JP5115569B2 - Optical drive device - Google Patents

Description

  The present invention relates to an optical drive device, and more particularly to an optical drive device that performs layer recognition of a multilayer optical disk using a pull-in signal.

  In an optical drive device for reproducing and recording an optical disc such as a CD (Compact Disc), DVD, or BD (Blu-ray Disc (registered trademark)), a focus servo for focusing on a recording layer of the optical disc, and a recording Tracking servo for focusing on the center of the track formed in the layer is performed.

  There are various specific methods for realizing these servos. In a typical example, the astigmatism method is used for the focus servo, and the differential push-pull method is used for the tracking servo. In this case, the optical system of the light beam is provided with a diffraction grating and a cylindrical lens. In addition, the photodetector for receiving the light beam reflected by the optical disc has three light receiving surfaces each having a square light receiving region.

  FIG. 39 is a plan view of the photodetector 100 having such three light receiving surfaces (the main beam light receiving surface 101 and the sub beam light receiving surfaces 102 and 103). The three light receiving surfaces are provided so as to be able to receive the three diffracted lights (0th order diffracted light and ± 1st order diffracted light) output from the diffraction grating, respectively. In the example of FIG. It is arranged at a position where it can receive folding light (hereinafter referred to as “main beam MB”), and the sub-beam light receiving surfaces 102 and 103 are respectively + 1st order diffracted light (hereinafter referred to as “subbeam SB1”) and −1st order diffracted light (hereinafter referred to as “subbeam SB1”). , “Sub-beam SB2”). FIG. 39 also shows the shape of a spot formed by each of these light beams on the photodetector 100.

  The sides of each light receiving surface are parallel to the X direction and the Y direction shown in FIG. The X direction is the moving direction of the spot on the photodetector 100 when the focal point of the light beam (signal light) focused on the recording layer moves in the tangential direction of the optical disc on the optical disc recording surface. Hereinafter, it is referred to as “signal light tangent direction”. The Y direction is a spot moving direction on the photodetector 100 when the focal point of the signal light moves in the radial direction of the optical disk on the optical disk recording surface, and is hereinafter referred to as “signal light radial direction”. .

  The main beam light receiving surface 101 is used for both focus servo and tracking servo.

First, the focus servo will be described. Since astigmatism is given to the main beam MB that has passed through the cylindrical lens, spots having different shapes are formed on the main beam light receiving surface 101 depending on whether or not the recording layer is focused. Is done. A spot MB ₀ shown in FIG. 39 shows an example in which the recording surface is focused, and the spot in this case is circular as shown in FIG. On the other hand, the spots MB ₁ and MB ₂ shown in FIG. 39 show an example in which the recording surface is not focused, and the spot in this case is the diagonal direction of the main beam receiving surface 101 as shown in FIG. It becomes an elongated shape. Focus servo by the astigmatism method is performed using such a difference in spot shape. For this purpose, the main beam light receiving surface 101 is divided into four light receiving regions 101A to 101D each having a square shape. By using a signal (focus error signal) obtained by subtracting the total signal of the light receiving area 101B and the light receiving area 101D from the total signal of the light receiving area 101A and the light receiving area 101C, a difference in spot shape can be detected.

  Next, the tracking servo will be described. Since the light beam applied to the optical disk is diffracted by the track, the spots formed on the photodetector 100 have both ends in the signal light radial direction as shown in FIG. Interference areas E1 and E2 called push-pull areas appear. There is no difference in the light intensity between the push-pull region E1 and the push-pull region E2 when the focal point of the light beam is at the track center, but there is a difference otherwise. Therefore, a signal (hereinafter referred to as “push-pull signal”) obtained by calculating the difference between the sum of the output signals of the light receiving areas 101A and 101D and the sum of the output signals of the light receiving areas 101B and 101C is referred to by the focus servo. Assuming that this is the case, the value is 0 when the focus of the light beam is at the center of the track, and takes a non-zero value only when it is not. The tracking servo is performed using such a property of the push-pull signal.

  The sub-beam light receiving surfaces 102 and 103 are light receiving surfaces that are particularly provided for performing tracking servo by the differential push-pull method. In the optical drive device, an objective lens is used to focus the light beam on the recording surface of the optical disc. The tracking servo is a technique for focusing the light beam on the track center by moving the objective lens in the radial direction of the signal light, but is formed on the photodetector 100 when the objective lens is moved. The spot also moves in the signal light radial direction. This is called lens shift, and tracking servo is greatly affected by lens shift because it uses a push-pull signal. The sub beam receiving surfaces 102 and 103 are used to reduce the influence of such lens shift. As shown in FIG. 39, since the relationship between the push-pull areas E1 and E2 is reversed between the main beam MB and the sub-beams SB1 and SB2, the lens shift can be achieved by using the output signals of the sub-beam receiving surfaces 102 and 103. This makes it possible to cancel the offset generated in the push-pull signal.

  Patent Documents 1 and 2 disclose examples of optical drive devices having light receiving surfaces corresponding to the sub-beam light receiving surfaces 102 and 103.

Japanese Patent Laying-Open No. 2005-346882 (Abstract) JP 2007-287232 A (Abstract)

  By the way, in recent years, multilayered optical discs having a plurality of recording layers have attracted attention. When reproducing / recording a multi-layered optical disk, the optical drive apparatus performs layer recognition processing for automatically recognizing the recording layer. The layer recognition processing includes, for example, layer number counting processing for obtaining the number of recording layers, objective lens focal length rough adjustment processing, and objective lens in-focus recognition processing performed as part of focus servo. .

  In the layer recognition process, a pull-in signal (a total addition signal obtained by adding all the output signals of the light receiving areas 101A to 101D) indicating the total light receiving amount of the main beam light receiving surface 101 is used. Usually, however, a low-pass filter is provided to remove RF signals and the like. The spot formed on the photodetector 100 by the main beam MB is sized to fit within the main beam receiving surface 101 when any recording layer is in focus, but gradually as the focus shifts. It becomes larger and protrudes from the main beam light receiving surface 101. For this reason, the pull-in signal becomes smaller as the focus shifts. When there are a plurality of recording layers, the pull-in signal becomes maximum when any recording layer is in focus, and the pull-in signal becomes minimum when the recording layer is in focus. The layer recognition process is performed using such a property of the pull-in signal.

  The layer recognition process will be specifically described with reference to FIG. FIG. 40A shows a pull-in signal PIM and a focus error signal FE when a multilayered optical disk having two recording layers with an interlayer distance of 20 μm is used. In the figure, the horizontal axis represents the focal length (μm) of the objective lens, and the vertical axis represents the amplitude of each signal. In the figure, the return optical magnification is 15 times, the spot diameter at the time of focusing is 50 μm, and the width of the main beam light receiving surface 101 in the signal light tangent direction is 100 μm. W1 shown in the figure legend is w1 shown in FIG. That is, the numerical value of w1 shown in parentheses in the legend uses the corresponding signal or the like only for the center w1 μm of the main beam light receiving surface 101 in the signal light tangential direction (when w1 = 100, the entire light receiving surface). It shows that it was generated. Usually, since the pull-in signal PIM is generated using the entire light receiving surface, the following description will be made on the assumption that w1 = 100 for a while.

  In the layer recognition process, first, a threshold value THM having a value that is approximately between the maximum value and the minimum value is determined. For example, the optical drive device determines the maximum value of the amplitude of the pull-in signal PIM by generating the pull-in signal PIM while changing the focal length of the objective lens from the minimum value to the maximum value. Then, for example, 70% of the determined maximum value is stored as the threshold value THM. In FIG. 40A, the threshold THM is 70% of the maximum value of the pull-in signal PIM.

  Next, the optical drive device generates a signal (slice signal PIMSL) that becomes high when the pull-in signal PIM becomes larger than the threshold value THM and becomes low otherwise. The layer number counting process is performed by counting the number of high sections of the slice signal PIMSL. In the example of FIG. 40A, since there are two high sections, 2 is acquired as the number of recording layers.

  On the other hand, in the coarse adjustment processing of the objective lens focal length performed as part of the focus servo, the focus of the light beam is controlled so that focus control can be performed by recognizing the number and position of the high section of the slice signal PIMSL. This is a process of moving to the vicinity. The in-focus recognition process of the objective lens is a process for recognizing whether or not the position where the focus error signal is zero is the in-focus point. That is, since the position where the focus error signal becomes zero exists in addition to the in-focus point, the position where the focus error signal is zero or zero-crossing is recognized as the in-focus point on condition that it is within the high section of the slice signal PIMSL. I have to.

  Note that the accuracy of pull-in signal generation is important when the in-focus recognition process is also performed. That is, it is necessary to generate a pull-in signal such that the focus error signal is only at the focal point within the high interval of the slice signal PIMSL.

  By performing the above processing, it is possible to prevent the focal length of the objective lens from greatly deviating from the recording layer to be accessed and the focus from being adjusted to another recording layer.

  However, in recent years, optical discs having a very small distance between recording layers (interlayer distance) have appeared, and it is difficult to perform layer recognition processing with such optical discs.

  FIG. 40B shows the signals drawn under the same conditions as in FIG. 40A except that the interlayer distance is 10 μm. As can be understood by comparing FIG. 40A and FIG. 40A, the drop in the pull-in signal PIM between layers decreases as the interlayer distance decreases. As a result, in the pull-in signal PIM (w1 = 100) shown in FIG. 40B, the high section of the first layer and the high section of the second layer are connected. In this case, the layer recognition process cannot be executed. This is because the influence of the reflected light (stray light) from other than the access target layer is increased as the interlayer distance is reduced.

