CN116027649A - Image multiplexing system - Google Patents
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- CN116027649A CN116027649A CN202310093692.8A CN202310093692A CN116027649A CN 116027649 A CN116027649 A CN 116027649A CN 202310093692 A CN202310093692 A CN 202310093692A CN 116027649 A CN116027649 A CN 116027649A
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Abstract
The application provides an image multiplexing system. The system comprises: a light source device, a beam modulation device, a time division multiplexing holographic device, a camera, and a computer; the computer is connected with the time division multiplexing holographic equipment and is used for encoding the target image to be reconstructed to obtain a binary orbital angular momentum hologram and transmitting the binary orbital angular momentum hologram to the time division multiplexing holographic equipment; the light source device is used for emitting Gaussian beams; the light beam modulation device is used for modulating the Gaussian light beam into a target light beam carrying orbital angular momentum and emitting the target light beam; the time division multiplexing holographic device is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so that the target beam decodes the binary orbital angular momentum hologram to obtain a decoded image; the camera is used for shooting the decoded image to obtain a target image. The image multiplexing system improves the resolution of the multiplexed image and improves the quality of the multiplexed image.
Description
Technical Field
The present application relates to holographic technology, and in particular, to an image multiplexing system.
Background
In recent years, computer-generated holograms have been receiving great attention due to their flexible manipulation of the beam wavefront, and are widely used in the fields of photoelectric computation, three-dimensional display, beam shaping, optical encryption, and the like.
The hologram multiplexing technology effectively solves various problems generated by holograms in real time. Holographic multiplexing refers to storing multi-channel information in one hologram using multiple degrees of physical freedom such as polarization, wavelength, angle of incidence, etc. Whether physical degrees of freedom can be used for holographic multiplexing is critical in the selective response of holograms to inputs of different orthogonal dimensions. Orbital angular momentum is particularly suited for holographic multiplexing techniques as a physical degree of freedom with infinite orthogonal dimensions.
However, in current orbital angular momentum holography techniques, it is often necessary to perform discrete sampling of the target image to be reconstructed so that the orbital angular momentum properties of each pixel location in the target image are not destroyed. However, this inevitably reduces the resolution of the target image, so that the quality of the reconstructed target image cannot be ensured.
Disclosure of Invention
The application provides an image multiplexing system which is used for solving the problem that the resolution of a target image is reduced when the target multiplexed image is multiplexed in the current orbital angular momentum holographic technology.
The application provides an image multiplexing system, comprising: a light source device, a beam modulation device, a time division multiplexing holographic device, a camera, and a computer; the computer is connected with the time division multiplexing holographic equipment, and is used for encoding a target image to be reconstructed to obtain a binary orbital angular momentum hologram and transmitting the binary orbital angular momentum hologram to the time division multiplexing holographic equipment; the light source device is used for emitting Gaussian beams; the light beam modulation device is positioned on the light path of the Gaussian light beam, and is used for modulating the Gaussian light beam into a target light beam carrying orbital angular momentum and emitting the target light beam; the time division multiplexing holographic device is positioned on the light path of the target light beam and is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so that the target light beam decodes the binary orbital angular momentum hologram to obtain a decoded image; the camera is used for shooting the decoded image to obtain the target image.
The image multiplexing system comprises a light source device, a light beam modulation device, a time division multiplexing holographic device, a camera and a computer, wherein the computer is connected with the time division multiplexing holographic device, and is used for encoding a target image to be reconstructed to obtain a binary orbital angular momentum hologram and transmitting the binary orbital angular momentum hologram to the time division multiplexing holographic device; the light source device is used for emitting Gaussian beams; the light beam modulation device is positioned on the light path of the Gaussian light beam, and is used for modulating the Gaussian light beam into a target light beam carrying orbital angular momentum and emitting the target light beam; the time division multiplexing holographic device is positioned on the light path of the target light beam and is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so that the target light beam decodes the binary orbital angular momentum hologram to obtain a decoded image; the camera is used for shooting the decoded image to obtain a target image. That is, when reconstructing through the image multiplexing system, the beam modulation device may receive the gaussian beam emitted by the light source device, modulate the gaussian beam into the target beam carrying orbital angular momentum, then make the target beam incident on the time division multiplexing holographic device, and at the same time, the time division multiplexing holographic device may display the binary orbital angular momentum hologram in a time division multiplexing manner. In addition, the time division multiplexing holographic device realizes reconstruction of the target image by using a time division multiplexing method, reduces multiplexing crosstalk of multiplexing images of the orbital angular momentum hologram, and effectively improves resolution of the multiplexing images.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and together with the description, serve to explain the principles of the application.
Fig. 1 is a schematic diagram showing a configuration of an image multiplexing system according to an exemplary embodiment;
FIG. 2 is a flowchart illustrating a method of image processing under an image multiplexing system, according to an example embodiment;
FIG. 3A is a flow diagram illustrating image processing under an image multiplexing system in accordance with an exemplary embodiment;
FIG. 3B is a flow diagram II illustrating image processing under an image multiplexing system according to another example embodiment;
FIG. 4A is a diffusion diagram of a current pixel of a signal window average error minimization algorithm, according to an exemplary embodiment;
FIG. 4B is a schematic diagram of a signal window shown according to an example embodiment;
FIG. 4C is a binary hologram generated by a signal window average error minimization algorithm according to an exemplary embodiment;
fig. 4D is a schematic diagram of a reconstruction result of a binary OAM hologram according to an exemplary embodiment;
fig. 5A is a schematic diagram showing reconstruction results for 7 OAM channels for three holographic techniques according to an example embodiment;
Fig. 5B is a schematic diagram showing reconstruction results for 11 OAM channels for three holographic techniques according to an example embodiment;
fig. 5C is a fluctuation factor diagram showing reconstruction results of 7 OAM channels and 11 OAM channels corresponding to three kinds of holographic techniques according to an exemplary embodiment;
fig. 5D is a graph showing the trend of intensity fluctuation factors corresponding to three kinds of holographic techniques with the number of OAM multiplexing channels according to an exemplary embodiment.
