Abstract:
An optical recording/reproducing apparatus comprises a light beam emitting unit which emits a plurality of light beams to the recording medium, a photodetection unit which detects the reflected light beams and output detection signals, a detection signal selection unit which selects one of the detection signals according to one of a plurality of tracks which is selected in order to record or reproduce data, the tracks being formed on at least one of the land and the groove, and a tracking control unit which make one of the light beams trace the track which is selected in order to record or reproduce data, according to the selected detection signal.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-293626, filed Sep. 26, 2001, the entire contents of which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to an optical recording and reproducing apparatus which records data on a recording medium and reproduces recorded data by means of a laser.  
           [0004]    2. Description of the Related Art  
           [0005]    In recent years, high density of optical disc progresses by short-wavelength of light source and high NA (Numerical Aperture) of objective lens. If recording density will be raised more in future, high line-density and high track-density become important. A PRML (Partial Response Maximum Likelihood) signal processing technique or superresolution technique is effective for high line-density. Further, the superresolution technique is promising in high track-density.  
           [0006]    The conventional technique makes one data track correspond to one groove or one land. Further, generation of a tracking error signal and data recording and reproducing are performed based on a push-pull method of detecting imbalance of diffraction light from a groove or land by means of a single light beam. For this reason, there is a problem that the amplitude of the tracking error signal is greatly deteriorated with narrowing of the tracks. As a result, stable tracking control cannot be realized.  
           [0007]    It is an object of the present invention to provide an optical data recording and reproducing apparatus which realizes stable tracking control for an optical data recording medium of high track density, for example, an optical disc which narrows a track pitch more than the conventional disc.  
         BRIEF SUMMARY OF THE INVENTION  
         [0008]    According to an aspect of the present invention, there is provided an optical data recording/reproducing apparatus using a recording medium having at least one of a land and a groove, the optical data recording/reproducing apparatus comprising: a light beam emitting unit configured to emit a plurality of light beams to the recording medium, the at least one of the land and groove containing a plurality of tracks corresponding to the light beams; a photodetection unit configured to detect the light beams reflected from the recording medium and output detection signals corresponding to the reflected light beams; a detection signal selection unit configured to select at least one of the detection signals detected by the photodetection unit according to one of a plurality of tracks which is selected in order to record or reproduce data, the tracks being formed on at least one of the land and the groove, and a tracking control unit configured to make one of the light beams trace the track which is selected in order to record or reproduce data, according to the selected detection signal.  
           [0009]    According to another aspect of the invention, there is provided an optical recording/reproducing method comprising: emitting a plurality of light beams to a recording medium; detecting the light beams reflected from the recording medium by a photodetector to output detection signals; selecting at least one detection signal of the detection signals detected by the photodetector, according to one of a plurality of tracks which is selected in order to record or reproduce data, the tracks being formed on at least one of the land and the groove; and tracking the track which is selected in order to record or reproduce data by means of one of the light beams, according to the detection signal selected. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0010]    [0010]FIGS. 1A to  1 D show states forming three tracks on a land and a groove by means of an optical recording and reproducing apparatus according to an embodiment of the present invention;  
         [0011]    [0011]FIGS. 2A, 2B and  2 C show positional relations between three tracks provided in a groove or a land and a focused beam;  
         [0012]    [0012]FIG. 3 shows a schematic configuration of the optical recording and reproducing apparatus according to the embodiment of the present invention;  
         [0013]    [0013]FIG. 4 shows a perspective view of an optical head of the optical recording and reproducing apparatus of FIG. 3;  
         [0014]    [0014]FIG. 5 shows a circuit block of a switching device configured to switch between a focal error signal and a tracking error signal;  
         [0015]    [0015]FIGS. 6A and 6B show positional relations between a focused beam and two tracks provided in a groove or a land;  
         [0016]    [0016]FIG. 7 shows a pit arrangement for detecting distances among three tracks; and  
         [0017]    [0017]FIG. 8 shows a pit arrangement for detecting a distance between two tracks. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    There will now be described embodiments of the present invention in conjunction with drawings.  
