Abstract:
A swing-arm type optical recording and reproducing apparatus and an optical disk applicable to the same. The optical disk includes a substrate having an information recording surface to record and reproduce an information signal, and a protective layer which is provided on the information recording surface and whose surface facing a slider is a flat even surface so that variations in a floating height of the slider can be reduced. The optical recording and reproducing apparatus further includes, an optical head having a light source provided at a swing arm to emit light of a predetermined wavelength; an optical path changing means provided in the optical path of the light emitted from the light source for changing the proceeding path of incident light; a collimating lens installed at the slider to preliminarily converge the light emitted from the light source and entering via the optical path changing means; an objective lens installed at the slider to converge the light which is emitted from the light source and enters via the optical path changing means to form an optical spot on the optical disk; and a photodetector to receive the light which is reflected from the optical disk and enters via the objective lens, the collimating lens, and the optical path changing means. The optical head detects an information signal and an error signal in order to reduce defocus due to variations in ambient temperature and variations in the wavelength of the light of the light source.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of Korean Application No. 00-42364, filed Jul. 24, 2000, in the Korean Patent 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 swing-arm type optical recording and reproducing apparatus and an optical disk applicable to the same. More particularly, the present invention relates to a swing-arm type optical recording and reproducing apparatus adapted to prevent defocus due to variations in the temperature and wavelength of illuminating light, and an optical disk which is applied to the optical recording and reproducing apparatus so that the swing arm of the optical recording and reproducing apparatus can swing stably.  
           [0004]    2. Description of the Related Art  
           [0005]    As shown in FIGS. 1 and 2, a conventional swing-arm type optical recording and reproducing apparatus  80  includes a swing arm  2  installed to pivot on a base  1 , an actuator  6  for providing a rotational driving force for the swing arm  2 , a slider  5  installed at an end portion of the swing arm  2  for scanning a track of an optical disk  20  while floating, due to a dynamic air pressure, on the optical disk  20  supported and rotated by a spindle motor  7 , and an optical head installed at the swing arm  2  and the slider  5  in order to optically record/reproduce information.  
           [0006]    The optical head includes a light source  11  installed on a mount  3  of the swing arm  2 , a beam splitter  12 , a photodetector  13 , and an objective lens  15  installed at the slider  5 . The beam splitter  12  changes the path of incident rays by passing or reflecting the incident rays. That is, the beam splitter  12  passes the rays entering from the light source  11  to direct the rays toward the objective lens  15 , and reflects the rays entering from the objective lens  15  to direct the rays toward the photodetector  13 . The photodetector  13  detects an information signal recorded on the optical disk  20  and a track error signal.  
           [0007]    In the swing-arm type optical recording and reproducing apparatus  80 , the swing arm  2  is swung by the driving force of the actuator  6  in a radial direction of the optical disk  20 . At this time, a beam L, having passed through the beam splitter  12  after being emitted from the light source  11 , is reflected from a reflecting member  14  installed at the end portion of the swing arm  2 . A reflected beam M enters and is converged by the objective lens  15  installed at the slider  5 , and is focused on a recording surface of the optical disk  20 . Subsequently, the beam reflected from the optical disk  20  travels toward the beam splitter  12  via the objective lens  15  and the reflecting member  14 , and is reflected toward the photodetector  13  from the beam splitter  12 . The photodetector  13  receives incident light, and detects the information signal and the track error signal of the objective lens  15 .  
           [0008]    In the optical recording and reproducing apparatus  80 , the focus position of a beam spot is adjusted by the floatation of the slider  5  due to the dynamic air pressure, thus a separate focusing servomechanism function is not performed. Therefore, in the optical head, there is no focusing servomechanism to correspond to a defocus amount representing a degree of variation in a focus position of a beam spot due to temperature or wavelength variations. Since, in the conventional optical recording and reproducing apparatus  80 , a wavelength of the beam varies with temperature variations within about ±15 nm, the optical head must be configured so that the defocus amount of the optical head can be sufficiently small with respect to the wavelength variations of about ±15 nm for stable recording and reproducing.  
