CN105096974A

CN105096974A - Holographic device and data reading device thereof

Info

Publication number: CN105096974A
Application number: CN201510595138.5A
Authority: CN
Inventors: 彭灯木
Original assignee: Qingdao Tai Gu Photoelectric Project Technology Co Ltd
Current assignee: Qingdao Tai Gu Photoelectric Project Technology Co Ltd
Priority date: 2015-09-17
Filing date: 2015-09-17
Publication date: 2015-11-25
Anticipated expiration: 2035-09-17
Also published as: CN105096974B

Abstract

The invention relates to a holographic device comprising a holographic storage device, a shearing interferometer and an optical receiver. The holographic storage device is arranged for providing reading light to a disk so that reading light is enabled to be diffracted at the disk to form diffraction light then. The shearing interferometer is arranged for receiving diffraction light and converting diffraction light into first light beams and second light beams. The optical receiver is arranged for receiving the first light beams and the second light beams which are provided by the shearing interferometer.

Description

Holographic device and data reading method thereof

Technical Field

The invention relates to a holographic device and a data reading method thereof.

Background

With the development of science and technology, the required storage capacity of the electronic file is also followed

And (4) rising. A common storage method is to record magnetic or optical changes on the surface of a storage medium as the basis of stored data, such as a magnetic disk or an optical disk. However, as the required storage capacity of electronic files increases, the development of holographic storage technology has become more and more attractive.

The holographic storage technique is to write image data into a storage medium (photosensitive material) after interference is generated between signal light and reference light. When reading data, diffracted light is generated by diffraction by re-irradiating the reference light onto the storage medium (photosensitive material). The diffracted light generated is then read by a receiver.

In the step of converting the diffracted light into digital data, since the diffracted light may be affected by noise, the reading step of the diffracted light by the receiver may be performed a plurality of times to more accurately calculate the data content and eliminate the noise. However, multiple reading steps will extend the time to translate the diffracted light into digital data, making the receiver inefficient at reading the data. Therefore, how to improve the reading efficiency of the holographic storage technology becomes a target of current research in the related art.

Disclosure of Invention

The present invention provides a holographic device, which converts diffracted light into a first light beam and a second light beam through a shearing interferometer, and forms a first imaging range and a second imaging range on an optical receiver. Through the data points corresponding to the initial reference signal points in the first imaging range and the second imaging range, the phase of the first data cell in the first imaging range can be calculated by the data points with known phases. When the phase of the first data cell in the first imaging range is calculated, the holographic device can read the data stored in the disk. By the above phase estimation method, the number of times the disk is read by the hologram device is one, so that the time for the disk fetching by the hologram device is shortened.

Preferably, the holographic device comprises a holographic storage device, a shearing interferometer and an optical receiver. The holographic storage device is configured to provide the reading light to the disk, so that the reading light is diffracted on the disk to become diffracted light. The shearing interferometer is configured to receive the diffracted light and convert the diffracted light into a first light beam and a second light beam, wherein the first light beam and the second light beam are parallel to each other. The optical receiver is configured to receive the first light beam and the second light beam provided by the shearing interferometer.

Preferably, the holographic storage device comprises a light source module. The light source module is arranged to provide signal light, wherein the signal light provided by the light source module has an initial reference signal point.

Preferably, the shearing interferometer comprises a reflective shearing plate or a transmissive shearing plate.

Preferably, the holographic device further comprises an afocal system. The afocal system is disposed between the shearing interferometer and the optical receiver, wherein the afocal system is used for reducing the image of the first light beam and the second light beam provided by the shearing interferometer on the optical receiver.

Preferably, the shearing interferometer comprises a transparent substrate and a dielectric layer. The transparent substrate has a first surface and a second surface which are opposite and not parallel. The dielectric layer is arranged on the first surface and is parallel to the first surface.

Preferably, the dielectric layer has a thickness greater than 0 micrometers (μm) and less than or equal to 10 micrometers (μm).

Preferably, the holographic device further comprises an afocal system. The afocal system is disposed between the shearing interferometer and the optical receiver, wherein the afocal system is used for amplifying images of the first light beam and the second light beam provided by the shearing interferometer on the optical receiver.

Preferably, the holographic device further comprises a first lens, a second lens and a low-pass filter. The first lens and the second lens are disposed between the holographic storage device and the shearing interferometer, and the diffracted light traveling from the holographic storage device to the shearing interferometer sequentially passes through the first lens and the second lens. The low-pass filter is arranged between the first lens and the second lens. The low pass filter has an aperture with a size ranging from 1X1 minimum pixel units of the optical receiver to 4X4 minimum pixel units of the optical receiver.

Preferably, the imaging ranges of the first light beam and the second light beam provided by the shearing interferometer on the optical receiver are a first imaging range and a second imaging range, respectively. The first imaging range and the second imaging range are rectangles with the same size, and the first imaging range and the second imaging range are partially overlapped.

Preferably, there is a longitudinal distance difference and a lateral distance difference between the first imaging range and the second imaging range. The ratio of the lateral distance difference to the longitudinal distance difference is a tangent of an angle, wherein the angle is greater than or equal to 0 degrees and less than or equal to 90 degrees.

Preferably, the shearing interferometer is disposed so that a lateral distance difference or a longitudinal distance difference between the first imaging range and the second imaging range is an integral multiple of a minimum pixel unit of the optical receiver.

Preferably, the shearing interferometer is composed of a first convergent lens, a second convergent lens and a grating unit. The first converging lens and the second converging lens are arranged between the holographic storage device and the optical receiver, and the diffracted light traveling from the holographic storage device to the optical receiver sequentially passes through the first converging lens and the second converging lens. The grating unit is arranged between the first convergent lens and the second convergent lens.

Preferably, the grating unit includes a first grating and a second grating. The second grating is parallel to the first grating, and the diffracted light from the first converging lens to the second converging lens passes through the first grating and the second grating in sequence.

Preferably, the grating unit includes a tilted grating (blazedgradgrating) or a dual frequency grating (doublefrequentrygrating).

Another technical problem to be solved by the present invention is to provide a data reading method for a holographic device, comprising the following steps. The holographic storage device provides a signal light to the disk, wherein the signal light has an initial reference signal point, so that information corresponding to the initial reference signal point is recorded in the disk. The reading light is provided to the disk through the holographic storage device, so that the reading light is diffracted on the disk to form diffracted light, wherein the diffracted light has data points corresponding to the initial reference signal points. The diffracted light is converted into a first light beam and a second light beam which are parallel to each other by a shearing interferometer. The first light beam and the second light beam are guided to the optical receiver. The imaging ranges of the first light beam and the second light beam on the optical receiver are the first imaging range and the second imaging range, respectively. The first imaging range and the second imaging range are rectangles with the same size, and the first imaging range and the second imaging range are partially overlapped.

