Abstract:
An optical disk recording apparatus includes a beam emitting unit operable to emit a first beam for irradiating a track on an optical disk so as to record data and second and third beams for irradiating spaces between the track and tracks on both sides of the track, respectively; a light detection mechanism operable to detect the first to third beams reflected from the optical disk; a tracking controller operable to control tracking of the first beam on the basis of results of the reflected first to third beams detected by the light detection mechanism; and a determination unit operable to determine whether the first beam records data on a white portion of the track or overwrites data on a recorded portion of the track based on changes in reflected light amounts of the second and third beams detected by the light detection mechanism.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present application claims priority from Japanese Patent Application No. JP 2005-086547 filed on Mar. 24, 2005, the disclosure of which is hereby incorporated by reference herein.  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a disk recording apparatus, a recording method, and a recording control program suitable for use in recording data by tracking control of an optical disk having multiple recording layers using a DPP (differential push-pull) system.  
         [0003]     Recently, recordable optical disks have been generally used as recording media for recording digital data. For example, in standards of CDs (compact disc) and DVDs (digital versatile disc), recordable optical disks are defined. In particular, the recordable DVD can store high-capacity data, so that it has been significantly in wide spread use as a recording medium replaceable from a conventional magnetic tape. Also, a recordable DVD with two recording layers capable of recording much higher capacity data has appeared.  
         [0004]     In a one side two-layered disk having two recording layers on one side, the two recording layers are respectively referred to as an L0 layer and an L1 layer from the incident side of laser light in that order. For example, in “DVD+R” standard, the L0 layer is accessed toward the outer periphery of the disk from the inner periphery in the same way as in a single layered disk while the L1 layer is accessed toward the inner periphery of the disk from the outer periphery. Thereby, the L1 layer can be easily accessed continuously from the L0 layer.  
         [0005]     In recordable DVDs, there are a write once DVD and a rewritable DVD rewritable data recorded before. The rewritable DVD will be described below unless otherwise specified. Rewritable DVD standards include a DVD-RW standard, a DVD+RW standard, and a DVD-RAM (random access memory) standard. The DVD-RW standard and the DVD+RW standard will be described below.  
         [0006]     In such a rewritable optical disk, a tracking error signal is detected so as to take tracking using a groove provided in the disk, and pits are formed on the groove by a laser beam emitted from an optical pick-up so that data are recorded by forming a track with a pit train.  
         [0007]     In the rewritable optical disk complying with DVD-RW standards and DVD+RW standards, the tracking error signal may be detected by a DPP (differential push-pull) system. A tracking control technique by the DPP system is disclosed in Japanese Unexamined Patent Application Publication No. 2005-25790.  
         [0008]     In the DPP system, a laser beam emitted from a laser diode is divided into a zero-order beam (main beam) and two first-order beams (side beams) using a diffraction grating. The three divided beams are arranged such that when the main beam is positioned on the groove, the two side beams are located on lands on both sides, respectively. The reflected beams from the respective beams of the optical disk are detected by a split-half light detector, respectively, so as to have a push-pull signal, and then, a tracking error signal DPP is obtained by the computation using equation (1). According to the DPP system, a satisfactory tracking error signal DPP can be obtained without being affected by the visual field deviation in an object lens of the optical pick-up. 
 
 DPP=mpp−G ×( spp   1   +spp   2 )  (1) 
 
 mpp: push-pull signal of the main beam 
 
 spp 1 , spp 2 : push-pull signals of the two side beams 
 
 G: a gain defined by the light quantity of the side beam and the gain of a photo-detector (DPP gain) 
 