  Whether or not the layer recognition process can be performed can be evaluated using a PI interlayer separation index. The PI interlayer separation index is defined for each of the two adjacent recording layers, and Δ1 (the smaller one of the maximum values of the two adjacent recording layers) and Δ2 (adjacent) shown in FIG. It is expressed as Δ2 / Δ1 × 100 (%) using the difference between the smaller one of the maximum values of the two recording layers and the minimum value between the layers. As a condition for appropriately executing the layer recognition process, the PI interlayer separation index is required to be 20% or more.

  FIG. 41 is a diagram showing the relationship between the width w1 and the PI interlayer separation index for each interlayer distance. D shown in the figure legend is the interlayer distance (μm). As shown in the figure, when the width w1 is 100 μm, that is, when the pull-in signal PIM is generated using the entire light-receiving surface of the main beam light-receiving surface 101, the problem particularly occurs when the interlayer distance is 20 μm and 15 μm. However, when the interlayer distance is 10 μm, the PI interlayer separation index is less than 20%, and the layer recognition process cannot be performed properly.

  Regarding the above problems, the inventor of the present invention has previously proposed that the pull-in signal PIM is generated using only the central portion of the main beam receiving surface 101 in the signal light tangent direction. As shown in FIG. 41, the PI interlayer separation index of the pull-in signal PIM has a property of becoming larger as the width w1 is smaller. Even if the interlayer distance is 10 μm, if the width w1 is approximately 90 μm or less, PI The interlayer separation index is 20% or more. This indicates that if the pull-in signal PIM is generated using only the central portion of the main beam light receiving surface 101 in the signal light tangent direction, the layer recognition process can be performed even if the interlayer distance is small. Yes.

  However, the use of only the central portion of the main beam light receiving surface 101 in the signal light tangent direction means that the main beam light receiving surface 101 is further divided. Since the main beam light receiving surface 101 is used for generating a data signal (RF signal) in addition to the focus servo and tracking servo, it is preferable not to divide the main beam light receiving surface 101 into four or more. In addition, when it is intended to use only the center 10 μm in the signal light tangent direction, it is difficult to manufacture the 5 μm width, so the dividing line along the center line in the signal light tangential direction is eliminated, and the center line A dividing line is inserted at a distance of 5 μm on both sides. Such a division affects the accuracy of the focus servo, so it is preferable not to do this if possible.

  Accordingly, one of the objects of the present invention is to provide an optical drive device that can perform layer recognition processing even when the interlayer distance is small while avoiding the division of the main beam light receiving surface as much as possible.

  In particular, regarding the in-focus recognition processing, when the interlayer distance is small, even if the high section of the slice signal PIMSL appears for each recording layer, the focal distance at which the focus error signal FE becomes zero is high for the slice signal PIMSL. It may not be included in the section. In this case, no matter how much the focal length of the objective lens is moved within the high interval of the slice signal PIMSL, the focal point (focal length at which the focus error signal FE becomes zero) cannot be reached. That is, the focus servo cannot be performed correctly.

  Accordingly, another object of the present invention is to provide an optical drive device capable of performing focus servo with in-focus recognition processing even when the interlayer distance is small.

  In order to achieve the above object, an optical drive device according to the present invention includes a diffraction grating that divides a light beam applied to a multilayer optical disk having a plurality of recording layers into a main beam and first and second sub beams, and the multilayer. A main beam light-receiving surface and a first and second sub-beam light-receiving surface arranged so as to be able to receive the main beam reflected by the optical disc and the first and second sub-beams, respectively. A light detector that outputs a signal indicating the amount of light received by the first sub-beam light-receiving surface, and a light output that indicates the amount of light received by the second sub-beam light-receiving surface. Pull-in signal generating means for generating a pull-in signal based on the sum signal with the second output signal of the device, and layer recognizing means for performing layer recognition processing based on the pull-in signal; Characterized in that it comprises.

  The main beam is also received by the first and second sub-beam receiving surfaces when the focal point is between the layers. However, the amount of main beam received on the first and second sub-beam receiving surfaces decreases as the interlayer distance decreases. It ’s a big drop. As a result, the pull-in signal generated based on the sum signal of the first and second sub-output signals also drops significantly between the layers as the interlayer distance is smaller. Therefore, the layer recognition process can be performed even when the interlayer distance is small while avoiding the division of the main beam light receiving surface as much as possible.

  The optical drive device according to the first aspect of the present invention is characterized in that, in the optical drive device, the pull-in signal is the total signal or a signal obtained by amplifying the total signal at a predetermined amplification factor. In this case, the length of the first and second sub beam light receiving surfaces in the signal light tangent direction may be 1.4 times or less the diameter of the spot formed on each light receiving surface by the corresponding sub beam. .

  In the optical drive device according to the second aspect of the present invention, in the optical drive device, the pull-in signal generating means is also based on a third output signal of the photodetector indicating the amount of light received by the main beam light receiving surface. The pull-in signal is generated. In this case, the pull-in signal may be a total signal of the third output signal and a signal obtained by amplifying the total signal with a predetermined amplification factor.

  In the optical drive device according to the first and second aspects of the present invention, the optical drive device includes an objective lens for condensing the main beam and the first and second sub beams onto the multilayered optical disk, and the pull-in signal generating means Generating a first slice signal having a first value when the pull-in signal is greater than a first threshold value and a second value otherwise, the layer recognizing means Acquiring the number of recording layers of the multilayered optical disc by counting the number of sections in which the first slice signal is the first value while moving in the normal direction of the multilayered optical disc. It is good.

  In the optical drive device according to the first and second aspects of the present invention, the optical drive device includes an objective lens for condensing the main beam and the first and second sub beams onto the multilayered optical disk, and the pull-in signal generating means Generating a first slice signal having a first value when the pull-in signal is greater than a first threshold value and a second value otherwise, the layer recognizing means By recognizing at least one of the number or position of the section where the first slice signal becomes the first value while moving in the normal direction of the multilayered optical disc, the focus of the light beam is recorded in the plurality of recordings. It is good also as moving to the access object layer vicinity of a layer.

  In the optical drive device according to the first and second aspects of the present invention, an objective lens for condensing the main beam and the first and second sub-beams on the multilayered optical disk, and light reception by the main beam receiving surface. A focus error signal generating unit configured to generate a focus error signal based on an output signal of the photodetector indicating the amount, and the pull-in signal generating unit is configured to output a first error when the pull-in signal is greater than a first threshold value. A first slice signal that becomes a value of 1 and a second value otherwise, the layer recognition means generates the focus error signal when the first slice signal is the first value. Recognizes whether the focus error signal is at the in-focus position by recognizing the position where the focus error signal is zero or zero-crossing as the in-focus position. It is also possible.

  In the optical drive device according to the third aspect of the present invention, in the optical drive device, the pull-in signal generating means has a first value when the total signal is larger than a second threshold value, and otherwise. A second slice signal that is a second value and a third value that is the first value if the third output signal is greater than a third threshold value, and that is the second value otherwise. And the pull-in signal becomes the first value when both the second and third slice signals are the first value, and the pull-in signal is the second value otherwise. It is the signal which becomes.

  In the optical drive device according to the third aspect of the present invention, the optical disk drive further comprises an objective lens for condensing the main beam and the first and second sub beams onto the multilayered optical disk, and the layer recognition means includes the objective lens. The number of recording layers of the multi-layered optical disk may be acquired by counting the number of sections in which the pull-in signal becomes the first value while moving in the normal direction of the multi-layered optical disk. Good.

  In the optical drive device according to the third aspect of the present invention, the optical disk drive further comprises an objective lens for condensing the main beam and the first and second sub beams onto the multilayered optical disk, and the layer recognition means includes the objective lens. By recognizing at least one of the number or position of the section in which the pull-in signal takes the first value while moving the optical disc in the normal direction of the multilayered optical disc, thereby focusing the light beam on the plurality of recording layers. It is good also as moving to the access object layer vicinity.

  In the optical drive device according to the third aspect of the present invention, an objective lens for condensing the main beam and the first and second sub-beams on the multilayered optical disk, and a light receiving amount of the main beam receiving surface are shown. Focus error signal generating means for generating a focus error signal based on an output signal of the photodetector, and the layer recognition means has a zero focus error signal when the pull-in signal is the first value. Alternatively, a process of recognizing whether or not the position where the focus error signal becomes zero may be performed by recognizing a position where the zero crossing is performed as a focal point.

  According to the present invention, the layer recognition process can be performed even when the interlayer distance is small while avoiding the division of the main beam light receiving surface as much as possible. Further, even when the interlayer distance is small, focus servo accompanied with in-focus recognition processing can be performed.

