Abstract:
A hybrid disk useable with a recording and or reproducible apparatus having an optical pickup. The hybrid disk includes a first recording layer having a first format on which data is recordable or readable by a first format beam and a second recording layer having a second format on which the data is recordable or readable by a second format beam. The transmivities and reflectivities of the first and second recording layers are interrelated to control relative intensities of the first and second format beams incident on the optical pickup.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of Korean Application No. 2005-27828, filed Apr. 2, 2005, 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]     Aspects of the present invention relate to an optical disk, and more particularly, to a hybrid disk including first and second recording layers that are different in format from each other.  
         [0004]     2. Description of the Related Art  
         [0005]     Generally, optical disks are manufactured by employing one of a variety of formats such as a compact disk (CD) format, a digital versatile disk (DVD) format, a high density digital versatile disk (HD-DVD) format, and a blu-ray disk (BD) format.  
         [0006]     Recently, a hybrid disk having recording layers that are different in format from each other has been proposed. Wavelengths of beams for writing and reading data on or from the respective recording layers are different from each other. For example, a recording layer having the CD format and a recording layer having the DVD format, or a recording layer having the DVD format and a recording layer having the BD format, or a layer having the CD format and a layer having the BD format can be formed on a single optical disk.  
         [0007]     Since the hybrid disk includes recording layers different in format from each other, the data written on the hybrid optical disk can be read by both an existing player and a new player. For example, when the hybrid disk includes recording layers respectively having CD and DVD formats, the hybrid disk can be used in a CD player or a DVD player.  
         [0008]     In the hybrid disk, focus servo control is performed using a focus error signal (FES) detected by irradiating a beam having a wavelength proper for each recording layer and using the amplitude of a radio frequency signal (RFS).  
         [0009]     However, when the focus servo control is performed by irradiating a beam having a predetermined wavelength to one of the recording layers of the hybrid disk, crosstalk may be generated since a beam reflected from another of the recording layers has a predetermined intensity. That is, in an S-curve, in addition to a signal component reflected from one of the recording layers, a beam having a predetermined intensity or more is reflected from another layer and detected to disturb the focus servo control. For example, in a hybrid disk including a first recording layer having the DVD format and a second recording layer having the HD-DVD format, when the focus servo control is performed by irradiating a beam having a wavelength of about 650 nm to read data from the first recording layer, a part of the beam transmitted through the first recording layer, which has a predetermined intensity or more, is reflected from the second recording layer. In this case, an optical pickup device erroneously determines the hybrid disk as a dual layer DVD disk. This may cause a malfunction of the player.  
         [0010]     Therefore, in the hybrid disk including recording layers that are different in format from each other, when the data is read from one of the recording layers, the reflectivity and transmissivity of the other recording layers must be properly set so that the intensity of the beams reflected from the other recording layers can be reduced to be lower than a predetermined level.  
       SUMMARY OF THE INVENTION  
       [0011]     As aspect of the present invention provides a hybrid disk that is compatible for writing and/or reading apparatuses that are different in format from each other. Other aspects of the present invention provide an apparatus for and method of writing data to and/or reading data from a hybrid disk.  
         [0012]     According to an aspect of the present invention, there is provided a hybrid disk having a plurality of recording layers that are different in a format from each other, including: a first recording layer to and/or from which data are written or read by a first format beam; and a second recording layer to and/or from which data are written or read by a second format beam, wherein a reflectivity of the second recording layer with respect to the first format beam and/or an intensity of the second format beam reflected from the first recording layer is less than a predetermined level.  
         [0013]     The reflectivity of the second recording layer with respect to the first format beam may be less than 1/7- 1/10 of that of the first recording layer with respect to the first format beam.  
