Abstract:
A CD-DVD compatible optical pickup in which both on-axis and off-axis light form a circular light spot on a recording surface of an optical recording medium, and an optical recording and/or reproducing apparatus using the same. The CD-DVD compatible optical pickup includes an optical output module, an objective lens, an optical path conversion unit, a photodetector, and an actuator. The optical output module has a mount and light sources emitting light of different wavelengths. The objective lens focuses the emitted light onto two types of optical recording media. The optical path conversion unit between the optical output module and objective lens, converts incident light. The photodetector receives beams emitted from the light sources, reflected from the optical recording media, and then passed through the optical path conversion unit, detecting data and error signals. The actuator has a movable member, moving the objective lens and compensating focusing and tracking error signals.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Patent Application No. 2002-65518, filed on Oct. 25, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a CD-DVD compatible optical pickup using a twin laser diode emitting light of two different wavelengths and an optical recording and/or reproducing apparatus using the same, and more particularly, to a CD-DVD compatible optical pickup in which both on-axis light and off-axis light form a circular light spot on an optical recording medium and an optical recording and/or reproducing apparatus using the same.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, optical pickups are used in compact disc players (CDPs), CD-random access memory (ROM) drives, digital versatile disc players (DVDPs), DVD-ROM drives, etc. and perform data recording and/or reproduction on recording media in a non-contact manner.  
           [0006]    An optical pickup used for the DVD-family recording media, such as a DVD or a DVD-ROM, should be compatible with that used for the CD-family recording media, such as a CD, a CD-R, a CD-RW, a CD-I, or a CD-G, to perform data recording and/or reproduction on two kinds of the recording media.  
           [0007]    However, a standard thickness of a DVD is different from that of a CD due to an allowable tolerance of tilt of a disc and numerical aperture (NA) of an objective lens, etc. That is, the thickness between an incident surface and an information recording surface in a conventional CD-family recording media is 1.2 mm, whereas a thickness in a DVD is 0.6 mm. Thus, if an optical pickup for the DVD is used for the conventional CD-family recording media, spherical aberration is generated due to a thickness difference between the conventional CD-family recording media and the DVD. As such, sufficient optical intensity required for recording a data signal cannot be obtained, and a reproduction signal is deteriorated due to the spherical aberration.  
           [0008]    Further, light sources for DVD and conventional CD family recording media reproduction have different standard wavelengths. That is, the wavelength of the light source for conventional CD-family recording media reproduction is about 780 nm, whereas the wavelength of the light source for DVD reproduction is about 650 nm.  
           [0009]    Since a conventional CDP cannot reproduce data recorded on the DVD due to the above-described differences, a separate optical pickup for a DVD is required. Here, the separate optical pickup for the DVD must be compatible with that for the conventional CD-family recording media.  
           [0010]    Considering the above-described problems, a CD-DVD compatible optical pickup as shown in FIG. 1 includes an optical output module  10  in which first and second light sources  11  and  13  are integrally formed, an objective lens  7  focusing light emitted from the first and second light sources  11  and  13  onto an optical recording medium  1 , a beam splitter  5  converting a traveling path of incident light, and a photodetector  9  which receives light reflected from the optical recording medium  1  and then passed through the beam splitter  5 .  
           [0011]    The CD-DVD compatible optical pickup further includes a grating  3 , a collimating lens  6 , and an astigmatism lens  8 .  
           [0012]    The grating  3  is installed on an optical path between the optical output module  10  and the beam splitter  5  and diffracts and transmits the incident light. The collimating lens  6 , disposed on an optical path between the beam splitter  5  and the objective lens  7 , converges the incident light, and focuses light directed toward the objective lens  7  into parallel light. The astigmatism lens  8  is disposed on an optical path between the beam splitter  5  and the photodetector  9 , and is inclined in a direction opposite to a direction in which the beam splitter  5  is inclined. The astigmatism lens  8  suppresses coma aberration and generates astigmatism in order to detect an error signal using an astigmatic method.  
           [0013]    The objective lens  7  is mounted in a moving member (not shown) on an actuator  20 . The actuator  20  drives the objective lens  7  in a tracking direction (direction along a X-axis in FIG. 1) of the optical recording medium  1  and a focusing direction (direction along a Y-axis in FIG. 1) based on a tracking error signal and a focusing error signal detected by the photodetector  9 .  
