CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims all benefits of Japanese Patent Application No. 2004-118856, filed on Apr. 14, 2004, in the Japanese Intellectual Property Office, and Korean Patent Application No. 2004-79209, filed on Oct. 5, 2004, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a memory medium, and, more particularly, to a method of recording and/or reproducing information with respect to a hologram memory medium, in which the information is recorded as interference fringes by using an object beam and a reference beam.  
         [0004]     2. Related Art  
         [0005]     Recently, a rewritable optical disk of a phase shift type or an optical magnetic type is widely used as an information recording medium. In order to increase the recording density of such an optical disk, reducing the diameter of a beam spot and the distance between adjacent tracks or adjacent bits is required.  
         [0006]     Although the recording density of an optical disk has been increased, the recording density of such an optical disk is physically limited by a diffraction limit of a beam, because data is recorded on a surface. Accordingly, a three-dimensional multi-recording including a depth direction is required to increase the recording density of an optical disk.  
         [0007]     Therefore, a hologram memory medium having a large capacity due to a three-dimensional multi-recording region and a high speed due to a two-dimensional recording/reproducing method has attracted public attention as a next generation of computer file memory. Such a hologram memory medium may be formed by inserting a recording layer, which is formed of a photopolymer, between two sheets of glass. In order to record data on such a hologram memory medium, an object beam corresponding to data to be recorded and a reference beam are irradiated to the hologram memory medium to form interference fringes or interference patterns of the object beam and the reference beam. In order to reproduce data from the hologram memory medium, the reference beam is irradiated to the interference fringes to extract optical data corresponding to the recorded data.  
         [0008]     In addition, hologram memory media having a cube shape and a card shape are provided. For example, Japanese Laid-open Patent No. 2000-67204 discloses a card shaped hologram memory including multiple recording layers on which waveguides are recorded to increase a recording capacity.  
         [0009]     However, when recording/reproducing data on/from such a hologram memory medium, data is recorded on or reproduced from a data recording/reproducing area (or data area) on the hologram memory medium in a horizontal direction along a reference line, also known as a recording route, as shown in  FIG. 1 . At the end of the reference line, the recording or the reproducing is stopped to move to an adjacent reference line, and then the recording or the reproducing of data is repeated in the horizontal direction along the adjacent reference line. However, such a method stops the recording or the reproducing of data at the ends of the reference lines. As a result, the operation continuity cannot be secured. Furthermore, the control of a data recording/reproducing optical system becomes complicated.  
       SUMMARY OF THE INVENTION  
       [0010]     Accordingly, the present invention advantageously provides methods of recording/reproducing information on/from a hologram memory medium in which a recording/reproducing optical system can be conveniently controlled to increase a recording capacity of the hologram memory medium.  
         [0011]     According to an aspect of the present invention, a method of recording information on a card or rectangular shaped hologram memory medium, comprises sequentially recording information on a data recording/reproducing area of the card shaped hologram memory medium along a predetermined route, while maintaining a predetermined distance between stripes of information.  
         [0012]     Accordingly, the information can be continuously recorded on the card shaped hologram memory medium. In addition, the information can be continuously reproduced without operating an optical system, such as an optical pickup, unnecessarily.  
         [0013]     The predetermined route may be formed in a spiral shape that spans the entire data recording/reproducing area of the card shaped hologram memory medium. Since the predetermined route is formed in the spiral shape, the data recording/reproducing area of the card shaped hologram memory medium can be effectively used, and the information may be continuously recorded in the data recording/reproducing area of the card shaped hologram memory medium.  
         [0014]     The information recorded in the data recording/reproducing area of the card shaped hologram memory medium may be sequentially recorded from a central portion to a circumference or periphery of the card shaped hologram memory medium or from the circumference or periphery to the central portion of the card shaped hologram memory medium.  
         [0015]     Accordingly, the data recording/reproducing area of the card shaped hologram memory medium can be effectively used, while continuously recording the information without operating an optical system unnecessarily.  