Preferably, the first imaging range has first data cells, each of which has a first phase or a second phase. The second imaging range has second data cells, each having either the first phase or the second phase. Each first data cell and each second data cell in the area where the first imaging range and the second imaging range overlap completely coincide.

Preferably, the data reading method further includes converting the first and second light beams provided by the shearing interferometer from a phase distribution form to an intensity distribution form by interference according to the completely overlapped first and second data cells in the overlapping region of the first and second imaging ranges.

Preferably, the step of converting the first beam and the second beam from a phase distribution form to an intensity distribution form by interference further comprises the following steps. When each set of the completely overlapped first data cell and the second data cell is the first phase or the second phase, the intensity of the set of the completely overlapped first data cell and the second data cell at the optical receiver is defined as the first intensity. When each set of the completely coincident first data cells and the second data cells is the first phase and the second phase, respectively, the intensity of the set of completely coincident first data cells and the second data cells at the optical receiver is defined as the second intensity.

Preferably, the data reading method further comprises the following steps. After the first and second light beams are converted from the phase distribution form to the intensity distribution form, the phase of each first data cell in the first imaging range is calculated through the intensity distribution form of the first and second light beams and the data point corresponding to the initial reference signal point.

Preferably, the step of estimating the phase of each first data cell in the first imaging range further comprises the following steps. The estimation is performed from one of the data points corresponding to the initial reference signal point in the first data cell to each of the other completely overlapped first data cell and second data cell.

Drawings

FIG. 1 is a schematic optical path diagram of a holographic device according to a first embodiment of the present invention.

FIG. 2A is a schematic view of the holographic memory device of the holographic device of FIG. 1 configured in a coaxial manner.

FIG. 2B is a schematic configuration diagram of the holographic storage device of the holographic device of FIG. 1 configured in an off-axis manner.

Fig. 3A is a schematic view of a first imaging range of the first light beam of fig. 1 on an optical receiver.

Fig. 3B is a schematic diagram of a second imaging range of the second light beam of fig. 1 on the optical receiver.

Fig. 4A and 4B are schematic diagrams illustrating the holographic device in fig. 1 reading the first light beam and the second light beam.

FIGS. 5A-5I are diagrams of embodiments of signal light having an initial reference signal point provided by a holographic storage device in the holographic device of FIG. 1.

FIG. 6 is a schematic optical path diagram of a holographic device according to a second embodiment of the present invention.

FIG. 7 is a schematic optical path diagram of a holographic device according to a third embodiment of the present invention.

FIG. 8 is a schematic configuration diagram of a holographic device according to a fourth embodiment of the present invention.

Fig. 9 is a schematic optical path diagram of a holographic device according to a fifth embodiment of the present invention.

Fig. 10A is a schematic optical path diagram of a holographic device according to a sixth embodiment of the present invention.

Fig. 10B is a schematic configuration diagram of the grating unit of fig. 10A.

Fig. 11A is a schematic optical path diagram of a holographic device according to a seventh embodiment of the present invention.

Fig. 11B is a schematic configuration diagram of the grating unit of fig. 11A.

Fig. 12 is a schematic optical path diagram of a holographic device according to an eighth embodiment of the present invention.

100 holographic devices; 102 a holographic storage device; 104 a low-pass filter; 105 light holes; 106 disks; 108 an optical receiver; 109 a first mirror; 110 a first lens; 111 a second lens; 112A, 112B guide lenses; 113 galvanometer; 114 a light source module; 115. 115A, 115B spatial light modulators; 116. 116A, 116B polarizing beam splitters; a 117 dichroic mirror; 118 a second mirror; 119 objective lens; a 120 shearing interferometer; 122 a reflective shear plate; 124 penetrating the shear plate; 126 an afocal system; a 128 transparent substrate; 130 a dielectric layer; 132 a first converging lens; 134 a second converging lens; 136 a grating unit; 138 a first grating; 140 a second grating; 142 inclined grating; 144 dual-frequency grating; a P1 first phase; p2 second phase; a1 first imaging range; a2 second imaging range; d, diffracted light; m, M_ijA first data cell; n, N_ijA second data cell; r initial reference signal points; l reading light; an L1 first light beam; l2 at the end ofTwo light beams; l3, L4, L5, L6, L7, L8, L9, L10, L11, L12 light beam; s1 first surface; s2 second surface; v longitudinal distance difference; h, difference of transverse distance; the angle theta.

Detailed Description

While the spirit of the invention will be described in detail and with reference to the drawings, those skilled in the art will understand that various changes and modifications can be made without departing from the spirit and scope of the invention as taught herein.

In a holographic storage system, when data is written to a holographic disk, a light beam consisting of a signal light and a reference light needs to interfere with and expose a photosensitive material in a certain range of the disk. When reading data, diffracted light is generated by diffraction by re-irradiating the reference light onto the photosensitive material in the disk. The diffracted light generated is then read by a receiver. In the step of reading the diffracted light by the receiver, the number of times of reading the diffracted light by the receiver may be multiple times in order to accurately calculate the diffracted light and avoid noise interference on the calculation result. However, the multiple reading steps will prolong the reading time of the disk by the holographic device, so that the reading efficiency and efficiency of the holographic device are low.

In view of the above, the holographic device of the present invention converts the diffracted light into the first light beam and the second light beam through the shearing interferometer, and forms the first imaging range and the second imaging range on the optical receiver. Through the data points corresponding to the initial reference signal points in the first imaging range and the second imaging range, the phase of the first data cell in the first imaging range can be calculated by the data points with known phases. When the phase of the first data cell in the first imaging range is calculated, the holographic device can read the data stored in the disk. In other words, the optical receiver can obtain the phase information stored in the disk by reading the diffraction light once, so that the fetching time of the disk by the holographic device is shortened. Moreover, the holographic device can still generate high-quality data under the condition of shortening fetching time, so that the reading efficiency and efficiency of the holographic device can be greatly improved.

Fig. 1 is a schematic optical path diagram of a holographic device 100 according to a first embodiment of the present invention. The holographic device 100 comprises a holographic storage device 102, a low pass filter 104, a shearing interferometer 120, an optical receiver 108, a first mirror 109, a first lens 110 and a second lens 111, wherein the holographic storage device 102 may be of an on-axis type or an off-axis type. In the optical path of the diffracted light D, the diffracted light D passes through the holographic storage device 102, the first lens 110, the low pass filter 104, the second lens 111, the first mirror 109, and the shearing interferometer 120 in this order, and then enters the optical receiver 108. In other embodiments, the diffracted light D may be passed from the holographic storage device 102 through the shearing interferometer 120 and into the optical receiver 108.

