Abstract:
The invention provides an effective method for improving accuracy of recording, tracking, and reproduction in a real-time correction in which correction is performed simultaneously with recording. A beam spot for recording, beam spots for reproduction, and beam spots for tracking are formed by branching a laser beam outputted from a laser diode by using a diffraction grating. In this manner, by providing the beam spots for recording, reproduction, and tracking independently, signals which are subjected to less reproduction degradation are obtained while maintaining tracking accuracy.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to an optical disk recording device and a pickup device, and more specifically, to an optical disk recording device and a pickup device which are effective for correction of a registration condition in real time.  
         [0003]     2. Description of the Related Art  
         [0004]     Information record to an optical recording media such as an optical disk is performed by modulating recorded data in an EFM (Eight to Fourteen Modulation) system, forming a record pulse based on a modulating signal, controlling the strength or irradiation timing of a laser beam based on the record pulse, and forming a recording pit on the optical disk.  
         [0005]     Formation of the recording pit in this case is performed by utilizing heat generated by irradiation of the laser beam, the record pulse is required to be set with a heat accumulation effect or heat interference, and the like taken into account.  
         [0006]     Therefore, in the related art, recording on the optical disk has been performed by defining a plurality of settings of various parameters which constitute the record pulse for each type of the optical disk in a form of a strategy, and selecting one of these strategies which is optimal for the record environment.  
         [0007]     Since the strategy depends not only on the individual difference among the optical disk recording devices such as variations in spot diameter of the pickup, variations in accuracy of the mechanism and the like, but also on manufacturers and types and the record speed of the optical disk used for record reproduction, setting of the optimal strategy may result in improvement of the recording quality.  
         [0008]     Therefore, a method of finding the optimal strategies for the optical disks corresponding to the respective manufacturers and types, storing the results corresponding to the respective manufacturers and types in a memory in advance, and when recording information on the optical disk, reading manufacturers and types of the optical disk stored in the optical disk, and reading the optimal strategy corresponding to the read manufacturers and types from the memory to use is proposed.  
         [0009]     However, according to the above-described method, although the optimal recording is achieved for the optical disk of manufactures and types stored in the memory in advance, the optimal recording cannot be achieved for the optical disk of manufacturers and types which are not recorded in the memory. In addition, even with the optical disk of manufacturers and types which are stored in the memory in advance, the optimal recording cannot be achieved if the record speed is different.  
         [0010]     Accordingly, as disclosed in JP-A-5-144001, JP-A-4-137224, JP-A-5-143999 and JP-A-7-235056 shown below, a plurality of methods which can cope with various types of optical disks by conducting a test record in advance for each registration condition and determining the optimal strategy based on the test record are proposed.  
         [0011]     However, in the methods shown in JP-A-5-144001, JP-A-4-137224, JP-A-5-143999 and JP-A-7-235056, since it is necessary to perform the test record before starting information record, the strategy cannot be corrected simultaneously with recording, and hence it is difficult to cope with the case in which the optimal condition is different between the outer periphery and the inner periphery.  
         [0012]     Since there is such a problem, that is, the fact that the storage characteristic of the optical disk is slightly different from the inner periphery to the outer periphery, and that the recording rate is different between the inner periphery and the outer periphery on the side of the record device, a technology to alleviate the difference between the inner periphery and the outer periphery by adjusting the laser output is shown in the following publications as a technology to solve the problem such that there arises a difference in recording quality between the inner periphery and the outer periphery.  
         [0013]     In JP-A-53-050707 and JP-A-2001-312822, a technology to optimize the laser output automatically by detecting the quantity of light change of the supplementary beam is disclosed, and the method of this type is referred to as OPC.  
         [0014]     Since the OPC as described above is a method of adjusting power, the correction conditions can be found with a statistic index such as an asymmetric value, and a real-time correction which performs correction while recording is also possible. However, in a case in which the pulse width or the phase conditions of the pulse are to be corrected, it is necessary to detect the amount of displacement between the record pulse and the pit formed on the optical disk, and hence it is difficult to cope with this case with the conventional OPC.  
         [0015]     Therefore, in order to perform the real-time correction of the pulse conditions, a technology to detect the position and the length of the pit simultaneously with recording is necessary.  
