CN113916792B - Far-field imaging method and system based on coherent structure - Google Patents
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Abstract
The scheme utilizes the joint regulation and control of the coherent structure and the cross phase structure of partial coherent light beams to realize that the coherent structure is used as a transmission carrier of image information, and regulates and controls the coherent structure after information is loaded; when the transmission path is blocked by the obstacle, the size of the coherence of the partial coherent light beam is regulated and controlled in real time in the far field through detecting the shape and the size of the obstacle after the transmission path is transmitted in the far field, the complete coherent structural information is recovered by using the information destroyed by the obstacle in the far field, and further, the far field imaging is realized by using the corresponding relation between the coherent structural information and the image information. The scheme can detect whether the far-field transmission path has the obstacle or not, including the shape, the size and the position of the obstacle. According to the size of the obstacle, the coherence size of the light source is regulated and controlled in real time, so that the coherence structure is ensured not to be damaged, and further far-field imaging is realized.
Description
Technical Field
The disclosure belongs to the technical field of far-field imaging, and particularly relates to a far-field imaging method and system based on a coherent structure.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
Optical imaging is a means for converting an objective object into an image by using light as a medium and using a certain technology, and is widely used in various fields such as biological cell imaging, microscopic imaging, medical imaging, astronomical imaging, cameras in daily life, projection imaging, and the like. In the conventional imaging technology, the 4f imaging system strictly comprises two fourier transform processes by using two lenses, and has three positions of an object plane, a frequency plane and an imaging plane, and can improve the imaging resolution to a certain extent and imaging in a complex environment by introducing a certain regulation and control means in the frequency domain, however, some complex processing and additional processing equipment such as a specific filter are often required to be introduced through the regulation and control in the frequency domain, so that the complexity of the system is greatly increased. On the other hand, optical imaging is most widely performed by using completely coherent light at present, however, imaging distortion can be caused by using completely coherent light under some complex environments, such as extreme environments of high temperature, high pressure and the like, under medium of atmospheric/ocean turbulence and the like, and when shielding is caused by obstacles and the like, resolution is reduced, and imaging quality is difficult to meet actual requirements.
At present, a partially coherent light beam is widely focused by researchers, the partially coherent light beam is used for an imaging technology, the partially coherent light beam contains rich adjustable degrees of freedom for controlling and manipulating light beam transmission characteristics, negative effects caused by media such as turbulence in a complex environment can be reduced, in addition, the partially coherent light beam has strong self-repairing characteristics when encountering obstacles, negative effects caused by the obstacles can be resisted, and the partially coherent light beam has important application in various fields.
In recent years, far field imaging has been widely studied in various application fields using degrees of freedom such as partially coherent beam amplitude, phase, polarization, and coherent structure. However, the inventors have found that in complex environments, such as extreme environments of high temperature and high pressure, under medium such as atmospheric/ocean turbulence, and when the light beam is blocked by obstacles, the characteristics of the light beam change after the light beam interacts with the complex environments, and information is easily lost by using a single degree of freedom, and although various improvements are proposed successively, these solutions often require complex optical systems or long processing times. The new degree of freedom of the partially coherent light coherent structure has a certain hiding property, and can show strong robustness even in a complex environment, however, after the coherent structure performs far-field transmission, the coherent structure is subjected to unavoidable light beam diffraction effect, has no transmission invariance, and is difficult to image by using the changed coherent structure, so that image information is lost. In addition, when the transmission path encounters an obstacle, such as a building, a forest, etc., the transmitted information is partially lost, so far-field imaging using the information after encountering the obstacle in the transmission is severely challenged. Meanwhile, if the coherent structure of the partially coherent light beam is intended to be used as a carrier of image information, far-field imaging is performed by far-field transmission after encountering an obstacle in transmission, which cannot be realized in the prior art.