           [0014]    Referring to FIGS. 2 and 3, the optical output module  10  further includes a monitor photodetector  17  for monitoring an optical output of the first and second light sources  11  and  13  which emit light of two different wavelengths.  
           [0015]    The first light source  11 , emitting a first light beam  11   a  having the wavelength of about 650 nm, is employed in a case where a thin optical disc  1   a  (refer to FIG. 4), a thickness between an incident surface and a recording surface is relatively thin, is used as the optical recording medium  1 . The second light source  13 , emitting a second light beam  13   a  having the wavelength of about 780 nm, is employed in a case where a thick optical disc  1   b  (refer to FIG. 4), a thickness between an incident surface and a recording surface is relatively thick, is used as the optical recording medium  1 . The second light source  13  is used in, for example, an optical pickup for a CD utilizing a relative long wavelength.  
           [0016]    The first and second light sources  11  and  13  are a twin laser diode and are installed on a mount  15  in a single chip shape. Further, the first and second light sources  11  and  13  are separately installed by grooves  12  so as to irradiate light of two different wavelengths. In the optical output module  10  having the above-described structure, the distance between an emitting point of the first light source  11  and an emitting point of the second light source  13  is optically about 110 μm. Thus, in a case where the optical elements are disposed such that a center of the first light beam  11   a  emitted from the first light source  11  travels along the optical axis of the light as indicated by the solid lines in FIG. 1, the second light beam  13   a  emitted from the second light source  13  deviates from the optical axis of the light as indicated by the dotted lines in FIG. 1.  
           [0017]    [0017]FIG. 4 shows that the first and second light beams  11   a  and  13   a  emitted from the first and second light sources  11  and  13  pass through the objective lens  7  and then are focused onto the optical recording medium  1 . As shown in FIG. 4, since the first light beam  11   a  traveling along the optical axis has an optical profile symmetric with respect to the optical axis, the first light beam  11   a  is incident on the incident surface of the optical recording medium  1  at substantially a right angle. On the other hand, since the second light  13   a  travels asymmetrically with respect to the optical axis, the second light beam  13   a  is incident on the incident surface of the optical recording medium  1  at a predetermined angle other than substantially a right angle.  
           [0018]    Thus, as shown in FIG. 5A, the first light beam  11   a  preferably forms a circular light spot SP 1  on a thin optical disc  1   a . However, as shown in FIG. 5B, the second light beam  13   a  forms a light spot SP 2  of a distorted shape on a thick optical disc  1   b . As a result, optical aberration and jitter increase in the light spot SP 2  formed by the second light beam  13   a  so that the signal reproduction performance of an optical recording and/or reproducing apparatus using the optical pickup is reduced.  
         SUMMARY OF THE INVENTION  
         [0019]    The present invention provides a CD-DVD compatible optical pickup having an off-axis light beam emitted from a light source forming a substantially circular light spot on an optical recording medium, using a twin laser diode as the light source, and an optical recording and/or reproducing apparatus using the same.  
           [0020]    According to an aspect of the present invention, a CD-DVD compatible optical pickup is provided comprising an optical output module having a mount and first and second light sources disposed so as to be adjacent to each other on the mount and emitting light beams having different wavelengths, an objective lens focusing light, emitted from the first and second light sources, onto two types of optical recording media, and an optical path conversion unit disposed on an optical path between the optical output module and the objective lens converting a traveling path of incident light. A photodetector receives the light beams emitted from the first and second light sources, reflected from the optical recording media, and passed through the optical path conversion unit, and detects a data signal and an error signal. An actuator, having a moving member in which the objective lens is mounted, moves the objective lens in a direction capable of compensating for a focusing error signal and a tracking error signal. The actuator rolls the moving member, in a case where recording and/or reproduction of data is performed using a light beam deviating from a main axis of the objective lens among the light beams emitted from the first and second light sources.  
