Abstract:
A holographic storage system. A low over-sampling technology and an adaptable gain-controlling unit are used in the holographic storage system for unequally amplifying signals generated by a detecting apparatus. Then the amplified signals generated by the detecting apparatus are summed in order to generate summing signals, which are used to detect original image frames for raising the resolution of the images and reducing the error rate of the data.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a holographic storage system, and more particularly to a detecting apparatus and a detecting method within the holographic storage system. 
       BACKGROUND OF THE INVENTION 
       [0002]      FIG. 1  depicts a holographic storage system diagram, wherein the holographic storage system  100  includes a signal beam  12 , a data plane  14 , a reference beam  16 , a storage medium  18 , a data beam  22 , and a detecting apparatus  20 . 
         [0003]    A light source, e.g. a laser light source, is split into two light beams by a beam splitter (not shown), wherein one of the two light beams is converted to the signal beam  12  after the light beam is emitted to the data plane  14 , which means an image frame presented on the data plane  14  is also contained in the signal beam  12 ; and another light beam is the reference beam  16 . When the signal beam  12  and the reference beam  16  are both focused on the storage medium  18 , an interference strip, generated by the signal beam  12  and the reference beam  16 , is formed on the focal point  24 , wherein the interference strip can be regarded as a grating. When only the reference beam  16  emits the storage medium  18 , the data beam  22  is generated and outputted from the extended direction of the signal beam  12 , and the image frame originally presented on the data plane  14  can be read out if the detecting apparatus  20  is placed on the path of the data beam  22 . 
         [0004]    A data-recording process in the holographic storage system  100  includes steps of: converting the original data to an image frame and presenting the image frame on the data plane  14 ; converting a light beam to the signal beam  12  via emitting the light beam to the data plane  14 ; and recording the focal point  24  with an interference strip in the storage medium via focusing the signal beam  12  and the reference beam  16  on the focal point  24 . A data-reading process in the holographic storage system  100  includes steps of: focusing the reference beam  16  on the focal point  24  in the storage medium  18  to generate the data beam  22  outputted from the extended direction of the signal beam  12 ; placing the detecting apparatus  20  on the path of the data beam  22  for presenting the image frame contained in the data beam  22  on the detecting apparatus  20 ; and converting the image frame presented on the detecting apparatus  20  to the original data. 
         [0005]    Generally, the data plane  14  is a SLM (spatial light modulator), wherein the SLM can be a DMD (digital micro-mirror device) or a LCD (liquid crystal display). Both the DMD and the LCD are composed by a plurality of presenting units arranged as an array, and these presenting units with different intensities can present an image frame. In addition, the storage medium  18  is a Photopolymer. The detecting apparatus  20  can be a CCD (charge-coupled device) or a CMOS (complementary metal oxide semiconductor). Both the CCD and the CMOS are also composed by a plurality of sensing units arranged as an array, wherein these sensing units are use for receiving the image frame presented on the resenting units of the data plane  14 . 
         [0006]    A deformation of the storage medium  18  may be happened during the process of data recording, and the deformation may be also happened when the temperature where the storage medium  18  within is varying. The deformation may further result in the vector or the size of the grating recorded in the storage medium change. Therefore, during the process of reading the data recorded in the storage medium  18 , an included angle mat be happened between the data beam  22  and the extended direction of the signal beam  12 . If the detecting apparatus  20  is still placed on the path of the extended direction of the signal beam  12 , a misalignment between the image frame presented on the detecting apparatus  20  and the sensing units will be happened, wherein the misalignment can be regarded as an image-frame shift. A serious image-frame shift may further result in the image frame cannot be restored back to the original data. 
         [0007]      FIG. 2(   a ) depicts a diagram of an original image frame presented on a data plane  14 . Assuming the resolution of the data plane  14  is 2×2, and the data plane  14  includes the presenting units  14   a  and  14   d  with a light state and presenting units  14   b ,  14   c  with a dark state. Moreover, as the depicted in the  FIG. 2(   b ), assuming the resolution of the detecting apparatus  20  is also 2×2, and the detecting apparatus includes the sensing units  20   a  and  20   b ,  20   c , and  20   d.    