           [0009]    Furthermore, the conventional optical disk  20  employed in the above swing-arm type optical recording and reproducing apparatus  80  has a structure shown in FIG. 3. Referring to FIG. 3, an optical disk  20  includes a substrate  21  provided with a spiral groove forming pits  24  on a surface thereof, and a protective layer  23  provided on the substrate  21 . In the protective layer  23 , recessed grooves  23   a  face the slider  5  and correspond to the pits  24 .  
           [0010]    The protective layer  23  has a thickness of about 50 to 100 nm, and a depth of the recessed grooves  23   a  is about 130 nm. Since the recessed grooves  23   a  are formed, a floatation height of the slider  5  is about 20 to 100 nm. Thus, there is a problem of unstable movement of the slider  5 .  
           [0011]    Furthermore, since the light source  11  and the photodetector  13  are installed on the mount  3 , the light beam reflected from the optical disk  20  directly passes through air while returning to the photodetector  13  Thus, there is a further problem of significant light loss along the optical path.  
           [0012]    Still further, since the focusing servochanism function is not performed, when defocus representing the degree of variation in the focus position due to variations in ambient temperature and variations in the wavelength of the light of the light source occurs, significant errors in the recording/reproducing of information may occur.  
           [0013]    Additionally, as a recording density of the optical disk  20  becomes denser, the optical recording and reproducing apparatus  80  requires a mechanism for performing precise servo tracking of the slider  5  so that an optical spot formed on the optical disk  20  can be precisely focused. However, the conventional optical recording and reproducing apparatus  80  performs servo tracking with the actuator  6 , which drives the swing arm  2  without a separate actuator for driving the slider  5  independently. Thus, the optical recording and reproducing apparatus  80  is problematic because it is difficult to control the slider  5  precisely.  
         SUMMARY OF THE INVENTION  
         [0014]    Accordingly, it is an object of the present invention to provide an optical disk which can be applied to a swing-arm type optical recording and reproducing apparatus adapted to minimizing variations in the floatation height of a slider floated by a dynamic air pressure.  
           [0015]    It is another object of the present invention to provide a swing-arm type optical recording and reproducing apparatus having an improved structure capable of restraining the amount of defocus due to variations in ambient temperature and the wavelength of the light of a light source.  
           [0016]    Additional objects 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 learned by practice of the invention.  
           [0017]    The foregoing objects of the present invention are achieved by providing an optical disk applicable to a swing-arm type optical recording and reproducing apparatus, which is rotatably installed on a spindle motor so that information can be recorded on or reproduced from the optical disk by a slider of the optical recording and reproducing apparatus. The slider moves while floating at a predetermined height due to a dynamic air pressure in order to reduce variations in the floating height of the slider. The optical disk includes a substrate having an information recording surface for recording and reproducing an information signal, and a protective layer provided on the information recording surface. The protective layer has a flat even surface that faces the slider.  
