JP2009009630A - Optical pickup device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device for obtaining a stable signal having an improved S/N ratio at low cost even for a multilayered optical disk. <P>SOLUTION: Second order diffracted light reflected on a first signal surface for reproducing an optical disk and diffracted by a diffraction type optical element is condensed at light reception cells 9A-9D in a photo detector 9 as spots 21a-21d. Light reflected on the first signal surface and diffracted in the order other than the secondorder and light reflected on a second signal surface and diffracted in the second order become crosstalk light. The generation of first diffracted light 23a-23d, negative first order diffracted light 24a-24d, negative second order diffracted light 25a-25d, third order diffracted light 26a-26d, and negative third order diffracted light 27a-27d from the first signal surface are prevented. The spots of the second-order diffracted light from the second signal surface are prevented from being formed onto all the light reception cells. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention includes a diffractive optical element having a plurality of divided regions between an objective lens and a photodetector, and is good not only for an optical disk having a signal surface on a single layer but also for an optical disk having a signal surface on multiple layers. The present invention relates to an optical pickup device that can perform proper recording or reproduction.

 In an optical disk, which is a disk-shaped optical recording medium, spiral or concentric tracks are formed on a transparent substrate. Since information such as video information, audio information, and computer data can be recorded with high density on this track, and a desired track can be accessed at high speed when the recorded track is reproduced, an optical disc is generally used. It is frequently used as a recording medium.

  CDs (Compact Discs) and DVDs (Digital versatile discs) are already on the market as optical discs of this type, and recently, two types of high-density optical recording media with higher densities and higher capacities have been distributed. Yes. That is, BD (Blu-ray Disc) and HD-DVD (High Definition DVD).

  In addition, in order to increase the capacity of each optical disc, development and standardization of a multilayer optical disc (hereinafter simply referred to as a multilayer optical disc) having a signal surface in a plurality of layers is progressing. Optical discs having a signal surface on one side and two layers of DVD-ROM and DVD-R (hereinafter referred to as single-sided dual-layer optical discs) are already on the market, and DVD-RW, BD, and HD-DVD are also being standardized on single-sided dual-layer optical discs. It is out. Furthermore, at a recent conference, the development of BD 4-layer optical disc and 8-layer optical disc was announced.

  By the way, in the above optical pickup device for reproducing a single-sided dual-layer optical disc of DVD, a tracking error signal called a DPD signal is detected using a DPD (Differential Phase Detection) method (phase difference tracking method) using one beam. The DPD method is a method for obtaining a DPD signal based on a phase difference of a light intensity modulation signal obtained by receiving light reflected from a signal surface of an optical disk (hereinafter referred to as reflected light). However, for recordable optical discs such as DVD-R and DVD-RW, DPD signals can be detected after signal recording, but DPD signals cannot be detected before signal recording. Therefore, a tracking error signal called a DPP signal is detected for a DVD recording type optical disc by using a 3-beam DPP (Differential Push Pull) method (differential push-pull method). The DPP method is a method of obtaining a tracking error signal without an offset by taking a difference between a push-pull signal of a main beam and a push-pull signal of front and rear sub-beams.

  In an HD-DVD that is recorded or reproduced using a blue laser light source having a wavelength of about 405 nm, the same tracking error signal detection method as that of the above-described DVD is used for the reproduction type and recording type optical discs. On the other hand, in the BD of another standard for recording or reproducing using a blue laser light source having a wavelength of about 405 nm, the DPD signal can be detected in the BD-ROM, but the DPD signal can be detected in the state after the signal recording in the recording optical disk. It is not guaranteed as a standard. Therefore, it is common to detect the DPP signal in both the recording type and the reproducing type.

  Here, when the DPP method is used in a single-sided dual-layer optical disc, there are the following problems. Reflected light from the signal surface of another layer that has not been recorded or reproduced, that is, a defocused layer (hereinafter referred to as another layer) enters the photodetector as unnecessary crosstalk light, and is recorded or reproduced. Coherent noise is generated by overlapping with the reflected light from the signal surface of the layer (hereinafter referred to as recording / reproducing layer). The behavior due to this coherent noise is determined by the optical path difference between two interfering lights, that is, the optical path difference due to the interlayer distance of the optical disk. Further, the behavior due to the noise is also affected by the fluctuation of the interlayer distance depending on the track position of the optical disc, the tilt state of the optical disc, and the recording track (groove) being reproduced.

  When the DPP signal is used, the light amount of the sub beam is set smaller than that of the main beam in order to prevent erroneous recording due to the sub beam at the time of recording and to use light efficiently. For this reason, since the sub-beam is more greatly affected by the crosstalk light than the main light, the above-mentioned problem occurs remarkably.

  The influence of the crosstalk light has also occurred in the case of a single-sided dual-layer optical disc of DVD. However, it has been reported that BD cannot perform more stable recording and reproduction as compared with DVD (for example, see Non-Patent Document 1). The reason is as follows. First, the interlayer distance is narrower than that of the DVD, the optical path difference is reduced, and the numerical aperture (NA) of the objective lens is higher than that of the DVD, so that the spot size of the crosstalk light is increased. Secondly, in the blue laser light source having a wavelength of 405 nm, the laser coherence is improved.

  Therefore, as a method for solving these problems, a tracking error signal detection method using an APP (Advanced Push Pull) method (advanced push pull method) using a one-beam method has been proposed (for example, see Non-Patent Document 2). .

  17 is a configuration diagram of an example of a detection system of a conventional optical pickup device described in Non-Patent Document 2, and FIG. 18 is a diagram of a HOE pattern (far field pattern) used in the detection system of the conventional optical pickup device described in Non-Patent Document 2. FIG. 19 is a diagram showing an example, and FIG. 19 is a diagram showing an example of the spread of crosstalk light in the conventional optical pickup device described in Non-Patent Document 2.

  The operation of the conventional optical pickup device until the reflected light from the optical disk is received by a PD (photodetector) will be briefly described with reference to FIGS. In FIG. 17, the focus error signal is detected as follows. Reflected light from the signal surface of the optical disk is transmitted without being diffracted by a hologram optical element (hereinafter referred to as “HOE”) 101, becomes convergent light through the lens 102, and astigmatism is given through the cylindrical lens 103. The light is received on the focus PD 104 and detected.

  On the other hand, the tracking error signal is detected as follows. The reflected light from the signal surface of the optical disk is diffracted by the HOE 101, passes through the lens 102, becomes convergent light, the astigmatism caused by the HOE 101 is canceled by the cylindrical lens 103, and is received by the tracking PD 105 (105A to 105D). Detected.

  FIG. 18 shows a pattern of the HOE 101, and the HOE 101 is divided into five areas 101A to 101E. FIG. 19 shows the states of the signal detection light spot and the crosstalk light spot in the focusing PD 104 and tracking PD 105. Light reflected from the signal surface of the recording / reproducing layer and not diffracted by the HOE 101 forms a spot 106 in the light receiving unit 104 and becomes signal detection light for detecting a focus error signal.

  The light reflected from the signal surface of the recording / reproducing layer and diffracted in the region 101A forms a spot 107A on the PD 105A, and the light diffracted in the region 101B forms a spot 107B on the PD 105B and diffracted in the region 101C. Forms a spot 107C on the PD 105C, and the light diffracted in the region 101D forms a spot 107D on the PD 105D, and each becomes a signal detection light for detecting a tracking signal. Further, the light reflected from the signal surface of the recording / reproducing layer and diffracted in the region 101E forms a spot 107E, and is not irradiated onto the focusing PD 104 and the tracking PD 105.

