CN114295227A - System and method for measuring orbital angular momentum light beam topology charge value - Google Patents
System and method for measuring orbital angular momentum light beam topology charge value Download PDFInfo
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Abstract
The invention provides a system and a method for measuring orbital angular momentum light beam topological charge value. The method comprises the steps that an orbital angular momentum light beam generating unit obtains an orbital angular momentum light beam carrying topological charges; the orbit angular momentum light beam coupling unit converts the orbit angular momentum light beam into a coherent state; and the orbital angular momentum light beam interference unit performs equal-thickness interference on the orbital angular momentum light beam on the basis to obtain a required orbital angular momentum light beam interference form for measurement. The invention realizes the measurement of the number and the positive and negative values of the orbital angular momentum topological charges, can measure the high-order topological charge value, reduces the cost of a measurement system and greatly improves the efficiency of the orbital angular momentum light beam in practical application.
Description
Technical Field
The invention relates to the technical field of quantum information and optical communication, in particular to a system and a method for measuring orbital angular momentum light beam topological charge value.
Background
Photons have multiple degrees of freedom, such as polarization, spin angular momentum, and orbital angular momentum. The spin angular momentum is related to the circular polarization state of the photon, and its eigenstates can be represented by the spin angular momentum operator left-handed circular polarization state | L>
And a right-handed circularly polarized state | R>
To show that a common two-dimensional hilbert space can be constructed using spin angular momentum. In 1992, orbital angular momentum was formally known and it was proved by research that a single photon contains definite orbital angular momentum
A characteristic quantum number, which is orbital angular momentum, may also be referred to as a topological charge number,
the value of (a) can be any integer. Of theoretical angular momentum of the track
The value is infinite, that is, the encoding in the infinite Weibull space in the quantum information and optical communication technology can be realized by using the orbital angular momentum. Photons as information carriers want to realize high-dimensional Hilbert space coding and can modulate orbital angular momentum of the photons, and therefore the amount of information carried by the photons is greatly improved. In the scheme of optical communication and quantum communication by using orbital angular momentum, measuring the photon orbital angular momentum for encoding is a key step and a last step in the orbital angular momentum communication. With the increasing research heat of orbital angular momentum, how to more conveniently and effectively measure the orbital angular momentum of photons becomes one of the hot areas of research nowadays.
The prior art discloses a patent of a detection system for identifying the topological charge number of an OAM light beam based on signal crosstalk distribution characteristics, wherein an OAM multiplexing module in the patent carries out orbital angular momentum multiplexing on a vortex light beam; the first optical antenna module transmits the vortex light beam signal into an optical communication channel; the second optical antenna receives the light beam, the OAM demultiplexing module decomposes the received optical signal into a group of OAM modes and converts the optical signal into a crosstalk distribution electric signal, the OAM light beam topology charge number detection module analyzes input data to obtain the topology charge number of the vortex light beam, and the patent makes full use of topology charge number information contained in the crosstalk distribution by utilizing the characteristics of the crosstalk distribution so that the vortex light beam topology charge number detection has high accuracy and high speed and realizes high-speed information transmission. However, the patent is rarely reported for measuring the magnitude and sign of the orbital angular momentum beam topological charge value.
In the existing application, the orbital angular momentum carried by the photon has a larger topological charge value, and the negative topological charge is widely used. Thus the topological charge value of orbital angular momentum
In the measurement, not only the magnitude of the absolute value of the topological charge value needs to be measured, but also the sign of the topological charge value needs to be measured, so that the simultaneous measurement of two variables is a challenge, and the lightweight measurement device is a problem to be overcome in practical application.
Disclosure of Invention
The invention provides a system for measuring a track angular momentum light beam topological charge value, which can measure the size and the sign of the track angular momentum light beam topological charge value.
It is another object of the present invention to provide a method for measuring orbital angular momentum beam topology charge values.
