JP2008065864A - Optical pickup device, focusing control method, and focusing jump method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical pickup device which carries out further efficient focal jump logic to clearly decide the focus search direction in a target area to jump when making a focusing jump by using a liquid crystal element. <P>SOLUTION: When jumping the focusing from a spot 41 on a signal recording layer L1 to a spot 43 on a signal recording layer L0, this pickup device always sets up the power of the liquid crystal element 25 producing discrete power aberration so as to set the spot like a spot 42 outside a ±5 μm margin from a desired location L0 on a light incident disk surface side 45. Then, it makes one directional adjustment of the liquid crystal element 24 producing continuous power aberration so as to set the spot within the jump position margin on the recording layer L0. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical pickup device applied to an optical disc apparatus for recording and / or reproducing information with respect to an optical disc having at least two signal recording layers. The present invention also relates to a focus control method and a focus jump method that are applied to the optical pickup device and focus a light beam on a desired signal recording device.

  As an optical disc having a plurality of recording surfaces, for example, a Blu-ray Disc (registered trademark), as a method of performing a focus jump from one recording surface to another recording surface, for example, various techniques such as Patent Documents 1 to 7 below. Is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses that when an optical disk having a plurality of recording surfaces is irradiated with a laser beam from an optical pickup to cause a focus jump from one recording surface to another recording surface, the focus actuator of the optical pickup or between the recording surfaces The task is to make the focus jump accurately even if the distance varies. Therefore, when generating the acceleration / deceleration signal for focus jump based on the focus error signal, the acceleration signal is started and stopped and the deceleration signal is started and stopped only by detecting the threshold value of the focus error signal.

  The layer interval of a BD double-layer disc, which is an example of the optical disc having a plurality of recording surfaces, is 25 μm ± 5 μm, and the spot position margin after the focus jump is ± 5 μm from the jump destination layer.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique that realizes stable interlayer jump by starting the change of the spherical aberration correction amount before the movement of the light spot focal position from the first recording layer to the second recording layer is completed. It is disclosed.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique that can perform stable interlayer jump by performing the focus jump operation of the actuator after the start of movement of the spherical aberration correction mechanism.

  Further, in Patent Document 4 below, after recording or reproduction with respect to the first recording layer, the tracking servo loop is opened, the driving signal of the spherical aberration adding means is changed, and then the focal position of the minute light spot is changed. There is disclosed a technique for starting movement to two recording layers.

  In Patent Document 5 below, when the focal position of the spot light is moved from one information recording layer to another information recording layer, the interlayer movement of the spot light is changed depending on the change rate of the SUM signal of the low frequency component of the RF signal. Disclosed is a technique for generating a focus switching operation by generating acceleration / deceleration switching timing and identifying a specific threshold of the SUM signal and a threshold of different positive and negative levels of the S-shaped signal. Yes.

  Patent Document 6 below discloses a technique for reliably detecting a desired recording layer in a dual-layer disc. The spherical aberration correction means corrects the spherical aberration generated in the light beam according to the recording layer on which information is recorded or reproduced. The light receiving means receives the reflected light of the light beam, and outputs a sum signal indicating the amount of the reflected light and a signal level corresponding to the distance from the focal position of the light beam to the recording layer within a predetermined range from the focal position. A focus error signal is generated, and the recording layer detection means moves the focus of the light beam closer to the optical disc from the cover layer side, and detects that the focus of the light beam approaches the recording layer based on the focus error signal To do. When the recording layer determination means does not re-detect the recording layer within the re-detection period after the recording layer detection means detects the recording layer and the focus of the light beam keeps approaching the optical disc. The recording layer detected last is determined to be the first recording layer.

  FIG. 12 is a block diagram of this optical disc apparatus. The optical disc apparatus 1 corresponds to a two-layer Blu-ray disc (hereinafter referred to as an optical disc D) in which two recording layers are laminated in the thickness direction of the disc, and reproduces information from the two recording layers of the optical disc D.

  The optical disk apparatus 1 includes an optical pickup apparatus 2, an analog signal processor 3 that performs predetermined signal processing on a signal read from the optical disk D by the optical pickup apparatus 2, and an analog that converts an analog signal from the analog signal processor 3 into digital data. A digital (AD) converter 4 and a controller 5 that performs control processing of the focal position of the light beam on the digital data from the AD converter 4 are provided.

  The optical disc D is based on a digital-analog (DA) converter 11 that converts control data generated based on the focal position control processing by the controller 5 into an analog signal, and an analog control signal from the DA converter 11. And a driver 12 for controlling the focus of the optical pickup device 2.

  The controller 5 includes a microprocessor, and includes a calculation unit 6, a nonvolatile memory 7, a focus search processing unit 8, a servo filter processing unit 9, and a changeover switch 10, and a basic program stored in the nonvolatile memory 7. And overall control of the optical pickup device 2 and the entire optical disc device 1 in accordance with an application program such as a focus search program. Further, it operates in accordance with a read / write command supplied from the outside, and controls data recording and reproduction processing with respect to the optical disc D. The nonvolatile memory 7 stores various data related to the focus control process, setting values, and the like.

  The optical disk D is placed on a turntable (not shown) and is rotationally driven by a spindle motor. The optical pickup device 2 reads out data recorded on the optical disc D, ADIP (Address In Pre Groove) information by wobbled groove, and the like. Further, data is recorded on the optical disc D by the optical pickup device 2.

