CN114235146B - Detection system and method for multiplexing vortex beam orbital angular momentum mode - Google Patents
Detection system and method for multiplexing vortex beam orbital angular momentum mode Download PDFInfo
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Abstract
The invention discloses a detection system and a detection method for a multiplexing vortex beam orbital angular momentum mode, and relates to the technical field of optical communication. The system comprises a Gaussian light source, a modulation device, a device for generating a multiplexing vortex light beam to be detected, a device for generating an auxiliary Gaussian light beam, a1 st detection device, a1 st receiving device, a2 nd detection device and a2 nd receiving device; the 1 st controller controls the 1 st spatial light modulator; the 2 nd controller controls the 2 nd spatial light modulator and the 1 st receiver and displays the 1 st detection result; the 3 rd controller controls the 3 rd spatial light modulator and the 2 nd receiver, and displays the 2 nd detection result. The method comprises (1) at the transmitting end: (2) at the detection end; (3) at the receiving end. The system simply and efficiently realizes the detection of the high-order OAM mode of the multiplexing vortex beam; the system has simple structure and is easy to realize; the method is suitable for detecting the OAM mode of the multiplexing vortex beam in the fields of optical micro-operation, optical imaging, optical communication and quantum information research.
Description
Technical Field
The invention relates to the technical field of optical communication, in particular to a detection system and a detection method for a multiplexing vortex beam orbital angular momentum mode.
Background
A Vortex beam (Vortex Beams) is a beam with a wave front having a spiral form along the propagation direction, the beam having a spiral phase factor exp (il phi) carrying orbital angular momentum (Orbital Angular Momentum, OAM), each photon carrying an orbital angular momentum lh, where phi is the direction angle, l is the topological charge value or the order of the orbital angular momentum, h is the reduced planck constant, and the spiral wavefront and center have phase singularities as its two main features.
Free-space optical communication is an important technology for high-speed information transmission in a spatial information network, and currently faces the problems of low spectrum utilization rate, insufficient channel capacity and the like. In theory, the above problems can be solved by using vortex beams as carriers and using newly added degrees of freedom of OAM to encode information, and OAM optical communication is focused by more and more researchers by virtue of its advantages of high spectrum utilization, high safety reliability and high transmission rate, so that the communication capacity and communication rate can be further improved by multiplexing OAM optical communication. Multiplexed vortex beams have been widely studied in various research areas, such as optical micro-operation, optical imaging, optical communication, quantum information, etc., and in most of these applications are extremely important for measuring the topology load (Topological Charges, TC) of multiplexed OAM. Up to the present, many methods for measuring single OAM mode have been found, but few methods for measuring compound vortex beam OAM mode have been found, for example Yang Chunyong, the phase distribution characteristics of two vortex beams after multiplexing transmission have been studied, and the association of the two vortex beams with topology load information has been revealed; ke Xizheng and the like, and the feasibility of detecting the positive and negative values and the numerical values of the topological charge numbers of the superimposed beams by using the superimposed vortex beam light field diffraction diagram is verified; wei Hongyan and the like utilize elliptic diaphragms to simulate and research composite vortex beams, and the measurable high-order mode range is-30 to +30; gao et al have studied the coaxial superimposed vortex beam by phase shift method simulation, can measure the multiplexing vortex beam that the two modes differ greatly, and the measurable range is-12 to 12. The methods are only stopped at the simulation stage at present, and are not proved by experiments, and the detectable mode range is low, so that the implementation method for measuring the multiplexing vortex beam is further explored. The detection method of the multimode multiplexing vortex beam mainly comprises the detection of a composite fork grating and a Dammann vortex grating; when a Gaussian beam passes through the composite fork grating, the far-field diffraction of the Gaussian beam is an array of light spots; if a multimode mixed vortex beam with opposite phases is adopted, a plurality of solid spots can appear in far field diffraction, and the OAM state distribution of the composite beam can be determined according to the positions of the solid spots; in 2009, moreno et al proposed a new diffraction grating, in which a plurality of diffraction orders from-3 to +3 can be simultaneously displayed by binarizing the periodic phase distribution of the phase grating, and by designing different forks, the detection of vortex beams can be realized; subsequently, zhang et al propose a novel dammann vortex grating whose far field diffraction is a 5 x 5 vortex beam array that can extend the continuous detectable range of OAM states to-12 to +12; subsequently, ke Xizheng et al propose an integrated dammann vortex grating that extends the multi-modal detection range to-24 to +24; since these methods mainly determine the OAM mode by observing whether there is a solid spot in the center of far-field diffraction and by determining the OAM mode according to the position of the solid spot, but in practical experiments, the spot energy is low and the effect is not well observed, and since the detected pattern is fixed and the detection range is low, these methods still cannot meet the application requirements of some applications such as optical communication along with the high-speed development of the information age, and therefore a practical system and a method thereof are needed to solve the above problems.
Disclosure of Invention
The invention aims to overcome the defects and shortcomings of the prior art and provide a detection system and a detection method for a multiplexing vortex beam orbital angular momentum mode, which simply and efficiently realize detection of a multiplexing vortex beam high-order OAM mode.
The purpose of the invention is realized in the following way:
on one hand, the multiplexing vortex beam to be detected is incident to the center or the vicinity of the center of a designed annular phase grating to generate diffraction, and the relationship between two modes in the multiplexing vortex beam to be detected is obtained through the number of uniformly distributed spiral stripes in the received far-field diffraction intensity mode: n= |l1-l2|, wherein L1, L2 are two OAM modes multiplexed, the direction of the spiral stripe is consistent with the sign of the larger of |l1|, |l2|; on the other hand, gaussian beams are used as auxiliary beams and multiplexed vortex beams to be tested to be combined to obtain a composite beam to be tested, then the composite beam to be tested is incident into the center or the vicinity of the center of another designed annular phase grating to generate diffraction, one OAM mode L1 or L2 in the multiplexed vortex beams to be tested is obtained through the number and the rotation direction of spiral stripes uniformly distributed in a received far-field diffraction intensity mode, the number and the rotation direction of the spiral stripes of an inner ring are consistent with those of |L1| and |L2|, and the number and the rotation direction of the spiral stripes of an outer ring are consistent with those of |L1| and |L2|; the OAM mode of the multiplexing vortex beam can be identified by combining the relation of the two aspects, so that the detection purpose is achieved.
