CN211788163U - Holographic storage device and storage medium based on angle-shift multiplexing - Google Patents

Abstract

The utility model discloses a holographic storage device and storage medium based on angle-aversion is multiplexing, holographic storage device based on angle-aversion is multiplexing includes light source, reference light path, signal light path and medium platform, the light that the light source sent forms the reference light sum that follows the reference light path conveying and the signal light that follows the signal light path conveying after passing through the beam splitting, and reference light and signal light produce on the storage medium that the medium platform supported and interfere, form holographic storage image information, still include a control mechanism for the incident angle of control reference light with write in the position, make the incident angle that the position corresponds of writing in of difference of reference light in same record cell different.

Description

Holographic storage device and storage medium based on angle-shift multiplexing

Technical Field

The utility model belongs to the technical field of the holographic storage of light, concretely relates to holographic storage device based on angle-aversion is multiplexing.

Background

The reference light wave used in the angular multiplexing recording method is a plane wave, and multiplexing/recording is realized by changing the incident angle of the reference light. In this method, the original hologram cannot be reproduced by changing the incident angle of the reference light by only 0.1 °, so that a new hologram is recorded at that angle, and thus, about 100 times of multiplex recording can be realized by repeating the operations several times. In this method, the angle selectivity is determined by the bragg condition, and since a thick film medium is used, the intensity of the reproduction light is very sensitive to angle variation, and the reproduction light intensity is greatly reduced in the case where the angle variation is 0.1 degree. However, in this method, the incident position of the signal light is not changed, and the cross write noise is accumulated continuously along with the multiplexing process, thereby reducing the signal-to-noise ratio. In addition, since the range of variation of the incident angle is limited, the number of multiplexing cannot be increased without limitation. Therefore, the accumulation of noise and the range of angle variation will limit the storage capacity of the medium. On the contrary, the shift-multiplex recording is free from these restrictions, and the medium capacity can be greatly increased.

SUMMERY OF THE UTILITY MODEL

The present invention is directed to overcome at least one of the above-mentioned drawbacks of the prior art, and provides a holographic storage device and a storage medium for improving the storage capacity of the storage medium.

The technical scheme firstly provides a holographic storage method based on angle-shift multiplexing, which is characterized in that the incident angles of reference light and the positions of the reference light are in one-to-one correspondence.

The incident angle of the reference light is different between the holograms overlapped in the recording area block.

The recording/reproducing position is accessed by translation and rotation of the medium.

The hologram sequences recorded by each cross-shift multiplexing are recorded with an angle of 45 ° or more therebetween.

The position and the crossing angle of the hologram at the time of cross shift multiplex recording/reproduction are determined by detecting the mark on the guide groove.

When the bragg condition formed by the signal light wave loss, the reference light wave and the grating vector is mismatched, correction can be performed by controlling the incident angle and incident wavelength of the reference light.

The present invention also provides a holographic recording/reproducing device combining angle multiplexing and shift multiplexing suitable for the method.

The utility model discloses still provide a holographic storage medium based on angle-aversion is multiplexing suitable for above-mentioned method and device, holographic information is saved in storage medium with the mode of unit, includes a plurality of holographic image information that averts multiplexing according to the law in every unit, and the grating vector angle that corresponds when the storage of holographic image information on the different positions is different in same unit.

The storage medium comprises a plurality of units which are mutually superposed, and in two different units which are mutually superposed, two pieces of holographic image information corresponding to the same grating vector angle are mutually staggered and do not overlap.

The rule is to shift multiplexing along a certain direction x direction and shift multiplexing along a y direction perpendicular to the x direction, a shift step dx of the x direction is different from a shift step dy of the y direction, a size width of the holographic image information in the x direction is defined to be Rx, a size width of the holographic image information in the y direction is Ry, dx is Rx/n, dy is Ry/m, n and m are the shift multiplexing times of the holographic image information in the x direction and the y direction respectively, and the size of the unit is 2Rx x2 Ry.