         [0019]    The present invention can apply to a groove recording scheme, a land recording scheme, or a land &amp; groove recording scheme. The first embodiment describes an optical recording and reproducing of the land &amp; groove scheme. FIGS. 1A to  1 D show states forming three data tracks on a land and a groove of an optical disc. In other words, FIG. 1A shows a state forming a first track  111  on the circumference side of the land, FIG. 1B shows a state forming a second track  112  on the center of the land, FIG. 1C shows a state forming a third track  113  on the internal circumference side of the land, and FIG. 1D shows a state forming a first track  111  on the circumference side of the groove. These tracks are formed in turn on the land and groove in units of one circuit of the optical disc.  
         [0020]    [0020]FIGS. 2A, 2B and  2 C show relative positional relations between the recording/reproducing of each track and three focused beams, in a case of arranging three tracks on the land or groove of the optical disc. In other words, FIG. 2A shows a case that performs data recording or data reproducing for the track  111  on the left side. (the circumference side) of the groove, FIG. 2B shows a case that performs data recording or data reproducing for the track  112  on the center of the groove, and FIG. 2C shows a case that performs data recording or data reproducing for the track  113  on the right side (the inner circumference side) of the groove.  
         [0021]    Three light beams  101 ,  102 , and  103  focused on the groove are generated through a diffraction grating, for example, the ratio of the optical intensities of the light beams  101  and  103  of each side that are shown by dashed lines (tracking controlling light beam) to a light intensity of the central light beam (light beam for exposure)  102  that is shown by a solid line is set at 1:10, and the recording and reproducing of data are performed by the central light beam  102  of the large light intensity.  
         [0022]    The light intensity ratio between the light beams is set usually at the above value. As a result, it can be avoided that the recorded data of adjacent tracks are erased by mistake by the side light beams  101  and  103  in a recording operation. Further, the beam diameter Φ becoming 1/e 2  of the center strength of each focused beam has a relation of Gw to 2Φ/3 with respect to a groove width Gw. For this reason, the amplitude of the tracking error signal is large, and a good tracking error signal can be obtained. As a result, stable tracking control can be realized.  
         [0023]    The distance W between the center positions of three light beams  101 ,  102  and  103  in a direction perpendicular to the track approximately coincides with the track pitch Tp between adjacent tracks  111  and  112  and between the tracks  112  and  113 . In other words, the center positions of three light beams  101 ,  102  and  103  shift in turn by the track pitch Tp in a radial direction of the optical disc. The distance D between the center positions of three light beams  101 ,  102  and  103  with respect to a direction along the data track is set to be D≧2Φ with respect to the focal beam diameter Φ.  
         [0024]    When the recording and reproducing for the track  111  are done by three light beams as above described, the tracking control are done using the light beam  101  shown by the thick dashed line in FIG. 2A, and the recording and reproducing are performed by the central light beam  102 . When data is recorded on or reproduced from the track  112  as shown in FIG. 2B, tracking control and data recording and reproducing is done using the central light beam  102  shown by a thick solid line. The light intensity of the central light beam  102  is changed between the tracking control and the recording/reproducing. When data is recorded on or reproduced from the track  113  as shown in FIG. 2C, the tracking control is done using the light beam  103  shown by the thick dashed line in FIG. 2C, and the recording and reproducing are performed by the central light beam  102 . In other words, when the center position of the light beam  101  is at the center position of the land or groove, the light beam  101  is used as a tracking control beam, and data is recorded on or reproduced from the track  111  by the light beam  102 . When the center position of the light beam  102  is at the center position of the land or groove, the light beam  102  is used as a tracking control beam and a data recording and reproducing beam and records data on or reproduces data from the center track  112 . When the center position of the light beam  103  is at the center position of the land or groove, the light beam  103  is used as a tracking control beam, and the light beam  102  records data on or reproduces data from the track  113 . In this way, three tracks are formed on each land and each groove, and data recording and reproducing are performed.  
         [0025]    By changing three kinds of light beams generate tracking error signals as described above, a conventional tracking control driver can be used. In addition, the focusing error signal may use the light beam for the tracking control or the central light beam in case of all of FIGS. 2A, 2B, and  2 C.  
         [0026]    [0026]FIG. 3 shows a schematic configuration of an optical data recording/reproducing apparatus according to the first embodiment of the present invention. In FIG. 3, a spindle motor  31  driven by a motor driver  3  rotates the optical disc  1 . An optical head  32  facing the optical disc  1  records data on or reproduces data from the optical disc  1 .  
