KR20000001661A - Data recording/reproducing method of holographic storage device - Google Patents

Abstract

PURPOSE: A data recording/reproducing method of a holographic storage device is provided to improve data processing speed. CONSTITUTION: The data recording/reproducing is made in the process; after separating each pick cell of the information element into plural groups of pick cells, the pick cells in the group are divided into a dummy pick cell which is indicated black at all times and the data pick cells which are indicated white or black depending upon the nature of the information; inputting reproduced pick cell images in the photo detector after reproducing the above hologram.

Description

Data recording / playback method of holographic storage device

The present invention relates to a data recording / reproducing method of a holographic storage device. Specifically, a holo that enables high-speed playback in a simple manner while preventing information loss due to distortion of an image generated during the reproduction of holographic information. A data recording / reproducing method of a graphics storage device.

Recently, as a high-speed, high-density recording technology capable of a storage capacity of more than 1 terabyte and a transmission speed of 1 Gbyte / sec, research on the storage device using the principle of holographic has been intensively performed.

As shown in FIG. 1, a holographic storage device generally includes a laser 1 as a light source, a beam splitter 3 for splitting incident light into two lights traveling in different directions, and a direction of incident light. Reflector 8, 9, SLM (Spatial Light Modulator) 6 for modulating the light intensity distribution of the incident laser light, FT lenses 10, 13 for Fourier Transform the incident light, holograms are recorded. The recording medium 11 and the CCD array 14 for reading out the reproduced information.

SLM 6 is composed of a set of unit pixels 50 arranged in a two-dimensional grid form, as shown in Figure 2-a, each pixel 'on' state and incident light that can pass incident light It can have an 'off' state that blocks it.

Since the state of each pixel can be adjusted by the SLM controller 7 connected to the SLM 6, if the 'on' state of the pixel corresponds to '1' and the 'off' state corresponds to '0', each pixel One bit of information can be represented and the SLM 6 can display any binary data arranged two-dimensionally.

In other words, the SLM displays certain binary data in the form of a two-dimensional image.

When the laser light 4 enters the SLM 6, the light amount is modulated to proceed with the image information displayed on the SLM 6.

The CCD array 14 is composed of an array of pixels 18. Each pixel 18 is arranged in a grid like the SLM pixels, and a signal generated from the CCD array 14 is transmitted to the signal processing device 15. It is supposed to be input.

In the above configuration, the process of recording information among operating principles of the holographic storage device is as follows.

That is, the laser light 2 generated by the laser 1 enters the beam splitter 3 and is separated into the object light 4 and the reference light 5.

The object light 4 is incident on the SLM 6 and the light quantity distribution is modulated to proceed with the constant image information 16. The laser light via the SLM 6 is Fourier transformed by the FT lens 10. It enters the recording medium 11 with the image information 16 '.

On the other hand, the reference light 5 enters the recording medium 11 by changing the traveling direction by the reflecting mirrors 8 and 9. At this time, the reference light 5 and the object light 4 containing the image information cause interference in the recording medium 11, and the interference fringe is recorded in the recording medium 11.

The reproduction process of the hologram recorded by the above process is as follows.

The object light 4 separated by the beam splitter 3 and the object light 4 of the reference light 5 are blocked using a shutter or the like not shown in the drawing. At this time, only the reference light 5 is incident on the recording medium 11, and the reproduction light 12 is generated by the principle of diffraction, passes through the FT lens 13, and enters the CCD array 14.

In accordance with the principle of holography, the reproduction light 12 has all of the image information 16 'that the original object light 4 had. Therefore, when the inverse Fourier transform is performed by the FT lens 13, it is displayed on the SLM 6 at the time of recording. The same image information 16 as the binary data is reproduced and incident on the CCD array 14.

Each pixel 18 of the CCD array 14 converts an optical signal according to an incident image into an electrical signal and sends the signal to the signal processing device 15 to process information. The displayed information can be played back.

2-A and 2-B, the SLM pixels 50 and the CCD pixels 18 correspond to one-to-one in a grid form, i.e., a constant rectangular pixel arrangement.