Specifically:
1. detection system for orbital angular momentum mode of multiplexing vortex beam (short for system)
The system comprises a Gaussian light source, a modulation device, a device for generating a multiplexing vortex light beam to be detected, a device for generating an auxiliary Gaussian light beam, a1 st detection device, a1 st receiving device, a2 nd detection device and a2 nd receiving device;
the Gaussian light source selects a1 st laser to generate a1 st Gaussian beam;
the modulation device comprises a beam expansion collimator and a1 st polarization beam splitter;
the device for generating the multiplexing vortex beam to be tested comprises a1 st spatial light modulator, a1 st beam splitter and a1 st controller;
the device for generating the auxiliary Gaussian beam comprises a2 nd laser and a2 nd polarization beam splitter;
the 1 st detection device comprises a2 nd spatial light modulator and a2 nd controller;
the 1 st receiving device comprises a1 st lens and a1 st receiver;
the 2 nd detection device comprises a2 nd beam splitter, a 3 rd spatial light modulator and a 3 rd controller;
the 2 nd receiving device comprises a2 nd lens and a2 nd receiver;
the interaction relation is as follows:
the 1 st laser, the beam expanding collimator, the 1 st polarization beam splitter, the 1 st spatial light modulator and the 1 st beam splitter are sequentially interacted, the 1 st controller controls the 1 st spatial light modulator, and the 1 st multiplexed vortex beam to be detected is divided into two paths after being generated, so that the 1 st multiplexed vortex beam to be detected and the 2 nd multiplexed vortex beam to be detected are obtained;
the 2 nd laser and the 2 nd polarization beam splitter are interacted back and forth to obtain a2 nd auxiliary Gaussian beam;
the 1 st beam splitter and the 2 nd polarization beam splitter are respectively interacted with the 2 nd beam splitter to obtain a composite light beam to be detected;
the 1 st beam splitter, the 2 nd spatial light modulator, the 1 st lens and the 1 st receiver are sequentially interacted to detect the 1 st multiplexing vortex beam to be detected, sequentially obtain a1 st far-field diffraction intensity mode and a2 nd far-field diffraction intensity mode, and receive a1 st detection result;
the 2 nd beam splitter, the 3 rd spatial light modulator, the 2 nd lens and the 2 nd receiver are sequentially interacted to detect the composite light beam to be detected, sequentially obtain a 3 rd far-field diffraction intensity mode and a 4 th far-field diffraction intensity mode, and receive a2 nd detection result;
the 1 st controller controls the 1 st spatial light modulator;
the 2 nd controller controls the 2 nd spatial light modulator and the 1 st receiver and displays the 1 st detection result;
the 3 rd controller controls the 3 rd spatial light modulator and the 2 nd receiver, and displays the 2 nd detection result.
2. Method for detecting vortex beam orbital angular motion high-order mode (short method)
The method comprises the following steps:
(1) at the transmitting end: the method comprises the steps that a1 st laser is arranged to emit a1 st Gaussian beam, a2 nd laser is arranged to emit a1 st auxiliary Gaussian beam, and a1 st multiplexing vortex beam to be detected and a2 nd multiplexing vortex beam to be detected are respectively obtained;
(2) at the detection end: respectively obtaining a1 st far-field diffraction intensity mode and a 3 rd far-field diffraction intensity mode;
(3) at the receiving end: focusing into a2 nd far-field diffraction intensity mode through a1 st lens, and then receiving a1 st detection result by a1 st receiver; focusing into a 4 th far field diffraction intensity mode through a2 nd lens, and then receiving a2 nd detection result by a2 nd receiver.
Compared with the prior art, the invention has the following advantages and positive effects:
(1) the system can realize the experimental verification of detecting the OAM mode of the multiplexing vortex beam, solves the difficult problem of detecting the OAM high-order mode of the multiplexing vortex beam to a certain extent, and has better practicability;
(2) the system does not need to add a filter to adjust the identification effect, so that the operation difficulty is reduced;
(3) in the system, the light beams to be detected are all incident to the center or near the center of the designed annular phase grating, so that the off-axis parameters of the grating do not need to be regulated, and the debugging complexity is reduced;
(4) the stripes obtained by the method are all spiral, so that the receiver is easier to receive when detecting the OAM high-order mode of the multiplexing vortex beam;
(5) the spiral stripes obtained by the method are uniformly distributed, have higher definition, and can detect higher-order multiplexing vortex beam OAM modes;
(6) the system has simple structure and is easy to realize.
(7) The method is suitable for detecting the OAM mode of the multiplexing vortex beam in the fields of optical micro-operation, optical imaging, optical communication and quantum information research.
Drawings
FIG. 1 is a block diagram of the architecture of the present system;
FIG. 2 is a structural light path diagram of the present system;
FIG. 3 is a1 st annular phase grating diagram designed by the present method;
FIG. 4 is a2 nd annular phase grating diagram designed by the present method;
fig. 5 is a schematic diagram of the results of detection of the 1 st and 2 nd of l= +10, +20 in the case obtained by the present method.
In the figure:
10-a gaussian light source, which is arranged at the bottom of the light source,
11-1 st laser;
20-a modulation device, which is used for modulating the signal,
21-a beam expansion collimator, 22-a 1 st polarization beam splitter;
30-generating a multiplexed vortex beam device to be tested,
31-1 st spatial light modulator, 32-1 st beam splitter, 33-1 st controller;
40-generating an auxiliary gaussian beam device,
41-2 nd laser, 42-2 nd polarization beam splitter;
50-the 1 st detection device, the first detection device,
51-2 nd spatial light modulator, 52-2 nd controller;
60-the 1 st receiving means,
61-1 st lens, 62-1 st receiver;
70-the 2 nd detection device,
71-2 nd beam splitter, 72-3 rd spatial light modulator, 73-3 rd controller;
80-the receiving device of the 2 nd,
81-2 nd lens, 82-2 nd receiver.