           [0021]    The actuator includes a base on which the optical output module, the optical path conversion unit, and the photodetector are installed. A holder is installed on the base, and a plurality of elastic members respectively have one end coupled to the holder and the other end coupled to the moving member such that the moving member is supported movably, and have different stiffnesses with respect to the center of the objective lens such that the moving, member asymmetrically moves in a focusing direction of the optical recording media. A magnetic driving unit drives the moving member in the focusing direction and the tracking direction of the optical recording media due to an electromagnetic force of the magnetic driving unit.  
           [0022]    According to one aspect of the present invention, the length of the elastic member positioned close to an inner circumference of the optical recording media with respect to the radius direction of the optical recording medium is different from that of the elastic member positioned close to an outer circumference of the optical recording medium such that the moving member asymmetrically moves in a focusing direction of the optical recording media. A magnetic driving unit drives the moving member in the focusing direction and a tracking direction of the optical recording media due to an interaction between the magnet and a current flowing in the focusing coils and an interaction between the magnet and a current flowing in the tracking coils.  
           [0023]    According to another aspect of the present invention, the optical recording and/or reproducing apparatus includes a spindle motor rotating an optical recording medium placed in a turntable, an optical pickup mounted so as to be movable in a radius direction of the optical recording medium and perform recording and reproduction of data with respect to the optical recording medium, a driving unit driving the spindle motor and the optical pickup and a controller controlling a focusing servo and a tracking servo of the optical pickup. The optical pickup includes an optical output module having a mount and first and second light sources, disposed so as to be adjacent to each other on the mount and emit light beams having different wavelengths, an objective lens focusing light emitted from the first and second light sources onto two types of optical recording media and an optical path conversion unit disposed on an optical path between the optical output module and the objective lens converting a traveling path of incident light. A photodetector receives the light beams, emitted from the first and second light sources, reflected from the optical recording media, and then passed through the optical path conversion unit, and detects a data signal and an error signal. An actuator, having a moving member in which the objective lens is installed, moves the objective lens in a direction capable of compensating a focusing error signal and a tracking error signal, and rolling the moving member in a case where recording and/or reproduction of data is performed using a light beam deviating from a main axis of the objective lens among the light beams emitted from the first and second light sources.  
           [0024]    Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    These features, and/or other aspects and advantages of the invention will become apparent and more readily appreciated from the following description of the embodiments taken in conjunction with accompanying drawings in which:  
         [0026]    [0026]FIG. 1 shows the disposition of optical elements of a CD-DVD compatible optical pickup using a twin laser diode;  
         [0027]    [0027]FIG. 2 is a perspective cut-away view of an optical output module of FIG. 1;  
         [0028]    [0028]FIG. 3 is an enlarged perspective view of first and second light sources of FIG. 1;  
         [0029]    [0029]FIG. 4 schematically shows an optical path of light beams emitted from the first and second light sources of FIG. 1 passing through an objective lens and focused onto an optical recording medium;  
         [0030]    [0030]FIGS. 5A and 5B schematically show shapes of light spots, which the light beams emitted from the first and second light sources of FIG. 1, form on the optical recording medium;  
         [0031]    [0031]FIG. 6 is a schematic perspective view of an actuator of a CD-DVD compatible optical pickup according to an embodiment of the present invention;  
         [0032]    [0032]FIGS. 7 and 8 illustrate positions of the actuator of FIG. 6 during operation;  
         [0033]    [0033]FIG. 9 illustrates the correction of an optical path of an off-axis light beam by the actuator of FIG. 6;  
         [0034]    [0034]FIG. 10 shows a shape of a light spot which the off-axis light beam shown in FIG. 9 emitted from a second light source forms on an optical recording medium;  
         [0035]    [0035]FIGS. 11 and 12 schematically show examples of deformed elastic members;  
         [0036]    [0036]FIG. 13 is a graph showing variation in inclination angles due to thickness differences between the elastic members, in the case where the elastic members are deformed as shown in FIG. 11;  
         [0037]    [0037]FIG. 14 is a schematic perspective view of an actuator of a CD-DVD compatible optical pickup according to an embodiment of the present invention;  
         [0038]    [0038]FIG. 15 is a plan view of the actuator of FIG. 14; and  
         [0039]    [0039]FIG. 16 shows an optical recording and/or reproducing apparatus using the CD-DVD compatible optical pickups according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0040]    Reference will now be made in detail to the present preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures.  