Specific embodiments thereof have been shown by way of example in the drawings and will herein be described in more detail. These drawings and the written description are not intended to limit the scope of the inventive concepts in any way, but to illustrate the concepts of the present application to those skilled in the art by reference to specific embodiments.
Detailed Description
Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, the same numbers in different drawings refer to the same or similar elements, unless otherwise indicated. The implementations described in the following exemplary examples are not representative of all implementations consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present application as detailed in the accompanying claims.
The terms referred to in this application are explained first:
OAM: orbital angular momentum, english is all: orbital Angular Momentum.
DMD: digital micromirror device, english is all: digital Micromirror Device.
TM: time division multiplexing, english is all: temporal Multiplexing, namely dividing the time provided for the transmission information of the whole channel into a plurality of time slices (time slots for short), and distributing the time slots to each signal source for use, so as to ensure the utilization rate of resources.
At present, holographic multiplexing technology is developed faster and faster, and the purpose of the development of the holographic multiplexing technology is to record as many holograms as possible in a medium, thereby not only improving the storage capacity, but also ensuring the reproduction performance of each hologram, and the crosstalk between each hologram is within an allowable range.
OAM is particularly suited for holographic multiplexing techniques as a physical degree of freedom with infinite orthogonal dimensions. However, according to the bragg diffraction formula, all OAM modes diffract in the same way. Thus, the selective response of OAM holograms cannot depend on the diffraction law of the hologram, but is derived from the law of OAM conservation that OAM itself has.
The key to implementing OAM holograms is to preserve the OAM properties of the incident beam entirely in the hologram in order to apply OAM conservation laws during the hologram reconstruction process. It has been pointed out in the related art that fourier holographic systems can preserve the properties of the incident OAM beam at each pixel location of the multiplexed image.
However, even though each pixel location theoretically possesses the OAM properties of the incident light beam, the OAM properties of each pixel location in the multiplexed image are destroyed by random interference between pixels.
Therefore, in the related art, OAM holography is proposed such that OAM properties of each pixel position in an image are not destroyed by performing discrete sampling on a target image, but this inevitably reduces resolution of an original image. Specifically, in the OAM holography of the related art, all multiplexed images must satisfy sampling conditions in the OAM holography, specifically, the sampling conditions are as follows:
wherein d max Is the largest addressable OAM mode diameter. L is the sampling distance of the image. Gamma is a scale factor, the value of which is the largest diameter d of the addressable OAM mode max And the ratio of the image sampling interval L. It is important for OAM holography to expand the value of γ even further, as it represents a higher multiplexing image resolution for a certain number of OAM channels, or a higher multiplexing capacity for the same multiplexing image resolution. In addition, even under the condition that γ is less than or equal to 1, the quality of the multiplexed image cannot be further improved by the influence of multiplexing crosstalk, so that the multiplexed image cannot be ensured to have higher resolution. It will be appreciated that the multiplexed image is reconstructed from the target image.
The image multiplexing system provided by the application aims at solving the technical problems in the prior art.
The following describes the technical solutions of the present application and how the technical solutions of the present application solve the above technical problems in detail with specific embodiments. The following embodiments may be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. Embodiments of the present application will be described below with reference to the accompanying drawings.
Fig. 1 is an image multiplexing system according to an exemplary embodiment, the image multiplexing system comprising: a light source device 1, a beam modulation device 2, a time division multiplexing holographic device 3, a camera 4 and a computer (not shown in fig. 1), wherein:
the computer is connected with the time division multiplexing holographic device 3, and is used for encoding the target image to be reconstructed to obtain a binary orbital angular momentum hologram and transmitting the binary orbital angular momentum hologram to the time division multiplexing holographic device 3. Wherein the computer may be communicatively coupled to the time division multiplexed holographic device 3 to transmit data to the time division multiplexed holographic device 3.
The light source device 1 is for emitting a gaussian beam.
The beam modulation device 2 is located on the optical path of the gaussian beam, and the beam modulation device 2 is configured to modulate the gaussian beam into a target beam carrying orbital angular momentum and emit the target beam.
The time division multiplexing holographic device 3 is located on the optical path of the target beam, and the time division multiplexing holographic device 3 is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so that the target beam decodes the binary orbital angular momentum hologram to obtain a decoded image.
The camera 4 is used for shooting the decoded image to obtain a reconstructed target image, i.e. a multiplexed image.
For example, in practical application, the computer may receive the target image to be reconstructed input by the user, and encode the target image to obtain a binary orbital angular momentum hologram, and then the computer may send the binary orbital angular momentum hologram to the time division multiplexing holographic device 3, and the time division multiplexing holographic device 3 may store the binary orbital angular momentum hologram. Alternatively, the time division multiplexing holographic device 3 may include a DMD, and the computer may write the binary orbital angular momentum hologram image as a binary hologram template to the DMD, and the DMD may display the binary orbital angular momentum hologram image by loading the binary orbital angular momentum hologram image in a TM manner on a display plane thereof.