1 is a schematic diagram of an optical drive device according to an embodiment of the present invention. It is explanatory drawing of the astigmatism provided by the sensor lens by embodiment of this invention. It is a top view of the photodetector by embodiment of this invention. It is a figure which shows the functional block of the process part by the 1st Embodiment of this invention. (A) and (b) are respectively simulated on the pull-in signal PIS and its main beam component PIS_M, assuming that the optical disk has a two-layer structure and the interlayer distance d is 10 μm, and the width w2 is 20 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M on the premise that the optical disk has a two-layer structure and the interlayer distance d is 10 μm and the width w2 is 100 μm. It is a figure which shows a result. (A) and (b) are respectively simulated on the pull-in signal PIS and its main beam component PIS_M with a width w2 of 50 μm on the assumption that the optical disk has a two-layer structure and the interlayer distance d is 10 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M on the premise that the optical disk has a two-layer structure and the interlayer distance d is 10 μm, and the width w2 is 10 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M on the premise that the optical disk has a two-layer structure and the interlayer distance d is 15 μm and the width w2 is 100 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M with a width w2 of 20 μm on the premise that the optical disk has a two-layer structure and the interlayer distance d is 15 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M with a width w2 of 10 μm on the premise that the optical disk has a two-layer structure and the interlayer distance d is 15 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M on the premise that the optical disk has a two-layer structure and the interlayer distance d is 20 μm and the width w2 is 100 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M with a width w2 of 20 μm on the assumption that the optical disk has a two-layer structure and the interlayer distance d is 20 μm. It is a figure which shows a result. (A) and (b) were respectively simulated on the pull-in signal PIS and its main beam component PIS_M with a width w2 of 10 μm on the premise that the optical disk has a two-layer structure and the interlayer distance d is 20 μm. It is a figure which shows a result. It is the figure which showed the relationship between PI interlayer isolation | separation parameter | index and width w2 for every interlayer distance d. It is a figure which shows an example of the laminated constitution of the optical disk by embodiment of this invention. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIS and its main beam component PIS_M, assuming that the optical disk has the layer configuration shown in FIG. 16 and having a width w2 of 100 μm. is there. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIS and its main beam component PIS_M, assuming that the optical disk has the layer structure shown in FIG. 16 and having a width w2 of 50 μm. is there. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIS and its main beam component PIS_M, assuming that the optical disk has the layer configuration shown in FIG. 16 and having a width w2 of 20 μm. is there. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIS and its main beam component PIS_M, assuming that the optical disk has the layer structure shown in FIG. 16 and having a width w2 of 10 μm. is there. It is a figure which shows the functional block of the process part by the 2nd Embodiment of this invention. The figure which shows the pull-in signal PIMS simulated about each when the width | variety w2 is 100 micrometers, 50 micrometers, 40 micrometers, 30 micrometers, 20 micrometers, and 10 micrometers on the assumption that an optical disk is 2 layer structure and interlayer distance d is 10 micrometers. It is. It is a figure which shows the pull-in signal PIMS simulated about each when the width | variety w2 is 100 micrometers, 20 micrometers, and 10 micrometers on the assumption that an optical disk is a 2 layer structure and interlayer distance d is 15 micrometers. It is a figure which shows the pull-in signal PIMS simulated about each when the width | variety w2 is 100 micrometers, 20 micrometers, and 10 micrometers on the assumption that an optical disk is a 2 layer structure and the interlayer distance d is 20 micrometers. It is the figure which showed the relationship between PI interlayer isolation | separation parameter | index and width w2 for every interlayer distance d. It is a figure which shows the result of having simulated the pull-in signal PIMS about each when width w2 is 100 micrometers, 50 micrometers, 20 micrometers, and 10 micrometers on the premise that the optical disk has the layer structure shown in FIG. Under the premise that the optical disk has the layer configuration shown in FIG. 16, the pull-in signal PIMS is simulated for each of the cases where the width w2 is 100 μm, 50 μm, 20 μm, and 10 μm, with the constant m being twice that of FIG. It is a figure which shows the result. Under the assumption that the optical disk has the layer structure shown in FIG. 16, the minimum of the PI interlayer separation index is obtained by changing the constant m between 5 and 50 for each of the cases where the width w2 is 100 μm, 50 μm, 20 μm, and 10 μm. It is a figure which shows the result of having simulated the value. It is a figure which shows the functional block of the process part by the 3rd Embodiment of this invention. (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disk has a two-layer structure and the interlayer distance d is 10 μm and the width w2 is 100 μm. . (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disk has a two-layer structure and the interlayer distance d is 10 μm and the width w2 is 20 μm. . (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disk has a two-layer structure and the interlayer distance d is 15 μm and the width w2 is 100 μm. . (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disk has a two-layer structure and the interlayer distance d is 15 μm and the width w2 is 20 μm. . (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disk has a two-layer structure and the interlayer distance d is 20 μm and the width w2 is 100 μm. . (A) and (b) are diagrams showing simulation results of the pull-in signal PIAND assuming that the optical disc has a two-layer structure and the interlayer distance d is 20 μm and the width w2 is 20 μm. . (A) and (b) are diagrams showing the results of simulation of the pull-in signal PIAND, assuming that the optical disk has the layer configuration shown in FIG. 16 and having a width w2 of 100 μm. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIAND with a width w2 of 50 μm on the premise that the optical disc has the layer configuration shown in FIG. (A) and (b) are diagrams showing the results of simulating the pull-in signal PIAND with a width w2 of 20 μm on the premise that the optical disc has the layer configuration shown in FIG. It is a top view of the photodetector by the background art of this invention. (A) and (b) are diagrams showing a pull-in signal PIM and a focus error signal FE when a multilayered optical disk having two recording layers with an interlayer distance of 20 μm and 10 μm is used. It is the figure which showed the relationship between the width | variety w1 and PI interlayer isolation | separation parameter | index for every interlayer distance.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram of an optical drive device 1 according to a first embodiment of the present invention.

  The optical drive device 1 performs reproduction and recording of the optical disk 11. Various optical recording media such as CD, DVD, and BD can be used as the optical disc 11. In this embodiment, a disc-shaped optical disc having a recording surface multilayered by a multilayer film is used.

  As shown in FIG. 1, the optical drive device 1 includes a laser light source 2, an optical system 3, an objective lens 4, a photodetector 5, and a processing unit 6a. Among these, the laser light source 2, the optical system 3, the objective lens 4, and the photodetector 5 constitute an optical pickup.

  The optical system 3 includes a diffraction grating 21, a polarizing beam splitter 22, a collimator lens 23, a quarter wavelength plate 24, and a sensor lens (cylindrical lens) 25. The optical system 3 functions as an outward optical system that guides the light beam emitted from the laser light source 2 to the optical disk 11, and also functions as a backward optical system that guides the return beam from the optical disk 11 to the photodetector 5.

  First, in the forward optical system, the diffraction grating 21 decomposes the light beam emitted from the laser light source 2 into three beams (0th-order diffracted light and ± 1st-order diffracted light) and causes the light beam to enter the polarization beam splitter 22 as P-polarized light. The polarization beam splitter 22 reflects the incident P-polarized light and bends its path in the direction of the optical disk 11. The collimator lens 23 converts the light beam incident from the polarization beam splitter 22 into parallel light. The quarter wavelength plate 24 converts the light beam that has passed through the collimator lens 23 into circularly polarized light. The light beam that has passed through the quarter-wave plate 24 enters the objective lens 4.

  The objective lens 4 condenses the light beam incident from the optical system 3 (a light beam in a parallel light state) on the optical disk 11 and returns the return light beam reflected by the recording surface of the optical disk 11 to parallel light. This return light beam is diffracted on the recording surface, and is decomposed into zero-order diffracted light and ± first-order diffracted light as described with reference to FIG. The 0th-order diffracted light and the ± 1st-order diffracted light are different from the 0th-order diffracted light and ± 1st-order diffracted light generated by the diffraction grating 21. The folded light is referred to as main beam MB, sub beam SB1, and sub beam SB2, respectively. In the case of 0th order diffracted light and ± 1st order diffracted light, it means diffracted light generated by diffraction on the recording surface. The main beam MB, the sub beam SB1, and the sub beam SB2 independently generate reflected light having a push-pull region as described in FIG. Each light intensity of the sub beams SB1 and SB2 is about 1/10 of the light intensity of the main beam MB.

  Next, in the return path optical system, a light beam that has passed through the objective lens 4 and has become S-polarized light by reciprocating the quarter-wave plate 24 is incident on the collimator lens 23. The light beam that has passed through the collimator lens 23 is incident on the polarization beam splitter 22 while being condensed. The polarization beam splitter 22 transmits the incident S-polarized light and makes it incident on the sensor lens 25. The sensor lens 25 gives astigmatism to the light beam incident from the polarization beam splitter 22. The light beam provided with astigmatism enters the photodetector 5.

  FIG. 2 is an explanatory diagram of astigmatism imparted by the sensor lens 25. As shown in the figure, the sensor lens 25 has a lens effect only in one direction (MY axis direction = subordinate direction). Therefore, the focal position of the optical system constituted by the collimator lens 23 (FIG. 1) and the sensor lens 25 differs between the MY axis direction and the MX axis direction (bus line direction) which is a direction perpendicular to the MY axis direction. (MY axis focus and MX axis focus shown in FIG. 2). A point where the lengths of the light beams in the MY axis direction and the MX axis direction are equal is referred to as a focal point.

  In the optical drive device 1, the objective lens 4 is arranged so that the joint point of the light beam (signal light) reflected by the layer to be focused (access target layer) is positioned on the photodetector 5. Position control is performed (focus servo). In other words, the joint point of the light beam (stray light) reflected by a layer other than the access target layer is not located on the photodetector 5, and the spot (stray light spot) that stray light forms on the photodetector 5 is As compared with a spot (signal light spot) formed on the photodetector 5 by the signal light, the signal light has a shape spreading in at least one of the MY axis direction and the MX axis direction.