         [0041]    A CD-DVD compatible optical pickup according to an aspect of the present invention includes some similar optical elements as those of a conventional CD-DVD compatible optical pickup shown in FIGS. 1 through 3. However, in the CD-DVD compatible optical pickup according to the present invention, the optical pickup actuator is improved in order to solve the above-described problems of the conventional CD-DVD compatible optical pickup. Description of the CD-DVD compatible optical pickup according to the present invention will include references to some components of FIGS. 1 through 3 which also show some components of the conventional CD-DVD compatible optical pickup.  
         [0042]    The CD-DVD compatible optical pickup according to an aspect of the present invention includes an optical output module  10  having first and second light sources  11  and  13 , an objective lens  7  focusing light emitted from the first and second light sources  11  and  13  onto two different optical recording media  1   a  and  1   b , an optical path conversion unit converting a traveling path of incident light, and a photodetector  9  receiving light reflected from an optical recording medium  1 .  
         [0043]    The optical output module  10  includes a mount  15  in which the first and second light sources  11  and  13  are mounted, and a monitor photodetector  17  receiving and monitoring a portion of the light emitted from the first and second light sources  11  and  13 .  
         [0044]    An optical path conversion unit is disposed on an optical path of the optical output module  10 , the objective lens  7 , and the photodetector  9  so that the light emitted from the optical output module  10  is directed toward the optical recording medium  1  and the light reflected from the optical recording medium  1  is directed toward the photodetector  9 . A plate-type beam splitter  5 , disposed to be inclined on the optical path, can be used as the optical path conversion unit. Further, it is possible to use a cubic beam splitter, a polarizing beam splitter, a hologram optical element, etc. as the optical path conversion unit.  
         [0045]    In a case where the thick optical disc  1   b , in which a thickness between an incident surface and a recording surface is relatively thick, is used as the optical recording medium  1 , the CD-DVD compatible optical pickup further includes a grating  3  disposed on an optical path between the optical output module  10  and the plate-type beam splitter  5 . The grating  3  diffracts and transmits the light emitted from the optical output module  10  into a 0-order light beam, ±1-order light beam, etc., in order to detect a tracking error signal using a three-light beam method. On the other hand, in a case where the thin optical disc  1   a  in which a thickness is relatively thin is used, the tracking error signal is detected by a differential phase detection method. A second light beam  13   a  emitted from the second light source  13  is incident on the thick optical disc  1   b , and a first light beam  11   a  emitted from the first light source  11  is incident on the thin optical disc  1   a.    
         [0046]    A mirror  4  and a collimating lens  6 , focusing the diverging light into parallel light are disposed on an optical path between the plate-type beam splitter  5  and the objective lens  7 . The mirror  4  reflects the light so the reflected light is perpendicular to the optical recording medium  1  even where the optical elements are disposed in a horizontal direction, thereby reducing the height of the optical elements.  
         [0047]    The photodetector  9  receives the light, emitted from the first and second light sources  11  and  13  and reflected from the optical recording medium  1 , and detects a data signal and a servo signal. The CD-DVD compatible optical pickup, according to an aspect of the present invention, includes an astigmatism lens  8 , disposed on an optical path between the plate-type beam splitter  5  and the photodetector  9 , detecting a focusing error signal using an astigmatic method. The astigmatism lens  8  is inclined in a direction opposite to a direction in which the plate-type beam splitter  5  is inclined, correcting for coma aberration generated due to the inclination disposition of the plate-type beam splitter  5 .  
         [0048]    An actuator  40  includes a moving member  45  (refer to FIG. 6), in which the objective lens  7  is mounted, driving the objective lens  7  in a direction to compensate for the tracking error signal and the focusing error signal.  
         [0049]    Referring to FIG. 6, the actuator  40  according to an embodiment of the present invention includes a base  41 , a holder  43  installed on the base  41 , and a moving member  45  in which the objective lens  7  is mounted. A plurality of elastic members  47  and  48  respectively have one end coupled to the holder  43  and the other end coupled to the moving member  45  such that the moving member  45  is supported movably. A magnetic driving unit (not shown) drives the moving member  45  in a focusing direction (direction along a Y-axis in FIG. 6) and a tracking direction (direction along a X-axis in FIG. 6) of the optical recording medium  1 .  