Disclosure of Invention
In order to solve the problems, the present disclosure provides a far-field imaging method and a system based on a coherent structure, where the scheme uses the coherent structure of a partially coherent light beam as an image transmission carrier, introduces a cross phase regulation function into the partially coherent light beam with a special correlation structure to regulate and control the coherent structure after loading information, so as to ensure that the coherent structure has transmission invariance, and after the transmission link is shielded by an opaque obstacle, the coherence of the light beam is regulated and controlled in real time by detecting the shape and the position of the obstacle, so as to ensure that the far field obtains complete coherent structure information, and the coherent structure can be used as the carrier of image transmission to conveniently hide information, and the information is shielded by the obstacle in transmission, and finally imaged in the far field by using the damaged information, thereby greatly improving the effectiveness of information transmission and effectively overcoming the shielding of the obstacle.
According to a first aspect of embodiments of the present disclosure, there is provided a far field imaging method based on a coherent structure, comprising:
acquiring image information to be transmitted;
loading the image information into a coherent structure of a partial coherent light beam through a complex screen method for transmission;
introducing a cross phase structure with controllable size into a coherent structure of a partially coherent light beam after image information is loaded;
regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
and obtaining the coherent structure of the partial coherent light beam in the far field, and realizing far-field imaging based on the relation between the coherent structure information and the image information.
Furthermore, the cross phase structure with controllable size is introduced into the coherent structure of the partially coherent light beam after the image information is loaded, specifically: the image information is encoded in a complex screen function in the electric field constituting the partially coherent light beam while introducing a cross-phase structure in the electric field, which is loaded by the spatial light modulator.
Further, the intensity factor of the cross phase structure is regulated and controlled based on the shape, size and position of the obstacle in the transmission path; the method comprises the following steps: the shape and the position of the obstacle are detected at first in the far field, and the coherence of the light beam is regulated in real time, so that the complete coherent structural information is obtained in the far field measurement when the obstacle exists.
Further, the acquiring the image information to be transmitted specifically includes: the laser output by the laser transmitter reaches the beam expander through the attenuation sheet; the laser beam expanded by the beam expander is loaded with the holographic sheet of the image information by the spatial light modulator.
Further, the image information is loaded into a coherent structure of a partially coherent light beam for transmission by a multi-screen method, specifically: firstly, generating an electric field of a partially coherent light beam carrying image information, then synthesizing the partially coherent light beam by adopting a complex screen method, realizing that the image information is loaded into a coherent structure of the partially coherent light beam, and further realizing that the coherent structure is used as a transmission carrier of the image information.
According to a second aspect of embodiments of the present disclosure, there is provided a far field imaging system based on a coherent structure, comprising:
an image acquisition unit for acquiring image information to be transmitted;
the image loading unit is used for loading the image information into a coherent structure of a partial coherent light beam through a multi-screen method for transmission;
the phase structure regulating and controlling unit is used for introducing a cross phase structure with controllable size into the coherent structure of the partially coherent light beam after the image information is loaded; regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
and the imaging unit is used for obtaining the coherent structure of the partial coherent light beam in the far field and realizing far-field imaging based on the relation between the coherent structure information and the image information.
According to a third aspect of the embodiments of the present disclosure, there is provided a far-field imaging system based on a coherent structure, which adopts the far-field imaging method based on a coherent structure described above, where the system includes a laser emitter, and laser emitted by the laser emitter reaches a beam expander through an attenuation sheet, and the laser after being expanded by the beam expander is led into a cross phase structure through a spatial light modulator;
the partially coherent light beam modulated by the spatial light modulator reaches the light source surface through a lens group consisting of lenses L1 and L2; the partially coherent light beam reaching the light source face impinges the light source through a thin lens L3 onto a lens L4 and finally to a charge coupled element, wherein an opaque barrier is arranged between the lens L3 and the charge coupled element.
