtain the same effect even if the region Z is formed in the diffraction grating as shown in FIG. 9 for the purpose of eliminating stray light outside the effective diameter of the signal light on the diffraction grating. Needless to say. At this time, the light incident on the region Z is configured not to be incident on the light receiving unit, and the region Z may have a lattice structure, a multilayer mirror, or a filter. . Although the description has been made with two layers here, it goes without saying that the same effect can be obtained even with an optical disk having two or more layers. Needless to say, the spherical aberration correction method is not limited. Furthermore, in this embodiment, two polarization diffraction gratings are arranged, but it goes without saying that the same effect can be obtained even if one element having the same function is arranged.

  In addition, the arrangement of the light receiving section of this embodiment is an example, and one polarization diffraction grating separates the reproduced signal and the servo signal light beam, and the other polarization diffraction grating separates one beam for servo use. Needless to say, there are similar effects. The stray light diffracted in the Rad direction with respect to the center of the diffraction grating is separated in the Rad direction, and the stray light diffracted in the Tan direction with respect to the center of the diffraction grating is separated in the Tan direction. Needless to say, the same effect can be obtained. When unnecessary diffracted light such as −1st order diffracted light is generated, the light receiving portions may be separated from each other so that the unnecessary diffracted light does not enter.

  In this embodiment, the diffracted light in the region Di is not specified, but other servo signals such as spherical aberration error signals and adjustment signals may be detected using the diffracted light. May be detected as Furthermore, it goes without saying that the output signal from the optical pickup device may be reduced by connecting the light receiving section. The light receiving portions for the RF signal and tracking error signal of the photodetector are shown as squares, but needless to say, they may be rectangular or other shapes instead of squares.

  In the twelfth embodiment, an optical reproducing device equipped with the optical pickup device 170 will be described. FIG. 36 shows a schematic configuration of the optical reproducing apparatus. The optical pickup device 170 is provided with a mechanism that can be driven along the Rad direction of the optical disc 100, and the position is controlled in accordance with an access control signal from the access control circuit 172.

  A predetermined laser driving current is supplied from the laser lighting circuit 177 to the semiconductor laser in the optical pickup device 170, and laser light is emitted from the semiconductor laser with a predetermined light amount according to reproduction. The laser lighting circuit 177 can be incorporated in the optical pickup device 170.

  A signal output from the photodetector 10 in the optical pickup device 170 is sent to the servo signal generation circuit 174 and the information signal reproduction circuit 175. The servo signal generation circuit 174 generates servo signals such as a focus error signal, a tracking error signal, and a tilt control signal based on the signal from the photodetector 10, and based on this generates an optical pickup device 170 via an actuator drive circuit 173. The actuator is driven to control the position of the objective lens.

  The information signal reproduction circuit 175 reproduces the information signal recorded on the optical disc 100 based on the signal from the photodetector 10.

  Some of the signals obtained by the servo signal generation circuit 174 and the information signal reproduction circuit 175 are sent to the control circuit 176. The control circuit 176 is connected to a spindle motor drive circuit 171, an access control circuit 172, a servo signal generation circuit 174, a laser lighting circuit 177, a spherical aberration correction element drive circuit 179, and the like, and the rotation of the spindle motor 180 that rotates the optical disc 100. Control, access direction and access position control, servo control of the objective lens, control of the amount of light emitted from the semiconductor laser in the optical pickup device 170, correction of spherical aberration due to the difference in disk substrate thickness, and the like are performed.

  In Example 13, an optical recording / reproducing apparatus equipped with the optical pickup device 170 will be described. FIG. 37 shows a schematic configuration of the optical recording / reproducing apparatus. 36 is different from the optical information recording / reproducing apparatus described in FIG. 36 in that an information signal recording circuit 178 is provided between the control circuit 176 and the laser lighting circuit 177, and a recording control signal from the information signal recording circuit 178 is provided. Based on the above, the lighting control of the laser lighting circuit 177 is performed, and a function of writing desired information to the optical disc 100 is added.

