Method and system for equalizing holographic data pages

Abstract

Methods and systems for equalizing a holographic image page and for compensating nonlinearity of a holographic data storage channel are disclosed. In one embodiment, a method for equalizing a holographic image page includes receiving the holographic image page and dividing the holographic image page into a plurality of local image regions. The method further includes generating a local alignment error vector for each local image region, computing a local finite impulse response kernel for each local image region according to the corresponding local alignment error vector, and adjusting misaligned pixels of each local image region using the corresponding local finite impulse response kernel.

1 .- 36 . (canceled) 
     
     
         37 . A method for compensating nonlinearity of a holographic data storage channel, comprising:
 selecting a metric for measuring data accuracy of a holographic image page;   computing a set of values of the metric over a predetermined set of linearization exponents;   selecting a desired linearization exponent for generating a desired value of the metric, wherein the desired value of the metric corresponds to a desired data accuracy of the holographic image page; and   adjusting the nonlinearity of the holographic data storage channel in accordance with the desired linearization exponent.   
     
     
         38 . The method of  claim 37 , wherein the metric for measuring data accuracy comprises one or more parameters selected from the group consisting of least-squares-error of signal intensity level, signal-to-noise ratio and bit error rate of the holographic image page. 
     
     
         39 . The method of  claim 38 , wherein the step of computing the least-squares-error of signal intensity level comprises:
 generating an expected signal intensity level vector;   measuring an actual signal intensity level vector;   computing a signal intensity deviation between the expected signal intensity level vector and the actual signal intensity level vector, wherein the signal intensity deviation is an absolute value; and   computing the least-squares-error of signal intensity level by taking the ratio of the signal intensity deviation to the expected signal intensity level vector.   
     
     
         40 . The method of  claim 38 , wherein the step of computing the signal-to-noise ratio comprises:
 dividing an actual signal intensity level vector into two groups, wherein a first group has a center pixel value equal to 1 and a second group has a center pixel value equal to 0;   calculating a first mean for the first group and a second mean for the second group;   calculating a first standard deviation for the first group and a second standard deviation for the second group; and   computing the signal-to-noise ratio in accordance with the means and the standard deviations of the first group and the second group respectively.   
     
     
         41 . The method of  claim 40 , wherein the signal-to-noise ratio is computed in response to intersymbol interferences. 
     
     
         42 . The method of  claim 40  further comprises computing the signal-to-noise ratio in accordance with empirical data collected from the holographic image page. 
     
     
         43 . The method of  claim 40  further comprises computing the signal-to-noise ratio in accordance with empirical data collected from a representative optical image system. 
     
     
         44 . The method of  claim 37  further comprises selecting the desired linearization exponent in response to a predetermined bit-error-rate at an output of the holographic data storage channel. 
     
     
         45 . The method of  claim 44 , wherein the predetermined bit-error-rate is determined analytically. 
     
     
         46 . The method of  claim 44 , wherein the predetermined bit-error-rate is determined empirically. 
     
     
         47 . The method of  claim 37 , wherein the step of adjusting comprises applying the desired linearization exponent to each measured pixel of the holographic image page. 
     
     
         48 . A system for compensating nonlinearity of a holographic data storage channel, comprising:
 at least one microprocessor unit for executing computer programs;   a memory for storing an operating system and an application layer;   a light source for providing a coherent beam of light;   a spatial light modulator for encoding the coherent beam of light;   a storage medium for storing an encoded holographic image page;   a detector for reading the encoded holographic image page;   one or more microcontrollers for controlling the spatial light modulator and the detector;   means for selecting a metric for measuring data accuracy of a holographic image page;   means for computing a set of values of the metric over a predetermined set of linearization exponents;   means for selecting a desired linearization exponent for generating a desired value of the metric, wherein the desired value of the metric corresponds to a desired data accuracy of the holographic image page; and   means for adjusting the nonlinearity of the holographic data storage channel in accordance with the desired linearization exponent.   
     
     
         49 . The system of  claim 48 , wherein the metric for measuring data accuracy comprises one or more parameters selected from the group consisting of least-squares-error of signal intensity level, signal-to-noise ratio and bit error rate of the holographic image page. 
     
     
         50 . The system of  claim 49 , wherein the means for computing the least-squares-error of signal intensity level comprise:
 means for generating an expected signal intensity level vector;   means for measuring an actual signal intensity level vector;   means for computing a signal intensity deviation between the expected signal intensity level vector and the actual signal intensity level vector, wherein the signal intensity deviation is an absolute value; and   means for computing the least-squares-error of signal intensity level by taking the ratio of the signal intensity deviation to the expected signal intensity level vector.   
     
     
         51 . The system of  claim 49 , wherein the means for computing the signal-to-noise ratio comprise:
 means for dividing an actual signal intensity level vector into two groups, wherein a first group has a center pixel value equal to 1 and a second group has a center pixel value equal to 0;   means for calculating a first mean for the first group and a second mean for the second group;   means for calculating a first standard deviation for the first group and a second standard deviation for the second group; and   means for computing the signal-to-noise ratio in accordance with the means and the standard deviations of the first group and the second group respectively.   
     
     
         52 . The system of  claim 51 , wherein the signal-to-noise ratio is computed in response to intersymbol interferences. 
     
     
         53 . The system of  claim 51  further comprises means for computing the signal-to-noise ratio in accordance with empirical data collected from the holographic image page. 
     
     
         54 . The system of  claim 51  further comprises means for computing the signal-to-noise ratio in accordance with empirical data collected from a representative optical image system. 
     