         [0009]     The push-pull signal is the difference between detected signals of the split-half light-receiving surfaces of the split-half light detector. A tracking servo moves the beams so as to be PD 1 =PD 2  for tracking. That is, the tracking servo moves the beams so as to be the tracking error signal DPP=zero in the above equation (1).  
         [0010]      FIG. 20  shows an example of the arrangement of the main beam and the two side beams on an optical disk  100  according to the DPP system. Referring to  FIG. 20 , the rotation direction of the optical disk  100  is assumed to be clockwise, and the optical disk  100  is provided with grooves  101 ,  101 , . . . formed roughly concentrically about the disk center in advance. Between the grooves  101  and  101 , a land  102  is formed. The grooves  101 ,  101 , . . . meander slightly in fact; however, they are shown by straight lines in  FIG. 20 .  
         [0011]     Two side beams  103 A and  103 B are arranged in front and in rear of a main beam  104  in the rotation direction of the optical disk  100 , respectively. In general, the side beam  103 A, which is positioned in front of the main beam  104  in the rotation direction, is arranged in the outer radial side than the main beam  104 , while the side beam  103 B, which is positioned in rear of the main beam  104  in the rotation direction, is arranged in the inner radial side than the main beam  104 . Hence, when recording from the inner radial side of the disk toward the outer radial side, the side beam  103 A precedes the main beam  104  while the side beam  103 B succeeds the main beam  104 .  
         [0012]     When data is recorded on a white area of the optical disk  100 , a track, through which the main beam  104  has passed, is the recorded track already having a pit formed thereon while a track preceding the main beam  104  is a white track having no pit yet. The white track generally has a reflectance of laser light higher than that of the recorded track.  
         [0013]     Accordingly, as shown in  FIG. 21 , in the side beam  103 A for example, if one side track of the beam is a white track and the other side track is a recorded track, even when the main beam  104  is positioned at the center of the track, the respective photo-acceptance amounts due to the side beam  103 A on the split-half light-receiving surfaces of the split-half light detector differ from each other. In the state of  FIG. 21 , the photo-acceptance amount PD 1  on the split-half light-receiving surface on the white track side of the split-half light detector is larger than that on the split-half light-receiving surface PD 2  on the recorded track side. As a result, the push-pull signal output from the split-half light detector has an offset.  
         [0014]     As described above, the tracking servo moves the beams so that the difference between detected signals due to the split-half light-receiving surfaces PD 1  and PD 2  of the split-half light detector becomes zero. Thus, in the example of  FIG. 21 , the tracking servo is operated so that the beam is moved toward the recorded track. As a result, the main beam deviates from the track so as to be de-tracking. The de-tracking is designated that although the main beam can trace the track, it deviates from the track center.  
         [0015]     The recording on the white track is referred to as a DOW (Direct Over Write)  0  while the recording on the recorded track is referred to as a DOW 1 .  
         [0016]     When the side beam  103 A, which is positioned in front of the main beam  104  in the rotation direction of the disk, is arranged in the outer radial side than the main beam  104 , a case where the L0 layer of a single-layered disk or the one side two-layered disk is recorded will be considered. In this case, the recording is executed from the inner radial side of the optical disk  100  toward the outer radial side. When recording on the white track (DOW0 state), as shown in  FIG. 22A , tracks on both sides of the side beam  103 A are white while tracks on both sides of the side beam  103 B are already recorded. Since the respective both sides of the side beam  103 A and the side beam  103 B are in the same states, the difference between photo-acceptance amounts of the split-half light-receiving surfaces of the split-half light detector is small so that push-pull signals spp 1  and spp 2  of the side beam  103 A and the side beam  103 B have no offset. Accordingly, when the beam is moved so as to be the tracking error signal DPP=zero, the main beam may not be detracked.  
         [0017]     Similarly, when the L0 layer of the single-layered disk or the one side two-layered disk is recorded, in the state that the recorded track is overwritten (DOW1 state), as shown in  FIG. 22B , both tracks on both sides of the side beam  103 A and tracks on both sides of the side beam  103 B are already recorded. In this case also, in the same way as that described above, the push-pull signals spp 1  and spp 2  of the side beam  103 A and the side beam  103 B have no offset, so that the main beam may not be detracked.  
         [0018]     Then, when the side beam  103 A is arranged in the outer radial side than the main beam  104 , a case where the L1 layer of the one side two-layered disk is recorded will be considered. In this case, the recording is executed from the outer radial side of the optical disk  100  toward the inner radial side. When recording on the white track, as shown in  FIG. 23A , in both the side beam  103 A and the side beam  103 B, the inner radial side of the disk is the white track while the outer radial side is the recorded track. Thus, the difference between photo-acceptance amounts of the split-half light-receiving surfaces of the split-half light detector is large in the side beam  103 A and the side beam  103 B, so that push-pull signals spp 1  and spp 2  have offsets. As a result, the main beam is detracked in the white track direction, i.e., in the outer radial direction of the disk.  
         [0019]     On the other hand, in the state that the recorded track is overwritten when the L1 layer of the one side two-layered disk is recorded, as shown in  FIG. 23B , both sides of the side beam  103 A and the side beam  103 B are recorded tracks. In this case also, in the same way as that described above, the push-pull signals spp 1  and spp 2  of the side beam  103 A and the side beam  103 B have no offset, so that the main beam may not be detracked.  
         [0020]     In such a manner, in the past system for obtaining the tracking error signal with the DPP system, when the L1 layer of the one side two-layered disk is recorded, the state that the white track is recorded (DOW0 state) other than the state the recorded track is overwritten (DOW1 state) leads to the detracking. This fact has not been reported as well as solving means therefore is not obviously reported.  
         [0021]      FIG. 24  shows example measured results of a detracking amount when the white track of the rewritable DVD is recorded. In  FIG. 24 , the relationship between the detracking amount (nm) and the jitter (%) during reproducing is shown for when recording from inner radial side of the disk toward the outer radial side (designated by symbol ♦ in the drawing) and for when recording from outer radial side of the disk toward the inner radial side (designated by symbol ▪ in the drawing). Desirable characteristics include that the most satisfactory reproducing signal (the jitter is small) is obtained when the detracking amount is zero, as shown in measured results when recording from the inner radial side toward the outer radial side. Whereas, when recording from the outer radial side toward the inner radial side, if the main beam is detracked rather in the outer radial direction, the jitter becomes smaller, obtaining favorable reproducing signals.  
         [0022]     In order to correct the detracking in such a way, under conditions in that the detracking may occur, an offset may be electrically applied to the tracking error signal. In this method, as described above, when the L1 layer of the one side two-layered disk is recorded, the detracking occurrence depends on the kind of the track to be recorded, whether it is white or recorded before. Accordingly, it needs to determine whether the track being recorded at present is white or recorded before.  
         [0023]     However, in the past, there was no method for determining whether the track being recorded at present is white or recorded before, i.e., whether the present recording is in the DOW0 state or the DOW1 state.  
         [0024]     It is possible to know part of the recorded track and part of the white track in advance on the basis of address information. However, the accuracy in reading address during recording is generally not so high, so that it is difficult to precisely detect the boundary between the recorded track and the white track using the address information. Moreover, there exits a system not reading address during recording.  
       SUMMARY OF THE INVENTION  
       [0025]     Thus, according to the present invention, it is desirable to provide a disk recording apparatus, a method, and a recording control program capable of determining whether a track being recorded at present is white or recorded before when data are recorded on an optical disk by tracking control using a DPP system.  
         [0026]     According to an embodiment of the present invention, there is provided an optical disk recording apparatus including beam emitting means for emitting a first beam for irradiating a track on an optical disk so as to record data and second and third beams for irradiating spaces between the track and tracks on both sides of the track, respectively; light detecting means for detecting the first to third beams reflected from the optical disk; tracking controlling means for controlling tracking of the first beam on the basis of results of the reflected first to third beams detected by the light detecting means; and determining means for determining whether the first beam records data on a white portion of the track or overwrites data on a recorded portion of the track based on changes in reflected light amounts of the second and third beams detected by the light detecting means.  
         [0027]     According to an embodiment of the present invention, there is provided an optical disk recording method including emitting a first beam for irradiating a track on an optical disk so as to record data and second and third beams for irradiating spaces between the track and tracks on both sides of the track, respectively; detecting the first to third beams reflected from the optical disk; controlling tracking of the first beam based on the reflected first to third beams; and determining whether the first beam records data on a white portion of the track or overwrites data on a recorded portion of the track based on changes in reflected light amounts of the second and third beams.  
         [0028]     According to an embodiment of the present invention, there is provided a recording control program for allowing a computer to execute an optical disk recording method, the optical disk recording method including emitting a first beam for irradiating a track on an optical disk so as to record data and second and third beams for irradiating spaces between the track and tracks on both sides of the track, respectively; detecting the first to third beams reflected from the optical disk; controlling tracking of the first beam based on the reflected first to third beams; and determining whether the first beam records data on a white portion of the track or overwrites data on a recorded portion of the track based on changes in reflected light amounts of the second and third beams.  
         [0029]     As described above, according to an embodiment of the present invention, on the basis of changes in reflected light amounts of the second and third beams irradiating spaces between a track and tracks on both sides of the track, respectively, for tracking control of the first beam irradiating the track on the optical disk so as to record data, it is determined whether the first beam records on a white portion of the track or overwrites on the recorded portion. Hence, the transition from the overwriting on the recorded portion of the track to the recording on the white portion can be detected during the recording. Thereby, suitable recording control can be performed on the overwriting on the recorded portion and the recording on the white portion, and also pre-existing hardware structures can be used as they are.  
         [0030]     According to an embodiment of the present invention, when recording on a rewritable optical disk by tracking control with the DPP system, based on the sum of the reflected light amounts of the two side beams, it is determined whether the present recording is in DOW0 state or in DOW1 state. Therefore, the detracking generated when the recording state is changed from DOW1 state to DOW0 state during recording for the outer radial side of the disk toward the inner radial side can be effectively prevented.  
         [0031]     Also, the detracking generated when recording on an L1 layer of the two-layered disk can thereby be prevented.  
         [0032]     Furthermore, according to an embodiment of the present invention, since it can be precisely determined whether the present recording is in DOW0 state or in DOW1 state, as described above, the optimum recording conditions (such as recording power, a strategy, and servo setting) can be established for the recording in DOW0 state and the recording in DOW1 state, respectively. Also, there is an advantage of improved quality of recording signals.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0033]      FIG. 1  is a block diagram of an example of an optical disk drive according to an embodiment of the present invention;  
         [0034]      FIG. 2  is a conceptual schematic diagram of an example of a light path in an optical pick-up;  
         [0035]      FIG. 3  is a schematic diagram of a structural example of a recording layer of an optical disk;  
         [0036]      FIGS. 4A and 4B  are schematic diagrams showing a disk layout of the optical disk complying with rewritable DVD standards;  
         [0037]      FIG. 5  is a schematic diagram showing an arrangement of a main beam and two side beams on the optical disk;  
         [0038]      FIG. 6  is a schematic diagram of a structural example of a photo-detector;  
         [0039]      FIG. 7  is a schematic diagram showing measured results of light receiving amounts in the photo-detector when conditions of tracks on both sides of the side beam are changed;  
         [0040]      FIGS. 8A  to  8 D are schematic diagrams showing situations of the main beam and two side beams irradiating the optical disk;  
         [0041]      FIG. 9  is a schematic diagram showing changes in reflected light amount of the side beam when recording from the inner radial side of the disk toward the outer radial side;  
         [0042]      FIGS. 10A  to  10 D are schematic diagrams showing situations of the main beam and two side beams irradiating the optical disk;  
         [0043]      FIG. 11  is a schematic diagram showing changes in reflected light amount of the side beam when recording from the outer radial side of the disk toward the inner radial side;  
         [0044]      FIGS. 12A and 12B  are schematic diagrams showing changes in sum of reflected light amounts of the two side beams;  
         [0045]      FIG. 13  is a schematic diagram showing the relationship among levels SPD 0  to SPD 4 ;  
         [0046]      FIG. 14  is a flowchart showing a setting method of a threshold value SPD th ;  
         [0047]      FIGS. 15A  to  15 D are schematic diagrams showing situations of the main beam and two side beams irradiating the optical disk;  
         [0048]      FIG. 16  is a schematic diagram showing changes in reflected light amount of the side beam when recording from the inner radial side of the disk toward the outer radial side;  
         [0049]      FIGS. 17A  to  17 D are schematic diagrams showing situations of the main beam and two side beams irradiating the optical disk;  
         [0050]      FIG. 18  is a schematic diagram showing changes in reflected light amount of the side beam when recording from the outer radial side of the disk toward the inner radial side;  
         [0051]      FIGS. 19A and 19B  are schematic diagrams showing changes in sum of reflected light amounts of the two side beams;  
         [0052]      FIG. 20  is a schematic diagram showing an arrangement of a main beam and two side beams on the optical disk with a DPP system;  
         [0053]      FIG. 21  is a schematic diagram for illustrating that when one side of the side beam is a white track and the other side is a recorded track, a difference is generated between light receiving amounts on the respective two-divided light receiving surfaces of a two-split photo-detector;  
         [0054]      FIGS. 22A and 22B  are schematic diagrams showing the relationship between the recording tracks, the main beam, and the two side beams;  
         [0055]      FIGS. 23A and 23B  are schematic diagrams showing the relationship between the recording tracks, the main beam, and the two side beams; and  
         [0056]      FIG. 24  is a graph showing measured results of detracking amounts when recording on a white track of a recordable DVD. 
     