  In addition, this invention is not limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. In addition, a part of the configuration of a certain embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of a certain embodiment. Further, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

2: objective lens, 5: actuator, 10: photodetector, 11: polarization diffraction grating, 12: polarization diffraction grating, 50: semiconductor laser, 51: collimating lens, 52: beam splitter, 53: front monitor, 54: beam Expander, 55: Raising mirror, 56: 1/4 wavelength plate, 170: Optical pickup device, 171: Spindle motor drive circuit, 172: Access control circuit, 173: Actuator drive circuit, 174: Servo signal generation circuit, 175 : Information signal reproduction circuit, 176: Control circuit, 177: Laser lighting circuit, 178: Information recording circuit, 179: Spherical aberration correction element driving circuit, 180: Spindle motor, Da to Di: Diffraction grating region, Dab, Dcd: Diffraction Lattice region, a1 to h1, a2 to h2, r to v, re, se, tg, ug tf, uf, rh, sh, ia1, ib1, ic1, ia2, ib2, ic2, i1, i2: the light-receiving part

Claims (21)

An optical pickup device,
A semiconductor laser that emits laser light;
An objective lens for irradiating an optical disk with a light beam emitted from the semiconductor laser;
At least two diffraction gratings for branching the light beam reflected from the information recording layer on the optical disc;
A photodetector having a plurality of light receiving portions for detecting a light beam branched from the at least two diffraction gratings;
With
Of the at least two diffraction gratings, two are polarization diffraction gratings;
The polarized light causing the diffraction action of the one polarization diffraction grating and the polarized light causing the diffraction action of the other polarization diffraction grating are substantially orthogonal,
An optical pickup device that detects a reproduction signal from the diffracted light of one of the two polarization diffraction gratings and detects a servo control signal from the diffracted light of the other polarization diffraction grating. The optical pickup device according to claim 1,
2. The optical pickup device according to claim 1, wherein the light beams incident on the two polarization diffraction gratings are polarized light that causes diffraction action in both polarization diffraction gratings. The optical pickup device according to any one of claims 1 to 2,
An optical pickup device characterized in that a light beam diffracted by one of the two polarization diffraction gratings and a light beam diffracted by the other polarization diffraction grating are simultaneously detected by the photodetector. In the optical pick-up apparatus as described in any one of Claims 1-3,
A reproduction signal is detected from the diffracted light of one of the two polarization diffraction gratings,
An optical pickup device, wherein a tracking error signal is detected from the diffracted light of the other polarization diffraction grating. The optical pickup device according to any one of claims 1 to 4,
Of the two polarization diffraction gratings,
One polarization diffraction grating is composed of a plurality of regions having different grating pitches and diffraction grating groove directions,
The other polarization diffraction grating is composed of one grating pitch and one diffraction grating groove direction. The optical pickup device according to claim 5, wherein
An optical pickup device, wherein a reproduction signal is generated from diffracted light of ± 1st order or more of a polarization diffraction grating composed of one grating pitch and one diffraction grating groove direction. The optical pickup device according to any one of claims 5 to 6,
An optical pickup device that generates a tracking error signal from diffracted light of ± 1st order or more of a polarization diffraction grating composed of a plurality of regions having different grating pitches. The optical pickup device according to any one of claims 5 to 7,
A polarization diffraction grating composed of a plurality of regions having different grating pitches,
It has at least three regions of region A, region B, and region C,
Of the disc diffracted light diffracted by the track on the optical disc,
In the area A, 0th-order disc diffracted light is incident,
At least ± first-order disc diffracted light is incident on the region B,
Among the light receiving portions of the photodetector that detects the + 1st order grating diffracted light or the −1st order grating diffracted light in the region A, at least two light receiving portions are arranged in a substantially straight line in a direction substantially coincident with the tangential direction of the optical disc. An optical pickup device characterized by that. The optical pickup device according to any one of claims 5 to 8,
A polarization diffraction grating composed of a plurality of regions having different grating pitches,
It has at least three regions of region A, region B, and region C,
Of the disc diffracted light diffracted by the track on the optical disc,
In the area A, 0th-order disc diffracted light is incident,
At least ± first-order disc diffracted light is incident on the region B,