  Next, crosstalk light from the signal surface of the other layer will be described. The spot 108 by the crosstalk light reflected from the signal surface of the other layer and not diffracted by the HOE 101 is irradiated on the focusing PD 104 but not on the tracking PD 105. The crosstalk light reflected from the signal surface of the other layer and diffracted in the region 101A is the spot 109A, the crosstalk light diffracted in the region 101B is the spot 109B, the crosstalk light diffracted in the region 101C is the spot 109C, Since the crosstalk light diffracted in the region 101D forms spots 107D and is located around the tracking PD 105, it is not irradiated onto the tracking PD 105.

Further, the crosstalk light diffracted in the region 101E forms a spot 109E, is positioned on the left and right of the focusing PD 104, and is not irradiated onto the tracking PD 105. The tracking error signal TAPP uses the APP method when the electrical signal obtained by the PD 105A is TA, the electrical signal obtained by the PD 105B is TB, the electrical signal obtained by the PD 105C is TC, and the electrical signal obtained by the PD 105D is TD. And is calculated by the following equation (2).
TAPP = TC-TD-Tk. (TA-TB) (2)
Here, Tk is a constant.

  As another method for solving the problem of crosstalk light, a tracking error signal detection method using the PP method using the one-beam method has been proposed as in Non-Patent Document 2 (for example, see Non-Patent Document 3). . FIG. 20 is a structural diagram of an example of a liquid crystal element used in the detection system of the conventional optical pickup device described in Non-Patent Document 3, and FIG. 21 shows a beam spot on the light receiving cell of the conventional optical pickup device described in Non-Patent Document 3. It is the figure which showed the state to form.

  The operation until the reflected light from the signal surface of the optical disk in the conventional optical pickup device described in Non-Patent Document 3 is detected will be briefly described with reference to FIGS. As shown in FIG. 20A, the liquid crystal element 110 has three layers, and is formed in the order of a non-polarization HOE 111, a liquid crystal active rotator 112, and a polarization HOE 113 from the optical disc (not shown) side.

  As shown in FIG. 20B, the non-polarized HOE 111 is a diffractive element having a lens effect in order to detect a focus error signal, and generates ± first-order diffracted light. The liquid crystal active rotator 112 changes the polarization direction according to voltage on (ON) and off (OFF). The polarization HOE 113 is composed of a stack of a recording pattern 113A shown in FIG. 20C and a reproduction pattern 113B shown in FIG.

  When a recording type tracking error signal is detected, the voltage is turned off by the liquid crystal active rotator 112, and the exit polarization direction is changed to a direction perpendicular to the incident polarization direction. Then, as shown in FIG. 21A, the recording pattern 113A of the polarized light HOE 113 is acted to receive the 0th order, 1st order and −1st order diffracted light on the PD 114, and the same APP as in Non-Patent Document 2. A tracking error signal is detected using the method. At this time, the central region 113E of the recording pattern 113A is excluded from the calculation of the tracking error signal to reduce the influence of the crosstalk light.

  On the other hand, when a regenerative tracking error signal is detected, the voltage is turned on by the liquid crystal active rotator 112 so that the incident polarization direction and the exit polarization direction are the same. Then, as shown in FIG. 21B, the reproduction-type pattern 113B of the polarization HOE 113 is acted to receive the 0th, 1st, and −1st order diffracted light on the PD 114, and the tracking error signal is detected using the DPD method. Is detected.

Alexander van der Lee, et.al., "Drive consideration for multilayer discs", ISOM06 Technical Digest P.30 Mo-C-5 Kousei SANO, et.al., "Novel One-Beam Tracking Detection Method for Dual-Layer Blu-ray Discs", Japanese Journal of Applied Physics Vol. 45, No. 2B, 2006, pp. 1174-1177 (Fig. 4 FIG. 6 and FIG. 7) Noriaki Nishi et.al., "Novel One-Beam Detection Method with Changeable Multi Division Patterns", Proc. Of SPIEVol.6282,62821H-1 (Figs. 4 and 5)

  In the conventional optical pickup device described in Non-Patent Document 2 described with reference to FIGS. 17 to 19, the tracking error signal is stabilized so that the tracking PD 105 is not affected by the crosstalk light. However, since the focus PD 104, the tracking PD 105, and the detection beam are divided into two and the signal obtained from the focus PD 104 cannot be used for the detection of the main signal, the signal output is reduced, and the S / N of the signal detection is reduced. Decreases. In particular, this is a significant problem when performing high-speed playback.

  Further, in the conventional optical pickup device described in Non-Patent Document 3 described with reference to FIGS. 20 and 21, it is possible to detect the recording type and the reproduction type tracking error signal while reducing the influence of the crosstalk light. However, since there are many expensive parts such as the liquid crystal active rotator 112 and the two patterns of polarization HOEs 113A and 113B, there is a problem that the entire apparatus becomes expensive.

  The present invention has been made in view of such problems, and obtains a stable signal with good S / N at low cost when information is recorded on or reproduced from a multilayer optical disk. An object of the present invention is to provide an optical pickup device that can be used.

The present invention provides an optical pickup device having the following configuration in order to solve the above-described problems of the prior art.
A laser light source (2) for emitting laser light, a collimator lens (4) for converting light (LS) emitted from the laser light source (2) into substantially parallel light, and collecting the substantially parallel light, the first An objective lens (7) for forming a spot on the first (10B1) or the second signal surface (10B2) with respect to the optical disc having the signal surface (10B1) and the second signal surface (10B2); (10B1) or a plurality of dividing lines (8i, 8j) in which at least two dividing lines (8i, 8j) are arranged so as to pass through the substantially luminous flux center of the reflected light (LT) from the second signal surface (10B2). And each region (8A to 8D) that is divided by a plurality of dividing lines (8i, 8j) and has a step-shaped diffraction structure with the number of steps q, and the reflected light (LT) is converted into a diffraction order m (m is Diffractive optical element that diffracts in a predetermined direction by an integer other than 0) (8) and signal detection light diffracted in a predetermined direction by the diffractive optical element (8) and provided with astigmatism are individually received, and signal detection light (21a to 21d) is generated by astigmatism 2 And a photodetector (9) having a plurality of light receiving cells (9A to 9D) arranged at a position where the circle of least confusion is approximately in the middle of two focal lines, and when q ≧ 4, the absolute value of m | m | Is an optical pickup device (1) that satisfies the following expression (1).
| M | ≦ INT [(q−2) / 2] (1)
Here, INT [(q-2) / 2] is an integer part of (q-2) / 2.

