CN110060707B - Optical signal coding method and access method and holographic storage device - Google Patents
Optical signal coding method and access method and holographic storage device Download PDFInfo
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- CN110060707B CN110060707B CN201810047857.7A CN201810047857A CN110060707B CN 110060707 B CN110060707 B CN 110060707B CN 201810047857 A CN201810047857 A CN 201810047857A CN 110060707 B CN110060707 B CN 110060707B
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- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
- G11B7/0065—Recording, reproducing or erasing by using optical interference patterns, e.g. holograms
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- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/13—Optical detectors therefor
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
- G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
- G11B7/135—Means for guiding the beam from the source to the record carrier or from the record carrier to the detector
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Abstract
The invention discloses an optical signal coding method, an optical signal access method and a holographic storage device. The method for encoding the optical signal uses a controller to control the arrangement relationship of the pixels of the spatial light modulator, so as to adjust the phase distribution of the light beam passing through the pixels, so that the sub-light beam leaving from the first phase pixel has a first phase, and the sub-light beam leaving from the second phase pixel has a second phase, wherein the phase difference between the first phase and the second phase is 180 degrees, and the method is characterized in that: between the first pixel and the last pixel arranged along the same straight line direction, at least two first phase pixels arranged in succession exist in three consecutive pixels, or at least two second phase pixels arranged in succession exist in three consecutive pixels. The invention can increase the total length of the continuously arranged and same-phase bit signals in the light beam, thereby reducing the Nyquist aperture size of the light beam for the storage disk, and further increasing the storage capacity density of the storage disk.
Description
Technical Field
The present invention relates to the field of optical information storage, and more particularly, to a method for encoding and accessing optical signals and a holographic storage device.
Background
With the development of technology, the required storage capacity of electronic files has increased. 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. As the amount of required storage for electronic files increases, the technical development of holographic storage has begun to be highlighted.
The hologram memory technology is an information memory technology for writing image data into a memory medium by causing interference between transmitted signal light and reference light. When reading data, the reference light is re-irradiated to the storage medium to generate image data. Then, the generated image data is read by the detector. How to increase the storage capacity of the holographic storage technology becomes the focus and hot spot of the current research in the related field.
A spatial light modulator is a device that modulates the spatial distribution of an optical wave. In general, spatial light modulators are capable of spatially and temporally transforming or modulating a one-or two-dimensional distribution of a certain property or properties of a light wave (e.g., phase, amplitude or intensity, frequency, polarization, etc.) to write information carried by the light wave into a corresponding storage device. The phase of the light wave passing through the spatial light modulator can be changed or arranged according to a certain rule by adopting a corresponding controller, so that the optical signal is encoded. However, how to record as much information as possible in a storage medium with a fixed capacity by encoding an optical signal is a technical problem that needs to be solved by those skilled in the art.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention discloses an optical signal encoding method, an optical signal access method and a holographic storage device.
The invention is realized by the following technical scheme:
a method for coding optical signals, wherein a controller is adopted to control the arrangement relation of a plurality of pixels arranged along a straight line direction of a spatial light modulator, wherein the pixels comprise a first phase pixel and a second phase pixel, so that the phase distribution of light beams passing through the pixels is adjusted, the sub-light beams leaving from the first phase pixel have a first phase, the sub-light beams leaving from the second phase pixel have a second phase, the phase difference between the first phase and the second phase is 180 degrees, at least two first phase pixels arranged in succession exist in three pixels arranged along the same straight line direction, or at least two second phase pixels arranged in succession exist in three pixels arranged in succession.
Further, between the first pixel and the last pixel arranged along the same straight line direction, there are at least three of the first phase pixels arranged in series, or there are at least three of the second phase pixels arranged in series.
Further, all the first phase pixels between the first pixel and the last pixel arranged along the same straight line direction are continuously arranged, and all the second phase pixels are continuously arranged.
When storing optical signal, the coding method codes the optical signal and makes the writing light provided by the light emitter pass through the space light modulator and the light guide module in turn and then enter the storage disc.
Furthermore, when optical signals are read, reading light provided by the light emitter is made to enter the storage disk after passing through the spatial light modulator and the light guide module in sequence and form diffracted light through the storage disk, the diffracted light enters the shearing interferometer through the light guide module, the shearing interferometer converts the diffracted light into a first light beam and a second light beam which are parallel to each other and have the same phase distribution, and then the first light beam and the second light beam are read by adopting a light detector.