Compared with the prior art, the beneficial effects of the present disclosure are:
(1) The scheme of the disclosure provides a far-field imaging method and a far-field imaging system based on a coherent structure, which utilize the joint regulation and control of the coherent structure and the cross phase structure of a partial coherent light beam to realize the coherent structure as a transmission carrier of image information, regulate and control the coherent structure after information is loaded, have obstacle shielding on a transmission path, regulate and control the size of the coherence of the partial coherent light beam in real time by detecting the shape and the size of the obstacle after far-field transmission, recover complete coherent structure information by utilizing the information destroyed by the obstacle in the far field, and further realize far-field imaging by utilizing the corresponding relation between the coherent structure information and the image information.
(2) The scheme disclosed by the disclosure can detect whether the far-field transmission path has an obstacle or not, including the shape, the size and the position of the obstacle. According to the size of the obstacle, the coherence size of the light source is regulated and controlled in real time, so that the coherence structure is ensured not to be damaged, and further far-field imaging is realized.
(3) The scheme of the present disclosure uses the hidden characteristic of the coherent structure, greatly improves the effectiveness of information transmission, and overcomes the robustness of complex environments (obstacles).
Additional aspects of the disclosure will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the disclosure.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate and explain the exemplary embodiments of the disclosure and together with the description serve to explain the disclosure, and do not constitute an undue limitation on the disclosure.
Fig. 1 is a flow chart of a far-field imaging method based on a coherent structure according to a first embodiment of the present disclosure;
FIG. 2 is a diagram of a far field imaging system based on a coherent architecture in accordance with a first embodiment of the present disclosure;
1.532nm laser (Nd: YAG); 2. an attenuation sheet; 3. a beam expander; 4. a computer (PC 1); 5. a Spatial Light Modulator (SLM); 6. a thin lens (L1); 7. round aperture (CA); 8. a thin lens (L2); 9. a planar mirror; a 10 thin lens (L3); 11. a thin lens (L4); 12 obstacles; 13. a Charge Coupled Device (CCD); 14. computer (PC 2).
Detailed Description
The disclosure is further described below with reference to the drawings and examples.
It should be noted that the following detailed description is illustrative and is intended to provide further explanation of the present disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments in accordance with the present disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise, and furthermore, it is to be understood that the terms "comprises" and/or "comprising" when used in this specification are taken to specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof.
Embodiments of the present disclosure and features of embodiments may be combined with each other without conflict.
Embodiment one:
it is an object of the present embodiment to provide a far field imaging method based on a coherent structure.
As shown in fig. 1, a far field imaging method based on a coherent structure includes:
acquiring image information to be transmitted;
loading the image information into a coherent structure of a partial coherent light beam through a complex screen method for transmission;
introducing a cross phase structure with controllable size into a coherent structure of a partially coherent light beam after image information is loaded;
regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
and obtaining the coherent structure of the partial coherent light beam in the far field, and realizing far-field imaging based on the relation between the coherent structure information and the image information.
Furthermore, the cross phase structure with controllable size is introduced into the coherent structure of the partially coherent light beam after the image information is loaded, specifically: the image information is encoded in a complex screen function in the electric field constituting the partially coherent light beam while introducing a cross-phase structure in the electric field, which is loaded by the spatial light modulator.
Further, the intensity factor of the cross phase structure is regulated and controlled based on the shape, size and position of the obstacle in the transmission path; the method comprises the following steps: the shape and the position of the obstacle are detected at first in the far field, and the coherence of the light beam is regulated in real time, so that the complete coherent structural information is obtained in the far field measurement when the obstacle exists.
Further, the acquiring the image information to be transmitted specifically includes: the laser output by the laser transmitter reaches the beam expander through the attenuation sheet; the laser beam expanded by the beam expander is loaded with the holographic sheet of the image information by the spatial light modulator.
Further, the image information is loaded into a coherent structure of a partially coherent light beam for transmission by a multi-screen method, specifically: firstly, generating an electric field of a partially coherent light beam carrying image information, then synthesizing the partially coherent light beam by adopting a complex screen method, realizing that the image information is loaded into a coherent structure of the partially coherent light beam, and further realizing that the coherent structure is used as a transmission carrier of the image information.