         [0016]     Alternatively, the predetermined route may be formed in a continuous zig-zag shape that spans the entire data recording/reproducing area of the card shaped hologram memory medium, by having a plurality of reference lines that are parallel to one another and connecting the ends of each reference lines with the start portions of the following reference lines.  
         [0017]     The information recorded on the data recording/reproducing area of the card shaped hologram memory medium may be sequentially recorded from an opened end of a reference line to an opened end of another reference line.  
         [0018]     Accordingly, the data recording/reproducing area of the card shaped hologram memory medium can be effectively used, while continuously recording the information without operating an optical system unnecessarily.  
         [0019]     A recording shape adjacent to a portion of converting a recording direction is a curve. Accordingly, a servo following property of an optical system, such as an optical pickup, may be sufficiently secured even in a portion of converting the recording direction.  
         [0020]     According to an aspect of the present invention, the information may be recorded utilizing a two-dimensional shift multi-recording method. Accordingly, a recording capacity of the card-shaped hologram memory medium may be increased. When the information is recorded utilizing a two-dimensional shift multi-recording method, the distance between the parallel reference lines, which are formed in a spiral shape, is the same as a shift amount of the two-dimensional shift multi-recording. Accordingly, the information may be continuously recorded on the card shaped hologram memory medium, while increasing a recording capacity of the card shaped hologram memory medium, and without operating an optical system unnecessarily.  
         [0021]     The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     A better understanding of the present invention will become apparent from the following detailed description of example embodiments and the claims when read in connection with the accompanying drawings, all forming a part of the disclosure of this invention. While the following written and illustrated disclosure focuses on disclosing example embodiments of the invention, it should be clearly understood that the same is by way of illustration and example only and that the invention is not limited thereto. The spirit and scope of the invention are limited only by the terms of the appended claims. The following represents brief descriptions of the drawings, wherein:  
         [0023]      FIG. 1  illustrates a conventional method of recording information on a hologram memory medium useful in gaining a more thorough appreciation of the present invention;  
         [0024]      FIG. 2  illustrates a method of recording/reproducing information on/from a data area of a card shaped hologram memory medium along a recording (reproducing) route in a spiral pattern according to a first embodiment of the present invention;  
         [0025]      FIG. 3  illustrates an adjacent distance according to the first embodiment of the present invention;  
         [0026]      FIG. 4  illustrates example interference fringes recorded in a spiral pattern according to the first embodiment of the present invention;  
         [0027]      FIG. 5  illustrates a method of recording/reproducing information on/from a data area of a card shaped hologram memory medium along a recording (reproducing) route in a continuous zig-zag pattern according to a second embodiment of the present invention;  
         [0028]      FIG. 6  illustrates an adjacent distance according to the second embodiment of the present invention;  
         [0029]      FIG. 7  illustrates example interference fringes according to the second embodiment of the present invention;  
         [0030]      FIG. 8  illustrates an example hologram memory medium according to an embodiment of the present invention;  
         [0031]      FIG. 9  is a block diagram of an example information recording/reproducing apparatus according to an embodiment of the present invention;  
         [0032]      FIG. 10  illustrates an example optical system according to an embodiment of the present invention; and  
         [0033]      FIG. 11  is a flowchart illustrating a method of recording/reproducing information on/from a hologram memory medium according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0034]     The present invention is applicable for use with all types of memory or computer-readable media, hologram memory media, data recording/reproducing apparatuses and computer systems implemented methods described according to various embodiments of the present invention. However, for the sake of simplicity, discussions will concentrate mainly on exemplary use of a hologram memory media having a card shape or a rectangular shape, although the scope of the present invention is not limited thereto.  