Further, there is a partial overlap or a complete overlap in the projection range of the first light beam and the second light beam on the light detector.
Further, the overlapping depth of the projection range of the first light beam and the second light beam on the light detector is an integral multiple of the length of the first phase pixel or an integral multiple of the length of the second phase pixel.
A holographic storage device of optical signal, the said holographic storage device adopts the said optical signal encoding method to store the optical signal; the holographic storage device comprises a light emitter, a spatial light modulator, a controller, a light guide module and a storage disk; the spatial light modulator is optically coupled between the light emitter and the storage disk, the controller is electrically connected with the spatial light modulator, and the light guide module is optically coupled between the spatial light modulator and the storage disk.
Further, the device comprises a light detector and a shearing interferometer optically coupled between the light guide module and the light detector.
Further, the light guide module comprises a polarizing beam splitter, a first guide lens, a low-pass filter, a second guide lens, a quarter-wave plate, a reflector and an objective lens.
The invention has the advantages that: the invention controls the arrangement position of the pixel, thereby enabling the spatial light modulator to carry out phase coding modulation on the light beam. By phase-coded modulating the light beam, the total length of the bit signals which are arranged in the light beam in series and have the same phase can be increased, so that the Nyquist aperture size of the light beam for the storage disk is reduced, and the storage capacity density of the storage disk is increased.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention.
FIG. 1 is a schematic optical path diagram illustrating an optical signal holographic storage device according to an embodiment of the present invention for data writing;
FIG. 2 is a schematic diagram of an arrangement of a light emitter and a spatial light modulator according to an embodiment of the invention;
FIG. 3 is a schematic optical path diagram illustrating an embodiment of a holographic storage device for optical signals for data reading;
FIG. 4 is a schematic diagram of the first light beam and the second light beam traveling to the light detector when the holographic storage device for optical signals reads data according to the embodiment of the present invention;
FIG. 5 is a schematic diagram illustrating phase distributions of a first beam and a second beam when a holographic storage device for optical signals reads data according to an embodiment of the present invention.
Description of reference numerals:
100-holographic storage; 102-a storage disk; 110-a light source module; 112-an optical transmitter; 114-a spatial light modulator; 116. 116a, 116b, 116c, 116 d-first phase pixels; 118. 118a, 118b, 118c, 118 d-second phase pixels; 120-a light guide module; 122-a polarizing beam splitter; 124-a first guiding lens; 125-a low-pass filter; 126-a second guidance lens; 128-quarter wave plate; 130-a mirror; 132-objective lens; 140-a light detector; 142-a shearing interferometer; 150-a controller; a1 — first projection range; a1a, A1b, A1c, A1d, A1e, A1f, A1g, A1h — a first subrange; a2 — second projection range; a2a, A2b, A2c, A2d, A2e, A2f, A2g, A2 h-second subrange; l reading light; l1 — first light beam; l2 — second light beam; r-write light; r1a, R1b, R1c, R1d, R1e, R1f, R1g, R1h sub-beams; s1 — first surface; s2 — a second surface; w-length; diffracted light-D.
Detailed Description
In order to make the technical means and functions of the present invention easy to understand, embodiments of the present invention are described in detail below with reference to specific drawings.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example embodiment," "an example," "a specific example," or "some examples" or the like, mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. In addition, the descriptions related to "first", "second", etc. in the present invention are for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated.
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.
The embodiment of the invention provides an optical signal encoding method, an optical signal access method and a holographic storage device.
The encoding method of the optical signal uses the controller 150 to control the arrangement relationship of a plurality of pixels arranged along a straight line of the spatial light modulator 114, wherein the pixels include a first phase pixel 116 and a second phase pixel 118, so as to adjust the phase distribution of the light beam passing through the pixels, such that the sub-beam exiting from the first phase pixel 116 has a first phase, and the sub-beam exiting from the second phase pixel 118 has a second phase, wherein the phase difference between the first phase and the second phase is 180 degrees, between the first pixel and the last pixel arranged along the same straight line direction, there are at least two first phase pixels 116 arranged in succession in three pixels, or there are at least two second phase pixels 118 arranged in succession in three pixels.