  Returning to FIG. The photodetector 5 is installed on a plane that intersects the optical path of the return light beam emitted from the optical system 3. The photodetector 5 includes three light receiving surfaces, and each light receiving surface is divided into a plurality of light receiving regions. The optical drive device 1 generates a pull-in signal by various generation processes using these light receiving areas. The specific contents will be described later.

  As an example, the processing unit 6a is configured by a DSP (Digital Signal Processor) having an A / D conversion function that converts analog signals for multiple channels into digital data, and receives an output signal of the photodetector 5, Various signals such as a pull-in signal, a focus error signal, a tracking error signal, and a data signal are generated. Details of the processing of the processing unit 6a will also be described later.

  The CPU 7 is a processing device incorporated in a computer, a DVD recorder, or the like, and transmits an instruction signal for specifying an access position on the optical disc 11 to the processing unit 6a via an interface (not shown). The processing unit 6a that has received this instruction signal controls the objective lens 4 and moves it in the normal direction of the optical disc, thereby focusing on the recording layer to be accessed (focus servo). When the focus servo is applied in this way, the processing unit 6a then realizes a track-on state by moving the objective lens parallel to the surface of the optical disk 11 (tracking servo). When the track is on, the processing unit 6a starts to acquire the data signal. The acquired data signal is output to the CPU 7.

  Hereinafter, details of the configuration of the photodetector 5 and details of the processing of the processing unit 6a will be described.

  First, FIG. 3 is a top view of the photodetector 5 according to the present embodiment, showing a light receiving surface and a light receiving region. In the figure, a spot of signal light is also drawn. As shown in the figure, the photodetector 5 has a main beam light receiving surface S1 and sub beam light receiving surfaces S2 and S3.

  The main beam light receiving surface S1 is a square whose side is x (≧ spot diameter r = 50 μm) and is arranged so as to receive the main beam MB. Specifically, it is point-symmetric with respect to the spot center of the main beam MB, and is symmetrical with respect to a straight line S1x passing through the spot center and parallel to the signal light tangential direction. Further, it is formed so as to be symmetric with respect to a straight line S1y passing through the spot center of the main beam MB and parallel to the signal light tangential direction. In general, the value of x is about twice the spot diameter (100 μm). This is because the area necessary for receiving the signal of the entire spot when performing the focus control using the astigmatism method is about twice the spot diameter.

  The main beam light receiving surface S1 is a so-called four-divided light receiving surface that is divided into four light receiving regions 1A to 1D each having a square shape.

  The sub beam light receiving surface S2 is a square having the same size as the main beam light receiving surface S1, and is arranged so as to be able to receive the sub beam SB1. Specifically, it is point-symmetric with respect to the spot center of the sub beam SB1, and is symmetrical with respect to a straight line S2x passing through the spot center and parallel to the signal light tangential direction. Further, it is formed so as to be symmetric with respect to a straight line S2y passing through the spot center of the sub beam SB1 and parallel to the signal light tangential direction. Similarly, the sub-beam light receiving surface S3 is a square having the same size as the main beam light-receiving surface S1, and is arranged to receive the sub-beam SB2. Specifically, it is point-symmetric with respect to the spot center of the sub beam SB2, and is line-symmetric with respect to a straight line S3x passing through the spot center and parallel to the signal light tangential direction. Further, it is formed so as to be symmetric with respect to a straight line S2y passing through the spot center of the sub beam SB2 and parallel to the signal light tangential direction. The sub beam receiving surface S3 is disposed on the opposite side of the sub beam receiving surface S2 with the main beam receiving surface S1 interposed therebetween.

  The sub-beam light receiving surfaces S2 and S3 are arranged so as to be slightly shifted in the opposite direction to the signal beam tangential direction with respect to the main beam light receiving surface S1. This reflects the deviation of the spot positions of the main beam MB and the sub beam SB1. Since the magnitude of the spot position deviation varies depending on the configuration of the optical system 3, the arrangement of the light receiving surfaces may be determined as appropriate according to the configuration of the optical system 3.

  The sub-beam light receiving surface S2 has six light receiving regions 2A to 2F divided along a straight line S2x and dividing lines L1 and L2 provided at w2 / 2 on both sides of the straight line S3y. Among these, the light receiving region 2A is located at the center of the three light receiving regions on the opposite side of the straight beam S2x from the main beam light receiving surface S1. The light receiving areas 2B to 2F are arranged counterclockwise from the light receiving area 2A.

  Similarly, the sub-beam light receiving surface S3 has six light receiving regions 3A to 3F that are divided along a straight line S3x and dividing lines L3 and L4 provided at w2 / 2 on both sides of the straight line S3y. . Among these, the light receiving region 3A is located at the center of the three light receiving regions on the main beam light receiving surface S1 side of the straight line S2x. The light receiving areas 3B to 3F are arranged counterclockwise from the light receiving area 3A.

As described above, each light receiving surface of the light detector 5 is divided into a plurality of light receiving regions, and the light detector 5 obtains a value obtained by dividing the intensity of the light beam in the light receiving region for each light receiving region. A signal having an amplitude of (amount of received light) is output. Hereinafter, an output signal corresponding to the light receiving region X (X is a code of the light receiving region) is described as I _X.

  The main beam light receiving surface S1 is used to generate various signals such as a pull-in signal, a focus error signal, a tracking error signal, and a data signal. On the other hand, as described above, the sub beam light receiving surfaces S2 and S3 are provided to cancel the offset generated in the push-pull signal due to the lens shift. However, in the present embodiment, the light receiving regions 2A and 2D (first sub-beam light receiving surface) and the light receiving regions 3A and 3D (second sub-beam light receiving surface) are also used for generating a pull-in signal.

  Next, FIG. 4 is a diagram showing a part of functional blocks of the processing unit 6a. As shown in the figure, the processing unit 6a includes a pull-in signal generation unit 61a (pull-in signal generation means), a focus error signal generation unit 62, a tracking error signal generation unit 63, a data signal generation unit 64, and an objective lens control unit 65. (Layer recognition means).

Pull-in signal generation unit 61a, the optical detector 5, the light receiving area 2A, the output signal _I 2A corresponding to _2D, and _{I 2D} (first output signal), the light receiving region 3A, the output signal _{I 3A} corresponding to 3D, I _3D (second output signal) is acquired. Then, a pull-in signal PIS is generated based on these total signals I _2A + I _2D + I _3A + I _3D . Specifically, as shown in Expression (1), the total signal I _2A + I _2D + I _3A + I _3D is used as it is as the pull-in signal PIS. Needless to say, a signal obtained by amplifying the total signal I _2A + I _2D + I _3A + I _3D with a predetermined amplification factor may be used as the pull-in signal PIS.

  FIG. 5 shows the result of a simulation of the pull-in signal PIS, assuming that the optical disk 11 has a two-layer configuration having recording layers L0 and L1, and the interlayer distance d is 10 μm, and the width w2 is 20 μm. FIG. Other conditions are as follows: the laser wavelength is 405 nm, the NA of the objective lens is 0.85, the spot light diameter is 50 μm, the return optical magnification is 15 times, and the center coordinates of the sub-beam light receiving surfaces S2 and S3 are the main beam light receiving surface S1. (X, y) = (10 μm, 155 μm) and (−10 μm, −155 μm), respectively, where (x, y) = (0, 0). The following simulations are all performed under the above conditions. The focal lengths corresponding to the recording layers L0 and L1 are about 1759 μm and about 1765 μm, respectively. The difference between them is not 10 μm because of the refractive index of the constituent material of the optical disk 11. In FIG. 5A, in addition to the pull-in signal PIS, the main beam component PIS_M of the pull-in signal PIS (a component generated when the main beam MB is applied to the sub-beam receiving surfaces S2 and S3) and the sub-beam component PIS_S (sub-beams SB1 and SB2 are included). A component generated by applying to the sub-beam light receiving surfaces S2 and S3), a threshold value THS (described later), a slice signal PISSL (described later), and a focus error signal FE are also shown. FIG. 5B shows the recording layer L0 reflection component PIS_L0 of the main beam component PIS_M (the component generated by the reflection component of the recording layer L0 in the main beam MB received by the sub beam light receiving surfaces S2 and S3) and the recording layer. Also shown is an L1 reflection component PIS_L1 (a component generated by the reflection component of the recording layer L1 in the main beam MB received by the sub-beam light receiving surfaces S2 and S3).

  When the PI interlayer separation ratio between the recording layers L0 and L1 is calculated using the pull-in signal PIS of FIG. 5, it is about 58.2%. Therefore, when the interlayer distance d is 10 μm and the width w2 is 20 μm, it can be said that the layer recognition can be sufficiently performed by using the pull-in signal PIS. Other cases will be described later.

  The pull-in signal generation unit 61a further determines a threshold value THS (first threshold value) having a value that is approximately between the maximum value and the minimum value of the pull-in signal PIS. For example, first, the pull-in signal PIS is generated through the objective lens controller 65 while changing the focal length of the objective lens 4 from the minimum value to the maximum value. The pull-in signal generation unit 61a acquires the maximum value based on the amplitude of the pull-in signal PIS thus generated. Then, for example, 70% of the acquired maximum value is calculated and stored as the threshold value THS. The ratio between the maximum value and the threshold value THS is determined in advance so that the layer recognition process can be reliably performed in consideration of fluctuations and errors in the pull-in signal PIS. However, it is difficult to determine such a threshold when the PI interlayer separation index is less than 20%. This is the reason why the layer recognition process cannot be performed properly when the PI interlayer separation index is less than 20%.