     
         55 . The system of  claim 48  further comprises means for selecting the desired linearization exponent in response to a predetermined bit-error-rate at an output of the holographic data storage channel. 
     
     
         56 . The system of  claim 55 , wherein the predetermined bit-error-rate is determined analytically. 
     
     
         57 . The system of  claim 55 , wherein the predetermined bit-error-rate is determined empirically. 
     
     
         58 . The system of  claim 48 , wherein the means for adjusting comprise means for applying the desired linearization exponent to each measured pixel of the holographic image page. 
     
     
         59 . A computer program product, comprising a medium storing programs for execution by one or more computer systems, the computer program product comprising:
 a linearization module for compensating nonlinearity of a holographic data storage channel, wherein the linearization module is used in conjunction with at least a microprocessor unit, a memory, a light source, a spatial light modulator, a storage medium, a detector, and one or more microcontrollers, and the linearization module includes one or more computer programs containing instructions for:   selecting a metric for measuring data accuracy of a holographic image page;   computing a set of values of the metric over a predetermined set of linearization exponents;   selecting a desired linearization exponent for generating a desired value of the metric, wherein the desired value of the metric corresponds to a desired data accuracy of the holographic image page; and   adjusting the nonlinearity of the holographic data storage channel in accordance with the desired linearization exponent.   
     
     
         60 . The computer program product of  claim 59 , wherein the metric for measuring data accuracy comprises one or more parameters selected from the group consisting of least-squares-error of signal intensity level, signal-to-noise ratio and bit error rate of the holographic image page. 
     
     
         61 . The computer program product of  claim 60 , wherein the instructions for computing the least-squares-error of signal intensity level comprise:
 generating an expected signal intensity level vector;   measuring an actual signal intensity level vector;   computing a signal intensity deviation between the expected signal intensity level vector and the actual signal intensity level vector, wherein the signal intensity deviation is an absolute value; and   computing the least-squares-error of signal intensity level by taking the ratio of the signal intensity deviation to the expected signal intensity level vector.   
     
     
         62 . The computer program product of  claim 60 , wherein the instructions for computing the signal-to-noise ratio comprise:
 dividing an actual signal intensity level vector into two groups, wherein a first group has a center pixel value equal to 1 and a second group has a center pixel value equal to 0;   calculating a first mean for the first group and a second mean for the second group;   calculating a first standard deviation for the first group and a second standard deviation for the second group; and   computing the signal-to-noise ratio in accordance with the means and the standard deviations of the first group and the second group respectively.   
     
     
         63 . The computer program product of  claim 62 , wherein the signal-to-noise ratio is computed in response to intersymbol interferences. 
     
     
         64 . The computer program product of  claim 62  further comprises instructions for computing the signal-to-noise ratio in accordance with empirical data collected from the holographic image page. 
     
     
         65 . The computer program product of  claim 62  further comprises instructions for computing the signal-to-noise ratio in accordance with empirical data collected from a representative optical image system. 
     
     
         66 . The computer program product of  claim 59  further comprises instructions for selecting the desired linearization exponent in response to a predetermined bit-error-rate at an output of the holographic data storage channel. 
     
     
         67 . The computer program product of  claim 66 , wherein the predetermined bit-error-rate is determined analytically. 
     
     
         68 . The computer program product of  claim 66 , wherein the predetermined bit-error-rate is determined empirically. 
     
     
         69 . The computer program product of  claim 59 , wherein the instructions for adjusting comprise applying the desired linearization exponent to each measured pixel of the holographic image page. 
     
     
         70 . A method for equalizing a holographic image page, comprising:
 receiving the holographic image page;   dividing the holographic image page into a plurality of image regions;   deriving an expected blur and an actual blur for each image region;   computing a pixel-signal-error-ratio between the actual blur and the expected blur for each image region;   computing a local finite impulse response kernel in accordance with the pixel-signal-error-ratio and a predetermined global final impulse response; and   adjusting pixels of each local image region using the corresponding local finite impulse response kernel.   
     
     
         71 . The method of  claim 70 , wherein the step of deriving the expected blur and the actual blur comprises:
 generating a covariance matrix comprising cross-correlation information between a measured image pattern and a corresponding known image pattern, wherein the covariance matrix represents the local pixel spread function;   deriving a first pixel signal error factor from the local pixel spread function, wherein the first pixel signal error factor is a ratio of signal landed in the intended pixel location to signal landed in the neighboring pixel locations; and   deriving a second pixel signal error factor from a global pixel spread function of the holographic image page, wherein the second pixel signal error factor is a ratio of signal landed in the intended pixel location to signal landed in the neighboring pixel locations.   
     
     
         72 . The method of  claim 71 , wherein the step of computing pixel-signal-error-ratio comprises dividing the first pixel signal error factor by the second pixel signal error factor. 
     
     
         73 . The method of  claim 71 , wherein the region of the measured image pattern is the nearest neighbors immediately above, below, to the left and to the right of the center pixel of interest. 
     
     
         74 . The method of  claim 71 , further comprising:
 equalizing the local pixel spread function in accordance with the pixel-signal-error-ratio; and   determining a local finite impulse response function in accordance with a predetermined linear transformation mechanism.   
     
     
         75 . The method of  claim 74 , wherein the predetermined linear transformation mechanism comprises a method selected from the group consisting of zero forcing method and linear minimum mean-squared-error method. 
     
     
         76 . The method of  claim 74  further comprising:
 equalizing the local pixel spread function in accordance with a scaled pixel-signal-error-ratio, wherein the range of the scale is a predetermined value between 0 and 1.