         [0035]     Attention now is directed to the drawings and particularly to  FIGS. 2 through 7 , in which hologram memory media having information recorded by methods of recording information such as video data, audio data, audio/visual (AV) data, computer files or meta information according to various embodiments of the present invention. Specifically,  FIG. 2  illustrates a method of recording/reproducing information on/from a data area of a card shaped hologram memory medium along a recording (reproducing) route in a spiral or concentric pattern according to a first embodiment of the present invention.  FIGS. 3-4  illustrate an example distance Ws between parallel reference lines established by an interference pattern which is a series of interference fringes that span the entire data area of the hologram memory medium, as shown in  FIG. 2 .  FIG. 5  illustrates another method of recording/reproducing information on/from a data area of a card shaped hologram memory medium along a recording (reproducing) route in a continuous zig-zag pattern according to a second embodiment of the present invention.  FIGS. 6-7  illustrate an example distance Ws between parallel reference lines established by an interference pattern which is a series of interference fringes that span the entire data area of the hologram memory medium, as shown in  FIG. 5 .  FIG. 8  illustrates a sectional view of a hologram memory medium having servo information i.e., location determination information, recorded thereon which is arranged on a surface facing a surface having a data area.  
         [0036]     In one example embodiment of the present invention, an interference pattern which is a series of interference fringes recorded on the hologram memory medium is formed in a spiral shape, as shown in  FIGS. 2 through 4 . Such interference fringes are recorded on the hologram memory medium due to an interference between an object beam and a reference beam during a recording operation. As a result, information can be continuously recorded on or reproduced from the hologram memory medium, starting from a central portion extending to a circumference or periphery of the hologram memory medium, or vice versa, without interruption, i.e., stopping recording or reproducing at an end of a reference line, and restarting at a next, adjacent reference line. In another example embodiment of the present invention, an interference pattern of interference fringes is formed in a continuous zig-zag shape by connecting end portions of reference lines to start portions of following references lines, while arranging the reference lines in parallel to one another, as shown in  FIGS. 5 through 7 .  
         [0037]     Referring to  FIG. 8 , a hologram memory medium  1  includes a substrate  2 , a hologram recording layer  3 , a total reflection layer  4 , a protective layer  5 , a coat layer (not shown), an adherence layer (not shown), and a substrate  6  having pits  7  in a concave shape or a convex shape. As shown in  FIG. 8 , the substrates  2  and  6  serve as bases of the hologram memory medium  1 . The hologram recording layer  3  is formed of a photosensitive material, for example, a photo polymer, a photorefractive crystal or any other material having a high recording/reproducing efficiency and resolution. Such a material should allow for repeated recording and erasing of data without causing a deterioration of the high recording/reproducing efficiency and resolution characteristics. Information of an object beam is recorded as interference fringes on the hologram recording layer  3  by irradiating the object beam and a reference beam to the same location on the hologram memory medium  1 .  
         [0038]     The total reflection layer  4  reflects the object beam and the reference beam that are irradiated to the hologram recording layer  3  to prevent the transmission of the object beam and the reference beam to a surface facing a surface having a data recording/reproducing area. The protective layer  5  physically protects servo information, in other words, the pits  7 , in a concave shape or a convex shape formed on the substrate  6  from the outside.  
         [0039]     The pits  7  include servo information of an optical system, such as an optical pickup, which records or reproduces information. Accordingly, the servo information can be optically read from the substrate  6  of the hologram memory medium  1  so as to properly control the location of the optical system, i.e., the irradiation location of the object beam and the reference beam from the optical system.  
         [0040]     The pit row shape is symmetrical with the recording shape of the interference fringes (interference stripes), which are recorded on the hologram memory medium. For example, when the interference fringes are formed in a spiral shape, the pit row is formed in a spiral shape symmetrical with the spiral shape of the interference stripes.  
         [0041]     Referring to  FIGS. 3 and 6 , the distance W S  between the parallel reference lines is applied to a two-dimensional multi-recording method. Therefore, the distance W s  may be the same as a shift amount of the two-dimensional multi-recording method. Accordingly, the distance between the pit rows is the same of the distance WS between the reference lines. The examples of the interference stripes, which are recorded by the two-dimensional shift multi-recording method, are shown in  FIGS. 4 and 7 .  
