CN101625874B - Multi-gray scale holographic storage method - Google Patents

Abstract

The present invention relates to a multi-gray scale volume holographic storage method which comprises the following steps: (1) selecting the information to be stored of K+1 gray scales and a volume holographic storage system with a binary space modulator, wherein K is larger than 1; (2) resolving a multi-gray scale matrix corresponding to the information to be stored of K+1 gray scales into the accumulation of a series of binary gray scale matrixes; (3) selecting and fixing all parameters of reference light; (4) dividing the illumination time of object light into K time section sequences; (5) respectively uploading different two-dimensional information pages with two-gray scale distribution on each time section by the binary space light modulator to form the object light and recording a series of holograms in a storage medium by the object light and selected reference light; and (6) accumulating the holograms obtained and recorded in the step (5) by the selected reference light to reproduce and obtain a two-dimensional information page in the same distribution with the information to be stored of the K+1 gray scales in the step (1). The multi-gray scale volume holographic storage method provided by the present invention not only improves the storage density, the transmission rate and the information uploading speed of the volume holographic storage system but also saves the cost, and has wide application prospect in the fields of computer data storage, database backup, movie image storage, and the like.

Description

A kind of multi-gray scale volume holographic storage method

Technical field

The present invention relates to a kind of volume holographic storage method, particularly about a kind of multi-gray scale volume holographic storage method.

Background technology

As shown in Figure 1, in the holographic memory light path, spatial modulator (SLM) 2 is positioned on the front focal plane of the preceding group 4 of fourier transform lens, thing light 1 obtains thing light 3 after modulating by spatial modulator 2, thing light 3 forms corresponding fourier transform spectrum 5 through group before the fourier transform lens 4 again, fourier transform spectrum 5 interferes on storage medium 7 with reference light 6, and this interference pattern forms hologram, is recorded on the storage medium 7.When independent employing reference light 6 irradiation storage mediums 7, be stored light field 8 that the hologram diffraction of storage on the medium 7 goes out through group 9 behind the fourier transform lenses after, on the detector 10 at the back focal plane place of group 9 behind the fourier transform lens, reproduce thing light 1.On record and reproduction effect, the front focal plane of group 4 is equivalent to object plane before the fourier transform lens, and the back focal plane of group 9 is equivalent to the picture plane behind the fourier transform lens.

Spatial light modulator 2 can be loaded as various forms of information the dimensional information pages of object plane, the input block of constituting body holographic memory.That is to say that the directional light behind the collimation is a thing light 1, after the pel array modulation through spatial light modulator 2, the optical field distribution of outgoing has just formed and the corresponding dimensional information pages of spatial light modulator 2 pel arrays, and just thing light 3.This dimensional information pages can be corresponding to an entire image of storage, also can be the page that becomes according to certain series arrangement by the represented data of each pixel (usually the intensity of pixel is represented the size of data), even can be to wait the page distribution of handling the 2-D data that the back forms through coding.

The two-value spatial light modulator is as the entering apparatus of extensive employing in the hologram memory system, and it has manufacturing, it is simple, cheap to use, the advantage that the information page upload rate is fast.But, the two-value spatial light modulator is to control the intensity of transmission/reflection light field by the state that changes each pixel, and each pixel only exists light tight/not reflective (OFF) and printing opacity/reflective (ON) two states (or two GTGs), that is to say, the two-value spatial light modulator can only be stored the dimensional information pages of two gray level information, and can't store the dimensional information pages of a plurality of gray level information.

So, many GTGs spatial modulator of the dimensional information pages of a plurality of gray level information has appearred expressing.Yet, many GTGs spatial modulator is compared with the two-value spatial light modulator, and it has some defectives of self, is difficult to distinguish each GTG such as the not high detector that causes 10 of the linearity, contrast is not high to make that the data signal to noise ratio (S/N ratio) of record is not high on the storage medium 7, and upload pictures speed waits slowly.