Further, a laser light source (2) for emitting laser light, a collimator lens (4) for converting light (LS) emitted from the laser light source (2) into substantially parallel light, and condensing the substantially parallel light, An objective lens (7) that forms a spot on the first (10B1) or the second signal surface (10B2) with respect to the optical disc (10) having the first signal surface (10B1) and the second signal surface (10B2). ) And the track of the optical disc (10), the first dividing line (50i) is arranged in a direction perpendicular to the track direction, and the second dividing line (50j) is the first dividing line (50i). ) And an angle direction of 40 ° or more and 50 ° or less, and the third dividing line (50k) is arranged at an angle direction of −50 ° or more and −40 ° or less with respect to the first dividing line (50i). The first, second and third dividing lines (50i, 50j, 50k) are 1 (10B1)) or three dividing lines (50i, 50j, 50k) arranged so as to pass through substantially the center of the luminous flux of the reflected light from the second signal surface (10B2) and three dividing lines. And a diffractive optical element that diffracts reflected light (LT) in a predetermined direction by a diffraction order m (m is an integer other than 0). (50) and signal detection lights (61a to 61f) diffracted in a predetermined direction by the diffractive optical element (50) and provided with astigmatism are individually received, and the signal detection lights (61a to 61f) are not received. A photodetector (51) having a plurality of light receiving cells (51A to 51F) arranged at a position where the circle of least confusion is approximately in the middle of two focal lines generated by point aberration, and when q ≧ 4, m The absolute value of | m | is light that satisfies the following equation (1) A pickup device (1).
| M | ≦ INT [(q−2) / 2] (1)
Here, INT [(q-2) / 2] is an integer part of (q-2) / 2.

  Furthermore, it is the reflected light from the signal surface which is not recorded or reproduced among the first (10B1) and the second signal surface (10B2), and any region (8A to 8D, 50A to 50F) of the diffractive optical element. ) So that the crosstalk light (28a to 28d, 66a to 66f) diffracted by the diffraction order m is not irradiated to any of the light receiving cells (9A to 9D, 51A to 51F). -9D, 51A-51F) is an optical pickup device (1).

  According to the optical pickup device of the present invention, the reflected light from the signal surface of the recording / reproducing layer is incident on the diffractive optical element, and the crosstalk light diffracted in the order other than the signal detection light is reflected on all the light receiving cells. It is set as the structure which does not irradiate. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained.

  In addition, the reflected light from the signal surface of the other layer is incident on the diffractive optical element, and the crosstalk light diffracted with the same order as the signal detection light is not irradiated onto all the light receiving cells. Therefore, a more stable focus error signal and tracking error signal with good S / N can be obtained.

  In addition, the cost is low because only one diffractive optical element is used without using expensive parts such as a liquid crystal element and crosstalk light is not irradiated onto the light receiving cell.

<First Embodiment>
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing an overall configuration of an optical pickup device 1 of the present invention. The optical pickup device 1 uses a laser beam LS having a wavelength λ = 405 nm emitted from a light source 2 to record on an optical disc (BD) 10 having a single-sided signal surface 10B of Blu-ray standard, or an optical disc 10 is a device that reproduces information from 10. The optical disk 10 has a thickness t1 = 0.075 mm from the light incident surface 10A to the first signal surface 10B1, and a thickness t2 = 0.1 mm from the second signal surface 10B2.

  The objective lens 7 is designed to focus the laser beam optimally when the thickness between the first and second signal surfaces is 0.0875 mm. When recording or reproducing is performed on the first signal surface 10B1, the collimator lens 4 is moved in the optical path direction, and the light emitted from the collimator lens 4 is slightly converged light, so that recording or reproduction can be performed satisfactorily. . Further, when recording or reproduction is performed on the second signal surface 10B2, the collimator lens 4 is moved in the optical path direction so that the light emitted from the collimator lens 4 is slightly divergent light, so that recording or reproduction can be performed satisfactorily. Can do. Hereinafter, the first signal surface 10B1 will be described as the signal surface of the recording / reproducing layer, and the second signal surface 10B2 will be described as the signal surface of the other layer.

  The laser light LS emitted from the light emitting point 2P of the laser light source 2 is p-polarized linearly polarized light and passes through the optical path separation element 3. The optical path separation element 3 may be a polarizing beam splitter, a half mirror, or the like as long as it has a function of separating light traveling from the laser light source 2 toward the optical disk 10 and light reflected from the optical disk 10 toward the photodetector 9. . The element shape may be square or flat. Here, the optical path separation element 3 will be described as a polarization beam splitter.

  The light incident on the polarization beam splitter 3 passes through the polarization-selective dielectric multilayer film 3A that transmits p-polarized light and reflects s-polarized light, and then is slightly converged by the collimator lens 4 and reflected by the flat mirror 5 The light is deflected at an angle of 90 ° by the film 5A, given a phase difference of λ / 4 by the quarter wavelength plate 6, becomes circularly polarized light, and enters the objective lens 7. The beam obtained by focusing by the objective lens 7 is incident from the light incident surface 10A of the optical disk 10, and is condensed on the signal surface 10B1 of the recording / reproducing layer with good aberration to be recorded or reproduced. .

  Then, the reflected light LT from the signal surface 10B1 of the recording / reproducing layer re-enters the objective lens 7, becomes slightly divergent light by the objective lens 7, enters the quarter-wave plate 6 and has a wavelength of λ / 4. A phase difference is given and it becomes s-polarized linearly polarized light. Thereafter, the light is deflected at an angle of 90 ° by the reflective film 5 A of the flat mirror 5, becomes convergent light by the collimator lens 4, and enters the polarizing beam splitter 3.

  FIG. 2 shows the detection system of the optical pickup device 1 in detail. As shown in FIG. 2, the s-polarized reflected light LT that has entered the polarization beam splitter 3 is reflected by the polarization-selective dielectric multilayer film 3A, is incident on the diffractive optical element 8, and is divided into each divided region of the HOE surface 8Z. And diffracted in a predetermined direction by the diffraction order m, and third-order astigmatism (hereinafter simply referred to as astigmatism) is given. As a means for giving astigmatism, each divided area of HOE8Z may be used, or a cylindrical lens or the like may be used, but in this embodiment, astigmatism is given to each divided area of HOE8Z. The diffracted light to which astigmatism is given is received as a spot of the signal detection light by the light receiving cell on the light receiving surface of the photodetector 9. Thereafter, photoelectric conversion is performed, and a tracking error signal, a focus error signal, and a main data signal are calculated for each electrical signal according to a predetermined arithmetic expression described later.

  Next, a detection system of the optical pickup device 1 which is a main part of the present invention will be described with reference to FIGS. 3 is a diagram showing the divided regions 8A to 8D of the HOE surface 8Z, FIG. 4 is a diagram showing a part of the cross section of the HOE surface 8Z in FIG. 3, and FIG. 5 is a light receiving cell of the photodetector 9. FIG. 6 is a diagram showing the arrangement of 9A to 9D, and FIG. 6 is a diagram showing the effective distance N1 on the emission side and the effective distance N2 on the detection side in FIG.

  In FIG. 3, the reflected light LT reflected by the polarization beam splitter 3 and incident on the diffractive optical element 8 is predetermined by the diffraction order m in the four divided regions 8A to 8D on the HOE surface 8Z of the diffractive optical element 8. Diffracted in the direction. As the diffraction order m, any integer other than 0 can be used.

  As shown in FIG. 3, the four divided regions 8A to 8D are divided by two dividing lines 8i and 8j passing through the optical axis center 8P. The two dividing lines 8i and 8j are arranged in an angle direction of ± 45 ° with respect to a direction perpendicular to the direction of the track when the track of the optical disk 10 is projected on the HOE surface 8Z (hereinafter referred to as a radial direction). Is done. Each of the divided regions 8A to 8D has a hologram pattern having a different staircase-shaped diffraction structure, and is configured to give astigmatism to light diffracted by the diffraction order m. Accordingly, diffracted light to which four astigmatisms are imparted is generated corresponding to each of the four divided regions 8A to 8D. In the state where there is no lens shift or lens tilt at the objective lens 7, the light flux center of the reflected light from the signal surface 10B1 of the recording / reproducing layer passes through the substantially optical axis center 8P of the HOE surface 8Z. In addition, the combination of the divided regions 8A to 8D is circular, but may be oval or rectangular.