In order to achieve the technical effects, the technical scheme of the invention is as follows:
a system for measuring orbital angular momentum light beam topological charge values comprises a pumping light source, an orbital angular momentum light beam generating unit, an orbital angular momentum light beam coupling unit, an orbital angular momentum light beam interference unit and a light detector which are connected in sequence;
the pump light source generates continuous Gaussian beams; the orbital angular momentum light beam generating unit generates an orbital angular momentum light beam carrying required topological charges; the orbit angular momentum light beam coupling unit is used for splitting and coupling the orbit angular momentum light beam to obtain a coherent orbit angular momentum light beam; the orbital angular momentum light beam interference unit performs secondary interference on the orbital angular momentum light beam to obtain a required interference pattern; and the optical detector observes the interference pattern to obtain the magnitude and the positive and negative of the orbit angular momentum topological charge value.
Further, the orbital angular momentum beam generating unit comprises a first lens, a second lens, a polarizing plate, a liquid crystal Spatial Light Modulator (SLM) and a computer PC which are connected in sequence; the pumping light source is connected with the first lens, and the first lens and the second lens form a lens group for expanding and collimating the input pumping light; the polaroid converts the Gaussian beam into linearly polarized light; and the computer PC transmits a calculation hologram to the liquid crystal spatial light modulator SLM to convert the linearly polarized light into a required orbital angular momentum beam.
Further, the orbital angular momentum beam coupling unit comprises a first beam splitter, a first total reflection mirror and a Faraday mirror; the first beam splitter divides the passing orbital angular momentum light beam into a first light beam and a second light beam; the first light beam is reflected at the first total reflection mirror, and the second light beam is rotated by 180 degrees and reflected at the Faraday mirror; and then the first light beam and the second light beam reenter the first beam splitter and are coupled into a light beam and then exit.
Further, the first total reflection mirror is equal to the distance between the Faraday mirror and the first beam splitter; the first total reflector and the Faraday reflector are all total reflectors plated with high-reflection films; the splitting ratio of the first splitter is 50: 50.
Further, the orbital angular momentum beam interference unit comprises a third lens, a second beam splitter, a plano-convex lens, a second total reflection mirror and a fourth lens; the third lens converges the parallel light into a divergent light beam; the plano-convex lens and the second holophote interfere the diverged orbital angular momentum light beam to obtain a required orbital angular momentum interference light beam; the second beam splitter receives the light beam, reflects the light beam and then enters a fourth lens; the fourth lens reconverges the divergent light into parallel light, obtains a required interference pattern and is used for measuring the topological charge value.
Further, the beam splitting ratio of the second beam splitter is 50: 50; the second holophote is a holophote plated with a high-reflection film; the third lens and the fourth lens are both convergent lenses; the position of the plano-convex lens is behind the focal point f of the third lens; the plano-convex lens is tightly connected with the second total reflector.
A method for measuring orbital angular momentum beam topological charge value comprises the following steps:
s1: using a pump light source to generate continuous Gaussian beams, and enabling the Gaussian beams to enter an orbital angular momentum beam generating unit;
s2: gaussian beams entering the orbital angular momentum beam generation unit respectively pass through a lens group consisting of a first lens and a second lens, the Gaussian beams are expanded and collimated after passing through the lens group, and then pass through a polaroid, and the Gaussian beams are converted into linearly polarized light; under the modulation of a computer PC, linearly polarized light enters a liquid crystal spatial light modulator SLM and is converted into a liquid crystal spatial light modulator
An orbital angular momentum beam of topological charges; the orbital angular momentum light beam enters an orbital angular momentum light beam coupling unit;
s3: the orbital angular momentum light beam entering the orbital angular momentum light beam coupling unit is divided into a first light beam and a second light beam at the first beam splitter, and the first light beam and the second light beam are coupled into a light beam at the first beam splitter again and emitted out through reflection of a first total reflection mirror and rotation and reflection of a Faraday reflection mirror and enter the orbital angular momentum light beam interference unit;
s4: the orbital angular momentum light beam entering the orbital angular momentum light beam interference unit is changed into divergent light from parallel light at the third lens, then is transmitted into the plano-convex lens at the second beam splitter, the light refracted by the plano-convex lens enters the plano-convex lens again after being reflected by a second total reflector close to the bottom of the plano-convex lens to generate interference phenomenon, then the interfered orbital angular momentum light beam returns to the second beam splitter, is reflected at the second beam splitter to enter the fourth lens, is changed into parallel light again, and leaves the orbital angular momentum light beam interference unit;
s5: and the orbit angular momentum light beam leaving the orbit angular momentum light beam interference unit enters the optical detector to obtain an interference pattern of the orbit angular momentum light beam after system modulation, so that the size and the positive and negative of the orbit angular momentum light beam topological charge value are respectively judged according to the interference pattern interference great bright spot number and the interference fringe rotation direction.