For example, the pixels 50, 51, 52, and 53 of the SLM shown in Figs. 2-A are adapted to correspond to the pixels 18, 19, 20, and 21 of the CCD array of Fig. 2-B, respectively. As shown in FIG. 3, the SLM images 54, 55, 56, and 67 corresponding to the pixels 50, 51, 52, and 53 of the SLM are respectively arranged in the CCD array pixels 18, 19, 20, and 21, respectively. Will be entered.

The FT lenses 10 and 13, which are actually used in the holographic storage device having the above structure, inevitably generate image distortion due to manufacturing error and the characteristics of the lens itself, and also the difference in partial refractive index distribution of the recording medium 11 is also image distortion. Generates.

As shown in FIG. 3, the position of the CCD array pixel 18 and the image 54 of the SLM pixel corresponding thereto is not completely matched and has a certain amount of offset.

In this case, the image 54 of the SLM pixel enters the region of the adjacent CCD pixels 19, 20, and 21.

For example, the SLM reproduced through the reproduction process in the case where the originally recorded binary data is in a state in which the pixel 50 of the SLM is '1' and the pixels 51, 52, and 53 of the SLM are '0'. The image 54 of the pixel 50 has a light quantity of '1' and the images 55, 56 and 57 of the pixels 51, 52 and 53 enter the CCD with a light quantity of '0'.

S18 is a signal generated from the CCD pixel 18, and S19, S20, and S21 are signals generated from the CCD pixels 19, 20, and 21, respectively. If there is no offset, that is, no position error, S18 = 1, S19 = S20 = S21 = 0 generates a signal.

If a distortion occurs in the reproduced image, a portion of the image 54 to be incident on the CCD pixel is incident on the CCD pixels 19, 20, 21, and so on. In the state of 0, an error signal is generated in S20 and the like.

As shown in FIG. 3, the distance between the center point P1 of the CCD pixel 18 and the center point P2 of the image 54 of the SLM pixel is called D1, and the distance between each pixel of the CCD array 14 is D2. The error signal depends on the degree of offset, that is, the relationship between D1 and D2.

For example, if the image 54 of the SLM pixel is moved to the right side of the drawing and enters the region of the CCD pixel 18 and becomes D1> D2 / 2, then S18 <S19, in which case S18 = '0 ', S19 =' 1 'is recognized so that the original data is not played properly.

Conventional methods for preventing such data errors include the methods proposed in US Pat. Nos. 5,511,058 and 5694488 shown in FIGS. 4 (a), (b) and 5 (a) to (c).

That is, all the pixels of the CCD 14 are divided into groups consisting of a certain number of pixels. 4A illustrates the CCD pixel group 65. The pixels 60, 61, and 62 are reference pixels allocated for position error measurement, and the CCD pixels 63, 64 and the like receive the recorded information. The pixels 60 to 64 form one pixel group 65 as data pixels.

As shown in FIG. 4B, the image group 71 is formed of the pixels 66 to 70 of the SLM 6 corresponding to the CCD pixels 63 and 65, and the pixels (of the pixel group 71) 66, 67, and 68 are pixels allocated for position error measurement, and pixels 69 and 70 are pixels allocated for information reproduction.

Each pixel 60 to 64 of the CCD pixel group 65 and each pixel 66 to 70 of the image group 71 have a one-to-one correspondence relationship.

That is, during reproduction, the image 67 'of the pixel 67 is incident on the pixel 61 of the CCD, and the remaining pixels 66, 68, 69, and 70 are also incident on the pixel 60, 62, 63, 64 of the CCD. Do it.

Pixel 67 always generates a signal of '1' and pixels 66 and 68 always generate a signal of '0'. The pixels 69 and 70 may have a state of '1' or '0' depending on the content of information to be stored.

As shown in Fig. 5A, when there is no error, the signals S60, S61, and S62 generated by the CCD pixels 60, 61, 62, etc. become S61 = 1, S60 = 0, S62 = 0.

However, as shown in Fig. 5B, when the image 67 'and the like of the pixel 67 are moved to the right, for example, signals S61 = 0.9 S60 = 0, S62 = 0.1 are generated.

On the contrary, as shown in FIG. 5C, when the image 67 'of the pixel 67 is moved to the left, signals S60 = 0.1, S61 = 0.9, and S62 = 0 are generated.