         [0014]     The first recording layer may include at least one metal layer and the second recording layer may include at least two metal layers and at leas one dielectric layer disposed between the metal layers. In this case, the metal layer of the first recording layer may be formed of Ni, the metal layers of the second recording layer may be formed of Al, and the dielectric layer of the second recording layer may be formed of ZnS—SiO 2 . In addition, a thickness of the metal layer of the first recording layer may be 35 nm, a thickness of each metal layer of the second recording layer may be 10 nm, and a thickness of the dielectric layer of the second recording layer may be less than 25 nm.  
         [0015]     Alternatively, the first recording layer may include at least two metal layers and at least one dielectric layer disposed between the metal layers and the second recording layer may include at least one metal layer. In this case, the metal layers of the first recording layer may be formed of Al, the dielectric layer of the first recording layer may be formed of ZnS—SiO 2 , and the metal layer of the second recording layer may be formed of Al. In addition, a thickness of each metal layer of the first recording layer may be 10 nm, a thickness of the dielectric layer of the first recording layer may be 38 nm, and a thickness of the metal layer of the second recording layer may be more than 12 nm.  
         [0016]     The first recording layer may have a DVD format and the second recording layer may have an HD-DVD format.  
         [0017]     According to another aspect of the present invention, there is provided an apparatus for writing data to and/or reading the data from a hybrid disk having a plurality of recording layers that are different in format from each other, the apparatus including: a writing/reading unit writing the data to and/or reading the data from a first recording layer using a first format beam, writing and/or reading the data on and/or from a second recording layer using a second format beam, and allowing reflectivity of the second recording layer with respect to the first format beam to be less than a predetermined level when writing the data to and/or reading the data from the first recording layer using the first format beam; and a control unit controlling the writing/reading unit to write or read the data to or from the hybrid disk.  
         [0018]     According to another aspect of the present invention, there is provided a method of writing data to and/or reading data from a hybrid disk having a plurality of recording layers that are different in format from each other, the method including: writing or reading the data to or from a first recording layer of the hybrid disk using a first format beam; writing or reading the data to or from a second recording layer of the hybrid disk using a second format beam, wherein a reflectivity of the second recording layer with respect to the first format beam is less than a predetermined level when writing or reading the data on or from the first recording layer using the first format beam.  
         [0019]     Additional aspects and/or 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  
       [0020]     These 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 the accompanying drawings of which:  
         [0021]      FIG. 1  is a schematic view of a hybrid disk according to an embodiment of the present invention;  
         [0022]      FIG. 2  is a graph illustrating the reflectivity and transmissivity of a first recording layer with respect to a first format beam and the transmissivity of the first recording layer with respect to a second format beam according to a variation of a thickness of a first metal layer in the hybrid disk shown in  FIG. 1 ;  
         [0023]      FIG. 3  is a graph illustrating the reflectivity of a second recording layer with respect to first and second format beams according to a variation of a thickness of a dielectric layer in the hybrid disk shown in  FIG. 1 ;  
         [0024]      FIG. 4  is a schematic view of a hybrid disk according to another embodiment of the present invention;  
         [0025]      FIG. 5  is a graph illustrating the reflectivity and transmissivity of a first recording layer with respect to a first format beam and the transmissivity of the first recording layer with respect to a second format beam according to a variation of a thickness of a dielectric layer in the hybrid disk shown in  FIG. 4 ;  
         [0026]      FIG. 6  is a graph illustrating the reflectivity of a second recording layer with respect to first and second format beams according to a variation of a thickness of a third metal layer in the hybrid disk shown in  FIG. 4 ;  
         [0027]      FIG. 7  is a block diagram of an apparatus for writing/reading data on/from a hybrid disk according to an embodiment of the present invention; and  
         [0028]      FIG. 8  is a view of a writing/reading unit shown in  FIG. 7  according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0029]     Reference will now be made in detail to the present 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.  
         [0030]     According to embodiments of the present invention, a hybrid disk comprises two recording layers that are different in format from each other and data can be written to and/or read from the recording layers.  
