CN111193552B - Vortex light beam topological charge number identification method - Google Patents
Vortex light beam topological charge number identification method Download PDFInfo
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- CN111193552B CN111193552B CN202010055352.2A CN202010055352A CN111193552B CN 111193552 B CN111193552 B CN 111193552B CN 202010055352 A CN202010055352 A CN 202010055352A CN 111193552 B CN111193552 B CN 111193552B
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Abstract
The invention discloses a vortex light beam topological charge number identification method, which comprises the following steps: extracting a light intensity diagram and a phase diagram of the vortex beam; processing the light intensity graph, finding the light ring with the strongest light intensity from the center of the graph from inside to outside, and counting the radius of the light ring; and (4) finding the corresponding phase on the circular ring in the phase diagram by taking the radius as a circle, and calculating the frequency of the phase change from 0-2 pi, wherein the frequency is the topological charge number of the vortex beam. The method of the invention not only can separate different vortex beams, but also can obtain the intensity information (such as OOK modulation signals) carried in the vortex optical beams in real time; the method does not need to convert the vortex light beam into the Gaussian light beam for identification, reduces the number of elements of the communication system, greatly reduces the complexity of the system, increases the identification rate of the vortex light, has high application value, and has important significance for promoting the application of the vortex optical rotation communication system.
Description
Technical Field
The invention relates to the technical field of communication, in particular to a vortex light beam topological charge number identification method.
Background
As the technology industry develops, the channel capacity required for communicating data becomes larger, which also poses a serious challenge to the conventional communication technology. To further improve the data transmission capabilities of existing communication networks, vortex rotation is introduced into the communication system. Vortex rotation has orbital angular momentum and can carry more information. Unlike the traditional polarization, frequency, phase dimensions, vortex beams require new techniques to generate and demodulate.
The concept of vortex rotation was first proposed in 1989, and it was discovered in 1992 that vortex beams contain orbital angular momentum, and that the Barreiro team, 2008, used orbital angular momentum beams to transmit signals to break through capacity limitations. The study of vortex light has been intensive over the last 30 years. At present, the application of vortex light in the communication field is greatly researched, for example, Wang and the like realize data transmission of 2TBit/s by vortex light multiplexing. Most of the existing orbital angular momentum communication technologies improve the communication speed through orbital angular momentum multiplexing. At present, Gaussian beams generated by lasers are converted into vortex beams for transmission, and the vortex beams are converted into the Gaussian beams for identification at a receiving end in a reverse process. This method is reliable and technically mature and efficient, but is structurally too cumbersome.
Disclosure of Invention
In view of the above, in order to solve the above problems in the prior art, the present invention provides a vortex light beam topological charge number identification method, in which a high-speed CCD camera is used to acquire vortex light intensity and phase information, and the topological charge of the vortex light beam is obtained through program identification.
The invention solves the problems through the following technical means:
a vortex light beam topological charge number identification method comprises the following steps:
extracting a light intensity diagram and a phase diagram of the vortex beam;
processing the light intensity graph, finding the light ring with the strongest light intensity from the center of the graph from inside to outside, and counting the radius R of the light ring;
and (4) finding the corresponding phase on the circular ring in the phase diagram by taking the radius as a circle, and calculating the frequency of the phase change from 0-2 pi, wherein the frequency is the topological charge number of the vortex beam.
Further, the direction of the phase change from 0 to 2 pi determines the positive and negative of the topological charge, and the counterclockwise direction is positive and the clockwise direction is negative.
Furthermore, after the topological charge number of the vortex light beam is identified, the intensity information of the light beam is extracted, and finally 0 and 1 signals carried by the corresponding vortex light beam at different times are demodulated.