In particular, for ease of understanding, the following detailed description of the aspects of the disclosure will be given with reference to specific examples:
the coherent structure of the partial coherent light beam is used as a carrier of image information, the coherent structure of the image information carrier is controlled by combining the coherent structure and a Cross phase (CP: cross-phase), the coherent structure of the image information carrier has transmission invariance, the coherent structure is shielded by an obstacle and transmitted by a far field, the shape and the size of the obstacle are detected in the far field, the coherent structure coherence of the incident light beam is designed, the complete coherent structure information is ensured to be measured in the far field, and finally the coherent structure information measured in the far field is equal to the coherent structure information at a measuring light source; far-field imaging is achieved using a correspondence of known coherence structures and image information.
First basic principle
First, describing how image information is loaded into the coherent structure of partially coherent light, the Cross Spectral Density (CSD) at the light source can be expressed as
Where P (v) defines any non-negative function, H (r, v) can be any function, in order to construct our optical system (Fourier transform system) and introduce a cross-phase regulatory function. H (r, v) is expressed as
H(r,v)＝τ(r)exp(-ikr·v)exp(iuxy)， (2)
Where k=2pi/λ defines wavenumber, λ defines wavelength, τ (r) is a complex function describing the light intensity term I (r) = |τ (r) | 2 To be general, the intensity term is defined as a gaussian function, i.e., τ (r) =exp (-r) 2 /4ω 0 2 ) (spot width omega) 0 =1 mm). Bringing equation (2) into equation (1) yields partially coherent light beams (PCBs) with image information, a type of partially coherent light beam (SMPCBs) of the schel-eye model, the Cross Spectral Density (CSD) after introducing the Cross Phase (CP) structure being expressed as:
W s (r 1 ,r 2 )＝τ(r 1 ) * τ(r 2 )μ 0 (Δr)exp[-iu(x 1 y 1 -x 2 y 2 )], (3)
wherein r is i ＝(x i ，y i ) I=1, 2 defines any two position vectors at the light source, Δr=r 1 -r 2 Is the vector difference operation of two positions of the light source surface, mu 0 (Δr) defines the coherence structure of the partially coherent beam, and the last term exp (iuxy) defines the cross-phase structure (CP), u being the CP structural intensity factor.
And the relationship between the coherent structure and the non-negative function P (v) is expressed as:
μ 0 (Δr)＝∫p(v)exp(-ikvΔr)d 2 v (4)
the image information is loaded into the coherent structure according to equation (4). And the coherent structure and the image information have a fourier transform relationship.
The following is to generate a partially coherent light beam carrying object information by using a multi-screen method, and the single electric field form of the partially coherent light beam is expressed as follows in combination with formulas (1) and (3):
U(r)＝τ(r)exp(iuxy)T(r), (5)
wherein T (r) is defined as a random complex function, obeying zero-mean, complex Gaussian random distribution. From equations (3) and (5), it is easy to derive
T is then expressed in the form of Fourier coefficients
Wherein T is zero mean, the circular complex Gaussian Fourier coefficients, m and n are discrete space frequency coefficients of the matrix T respectively, and L is the actual size of the discrete grid. Carrying out autocorrelation operation by carrying out the formula (6) to obtain,
because of the fact that,<|T| 2 >equal to the variance of the Fourier coefficients, and T is a circular complex Gaussian function, so the real and imaginary parts of the variance of the T function are equal, thus yielding
In combination with the above results, the complex screen T for generating a partially coherent beam can be expressed as
Where j, l is the discrete space coefficient of the complex screen T, N is the total number of points of the complex screen, r is a zero-mean value of N, and the variance is a round complex Gaussian random function of 1.
Equation (10) is an inverse discrete fourier transform form, so a fast fourier transform algorithm may be used to synthesize the complex screen function in order to increase computational efficiency and reduce computational complexity.
