JP2010009701A - Optical pickup device and optical disk device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device which is less subject to return light from an irrelevant information recording layer or the like in the optical pickup device using a hologram element. <P>SOLUTION: The optical pickup device is equipped with a light shielding part 153 which blocks the light which enters into a center of a polarization hologram 152 of an accumulation unit 101. The polarization hologram is divided into six areas and a push-pull signal, a lens shift signal and a focus error signal are detected by computing a diffraction light from each area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical pickup device used in an optical disk device that optically records or reproduces information on an information recording medium such as an optical disk, and an optical disk device equipped with the optical pickup device.

  As a tracking servo method of the optical pickup device, a push-pull method (PP method) can be cited. The PP method is a method for detecting a detrack amount by detecting a light amount difference between a plurality of light receiving units. A case where there is no light amount difference is determined as a just track.

  In order to make the optical pickup device using the PP method small, thin, and highly reliable, one using a hologram has been proposed.

  The basic structure of an optical pickup device using such a hologram is described in Patent Document 1. The optical pickup device described in the publication is for a DVD, in which a hologram is divided into two in the disc radial direction, and one of them is further divided into two in the track direction. This optical pickup device detects a focus error signal with half of the reflected beam from the disk, a track error signal with the other half, and an information signal over the entire beam.

  In this optical pickup device, the track error signal includes a position signal for the track, a so-called push-pull signal (PP signal). This PP signal is detected by comparing the amount of light obtained by further dividing the beam divided in half in the disk radial direction into two in the track direction.

  In the optical pickup device, the hologram having such a configuration is arranged in the optical integrated unit, and the laser light emitted from the optical integrated unit is condensed on the optical disk by the objective lens.

  10 and 11 are diagrams showing an example of a conventional optical pickup device 400 using a hologram. FIG. 10 is a schematic diagram showing a configuration of the optical pickup device 400, and FIG. 11 is a schematic diagram showing a beam shape on the hologram element 52 and the light receiving unit 31 of the photodetector 30 in the optical pickup device 400. As shown in FIG. 10, in the optical pickup device 400, the integrated unit 1 includes a semiconductor laser chip 2, a photodetector 30, and a hologram element 52. The light emitted from the semiconductor laser chip 2 is diffracted by the hologram element 52, and the 0th-order diffracted light is condensed on the optical disk 12 through the collimator lens 8 and the objective lens 10. The return light is guided to the light receiving unit 31 of the photodetector 30 by the hologram element 52 through the objective lens 10 and the collimating lens 8.

  Further, as shown in FIG. 11, the hologram element 52 includes a dividing line extending in the x direction corresponding to the radial direction of the optical disk 12 and a y direction orthogonal to the radial direction of the optical disk 12 from the center of the dividing line, that is, the optical disk. It is divided into three divided regions 52a, 52b, and 52c by dividing lines extending in a direction corresponding to twelve track directions.

  The light receiving unit 31 of the photodetector 30 includes four rectangular light receiving elements 31 a, 31 b, 31 c, and 31 d arranged in the y direction corresponding to the track direction of the optical disk 12. The central light receiving elements 31c and 31d are divided by a dividing line extending in the x direction. Light receiving elements 31a and 31b are provided on both sides in the y direction of the light receiving elements 31c and 31d. Each light receiving element 31a, 31b, 31c, 31d extends in the y direction.

  The light diffracted by the divided region 52c of the hologram element 52 forms an image on the light receiving element 31c or 31d, and the light diffracted by the divided regions 51a and 51b forms an image on the light receiving elements 31a and 31b, respectively. . Here, if the output signals of the light receiving elements 31a, 31b, 31c, and 31d are Sa, Sb, Sc, and Sd, respectively, the focus error signal FES is calculated by (Sc-Sd), and the tracking error signal RES is (Sa-Sb). ).

  However, when the PP method is employed, if the objective lens is shifted, the position of the return light at the light receiving portion changes. Therefore, if the objective lens is shifted even if detracking is not performed, an offset occurs in the track error signal.

  On the other hand, in the differential push-pull method (DPP method), it is possible to suppress an offset that occurs when the PP method is used. In this DPP method, a beam from a light emitting unit that emits laser light is divided into three beams of a main beam and front and rear sub-beams, and the main beam and the front and rear sub-beams are divided in a direction across the track. A track error is detected from the signal. For this reason, the offset generated in the PP method can be suppressed, and the DPP method is used as a tracking servo method.

  However, in the DPP method, since three beams are generated from one light source, the amount of light of the main beam involved in recording decreases, resulting in a slow recording speed and hinders an increase in recording speed. There is a problem of becoming.

Accordingly, various methods have been proposed for correcting an offset signal generated by the PP method by using an objective lens shift signal, even though it is a one-beam PP method. For example, in Patent Document 2, return light from an objective lens is detected by a 6-divided photodetector, and an output signal corresponding to the amount of light received by the 6-divided photodetector is calculated, so that even if the objective lens is shifted. An optical head with a small offset of the track servo signal has been proposed.
JP 9-161282 (release date: June 20, 1997) JP-A-8-306057 (Publication date: November 22, 1996)

  2. Description of the Related Art In recent years, an optical disk device that optically records or reproduces information on an optical information recording medium called a BD (Blu-ray Disc) whose light transmission layer has a thickness of 0.1 mm is known. When the information recording surface is one layer, the thickness of the light transmission layer is 0.1 mm. However, when the information recording surface is two layers, the information recording layer on the side far from the objective lens is the first information recording layer (L0). Layer), and the information recording layer close to the objective lens is the second information recording layer (L1 layer), the information recording layer of the first information recording layer (L0 layer) and the second information recording layer (L1 layer) Since the interval is 0.025 mm, the thickness of the light transmission layer is 0.100 mm for the first information recording layer (L0 layer), and the thickness of the light transmission layer is for the second information recording layer (L1 layer). 0.075 mm.