         [0031]     In the following description of the embodiments, one of the two recording layers will be referred to as a first recording layer L 0  and the other recording layer will be referred to as a second recording layer L 1 . The recording layer L 0  is closer to the optical pickup than the second recording layer L 1  Light beams, each having a predetermined wavelength, that are appropriate for writing data to and/or reading data from the first and second recording layers L 0  and L 1 , will be referred to as first and second format beams.  
         [0032]     Optical constants used in describing the embodiments of the present invention are shown in Table 1.  
                                                                                           TABLE 1                                       Wavelength of   650 nm       413 nm                    beam   n   k   n   k                            Al   1.488   7.821   0.523   5.024           Ni   2.02   3.82   2.44   0.495           ZnS—SiO 2     2.32   0   2.32   0           Polycarbonate   1.55   0   1.55   0                      
 
         [0033]     In the hybrid disk using the beams that are different in wavelength from each other, the intensity of the first format beam transmitted through the first recording layer and reflected from the second recording layer must be lowered to be less than a predetermined level to prevent focus servo control errors caused by crosstalk. It can be shown experimentally that the reflectivity of the second recording layer with respect to the first format beam should be set to be less than 1/7- 1/10 of a reflectivity of the first recording layer and the reflectivity of the second recording layer with respect to the second format beam should be set to be more than 10% of the reflectivity of the first recording layer so that a signal having a sufficient intensity can be detected. Although the embodiments of the invention are explained with respect to wavelengths related to the HD-DVD and the bluray disks, a hybrid disk may be formed to use other combinations of wavelengths.  
         [0034]      FIG. 1  is a schematic view of a hybrid disk  100  according to an embodiment of the present invention. Referring to  FIG. 1 , the hybrid disk  100  includes a first substrate  101 , a first metal layer  103 , a space layer  105 , a second metal layer  107 , a dielectric layer  109 , a third metal layer  111 , and a second substrate  113 .  
         [0035]     As illustrated in  FIG. 1 , a beam having a predetermined wavelength is focused by an object lens OL and incident on the hybrid disk  100  through the first substrate  101  to write data to and/or read data from the hybrid disk  100 .  
         [0036]     The first substrate  101 , the space layer  105 , and the second substrate  113  are formed of a material selected from the group consisting of polycarbonate, polymethylmetyacrylate (PMMA), amorphous polyolefin (APO), and glass.  
         [0037]     The first, second and third metal layers  103 ,  107  and  111  are formed of a material selected from the group consisting of Ni, Al, Au, Ag, Cu and an alloy thereof. The data is written on the first, second and third metal layers  103 ,  107  and  111  in a form of pits.  
         [0038]     The dielectric layer  109  is formed of a material selected from the group consisting of SiOx, MgOx, AlOx, TiOx, VOx, CrOx, NiOx, ZrOx, GeOx, ZnOx, SiNx, AlNx, TiNx, ZrNx, GeNx, SiC, ZnS, ZnS—SiO 2 , and MgF 2 , where x is an integer.  
         [0039]     The first metal layer  103  corresponds to the first recording layer L 0  having a first format among a variety of formats such as CD, DVD, HD-DVD, and BD, and the second metal layer, the dielectric layer and the third metal layer  107 ,  109  and  111  correspond to the second recording layer L 1  having a second format among the variety of formats. For example, two of the variety formats are respectively selected as formats of the first and second recording layers L 0  and L 1 .  
         [0040]     The wavelength of the first format beam for writing data to and/or reading data from the first recording layer L 0  may be longer than the wavelength of the second format beam for writing data to and/or reading data from the second recording layer L 1 . For example, the first recording layer L 0  may have a DVD format using a beam (i.e., the first format beam) having a wavelength of 650 nm and the second recording layer L 1  may have an HD-DVD format using a beam (i.e., the second format beam) having a wavelength of 413 nm.  
         [0041]     In the above-described hybrid disk, when the first format beam is irradiated to write data to and/or read data from the first recording layer L 0 , the reflectivity of the second recording layer L 0  with respect to the first format beam reflected from the second recording layer L 0  is limited to be lower than a predetermined level, thereby preventing focus crosstalk caused by the reflected beam.  