  FIG. 4 shows an example of the staircase shape of the divided regions 8A to 8D on the HOE surface 8Z. The number of stages q in FIG. 4 shows a case where q = 4, but the number of stages q may be an arbitrary integer of 4 or more. Note that if the light amounts of the diffracted lights diffracted in the divided regions 8A to 8D are different, the S / N of a focus error signal and a tracking error signal described later deteriorates. Therefore, it is desirable that the number of stages q of the divided regions 8A to 8D is the same.

  Thereafter, the four diffracted lights to which astigmatism is given are received by forming spots of signal detection light on the light receiving cells 9A to 9D arranged on the light receiving surface of the photodetector 9 shown in FIG. The The light receiving cells 9A to 9D are arranged according to the diffraction directions of the divided regions 8A to 8D of the HOE surface 8Z, and the light diffracted by the diffraction order m in the divided region 8A spans the light receiving cells 9A (9A1 and 9A2). A spot of signal detection light is formed and received. Similarly, the light diffracted by the diffraction order m in the divided region 8B is on the light receiving cell 9B (straddles 9B1 and 9B2), and the light diffracted by the diffraction order m in the divided region 8C is on the light receiving cell 9C. The light diffracted by the diffraction order m at 8D is received on the light receiving cell 9D by forming a spot of signal detection light.

  The optical axis center 8P of the HOE surface 8Z and the light receiving surface center 9P on the light receiving surface of the photodetector 9 substantially coincide with each other in the optical axis direction. The light receiving surface center 9P is a position where the 0th-order diffracted light transmitted without being diffracted in the divided regions 8A to 8D is substantially condensed. Further, it is desirable that the distance from the middle point 9R of the light receiving cells 9A and 9B to the light receiving surface center 9P is substantially equal to the distance from the middle point 9S of the light receiving cells 9C and 9D to the light receiving surface center 9P. The reason is that if the distances are greatly different, the diffraction pitches of the hologram patterns in the divided regions 8A to 8D are changed, and the respective light amounts in the light receiving cells 9A to 9D are different.

  When the track of the optical disk 10 is projected onto the light receiving surface of the photodetector 9, the light receiving cell 9A is divided into two light receiving cells 9A1 and 9A2 in the radial direction. Similarly, the light receiving cell 9B is divided into two light receiving cells 9B1 and 9B2 in the radial direction. In order to calculate the focus error signal using the astigmatism method described later, each of the light receiving cells 9A and 9B needs to be divided into two. Further, astigmatism is generally given in the 45 ° direction, and when the astigmatism is given in the 45 ° direction in the divided regions 8A and 8B, the spot at the position of the minimum circle of confusion rotates 90 °. . Therefore, it is desirable that the light receiving cells 9A and 9B are divided in the radial direction.

  The spot of each signal detection light on each of the light receiving cells 9A to 9D has a fan shape corresponding to the divided areas 8A to 8D as will be described later. However, there is no divided area, and a circular holographic pattern forms a minimum circle of confusion. When considered as a circular spot, it has appropriate astigmatism and no other aberration occurs. Then, since the spot becomes a minimum circle of confusion in the middle of two focal lines generated by astigmatism, the light receiving cells 9A to 9D are arranged at this intermediate position. Further, the astigmatism given in the divided regions 8A to 8D is good in the same direction and at 45 ° in at least 8A and 8B. However, in consideration of adjustment of the optical pickup device 1 by servo signals such as a focus error signal and a tracking error signal, astigmatism given in all the divided regions 8A to 8D is in the same direction and in a 45 ° direction. Is desirable. Astigmatism may be given by inserting a cylindrical lens separately from the hologram pattern.

  In FIG. 6, the effective distance N1 is the effective distance from the light emitting point 2P of the laser light source 2 to the incident surface of the polarizing beam splitter 3, and the effective distance N2 is the effective distance N2 from the exit surface of the polarizing beam splitter 3 to the light receiving surface center 9P. Show. The effective distances N1 and N2 mean air conversion distances determined by the refractive index of the glass material. When the effective distances N1 and N2 are equal, the 0th-order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and transmitted through the divided regions 8A to 8D on the HOE surface 8Z without any diffraction action is received. Light is collected at the surface center 9P. That is, the light emitting point 2P of the laser light source 2 and the light receiving surface center 9P of the photodetector 9 have a conjugate arrangement.

  Further, the distance from the middle point 9R to the light receiving surface center 9P shown in FIG. 4 is substantially equal to the distance from the middle point 9S to the light receiving surface center 9P. However, the distances from the divided regions 8A to 8D to the corresponding light receiving cells 9A to 9D are slightly different from each other. Therefore, in order to receive the light diffracted by the diffraction order m in each divided region 8A to 8D on the same plane and with the same spot radius, different power components are required in each divided region 8A to 8D. The power component corresponds to a lens action and means the diffractive surface power.

  Next, crosstalk light will be described. The crosstalk light includes reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted by a diffraction order other than m in each of the divided regions 8A to 8D on the HOE surface 8Z, and signals of other layers. There is crosstalk light that is reflected from the surface 10B2 and diffracted by the diffraction order m in each of the divided regions 8A to 8D on the HOE surface 8Z.

  The spots generated from the signal surface 10B1 of the recording / reproducing layer will be described with reference to FIG. In the first embodiment, the diffraction order m used as the signal detection light is m = 2. Therefore, the second-order diffracted light reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 8A to 8D of the HOE surface 8Z forms spots 21a to 21d and becomes signal detection light.

  Diffracted light other than the signal detection light becomes crosstalk light and forms spots around the light receiving cells 9A to 9D. The zero-order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and transmitted through the divided regions 8A to 8D of the HOE surface 8Z without any diffraction action forms a spot 22. Since the spot 22 is focused on the light receiving surface center 9P of the photodetector 9 and is not irradiated onto the light receiving cells 9A to 9D, it does not affect each signal described later.

  The second-order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 8A to 8D of the HOE surface 8Z is spotted at a position that is in contrast to the spots 21a to 21d when viewed from the light receiving surface center 9P. 23a to 23d are formed. The first-order diffracted light reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 8A to 8D of the HOE surface 8Z is closer to the light receiving surface center 9P than the spots 21a to 21d. Form. Since the first-order diffracted light has a diffraction angle that is ½ times that of the second-order diffracted light, the distance between the light receiving surface center 9P and the spots 24a to 24d is approximately ½ times the distance between the light receiving surface center 9P and the spots 21a to 21d. is there. The −1st order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted in each of the divided regions 8A to 8D of the HOE surface 8Z is spotted at positions symmetrical to the spots 24a to 24d when viewed from the light receiving surface center 9P. 25a to 25d are formed. Similarly, the third-order diffracted light reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 8A to 8D of the HOE surface 8Z is the spots 26a to 26d, and the third-order diffracted light is the spots 27a to 27d. Form. These crosstalk lights form spots with more aberrations than the signal detection lights 21a to 21d. Therefore, the size of the spot due to the crosstalk light is larger than the size of the spot serving as the signal detection light.