Preferably, between the first pixel and the last pixel arranged along the same straight line direction, there are at least three first phase pixels 116 arranged in series, or there are at least three second phase pixels 118 arranged in series.
Further preferably, all the first phase pixels 116 between the first pixel and the last pixel arranged in the same straight line direction are arranged in series, and all the second phase pixels 118 are arranged in series.
By the coding method, when the total length of the sub-beams which are continuously arranged and have the same phase is increased and is larger than the length of a single bit signal, the imaging range of the focusing bright point on the storage disk can be reduced, so that the Nyquist aperture size of the beam relative to the storage disk is reduced, and the storage capacity density of the storage disk is increased.
The embodiment of the present invention further provides an optical signal accessing method, when storing an optical signal, the optical signal is encoded by using the optical signal encoding method, that is: the arrangement of the pixels is controlled, and the writing light R provided by the light emitter 112 is incident to the storage disk 102 after passing through the spatial light modulator 114 and the light guide module 120 in sequence. In the optical signal reading, the reading light L provided by the optical transmitter 112 is made to enter and transmit through the storage disk 102 after passing through the spatial optical modulator 114 and the light guide module 120 in sequence to form a diffracted light D, the diffracted light D enters the shearing interferometer 142 through the light guide module 120, the shearing interferometer 142 converts the diffracted light D into a first light beam L1 and a second light beam L2 which are parallel to each other and have the same phase distribution, and then the first light beam L1 and the second light beam L2 are read by the optical detector 140.
The projection ranges of the first light beam L1 and the second light beam L2 on the light detector are partially overlapped or completely overlapped. The depth of the overlap is an integer multiple of the length of the first phase pixel 116 or an integer multiple of the length of the second phase pixel 118.
The embodiment of the invention also provides a holographic storage device of the optical signal, wherein the holographic storage device stores the optical signal by adopting the coding method of the optical signal; the holographic storage device comprises a light emitter 112, a spatial light modulator 114, a controller 150, a light guide module 120 and a storage disc 102; the spatial light modulator 114 is optically coupled between the light emitter 112 and the storage disk 102, the controller 150 is electrically connected to the spatial light modulator 114, and the light guide module 120 is optically coupled between the spatial light modulator 114 and the storage disk 102. The light guide module 120 includes a polarization beam splitter 122, a first guide lens 124, a low pass filter 125, a second guide lens 126, a quarter wave plate 128, a mirror 130, and an objective lens 132. Preferably, the holographic storage device for optical signals further includes a light detector 140, and a shearing interferometer 142 optically coupled between the light guide module 120 and the light detector 140.
As shown in fig. 1, the holographic storage device 100 according to the embodiment of the present invention is a coaxial architecture, and the holographic storage device 100 performs data writing and data reading on a storage disk 102. The holographic storage device 100 comprises a light source module 110, a light guide module 120, a light detector 140 and a shearing interferometer 142.
The light source module 110 includes a light emitter 112 and a spatial light modulator 114, the light emitter 112 can provide a light beam to the spatial light modulator 114, and a person skilled in the art can select a model of the spatial light modulator 114 according to actual conditions, for example, a transmissive spatial light modulator or a reflective spatial light modulator, and a spatial light modulation module formed by combining the transmissive spatial light modulator or the reflective spatial light modulator.
The light guide module 120 is optically coupled between the light source module 110 and the light detector 140, and is used for receiving and guiding the light beam from the light source module 110. The light guide module 120 includes a polarization beam splitter 122, a first guiding lens 124, a low pass filter 125, a second guiding lens 126, a quarter wave plate 128, a mirror 130, and an objective lens 132.
The shearing interferometer 142 is optically coupled between the light guide module 120 and the light detector 140, and is used for receiving and converting the light beam from the light guide module 120.
It should be noted that the components and their configuration shown in fig. 1 are only for illustration and are not meant to limit the configuration of the components in the holographic storage device 100 according to the present invention. The relative position relationship between the components can be adjusted by those skilled in the art according to different optical path designs.