In addition, the holographic device 100 depicted in fig. 1 is configured to show the sequential relationship of the components that the diffracted light D passes through in its optical path, rather than the relative positional relationship of the actual components. That is, one skilled in the art can adjust the actual relative position relationship between the components according to the design of the optical path of the diffracted light D. For example, the first reflecting mirror 109 may be omitted in different optical path designs of the diffracted light D.

Please see fig. 2A and fig. 2B first. FIG. 2A is a schematic diagram of the holographic storage device 102 of the holographic device 100 of FIG. 1 configured in a coaxial manner. FIG. 2B is a schematic diagram of the holographic storage device 102 of the holographic device 100 of FIG. 1 configured in an off-axis manner.

In fig. 2A, the holographic storage device 102 of the holographic device 100 is a coaxial structure, wherein the holographic storage device 102 includes a light source module 114, a spatial light modulator 115, a polarization beam splitter 116, a dichroic mirror 117, a second reflecting mirror 118 and an objective 119, and the low pass filter 104, the first lens 110 and the second lens 111 are disposed between the polarization beam splitter 116 and the dichroic mirror 117. In addition, in the holographic storage device 102 of the holographic device 100, which is coaxially disposed, the first mirror 109 in fig. 1 may be omitted.

During reading, the light source module 114 provides reading light L, so that the reading light L can pass through the spatial light modulator 115, the polarization beam splitter 116, the first lens 110, the low pass filter 104, the second lens 111, the dichroic mirror 117, the second reflecting mirror 118 and the objective lens 119 in sequence from the light source module 114 and enter the disc 106. The reading light L is diffracted by the disk 106 to become diffracted light D. Then, the diffracted light D travels along the original optical path to the polarization beam splitter 116 and is guided to the shearing interferometer 120 by the polarization beam splitter 116. The optical receiver 108 is configured to receive the light beam provided by the shearing interferometer 120.

In fig. 2B, the holographic storage device 102 of the holographic device 100 is an off-axis structure, wherein the holographic storage device 102 includes a galvanometer 113, a light source module 114, spatial light modulators 115A and 115B, guiding lenses 112A and 112B, polarization beam splitters 116A and 116B, a dichroic mirror 117 and an objective lens 119, and the low pass filter 104, the first lens 110 and the second lens 111 are disposed between the dichroic mirror 117 and the first reflecting mirror 109.

Similarly, when reading, the light source module 114 provides the reading light L, so that the reading light L can pass through the guiding lens 112A, the spatial light modulator 115A, the polarization beam splitters 116A and 116B, the galvanometer 113, the guiding lens 112B, and the objective lens 119 in sequence from the light source module 114 and enter the disk 106. The reading light L is diffracted by the disk 106 to become diffracted light D. Then, the diffracted light D travels from the disk 106 to the first mirror 109 along the objective lens 119, the dichroic mirror 117, the spatial light modulator 115B, the dichroic mirror 117, the first lens 110, the low pass filter 104, and the second lens 111 in this order, and is guided to the shearing interferometer 120 by the first mirror 109. The optical receiver 108 is configured to receive the light beam provided by the shearing interferometer 120.

In addition, the arrangement of the components in the holographic device 100 shown in fig. 2A and fig. 2B is only illustrative, and not limiting. The skilled person can adjust the relative position relationship between the components according to different designs of the light path of the diffracted light D.

Please return to fig. 1. The shearing interferometer 120 is configured to receive the diffracted light D and convert the diffracted light D into a first light beam L1 and a second light beam L2, wherein the first light beam L1 and the second light beam L2 are parallel to each other. In this embodiment, the shearing interferometer 120 includes a reflective shearing plate 122. That is, the diffracted light D is converted into the first light beam L1 and the second light beam L2 which are parallel to each other through the reflective shear plate 122. The reflective shear plate 122 has a first surface S1 and a second surface S2 that are parallel. The diffracted light D is reflected by the first surface S1 of the reflective shear plate 122 and becomes the first light beam L1, and the diffracted light D is reflected by the second surface S2 of the reflective shear plate 122 and becomes the second light beam L2. The optical receiver 108 is disposed to receive the first light beam L1 and the second light beam L2 provided by the reflective shear plate 122.

The first lens 110 and the second lens 111 are disposed between the holographic storage device 102 and the shearing interferometer 120, and the diffracted light D traveling from the holographic storage device 102 to the optical receiver 108 sequentially passes through the first lens 110 and the second lens 111. The low pass filter 104 is disposed between the first lens 110 and the second lens 111. The low pass filter 104 has an aperture 105, and the size of the aperture 105 is between 1X1 minimum pixel units of the optical receiver 108 and 4X4 minimum pixel units of the optical receiver 108. The low pass filter 104 is used to leave the diffracted light D passing through with low spatial frequency noise, so as to increase the accuracy of the holographic device 100 in reading data from the disk 106 (see fig. 2A and 2B).

Please refer to fig. 1, fig. 3A and fig. 3B simultaneously. FIG. 3A is a schematic diagram illustrating a first imaging range A1 of the first light beam L1 on the optical receiver 108 shown in FIG. 1. FIG. 3B is a schematic diagram illustrating a second imaging range A2 of the second light beam L2 on the optical receiver 108 shown in FIG. 1.

When the reading light L diffracts on the disk 106 to form a diffracted light D, the diffracted light D has (or carries) data stored on the disk 106. Therefore, the first light beam L1 and the second light beam L2 converted from the diffracted light D by the shearing interferometer 120 also have (or carry) the data stored on the disk 106. For the parallel first and second light beams L1 and L2, the difference between the first and second light beams L1 and L2 is a distance difference from each other in a direction perpendicular to the traveling direction.

When the optical receiver 108 receives the first light beam L1 and the second light beam L2, the data stored on the disk 106 and carried by the first light beam L1 and the second light beam L2 are represented as data cells in a phase format, as shown in fig. 3A and 3B.

The data reading method of the present invention can be roughly divided into three steps. The first step is to form the overlapped imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108. The second step is to obtain the intensity distribution form of the first light beam L1 and the second light beam L2 on the optical receiver 108 by the overlapped imaging ranges. The third step is to calculate the intensity distribution form to calculate the data of the first light beam L1 stored on the disk 106, wherein the calculation is performed by calculating the known phase to the unknown phase (or to be calculated). When the data content of the first light beam L1 is estimated, the data content stored on the disc 106 can be read by the holographic device 100.

As mentioned above, in order to derive the unknown phase from the known phase, the holographic device 100 records the information of the initial reference signal point on the disc 106. In this embodiment, when the holographic device 100 performs writing, the light source module 114 of the holographic storage device 102 may provide a signal light (not shown), wherein the signal light provided by the light source module 114 has an initial reference signal point. Therefore, when the signal light is written in the disc 106, the disc 106 will record the information corresponding to the initial reference signal point.