  FIG. 13 shows the configuration of the optical pickup device 2. The optical pickup device 2 emits a light beam from a laser diode 61, a collimator lens 62, a beam splitter 63, a fixed lens 64a and a movable lens 64b of an expander 64 that corrects spherical aberration of the laser light, and a quarter wavelength plate 65. Then, the optical disk D is irradiated sequentially through the objective lens 66 that becomes the laser beam emission end.

  In the optical pickup device 2, since the numerical aperture of the objective lens 66 is as large as 0.85, for example, the spherical aberration of the generated laser light is corrected by an expander 64 as spherical aberration correcting means.

  That is, the movable lens 64b of the expander 64 is held movably by an actuator, and the spherical aberration of the light beam is appropriately corrected by driving the actuator based on the expander servo signal CE from the controller 5. It is made to do.

  The objective lens 66 is held by a biaxial actuator 70 so as to be movable in the focus direction, that is, in the direction of contact with and away from the disk, and in the tracking direction, that is, in the radial direction of the disk. By driving the biaxial actuator 70 based on the CF, the focal point of the light beam is made to coincide with the recording surface of the optical disc.

  Then, the optical pickup device 2 sequentially starts the reflected light beam reflected from the recording surface of the optical disc D by the objective lens 66 and the expander 64, reflects the reflected light beam by the beam splitter 63, and transmits the focusing lens 67 and the cylindrical lens 68. It reaches the light receiving surface of the photodetector 69.

  The optical disc apparatus 1 performs the focus servo pull-in (focus search) with respect to the target recording layer in the optical disc D when the optical disc D is mounted or when the focus servo is lost due to disturbance or the like during recording / reproduction. The reproduction RF signal corresponds to a sum signal (SUM) as a reflected light intensity signal, and the controller 5 performs a focus search using the reproduction RF signal as the sum signal SUM.

  The sum signal is the sum of the detection signals output from the photodetector of the optical pickup device 2, and a signal level corresponding to the amount of reflected light from the optical disc D is obtained. When close to a reflector such as a layer, its signal level increases. The focus error signal outputs a signal proportional to the distance from the focal point of the light beam to the recording layer up to a certain distance from the in-focus position. As a result, the focus error signal draws a substantially S-shaped curve when the focal point of the light beam passes through the recording layer.

  For this reason, as shown in FIG. 14, in the optical disc apparatus, basically, the objective lens is brought close to the optical disc while monitoring the sum signal SUM and the focus error signal FE, and the first increase of the sum signal is detected. Suppose that the surface of the cover layer CLV is detected. Further, when the objective lens is further brought closer to the optical disc and the increase of the focus error signal FE is detected in a state where the signal level of the sum signal is equal to or higher than the predetermined sum signal threshold, the focus of the light beam approaches the recording layer. Shall be.

  Naturally, the increase in the focus error signal FE occurs twice when the optical disk D has two layers. When the focus search is performed on the recording layer on the near side of the dual-layer disc, the first increase in the focus error signal FE detected is determined as the target recording layer.

  On the other hand, when a focus search is performed on the recording layer on the far side of the dual-layer disc, the sum error signal temporarily falls below the above-mentioned sum signal threshold value, and then the focus error signal is output when the sum signal threshold value is exceeded again. When an increase is detected, this can be determined as a target recording layer.

  Next, as a technique for generating power aberration, that is, defocus aberration by a voltage applied to one liquid crystal element, for example, there is Patent Document 7 below. Liquid crystal lens element for correcting spherical aberration caused by interlayer thickness in a two-layer optical disc having two recording layers, regardless of the incident polarization direction, and also correcting spherical aberration caused by variations in the cover thickness of the recording layer In order to obtain an optical head, the spherical aberration due to the recording interlayer thickness is corrected by the voltage applied to the Fresnel lens portion, and the cover thickness varies depending on the voltage applied to the composite electrode provided in the electrode lens portion. The spherical aberration due to is corrected.

  With reference to FIG. 15, an optical pickup apparatus 2 'configured to correct spherical aberration using one liquid crystal element will be described. The optical pickup device 2 ′ differs from the optical pickup device 2 described in Patent Document 6 in that a single liquid crystal element 71 is used instead of the expander 64 for spherical aberration correction. It is assumed that a liquid crystal element whose correction amount corresponds to a layer interval, for example, 25 μm ± 5 μm is used for spherical aberration correction.

  However, as shown in FIG. 16, if the power generation amount of the liquid crystal element reported in Patent Document 7 corresponds to the layer spacing, that is, the above-mentioned 25 μm ± 5 μm, the focus jump using this liquid crystal element There is a great possibility that the later spot position is somewhat deviated from the position of the desired jump destination layer even in the spot position margin due to disc manufacturing errors and various perturbations. That is, when the spot 41 on the signal recording layer L1 in FIG. 16 is focus-jumped to L0, the spot position after the focus jump by the spherical aberration correction unit 71 made of power liquid crystal is a spot position margin of ± 5 μm. Among them, there is a possibility that the spot 47 or 48 is slightly off.