Summary of the invention

At the problems referred to above, the purpose of this invention is to provide a kind of employing two-value spatial modulator and realize multi-gray scale volume holographic storage method.

For achieving the above object, the present invention takes following technical scheme: a kind of multi-gray scale volume holographic storage method, and it may further comprise the steps:

1) body hologram memory system of the information to be stored and one of a selected K+1 GTG with two-value spatial modulator, K is greater than 1 and be integer;

2) the many GTGs matrix decomposition with the information correspondence to be stored of K+1 GTG is adding up of a series of two-value GTG matrixes;

3) selected also each parameter constant of fixed reference light;

4) light-struck time of thing is divided into K time period sequence, is specially:

K time period sequence is respectively T _E1, T _E2..., T _Ek..., T _EK,

T _E1＝Δt，

${\mathrm{<figure-callout\; id="2"\; label="T\; E"\; filenames="H2009100904113E00011.png,H2009100904113E00012.png"\; state="\{\{state\}\}">T</figure-callout>}}_E=(\sqrt{2}-1)\mathrm{\&Delta;t},$

$T_{\mathrm{Ek}}=(\sqrt{k}-\sqrt{k-1})\mathrm{\&Delta;t},$

$T_{\mathrm{EK}}=(\sqrt{K}-\sqrt{K-1})\mathrm{\&Delta;t}.$

Wherein Δ t is a set time unit of setting according to the response characteristic of storage medium and detector; 1＜2＜...＜k＜... K;

5) on each time period, upload different dimensional information pages with the two-value spatial light modulator respectively, constitute thing light, and in storage medium, write down a series of hologram, be specially with this thing light and selected reference light with two gray-scale distribution:

(1) at time period T _E1In, the two-value spatial light modulator is uploaded the two-value GTG matrix A of a width of cloth dimensional information pages correspondence ₁Element a _1mnDetermine by following formula:

(2) at time period T _E2In, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth ₂Element a _2mnDetermine by following formula:

(k) at k time period T _EkIn, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth _kElement a _KmnDetermine by following formula:

(K) time period T in the end _EKIn, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth _KElement a _KmnDetermine by following formula:

Wherein, the GTG value that K+1 GTG information to be stored comprises is respectively integer 0,1,2 ..., k ..., K, the element in its corresponding GTG matrix A is a _Mn, and a _MnSpan be integer in the GTG value;

6) utilize selected reference light that a series of hologram that record in the step 5) obtains is added up, reproduce draw one with step 1) in the identical dimensional information pages of information distribution to be stored of K+1 GTG.

The present invention has following technological merit: 1, because the inventive method is with the pairing many GTGs matrix of information to be stored, be decomposed into adding up of a series of two-value GTG matrixes, in recording process, each parameter constant of fixed reference light, time with record is divided into a series of continuous time periods according to certain rule simultaneously, on each time period, upload the different dimensional information pages that two-value intensity (two GTGs) distributes that has with the two-value spatial light modulator respectively, constitute thing light, and in storage medium, store a series of hologram with this thing light and reference light, again by appropriate design time period sequence and the corresponding dimensional information pages sequence of uploading, when make reproducing behind the used reference light and these a series of hologram accumulative actions, draw a dimensional information pages, its intensity distributions situation is with consistent with the pairing many GTGs matrix of information to be stored, so dimensional information pages contrast height that reveals again, the signal to noise ratio (S/N ratio) height, and cost is low, is fit to apply.2, do not need original body hologram memory system structure and light path are made any modification owing to the inventive method, only pass through the reasonably optimizing of sequence storage time, just can make reproduction dimensional information pages gray-scale distribution and when storage the specified matrix correspondence that comprises many gray level information, simple to operate, the storage density height, transfer rate is fast, and upload speed is fast, and implementation result is remarkable.The present invention can be used for mass data storage and the storage of magnanimity gray level image, has wide practical use in fields such as computer data storage, DB Backup, video image storages.