         [0050]    The magnetic driving unit includes magnets  51  and  52  positioned opposite to each other, with the moving member  45  interposed therebetween, an internal yoke  53  and an external yoke  54  installed inside and outside respectively the magnets  51  and  52  on the base  41  and guiding the formation of a magnetic path, focusing coils  55  wound around the outside of the moving member  45 , and tracking coils  57  wound at sidewalls of the moving member  45  positioned opposite to the magnet  51 .  
         [0051]    The plurality of elastic members  47  and  48  include the first elastic member  47  positioned nearer an inner circumference, than an outer circumference, of the optical recording medium  1  with respect to the radius direction of the optical recording medium  1 , and the second elastic member  48  positioned nearer an outer circumference, than an inner circumference, of the optical recording medium  1 .  
         [0052]    The first and second elastic members  47  and  48  have different stiffnesses with respect to the center of the objective lens  7  such that the moving member  45  asymmetrically moves in the focusing direction Y. The stiffness of the second elastic member  48  is relatively less than that of the first second elastic member  47 . This difference in stiffness between the first and second elastic members  47  and  48  may be achieved by making the thickness of the second elastic member  48  thinner that of the first elastic member  47 .  
         [0053]    The actuator  40 , having the above-described structure, drives the moving member  45  in the focusing direction Y according to the focusing error signal, normally input, without the rolling of the moving member  45 , in a case of using the first light beam  11   a , the on-axis light. On the other hand, in a case of using the second light beam  13   a , the off-axis light, a substantially circular light spot is formed on the optical recording medium  1   b  due to the rolling of the moving member  45 .  
         [0054]    The determination of whether the moving member  45  is rolled is achieved by a difference in working distances between the two kinds of optical recording media used, the electromagnetic force of the magnetic driving unit, and a distance in elastic force between the first and second elastic members  47  and  48 .  
         [0055]    Referring to FIGS. 7 and 8, the working distance is referred to as a distance between the objective lens  7  and optical incident surfaces A and C of the optical recording media  1   a  and  1   b.    
         [0056]    In FIG. 7, the optical recording medium  1   a , a thickness d 1  between a data recording surface B and the optical incident surface A is relatively thin. In FIG. 8, the optical recording medium  1   b , a thickness d 3  between a data recording surface D and the optical incident surface C is relatively thicker than the thickness d 1  of the optical recording medium  1   a . The optical recording medium  1   a  of FIG. 7 is an example of a digital versatile disc (DVD) having a thickness d 1  of 0.6 mm, and the optical recording medium  1   b  of FIG. 8 is an example of a compact disc (CD) having a thickness d 3  of 1.2 mm.  
         [0057]    In a case where an objective lens  7  is used such as a T565 model product manufactured by KONICA CO., LTD., a working distance WD 1  in FIG. 7 is 1.71 mm whereas a working distance WD 2  in FIG. 8 is 1.35 mm and longer than the working distance WD 1  in FIG. 7. Thus, when distances d 2  and d 4  of FIGS. 7 and 8 between the base  41 , which does not move in a focusing direction, and the moving member  45 , which can move, as shown in FIG. 8, are compared, the distance d 2  in FIG. 7 is shorter than the distance d 4  in FIG. 8.  
         [0058]    Thus, in a case where the intensity of current applied to the focusing coils  55  is substantially the same in FIGS. 7 and 8, the intensity of an electromagnetic force between the focusing coils  55  and the magnet  51 , indicated by a dotted line, in FIG. 7 is stronger than the intensity of an electromagnetic force in FIG. 8. That is, because, a facing area of the focusing coils  55  and the magnet  51  in FIG. 7 is greater than that in FIG. 8.  
         [0059]    Therefore, in FIG. 7, the difference in stiffness between the first and second elastic members  47  and  48  is overcome due to the stronger electromagnetic force than that in FIG. 8, thereby suppressing the rolling of the moving member  45 .  