JP 2000-298446 A JP 2002-157750 A JP 2003-022545 A JP 2004-326936 A JP 2005-293698 A JP 2006-155792 A JP 2006-085801 A

  As described above, in the prior art, for example, as shown in FIG. 16, the spot position after the focus jump is the area on the disk surface side where the beam is incident, with the jump destination layer L1 (there is a spot 47). It is impossible to determine which of the opposite areas (the spot 48 is). For example, when the beam is in an area on the disk surface side where the beam is incident as in the spot 47, the focus error signal FE can be detected and the focus can be pulled in by setting the focus search direction to the upper side of the paper. However, if the beam is on the opposite side of the disk surface side area as the spot 48, the focus error signal FE cannot be detected even if a focus search is performed on the upper side of the paper. Thus, conventionally, when performing a focus search at a jump destination, there is a concern that the direction of the search cannot be uniquely determined and the focus error signal cannot be detected efficiently.

  It is an object of the present invention to provide an optical pickup device that executes a more efficient focus jump logic that uniquely determines a focus search direction at a jump destination in a focus jump using the liquid crystal element. Another object of the present invention is to provide a focus control method and a focus jump method for executing a more efficient focus jump logic that uniquely determines a focus search direction at a jump destination in a focus jump using the liquid crystal element. And

  In order to solve the above problems, an optical pickup according to the present invention performs an information signal recording and / or reproduction with respect to a selected signal recording layer of an optical disc having at least two or more signal recording layers. In the apparatus, a light source that emits a light beam having a predetermined wavelength, an objective lens that focuses the light beam emitted from the light source on the signal recording layer, and a liquid crystal that passes through the liquid crystal according to the magnitude of an applied voltage. A voltage applied by the liquid crystal element between the predetermined two layers of the at least two or more signal recording layers, and at least one liquid crystal element that changes the focal length of light discretely and / or continuously. The focus of the light beam is moved outside the possible range of the desired layer from the layer where the light beam is focused by the focus servo based on the change in the size of the light beam. From focusing of the light beam to the desired layer.

  In this optical pickup device, the magnitude of the voltage applied by at least one liquid crystal element that discretely and / or continuously changes the focal length of the light transmitted through the liquid crystal according to the magnitude of the applied voltage. Based on the change, the focus of the light beam is moved outside the range where the desired layer can exist from the layer on which the light beam is focused by the focus servo, and then the light beam is focused on the desired layer.

  In order to solve the above problems, a focus control method according to the present invention includes an objective lens that focuses a light beam emitted from a light source that emits a light beam having a predetermined wavelength on a signal recording layer, and an applied voltage. And at least one liquid crystal element that discretely and / or continuously changes the focal length of the light transmitted through the liquid crystal according to the size, and the optical disc having at least two signal recording layers is selected. In a focus control method executed in an optical pickup device that records and / or reproduces an information signal with respect to a signal recording layer, the liquid crystal element is provided between two predetermined signal recording layers among the at least two signal recording layers. Based on the change in the magnitude of the applied voltage, the layer where the light beam is focused by the focus servo is outside the range where the desired layer can exist. A first step of moving the focus of the light beam to a second layer, and a second step of focusing the light beam moved outside the possible range of the desired layer by the first step on the desired layer, and Is provided.

  According to this focus control method, the first step is outside the range where the desired layer can exist from the layer where the light beam is focused by the focus servo based on the change in the magnitude of the voltage applied by the liquid crystal element. And the second step focuses the light beam that has been moved outside the possible range of the desired layer by the first step to the desired layer. Since the optical pickup device can grasp the position of the spot moved in the first step, the direction in which the focal point is moved can be uniquely determined in the second step.

  In order to solve the above problem, the focus jump method according to the present invention changes at least one or more liquid crystal elements that move the focal point of the light beam discretely and / or continuously by changing the voltage applied to the liquid crystal. A focus jump method that is used in an optical pickup device that records and / or reproduces an information signal with respect to a selected signal recording layer of an optical disc having at least two or more signal recording layers. The first step of adjusting the one direction toward the desired layer by the liquid crystal element that discretely moves the focal point of the beam, and the desired layer by the liquid crystal element that continuously moves the focal point of the light beam And a second step of performing adjustment with respect to the one direction to go.

  According to this focus jump method, the liquid crystal element that discretely moves the focus of the light beam in the first step performs adjustment in one direction toward the desired layer, and the focus of the light beam in the second step. Is adjusted in one direction toward a desired layer by the liquid crystal element that continuously moves the liquid crystal.

  In order to solve the above problem, the focus jump method according to the present invention uses at least one liquid crystal element that moves the focal point of the light beam discretely and / or continuously by changing the applied voltage of the liquid crystal. And a focus jump method executed in an optical pickup device that records and / or reproduces an information signal using an objective lens with respect to a selected signal recording layer of an optical disc having at least two signal recording layers. A first step of adjusting the liquid crystal element in one direction toward the desired layer, and moving the objective lens in a direction perpendicular to the signal recording layer toward the desired layer. And a second step for adjusting the direction.

  According to this focus jump method, adjustment is performed in one direction toward the desired layer by the liquid crystal element in the first step, and the objective lens is adjusted in one direction perpendicular to the signal recording layer in the second step. By moving, adjustment is made with respect to the direction toward the desired layer.

  According to the present invention, it is possible to accurately grasp on which side the spot position after the focus jump is with respect to the desired layer of the jump destination. As a result, the direction of the focus search at the jump destination can be uniquely determined, and an efficient focus jump is possible.

  The best mode for carrying out the present invention will be described below with reference to the drawings. This embodiment is an optical pickup device applied to an optical disc apparatus that records and / or reproduces an information signal with respect to a selected signal recording layer of an optical disc having two signal recording layers. Of course, the optical pickup device of the present invention can record and / or reproduce an information signal even on an optical disc having three or more signal recording layers.