Description of drawings

Fig. 1 is the principle schematic of holographic memory light path

Fig. 2 is a principle schematic of the present invention

Fig. 3 is a GTG matrix and a dimensional information pages synoptic diagram of uploading and reproducing of information correspondence to be stored

Fig. 4 is the image that the two-value spatial light modulator is uploaded and revealed in Fig. 3 recording process

Fig. 5 is that the two-value spatial light modulator receives gray distribution of image in Fig. 3 recording process

Embodiment

Below in conjunction with drawings and Examples, the inventive method is described in detail.

As shown in Figure 2, the inventive method may further comprise the steps:

1) body hologram memory system of the information to be stored and one of the selected individual GTG of a K+1 (K is greater than 1) with two-value spatial modulator: the GTG value that K+1 GTG information to be stored comprises is respectively integer 0,1,2,, k ... K, its corresponding GTG matrix is A, the element in the GTG matrix A is a _Mn, and a _MnSpan be integer in the GTG value.

2) the many GTGs matrix decomposition with the information correspondence to be stored of K+1 GTG is adding up of a series of two-value GTG matrixes.

3) selected and fix the reference light 6 of a complex amplitude R, and each parameter of reference light 6 remains constant in subsequently record and reproduction process.Because the reproduction of volume hologram is very responsive to parameters such as the angle of reference light 6, wavelength.

4) with the time of thing light 1 irradiation, promptly be divided into K time period sequence T writing time _E1, T _E2..., T _Ek..., T _EK, wherein

T _E1＝Δt，

${\mathrm{<figure-callout\; id="2"\; label="T\; E"\; filenames="H2009100904113E00011.png,H2009100904113E00012.png"\; state="\{\{state\}\}">T</figure-callout>}}_E=(\sqrt{2}-1)\mathrm{\&Delta;t},$

$T_{\mathrm{Ek}}=(\sqrt{k}-\sqrt{k-1})\mathrm{\&Delta;t},$

$T_{\mathrm{EK}}=(\sqrt{K}-\sqrt{K-1})\mathrm{\&Delta;t}.$

Wherein Δ t be one regular time the unit, its value should guarantee the response of storage medium 7 within its dynamic range, the response of detector 10 also is in the linear zone in the reproduction process simultaneously.

5) opening entry is uploaded the different dimensional information pages with two gray-scale distribution with the two-value spatial light modulator respectively on each time period, constitute thing light 1, and writes down a series of hologram with this thing light and selected reference light 6 in storage medium 7:

(1) first time period T of record _E1In, the two-value spatial light modulator is uploaded a width of cloth dimensional information pages, the two-value GTG matrix A that it is corresponding ₁Element a _1mnDetermine by following formula:

(2) second time period T of record _E2In, the two-value spatial light modulator is uploaded the new dimensional information pages of a width of cloth, the two-value GTG matrix A that it is corresponding ₂Element a _2mnDetermine by following formula:

(k) k the time period T of record _EkIn, the two-value spatial light modulator is uploaded the new dimensional information pages of a width of cloth, the two-value GTG matrix A that it is corresponding _kElement a _KmnDetermine by following formula:

(K) the final time section T of record _EKIn, the two-value spatial light modulator is uploaded the new dimensional information pages of a width of cloth, the two-value GTG matrix A that it is corresponding _KElement a _KmnDetermine by following formula:

6) close the two-value spatial light modulator, only with reference light 6 irradiation storage mediums 7, a series of hologram that record in the step 5) is obtained adds up, just the dimensional information pages that contains K+1 gray level information that can be revealed again on detector 10.

In above-mentioned steps 5) in, each time period T _EkOrder can upset arbitrarily, as long as guarantee to load the corresponding two-value GTG matrix A that is distributed as _kData page.

As shown in Figure 3, by a specific embodiment the inventive method is further set forth below.