  When the threshold value THS is determined, the pull-in signal generation unit 61a becomes high (first value) when the pull-in signal PIS becomes larger than the threshold value THS, and becomes low (second value) otherwise. A slice signal PISSL (first slice signal) is generated. The slice signal PISSL thus generated is input to the objective lens control unit 65.

The focus error signal generation unit 62 acquires output signals I _{1A to} I _1D corresponding to the light receiving areas _{1A to 1D} from the photodetector 5. Then, a total signal is generated for each diagonal component (output signals I _1A and I _1C , output signals I _1B and I _1D ), and a focus error signal FE is generated based on the difference signal. Specifically, the focus error signal FE is generated by the following equation (2). A focus error signal FE is also input to the objective lens control unit 65.

The tracking error signal generation unit 63 acquires output signals I _{1A to} I _1D , I _{2A to} I _2F , and I _{3A to} I _3F corresponding to all the light receiving areas from the photodetector 5. Then, the push-pull signal PP is generated based on the output signals I _{1A to} I _1D corresponding to the main beam receiving surface S1, and the output signals I _{2A to} I _2F and I _{3A to} I corresponding to the sub beam receiving surfaces SB1 and SB2. _The sub push-pull signal SPP is generated by _3F, and the tracking error signal TE is generated based on these difference signals. Specifically, the push-pull signal PP, the sub push-pull signal SPP, and the tracking error signal TE are generated by the following formulas (3) to (5). However, the constant k in the equation (5) is determined so that the effect of canceling the lens shift is exhibited to the maximum. For example, a value equal to the ratio between the light intensity of the main beam MB and the total light intensity of the sub beams SB1 and SB2 may be used. The generated tracking error signal TE is input to the objective lens control unit 65.

The data signal generation unit 64 acquires output signals I _{1A to} I _1D corresponding to the light receiving regions _{1A to 1D} from the photodetector 5. Then, a data signal RF is generated based on these total signals I _1A + I _1B + I _1C + I _1D . Specifically, as shown in the equation (6), the total signal I _1A + I _1B + I _1C + I _1D may be used as the data signal RF as it is. The generated data signal RF is input to the CPU 7.

  The objective lens control unit 65 performs layer recognition processing based on the input slice signal PISSL. The layer recognition process includes a layer number counting process for acquiring the number of recording layers, a rough adjustment process of the objective lens focal length and an in-focus recognition process of the objective lens, which are performed as part of the focus servo. The objective lens control unit 65 performs focus servo using the input focus error signal FE, and further performs tracking servo using the input tracking error signal TE. In the following, description will be given in order.

  First, the objective lens control unit 65 performs the layer number counting process by counting the number of sections (high section) in which the slice signal PISSL is high. That is, as shown in FIG. 5, the number of high sections equal to the number of recording layers appears in the slice signal PISSL. The objective lens control unit 65 obtains the number of recording layers of the optical disc 11 by counting the number of high sections while changing the focal length of the objective lens 4 from the minimum value to the maximum value.

  Next, the objective lens control unit 65 performs focus servo. The focus servo is started when an instruction signal for specifying an access position on the optical disk 11 is input from the CPU 7. When focus servo is started, the objective lens control unit 65 first performs rough adjustment processing of the objective lens focal length. Specifically, the layer number of the recording layer to be accessed (the serial number from the recording layer on the side farthest (or close) from the objective lens) is acquired from the instruction signal. Then, the focal length of the objective lens 4 is moved from the minimum value (or maximum value), and the number of high sections is counted. Then, when the count value becomes equal to the layer number of the access target layer, the rough adjustment process is terminated.

When the rough adjustment process is completed, the objective lens control unit 65 starts the focal point recognition process of the objective lens 4. Position the focus error signal becomes zero is the process of recognizing whether focus. Since the position where the focus error signal becomes zero are present in addition to the focal point, the objective lens controller 65, as a condition to be within the high period of the slice signal PI S SL, the position where the focus error signal is zero or zero-crossing Is recognized as the focal point. Thus when performing focus recognition processing such, in the high period of the slice signal PI S SL, it is necessary to position the focus error signal becomes zero to generate a pull-in signal such that only the focal point.

When the slice signal PI S SL that can perform the in-focus recognition processing is generated, the objective lens control unit 65 performs fine adjustment processing of the objective lens focal length. Specifically, moving the focal length of the objective lens 4 in the high period of the slice signal PI S SL, to search for a focal length of the focusing error signal FE becomes 0. After the focal length of 0 is found, the position of the objective lens 4 is continuously finely adjusted so that the state where the focus error signal FE is 0 is maintained. This state is referred to as a “focus servo applied state”.

  When focus servo is applied, the objective lens control unit 65 starts tracking servo. In the tracking servo, the objective lens control unit 65 moves the objective lens 4 in the radial direction of the optical disc 11 so that the tracking error signal TE becomes zero. The tracking servo is also continuously performed, and the data signal RF is acquired in parallel.

  The functional block of the processing unit 6a has been described above. Next, the pull-in signal PIS will be described again in detail with specific examples.

  6 to 8 show the conditions of the optical disk 11 that are the same as the example shown in FIG. 5 (two-layer configuration and interlayer distance d = 10 μm), and the width w2 is 100 μm, 50 μm, and 10 μm. It is a figure which shows the result of having performed PIS simulation. (A) and (b) of these drawings show the main beam component PIS_M of the pull-in signal PIS and the like, as in (a) and (b) of FIG. The PI interlayer separation ratio between the recording layers L0 and L1 in the example of each figure is about 36.4% in FIG. 6 (w2 = 100 μm), about 52.8% in FIG. 7 (w2 = 50 μm), and FIG. = 10 μm), which is about 58.3%. Although not shown, the PI interlayer separation ratios when w2 = 30 μm and 40 μm are about 55.8% and about 57.5%, respectively.

  9 to 11 show a case where the optical disk 11 has a two-layer structure having recording layers L0 and L1, and the width w2 is 100 μm, 20 μm, and 10 μm on the assumption that the interlayer distance d is 15 μm. It is a figure which shows the result of having simulated the pull-in signal PIS about each. The focal lengths corresponding to the recording layers L0 and L1 are about 1754.8 μm and about 1765 μm, respectively. Similarly to FIGS. 5A and 5B, FIGS. 5A and 5B also show the main beam component PIS_M of the pull-in signal PIS. The PI interlayer separation ratio between the recording layers L0 and L1 in the example of each figure is about 41.5% in FIG. 9 (w2 = 100 μm), about 63.5% in FIG. 10 (w2 = 20 μm), and FIG. 11 (w2). = 6 μm), which is about 64.2%.

  Further, FIGS. 12 to 14 show a case where the optical disk 11 has a two-layer configuration having recording layers L0 and L1, and the width w2 is 100 μm, 20 μm, and 10 μm on the assumption that the interlayer distance d is 20 μm. It is a figure which shows the result of having simulated the pull-in signal PIS about each. The focal lengths corresponding to the recording layers L0 and L1 are about 1752.5 μm and about 1765 μm, respectively. Similarly to FIGS. 5A and 5B, FIGS. 5A and 5B also show the main beam component PIS_M of the pull-in signal PIS. The PI interlayer separation ratio between the recording layers L0 and L1 in the example of each figure is about 3.1% in FIG. 12 (w2 = 100 μm), about 41.9% in FIG. 10 (w2 = 20 μm), and FIG. = 10 μm), which is about 42.6%.

  As shown in FIG. 12, when the width w2 is 100 μm, the maximum value of the pull-in signal PIS occurs in areas other than the vicinity of the focal point. When such a maximum value occurs, it is difficult to execute the layer recognition process. Note that the PI interlayer separation rate in the example of FIG. 12 is calculated based on the maximum value between the focal points and the smaller value of the two maximum values that appear in the vicinity of the original focal point. On the other hand, as shown in FIGS. 13 and 14, such a maximum value does not occur when the width w2 is 20 μm or less.

  FIG. 15 is a diagram showing the relationship between the PI interlayer separation index between the recording layers L0 and L1 and the width w2 calculated based on FIGS. 5 to 14 for each interlayer distance d. However, FIG. 15 also shows the PI interlayer separation rate when w2 = 90 μm, 80 μm, and 70 μm when the interlayer distance d is 20 μm. Specific numerical values are 9.4%, 15.6%, and 20.9% for w2 = 90 μm, 80 μm, and 70 μm, respectively.

  As can be understood from FIG. 15, the PI interlayer separation index increases as the width w <b> 2 decreases when the interlayer distance d is the same. Further, the PI interlayer separation index hardly changes between the case where the interlayer distance d is 10 μm and the case where the interlayer distance d is 15 μm, but the PI interlayer separation index becomes small when the interlayer distance d is 20 μm. The point that the PI interlayer separation index decreases as the interlayer distance d increases, which is the opposite of the example of the pull-in signal PIM shown in FIG. The reason for this is as follows.

  As shown in (b) of each figure, the recording layer L0 reflection component PIS_L0 and the recording layer L1 reflection component PIS_L1 are substantially zero near the in-focus point, but the intensity increases as the distance from the in-focus point increases, and the maximum value is obtained. In other words, as the interlayer distance increases, this maximum value is just between the focal points, and also overlaps with the maximum value of the other layers. When the interlayer distance is reduced, the position of the maximum value is shifted from between the focal points and is in the vicinity of the focal point, so that the maximum value does not occur between the focal points. That is, these components are due to the reflected light of the main beam MB, that is, stray light. However, when considering the interlayer separation between PI, if the interlayer distance d increases on the sub-beam light receiving surfaces S2 and S3, the influence of stray light is exerted. Becomes larger and the PI interlayer separation index becomes smaller.