         [0042]     In particular, in the hybrid disk according to the current embodiment of the present invention, since the second recording layer L 1  includes the second and third metal layers  107  and  111  and the single dielectric layer  109 , a selective wavelength property can be realized by adjusting the reflectivity and transmissivity of the first and second recording layers L 0  and L 1  with respect to the first and second format beams that are different in wavelength from each other.  
         [0043]     In a conventional multi-layer read-only or recording medium, since a beam having a single wavelength is used to read data from a plurality of recording layers, the reflectivity and transmissivity of each recording layer can be adjusted by properly adjusting a thickness of each recording layer.  
         [0044]     However, in the embodiment shown in  FIG. 1 , since the recording medium is the hybrid disk having the two recording layers that are different in format from each other and thus the first and second format beams that are different in wavelength from each other are used for performing the writing and reading, it is difficult to properly adjust the reflectivity and transmissivity of the first and second recording layers L 0  and L 1  by simply adjusting the thickness of the first and second recording layers L 0  and L 1 .  
         [0045]     Therefore, in the hybrid disk shown in  FIG. 1 , the second recording layer L 1  includes at least two metal layers, the second and third metal layers  107  and  111 , and at least one dielectric layer  109 . Therefore, the reflectivity and transmissivity of each recording layer can be set such that, when the first format beam is irradiated to write and/or read data to/from the first recording layer L 0 , the intensity of the beam reflected from the second recording layer L 1  can be lower than a predetermined level.  
         [0046]      FIG. 2  is a graph illustrating the reflectivity and transmissivity of the first recording layer L 0  with respect to the first format beam and the transmissivity of the first recording layer L 0  with respect to the second format beam according to a variation of the thickness of the first metal layer  103  in the hybrid disk according to the embodiment shown in  FIG. 2 . Here, the first recording layer L 0  has the DVD format and the second recording layer L 1  has the HD-DVD format. In addition, the first recording layer L 0  is formed of Ni, the wavelength of the first format beam is 650 nm, and the wavelength of the second format beam is 413 nm.  
         [0047]     Referring to  FIG. 2 , as the thickness of the first recording layer L 0  and the reflectivity of the first format beam gradually increase, the transmissivity of the first and second format beams is gradually reduced. For example, when the thickness of the first recording layer L 0  is 35 nm, the reflectivity and transmissivity of the first recording layer L 0  with respect to the first format beam having the wavelength of 650 nm are respectively 50% and 8% and the transmissivity of the first recording layer L 0  with respect to the second format beam having the wavelength of 413 nm is 50%.  
         [0048]      FIG. 3  is a graph illustrating the reflectivity of the second recording layer L 1  with respect to the first and second format beams according to a variation of the thickness of the dielectric layer in the hybrid disk shown in  FIG. 2 . Here, each of the second and third metal layers  107  and  111  of the second recording layer L 1  is formed of an Al layer having a thickness of 10 nm and the dielectric layer  109  is formed of ZnS—SiO 2 . In addition, as in the case of  FIG. 2 , a red beam having a wavelength of 650 n is used as the first format beam and a blue beam having a wavelength of 413 nm is used as the second format beam.  
         [0049]     Referring to  FIG. 3 , it can be noted that, as the thickness of the dielectric layer  109  is increased, the reflectivity of the second recording layer L 1  with respect to the first and second format beams is reduced.  
         [0050]     In order to write data to and/or read data from the second recording layer L 1 , more than 18% of the second format beam incident on the hybrid disk must be reflected from the second recording layer L 1 . When the thickness of the first recording layer L 0  formed of Ni is 35 nm, 50% of the second format beam reaches the second recording layer L 1  through the first recording layer L 0 .  