Therefore, by comparing the signals generated in the reference pixels 60, 61, 62, etc. belonging to the CCD pixel group 65 with each other, the degree of error in the left and right directions can be grasped in the direction of the light error.

In addition, when the pixels 61 in the vertical direction of the pixel 61 are included in the CCD pixel group 65, the vertical errors may be detected in a similar manner. That is, since the magnitude and direction of the error occurring in the region of the specific CCD pixel group 65 can be calculated, the original signal incident on the data pixels 63 and 64 can be restored using the same.

However, the above conventional technology has the following problems.

First, since the magnitude of the error and its rate of change over the entire area of the CCD array 14 vary depending on the part, the reference pixels 60, 61, 62 and the data pixels 63, The magnitude of the error occurring in 64) may vary, so that an error occurs in the restored signal. In order to restore the information, a series of calculations should be performed using signals generated in all pixels of all groups of the CCD array 14. As a result, the computational process is complicated, which inevitably slows down the data processing rate, making it difficult to realize high-speed reproduction of information, which is an advantage of holographic storage.

Accordingly, the present invention has been invented in view of such a conventional problem, and an object of the present invention is to prevent an error of a reproduction signal and at the same time increase the data processing speed of a holographic storage device. It is to provide a recording / reproducing method.

1 is an exploded view showing the structure of a holographic storage device;

2 (a) is a view showing pixels of an optical modulator,

2B is a view showing pixels of the photodetector device CCD;

3 is a diagram showing an offset between an optical modulator and an array of the corresponding optical detector by image distortion;

4 (a) to 4 (b) show offsets when there is no error between a SLM pixel and a corresponding CCD pixel in the prior art;

5 (a) to 5 (c) show offsets when there is an error between a SLM pixel and a corresponding CCD pixel in the prior art;

6 and 7 illustrate an SLM pixel group and a corresponding CCD pixel group, and an offset between an SLM pixel image and a CCD pixel according to one embodiment of the present invention;

8 and 9 are diagrams illustrating an SLM pixel group and a corresponding CCD pixel group, and an offset between the SLM pixel image and the CCD pixel according to another embodiment of the present invention.

Explanation of symbols for main parts of the drawings

1 laser 2 laser light

3: beam splitter 4: object light

5: reference light 6: SLM

7: SLM controller 8,9: Reflector

10,13: FT lens 11: recording medium

12: reproduction light 14: CCD array

15: signal processing device 16: image information

16 ': Fourier transformed image information

The data recording / reproducing method of the holographic storage device of the present invention for achieving the above object is to divide each pixel of the information display element arranged in a grid form with pixels capable of displaying black or white information into a plurality of groups of pixels. Thereafter, the pixels in each group are classified into a dummy pixel in which a black state is always displayed and a data pixel in a black or white state according to the content of the information, and the information to be recorded is displayed as a black and white image using the respective data. And storing the image in the form of a hologram, reproducing the hologram, and then inputting an image of the reproduced pixels to a light detecting device including pixels having pixels corresponding to the information display elements. Separate each pixel into a data pixel and a dummy pixel, and then use only the signal generated from the data pixel to And a process of playing the black and white image of the.

EMBODIMENT OF THE INVENTION Hereinafter, the Example of this invention is described based on an accompanying drawing.

The position error between the CCD pixel 18 shown in FIG. 3 and the image 54 of the corresponding SLM pixel shown in FIG. 3 when used as a camera lens commercialized with the FT lenses 10 and 13 in the holographic storage device shown in FIG. Usually, the size and direction are limited to a certain range.

In most cases, as shown in FIG. 3, the center position of the CCD pixel 13 is P ₁ , and the center position of the image 54 of the SLM pixel is P ₂ , and the distance between P ₁ and P ₂ is D ₁ , between the CCD pixels. When the interval is referred to as D ₂ , the relationship as in Equation 1 is satisfied.

D ₁ <D ₂

The present invention has been made in view of the above, and one embodiment of the present invention is as follows.

The data recording / reproducing method of the holographic storage device according to the present invention is implemented using the holographic device shown in FIG.