A1-1 st Gaussian beam;
b1-2 Gauss beam;
c1_3rd gaussian beam;
a2-1 st auxiliary Gaussian beam;
b2—2nd auxiliary gaussian beam;
c2-a composite beam to be measured;
d, multiplexing vortex light beams to be detected;
d1-1 st multiplexing vortex beam to be measured;
d2-2 nd multiplexing vortex beam to be tested;
e1-1 st far field diffraction intensity pattern;
f1-2 nd far field diffraction intensity pattern;
e2-3 rd far field diffraction intensity pattern;
f2—4 far field diffraction intensity pattern.
English-Chinese translation
1. Vortex Beams: swirling the light beam;
2. OAM: full scale Orbital Angular Momentum, orbital angular momentum;
3. topological Charges: topology payload.
Detailed Description
The following detailed description refers to the accompanying drawings and examples.
1. Detection system
1. Overall (L)
As shown in fig. 1 and 2, the system comprises a gaussian light source 10, a modulation device 20, a device 30 for generating a multiplexed vortex beam to be tested, a device 40 for generating an auxiliary gaussian beam, a1 st detection device 50, a1 st receiving device 60, a2 nd detection device 70 and a2 nd receiving device 80;
the Gaussian light source 10 selects A1 st laser 11 to generate A1 st Gaussian beam A1;
the modulation device 20 includes a beam expansion collimator 21 and a1 st polarization beam splitter 22;
the device 30 for generating the multiplexed vortex beam to be measured comprises a1 st spatial light modulator 31, a1 st beam splitter 32 and a1 st controller 33;
the means 40 for generating an auxiliary gaussian beam comprises a2 nd laser 41 and a2 nd polarizing beam splitter 42;
the 1 st detection means 50 includes a2 nd spatial light modulator 51 and a2 nd controller 52;
the 1 st receiving device 60 includes a1 st lens 61 and a1 st receiver 62;
the 2 nd detection device 70 includes a2 nd beam splitter 71, a 3 rd spatial light modulator 72, and a 3 rd controller 73;
the 2 nd receiving means 80 comprises a2 nd lens 81 and a2 nd receiver 82;
the interaction relation is as follows:
the 1 st laser 11, the beam expanding collimator 21, the 1 st polarization beam splitter 22, the 1 st spatial light modulator 31 and the 1 st beam splitter 32 are sequentially interacted, the 1 st controller 33 controls the 1 st spatial light modulator 31, and the 1 st multiplexed vortex beam D to be detected is generated and then split into two paths to obtain a1 st multiplexed vortex beam D1 to be detected and a2 nd multiplexed vortex beam D2 to be detected;
the 2 nd laser 41 and the 2 nd polarization beam splitter 42 interact back and forth to obtain a2 nd auxiliary Gaussian beam B2;
the 1 st beam splitter 32 and the 2 nd polarization beam splitter 42 interact with the 2 nd beam splitter 71 respectively to obtain a composite light beam C2 to be measured;
the 1 st beam splitter 32, the 2 nd spatial light modulator 51, the 1 st lens 61 and the 1 st receiver 62 are sequentially interacted to detect the 1 st multiplexing vortex beam D1 to be detected, sequentially obtain a1 st far-field diffraction intensity pattern E1 and a2 nd far-field diffraction intensity pattern F1, and receive a1 st detection result;
the 2 nd beam splitter 71, the 3 rd spatial light modulator 72, the 2 nd lens 81 and the 2 nd receiver 82 are sequentially interacted to detect the composite light beam C2 to be detected, sequentially obtain a 3 rd far-field diffraction intensity pattern E2 and a 4 th far-field diffraction intensity pattern F2, and receive a2 nd detection result;
the 1 st controller 33 controls the 1 st spatial light modulator 31;
the 2 nd controller 52 controls the 2 nd spatial light modulator 51 and the 1 st receiver 62, and displays the 1 st detection result;
the 3 rd controller 73 controls the 3 rd spatial light modulator 72 and the 2 nd receiver 82, and displays the 2 nd detection result.
Therefore, the system can realize the experimental verification of detecting the OAM mode of the multiplexing vortex beam, and has simple structure and better practicability; the system does not need to add a filter and adjust the off-axis parameters of the grating, thereby reducing the complexity and debugging difficulty of the system; the two detection results obtained by the system are presented as spiral stripes with uniform light intensity distribution and uniform thickness distribution, so that the stripes can be more clearly identified, and a receiver can better receive a multiplexed vortex beam OAM high-order mode; the system solves the problem of detecting the OAM high-order mode of the multiplexing vortex beam to a certain extent, is favorable for further improving the communication capacity and the communication speed, and can be applied to the research fields of optical communication and the like needing to identify the OAM high-order mode of the multiplexing vortex beam.
2. Functional device
1) Gaussian light source 10
As shown in fig. 1 and 2, A1 st laser 11 is selected to emit A1 st gaussian beam A1.
2) Modulating device 20
As shown in fig. 1 and 2, the modulation device 20 includes a beam expansion collimator 21 and a1 st polarization beam splitter 22.
The interaction relation is as follows:
the 1 st laser 11, the beam expanding collimator 21, the 1 st polarizing beam splitter 22 and the 1 st spatial light modulator 31 are sequentially interacted to sequentially obtain A1 st gaussian beam A1, a2 nd gaussian beam B1 and a 3 rd gaussian beam C1.
The working mechanism is as follows:
the 1 st laser 11 emits A1 st gaussian beam A1; because the beam prepared by the laser has a certain divergence angle, the 1 st Gaussian beam A1 needs to pass through the beam expansion collimator 21 to increase the beam waist radius of the beam and reduce the divergence angle of the beam, so as to obtain the 2 nd Gaussian beam B1 after beam expansion collimation; since the 1 st spatial light modulator 31 can modulate only the P-polarized light beam, the 2 nd gaussian beam B1 passes through the 1 st polarization beam splitter 22 to obtain the P-polarized 3 rd gaussian beam C1 propagating along the original optical path and the S-polarized gaussian beam propagating perpendicular to the original optical path, where the P-polarized 3 rd gaussian beam C1 is used to generate the multiplexed vortex beam D to be measured.
Functional components:
(1) The 1 st laser 11 is a light source for generating a gaussian beam, and obtains A1 st gaussian beam A1;
the wavelength of Gaussian beam is 600-2000nm, and the specific wavelength is 1550nm.