         [0016]     As an approach for this necessity, a method of reproducing simultaneously with recording by employing a beam for recording and a beam for reproduction independently is disclosed in JP-A-7-129956 and JP-A-9-147361.  
         [0017]     In JP-A-7-129956, a method of recording with a main beam and reproducing with a sub-beam is disclosed, and in JP-A-9-147361, a method of recording with a main beam and reproducing and tracking with a sub-beam is disclosed.  
         [0018]     However, in the method disclosed in JP-A-7-129956, tracking is not taken into consideration, and in the method disclosed in JP-A-9-147361, since reproduction is performed using a beam arranged on a boundary between a land and a groove for tracking, deterioration of a regenerative signal during tracking can easily be occurred.  
       SUMMARY OF THE INVENTION  
       [0019]     Accordingly, the present invention provides a method effective in improvement of accuracy of recording, tracking and reproduction in the real-time correction for correcting the registration condition simultaneously with recording.  
         [0020]     In order to achieve the above-described object, a first aspect of the invention is an optical disk recording device for forming a pit on an optical recording media by a pulse irradiation of a laser beam for recording and simultaneously, detecting the pit by irradiation of a laser beam for reproduction, characterized in that tracking of the laser beam for recording and the laser beam for reproduction is performed by irradiating a laser beam for tracking on the media in addition to the laser beam for recording and the laser beam for reproduction.  
         [0021]     In this manner, by providing the laser beam for reproduction and the laser beam for tracking separately, reproduction with less signal deterioration is achieved while performing tracking.  
         [0022]     Tracking objects here are the laser beam for recording and the laser beam for reproduction, and preferably, both of these laser beams are determined as the tracking objects.  
         [0023]     The method of tracking may be any one of a known three beam technique or a differential push-pull method.  
         [0024]     A second aspect of the invention is an optical disk recording device for generating a laser beam for recording and a laser beam for reproduction by branching one laser beam, forming a pit on an optical recording media by pulse irradiation of the laser beam for recording, and detecting the pit by irradiating the laser beam for reproduction, characterized in that tracking of the one laser beam is performed by further branching the one laser beam to generate a laser beam for tracking and irradiating the laser beam for tracking on to the media.  
         [0025]     In this manner, when employing a branch configuration, tracking of the laser beam for recording and the laser beam for reproduction can be substantially achieved by generating the laser beam for tracking by branching and determining the one laser beam which corresponds to a branching source as the tracking object.  
         [0026]     As information as a basis of the tracking, any of reflective light of the laser beam for recording and reflective light of the laser beam for reproduction may be used.  
         [0027]     The one laser beam here includes a laser beam which becomes a source when the laser beam irradiated from the specific light source is branched in several steps. In other words, a case in which the laser beam for recording and the laser beam for reproduction are generated from a certain laser beam via an intermediate branching step is also included.  
         [0028]     A third aspect of the invention is an optical disk recording device for generating a pit on an optical recording media by pulse irradiation of a laser beam for recording and simultaneously, detecting the pit by irradiating a laser beam for reproduction, characterized in that a distance H between a recording spot formed on the media by irradiating the laser beam for recording and a reproduction spot formed on the media by irradiating the laser beam for reproduction is determined by an expression H≧V×T, where T represents a time required for forming the pit, and V represents a linear velocity of the media.  
         [0029]     As described above, the pit of the final state in which an influence of a record environment is reflected can be regenerated by arranging the recording spot and the reproduction spot while taking a pit formation time into consideration, the real-time correction with higher degree of accuracy is realized.  
         [0030]     The time required for forming the pit is preferably determined by considering the relation between heat characteristics of a recording material and registration conditions in the case of dye type media, and is determined by considering phase change characteristics of an inorganic material in the case of phase change type media. More preferably, it is defined in advance for each pit length by testing a plurality of types of media.  