  Therefore, when recording / reproducing the first information recording layer (L0 layer), as described above, since the information recording layer interval is 0.025 mm, the reflected light from the second information recording layer (L1 layer) is not reflected. It enters the photodetector as stray light. The reverse is also true.

  In particular, in an optical pickup device using a hologram element having high efficiency of 0th-order diffracted light with respect to ± 1st-order diffracted light, the light intensity of ± 1st-order diffracted light is much smaller than that of 0th-order diffracted light. When reflected light from another information recording layer is incident on the element, the ratio of stray light to signal light increases. Therefore, special attention is required when focus servo or track servo is formed using ± first-order diffracted light.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to record an information recording layer other than the information recording layer of an optical disc, which is an object of recording or reproduction, in an optical pickup device using a hologram element. Another object of the present invention is to provide an optical pickup device that is not easily affected by the reflected light from the surface of the optical disc and an optical disc device equipped with the optical pickup device.

  In order to solve the above problems, an optical pickup device according to the present invention collects a light source and a light beam from the light source in a target recording layer that is one of a plurality of recording layers of an optical information recording medium. An objective lens that emits light, a photodetector that receives reflected light reflected by the target recording layer, and a hologram element that is disposed between the objective lens and the photodetector and guides the reflected light to the photodetector The optical pickup device further includes a light shielding portion that blocks light incident on the central portion of the hologram element.

  According to said structure, the light beam radiate | emitted from the light source is condensed on the target recording layer which an optical information recording medium has with an objective lens. The reflected light reflected by the target recording layer is guided to the photodetector by the hologram element. At this time, the reflected light from a layer different from the target recording layer is collected near the center of the hologram element.

  Therefore, by providing a light blocking portion that blocks light incident on the central portion of the hologram element, it is possible to reduce the influence of stray light from a layer different from the target recording layer. As a result, an optical pickup device with a high S / N ratio can be realized.

  The light shielding portion is circular, and its diameter D1 is formed so as to satisfy D2 / 6 <D1 <D2 / 4, where D2 is the diameter of the light beam projected onto the hologram element. preferable.

  According to said structure, since the diameter of a light-shielding part is larger than 1/6 of the diameter of a light beam, the light which injects into the center part of a hologram element can be interrupted | blocked effectively. Further, since the diameter of the light shielding portion is smaller than ¼ of the diameter of the light beam, it is possible to reduce the possibility of preventing the generation of a signal such as a push-pull signal.

  Moreover, it is preferable that the said light-shielding part is formed by reducing the transmittance | permeability of the light of the said center part.

  According to said structure, the light-shielding part is formed as a part of hologram element in the center part of a hologram element. Therefore, the light can be blocked more reliably than when the light shielding portion is formed as a member different from the hologram element.

  Further, the reflectance of the light shielding part is preferably larger than 0.15 and smaller than 0.3.

  There is a possibility that the reflected light at the light shielding portion becomes unnecessary stray light. By limiting the reflectance of the light shielding portion to the above range, the possibility of unnecessary stray light occurring in the light shielding portion can be reduced.

  The light transmittance of the light shielding part is preferably greater than 0 and less than 0.2.

  With the above configuration, it is possible to effectively block light incident on the central portion of the hologram element.

  The efficiency of the + 1st order diffracted light, 0th order diffracted light and −1st order diffracted light transmitted through the hologram element is preferably in the range of 1: 8: 1 to 1: 12: 1.

  With the above configuration, the focus servo signal and the track servo signal can be obtained by the ± first-order diffracted light from the hologram element, and a sufficient S / N ratio can be secured for the reproduction signal.

  The hologram element is preferably divided into a plurality of regions for generating a plurality of types of signals.

  With the above configuration, it is possible to generate a light beam for generating a plurality of types of signals such as a push-pull signal, a focus error signal, and a lens shift signal from the hologram element.

  An optical disk apparatus according to the present invention includes the above-described optical pickup device, a rotating unit that rotates an optical information recording medium, and a reproduction control unit that reproduces information recorded on the optical information recording medium.

  With the above configuration, it is possible to reduce the influence of stray light from a layer different from the target recording layer. As a result, an optical disk device including an optical pickup device having a high S / N ratio can be realized.

  As described above, the optical pickup device according to the present invention is configured to include the light blocking unit that blocks the light incident on the central portion of the hologram element.

  Therefore, the influence of stray light from a layer different from the target recording layer can be reduced.

[Embodiment 1]
An embodiment of the present invention will be described below with reference to FIGS.

(Configuration of optical disc apparatus 200)
FIG. 2 is a schematic diagram showing a configuration of an optical disc device 200 including the optical pickup device 100 according to an embodiment of the present invention. As shown in the figure, an optical disc device 200 includes an optical pickup device 100 for recording and reproducing information on an optical disc (optical information recording medium) 112, a spindle motor (rotating means) 4 for rotating the optical disc 112, A control unit 20 that controls each unit of the optical disc apparatus 200 is provided. Details of the control unit 20 will be described later.

  The optical disc apparatus 200 also has other functions necessary for recording information on the optical disc 112 and reproducing information on the optical disc 112, but the description thereof is omitted because it is not directly related to the features of the present invention. To do.

(Configuration of optical disc 112)
FIG. 3 is a schematic diagram illustrating a configuration of the optical pickup device 100. In the present embodiment, as shown in FIG. 3, an optical disk device 200 for recording and reproducing information with respect to an optical disk 112 having two information recording layers will be described as an example. It may have three or more information recording layers.