Further, the light intensity graph is processed, and the halo with the strongest light intensity is found from the center of the graph from inside to outside to calculate the radius of the halo, which specifically comprises the following steps:
after a vortex light beam light intensity graph and a phase graph are collected, the graph is read in through a computing platform, an RGB (red, green and blue) graph is converted into a 0-255 gray scale graph, the center of a square which is the center of a vortex light beam is cut into an n multiplied by n square matrix, R is taken as a radius to be taken as a circle, all data points on the circle form a one-dimensional data set, the radius is sequentially increased to traverse the whole graph, finally n/2 groups of data are obtained, each group of data are summed firstly and then averaged to obtain n/2 single values, the n/2 single values are compared to find the maximum value, and the radius corresponding to the maximum value is the radius with the strongest light.
Further, the corresponding phase on the circular ring is found in the phase diagram by taking the radius as a circle, and the number of times that the phase changes from 0 pi to 2 pi is calculated, and the number is the topological charge number of the vortex beam, and the method specifically comprises the following steps:
finding out the phase corresponding to the ring with the strongest light intensity according to the radius, and taking out the data on the ring to form a one-dimensional array, wherein the data of the array represents the change condition of the phase of 0-2 pi; each sawtooth of the waveform is sawtooth-shaped and represents the change of 0 to 2 pi once, and the total change times are the topological charge number of the light beam; and carrying out one-time derivation on the obtained one-dimensional array, forming a delta function by 0-2 pi mutation in the derived one-dimensional array, filtering to obtain a pure oscillogram only containing a plurality of delta functions, and calculating the number of the delta functions to obtain the topological charge number.
Further, the computing platform comprises a computing platform based on MATLAB, C program and Python.
Further, n takes the value of 500.
Compared with the prior art, the invention has the beneficial effects that at least:
the method not only can separate different vortex beams, but also can obtain the intensity information (such as OOK modulation signals) carried in the vortex optical beams in real time. The method does not need to convert the vortex beam into the Gaussian beam and then identify the Gaussian beam, greatly reduces the complexity of the system and has high application value.
Compared with the original Gauss-OAM-Gauss scheme, the method provided by the invention reduces the OAM-Gauss steps, and can directly identify vortex beams to obtain signals. The vortex optical rotation topological charge number can be automatically identified by acquiring a light intensity and phase diagram in the identification process, and the method can be operated under MATLAB, C programs, Python and other platforms.
The method is specifically tested under an MATLAB platform, the highest recognition rate in the vortex light from l to 8 can reach 99.2%, and the average recognition rate can reach 93.58%. The identification scheme adopts image identification analysis signals, reduces the number of elements of a communication system, reduces the complexity of the system and increases the identification rate of vortex light. It is of great significance to the application of vortex optical rotation communication system.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
FIG. 1 is a flow chart of a vortex beam topological charge number identification method of the present invention;
FIG. 2(a) is a graph of vortex beam intensity obtained at the receiving end of the communication system of the present invention;
FIG. 2(b) is a phase diagram of a vortex beam obtained at the receiving end of the communication system of the present invention;
FIG. 3(a) is a diagram of the position where the strongest vortex beam light field is found by calculation according to the present invention;
FIG. 3(b) is a diagram of the phase change corresponding to the position of the highest light intensity in the phase diagram according to the present invention;
FIG. 4(a) is a statistical intensity plot for the direction of increasing radius according to the present invention;
FIG. 4(b) is a light intensity distribution diagram at a corresponding radius of the present invention, wherein the highest point in the diagram represents the radius of the light ring where the light intensity is strongest;
FIG. 5(a) is a vortex beam phase diagram for the present invention with a topological charge of + 8;
FIG. 5(b) is a diagram showing the variation of the phase at the strongest light intensity according to the present invention;
FIG. 5(c) is a waveform of the invention after phase derivation, including a plot of the delta function corresponding to the amount of topological charge;
fig. 6(a) is a graph of the identification and distribution of the present invention, l +1 to l + 8;
fig. 6(b) is a graph showing the discrimination and average discrimination of each vortex rotation of +1 to +8 according to the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art without any inventive work based on the embodiments of the present invention belong to the protection scope of the present invention.