The storage medium comprises a plurality of units which are mutually overlapped, the overlapping direction is along the x direction and/or the y direction, and the overlapping area size of two different units which are mutually overlapped is not smaller than Rx and/or Ry.

The holographic image information is a circular holographic image, Rx (Ry) is D, D is the diameter of the circular holographic image, in the same unit, the x direction is a shift multiplexing direction, the y direction is perpendicular to the x direction, and dy is larger than dx.

The cells have a size of 2D x 2D and comprise a plurality of cells stacked on each other in the x-direction and/or the y-direction, the width of the stack being D.

The cells are continuously stacked along the x-direction with a stacking width D to form a cell row.

The storage medium is rectangular and stores a plurality of unit rows which are distributed in parallel.

The storage medium is circular and is provided with a plurality of concentrically distributed storage rings, each storage ring at least comprises a plurality of unit rows distributed along the radial direction, and the x direction of the unit rows distributed along the radial direction is defined as x 1.

The memory ring also comprises a plurality of unit rows with a certain x direction and an angle of x1, and the unit rows realize angle cross multiplexing, and the x direction of the unit rows along the radial direction is defined as xi, i is 2, 3, 4 … ….

The certain angle is greater than 45 °.

The storage medium is circular and is provided with at least one storage ring, the storage ring comprises six unit rows with different x directions, the x directions are defined as x1 and x2 … … x6, and the difference between every two units is 60 degrees.

In the holographic storage method based on angle-shift multiplexing, in the writing process, the incident angle of the reference light corresponds to the writing position of the reference light on the storage medium one by one, and the one-to-one correspondence is realized by simultaneously changing the incident angle of the reference light and the writing position of the reference light on the storage medium.

Dividing the reference light into a plurality of sub-beams with the same angle delta theta; and making the writing position of the sub-beam on the storage medium change equidistantly by dx, or moving the storage medium to make the writing position of the sub-beam on the storage medium change equidistantly by dx; only one sub-beam is controlled to irradiate the storage medium at each writing, and dx is the shift step of the shift multiplexing.

And performing shift multiplexing for n times in the x direction of the shift multiplexing direction to form rows with the size width of 2Rx, performing shift multiplexing for m times in the y direction perpendicular to the x direction by the shift step dy, and forming units with the size of 2Rx x 2Ry, wherein the incidence angles of the reference light at different writing positions in the units are different.

Dividing the reference light into a plurality of sub-beams with equal angle delta theta change, wherein the sub-beams are arranged in a matrix; and making the sub-beams change equidistantly in the two mutually perpendicular directions of x and y on the storage medium, or moving the storage medium to make the sub-beams change equidistantly in the two mutually perpendicular directions of dx and dy on the storage medium; only one sub-beam is controlled to irradiate the storage medium at a time of writing, and dx and dy are respectively the shift steps of the horizontal and vertical shift multiplexing.

The reference light is irradiated by a galvanometer in a linear scanning manner, wherein the angle is equal to delta theta and the writing position on the storage medium is equal to dx.

The reference light is irradiated by a double-vibration mirror in a matrix scanning mode, wherein the angle delta theta is equal and the distance dx and dy are equal to each other in two perpendicular x and y directions on the storage medium.

After the reference light completes a row shift multiplexing writing along the x direction, the storage medium is moved to make the reference light writing position return to the initial position in the x direction, and the position is shifted by dy in the y direction to write a new row, and the steps are repeated until the whole matrix scanning type irradiation is completed.

In the writing process, a 2Rx × 2Ry unit is taken as a storage unit, the shift steps of the unit in the horizontal direction and the vertical direction shift multiplexing are dx and dy respectively, and the incidence angles of the reference light at different writing positions in the unit are different.

In the method, the size width of the holographic image information in the x direction is Rx, the size width of the holographic image information in the y direction is Ry, dx is Rx/n, dy is Ry/m, and n and m are the shift multiplexing times of the holographic image information in the x direction and the y direction respectively.