Among the light receiving portions of the photodetector that detects the first-order grating diffracted light or the minus first-order grating diffracted light in the region B, at least two light receiving portions are arranged in a substantially straight line in a direction substantially coincident with the radial direction of the optical disc. An optical pickup device characterized by that. The optical pickup device according to any one of claims 5 to 9,
A polarization diffraction grating composed of a plurality of regions having different grating pitches,
It has at least three regions of region A, region B, and region C,
Of the disc diffracted light diffracted by the track on the optical disc,
In the area A, 0th-order disc diffracted light is incident,
At least ± first-order disc diffracted light is incident on the region B,
When recording / playing back two or more optical discs,
The light beam reflected from the recording / reproducing layer on the optical disc and diffracted by the region A is converged on the light receiving portion on the photodetector,
A light beam reflected from a layer other than the recording / reproducing layer on the optical disc and diffracted by the region A is irradiated to a position substantially deviated in the disc radial direction from the light receiving portion on the photodetector. An optical pickup device characterized by the above. The optical pickup device according to any one of claims 5 to 10,
A polarization diffraction grating composed of a plurality of regions having different grating pitches,
It has at least three regions of region A, region B, and region C,
Of the disc diffracted light diffracted by the track on the optical disc,
In the area A, 0th-order disc diffracted light is incident,
At least ± first-order disc diffracted light is incident on the region B,
When recording / playing back two or more optical discs,
The light beam reflected from the recording / reproducing layer on the optical disc and diffracted by the region A is converged on the light receiving portion on the photodetector,
A light beam reflected from a layer other than the reproducing layer on the optical disc and diffracted in the region A is irradiated to a position substantially deviated in the disc tangential direction from the light receiving portion on the photodetector. Optical pickup device. The optical pickup device according to any one of claims 5 to 11,
The tracking error signal is
An optical pickup device generated from a signal obtained by detecting a grating diffracted light diffracting the diffraction grating region A and a signal obtained by detecting a grating diffracted light diffracted by the diffraction grating region B. The optical pickup device according to claim 1, wherein:
An optical pickup device characterized in that -1st order diffracted light: 0th order diffracted light: + 1st order diffracted light of at least one of the two polarization diffraction gratings is approximately 1: 0: 1. The optical pickup device according to claim 1, wherein:
Light characterized in that −1st order diffracted light: 0th order diffracted light: + 1st order diffracted light of at least one of the two polarization diffraction gratings is approximately 1: 0: 0 or approximately 0: 0: 1. Pickup device. The optical pickup device according to claim 1, wherein:
One of the two polarization diffraction gratings is a polarization hologram element for adding defocus, and an optical pickup device. The optical pickup device according to any one of claims 1 to 15,
An optical pickup device that detects a diffracted light of one of the two polarization diffraction gratings as a spot size type focus error signal. The optical pickup device according to claim 1, wherein:
An optical pickup device that detects diffracted light of one of the two polarization diffraction gratings as a double knife edge type focus error signal. The optical pickup device according to any one of claims 1 to 17,
A plurality of detection units on the photodetector for detecting diffracted light of one of the two polarization diffraction gratings are arranged in the form of “I”. The optical pickup device according to any one of claims 1 to 17,
An optical pickup device, wherein a plurality of detection units on the photodetector for detecting the diffracted light of one of the two polarization diffraction gratings are arranged in a “T” shape. The optical pickup device according to any one of claims 1 to 19,
Of the light beams detected by a plurality of light receiving portions of the photodetector,
An optical pickup device characterized in that the polarization of the light beam used for the reproduction signal and the polarization of the light beam used for the tracking error signal are substantially orthogonal.   21. The optical pickup device according to any one of claims 1 to 20, a laser lighting circuit that drives the semiconductor laser in the optical pickup device, and the photodetector in the optical pickup device. An optical disc apparatus including a servo signal generation circuit that generates a focus error signal and a tracking error signal using a signal, and an information signal reproduction circuit that reproduces an information signal recorded on the optical disc.

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