(2) The beam expansion collimator 21 is composed of two lenses, and is an optical combination device capable of changing the beam waist radius and the divergence angle of a Gaussian beam;
the function of the method is that the beam waist radius of the 1 st Gaussian beam A1 is increased, the divergence angle is reduced, and the 2 nd Gaussian beam B1 after beam expansion and collimation is obtained.
(3) The 1 st polarization beam splitter 22 is an optical device capable of vertically separating the P-polarization and the S-polarization of an incident light beam;
its function is to obtain a P-polarized 3 rd gaussian beam C1 and to be incident on the 1 st spatial light modulator 31.
3) Device 30 for generating multiplexed vortex beam to be measured
As shown in fig. 1 and 2, the device 30 for generating the multiplexed vortex beam to be measured includes a1 st spatial light modulator 31, a1 st beam splitter 32, and a1 st controller 33.
The interaction relation is as follows:
the 1 st controller 33 controls the 1 st spatial light modulator 31; the 1 st spatial light modulator 31 and the 1 st beam splitter 32 interact to generate a multiplexed vortex beam D to be measured, and obtain a1 st multiplexed vortex beam D1 to be measured and a2 nd multiplexed vortex beam D2 to be measured, respectively.
The working mechanism is as follows:
the 3 rd Gaussian beam C1 of P polarization is incident on the 1 st spatial light modulator 31 loaded with multiplexed holograms for phase modulation by superimposing the spiral phase factor exp (il 1 φ)+exp(il 2 Phi) to generate a multiplexed vortex beam D to be measured, then vertically enterAnd the light enters the 1 st beam splitter 32 and is divided into two paths to obtain a1 st multiplexing vortex beam D1 to be detected and a2 nd multiplexing vortex beam D2 to be detected.
Functional components:
(1) The 1 st spatial light modulator 31 is an optical device that modulates the phase, polarization, and intensity of a light field by controlling the voltage across liquid crystal molecules;
its function is to add the spiral phase factor exp (il) to the incident P-polarized 3 rd Gaussian beam C1 after modulation by loading a multiplexed hologram on it 1 φ)+exp(il 2 Phi) to generate a multiplexed vortex beam D to be measured.
(2) The 1 st beam splitter 32 is an optical device that splits an incident light beam into two identical light beams having mutually perpendicular propagation directions;
the function of the method is to divide the incident multiplexing vortex beam D to be detected into two paths to obtain the 1 st multiplexing vortex beam D1 to be detected which propagates along the original light path and the 2 nd multiplexing vortex beam D2 to be detected which propagates perpendicular to the original light path.
(3) The 1 st controller 33 is a computer or a scale integrated circuit;
its function is to load the multiplexed holograms onto the 1 st spatial light modulator 31.
4) Device 40 for generating auxiliary gaussian beam
As shown in fig. 1 and 2, the means 40 for generating an auxiliary gaussian beam comprises a2 nd laser 41 and a2 nd polarizing beam splitter 42.
The interaction relation is as follows:
the 2 nd laser 41, the 2 nd polarizing beam splitter 42 and the 2 nd beam splitter 71 are sequentially interacted to obtain a2 nd auxiliary gaussian beam B2.
The working mechanism is as follows:
the 2 nd laser 41 emits the 1 st auxiliary gaussian beam A2, and the 2 nd auxiliary gaussian beam B2 of P polarization is obtained by the 2 nd polarization beam splitter 42 and is perpendicularly incident on the 2 nd beam splitter 71.
Functional components:
(1) The 2 nd laser 41 is a light source for generating a gaussian beam, namely, the 1 st auxiliary gaussian beam A2 is used as an auxiliary beam of the 2 nd multiplexed vortex beam D2 to be measured;
the wavelength of the gaussian beam emitted by the 2 nd laser 41 and the wavelength of the gaussian beam emitted by the 1 st laser 11 are not equal;
the wavelength of the Gaussian beam emitted by the 2 nd laser 41 is 600-2000nm, and specifically 1570nm.
(2) The 2 nd polarization beam splitter 42 is an optical device capable of vertically separating the P-polarization and the S-polarization of an incident light beam;
its function is to obtain a P-polarized 2 nd auxiliary gaussian beam B2 and to be incident perpendicularly to the 2 nd beam splitter 71.
5) 1 st detection device 50
As shown in fig. 1 and 2, the 1 st detection device 50 includes a2 nd spatial light modulator 51 and a2 nd controller 52.
The interaction relation is as follows:
the 2 nd spatial light modulator 51 and the 1 st lens 61 interact back and forth, and the 2 nd controller 52 controls the 2 nd spatial light modulator 51 to modulate the 1 st multiplexed vortex beam D1 to be tested to obtain a1 st far-field diffraction intensity pattern E1.
The working mechanism is as follows:
the 1 st multiplexing vortex beam D1 to be detected is incident on the 2 nd spatial light modulator 51 loaded with the designed 1 st annular phase grating to generate diffraction, so as to obtain a1 st far-field diffraction intensity mode E1, wherein the process of generating the 1 st annular phase grating is completed by designing a grating function by the 2 nd controller 52.
Functional components:
(2) The 2 nd spatial light modulator 51 is an optical device that modulates the phase, polarization and intensity of a light field by controlling the voltage on liquid crystal molecules;
the function of the method is that when the 1 st multiplexing vortex beam D1 to be detected is incident on the center or the vicinity of the center of the 1 st annular phase grating loaded on the 1 st multiplexing vortex beam D1, diffraction is generated, and a1 st far-field diffraction intensity mode E1 is obtained.
(3) The 2 nd controller 52 is a computer or a scale integrated circuit;
its function is to load a designed 1 st annular phase grating onto a2 nd spatial light modulator 51, wherein the designed 1 st annular phase grating is shown in fig. 3.
6) 1 st receiving device 60
As shown in fig. 1 and 2, the 1 st receiving device 60 includes a1 st lens 61 and a1 st receiver 62.
The interaction relation is as follows:
the 1 st lens 61 and the 1 st receiver 62 interact back and forth, the 1 st receiver 62 is controlled by the 2 nd controller 52 to obtain a2 nd far-field diffraction intensity pattern F1, and the 1 st detection result is received.