  First, a schematic configuration of the optical disc apparatus 81 will be described with reference to FIG. The optical disk device 81 includes an optical pickup device 20 that records and reproduces information from the optical disk D, a spindle motor 82 as a driving unit that rotates the optical disk D, and a feed motor that moves the optical pickup device 20 in the radial direction of the optical disk D. 83.

  The optical disk device 81 has, for example, two signal recording layers, and can record or reproduce information on an optical disk D capable of high-density recording using a semiconductor laser having a wavelength of about 405 nm (blue purple). It is configured to be able to. In this optical disc D, specifically, the signal recording layer has an interlayer thickness of 25 ± 5 μm as will be described later. Here, the interlayer thickness of the signal recording layer is a distance between the centers of the signal recording layers.

  In the optical disk device 81, the spindle motor 82 and the feed motor 83 are driven and controlled at a predetermined rotational speed by a drive control circuit 85 that is controlled based on a command from the system controller 84. The optical pickup device 20 irradiates a light beam having a predetermined wavelength and detects reflected light of the light beam on the recording layer. The optical pickup device 20 supplies a signal corresponding to each light beam from the detected reflected light to the preamplifier unit 86.

  The output of the preamplifier unit 86 is sent to a signal modulator / demodulator and error correction code block (hereinafter referred to as signal modulation / demodulation & ECC block) 87. The signal modulation / demodulation and ECC block 87 performs signal modulation, demodulation, and addition of ECC (error correction code). The optical pickup device 20 irradiates the recording layer of the optical disc D rotating according to the signal modulation / demodulation and the command of the ECC block 87, and records or reproduces the signal on the optical disc D.

  The preamplifier unit 86 is configured to generate a focus error signal FE, a tracking error signal TE, an RF signal, and the like based on signals corresponding to light beams detected differently for each format.

  Here, for example, if the recording signal demodulated by the signal modulation / demodulation & ECC block 87 is for computer data storage, it is sent to the external computer 89 via the interface 88. Thereby, the external computer 89 or the like can receive a signal recorded on the optical disc D as a reproduction signal.

  In addition, if the recording signal demodulated by the signal modulation / demodulation & ECC block 87 is for audio visual, it is converted from digital to analog by the D / A converter of the D / A and A / D converter 90 and supplied to the audio visual processor 91. Is done. Audio visual processing is performed by the audio visual processing unit 91 and transmitted to an external imaging / projection device (not shown) or the like via the audio visual signal input / output unit 92.

  In the optical pickup device 20, for example, control of the feed motor 83 for moving to a predetermined recording track on the optical disc D, control of the spindle motor 82, and an objective lens serving as light condensing means in the optical pickup device 20 are held. Driving control of the biaxial actuator in the focusing direction and driving control in the tracking direction are performed by the drive control circuit 85, respectively.

  The laser control unit 93 controls the laser light source of the optical pickup device 20. In particular, in this specific example, the laser control unit 93 performs control to vary the output power of the laser light source between the recording mode and the reproduction mode.

  The system controller 84 discriminates the type and number of signal recording layers in the optical disc based on information based on inventory information (Table Of Contents; TOC) recorded in the premastered pits and grooves in the innermost circumference of the optical disc. From which address signals are recorded by track wobbling or the like, it is possible to determine which signal recording layer the recording / reproduction is performed on.

  The drive control circuit 85 is controlled by the system controller 84 and can determine a recording area to be recorded and / or reproduced by detecting a relative position between the optical pickup device 20 and the optical disc D, for example. Here, detecting the relative position between the optical pickup device 20 and the optical disk D includes a case where the position is detected based on an address signal recorded on the optical disk D.

  The optical disk device 81 configured as described above rotates the optical disk D by the spindle motor 82, drives and controls the feed motor 83 according to the control signal from the drive control unit 85, and controls the optical pickup device 20 to the optical disk D. By moving to the position corresponding to the desired recording track of the selected signal recording layer, information is recorded on and reproduced from the selected signal recording layer of the optical disc D.

  As shown in FIG. 2, the optical pickup device 20 has a light source 21 that emits a light beam having a predetermined short wavelength, for example, λ = 405 nm, and a focal length of the light beam emitted from the light source 21 in a discrete and / or continuous manner. The two liquid crystal elements 25 and 24 that change with each other, and the light beam whose focal length is discretely and / or continuously changed by the two liquid crystal elements 25 and 24 is condensed on the signal recording layer of the optical disc D An objective lens 27 that transmits the return light from the optical disk D and a photodetector 30 that detects the amount of return light transmitted through the objective lens 27 are provided.

  Further, the optical pickup device 20 includes a collimator lens 22 that converts laser light emitted from the light source 21 into a parallel light beam between the light source 21 and the liquid crystal element 24, and a parallel light beam from the collimator lens 22 as an objective lens. And a polarization beam splitter 23 that transmits in the 27 direction and reflects the return light from the optical disk D via the objective lens 27 perpendicularly to the direction of the photodetector 30. A quarter wavelength plate 26 is provided between the liquid crystal element 25 and the objective lens 27. Further, the optical pickup device 20 includes a focusing lens 28 and a cylindrical lens 29 between the polarization beam splitter 23 and the photodetector 30.