         [0031]     A fourth aspect of the invention is a pickup device which receives and processes first and second beam spots irradiated on an optical recording media via an objective lens, a collimating lens, and a toroidal lens via the first and second detectors respectively, characterized in that where Y 1  represents a distance between the first and second beam spots in the vertical direction of optical axis, X 1  represents a distance between the same in the horizontal direction of optical axis, Ly represents a distance between the first and second detectors in the vertical direction of optical axis, Lx represents a distance between the same in the horizontal direction of optical axis, f 1  represents a focal distance of the objective lens, f 2  represents a focal distance of the collimating lens, f 3   y  represents a focal distance of the toroidal lens in the vertical direction, f 3   x  represents a focal distance thereof in the horizontal direction, f 3  is a focal distance synthesized by f 3   x  and f 3   y  and d represents a distance between principal points of the collimating lens and the toroidal lens, and when the aforementioned Y 2  and X 2  are defined by following expression: 
 
 Y   2 ={ f   1 · f   2 · f   3   y /( f   2 + f   3 − d )}· Y   1  
 
 X   2 ={ f   1 · f   2 − f   3   x /( f   2 + f   3 − d )}· X   1 , 
 
 if the toroidal lens is a convex lens, and f 3   y &gt;f 3   x  is satisfied, the aforementioned Y 2 , X 2 , Ly, X 2  satisfy relations Y 2 &gt;Ly and X 2 &lt;Lx. 
 
         [0032]     As described above, by providing conditions which satisfy the relations Y 2 &gt;Ly and X 2 &lt;Lx when the toroidal lens is the convex lens, mechanical overlapping of the first and second detectors can be avoided.  
         [0033]     More specifically, when Wy represents the width of the first and second detectors in the vertical direction of optical axis and Wx represents the width of the same in the horizontal direction of optical axis, arrangement under the conditions in which the aforementioned Lx and Wx satisfy a relation Lx≧Wx is preferred, and a detection side of the first detector and a detection side of the second detector are arranged on different Z-coordinates, where Y-axis represents the vertical direction of the optical axis, X-axis represents the horizontal direction of optical axis, and Z-axis represents the direction of optical axis.  
         [0034]     A fifth aspect of the invention is a pickup device which receives and processes first and second beam spots irradiated on an optical recording media via an objective lens, a collimating lens, and a toroidal lens via the first and second detectors respectively, characterized in that where Y 1  represents a distance between the first and second beam spots in the vertical direction of optical axis, X 1  represents a distance between the same in the horizontal direction of optical axis, Ly represents a distance between the first and second detectors in the vertical direction of optical axis, Lx represents a distance between the same in the horizontal direction of optical axis, f 1  represents a focal distance of the objective lens, f 2  represents a focal distance of the collimating lens, f 3   y  represents a focal distance of the toroidal lens in the vertical direction, f 3   x  represents a focal distance thereof in the horizontal direction, f 3  is a focal distance synthesized by f 3   x  and f 3   y,  and d represents a distance between principal points of the collimating lens and the toroidal lens, and when the aforementioned Y 2  and X 2  are defined by following expression: 
 
 Y   2 ={ f   1 · f   2 · f   3   y /( f   2 + f   3 − d )}· Y   1  
 
 X   2 ={ f   1 · f   2 · f   3   x /( f   2 + f   3 − d )}· X   1 , 
 
 if the toroidal lens is a concave lens, and f 3   y &gt;f 3   x  is satisfied, the aforementioned Y 2 , X 2 , Ly, X 2  satisfy relations Y 2 &lt;Ly and X 2 &gt;Lx. 
 
         [0035]     As described above, by providing conditions which satisfy the relations Y 2 &lt;Ly and X 2 &gt;Lx when the toroidal lens is a concave lens, mechanical overlapping of the first and second detectors can be avoided.  
         [0036]     More specifically, when Wy represents the width of the first and second detectors in the vertical direction of optical axis and Wx represents the width of the same in the horizontal direction of optical axis, arrangement under the conditions in which the aforementioned Ly and Wy satisfy a relation Ly≧Wy is preferred, and a detection side of the first detector and a detection side of the second detector are arranged on different Z-coordinates, where Y-axis represents the vertical direction of the optical axis, X-axis represents the horizontal direction of optical axis, and Z-axis represents the direction of optical axis.  
         [0037]     A sixth aspect of the invention is a pickup device which receives and processes a beam spot irradiated on an optical recording media by a detector, via an objective lens a collimating lens, and a toroidal lens, characterized in that where dy represents a distance between an image surface of the beam spot in the vertical direction and a principal point of the toroidal lens, dx represents a distance between an image surface of the beam spot in the horizontal direction and the principal point of the toroidal lens, and D represents a distance between the detection side of the detector and the principal point of the toroidal lens, if the toroidal lens is a convex lens, and f 3   y &gt;f 3   x  is satisfied, the aforementioned dx, dy, and D satisfy a relation dx&lt;D&lt;dy.  