The working mechanism is as follows:
the 1 st far-field diffraction intensity pattern E1 is focused into a2 nd far-field diffraction intensity pattern F1 through the 1 st lens 61, and finally received by the 1 st receiver 62 and subjected to photoelectric signal conversion, wherein the 2 nd spatial light modulator 51 and the 1 st receiver 62 are located at two focal points of the 1 st lens 61, respectively.
Functional components:
(1) The 1 st lens 61 is a plane convex lens with a convex surface and a plane surface, and has the functions of beam expansion, imaging, beam collimation and focusing collimation;
the function of the system is to concentrate the 1 st far-field diffraction intensity pattern E1 into the 2 nd far-field diffraction intensity pattern F1 on the 1 st receiver 62 on the focal plane of the image side, so that the system is easier to receive.
(2) The 1 st receiver 62 is a photoelectric charge converter;
its function is to receive the 2 nd far field diffraction intensity pattern F1, convert the optical signal into an electrical signal, and display the 1 st detection result on the 2 nd controller 52.
(3) The 2 nd controller 52 is a computer or a scale integrated circuit;
the function of the method is to observe the number and the direction of spiral stripes in the 1 st detection result to obtain the relation between two OAM modes in the multiplexing vortex beam D to be detected.
7) 2 nd detection device 70
As shown in fig. 1 and 2, the 2 nd detection device 70 includes a2 nd beam splitter 71, a 3 rd spatial light modulator 72, and a 3 rd controller 73.
The interaction relation is as follows:
the 1 st beam splitter 32 and the 2 nd polarization beam splitter 42 interact with the 2 nd beam splitter 71 respectively to obtain a composite light beam C2 to be measured; the 2 nd beam splitter 71, the 3 rd spatial light modulator 72 and the 2 nd lens 81 are sequentially interacted, and the 3 rd controller 73 controls the 3 rd spatial light modulator 72 to modulate the composite light beam C2 to be detected, so as to obtain a 3 rd far-field diffraction intensity pattern E2.
The working mechanism is as follows:
the 2 nd multiplexing vortex beam D2 to be detected and the 2 nd auxiliary Gaussian beam B2 are incident on the 2 nd beam splitter 71 to obtain a P-polarized composite beam C2 to be detected, then are incident on the 3 rd spatial light modulator 72 loaded with the designed 2 nd annular phase grating to generate diffraction, so as to obtain a 3 rd far-field diffraction intensity mode E2, wherein the process of generating the 2 nd annular phase grating is completed by designing a grating function by the 3 rd controller 73.
Functional components:
(1) The 2 nd beam splitter 71 is an optical device that combines two incident lights having mutually perpendicular propagation directions into one light;
the function of the device is to compound the 2 nd auxiliary Gaussian beam B2 polarized by the 2 nd multiplexing vortex beam D2 to be tested and the P polarized 2 nd auxiliary Gaussian beam B2 into a compound beam C2 to be tested.
(2) The 3 rd spatial light modulator 72 is an optical device that modulates the light field phase, polarization and intensity by controlling the voltage across the liquid crystal molecules;
the function of the device is to generate diffraction when the composite light beam C2 to be detected is incident on the center or near the center of the 2 nd annular phase grating loaded on the composite light beam C2 to be detected, so as to obtain a 3 rd far-field diffraction intensity mode E2.
(3) The 3 rd controller 73 is a computer or a scale integrated circuit;
its function is to load a designed 2 nd annular phase grating onto the 3 rd spatial light modulator 72, wherein the designed 2 nd annular phase grating is shown in fig. 4.
8) 2 nd receiving device 80
As shown in fig. 1 and 2, the 2 nd receiving device 80 includes a2 nd lens 81 and a2 nd receiver 82.
The interaction relation is as follows:
the 2 nd lens 81 and the 2 nd receiver 82 interact back and forth, and the 2 nd receiver 82 is controlled by the 3 rd controller 73 to receive the 2 nd detection result.
The working mechanism is as follows:
the 3 rd far field diffraction intensity pattern E2 is focused into a 4 th far field diffraction intensity pattern F2 through the 2 nd lens 81, and finally received by the 2 nd receiver 82 and subjected to photoelectric signal conversion, wherein the 3 rd spatial light modulator 72 and the 2 nd receiver 82 are respectively located at two focal points of the 2 nd lens 81.
Functional components:
(1) The 2 nd lens 81 is a plano-convex lens with a convex surface and a plane surface, and has the functions of beam expansion, imaging, beam collimation, focusing collimation and the like;
the function of the method is to concentrate the 3 rd far-field diffraction intensity pattern E2 into a 4 th far-field diffraction intensity pattern F2 on the 2 nd receiver 82 on the focal plane of the image side, so that the 2 nd receiver is easier to receive.
(2) The 2 nd receiver 82 is a photoelectric charge converter;
its function is to receive the 4 th far field diffraction intensity pattern F2, convert the optical signal into an electrical signal, and display the 2 nd detection result on the 3 rd controller 73.
(3) The 3 rd controller 73 is a computer or a scale integrated circuit;
the method has the function of observing the number and the direction of the spiral stripes of the inner ring and the outer ring in the displayed 2 nd detection result to obtain one or two OAM modes in the multiplexed vortex beam D to be detected.