    
     DETAILED DESCRIPTION  
       [0057]     Embodiments according to the present invention will be described below with reference to the drawings. According to the present invention, when data are recorded on a rewritable optical disk by tracking control using a DPP (differential push-pull) system, in a configuration that in two side beams by the DPP system, the side beam positioned in front of a main beam in the rotation direction of the disk is arranged in the outer radial side of the disk than the main beam, a track being recorded at present is determined whether white or recorded before on the basis of change in light amount of the side beam.  
         [0058]     According to the present invention, a tracking offset can be prevented, which is generated when recording on a white track from the outer radial side of the disk toward the inner radial side, such as recording on the L1 layer of a rewritable one side two-layered disk.  
         [0059]      FIG. 1  shows a configuration of an optical disk drive  1  according to an embodiment of the present invention. An optical disk  10  is brought into engagement with a shaft  21  of a spindle motor  20  with a cramp mechanism (not shown) rotatably by being driven by the spindle motor  20 .  
         [0060]     An optical pick-up  22  is arranged at a position opposing the recording surface of the optical disk  10 . The optical pick-up  22  is placed on a thread  24 , which is movable in the radial direction of the optical disk  10  by a thread motor  23 , so as to move in the radial direction of the optical disk  10  together with the thread  24 .  
         [0061]     The optical pick-up  22  includes a laser light source, a beam splitter, a grating, a photo-detector, and an object lens. A laser beam emitted from the laser light source is divided into three components that are a main beam and two side beams, and enters the object lens after passing through the beam splitter. The object lens irradiates the incident main beam and the two side beams on the recording surface of the optical disk  10 . The laser beam is reflected on the recording surface of the optical disk  10  and then, is entered in the beam splitter via the object lens so as to arrive at the photo-detector by being reflected at the beam splitter. The photo-detector takes out respective push-pull signals of the main beam and the two side beams for outputting.  
         [0062]     The output of the optical pick-up  22  is supplied to a signal processing unit  25 . The signal processing unit  25  produces a focus error signal, a tracking error signal, etc., on the basis of the output of the optical pick-up  22  so as to feed them to a microcomputer  27 . The microcomputer  27  supplies control signals to a servo control unit  28  on the basis of these focus error signal and tracking error signal. The servo control unit  28  performs various servo controls, such as spindle servo, thread servo, servo for the object lens (focus servo and tracking servo), on the basis of supplied control signals.  
         [0063]     During recording, the signal processing unit  25  performs error-correction encoding processing and record encoding processing on recording data supplied via a host interface (I/F), and further it performs predetermined signal processing, such as modulation processing, thereon so as to produce a recording signal. The recording signal is fed to the optical pick-up  22  so as to modulate the laser beam. During reproducing, predetermined processing, such as RF signal processing, binarization processing, PLL (phase locked loop) synchronous processing, and decryption processing of recording codes, is performed on the signal output from the optical pick-up  22  so as to take out digital data. The digital data output from the signal processing unit  25  are fed to an external device via the host I/F  26 .  
         [0064]     Furthermore, during recording, recording instructions are given via the host I/F  26  so as to feed them to the microcomputer  27 . The microcomputer  27  instructs the servo control unit  28  to start recording on the basis of the recording instructions. The servo control unit  28  controls the position of the optical pick-up  22  on the basis of the instructions from the microcomputer  27 . Also, the microcomputer  27  establishes various recording conditions, such as a write strategy, recording power, and a defocus amount, for the signal processing unit  25 . According to the established recording conditions, the signal processing unit  25  controls the modulation of the recording signal and the laser light source drive. During reproducing, the signal processing unit  25  and the servo control unit  28  are also controlled by the microcomputer  27  in the same way.  
         [0065]     The microcomputer  27  is composed of a microprocessor for example, and on the basis of programs stored in an ROM (read only memory) (not shown) in advance, it controls the operation of the optical disk drive  1  as described above. When the ROM is replaced by a rewritable memory such as an EEPROM (electrically erasable programmable read only memory), the stored programs can be desirably updated. The program data to be updated are supplied from the host I/F  26 .  
         [0066]     As will be described later in detail, during recording, the microcomputer  27  detects the state of a recording part on the basis of the output of the optical pick-up  22  so as to be able to establish the recording conditions corresponding to the detected state for the servo control unit  28 .  
         [0067]      FIG. 2  conceptually shows a light path in the optical pick-up  22 . Laser light emitted from a laser light source  30  made of a laser diode is divided into a zero-order main beam and two first-order side beams by a grating  31 , and enters a collimator lens  33  via a beam splitter  32 . The laser light is converted into parallel rays by the collimator lens  33 , and converged by an object lens  34  so as to irradiate the recording surface of the optical disk  10 . The laser light is reflected on the recording surface of the optical disk  10 , and is incident in the beam splitter  32  via the object lens  34  and the collimator lens  33 . The reflected laser light is reflected by the beam splitter  32  in a predetermined manner and incident in a photo-detector  40  via a cylindrical lens  35 .  
         [0068]      FIG. 3  schematically shows the structure of a recording layer of the optical disk  10 . On the recording layer, grooves  70 ,  70 , . . . wobbled at a predetermined frequency are formed as guide grooves for introducing laser light to a track. Between the grooves  70  and  70 , a land  71  is formed. The address information is indicated by a pre-pit (not shown) formed on the land  71  in the DVD-RW standard, and is indicated by a high-frequency (not shown) superposed on a wobble in the DVD+RW standard.  
         [0069]     Data is recorded by forming a record mark  72  on the groove  70  with the laser light introduced to the track. In a rewritable optical disk conforming with the DVD-RW standard and the DVD+RW standard, the recording layer is made of a phase change film, and the forming the record mark  72  and the erasing the formed record mark  72  can be executed using the reversible change between the crystalline substance and the non-crystalline substance of the phase change film. By changing the emission intensity of the laser light in a predetermined manner, changes in the phase change film are controlled. A new record mark  72  is formed directly after the record mark  72  is erased thereon, so that data can be overwritten thereon.  
         [0070]      FIGS. 4A and 4B  are schematic layouts of the optical disk  10  conforming to a rewritable DVD standard. According to the DVD-RW standard, as schematically shown in  FIG. 4A , in the most inside periphery of the disk, a recording information management area (R-information area) is provided and a data area (information area) is provided outside the R-information area for use in recording user data. In the R-information area, a PCA (power calibration area) and an RMA (recording management area) are provided. The PCA is used by the optical disk drive  1  for testing the optimization of the laser power during recording. In the RMA, power calibration information, a recorder ID, and a recording history are recorded. The RMA of the white optical disk  10  has no signal recorded thereon.  
         [0071]     The information area is composed of a lead-in area, a data area, and a lead-out area, in that order from the inside periphery. In the lead-in area, pieces of information about the optical disk  10 , such as a format version, a disk type (such as DVD-R, DVD+R, DVD-RW, and DVD+RW), and the number of initiation/completion sectors, are recorded.  
         [0072]      FIG. 4B  schematically shows the disk layout conforming to the DVD+RW standard. In the DVD+RW standard, the R-information area is not provided as in the DVD-RW standard. In the lead-in area, the information about the optical disk  10  is recorded in the same way in the DVD-RW standard.  
         [0073]     As described above, the laser light emitted from the laser light source  30  is divided into the main beam and the two side beams by the grating  31  so as to irradiate the optical disk  10 .  FIG. 5  schematically shows the arrangement of the three beams on the optical disk  10 . The crosswise direction of the drawing indicates the radial direction of the optical disk  10 . The left of  FIG. 5  is assumed to be the inside periphery of the optical disk  10  and the right the outside. In  FIG. 5 , the wobble of grooves  50  is omitted.  
         [0074]     A main beam  60  is for recording/reproducing data in practice, and the position of an optical spot of the main beam  60  is controlled so as to irradiate the track  50 . On the other hand, side beams  61 A and  61 B are arranged so that optical spots thereof irradiate lands on both sides of the main beam  60 , respectively. For example, when the center of the track  50  is irradiated by the optical spot of the main beam  60 , the side beams  61 A and  61 B are arranged so that optical spots thereof irradiate respective centers of spaces  51 A and  51 B between the track  50  and tracks on both sides of the track  50 .  
         [0075]     The side beams  61 A and  61 B are displaced to the main beam  60  in front and rear in the rotation direction of the optical disk  10 . According to the embodiment, when the rotation direction of the optical disk  10  is assumed to be clockwise in  FIG. 5 , the side beam  61 A precedes the main beam  60  while the side beam  61 B succeeds the main beam  60 .  
         [0076]     In order to avoid some complexity, an optical spot by a laser beam is simply referred to a beam bellow. That is, “the main beam  60 ” and “the side beams  61 A and  61 B” indicate optical spots by the main beam  60  and the side beams  61 A and  61 B below, respectively, unless otherwise specified.  
         [0077]      FIG. 6  schematically shows the structural example of the photo-detector  40 . The photo-detector  40  has a four-piece shape in the center having four-divided components A to D, and two-piece shapes on both sides having half-divided components E and F and half-divided components G and H. The four-divided components A to D receive the reflected main beam  60  so as to obtain a push-pull signal mpp from the difference between light-receiving amounts by the elements A and D and the elements B and C. The half-divided components E and F receive the reflected side beam  61 A, for example, to obtain a push-pull signal spp 1  from the difference between light-receiving amounts by the elements E and F. Similarly, the half-divided components G and H receive the reflected side beam  61 B, for example, to obtain a push-pull signal spp 2  from the difference between light-receiving amounts by the elements G and H.  
         [0078]     Referring to  FIG. 5  described above, each push-pull signal is obtained from signals divided in the radial direction of the optical disk  10 . The reflected beams of the beams  60 ,  61 A, and  61 B arranged as shown in  FIG. 5  are condensed in a line by the cylindrical lens  35  so as to irradiate the photo-detector  40  as shown in  FIG. 6 . In the example of  FIGS. 5 and 6 , the half-divided elements E and G and the half-divided elements A and D of the photo-detector  40  correspond to the outer radial side of the optical disk  10 . The half-divided elements F and H and the half-divided elements B and C of the photo-detector  40  correspond to the inner radial side of the optical disk  10 .  
         [0079]     The tracking error signal DPP is obtained from the following equation (2) when output signals from the components A to H are referred to characters A to H, respectively. 
 