In writing data, a write light R is provided by the optical transmitter 112, wherein the write light R includes a signal light and a reference light. The write light R passes through the spatial light modulator 114, the polarization beam splitter 122, the first guide lens 124, the low pass filter 125, the second guide lens 126, the quarter wave plate 128, the mirror 130, and the objective lens 132 in this order by the light emitter 112, and then enters the storage disk 102.
The signal light and the reference light contained in the writing light R interfere with each other in the storage disc 102, and form an interference pattern in the storage disc 102, thereby recording data. Specifically, the holographic memory device 100 may perform phase modulation on the signal light and the reference light included in the writing light R through the spatial light modulator, and perform a writing process on the storage disc 102 by using the writing light R modulated.
As shown in fig. 2, fig. 2 shows a schematic configuration of the light emitter 112 and the spatial light modulator 114, and for convenience of understanding and describing the present invention, the pixels of the spatial light modulator 114 of fig. 2 are shown in a single row, however, the present invention is not limited thereto, and those skilled in the art can adjust or expand the pixel range of the spatial light modulator 114 according to the teachings of the present invention.
As shown in fig. 2, the light emitter 112 first provides write light R to the spatial light modulator 114. The spatial light modulator 114 includes a plurality of first phase pixels 116a, 116b, 116c and 116d and a plurality of second phase pixels 118a, 118b, 118c and 118d, wherein the pixels can be used to modulate the phase distribution of the passing write light R so that the write light R becomes a phase-encoded optical signal. Specifically, in the write light R, the portion passing through the first phase pixels 116a-116d has a first phase and the portion passing through the second phase pixels 118a-118d has a second phase, and the first phase is 180 degrees out of phase (or π out of phase) with the second phase.
In some embodiments of the invention, the first phase is at 0 degrees (or at 0) and the second phase is at 180 degrees (or at π). In addition, the first phase pixels 116a-116d and the second phase pixels 118a-118d of the spatial light modulator 114 have the same size, and both have a length W.
In addition, the spatial light modulator 114 is electrically connected to the controller 150, wherein the controller 150 is capable of controlling the arrangement relationship between the first phase pixels 116a to 116d and the second phase pixels 118a to 118d of the spatial light modulator 114, so that the arrangement relationship between the first phase pixels 116a to 116d and the second phase pixels 118a to 118d of the spatial light modulator 114 can meet a certain encoding rule.
The encoding rule means that the first phase pixels 116a to 116d and the second phase pixels 118a to 118d are arranged in a staggered manner along the linear direction, and at least two pixels which are arranged in series and correspond to the same phase exist among three consecutive pixels between the first pixel and the last pixel which are arranged along the linear direction. For example, there may be at least two first phase pixels arranged in series among the three consecutive pixels, or there may be at least two second phase pixels arranged in series. That is, for two pixels corresponding to the same phase, there is no single pixel corresponding to the other phase between them.
Taking fig. 2 as an example, the first phase pixels 116a to 116d and the second phase pixels 118a to 118d are arranged along a straight line in a staggered manner, wherein the first pixel from left to right to the last pixel are the second phase pixel 118a, the second phase pixel 118b, the first phase pixel 116a, the first phase pixel 116b, the first phase pixel 116c, the second phase pixel 118d and the first phase pixel 116d in sequence, three first phase pixels 116a to 116c arranged in series exist between the second phase pixel 118b and the second phase pixel 118c, and two second phase pixels 118c to 118d arranged in series also exist between the first phase pixel 116c and the first phase pixel 116 d.
Under this configuration, after the writing light R passes through the spatial light modulator 114 shown in fig. 2, the writing light R can be divided into eight sub-light beams R1a, R1b, R1c, R1d, R1e, R1f, R1g, R1h, and the phases thereof are pi, 0, pi, 0, respectively. When the write light R is incident on the storage disc 102, the phase modulated by the spatial light modulator 114 is recorded in the storage disc 102.
It should be noted that the arrangement relationship between the first phase pixels 116a to 116d and the second phase pixels 118a to 118d of the spatial light modulator 114 according to the present invention is not limited to that shown in fig. 2, and in other embodiments, the arrangement relationship between the first phase pixels 116a to 116d and the second phase pixels 118a to 118d may also be changed under the condition of meeting the encoding rule, for example, the order from the first pixel to the last pixel from left to right may also be two first phase pixels, two second phase pixels, two first phase pixels, and two second phase pixels, that is, the corresponding phases may be 0, pi, 0, pi, and pi, respectively.