           [0018]    The above objects of the present invention may also be achieved by providing a swing-arm type optical recording and reproducing apparatus including a swing arm installed in order to be pivoted in a radial direction of an optical disk by a driving source; a suspension with one end fixed to the swing arm for elastically biasing the other end thereof; a slider installed on a surface of the end portion of the suspension facing the optical disk; and an optical head installed at the swing arm and the slider for recording and reproducing information. The optical head restrains defocus due to variations in ambient temperature and variations in the wavelength of the light of a light source, and includes a light source provided at the swing arm for emitting light of a predetermined wavelength; an optical path changing unit provided in the optical path of the light emitted from the light source, changing the proceeding path of incident light; an objective lens installed at the slider, converging the light which is emitted from the light source and enters via the optical path changing unit to form an optical spot on the optical disk; and a photodetector receiving the light which is reflected from the optical disk and enters via the objective lens and the optical path changing unit to detect an information signal and an error signal. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    These and other objects and advantages of the invention will become apparent and more readily appreciated from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings of which:  
         [0020]    [0020]FIG. 1 is a schematic plan view illustrating a conventional swing-arm type optical recording and reproducing apparatus;  
         [0021]    [0021]FIG. 2 is a sectional view schematically illustrating an essential portion of FIG. 1;  
         [0022]    [0022]FIG. 3 is a sectional view schematically illustrating a conventional optical disk which can be recorded and reproduced by an optical recording and reproducing apparatus;  
         [0023]    [0023]FIG. 4 is a sectional view schematically illustrating an optical disk according to one embodiment of the present invention, which can be recorded and reproduced by an optical recording and reproducing apparatus;  
         [0024]    [0024]FIG. 5 is a sectional view illustrating the operation of an optical recording and reproducing apparatus when the apparatus employs the optical disk of FIG. 4;  
         [0025]    [0025]FIG. 6 is an exploded perspective view schematically illustrating a swing-arm type optical recording and reproducing apparatus according to a first embodiment of the present invention;  
         [0026]    [0026]FIG. 7 is an exploded perspective view schematically illustrating an optical head of the optical recording and reproducing apparatus shown in FIG. 6;  
         [0027]    [0027]FIG. 8 is a schematic diagram illustrating an optical layout of a portion of optical elements of the optical head shown in FIG. 6;  
         [0028]    [0028]FIG. 9 is a schematic diagram illustrating a first embodiment of an objective lens of FIG. 6;  
         [0029]    [0029]FIG. 10 is a schematic diagram illustrating a second embodiment of an objective lens of FIG. 6;  
         [0030]    [0030]FIG. 11 is a schematic diagram illustrating a third embodiment of an objective lens of FIG. 6;  
         [0031]    [0031]FIG. 12 is an exploded perspective view schematically illustrating an optical head of a swing-arm type optical recording and reproducing apparatus according to another embodiment of the present invention; and  
         [0032]    [0032]FIG. 13 is an exploded perspective view schematically illustrating an optical head of a swing-arm type optical recording and reproducing apparatus according to still another embodiment of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]    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 like elements throughout.  
         [0034]    Referring to FIGS. 4 and 5, an optical disk  30  which can be applied to a swing-arm type optical recording and reproducing apparatus according to an embodiment of the present invention is rotatably installed on a spindle motor (not shown) similar to spindle motor  1  of FIGS. 1 and 2, and includes a substrate  31  having an information recording surface  31   a , and a protective layer  33  provided on the substrate  31 .  
         [0035]    An information signal is recorded on or reproduced from the information recording surface  31   a . A spiral groove for defining a track and pits, which comprise an information signal, are formed on the information recording surface  31   a . The protective layer  33  is provided on the information recording surface  31   a , and a surface  33   a  facing a slider  5  is a flat surface. Therefore, when the slider  5  is floated by dynamic air pressure, variations in a floatation height of the slider  5  can be reduced.  
         [0036]    In order to reduce the effect of a dust particle (D), having a diameter R1, adhering to the surface  33   a  of the protective layer  33 , it is preferable that a thickness d1 of the protective layer  33  satisfies the following formula:  
         1 ≦d 1≦5 μm.  (1)  
         [0037]    Furthermore, when R1 is less than or equal to 1.4 mm, the dust particle has almost no influence on the information reproduction from the optical disk  30  when the thickness d1 of the protective layer  33  follows Equation 1.  
         [0038]    Here, the conditional range of the thickness d1 of the protective layer  33  is determined by a range of a thickness variation Δd1 of the protective layer  33  according to the following formula:  
               Δ                 d1     &lt;     λ     2        NA   2                 (   2   )                               
 
         [0039]    where λ is a wavelength of light of a light source, and NA is a numerical aperture of an objective lens. Following formula 2 minimizes defocus of an optical spot.  
         [0040]    On the other hand, when the maximum distance between the surface  33   a  of the protective layer  33  and the slider  5  is d3, a dust particle having an R1 greater than 1.4 mm would be removed by the slider  5  since d3 is kept to within about 0.7 μm. Here, when the distance between the slider  5  and the optical disk  30  along an optical axis of the light converged by an objective lens  15  is d2, d2 is kept to about 0.05 μm.  