First, a plurality of pixels in which each pixel of the SLM 6, which is an information display element in which binary information, which is black '0' or white '1', is arranged in a grid form, is 2x2, that is, four pixels are used as a unit. After dividing the pixels of each group of pixels into pixels of each group, for example, as shown in FIG. 6, the pixels of the pixel group 17 of the SLM are always dummy pixels in which binary information of black '0' is displayed. 32) and data pixels 31 in which binary information of black '0' and binary information of white '1' are displayed.

In addition, as shown in FIG. 7, the pixels of the CCD array 14 also correspond to each pixel of the SLM. As shown in FIG. 7, the CCD pixel groups 23, 24, 25, and 26 each having 4 pixels as a unit Separated by.

One data pixel and three dummy pixels are allocated to all pixel groups. For example, the pixel group 23 of the CCD is composed of one data pixel 23 and three dummy pixels 22, which is one data pixel 31 and three of the pixel group 17 of the SLM. Each of the dummy pixels 32 is configured to correspond to each other.

Each pixel of the SLM 6 is divided into a plurality of groups so that some pixels of each group are divided into data pixels and others are dummy pixels, and each pixel of the CCD 14 which is an optical sensing device is also assigned to the SLM. Each pixel is divided into a plurality of groups so as to correspond to each pixel in (6), and each group is divided into data pixels and dummy pixels.

The data display of '0' and '1' on each pixel of the SLM 6 is performed by the SLM controller 7 as shown in FIG.

That is, the object light 4 incident on the SLM 6 modulates the light quantity distribution in the SLM 6 according to the control signal of the SLM controller 7 to obtain constant image information 16, and the image information 16 ) Is incident on the recording medium (11) via the FT lens (10), and is separated by the beam splitter (3) and then the recording medium (11) as the reference light (5) incident through the reflectors (8,9). By interfering with the image information 16 to form an interference fringe, the image information in the recording medium 11 is stored in the holographic form.

On the other hand, the image information stored in the recording medium 11 is blocked at the object light 4 using a shutter (not shown) or the like in the same manner as described above, and then recorded using the reference light 5 at the same incident angle as when stored. After irradiating the medium 11 to obtain the reproduction light 12 identical to the image information 16 ', the reproduction light is inverse Fourier transformed through the FT lens 13 to obtain the image of the binary data identical to the image information 16. Get information.

Subsequently, the image information represented by the binary data is incident on the CCD array 14 to separate each of the input pixels into data pixels and derby pixels using the signal processing apparatus 15, and then only signals generated from the data pixels are generated. Play back the original black and white image.

For example, when the image 31 'of the data pixel 31 of the SLM pixel group 17 is incident on the CCD 14, the reproduced image 31' of the data pixel 31 is the data pixel of the CCD. Assuming that an incident occurs on the right side of FIG. 6 and an offset occurs in the lower right side of FIG. 6, the reproduced image 31 ′ is not only a data pixel 27 of the CCD pixel group 23, but also a dummy pixel of the pixel group 23. (22), but as long as [Equation 1] described above is satisfied, the reproduced image 31 'is a data pixel (28,) of the pixel group (24, 25, 26) adjacent to the pixel group (23) 29, 30) will not have any effect.

That is, the signal generated in the data pixels 27 and 28 may be smaller than the original signal value but is not affected by the amount of light incident on the adjacent data pixels.

If the generated signal to the data pixel 27 is S27, the value of Equation 2 is obtained as long as the condition of Equation 1 is maintained.

0≤S27 <1

Here, the equal sign only occurs in a state where the data of the original SLM pixel 31 is '0'.

Therefore, only the signals generated from the pixels 27 and 28 are sent to the signal processing device 15, and the non-zero minimum value is referred to as Smin, and binarized with respect to the received information with Smin as the threshold. All true data will be restored.

And even if the offset occurs in a direction other than the lower right, the same principle can restore the original data without error.

8 and 9 are diagrams for explaining a data recording / reproducing method of another embodiment of the present invention.

In the above-described embodiment, one-quarter of all pixels of the CCD array 14 are used as data pixels.

However, this embodiment is a case where half of all pixels are used as data pixels.