         [0008]    If there is no image-frame shift between the image frame presented on the detecting apparatus  20  and the sensing units  20   a ˜ 20   d , each single sensing unit can receive an image generated by each corresponding single presenting unit, which means the images generated by the presenting units  14   a ,  14   b ,  14   c , and  14   d  are received by the sensing units  20   a ,  20   b ,  20   c , and  20   d , respectively. Each sensing unit,  20   a ,  20   b ,  20   c , and  20   d  can output a sensing signal corresponding to the intensity received by each sensing unit. Therefore, the sensing units  20   a ,  20   d  will output a sensing signal representing a light state, and the sensing units  20   b ,  20   c  will output a sensing signal representing a dark state. There is a processing circuit for processing these sensing signals to restore back to the original data. 
         [0009]    However, if a misalignment is happened between the image frame presented on the detecting apparatus  20  and the sensing units  20   a ˜ 20   d , each single sensing unit is not able to receive the image generated by each corresponding presenting unit, respectively. As depicted in  FIG. 2(   c ), there is a misalignment between the image frame  30  and the sensing units  20   a ˜ 20   d , the image with a light state originally presented on the presenting unit  14   a  is received by the sensing units  20   a  and  20   c ; the image with a dark state originally presented on the presenting unit  14   b  is received by the sensing units  20   a ,  20   b ,  20   c , and  20   d ; the image with a dark state originally presented on the presenting unit  14   c  is received by the sensing unit  20   c ; and the image with a light state originally presented on the presenting unit  14   d  is received by the sensing units  20   c  and  20   d , which means the sensing units  20   a ˜ 20   d  within the detecting apparatus  20  may receive images generated from different presenting units at the same time. Because the sensing signal outputted from each sensing unit is determined according to the intensity received by the sensing unit itself, therefore, it is difficult for the processing circuit to process the sensing signals back to the original image frame, which means when the processing circuit process these sensing signals, it is hard to identify these sensing signals are representing light states or dark states. Therefore, reading errors will be happened during the process of image frames converting to the original data. 
         [0010]    The conventional problem, a misalignment between the image frame and the sensing unit, can be fixed by an over-sampling technology, wherein the over-sampling technology is use for providing a detecting apparatus having a higher resolution than the data plane.  FIG. 3  depicts a diagram of a detecting apparatus adopting 3× over-sampling technology. The detecting apparatus  40  uses nine (3×3) sensing units for processing an image generated by a single presenting unit, which means the detecting apparatus  40  with 6×6 resolution is use for the data plane  14  with 2×2 resolution depicted in  FIG. 2(   a ). As depicted in  FIG. 3 , nine sensing units detect one single image, and each of these nine sensing units outputs a sensing signal, and these nine sensing signals are summed by a SUM (summing unit). After these nine sensing signals are summed as a summing signal, the SUM outputs the summing signal to the processing circuit for identifying the original image presented on the presenting unit. 
         [0011]    It is understood that more sensing units use for detecting an intensity generated by a presenting unit, the corresponding summing signal has a higher identification. However, the over-sampling technology may consume more computation power of the processing circuit, so as to reduce the performance of the holographic storage system. Therefore, reaching higher image identification by a lower over-sampling technology is the main purpose of this present invention. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention relates to a holographic storage system, the holographic storage system is use for raising the identifying rate of an image frame by adopting a low over-sampling technology and a gain-controlling unit capable of providing a changeable gain. The present invention relates to a holographic storage system including: a first light beam; a second light beam; a data plane including n presenting units for presenting an image frame, wherein the second light beam is converted to a signal beam containing the image frame after the second light beam is emitted to the data plane, and each presenting unit is capable of outputting a light state or a dark state; a storage medium, wherein the first light beam and the signal beam are both focused on a focal point in the storage medium when the storage medium is use for data recording, and a data beam is generated if only the first light beam is focused on the focal point in the storage medium when the storage medium is use for data reading; a detecting apparatus including m sensing units for receiving the image frames contained in the data beam and each sensing unit is capable of generating a corresponding sensing signal, wherein the m/n is an integer or a rational; m gain-controlling units, connected to the m sensing units, for providing different gains to respectively amplify the corresponding sensing signals outputted from the sensing units; and n SUMs, wherein each SUM is capable of outputting a summing signal which is a sum of partial amplified sensing signals within the m amplified sensing signals. 