Therefore, when the holographic device 100 performs reading, the diffracted light D diffracted from the reading light L in the disk 106 has a data point corresponding to the initial reference signal point. By using the diffracted light D having the data point corresponding to the initial reference signal point, the data content stored in the disk 106 can be estimated and read by the holographic device 100. The following description will further describe the data reading method of the present invention.

In FIG. 3A, the imaging range of the first light beam L1 provided by the shearing interferometer 120 on the optical receiver 108 is the first imaging range A1. The first imaging range a1 has a first data cell M. In this embodiment, the first imaging range a1 can be regarded as the first imaging range a1 of 8 rows by 8 columns, and the number of the first data cells M therein is 64.

Each of the first data cells M has a first phase P1 or a second phase P2. In the first imaging range a1 illustrated in fig. 3A, the first data cell M without shading is represented as the first phase P1, and the first data cell M with shading is represented as the second phase P2. The first phase P1 may be a 0 degree phase and the second phase P2 may be a 180 degree (π) phase.

For convenience of illustration, the first data cell M in fig. 3A is represented in a matrix-like manner. For example, in the first row of the first imaging range A1, the first data cell M may be sequentially represented as M₁₁、M₁₂、M₁₃、M₁₄、M₁₅、M₁₆、M₁₇、M₁₈Wherein M is₁₁、M₁₂、M₁₄、M₁₆、M₁₈A first phase P1 (no shading), and M₁₃、M₁₅、M₁₇A second phase P2 (with shading). Likewise, in the second column of the first imaging range a1, the first data cell M may be sequentially represented as M₂₁、M₂₂、M₂₃、M₂₄、M₂₅、M₂₆、M₂₇、M₂₈Wherein M is₂₁、M₂₃、M₂₅、M₂₆A first phase P1 (no shading), and M₂₂、M₂₄、M₂₇、M₂₈A second phase P2 (with shading).

In FIG. 3B, the imaging range of the second light beam L2 provided by the shearing interferometer 120 on the optical receiver 108 is a second imaging range A2, wherein the first imaging range A1 and the second imaging range A2 are rectangles with the same size. The second imaging range a2 has a second data cell N. Since the first imaging range a1 and the second imaging range a2 are rectangles of the same size, the second imaging range a2 can also be regarded as the second imaging range a2 of 8 columns by 8 rows, and the number of the second data cells N therein is 64.

Each second data cell N also has the first phase P1 or the second phase P2. Similarly, in the second imaging range a2 shown in fig. 3B, the second data cell N without shading is represented as the first phase P1, and the second data cell N with shading is represented as the second phase P2.

The second data cell N in fig. 3B is also represented in a matrix-like manner. For example, in the first row of the second imaging range A2, the second data cell N may be sequentially represented as N₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈In which N is₁₁、N₁₂、N₁₄、N₁₆、N₁₈A first phase P1 (no shading), and N₁₃、N₁₅、N₁₇A second phase P2 (with shading).

In addition, as described above, since the information corresponding to the initial reference signal point is recorded in the disk 106, the diffracted light D and the first and second light beams L1 and L2 converted from the diffracted light D each have data points corresponding to the initial reference signal point.

For example, in the first imaging range A1 of the first light beam L1 on the optical receiver 108, the first data cell M₁₁、M₁₂、M₁₃、M₁₄、M₁₅、M₁₆、M₁₇、M₁₈May be the data point corresponding to the initial reference signal point. For convenience of explanation, the first data cell M₁₁、M₁₂、M₁₃、M₁₄、M₁₅、M₁₆、M₁₇、M₁₈Upper labelThere is an initial reference signal point R.

Similarly, in the second imaging range A2 of the second light beam L2 on the optical receiver 108, the second data cell N₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈There are also data points corresponding to the initial reference signal points. For convenience of explanation, the second data cell N₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈The initial reference signal point R is marked on the graph.

In other words, in the first imaging range A1 and the second imaging range A2, the first data cell M₁₁、M₁₂、M₁₃、M₁₄、M₁₅、M₁₆、M₁₇、M₁₈And a second data cell N₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈Is known, while the phases of the remaining first data cells M and second data cells N are unknown.

Fig. 4A and 4B are schematic diagrams illustrating the holographic device 100 of fig. 1 reading the first light beam L1 and the second light beam L2. In fig. 4A and 4B, the first imaging range a1 and the second imaging range a2 are illustrated to correspond to the first imaging range a1 and the second imaging range a2 of fig. 3A and 3B, respectively. In addition, the second imaging range a2 is indicated by a dashed line frame so as not to complicate the drawing.

As mentioned above, the diffracted light D can be converted into the first light beam L1 and the second light beam L2 by the shearing interferometer 120 (see fig. 1), and imaged on the optical receiver 108 (see fig. 1) to form the first imaging range a1 and the second imaging range a2, respectively, as mentioned above in the first step. In fig. 4A and 4B, the first imaging range a1 and the second imaging range a2 formed by the first light beam L1 and the second light beam L2 on the optical receiver 108 are partially overlapped.

First imaging range on the optical receiver 108When a1 partially overlaps the second imaging range a2, in the overlapping area of the first imaging range a1 and the second imaging range a2, each first data cell M overlapping the first imaging range a1 and the second imaging range a2 completely overlaps each second data cell N. For example, the first data cell M of the second row of the first imaging range A1 (corresponding to the first data cell M of FIG. 3A)₂₁、M₂₂、M₂₃、M₂₄、M₂₅、M₂₆、M₂₇、M₂₈) Respectively correspond to the second data cells N of the first row of the second imaging range A2 (corresponding to the second data cells N of FIG. 3B)₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈) And completely overlapping.

Then, the data reading method is to convert the first light beam L1 and the second light beam L2 provided by the shearing interferometer 120 from the phase distribution form to the intensity distribution form by interference according to the completely overlapped first data cell M and second data cell N in the area where the first imaging range a1 and the second imaging range a2 overlap, and record in the form of intensity signals, as the second step mentioned above.

In the step of converting the first light beam L1 and the second light beam L2 from the phase distribution form to the intensity distribution form by interference, the conversion step has the following steps. When each of the completely overlapped sets of the first data cell M and the second data cell N is the first phase P1 or the second phase P2, the intensity of the completely overlapped set of the first data cell M and the second data cell N at the optical receiver 108 is defined as the first intensity. When the first phase P1 and the second phase P2 are defined for each set of the completely overlapped first data cell M and the completely overlapped second data cell N, respectively, the intensity of the set of the completely overlapped first data cell M and the second data cell N at the optical receiver 108 is defined as the second intensity.