  By the way, the position of each spot may be shifted from the design position due to a wavelength shift from the design wavelength in the optical pickup device 1, a temperature change, an adjustment error during assembly, and the like. Therefore, it is necessary to prevent the spots formed by the crosstalk light from shifting and irradiating the light receiving cells 9A to 9D.

  As described above, the distance from the midpoint 9R of the light receiving cells 9A and 9B to the light receiving surface center 9P is substantially equal to the distance from the midpoint 9S of the light receiving cells 9C and 9D to the light receiving surface center 9P. Therefore, it is necessary to take care not to irradiate the light receiving cells 9A to 9D by shifting the spot formed by the crosstalk light to the periphery of the position symmetrical to the signal detection light when viewed from the light receiving surface center 9P. .

  As shown in FIG. 7, spots 23a to 23d, 24a to 24d, 25a to 25d, 26a to 26d, and 27a to 27d are formed around the light receiving cells 9A to 9D by crosstalk light. Spots around these light receiving cells 9A to 9D are formed by crosstalk light diffracted by the diffraction order | m ± 1 | in the divided regions 8A to 8D on the HOE surface 8Z. Here, | m ± 1 | represents the absolute value of m ± 1. Therefore, in order to prevent the spots formed by the crosstalk light from being irradiated on the light receiving cells 9A to 9D, diffracted light of the diffraction order | m ± 1 | is not generated.

表１より、段数ｑ＝３の場合、回折次数３の周期で回折光が生じる。 Next, the relationship between the step number q of the staircase shape of the HOE surface 8Z and the diffraction efficiency will be described with reference to Tables 1 to 3. Table 1 shows the diffraction efficiency of each diffraction order when the maximum diffraction efficiency is obtained with the number of stages q = 3 and the diffraction order m = 1.

From Table 1, when the number of stages q = 3, diffracted light is generated with a period of diffraction order 3.

表２より、段数ｑ＝４の場合、回折次数４の周期で回折光が生じる。 Table 2 shows the diffraction efficiency of each diffraction order when the maximum diffraction efficiency is obtained with the number of stages q = 4 and the diffraction order m = 1.

From Table 2, when the number of stages q = 4, diffracted light is generated with a period of diffraction order 4.

表３より、段数ｑ＝８の場合、回折次数８の周期で回折光が生じる。 Table 3 shows the diffraction efficiency of each diffraction order when the maximum diffraction efficiency is obtained with the number of stages q = 8 and the diffraction order m = 2.

From Table 3, when the number of stages q = 8, diffracted light is generated with a period of diffraction order 8.

As shown in Tables 1 to 3, diffracted light is generated with a period of the diffraction order q with respect to the stage number q. Therefore, the condition that diffracted light of the diffraction order | m ± 1 | is not generated is that when q ≧ 4, the absolute value | m | of m satisfies the following expression (3).
| M | ≦ INT [(q−2) / 2] (3)
Here, INT [(q-2) / 2] represents the integer part of (q-2) / 2.

  By satisfying the expression (3), a stable signal with good S / N can be obtained without irradiating the spot formed by shifting the crosstalk light on the light receiving cells 9A to 9D.

  The crosstalk light generated from the signal surface 10B2 of the other layer will be described with reference to FIG. Since the crosstalk light from the other layer 10B2 spreads greatly according to the magnification and the local light quantity is small, there is no need to consider the crosstalk light having a low diffraction efficiency. Therefore, only the diffracted light having the same diffraction order m = 2 as that of the signal detection light needs to be considered as the crosstalk light. In FIG. 8, the light reflected from the signal surface 10B2 of the other layer and diffracted by the diffraction order m = 2 in the divided regions 8A to 8D of the HOE surface 8Z forms spots 28a to 28d. And the spots 28a-28d spread in a fan shape in the direction rotated 90 degrees with respect to the spots 21a-21d. Therefore, the spots 28a to 28d can be hardly irradiated onto the light receiving cells 9A to 9D by the HOE dividing method of FIG. 3 and the arrangement of the light receiving cells of FIG. Therefore, a more stable signal with good S / N can be obtained without irradiating the light receiving cells 9A to 9D with the crosstalk light from the other layer 10B2.

  FIG. 9 is a diagram showing an S curve and a spot shape for obtaining a focus error signal. FIG. 9A shows a spot shape on the light receiving cells 9A and 9B when the optical disk 10 is close to the objective lens 7 and the S curve is maximized. At this time, most of the spots 21a and 21b of the signal detection light are irradiated to the light receiving cells 9A1 and 9B2, and only a few spots 21a and 21b are irradiated to the light receiving cells 9A2 and 9B1. FIG. 9B shows a spot shape on the light receiving cells 9A and 9B when the optical disk 10 is far from the objective lens 7 and the S curve is minimized. At this time, most of the spots 21a and 21b are irradiated to the light receiving cells 9A2 and 9B1, and only a few spots 21a and 21b are irradiated to the light receiving cells 9A1 and 9B2. Then, by changing the focus and calculating the focus error signal FE, a good S curve characteristic can be obtained as shown in FIG. In FIG. 9C, the horizontal axis indicates the defocus amount (one scale of 4 μm), and the vertical axis indicates the level of the focus error signal FE1. This is when the maximum level of the focus error signal FE1 in FIG. 9C is shown in FIG. 8A and the minimum level is shown in FIG. 9B. When there is no defocus at all, the uniform fan-shaped spots 21a and 21b shown in FIG. 7 are formed.

FIG. 10 shows a circuit system diagram of an arithmetic circuit in the photodetector 9. This circuit calculates a focus error signal FE1, tracking error signals PP1 and APP1, and a main signal RF1. First, a method for calculating the focus error signal FE1 will be described with reference to FIG. An electric signal A11 obtained from the light receiving cell 9A1, an electric signal A12 obtained from the light receiving cell 9A2, an electric signal B11 obtained from the light receiving cell 9B1, an electric signal B12 obtained from the light receiving cell 9B2, an adder 31, 32 and a subtractor 37. And is calculated by the following equation (4).
FE1 = (A11 + B12) − (A12 + B11) (4)
As shown in equation (4), since a general astigmatism method can be used for focus error detection, the optical pickup device 1 can easily cope with a conventional FEP (front end processor).

  FIG. 11 is a diagram showing spots 45 and 46 formed by reflection from the signal surface 10B1 of the recording / reproducing layer on the HOE surface 8Z. 11A shows a case where recording or playback is performed on a Blu-ray standard optical disc (BD), and FIG. 11B shows a case where recording or playback is performed on an HD-DVD standard optical disc (HD-DVD). is there. Reflected light spots 45 and 46 from the signal surface 10B1 of the recording / reproducing layer have overlapping portions 45a of primary light diffracted by tracks and pits (hereinafter referred to as tracks) and zero-order light not subjected to diffraction action. , 46a. A so-called push-pull signal component is obtained when the overlapping portions 45a and 46a interfere with each other to cause a difference in right and left light intensity.

  The size of the overlapping portions 45a and 46a is determined by the standard of the optical disc, and the ratio of the overlapping portions 45a and 46a differs between BD and HD-DVD. The overlapping ratio of the 0th order light and the 1st order light is uniquely determined by the numerical aperture of the objective lens 7, the wavelength of the laser light LS, and the track pitch on the signal surface 10B1 of the recording / reproducing layer.