  The optical disc 112 includes a light transmission layer 112a, a second information recording layer (L1 layer) 112b, a first information recording layer (L0 layer) 112c, and a substrate 112e. The first information recording layer 112c is formed at a position closer to the substrate 112e than the second information recording layer 112b (a side far from the objective lens).

  Regarding the thickness of the light transmission layer, the distance between the information recording layers of the first information recording layer 112c and the second information recording layer 112b is 0.025 mm, and therefore the light transmission layer for the first information recording layer 112c. Is 0.100 mm, and the thickness of the light transmission layer is 0.075 mm for the second information recording layer 112b.

(Configuration of optical pickup device 100)
As shown in FIG. 3, the optical pickup device 100 includes an integrated unit 101, a collimating lens 108, and an objective lens unit 115.

  The objective lens unit 115 includes a quarter-wave plate 109, an objective lens 110, an actuator 111, and an aperture stop 116. The quarter-wave plate 109, the objective lens 110, and the aperture stop 116 are fixed to the holder 120 of the actuator 111, and with respect to the target track of the first information recording layer 112c or the second information recording layer 112b of the optical disc 112. During the focusing operation and tracking operation of the objective lens 110, they are driven together.

  The objective lens 110 condenses the light beam from the semiconductor laser chip 102 that is a light source on a target recording layer that is one of a plurality of recording layers that the optical disc 112 has.

  The collimating lens 108 is disposed between the integrated unit 101 including the semiconductor laser chip 102 as a light source and the objective lens 110, and is a diffractive collimating lens in which chromatic aberration is corrected together with the objective lens 110.

  FIG. 1 is a perspective view showing the configuration of the integrated unit 101 and the photodetector 130. As shown in FIGS. 3 and 1, the integrated unit 101 includes a semiconductor laser chip 102, a photodetector 130, an optical branching element 140, and a polarization hologram (hologram element) 152.

  The semiconductor laser chip 102 functions as a light source and emits light in the 405 nm band.

  The photodetector 130 is provided between the semiconductor laser chip 102 and the polarization hologram 152, and the light reflected by the target recording layer of the optical disc 112 and diffracted by the polarization hologram 152 is received by the light receiving unit 131. Details of the photodetector 130 will be described later.

  The optical branching element 140 is provided between the semiconductor laser chip 102 and the photodetector 130 and has a role of an optical branching unit that transmits or reflects light depending on the polarization direction and branches the forward light and the backward light. is doing.

  The polarization hologram 152 is a hologram element that selectively performs an action of transmitting or diffracting light according to the polarization direction, and is between the objective lens 110 and the photodetector 130 (more precisely, the collimating lens 108 and Between the light detector 130 and the glass substrate 150. The efficiency of the + 1st order diffracted light, the 0th order diffracted light, and the −1st order diffracted light transmitted through the polarization hologram 152 is preferably in the range of 1: 8: 1 to 1: 12: 1.

  FIG. 4 is a schematic diagram showing divided areas of the polarization hologram 152. In the figure, the beam falling on the polarization hologram 152 is shown as a beam spot 155.

  The polarization hologram 152 includes a split line 157 passing through the center of the polarization hologram 152, split lines 158 and 159 that are parallel to the split line 157 and located on both sides of the split line 157 at a predetermined interval, and the polarization hologram 152 It is divided into six regions (regions 152a, 152b, 152c, 152d, 152e, and 152f) by a dividing line 160 that passes through the center and is orthogonal to the dividing line 157.

  Among these six regions, a push-pull signal is generated with the light transmitted through the regions 152c and 152d of the polarization hologram 152, and the light diffracted in the four regions 152a, 152b, 152e and 152f is calculated. A lens shift signal is generated. Further, a focus error signal is generated using the regions 152c and 152d.

  These six regions diffract the reflected light from the optical disk 112 in different directions. The light diffracted from each region is guided to the photodetector 130 together with ± 1st order light and used for signal generation. As a result, a total of 13 beams are generated by the polarization hologram 152 including the 0th-order diffracted light.

  That is, the polarization hologram 152 is divided into a plurality of regions for generating a plurality of types of signals.

  The light shielding unit 153 is a member that almost completely shields part of the light incident on the polarization hologram 152, and is a circular member having an intersection between the optical axis 113 passing through the center of the polarization hologram 152 and itself as a center. That is, the light shielding unit 153 blocks the reflected light that enters the vicinity of the center of the polarization hologram 152.

  The outer shape of the light shielding portion 153 may be circular, rectangular, or a combination of a straight line and an arc. However, the circular shape is a target for information recording or reproduction. Reflected light from information recording layers other than the information recording layer can be efficiently removed or reduced.

  The diameter D1 of the light shielding portion 153 is preferably configured to satisfy the relationship of D2 / 6 <D1 <D2 / 4, where D2 is the beam diameter on the polarization hologram 152.

  With this configuration, it is possible to obtain an objective lens shift signal that minimizes the signal light amount decrease in the return path and is not easily affected by the surface reflection of the light transmission layer 112a of the optical disc 112.

  Further, since the transmittance of the light shielding portion 153 is set to almost zero, if the diameter D1 of the light shielding portion 153 exceeds the above range, the light use efficiency is lowered in both the forward path and the backward path, and the reproduction signal characteristics are degraded. End up. Also in this respect, the diameter D1 of the light shielding part 153 is preferably within the above range.