         [0038]     As described above, by providing conditions which satisfy the relation dx&lt;D&lt;dy when the toroidal lens is the convex lens, the detector can be arranged in a range in which an astigmatism method can be implemented.  
         [0039]     In this case, the image surface in the horizontal direction represents a focusing position at which a spot width in the horizontal direction becomes minimum, and the image surface in the vertical direction represents a focusing position where the spot width in the vertical direction becomes minimum.  
         [0040]     A seventh aspect of the invention is a pickup device which receives and processes a beam spot irradiated on an optical recording media via an objective lens, a collimating lens, and a toroidal lens by a detector, characterized in that where dy represents a distance between an image surface in the vertical direction of the beam spot and a principal point of the toroidal lens, dx represents a distance between the image surface in the horizontal direction of the beam spot and the principal point of the toroidal lens, and D represents a distance between a detection side of the detector and the principal point of the toroidal lens, if the toroidal lens is a concave lens, and f 3   y &gt;f 3   x  is satisfied, the aforementioned dx, dy, and D satisfy a relation dx&gt;D&gt;dy.  
         [0041]     As described above, by providing conditions which satisfy the relation dx&gt;D&gt;dy when the toroidal lens is the concave lens, the detector can be arranged in a range in which an astigmatism method can be implemented.  
         [0042]     As described above, according to the invention, since the tracking and reproduction are performed independently, the real-time correction with higher degree of accuracy is achieved.  
         [0043]     The invention is not limited to embodiments described below, and may be modified as needed. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0044]      FIG. 1  is a block diagram showing an internal composition of a drive according to the present invention;  
         [0045]      FIG. 2  is an exploded perspective view showing a structure of a pickup built in the drive shown in  FIG. 1 ;  
         [0046]      FIG. 3  is a plan view showing an arrangement of spots irradiated on a disk surface of an optical disk;  
         [0047]      FIG. 4  shows a conceptual diagram showing a relation between the spot irradiated on the disk surface of the optical disk and a detector;  
         [0048]      FIG. 5  is a conceptual diagram showing a relation between the respective spots and the detector in the case of irradiating four spots on the disk surface of the optical disk;  
         [0049]      FIG. 6  is a conceptual diagram showing a relation between the respective spots and the detector in the case of irradiating nine spots on the disk surface of the optical disk;  
         [0050]      FIG. 7  is a plan view showing a distance between a beam for recording and a beam for reproduction;  
         [0051]      FIG. 8  is an exploded perspective view showing a positional relation of the respective optical elements provided in the pickup shown in  FIG. 1 ;  
         [0052]      FIG. 9  is a conceptual diagram showing a relation between vertical and horizontal layouts of an objective lens  118 , a collimating lens  119 , and a toroidal lens  120 , and distances between the respective detectors;  
         [0053]      FIG. 10  is a perspective diagram showing an example of arrangement of a first detector and a second detector;  
         [0054]      FIG. 11  is a conceptual diagram showing an image of ranges of maximum distance between the detectors;  
         [0055]      FIG. 12  is a perspective diagram showing the relation between the width and the distance of the first and second detectors;  
         [0056]      FIG. 13  is a perspective diagram showing an example of another arrangement of the first detector and the second detector;  
         [0057]      FIG. 14  is a conceptual diagram showing a relation between the vertical and horizontal layouts of the objective lens  118 , the collimating lens  119 , and the toroidal lens  120  shown in  FIG. 8  and the position of the detectors in the direction of optical axis;  
         [0058]      FIG. 15  is a conceptual diagram showing a concept of focusing using an astigmatism method;  
         [0059]      FIG. 16  is a circuit block diagram showing an internal composition of a pulse generation circuit shown in  FIG. 1 ;  
         [0060]      FIG. 17  is a circuit drawing showing an internal composition of a LD driver shown in  FIG. 1 ;  
         [0061]      FIG. 18  is a timing chart showing a process of generation of a record pulse shown in  FIG. 17 ; and  
         [0062]      FIG. 19  is a timing chart showing a relation between a main beam for recording and a sub-beam for reproduction. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0063]      FIG. 1  is a block diagram showing an internal composition of a drive according to the present invention.  