In reconstructing the target image, the light source device 1 emits a gaussian beam, which the beam modulation device 2 can receive and modulate into a target beam carrying orbital angular momentum and transmit to the time division multiplexing holographic device 3. Meanwhile, the time division multiplexing holographic device 3 displays the binary orbital angular momentum holographic image on the display plane by loading the binary orbital angular momentum holographic image in a TM mode, and when the target beam carries the orbital angular momentum and is incident on the binary orbital angular momentum holographic image displayed by the time division multiplexing holographic device 3, the binary orbital angular momentum holographic image can be decoded to reconstruct a target image corresponding to the binary orbital angular momentum holographic image, and finally, the target image is shot by the camera 4, so that the reconstructed target image can be obtained.
It can be seen that, in this embodiment, the image multiplexing system includes a light source device 1, a light beam modulating device 2, a time division multiplexing holographic device 3, a camera 4, and a computer, where the computer is connected to the time division multiplexing holographic device 3, and the computer is configured to encode a target image to be reconstructed to obtain a binary orbital angular momentum hologram, and send the binary orbital angular momentum hologram to the time division multiplexing holographic device 3; the light source device 1 is for emitting a gaussian beam; the beam modulation device 2 is located on the optical path of the gaussian beam, and the beam modulation device 2 is used for modulating the gaussian beam into a target beam carrying orbital angular momentum and emitting the target beam; the time division multiplexing holographic device 3 is positioned on the light path of the target light beam, and the time division multiplexing holographic device 3 is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so as to enable the target light beam to decode the binary orbital angular momentum hologram to obtain a decoded image; the camera 4 is used for shooting the decoded image to obtain a target image. That is, when reconstructing through the image multiplexing system, the beam modulating device 2 may receive the gaussian beam emitted by the light source device 1, modulate the gaussian beam into a target beam carrying orbital angular momentum, then make the target beam incident on the time division multiplexing holographic device 3, and at the same time, the time division multiplexing holographic device 3 may display a binary orbital angular momentum hologram in a time division multiplexing manner, and since the target beam carries orbital angular momentum, the binary orbital angular momentum hologram can be decoded by using the target beam, and then the camera 4 photographs the decoded image, so as to obtain the target image. In addition, the time division multiplexing holographic device 3 realizes reconstruction of the target image by using a time division multiplexing method, reduces multiplexing crosstalk of multiplexing images of the orbital angular momentum hologram, and effectively improves resolution of the multiplexing images.
In some embodiments, as shown in fig. 1, the light beam modulating device 2 in the image multiplexing system described above may include a spatial light modulator 21 and a first lens 22, where:
the spatial light modulator 21 is located on the optical path of the gaussian beam, and the spatial light modulator 21 is configured to perform phase modulation on the gaussian beam to obtain a first beam, and emit the first beam.
The first lens 22 is located on the optical path of the first light beam, and the first lens 22 is used for performing fourier transform on the first light beam to obtain a target light beam and transmitting the target light beam.
For example, in practical applications, the spatial light modulator 21 may be a phase spatial light modulator 21, where a preset phase hologram template is stored in the spatial light modulator 21, and when the spatial light modulator 21 receives the gaussian beam, the specific pure phase modulation may be performed on the gaussian beam by loading the phase hologram template, so as to obtain the first beam. Wherein the gaussian beam may be spread into a near-field plane and then incident into the spatial light modulator 21.
Alternatively, a plurality of phase hologram templates may be stored in the spatial light modulator 21, and the desired target beam of orbital angular momentum of various spiral phase orders may be obtained by replacing the phase hologram template loaded into the spatial light modulator 21.
Alternatively, the light source device 1 may be a laser, and the center wavelength of the spatial light modulator 21 may be matched with the center wavelength of the laser.
After the spatial light modulator 21 emits the first light beam, the first lens 22 may receive the first light beam, perform fourier transform on the first light beam, and perform series separation to obtain a target light beam carrying orbital angular momentum.
In the present embodiment, the beam modulation device 2 is constituted by the spatial light modulator 21 and the first lens 22, and not only is the structure simple, but also the target beam carrying the orbital angular momentum can be stably modulated.
In some embodiments, referring again to fig. 1, the beam modulating device 2 further comprises a polarization selector 23;
a polarization selector 23 is located between the light source device 1 and the spatial light modulator 21, the polarization selector 23 being configured to adjust the polarization of the gaussian beam to a target direction and then transmit to the spatial light modulator 21; the target direction is the direction in which the modulation efficiency of the spatial light modulator 21 is maximum.
Illustratively, the polarization selector 23 may include a polarizer 231 and a half-wave plate 232, and the gaussian beam emitted from the light source device 1 may sequentially pass through the polarizer 231 and the half-wave plate 232, thereby obtaining the gaussian beam after polarization adjustment.
In the present embodiment, the polarization of the gaussian beam is adjusted by the polarization selector 23 to the direction in which the modulation efficiency of the spatial light modulator 21 is maximum, thereby improving the modulation efficiency of the spatial light modulator 21 at the time of modulation.
In some embodiments, referring again to fig. 1, the beam modulating device 2 further comprises a magnifying lens assembly 24;
the magnifying lens assembly 24 is located between the polarization selector 23 and the spatial light modulator 21, and the magnifying lens assembly 24 is used for magnifying the light beam emitted by the polarization selector 23 according to a specified magnification and then emitting the light beam to the spatial light modulator 21.
Illustratively, the magnifying lens assembly 24 may be composed of a plurality of lenses, and the gaussian beam adjusted by the polarization selector 23 may be magnified according to a predetermined magnification after passing through the plurality of lenses, thereby obtaining the near-field plane wave. Alternatively, the specified magnification may be 1:12.