  When the HOE plane 8Z is divided at the dividing lines 8i and 8j in FIG. 3 (the angle between the dividing lines is ± 45 ° with respect to the radial direction), the dividing lines 8i and 8j in the case of BD The dividing lines 8i and 8j in the case of HD DVD only have a margin of about 14% with respect to the radius of the spot 46. However, in the case of BD, the wavelength is 405 nm, the track pitch is 0.32 μm, the numerical aperture is 0.85, and in the case of HD DVD, the wavelength is 405 nm, the track pitch is 0.4 μm, and the numerical aperture is 0.65.

  According to the dividing lines 8i and 8j in FIG. 3, the overlapping portions 45a and 46a are not irradiated onto the dividing regions 8A and 8B used in the calculation of the focus error signal FE. Therefore, since the light quantity change hardly occurs when crossing the track, the fluctuation of the focus error signal FE due to the track crossing does not occur. On the contrary, since the overlapping portions 45a and 46a are not included more than necessary, the influence of the diffracted light due to the period twice the track pitch can be excluded from the focus error signal FE. In the case of BD, when the angle formed by the dividing line 8i and the radial direction is 41.8 ° or less, the overlapping portions 45a and 46a intersect with the dividing line 8i. Similarly, when the angle formed by the dividing line 8j and the radial direction is −41.8 ° or more, the overlapping portions 45a and 46a intersect with the dividing line 8j.

  In the case of HD-DVD, when the angle formed by the dividing line 8i and the radial direction is 39.7 ° or less, the overlapping portions 45a and 46a intersect with the dividing line 8i. Similarly, when the angle formed by the dividing line 8j and the radial direction is −39.7 ° or more, the overlapping portions 45a and 46a intersect with the dividing line 8j. It is not preferable that the dividing lines 8i and 8j slightly intersect the divided areas 8A and 8B, and that the portion where the 0th-order light and the primary light do not overlap is included more than necessary. Considering the above conditions, it is preferable that the angle formed between the dividing line 8i and the radial direction is 40 ° to 50 °, and the angle formed between the dividing line 8j and the radial direction is −50 ° to −40 °. As shown in FIG. 3, it is most desirable that the angle formed between the dividing line 8i and the radial direction is 45 °, and the angle formed between the dividing line 8j and the radial direction is −45 °.

Next, a method for calculating the tracking error signal will be described. An electric signal C1 is obtained by the light receiving cell 9C, and an electric signal D1 is obtained by the light receiving cell 9D. The electric signals C1 and D1 include a push-pull signal component. Therefore, the tracking error signal PP1 by the normal PP (Push Pull) method (push pull method) is calculated by the following equation (5) using the electric signals C1 and D1 and the subtractor 36.
PP1 = C1-D1 (5)

By the way, a tracking error signal based on the normal PP method or DPP method is known as a signal in which an offset occurs when the optical disc is tilted or shifted in the radial direction. The aforementioned APP method is known as a tracking error detection method in which the offset is reduced. The tracking error signal APP1 by the APP method is calculated by the following equation (6) using the electric signals A11 to D1, adders 33 and 34, subtractors 36, 39, and 42, and a multiplier 40.
APP1 = (C1-D1) -k1. [(A11 + B11)-(A12 + B12)] (6)
Here, k1 is a multiplication coefficient of the multiplier 40.

  The tracking error signal APP1 can reduce not only the offset such as the lens shift described above but also the offset generated at the boundary of the recording mark. That is, the offset generated at the boundary of the recording mark can be reduced by correcting with the DC component obtained by taking the difference between the signal A12 and the signal B12 from the sum of the signal A11 and the signal B11. Note that the multiplication coefficient k1 is optimized to correct the offset at the lens shift and the recording boundary, and to reduce the occurrence of the offset even if there is a disturbance or the like. As described above, the tracking error signals PP1 and APP1 can be obtained by the 1-beam method without using the 3-beam method.

The main signal RF1 is calculated by the following equation (7) using the electrical signals A11 to D1 and the adders 31, 32, 33, 38, and 41.
RF1 = A11 + A12 + B11 + B12 + C1 + D1 (7)

  As described above, when the expression (3) is satisfied, a spot formed by crosstalk light reflected from the signal surface of the recording / reproducing layer and diffracted by the HOE surface is generated around the light receiving cell. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained. Further, as shown in FIG. 8, the spot formed by the crosstalk light reflected from the signal surface of the other layer and diffracted by the HOE surface is not irradiated on all the light receiving cells. A more stable focus error signal and tracking error signal with good S / N can be obtained.

  Further, as shown in FIGS. 3 and 5, since it is composed of one diffractive optical element and a small number of light receiving cells, it is possible to prevent the crosstalk light from being irradiated onto the light receiving cells at low cost. In addition, since the single beam system is used, there is an advantage that a grating is not necessary, and it is possible to cope with a plurality of types of optical disks having different track pitches such as BD and HD-DVD.

<Second Embodiment>
The second embodiment of the present invention will be described in detail with reference to FIGS. 12 to 16 with a focus on differences from the first embodiment. In the second embodiment, a diffractive optical element 50 is used in place of the diffractive optical element 8 of the first embodiment, and a photodetector 51 is used in place of the photodetector 9 (FIGS. 1 and 2). reference). Other components are the same as those in FIGS. 1 and 2, and the arrangement of optical components is also the same.

FIG. 12 is a diagram showing a six-divided pattern of the diffractive optical element 50, and FIG. 13 is a diagram showing the arrangement of the light receiving cells 51 </ b> A to 51 </ b> F of the photodetector 51. The six divided regions 50A to 50F of the HOE surface 50Z are divided by three dividing lines 50i, 50j, and 50k passing through the optical axis center 50P. The dividing line 50i is in the same direction as the radial direction, and the dividing lines 50j and 50k are arranged in the ± 45 ° direction with respect to the dividing line 50i. Each of the divided regions 50A to 50F has a hologram pattern having a different diffraction structure, and is configured to give astigmatism to light diffracted by the diffraction order m. Therefore, six diffracted lights to which astigmatism is imparted corresponding to the six divided regions 50A to 50F are generated. Similar to the first embodiment, in the state where there is no lens shift or lens tilt at the objective lens 7, the light beam center of the reflected light from the optical disk 10 passes through the substantially optical axis center 50P of the HOE surface 50Z. As in FIG. 4 of the first embodiment, the divided regions 50A to 50F on the HOE surface 50Z are formed of a step-shaped diffraction structure having the number of steps q.

  After that, the diffracted light to which the six astigmatisms are given is received by forming signal detection light spots on the light receiving cells 51A to 51F arranged on the light receiving surface of the photodetector 51 shown in FIG. The light receiving cells 51A to 51F are arranged according to the diffraction directions of the divided regions 50A to 50F of the HOE surface 50Z, and the light diffracted by the diffraction order m in the divided region 50A spans the light receiving cells 51A (51A1 and 51A2). Is received. Similarly, the light diffracted by the diffraction order m in the divided region 50B is received by the light receiving cell 51B (stretches 51B1 and 51B2), and the light diffracted by the diffraction order m in the divided region 50C is diffracted by the light receiving cell 51C by the divided region 50D. The light diffracted by the order m is received by the light receiving cell 51D, the light diffracted by the diffraction order m in the divided region 50E is received by the light receiving cell 51E, and the light diffracted by the diffraction order m in the divided region 50F is received by the light receiving cell 51F. Spots of detection light are formed and received respectively.