The single-pass electric field of the synthesized partially coherent light source can be easily obtained by bringing the formula (10) into the formula (5), and then the cross spectral density of the light source can be obtained by bringing the formula (1).
Theoretical deductions were made in order to obtain the effect of obstacles in the transmission path on the coherent structure of SMPCBs. Under paraxial approximation, a single electric field realization of the beam transmitted through free space to the front surface of an obstacle can be expressed by the generalized Huygens-Fresnel principle as
Wherein ρ is i ＝(ρ xi ，ρ yi ) I=1, 2 defines any two position vectors of the obstacle plane, a 1 ，B 1 And D 1 Optical system transmission from light source surface to obstacle surfaceThe matrix elements, FT, represent the fourier transform operation.
After being blocked by the barrier, the single electric field implementation of the light beam on the rear surface of the barrier is expressed as,
U on (ρ i )＝O(θ i )U n (ρ i ), (12)
o (θ) is expressed as an obstacle transmission function, where the obstacle function selects a sector of opaque obstacles, expressed as,
where ρ= (ρ, θ), θ is the angular angle of the position vector ρ.
Next, again using the generalized Huygens-Fresnel principle, the single electric field transmission of the light source from the obstacle surface to the far surface is realized, expressed as
Wherein,ρ’ i ＝(ρ’ xi ，ρ’ yi ) I=1, 2, defined as any two position vectors of far scene, a 2 ，B 2 And D 2 Matrix elements are transmitted for the optical system from the object plane of the obstacle to the far scene.
The average light intensity can be expressed as
Wherein I is rn (ρ’)＝U * n (ρ’)U n (ρ') represents the single-pass light intensity at the far field.
By Gaussian moment theory, the coherent structure at the far field can be expressed as
Wherein g 2 (ρ’ 1 ,ρ’ 2 ) Is a fourth-order correlation operation at two points in the far field, expressed as
From equations (15) and (16), we can conveniently derive the average light intensity and the coherent structure information at the far field.
The optical system in this embodiment selects a lens focusing system, specifically, a focusing lens with a focal length f is placed on the light source surface, and the distance between the light source surface and the obstacle is assumed to be Δz, and the distance between the obstacle surface and the far scene is assumed to be f- Δz. The matrix elements of the optical system are correspondingly represented as
However, as can be seen from equation (16), the measured coherent structure can only be obtained as a modulus of the coherent structure, and all phase information corresponding to the coherent structure has been lost. In the far field, even after the modulus of the coherent structure is measured, the fourier transform and inverse transform relationship (formula (4)) of the coherent structure and the image information is directly utilized without knowing the phase information thereof, so that the image information hidden in the coherent structure is not recovered.
Here we iterate out the phase information of the coherent structure by Fienup Phase Recovery (FPR) algorithm after knowing the information of the far field coherence modulus, thereby realizing the recovery of the image information.
The algorithm starts with any initial guess of the object P 1 (x, y) and then performing a four-step operation, at the kth iterationRepresented as
μ k (u,v)＝FT{P k (x,y)}, (19)
Wherein P is k (x, y) represents object information at the kth iteration, and FT represents a fourier transform operation. The coherent structure information of the kth estimate is obtained and its phase is expressed as
θ k (u,v)＝arg{μ k (u,v)}, (20)
Wherein arg represents a phase extraction operation. θ k Representing fourier spectrum phase information at the kth iteration. Then, a new coherent structure is formed by using the mode of the measured coherent structure and the phase information estimated at the kth time, which is expressed as
Wherein, |mu m I represents the measured or known model of DOC, μ k ' represents the newly derived estimated fourier spectrum of the kth iteration,
then, the new obtained coherent structure is utilized to carry out Fourier inverse transformation to obtain a new estimated object which is used as the estimated object of the next iteration and expressed as
P k '(x,y)＝IFT{μ k '(μ,ν)}, (22)
Wherein P is k ' represents the newly derived estimated object of the kth iteration.