         [0013]    In an embodiment, the first light beam and the second light beam are from a laser beam split by a beam splitter. 
         [0014]    In an embodiment, the spatial light modulator can be a digital micro-mirror device or a liquid crystal display 
         [0015]    In an embodiment, the storage medium is a Photopolymer. 
         [0016]    In an embodiment, the detecting apparatus is a charge-coupled device or a complementary metal oxide semiconductor. 
         [0017]    In an embodiment, the n summing signals are use for identifying the images presented on the n corresponding presenting units. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The above contents of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
           [0019]      FIG. 1  is a diagram of a holographic storage system. 
           [0020]      FIG. 2(   a ) is a diagram of an original image frame presented on a data plane. 
           [0021]      FIG. 2(   b ) is a diagram of a detecting apparatus. 
           [0022]      FIG. 2(   c ) is a diagram of a misalignment happened between an image frame and a detecting apparatus. 
           [0023]      FIG. 3  is a diagram of a detecting apparatus adopting a 3× over-sampling technology. 
           [0024]      FIG. 4  is a diagram of a holographic storage system of this present invention. 
           [0025]      FIG. 5(   a ) is a diagram of an image frame presented on a data plane of this present invention. 
           [0026]      FIG. 5(   b ) is a diagram of a detecting apparatus of this present invention. 
           [0027]      FIG. 5(   c ) is a diagram of a misalignment happened between an image frame and a detecting apparatus. 
           [0028]      FIG. 6  is a diagram of a identifying rate resulted from a 2× over-sampling technology adopted with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]      FIG. 4  depicts a holographic storage system of the present invention, wherein the holographic storage system  500  includes a signal beam  52 , a data plane  54 , a reference beam  56 , a storage medium  58 , a data beam  68 , a detecting apparatus  60 , a gain-controlling unit  62 , and a SUM  64 . 
         [0030]    Because a higher over-sampling technology can provide a better resolution, but also consumes more computation power, therefore, a 2× over-sampling technology is adopted in the detecting apparatus  60  of this present invention, so as there are four (2×2) sensing units use for processing an image generated by a single presenting unit. In addition, every sensing signal outputted from each sensing unit is connected to a corresponding gain-controlling unit  62 , and each gain-controlling unit  62  can provide a changeable gain to the sensing signal. The SUM  64  sums the four sensing signals, amplified by the corresponding gain-controlling unit  62 , as a summing signal, and the summing signal is outputted to a processing circuit for further identifying. 
         [0031]      FIG. 5(   a ) depicts an image frame presented on the data plane  54 , wherein the presenting units  54   a  and  54   d  present an image with a light state, and the presenting units  54   b  and  54   c  present an image with a dark state.  FIG. 5(   b ) depicts a diagram of the detecting apparatus  60  of this present invention. There are 16 sensing units  60   a ˜ 60   p  in the detecting apparatus  60 , wherein the sensing signals from the sensing units  60   a ˜ 60   d  are inputted to the four gain-controlling units  62   a ˜ 62   d  and amplified by the four gain-controlling units  62   a ˜ 62   d , respectively, and the four amplified sensing signals are summed as a summing signal and outputted by the SUM  64   a ; the sensing signals from the sensing units  60   e ˜ 60   h  are inputted to the four gain-controlling units  62   e ˜ 62   h  and amplified by the four gain-controlling units  62   e ˜ 62   h , respectively, and the four amplified sensing signals are summed as a summing signal and outputted by the SUM  64   b ; the sensing signals from the sensing units  60   i ˜ 60   l  are inputted to the four gain-controlling units  62   i ˜ 62   l  and amplified by the four gain-controlling units  62   i ˜ 62   l , respectively, and the four amplified sensing signals are summed as a summing signal and outputted by the SUM  64   c ; the sensing signals from the sensing units  60   m ˜ 60   p  are inputted to the four gain-controlling units  62   m ˜ 62   p  and amplified by the four gain-controlling units  62   m ˜ 62   p , respectively, and the four amplified sensing signals are summed as a summing signal and outputted by the SUM  64   d ; and each of the gain-controlling units  62   a ˜ 62   p  can provide different gains. 