 The optical axis center 50P of the HOE surface 50Z and the light receiving surface center 51P on the light receiving surface of the photodetector 51 substantially coincide with each other in the optical axis direction. The light receiving surface center 51P is a position where the 0th-order diffracted light transmitted without being diffracted by the divided regions 51A to 51F is substantially condensed. For the same reason as in the first embodiment, the distance from the midpoint 51Q of the light receiving cells 51A, 51B to the light receiving surface center 51P, the distance from the midpoint 51R of 51C, 51E to the light receiving surface center 51P, the light receiving cell 51D. , 51F from the midpoint 51S to the light receiving surface center 51P are substantially equal.

  When the track of the optical disk 10 is projected onto the light receiving surface of the photodetector 51, the light receiving cell 51A is divided into two light receiving cells 51A1 and 51A2 in the radial direction. Similarly, the light receiving cell 51B is divided into two light receiving cells 51B1 and 51B2 in the radial direction. Also, the direction of astigmatism is the same as in the first embodiment.

  The spot of each signal detection light on each of the light receiving cells 51A to 51F has a fan shape corresponding to the divided areas 50A to 50F, but has a circular spot that has no divided area and is a circle of minimum confusion with a circular hologram pattern. When considered, it has appropriate astigmatism and no other aberration occurs. Then, since the spot becomes a minimum circle of confusion approximately in the middle of two focal lines caused by astigmatism, the light receiving cells 51A to 51F are arranged at the intermediate position. Similarly to the first embodiment, the light emission point 2P of the laser light source 2 and the light receiving surface center 51P of the photodetector 51 have a conjugate arrangement.

  The spots generated from the signal surface 10B1 of the recording / reproducing layer will be described with reference to FIG. In the second embodiment, the diffraction order m used as the signal detection light is m = 1. Therefore, the first-order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 8A to 8D of the HOE surface 8Z forms spots 61a to 61f and becomes signal detection light.

  Diffracted light other than the signal detection light becomes crosstalk light and forms spots around the light receiving cells 51A to 51F. The zero-order diffracted light that is reflected from the signal surface 10B1 of the recording / reproducing layer and transmitted through the divided regions 50A to 50F of the HOE surface 8Z without receiving any diffraction action forms a spot 62. Since the spot 62 is focused on the light receiving surface center 51P of the photodetector 51 and is not irradiated on the light receiving cells 51A to 51F, it does not affect each signal described later.

  The minus first-order diffracted light, which is reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted in each of the divided regions 50A to 50F of the HOE surface 50Z, is spot 63a at a position contrasted with the spots 61a to 61f when viewed from the light receiving surface center 9P. ~ 63f are formed. Similarly, the second-order diffracted light reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the divided regions 50A to 50F of the HOE surface 50Z is the spots 64a to 64f, and the -second-order diffracted light is the spots 65a to 65f. Form. These crosstalk lights form spots with more aberrations than the signal detection lights 61a to 61f. Therefore, the size of the spot due to the crosstalk light is larger than the size of the spot serving as the signal detection light.

  As in the first embodiment, it is necessary to prevent the spots formed by these crosstalk lights from shifting and irradiating the light receiving cells 51A to 51F. As shown in FIG. 15, spots 62, 63a to 63f, 64a to 64f, and 65a to 65f are formed around the light receiving cells 51A to 51F by crosstalk light. Spots around these light receiving cells 51A to 51F are formed by crosstalk light diffracted by the diffraction order | m ± 1 | in the divided regions 50A to 50F on the HOE surface 50Z. Therefore, in order to prevent the spots formed by these crosstalk lights from being irradiated on the light receiving cells 51A to 51F, diffracted light of the diffraction order | m ± 1 | is not generated.

  As in the first embodiment, diffracted light is generated with a period of the diffraction order q with respect to the stage number q. Therefore, the condition that diffracted light of the diffraction order | m ± 1 | is not generated when q ≧ 4 (3 ) Is satisfied. By satisfying the expression (3), a stable signal with good S / N can be obtained without irradiating the spot formed by shifting the crosstalk light on the light receiving cells 51A to 51F.

  The crosstalk light generated from the signal surface 10B2 of the other layer will be described with reference to FIG. Similar to the first embodiment, the crosstalk light from the signal surface 10B2 of the other layer greatly spreads in accordance with the magnification, and the local light quantity is small. Therefore, it is not necessary to consider the crosstalk light with low diffraction efficiency. Therefore, only the diffracted light having the same diffraction order m = 1 as the signal detection light needs to be considered as the crosstalk light. In FIG. 15, the light reflected from the signal surface 10B2 of the other layer and diffracted by the diffraction order m = 1 in the divided regions 50A to 50F of the HOE surface 50Z forms spots 66a to 66f. And the spots 66a-66f spread in a fan shape in the direction rotated 90 degrees with respect to the spots 61a-61f. Therefore, the spots 66a to 66f can be hardly irradiated onto the light receiving cells 51A to 51F by the HOE dividing method of FIG. 12 and the arrangement of the light receiving cells of FIG. Therefore, a more stable signal with good S / N can be obtained without irradiating the light receiving cells 51A to 51F with the crosstalk light from the other layer 10B2.

FIG. 16 shows a circuit system diagram of an arithmetic circuit in the photodetector 51. This circuit calculates a focus error signal FE2, tracking error signals PP2 and APP2, and a main signal RF2. First, a method for calculating the focus error signal FE2 will be described with reference to FIG. An electric signal A21 obtained from the light receiving cell 51A1, an electric signal A22 obtained from the light receiving cell 51A2, an electric signal B21 obtained from the light receiving cell 51B1, an electric signal B22 obtained from the light receiving cell 51B2, an adder 71, 72 and a subtractor 77 And is calculated by the following equation (8).
FE2 = (A21 + B22)-(A22 + B21) (8)
As shown in the equation (8), since a general astigmatism method can be used for focus error detection, the optical pickup device 1 can easily cope with the conventional FEP.

  As in FIG. 11 of the first embodiment, the spot formed by reflecting from the signal surface 10B1 of the recording / reproducing layer on the HOE surface 50Z is not subjected to the diffraction effect with the primary light diffracted by the track. Since an overlapping portion with the next light occurs, a push-pull signal component can be obtained. Therefore, the angle formed by the dividing line 50i and the dividing line 50j is preferably 40 ° or more and 50 ° or less. Similarly, the angle formed by the dividing line 50i and the dividing line 50k is preferably -50 ° or more and -40 ° or less. The angles formed by the dividing lines 50i and 50j are most preferably 45 °, and the angles formed by the dividing lines 50i and 50k are most preferably −45 °.

The first-order diffracted light diffracted by the four divided regions 50C to 50F of the HOE surface 50Z is received by the light detection cells 51C to 51F, forming signal detection light spots 61c to 61f. Then, electrical signals C2 to F2 corresponding to the respective light receiving cells 51C to 51F are obtained. The electric signals C2 to F2 include push-pull signal components. Therefore, the tracking error signal PP2 by the normal push-pull method is calculated by the following equation (9) using the electrical signals C2 to F2, the adders 75 and 76, and the subtracter 80.
PP2 = (C2 + D2) − (E2 + F2) (9)

The tracking error signal APP2 is calculated by the following equation (10) using the electrical signals A21 to F2, adders 73, 74, 75, and 76, subtractors 79, 80, and 83, and a multiplier 81.
APP2 = (C2 + D2) − (E2 + F2) −k2 {(A21 + B21) − (A22 + B22)} (10)

Further, the main signal RF is calculated by the following equation (11) using the electrical signals A21 to F2 and the adders 71, 72, 75, 76, 78, 81 and 83.
RF2 = A21 + A22 + B21 + B22 + C2 + D2 + E2 + F2 (11)

  In the case of the second embodiment, it is possible to detect a tracking error signal by the DPD method corresponding to a reproduction type optical disc such as a BD-ROM. The DPD signal is obtained by comparing and calculating the sum of the electric signal C2 and the electric signal E2 (C2 + E2) and the sum of the electric signal D2 and the electric signal F2 (D2 + F2). Therefore, the second embodiment has a configuration in which the APP method and the DPD method can be compatible, and can cope with various media than the first embodiment.