Repeating the four steps until the algorithm meets the judgment condition, wherein the judgment condition of the algorithm requires that the object is a real value and is not negative. In the case that we construct the real illuminant condition, we define the image information P to be a real valued non-negative function and to satisfy the algorithm decision condition. Let Γ be P k (x, y) points that violate the constraint; for points against constraint we first process the points against constraint using a hybrid input output algorithm, expressed as
Wherein beta is a feedback parameter for controlling the convergence of the algorithm, when P k+1 After calculation of (x, y), he can be used as (k+1) th The starting point of the iteration. The algorithm takes only a few microseconds for a single iteration in a modern computer, and in an actual iteration operation, the optimal iteration parameter can be selected to be beta, and the beta is changed from 2 to 0 in a step size of 0.05. 10 iterations are performed for each beta value, followed by running 100 an error reduction algorithm to reduce the recovered information background noise.
The level of convergence of the algorithm can be monitored by calculating the square difference of the self-correlation of the recovered information with the known object information. Represented as
(II) detailed description
The scheme mainly comprises the following steps that image information is loaded into a coherent structure of partial coherent light, the coherent structure of the partial coherent light is used as a carrier for image transmission, far-field transmission obstacle shielding is realized in the step II, and image information is recovered by the step III through coherent structure measurement and FPR algorithm. As shown in fig. 2:
a first section in which a 532nm wavelength laser light is emitted from a Nd: YAG laser, passes through an attenuator pad (NDFM) to reach a Beam Expander (BE), and then reaches a Spatial Light Modulator (SLM); the SLM is used for loading an electric field hologram which synthesizes partial coherent light beams containing image information, a computer (PC 1) is used for generating and controlling the hologram, a CP structural strength factor u can be controlled by controlling the hologram on the SLM, then the hologram reaches a light source surface through a 4f optical system consisting of imaging lenses (L1) and (L2), a first-order diffraction light spot is filtered out from the circular aperture, and then object information is loaded into a SMPCBs coherent structure. The resulting SMPCBs are illuminated onto detection system lens L4 by a 2f imaging system consisting of lens L3.
The second part is used for detecting far-field light intensity and coherent structural information through the thin lens L4 and the CCD, an opaque obstacle is arranged in a transmission path, the light intensity and coherence degree are measured through scattered spots shot by the CCD and sent into the PC2, the light intensity is measured according to the measured light intensity to judge the shape and the position (the light intensity of the detected damaged part corresponds to the shape and the size of the obstacle under the influence of the obstacle due to the regulation and control action of the cross phase) of the obstacle (the distance between the obstacle and the light source can be calculated according to the rotation angle of the light intensity), and the coherence degree of the light source is regulated in real time, so that the intact coherent structural information which is not destroyed can be measured under the shielding of the obstacle.
And thirdly, obtaining a complete coherent structural module through intensity correlation measurement on a receiving surface by adjusting the proper coherence size, and then calling an FPR algorithm. Performing far-field image recovery.
Embodiment two:
it is an object of this embodiment to provide a far field imaging system based on a coherent structure.
A far field imaging system based on a coherent structure, comprising:
an image acquisition unit for acquiring image information to be transmitted;
the image loading unit is used for loading the image information into a coherent structure of a partial coherent light beam through a multi-screen method for transmission;
the phase structure regulating and controlling unit is used for introducing a cross phase structure with controllable size into the coherent structure of the partially coherent light beam after the image information is loaded; regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
and the imaging unit is used for obtaining the coherent structure of the partial coherent light beam in the far field and realizing far-field imaging based on the relation between the coherent structure information and the image information.
Embodiment III:
it is an object of this embodiment to provide a far field imaging system based on a coherent structure.