According to the method, unit superposition multiplexing is respectively carried out in a square storage medium along the x direction and the y direction, the superposition width in the x direction is Rx, and the superposition width in the y direction is Ry.

In the method, cell superposition multiplexing and cross multiplexing are performed in a circular storage medium.

Firstly, the units are overlapped and multiplexed along the x direction to form a unit row, the overlapping width is Rx, and then the circular storage medium is rotated to realize the cross multiplexing of the unit row.

The utility model provides a holographic storage device based on angle-aversion is multiplexing, including light source, reference light path, signal light path and medium platform, the light that the light source sent forms the reference light that follows the reference light path conveying and the signal light that follows the signal light path conveying after passing through the beam, and the reference light produces with the signal light and interferes on the storage medium that the medium platform supported, forms holographic storage image information, and its improvement part lies in, still includes a control mechanism for the incident angle of control reference light, make the incident angle of reference light and the write-in position one-to-one of reference light on storage medium.

The control mechanism is a beam splitter which divides the reference light into a plurality of sub-beams with equal angle delta theta change, and the beam splitter controls only one sub-beam to irradiate the storage medium at each writing.

The control mechanism is a beam splitter which divides the reference light into a plurality of sub-beams which are in equal angle delta theta change and are arranged in a matrix mode, and the beam splitter controls only one sub-beam to irradiate the storage medium during writing each time.

The control mechanism is a galvanometer structure which reflects reference light with equal angle delta theta change and controls the reference light to realize equidistant dx scanning on the storage medium.

The control mechanism further comprises another galvanometer structure for realizing the shift multiplexing of the reference light in the vertical direction.

The medium platform also comprises a translation mechanism for driving the storage medium to translate so as to realize superposition multiplexing.

The medium platform also comprises a rotating mechanism for driving the storage medium to rotate so as to realize superposition multiplexing.

Compared with the prior art, the beneficial effects of the utility model are that: the utility model discloses a holographic multiplexing recording method, this method has combined the advantage of angle multiplexing and aversion multiplexing technique, has improved the capacity and the stability of system. Since the medium shrinkage and expansion caused by the environmental temperature fluctuation can cause the Bragg condition mismatch, the angle multiplexing recording has the advantages that the Bragg condition mismatch caused by the medium shrinkage and expansion can be corrected by controlling the incident angle of the reference beam and the emergent wavelength of the laser, and the problem of weak reproduction signals caused by the environmental temperature fluctuation is solved. On the other hand, the shift multiplex recording has an advantage in that cross write noise is not accumulated, and the multiplex number can be increased by the cross shift multiplex method. The utility model discloses combine both, realized a recorder of large capacity, high stability.

Drawings

Fig. 1 is a schematic diagram of angle multiplexing recording.

Fig. 2 is a diagram showing an optical path system structure using an angle multiplexing recording method.

Fig. 3 is a schematic diagram of shift multiplexing recording.

Fig. 4 is a schematic diagram of cross-shift multiplex recording.

FIG. 5 is a method of correcting for medium shrinkage and wavelength fluctuations.

FIG. 6 is a schematic diagram illustrating a method for changing the incident angle of the reference light.

Fig. 7 is a schematic diagram of an angle-shift multiplexing recording method.

Fig. 8 is a schematic diagram of a two-dimensional recording method of angle-shift multiplexing.

Fig. 9 is an overview of an angle-shift multiplexing recording method.

FIG. 10 is a schematic diagram of a holographic multiplexing recording process.

Fig. 11 is a light path diagram of the reference light incident angle adjusting system.

Fig. 12 is a schematic diagram of a method for estimating the number of multiplexes in angle multiplex recording.

Fig. 13 is a schematic diagram of a cross-shift multiplexing recording method in an optical disc medium.

Fig. 14 is a diagram showing an optical path system configuration of a holographic memory device based on angle-shift multiplexing of gratings.