(Configuration of the photodetector 130)
FIG. 5 is a schematic diagram showing the arrangement of light receiving elements included in the photodetector 130. As shown in the figure, the light receiving unit 131 receives a reproduction signal and generates a push-pull signal, and receives a zero-order diffracted light transmitted through the polarization hologram 152 (first light receiving element). Elements) 131a, 131b, 131c, 131d and an objective lens shift signal light receiving element (second light receiving element) 131i for receiving ± first-order diffracted light diffracted by the polarization hologram 152 in order to generate an objective lens shift signal. , 131j, 131k, 131l, 131m, 131n, 131o, and 131p, and a focus error signal light receiving element (second light receiving element) that receives ± first-order diffracted light diffracted by the polarization hologram 152 to generate a focus error signal. Element) 131e, 131f, 131g, 131h, 133, 134.

  The light receiving elements 131o and 131p receive ± 1st order diffracted light from the region 152a of the polarization hologram 152, the light receiving elements 131m and 131n receive ± 1st order diffracted light from the region 152b, and the light receiving elements 131g, 131h and 133 receive the region 152c. The light receiving elements 131e, 131f and 134 receive the ± 1st order diffracted light from the region 152d, and the light receiving elements 131k, 131l receive the ± 1st order diffracted light from the region 152e. 131 i and 131 j receive ± first-order diffracted light from the region 152 f.

  The objective lens shift signal light receiving elements 131i and 131j are internally connected, and after signals from these light receiving elements are added, they are output to an objective lens shift signal generating unit 25 described later. Similarly, the objective lens shift signal light receiving elements 131k and 131l, the objective lens shift signal light receiving elements 131m and 131n, and the objective lens shift signal light receiving elements 131o and 131p are added together, and then the objective lens shift is performed. The signal is output to the signal generator 25.

(Configuration of control unit 20)
As shown in FIG. 2, the control unit 20 includes a rotation control unit 21 and an optical pickup control unit 22.

  The rotation control unit 21 rotates the optical disc 112 by driving the spindle motor 4 under the control of the optical pickup control unit 22.

  The optical pickup control unit 22 is a reproduction control unit that reproduces information recorded on the optical disc 112 by controlling the optical pickup device 100, and includes a focus error signal generation unit 23, a main push-pull signal generation unit 24, and an objective lens shift. A signal generation unit 25, a track error signal generation unit 26, and a reproduction signal generation unit 27 are provided.

  Although the optical pickup control unit 22 has other functions for performing focus servo, tracking servo, and the like, the description thereof is omitted because it is not directly related to the feature point of the present invention.

  The focus error signal generation unit 23 generates a focus error signal FES based on a signal output from the focus error signal light receiving element. Specifically, assuming that the output signals based on the received light amounts at the focus error signal light receiving elements 131e, 131f, 131g, and 131h are S5, S6, S7, and S8, respectively, the focus error signal generation unit 23 is (S5 + S8). A focus error signal is generated by the calculation of-(S6 + S7).

  The main push-pull signal generation unit 24 generates a main push-pull signal based on the signal output from the push-pull signal light receiving element. Specifically, assuming that the output signals based on the amounts of light received by the push-pull signal light receiving elements 131a, 131b, 131c, and 131d are S1, S2, S3, and S4, respectively, the main push-pull signal generator 24 has (S1 + S2 )-(S3 + S4) to generate a main push-pull signal.

  The objective lens shift signal generation unit 25 generates an objective lens shift signal based on the signal output from the objective lens shift signal light receiving element. Specifically, the sum of the output signals of the objective lens shift signal light receiving elements 131i and 131j, the sum of the output signals of 131k and 131l, the sum of the output signals of 131m and 131n, and the sum of the output signals of 131o and 131p, respectively, Assuming S9, S10, S11, and S12, the objective lens shift signal generation unit 25 generates an objective lens shift signal by a calculation of (S9 + S11) − (S10 + S12).

  The track error signal generator 26 generates a track error signal based on the main push-pull signal generated by the main push-pull signal generator 24 and the objective lens shift signal generated by the objective lens shift signal generator 25. Specifically, the track error signal generation unit 26 generates a track error signal by an operation of {(S1 + S2) − (S3 + S4)} − α {(S9 + S11) − (S10 + S12)}. Here, α is a predetermined coefficient, and is a value set as appropriate by the user.

  The reproduction signal generation unit 27 generates a reproduction signal based on the signal output from the push-pull signal light receiving element. Specifically, the reproduction signal generation unit 27 generates a reproduction signal by performing a calculation of (S1 + S2 + S3 + S4).

(Processing in optical disc apparatus 200)
Next, an example of a processing flow in the optical disc apparatus 200 will be described in detail. In the following, a case where recording / reproduction is performed on the second information recording layer 112b will be described. However, similar processing is performed when recording / reproduction is performed on the first information recording layer 112c.

  First, the linearly polarized light in the X direction in FIG. 3 emitted from the semiconductor laser chip 102 passes through the optical branching element 140, the polarization hologram 152, and the collimating lens 108, and then the polarization direction is circular by the quarter wavelength plate 109. Converted to polarized light.

  Thereafter, the emitted light passes through the objective lens 110 and is condensed on the second information recording layer 112b of the optical disc 112.

  The circularly polarized reflected light (returned light) reflected by the second information recording layer 112b is converted into linearly polarized light in the Y direction in FIG. That is, the reflected light from the second information recording layer 112b is not the X-direction linearly polarized light emitted from the semiconductor laser chip 2, but the Y-direction linearly polarized light. Therefore, the return light is diffracted by the polarization hologram 152 due to the difference in polarization direction.