         [0042]     In addition, recording information corresponding to table of content (TOC) data of a compact disk (CD) or a DVD is recorded in a predetermined location of the data recording/reproducing area. Such recording information recorded in the data recording/reproducing area includes location information, in other words, address data, recorded in each data row as well as actual recording information. Accordingly, an access to a predetermined data row can be performed by using the information corresponding to the TOC data and the address data of each data row.  
         [0043]     Turning now to  FIG. 9 , an information recording/reproducing apparatus for recording/reproducing information on/from a hologram memory medium according to an embodiment of the present invention is illustrated. As shown in  FIG. 9 , the information recording/reproducing apparatus includes a hologram memory medium transferring motor  10 , an optical pickup  11 , a feed motor  12 , a signal process integrated circuit (IC)  13 , a central processing unit (CPU)  14 , and a driver integrated circuit (IC)  15 .  
         [0044]     The hologram memory medium transferring motor  10  transfers a hologram memory medium  1  in a different direction from a reference line to the same distance as the shift amount of a shift multi-recording, at the end portion of the reference line. In addition, the transfer of the hologram memory medium transferring motor  10  is controlled by the output of the driver IC  15 .  
         [0045]     The optical pickup  11  includes optical elements such as a laser light source, for example, a semiconductor laser, a collimator lens, an object lens, which is driven by a focus actuator or a tracking actuator, and a polarizing beam splitter, and a light receiving device.  
         [0046]     The feed motor  12  moves the optical pickup  11  to a predetermined location along the hologram memory medium  1 . More specifically, in a search operation, the feed motor  12  controls the location of the optical pickup  11  by using a driving voltage supplied from the driver IC  15 . The driving voltage may be obtained, for example, based on the address data recorded on the hologram memory medium  1 .  
         [0047]     The signal process IC  13  generates a reproducing signal based on a return light quantity from the hologram memory medium  1  that is received by the light receiving device (not shown) in the optical pickup  11 , while generating a focus error (FE) signal obtained by detecting a focus error of a radiation laser from the optical pickup  11  by an astigmatism method based on the return light quantity obtained by the light receiving device (not shown) in the optical pickup  11 . Furthermore, the signal process IC  13  generates a track error (TE) signal obtained by detecting an error in the radiation laser from the optical pickup  11  in a reference line direction by a push-pull method. In addition, the signal process IC  13  generates a focus driving (FODRV) signal and a tracking driving (TRDRV) signal based on the FE and TE signals.  
         [0048]     The CPU  14  controls the information recording/reproducing apparatus based on a control program stored in an internal memory such as a read only memory (ROM). According to an embodiment of the present invention, the CPU  14  controls various servo operations when recording information on the hologram memory medium  1 . More specifically, the CPU  14  calculates a driving voltage of the feed motor  12  that is required to move the optical pickup  11  based on the present address data and the address data of a target location in a search operation, and supplies the driving voltage of the feed motor  12  to the driver IC  15  through the signal process IC  13 .  
         [0049]     The driver IC  15  inputs the focus driving (FODRV) signal or the tracking driving (TRDRV) signal that are generated in the signal process IC  13 , and amplifies the input focus driving (FODRV) signal or tracking driving (TRDRV) signal to a predetermined size. Thereafter, the driver IC  15  supplies the amplified signal to a focus actuator or a tracking actuator.  
         [0050]     Referring to  FIG. 10 , an example optical system, such as an optical pickup  11 , shown in  FIG. 9 , for use in an information recording/reproducing apparatus according to an embodiment of the present invention is illustrated. As shown in  FIG. 10 , such an optical system includes a data recording/reproducing optical system  20  and a location determination controlling optical system  30 . The data recording/reproducing optical system  20  records information in the data recording/reproducing area of the hologram memory medium  1  and reproduces information from the data recording/reproducing area of the hologram memory medium  1 . The location determination controlling optical system  30  performs the location determination control of the object beam and the reference beam irradiated from the data recording/reproducing system  20  based on the servo information, when recording/reproducing information on/from the hologram memory medium  1 . In addition, the data recording/reproducing optical system  20  and the location determination controlling optical system  30  are integrally formed. In such a situation, the location determination controlling optical system  30  transfers inconnection with the transfer of the data recording/reproducing optical system  20 . However, the data recording/reproducing optical system  20  and the location determination controlling optical system  30  can also be physically separated. In such a situation, a control signal may be fed back from the location determination controlling optical system  30  to the data recording/reproducing optical system  20  so as to determine the location of the optical system.  