2. Method of
The method comprises the following steps:
(1) at the transmitting end:
the 1 st laser 11 emits A1 st Gaussian beam A1, after passing through the beam expansion collimator 21, the beam waist radius is increased, the divergence angle is reduced, a2 nd Gaussian beam B1 which is subjected to beam expansion collimation is obtained, a 3 rd Gaussian beam C1 which is subjected to P polarization is obtained through the 1 st polarization beam splitter 22, then the 1 st Gaussian beam C1 is incident on the 1 st spatial light modulator 31 which is controlled by the 1 st controller 33 and is loaded with a multiplexing hologram to generate a multiplexing vortex beam D to be detected, and the multiplexing vortex beam D to be detected is vertically incident on the 1 st beam splitter 32 and then is split into two paths, and A1 st multiplexing vortex beam D1 to be detected and a2 nd multiplexing vortex beam D2 to be detected are obtained;
the 1 st auxiliary gaussian beam A2 emitted by the 2 nd laser 41 is used as an auxiliary beam of the 2 nd multiplexing vortex beam D2 to be detected, and the 2 nd auxiliary gaussian beam B2 with P polarization is obtained after passing through the 2 nd polarization beam splitter 42 and is vertically incident to the 2 nd beam splitter 71;
(2) at the detection end:
the 1 st multiplexing vortex beam D1 to be detected is incident on the 2 nd spatial light modulator 51 which is controlled by the 2 nd controller 52 and is loaded with the 1 st annular phase grating to generate diffraction, so as to obtain a1 st far-field diffraction intensity mode E1, wherein the process of generating the 1 st annular phase grating is completed by designing a grating function by the 2 nd controller 52;
the 2 nd multiplexing vortex beam D2 to be detected and the 2 nd auxiliary Gaussian beam B2 are compounded through the 2 nd beam splitter 71 to obtain a compound beam C2 to be detected, the compound beam C2 to be detected cannot interfere due to the difference of the frequencies of the two beams of light, and then the compound beam C2 to be detected is incident on the 3 rd spatial light modulator 72 which is controlled by the 3 rd controller 73 and is loaded with the 2 nd annular phase grating to generate diffraction, so that a 3 rd far field diffraction intensity mode E2 is obtained, wherein the process of generating the 2 nd annular phase grating is completed by designing a grating function by the 3 rd controller 73;
(3) at the receiving end:
focusing the 1 st far-field diffraction intensity pattern E1 obtained at the detection end into a2 nd far-field diffraction intensity pattern F1 through a1 st lens 61, and then receiving a1 st detection result by a1 st receiver 62; the relationship between the two modes in the multiplexed vortex beam D to be measured is obtained by observing the number of uniformly distributed spiral fringes in the 1 st detection result on the 2 nd controller 52: n= |l1-l2|, wherein N is the number of spiral stripes, L1, L2 are two OAM modes of multiplexing, the direction of the spiral stripes is consistent with the sign of the larger of |l1|, |l2|;
focusing a 3 rd far-field diffraction intensity pattern E2 obtained at a detection end into a 4 th far-field diffraction intensity pattern F2 through a2 nd lens 81, then receiving a2 nd detection result by a2 nd receiver 82, and observing the number and the rotation direction of spiral stripes uniformly distributed in the 2 nd detection result on a 3 rd controller 73 to obtain one OAM pattern L1 or L2 in the multiplexed vortex beam D to be detected, wherein the number and the rotation direction of the spiral stripes of an inner ring are consistent with those of |L1| and |L2| and the number and the rotation direction of the spiral stripes of an outer ring are consistent with those of |L1| and |L2|; by combining the relationship between the two modes and knowing one of the OAM modes, a multiplexed vortex beam OAM mode can be identified.
The 2 nd controller 52 design grating function in step (2) generates a1 st annular phase grating and the 3 rd controller 73 design grating function generates a2 nd annular phase grating: derived from a circular phase grating function t (r) =exp (i 2 pi r/a), where r is the radial coordinate and a is the grating period.
3. Detection result
FIG. 5 is a schematic diagram showing the results of detection of the 1 st and 2 nd steps according to the present invention, wherein L= +10, +20;
the relation between the two modes in the multiplexed vortex beam D can be obtained by the 1 st detection result: n= |l1-l2|, wherein n=10 is the number of spiral stripes, l1= +10, l2= +20 are two OAM modes of multiplexing, the direction of the spiral stripes is the symbol of the left hand and the larger of |l1|, |l2| is the same, namely L2;
one OAM mode L1 or L2 in the multiplexed vortex beam D to be detected can be obtained through the 2 nd detection result, wherein the number of spiral stripes of the inner ring is 10, and the rotation direction is the same as those of L1 and L2, namely L1= +10; the number of the outer ring spiral stripes is 20, and the rotation direction is the same as that of the large one of the L1 and L2, namely L2 = +20; in most cases, only one OAM mode L1 or L2 in the multiplexed vortex beam D to be detected is obtained in the 2 nd detection result, so that the OAM mode of the multiplexed vortex beam can be detected by combining the relationship between the two OAM modes obtained in the 1 st detection result; under a part of conditions, two OAM modes in the multiplexed vortex beam can be detected directly through the 2 nd detection result, and the method is more convenient and quicker at the moment; the two detection results show that the obtained stripes are spiral, the receiver can receive the stripes more conveniently, the thickness distribution and the light intensity distribution of the stripes are uniform, and the definition is high, so that the OAM high-order mode of the multiplexing vortex beam can be detected.