In the present embodiment, the gaussian beam adjusted by the polarization selector 23 is expanded by the magnifying lens unit 24, so that a gaussian beam having a large beam waist size can be obtained, and the gaussian beam having a large beam waist size can be considered to be close to an ideal plane wave. Therefore, the OAM degree of freedom of the optical field is utilized, and the bandwidth of the calculation hologram is greatly expanded.
Optionally, referring again to fig. 1, the magnifying lens assembly 24 includes a first magnifying lens 241 and a second magnifying lens 242.
The first amplifying lens 241 and the second amplifying lens 242 are both positioned on the optical path of the light beam emitted by the polarization selector 23, the distance between the first amplifying lens 241 and the polarization selector 23 is greater than the distance between the second amplifying lens 242 and the polarization selector 23, and the focal length of the first amplifying lens 241 is 25mm; the focal length of the second magnifier lens 242 is 300mm.
Illustratively, the gaussian beam adjusted by the polarization selector 23 may sequentially pass through the first amplifying lens 241 and the second amplifying lens 242, and then may be amplified according to a specified magnification, so that a simple telescope structure is formed by using the first amplifying lens 241 and the second amplifying lens 242, and beam expansion of the gaussian beam is achieved.
In some embodiments, referring again to fig. 1, the beam modulating device 2 further comprises a pinhole filter 25.
A pinhole filter 25 is located between the first lens 22 and the time division multiplexing holographic device 3, and the pinhole filter 25 is configured to spatially filter the light beam transmitted by the first lens 22 and then transmit the light beam to the time division multiplexing holographic device 3.
Illustratively, the pinhole filter 25 may spatially filter the light beam transmitted by the first lens 22 to pass only the light beam of the target frequency, thereby obtaining a pure OAM light beam. Alternatively, the target frequency may be a first order fourier frequency.
In some embodiments, referring again to fig. 1, the time division multiplexing holographic apparatus 3 comprises a second lens 31, a digital micromirror device 32, and a third lens 33.
The second lens 31 is located on the optical path of the target beam, and the second lens 31 is configured to perform inverse fourier transform on the target beam to obtain a second beam, and transmit the second beam.
The digital micro-mirror device 32 is connected with the computer and is positioned on the optical path of the second light beam, and the digital micro-mirror device 32 is used for receiving the binary orbital angular momentum hologram sent by the computer and displaying the binary orbital angular momentum hologram on the display plane thereof in a time division multiplexing mode; the second light beam is used for being incident on the display plane so as to decode the binary orbital angular momentum hologram displayed on the display plane and reflect the third light beam.
The third lens 33 is located on the optical path of the third light beam, and the third lens 33 is configured to fourier transform the third light beam to obtain a fourth light beam, and transmit the fourth light beam.
The camera 4 is located on the optical path of the fourth light beam, and the camera 4 is used for shooting the binary orbital angular momentum hologram displayed on the display plane through the fourth light beam to obtain a target image.
Along the above example, the second lens 31 may receive the target beam filtered by the pinhole filter and perform inverse fourier transform on the target beam to obtain a second beam, so that the spot size corresponding to the second beam is exactly equal to the size of the modulation surface of the digital micromirror device 32. The digital micromirror device 32 can load the binary orbital angular momentum hologram transmitted from the computer and realize the display of the binary orbital angular momentum hologram on its display plane in a time division multiplexing manner in its high-speed mode. Then, the second light beam is incident on the time-division multiplexed binary orbital angular momentum hologram, the target image encoded in the binary orbital angular momentum hologram is decoded, thereby obtaining a decoded complex amplitude distribution, that is, the above decoded image, on the display plane of the digital micromirror device 32, and the third light beam is reflected according to the complex amplitude distribution. Then, when the third light beam passes through the third lens 33, the decoded complex amplitude distribution is fourier transformed by the third lens 33, and finally a target image is obtained, and the target image is transmitted to the camera 4 through the fourth light beam, so that the camera 4 photographs the binary orbital angular momentum hologram displayed on the display plane through the fourth light beam, and the target image is obtained. Alternatively, the camera 4 may be a high resolution camera.
In the present embodiment, by constructing the time division multiplexing hologram device 3 based on the digital micromirror device 32, it can be conveniently applied to various general display devices such as portable hologram projectors, head-up display devices, etc., with the benefit of the strong programmability and low cost advantage of the digital micromirror device 32.
In some embodiments, the computer may be further configured to perform a method for generating a binary orbital angular momentum hologram, as shown in fig. 2, the method comprising:
110. and receiving a plurality of target images input by a user, and sampling the target images by a sampling array with random phase aiming at each target image in the plurality of target images to obtain a sampling image.
Illustratively, the user may input a plurality of target images to the computer by way of human-computer interaction. As shown in fig. 3A, for each of a plurality of target images, the computer may sample the target image by a random phase sampling array after receiving the target image, to obtain a sampled image. The sampling array may be stored in a computer in advance. As an example, the computer may superimpose a random phase matrix, i.e., the random phase in fig. 3A, on the target image to generate the image to be multiplexed. The image to be multiplexed is then sampled, resulting in a sampled image, i.e. the sampling array in fig. 3A.
120. And performing inverse Fourier transform on the sampling image to obtain first complex amplitude distribution information corresponding to the sampling image.