  The light source 21 is driven by a drive circuit (not shown), can emit blue-violet laser light having a wavelength λ of 405 nm, and emits a light beam having an emission power suitable for recording characteristics and reproduction characteristics.

  The objective lens 27 having NA (numerical aperture) = 0.85 is adopted, and a light beam whose aperture is limited to an appropriate numerical aperture can be condensed on a selected signal recording layer of the optical disc D. it can. The objective lens 27 is held by an objective lens driving mechanism such as a biaxial actuator (not shown), and is driven and displaced in the focusing direction parallel to the optical axis of the objective lens based on the focusing servo signal. The objective lens 27 is also based on the tracking servo signal. Thus, it is driven and displaced in the tracking direction orthogonal to the optical axis of the objective lens.

  The collimator lens 22 converts the divergence angle of the light beam emitted from the light source unit 21 and emits it to the liquid crystal element 24 side through the PBS 23.

  The laser light emitted from the light source 21 becomes a parallel light beam through the collimator lens 22 and enters the polarization beam splitter 23. The polarizing beam splitter 23 transmits the parallel light flux and makes it incident on the liquid crystal elements 24 and 25.

  The liquid crystal element 24 generates a continuous power aberration, that is, a defocus aberration depending on the applied voltage. Further, the liquid crystal element 25 generates power aberrations discretely according to the applied voltage. The light beams transmitted through the liquid crystal elements 24 and 25 are converted into circularly polarized light by the quarter wavelength plate 26 and reach the objective lens 27. The objective lens 27 converges the light beam on the recording surface of the optical disc 7.

  The light beams reflected by the signal recording layer L0 and the signal recording layer L1 of the optical disc D are converted into parallel light beams by the objective lens 27 and then transmitted through the quarter-wave plate 26 again. After being converted into polarized light and transmitted through the liquid crystal elements 25 and 24, the light enters the polarizing beam splitter 23. The light beam reflected by the polarizing beam splitter 23 passes through the focusing lens 28 and the cylindrical lens 29 and then reaches the light receiving surface of the photodetector 30.

  FIG. 3 is a structural diagram of the optical disc D. As described above, the optical disc D has two recording layers. The disc thickness is 1.2 mm. For example, the thickness of the substrate RL, which is polycarbonate, is about 1.1 mm. The light beam OB from the optical pickup device 20 is irradiated from the transparent cover layer CLV side.

  In addition, the optical disk D is formed with a recording layer L0 formed of a first phase change recording film on a substrate RL having a thickness of about 1.1 mm, and a second phase change recording film sandwiched by a 25 μm intermediate layer ML. The recording layer L1 is formed. A 75 μm cover layer CVL is formed on the recording layer L1. The first recording layer L0 is located 100 um from the surface of the cover layer CVL, as in the case of a single-layer disc.

  The optical disk D can realize a capacity exceeding 20 GB, for example, by shortening the wavelength of the light source of the optical pickup device, increasing the numerical aperture of the objective lens, and further forming two layers. However, a short wavelength laser (wavelength 405 nm) and a high numerical aperture (for example, 0.7 or more) of the objective lens cause spherical aberration.

  In particular, the thickness of the interlayer distance (corresponding to the thickness of the intermediate layer ML) required for reasons such as a change in the thickness of the transparent cover layer CLV on the light incident side and prevention of interlayer interference between the two recording layers. Spherical aberration due to change. Accordingly, in order to correct the spherical aberration due to the transparent cover layer CLV and the intermediate layer ML, spherical aberration correction means is required.

  In the configuration shown in FIG. 2, the two liquid crystal elements 25 and 24 generate spherical aberration for correcting spherical aberration generated by the transparent cover layer CLV and the intermediate layer ML of the optical disc D. Specifically, the liquid crystal elements 25 and 24 change the refractive power and change the divergence convergence angle of the light beam incident on the objective lens 27 by changing the refractive power. In other words, by changing the imaging magnification of the objective lens 27, the spherical aberration generated in the light beam emitted from the objective lens 27 is used to generate the change in the thickness of the transparent cover layer CLV and the intermediate layer ML of the optical disc D. To correct spherical aberration. One liquid crystal element is formed by sandwiching liquid crystal molecules between two glass substrates on which transparent electrodes are formed.

  When a driving voltage is applied to each transparent electrode, the orientation of the liquid crystal molecules is deviated according to the electric field generated by the applied voltage, thereby arbitrarily changing the refractive power given to the light beam passing through the liquid crystal element. That is, the liquid crystal element can change the divergence angle of the transmitted light beam. By changing the refractive power, the divergence angle can be changed to arbitrarily change the power aberration, that is, the defocus aberration component. Thereby, the amount of spherical aberration generated in the light beam emitted from the objective lens 27 can be changed. Here, the power aberration and defocus aberration components mean power aberration and defocus aberration as a wavefront aberration classification corresponding to the Z4 term in the fringes Zernike aberration polynomial.

  The liquid crystal element 25 generates discrete power aberrations such as binary values, and focuses a spot 41 on the signal recording layer L1 to a spot 43 on the signal recording layer L0 as shown in FIG. When jumping, first, the spot 42 is set so that it is always located outside the margin from the position of the jump destination L0 and in the area 45 on the disk surface side where light enters.