 DPP =( A+D )−( B+C )−α×{( E−F )+( G−H )}  (2) 
 
 where factor α is a DPP gain determined by the light amount of the side beam and the gain of the photo-detector  40 . 
 
         [0080]     Then, the embodiment of the present invention will be described more in detail.  FIG. 7  shows measured light-receiving amounts in the photo-detector when conditions of tracks on both sides of the side beam are changed. That is, in  FIG. 7 , the abscissa indicates the radial direction of the optical disk  10 , in which the first and second tracks from the left are recorded (shown by oblique lines) and subsequent tracks including the third track are white. The side beam sequentially irradiates the land (shown by character L) between tracks, and light amounts reflected from the optical disk  10  are indicated by vertical bars (shown by L 1  to L 4  in convenience sake).  
         [0081]     From the example of  FIG. 7 , it is understood that if the reflected light amount, when tracks on both sides of an optical spot by the side beam are white, is assumed to be “1” (the bars L 3  and L 4 ), when tracks on both sides of an optical spot by the side beam are both recorded, the reflectance is approximately 0.70 (the bar L 1 ); and when the tracks are white and recorded combined, the reflectance is approximately 0.85 (the bar L 2 ). That is, in comparison with the case where tracks on both sides of an optical spot by the side beam are white, the reflected light amount in the state that tracks on both sides are recorded is lower by approximately 30% while the reflected light amount in the state that one side track is only recorded is lower by approximately 15%.  
         [0082]     Then, changes in reflected light amount of the side beam during recording will be described. The change in reflected light amount of the side beam is different between cases in recording from the inner side toward the outer side and in recording from the outer side toward the inner side.  
         [0083]     In addition, the preceding side beam  61 A to the main beam  60  in the rotation direction of the optical disk  10  is referred to as the preceding beam below in convenience sake. Similarly, the succeeding side beam  61 B to the main beam  60  in the rotation direction of the optical disk  10  is referred to as the succeeding beam. The preceding side beam  61 A is assumed to be arranged in the outer radial side of the disk further than the main beam  60 .  
         [0084]     First, with reference to  FIGS. 8A  to  9 , changes in reflected light amounts of the side beams  61 A and  61 B when recording from the inner radial side toward the outer radial side of the optical disk  10  will be described.  
         [0085]      FIGS. 8A  to  8 D schematically show respective situations in that the optical disk  10  is irradiated with optical spots by the main beam  60  and the side beams  61 A and  61 B for every one revolution of the optical disk  10 . On the optical disk  10  herein from the outer radial side to a boundary position “a”, data is assumed to be already recorded before the present recording. The area from the boundary position “a” to the inner radial side is a white portion of the track. In  FIGS. 8A  to  8 D, the revolution direction of the optical disk  10  is clockwise, and the left of the drawing is the outer radial side of the optical disk  10 . In the tracks  50 ,  50 , . . . , portions painted black are newly recorded on white tracks; obliquely lined portions are already recorded before the present recording; and other portions designate white portions. These indications in  FIGS. 8A  to  8 D are common to the similar drawings below.  
         [0086]     That is, in  FIGS. 8A  to  8 D, already recorded portions are overwritten (DOW1 state) at first, and then, after the optical spot of the main beam  60  passed the boundary position “a”, the newly recording on white portions starts (DOW0 state).  
         [0087]     When recording on the optical disk  10  from the inner radial side toward the outer radial side of the disk, as shown in  FIGS. 8A  to  8 D, the position succeeding the main beam  60  in the rotation direction of the disk and the track is irradiated with the side beam  61 B. Hence, portions on both sides of the side beam  61 B are typically recorded.  
         [0088]     Also, the position preceding the main beam  60  in the rotation direction of the disk and the track is irradiated with the side beam  61 A. Hence, as shown in  FIG. 8D , when the main beam  60  is white and the present recording is in DOW0 state, portions on both sides of the side beam  61 A are typically white.  
         [0089]     On the other hand, when the main beam  60  includes portions already recorded before the present recording, these portions are to be in an overwritten state (DOW1 state). In the overwritten state, if the outer radial side of the side beam  61 A has already recorded portions, portions on both sides of the side beam  61 A are recorded (see  FIG. 8A ). If the outer radial side of the side beam  61 A reaches the white portion beyond the boundary position “a”, the outer radial side of the side beam  61 A is white while the inner radial side is recorded (see  FIG. 8B ). From this state, if the recording progresses by an amount equivalent to one track so that the inner radial side of the side beam  61 A reaches the white portion beyond the boundary position “a”, portions on both sides of the side beam  61 A are white (see  FIG. 8C ).  
         [0090]     When recording on the optical disk  10  from the inner radial side toward the outer radial side of the disk  10  in such a manner, the reflected light amount of the side beam  61 A changes in three steps in accordance with the state of portions on both sides of the side beam  61 A.  
         [0091]      FIG. 9  shows changes in reflected light amounts of the side beams  61 A and  61 B when recording on the disk from the inner radial side toward the outer radial side of the disk. The ordinate designates the reflected light amount level while the abscissa indicates time.  
         [0092]     As is already described with reference to  FIG. 7 , the reflected light amounts of the side beams  61 A and  61 B change stepwise corresponding to the state of portions on both sides of the beam. That is, when portions on both sides are white, the reflected light amount has the highest level (indicated by LV 2  in  FIG. 9 ); when portions on both sides are recorded, it has the lowest level (indicated by LV 0  in  FIG. 9 ); and when one side of the beam is white and the other is recorded, it has the intermediate level (indicated by LV 1  in  FIG. 9 ).  
         [0093]     In the state of  FIG. 8A  at first, the reflected light amount (indicated by the dotted line in  FIG. 9 ) of the preceding side beam  61 A is at Level LV 0  in which portions on both sides of the beam are recorded. For example, at a time “s” in  FIG. 9 , the outer radial side of the side beam  61 A reaches the boundary position “a”, so that the outer radial side of the side beam  61 A is white while the inner radial side becomes recorded (see  FIG. 8B ) and the reflected light amount of the side beam  61 A is to be at level LV 1 . When the recording further progresses so that the inner radial side of the side beam  61 A reaches the boundary position “a”, portions on both sides of the side beam  61 A are white (see  FIG. 8C ) and the reflected light amount of the side beam  61 A is to be at level LV 2  in which portions on both sides of the beam are white, and this state is maintained thereafter.  
         [0094]     Since portions on both sides of the succeeding side beam  61 B are typically recorded, the reflected light amount is at level LV 0  in which portions on both sides are typically recorded.  
         [0095]     Then, with reference to  FIGS. 10A  to  11 , changes in reflected light amounts of the side beams  61 A and  61 B when recording from the outer radial side toward the inner radial side of the disk will be described. In addition, designations of portions in  FIGS. 10A  to  11  are common to those in  FIGS. 8A  to  9  described above, so that the description thereof is omitted for avoiding complexity.  
         [0096]     When recording on the optical disk  10  from the outer radial side toward the inner radial side, the side beam  61 B is arranged at a position preceding the main beam  60  in the tracking direction of the disk  10  as well as in the rotation direction of the optical disk  10 . On the other hand, the side beam  61 A is arranged at a position succeeding the main beam  60  in the tracking direction of the optical disk  10 .  
         [0097]     When recording on the optical disk  10  from the outer radial side toward the inner radial side, the succeeding position in the tracking direction of the disk  10  is irradiated with the side beam  61 A while the preceding position is irradiated with the side beam  61 B. Also, the preceding position in the rotation direction of the disk  10  is irradiated with the side beam  61 A while the succeeding position is irradiated with the side beam  61 B. Hence, as shown in  FIGS. 10A  to  10 D, the outer radial side of the side beams  61 A and  61 B is typically in a state in that the main beam  60  has passed, so that the outer radial side becomes recorded by the present recording. The state of the inner radial side of the side beams  61 A and  61 B depends on the fact that whether this portion is already recorded before the present recording or not.  
         [0098]     Accordingly, as shown in  FIG. 10D , when the main beam  60  includes a white portion and is in state DOW 0 , the outer radial side of the side beams  61 A and  61 B is recorded while the inner radial side is white, differently from the example shown in  FIG. 8D .  
         [0099]      FIG. 11  shows changes in reflected light amounts of the side beams  61 A and  61 B when recording on the disk from the outer radial side toward the inner radial side of the disk. In the state of  FIG. 10A  at first, the reflected light amounts of both the preceding side beam  61 B and the succeeding side beam  61 A are at Level LV 0  in which portions on both sides of the beam are recorded. When the recording progresses from the state of  FIG. 10B , at a time “t” in  FIG. 11 , for example, the inner radial side of the side beam  61 B reaches the boundary position “a” so as to become white. Since the outer radial side of the side beam  61 B is typically recorded, the reflected light amount of the side beam  61 B is to be at level LV 1 . After the inner radial side of the side beam  61 B reached the boundary position “a” (see  FIGS. 10C and 10D ), the reflected light amount of the side beam  61 B is maintained at level LV 1 .  
         [0100]     On the other hand, at a time “u” after an elapsed time equivalent to one track from the time “t”, the inner radial side of the succeeding side beam  61 A reaches the boundary position “a” so as to become white (see  FIG. 10C ). The time from the time “t” to the time “u” is in fact shorter than the time equivalent to one track by a time corresponding to the space between the side beams  61 A and  61 B. Since the outer radial side of the side beam  61 A is typically recorded, the reflected light amount of the side beam  61 A is to be at level LV 1 . After the inner radial side of the side beam  61 A reached the boundary position “a” (see  FIG. 10D ), the reflected light amount of the side beam  61 A is maintained at level LV 1 .  
         [0101]     As is described with reference to  FIGS. 9 and 11 , the changes in reflected light amounts of the side beams  61 A and  61 B are different between cases in recording from the inner side toward the outer side and in recording from the outer side toward the inner side. The sum of the reflected light amounts of the side beams  61 A and  61 B in both the recording cases is figured out now.  