Device description: 10: laser, 20: shutter (AOM), 30: polarizing plate, 40: anamorphic prism set, 50: polarizing beam splitter prism, 51: first polarizing beam splitting prism, 52: second polarizing beam splitter prism, 60: attenuator, 70: half wave plate, 80: mirror, 81: first mirror, 82: second mirror, 90: galvanometer, 100: beam expanding collimator, 101: first beam expander collimator, 102: second beam expander collimator, 110: spatial light modulator, 120: relay lens group, 130: fourier lens, 131: first fourier lens, 132: second fourier lens, 140: holographic disk, 150: camera, 160: the acousto-optic modulator (AOM) can be replaced by a vibrating mirror.

Detailed Description

The drawings of the present invention are for illustration purposes only and are not to be construed as limiting the invention. For a better understanding of the following embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.

Examples

A conventional angle multiplexing recording method uses a plane wave as a reference light to perform multiplexing recording of holograms at the same position on a medium while changing an incident angle, as shown in fig. 1. After the hologram is recorded a predetermined number of times, the next round of hologram angle-multiplexing recording is performed at another place not coinciding with the position. In reproduction, the medium is illuminated with only the reference beam, and filters are used to block cross-talk from other location holograms. A typical angle-multiplexed hologram recording/reproducing apparatus is shown in fig. 2, in which the incident angle of the reference light is adjusted by a galvanometer mirror 90.

The shift-multiplex recording principle using a spherical wave as reference light is shown in fig. 3, which is a method of shift-multiplex recording and reproducing a hologram using a spherical reference wave. If the medium is moved a distance after the hologram has been recorded, the hologram cannot be reproduced, i.e. it is possibleTo re-record a new hologram. In particular, the signal beam k can be known from the bragg principle_sReference beam k_rSum raster vector k_gThe medium only needs to move by several microns, the original triangle is damaged, and the hologram can not be reproduced. In the method, the intersection line of the plane where the reference light optical axis and the signal light optical axis are located and the surface of the medium is taken as an axis, the medium is subjected to displacement multiplexing along the axial direction, the displacement selectivity in the axial direction is determined by a Bragg condition, and the displacement distance of several micrometers can meet the condition. In the direction perpendicular to this axis, the diffraction intensity is insensitive to the shift distance, and it is difficult to improve the storage density. Fig. 4 shows a cross shift multiplex recording method related to this patent, which solves the problem of insufficient multiplex number of the spherical wave shift multiplex recording method by performing shift multiplex recording in the axial direction to obtain a two-dimensional hologram array, then rotating the medium by a certain angle around the center normal of the medium surface, and then performing a second shift multiplex overlay recording, which is called cross shift multiplex recording. Compared with the angle multiplexing method, the spherical wave reference light shift multiplexing method has higher signal-to-noise ratio and larger storage capacity.

In practical applications but in holographic storage, both methods are compared, since the medium shrinks and expands due to changes in ambient temperature, and since the laser wavelength fluctuates, reconstruction of the hologram becomes difficult, which degrades the signal quality.

Fig. 5 describes a method of correcting medium shrinkage, wavelength fluctuation, and the like. Wherein k is_rDenotes the wave vector of the reference light, k_sDenotes the signal light wave vector, k_gRepresenting the grating vector and the circles represent the change in the Ewaldsphere (Ewaldsphere) caused by a change in wavelength. As the wavelength increases, the radius of the Everdet sphere decreases, and therefore k, which is most advantageous for hologram reconstruction_rThe direction is changed and the diffraction efficiency of the hologram is reduced. In contrast, angular multiplexing with a plane wave reference beam can very easily re-satisfy the bragg condition by changing the incident angle of the reference beam.On the other hand, in shift multiplexing using spherical waves as reference light, the wavefront is a superposition of sub-wavefronts propagating in multiple directions, and even if the tilt angle of the reference light is changed, only partial optimization is performed, and it is difficult to perform all k-ray images_rAnd optimizing the direction. Therefore, it is substantially impossible to recover the deteriorated signal, and the margin of the signal is reduced.