         [0064]     As shown in the same drawing, a drive  100  performs record reproduction of information on an optical disc  500  using a laser beam outputted from a laser diode  110 , and transmits and receives data with respect to an external device such as a personal computer  600  or the like.  
         [0065]     When recording the information on the optical disk  500 , a strategy which corresponds to registration conditions for the optical disk  500  is determined by encoding recorded data received from the personal computer  600  via an interface circuit  218  by an EFM encoder/decoder  216 , and processing the encoded recorded data by a CPU  212 , the strategy is converted into a record pulse in a pulse generation circuit  300 , and the record pulse is outputted to a LD driver  124 .  
         [0066]     A LD driver  124  drives the laser diode  110  based on the inputted record pulse, the laser diode  110  controls the output laser beam corresponding to the record pulse, and irradiates the controlled laser beam via a diffraction grating  114 , a polarized beam splitter  116 , and an objective lens  118  onto the optical disk  500  which rotates at a constant linear velocity or at a constant rotary velocity, whereby a record pattern including pit and land rows corresponding to a desired recorded data is recorded on the optical disk  500 .  
         [0067]     On the other hand, when reproducing information recorded on the optical disk  500 , a reproduction laser beam is irradiated on the optical disk  500  via the diffraction grating  114 , the polarized beam splitter  116 , and the objective lens  118  from the laser diode  110 .  
         [0068]     At this time, a laser beam which is low in strength than the laser beam used at the time of recording is used as the reproduction laser beam, reflective light of the reproduction laser beam from the optical disk  500  is received by a detector  122  via the objective lens  118 , the polarized beam splitter  116 , the toroidal lens  120 , thereby being converted into an electrical signal.  
         [0069]     The electrical signal outputted from the detector  122  corresponds to the record pattern including pits and lands recorded on the optical disk  500 , and the electrical signal is binarized by a slicer  210 , then decoded by the EFM encoder/decoder  216 , and then outputted as the regenerative signal.  
         [0070]     A pickup  102  includes optical elements such as the above-described laser diode  110 , the diffraction grating  114 , the polarized beam splitter  116 , the objective lens  118 , the collimating lens  119 , the toroidal lens  120 , the detector  122 , and the optical elements provided in the pickup are driven by an actuator  123 .  
         [0071]     The control positions of the respective optical elements are detected by a servo detecting unit  202  and, based on the detection results of the servo detecting unit  202 , a tracking control unit  204  drives the actuator  123  to perform tracking control, and a focusing control unit  206  drives the actuator  123  to perform focusing control.  
         [0072]      FIG. 2  is an exploded perspective view showing a structure of a pickup built in the drive shown in  FIG. 1 .  
         [0073]     As shown in  FIG. 2 , the diffraction grating provided between the laser diode  110  and a disc surface of the optical disk  500  includes two diffraction gratings  114 - 1 ,  114 - 2 , and the respective diffraction gratings are formed with grooves  115 - 1 ,  115 - 2  extending in the different directions, respectively.  
         [0074]     When a laser beam  20  enters the diffraction gratings configured as described above, the laser beam is branched into three laser beams by the first diffraction grating  115 - 1 , and then branched further into three laser beams by the second diffraction grating  115 - 2 , whereby nine laser beams in total are formed. Then, five spots  20 A to  20 E out of these beams which are irradiated on the disk surface of the optical disk are used.  
         [0075]      FIG. 3  is a plan view showing an arrangement of spots irradiated on the disk surface of the optical disk.  
         [0076]     As shown in  FIG. 3 , a main beam for recording  20 A, a precedent sub-beam for tracking  20 B, a following sub-beam for tracking  20 C, a precedent sub-beam for reproduction  20 D, and a following sub-beam for reproduction  20 E are irradiated on the disk surface of the optical disk  500 .  
         [0077]     Here, the main beam for recording  20 A is irradiated on a groove  502 - 2  formed on the optical disk  500 , and by this irradiation of the beam spot, pits  506  are formed in the groove  502 - 2 .  
         [0078]     The main beam for recording  20 A is set to the highest luminescence intensity to enable formation of a pit by a heat mode.  
