JP2009015954A - Optical pickup device and its adjusting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device with which a stable signal of satisfactory S/N can be obtained at a low cost even for a multilayered disk. <P>SOLUTION: An effective distance from a light emission point of a laser light source up to a collimator lens and an effective distance from the collimator lens up to a light reception center point 9P of a photodetector 9 are made approximately equal. First order diffracted light reflected on a first signal face for replaying the optical disk and diffracted with a diffraction optical element converges to spots 21a to 21d on light receiving cells 9A to 9D of the photodetector 9, while light reflected on the first signal face and diffracted by orders other than first-order and light reflected on a second signal face become crosstalk light. Spots 23a to 23d by the first order diffracted light from the first signal face and spots 24a to 24d by the first order diffracted light from the second signal face are not radiated on all the light receiving 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 apparatus capable of performing proper recording or reproduction and an adjustment method thereof.

 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). .

  16 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. 17 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. 18 is a diagram illustrating an example, and FIG. 18 is a diagram illustrating 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 apparatus until the reflected light from the optical disk is received by a PD (light detector) will be briefly described with reference to FIGS. In FIG. 16, 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. 17 shows a pattern of the HOE 101, and the HOE 101 is divided into five areas 101A to 101E. FIG. 18 shows the states of signal detection light spots and crosstalk light spots 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 diffracts in the region 101C. The light thus formed forms a spot 107C on the PD 105C, and the light diffracted in the region 101D forms a spot 107D on the PD 105D, which 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 (1).
TAPP = TC-TD-Tk. (TA-TB) (1)
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. 19 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. 20 is a diagram showing 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 disc 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. 19A, 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. 19B, 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. 19C and a reproduction pattern 113B shown in FIG. 19D.

  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. 20A, the recording pattern 113 </ b> A of the polarization HOE 113 is acted to receive 0th-order, first-order, and −1st-order diffracted light, 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. 20B, 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 received 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. 16 to 18, 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. 19 and 20, it is possible to reduce the influence of crosstalk light and perform recording type and reproduction type tracking error signal detection. 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 and an adjustment method thereof.

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 light emitting point (2P) of the laser light source into substantially parallel light, and collecting the substantially parallel light. Objective lens for forming spots on the first (10B1) or second signal surface (10B2) with respect to the optical disc (10) having the first signal surface (10B1) and the second signal surface (10B2). 7), a plurality of dividing lines (8i, 8j) arranged so as to pass through a substantially luminous flux center of the reflected light (LT) from the first (10B1) or the second signal surface (10B2), and a plurality of divisions A diffractive optical element (8) having a plurality of regions (8A to 8D) divided by lines (8i, 8j) and diffracting the reflected light (LT) in a predetermined direction, and a diffractive optical element (8 ) Is diffracted in a predetermined direction and given astigmatism The signal detection lights (21a to 21d) are individually received, positioned at the periphery of the center point (9P) on the light receiving surface, and the signal detection lights (21a to 21d) are two focal lines generated by astigmatism. A light detector (9) having a plurality of light receiving cells (9A to 9D) arranged at a position that is a minimum circle of confusion in the middle of the first (10B1) and the second signal surface (10B2) The 0th-order diffracted light (22) that is reflected from the signal surface being recorded or reproduced (LT) and transmitted without being diffracted in the plurality of regions (8A to 8D) of the diffractive optical element is condensed. And the effective distance from the collimator lens (4) to the light emission point (2P) of the laser light source (2) and the collimator lens (4). The effective distance to the light receiving center point (9P) is made approximately equal. A pickup device (1).