         [0027]    The optical head  32  comprises a laser diode (LD)  33  as a light source, a diffraction grating  34  which diffracts a laser beam in three light beams  101 ,  102  and  103 , a polarized light beam splitter  36  which separates an incident light to the optical disc  1  and a reflected light from the optical disc  1 , a ¼ wavelength plate  37  that changes the polarization of the light beam passed through the polarization light beam splitter  36 , and an objective lens  38  that focuses the light beam to form a minute light beam spot on the optical disc  1 , a condenser lens  50  that condenses the light reflected from the optical disc  1  and led by the beam splitter  36 , and a photodetector unit  39  which receives focused beams, as shown in FIGS. 3 and 4.  
         [0028]    An optical lens actuator  4  moves the objective lens  38  to an optical axis direction (a focusing direction) and a tracking direction according to a focusing error and a tracking error. A diffraction grating actuator  41  rotates the diffraction grating  34  according to the tracks  111 ,  112  and  113 .  
         [0029]    The photodetector unit  39  comprises three multiple-photodetectors, for example, three quadrant-photodetectors each having four detection regions. The three quadrant-photodetectors are provided for three light beams, respectively. A plurality of output signals output from the photodetector  39  are input to an analog operation circuit  42 . The analog operation circuit  42  generates a reproduced signal corresponding to data recorded on the optical disc  1 , and focusing error signals and tracking error signals corresponding to three light beams. The focusing error signal and tracking error signal are selected by a switching circuit  45  configured to switch the focusing error to the tracking error signal or vice versa.  
         [0030]    The focusing error signal and tracking error signal are input to a lens servo circuit  43 . The lens servo circuit  43  controls the lens actuator  4  so that the objective lens  38  is adjusted in a focusing direction and a tracking direction. A diffraction grating servo circuit  44  controls the diffraction grating actuator  41  according to a signal indicating a beam distance deviation that is output from the reproduced data processor  48 , and drives the diffraction grating  34  so that three light beams trace the tracks  111 ,  112  and  113  as shown in FIG. 2.  
         [0031]    The laser diode driver  46  drives the laser diode  33  according to the recording data from the recording data processor  47 . The reproduced data processor  48  processes the reproduced signal from the arithmetic circuit  42  to generate a reproduced output signal.  
         [0032]    The tracking error signals are described hereinafter. The tracking error signals  221 ,  222  and  223  are generated by three light beams  101 ,  102  and  103  using a push-pull method, for example. When the tracking error signals  221 ,  222  and  223  are input to the switching circuit  45 , one of the tracking error signals  221 ,  222  and  223  is selected by a track discrimination signal  24  corresponding to three tracks  111 ,  112  and  113 . In other words, when data is recorded on or reproduced from the track  111 , the switching circuit  45  selects the tracking error signal  221  and supplies it to the lens servo circuit  43  as a tracking control signal  23 . In case of recording or reproducing of the track  112  or  113 , the switching circuit  45  selects the tracking error signal  222  or  223  and outputs the tracking control signal  23 .  
         [0033]    The second embodiment will be described referring to FIGS. 6A and 6B hereinafter. The second embodiment can apply to the groove recording scheme, land recording scheme, and land &amp; groove recording scheme similarly to the first embodiment. In this second embodiment, two tracks are provided on the groove of the land &amp; groove recording scheme.  
         [0034]    [0034]FIGS. 6A and 6B each show a relative positional relation between the track to be recorded or reproduced and three beams in a case of providing two tracks on the groove of the land &amp; groove recording scheme. In FIGS. 6A and 6B, two tracks  311  and  312  are provided on the groove as shown by a dash-and-dot line in FIGS. 6A and 6B In other words, FIG. 6A shows a state that data is recorded on or reproduced from the track  311  on the left side (the circumference side of the optical disc) with respect to the groove center. FIG. 6B shows a case that data is recorded on or reproduced from the track  312  on the right side (the internal circumference side of the optical disc) with respect to the groove center. Diffracting the laser beam from the laser diode  33  by means of the diffraction grating  34  generates three light beams  31 ,  32  and  33  condensed on the groove. The ratio between the light intensities of the side light beams  31  and  33  shown by dashed lines and the light intensity of the central light beam  32  shown by the solid line is set to 1:1, and the recording and reproducing of data are performed by the central light beam  32  of the high light intensity.  