A hole horizontally in the error of the reproduced video special conditions according to the characteristics of the optical system, i.e., FIG. 3 of the graphic storage device shown in Figure 1 X-axis, called the axis of the vertical direction Y, and (X ₁ the coordinates of P _1, Y ₁ ), when the coordinate of P ₂ is (X ₂ , Y ₂ ), an image reproduction error satisfies Equation 1 and at the same time satisfies the relationship represented by Equation 3 as follows. Record / replay data through the process.

X ₂ -X ₁ = 0 or Y ₂ -Y ₁ = 0

In this embodiment, the pixels of the SLM 6 are defined as 1 × 2, that is, two pixels as one pixel group 33 as shown in FIG.

One pixel in the pixel group 33 is defined as a data pixel 34 and the other pixel is a dummy pixel 35.

In addition, '1' or '0' is displayed on the data pixel 34 of the SLM, and the dummy pixel 35 of the SLM is always '0'.

Meanwhile, as shown in FIG. 9, the pixels of the CCD array 14 are grouped in units of two pixels to correspond one-to-one to the pixels of the SLM, but the pixels of the SLM corresponding to the SLM data pixel 34 are separated. The pixel is referred to as the pixel 37, and the pixel of the SLM corresponding to the dummy pixel 35 of the SLM is referred to as the dummy pixel 42.

At the time of reproduction, the signal generated from the dummy pixel 42 of the CCD array 14 is discarded and only the signal of the data pixel 34 is used.

In addition, the up and down groups adjacent to one pixel group 36 are shifted by one pixel to the left or right of the pixel group 36 so that the adjacent data pixels 37 and 39 are positioned diagonally.

Therefore, only the image 40 of the data pixel 34 of the SLM is reproduced during the reproduction of the information.

As shown in FIG. 9, when the image 40 of the data pixel 34 of the SLM enters the data pixel 37 of the CCD with an error in the right direction, as long as the equations (1) and (3) are satisfied, The image 39 of the data pixel 34 of the SLM does not leave the area defined by the data pixel 37 and the dummy pixel 42 of the CCD and therefore does not affect the data pixels 38 and 39 of the adjacent group at all. .

As shown in FIG. 8, even when the image 40 of the data pixel 34 of the SLM is reproduced with an error downward, the data pixels 38 and 39 of the adjacent group are not affected at all.

Therefore, the signal S37 generated from the data pixel 37 has a value as shown in equation (4).

0≤S37 <1

Here, the equal sign applies only when the data of the data pixel 34 of the original SLM is '0'.

Therefore, the signal generated from all the data pixels of the CCD array 14 is sent to the signal processing device 15, and the non-zero minimum value of Smin is referred to as Smin, and binarized with respect to the received signal with Smin as the threshold. All original binary data will be restored.

As described above, according to the data recording / reproducing method of the holographic storage device of the present invention, the original recorded signal can be reproduced without error without any complicated comparison process with respect to the signal generated in each pixel of the CCD array. There is.

Claims (5)

After dividing each pixel of the information display element in which the pixels capable of displaying black or white information in a grid form into a plurality of groups of pixels, the pixels in each group are always assigned to the dummy pixels and the contents of the information. According to the data pixels indicating the black or white state to indicate the information to be recorded as a black and white image using the respective data; Storing the image in the form of a hologram, Reproducing the hologram and inputting an image of the reproduced pixels to a photodetector including pixels having pixels corresponding to the information display elements; And dividing each input pixel into a data pixel and a dummy pixel, and reproducing the original black and white image using only a signal generated from the data pixel. The method of claim 1, And said information display element is a light amount modulator and said photodetector device is a CCD. The method of claim 1, In the process of displaying the recording information on the information display device as a black and white image, each of the plurality of group pixels is divided into 2x2 pixels, one pixel of which is designated as a data pixel, and the other three pixels are designated as dummy pixels. Data recording / reproducing method of the holographic storage device characterized in that. The method of claim 1, In the process of displaying the recording information on the information display device as a black and white image, each of the plurality of group pixels is designated by 1 × 2 pixel or 2 × 1 pixel, one pixel of which is a data pixel, and the other one pixel A data recording / reproducing method of a holographic storage device, characterized in that it is specified as a dummy pixel. The method according to any one of claims 1 to 4, And specifying the dummy pixel to display '0' and the data pixel to display '1' or '0' according to the information content to be recorded.