In other words, the step of converting the first light beam L1 and the second light beam L2 from the phase distribution form to the intensity distribution form through interference is defined by the phase relationship between the completely overlapped first data cell M and the completely overlapped second data cell N. The phase relationship is, for example, constructive or destructive interference between the first data cell M and the second data cell N. For example, when the first data cell M and the second data cell N have the same phase, the phase relationship can be regarded as constructive interference. Conversely, when the first data cell M and the second data cell N which are coincident have opposite phases, the phase relationship thereof can be regarded as destructive interference.

In this embodiment, the converted intensity signal is recorded in a binary form as an example, that is, the first intensity and the second intensity of the converted intensity distribution form can be regarded as 1 and 0, respectively. During the step of converting the first light beam L1 and the second light beam L2 from the phase distribution form to the intensity distribution form through interference, the data reading method is to subtract the phases of the first data cell M and the second data cell N to define the intensity of each datum. For example, when the phase of a group of data cells overlapped is pi and 0 (or 0 and pi), the intensity of the group of data cells is defined as 1. When the phases of a set of data cells are both pi (pi and pi) or both 0(0 and 0), the intensity of the set of data cells is defined as 0.

After the optical receiver 108 converts the first light beam L1 and the second light beam L2 from the phase distribution form to the intensity distribution form through interference, the phase of each first data cell M in the first imaging range a1 can be estimated through the intensity distribution form of the first light beam L1 and the second light beam L2 and the data point corresponding to the initial reference signal point R, as mentioned above in the third step.

Please see the arrows in FIG. 4A (the second row of the first imaging range A1 and the first row of the second imaging range A2), in which the optical receiver 108 will detect the first data cell M in the second row of the first imaging range A1 (corresponding to the first data cell M in FIG. 3A)₂₁、M₂₂、M₂₃、M₂₄、M₂₅、M₂₆、M₂₇、M₂₈) And second imagingThe second data cell N of the first row of range A2 (corresponding to the second data cell N of FIG. 3B)₁₁、N₁₂、N₁₃、N₁₄、N₁₅、N₁₆、N₁₇、N₁₈) The data cells are completely overlapped, and the data cells at different positions receive a plurality of intensity signals. For example, the optical receiver 108 is connected to the optical network by M₂₁And N₁₁Intensity after superposition, M₂₂And N₁₂Intensity after superposition, M₂₃And N₁₃Intensity after superposition, M₂₄And N₁₄Intensity after superposition, M₂₅And N₁₅Intensity after superposition, M₂₆And N₁₆Intensity after superposition, M₂₇And N₁₇Intensity after superposition, M₂₈And N₁₈The intensities after the superposition are respectively 0, 1, 0 and 1.

Since the phase of the second data cell N in the first row of the second imaging range a2 is known (marked with the initial reference signal point R), the phase of the first data cell M in the second row of the first imaging range a1 can be calculated by the operation rule of phase subtraction.

For example, due to M₂₁And N₁₁In the superposition, due to M₂₁And N₁₁The intensity after superposition is 0, so that M can be deduced₂₁And N₁₁The phases are the same. Then, due to N₁₁Is known and is 0 phase, so M₂₁The phase of which can be estimated as the 0 phase.

On the contrary, since M₂₂And N₁₂The intensity after superposition is 1, so that M can be deduced₂₁And N₁₁The phases are different. Then, due to N₁₁Is known and is 0 phase, so M₂₁The phase of which can be estimated as the pi phase. By deriving the rule from this, the phase of the first data cell M in the second row of the first imaging range a1 can be derived.

Similarly, when the phase of the first data cell M in the second row of the first imaging range a1 is calculated, the phase of the second data cell N in the second row of the second imaging range a2 can be obtained because the phase distribution of the first imaging range a1 is the same as that of the second imaging range a 2.

Then, please see the arrow in fig. 4B (the third row of the first imaging range a1 and the second row of the second imaging range a 2), where the first data cell M in the third row of the first imaging range a1 and the second data cell N in the second row of the second imaging range a2 are completely overlapped, respectively.

The optical receiver 108 is connected to the optical fiber M₃₁And N₂₁(not shown, the first data cell M of FIG. 3A and the second data cell N of FIG. 3A are labeled as a matrix rule)₃₂And N₂₂Intensity after superposition, M₃₃And N₂₃Intensity after superposition, M₃₄And N₂₄Intensity after superposition, M₃₅And N₂₅Intensity after superposition, M₃₆And N₂₆Intensity after superposition, M₃₇And N₂₇Intensity after superposition, M₃₈And N₂₈The intensities after the superposition are 0, 1, 0, 1, 0, respectively. According to the above estimation rule, since the intensity distribution and the phase of the second data cell N in the second row of the second imaging range A2 are known, the phase of the first data cell M in the third row of the first imaging range A1 can be estimated.

Specifically, in the present embodiment, the step of estimating the phase of each first data cell M in the first imaging range a1 is as follows. The estimation is performed from one of the data points corresponding to the initial reference signal point R in the first data cell M to each of the other completely overlapped first data cell M and second data cell N. In other words, since the phase of the first data cell M in the first row of the first imaging range a1 of the present embodiment is known, the phases of the other first data cells M in the first imaging range a1 are estimated from the first row to the second row, the third row, the fourth row, the fifth row, the sixth row, the seventh row and the eighth row in sequence.

In summary, the data reading method of the present invention can form an overlapped area after the first light beam L1 and the second light beam L2 are overlapped, wherein the overlapped area is received by the optical receiver 108 in the form of an intensity distribution. Then, through the data points of the first and second light beams L1 and L2 corresponding to the initial reference signal point R in the first and second imaging ranges a1 and a2 on the optical receiver 108, the phase of the first data cell M in the first imaging range a1 can be calculated from the data points with known phases.

When the phase of the first data cell M of the first imaging range a1 is estimated, the holographic device 100 can read the data stored in the disk 106. By the data reading method of the present invention, the optical receiver 108 can read the phase information stored in the disk 106 by reading the diffracted light D once, so that the time for the holographic device 100 to pick up from the disk 106 is shortened. Moreover, the holographic device 100 can still generate high quality data with shortened fetching time, so that the reading performance and efficiency of the holographic device 100 are greatly improved.

In addition, since the first light beam L1 and the second light beam L2 are the same diffracted light D before being converted by the shearing interferometer 120, the destructive interference of the first light beam L1 and the second light beam L2 caused by the aberration of the optical elements or the noise generated by the disk offset can be eliminated by the calculation rule of phase subtraction, thereby improving the signal-to-noise ratio of the holographic device 100.

However, it should be understood that the calculation rule of phase subtraction is only an example and not intended to limit the present invention, and those skilled in the art can flexibly select the calculation rule to define the intensity signal of the overlapped imaging range according to the actual requirement. For example, the intensity signals of the overlapped imaging ranges can be defined by the estimation rule of phase addition.