         [0079]     The precedent sub-beam for tracking  20 B is irradiated on a land  504 - 3  which is situated next to the groove  502 - 2  on which the main beam  20 A is irradiated, and the following sub-beam for tracking  20 C is irradiated on a land  504 - 2  which is a land situated next to the groove  502 - 2  on which the main beam  20 A is irradiated, that is, the land on the opposite side from the land on which the sub-beam  20 B is irradiated.  
         [0080]     The precedent sub-beam for reproduction  20 D is irradiated on the groove  502 - 2  which is the same groove on which the main beam  20 A is irradiated at a position preceding the main beam  20 A, and the following sub-beam for reproduction  20 E is irradiated on the groove  502 - 2  which is the same as the groove on which the main beam  20 A is irradiated at a position following the main beam  20 A.  
         [0081]     By disposing the respective spots as described above, the record pattern formed by the main beam  20 A, that is, the record pattern composed of combination of the pit  506  and a land  508  can be detected by the following sub-beam for reproduction  20 E.  
         [0082]      FIG. 4  shows a conceptual diagram showing a relation between the spot irradiated on the disk surface of the optical disk and the detector. As shown in  FIG. 4 , the detector  122  shown in  FIG. 1  includes five light receiving portions from  122 A to  122 E, and reflective lights  22 A to  22 E corresponding to the spots  20 A to  20 E are irradiated on the respective light receiving portions, thereby being converted into the electrical signals.  
         [0083]      FIG. 5  is a conceptual diagram showing a relation between the respective spots and the detector in the case of irradiating four spots on the disk surface of the optical disk. As shown in  FIG. 5 , the invention may be configured without using the precedent sub-beam for reproduction  20 D shown in  FIG. 4 .  
         [0084]      FIG. 6  is a conceptual diagram showing a relation between the respective spots and the detector in the case of irradiating nine spots on the disk surface of the optical disk.  
         [0085]     As shown in  FIG. 6 , the invention may be configured to generate nine branched lights by the diffraction grating and use five of them.  
         [0086]     In this case, a configuration in which spots shown in broken lines in the drawing are not received by the detector is employed.  
         [0087]      FIG. 7  is a plan view showing a distance between the beam for recording and the beam for reproduction.  
         [0088]     As shown in  FIG. 7 , a distance H between the main beam for recording  20 A and the sub-beam for reproduction  20 E is set to a range of H≧V×T, where T represents a time required for formation of a pit, and V represents a linear velocity of the media.  
         [0089]     This configuration is devised by focusing attention to a point that there arises a problem such that passage of time until completion of recording is necessary in the optical recording media, and hence in a state of imperfect recording, the laser output and the regenerative signal for pulse adjustment are deteriorated, and a distance between the beam spot for recording and the beam spot for reproduction is determined in order to avoid the regenerative signal acquisition in the state of incomplete recording as described above.  
         [0090]     While media using thermal reaction or phase change for data recording are known in the optical recording media, by setting the distance between the record spot and the regenerative signal acquisition spot on the optical recording medium as shown in  FIG. 7 , acquisition of regenerative signals after completion of data recording is ensured.  
         [0091]      FIG. 8  is an exploded perspective view showing a positional relation of the respective optical elements provided in the pickup shown in  FIG. 1 .  
         [0092]     As shown in  FIG. 8 , when Y-axis represents the vertical direction of optical axis, X-axis represents the horizontal direction of optical axis, and the Z-axis represents the direction of optical axis, the objective lens  118 , the collimating lens  119 , and the toroidal lens  120  are disposed on the Z-axis and the detectors  122 A- 122 E are disposed on the Y-axis.  
         [0093]     In this arrangement, the spots  20 A to  20 E irradiated on the disk surface of the optical disk are irradiated on the detection sides of the respective detectors via the objective lens  118 , the collimating lens  119 , and the toroidal lens  120 .  
         [0094]      FIG. 9  is a conceptual diagram showing a relation between vertical and horizontal layouts of the objective lens  118 , the collimating lens  119 , and the toroidal lens  120 , and the distances between the respective detectors.  FIG. 9A  shows a vertical layout of the respective optical elements, and FIG.  9 B shows a horizontal layout of the respective optical elements.  