  Also, a laser light source (2) that emits laser light, a collimator lens (4) that converts light (LS) emitted from the light emission point (2P) of the laser light source (2) into substantially parallel light, and substantially parallel light The optical disc (10) having the first signal surface (10B1) and the second signal surface (10B2) is focused on the first (10B1) or the second signal surface (10B2). When the objective lens (7) to be formed and the track of the optical disc (10) are projected, a first dividing line (50i) and a first dividing line (50i) arranged in a direction perpendicular to the track direction A second dividing line (50j) arranged in an angular direction of 40 ° or more and 50 ° or less, and a third dividing line (50j) arranged in an angular direction of an angle of −50 ° or more and −40 ° or less with the first dividing line (50i). Dividing line (50k) and the first, second and third dividing lines (50 , 50j, 50k) are arranged so as to pass through the approximate luminous flux center of the reflected light (LT) from the first (10B1) or second signal surface (10B2), and the first, second, and third dividing lines ( A diffractive optical element (50) having six regions (50A to 50F) divided by 50i, 50j, and 50k) and diffracting reflected light (LT) in a predetermined direction, and a diffractive optical element (50 ) Are individually received by the signal detection light (61a to 61f) diffracted in a predetermined direction and provided with astigmatism, positioned at the periphery of the center point (9P) on the light receiving surface, and the signal detection light ( 61a to 61f) includes a photodetector (51) having a plurality of light receiving cells (51A to 51F) arranged at positions where the circle of least confusion is approximately in the middle of two focal lines caused by astigmatism, 1 (10B1) and the second signal plane (10B2) Among them, the position where the 0th-order diffracted light (22) which is reflected from the signal surface being recorded or reproduced and transmitted without being diffracted in the six regions (50A to 50F) of the diffractive optical element is condensed. Is the effective distance from the collimator lens (4) to the light emission point (2P) of the laser light source and the effective distance from the collimator lens (4) to the light reception center point (9P). This is an equal optical pickup device (1).

  The laser light source (2) that emits laser light on the first optical axis, the light emitted from the light emission point (2P) of the laser light source (2), and the first optical axis (L1) direction, A first optical axis direction separated by an optical path separating element (3) and a second optical axis (L2) direction intersecting the first optical axis (L1) direction; A collimator lens (4) to which the light of the first light is incident, a diffractive optical element (8) to which light in the direction of the second optical axis (L2) separated by the optical path separating element (3) is incident, and a diffractive optical A light detector (9) to which light emitted from the element (8) is incident, and the light incident on the light detector (9) is reflected from the light detector (9) to be a diffractive optical element ( 8), is reflected by the optical path separation element (3), and is emitted as light in the direction of the first optical axis (L1). A method of adjusting the optical pickup device for adjusting the position of the photodetector (9) in the optical pickup device (1) incident on the optical pickup device (4), the first light facing the collimator lens (4) An arrangement step of arranging an image pickup device (11) having an image pickup surface (11A) on the side opposite to the laser light source (2) in the axis (L1) direction, and light from a light emitting point (2P) of the laser light source (2) The imaging step (11A) of the imaging device (11) is made by combining the emission step to be emitted, the light emitted from the light emitting point (2P) of the laser light source (2) and the light reflected from the photodetector (9). A light receiving step for receiving light, a determination step for determining whether or not both the light emitting point (2P) of the laser light source (2) and the photodetector (9) are in focus, and if the focus is not in the determination step If determined, the position of the photodetector (9) A method of adjusting an optical pickup device including an adjustment step of adjusting.

  According to the optical pickup device of the present invention, the light source point of the laser light source and the light receiving center point of the photodetector are conjugated, and the position error of the spot that becomes the signal detection light with respect to the position error of the diffractive optical element is reduced. There are few configurations. 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 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 not irradiated onto all the light receiving cells. In addition, it is configured such that 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 components such as a liquid crystal element, and the crosstalk light is not irradiated onto the light receiving cell.

  Further, according to the method for adjusting an optical pickup device of the present invention, the light emission point of the laser light source and the light receiving center point of the photodetector are easily conjugated to each other. Therefore, it is possible to manufacture an optical pickup device that obtains a stable signal with good S / N at low cost.