         [0035]    By setting the light intensity ratio between the light beams to 1:1, it is avoided that the side light beams  31  and  33  erroneously erase data recorded on adjacent tracks, in the recording operation.  
         [0036]    Further, the beam diameter Φ corresponding to 1/e 2  of the center light intensity of each focal beam has a relation of Gw to 2Φ/3 with respect to the groove width Gw. This means to provide a good tracking error signal with a large amplitude. Therefore, a stable tracking control can be realized.  
         [0037]    A point different from the first embodiment is the distance W between the center position of each of three light beams  101 ,  102  and  103  and the track with respect to a vertical direction. The distance W makes ½ of the track pitch Tp between the tracks  311  and  312  substantially coincide. Further, the distance D between the center positions of three light beam  31 ,  32  and  33  with respect to a direction along the track is set to D≧2Φ with respect to the focused beam diameter Φ.  
         [0038]    In the second embodiment, when data is recorded on or reproduced from the track  311  as shown in FIG. 6A, the tracking control is performed using the light beam  31  shown by a thick dashed line in FIG. 6A, and the recording or reproducing of data is performed using the central light beam  32 . When data is recorded on or reproduced from the track  312  as shown in FIG. 6B, the tracking control is performed using the light beam  33  shown by a thick dashed line in FIG. 6B, and the recording and reproducing of data are performed using the central light beam  32 . It is possible to form two tracks on the groove using the conventional tracking control driver by changing two kinds of light beams to generate a tracking error signal as described above. In addition, the focusing error signal may be generated using the light beam used for the tracking control or the central light beam in either of FIGS. 6A and 6B. In a case of forming four or more data tracks on the same groove or land, it is obvious that the formation of odd-numbered tracks may expand the first embodiment of FIG. 2, and the formation of even-numbered tracks may expand the second embodiment of FIG. 6. FIG. 7 shows a track format providing pits for detecting each track distance of the first embodiment on a header portion on which addresses or sector numbers of the tracks are recorded by pits. The track distance detection pits  451 ,  452  and  453  are preformed in correspondence with the track centers of the tracks  111 ,  112  and  113 .  
         [0039]    Further, the address pits of a groove or land on which three tracks are formed are formed consistent with the center of the track distance detection pit  452  of the track  112 . The three light beams  101 ,  102  and  103  detect the reproduced signal corresponding to the track distance detection pit. If the distance between the center positions of the light beams in a direction perpendicular to the track is adjusted so that the reproduced signal amplitudes corresponding to two of three light beams become the same, the recording/reproducing apparatus of the present embodiment can deal with the track distance every disc and improve reliability of a recording/reproducing operation. As a method of adjusting the distance between the center positions of the light beams in the direction perpendicular to the track, there is a method of spinning the diffraction grating which generates, for example, a plurality of beams.  
         [0040]    [0040]FIG. 8 shows an arrangement of pits to detect each track distance according to the second embodiment. In this time, track distance detection pits  551  and  552  are preformed corresponding to the track distance of the tracks  311  and  312 . Further, a pit  553  is formed between the track  311  and  312 . The diffraction grating is rotated so that the amplitudes of the reproduced signals of the pits  553  and  551  that are reproduced by two light beams  31  and  32  of three light beams  31 ,  32  and  33  are coincide with each other. The address pits of a groove or land containing two tracks are formed consistent with the center of the track distance detection pit  551  of the track  311 . However, the address pits may be formed on the center of the groove or land that is between the tracks  311  and  312 . Furthermore, FIGS. 7 and 8 show the embodiment wherein the track distance detection pits are arranged on the disc every header. It is possible to adjust the vertical distance of the track at the center position of the light beam by preforming the track distance detection pits on a part of the disc such as the most internal circumferential portion or the most outer circumferential portion of the track, and reproducing the track distance detection pits after inserting a disc into a drive apparatus or in an idle-time of the recording/reproducing operation.  
         [0041]    As described above, according to the present invention, a stable tracking control can be realized in the optical disc of high track density. As a result, it is possible to provide an optical data recording/reproducing apparatus with high data reliability and high recording density.  
         [0042]    Additional advantages and modifications will readily occur to those skilled in the art Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.