  As described above, in order to properly execute the layer recognition process, the PI interlayer separation index needs to be 20% or more. From FIG. 15, it is understood that the layer recognition process can be performed regardless of the width w2 when the interlayer distance d is 10 μm and 15 μm. On the other hand, when the interlayer distance is 20 μm, if the width w2 is greater than 70 μm, the PI interlayer separation index is less than 20%, and the layer recognition process cannot be performed properly.

  Generally speaking, an interlayer distance of about 20 μm is a practical upper limit of the interlayer distance. Further, as described above, the PI interlayer separation index of the pull-in signal PIS increases as the width w2 decreases as the interlayer distance d is the same. Therefore, by setting the width w2 to 70 μm or less, that is, 1.4 times or less of the spot diameter r = 50 μm, it is possible to obtain a pull-in signal PIS that can execute the layer recognition process regardless of the structure of the optical disc 11.

  Here, a simulation result of the pull-in signal PIS in the case of using the optical disc 11 having a four-layer structure is also shown. First, FIG. 16 is a diagram showing a layer structure of the optical disc 11 on which this simulation is based. As shown in the figure, the optical disc 11 according to this example has a four-layer configuration having layers L0 to L3 in order from the side far from the objective lens 4, and the layer spacing is 16 μm, 21 μm, in order from between the layers L0 and L1. 10 μm.

  FIGS. 17 to 20 show the results of the simulation of the pull-in signal PIS for each of the cases where the width w2 is 100 μm, 50 μm, 20 μm, and 10 μm on the assumption that the optical disk 11 has the layer configuration shown in FIG. FIG. The focal lengths corresponding to the recording layers L0 to L3 are about 1735 μm, about 1746 μm, about 1759 μm, and about 1765 μm, respectively. (A) and (b) of these figures also show the main beam component PIS_M of the pull-in signal PIS and the like, similarly to (a) and (b) of FIGS.

  As can be understood from FIGS. 17 to 20, even if the optical disk 11 has a four-layer structure, the PI interlayer separation index between the recording layers has a property of becoming larger as the width w2 is smaller.

  When the width w2 is 100 μm and the threshold value THS is set so that the in-focus recognition process can be performed, there is one high section, and layer recognition cannot be performed. Also, if the threshold value is increased for the number of layers counting process, etc., there are four high intervals depending on the value, but there is a possibility that it will be recognized as five because the maximum value appears between the focal points. come. Therefore, when the width w2 is 100 μm, it is difficult to execute the layer recognition process. On the other hand, when the width w2 is 50 μm, 20 μm, or 10 μm, the width w2 can be separated to the extent that the in-focus recognition process can be performed.

  In the optical disk 11 shown in FIG. 16, since a part of the interlayer distance is about 20 μm, when the width w2 is larger than 70 μm as in the case of the two-layer configuration with the interlayer distance d = 20 μm described above, the PI interlayer The minimum value of the separation index (the minimum value among the PI interlayer separation index between the recording layers L0 and L1, the PI interlayer separation index between the recording layers L1 and L2, and the PI interlayer separation index between the recording layers L2 and L3) is 20. %, The layer recognition process cannot be performed properly. On the other hand, as in the case of using the optical disc 11 having the two-layer structure, the layer recognition process can be executed regardless of the structure of the optical disc 11 by setting the width w2 to 1.4 times or less of the spot diameter r. .

  As described above, according to the optical drive device 1 according to the present embodiment, it is possible to perform the layer recognition process regardless of the interlayer distance without dividing the main beam light receiving surface S1 into four or more. In addition, focus servo with in-focus recognition processing can be performed.

  FIG. 21 is a diagram illustrating a part of functional blocks of the processing unit 6b provided in the optical drive device 1 according to the second embodiment of the present invention.

  As shown in FIG. 21, the processing unit 6b is different from the processing unit 6a according to the first embodiment in that a processing unit 6b includes a pull-in signal generation unit 61b instead of the pull-in signal generation unit 61a. Hereinafter, the difference will be mainly described.

The pull-in signal generation unit 61b is the same as the pull-in signal generation unit 61a in that it generates a pull-in signal PIS. In addition to this, the pull-in signal generation unit 61b also generates a pull-in signal PIM. Specifically, output signals I _{1A to} I _1D (third output signals) corresponding to the light receiving areas _{1A to 1D} are also acquired. Then, a pull-in signal PIM is generated based on these total signals I _1A + I _1B + I _1C + I _1D . Specifically, as shown in Expression (7), the total signal I _1A + I _1B + I _1C + I _1D is used as it is as the pull-in signal PIM. The pull-in signal PIM is a signal conventionally used as a pull-in signal.

  The pull-in signal generator 61b further generates a pull-in signal PIMS based on the two pull-in signals PIS and PIM. Specifically, the pull-in signal PIMS is generated by the equation (8). Here, m is a constant.

  FIG. 22 shows a two-layer configuration in which the optical disc 11 has recording layers L0 and L1, an interlayer distance d is 10 μm, the main beam light receiving surface S1 is divided into four, and the width w1 is 100 μm. It is a figure which shows the pull-in signal PIMS simulated about each in the case of 100 micrometers, 50 micrometers, 40 micrometers, 30 micrometers, 20 micrometers, and 10 micrometers. In the figure, in addition to the pull-in signal PIMS, a threshold value THMS (described later) and a focus error signal FE are also shown. In this example, the constant m is set to 5, 6.5, 7.6, 9.8, 14.2, and 28.2 for each width w2. Moreover, the value plotted in each figure is 1/2 of the value calculated | required by Formula (8).

  Note that the constant m = 5 when the width w2 is 100 μm. As an example, in the pull-in signal PIMS, the sum of the sub beams SB1 and SB2 has the same intensity as the main beam MB. A value equal to the ratio between the light intensity and the total light intensity of the sub beams SB1 and SB2 is used. In addition, the value of the constant m when the width w2 is 50 μm, 40 μm, 30 μm, 20 μm, and 10 μm is the minimum of the plurality of maximum values that each has so that the dependency on the width w2 of the PI interlayer separation can be easily compared. Is determined to be the same as the minimum value among the plurality of maximum values that the pull-in signal PIMS has when the width w2 is 100 μm.

  When the PI interlayer separation ratio between the recording layers L0 and L1 in the example of FIG. 22 is calculated, the width w2 is about 29.7% and about 38. 7%, about 40.3%, about 40.4%, about 40.8%, and about 40.8%. Therefore, when the interlayer distance d is 10 μm, it can be said that the layer recognition can be sufficiently performed by using the pull-in signal PIMS even if the width w2 is 100 μm.

  As shown in FIG. 41, when the main beam receiving surface S1 is divided into four parts, the width w1 = 100 μm and only the pull-in signal PIM is used, layer recognition cannot be performed, but the sub beam receiving surfaces S2 and S3 are combined. Thus, layer recognition can be performed for all widths w2.

  The pull-in signal generation unit 61b further determines a threshold value THMS (first threshold value) having a value that is approximately between the maximum value and the minimum value of the pull-in signal PIMS. The specific determination method is the same as the threshold value THS determination method described in the first embodiment, and thus detailed description thereof is omitted.

  When the threshold value THMS is determined, the pull-in signal generation unit 61b is not shown, but becomes high (first value) when the pull-in signal PIMS is larger than the threshold value THMS, and low (first value) otherwise. 2), a slice signal PIMSSL (first slice signal) is generated. The slice signal PIMSSL generated in this way is input to the objective lens controller 65. The objective lens controller 65 uses the input slice signal PIMSSL instead of the slice signal PISSL, and performs the same processing as that described in the first embodiment.

  FIG. 23 shows a two-layer configuration in which the optical disk 11 has recording layers L0 and L1, an interlayer distance d is 15 μm, the main beam light receiving surface S1 is divided into four parts, and the width w1 is 100 μm. It is a figure which shows the pull-in signal PIMS simulated about each in the case of 100 micrometers, 20 micrometers, and 10 micrometers. In this example, the constant m is set to 5, 15.4, 31.1 for each width w2. Moreover, the value plotted in each figure is 1/2 of the value calculated | required by Formula (8). The PI interlayer separation ratio between the recording layers L0 and L1 in the examples in each figure is about 45.4%, about 57.5%, and about 56.9%, respectively.

  FIG. 24 shows that the optical disk 11 has a two-layer configuration having recording layers L0 and L1, the interlayer distance d is 20 μm, the main beam light receiving surface S1 is divided into four, and the width w1 is 100 μm. It is a figure which shows the pull-in signal PIMS simulated about each in the case of 100 micrometers, 20 micrometers, and 10 micrometers. In this example, the constant m is set to 5, 16.2 and 31.7 for each width w2. Moreover, the value plotted in each figure is 1/2 of the value calculated | required by Formula (8). The PI interlayer separation ratios between the recording layers L0 and L1 in the examples in the drawings are about 30.4%, about 47.1%, and about 48.1%, respectively.