<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 the laser light LS having a wavelength λ = 405 nm emitted from the laser light source 2 to record on the optical disc (BD) 10 having the two-sided signal surface 10B of the Blu-ray standard, or This is a device for reproducing information from the optical disc 10. The optical disk 10 has a thickness t1 = 0.075 mm from the light incident surface 10A to the first signal surface, and a thickness t2 = 0.1 mm from the second signal surface.

  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. In the present embodiment, the optical path separation element 3 is 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 to give third-order astigmatism (hereinafter simply referred to as astigmatism). 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. Here, FIG. 3 is a diagram showing the divided regions 8A to 8D of the HOE surface 8Z, FIG. 4 is a diagram showing the arrangement of the light receiving cells 9A to 9D of the photodetector 9, and FIG. 5 is a diagram of the emission system in FIG. It is the figure which showed the effective distance and the effective distance of a detection system.

  In FIG. 3, the reflected light LT reflected by the polarization beam splitter 3 and incident on the diffractive optical element 8 is diffracted light of order ma in the four divided regions 8A to 8D on the HOE surface 8Z of the diffractive optical element 8. Is diffracted in a predetermined direction. Note that the order ma diffracted as signal detection light in the divided regions 8A to 8D can be any integer other than 0, but in the present embodiment, it will be described as ma = 1.

  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 diffraction structure, and is configured to give astigmatism to the first-order diffracted light with ma = 1. Therefore, four first-order diffracted lights to which astigmatism is imparted corresponding to the four divided regions 8A to 8D are generated. 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.

  Thereafter, the four first-order diffracted lights are received by forming signal detection light spots 21a to 21d on the light receiving cells 9A to 9D arranged on the light receiving surface of the photodetector 9 shown in FIG. 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 first-order diffracted light diffracted by the divided region 8A is on the light receiving cell 9A (9A1 and 9A2). Spots 21a are formed and received. Similarly, the first-order diffracted light diffracted in the divided region 8B forms a spot 21b on the light-receiving cell 9B (straddles 9B1 and 9B2), and the first-order diffracted light diffracted in the divided region 8C forms a spot 21c on the light-receiving cell 9C. The first-order diffracted light diffracted in the divided region 8D is received by forming spots 21d on the light receiving cell 9D.

  The light receiving center point 9P is a position where 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 without being diffracted forms a spot 22 and is substantially condensed. It is. The optical axis center 8P of the HOE surface 8Z and the light receiving center point 9P of the photodetector 9 substantially coincide with each other in the optical axis direction. On the light receiving surface, it is desirable that the distance from the middle point 9R of the light receiving cells 9A and 9B to the light receiving center point 9P and the distance from the middle point 9S of the light receiving cells 9C and 9D to the light receiving center point 9P are substantially equal. 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 21a to 21d of each signal detection light on each of the light receiving cells 9A to 9D has a fan shape corresponding to the divided regions 8A to 8D. However, there is no divided region, and the circle is a circle of minimum confusion with a circular hologram pattern. When it is considered as a shape 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.

 Astigmatism given by the divided regions 8A to 8D of the HOE surface 8Z 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. 5, the center point 3P of the polarization beam splitter is the intersection of the optical axis and the polarization-selective dielectric multilayer film 3A. N1 represents an effective distance from the light emitting point 2P of the laser light source 2 to the center point 3P of the polarizing beam splitter 3, and N2 represents an effective distance from the center point 3P of the polarizing beam splitter 3 to the light receiving center point 9P of the photodetector. ing. The effective distance is an air equivalent distance determined by the refractive index of the glass material. When the effective distance from the collimator lens 4 to the light emitting point 2P of the laser light source 2 is equal to the effective distance from the collimator lens 4 to the light receiving center point 9P of the photodetector 9, that is, the effective distance N1 is equal to the effective distance N2. In this case, the light emission point 2P of the laser light source 2 and the light receiving center point 9P of the photodetector 9 are conjugated.