         [0060]    Since the electromagnetic force in FIG. 8 is weaker than that in FIG. 7, the moving member  45  is rolled due to the difference in stiffness between the first and second elastic members  47  and  48 . In a case where the second light beam  13   a  is focused onto the optical recording medium  1   b , in a state of the rolling of the moving member  45 , as shown in FIG. 9, due to the inclination disposition of the objective lens  7 , the travelling path of the second light beam  13   a , directed toward the optical recording medium  1   b  through the objective lens  7 , changes from an optical path indicated by a dotted line into an optical path indicated by a solid line. Thus, as shown in FIG. 10, a substantially circular light spot is formed on the optical recording medium  1   b.    
         [0061]    The present invention is not limited to the description of the light for the CD as off-axis light. The present invention can be applied to an optical pickup in which light for the CD is referred to as on-axis light and light for the DVD is referred to as off-axis light.  
         [0062]    Example coefficients for making the stiffnesses of the first and second elastic members  47  and  48  different can be found as follows.  
         [0063]    The following Equation 1 indicates the electromagnetic force generated between the focusing coils  55  and the magnets  51  and  52 . 
         F=nilB . . .   (1) 
         [0064]    In Equation 1, n represents the number of turns of the focusing coils  55 , i represents current, l represents the effective length of the elastic members  47  and  48 , and B represents a magnetic field.  
         [0065]    The following Equation 2 indicates the elastic force generated in the elastic members  47  and  48 . 
         F=kx . . .   (2) 
         [0066]    In Equation 2, k represents an elastic coefficient of the elastic members  47  and  48  and x represents the deformation amount of the elastic members  47  and  48 .  
         [0067]    The following Equation 3 indicates a deformation amount of the elastic members  47  and  48  in a case where the electromagnetic force obtained by Equation 1 is the same as the elastic force obtained by Equation 2.  
             x   =       nil                 B     k             (   3   )                               
 
         [0068]    [0068]FIG. 11 shows an example of the deformation of the elastic members  47  and  48 . An elastic coefficient k used in FIG. 11 is given by the following Equation 4.  
             k   =       12      E                 π                   d   4           L   3        64               (   4   )                               
 
         [0069]    In Equation 4, L represents the length of the elastic members  47  and  48 , E represents Young&#39;s modulus, and d represents the diameter of the elastic members  47  and  48 .  
         [0070]    [0070]FIG. 12 shows another example of the deformation of the elastic members  47  and  48 . An elastic coefficient k used in FIG. 12 is given by the following Equation 5.  
             k   =       3      E                 π                   d   4           L   3        64               (   5   )                               
 
         [0071]    An angle θ generated due to the deformation of the elastic members  47  and  48  is given by the following Equation 6. 
         tanθ=x/L . . .   (6) 
         [0072]    The following Equation 7 indicates an angle θ 1  (refer to FIG. 8) of inclination of the moving member  45  generated due to the difference in thickness between the first and second elastic members  47  and  48 . Further, the angle θ 1  of inclination changes according to change in the elastic coefficient caused by the difference in length or material between the first and second elastic members  47  and  48  as well as the difference in thickness.  
               sin                 θ                 1     =       x2   -   x1     L             (   7   )                               
 
         [0073]    In Equation 7, x 1  represents a deformation length of the first elastic member  47  and x 2  represents a deformation length of the second elastic member  48 .  
         [0074]    The amount of change in the rolling of the moving member  45  can be obtained as follows.  
         [0075]    [0075]FIG. 13 shows variations of the angle θ 1  of inclination of the moving member  45  according to the difference Δd in diameter between the elastic members  47  and  48  based on example data in Table 1. In this example, the angle θ 1  of inclination of the moving member  45  indicates that the elastic members  47  and  48  have the deformation shown in FIG. 11. The elastic coefficient k used in the angle θ 1  of inclination is given by Equation 4.  
                           TABLE 1                                       The number of turning   53 (turns)           of coils (n)           Magnetic field (B)   0.2 (T)           Effective length of   0.011 (m)           elastic members (L)           Current (I)   0.01 (A)           Young&#39;s Modulus (E)   1.10 × 10 11  (N/m 2 )           Diameter of first   0.1 (mm)           elastic member (d1)           Diameter of second   0.1-0.15 (mm)           elastic member (d2)   {d2 is changed in               units of 0.02 mm}                      
 
         [0076]    As described above, since the angle θ 1  of inclination of the moving member  45  is dependent on the different thicknesses of the elastic members  47  and  48  from each other so that the light spot of the off-axis light beam is formed into a substantially circular shape.  
