Patent Publication Number: US-7593310-B2

Title: Method for manufacturing multilayered disk

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of manufacturing a multilayered disk capable of refraining from an interlayer interference between adjacent layers when a specific layer of the multilayered layers is recorded or regenerated in an optical disk. 
   2. Background of the Related Art 
   As a request for high quality moving pictures is increased in accordance with an improvement of consumers&#39; lifestyle along with a speed doubling and an increase of storing density of an optical storing device, a larger volume of storing data of an optical storing disk is required. 
     FIG. 1  is a schematic block diagram of a general optical pickup device. 
   Referring to  FIG. 1 , the optical pickup device comprises a laser diode  101  emitting a beam with a regular wavelength, a beam splitter  102  reflecting or transmitting the beam, a collimator lens  103  emitting the beam impinged from the beam splitter  102  into a parallelized beam, an object lens  104  condensing the beam impinged from the collimator lens  103  to the optical disk  105  and transmitting the reflected beam to the collimator lens  103  and a photo detector  106  detecting the beam reflected by the beam splitter  102  and emitting it as an electric signal. 
   The above configured optical pickup device is shown in  FIG. 1 . As shown in  FIG. 1 , a laser beam emitted from the laser diode LD  101  is transmitted through the beam splitter  102  and the transmitted beam is impinged to an object lens  104  from the collimator lens  103  as a parallel beam. The object lens  104  condenses an impinged beam to a point on the optical disk  105  to record and regenerate the information, and a beam formed from the optical disk  105  is reflected. The reflected beam is transmitted through the object lens  104  and the collimator lens  103  to be reflected to the photo detector  106  by the beam splitter  102 . The photo detector  106  changes the information which is reflected and input into an electric signal. 
   In a recent optical system, a lot of methods are attempted in order to increase a recording volume of an optical disk. A representative method is to increase a recording density by decreasing the size of a light condensed on a disk. The object can be obtained by decreasing a wavelength of a laser and increasing a numerical aperture of the object lens for condensing a light. 
   The recently developed recording and regenerating device of an optical disk for Blu-ray Disk BD employs a laser wavelength of 450 nm and a numerical aperture of the object lens of 0.85 to have a recording volume of 25 GB per one disk of 12 cm. 
   In addition, researches on a method using a UV laser with a shorter wavelength or a method for recording a near field for further widening a numerical aperture of an object lens have been carried out in order to further increase a recording volume. 
   As another method for increasing the total recording volume in the process, the number of recording layers is increased by making the recording layer of an optical disk have multiple layers, with maintaining the two dimensional recording densities. 
     FIG. 2  schematically shows a Blu-ray disk where the dual layers are formed and a pickup device thereof. 
   Referring to  FIG. 2 , the Blu-ray disk  30  is formed to have two recording layers  1  and  2  with a predetermined distance d 2  therebetween. The recording layer  1  is formed in the same direction of the object lens  11  of an optical pickup with a predetermined distance d 1 . 
   An optical disk device for reading or recording the recorded data onto a recording layer of the Blu-ray disk  30  is variably controlled to be suitable for recording or regenerating a laser power of a laser diode LD  13  included in the pickup. For example, the optical pickup performs the operations of recording or regenerating by transforming a light source emitted from the laser diode  13  into a parallelized light in the collimator lens CL  12 , and condensing the parallelized light on the recording layer of a disk in the object lens OL  11  and reflecting it again. 
   As described above, in the case of DVD or BD disks, a method for increasing a recording volume using two layers has been already completed, and a method for increasing a recording layer of a BD disk to have six or eight layers or further is developed. 
   However, the most serious problem of the above described multilayered disk is that a light reflected from an undesired layer is received to a photo detector to operate as a noise when a laser light is condensed on a layer to be recorded or regenerated. Thus, it is required to adjust a shape of a photo detector and a range of a reflective signal or S-curve range and so on in order to decrease the noise. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide with a method for removing an interlayer interference in an optical pickup device where noise characteristics of all signals can be decreased by adjusting the range of a reflective signal. In the device, the disk recording layers has a regular space in order to decrease an interlayer interference in the multilayered disk. 
   In order achieve the above object, a method for manufacturing a multilayered disk according to the present invention is characterized by that a space between the recoding layers is set to less than 10 μm to refrain from an interference at the adjacent layer when one of the recording layers is recorded or regenerated. 
   It is preferable that the space between the recording layers of the disk be the same. 
   It is preferable that the range of a reflective signal from the recording layer of the disk be less than 1.7 μm. 
   It is preferable that the reflective signal be detected using an astigmatism method that a focus server is used to pick up a light. 
   It is preferable that the method for detecting the reflective signal use a focus server to pick up a light by a knife edge method or a foucault method. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic block diagram of a conventional optical pickup device. 
       FIG. 2  shows a focusing state of the conventional multilayered disk. 
       FIG. 3  shows an interlayer interference from the multilayered disk according to the present invention. 
       FIG. 4  shows a reflective beam size from a photo detector according to the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, embodiments of the present invention will now be described in detail with reference to the attached drawings. Reference now should be made to the drawings, in which the same reference numerals are used throughout the different drawings to designate the same or similar components. In the following description of the present invention, detailed descriptions may be omitted if it is determined that the detailed descriptions of related well-known functions and construction may make the gist of the present invention unclear. 
     FIG. 3  shows an example of a reflective beam from a multilayered disk from which an interlayer interference is removed according to the present invention, and  FIG. 4  shows the shape of a beam received from a photo detector according to the present invention. 
   Referring to  FIGS. 3 and 4 , when mth recording layer of the multilayered optical disk  30  in an optical pickup device is recorded or regenerated, the light is reflected on the (m+1)th layer and (m−1)th layer, also. Here, a signal reflected from other layers barely has an effect, thus is excluded from the consideration. 
   The beam reflected from the mth recording layer is received by the photo detector  20 , the light RB 0  reflected from the mth recording layer is received in the center of the photo detector and the light RB 1  reflected from the (m+1)th recording layer is received in the center of the photo detector with a larger size than the light detected by the photo detector. 
   A beam size of the photo detector is as follows. If a reflectivity from the real recording layer m is Rm and an interlayer space of a disk is d, the beam from the photo detector is focused as illustrated in  FIG. 2 . 
   At this time, if the beam size is D, a numerical aperture of an object lens is NA, a ratio of a light receiving system is M, a reflective signal range or S-curve range is s, and a detecting size of a photo detector is L, the beam size D of a light reflected from m layer in the photo detector is represented in the following mathematic formula 1.
 