  FIG. 25 is a diagram illustrating the relationship between the PI interlayer separation index between the recording layers L0 and L1 and the width w2 calculated based on FIGS. 29 to 40 for each interlayer distance d. However, FIG. 25 also shows the PI interlayer separation ratio when w2 = 90 μm, 80 μm, and 70 μm when the interlayer distance d is 20 μm. Specific numerical values are 35.7%, 39.5%, and 42% for w2 = 90 μm, 80 μm, and 70 μm, respectively. In calculating these numerical values, the constant m was set to 5.2, 5.3, and 5.7 for w2 = 90 μm, 80 μm, and 70 μm.

  As can be understood from FIG. 25, regarding the pull-in signal PIMS, the PI interlayer separation index increases as the width w2 decreases as the interlayer distance d is the same. Further, the layer recognition process can be performed for all the widths w2 regardless of the interlayer distance d. That is, in the pull-in signal PIMS, unlike the pull-in signal PIS, a PI interlayer separation index of 20% or more is obtained even when the interlayer distance d is 20 μm. Therefore, if the pull-in signal PIMS is used, even if the dividing lines L1 to L4 shown in FIG. 3 are not provided, that is, the conventional sub-beam light receiving surfaces S1 and S2 are used, the layer recognition process is performed regardless of the interlayer distance. It becomes possible to do. However, since the contribution of the pull-in signals PIM and PIS changes by changing the value of the constant m, the PI interlayer separation index also changes. In consideration of the interlayer distance of the multilayered optical disk, it is necessary to appropriately set the constant m appropriately.

  Next, FIG. 26 shows that the optical disk 11 has the four-layer configuration shown in FIG. 16 and that the main beam light receiving surface S1 is divided into four and the width w1 is 100 μm, and the width w2 is 100 μm, 50 μm, It is a figure which shows the result of having performed the simulation of the pull-in signal PIMS about each in the case of 20 micrometers and 10 micrometers. The same applies to FIG. However, in FIG. 26, the constant m is set to 15.5, 23.5, 49.3, 95.8, respectively, and the value 1 / 5.4 of the value obtained by the equation (8) is plotted. On the other hand, in FIG. 27, the constant m is doubled (31, 47, 98.6, 191.6) of FIG.

  In any case, if the threshold value THMS is set small so that the in-focus recognition process can be performed, when the width w2 is 100 μm, the recording layer L3 and the recording layer L2 cannot be separated, and layer recognition cannot be performed. Therefore, it is necessary to make the width w2 smaller than 100 μm. However, for specific processing such as layer count processing, layer recognition can be performed even if the width w2 is 100 μm.

  Here, the case where the main beam receiving surface S1 is divided into four and the width w1 is 100 μm is considered, but if the width w1 is similarly reduced, all layers can be separated. At the same time, in-focus recognition processing in the recording layer L0 becomes easier and the threshold value THMS can be increased, so that layer recognition processing including in-focus recognition processing is facilitated.

  The dependency of the pull-in signal PIM on the width w1 is shown in FIG. 5 to 14 and FIGS. 17 to 20 show the sub-beam component PIS_S, which is a signal obtained by multiplying the pull-in signal PIM by a constant, and thus shows the state of interlayer separation of the pull-in signal PIM. It is also a figure. That is, when the width w1 is reduced, the interlayer separation of the pull-in signal PIM is improved. Although not shown, the interlayer separation of the pull-in signal PIMS is also improved.

  28, the optical disk 11 has the four-layer configuration shown in FIG. 16, and the main beam light receiving surface S1 is divided into four parts and the width w1 is 100 μm. The width w2 is 100 μm, 50 μm, and 20 μm. FIG. 27 is a diagram illustrating a result of simulating a PI interlayer separation index by shaking the constant m between 0.2 times and 2 times the value used in FIG. The horizontal axis α indicates a value that is five times the magnification. Further, since the separation between the recording layers L3 and L2 has become a problem, the PI interlayer separation index between the recording layers L3 and L2 is plotted.

  As can be understood from FIG. 28, the minimum value of the PI interlayer separation index in the case of using the optical disc 11 having the four-layer structure has the property that the smaller the width w2, the larger the value as in the case of the two-layer structure. However, it hardly changes when the width w2 is 20 μm or less. Further, since the PI interlayer separation index is always 20% or more, the pull-in signal PIMS is used, so that at least the layer count processing can be performed even if the conventional sub-beam light receiving surfaces S1 and S2 are used. It is understood that the layer recognition process can be performed regardless of the distance.

  Further, the PI interlayer separation index has a property of increasing as the value of the constant m increases. However, even if α = 1, the PI interlayer separation index is maintained at 20% or more, so that the layer recognition process can be performed regardless of the value of the constant m.

FIG. 29 is a diagram illustrating a part of functional blocks of the processing unit 6c provided in the optical drive device 1 according to the third embodiment of the present invention.

  As illustrated in FIG. 29, the processing unit 6c is different from the processing units 6a and 6b according to the first and second embodiments in that a processing unit 6c includes a pull-in signal generation unit 61c instead of the pull-in signal generation units 61a and 61b. To do. Hereinafter, the difference will be mainly described.

  The pull-in signal generation unit 61c is the same as the pull-in signal generation unit 61b in that it generates the pull-in signal PIS and the pull-in signal PIM.

  The pull-in signal generation unit 61c further determines a threshold value THS (second threshold value) having a value that is approximately between the maximum value and the minimum value of the pull-in signal PIS. Further, a threshold value THM (third threshold value) having a value that is approximately between the maximum value and the minimum value of the pull-in signal PIM is also determined. The specific determination method is the same as the threshold value THS determination method described in the first embodiment, and thus detailed description thereof is omitted.

  When the threshold values THS and THM are determined, the pull-in signal generation unit 61c becomes high (first value) when the pull-in signal PIS becomes larger than the threshold value THS, and low (second value) otherwise. A slice signal PISSL (second slice signal) that becomes and a slice that becomes high (first value) when the pull-in signal PIM is greater than the threshold value THM, and low (second value) otherwise. A signal PIMSL (third slice signal) is generated.

  Finally, the pull-in signal generation unit 61c becomes high (first value) when the slice signals PISSL and PIMSL are both high (first value), and becomes low (second value) otherwise. A pull-in signal PIAND is generated. In short, the pull-in signal PIAND is a signal obtained as a result of an OR operation between the slice signal PISSL and the slice signal PIMSL. The pull-in signal PIAND thus generated is input to the objective lens control unit 65. The objective lens controller 65 uses the input pull-in signal PIAND instead of the slice signal PISSL, and performs the same processing as that described in the first embodiment.

  Hereinafter, the pull-in signal PIAND will be described in detail with specific examples.

  30 and 31, the conditions of the optical disk 11 are the same as the example shown in FIG. 5 (two-layer configuration and interlayer distance d = 10 μm), and the main beam light receiving surface S1 is divided into four parts with a width w1 of 100 μm. It is a figure which shows the result of having performed the simulation of the pull-in signal PIAND about each when w2 is 100 micrometers and 20 micrometers. In each figure, (a) shows pull-in signals PIS and PIM, threshold values THS and THM, and a focus error signal FE. Further, (b) of each figure shows slice signals PISSL and PIMSL and a pull-in signal PIAND.

  32 and 33, the conditions of the optical disk 11 are the same as in the example shown in FIG. 9 (two-layer configuration and interlayer distance d = 15 μm), and the main beam light receiving surface S1 is divided into four and the width w1 is 100 μm. FIG. 6 is a diagram illustrating a result of simulation of the pull-in signal PIAND for each of the cases where the width w2 is 100 μm and 20 μm. The signals shown in (a) and (b) of these figures are the same as those in (a) and (b) of FIG.

  34 and 35, the conditions of the optical disk 11 are the same as in the example shown in FIG. 12 (two-layer configuration and interlayer distance d = 20 μm), and the main beam light receiving surface S1 is divided into four parts with a width w1 of 100 μm. FIG. 6 is a diagram illustrating a result of simulation of the pull-in signal PIAND for each of the cases where the width w2 is 100 μm and 20 μm. The signals shown in (a) and (b) of these figures are also the same as (a) and (b) of FIG.

  As shown in FIGS. 30 to 35, when the interlayer distance d becomes smaller and 10 μm, the pull-in signal PIM cannot sufficiently perform interlayer separation, but the pull-in signal PIS can perform interlayer separation. On the other hand, when the interlayer distance d is increased and is 20 μm, the pull-in signal PIM can sufficiently perform interlayer separation. However, when the w2 is 100 μm in the pull-in signal PIS, the threshold value increases. It becomes difficult to perform interlayer separation because there are three sections, or even two sections, and the high section becomes long. However, even if the interlayer distance d changes, one of the pull-in signals is always generated normally. Therefore, it can be understood that the layer recognition process can be performed when both ANDs are set as the pull-in signal AND.

  Next, in FIGS. 36 to 38, the optical disk 11 has the four-layer configuration shown in FIG. 16, and the main beam light-receiving surface S1 is divided into four and the width w1 is 100 μm. It is a figure which shows the result of having performed the simulation of the pull-in signal PIAND about each in the case of 50 micrometers and 20 micrometers. The signals shown in (a) and (b) of these figures are also the same as (a) and (b) of FIG.