Fig. 5A to 5I are schematic diagrams illustrating various embodiments of signal light having an initial reference signal point R provided by the holographic storage device 102 in the holographic device 100 of fig. 1.

In light of the foregoing, in fig. 3A, the phase of the first data cell M of the first imaging range a1 is estimated from the data points with known phases. Fig. 3A and 3B correspond to the position of the initial reference signal point R of the signal light being in the first row of the imaging range, however, the position of the initial reference signal point R of the signal light may be in different positions according to different designs, as shown in fig. 5A to 5H. In different configurations of the initial reference signal points R, the accuracy of reading the disk by the holographic device can be increased when the number of the initial reference signal points R is increased.

In fig. 5A, the signal light has one initial reference signal point R and is located in a single data point. In fig. 5B, the signal light has a plurality of initial reference signal points R located among a plurality of data points. In fig. 5C, the signal light has a plurality of initial reference signal points R and is located in the same column of the imaging range. In fig. 5D, the signal light has a plurality of initial reference signal points R, and is located in two rows of the imaging range. In fig. 5E, the signal light has a plurality of initial reference signal points R, and is located in the data points on the diagonal line of the imaging range. In fig. 5F, the signal light has a plurality of initial reference signal points R, and is arranged in an interlaced manner. In fig. 5A, the signal light has a plurality of initial reference signal points R and is located in a block of the imaging range. In fig. 5H, the signal light has a plurality of initial reference signal points R, and is arranged among the data points in a parallel manner.

According to the number and arrangement of the initial reference signal points R of the signal light, the first imaging range a1 and the second imaging range a2 of the first light beam L1 and the second light beam L2 on the optical receiver 108 may have different overlapping manners, wherein the overlapping area of the first imaging range a1 and the second imaging range a2 may be adjusted by the shearing interferometer 120.

For example, in fig. 4A and 4B, the first imaging range a1 and the second imaging range a2 of the first light beam L1 and the second light beam L2 on the optical receiver 108 are different by a row distance (or by one data cell). In some embodiments, the shearing interferometer 120 is configured such that the lateral distance difference or the longitudinal distance difference between the first imaging range a1 and the second imaging range a2 is an integer multiple of the minimum pixel unit of the optical receiver 108.

In addition, a lateral distance difference and a longitudinal distance difference may exist between the first imaging range a1 and the second imaging range a2 at the same time, as shown in fig. 5I. In fig. 5I, there are a longitudinal distance difference V and a lateral distance difference H between the first imaging range a1 and the second imaging range a 2. The ratio of the lateral distance difference H to the longitudinal distance difference V is a tangent of an angle θ, wherein the angle θ is greater than or equal to 0 degrees and less than or equal to 90 degrees.

Referring to fig. 6, fig. 6 is a schematic optical path diagram of a holographic device 100 according to a second embodiment of the present invention. The difference between this embodiment and the first embodiment is that the holographic device 100 of this embodiment further includes an afocal system 126.

When the diffracted light D is converted into the first light beam L1 and the second light beam L2 through the reflective shear plate 122, the first light beam L1 and the second light beam L2 are generated by being reflected through the first surface S1 and the second surface S2 of the reflective shear plate 122, respectively. Due to the spacing between the first surface S1 and the second surface S2 of the reflective shear plate 122, the imaging relationship between the first light beam L1 and the second light beam L2 on the optical receiver 108 may be out of focus.

The afocal system 126 is disposed between the shearing interferometer 120 and the optical receiver 108, wherein the afocal system 126 is used for reducing the image of the first light beam L1 and the second light beam L2 provided by the shearing interferometer 120 on the optical receiver 108. In this embodiment, the afocal system 126 can be considered a zoom-out imaging system. By reducing the image on the optical receiver 108 by the afocal system 126, the possible out-of-focus problem of the first light beam L1 and the second light beam L2 on the optical receiver 108 can be effectively prevented. Furthermore, since the magnification of the first light beam L1 and the second light beam L2 in the longitudinal direction (parallel to the optical axis of the afocal system 126) is the square times of the magnification in the transverse direction (perpendicular to the optical axis of the afocal system 126), the phase shift (pisohaseshift) between the images of the first light beam L1 and the second light beam L2 on the optical receiver 108 is not affected.

Fig. 7 is a schematic optical path diagram of the holographic device 100 according to the third embodiment of the present invention. The difference between this embodiment and the first embodiment is that the shearing interferometer 120 of the holographic device 100 of this embodiment includes a transmissive shearing plate 124.

In fig. 7, the diffracted light D provided by the holographic storage device 102 is incident on the first mirror 109 through the first lens 110, the low pass filter 104 and the second lens 111, and then the diffracted light D is reflected by the first mirror 109 to the transmissive shear plate 124. In this embodiment, the diffracted light D passing through the transmissive shear plate 124 will become the first light beam L1, and the diffracted light D sequentially reflected from the first surface S1 and the second surface S2 of the transmissive shear plate 124 will become the second light beam L2. Then, the first light beam L1 enters the optical receiver 108 in parallel with the second light beam L2.

In addition, since there is a distance between the first surface S1 and the second surface S2 of the transmissive shear plate 124, there may be a problem of defocusing in the imaging relationship between the first light beam and the L1 and the second light beam L2 on the optical receiver 108. To prevent this out-of-focus problem, an afocal system (not shown) may be disposed between the shearing interferometer 120 and the optical receiver 108. Similarly, the afocal system is used to reduce the image of the first light beam L1 and the second light beam L2 provided by the shearing interferometer 120 on the optical receiver 108, so as to effectively prevent the out-of-focus problem.

Fig. 8 is a schematic configuration diagram of a holographic device 100 according to a fourth embodiment of the present invention. The difference between the present embodiment and the first embodiment is that the shearing interferometer 120 of the present embodiment is composed of a transparent substrate 128 and a dielectric layer 130, whereas the shearing interferometer 120 of the first embodiment is a shearing plate.

The shearing interferometer 120 includes a transparent substrate 128 and a dielectric layer 130. The transparent substrate 128 has a first surface S1 and a second surface S2 that are opposite and non-parallel. The dielectric layer 130 is disposed on the first surface S1 and is parallel to the first surface S1.

In this embodiment, when the diffracted light D enters the shearing interferometer 120, the diffracted light D reflected by the dielectric layer 130 will become the first light beam L1, and the diffracted light D transmitted through the dielectric layer 130 and reflected at the interface between the dielectric layer 130 and the transparent substrate 128 will become the second light beam L2. By adjusting the characteristics of the dielectric layer 130, the accuracy of the holographic device 100 in data reading can be improved. For example, the possible defocus problem mentioned above can be prevented by adjusting the thickness of the dielectric layer 130. Furthermore, by adjusting the reflectivity of the medium layer 130, the interference contrast between the first light beam L1 and the second light beam L2 can be improved.