Examples
The method is different from the traditional vortex optical communication system in that different topological charge states of vortex light beams are separated and converted into Gaussian light beams to be identified, and the vortex light beams can be directly identified to obtain information. The specific method is that a high-speed CCD camera is used at a signal receiving end to continuously acquire the intensity and phase diagram of the vortex light beam, each group of intensity and phase diagram is processed in real time, the topological charge state of the light beam is judged, and carried digital 0 and 1 signals are obtained.
As shown in FIG. 1, the invention provides a vortex beam topological charge number identification method, which comprises the following steps:
s1, extracting a light intensity diagram and a phase diagram of the vortex light beam;
s2, processing the light intensity graph, finding the light ring with the strongest light intensity from the center of the graph from inside to outside, and counting the radius of the light ring;
s3, finding the corresponding phase on the circular ring in the phase diagram by taking the radius as a circle, and calculating the times of the phase change from 0-2 pi, wherein the times is the topological charge number of the vortex beam.
The computer extracts the light intensity and phase maps from the CCD as shown in fig. 2. The intensity map is first processed, and the halo with the strongest intensity is found from the center of the map from inside to outside, and the radius of the halo is counted, as shown in fig. 3 (a). The corresponding phase on the circular ring is found in the phase diagram (b) by taking the radius as a circle, and the number of times that the phase changes from 0 to 2 pi is calculated, and the number is the topological charge number of the vortex rotation. And the direction of the phase change from 0 to 2 pi determines the positive and negative of the topological load, namely, the counterclockwise direction is positive, and the clockwise direction is negative. When the high-speed camera acquires the light intensity signal in real time, if the light beam is observed from the time axis to carry the intensity information, the carried information can be obtained through demodulation. Using this method it is possible to distinguish vortex spins of different topological charges and identify the signal carried in the beam.
The specific flow of the program execution of the method is based on computation platforms such as MATLAB, C program, Python and the like, and the computation of the invention takes the MATLAB platform as an example. After acquiring a vortex light beam light intensity and phase diagram, the CCD reads in the image through MATLAB, converts the RGB image into a gray scale image of 0-255, and cuts the image into an n multiplied by n square matrix (in the invention, the value of n is 500, and the value can be changed) by taking the vortex light beam center as the center of the square. All data points on a circle taken by taking R as a radius form a one-dimensional data set, the radius is sequentially increased to traverse the whole graph, and finally n/2 groups of data are obtained, as shown in fig. 4 (a). Each set of data is summed and then averaged to obtain n/2 individual values. Comparing n/2 single values to find the maximum value, the radius corresponding to the maximum value is the radius with the strongest light intensity, as shown in fig. 4 (b). The radius obtained by the scheme is the light ring with the strongest light intensity distribution and the most concentrated energy, and the corresponding phase on the circular ring is the phase which can represent the topological load of the light beam theoretically, so that the phase diagram is further identified.
In fig. 4(b), the phase corresponding to the ring with the strongest light intensity is found according to the radius, and the data on the ring is taken out to form a one-dimensional array, wherein the data of the array represents the change situation of the phase 0-2 pi. Taking the topological charge as +8 as an example, the phase change on the circular ring is shown in fig. 5(b), the waveform is zigzag, each sawtooth represents a change of 0 to 2 pi once, and the total times of the changes are the topological charge number of the light beam. And (3) carrying out derivation once on the obtained one-dimensional array in the program, forming a delta function by 0-2 pi mutation in the derived one-dimensional array, as shown in fig. 5(c), filtering to obtain a pure oscillogram only containing a plurality of delta functions, and calculating the number of the delta functions to obtain the topological charge number.
The work of the step can enable a computer to successfully identify the topological charge number of the vortex light beam, and the high-speed CCD camera can not only obtain phase information but also obtain real-time light intensity information. And further extracting intensity information of the light beam, and finally demodulating 0 and 1 signals carried by the corresponding vortex light beam at different times.