As shown in fig. 3, when data is read, the light beam from the light guiding module 120 can be guided to the optical detector 140 by the shearing interferometer 142, wherein the shearing interferometer 142 can be a reflective shearing plate.
Specifically, during reading, the optical transmitter 112 provides the reading light L, so that the reading light L can sequentially pass through the spatial light modulator 114, the polarization beam splitter 122, the first guiding lens 124, the low pass filter 125, the second guiding lens 126, the quarter wave plate 128, the second reflecting mirror 130 and the objective lens 132 from the optical transmitter 112 and enter the storage disk 102, so that the reading light L is diffracted into the diffracted light D by the storage disk 102. Then, the diffracted light D travels along the original optical path to the polarization beam splitter 122 and is guided to the shearing interferometer 142 by the polarization beam splitter 122.
The shearing interferometer 142 is used for receiving the diffracted light D from the polarization beam splitter 122 of the light guide module 120 and converting the diffracted light D into a first light beam L1 and a second light beam L2 which are parallel to each other. Specifically, the shearing interferometer 142 has a first surface S1 and a second surface S2 that are parallel, wherein when the diffracted light D travels to the shearing interferometer 142, a portion of the diffracted light D reflects off the first surface S1 of the shearing interferometer 142 and becomes the first light beam L1, and another portion of the diffracted light D reflects off the second surface S2 of the shearing interferometer 142 and becomes the second light beam L2. Since the first beam L1 and the second beam L2 are converted from the diffracted light D, the phase distribution of the first beam L1, and the phase distribution of the second beam L2 are substantially the same. In other words, 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.
In addition, the first light beam L1 and the second light beam L2 converted by the shearing interferometer 142 overlap each other. Specifically, the first light beam L1 may travel from the shearing interferometer 142 to the light detector 140 along a first optical path, the second light beam L2 may travel from the shearing interferometer 142 to the light detector 140 along a second optical path, and the first optical path and the second optical path may partially overlap, wherein the overlapping depth of the first optical path and the second optical path may be an integer multiple of the length W of the first phase pixels 116a-116d or the second phase pixels 118a-118d, i.e., the misalignment distance between the first light beam L1 and the second light beam L2 exiting from the shearing interferometer 142 is an integer multiple of the length W of the first phase pixels 116a-116d or the second phase pixels 118a-118 d. Then, the first light beam L1 and the second light beam L2 converted by the shearing interferometer 142 travel toward the light detector 140 and are received and read by the light detector 140.
As shown in fig. 3, 4 and 5, when the first light beam L1 and the second light beam L2 travel from the shearing interferometer 142 to the photo detector 140, the projection ranges of the first light beam L1 and the second light beam L2 on the photo detector 140 overlap each other.
The projection range of the first light beam L1 on the light detector 140 is represented by a first projection range A1, and the first projection range A1 is divided into eight first sub-ranges A1a, A1b, A1c, A1d, A1e, A1f, A1g, and A1h, wherein the phases of the first sub-ranges A1a-A1h respectively correspond to the phases of the sub-beams R1a-R1h of the writing light R in fig. 2, i.e., the phases of the first sub-ranges A1a-A1h are pi, 0, pi, 0 as shown in fig. 5, and the phase distribution can be regarded as the phase code of the first light beam L1.
The projection range of the second light beam L2 on the light detector 140 is represented by a second projection range A2, and the second projection range A2 is divided into eight second sub-ranges A2a, A2b, A2c, A2d, A2e, A2f, A2g and A2h, wherein the phases of the second sub-ranges A2a-A2h respectively correspond to the phases of the sub-light beams R1a-R1h of the writing light R in fig. 2, i.e. the phases of the second sub-ranges A2a-A2h are pi, 0, pi, 0 as shown in fig. 5, and the phase distribution can be regarded as the phase code of the second light beam L2.