         [0077]    Referring to FIGS. 14 and 15, an actuator  40  according to an aspect of the present invention includes a base  41 , a holder  43  installed on the base  41 , and a moving member  45  in which an objective lens  7  is mounted. A plurality of elastic members  147  and  148  respectively having one end coupled to the holder  43  and the other end coupled to the moving member  45  such that the moving member  45  is supported movably. A magnetic driving unit drives the moving member  45  in a focusing direction (direction along a Y-axis in FIG. 14) and a tracking direction (direction along a X-axis in FIG. 14) of the optical recording medium  1 . Structures of the elements, other than the elastic members  147  and  148 , are as previously described.  
         [0078]    The plurality of elastic members  147  and  148  include the first elastic member  147  positioned nearer an inner circumference, than an outer circumference, of the optical recording medium  1  with respect to the radius direction of the optical recording medium  1 , and the second elastic member  148  positioned nearer an outer circumference, than an inner circumference, of the optical recording medium  1 .  
         [0079]    The deformation amounts of the first and second elastic members  147  and  148  are different from each other with respect to the center of the objective lens  7  such that the moving member  45  asymmetrically moves with respect to the focusing direction Y of the optical recording medium  1 . To make the deformation amounts of the first and second elastic members  147  and  148  different from each other, according to an aspect of the present invention lengths of the first and second elastic members  147  and  148  are different from each other. The length of the second elastic member  148  is longer than that of the first elastic member  147  such that the second elastic member  148  deforms more than the first elastic member  147 .  
         [0080]    The deformation amount of the first and second elastic members  147  and  148  are determined with reference to Equations 1 through 7. The actuator  40  operates as previously described.  
         [0081]    The deformation amounts of the first and second elastic members  147  and  148  can be set different from each other by using different materials for the first and second elastic members  147  and  148 .  
         [0082]    Referring FIG. 16, an optical recording and/or reproducing apparatus using the CD-DVD compatible optical pickup according to an aspect of the present invention includes a turntable  203  accommodating a circular optical recording medium  1 , a damper  205  fixing the optical recording medium  1 , a spindle motor  201  rotating the optical recording medium  1 . An optical pickup  200  is installed so as to be movable in a radius direction of the optical recording medium  1  performing recording and reproduction of data. A driving unit  210  drives the spindle motor  201  and the optical pickup  200 , and a controller  220  controls a focusing servo and a tracking servo of the optical pickup  200 .  
         [0083]    The optical pickup  200  includes an optical unit including an objective lens  7  and an actuator driving the objective lens  7  in focusing and tracking directions of the optical recording medium  1 . The structures and operations of the optical pickup and the actuator are as previously described.  
         [0084]    A signal detected through the optical pickup  200  is converted and input to the controller  220  through the driving unit  210 . The driving unit  210  controls the rotating speed of the spindle motor  201  and drives the optical pickup  200 . The controller  220  sends a focusing servo instruction and a tracking servo instruction controlled based on the signal input from the driving unit  210  to the driving unit  210  performs as a focusing servo and a tracking servo.  
         [0085]    As described above, a CD-DVD compatible optical pickup using a twin laser diode as a light source and an optical recording and/or reproducing apparatus using the same includes a first elastic member positioned close to an inner circumference of an optical recording medium with respect to the radius direction of the optical recording medium, and a second elastic member positioned close to an outer circumference of the optical recording medium. The deformation amounts of the first and second elastic members are different from each other. Further, it is determined whether a moving member is rolled using a magnetic driving unit. Thus, even if optical recording media of two types are used, particularly, thickness between an incident surface and a recording surface of the optical recording media of two types are different from each other, a substantially circular light spot, or a circle-like light spot, is formed on the optical recording media of two types.  
         [0086]    Since a skew characteristic, according to an off-axis light, can be improved, an optical recording and/or reproducing apparatus can be improved. Further, the defective rate of the moving member due to the rolling thereof is reduced during manufacturing an optical pickup actuator, the defective rate of the actuator is reduced and a jitter characteristic is improved in the optical pickup, thereby increasing the productivity of the optical pickup.  
         [0087]    Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that various may be made in this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.