 D=s×NA×M× 2  [Mathematic formula 1]
 
   In addition, the beam size D′ of a light reflected from (m+1) or (m−1) layer in the photo detector is represented in the following mathematic formula 2.
 
 D′= 2 d×NA×M× 2  [Mathematic formula 2]
 
   The mathematic formula 2 is obtained by applying the value of 2d in consideration of an adjacent layer with respect to a reflective signal range in the mathematic formula 1. 
   Therefore, a light amount R PD  which is reflected from the (m+1) layer and is input to the photo detector is represented in the following mathematic formula 3. 
   
     
       
         
           
             
               
                 
                   R 
                   PD 
                 
                 = 
                 
                   
                     R 
                     
                       m 
                       + 
                       1 
                     
                   
                   ⁢ 
                   
                     
                       L 
                       2 
                     
                     
                       
                         π 
                         ⁡ 
                         
                           ( 
                           
                             4 
                             ⁢ 
                             dNAM 
                           
                           ) 
                         
                       
                       2 
                     
                   
                 
               
             
             
               
                 [ 
                 
                   Mathematic 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   3 
                 
                 ] 
               
             
           
         
       
     
   
   In addition, the proportion P of a noise light reflected from the adjacent layer to the main light reflected to the mth layer is represented in the formula 4 as follows, 
   
     
       
         
           
             
               
                 
                   
                     
                       P 
                       = 
                       
                         
                           
                             
                               
                                 
                                   
                                     R 
                                     
                                       m 
                                       + 
                                       1 
                                     
                                   
                                   ⁢ 
                                   
                                     
                                       L 
                                       2 
                                     
                                     
                                       π 
                                       ⁢ 
                                       
                                         
                                           { 
                                           
                                             4 
                                             ⁢ 
                                             dNAM 
                                           
                                           } 
                                         
                                         2 
                                       
                                     
                                   