  At this time, the stray light 117 reflected by the first information recording layer 112 c is substantially condensed on the polarization hologram 152. Since a light shielding portion 153 that completely shields light is formed above the center portion of the polarization hologram 152, light that becomes stray light reflected from the first information recording layer 112 c by the light shielding portion 153 is converted into the polarization hologram 152. Can be cut above.

  Next, a plurality of light beams generated by the polarization hologram 152 are reflected by the light branching element 140 (reflected light 161), and the corresponding light receiving elements (push-pull signal light receiving elements 131a, 131b, 131c) included in the photodetector 130 are provided. , 131d, 131n, 131o, 131p, any one of focus error signal light receiving elements 131e, 131f, 131g, 131h, and objective lens shift signal light receiving elements 131i, 131j, 131k, 131l, 131m).

  The push-pull signal light receiving elements 131a, 131b, 131c, and 131d output an output signal based on the amount of received light to the main push-pull signal generation unit 24 and the reproduction signal generation unit 27.

  The main push-pull signal generation unit 24 generates a main push-pull signal by the above calculation using an output signal from the light receiving element for push-pull signal, and outputs the generated main push-pull signal to the track error signal generation unit 26. To do.

  The reproduction signal generation unit 27 generates a reproduction signal by the above-described calculation using the output signal from the push-pull signal light receiving element. The generated reproduction signal is output to a host computer (not shown) provided in the optical disc apparatus 200.

  On the other hand, the focus error signal light receiving elements 131e, 131f, 131g, and 131h output an output signal based on the amount of received light to the focus error signal generation unit 23.

  The focus error signal generation unit 23 generates a focus error signal by the above-described calculation using the output signal from the focus error signal light receiving element.

  On the other hand, the objective lens shift signal light receiving elements 131i, 131j, 131k, 131l, 131m, 131n, 131o, and 131p output an output signal based on the amount of received light to the objective lens shift signal generation unit 25.

  The objective lens shift signal generation unit 25 uses the output signal from the objective lens shift signal light receiving element to generate an objective lens shift signal by the above-described calculation, and sends the generated objective lens shift signal to the track error signal generation unit 26. Output.

  The track error signal generation unit 26 uses the main push-pull signal output from the main push-pull signal generation unit 24 and the objective lens shift signal output from the objective lens shift signal generation unit 25 to perform the track error signal by the above calculation. Is generated.

  The optical pickup control unit 22 adjusts the focus of the objective lens 110 based on the generated focus error signal and adjusts the position of the objective lens 110 based on the track error signal.

  The light intensity ratio of -1st order diffracted light: 0th order diffracted light: 1st order diffracted light at the polarization hologram 152 is 1: 8: 1 to 1: 12: 1, so that the focus servo is performed by ± 1st order diffracted light at the polarization hologram. A signal and a track servo signal can be obtained, and a sufficient S / N ratio can be secured for the reproduction signal.

  In the configuration of the polarization hologram 152 described above, the light amount of the 0th-order diffracted light is 8 to 12 times larger than the light amount of the ± 1st-order diffracted light. Therefore, care must be taken so that the 0th-order diffracted light from the polarization hologram 152 does not enter the light-receiving elements (the objective lens shift signal light-receiving element and the focus error signal light-receiving element) for receiving ± first-order diffracted light.

(Arrangement of light receiving elements in photodetector 130)
Here, the arrangement of the light receiving element for the objective lens shift signal and the light receiving element for the focus error signal will be described.

  During recording or reproduction of the optical disc 112, reflected light from an information recording layer (referred to as a non-target recording layer) other than an information recording layer (referred to as a target recording layer) that is a target of information recording or reproduction is reflected on the photodetector 130. May be incident on the light receiving part.

  For example, during reproduction of the first information recording layer 112c, reflected light from the second information recording layer 112b may pass through the polarization hologram 152 (0th order diffraction) and enter the photodetector 130.

  When the reflected light from the non-target recording layer, which is diffracted by the 0th order by the polarization hologram 152, enters the light receiving element for the objective lens shift signal and the light receiving element for the focus error signal that receive the ± 1st order diffracted light, The ratio increases and the S / N ratio decreases.

  Therefore, it is preferable to dispose these light receiving elements at a position where there is a low possibility that the reflected light from the non-target recording layer is incident on the objective lens shift signal light receiving element and the focus error signal light receiving element.

  Specifically, when the focal length of the objective lens 110 is f1, the focal length of the collimating lens 108 is f2, the recording layer interval of the optical disk 112 is S, and the refractive index of the light transmission layer 112a is n, the photodetector 130 is. The objective lens shift signal is received outside the circular region of radius R2 = (2 × s / n) (f2 / f1), centered on the intersection of the optical axis of the 0th-order diffracted light incident on the substrate and the substrate of the light receiving unit 131. It is preferable to arrange an element and a light receiving element for focus error signal.

  With this configuration, it is possible to reduce the possibility that the reflected light from the non-target recording layer enters the light receiving element of the photodetector 130, and the signal quality of the focus error signal and / or the track error signal by the reflected light from the non-target recording layer. Can be reduced.

(Influence of reflected light on light transmitting layer surface 112d)
Next, the influence of the reflected light on the light transmission layer surface 112d will be described.

  When the thickness of the light transmission layer is about 0.1 to 0.075 mm, the influence of the reflected light on the light transmission layer surface 112d cannot be ignored. In view of this, it is preferable to dispose these light receiving elements at positions where it is unlikely that the reflected light from the surface 112d of the light transmission layer is incident on the light receiving element for the objective lens shift signal and the light receiving element for the focus error signal.