  As described above, when the expression (3) is satisfied, a spot formed by crosstalk light reflected from the signal surface of the recording / reproducing layer and diffracted by the HOE surface is generated around the light receiving cell. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained. Further, as shown in FIG. 15, the spot formed by the crosstalk light diffracted by the signal surface of the other layer and diffracted by the HOE surface is not irradiated on all the light receiving cells. A more stable focus error signal and tracking error signal with good S / N can be obtained.

  Further, as shown in FIG. 12 and FIG. 13, since it is composed of one diffractive optical element and a small number of light receiving cells, it is possible to prevent the crosstalk light from being irradiated onto the light receiving cells at low cost. In addition, since the single beam system is used, there is an advantage that a grating is not necessary, and it is possible to cope with a plurality of types of optical disks having different track pitches such as BD and HD-DVD.

  In the first and second embodiments, the configuration of the optical pickup device corresponding to the single-sided two-layer BD is shown using one blue laser light source having a wavelength of 405 nm, but the present invention is the first and second embodiments. The form is not limited. For example, the same blue laser light source can be used for an optical pickup device compatible with both BD and HD-DVD, an optical pickup device compatible with DVD and CD, and an optical pickup device compatible with three or more layers of optical disks. is there.

It is a whole block diagram of the optical pick-up apparatus of this invention. It is the figure which showed the detection system of the optical pick-up apparatus of this invention. It is the figure which showed the 4-part dividing pattern of the HOE surface in FIG. It is the figure which showed the cross section of the HOE surface in FIG. It is the figure which showed the pattern of the light reception cell corresponding to the 4-part dividing pattern in FIG. It is the figure which showed the effective distance of the injection | emission side in FIG. 1, and a detection side. FIG. 6 is a diagram showing a positional relationship between a light receiving cell in FIG. 5 and spots due to crosstalk light from a recording / reproducing layer. It is the figure which showed the positional relationship of the light reception cell in FIG. 5, and the spot by the crosstalk light from another layer. It is the figure which showed the example of the focus error signal in this invention apparatus, and the spot shape on the light reception cell at that time. It is a block diagram of the arithmetic circuit of the electric signal in the photodetector in FIG. It is the figure which showed the spot shape containing the overlap part of the 0th order light and the primary light which were diffracted with the track | truck on the HOE surface in FIG. It is the figure which showed the 6 division | segmentation pattern of the HOE surface in FIG. It is the figure which showed the pattern of the light reception cell corresponding to the 6 division | segmentation pattern in FIG. It is the figure which showed the positional relationship of the light reception cell in FIG. 13, and the spot by the crosstalk light from a recording / reproducing layer. It is the figure which showed the positional relationship of the light reception cell in FIG. 13, and the spot by the crosstalk light from another layer. It is a block diagram of the arithmetic circuit of the electric signal in the photodetector in FIG. It is the figure which showed the detection system of the conventional optical pick-up apparatus. It is the figure which showed the HOE pattern (far field pattern) used for the detection system of the conventional optical pick-up apparatus. It is the figure which showed the state of the spot by the signal detection light of the conventional optical pick-up apparatus, and crosstalk light. It is the figure which showed the structure of the liquid crystal element used for the detection system of the conventional optical pick-up apparatus. It is the figure which showed the state which condenses the beam of the conventional optical pick-up apparatus to a light reception cell.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical pick-up apparatus 2 Laser light source 4 Collimator lens 7 Objective lens 8, 50 Diffractive optical element 8Z, 50Z HOE surface 8A-8D, 50A-50F Divided area 8i, 8j, 50i, 50j, 50k Dividing line 8P, 50P Optical axis Center 9, 51 Photodetector 9A-9D, 51A-51F Light receiving cell 9P, 51P Light receiving surface center 10 Optical disk 10A Light incident surface 10B Signal surface 10B1 First signal surface (signal surface of recording / reproducing layer)
10B2 Second signal surface (signal surface of other layer)
21a to 21d, 61a to 61f Spots caused by signal detection light 28a to 28d, 66a to 66f Spots caused by crosstalk light from other layers
LS Emission light LT Reflected light

Claims (3)

A laser light source for emitting laser light;
A collimator lens that converts light emitted from the laser light source into substantially parallel light;
An objective lens that collects the substantially parallel light and forms a spot on the first or second signal surface with respect to the optical disc having the first signal surface and the second signal surface;
A plurality of dividing lines arranged so as to pass through a substantially luminous flux center of reflected light from the first or second signal surface, and a step-shaped diffraction structure having a number of steps q divided by the plurality of dividing lines. A diffractive optical element that diffracts the reflected light in a predetermined direction by a diffraction order m (m is an integer other than 0),
The signal detection light diffracted in a predetermined direction by the diffractive optical element and provided with astigmatism is individually received, and the signal detection light is a minimum circle of confusion approximately in the middle of two focal lines generated by the astigmatism. And a photodetector having a plurality of light receiving cells arranged at a position,
When q ≧ 4, the absolute value | m | of m satisfies the following expression (1).
| M | ≦ INT [(q−2) / 2] (1)
Here, INT [(q-2) / 2] is an integer part of (q-2) / 2. A laser light source for emitting laser light;
A collimator lens that converts light emitted from the laser light source into substantially parallel light;
An objective lens that collects the substantially parallel light and forms a spot on the first or second signal surface with respect to the optical disc having the first signal surface and the second signal surface;
When the track of the optical disc is projected, the first dividing line is arranged in a direction perpendicular to the direction of the track, and the second dividing line is at an angle direction of 40 ° to 50 ° with respect to the first dividing line. And the third dividing line is arranged at an angle of -50 ° to -40 ° with respect to the first dividing line, and the first, second, and third dividing lines are the first or second Two dividing lines arranged so as to pass through substantially the center of the luminous flux of the reflected light from the signal surface of 2, and each region formed by the three dividing lines and having a step-shaped diffraction structure with the number of steps q. A diffractive optical element that diffracts the reflected light in a predetermined direction with a diffraction order m (m is an integer other than 0);
The signal detection light diffracted in a predetermined direction by the diffractive optical element and provided with astigmatism is individually received, and the signal detection light is a minimum circle of confusion approximately in the middle of two focal lines generated by the astigmatism. And a photodetector having a plurality of light receiving cells arranged at a position,
When q ≧ 4, the absolute value | m | of m satisfies the following expression (1).
| M | ≦ INT [(q−2) / 2] (1)
Here, INT [(q-2) / 2] is an integer part of (q-2) / 2.   Of the first and second signal surfaces, crosstalk light that is reflected from a signal surface that is not recorded or reproduced and is diffracted by a diffraction order m in any region of the diffractive optical element is arbitrary. 3. The optical pickup device according to claim 1, wherein all the light receiving cells are arranged so as not to irradiate the light receiving cells.

Images