  On the other hand, the distance from the light receiving center point 9P to each of the light receiving cells 9A to 9D is within several hundred μm. Therefore, the effective distance from the light emitting point 2P of the laser light source 2 to the collimator lens 4 and the effective distance from the collimator lens 4 to each of the light receiving cells 9A to 9D of the photodetector 9 are substantially equal. Therefore, the power component in each of the divided regions 8A to 8D is very small. The power component corresponds to a lens action and means the diffractive surface power. The smaller the power component in the divided regions 8A to 8D, the smaller the position error of the spot with respect to the position error between the HOE surface 8Z of the diffractive optical element 8 and the optical axis. The reason is that when there is no power component, the HOE surface 8Z of the diffractive optical element 8 can be regarded as a flat plate without a hologram pattern.

  As described above, by arranging the light emitting point 2P of the laser light source 2 and the light receiving center point 9P of the photodetector 9 in a conjugate arrangement, the divided regions 8A to 8D have only a minimum minute power component. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained.

  Next, an example of an adjustment method in which the light emission point 2P of the laser light source 2 and the light receiving center point 9P of the photodetector 9 are conjugatedly arranged will be described with reference to FIGS. FIG. 6 is a diagram for explaining a method for adjusting the position of the photodetector 9 in the optical pickup device 1, and FIG. 7 is a flowchart showing a method for adjusting the position of the photodetector 9 in the optical pickup device 1.

  As shown in FIG. 6, before adjusting the photodetector 9, the laser light source 2, the optical path separation element (polarization beam splitter) 3, the collimator lens 4, the diffractive optical element 8, and the photodetector 9 are arranged. . The polarization beam splitter 3 separates the light into the first optical axis L1 direction and the second optical axis direction L2, and the first optical axis L1 direction and the second optical axis L2 direction are polarized beams. Cross at splitter 3. In FIG. 6, the first optical axis L1 direction and the second optical axis L2 direction are orthogonal to each other, but the intersecting angle is not limited to the orthogonal direction. The laser light source 2 and the collimator lens 4 are arranged in the direction of the first optical axis L1, and the diffractive optical element 8 and the photodetector 9 are arranged in the direction of the second optical axis L2.

  With the components such as the laser light source 2 disposed as described above, the photodetector 9 in the optical pickup device is adjusted as shown in FIG. First, the imaging element 11 having the imaging surface 11A is arranged on the opposite side of the laser light source 2 in the first optical axis L1 direction so as to face the collimator lens 4 (step S1 in FIG. 7). Next, light is emitted in the LED (Light Emitting Diode) mode from the light emitting point 2P of the laser light source 2 (FIG. 7, step 2).

  The light in the LED mode is light having a lower output than the laser mode used when recording or reproduction is performed on the first signal surface 10B1, and does not have linear polarization characteristics. Therefore, the light emitted from the light emitting point 2P of the laser light source 2 is separated into two lights by the polarization selective dielectric multilayer film 3A of the polarization beam splitter 3. One is light that passes through the polarization-selective dielectric multilayer film 3 </ b> A on the first optical axis L <b> 1 and enters the collimator lens 4. The other is reflected by the polarization-selective dielectric multilayer film 3A, travels on the second optical axis L2, passes through the diffractive optical element 8, and is reflected by the light receiving surface of the photodetector 9. The light reflected on the light receiving surface of the photodetector again travels on the second optical axis L2, passes through the diffractive optical element 8, and is reflected by the polarization-selective dielectric multilayer film 3A. The light returns to the upper side of the optical axis L1 and enters the collimator lens 4.

  Next, the above-described two lights are received and imaged together on the imaging surface 11A of the imaging device 11 (FIG. 7, step S3). Then, it is visually or mechanically determined whether or not the light emitting point 2P of the laser light source 2 and the light receiving surface of the photodetector 9 are in focus (FIG. 7, step S4). When focus is not achieved in step S4 (N), the position of the photodetector 9 is adjusted in the second optical axis L2 direction (FIG. 7, step S5), and the process returns to step S4 again. If both are focused in step S5 (Y), the light emission point 2P of the laser light source 2 and the light receiving center point 9P of the photodetector 9 are conjugated, and the adjustment ends.