         [0095]     As indicated in the respective drawings, where Y 1  represents a distance between the first and second beam spots in the vertical direction of optical axis, X 1  represents a distance between the same in the horizontal direction of optical axis, Ly represents a distance between the first and second detectors in the vertical direction of optical axis, Lx represents a distance between the same in the horizontal direction of optical axis, f 1  represents a focal distance of the objective lens, f 2  represents a focal distance of the collimating lens, f 3   y  represents a focal distance of the toroidal lens in the vertical direction, f 3   x  represents a focal distance between the same in the same horizontal direction, f 3  is a focal distance synthesized by f 3   x  and f 3   y  and d represents a distance between principal points of the collimating lens and the toroidal lens, Y 2  and X 2  are defined by following expression. 
 
 Y   2 ={ f   1 · f   2 · f   3   y /( f   2 + f   3 − d )}· Y   1  
 
 X   2 ={ f   1 · f   2 · f   3   x /( f   2 + f   3 − d )}· X   1  
 
         [0096]     Therefore, when the toroidal lens is a convex lens and f 3   y &gt;f 3   x,  the first and second detectors are arranged under conditions where Y 2 &gt;Ly and X 2 &lt;Lx are satisfied, while when the toroidal lens is a concave lens and f 3   y &gt;f 3   x  is satisfied, the first and second detectors are arranged under conditions where Y 2 &lt;Ly and X 2 &gt;Lx are satisfied.  
         [0097]      FIG. 10  is a perspective diagram showing an example of arrangement of the first detector and the second detector.  
         [0098]     As shown in  FIG. 10 , imaging a case in which a first detector  122 - 1  and a second detector  122 - 2  are disposed obliquely on a XY plane, a distance L between the respective detectors is set to a distance larger than Lx and Ly, thereby achieving a configuration in which the respective detectors are prevented from being mechanically overlapped with each other, and light receiving of the spots is enabled.  
         [0099]      FIG. 11  is a conceptual diagram showing an image of ranges of maximum distance between the detectors.  
         [0100]     As shown in the respective drawings, when the toroidal lens is a convex lens, the distance between the detectors are to be in the range shown in  FIG. 11A , and when the toroidal lens is the concave lens, the distance between the detectors are to be in the range shown in  FIG. 11B .  
         [0101]      FIG. 12  is a perspective diagram showing the relation between the width and the distance of the first and second detectors.  
         [0102]     As shown in  FIG. 12 , when Wy represents the width of the first and second detectors in the vertical direction of optical axis and Wx represents the width of the same in the horizontal direction of optical axis, a configuration in which the respective detectors are prevented from being mechanically overlapped with the each other, and light receiving of the spots is enabled is achieved with the arrangement under conditions which satisfy Ly≧Wy in the case of the concave lens and Lx&gt;Wx in the case of the convex lens.  
         [0103]      FIG. 13  is a perspective diagram showing an example of another arrangement of the first detector and the second detector.  
         [0104]     As shown in  FIG. 13 , when the detection side of the first detector  122 - 1  and the detection side of the second detector  122 - 2  are arranged on different Z-coordinate, even when it is overlapped in a plane, spatial overlapping can be avoided, thereby achieving a configuration in which the respective detectors are prevented from being mechanically overlapped with each other, and light receiving of the spots is enabled.  
         [0105]      FIG. 14  is a conceptual diagram showing a relation between the vertical and horizontal layouts of the objective lens  118 , the collimating lens  119 , and the toroidal lens  120  shown in  FIG. 8  and the position of the detectors in the direction of optical axis.  
         [0106]     As shown in  FIG. 14 , when dy represents a distance between the image surface of the beam spot-in the vertical direction and the principal point of the toroidal lens, dx represents a distance between the image surface in the horizontal direction of the beam spot and the principal point of the toroidal lens, and D represents the distance between the detection side of the first and second detectors and the principal point of the toroidal lens, if the toroidal lens is a convex lens, and f 3   y &gt;f 3   x  is satisfied, the respective detectors are arranged under conditions where dx&lt;D&lt;dy is satisfied, and when the toroidal lens is a concave lens and f 3   y &gt;f 3   x  is satisfied, the respective detectors are arranged under conditions where dx&gt;D&gt;dy is satisfied.  
         [0107]      FIG. 15  is a conceptual diagram showing a concept of focusing using an astigmatism method.  