The far-field imaging system based on the coherent structure adopts the far-field imaging method based on the coherent structure, and comprises a laser emitter, wherein laser emitted by the laser emitter reaches a beam expander through an attenuation sheet, and the laser after being expanded by the beam expander is led into a cross phase structure through a spatial light modulator;
the partially coherent light beam modulated by the spatial light modulator reaches the light source surface through a lens group consisting of lenses L1 and L2; the partially coherent light beam reaching the light source face impinges the light source through a thin lens L3 onto a lens L4 and finally to a charge coupled element, wherein an opaque barrier is arranged between the lens L3 and the charge coupled element.
In particular, for ease of understanding, the system of the present disclosure is described in detail below with reference to the accompanying drawings:
as shown in fig. 2, a far-field imaging system based on a coherent structure includes a laser emitter, laser emitted by the laser emitter reaches a beam expander through an attenuation sheet, the laser after being expanded by the beam expander loads image information through a spatial light modulator and introduces a cross phase structure, and the image information is loaded into the coherent structure of a partial coherent beam for transmission through a multi-screen method, specifically: firstly, an electric field carrying image information and a cross phase partial coherent light beam is generated, then, the partial coherent light beam is synthesized by adopting a complex screen method, so that the image information is loaded into a coherent structure of the partial coherent light beam, the coherent structure is further used as a transmission carrier of the image information, and the CP structural strength factor u can be controlled by controlling a hologram on an SLM.
The partial coherent light beam modulated by the spatial light modulator passes through a 4f system formed by lenses L1 and L2, and a first-order diffraction light spot filtered out by a diaphragm reaches a light source surface (the surface of a plane reflector); the partial coherent light beam reaching the light source surface is transmitted to the detection system lens L4 through the 2f imaging system formed by the thin lens L3 and then reaches the charge coupling element (far field), wherein an opaque barrier is arranged between the lens L3 and the charge coupling element, the shot speckle shielded by the barrier is obtained through the charge coupling element, the speckle is transmitted to the PC, the shape and the position of the barrier are detected through average light intensity, the coherence of the light source is regulated and controlled in real time, the complete coherent structural information at the position can be recovered from the damaged speckle is ensured, and further far field imaging is carried out by utilizing the relation between the measured coherent structural information and the loaded image information.
Further, the 4f system formed by the lenses comprises a first thin lens and a second thin lens, and a circular aperture for filtering out first-order diffraction spots is arranged between the first thin lens and the second thin lens. The distance from the spatial light modulator to the thin lens L1 and the thin lens L1 to the circular aperture, and the distance from the circular aperture to the thin lens L2 and the distance from the thin lens L2 to the plane mirror are respectively f, and f is 250mm.
Further, the 2f imaging system formed by transmitting the partially coherent light beam through the plane mirror to transmit the partially coherent light beam L3 transmits the light source to the detection system lens L4, wherein the distances from the plane mirror to the thin lens L3 and the distances from the thin lens L3 to the thin lens L4 are 2 times f, and f is 250mm.
Further, the light source is applied to the lens L4 of the detection system and then reaches the charge coupled device (far field), wherein an opaque barrier is arranged between the lens L3 and the charge coupled device, the barrier is formed by a sector-shaped opaque barrier, and the size and the position of the barrier are controllable.
Those of ordinary skill in the art will appreciate that the elements of the various examples described in connection with the present embodiments, i.e., the algorithm steps, can be implemented as electronic hardware or combinations of computer software and electronic hardware. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.
The far-field imaging method and the far-field imaging system based on the coherent structure can be realized, and have wide application prospects.