         [0051]     A percentage of the second format beam that is transmitted through the first recording layer L 0 , reflected from the second recording layer L 1  and detected by an optical pickup device becomes (T 12 ) 2 ×R 22 ×100, where T 12  is the transmissivity of the first recording layer L 0  with respect to the second format beam and R 22  is the reflectivity of the second recording layer with respect to the second format beam. Therefore, where the reflectivity of the second recording layer L 1  with respect to the second format beam (T 12 ) is 0.50, the percentage of the second format beam reflected from the second recording layer L 1  and incident on the optical pickup becomes (0.5) 2 ×R 22 ×100, which must be more than 18%. That is, (0.5) 2 ×R 22 &gt;0.18 must be satisfied. Therefore, R 22  must be greater than 0.72. That is, in order to normally write data to and/or read data from the second recording layer L 1 , the reflectivity of the second recording layer L 1  with respect to the second format beam must be more than 0.72.  
         [0052]     Meanwhile, in order to prevent focus cross-talk, the intensity of the first format beam transmitted through the first recording layer L 0  and reflected from the second recording layer L 1  must be lower than a predetermined level. A percentage of the first format beam reflected from the second recording layer L 1  and detected by the optical pickup device is (T 11 ) 2 ×R 21 ×100, where T 11  is the transmissivity of the first recording layer L 0  with respect to the first format beam and R 21  is the reflectivity of the second recording layer L 1  with respect to the first format beam. Therefore, where the percentage of the first format beam transmitted through the first recording layer L 0  is 8%, (T 11 =0.08), the percentage of the first format beam reflected from the second recording layer L 1  and incident on the optical pickup becomes (0.08) 2 ×R 21 . When the percentage of the first format beam reflected from the second recording layer L 1  and incident on the optical pickup is set to be less than 5%, 0.08 2 ×R 21 &lt;0.05 must be satisfied. Therefore, R 21  may be any value in a range of 0-1. As shown in  FIG. 3 , when the thickness of the dielectric layer  109  is less than 25 nm, the reflectivity of the second recording layer L 1  with respect to the first and second format beams becomes more than 0.72.  
         [0053]      FIG. 4  is a schematic view of a hybrid disk  200  according to another embodiment of the present invention. The hybrid disk  200  is constructed of similar materials as the hybrid disk  100  of the embodiment illustrated in  FIG. 1 . However in the embodiment shown in  FIG. 4 , the dielectric layer  205  and the space layer  209  are located in a same position as the space layer  105  and the dielectric layer  209 , respectively, in the embodiment shown in  FIG. 1 . Thus, the first recording layer L 0  of the embodiment shown in  FIG. 4  includes first and second metal layers  203  and  207  and the dielectric layer  205  and the second recording layer L 1  includes a third metal layer  211 . The first and second recording layers L 0  and L 1  in the embodiment shown in  FIG. 4  are separated by the space layer  209 . A first substrate  201  is located adjacent the first metal layer  203  and a second substrate  213  is located adjacent the third metal layer  211 . The first substrate  201 , the first metal layer  203 , the dielectric layer  205 , the second metal layer  207 , the space layer  209 , the third metal layer  211  and the second substrate  213  of the hybrid disk  200  may be formed of the same materials as the first substrate  101 , the first metal layer  103 , the dielectric layer  109 , the second metal layer  107 , the space layer  105 , the third metal layer  111  and the second substrate  113  of the hybrid disk  100 , respectively  
         [0054]      FIG. 5  is a graph illustrating the reflectivity and transmissivity of the first recording layer L 0  with respect to a first format beam and the transmissivity of the first recording layer L 0  with respect to a second format beam according to a variation of the thickness of the dielectric layer  205  in the hybrid disk  200 . As in the hybrid disk  100 , the first recording layer L 0  of the hybrid disk  200  has the DVD format and the second recording layer L 1  has the HD-DVD format. In addition, the first and second metal layers  203  and  207  are formed of Al, the wavelength of the first format beam is 650 nm, and the wavelength of the second format beam is 413 nm.  