  As shown in FIGS. 36 to 38, consider a case where a threshold value is set so that the in-focus recognition process can be performed. When the width w2 is 100 μm (FIG. 36), there is only one section in which the slice signal PISSL of the pull-in signal PIS is high. On the other hand, since the main beam receiving surface S1 is divided into four and w1 is 100 μm, layer recognition cannot be sufficiently performed, and there are two sections in which the slice signal PIMSL of the pull-in signal PIM is high. Therefore, even if these are ORed to generate the pull-in signal PIAND, layer recognition cannot be performed as shown in FIG. On the other hand, when the width w2 is reduced to 50 μm and 20 μm, layer recognition can be performed as shown in FIGS. Therefore, it is understood that when the pull-in signal PIAND is used, the focal point recognition process can be performed by reducing the width w2. Specifically, the width w2 is preferably 50 μm or less, that is, the spot diameter or less.

  When the in-focus recognition process is not performed (when only the layer number counting process or the like is performed), the threshold value can be set to a higher value. Accordingly, since it is possible to provide a high section of the pull-in signal PIAND for each recording layer, it is possible to perform layer recognition using the pull-in signal PIAND even if the width w2 is 100 μm.

  Here, the case where the main beam receiving surface S1 is divided into four and w1 is 100 μm is considered. However, if the width w1 is similarly reduced, interlayer separation can be performed between the recording layer L1 and the recording layer L0. At the same time, in-focus recognition processing in the recording layer L0 becomes easier, and the threshold value can be increased as compared with the case where the width w1 is 100 μm. Layer recognition processing becomes easier.

  The dependency of the pull-in signal PIM on the width w1 is shown in FIG. 5 to 14 and FIGS. 17 to 20 show the sub-beam component PIS_S, which is a signal obtained by multiplying the pull-in signal PIM by a constant, and thus shows the state of interlayer separation of the pull-in signal PIM. It is also a figure. That is, as the width w1 becomes smaller, the interlayer separation of the pull-in signal PIM is improved, and although not shown, the king recognition process including the in-focus recognition process of the pull-in signal PIAND can be easily performed at the same time. It becomes.

  As described above, according to the optical drive device 1c according to the present embodiment, similarly to the pull-in signal PIMS, the pull-in signal PIAND has the disadvantage of the pull-in signal PIS that the PI interlayer separation index decreases as the interlayer distance increases. Since the defect of the pull-in signal PIM that the PI interlayer separation index becomes smaller as the interlayer distance is smaller is compensated for each other, the main beam light receiving surface S1 is not divided into four or more parts, but depending on the interlayer distance. It is possible to perform layer recognition processing. At the same time, focus servo with in-focus recognition processing can be performed.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to such embodiment at all, and this invention can be implemented in various aspects in the range which does not deviate from the summary. Of course.

DESCRIPTION OF SYMBOLS 1 Optical drive apparatus 1A-1D, 2A-2F, 3A-3F Light-receiving area | region 2 Laser light source 3 Optical system 4 Objective lens 5 Photodetector 6a, 6b, 6c Processing part 11 Optical disk 21 Diffraction grating 22 Polarization beam splitter 23 Collimator lens 24 1/4 wavelength plate 25 Sensor lenses 61a, 61b, 61c Pull-in signal generator 62 Focus error signal generator 63 Tracking error signal generator 64 Data signal generator 65 Objective lens controller

Claims (11)

A diffraction grating that divides a light beam applied to a multilayer optical disk having a plurality of recording layers into a main beam and first and second sub-beams;
A main beam receiving surface and a first and second sub beam receiving surface arranged to receive the main beam reflected by the multilayered optical disc and the first and second sub beams, respectively; A photodetector that outputs a signal indicating the amount of received light;
A total signal of the first output signal of the photodetector indicating the amount of light received by the first sub-beam light-receiving surface and the second output signal of the photodetector indicating the amount of light received by the second sub-beam light-receiving surface. A pull-in signal generating means for generating a pull-in signal having a maximum value in the vicinity of the focal point ,
Layer recognition means for performing layer recognition processing based on the pull-in signal ,
The lengths of the first and second sub-beam light-receiving surface of the signal light tangential optical wherein said sub-beams corresponding the Ru der 1.4 times the diameter of the spot formed on the light receiving surface Drive device. The optical drive apparatus according to claim 1, wherein the pull-in signal is the total signal or a signal obtained by amplifying the total signal with a predetermined amplification factor. A diffraction grating that divides a light beam applied to a multilayer optical disk having a plurality of recording layers into a main beam and first and second sub-beams;
A main beam receiving surface and a first and second sub beam receiving surface arranged to receive the main beam reflected by the multilayered optical disc and the first and second sub beams, respectively; A photodetector that outputs a signal indicating the amount of received light;
A total signal of the first output signal of the photodetector indicating the amount of light received by the first sub-beam light-receiving surface and the second output signal of the photodetector indicating the amount of light received by the second sub-beam light-receiving surface. A pull-in signal generating means for generating a pull-in signal having a maximum value in the vicinity of the focal point,
Layer recognition means for performing layer recognition processing based on the pull-in signal,
The pull-in signal generating means, the main beam light receiving surface of the light receiving quantity optical science drive and generates the pull-in signal based also on the third output signal of the light detector shown a. The optical drive apparatus according to claim 3 , wherein the pull-in signal is a total signal of the third output signal and a signal obtained by amplifying the total signal with a predetermined amplification factor. A diffraction grating that divides a light beam applied to a multilayer optical disk having a plurality of recording layers into a main beam and first and second sub-beams;
A main beam receiving surface and a first and second sub beam receiving surface arranged to receive the main beam reflected by the multilayered optical disc and the first and second sub beams, respectively; A photodetector that outputs a signal indicating the amount of received light;
A total signal of the first output signal of the photodetector indicating the amount of light received by the first sub-beam light-receiving surface and the second output signal of the photodetector indicating the amount of light received by the second sub-beam light-receiving surface. A pull-in signal generating means for generating a pull-in signal having a maximum value in the vicinity of the focal point,
Layer recognition means for performing layer recognition processing based on the pull-in signal;
And an objective lens for focusing the main beam and the first and second sub-beams to said multi-layer optical disc,
The pull-in signal generating means generates a first slice signal having a first value when the pull-in signal is larger than a first threshold value, and a second value otherwise;
The layer recognizing means counts the number of sections in which the first slice signal becomes the first value while moving the objective lens in the normal direction of the multilayered optical disk, whereby the multilayered optical disk is An optical drive device, wherein the number of the recording layers is acquired. A diffraction grating that divides a light beam applied to a multilayer optical disk having a plurality of recording layers into a main beam and first and second sub-beams;
A main beam receiving surface and a first and second sub beam receiving surface arranged to receive the main beam reflected by the multilayered optical disc and the first and second sub beams, respectively; A photodetector that outputs a signal indicating the amount of received light;
A total signal of the first output signal of the photodetector indicating the amount of light received by the first sub-beam light-receiving surface and the second output signal of the photodetector indicating the amount of light received by the second sub-beam light-receiving surface. A pull-in signal generating means for generating a pull-in signal having a maximum value in the vicinity of the focal point,
Layer recognition means for performing layer recognition processing based on the pull-in signal;
And an objective lens for focusing the main beam and the first and second sub-beams to said multi-layer optical disc,
The pull-in signal generating means generates a first slice signal having a first value when the pull-in signal is larger than a first threshold value, and a second value otherwise;
The layer recognizing means recognizes at least one of the number or the position of the section where the first slice signal becomes the first value while moving the objective lens in the normal direction of the multilayered optical disk. An optical drive device, wherein the focal point of the light beam is moved to the vicinity of an access target layer among the plurality of recording layers. An objective lens for condensing the main beam and the first and second sub-beams on the multilayer optical disc;
A focus error signal generating means for generating a focus error signal based on an output signal of the photodetector indicating the amount of light received by the main beam light receiving surface;
The pull-in signal generating means generates a first slice signal having a first value when the pull-in signal is larger than a first threshold value, and a second value otherwise;
The layer recognizing unit recognizes a position where the focus error signal is zero or zero crossing as a focal point when the first slice signal is the first value, and thereby a position where the focus error signal becomes zero. There optical drive apparatus according to any one of claims 1 to 4, characterized in that performing the process of recognizing whether focus. The pull-in signal generating means has a second slice signal having a first value when the total signal is larger than a second threshold value, and a second value otherwise, and the third output signal. Generating a first slice value that is greater than a third threshold and a second slice signal that is the second value otherwise.
The pull-in signal is a signal that becomes the first value when both of the second and third slice signals are the first value, and becomes the second value otherwise. The optical drive device according to claim 3 . An objective lens for condensing the main beam and the first and second sub-beams on the multilayer optical disc;
The layer recognizing means counts the number of sections in which the pull-in signal takes the first value while moving the objective lens in the normal direction of the multilayered optical disk, so that the recording of the multilayered optical disk is performed. The optical drive device according to claim 8 , wherein the number of layers is acquired. An objective lens for condensing the main beam and the first and second sub-beams on the multilayer optical disc;
The layer recognizing means recognizes at least one of the number or the position of the section where the pull-in signal is the first value while moving the objective lens in the normal direction of the multilayered optical disc, so that the light beam The optical drive apparatus according to claim 8 , wherein the focal point of the optical recording medium is moved to the vicinity of an access target layer among the plurality of recording layers. An objective lens for condensing the main beam and the first and second sub-beams on the multilayer optical disc;
A focus error signal generating means for generating a focus error signal based on an output signal of the photodetector indicating the amount of light received by the main beam light receiving surface;
The layer recognizing means recognizes a position where the focus error signal is zero or zero crossing as a focal point when the pull-in signal is the first value, so that a position where the focus error signal becomes zero is a focal point. The optical drive apparatus according to claim 8 , wherein a process for recognizing whether or not is is performed.

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