  FIG. 4 shows the principle of the present invention using the above embodiment. In FIG. 4, the distance between the signal recording layer L0 and the signal recording layer L1 of the optical disc D is 25 μm ± 5 μm, and the spot position margin after the jump in the focus jump is two above and below the recording layer L0 in the figure. The range is ± 5 μm as indicated by the dotted line. For example, considering that the current spot is in the recording layer L1 and a focus jump is made to the recording layer L0, the distance is ± 5 μm from the position of the jump destination layer L0.

  When the spot 41 on the signal recording layer L1 is focus-jumped to the spot 43 on L0, the power generation amount of the liquid crystal element 25 that generates discrete power aberration is set to the position of the jump destination L0 like the spot 42. From the margin, it is set so that it is always located in the area on the disk surface side 45 where light enters. This setting is called rough adjustment. That is, in this rough adjustment, it is possible to reliably grasp whether the spot position is in front of or behind the desired jump destination layer position.

  Thereafter, the liquid crystal element 24 that generates continuous power aberration is adjusted in one direction so as to be within the jump position margin of the recording layer L0. This adjustment is called fine adjustment.

  Next, the calculation of the focus error signal FE will be described with reference to FIG. The four-divided light receiving region in the light detector 30 includes light receiving portions A, B, C, and D, and outputs light receiving signals A, B, C, and D corresponding to the amount of received light. The analog signal processor 3 generates a focus error signal FE, a reproduction RF signal RF, and the like using these light reception signals A, B, C, and D, and supplies them to the AD converter 4.

The focus error signal FE and the reproduction RF signal are
FE = (A + C)-(B + D)
RF = A + B + C + D
It is calculated as follows. Further, the tracking error signal TE is calculated by a push-pull signal using the above-described four-divided light reception signal.

  In the optical disk device 1 of the present embodiment, the optical pickup device 20 used is between two layers, and a light beam is emitted by a focus servo based on a change in the magnitude of a voltage applied by the liquid crystal elements 24 and 25. The focus of the light beam is moved from the focused layer to the outside of the possible range of the desired layer, and then the light beam is focused on the desired layer.

  FIG. 6 is a diagram for explaining rough adjustment and fine adjustment, and schematically illustrates a state in which the optical pickup device 20 causes the spot 41 on the signal recording layer L1 in the optical disc D to focus jump to the spot on L0. FIG. FIG. 7 is a flowchart showing a processing procedure for causing the spot 41 on the signal recording layer L1 in the optical disc D to focus jump to the spot on L0.

  First, the optical pickup device 20 sets the power generation amount of the liquid crystal element 25 that generates discrete power aberration in step S1 in FIG. 7 with a margin of +5 μm from the position of the recording layer L0 that is the jump destination like the spot 42. The coarse adjustment is performed so that the outer surface is located in a region on the disk surface side where light enters. For example, if the layer spacing is 25 μm ± 5 μm, the correction amount is set to 20 μm or less. As a result, the spot position always exists in front of the jump destination layer. As described above, the optical pickup device 20 grasps that the light spot is currently outside the margin of +5 μm from the position of the recording layer L0 that is the jump destination, and is located in the area on the disk surface side where the light is incident. is made of. Therefore, in the next step S2, the adjustment direction of the light spot can be uniquely determined.

  In an actual interlayer jump, the coarse adjustment liquid crystal element generates a power aberration designed in advance at the moment of the jump, and the SA shortage in the coarse adjustment is corrected by the fine adjustment liquid crystal element.

  As described above, since the optical pickup device 2 knows the current position of the light spot, in step S2, the range of the jump position margin of the recording layer L0 by the liquid crystal element 24 that generates continuous power aberration. Fine adjustments can be made in a unique direction so that they fall within the range. At this time, the adjustment can be confirmed by the waveform shown in FIG. In step S4, the focus pull-in is completed and the focus is turned on.

  FIG. 8 shows a driving voltage waveform for the liquid crystal element 25. The liquid crystal element 25 is a so-called binary power liquid crystal that generates discrete power aberrations like binary values. As a driving condition, the driving waveform is an AC wave having a 50% duty rectangular shape. The drive frequency is 1000 Hz, and the drive voltage V is 4.0 Vrms. The drive waveform will be described in detail. After an acceleration pulse of an arbitrary form is generated at the timing when the liquid crystal is turned on, the post-acceleration drive voltage V is kept constant at 4.0 Vrms. Then, the drive voltage is set to 0 V at the timing when the liquid crystal is turned off. It should be noted that the acceleration driving described here is merely an example and is not limited to this.

  As described above, according to the optical pickup device 20 shown in FIG. 2, it is possible to accurately grasp which side the spot position by the coarse adjustment is on the desired layer of the focus jump destination. As a result, the direction of the focus search at the jump destination can be uniquely determined, and an efficient focus jump is possible.

  Next, another specific example (referred to as an optical pickup device 20 ′) that can be applied to the optical disc device 81 will be described with reference to FIGS. 9 to 11.

  FIG. 9 shows an aspect of another embodiment of the optical pickup device of the present invention. The difference from the optical pickup device 20 shown in FIG. 2 is that one liquid crystal element 51 is used instead of the two liquid crystal elements 25 and 24. The liquid crystal element 51 discretely changes the focal length of light transmitted through the liquid crystal according to the magnitude of the applied voltage. The optical pickup device 20 ′ is characterized in that the liquid crystal element 51 discretely generates power aberration 25 μm ± 5 μm corresponding to the layer spacing corresponding to the intermediate layer ML and at the same time the objective lens 27 is moved away from the disk D. To reduce the substantial spherical aberration correction amount. The shift of the objective lens 27 at the time of jump is characteristic.