         [0102]      FIGS. 12A and 12B  show changes in sum of the reflected light amounts of the side beams  61 A and  61 B.  FIG. 12A  shows the example when recording from the inner side toward the outer side while  FIG. 12B  shows the example when recording from the outer side toward the inner side. In  FIGS. 12A and 12B , “preceding beam light amount” schematically designates the reflected light amount by the side beam  61 A; “succeeding beam light amount” the reflected light amount by the side beam  61 B; and “side beam quantity sum” the sum of the reflected light amounts of the side beams  61 A and  61 B.  
         [0103]     From  FIGS. 12A and 12B , it is understood that the sum of the reflected light amounts of the side beams  61 A and  61 B be changed in a predetermined manner at the boundary position “a”, i.e., in front and rear of DOW 0  despite of the radial recording direction of the optical disk  10 .  
         [0104]     On the basis of the state of tracks adjacent to the side beams  61 A and  61 B, changes in sum of the reflected light amounts of the side beams  61 A and  61 B in front and rear of DOW 0  will be considered. Two tracks neighbor on one side beam so that the sum of the tracks neighboring to the side beams  61 A and  61 B is four in maximum.  
         [0105]     First, DOW0 state in that the main beam  60  is located in a white portion of a track will be considered.  
         [0000]     (1) In DOW0 State when Recording from the Inner Radial Side Toward the Outer Radial Side  
         [0106]     As is already described with reference to  FIGS. 8A  to  9 , since the side beam  61 A precedes the main beam  60  in the tracking direction and the revolution direction of the disk in this case, portions on both sides are white in DOW0 state. Also, since the side beam  61 B succeeds the main beam  60  in the tracking direction and the revolution direction of the disk, portions on both sides are recorded. Hence, the number of the recorded portions (recorded tracks) neighboring to the side beams  61 A and  61 B is two.  
         [0000]     (2) In DOW0 State when Recording from the Outer Radial Side Toward the Inner Radial Side:  
         [0107]     As is already described with reference to  FIGS. 10A  to  11 , since the side beam  61 A succeeds the main beam  60  in the tracking direction, and it precedes the main beam  60  in the revolution direction of the disk in this case, a portion on the outer radial side is recorded and a portion on the inner radial side is white in DOW0 state. Also, since the side beam  61 B precedes the main beam  60  in the tracking direction and succeeds the main beam  60  in the revolution direction of the disk, a portion on the outer radial side is recorded and a portion on the inner radial side is white in DOW0 state. Hence, the number of the recorded portions neighboring to the side beams  61 A and  61 B is two.  
         [0108]     In such a manner, in DOW0 state, the number of the recorded portions neighboring to the side beams  61 A and  61 B is typically two despite of the recording direction, the side beam  61 A, and the main beam  60 .  
         [0109]     Then, the state in that the main beam  60  is not located in a white portion is considered. In this case, an already recorded portion before the present recording is irradiated with the main beam  60  so as to be overwritten.  
         [0000]     (1) When Recording from the Inner Radial Side Toward the Outer Radial Side  
         [0110]     As is already described with reference to  FIGS. 8A  to  9 , in this case, the number of the recorded portions neighboring to the side beam  61 A depends on the fact that whether the outer side and/or the inner side of the beam have passed through the boundary position “a” between the white portion and the recorded portion, or not, so that the number is to be 0, 1, and 2 in that order from the furthest position of the side beam  61 A from the boundary position “a”.  
         [0111]     In addition, before DOW0 state, the state that the number of the recorded portions is 0 exists for an extremely short time while the boundary position “a” passes through a predetermined section between the inner side of the side beam  61 A and the main beam  60 .  
         [0112]     Since portions on both sides of the side beam  61 B are typically recorded as described above, the number of the recorded portions neighboring to the side beams  61 A and  61 B is 2.  
         [0113]     Hence, the number of the recorded portions neighboring to the side beams  61 A and  61 B is to be 4, 3, and 2 in that order from the furthest position of the side beam  61 A from the boundary position “a”, as shown in  FIG. 12A . Before DOW0 state, the state that the number of the recorded portions is 2 exists for an extremely short time while the boundary position “a” passes through from the inner side of the side beam  61 A to the main beam  60 .  
         [0000]     (2) When Recording from the Outer Radial Side Toward the Inner Radial Side  
         [0114]     As is already described with reference to  FIGS. 10A  to  11 , since the side beam  61 A succeeds the main beam  60  in the tracking direction, and it precedes in the revolution direction of the disk in this case, the outer radial side is typically recorded, and the number of the neighboring recorded portions depends on the fact that whether the inner side has passed through the boundary position “a” to the white portion or not. That is, the number of the recorded portions neighboring to the side beam  61 B is to be 2 until the inner side of the side beam  61 A passes through the boundary position “a” and to be 1 after it passed through the boundary position “a”, as shown in  FIGS. 10A  to  10 D.  
         [0115]     In addition, before DOW0 state, the state that the number of the recorded portions is 1 exists for an extremely short time while the boundary position “a” passes through a predetermined section between the inner side of the side beam  61 A and the main beam  60 .  
         [0116]     On the other hand, since the side beam  61 B precedes the main beam  60  in the tracking direction and succeeds the main beam  60  in the revolution direction of the disk, the outer radial side is typically recorded, so that the number of the neighboring recorded portions depends on the fact that whether the inner side has passed through the boundary position “a” to the white portion or not. That is, the number is to be 2 until the side beam  61 B passes through the boundary position “a”, and to be 1 after it passed through the boundary position “a”, as shown in  FIGS. 10A  to  10 D.  
         [0117]     Accordingly, the number of the recorded portions neighboring to the side beams  61 A and  61 B is to be 4 until the outer side of the side beam  61 B passes through the boundary position “a” as shown in  FIG. 12B ; to be 3 until the outer side of the side beam  61 B passes through the boundary position “a” as well as until the inner side of the side beam  61 A passes through the boundary position “a”; and to be 2 thereafter. In DOW0 state, the number of the recorded portions is to be 2 for an extremely short time while the boundary position “a” passes through between the inner side of the side beam  61 A and the main beam  60 .  
         [0118]     In such a manner, the sum of the reflected light amounts by the side beams  61 A and  61 B has the highest level in DOW0 state in that the white track is recorded, despite of the recording direction. Also, in states between DOW0 state and that before DOW0 state by approximately one track, it has a second highest level, and the lowest level there before. Thus, by monitoring the sum of the reflected light amounts by the side beams  61 A and  61 B during recording, the present recording can be determined whether it is overwriting (DOW 1 ) or the recording on a white portion (DOW 0 ), during the recording.  
         [0119]     More specifically, as is understood from  FIGS. 12A and 12B , by detecting the level change from the level of the sum of the reflected light amounts of the side beams  61 A and  61 B when the number of the recorded portions neighboring to the side beams  61 A and  61 B is 3 to the level when the number of the recorded portions is 2, the recording state transition from DOW1 state to DOW0 state can be known.  
         [0120]     That is, by detecting whether the sum of the reflected light amounts of the side beams  61 A and  61 B exceeds a predetermined threshold value or not, the present recoding can be determined whether it is in DOW0 state or in DOW1 state, so that the recording conditions can be changed on the basis of the determined result.  
         [0121]     For example, about the detracking, when recording from outer radial side of the disk toward the inner radial side, if it is in DOW0 state, the recording conditions are established so that an offset is electrically applied to the tracking error signal for tracking in the inner radial direction. Also, when recording from outer radial side of the disk toward the inner radial side and overwriting at the start of the recording, i.e., in DOW1 state, the recording conditions are established so that an offset is not electrically applied to the tracking error signal at the start of the recording. Then, at a time when it is determined that, the recording conditions be changed to DOW0 state so that an offset is electrically applied to the tracking error signal for tracking in the inner radial direction. By doing so, when the L1 layer of the one side two-layered disk is recorded, the detracking generating during recording state transition from DOW1 state to DOW0 state can be prevented.  
         [0122]     A method for determining a threshold value for determining whether the present recording is in DOW0 state or in DOW1 state will be described more specifically. As described above, the sum of the reflected light amounts of the side beams  61 A and  61 B changes stepwise corresponding to the number of the recorded tracks (recorded portions) neighboring to the side beams  61 A and  61 B. During the recording, as is already described with reference to  FIGS. 12A and 12B , the number of the recorded portions neighboring to the side beams  61 A and  61 B is to be 2 to 4, and the sum of the reflected light amounts of the side beams  61 A and  61 B also has three-step values.  
         [0123]     If including during reproducing, the sum of the reflected light amounts of the side beams  61 A and  61 B may have five-step values. That is, during reproducing, in a state in that the main beam  60  is located in a white portion, there are cases where portions on both sides of the side beams  61 A and  61 B are white so that the number of the neighboring recorded portions is 0, and where only one side of any one of the side beams  61 A and  61 B neighbors to the recorded portion so that the number of the neighboring recorded portions is 1. If the cases are included where during the reproducing, the number of the neighboring recorded portions is 0 and the number of the neighboring recorded portions is 1, the sum of the reflected light amounts of the side beams  61 A and  61 B has five-step values.  
         [0124]     The level of the sum of the reflected light amounts of the side beams  61 A and  61 B is assumed to be SPDn (n=0 to 4) when the number of the recorded portions neighboring to the side beams  61 A and  61 B is to be n.  FIG. 13  shows the relationship among example levels SPD 0  to SPD 4 . The change ΔSPD in sum of the reflected light amounts of the recorded portions neighboring to the side beams  61 A and  61 B can be obtained by equation (3). 
 