         [0051]     Turning now to  FIG. 11 , a method of recording information on a hologram memory medium utilizing an information recording/reproducing apparatus according to an embodiment of the present invention will now be described as follows.  
         [0052]     When a hologram memory medium  1  is mounted in an information recording/reproducing apparatus in S 101 , a CPU  14  calculates a driving voltage of a feed motor  12  for transferring an optical pickup  11  based on address data from a location determination controlling optical system  30  in order to transfer the optical pickup  11  to a home position having recording information in the hologram memory medium  1  by supplying the driving voltage of the feed motor  12  to a driver IC  15  through a signal process IC  13 , in S 102 .  
         [0053]     Thereafter, the CPU  14  reads information corresponding to table of content (TOC) data, which is recorded around the home position, from a reproducing signal from the location determination controlling optical system  30  in order to determine whether the information is preliminarily recorded on the hologram memory medium  1 , in S 103 . In the case where the information is not recorded on the hologram memory medium  1 , the data recording/reproducing optical system  20  is transferred to a predetermined recording start location, in S 104 .  
         [0054]     In the case where the information is recorded on the hologram memory medium  1 , the data recording/reproducing optical system  20  is transferred to an address, which is obtained by shifting from the address of the last information by the amount corresponding to the shift amount of a shift multi-recording, in S 105 . When the recording/reproducing optical system  20  is transferred to a predetermined location, the data recording/reproducing optical system  20  radiates an object beam and a reference beam to the data recording/reproducing area of the hologram memory medium  1  to record predetermined information as interference stripes, in S 106 . Thereafter, the data recording/reproducing optical system  20  records information, while shifting by a predetermined amount based on location determination information, which is obtained from the location determination controlling optical system  30 .  
         [0055]     As described from the foregoing, the present invention advantageously provides methods of recording/reproducing information on/from a card type hologram memory medium, in which a data recording/reproducing area of the hologram memory medium can be effectively used, and information can be continuously recorded and reproduced. As a result, the operation continuity can be secured, and the control of a data recording/reproducing optical system can be simplified. In addition, such recording/reproducing methods can advantageously utilize two-dimensional shift multi-recording and reproducing techniques.  
         [0056]     While there have been illustrated and described what are considered to be example embodiments of the present invention, it will be understood by those skilled in the art and as technology develops that various changes and modification may be made, and equivalents may be substituted for elements thereof without departing from the spirit and scope of the present invention. Many modifications may be made to adapt the teachings of the present invention to a particular situation without departing from the scope thereof. For example, the hologram memory medium can be formed in different sizes and shapes, such as square, cube, spherical and elliptical shape, as long as information can be continuously recorded on or reproduced from the hologram memory medium without interruption. In addition, the hologram memory medium can be a recordable medium formed of a photo-polymer, a multi-waveguide type medium or a rewritable medium formed of photorefractive crystals, such as LiNbO 3  (lithium niobate). Similarly, the CPU can be implemented as a chipset having firmware, or alternatively, a general or special purposed computer programmed to perform the methods as described with reference to  FIGS. 2-7 . Moreover, such a hologram memory medium can also have a wide range of applications, including multimedia computing, video-on demand, high-definition televisions, portable computing and consumer video. Accordingly, it is intended, therefore, that the present invention not be limited to the various example embodiments disclosed, but that the present invention includes all embodiments falling within the scope of the appended claims.
A method of recording/reproducing information on/from a card-shaped hologram memory medium is provided in which an information recording/reproducing optical system can be conveniently controlled to increase a recording capacity of the card-shaped hologram memory medium. In the method, pieces of information are sequentially recorded in a data recording/reproducing area of the card shaped hologram memory medium along a predetermined route, while maintaining a predetermined distance between pieces of information.