  FIG. 10 is a diagram schematically showing how the spot 41 on the signal recording layer L1 in the optical disc D is focus-jumped to the spot on L0 by the optical pickup device 20 '. FIG. 11 is a diagram showing a processing procedure of the optical pickup device at this time.

  When a focus jump is made from the signal recording layer L1 to the signal recording layer L0, in step S11, the optical pickup device 20 'discretely generates power aberration 25 μm ± 5 μm corresponding to the layer interval by the liquid crystal element 51. At the same time, the objective lens 27 is shifted away from the disk D in step S2 to reduce the substantial spherical aberration correction amount.

  The lens shift amount here is set so that it is always located outside the spot position margin after the jump, that is, in the area on the disk surface side where light enters, as in the spot example 42 in FIG.

  When jumping to a desired layer, that is, when the liquid crystal element 51 generates power aberration, the objective lens 27 is shifted in the direction away from the optical disc D, thereby reducing the substantial correction amount. For example, if the layer spacing is 25 μm ± 5 μm, the correction amount is set to 20 μm or less. As a result, the spot is always positioned in front of the jump destination layer. Further, fine adjustment is performed for the shortage of the spherical aberration correction amount while returning the lens shifted at the time of jump to the original position.

  As described above, the optical pickup device 20 ′ is located outside the margin of +5 μm from the position of the recording layer L0 where the light spot is the jump destination, and is located in the area on the disk surface side where the light enters. I know. Therefore, in the next step S13, the adjustment direction of the light spot can be uniquely determined.

  As described above, since the optical pickup device 20 ′ knows the current position of the light spot, it returns to the range of the jump position margin of L0 while returning the lens shifted in step S13 to the original position. Thus, fine adjustment can be performed in a unique direction. Then, in step S14, the adjustment can be confirmed by the waveform as shown in FIG. 14, and the focus pull-in is completed and the focus is turned on.

  The drive voltage control for the liquid crystal element 51 can be performed using the waveform shown in FIG.

  The focus jump by the optical pickup device 20 does not need to shift the objective lens, and thus is not affected by various characteristics of the actuator. In the focus jump by the optical pickup device 20 ', the number of liquid crystal elements to be used can be reduced.

  In any case, since it is not possible to determine whether the spot position is nearer or farther than the jump destination layer, the above two methods are different from the conventional technique in which the direction of spherical aberration correction is not uniquely determined. By using two focus jump methods, the correction direction is determined as one direction, and as a result, quick and stable layer jump is possible.

  In the optical pickup device 20 and the optical pickup device 20 ′ shown in FIGS. 2 and 9, a liquid crystal element is used as the power aberration generating means. However, the amount of power aberration generated can be changed by control. What is necessary is just to be not restricted to a liquid crystal element. For example, a liquid lens may be used as the power aberration generating means.

  Further, in the first embodiment (optical pickup device 20) of FIG. 2, the power aberration generated by the applied voltage changes discretely, for example, a liquid crystal element 25 that takes only a binary state (binary power liquid crystal). Although the liquid crystal element 24 (continuous power liquid crystal) that changes continuously is used, the order of this arrangement is shown in a range in which the optical coupling efficiency and the imaging magnification are not greatly changed, for example, Japanese Patent Laid-Open No. 2006-54007. Any one of them may be disposed on the objective lens 27 side as long as it is arranged at an interval between the aperture stop and the liquid crystal element.

Japanese Patent Application Laid-Open No. 2006-54007 discloses an optical pickup device that records and / or reproduces an information signal with respect to a selected signal recording layer of an optical disc having at least two signal recording layers, and enters an objective lens. An aperture limiting element that regulates the aperture diameter of the light beam, and provided between the light source and the objective lens, the refractive power is variable, and the refractive power is changed to change the divergence angle of the light beam emitted from the light source. Spherical aberration generated due to the difference in thickness from the disk surface on which the light beam is incident to the signal recording layer between the two most separated signal recording layers among the two or more signal recording layers. The difference in quantity, NA is the numerical aperture of the objective lens, λ is the wavelength of the light beam emitted from the light source, L is the distance between the refractive power variable element and the aperture limiting element, and φ When the aperture diameter is restricted by the aperture limiting element,
((1.5 / 4.4) × 103) · (ΔSA3 / NA3) (λ · L / φ2) ≦ 0.1
It becomes. Further, the distance L between the refractive power variable element and the aperture limiting element is
In this technique, L / (φ2) ≦ 1.8.

  In FIG. 4, the principle of the present invention has been described using the focus jump from the signal recording surface L1 to the signal recording surface L0 of the dual-layer disc as an example. However, the basic principle is also applied to the jump from the signal recording surface L0 to the signal recording surface L1. Are the same.

  In FIG. 4, the spot position after the jump is an area close to the disk surface on which light is incident, such as the spot 42. However, in principle, the spot position after the jump is always either on the front side or the back side of the jump destination layer. There is a spot and it is only necessary to grasp the spot, and the power generation amount of the binary power liquid crystal (liquid crystal element 25) of the first embodiment and the embodiment so that the spot position after the jump is always at the position on the spot 44 side. It is also possible to determine the objective lens shift amount of 2.

  In FIG. 9, the liquid crystal element 51 is used as the power aberration generating means. This generates the power aberration corresponding to the layer spacing discretely, but any power aberration corresponding to the layer spacing may be used, and a continuous power liquid crystal may be used.