         [0055]     Referring to  FIG. 5 , as the thickness of the dielectric layer  205  is increased, the reflectivity of the first recording layer L 0  with respect to the first format beam is gradually reduced and the transmissivity of the first recording layer L 0  with respect to second format beam is gradually increased. The transmissivity of the first recording layer L 0  with respect to the first format beam gradually decreases to a thickness of the dielectric layer  205  of about 30 nm and then gradually increases thicknesses of the dielectric layer  205  greater than about 30 nm, remaining within a range of about 20% of the transmissivity at about 30 nm.  
         [0056]     For example, where the thickness of the first recording layer L 0  is 35 nm, the reflectivity of the first recording layer L 0  with respect to the first format beam having the wavelength of 650 nm is 50% and the transmissivity of the first recording layer L 0  with respect to the first format beam is 12%. The transmissivity of the first recording layer L 0  with respect to the second format beam having the wavelength of 413 nm is 50%.  
         [0057]      FIG. 6  is a graph illustrating the reflectivity of the second recording layer L 1  with respect to the first and second format beams according to a variation of the thickness of the third metal layer  211 .  
         [0058]     In the example shown in  FIG. 6 , each of the second and third metal layers  207  and  211  of the second recording layer L 1  is formed of an Al layer having a thickness of 10 nm and the dielectric layer  205  is formed of ZnS—SiO 2 . In addition, as in  FIG. 5 , a red beam having a wavelength of 650 n is used as the first format beam and a blue beam having a wavelength of 413 nm is used as the second format beam.  
         [0059]     Referring to  FIG. 6 , it can be noted that, as the thickness of the third metal layer  211  is increased, the reflectivity of the second recording layer L 1  with respect to the first and second format beams gradually increases and saturates at about 90% at a predetermined thickness above about 30 nm.  
         [0060]     In order to write data to and/or read data from the third metal layer  211  corresponding to the second recording layer L 1 , more than 18% of the second format beam incident on the hybrid disk  200  should be reflected from the second recording layer L 1  and be detected by the optical pickup. When the thickness of the dielectric layer  205  of the first recoding layer L 0  is 35 nm, 50% of the second format beam reaches the second recording layer L 1  through the first recording layer L 0 .  
         [0061]     A percentage of the second format beam that is transmitted through the first recording layer L 0 , reflected from the second recording layer L 2  and detected by the optical pickup device becomes (T 12 ) 2 ×R 22 ×100 where T 12  is the transmissivity of the first recording layer with respect to the second format beam and R 22  is the reflectivity of the second recording layer with respect to the second format beam. Therefore, where the reflectivity of the second recording layer L 1  with respect to the second format beam is R 22 , the percentage of the second format beam reflected from the second recording layer L 1  and incident on the optical pickup device becomes 0.5 2 ×R 22 ×100. This percentage must be more than 18%. That is, 0.5 2 ×R 22 &gt;0.18 must be satisfied. Therefore, R 22  must be greater than 0.72. That is, in order to normally write data to and/or read data from the second recording layer L 1 , the reflectivity of the second recording layer L 1  must be more than 0.72.  
         [0062]     Meanwhile, in order to prevent focus cross-talk, the intensity of the first format beam transmitted through the first recording layer L 0  and reflected from the second recording layer L 1  must be lower than a predetermined level. A percentage of the first format beam reflected from the second recording layer L 1  and detected by the optical pickup device is (T 11 ) 2 ×R 21 ×100 where T 11  is the transmissivity of the first recording layer with respect to the first format beam and R 21  is the reflectivity of the second recording layer with respect to the first format beam.  
         [0063]     As shown in  FIG. 5 , the percentage of the first format beam transmitted through the first recording layer L 0  is about 12%, thus the percentage of the first format beam reflected from the second recording layer L 1  and incident on the optical pickup device becomes 0.12 2 ×R 21 . When the percentage of the first format beam reflected from the second recording layer L 1  and incident on the optical pickup is set to be less than 5%, 0.12 2 ×R 21 &lt;0.05 must be satisfied. Therefore, R 21 , the reflectivity of the second recording layer L 1  with respect to the first format beam, may be any value within a range of 0-1. As shown in  FIG. 6 , when the thickness of the third metal layer  211  corresponding to the second recording layer L 1  is greater than 12 nm, the reflectivity of the second recording layer L 1  with respect to the first and second format beams becomes more than 0.72.  