         [0041]    Referring to FIG. 6, a swing-arm type optical recording and reproducing apparatus  82  according to one embodiment of the present invention includes a first driving source  50 , a swing arm  41  installed to be pivoted in a radial direction of the optical disk  30  by the first driving source  50 , a suspension  43 , one end of which is fixed to the swing arm  41 , and the other end thereof being elastically biased, a slider  49  installed at one surface of the other end of the suspension  43 , which faces the optical disk  30 , and an optical head for recording and reproducing information. The optical disk  30  is rotatably installed on a spindle motor installed on a base (not shown), and it is preferable that the optical disk  30  has a structure as shown in FIGS. 4 and 5.  
         [0042]    The first driving source  50  is intended to drive the slider  49  in the radial direction of the optical disk  30  (in the direction of arrow A) by pivoting the swing arm  41 . The first driving source  50  is comprised of a first magnet  51  fixedly disposed on the base, and a first coil member  53  provided at the end portion of the swing arm  41  corresponding to the first magnet  51 .  
         [0043]    The suspension  43  has a structure of a leaf spring, and allows the slider  49 , installed at one end thereof by means of a fixing plate  47 , to be aerodynamically suspended over the optical disk  30 . Therefore, when the slider  49  is operated, the floatation height of the slider  49  due to dynamic air pressure is determined at a position where the elastic force of the suspension  43  is in equilibrium with the dynamic air pressure. One end of the fixing plate  47  is connected to the suspension  43 , and the fixing plate  47  is intended to secure a space for installing the slider  49  and an objective lens  66 .  
         [0044]    Furthermore, it is preferable that a hinge portion  45  is provided at the suspension  43  so that the end of the suspension  43  where the slider  49  is installed can be pivoted slightly with respect to the swing arm  41 , and a second driving source is provided for driving the end of the suspension  43  so that a track error can be corrected. To this end, the second driving source is comprised of a second magnet  55  installed at one end of the swing arm  41 , and a second coil member  57  installed at one end of the suspension  43 .  
         [0045]    The mechanical operation of the optical recording and reproducing apparatus  82  will now be described. First, when information is recorded on or reproduced from the optical disk  30 , the optical disk  30  is rotated at a high speed. At this time, the slider  49  is floated from the optical disk  30  due to the dynamic air pressure, and the distance between the optical disk  30  and the slider  49  along the optical axis is approximately 0.05 μm. In this state, the first driving source  50  is operated to pivot the swing arm  41  in the direction of arrow A so that the objective lens  66  can be positioned on the track where information is required to be recorded/reproduced. At this time, correction of a track error of the objective lens  66  with respect to the track direction of the optical disk  30  is performed by an interactive electromagnetic force between the second coil member  57  provided at the suspension  43  and the second magnet  55  provided at the swing arm  41 . That is, the track error is corrected by slight pivoting of the suspension  43  with respect to the swing arm  41  by the interactive electromagnetic force.  
         [0046]    Now, preferred embodiments of the optical head will be described in detail with reference to FIGS. 7 through 13.  
         [0047]    The optical head includes a light source  61  provided at the swing arm  41  for emitting light having a predetermined wavelength, an optical path changing unit  70  changing the path of light, a collimating lens  65  converging incident light, an objective lens  66  installed on the slider  49 , and a photodetector  67  receiving the light reflected from the optical disk  30 , and detecting an information signal and an error signal. The collimating lens  65  is installed at the slider  49 , converging incident light, and preventing defocus due to variations in ambient temperature and variations in the wavelength of the light of the light source  61 . The objective lens  66  converges the light converged by the collimating lens  65  again, and forms an optical spot on the optical disk.  
         [0048]    Referring to FIG. 7, the light emitted from the light source  61  is transferred to the optical path changing unit  70  via an optical fiber  63 . One end of the optical fiber  63  is connected to the light outputting end of the light source  61 , and the other end is connected to a glass ferule  64 , and the glass ferule  64  is fixedly disposed in the optical path between the light source  61  and the optical path changing unit  70 . When the optical fiber  63  is used in this manner, the light emitted from the light source  61  can change direction and be transferred to the optical path changing unit  70  without requiring a reflecting member, thereby realizing the advantage of a compact structure.  