Along with the above example, the computer may perform inverse fourier transform on the sampled image to obtain complex amplitude distribution information of one OAM reservation hologram corresponding to the sampled image, that is, the amplitude distribution of the OAM hologram in fig. 3A, and determine the complex amplitude distribution information as the first complex amplitude distribution information. The complex amplitude distribution information may specifically be a complex amplitude distribution matrix.
130. And processing the first complex amplitude distribution information through a preset spiral phase mask to obtain second complex amplitude distribution information.
Along with the above example, a preset spiral phase mask may be stored in the computer, where the spiral phase mask corresponds to the OAM phase in fig. 3A, where the masking process is performed on the first complex amplitude distribution information through the preset spiral phase mask, so as to obtain a complex amplitude distribution of an OAM selective hologram, and determine the complex amplitude distribution of the OAM selective hologram as the second complex amplitude distribution information. It will be appreciated that step 130 may be considered as a process of performing an OAM encoding of the target image. The masking process may specifically include: superimposing a spiral phase mask over the OAM reservation hologram creates the complex amplitude profile of the OAM selective hologram.
140. And superposing the second complex amplitude distribution information corresponding to each target image to obtain target complex amplitude distribution information, and converting the target complex amplitude distribution information into amplitude distribution information by correcting an off-axis coding method.
Along with the above example, through the above steps 110 to 130, the second complex amplitude distribution information corresponding to each of the plurality of target images may be obtained. Then, the computer may obtain a complex amplitude distribution of the OAM multiplexing hologram by performing superposition processing on the second complex amplitude distribution information corresponding to each of the target images, and determine the complex amplitude distribution of the OAM multiplexing hologram as the target complex amplitude distribution information. Referring again to fig. 3A, after obtaining the target complex amplitude distribution information, the calculation may convert the target complex amplitude distribution information into an amplitude-type OAM hologram as in fig. 3A by correcting the off-axis encoding method for the target complex amplitude distribution information, and determine the amplitude-type OAM hologram as the amplitude distribution information.
150. And performing binarization processing on the amplitude distribution information to obtain a binary orbital angular momentum hologram.
With the above example, the computer may perform binarization processing on the above amplitude distribution information, so that a binary orbital angular momentum hologram, that is, a binary OAM hologram as in fig. 3A, may be obtained.
Thereafter, the computer may replace the sampling array with the random phase, and then repeatedly execute steps 110 to 150 based on the replaced sampling array with the random phase, so as to obtain a plurality of binary orbital angular momentum holograms, where each binary orbital angular momentum hologram in the plurality of binary orbital angular momentum holograms corresponds to a sampling array with a random phase.
Then, the computer transmits the obtained plurality of binary orbital angular momentum holograms to the digital micromirror device 32 of the image multiplexing system, thereby sequentially writing the plurality of binary orbital angular momentum holograms to the digital micromirror device 32. So that the image multiplexing system can reconstruct a target image based on a plurality of binary orbital angular momentum holograms using a time division multiplexing method.
Optionally, the user may also input a signal-to-noise ratio of the target image, and the computer may determine the number of binary orbital angular momentum holograms required for time division multiplexing according to the signal-to-noise ratio. Optionally, the computer may also determine the OAM channels, the multiplexing number of multiplexed images, and the sampling interval through the basic principles of OAM holography.
As an example, fig. 3B illustrates a more specific process of generating a binary orbital angular momentum hologram, and as shown in fig. 3B, the computer may acquire a plurality of received target images (e.g., target image # 1, target image # 5 of …, etc.) through different random phase arrays, to obtain a sampling array. Then, the sampling array is subjected to inverse Fourier transform to obtain complex amplitude distribution of a plurality of OAM holograms, and then, the complex amplitude distribution of the plurality of OAM holograms is subjected to OAM coding and then subjected to complex amplitude superposition to obtain the target complex amplitude distribution information. And finally, correcting off-axis coding is carried out on the target complex amplitude distribution information, and binarization processing is carried out through a signal window average error minimum algorithm, so that the binary OAM multiplexing hologram can be obtained. It can be seen that by replacing the random initial phase of the multiplexed image with respect to the sample array, a plurality of binary OAM multiplexed holograms containing the same multiplexed image but having different complex amplitude distributions are calculated.
Illustratively, the above-described modified off-axis encoding method may specifically include the following three steps:
step one, determining the complex amplitude distribution of the OAM multiplexing hologram as follows:
s(x，y)＝a(x，y)exp[iφ(x，y)]
where s (x, y) is the complex amplitude distribution of the OAM multiplexed holograms described above, x represents the abscissa in the spatial domain, and y represents the ordinate in the spatial domain, that is, x and y are the spatial coordinates. a (x, y) is the amplitude part of the object light wave, and the value is [0,1]. Phi (x, y) is the phase function of the object light wave, the value is [0,2 pi ], and i is the imaginary unit. The amplitude distribution when off-axis interference can be written off-axis according to the optical holographic interference process is as follows:
h(x，y)＝0.5+0.5a(x，y) 2 +a(x，y)cos[φ(x，y)-2π(u 0 x+v 0 y)]
wherein u is 0 Is the abscissa in the spatial frequency domain, v 0 The first two items of the above expression do not contain information of the object light wave itself, and only function to make h (x, y) positive, called offset item of hologram, as ordinate in spatial frequency domain:
b(x，y)＝0.5+0.5a(x，y) 2
correcting the offset term into a constant form, wherein the form occupies less bandwidth in a space frequency domain:
b(x，y)＝-min{a(x，y)}
step three, finally determining amplitude distribution as follows:
h(x，y)＝a(x，y)cos[φ(x，y)-2π(u 0 x+v 0 y)]-min{a(x，y)}
in some embodiments, referring again to fig. 3A, the implementation of step 150 may include: and carrying out binarization processing on the amplitude distribution information through a signal window average error minimum algorithm to obtain a binary orbital angular momentum hologram.