         [0032]    When there is a misalignment between the image frame presented on the detecting apparatus  60  and the sensing units  60   a ˜ 60   p , the different gains provides by the gain-controlling units  62   a ˜ 62   p  will be respectively applied to the sensing signals outputted from the sensing units  60   a ˜ 60   p  to make the summing signals outputted from the SUM  64   a ˜ 64   d  are easier to be identified.  FIG. 5(   c ) depicts a misalignment happened when the image frame  70  is presented on the detecting apparatus  60 . For convenience, the gain-controlling units and the SUM are ignored in the  FIG. 5(   c ). For increasing the identification of the images frame presented on the detecting apparatus  60 , the gain-controlling unit  62   c  is designed to provide a gain higher than the gains provided by the gain-controlling units  62   a  and  62   b , and the gain-controlling unit  62   d  is designed to provide a lowest gain, therefore, the processing circuit can have a higher identifying ability to the image presented on the presenting unit  54   a  after the summing signal is outputted from the SUM  64   a ; the gain-controlling unit  62   g  is designed to provide a gain higher than the gains provided by the gain-controlling units  62   e  and  62   h , and the gain-controlling unit  62   f  is designed to provide a lowest gain, therefore, the processing circuit can have a higher identifying ability to the image presented on the presenting unit  54   b  after the summing signal is outputted from the SUM  64   b ; the gain-controlling unit  62   k  is designed to provide a gain higher than the gains provided by the gain-controlling units  62   i  and  62   l , and the gain-controlling unit  62   j  is designed to provide a lowest gain, therefore, the processing circuit can have a higher identifying ability to the image presented on the presenting unit  54   c  after the summing signal is outputted from the SUM  64   c ; the gain-controlling unit  62   o  is designed to provide a gain higher than the gains provided by the gain-controlling units  62   m  and  62   p , and the gain-controlling unit  62   n  is designed to provide a lowest gain, therefore, the processing circuit can have a higher identifying ability to the image presented on the presenting unit  54   d  after the summing signal is outputted from the SUM  64   d.    
         [0033]      FIG. 6  is a diagram of an identifying rate resulted from a 2× over-sampling technology adopted with the present invention, wherein the x-coordinate represents the image-frame shift, and the unit of the x-coordinate is ⅙ sensing-unit length; and the y-coordinate represents the error-data rate. As depicted in the  FIG. 6 , the worst image-frame shift is ½ sensing-unit length. If the image-frame shift is over than ½ sensing-unit length, another a plurality of sensing units can be chosen for making the image-frame shift less than ½ sensing-unit length. For example, if the image frame  70 , depicted in  FIG. 5(   c ), has a right image-frame shift with ⅔ sensing-unit length, the sensing units  60   g ,  60   h ,  60   m , and  60   n  are proper to be chosen for detecting the image presented on a single presenting unit, therefore, the image frame  70  is converted to having a left image-frame shift with ⅓ sensing-unit length. 
         [0034]    As depicted in the  FIG. 6 , the error-data rate is increasing with the value of the image-frame shift (the dotted line) in conventional holographic storage system without the gain-controlling unit; however, the error-data rate is fixed within a range by the gain-controlling unit of the present invention. 
         [0035]    Moreover, the misalignment between the image frame presented on the detecting apparatus and the image frame presented on the data plane is not always horizontal or vertical, the misalignment may result from the image frame is rotated. Under a 2× over-sampling technology, if the image frame is rotated, more than four sensing signals can be chosen for amplified, and these amplified sensing signals are summed as a summing signal for identifying. 
         [0036]    While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.