Fig. 6 illustrates a method of changing the optical axis of a spherical reference beam by mounting a lens on a motor to change the optical axis in three spatial dimensions. However, this method is theoretically impossible to correct all wave vectors k in the reference beam_rIn the direction of (a). Therefore, the present patent establishes a large-capacity storage method capable of correcting the above situation by combining two advantageous methods, angle multiplexing and shift multiplexing.

This patent discloses a method of changing the reference beam angle to record shift multiplexed recording. As shown in FIG. 7, the hologram is represented by a circle having a diameter of 500. mu.m. The system light source uses a short pulse laser to record the hologram while the medium is moving to the left. In the method proposed in this patent, 800 multiplexing can be realized. As can be seen from the figure, the hologram information is a circular hologram, i.e., Rx, Ry, D, 500 μm.

As shown in fig. 7, a first hologram is recorded at a reference angle of 0 (first angle), and then, one hologram may be recorded while changing the angle of the reference beam by 0.1 degrees every 5 μm, which is repeated, for a total of 100 holograms. Since each hologram has a different reference light angle, crosstalk does not occur even if a plane wave is used as the reference light. This recording sequence is multiplex recorded to the right in fig. 7. In this hologram sequence, the recording of holograms is performed with a variation of the reference beam angle from 0 degrees (first angle) to +9.9 degrees, this form being arranged consecutively to the right. That is, the shift step dx in the x direction is 5 μm, the number of times of shift multiplexing the hologram information in the x direction is 100, and the angle Δ θ of the reference light changes at 0.1 degrees for each multiplexing.

The two-dimensional recording process of this method is shown in fig. 8, and after performing right-direction continuous shift multiplexing using the method shown in fig. 7, the storage medium is moved in a direction perpendicular to the medium shift direction, and then the second continuous shift multiplexing is continuously repeated, as shown in fig. 8. Specifically, the reference light incident angle of the first hologram sequence (solid line) was 0 to +9.9 degrees, the second hologram sequence (dotted line) was spaced from the center of the first hologram sequence by 62.5 μm, and the second hologram sequence also included 100 holograms whose reference light incident angle varied from +10 degrees to +19.9 degrees. Repeating the above process can obtain a hologram recording unit consisting of 8 hologram sequences, and realize 800 times of multiplexing. That is, the shift step dy in the y direction is 62.5 μm, the shift multiplexing number m of the hologram information in the y direction is 8, the angle Δ θ of the reference light is changed to 0.1 degrees every time the hologram information is laterally multiplexed, and the reference light start angles of the hologram sequences in two adjacent rows are different by 10 degrees.

Shift multiplexing is performed in the shift direction, and a plurality of hologram sequences superimposed on each other are obtained, each sequence including 100 holograms, and the arrangement is shown in fig. 9. The shift distance for multiplex recording is 5 μm, and the first holograms of two adjacent sequences are spaced by 500 μm, i.e., the diameter of the hologram, so that although the reference light incident angles for forming the two holograms are the same, since they do not overlap with each other, crosstalk does not occur. In the area where the holograms overlap, no crosstalk occurs between the holograms due to the difference in the incident angle of the reference light. Therefore, the holograms recorded by the angle-shift multiplexing method proposed in this patent can be reproduced individually, and the recording flow of this method is shown in fig. 10. That is, the size of the cell is 2D × 2D 1mm × 1mm, and a plurality of cells are stacked on each other in the x direction in the storage medium, and the width of the stack is 0.5 mm.

The patent also provides a method and a device for adjusting the incident angle of the reference light. In view of the high speed angular transformation required by this patent, it is proposed to use an acousto-optic modulator (AOD) for angular transformation. The AOD modulates the amplitude of the carrier wave to generate a spectrum consisting of the carrier wave and sidebands, producing diffracted light corresponding to the sidebands, i.e., the reference beam. Then, the angle is changed by changing the frequency of the amplitude modulation signal.