Claims (5)
1. A detection system for a multiplexed vortex beam orbital angular momentum mode, characterized by:
the device comprises a Gaussian light source (10), a modulation device (20), a device (30) for generating a multiplexing vortex light beam to be detected, a device (40) for generating an auxiliary Gaussian light beam, a1 st detection device (50), a1 st receiving device (60), a2 nd detection device (70) and a2 nd receiving device (80);
the Gaussian light source (10) selects A1 st laser (11) to generate A1 st Gaussian beam (A1);
the modulation device (20) comprises a beam expansion collimator (21) and a1 st polarization beam splitter (22);
the device (30) for generating the multiplexing vortex beam to be tested comprises a1 st spatial light modulator (31), a1 st beam splitter (32) and a1 st controller (33);
-the means (40) for generating an auxiliary gaussian beam comprises a2 nd laser (41) and a2 nd polarizing beam splitter (42);
the 1 st detection device (50) comprises a2 nd spatial light modulator (51) and a2 nd controller (52);
the 1 st receiving device (60) comprises a1 st lens (61) and a1 st receiver (62);
the 2 nd detection device (70) comprises a2 nd beam splitter (71), a 3 rd spatial light modulator (72) and a 3 rd controller (73);
the 2 nd receiving device (80) comprises a2 nd lens (81) and a2 nd receiver (82);
the communication relation is as follows:
the 1 st laser (11), the beam expanding collimator (21), the 1 st polarization beam splitter (22), the 1 st spatial light modulator (31) and the 1 st beam splitter (32) are sequentially communicated, the 1 st controller (33) controls the 1 st spatial light modulator (31) to generate a multiplexing vortex beam (D) to be detected, and then the multiplexing vortex beam (D1) to be detected and the multiplexing vortex beam (D2) to be detected are obtained by dividing the multiplexing vortex beam into two paths;
the 2 nd laser (41) is communicated with the 2 nd polarization beam splitter (42) in front-back to obtain a2 nd auxiliary Gaussian beam (B2);
the 1 st beam splitter (32) and the 2 nd polarization beam splitter (42) are respectively communicated with the 2 nd beam splitter (71) to obtain a composite light beam (C2) to be detected;
the 1 st beam splitter (32), the 2 nd spatial light modulator (51), the 1 st lens (61) and the 1 st receiver (62) are sequentially communicated, the 1 st multiplexing vortex beam (D1) to be detected is detected, a1 st far-field diffraction intensity mode (E1) and a2 nd far-field diffraction intensity mode (F1) are sequentially obtained, and a1 st detection result is received;
the 2 nd beam splitter (71), the 3 rd spatial light modulator (72), the 2 nd lens (81) and the 2 nd receiver (82) are sequentially communicated, a composite light beam (C2) to be detected is detected, a 3 rd far-field diffraction intensity mode (E2) and a 4 th far-field diffraction intensity mode (F2) are sequentially obtained, and a2 nd detection result is received;
a1 st controller (33) controls the 1 st spatial light modulator (31);
the 2 nd controller (52) controls the 2 nd spatial light modulator (51) and the 1 st receiver (62), and displays the 1 st detection result;
a3 rd controller (73) controls the 3 rd spatial light modulator (72) and the 2 nd receiver (82), and displays the 2 nd detection result.
2. The system for detecting orbital angular momentum patterns of a multiplexed vortex beam according to claim 1, wherein:
the 1 st laser (11) is a light source for generating Gaussian beam, and emits 1 st Gaussian beam (A1) with wavelength of 600-2000 nm;
the beam expansion collimator (21) consists of two lenses, and is an optical combination device capable of changing the beam waist radius and the divergence angle of the Gaussian beam; the beam waist radius of the 1 st Gaussian beam (A1) is increased, the divergence angle is reduced, and the 2 nd Gaussian beam (B1) after beam expansion collimation is obtained;
the 1 st polarization beam splitter (22) is an optical device capable of vertically separating the P-polarization and the S-polarization of an incident light beam; obtaining a 3 rd Gaussian beam (C1) polarized by P and incidence to a1 st spatial light modulator (31);
the 1 st spatial light modulator (31) is an optical device that modulates the phase, polarization and intensity of a light field by controlling the voltage across liquid crystal molecules; by modulating the incident P-polarized 3 rd Gaussian beam (C1) with a multiplexed hologram applied thereto, adding a spiral phase factor exp (il) 1 φ)+exp(il 2 Phi), generating a multiplexing vortex beam (D) to be detected;
the 1 st beam splitter (32) is an optical device that splits an incident light beam into two identical light beams having mutually perpendicular propagation directions; dividing an incident multiplexing vortex beam (D) to be detected into two paths to obtain a1 st multiplexing vortex beam (D1) to be detected which propagates along an original optical path and a2 nd multiplexing vortex beam (D2) to be detected which propagates perpendicular to the original optical path;
the 1 st controller (33) is a computer or a certain scale integrated circuit; loading the multiplexed holograms onto a1 st spatial light modulator (31);
the 2 nd laser (41) is a light source for generating a Gaussian beam; emitting a1 st auxiliary Gaussian beam (A2) with the wavelength of 600-2000nm as an auxiliary beam of A2 nd multiplexing vortex beam (D2) to be detected;
the wavelength of the Gaussian beam emitted by the 2 nd laser (41) is unequal to the wavelength of the Gaussian beam emitted by the 1 st laser (11);
the 2 nd polarization beam splitter (42) is an optical device capable of vertically separating the P polarization and the S polarization of an incident light beam, and obtains a2 nd auxiliary gaussian light beam (B2) of the P polarization, and vertically enters the 2 nd beam splitter (71);
the 2 nd spatial light modulator (51) is an optical device that modulates the phase, polarization and intensity of a light field by controlling the voltage across liquid crystal molecules; when the 1 st multiplexing vortex beam (D1) to be detected is incident to the center or the vicinity of the center of the 1 st annular phase grating loaded on the 1 st multiplexing vortex beam, diffraction is generated, and a1 st far-field diffraction intensity mode (E1) is obtained;
the 2 nd controller (52) is a computer or a scale integrated circuit; loading a designed 1 st annular phase grating onto a2 nd spatial light modulator (51);
the 1 st lens (61) is a plano-convex lens with a convex surface and a plane surface, and has the functions of beam expansion, imaging, beam collimation and focusing collimation; converging the 1 st far field diffraction intensity pattern (E1) into a2 nd far field diffraction intensity pattern (F1) to be concentrated on a1 st receiver (62) on an image side focal plane, so that the 1 st far field diffraction intensity pattern (F1) is easier to receive;
the 1 st receiver (62) is a photoelectric charge converter; receiving a2 nd far field diffraction intensity pattern (F1), converting the optical signal into an electrical signal, so as to display a1 st detection result on a2 nd controller (52);
the 2 nd controller (52) is a computer or a scale integrated circuit; observing the number and the direction of the spiral stripes in the displayed 1 st detection result to obtain the relation between two OAM modes in the multiplexed vortex beam (D) to be detected;
the 2 nd beam splitter (71) is an optical device for combining two incident lights having mutually perpendicular propagation directions into one light beam; compounding the 2 nd multiplexing vortex beam (D2) to be detected and the P polarized 2 nd auxiliary Gaussian beam (B2) into a compound beam (C2) to be detected;
the 3 rd spatial light modulator (72) is an optical device that modulates the light field phase, polarization and intensity by controlling the voltage across the liquid crystal molecules; when the composite light beam (C2) to be detected is incident on the center or near the center of the 2 nd annular phase grating loaded on the composite light beam, diffraction is generated, and a 3 rd far-field diffraction intensity mode (E2) is obtained;
the 3 rd controller (73) is a computer or a scale integrated circuit; loading a designed 2 nd annular phase grating onto a 3 rd spatial light modulator (72);
the 2 nd lens (81) is a plano-convex lens with a convex surface and a plane surface, and has the functions of beam expansion, imaging, beam collimation and focusing collimation; converging the 3 rd far field diffraction intensity pattern (E2) into a 4 th far field diffraction intensity pattern (F2) which is concentrated on a2 nd receiver (82) on the focal plane of the image side, so that the 2 nd receiver is easier to receive;
the 2 nd receiver (82) is a photoelectric charge converter; receiving a 4 th far field diffraction intensity pattern (F2), converting the optical signal into an electrical signal, so as to display a2 nd detection result on a 3 rd controller (73);
the 3 rd controller (73) is a computer or a scale integrated circuit; and observing the number and the direction of the spiral stripes of the inner ring and the outer ring in the displayed 2 nd detection result to obtain one or two OAM modes in the multiplexed vortex beam (D) to be detected.