Δ SPD =( SPD 0− SPD 4)/4  (3) 
 
         [0125]     On the other hand, as described above, during transition from DOW1 state to DOW0 state, the level SPD 3  when the number of the recorded portions of the side beams  61 A and  61 B is 3 is changed to the level SPD 2  when the number of the recorded portions is 2. Thus, if a threshold value for determining whether the present recording is in DOW0 state or in DOW1 state is to be a threshold value SPD th , the relationship between the threshold value SPD th , the level SPD 2 , and the level SPD 3  is obtained from equation (4). 
 
 SPD 3&lt; SPD   th   &lt;SPD 2  (4) 
 
         [0126]     From the equations (4) and (3), the threshold value SPD th  can be established as equation (5), for example. 
 
 SPD   th   =SPD 4+1.5×Δ SPD   (5). 
 
         [0127]     Then, a practical setting method of the threshold value SPD th  will be described with reference to the flowchart of  FIG. 14 . In addition, various determinations and controls in the flowchart of  FIG. 14  are executed by a microcomputer.  
         [0128]     When the optical disk  10  is loaded in the optical disk drive  1 , the laser light source  30  is activated by reproducing power so as to emit a laser beam. On the basis of the laser beam reflected from the optical disk  10 , focus servo and tracking servo are performed (Step S 10 ). The description below will be when recording from outer radial side of the optical disk  10  toward the inner radial side.  
         [0129]     At next Step S 11  and Step S 12 , the sums (SPDs) of reflected light amounts of the side beams  61 A and  61 B by the laser light with reproducing power in white portions and recorded portions of the optical disk  10  are measured. In the example in  FIGS. 5 and 6  described above, the sum SPD of the reflected light amounts of the side beams  61 A and  61 B can be obtained by adding the outputs of the half-divided components E to H of the photo-detector  40 . That is, the sum of the reflected light amounts SPD can be obtained from the following equation (6). 
 
 SPD=E+F+G+H   (6) 
 