The spectrum of the sidebands is determined by the Numerical Aperture (NA) of lens L1 and can reach a bandwidth of tens of megahertz. Fig. 12 shows the estimation of the multiplexing number in the method of implementing angle multiplexing using AOD, and if an objective lens with NA of 0.85 is used, the multiplexing number can reach 800.

In order to further increase the recording density of holograms, the patent proposes a method of cross-shift multiplexing. As shown in fig. 13, a guide groove is provided in the storage medium, and an initial position mark is provided in the guide groove, so that the storage medium is shifted and multiplexed rightward in the directions of arrows (r), (c), and (c) in fig. 13 with the initial position mark. The medium is rotated little by little, and after each rotation, the initial position mark is positioned and shift multiplex recording is performed. The relative position of the storage medium and the optical head is changed, the included angle between the vector direction of the recording grating and the displacement direction of the storage medium can be changed, the crossing angle of the hologram sequence obtained by carrying out the displacement multiplexing at the positions of the first, the second and the third can be set to be 50 degrees or higher, thus, six times of cross displacement multiplexing can be realized on the whole surface of the optical disc, namely, the multiplexing times are 6 times.

Specifically, referring to the right enlarged view in fig. 13, it can be seen that an arrow (r) is a radial direction of the storage ring, the direction is a first x direction, the arrow (r) is positioned as x1, the inside of the storage ring is used as a starting point, the superposition recording of a plurality of storage units is realized along the direction of the arrow (r), each unit has a size of 1mm × 1mm, the width of the superposition is 0.5mm, each unit contains 100 × 8 holograms, 800 holograms are arranged in a 100 × 8 array, a shift step dx in the x1 direction is 5 μm, a shift step dy in the y1 direction perpendicular to the x1 direction is 62.5 μm, the recording reference light of two adjacent holograms in the same row changes at an equal angle Δ θ of 0.1 degree, and the reference light starting angles of two adjacent hologram sequences differ by 10 degrees.

After the next unit row is recorded from inside to outside by the storage ring along the direction of the arrow, the rotation is carried out by a slight angle, and the rotation, the shift and the multiplexing are continuously carried out along the same direction arrow at the same initial position until the storage ring is completely recorded along the direction of the arrow, namely, the storage ring is rotated by one circle.

And then moving the storage medium to move the reference light to an arrow II initial position, wherein an included angle formed by the arrow II initial position, the arrow I initial position and the circle center is 60 degrees, the superposition recording of a plurality of storage units is realized along the arrow II direction, the unit rows recorded from the storage ring from inside to outside along the arrow II direction and the unit rows recorded by the arrow I are in a cross multiplexing angle of 60 degrees. Similarly, the storage medium is rotated by a small angle, and the rotation, displacement and multiplexing are continuously carried out at the same initial position along the same direction arrow (II), until the storage ring is fully recorded along the direction of the arrow (II), namely, the storage ring is rotated by one circle, and the cross multiplexing of the two directions of the arrow (II) and the arrow (I) is completed.

In the same way, the method can realize the cross multiplexing of the arrow (c) and the first two direction arrows (c)/the arrow (r), and repeats the steps for six times by taking 60 degrees as a cross multiplexing included angle.

Fig. 14 is an exemplary structure of an angle-shift multiplexing system proposed in this patent, which can be implemented in an optical system for conventional angle multiplexing recording. As shown in the figure, the holographic memory device based on angle-shift multiplexing includes a laser 10 as light, the light emitted from the laser passes through a shutter 20 and an anamorphic prism set 40 in sequence, and is divided into a reference optical path and a signal optical path by a first polarization beam splitter prism 51. The signal light passes through the second beam expanding collimator 102, is reflected to the spatial light modulator 110 by the second polarization beam splitting prism 52 to load the signal, passes through the relay lens group 120 and the first fourier lens 131 in sequence by the second polarization beam splitting prism 52 again, and reaches the holographic disk 140. The reference light is reflected by the first mirror 81 after passing through the attenuator 60 and the half-wave plate 70 in sequence, then enters an Acoustic Optical Modulator (AOM)160 or a galvanometer for angle modulation, and then reaches the holographic disk 140 after being expanded and collimated by a collimating structure composed of the second mirror 82 and the first beam expanding collimator 101. The reference light and the signal light interfere on the holographic disk 140 supported by the medium platform to form holographic storage image information, and the acousto-optic modulator (AOM)160 or the galvanometer is used to control the incident angle of the reference light, so that the incident angle of the reference light and the writing position of the reference light on the storage medium are in one-to-one correspondence.