  By the adjustment method described above, the light emission point 2P of the laser light source 2 and the light receiving center point 9P of the photodetector 9 can be easily conjugated. Therefore, the position error of the spot serving as the signal detection light is small with respect to the position error of the diffractive optical element. Therefore, an optical pickup device that obtains a stable signal with good S / N at low cost can be easily manufactured. FIG. 7 shows an example of an adjustment method, and a light source for light used for imaging may be provided separately from the laser light source 2. Moreover, it is good also as a method of observing using the lens of a microscope instead of the image pick-up element 11.

  FIG. 8 is a diagram showing an S curve and a spot shape for obtaining a focus error signal. FIG. 8A 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. 8B 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. 8C, 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. 8C is shown in FIG. 8A and the minimum level is shown in FIG. 8B. When there is no defocus at all, uniform fan-shaped spots 21a and 21b are formed.

FIG. 9 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 (2).
FE1 = (A11 + B12) − (A12 + B11) (2)
As shown in equation (2), since a general astigmatism method can be used for focus error detection, the optical pickup apparatus 1 can easily cope with a conventional front-end processor (hereinafter referred to as FEP).

  FIG. 10 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. 10A shows a case where recording or reproduction is performed on a Blu-ray standard optical disk (BD), and FIG. 10B shows a case where recording or reproduction is performed on an HD-DVD standard optical disk (HD-DVD). is there. In the spots 45 and 46 of reflected light from the signal surface 10B1 of the recording / reproducing layer, overlapping portions 45a and 46a of primary light diffracted by tracks and pits (hereinafter referred to as tracks) and non-diffracted zero-order light are generated. . 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. Here, 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. The light receiving cell 9C obtains an electric signal C1 and the light receiving cell 9D obtains an electric signal D1, and 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 (3) using the electric signals C1 and D1 and the subtractor 36.
PP1 = C1-D1 (3)

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 (4) using the electrical 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)} (4)
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 RF is calculated by the following equation (5) using the electrical signals A11 to D1 and the adders 31, 32, 33, 38, and 41.
RF1 = A11 + A12 + B11 + B12 + C1 + D1 (5)

  Next, crosstalk light on the light receiving surface of the photodetector 9 will be described. The crosstalk light includes reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted by the HOE surface 8Z except for the order ma of the signal detection light, and reflected from the signal surface 10B2 of the other layer. There is crosstalk light that is light and diffracted by the HOE surface 8Z at the order mb.

  The first-order diffracted light diffracted in the divided regions 8A to 8D is desirably 70% or more, but even in this case, diffracted light other than the order ma = 1 is generated with a slight diffraction efficiency. The diffracted light of an arbitrary order ma forms a spot at a position away from the light receiving cells 9A to 9D as the value of ma increases. For this reason, the crosstalk light that is reflected from the signal surface 10B1 of the recording / reproducing layer and diffracted by the HOE surface 8Z except for the order ma = 1 of the signal detection light is considered when the order ma = 0, −1. Good.

  Further, the crosstalk light that is reflected from the signal surface 10B1 of the other layer and diffracted by the HOE surface 8Z at an arbitrary order mb of the signal detection light spreads in accordance with the magnification and has a small local light amount. Therefore, the case where the same order mb = 1 as that of the signal detection light having high diffraction efficiency may be considered.

  FIG. 11 is a diagram showing a state of spots formed by crosstalk light on the light receiving surface of the photodetector 9. The spots 21a to 21d and the spot 22 generated from the signal surface 10B1 of the recording / reproducing layer are as described in FIG. Spots 23a to 23d formed by the reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted by the order ma = −1 in the divided regions 8A to 8D of the HOE surface 8Z are the spots 21a when viewed from the light receiving center point 9P. It occurs at a position symmetrical to ~ 21d. Therefore, it is possible to prevent the spots 23a to 23d from being irradiated on the light receiving cells 9A to 9D. Therefore, a stable signal with a good S / N can be obtained.