         [0130]     The signal processing unit  25  obtains the sum of the reflected light amounts SPD on the basis of the output of the photo-detector  40  so as to feed it to the microcomputer  27 . The processing order of Step S 11  and Step S 12  may be reversed.  
         [0131]     For example, at Step S 11 , the optical pick-up  22  is moved so that the number of white portions neighboring to the side beams  61 A and  61 B of the optical disk  10  is 0, and the sum of the reflected light amounts SPD 0   r  of the side beams  61 A and  61 B by the reproducing power is measured. Similarly, at Step S 12 , the optical pick-up  22  is moved so that the number of white portions neighboring to the side beams  61 A and  61 B of the optical disk  10  is 4, and the sum of the reflected light amounts SPD 4   r  of the side beams  61 A and  61 B by the reproducing power is measured.  
         [0132]     When the optical disk  10  is complying with the DVD-RW standard, after loading the optical disk  10  in the optical disk drive  1 , the RMA is accessed at first so as to read out the recording management information stored in the RMA. During the reading the recording management information, the sum of the reflected light amounts of the recorded portions of the side beams  61 A and  61 B SPD 4   r  can be measured at Step S 12 .  
         [0133]     In the RMA, information is added every time when the optical disk  10  is rewritten, so that if the number of rewriting times is small, the RMA has a sufficient free space. Consequently, the sum of the reflected light amounts of the white portions SPD 0   r  can be measured using the white space of the RMA at Step S 11 .  
         [0134]     On the basis of the disk information stored in the lead-in area, the white and recorded portions of the optical disk  10  may also be accessed so as to measure the sums of the reflected light amounts SPD 0   r  and SPD 4   r . Furthermore, depending on the information management format, the RMA may store positional information indicating the positions of the recorded and white portions of the data area, so that the sums of the reflected light amounts SPD 0   r  and SPD 4   r  may also be measured on the basis of the RMA information.  
         [0135]     On the other hand, when the optical disk  10  is complying with the DVD+RW standard, after loading the optical disk  10  in the optical disk drive  1 , the lead-in area is accessed at first. The lead-in area, as described above, stores the positional information indicating the positions of the recorded and white portions of the data area such as the number of initiation/completion sectors of the optical disk  10 . On the basis of the information of the lead-in area, the sums of the reflected light amounts of the recorded and white portions of the data area SPD 0   r  and SPD 4   r  can be measured at Step S 11  and Step S 12 .  
         [0136]     When there is no recorded portion, the sum of the reflected light amounts can be measured after trial writing. In this case, it is necessary to record on the entire groups neighboring to the side beams  61 A and  61 B so that the number of recorded portions neighboring to the side beams  61 A and  61 B is to be 4.  
         [0137]     After the sums of the reflected light amounts SPD 0   r  and SPD 4   r  are measured, at Step S 13 , the change in sum of the reflected light amounts of the recorded portions by the reproducing power ΔSPD r  is obtained. The change in sum of the reflected light amounts ΔSPD r  can be obtained from the following equation (7) on the basis of the equation (3). 
 
Δ SPDr =( SPD 0 r−SPD 4 r )/4  (7) 
 
         [0138]     At next Step S 14 , the record start portion is determined whether it is white or not. If the optical disk  10  to be recorded is white, for example, the lead-in area has no recorded signal. Thus, on the basis of the reproducing signal when the lead-in area is accessed after loading the optical disk  10  in the optical disk drive  1 , the optical disk  10  can be determined whether it is white or not. If it is white, the record start portion is determined to be white.  
         [0139]     If the record start portion is determined to be white at Step S 14 , the process proceeds to Step S 15 . At Step S 15 , it is assumed to record in DOW0 state so as to establish the recording conditions in DOW0 state. For example, the microcomputer  27  controls the signal processing unit  25  so as to apply a predetermined electrical offset to a tracking error signal for tracking in the inner radial direction.  
         [0140]     When the recording conditions are set in DOW0 state at Step S 15 , the recording is continued thereafter under the recording conditions of DOW0 state until the record stopping is instructed via the host I/F  26  (Step S 16 ).  
         [0141]     On the other hand, if the record start portion is determined to be not white at Step S 14 , the process is shifted to Step S 17 . At Step S 17 , it is assumed to overwrite because the record start portion is recorded, so that the recording conditions are set in DOW1 state so as to start recording. For example, the microcomputer  27  controls the signal processing unit  25  so as not to apply an electrical offset to the tracking error signal on the basis of the determined results at Step S 14 . Then, the exiting power of the laser light source  30  is switched to the recording power so as to start recording under the recording conditions of DOW1 state.  
         [0142]     Upon starting the record, during the overwriting, the sum of the reflected light amounts of the side beams  61 A and  61 B is measured (Step S 18 ). As is understood from  FIGS. 12A and 12B , in the overwriting (DOW1 state), the probability is very high in that the number of recorded portions neighboring to the side beams  61 A and  61 B is 4. Hence, the sum of the reflected light amounts to be measured at Step S 18  is assumed to be the value when the number of recorded portions neighboring to the side beams  61 A and  61 B is 4. The sum of the reflected light amounts obtained at Step S 18  is designated to be the sum of the reflected light amounts SPD 4   w . The reflected light amounts SPD 4   w  is an average value during the recording.  
         [0143]     At next Step S 19 , a light amount ratio α=SPD 4   w /SPD 4   r  of the sum of the reflected light amounts SPD 4   w  by the recording power to the sum of the reflected light amounts SPD 4   r  by reproducing power is obtained.  
         [0144]     At Step S 20 , a threshold value SPDth for determining whether the present recording is in DOW0 state or in DOW1 state is obtained. The threshold value SPDth can be calculated from the following equation (8) using the equation (3), the equation (7), and the light amount ratio α: 
 
 SPD   th =α×( SPD 4 r+ 1.5×Δ SPDr )  (8) 
 