         [0108]     As shown in  FIG. 15 , a reflection spot  22  irradiated on the detection side of the detector assumes a shape as shown by  22 - 1  to  22 - 7  according to the adjusted position of focusing, and a range from  22 - 6  which is an image surface in the horizontal direction to  22 - 3  which is an image surface in the vertical direction is a range in which the astigmatism method can be conducted.  
         [0109]     Therefore, when performing focusing using the astigmatism method, the respective detectors are arranged between dx and dy.  
         [0110]      FIG. 16  is a circuit block diagram showing an internal composition of the pulse generation circuit shown in  FIG. 1 .  
         [0111]     As shown in  FIG. 16 , in a pulse generation circuit  300 , strategy conditions SD 1 , SD 2  sent from the CPU  212  in  FIG. 1  are received respectively in a pulse unit generation circuits  310 - 1 ,  310 - 2 , and pulse signals PW 1 , PW 2  synchronized with a clock signal CLK are generated.  
         [0112]     The strategy conditions SD 1 , SD 2  are defined as numerical value data representing the length of ON-period and OFF-period of the pulse by clock numbers, and the pulse unit generation circuits  310 - 1 ,  310 - 2  receiving these data generate pulse signals under conditions indicated by the strategy conditions SD 1 , SD 2  using the clock signal CLK generated in the drive. These pulse signals PW 1 , PW 2  are outputted to the LD driver  124  in  FIG. 1 .  
         [0113]      FIG. 17  is a circuit drawing showing an internal composition of the LD driver shown in  FIG. 1 .  
         [0114]     As shown in  FIG. 17 , the LD driver  124  includes a partial pressure circuit using resistances R 1 , R 2 , and a synthesizer  126  for synthesizing the output voltages therefrom. The pulse signals PW 1 , PW 2  from the pulse generation circuit  300  are amplified to a predetermined output level via the resistances R 1 , R 2 , and then synthesized in a logical addition manner by the synthesizer  126 . Accordingly, a record pulse PWR is generated and outputted to the laser diode  110  in  FIG. 1 .  
         [0115]      FIG. 18  is a timing chart showing a process of generation of the record pulse shown in  FIG. 17 .  
         [0116]     As shown in the respective drawings, the record pulse PWR outputted to the laser diode is generated using the pulse signals PW 1 , PW 2  which constitute the record pulse. In other words, as shown in  FIG. 18B and 18C , the pulse signals PW 1 , PW 2  are generated synchronously with the clock signal CLK in  FIG. 18A , and as shown in  FIG. 18D , the record pulse PWR is generated by synthesizing these pulse signals PW 1 , PW 2 .  
         [0117]      FIG. 19  is a timing chart showing a relation between the main beam for recording and the sub-beam for reproduction. As shown in  FIG. 19A , the output of the main beam for recording assumes a pulse pattern of a high output required for formation of the pit, and the pit pattern formed on the optical disk by the pulse irradiation will be as shown in  FIG. 19B .  
         [0118]     On the other hand, as shown in  FIG. 19C , the output of the sub-beam for reproduction is the same timing as the output pattern of the main beam for recording, thereby becoming a pulse pattern in which the output is reduced by an amount corresponding to a branching fraction with respect to the main beam for recording. Therefore, the pit pattern reproduced by the sub-beam for reproduction will be a pattern delayed by a time difference τ from the pit which is being recorded as shown in  FIG. 19D .  
         [0119]     Therefore, for example, when detecting a land  4 T reproduced during recording of a pit  14 T, as shown in  FIG. 19E , a position where the land  4 T of the pulse obtained by delaying the pattern of the record pulse by the time difference τ and a constant output area of the pit  14 T of the record pulse overlap with each other may be specified.  
         [0120]     In other words, a configuration of generating a first gate signal from the constant output area of the longer pit in the record pulse and generating a second gate signal from the pulse corresponding to the short pit or the land as the detection objects in the pulse pattern obtained by delaying the record pulse by the time difference τ, and then masking an RF signal obtained from the sub-beam for reproduction using the first and second gate signals becomes effective.  
         [0121]     According to the invention, since the real-time correction with higher degree of accuracy is enabled, application to the record environment in which the registration condition is different between the inner periphery and the outer periphery of the optical disk is expected.