                                 
                                 + 
                               
                             
                           
                           
                             
                               
                                 
                                   R 
                                   
                                     m 
                                     - 
                                     1 
                                   
                                 
                                 ⁢ 
                                 
                                   
                                     L 
                                     2 
                                   
                                   
                                     π 
                                     ⁢ 
                                     
                                       
                                         { 
                                         
                                           4 
                                           ⁢ 
                                           dNAM 
                                         
                                         } 
                                       
                                       2 
                                     
                                   
                                 
                               
                             
                           
                         
                         
                           R 
                           m 
                         
                       
                     
                   
                 
                 
                   
                     
                       = 
                       
                         
                           
                             
                               R 
                               
                                 m 
                                 + 
                                 1 
                               
                             
                             + 
                             
                               R 
                               
                                 m 
                                 - 
                                 1 
                               
                             
                           
                           
                             R 
                             m 
                           
                         
                         ⁢ 
                         
                           
                             
                               L 
                               2 
                             
                             ⁢ 
                             
                               s 
                               2 
                             
                           
                           
                             4 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             π 
                             ⁢ 
                             
                                 
                             
                             ⁢ 
                             
                               d 
                               2 
                             
                             ⁢ 
                             
                               D 
                               2 
                             
                           
                         
                       
                     
                   
                 
               
             
             
               
                 [ 
                 
                   Mathematic 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   4 
                 
                 ] 
               
             
           
         
       
     
   
   R=R m+1 =R m−1 , and if an interference at the adjacent layer is refrained less than P, a reflective signal range should be limited in the following mathematic formula 5, 
   
     
       
         
           
             
               
                 s 
                 &lt; 
                 
                   
                     D 
                     L 
                   
                   ⁢ 
                   d 
                   ⁢ 
                   
                     
                       2 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       P 
                     
                   
                 
               
             
             
               
                 [ 
                 
                   Mathematic 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   5 
                 
                 ] 
               
             
           
         
       
     
   
   It is possible to design and manufacture an optical pickup satisfying the mathematic formula 5. 
   For example, a widely used proportion (D/L) of a photo detector size to a beam size in the photo detector is 0.7, and if the proportion P of a noise light to a main light is less than 1%, there are no difficulties in the capabilities. 
   Accordingly, if an optical disk is manufactured to have an interlayer space d of 10 μm, the reflective signal range s becomes less than 1.75 (s&lt;1.75 μm). In other words, if the reflective signal range is less than 1.7 μm, an interlayer interference can be refrained below 1%. 
   The above formulas are obtained under a condition that a focus server is obtained using an astigmatism. If a knife edge method or a fouault method is used, the above formula is changed into the following mathematic formula 6, 
   
     
       
         
           
             
               
                 P 
                 = 
                 
                   
                     
                       
                         R 
                         
                           m 
                           + 
                           1 
                         
                       
                       + 
                       
                         R 
                         
                           m 
                           - 
                           1 
                         
                       
                     
                     Rm 
                   
                   ⁢ 
                   
                     
                       s 
                       2 
                     
                     
                       4 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       π 
                       ⁢ 
                       
                           
                       
                       ⁢ 
                       
                         d 
                         2 
                       
                     
                   
                 
               
             
             
               
                 [ 
                 
                   Mathematic 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   formula 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   6 
                 
                 ] 
               
             
           
         
       
     
   
   In addition, a reflective signal range is obtained in the mathematic formula 7.
 
 s&lt;d √{square root over (2π P )}  [Mathematic formula 7]
 
   In the above case, in order to make D/L be 0.7 and P be less than 1%, d=10 μm, and s&lt;2.51 μm. 
   As described above, if an interlayer space d is manufactured to be 10 μm in order to remove an interlayer interference when manufacturing a multilayered disk, a reflective signal range becomes less than 1.7 μm and interlayer interference can be refrained below 1%. At this time, a focus server is detected using an astigmatism method. 
   The present invention has been described with reference to the preferred embodiments, but it is apprehended that the present invention can be modified and changed in various ways within the spirit and scope of the present invention described in the claims by those skilled in the art. 
   According to a method for manufacturing a multilayered disk and a method for removing an interlayer interference using the disk in the present invention, it is possible to design and manufacture a multilayered disk within a reflective signal range.