Further, the thickness of the dielectric layer 130 may be determined by the distance difference between the imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108 (see fig. 1), the phase difference between the first light beam L1 and the second light beam L2, the wavelength provided by the light source module 114 (see fig. 1), the refractive index of the dielectric layer 130, and the installation angle of the shearing interferometer 120.

The relationship between the above parameters is shown by the following equation:

………………………………..(1)

………………………...………..(2)

wherein λ₀W is a distance difference between imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108, phi is a phase difference between the first light beam L1 and the second light beam L2; t is the thickness of the dielectric layer 130；θ₀Is the incident angle of the light beam; theta₁Is the angle of refraction of the beam in dielectric layer 130; n is₁Is the refractive index of the dielectric layer 130; n is₀Is the refractive index of air.

When the difference between the distance between the imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108 is 5 μm, then a minimum of 5 μm is required for w to be able to resolve the interference pattern. Under the condition w of 5 μm, λ₀Is 405nm, n₁Is 1.56, n₀For 1, psi (2N-1) pi, and N is positive , it can be calculated according to equations (I) and (II):

wherein,. That is, when the incident angle is

At 41.6 ° ± 0.2 °, the phase difference between the first light beam L1 and the second light beam L2 is about pi ± 0.1 pi, and the thickness of the dielectric layer 130 is 7 micrometers (μm). In other words, in some embodiments, the thickness of the dielectric layer 130 is greater than 0 micrometer (μm) and less than or equal to 10 micrometers (μm).

In addition, since the transparent substrate 128 has the first surface S1 and the second surface S2 that are opposite and non-parallel to each other, ghost images generated by the diffracted light D in the shearing interferometer 120 can be effectively separated, as shown by the light beams L3, L4, L5 and L6. Since the noise caused by the ghost can be effectively eliminated, the accuracy of the holographic device 100 in data reading is also improved.

Fig. 9 is a schematic optical path diagram of a holographic device 100 according to a fifth embodiment of the present invention. The difference between the present embodiment and the fourth embodiment is that the holographic device 100 of the present embodiment further includes an afocal system 126.

According to the above formula (I), the distance difference between the imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108 is proportional to the thickness T of the medium layer 130. If the distance difference between the imaging ranges of the first light beam L1 and the second light beam L2 on the optical receiver 108 is to be increased while maintaining the thickness of the medium layer 130, the distance difference can be increased by the magnifying imaging system.

The afocal system 126 is disposed between the shearing interferometer 120 and the optical receiver 108, wherein the afocal system 126 is used for magnifying the image of the first light beam L1 and the second light beam L2 provided by the shearing interferometer 120 on the optical receiver 108. That is, the afocal system 126 can be considered a magnifying imaging system.

Through the afocal system 126, the distance between the first imaging range and the second imaging range of the first light beam L1 and the second light beam L2 on the optical receiver 108 can be adjusted. Furthermore, since the dielectric layer 130 can be regarded as a thin film, the out-of-focus problem generated between the first light beam L1 and the second light beam L2 can be ignored.

Fig. 10A is a schematic optical path diagram of a holographic device 100 according to a sixth embodiment of the present invention. FIG. 10B is a schematic diagram of the arrangement of the grating unit 136 shown in FIG. 10A. The difference between the present embodiment and the first embodiment is that the shearing interferometer 120 of the present embodiment is composed of a first focusing lens 132, a second focusing lens 134, and a grating unit 136.

The first converging lens 132 and the second converging lens 134 are disposed between the holographic storage device 102 and the optical receiver 108, and the diffracted light D traveling from the holographic storage device 102 to the optical receiver 108 sequentially passes through the first converging lens 132 and the second converging lens 134. The grating unit 136 is disposed between the first condensing lens 132 and the second condensing lens 134. The grating unit 136 includes a first grating 138 and a second grating 140. The second grating 140 is disposed parallel to the first grating 138, and the diffracted light D from the first converging lens 132 to the second converging lens 134 passes through the first grating 138 and the second grating 140 sequentially.

In fig. 10B, when the diffracted light D passes through the first grating 138, the diffracted light D is converted into light beams L7 and L8. When the light beams L7 and L8 pass through the second grating 140, the light beam L7 is converted into light beams L9 and L10, wherein the first light beam L1 is composed of light beams L9 and L10. When the light beam L8 passes through the second grating 140, the light beam L8 is converted into light beams L11 and L12, wherein the second light beam L2 is composed of light beams L11 and L12.

When the holographic storage device 102 provides the tilted diffracted light D (tilted to the optical axis of the first focusing lens 132) to the first focusing lens 132, the first focusing lens 132 guides the diffracted light D to the grating unit 136. Then, after the first light beam L1 and the second light beam L2 provided by the grating unit 136 are guided to the optical receiver 108 through the second converging lens 134, the first light beam L1 and the second light beam L2 are imaged on the optical receiver 108 to form a first imaging range and a second imaging range, respectively.

In this embodiment, by adjusting the horizontal distance between the first grating 138 and the second grating 140 of the grating unit 136, the relation of the distance difference between the first light beam L1 and the second light beam L2 can be changed. In addition, by adjusting the vertical distance between the first grating 138 and the second grating 140 of the grating unit 136, the phase difference between the first light beam L1 and the second light beam L2 can be changed.

Fig. 11A is a schematic optical path diagram of a holographic device 100 according to a seventh embodiment of the present invention. FIG. 11B is a schematic diagram of the configuration of the grating unit 136 shown in FIG. 11A. The difference between the present embodiment and the sixth embodiment is that the grating unit 136 of the present embodiment includes a tilted grating 142 (blazedgradling).

In this embodiment, the diffracted light D can be transmitted through the tilted grating 142 to generate beams of different orders, so as to convert the diffracted light D into the first beam L1 and the second beam L2. In addition, the holographic storage device 102 provides parallel diffracted light D (parallel to the optical axis of the first focusing lens 132) to the first focusing lens 132.

Fig. 12 is a schematic optical path diagram of a holographic device 100 according to an eighth embodiment of the present invention. The difference between the present embodiment and the sixth embodiment is that the grating unit 136 of the present embodiment includes a double frequency grating 144(double frequency grating).

In this embodiment, the diffracted light D can be converted into the first light beam L1 and the second light beam L2 through two spatial frequencies on the dual-frequency grating 144. In addition, controlling the two spatial frequencies can change the phase difference between the first beam L1 and the second beam L2.

In summary, the holographic device of the present invention converts the diffracted light into the first light beam and the second light beam through the shearing interferometer. The first light beam and the second light beam are partially overlapped to form an overlapped area after the optical receiver is partially overlapped, wherein the overlapped area is in the form of intensity distribution. The phase of the first data cell of the first imaging range can be calculated from the data points with known phases by passing the data points of the first and second imaging ranges of the first and second beams on the optical receiver corresponding to the initial reference signal point. When the phase of the first data cell in the first imaging range is calculated, the holographic device can read the data stored in the disk.