  Spots 24a to 24d formed by the reflected light from the signal surface 10B2 of the other layer and diffracted at the order mb = 1 in each of the divided regions 8A to 8D of the HOE surface 8Z are 90 ° with respect to the spots 21a to 21d. Spreads in a fan shape in the direction of rotation. Therefore, the spots 24a to 24d can be hardly irradiated on the light receiving cells 9A to 9D. As a result, a stable signal with a better S / N can be obtained.

  As described above, the position error of the spot is small with respect to the position error of the diffractive optical element by making the light emission point of the laser light source and the light receiving center point of the photodetector conjugate. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained.

  Moreover, as shown in FIG. 11, it is set as the structure which crosstalk light does not irradiate on all the light reception cells. Therefore, a more stable focus error signal and tracking error signal with good S / N can be obtained.

Further, as shown in FIG. 3 and FIG. 4, since it is composed of one diffractive optical element and few 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 15 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 diffracted light of the order ma = 1. Therefore, six first-order diffracted lights to which astigmatism is given corresponding to the six divided regions 50A to 50F are generated. As in the first embodiment, 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 50P of the HOE surface 50Z. .

  After that, the six first-order diffracted lights are received by the light detection cells 51A to 51F arranged on the light receiving surface of the photodetector 51 to form signal detection light spots 61a to 61f. 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 first-order diffracted light diffracted by the divided region 50A is on the light receiving cell 51A (51A1 and 51A2). Spot 61a is formed and received. Similarly, the first-order diffracted light diffracted in the divided region 50B divides the spot 61b on the light receiving cell 51B (striding 51B1 and 51B2), and the first-order diffracted light diffracted in the divided region 50C divides the spot 61c on the light receiving cell 51C. The first-order diffracted light diffracted in the region 50D is a spot 61d on the light-receiving cell 51D, the first-order diffracted light diffracted in the divided region 50E is a spot 61e on the light-receiving cell 51E, and the first-order diffracted light diffracted in the divided region 50F is Spots 61f are formed on the light receiving cell 51F and received.

  The light receiving center point 51P is a position where reflected light from the signal surface 10B1 of the recording / reproducing layer and zero-order diffracted light transmitted without being diffracted by the divided regions 51A to 51F forms a spot 62 and is substantially condensed. It is. 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 50P of the HOE surface 50Z. For the same reason as in the first embodiment, the distance from the middle point 51Q of the light receiving cells 51A and 51B to the light receiving center point 51P, and the distance from the middle point 51R to the light receiving center point 51P of the light receiving cells 51C and 51E The distances from the midpoint 51S of the light receiving cells 51D and 51F to the light receiving center point 51P are preferably substantially equal.

  When the track of the optical disc 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, and the light receiving cell 51B is divided into two light receiving cells 51B1 and 51B2 in the radial direction. Is done. Also, the direction of astigmatism is the same as in the first embodiment.

  The spot 61a to 61f of each signal detection light on each light receiving cell 51A to 51F has a fan shape corresponding to the divided areas 50A to 50F. However, there is no divided area, and the circle is a circle of minimum confusion with a circular hologram pattern. When it is considered as a shape spot, 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.

  In FIG. 5, as in the first embodiment, the effective distance N1 and effective distance N2 of the injection system are equal. Therefore, the light emission point 2P of the laser light source 2 and the light receiving center point 51P of the photodetector 51 are conjugated, and the divided regions 8A to 8D have only a minimum minute power component. Therefore, the optical pickup device 1 has a configuration in which the position errors of the spots 61a to 61f serving as signal detection light are small with respect to the position error of the diffractive optical element 50, and a stable focus error signal and tracking error signal with good S / N. Can be obtained. An adjustment method in which the light emitting point 2P of the laser light source 2 and the light receiving center point 51P of the photodetector 51 are conjugated is also the same as in the first embodiment shown in FIGS.