         [0049]    The optical path changing unit  70  is comprised of first and second beam splitters  71  and  73 , respectively, which are integrally formed and have first and second mirror surfaces  71   a  and  73   a , respectively. The optical path changing unit  70  further comprises first and second reflecting members  75  and  77 , respectively for totally reflecting incident light and changing the direction of the light.  
         [0050]    The first beam splitter  71  reflects and transmits, and therefore splits the incident light onto the first mirror surface  71   a  in a predetermined ratio. Therefore, the transmitting light of the light entering from the light source  61  is used as an effective light, and the reflecting light of the light entering from the objective lens  66  is used as an effective light. The first mirror surface  71   a  is disposed to reflect incident light in a direction on a plane parallel to the information recording surface  31   a  of the optical disk  30 . The first reflecting member  75  is provided in the optical path between the first beam splitter  71  and the objective lens  66 , and reflects the light after passing through the first beam splitter  71  and the collimating lens  65  toward the information recording surface  33   a  of the optical disk  30 . The second beam splitter  73  is reflects and transmits, and therefore splits the incident light onto the second mirror surface  73   a  in a predetermined ratio. The second beam splitter  73  reflects the light entering via the first reflecting member  75 , the collimating lens  65 , and the first beam splitter  71  after being reflected from the optical disk  30  in a direction parallel to a lengthwise direction of the slider  49 . The second reflecting member  77  reflects the incident beam from the second beam splitter  73  toward the photodetector  67 .  
         [0051]    Since the direction of the light emitted from the light source  61  and the direction of the light reflected from the optical disk  30  can be separated from each other and be parallel to each other by employing the optical path changing unit as described above, there is an advantage in that the optical head can be easily disposed in a small space on the swing arm.  
         [0052]    It is preferable that the collimating lens  65  is configured as shown in FIG. 8 so that defocus can be prevented. Referring to FIG. 8, the collimating lens  65  includes a first collimating lens  65   a , and a second collimating lens  65   b  integrally bonded to the objective lens side surface of the first collimating lens  65   a . Here, when the Abbe numbers of the first and second collimating lenses  65   a  and  65   b  are ν CL1  and ν CL2 , respectively, it is preferable that the difference |ν CL2 −ν CL1 | satisfies the following Equation  
         |ν CL2 −ν CL1 |&gt;18.0.  (3)  
         [0053]    Here, an Abbe number is an integer representing an optical dispersion of an optical element. When the difference between the Abbe numbers of the first and second collimating lenses  65   a  and  65   b  is greater than 18.0, differences in the optical path due to variations in the wavelength of the light emitted from the light source  62  according to variations in ambient temperature can be significantly reduced.  
         [0054]    Furthermore, the collimating lens  65  changes incident diverging light into parallel light, and it is preferable that the numerical aperture thereof satisfies the following equation:  
           NA   CL &lt;0.4.  (4)  
         [0055]    Furthermore, the diameter of the collimating lens  65  is preferably 2.5 mm or less. Thus, the total height of the optical recording and reproducing apparatus  82  measured from the optical disk  30 , is 4.0 mm or less, resulting in a thinner structure for the optical recording and reproducing apparatus  82 .  
         [0056]    Furthermore, the objective lens  66  can be configured as shown in FIGS. 9 through 11 so that the above-mentioned defocus can be prevented.  
         [0057]    Referring to FIG. 9, an objective lens  166  according to a first embodiment includes a first objective lens  166   a  having an Abbe number ν OL1 , and a second objective lens  166   b  integrally formed at a surface of the first objective lens  166   a  facing an optical disk  30 , and having an Abbe number ν OL2 .  
         [0058]    Here, it is preferable that the difference |ν OL2 −ν OL1 | between the Abbe numbers of the first and second objective lenses  166   a  and  166   b  satisfies:  
         |ν OL2 −ν OL1 |&gt;18.0.  (5)  
         [0059]    By establishing this difference between Abbe numbers, it is possible to significantly reduce the defocus amount that occurs due to variations in the wavelength of the light emitted from the light source  61  according to variations in ambient temperature.  