         [0064]     In the above embodiments, although one of the first and second recording layers L 0  and L 1  includes two or more metal layers and one or more dielectric layers, the hybrid disk of the present invention is not limited thereto. That is, the recording layer can have a variety of structures.  
         [0065]      FIG. 7  is a block diagram of an apparatus  300  for writing/reading data to/from a hybrid disk  301  according to an embodiment of the present invention. Referring to  FIG. 7 , the writing/reading apparatus  300  includes a writing/reading unit  303  and a control unit  305 .  
         [0066]     The writing/reading unit  303  writes and reads data to and from the hybrid disk  301 , respectively, according to the control of the control unit  305 . The control unit  305  controls the writing/reading unit  303  or processes the data read by the writing/reading unit  303  to provide effective data.  
         [0067]     The writing/reading unit  303  includes an optical pickup device for writing and reading data. The hybrid disk  301  is loaded on the optical pickup device. The optical pickup device outputs an optical signal from the control unit  305  by emitting a laser beam to the hybrid disk  301  and receiving the laser beam reflected from the hybrid disk  301 . Examples of the hybrid disk  301  include the hybrid disk  100  and the hybrid disk  200  as described above.  
         [0068]     In particular, the writing/reading unit  303  uses a first format beam having a first wavelength to write and read data to and from a first recording layer of the hybrid disk  301  and a second format beam having a second wavelength to write and read data to and from a second recording layer of the hybrid disk  301 . In addition, as described above, when data is written or read to or from the first recording layer using the first format beam, the writing/reading unit  303  controls the first format beam in consideration of the reflectivity of the second recording layer with respect to the first format beam so that first format light reflected from the second recording layer is less than a predetermined level.  
         [0069]     The writing/reading unit  303  will now be described in more detail.  FIG. 8  is a block diagram of an example of the writing/reading unit  303  shown in  FIG. 7 . In order for one or more object lens units to be compatible with the recording layers that are different in format from each other, the writing/reading unit  303  emits beams each having a wavelength appropriate for each recording layer to the hybrid disk  301  and receives the beams reflected from the hybrid disk  301  to detect an information signal and/or an error signal.  
         [0070]     Referring to  FIG. 8 , the writing/reading unit  303  includes an object lens  405  forming a light spot on a recording surface of the hybrid disk  301  by focusing incident light, a first light source  401  emitting a first beam having a first wavelength, a second light source  403  emitting a beam having a second wavelength, first and second optical path converters  407  and  409  converting light paths of the beams emitted from first and second light sources  401  and  403 , respectively, and an optical detector  411  detecting the information and/or error signal by receiving the beam reflected from the recording surface of the hybrid disk  301 .  
         [0071]     For example, when the first recording layer of the hybrid disk  301  has the DVD format, the first light source  401  is used as the DVD format light source emitting a beam having a wavelength of 650 nm to write and read data to and from the first recording layer. When the second recording layer of the hybrid disk  301  has the HD-DVD format, the second light source  403  is used as the HD-DVD format light source emitting a beam having a wavelength of 413 nm to write and read the data to and from the second recording layer.  
         [0072]     By preventing the deterioration of the focus error signal caused by cross-talk between two or more recording layers of a hybrid disk that are different in format from each other, focus servo control can be stably performed.  
         [0073]     Further, since two or more recording layers having different formats such as CD, DVD, HD-DVD, and BD are formed on a single disk, a user can enjoy the multimedia data using a system supporting a specific one of the formats or a system supporting all of the formats.  
         [0074]     Although a few 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 this embodiment without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.