For example, a signal window average error minimization algorithm may be stored in the computer in advance, and when the amplitude distribution information needs to be binarized, the signal window average error minimization algorithm may be called to perform binarization processing on the amplitude distribution information, so as to obtain a binary orbital angular momentum hologram.
The amplitude distribution of the hologram is converted into a binary orbital angular momentum hologram, which causes a reduction in modulation depth and inevitably reduces the quality of the multiplexed image. Specifically, the binary noise introduced by the binarization process is superimposed on the multiplexed image, so that the image quality is degraded. Because the multiplexed image is the fourier spectrum of the hologram, the goal of the binarization algorithm is to reduce the binary noise of the hologram in the spatial frequency domain.
As one example, in the field of computational holography, the most effective non-iterative binarization algorithm for the above-mentioned problem is the error diffusion algorithm. The algorithm performs the binarization process on each pixel of the hologram in turn and spreads the binarization error for the current pixel to adjacent non-binarized pixels. The error diffusion algorithm can significantly reduce binary noise in a portion of the spatial frequency domain, which is referred to as a signal window. The coordinates and shape of the signal window are related to the error diffusion coefficient (hereinafter referred to as diffusion coefficient).
Therefore, in the present embodiment, the amplitude distribution information is binarized by the signal window average error minimization algorithm, so that the binary noise can be effectively reduced.
In some embodiments, the implementation of step 150 may include:
151. and determining the target carrier frequency and the target resolution corresponding to the target image.
For example, the computer may receive a user-set target carrier frequency and a target resolution, wherein the target resolution characterizes a resolution that the user wants the target image to reach. The target carrier frequency may be determined by the user according to the device parameters of each device in the image multiplexing system, and then input into the computer. Optionally, the computer may further receive device parameters for respective devices in the input image multiplexing system, and generate the target carrier frequency according to the device parameters.
152. And determining the diffusion coefficient of the signal window average error minimum algorithm according to the target carrier frequency and the target resolution.
In some embodiments, the implementation of step 152 may include:
determining the size of a signal window corresponding to a signal window average error minimum algorithm in a spatial frequency domain according to the target resolution; the signal window is a partial region in the spatial frequency domain; determining the distribution position of a signal window in a space frequency domain according to the target carrier frequency; determining a space frequency domain coordinate corresponding to the signal window according to the size and the distribution position; and carrying out Fourier transform on the space frequency domain coordinates to obtain diffusion coefficients.
For example, the amplitude distribution information may be a holographic amplitude distribution image, and the spatial frequency domain corresponding to the holographic amplitude distribution image is taken as an example, and the target resolution determines the shape and the size of a signal window in the spatial frequency domain, and the target carrier frequency determines the distance between the signal window and the center point of the spatial frequency domain. Therefore, the computer can determine the size of the signal window corresponding to the signal window average error minimum algorithm according to the target resolution, and can determine the distribution position of the signal window in the space frequency domain according to the target carrier frequency. And then, combining the size and the distribution position, and calculating to obtain the space frequency domain coordinates corresponding to the signal window, namely the coordinates of the region corresponding to the signal window in the space frequency domain. Finally, the computer performs Fourier transform on the spatial frequency domain coordinates corresponding to the signal window, so that the diffusion coefficient can be obtained.
153. And performing binarization processing on the amplitude distribution information through a diffusion coefficient and signal window average error minimum algorithm to obtain a binary orbital angular momentum hologram.
As an example, the manner in which the expansion coefficient is determined may be as follows:
step a, the value of a pixel position of the holographic amplitude distribution image may be represented by f (i, j), the binarized value of f (i, j) may be represented by b (i, j), and the error e (i, j) at the pixel position may be represented as:
e(i，j)＝f(i，j)-b(i，j)
Where i denotes the abscissa in the spatial domain of the holographic amplitude distribution image, i.e. the abscissa in the planar coordinate system to which the holographic amplitude distribution image corresponds, and j denotes the ordinate in the spatial domain of the holographic amplitude distribution image.
In step b, in the signal window minimum average error algorithm, the pixel error under study will be spread into the area a as in fig. 4A, so the absolute quantization error is the sum of the error generated at that location and the error spread into that location by the area a, and can be expressed as:
where r is the abscissa in region A, s is the ordinate in region A, A is the set of coordinates in region A; d (r, s) is an expansion coefficient, and if the expansion coefficient defining the position is d (0, 0) =1, the absolute quantization error can be expressed as a form of convolution of the expansion coefficient:
wherein A is 0 Representing the set of coordinates in the region containing the current quantized pixel. The above equation illustrates that the effect of the signal window minimum average error algorithm is to reduce the convolution between the diffusion coefficient and the error.
In the spatial frequency domain, the target image expected to be reconstructed is denoted as F (I, J), the reconstruction result (hereinafter may be abbreviated as multiplexed image) of the binary orbital angular momentum hologram (hereinafter may be abbreviated as binary hologram) is denoted as B (I, J) by the above-mentioned image multiplexing system, and then the error of the reconstruction result, that is, the error of the expected target image F (I, J) and the reconstruction result B (I, J) of the binary hologram may be denoted as:
E 2 (I，J)＝[F(I，J)-B(I，J)] 2
Where I represents the abscissa in the spatial frequency domain and J represents the ordinate in the spatial frequency domain.