         [0060]    Referring to FIG. 10, an objective lens  266  is comprised of a solid immersion lens (SIL) having a lens performance of a high numerical aperture, greater than 1.0. The objective lens  266  includes a transmitting portion  266   a  for transmitting and diverging the light entering from the collimating lens  65  (FIG. 7), a transmitting/reflecting portion  266   b  transmitting or reflecting incident light according to an angle of incidence of the light, and a reflecting portion  266   c  reflecting and converging incident light. The reflecting portion  266   c  is provided around the transmitting portion  266   a , and converges and reflects the diverging light entering from the transmitting/reflecting portion  266   b . The transmitting/reflecting portion  266   b  is provided on a surface of the objective lens  266  which faces an optical disk  30 , and reflects and diverges the diverging light that has passed through and is entering from the transmitting portion  266   a , and transmits the converging light from the reflecting portion  266   c . As described above, since the size of the optical spot formed on the optical disk  30  can be reduced by employing an objective lens having a high numerical aperture, the allowable amount of defocus is greater. Therefore, this design is advantageous because a greater error in the wavelength of the light of a light source  61  can be tolerated.  
         [0061]    Referring to FIG. 11, an objective lens  366  according a third embodiment includes a first objective lens  366   a  having an Abbe number ν OL3 , and a second objective lens  366   b  provided between the first objective lens  366   a  and an optical disk  30 , and having an Abbe number ν OL4 . The second objective lens  366   b  is disposed to be close to the optical disk  30 , further converging the light converged by the first objective lens  366   a . Here, it is preferable that the difference |ν OL4 −ν OL3 | between the Abbe numbers of the first and second objective lenses  366   a  and  366   b  satisfies:  
         |ν OL4 −ν OL3 |&gt;18.0.  (6)  
         [0062]    By establishing this difference between Abbe numbers, it is possible to significantly reduce the defocus amount occurring due to variations in the wavelength of the light emitted from the light source  61  according to variations in ambient temperature.  
         [0063]    The above-mentioned optical head can also be modified as shown in FIGS. 12 and 13.  
         [0064]    Referring to FIG. 12, in an optical head according to another embodiment, the light emitted from a light source  61  is transmitted to an optical path changing unit  170  through free space without the previously described optical fiber  63 .  
         [0065]    The optical path changing unit  170  is comprised of one beam splitter  171 , and one reflecting member  175 . The beam splitter  171  has a mirror surface  171   a  adapted to transmit the light from the light source  61 , and to reflect the light from an objective lens  66  toward a photodetector  67 . The reflecting member  175  is provided in the optical path between the beam splitter  171  and the objective lens  66  for changing the path of the light that has passed through the beam splitter  171  from a lengthwise direction of a swing arm to a vertical direction of an optical disk  30 .  
         [0066]    Referring to FIG. 13, an optical head according to still another embodiment further comprises an optical fiber  63  in addition to the structure of the optical head described with reference to FIG. 12. The optical fiber  63  is disposed between a light source  61  and an optical path changing means  170  so that the optical disposition between the light source  61  and a beam splitter  171  can be easily performed. In this case, one end of the optical fiber  63  is connected to the light outputting end of the light source  61 , and the other end is connected to a glass ferule  64 , and the glass ferule  64  is fixedly disposed in the optical path between the light source  61  and the optical path changing means  170 .  
         [0067]    The above-described optical disk according to the present invention is is advantageous as compared to the prior art because variations in the floatation height of the slider are reduced as a result of the surface facing the slider being a flat even surface. A further advantage is that dust accumulated on the flat surface can be removed.  
         [0068]    Furthermore, in the optical recording and reproducing apparatus configured as described above, optical elements can be effectively disposed in the small space on a swing arm by improving a structure of an optical path changing unit. Still further, by employing an optical fiber, loss of the light emitted from a light source is reduced. Further, defocus due to variations in the wavelength of the light of a light source, and, therefore, errors in recording and reproducing an information signal, can be reduced.  
         [0069]    Although a few preferred embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.