  Specifically, when the focal length of the objective lens 110 is f1, the focal length of the collimating lens 108 is f2, the maximum thickness of the light transmission layer 112a is t, and the refractive index of the light transmission layer 112a is n, The objective lens is shifted to the outside of a circular region having a radius R3 = (2 × t / n) (f2 / f1), with the intersection of the optical axis of the 0th-order diffracted light incident on the detector 130 and the substrate of the photodetector 130 as the center. It is preferable to arrange a signal light receiving element and a focus error signal light receiving element.

  The refractive index of the light transmission layer 112a is, for example, 1.59, and the maximum value of the thickness of the light transmission layer is the distance between the light transmission layer surface 112d and the information recording layer farthest from the light incident surface. Here, the layer interval between the light transmission layer surface 112d and the first information recording layer 112c is 0.1 mm.

  Here, the reason why the maximum value t of the light transmission layer thickness is used is that the thickness of the light transmission layer 112a is larger when the size of the reflected light from the light transmission layer surface 112d on the photodetector 130 is considered. This is because the irradiation range of the reflected light from the light transmission layer surface 112d on the photodetector 130 becomes larger in the case of being larger (here, in the case of reproducing the information of the first information recording layer 112c).

  Note that the layer between the second information recording layer 112b and the first information recording layer 112c also has a role as a light transmission layer.

(Example of arrangement change)
In the above description, the arrangement in which the reflected light from the light transmission layer surface 112d does not enter the objective lens shift signal light receiving element and the focus error signal light receiving element has been described, but at least the objective lens shift signal light receiving element is It is preferable to arrange it outside the circular region of radius R3 = (2 × t / n) (f2 / f1).

  The reason for this is that in the case of a light receiving element for focus error signal, even if the reflected light on the light transmitting layer surface 112d is incident, if the change due to the amount of light reflected on the light transmitting layer surface 112d is Δ, the focus error The signal FES becomes (S5 + ΔA + S8 + ΔB) − (S6 + ΔC + S7 + ΔD), and since ΔA≈ΔC and ΔB≈ΔD, the influence is cancelled.

  On the other hand, in the case of the light receiving element for the objective lens shift signal, the objective lens shift signal is (S9 + ΔE + S11 + ΔF) − (S10 + ΔG + S12 + ΔH), and ΔG and ΔH increase / decrease with respect to ΔE and ΔF (ΔE and ΔF When the value is positive, the values of ΔG and ΔH are negative, and when the values of ΔE and ΔF are negative, the values of ΔG and ΔH are positive.

  Therefore, when the position of the reflected light on the light transmission layer surface 112d moves on the objective lens shift signal light receiving element during the objective lens shift, an offset occurs in the objective lens shift signal compared to the focus error signal FES. It becomes easy. Therefore, it is preferable to dispose the light receiving element for objective lens shift signal outside the circular region having the radius R3 = (2 × t / n) (f2 / f1).

  The light receiving element for focus error signal is less affected by reflected light than the light receiving element for objective lens shift signal. However, when the thickness of the light transmission layer 112a varies by several μm around 100 μm, the light receiving element Since the irradiation range and intensity of the reflected light from the surface of the light transmission layer above change, it becomes a disturbance to the focus error signal. In this respect, it is preferable that the reflected light from the light transmission layer surface 112d is not received by the focus error signal light receiving element.

(Lens shift characteristics of optical pickup device 100)
FIG. 6A is a diagram showing the objective lens shift characteristic of the optical pickup device 100 having the light shielding portion 153. When compared with the objective lens shift characteristic of the optical pickup device having no light shielding portion in FIG. 6B, it can be seen that the amount of offset generation of the tracking signal with respect to the objective lens shift is reduced.

(Example of change)
Instead of disposing the light-shielding part 153 above the center part of the polarization hologram 152, the center part 156 (see FIG. 4) of the polarization hologram 152 itself may be set so that its transmittance is lower than other areas. That is, a light shielding portion that cuts the stray light component from the other layer of the optical disk 112 by lowering the transmittance may be formed in the central portion of the polarization hologram 152. In this case, the same effect can be obtained.

  At this time, as described above, the diameter D1A of the central portion 156 of the polarization hologram 152 is configured to satisfy the relationship of D2 / 6 <D1A <D2 / 4, where D2 is the beam diameter on the polarization hologram 152. It is preferred that

  Further, if the reflectance of the central portion 156 of the polarization hologram 152 is RA and the transmittance is TA, both are defined to satisfy 0.15 <RA <0.3 and 0 <TA <0.2, respectively. Is preferred.

  When reproducing a two-layer disc, the reflected light from a recording layer different from the reproducing layer is collected on the polarization hologram, so that the influence of other layer stray light can be reduced by lowering the transmittance at the center. it can. Further, since the reflected light from the polarization hologram 152 may become unnecessary stray light, the allowable range of the reflectance of the central portion 156 is limited to the above range. Each of the above numerical values is obtained by experiment.

  Thereby, even if the objective lens 110 is shifted, a change in the amount of light received by the light receiving element for push-pull signal can be reduced, and a push-pull signal with a small offset can be obtained.

[Embodiment 2]
The following will describe another embodiment of the present invention with reference to FIGS. In addition, about the member similar to Embodiment 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

(Configuration of optical pickup device 300)
FIG. 7 is a schematic diagram showing the configuration of the optical pickup device 300 according to the second embodiment of the present invention. Unlike the optical pickup device 100, the optical pickup device 300 includes an integrated unit 201.

  In the integrated unit 201, an aperture limiting element 270 is provided on the surface of the polarization hologram 252 to shield the outer peripheral portion of the reflected light from the light transmission layer surface 112d. Other configurations of the integrated unit 201 are the same as those of the integrated unit 101.