FIG. 14 shows a circuit system diagram of an arithmetic circuit in the photodetector 9. 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 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 71, 72 and a subtractor 77 And is calculated from the following equation (6).
FE2 = (A21 + A22) − (A22 + B21) (6)
As shown in the equation (6), since a general astigmatism method can be used for focus error detection, the optical pickup device 1 can easily cope with the conventional FEP.

  Similar to FIG. 10 of the first embodiment, on the HOE surface 50Z, the spot formed by reflecting from the signal surface 10B1 of the recording / reproducing layer is composed of the first-order light diffracted by the track and the zero-order light not diffracted. Since an overlapping portion 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 °.

Next, a method for calculating the tracking error signal will be described. The light receiving cell 51C obtains the electric signal C2, the light receiving cell 51D obtains the electric signal D2, the light receiving cell 51E obtains the electric signal E2, and the light receiving cell 51F obtains the electric signal F2. The electric signals C2 to F2 include push-pull signal components. Therefore, the tracking error signal PP2 by the normal PP method is calculated by the following equation (7) using the electrical signals C2 to F2, the adders 75 and 76, and the subtracter 80.
PP2 = (C2 + D2) − (E2 + F2) (7)

The tracking error signal APP2 is calculated by the following equation (8) using the electrical signals A21 to F2, adders 73, 74, 75, and 76, subtractors 79, 80, and 84, and a multiplier 82.
APP2 = (C2 + D2) − (E2 + F2) −k2 {(A21 + B21) − (A22 + B22)} (8)
Here, k2 is a multiplication coefficient of the multiplier 82. The multiplication coefficient k2 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.

Further, the main signal RF is calculated by the following equation (9) 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 (9)

  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.

  Next, crosstalk light on the light receiving surface of the photodetector 51 will be described. The crosstalk light includes reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted by the HOE surface 50Z except for the order ma of the signal detection light, and reflected from the signal surface 10B2 of the other layer. And crosstalk light diffracted by the HOE surface 50Z at the order mb. Similar to the first embodiment, the case of the order ma = 0, −1 and the case of the order mb = 1 may be considered.

  FIG. 15 is a diagram showing a state of spots formed by crosstalk light on the light receiving surface of the photodetector 9. The spots 61a to 61f and the spot 62 generated from the signal surface 10B1 of the recording / reproducing layer are as described in FIG. Spots 63a to 63f formed by the reflected light from the signal surface 10B1 of the recording / reproducing layer and diffracted by the order ma = −1 in the divided regions 50A to 50F of the HOE surface 50Z are spots 61a as viewed from the light receiving center point 51P. It occurs at a position symmetrical to ~ 61f. Therefore, the spots 63a to 63f can be prevented from being irradiated on the light receiving cells 51A to 51F. Therefore, a stable signal with a good S / N can be obtained.

  Spots 64a to 64f formed by the reflected light from the signal surface 10B2 of the other layer and diffracted by the order mb = 1 in each of the divided regions 50A to 50F of the HOE surface 50Z are 90 ° with respect to the spots 61a to 61f. Spreads in a fan shape in the direction of rotation. Therefore, the spots 64a to 64f can be hardly irradiated on the light receiving cells 51A to 51F. As a result, a stable signal with a better S / N can be obtained.

  As described above, the positional error of the spot serving as the signal detection light is small with respect to the positional error of the diffractive optical element by making the light emitting point of the laser light source and the light receiving center point of the photodetector conjugate. It is configured. Therefore, a stable focus error signal and tracking error signal with good S / N can be obtained.