Based on this identification scheme, a topological charge identification test was performed in MATLAB. As a map, 500 intensity and phase maps were acquired from l +1 to l +8, respectively. Firstly, a program reads each picture to identify and obtain a topological charge value and calculates the probability of identification. As a result, as shown in fig. 6, the recognition rate reached 92.3% when l is +1, and the recognition rate reached 99.2% at the highest when l is + 7. The average recognition rate of l-1 to l-8 can reach 93.58%. The method has the advantage that the average recognition rate of more than 93% is obtained, so that the method has high recognition rate on the identification of the topological load. If an error correction code sequence is added to the communication, the communication signal accuracy is higher. The scheme provides a new approach for receiving and separating vortex beams, and has important application value in orbital angular momentum communication.
The method is different from the traditional Gauss-OAM-Gauss scheme, and directly identifies and analyzes the vortex light beams. The vortex optical rotation topological charge number can be automatically identified by acquiring a light intensity and phase diagram in the identification process, and the method can be operated under MATLAB, C programs, Python and other platforms. The method is specifically tested under an MATLAB platform, the highest recognition rate in the vortex light from l to 8 can reach 99.2%, and the average recognition rate can reach 93.58%. The identification scheme adopts image identification analysis signals, reduces the number of elements of a communication system, reduces the complexity of the system and increases the identification rate of vortex light. It is of great significance to the application of vortex optical rotation communication system.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (5)
1. A vortex beam topological charge number identification method is characterized by comprising the following steps:
extracting a light intensity diagram and a phase diagram of the vortex beam;
processing the light intensity graph, finding the light ring with the strongest light intensity from the center of the graph from inside to outside, and counting the radius of the light ring; the method specifically comprises the following steps: after a vortex light beam light intensity graph and a phase graph are collected, reading in the graph through a computing platform, converting an RGB (red, green and blue) picture into a 0-255 gray scale graph, cutting the graph into an n multiplied by n square matrix by taking the center of a vortex light beam as the center of a square, taking R as a radius as a circle, taking all data points on the circle to form a one-dimensional data set, sequentially increasing the radius and traversing the whole graph, finally obtaining n/2 groups of data, summing each group of data, then calculating an average value to obtain n/2 single values, comparing the n/2 single values to find out the maximum value, wherein the radius corresponding to the maximum value is the strongest radius;
finding out the corresponding phase on the circular ring in the phase diagram by taking the radius as a circle, and calculating the frequency of the phase change from 0-2 pi, wherein the frequency is the topological charge number of the vortex beam; the method specifically comprises the following steps: finding out the phase corresponding to the ring with the strongest light intensity according to the radius, and taking out the data on the ring to form a one-dimensional array, wherein the data of the array represents the change condition of the phase of 0-2 pi; each sawtooth of the waveform is sawtooth-shaped and represents the change of 0 to 2 pi once, and the total change times are the topological charge number of the light beam; and carrying out one-time derivation on the obtained one-dimensional array, forming a delta function by 0-2 pi mutation in the derived one-dimensional array, filtering to obtain a pure oscillogram only containing a plurality of delta functions, and calculating the number of the delta functions to obtain the topological charge number.
2. The vortex beam topological charge number identification method according to claim 1, wherein the direction of the phase change from 0 to 2 pi determines the positive and negative of the topological charge, and the counterclockwise direction is positive and the clockwise direction is negative.
3. The vortex light beam topological charge number identification method according to claim 1, characterized in that after identifying the topological charge number of the vortex light beam, extracting the intensity information of the light beam, and finally demodulating the 0, 1 signals carried by the corresponding vortex light beam at different times.
4. The vortex beam topological charge number identification method according to claim 1, wherein the computing platform comprises a computing platform based on MATLAB, C program, Python.
5. The vortex beam topological charge number identification method according to claim 1, wherein n is 500.
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| CN110146182A (en) * | 2019-05-28 | 2019-08-20 | 北京建筑大学 | The measurement method of zeroth order vortex beams topological charge, apparatus and system |
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| CN109115336A (en) * | 2018-09-28 | 2019-01-01 | 哈尔滨理工大学 | A kind of detection method of higher-dimension vortex beams topology charge values |
| CN110146182A (en) * | 2019-05-28 | 2019-08-20 | 北京建筑大学 | The measurement method of zeroth order vortex beams topological charge, apparatus and system |
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