(Significance of aperture limiting element 270)
As described above, when the thickness of the light transmission layer 112a is about 0.1 to 0.075 mm, the influence of the reflected light on the light transmission layer surface 112d cannot be ignored. Therefore, in the first embodiment, as shown in FIG. 5, the focal length of the objective lens 110 is f1, the focal length of the collimating lens 108 is f2, the maximum thickness of the light transmission layer 112a is t, and the refractive index is n. In this case, the objective lens shift signal light receiving element and the focus outside the circular region of radius R3 = (2 × t / n) (f2 / f1) centering on the optical axis of the 0th-order diffracted light on the photodetector 130. It has been described that it is preferable to arrange an error signal light receiving element.

  On the other hand, the light receiving element for the objective lens shift signal and the light receiving element for the focus error signal are arranged outside the circular region having the radius R3 = (2 × t / n) (f2 / f1) due to the package size limitation of the photodetector 130. It also occurs when it is not possible. In such a case, the reflected light on the light transmission layer surface 112d is relatively reduced in size on the photodetector, so that the reflected light on the light transmission layer surface 112d becomes a focus error signal or a track error signal. It can be made to have no effect.

  As a means for this, as shown in FIG. 7, an aperture limiting element 270 that shields the outer peripheral portion of the reflected light from the light transmitting layer surface 112 d is added to the surface of the polarization hologram 252.

  Here, the reason for shielding the outer peripheral portion of the reflected light from the light transmitting layer surface 112d will be described. The reflected light from the surface 112d of the light transmission layer is reflected from a layer in front of the first information recording layer 112c and the second information recording layer 112b, and therefore returns from the objective lens 110 to the photodetector 130. The return optical system is not limited to one point. Therefore, it is not possible to use a light shielding film (such as the light shielding part 153 of the first embodiment) that cuts only the stray light component. Further, since the reflected light from the light transmitting layer surface 112d has both the signal light and the optical axis, it is preferable to shield the outer peripheral portion of the reflected light from the light transmitting layer surface 112d.

(Configuration and arrangement of aperture limiting element 270)
FIG. 8 is a schematic diagram showing the configuration of the aperture limiting element 270. As shown in the figure, the opening limiting element 270 has an opening 271 and a light shielding part 272.

  The material of the light shielding part 272 may be any material as long as it can shield the reflected light from the light transmitting layer surface 112d. However, in the case of a reflective film, the light reflected by the reflective film part causes stray light. A material that absorbs the wavelength 405 nm band of the light source is preferable.

  As shown in FIG. 7, the aperture limiting element 270 is preferably disposed between the polarization hologram 252 and the collimating lens 108 or between the polarization hologram 252 and the light branching element 140.

  The difference in the beam diameter between the signal light from the first information recording layer 112c or the second information recording layer 112b and the reflected light from the light transmission layer surface 112d becomes closer to the photodetector 130 side. Thus, when the outer peripheral portion of the reflected light from the light transmission layer surface 112d is shielded, it is conceivable to place the aperture limiting element 270 as close to the photodetector 130 as possible.

  However, if the aperture limiting element 270 is disposed immediately before the photodetector 130 (for example, between the photodetector 130 and the optical branching element 140), the ± first-order diffracted light generated by the polarization hologram 252 is generated by the aperture limiting element 270. Light shielding is performed by the light shielding portion 272.

  Conversely, when the aperture limiting element 270 is disposed immediately after the collimating lens 108, the signal light from the first information recording layer 112c or the second information recording layer 112b and the reflection from the light transmission layer surface 112d. The light cannot be separated sufficiently.

  From the above, the position h of the aperture limiting element 270 shown in FIG. 6 is 0.25 × f2 or more and 0.5 × f2 or less from the semiconductor laser chip 102 when the focal length of the collimating lens 108 is f2. Is preferred.

(Example of change)
The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and embodiments obtained by appropriately combining technical means disclosed in different embodiments. Is also included in the technical scope of the present invention.

  For example, the polarization hologram 252 and the aperture limiting element 270 can be integrated. In this case, as shown in FIG. 8, the aperture can be limited so as to have an asymmetric shape in at least one direction. By doing so, it is possible to easily determine the vertical direction, the left-right direction, and the front and back of the polarization hologram 252 with respect to the optical pickup device 300, so that workability is improved.

  The asymmetric shape may be other than the shape shown in FIG. Although the opening 271 has been described as a circle, the shape of the opening 271 is not limited to a circle, and may be an ellipse or a polygon as long as the reflected light from the surface 112d of the light transmission layer can be blocked.

  Further, when a single semiconductor laser and a packaged photodetector are used, the same effect as that of the above-described embodiment can be obtained.

  In the above description, the case where a two-layer optical disk is used as the optical disk has been described. However, the same effect can be obtained when a multilayer optical disk having three or more layers is used.

  The present invention can also be expressed as follows.

That is, the optical pickup device of the present invention is disposed between a light source, an objective lens for condensing a light beam from the light source on an information recording surface of an optical information recording medium, the light source and the objective lens, A diffractive collimating lens corrected with chromatic aberration in combination with an objective lens, a light splitting element disposed between the light source and the collimating lens, a hologram element having high efficiency of zero-order diffracted light with respect to ± first-order diffracted light, and the information recording A first light-receiving element that receives 0th-order diffracted light that is reflected by the surface and then passes through the hologram element; and second and third light-receiving elements that receive ± 1st-order diffracted light diffracted by the hologram element Having a photodetector,
While obtaining a reproduction signal and a push-pull signal from the information recording surface according to the amount of light received by the first light receiving element of the zero-order diffracted light from the hologram element,
An objective lens shift signal is detected according to the amount of light received by the second light receiving element when ± 1st order diffracted light from the hologram element is received, and a focus error signal is generated according to the amount of light received by the third light receiving element. It is characterized by obtaining.