  Further, as shown in FIG. 15, the crosstalk 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, 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 a 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 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 system in FIG. 1, and a detection system. It is a figure for demonstrating the adjustment method of the optical pick-up apparatus of this invention. It is the figure which showed the flowchart of the adjustment method of the optical pick-up apparatus of this invention. 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 this invention apparatus. 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. FIG. 5 is a diagram showing the spread of crosstalk light on the light receiving cell in FIG. 4. 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 another block diagram of the arithmetic circuit of the electric signal in this invention apparatus. It is the figure which showed the spread of the crosstalk light on the light receiving cell 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 of 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 3 Optical path separation element (polarization beam splitter)
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 Photo detector 9A to 9D, 51A to 51F Light receiving cell 9P, 51P Light receiving center point 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)
DESCRIPTION OF SYMBOLS 11 Image pick-up element 11A Image pick-up surface 21a-21d, 61a-61f Spot by signal detection light LS Emission light LT Reflected light L1 1st optical axis L2 2nd optical axis

Claims (3)

A laser light source for emitting laser light;
A collimator lens that converts light emitted from the light emitting point of 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 substantially the center of light flux of the reflected light from the first or second signal surface, and a plurality of regions divided by the plurality of dividing lines, and the reflected light A diffractive optical element that diffracts each in a predetermined direction;
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 at least halfway between two focal lines caused by the astigmatism. A photodetector having a plurality of light receiving cells arranged in a circular position,
Of the first and second signal surfaces, the 0th-order diffracted light that is reflected from the signal surface being recorded or reproduced and transmitted without being diffracted in the plurality of regions of the diffractive optical element is collected. When the light-receiving position on the photodetector is the light reception center point, the effective distance from the collimator lens to the light emission point of the laser light source is substantially equal to the effective distance from the collimator lens to the light reception center point. An optical pickup device characterized by that. A laser light source for emitting laser light;
A collimator lens that converts light emitted from the light emitting point of 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, a first dividing line arranged in a direction perpendicular to the direction of the track, and a second dividing line arranged in an angle direction of 40 ° to 50 ° with respect to the first dividing line. And a first parting line and a third parting line arranged in an angle direction of not less than −50 ° and not more than −40 °, and the first, second and third parting lines Is arranged so as to pass through a substantially luminous flux center of the reflected light from the first or second signal surface, and has six regions divided by the first, second and third dividing lines, A diffractive optical element that diffracts each reflected light in a predetermined direction;
The signal detection light diffracted in a predetermined direction by the diffractive optical element and provided with astigmatism is individually received, located at the periphery of the center point on the light receiving surface, and the signal detection light is the astigmatism. A photodetector having a plurality of light receiving cells arranged at a position where the circle of least confusion is approximately in the middle of two focal lines caused by aberration,
Of the first and second signal surfaces, the 0th-order diffracted light that is reflected from the signal surface being recorded or reproduced and transmitted without being diffracted in the six regions of the diffractive optical element is collected. When the light-receiving position on the photodetector is the light reception center point, the effective distance from the collimator lens to the light emission point of the laser light source is substantially equal to the effective distance from the collimator lens to the light reception center point. An optical pickup device characterized by that. A laser light source for emitting laser light onto the first optical axis;
An optical path separation element that separates light emitted from a light emitting point of the laser light source into the first optical axis direction and a second optical axis direction intersecting the first optical axis direction;
A collimator lens on which the light in the first optical axis direction separated by the optical path separation element is incident;
A diffractive optical element on which the light in the second optical axis direction separated by the optical path separating element is incident;
A photodetector on which light emitted from the diffractive optical element is incident,
The light incident on the photodetector is reflected from the photodetector, passes through the diffractive optical element, is reflected by the optical path separation element, and is emitted as light in the first optical axis direction, and the collimator An adjustment method of an optical pickup device for adjusting a position of the photodetector in an optical pickup device incident on a lens,
An arrangement step of disposing an imaging element having an imaging surface facing the collimator lens and on the side opposite to the laser light source in the first optical axis direction;
An emission step of emitting light from a light emitting point of the laser light source;
A light receiving step of combining the light emitted from the light emitting point of the laser light source and the light reflected from the photodetector, and receiving the light on the imaging surface of the imaging element;
A determination step of determining whether both the light emitting point of the laser light source and the photodetector are in focus;
An adjustment method of an optical pickup device, comprising: an adjustment step of adjusting a position of the photodetector when it is determined that the focus is not achieved by the determination step.

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