And d, introducing a weight function W (I, J) into the expression of the error of the reconstruction result to distinguish the importance degrees of different areas in the space frequency domain. In general, W (I, J) is set to 1 in the signal window, and the other area is 0, as shown in fig. 4B. After defining the weighting function, the total error of the multiplexed image can be written as:
wherein signal represents the coordinate set of the corresponding region of the signal window in the spatial frequency domain. The other represents a set of coordinates in the spatial frequency domain except for a signal window. N represents the total number of pixels.
Step e, through pasmodic inequality, the total error of the multiplexed image in the spatial frequency domain can be converted into the spatial domain:
where W (I, J) is the fourier transform of the weighting function W (I, J), and W (I, J) may also represent the signal window, so W (I, J) may be considered the fourier transform of the signal window.
Step f, in combination with step e and step b above, shows that when d (i, j) =w (i, j), the sum of the binary errors on the binary orbital angular momentum hologram is virtually equal to the sum of the quantization errors of the multiplexed image. Wherein w (i, j) is the fourier transform of the signal window, which is determined based on the target resolution and the target carrier frequency. W (i, j) is also determined based on the target resolution and the target carrier frequency. Therefore, the computer can determine w (i, j) as the expansion coefficient d (i, j) according to the target resolution and the target carrier frequency, so that the spatial-domain error and the spatial-domain error can be equal, and the spatial-frequency-domain error, that is, the error between the multiplexed image and the target image, is reduced. Thereby setting the appropriate diffusion coefficient for the signal window average error minimization algorithm. Thus, the present embodiment substantially reduces the binary quantization noise of the signal window in the hologram reconstruction plane by the improved signal window minimum average error algorithm.
As an example, a specific implementation of binarizing the amplitude distribution information by the signal window average error minimization algorithm may include:
the amplitude distribution of the OAM hologram is sequentially binarized according to the spreading factor of the signal window average error minimization algorithm, and the binarized error of the current pixel is spread to adjacent non-binarized pixels, as shown in fig. 4A, the black square in fig. 4A may represent the current pixel, the current pixel may be spread to a white square representing the adjacent pixel, the spreading direction may be represented by d (0, 1), for example, and if the coordinates of the current pixel are (0, 0), the direction of the spreading d (0, 1) may represent the direction of the (0, 0) toward (0, 1). The error diffusion algorithm may substantially reduce binary noise in a portion of the spatial frequency domain, which is referred to as a signal window, where the signal window may be as shown in region a of fig. 4A. The signal window may be shown as a white area in fig. 4B, that is, an area corresponding to the signal window is set to 1 in fig. 4B, and the other areas are set to 0. Illustratively, a binary hologram generated by a signal window average error minimization algorithm may be as shown in fig. 4C. In particular, the reconstruction result of the binary OAM hologram transformed by the above-mentioned signal window average error minimization algorithm may be as shown in fig. 4D.
Illustratively, the performance of three types of OAM holographic techniques is compared in detail in this embodiment: phase OAM holographic technique, complex amplitude OAM holographic technique, and time division multiplexed binary OAM holographic scheme (hereinafter referred to as new scheme) proposed in the present embodiment.
Wherein a set of binary images of winter motion icons with a resolution of 300 x 300 are encoded into a plurality of OAM channels, respectively, with a sampling interval of 8λ/NA, where λ is the laser wavelength and NA is the numerical aperture of the fourier holographic system. The interval al of the spiral pattern sequence numbers=1. Fig. 5A and 5B show the reconstruction results for 7 and 11 OAM channels, respectively, for the three schemes described above.
As can be seen from the reconstruction results of fig. 5A and 5B, the binary OAM holographic scheme of the time division multiplexing provided by this embodiment clearly has the best multiplexing image quality.
In addition, as can be seen from fig. 5C, the time division multiplexing binary OAM holographic scheme provided in this embodiment has the best lowest intensity fluctuation factor per channel compared to the other two schemes.
As can be seen from the trend chart of the intensity fluctuation factor with the number of OAM multiplexing channels shown in fig. 5D, the time division multiplexing binary OAM holographic scheme of the present embodiment has an intensity fluctuation factor value of 8.1% at the conventional limit of the scale factor γ=1 (having 7 channels) and an intensity fluctuation factor value of 10.1% at the scale factor γ=2 (having 11 channels). Therefore, the time division multiplexing binary OAM holographic technique of the present embodiment exhibits significantly better performance than the phase OAM holographic technique, the complex amplitude OAM holographic technique. Wherein, the abscissa in fig. 5D is the number of OAM multiplexing channels, and the ordinate is the intensity fluctuation factor.
In summary, the image multiplexing system provided in this embodiment greatly expands the bandwidth of the conventional calculation hologram by using the degree of freedom of OAM of the optical field. Further, by using the time division multiplexing method, multiplexing crosstalk of multiplexing images of the OAM hologram is reduced, resolution of the multiplexing images is improved, and a holographic information system with high information capacity is realized. In addition, the scheme of the embodiment breaks through the sampling condition (gamma is less than or equal to 1) required in OAM holography in the related technology. The method realizes high-quality reconstruction of OAM holograms under the condition that gamma exceeds 1, greatly expands the bandwidth of the traditional calculation hologram, and enables a holographic information system with high information capacity to be realized.
Other embodiments of the present application will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the application following, in general, the principles of the application and including such departures from the present disclosure as come within known or customary practice within the art to which the application pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the application being indicated by the following claims.
It is to be understood that the present application is not limited to the precise arrangements and instrumentalities shown in the drawings, which have been described above, and that various modifications and changes may be effected without departing from the scope thereof. The scope of the application is limited only by the appended claims.