Further, in step S2, the computer PC provides a computer hologram to be projected onto the liquid crystal spatial light modulator SLM to generate a desired orbital angular momentum beam by changing the liquid crystal array.
Further, in step S4, the planoconvex lens generates a desired interference phenomenon by a refraction phenomenon caused by a difference in refractive index of different media and an optical path difference caused by a height difference between the planoconvex lens curved surface and the total reflection mirror.
Furthermore, the relationship between the number n of the interference maximum bright spots and the topological charge value l is n ═ 2| l |, and the relationship between the rotation direction of the interference fringes and the positive and negative values of the topological charge value is that the clockwise rotation is a positive value and the counterclockwise rotation is a negative value.
Compared with the prior art, the technical scheme of the invention has the beneficial effects that:
(1) according to the invention, the separation characteristic and the convergence characteristic of the beam splitter are used, so that the generation of the orbital angular momentum light beam which can be stably coupled is realized, and the interference of the orbital angular momentum light beam can be stably carried out; (2) the equal-thickness interference of the orbital angular momentum beams is realized by using the plano-convex lens, and the generated interference pattern is visual and clear and is beneficial to resolution; (3) the topological charge value of orbital angular momentum is measured by adopting an optical interference method, and the positive value and the negative value of the topological charge value can be measured under the condition of keeping the advantage of high topological charge value measurable by interference measurement.
Drawings
FIG. 1 is a block diagram of the system of the present invention;
FIG. 2 is a flow chart of the method of the present invention;
FIG. 3 is a graph showing the results of the example of the present invention.
Detailed Description
The drawings are for illustrative purposes only and are not to be construed as limiting the patent;
for the purpose of better illustrating the embodiments, certain features of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product;
it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The technical solution of the present invention is further described below with reference to the accompanying drawings and examples.
Example 1
As shown in fig. 1, a system for measuring orbital angular momentum beam topological charge value includes a pump light source 10, an orbital angular momentum beam generating unit 11, an orbital angular momentum beam coupling unit 12, an orbital angular momentum beam interference unit 13 and a light detector 14, which are connected in sequence;
the pump light source 10 generates a continuous gaussian beam; the orbital angular momentum light beam generating unit 11 generates an orbital angular momentum light beam carrying required topological charges; the orbital angular momentum light beam coupling unit 12 is configured to split and couple the orbital angular momentum light beams to obtain coherent orbital angular momentum light beams; the orbital angular momentum light beam interference unit 13 performs secondary interference on the orbital angular momentum light beam to obtain a required interference pattern; the optical detector 14 observes the interference pattern to obtain the magnitude and the positive and negative of the orbit angular momentum topological charge value.
The orbital angular momentum beam generating unit 11 includes a first lens 110, a second lens 111, a polarizing plate 112, a liquid crystal spatial light modulator SLM113, and a computer PC114 connected in this order; the pump light source 10 is connected with the first lens 110, and the first lens 111 and the second lens 112 form a lens group to expand and collimate the input pump light; the polarizer 112 converts the gaussian beam into linearly polarized light; the computer PC114 sends a computer hologram to the liquid crystal spatial light modulator SLM113, converting linearly polarized light into a desired orbital angular momentum beam.
The orbital angular momentum beam coupling unit 12 includes a first beam splitter 120, a first total reflection mirror 121, and a faraday mirror 122; the first beam splitter 120 splits the passing orbital angular momentum beam into a first beam and a second beam; the first beam is reflected at the first total reflection mirror 121, and the second beam is rotated by 180 ° and reflected at the faraday mirror 122; the first and second light beams then re-enter the first beam splitter 120 to be coupled into a beam of light and then exit.
The first total reflection mirror 121 is equidistant from the faraday mirror 122 and the first beam splitter 120; the first total reflector 121 and the faraday reflector 122 are all total reflectors plated with high reflective films; the splitting ratio of the first beam splitter 120 is 50: 50.