11 is the pairing GTG matrix A of gray level information to be stored among Fig. 3, and it is 2 * 2 square formations of a low dimension, comprises grey-scale range between 0～3, i.e. K=3.Adopt the inventive method among the figure in 11 the gray level information to be stored of GTG matrix A correspondence carry out record, its step is as follows:

1) will be divided into 3 time period sequence T writing time _E1, T _E2, T _E3, wherein

T _E1＝Δt，

${\mathrm{<figure-callout\; id="2"\; label="T\; E"\; filenames="H2009100904113E00011.png,H2009100904113E00012.png"\; state="\{\{state\}\}">T</figure-callout>}}_E=(\sqrt{2}-1)\mathrm{\&Delta;t},$

${\mathrm{<figure-callout\; id="3"\; label="T\; E"\; filenames="H2009100904113E00011.png,H2009100904113E00012.png"\; state="\{\{state\}\}">T</figure-callout>}}_E=(\sqrt{3}-\sqrt{2})\mathrm{\&Delta;t}.$

Wherein Δ t be one regular time the unit.

2) reference light 6 of a selected complex amplitude R, and in subsequently record and reproduction process, remain constant.

3) opening entry is at first storage time of section T _E1In, the two-value spatial light modulator is uploaded a width of cloth dimensional information pages, and this dimensional information pages is corresponding to two-value GTG matrix A ₁(shown among Fig. 3 12), the black box among Fig. 3 in 12 represents that the pixel of two-value spatial light modulator is in the OFF state; Beat the grid of oblique line and represent that the pixel of two-value spatial light modulator is in the ON state of brightness constancy, its corresponding complex amplitude is Am.

4) at second recording period T _E2In, the two-value spatial light modulator is uploaded the new dimensional information pages of a width of cloth, and this dimensional information pages is corresponding to two-value GTG matrix A ₂(shown among Fig. 3 13).

5) the final time section T of record _E3In, the two-value spatial light modulator is uploaded the new dimensional information pages of a width of cloth, and this dimensional information pages is corresponding to two-value GTG matrix A ₃(shown among Fig. 3 14).

6) close the two-value spatial light modulator, only with reference light 6 irradiation storage mediums 7, the dimensional information pages that contains 4 GTGs that can be revealed again at detector 10 just.This dimensional information pages and GTG matrix A ' (shown among Fig. 3 15) corresponding, each grid internal oblique line density in the dimensional information pages is big more, the complex amplitude of expression correspondence is more little, it is different relatively that grid oblique line density difference only represents to reproduce the complex amplitude of pixel of dimensional information pages inside, do not represent the dimensional information pages in 15 and 12,13,14 the pixel complex amplitude between size, therefore A ' and A are identical, promptly utilize the two-value spatial modulator successfully to realize the many gray level information of storage.

The experimental result of the foregoing description is shown in Fig. 4～5.Among Fig. 4 16,17,18 is three width of cloth images that the two-value spatial light modulator is uploaded in the recording process, is respectively writing time 20 seconds, 8.3 seconds, 6.3 seconds.The image that among Fig. 4 19 receives for detector 10 in the reproduction process, circular fringes among the figure and speck are that the noise in the light path causes.Fig. 5 is 4 area grayscale mean values of 19 in the corresponding diagram 4, is respectively 9.5,54.4,100.8,132.9, and corresponding to input GTG 0,1,2,3, its linearly dependent coefficient is 0.9969, and is consistent with the input gray-scale distribution.