Since the first projection range a1 overlaps the second projection range a2, interference occurs on the light detector 140, and the interference result is related to the phase distribution. Specifically, the first light beam L1 and the second light beam L2 can be converted from a phase distribution to an intensity distribution by interference on the light detector 140. For example, when the phases corresponding to the overlapping first sub-range A1a-A1h and the overlapping second sub-range A2a-A2h are pi and 0 (or 0 and pi), the intensity on the photodetector 140 is defined as 1, wherein the intensity defined as 1 can generate a focused bright spot on the photodetector 140, and when the phases corresponding to the overlapping first sub-range A1a-A1h and the overlapping second sub-range A2a-A2h are both pi (pi and pi) or both 0(0 and 0), the intensity on the photodetector 140 is defined as 0. By this conversion, the phase information of the overlapped second light beam L2 and the first light beam L1 can be converted into an intensity-encoded optical signal, so that the light detector 140 can read and record the signal in a binary form.
For example, since the number of the sub-ranges overlapped with each other between the first projection range a1 and the second projection range a2 is seven, seven intensity signals can be generated, which will be described below. In the overlapping range of the first projection range A1 and the second projection range A2, the phases of the first sub-range A1b and the second sub-range A2a overlapping each other are pi and pi, respectively, so that the intensity signal converted by interference is 0; the phases of the first sub-range A1c and the second sub-range A2b overlapped with each other are 0 and pi, respectively, so that the intensity signal converted by interference is 1; the phases of the first sub-range A1d and the second sub-range A2c that overlap each other are 0 and 0, respectively, so that the intensity signal converted by interference is 0; the phases of the first sub-range A1e and the second sub-range A2d overlapped with each other are 0 and 0, respectively, so that the intensity signal converted by interference is 0; the phases of the first sub-range A1f and the second sub-range A2e overlapped with each other are pi and 0, respectively, so that the intensity signal converted by interference is 1; the phases of the first sub-range A1g and the second sub-range A2f overlapped with each other are pi and pi, respectively, so that the intensity signal converted by interference is 0; the phases of the first sub-range A1h and the second sub-range A2g overlapped with each other are 0 and pi, respectively, so that the intensity signal converted by the interference is 1, i.e., the intensity code recorded by the first light beam L1 and the second light beam L2 in the light detector 140 is 0100101, and is recorded in a binary form.
With the above arrangement, for phase encoding of the first and second light beams L1 and L2, since there is no single sub-range corresponding to the other phase between two sub-ranges corresponding to the same phase, the total length of the sub-ranges arranged consecutively and having the same phase exceeds the length of a single bit signal.
When the recorded phase-encoded information generates a focusing spot on the storage disc 102, the intensity of the focusing spot can be represented as g (u), wherein:
w is the total length of the sub-beams with the same phase and arranged in series in the beam, U is the coordinate of the focused spot on the storage disk, λ is the wavelength of the beam traveling to the storage disk, and f is the focal length of the objective lens.
When the first zero point of the focusing bright point is to be taken, G (U) can be made zero, i.e.
Since sinc 1 is 0, it can be seen that this is the case
After finishing, the product can be obtained
According to
The coordinate of the focusing bright spot on the storage disk is inversely proportional to the total length of the sub-beams which are continuously arranged and have the same phase, so that the imaging range of the focusing bright spot on the storage disk can be reduced when the total length of the sub-beams which are continuously arranged and have the same phase is increased and is larger than the length of a single bit signal.
For example, in FIG. 2, the sub-beams R1c-R1e are three sub-beams arranged in series and having the same phase, and the total length of the signal exiting from the spatial light modulator 114 is 3W. That is, the minimum period of the entire string of encoded signals is greater than or equal to 2W, i.e., no encoded signal with period W is present. Thus, the first null width after focusing is at least halved, and the Nyquist aperture, which can be considered the area of minimum focus of the beam for writing data to the storage disk, is also at least halved. The Nyquist aperture size of the focusing bright spot is reduced, so that the data writing amount per unit volume of the storage disk can be increased, namely, the storage capacity density of the storage disk is increased. In addition, because the first light beam and the second light beam convert the phase code into the intensity code by the interference mode, the noise generated by the aberration of the optical component or the offset of the storage disk can be eliminated when the interference is carried out, thereby improving the signal-to-noise ratio of the holographic storage device.