  In the above-described embodiment, it is needless to say that an optical disc having three or more signal recording layers, which is a two-layer optical disc composed of signal recording layers L0 and L1, can be used as an optical disc. In addition, it is obvious that the present invention can be applied to a focus jump from the current signal recording layer L4 to the signal recording layer L0 that is two layers.

It is a schematic block diagram of an optical disk device. It is a block diagram of an optical pick-up apparatus. It is a block diagram of an optical disk. It is principle explanatory drawing of an optical pick-up apparatus. It is a figure which shows the light-receiving area | region of a photodetector. It is a figure for demonstrating rough adjustment and fine adjustment. It is a flowchart which shows the process sequence of the optical pick-up apparatus of FIG. It is a drive voltage waveform figure with respect to the liquid crystal element as a binary power liquid crystal. It is a block diagram of the optical pick-up apparatus used as another specific example. It is principle explanatory drawing of the optical pick-up apparatus of another specific example. It is a flowchart which shows the process sequence of the optical pick-up apparatus of FIG. FIG. 11 is a configuration diagram of an optical disc device disclosed in Patent Document 6. 10 is a configuration diagram of an optical pickup device disclosed in Patent Document 6. FIG. FIG. 10 is a characteristic diagram of a sum signal and a focus error signal disclosed in Patent Document 6. 10 is a configuration diagram of an optical pickup device disclosed in Patent Document 7. FIG. It is a figure for demonstrating the subject of this invention.

Explanation of symbols

20 optical pickup device, 21 light source, 22 collimator lens, 23 polarization beam splitter, 24 liquid crystal element (continuous change), 25 liquid crystal element (discrete change), 27 objective lens, 30 photodetector, D optical disk, L0, L1 Signal recording layer

Claims (7)

In an optical pickup apparatus for recording and / or reproducing information signals with respect to a selected signal recording layer of an optical disc having at least two signal recording layers,
A light source that emits a light beam of a predetermined wavelength;
An objective lens that focuses the light beam emitted from the light source on the signal recording layer;
And at least one liquid crystal element that discretely and / or continuously changes the focal length of the light transmitted through the liquid crystal according to the magnitude of the applied voltage,
Presence of a desired layer between the predetermined two layers of the at least two signal recording layers and the light beam focused by the focus servo based on the change in the magnitude of the voltage applied by the liquid crystal element An optical pickup device, wherein the focus of the light beam is moved outside a possible range, and then the light beam is focused on a desired layer. The liquid crystal element can be used in any of the cases where the focus is focus-jumped from the layer on which the light beam is focused between the predetermined two layers to a layer farther or closer to the disk surface on which the light beam is incident. And
2. The apparatus according to claim 1, wherein the movement is limited to a position separated by a predetermined distance or more from the jump destination layer, either in an area near or far from the disk surface, with the jump destination layer interposed therebetween. Optical pickup device. An objective lens for condensing the light beam emitted from a light source that emits a light beam of a predetermined wavelength on the signal recording layer, and the focal length of the light transmitted through the liquid crystal according to the magnitude of the applied voltage is discrete and And / or recording and / or reproducing information signals with respect to a selected signal recording layer of an optical disc comprising at least one or more continuously changing liquid crystal elements and having at least two or more signal recording layers. In the focus control method executed in the optical pickup device,
Presence of a desired layer between the predetermined two layers of the at least two signal recording layers and the light beam focused by the focus servo based on the change in the magnitude of the voltage applied by the liquid crystal element A first step of moving the focus of the light beam outside of the possible range;
A focus control method comprising: a second step of focusing the light beam moved outside the range in which the desired layer can exist in the first step on the desired layer.   In the first step, the focus of the light beam is moved discretely and / or continuously by changing the voltage applied to the liquid crystal element, and in the second step, the objective lens is perpendicular to the signal recording layer. 4. The focus control method according to claim 3, wherein the focus control method is moved in a direction. In any of the cases where the focus jumps from the layer where the light beam is focused between the two predetermined layers by the liquid crystal element to a layer farther and / or closer to the disk surface on which the light beam is incident,
In the first step, the movement is limited to a position at least a predetermined distance away from the jump destination layer in either the area close to and / or the area far from the disk surface with the jump destination layer in between. 5. The focus control method according to claim 3, wherein the focus control method is characterized in that: By changing the voltage applied to the liquid crystal, at least one liquid crystal element that moves the focus of the light beam discretely and / or continuously is used, and an optical disc having at least two signal recording layers is selected. A focus jump method executed in an optical pickup device for recording and / or reproducing information signals with respect to the signal recording layer,
A first step of adjusting one direction toward a desired layer by the liquid crystal element that discretely moves the focal point of the light beam;
A focus jump method comprising: a second step of performing adjustment in one direction toward a desired layer by the liquid crystal element that continuously moves the focal point of the light beam. A selected signal of an optical disc using at least one liquid crystal element that discretely and / or continuously moves the focal point of the light beam by changing the voltage applied to the liquid crystal and having at least two signal recording layers A focus jump method executed in an optical pickup device that records and / or reproduces an information signal using an objective lens with respect to a recording layer,
A first step of adjusting the one direction toward the desired layer by the liquid crystal element;
A focus jump method comprising: a second step of adjusting the direction toward a desired layer by moving the objective lens in a direction perpendicular to the signal recording layer.

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