Claims (11)
1. An image multiplexing system, comprising: a light source device, a beam modulation device, a time division multiplexing holographic device, a camera, and a computer;
the computer is connected with the time division multiplexing holographic equipment, and is used for encoding a target image to be reconstructed to obtain a binary orbital angular momentum hologram and transmitting the binary orbital angular momentum hologram to the time division multiplexing holographic equipment;
the light source device is used for emitting Gaussian beams;
the light beam modulation device is positioned on the light path of the Gaussian light beam, and is used for modulating the Gaussian light beam into a target light beam carrying orbital angular momentum and emitting the target light beam;
the time division multiplexing holographic device is positioned on the light path of the target light beam and is used for displaying the binary orbital angular momentum hologram in a time division multiplexing mode so that the target light beam decodes the binary orbital angular momentum hologram to obtain a decoded image;
The camera is used for shooting the decoded image to obtain the target image.
2. The system of claim 1, wherein the beam modulating device comprises a spatial light modulator and a first lens;
the spatial light modulator is positioned on the light path of the Gaussian beam, and is used for carrying out phase modulation on the Gaussian beam to obtain a first beam and emitting the first beam;
the first lens is located on the optical path of the first light beam, and is used for carrying out Fourier transform on the first light beam to obtain the target light beam and transmitting the target light beam.
3. The system of claim 2, wherein the beam modulating device further comprises a polarization selector;
the polarization selector is positioned between the light source device and the spatial light modulator and is used for adjusting the polarization of the Gaussian beam to a target direction and then transmitting the Gaussian beam to the spatial light modulator; the target direction is the direction in which the modulation efficiency of the spatial light modulator is maximum.
4. The system of claim 3, wherein the beam modulating device further comprises a magnifying lens assembly;
The amplifying lens component is positioned between the polarization selector and the spatial light modulator, and is used for amplifying the light beam emitted by the polarization selector according to a specified amplification rate and then emitting the light beam to the spatial light modulator.
5. The system of claim 4, wherein the magnifying lens assembly comprises a first magnifying lens and a second magnifying lens;
the first amplifying lens and the second amplifying lens are both positioned on the light path of the light beam emitted by the polarization selector, the distance between the first amplifying lens and the polarization selector is larger than the distance between the second amplifying lens and the polarization selector, and the focal length of the first amplifying lens is 25mm; the focal length of the second magnifier lens is 300mm.
6. The system of claim 2, wherein the beam modulating device further comprises a pinhole filter;
the pinhole filter is positioned between the first lens and the time division multiplexing holographic device, and the pinhole filter is used for spatially filtering the light beam transmitted by the first lens and then transmitting the light beam to the time division multiplexing holographic device.
7. The system of any one of claims 1 to 6, wherein the time division multiplexed holographic device comprises a second lens, a digital micromirror device, and a third lens;
The second lens is positioned on the light path of the target light beam, and is used for obtaining a second light beam after performing inverse Fourier transform on the target light beam and transmitting the second light beam;
the digital micro-mirror device is connected with the computer and is positioned on the optical path of the second light beam, and is used for receiving the binary orbital angular momentum hologram sent by the computer and displaying the binary orbital angular momentum hologram on a display plane thereof in a time division multiplexing mode; the second light beam is used for being incident on the display plane to decode the binary orbital angular momentum hologram displayed on the display plane and then reflect a third light beam;
the third lens is positioned on the light path of the third light beam, and is used for obtaining a fourth light beam after carrying out Fourier transform on the third light beam and transmitting the fourth light beam;
the camera is located on the light path of the fourth light beam, and is used for shooting the binary orbital angular momentum hologram displayed on the display plane through the fourth light beam to obtain the target image.
8. The system of any one of claims 1 to 6, wherein the computer is further configured to:
Receiving a plurality of target images input by a user, and sampling the target images through a sampling array with random phase aiming at each target image in the plurality of target images to obtain a sampling image;
performing inverse Fourier transform on the sampling image to obtain first complex amplitude distribution information corresponding to the sampling image;
processing the first complex amplitude distribution information through a preset spiral phase mask to obtain second complex amplitude distribution information;
superposing the second complex amplitude distribution information corresponding to each target image to obtain target complex amplitude distribution information, and converting the target complex amplitude distribution information into amplitude distribution information by correcting an off-axis coding method;
and carrying out binarization processing on the amplitude distribution information to obtain the binary orbital angular momentum hologram.
9. The system of claim 8, wherein the computer is further configured to: and carrying out binarization processing on the amplitude distribution information through a signal window average error minimum algorithm to obtain the binary orbital angular momentum hologram.
10. The system of claim 9, wherein the computer is further configured to:
Determining a target carrier frequency and a target resolution corresponding to the target image;
determining a diffusion coefficient of the signal window average error minimum algorithm according to the target carrier frequency and the target resolution;
and carrying out binarization processing on the amplitude distribution information through the diffusion coefficient and the signal window average error minimum algorithm to obtain the binary orbital angular momentum hologram.
11. The system of claim 10, wherein the computer is further configured to:
determining the size of a signal window corresponding to the signal window average error minimum algorithm in a spatial frequency domain according to the target resolution; the signal window is a partial region in the spatial frequency domain;
determining the distribution position of the signal window in the space frequency domain according to the target carrier frequency;
determining a spatial frequency domain coordinate corresponding to the signal window according to the size and the distribution position;
and carrying out Fourier transform on the space frequency domain coordinates to obtain the diffusion coefficient.
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