Below by theoretical derivation, verify the storage effect of the inventive method:

Usually, in the holographic memory light path, if forward and backward group 5 of the characteristic of storage medium 7 and fourier transform lens, components and parts such as 9 are all definite, use the two-value spatial light modulator to upload a width of cloth dimensional information pages, and record, each key physical amount of reproducing are provided by formula (1) and (2):

$S\&Proportional;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}(a_{\mathrm{mn}}\&times;\mathrm{Am})\mathrm{rect}\left(\frac{x-(n-1)p-x_0}{p}\right)\mathrm{rect}\left(\frac{y-(m-1)p-y_0}{p}\right)---\left(1\right)$

$S^{\&prime;}\&Proportional;c\left(R^{*}R\right)t_E\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}(a_{\mathrm{mn}}\&times;\mathrm{Am})\mathrm{rect}\left(\frac{x^{\&prime;}+(n-1)p+x_0}{p}\right)\mathrm{rect}\left(\frac{y^{\&prime;}+(m-1)p+y_0}{p}\right)---\left(2\right)$

Wherein, S is the COMPLEX AMPLITUDE of the dimensional information pages to be stored on the object plane, and S ' then is the COMPLEX AMPLITUDE as the dimensional information pages that reveals again on the plane; The number of pixels of two-value spatial light modulator is M * N, and Pixel Dimensions is p, and Am is in the pairing complex amplitude of ON state for the two-value spatial light modulator pixel; Rectangular coordinate system on the object plane is an initial point with the intersection point of object plane and optical axis, the positive dirction of x axle and y axle to the right, the positive dirction of x ' axle and y ' axle is (as shown in Figure 1) upwards; (x ₀, y ₀) be the coordinate of the geometric center of the lower left corner of dimensional information pages pixel; R is the complex amplitude of plane wave reference light, R ^*The complex conjugate of expression reference light complex amplitude; C is the change coefficient of storage medium 7 complex amplitude transmitances due to the unit exposure amount, by factor decisions such as the light intensity of the characteristic of storage medium 7 itself, storage and storage times; t _EThe time shutter of this dimensional information pages of expression storage.a _MnBe the element of the GTG matrix A corresponding, for two value informations, a with dimensional information pages complex amplitude to be stored _MnValue has only 1 or 0 two GTG.As seen, dimensional information pages that reveals again and former dimensional information pages pixel gray level value are corresponding one by one, and have two GTGs.

According to the inventive method, correlation formula (1) and (2) according to using two-value spatial light modulator record and reproducing draw at time period T _EkIn upload the corresponding two-value GTG of width of cloth matrix A _kDimensional information pages, the complex amplitude S that contributes in the dimensional information pages that finally reveals again _k' be:

${S_k}^{\&prime;}\&Proportional;T_{\mathrm{Ek}}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}(a_{\mathrm{kmn}}\&times;\mathrm{Am})\mathrm{rect}\left(\frac{x^{\&prime;}+(n-1)p+x_0}{p}\right)\mathrm{rect}\left(\frac{y^{\&prime;}+(m-1)p+y_0}{p}\right)$

Contrast (2) formula, in the present embodiment, because reference light 6 is constant all the time, and c is constant, therefore the two relevant proportionality constant can be ignored with this.

After the dimensional information pages sequence with a series of correspondences of certain period of time sequential recording in the present embodiment, the complex amplitude S ' of the reproduction dimensional information pages that the reproduction effect after each hologram stack is just final is:

$S^{\&prime;}=\underset{k=1}{\overset{K}{\mathrm{\&Sigma;}}}{S_k}^{\&prime;}$

$\&Proportional;\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}[\left(\underset{k=1}{\overset{K}{\mathrm{\&Sigma;}}}{T}_{\mathrm{Ek}}{a}_{\mathrm{kmn}}\right)\&times;\mathrm{Am}]\mathrm{rect}\left(\frac{x^{\&prime;}+(n-1)p+x_0}{p}\right)\mathrm{rect}\left(\frac{y^{\&prime;}+(m-1)p+y_0}{p}\right)$

Wherein, if the corresponding GTG matrix A of information to be stored, its general element GTG is a _Mn, then, obtain and a according to the section sequence and corresponding two-value dimensional information pages sequence storage time in this example _MnThe corresponding coefficient of location of pixels of living in is:

$\underset{k=1}{\overset{K}{\mathrm{\&Sigma;}}}{T}_{\mathrm{Ek}}{a}_{\mathrm{kmn}}=\underset{k=1}{\overset{a_{\mathrm{mn}}}{\mathrm{\&Sigma;}}}{T}_{\mathrm{Ek}}{a}_{\mathrm{kmn}}+\underset{k=a_{\mathrm{mn}}+1}{\overset{K}{\mathrm{\&Sigma;}}}{T}_{\mathrm{Ek}}{a}_{\mathrm{kmn}}=\underset{k=1}{\overset{a_{\mathrm{mn}}}{\mathrm{\&Sigma;}}}{T}_{\mathrm{Ek}}+0=\sqrt{a_{\mathrm{mn}}}\mathrm{\&Delta;t}$

Therefore, the final expression of results of reproduction dimensional information pages complex amplitude is:

$S^{\&prime;}\&Proportional;\mathrm{\&Delta;t}\underset{m=1}{\overset{M}{\mathrm{\&Sigma;}}}\underset{n=1}{\overset{N}{\mathrm{\&Sigma;}}}(\sqrt{a_{\mathrm{mn}}}\&times;\mathrm{Am})\mathrm{rect}\left(\frac{x^{\&prime;}+(n-1)p+x_0}{p}\right)\mathrm{rect}\left(\frac{y^{\&prime;}+(m-1)p+y_0}{p}\right)$

Then for the intensity of each pixel of dimensional information pages (mould of the complex amplitude square) regularity of distribution then just in time with the pixel a of GTG matrix A to be stored _MnCorresponding one by one, just reached the purpose that GTG is stored.

Claims (1)

1. multi-gray scale volume holographic storage method, it may further comprise the steps:

1) body hologram memory system of the information to be stored and one of a selected K+1 GTG with two-value spatial modulator, K is greater than 1 and be integer;

2) the many GTGs matrix decomposition with the information correspondence to be stored of K+1 GTG is adding up of a series of two-value GTG matrixes;

3) selected also each parameter constant of fixed reference light;

4) light-struck time of thing is divided into K time period sequence, is specially:

K time period sequence is respectively T _E1, T _E2..., T _Ek..., T _EK,

T _E1＝Δt，

$T_{E2}=(\sqrt{2}-1)\mathrm{\&Delta;t},$

...

$T_{\mathrm{Ek}}=(\sqrt{k}-\sqrt{k-1})\mathrm{\&Delta;t},$

...

$T_{\mathrm{EK}}=(\sqrt{K}-\sqrt{K-1})\mathrm{\&Delta;t}.$

Wherein Δ t is a set time unit of setting according to the response characteristic of storage medium and detector; 1＜2＜...＜k＜... K;

5) on each time period, upload different dimensional information pages with the two-value spatial light modulator respectively, constitute thing light, and in storage medium, write down a series of hologram, be specially with this thing light and selected reference light with two gray-scale distribution:

(1) at time period T _E1In, the two-value spatial light modulator is uploaded the two-value GTG matrix A of a width of cloth dimensional information pages correspondence ₁Element a _1mnDetermine by following formula:

(2) at time period T _E2In, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth ₂Element a _2mnDetermine by following formula:

...

(k) at k time period T _EkIn, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth _kElement a _KmnDetermine by following formula:

...

(K) time period T in the end _EKIn, the two-value spatial light modulator is uploaded the two-value GTG matrix A of the new dimensional information pages correspondence of a width of cloth _KElement a _KmnDetermine by following formula:

Wherein, the GTG value that K+1 GTG information to be stored comprises is respectively integer 0,1,2 ..., k ..., K, the element in its corresponding GTG matrix A is a _Mn, and a _MnSpan be integer in the GTG value;

6) utilize selected reference light that a series of hologram that record in the step 5) obtains is added up, reproduce draw one with step 1) in the identical dimensional information pages of information distribution to be stored of K+1 GTG.

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