The orbital angular momentum beam interference unit 13 includes a third lens 130, a second beam splitter 131, a plano-convex lens 132, a second total reflection mirror 133, and a fourth lens 134; the third lens 130 converges the parallel light to become a diverging light beam; the plano-convex lens 132 and the second total reflector 133 interfere the diverged orbital angular momentum beams to obtain required orbital angular momentum interference beams; the second beam splitter 131 receives the light beam, reflects the light beam and enters a fourth lens 134; the fourth lens 134 reconverges the diverging light into parallel light to obtain a desired interference pattern and is used for measurement of the topological charge value.
The splitting ratio of the second beam splitter 131 is 50: 50; the second holophote 133 is a holophote plated with a high reflection film; the third lens 130 and the fourth lens 134 are both converging lenses; the position of the plano-convex lens 132 is behind the focal point f of the third lens; the plano-convex lens 132 is closely coupled to the second total reflecting mirror 133.
Example 2
As shown in fig. 2, a method for measuring orbital angular momentum beam topological charge value comprises the following steps:
s1: using a pump light source 10 to generate a continuous Gaussian beam, and enabling the Gaussian beam to enter an orbital angular momentum beam generating unit 11;
s2: the gaussian beams entering the orbital angular momentum beam generating unit 11 pass through a lens group consisting of a first lens 110 and a second lens 111 respectively, the gaussian beams realize beam expansion and collimation after passing through the lens group, and then are converted into linearly polarized light through a polarizing film 112; under the modulation of the computer PC114, the linearly polarized light enters the liquid crystal spatial light modulator SLM113 and is converted into a light beam with a polarization direction
An orbital angular momentum beam of topological charges; the orbital angular momentum light beam enters an orbital angular momentum light beam coupling unit 12;
s3: the orbital angular momentum beam entering the orbital angular momentum beam coupling unit 12 is divided into a first beam and a second beam at the first beam splitter 120, and the first beam and the second beam are coupled into a beam again at the first beam splitter 120 and emitted out through reflection of the first total reflection mirror 121 and rotation and reflection of the faraday reflection mirror 122, and enter the orbital angular momentum beam interference unit 13;
s4: the orbital angular momentum light beam entering the orbital angular momentum light beam interference unit 13 is changed into divergent light from parallel light at the third lens 130, then is transmitted into the plano-convex lens 132 at the second beam splitter 131, the light refracted by the plano-convex lens 132 reenters the plano-convex lens 132 after being reflected by the second total reflection mirror 133 next to the bottom of the plano-convex lens 132 to generate interference phenomenon, and then the interfered orbital angular momentum light beam returns to the second beam splitter 131, is reflected at the second beam splitter 131, enters the fourth lens 134, is changed into parallel light again, and leaves the orbital angular momentum light beam interference unit 13;
s5: the orbital angular momentum light beam leaving the orbital angular momentum light beam interference unit 13 enters the optical detector 14 to obtain an interference pattern of the system modulated orbital angular momentum light beam, so that the size and the positive and negative of the orbital angular momentum light beam topological charge value are respectively judged according to the interference pattern interference maximum bright spot number and the interference fringe rotation direction.
In step S2, the computer PC114 provides a computer hologram that is projected onto the liquid crystal spatial light modulator SLM113 to generate a desired orbital angular momentum beam by changing the liquid crystal array.
In step S4, the plano-convex lens 132 generates a desired interference phenomenon by a refraction phenomenon caused by a difference in refractive index between different media and an optical path difference caused by a difference in height between the curved surface of the plano-convex lens 132 and the total reflection mirror.
The relationship between the number n of the interference maximum bright spots and the topological charge value l is 2| l |, and the relationship between the rotation direction of the interference fringes and the positive and negative values of the topological charge value is that the clockwise rotation is a positive value and the anticlockwise rotation is a negative value. Fig. 3 is a graph of the results of the embodiment, and it can be seen from the graph that there are 14 interference maximum bright spots, and the interference fringes rotate clockwise, so that the orbital angular momentum topological charge value l is + 7.