3. The system for detecting orbital angular momentum patterns of a multiplexed vortex beam according to claim 1, wherein:
the wavelength of Gaussian beam emitted by the 1 st laser (11) is 1550nm;
the wavelength of Gaussian beam emitted by the 2 nd laser (41) is 1570nm.
4. A detection method based on the detection system of claim 1, 2 or 3, characterized by comprising the steps of:
(1) at the transmitting end: the device is provided with A1 st laser (11) for emitting A1 st Gaussian beam (A1), A2 nd laser (41) for emitting A1 st auxiliary Gaussian beam (A2) for respectively obtaining A1 st multiplexing vortex beam (D1) to be detected and A2 nd multiplexing vortex beam (D2) to be detected;
(2) at the detection end: respectively obtaining a1 st far-field diffraction intensity mode (E1) and a 3 rd far-field diffraction intensity mode (E2);
(3) at the receiving end: focusing into a2 nd far-field diffraction intensity mode (F1) through a1 st lens (61), and then receiving a1 st detection result by a1 st receiver (62); focusing into a 4 th far field diffraction intensity pattern (F2) through a2 nd lens (81), and then receiving the 2 nd detection result by a2 nd receiver (82).
5. The method of claim 4, wherein the steps (1) (2) (3) are respectively:
(1) at the transmitting end:
the 1 st laser (11) emits A1 st Gaussian beam (A1), after passing through a beam expansion collimator (21), the beam waist radius is increased, the divergence angle is reduced, a2 nd Gaussian beam (B1) which is collimated by beam expansion is obtained, a 3 rd Gaussian beam (C1) which is polarized by P is obtained through A1 st polarization beam splitter (22), then the 3 rd Gaussian beam is incident on A1 st spatial light modulator (31) which is controlled by A1 st controller (33) and is loaded with a multiplexing hologram to generate a multiplexing vortex beam (D) to be detected, and the multiplexing vortex beam (D1) to be detected and the multiplexing vortex beam (D2) to be detected are vertically incident on A1 st beam splitter (32) and then are divided into two paths to obtain the 1 st multiplexing vortex beam (D1) to be detected and the 2 nd multiplexing vortex beam (D2) to be detected;
the 2 nd laser (41) emits a1 st auxiliary Gaussian beam (A2) as an auxiliary beam of A2 nd multiplexing vortex beam (D2) to be detected, and the 2 nd auxiliary Gaussian beam (B2) with P polarization is obtained after passing through A2 nd polarization beam splitter (42) and is vertically incident to the 2 nd beam splitter (71);
(2) at the detection end:
the 1 st multiplexing vortex beam (D1) to be detected is incident on a2 nd spatial light modulator (51) which is controlled by a2 nd controller (52) and is loaded with a1 st annular phase grating to generate diffraction, so as to obtain a1 st far-field diffraction intensity mode (E1), wherein the process of generating the 1 st annular phase grating is completed by designing a grating function by the 2 nd controller (52);
the 2 nd multiplexing vortex beam (D2) to be detected and the 2 nd auxiliary Gaussian beam (B2) are compounded through a2 nd beam splitter (71) to obtain a compound beam (C2) to be detected, the compound beam (C2) to be detected cannot interfere due to the difference of the frequencies of the two beams of light, and then the compound beam is incident on a 3 rd spatial light modulator (72) which is controlled by a 3 rd controller (73) and is loaded with a2 nd annular phase grating to generate diffraction, so as to obtain a 3 rd far field diffraction intensity mode (E2), wherein the process of generating the 2 nd annular phase grating is completed by designing a grating function by the 3 rd controller (73);
(3) at the receiving end:
focusing the 1 st far-field diffraction intensity pattern (E1) obtained at the detection end into a2 nd far-field diffraction intensity pattern (F1) through a1 st lens (61), and then receiving a1 st detection result by a1 st receiver (62); the relationship between two modes in the multiplexed vortex beam (D) to be detected is obtained by observing the number of uniformly distributed spiral stripes in the detection result of the 1 st step on a2 nd controller (52): n= |l1-l2|, wherein N is the number of spiral stripes, L1, L2 are two OAM modes of multiplexing, the direction of the spiral stripes is consistent with the sign of the larger of |l1|, |l2|;
focusing a 3 rd far-field diffraction intensity mode (E2) obtained at a detection end into a 4 th far-field diffraction intensity mode (F2) through a2 nd lens (81), then receiving a2 nd detection result by a2 nd receiver (82), and observing the number and the rotation direction of spiral stripes uniformly distributed in the 2 nd detection result on a 3 rd controller (73) to obtain one OAM mode L1 or L2 in the multiplexed vortex beam D to be detected, wherein the number and the rotation direction of the spiral stripes of an inner ring are consistent with those in |L1| and |L2|, and the number and the rotation direction of the spiral stripes of an outer ring are consistent with those in |L1| and |L2|; combining the relation between the two modes and knowing one OAM mode, the multiplexing vortex beam OAM mode can be identified;
the 2 nd controller (52) design grating function in the step (2) generates a1 st annular phase grating and the 3 rd controller (73) design grating function generates a2 nd annular phase grating: derived from a circular phase grating function t (r) =exp (i 2 pi r/a), where r is the radial coordinate and a is the grating period.
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