In addition, a beam splitter may be used which is composed of a grating which splits the reference light into a plurality of sub-beams varying at equal angles Δ θ and a shutter switch which controls that only one sub-beam is irradiated on the storage medium at a time of writing.

It is obvious that the above embodiments of the present invention are only examples for clearly illustrating the technical solutions of the present invention, and are not limitations to the specific embodiments of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (10)

1. A holographic storage device based on angle-shift multiplexing comprises a light source, a reference light path, a signal light path and a medium platform, wherein light emitted by the light source forms reference light transmitted along the reference light path and signal light transmitted along the signal light path after passing beams, and the reference light and the signal light generate interference on a storage medium supported by the medium platform to form holographic storage image information.

2. The holographic storage device of claim 1, wherein the control mechanism is a beam splitter that splits the reference light into a plurality of sub-beams of equal angular delta-theta variation, and the beam splitter controls only one of the sub-beams to illuminate the storage medium at a time for writing; or the control mechanism is a beam splitter which divides the reference light into a plurality of sub-beams which are changed at equal angles delta theta and are arranged in a matrix manner, and the beam splitter controls only one sub-beam to irradiate the storage medium during writing each time.

3. The holographic storage device of claim 1, in which the control mechanism is an acousto-optic modulator or a galvanometer that reflects the reference light at an equal angle Δ θ and controls the reference light to realize a matrix scan on the storage medium.

4. The holographic storage device of any of claims 1-3, wherein the media platform further comprises a translation mechanism for translating the storage media to achieve superposition multiplexing.

5. The holographic storage device of any of claims 1-3, wherein the media platform further comprises a rotation mechanism for rotating the storage media to achieve cross-multiplexing.

6. The holographic storage medium based on angle-shift multiplexing is characterized in that the holographic storage medium is divided into a plurality of unit line storage areas, each unit line comprises a plurality of units which are overlapped with each other, each unit comprises a plurality of holographic images which are regularly shifted and multiplexed, grating vector angles corresponding to the holographic images at different positions in the same unit are different, and two holographic images corresponding to the same grating vector angle in two different units which are overlapped with each other are staggered with each other.

7. The medium of claim 6, wherein the rules are shift multiplexing in a certain x direction and shift multiplexing in a y direction perpendicular to the x direction, the shift step dx in the x direction is different from the shift step dy in the y direction, a dimension width in the x direction of the hologram information is defined as Rx, a dimension width in the y direction is defined as Ry, dx is Rx/n, dy is Ry/m, n and m are shift multiplexing times of the hologram information in the x direction and the y direction, respectively, and the size of the cell is 2Rx x2 Ry.

8. The medium of claim 7, wherein the hologram image is a circular hologram image, Rx, Ry, D and D are diameters of the circular hologram images, the x direction is a direction in which a row of the circular hologram images in the unit are shift-multiplexed along a projection direction of a grating vector on a surface of the storage medium in the same unit, the y direction is a direction in which a plurality of rows of the shift-multiplexed circular hologram images in the x direction are shifted, and dy > dx.

9. The medium according to any one of claims 6-8, wherein the storage medium is rectangular and stores a plurality of rows of cells arranged in parallel.

10. A medium according to any of claims 6-8, characterized in that the storage medium is circular with at least one storage ring comprising six rows of cells differing in x-direction, defining x-direction x1, x2 … … x6, two by 60 °.

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