The shearing interferometer used in the above embodiment may be replaced with another type of optical element, for example, a dual-frequency grating may be used instead of the shearing interferometer, so that the diffracted light can be transmitted through two spatial frequencies on the dual-frequency grating and converted into the first and second beams.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A method for encoding an optical signal, wherein a controller (150) is used to control the arrangement of a plurality of pixels arranged along a linear direction of a spatial light modulator (114), wherein the pixels comprise a first phase pixel (116) and a second phase pixel (118), so as to adjust the phase distribution of a light beam passing through the pixels, such that a sub-light beam exiting from the first phase pixel (116) has a first phase and a sub-light beam exiting from the second phase pixel (118) has a second phase, wherein the phase difference between the first phase and the second phase is 180 degrees, the method comprising: between the first pixel and the last pixel arranged along the same straight direction, at least two first phase pixels (116) arranged in succession exist in three consecutive pixels, or at least two second phase pixels (118) arranged in succession exist in three consecutive pixels.
2. The method of claim 1, wherein: between the first pixel and the last pixel arranged along the same straight line direction, at least three first phase pixels (116) arranged in succession exist, or at least three second phase pixels (118) arranged in succession exist.
3. The method of claim 1, wherein: all the first phase pixels (116) between the first pixel and the last pixel arranged along the same straight line direction are arranged continuously, and all the second phase pixels (118) are arranged continuously.
4. An optical signal accessing method, comprising: in the optical signal storage, the optical signal is encoded by the method of encoding an optical signal according to any one of claims 1 to 3, and the writing light (R) provided by the light emitter (112) is incident on the storage disk (102) after passing through the spatial light modulator (114) and the light guide module (120) in sequence.
5. The method according to claim 4, wherein: during optical signal reading, reading light (L) provided by the light emitter (112) is made to sequentially pass through the spatial light modulator (114) and the light guide module (120) and then is incident on and penetrates through the storage disk (102) to form diffracted light (D), the diffracted light (D) is made to enter the shearing interferometer (142) through the light guide module (120), the shearing interferometer (142) converts the diffracted light (D) into a first light beam (L1) and a second light beam (L2) which are parallel to each other and have the same phase distribution, and then the first light beam (L1) and the second light beam (L2) are read by using the light detector (140).
6. The method of claim 5, wherein: the projection ranges of the first light beam (L1) and the second light beam (L2) on the light detector are partially overlapped or completely overlapped.
7. The method according to claim 6, wherein: the overlapping depth of the projection range of the first light beam (L1) and the second light beam (L2) on the light detector is integral multiple of the length of the first phase pixel (116) or integral multiple of the length of the second phase pixel (118).
8. A holographic storage device for optical signals, comprising: the holographic storage device stores the optical signal by using the method for encoding the optical signal according to any one of claims 1 to 3; the holographic storage device comprises a light emitter (112), a spatial light modulator (114), a controller (150), a light guide module (120) and a storage disc (102); the spatial light modulator (114) is optically coupled between the light emitter (112) and the storage disk (102), the controller (150) is electrically connected to the spatial light modulator (114), and the light guide module (120) is optically coupled between the spatial light modulator (114) and the storage disk (102).
9. The apparatus of claim 8, wherein: further includes a light detector (140), and a shearing interferometer (142) optically coupled between the light guide module (120) and the light detector (140).
10. The apparatus of claim 8, wherein: the light guide module (120) comprises a polarization beam splitter (122), a first guide lens (124), a low-pass filter (125), a second guide lens (126), a quarter-wave plate (128), a reflector (130) and an objective lens (132).
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| US5914802A (en) * | 1997-07-18 | 1999-06-22 | Northrop Grumman Corporation | Combined spatial light modulator and phase mask for holographic storage system |
| EP1551011A1 (en) * | 2002-10-09 | 2005-07-06 | Optware Corporation | Information recording method, reproducing method and recording/reproducig method utilizing holography |
| TW200801865A (en) * | 2006-03-29 | 2008-01-01 | Koninkl Philips Electronics Nv | Setup for storing data in a holographic storage medium and phase plate |
| EP1962285A1 (en) * | 2007-02-21 | 2008-08-27 | Deutsche Thomson OHG | Data page with increased data capacity |
| EP2028653A1 (en) * | 2007-08-21 | 2009-02-25 | Deutsche Thomson OHG | Phase mask for holographic data storage |
| CN106647214B (en) * | 2017-03-17 | 2019-02-12 | 京东方科技集团股份有限公司 | Addressing method, holographic display and its control method of spatial light modulator |
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