  In the optical pickup device, it is preferable that the efficiency of the + 1st order diffracted light: 0th order diffracted light: -1st order diffracted light of the hologram element is in a range of 1: 8: 1 to 1: 12: 1.

  In the optical pickup device, the hologram element is divided into first, second, third, and fourth regions by first, second, and third dividing lines orthogonal to a track tangential direction of the optical information recording medium. The first and fourth regions are further divided into two by a fourth dividing line substantially parallel to the track tangential direction, and two regions including push-pull signals; Preferably, the objective lens shift signal is obtained from ± 1st order diffracted light of the hologram element, and a track error signal is obtained from the push-pull signal and the objective lens shift signal.

  In the optical pickup device, it is preferable that the hologram element has a light shielding portion at a central portion.

  In the optical pickup device, the diameter D1 of the light shielding portion of the hologram element is preferably configured to satisfy D2 / 6 <D1 <D2 / 4, where D2 is a beam diameter on the hologram element.

  In the optical pickup device, it is preferable that the hologram element is set to have a lower transmittance in the central portion than in other regions.

  In the optical pickup device, the diameter D1 of the light shielding portion of the hologram element is preferably configured to satisfy D2 / 6 <D1 <D2 / 4, where D2 is a beam diameter on the hologram element.

In the optical pickup device, the reflectance RA and the transmittance TA of the central portion A of the hologram element are:
0.15 <RA <0.3,
0 <TA <0.2
It is preferable that

  The drive device of the present invention comprises at least rotation means and reproduction control means for the optical information recording medium in addition to the optical pickup device.

  According to the present invention, when optically recording or reproducing information with respect to an information recording medium having a plurality of information recording layers, it is difficult to be influenced by reflected light from portions other than the target information recording layer. An optical pickup device can be realized.

It is a perspective view which shows the structure of the integrated unit with which the optical pick-up apparatus which concerns on one Embodiment of this invention is equipped, and a photodetector. It is the schematic which shows the structure of an optical disk apparatus provided with the said optical pick-up apparatus. It is the schematic which shows the structure of the said optical pick-up apparatus. It is the schematic which shows the division area | region of the hologram element with which the said optical pick-up apparatus is provided. It is the schematic which shows arrangement | positioning of the light receiving element which the photodetector with which the said optical pick-up apparatus is provided has. 6 is a graph showing the amount of tracking signal offset generated with respect to the objective lens shift, where (a) relates to an optical pickup device having a light shielding portion, and (b) relates to a conventional optical pickup device having no light shielding portion. It is. It is the schematic which shows the structure of the optical pick-up apparatus which concerns on another embodiment of this invention. It is the schematic which shows the structure of the aperture limiting element with which the said optical pick-up apparatus is provided. It is the schematic which shows the structure of the conventional optical pick-up apparatus. It is the schematic which shows the hologram element with which the conventional optical pick-up apparatus is provided, and a photodetector.

Explanation of symbols

22 Optical pickup control unit (reproduction control means)
100 Optical Pickup Device 101 Integrated Unit 102 Semiconductor Laser Chip (Light Source)
108 collimating lens 110 objective lens 112 optical disc (optical information recording medium)
112a Light transmission layer 112b Second information recording layer 112c First information recording layer 130 Photodetectors 131a, 131b, 131c, 131d Push-pull signal light receiving elements 131e, 131f, 131g, 131h Focus error signal light receiving elements 131i, 131j, 131k, 131l Objective lens shift signal light receiving element 131m, 131n, 131o, 131p Objective lens shift signal light receiving element 152 Polarization hologram (hologram element)
153 Shading part 156 Center part (shading part)
200 Optical Disk Device 200 Optical Pickup Device 201 Integrated Unit 252 Polarization Hologram (Hologram Element)
270 Opening limiting element 271 Opening 272 Light-shielding part

Claims (8)

A light source;
An objective lens that focuses the light beam from the light source onto a target recording layer that is one of a plurality of recording layers of the optical information recording medium;
A photodetector for receiving the reflected light reflected by the target recording layer;
An optical pickup device including a hologram element that is disposed between the objective lens and the photodetector and guides the reflected light to the photodetector,
An optical pickup device, further comprising a light blocking portion that blocks light incident on a central portion of the hologram element.   The light-shielding portion is circular, and the diameter D1 is formed so as to satisfy D2 / 6 <D1 <D2 / 4, where D2 is the diameter of the light beam projected onto the hologram element. The optical pickup device according to claim 1.   3. The optical pickup device according to claim 1, wherein the light shielding portion is formed by reducing light transmittance of the central portion.   4. The optical pickup device according to claim 1, wherein a reflectance of the light shielding portion is larger than 0.15 and smaller than 0.3. 5.   5. The optical pickup device according to claim 1, wherein the light transmittance of the light shielding portion is greater than 0 and smaller than 0.2.   6. The efficiency of + 1st order diffracted light, 0th order diffracted light, and −1st order diffracted light transmitted through the hologram element is in the range of 1: 8: 1 to 1: 12: 1. 2. An optical pickup device according to item 1.   The optical pickup device according to claim 1, wherein the hologram element is divided into a plurality of regions for generating a plurality of types of signals. The optical pickup device according to any one of claims 1 to 7,
A rotating means for rotating the optical information recording medium;
An optical disc apparatus comprising: reproduction control means for reproducing information recorded on the optical information recording medium.

Images