The foregoing description of the preferred embodiments of the present disclosure is provided only and not intended to limit the disclosure so that various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims (3)
1. A far field imaging method based on a coherent structure, comprising:
acquiring image information to be transmitted;
loading the image information into a coherent structure of a partial coherent light beam through a complex screen method for transmission;
introducing a cross phase structure with controllable size into a coherent structure of a partially coherent light beam after image information is loaded;
regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
obtaining a coherent structure of a partial coherent light beam in a far field, and realizing far-field imaging based on the relation between coherent structure information and image information;
the cross phase structure with controllable size is introduced into the coherent structure of the partially coherent light beam after the image information is loaded, and specifically comprises the following steps: encoding image information in a complex screen function in an electric field constituting a partially coherent light beam while introducing a cross-phase structure in the electric field, the electric field being loaded by a spatial light modulator;
the intensity factor of the cross phase structure is regulated and controlled based on the shape, the size and the position of the obstacle in the transmission path; the method comprises the following steps: firstly detecting the shape and the position of an obstacle in a far field, and ensuring that complete coherent structural information is obtained in the far field measurement when the obstacle exists by regulating and controlling the coherence of a light beam in real time;
the obtaining of the image information to be transmitted specifically includes: the laser output by the laser transmitter reaches the beam expander through the attenuation sheet; the laser beam expanded by the beam expander is loaded with an electric field hologram carrying image information and a cross phase partial coherent beam by a spatial light modulator;
the image information is loaded into a coherent structure of a partial coherent light beam for transmission by a multi-screen method, and the method specifically comprises the following steps: firstly, generating an electric field of a partially coherent light beam carrying image information, then synthesizing the partially coherent light beam by adopting a complex screen method, realizing that the image information is loaded into a coherent structure of the partially coherent light beam, and further realizing that the coherent structure is used as a transmission carrier of the image information.
2. A far field imaging system based on a coherent structure, comprising:
an image acquisition unit for acquiring image information to be transmitted;
the image loading unit is used for loading the image information into a coherent structure of a partial coherent light beam through a multi-screen method for transmission;
the phase structure regulating and controlling unit is used for introducing a cross phase structure with controllable size into the coherent structure of the partially coherent light beam after the image information is loaded; regulating and controlling the intensity factor of the cross phase structure based on the shape and the position of the obstacle in the transmission path;
an imaging unit for obtaining a coherent structure of a partially coherent light beam in a far field, and realizing far field imaging based on a relation between the coherent structure information and image information;
the cross phase structure with controllable size is introduced into the coherent structure of the partially coherent light beam after the image information is loaded, and specifically comprises the following steps: encoding image information in a complex screen function in an electric field constituting a partially coherent light beam while introducing a cross-phase structure in the electric field, the electric field being loaded by a spatial light modulator;
the intensity factor of the cross phase structure is regulated and controlled based on the shape, the size and the position of the obstacle in the transmission path; the method comprises the following steps: firstly detecting the shape and the position of an obstacle in a far field, and ensuring that complete coherent structural information is obtained in the far field measurement when the obstacle exists by regulating and controlling the coherence of a light beam in real time;
the obtaining of the image information to be transmitted specifically includes: the laser output by the laser transmitter reaches the beam expander through the attenuation sheet; the laser beam expanded by the beam expander is loaded with an electric field hologram carrying image information and a cross phase partial coherent beam by a spatial light modulator;
the image information is loaded into a coherent structure of a partial coherent light beam for transmission by a multi-screen method, and the method specifically comprises the following steps: firstly, generating an electric field of a partially coherent light beam carrying image information and a cross phase, and then synthesizing the partially coherent light beam by adopting a complex screen method, so that the image information is loaded into a coherent structure of the partially coherent light beam, and further the coherent structure is used as a transmission carrier of the image information.
3. A far-field imaging system based on a coherent structure, which adopts the far-field imaging method based on the coherent structure as set forth in claim 1, wherein the system comprises a laser emitter, laser emitted by the laser emitter reaches a beam expander through an attenuation sheet, and the laser after being expanded by the beam expander is led into a cross phase structure through a spatial light modulator;
the partially coherent light beam modulated by the spatial light modulator reaches the light source surface through a lens group consisting of lenses L1 and L2; the partially coherent light beam reaching the light source face impinges the light source through a thin lens L3 onto a lens L4 and finally to a charge coupled element, wherein an opaque barrier is arranged between the lens L4 and the charge coupled element.
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