By the data reading method of the present invention, the optical receiver can read the phase information stored in the disk by reading the diffracted light once, so that the retrieving time of the disk is shortened. Moreover, the holographic device can still generate high-quality data under the condition of shortening fetching time, so that the reading performance of the holographic device is greatly improved.

In addition, the overlapping area of the first imaging range and the second imaging range of the first light beam and the second light beam on the optical receiver can be adjusted through the shearing interferometer, so as to be matched with different holographic device designs. In addition, the holographic device has an afocal system, which is configured as a zoom-out imaging system or a zoom-in imaging system, so that the imaging of the first light beam and the second light beam on the optical receiver can be adjusted to effectively prevent the out-of-focus problem and suppress noise.

While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

1. A holographic device, comprising:

a holographic storage device, configured to provide a reading light to a disk, so that the reading light is diffracted on the disk to become a diffracted light;

a shearing interferometer, configured to receive the diffracted light and convert the diffracted light into a first light beam and a second light beam, wherein the first light beam and the second light beam are parallel to each other; and an optical receiver configured to receive the first light beam and the second light beam provided by the shearing interferometer.

2. The holographic device of claim 1, wherein the holographic storage device comprises a light source module configured to provide a signal light, wherein the signal light provided by the light source module has an initial reference signal point.

3. The holographic device of claim 1, wherein the shearing interferometer comprises a reflective shearing plate or a transmissive shearing plate.

4. The holographic device of claim 3, further comprising an afocal system disposed between the shearing interferometer and the optical receiver, wherein the afocal system is configured to reduce the imaging of the first and second beams provided by the shearing interferometer on the optical receiver.

5. The holographic device of claim 1, wherein the shearing interferometer comprises: a transparent substrate having a first surface and a second surface which are opposite and nonparallel; and a dielectric layer disposed on the first surface and parallel to the first surface.

6. The holographic device of claim 5, in which the dielectric layer has a thickness greater than 0 microns and less than or equal to 10 microns.

7. The holographic device of claim 5, further comprising an afocal system disposed between the shearing interferometer and the optical receiver, wherein the afocal system is configured to magnify the images of the first and second beams provided by the shearing interferometer onto the optical receiver.

8. The holographic device of claim 1, further comprising a first lens; a second lens, wherein the first lens and the second lens are disposed between the holographic storage device and the shearing interferometer, and the diffracted light traveling from the holographic storage device to the shearing interferometer sequentially passes through the first lens and the second lens; and a low pass filter disposed between the first lens and the second lens, wherein the low pass filter has an aperture, and the size of the aperture is between 1X1 minimum pixel units of the optical receiver and 4X4 minimum pixel units of the optical receiver.

9. The apparatus of claim 1, wherein the first and second light beams provided by the shearing interferometer have a first and second imaging ranges on the optical receiver, respectively, the first and second imaging ranges have the same size, and the first and second imaging ranges partially overlap.

10. The holographic device of claim 9, wherein a longitudinal distance difference and a transverse distance difference exist between the first imaging range and the second imaging range, wherein a ratio of the transverse distance difference to the longitudinal distance difference is a tangent of an angle, wherein the angle is greater than or equal to 0 degrees and less than or equal to 90 degrees.

11. The holographic apparatus of claim 9, wherein the shearing interferometer is configured such that the lateral distance difference or the longitudinal distance difference between the first imaging range and the second imaging range is an integer multiple of the smallest pixel unit of the optical receiver.

12. The holographic device of claim 1, wherein the shearing interferometer comprises a first converging lens, a second converging lens and a grating unit, the first and second converging lenses are disposed between the holographic storage device and the optical receiver, and the diffracted light traveling from the holographic storage device to the optical receiver passes through the first and second converging lenses in sequence, the grating unit is disposed between the first and second converging lenses.

13. The holographic device of claim 12, wherein the grating unit comprises: a first grating; and a second grating parallel to the first grating, wherein the diffracted light from the first converging lens to the second converging lens passes through the first grating and the second grating in sequence.

14. The holographic device of claim 12, wherein the grating unit comprises a tilted grating or a dual frequency grating.

15. A data reading method of a holographic device comprises providing a signal light to a disk through a holographic storage device, wherein the signal light has an initial reference signal point, so that information corresponding to the initial reference signal point is recorded in the disk; providing a reading light to the disk through the holographic storage device, so that the reading light is diffracted on the disk to form a diffracted light, wherein the diffracted light has a data point corresponding to the initial reference signal point;

converting the diffracted light into a first light beam and a second light beam which are parallel to each other through a shearing interferometer; and guiding the first light beam and the second light beam to an optical receiver, wherein imaging ranges of the first light beam and the second light beam on the optical receiver are a first imaging range and a second imaging range respectively, the first imaging range and the second imaging range have the same size, and the first imaging range and the second imaging range are partially overlapped.

16. The method of claim 15, wherein the first imaging range has a plurality of first data cells, each of the first data cells has a first phase or a second phase, the second imaging range has a plurality of second data cells, each of the second data cells has the first phase or the second phase, and each of the first data cells and each of the second data cells in an area where the first imaging range and the second imaging range overlap completely overlap.

17. The data reading method as claimed in claim 16, further comprising converting the first and second light beams provided by the shearing interferometer from a phase distribution form to an intensity distribution form by interference based on the first and second data cells being completely coincident in a region where the first and second imaging ranges overlap.

18. The method of claim 17, wherein the step of converting the first and second beams from a phase profile to an intensity profile by interference further comprises defining the intensity of each of the completely coincident first and second data cells at the optical receiver as a first intensity when the first and second data cells are both in the first phase or the second phase; and defining the intensity of the set of completely coincident first data cells and second data cells at the optical receiver as a second intensity when each set of completely coincident first data cells and second data cells are the first phase and the second phase, respectively.

19. The method of claim 17, further comprising transforming the first and second beams from a phase distribution to an intensity distribution, and calculating the phase of each of the first data cells in the first imaging range according to the intensity distribution and the data point corresponding to the initial reference signal point.

20. The method of claim 19, wherein the step of estimating the phase of each of the first data cells in the first imaging range further comprises estimating from one of the data points of the first data cells corresponding to the initial reference signal point to each of the other completely coincident first data cell and second data cell.

21. The method of claim 15, wherein a longitudinal distance difference and a transverse distance difference exist between the first imaging range and the second imaging range, and wherein a ratio of the transverse distance difference to the longitudinal distance difference is a tangent of an angle, wherein the angle is greater than or equal to 0 degrees and less than or equal to 90 degrees.