         [0145]     Then, during the recording, the sum of the reflected light amounts SPDw of the side beams  61 A and  61 B by the recording power is continuously measured, and it is compared with the threshold value SPDth obtained at Step S 20  (Step S 21 ). From the compared result, if the sum of the reflected light amounts SPDw does not exceed the threshold value SPDth, the process is shifted to Step S 22 , and the present recording is determined to be the overwriting on the recorded portions, so that under the present recording conditions, that is the recording conditions in DOW1 state established at Step S 17 , the recording is continued (Step S 23 ).  
         [0146]     On the other hand, as a compared result, if the sum of the reflected light amounts SPDw exceeds the threshold value SPD th , the process is shifted to Step S 24 , and the present recording is determined to enter a white portion, so that the recording conditions are changed to the conditions in DOW0 state so as to continue the recording (Step S 25 ). For example, the microcomputer  27  controls the signal processing unit  25  so as to apply a predetermined electrical offset to the tracking error signal for tracking in the inner radial direction on the basis of the determination at Step S 21 .  
         [0147]     As described above, the timing at which the sum of the reflected light amounts changes from the sum of the reflected light amounts SPD 3   w  to the sum of the reflected light amounts SPD 2   w  is different from the timing at which the practical recording state changes from DOW0 state to DOW1 state by the space between the side beams  61 A and  61 B. Since this difference is known, the timing in changing the recording conditions can be delayed in advance.  
         [0148]     In the above-description, by detecting the change from the sum of the reflected light amounts SPD 3   w  to the sum of the reflected light amounts SPD 2   w , the transition from DOW1 state to DOW0 state is determined so as to change the recording conditions. However, the invention is not limited to this, so that on the basis of the change from the sum of the reflected light amounts SPD 4   w  to the sum of the reflected light amounts SPD 3   w , the recording conditions may be changed, for example. In this case, after a lapse of time corresponding to approximately one track since the change is detected, DOW1 state is changed to DOW0 state. Thus, this method is desirable for using in a case where the change in recording conditions requires some extent of time.  
         [0149]     In such a manner, according to the embodiment, by monitoring changes in sum of the reflected light amounts of the side beams  61 A and  61 B, the transition of the recording state from DOW1 state to DOW0 state can be detected. The detracking generated when recording from the outer radial side of the disk toward the inner radial side is thereby prevented.  
         [0150]     In the above-description, the recording condition established at Step S 15 , Step S 17 , and Step S 24  is an electrical offset for the tracking error signal; however, the invention is not limited to this. For example, in the recording conditions such as recording power of laser light, a strategy, and servo setting, the optimum setting may be different in between DOW0 recording and DOW1 recording.  
         [0151]     On the basis of the sum SPD of the reflected light amounts of the side beams  61 A and  61 B, the present recording is detected whether it is in DOW0 state or in DOW1 state so as to establish the recording conditions corresponding to detected results. For example, on the basis of the determinations at Step S 14  and Step S 21 , the microcomputer  27  feeds control signals to the servo control unit  28  and the signal processing unit  25  for establishing the recording conditions corresponding to the present recording state.  
         [0152]     The processing according to the flowchart of  FIG. 14  described above may also be applied to the recording from the inner radial side of the optical disk  10  toward the outer radial side. However, when recording from the inner radial side of the optical disk  10  toward the outer radial side, as described earlier, even in DOW0 state, in the respective side beams  61 A and  61 B, the recording states of portions on both sides are the same. Thus, the detracking due to the difference between receiving light amounts of the two-divided element due to the recording state difference between the beam portions on both sides may not occur. Accordingly, when recording from the inner radial side of the optical disk  10  toward the outer radial side, the applications at Step S 15  and Step S 25  of a predetermined electrical offset to the tracking error signal are omitted.  
         [0153]     Next, a modification of the embodiment of the present invention will be described. According to the embodiment, the recording state shifting from DOW0 state to DOW1 state has been described; however, the present invention is not limited to this, so that the recording state shifting from DOW1 state to DOW0 state may also incorporate the invention. With reference to  FIGS. 15A  to  19 , a recording state shifting from DOW1 state to DOW0 state according to the modification of the embodiment of the present invention will be described.  
         [0154]     First, with reference to  FIGS. 15A  to  16 , changes in reflected light amounts of the side beams  61 A and  61 B when recording from the inner radial side of the optical disk  10  toward the outer radial side will be described. In addition, designations of portions in  FIGS. 15A  to  16  are common to those in  FIGS. 8A  to  9  described above, so that the description thereof is omitted.  
         [0155]     In an initial DOW0 state in that the main beam  60  is located in a white portion, as shown in  FIG. 15A , portions on both sides of the side beam  61 A preceding the main beam  60  are white while portions on both sides of the side beam  61 B succeeding the main beam  60  are recorded. As the recording process proceeds, as shown in  FIG. 15B , the outer radial side of the preceding side beam  61 A reaches the recorded portion. When the recording process further proceeds beyond the state of  FIG. 15C  from that of  FIG. 15B , the main beam  60  reaches the recorded portion so as to be in DOW1 state. The DOW0 recording state is maintained thereafter ( FIG. 15D ).  
         [0156]     As shown in  FIG. 16 , the changes in reflected light amounts of the side beams  61 A and  61 B are reverse to those shown in  FIG. 9 . That is, since the initial recording is in DOW0 state, portions on both sides of the side beam  61 A are white (see  FIG. 15A ) and the reflected light amount is at level LV 2 . At a time when the outer radial side of the side beam  61 A reaches the recorded portion (see  FIG. 15B ), the reflected light amount becomes level LV 1 . After the optical disk  10  is rotated by one revolution from this state, and thereafter, the reflected light amount becomes level LV 0  (see  FIGS. 15C and 15D ).  
         [0157]     On the other hand, since portions on both sides of the succeeding side beam  61 B are typically recorded, the reflected light amount is at level LV 0 .  
         [0158]     Then, with reference to  FIGS. 17A  to  18 , changes in reflected light amounts of the side beams  61 A and  61 B when recording from the outer radial side of the optical disk  10  toward the inner radial side will be described. In addition, designations of portions in  FIGS. 17A  to  18  are common to those in  FIGS. 8A  to  9  described above, so that the description thereof is omitted.  
         [0159]     As described above, when recording from the outer radial side of the optical disk  10  toward the inner radial side, the side beam  61 A precedes the main beam  60  in the revolution direction of the disk  10  and succeeds the main beam  60  in the tracking direction. Also, the side beam  61 B succeeds the main beam  60  in the revolution direction of the disk  10  and precedes the main beam  60  in the tracking direction. Therefore, in an initial DOW0 state in that the main beam  60  is located in a white portion, as shown in  FIG. 17A , in both the side beams  61 A and  61 B, a portion on the outer radial side is recorded and a portion on the inner radial side is white.  
         [0160]     As the recording process proceeds from the state of  FIG. 17A , as shown in  FIG. 17B , the inner radial side of the side beam  60 B reaches the recorded portion. When the recording process further proceeds from this state, the main beam  60  reaches the recorded portion so as to move to DOW1 state from DOW0 state ( FIG. 17C ). The DOW1 recording state is maintained thereafter ( FIG. 17D ).  
         [0161]     When recording from the outer radial side of the disk  10  toward the inner radial side, as shown in  FIG. 18 , the changes in reflected light amounts of the side beams  61 A and  61 B are also reverse to those shown in  FIG. 11 .  
         [0162]     That is, since the initial recording is in DOW0 state, in the side beam  61 A, a portion on the outer radial side is recorded and a portion on the inner radial side is white (see  FIG. 17A ), and the reflected light amount is at level LV 1  and becomes level LV 0  at a time when the inner radial side reaches the recorded portion. Then, slightly thereafter, the main beam  60  reaches the recorded portion so as to move to DOW1 state from DOW0 state (see  FIG. 17C ).  
         [0163]     Also, in the side beam  61 B, initially a portion on the outer radial side is recorded and a portion on the inner radial side is white (see  FIG. 17A ), and the reflected light amount is at level LV 1  and becomes level LV 0  at a time when the beam reaches the recorded portion (see  FIG. 17B ).  
         [0164]      FIGS. 19A and 19B  show changes in sum of the reflected light amounts of the side beams  61 A and  61 B. FIG.  19 A shows the example when recording from the inner side toward the outer side while  FIG. 19B  shows the example when recording from the outer side toward the inner side. When the recording state moves from DOW0 state to DOW1 state in such a manner, in the same way as in the example of  FIGS. 12A and 12B , the sum of the reflected light amounts changes in a predetermined manner at the boundary position “a”, i.e., in front and rear of DOW 0 . In this case, differently from the example of  FIGS. 12A and 12B , after the sum of the reflected light amounts of the side beams  61 A and  61 B is reduced from level SPD 3  to level SPD 4 , the recording state moves from DOW0 state to DOW1 state.  
         [0165]     Therefore, during transition from DOW0 state to DOW1 state, a threshold value SPDth for determining whether the present recording is in DOW0 state or in DOW1 state is to be: 
 
 SPD 3&gt; SPD   th   &gt;SPD 4  (9), 
 
 the equation (10) can be established as follows: 
 
 SPD   th   =SPD 4+0.5×Δ SPD   (10). 
 
         [0166]     The method according to the modification of the embodiment of the present invention may be combined with the method according to the embodiment of the present invention. For example, on the basis of the sums of the reflected light amounts of the side beams  61 A and  61 B in the state of the present recording, it can be determined that any of the method according to the modification of the embodiment of the present invention and the method according to the embodiment of the present invention be incorporated. If the sums of the reflected light amounts is at level SPD 4 , the method according to the embodiment of the present invention is applied, while the sums of the reflected light amounts is at level SPD 2 , the method according to the modification of the embodiment of the present invention is applied. Then, in the respective methods, if DOW state is changed, the applied method is also switched.  
         [0167]     In the above, recording media incorporating the invention have been described as rewritable DVDs complying with DVD-RW standards and DVD+RW standards; however, the invention is not limited to these examples. That is, other than the rewritable DVDS, a rewritable CD (compact disc) such as a CDRW (compact disc-rewritable) and other recording media tracking by the DPP system such as a Blu-ray disk may incorporate the present invention.  
         [0168]     Also, one-side two-layered disks have been described as the recording medium according to the embodiment; however, the invention is not limited to these examples. A single layered disk having one recording layer and a multiple-layered disk having three or more recording layers may incorporate the present invention.  
         [0169]     Moreover, in the above-description, the side beam  61 A preceding the main beam  60  in the revolution direction of the optical disk  10  is arranged on the outer radial side of the disk  10 ; however, the invention is not limited to the example. The reverse arrangement in that the side beam preceding the main beam  60  in the revolution direction of the disk  10  is arranged on the inner radial side of the disk  10  may easily incorporate the invention.  
         [0170]     In this case, in DOW0 state recording on the white portion, the side beam  61 A succeeds the main beam  60  in the revolution direction of the optical disk  10  while the side beam  61 B succeeds the main beam  60  in the tracking direction.  
         [0171]     Accordingly, when recording from the inner radial side of the optical disk  10  toward the outer radial side, although not shown, in both the side beams  61 A and  61 B, the inner radial side is recorded and the outer radial side is white, so that when an offset is not applied to the tracking, the main beam  60  is detracked in the inner radial side. Then, in recording DOW0 state, the recording conditions are established so as to apply an electrical offset to the tracking error signal for tracking in the outer radial side.  
         [0172]     Similarly, when recording from the outer radial side of the optical disk  10  toward the inner radial side, in recording DOW0 state, although not shown, portions on both sides of the side beam  61 A are recorded and portions on both sides of the side beam  61 B are white, so that the application of the electric offset to the tracking error signal is not required.  
         [0173]     In this case, during transition from DOW1 state to DOW0 state, the change in number of recorded portions neighboring to the side beams  61 A and  61 B is the same as that shown in  FIG. 9 . Also, during transition from DOW1 state to DOW0 state, the change in number of recorded portions neighboring to the side beams  61 A and  61 B is the same as that shown in  FIG. 11 . Hence, as described above with reference to  FIGS. 12A and 12B , by detecting the change from the sum of the reflected light amounts SPD 3   w  to the sum of the reflected light amounts SPD 2   w , the transition from DOW1 state to DOW0 state can be determined.  
         [0174]     It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.