Example 3
As shown in fig. 2, a method for measuring orbital angular momentum beam topological charge value comprises the following steps:
s1: using a pump light source 10 to generate a continuous Gaussian beam, and enabling the Gaussian beam to enter an orbital angular momentum beam generating unit 11;
s2: the gaussian beams entering the orbital angular momentum beam generating unit 11 pass through a lens group consisting of a first lens 110 and a second lens 111 respectively, the gaussian beams realize beam expansion and collimation after passing through the lens group, and then are converted into linearly polarized light through a polarizing film 112; under the modulation of the computer PC114, the linearly polarized light enters the liquid crystal spatial light modulator SLM113 and is converted into a light beam with a polarization direction
An orbital angular momentum beam of topological charges; the orbital angular momentum light beam enters an orbital angular momentum light beam coupling unit 12;
s3: the orbital angular momentum beam entering the orbital angular momentum beam coupling unit 12 is divided into a first beam and a second beam at the first beam splitter 120, and the first beam and the second beam are coupled into a beam again at the first beam splitter 120 and emitted out through reflection of the first total reflection mirror 121 and rotation and reflection of the faraday reflection mirror 122, and enter the orbital angular momentum beam interference unit 13;
s4: the orbital angular momentum light beam entering the orbital angular momentum light beam interference unit 13 is changed into divergent light from parallel light at the third lens 130, then is transmitted into the plano-convex lens 132 at the second beam splitter 131, the light refracted by the plano-convex lens 132 reenters the plano-convex lens 132 after being reflected by the second total reflection mirror 133 next to the bottom of the plano-convex lens 132 to generate interference phenomenon, and then the interfered orbital angular momentum light beam returns to the second beam splitter 131, is reflected at the second beam splitter 131, enters the fourth lens 134, is changed into parallel light again, and leaves the orbital angular momentum light beam interference unit 13;
s5: the orbital angular momentum light beam leaving the orbital angular momentum light beam interference unit 13 enters the optical detector 14 to obtain an interference pattern of the system modulated orbital angular momentum light beam, so that the size and the positive and negative of the orbital angular momentum light beam topological charge value are respectively judged according to the interference pattern interference maximum bright spot number and the interference fringe rotation direction.
The method is applied to a system for measuring orbital angular momentum light beam topological charge value, and comprises a pump light source 10, an orbital angular momentum light beam generating unit 11, an orbital angular momentum light beam coupling unit 12, an orbital angular momentum light beam interference unit 13 and a light detector 14 which are connected in sequence;
the pump light source 10 generates a continuous gaussian beam; the orbital angular momentum light beam generating unit 11 generates an orbital angular momentum light beam carrying required topological charges; the orbital angular momentum light beam coupling unit 12 is configured to split and couple the orbital angular momentum light beams to obtain coherent orbital angular momentum light beams; the orbital angular momentum light beam interference unit 13 performs secondary interference on the orbital angular momentum light beam to obtain a required interference pattern; the optical detector 14 observes the interference pattern to obtain the magnitude and the positive and negative of the orbit angular momentum topological charge value.
The orbital angular momentum beam generating unit 11 includes a first lens 110, a second lens 111, a polarizing plate 112, a liquid crystal spatial light modulator SLM113, and a computer PC114 connected in this order; the pump light source 10 is connected with the first lens 110, and the first lens 111 and the second lens 112 form a lens group to expand and collimate the input pump light; the polarizer 112 converts the gaussian beam into linearly polarized light; the computer PC114 sends a computer hologram to the liquid crystal spatial light modulator SLM113, converting linearly polarized light into a desired orbital angular momentum beam.
The orbital angular momentum beam coupling unit 12 includes a first beam splitter 120, a first total reflection mirror 121, and a faraday mirror 122; the first beam splitter 120 splits the passing orbital angular momentum beam into a first beam and a second beam; the first beam is reflected at the first total reflection mirror 121, and the second beam is rotated by 180 ° and reflected at the faraday mirror 122; the first and second light beams then re-enter the first beam splitter 120 to be coupled into a beam of light and then exit.
The first total reflection mirror 121 is equidistant from the faraday mirror 122 and the first beam splitter 120; the first total reflector 121 and the faraday reflector 122 are all total reflectors plated with high reflective films; the splitting ratio of the first beam splitter 120 is 50: 50.
The orbital angular momentum beam interference unit 13 includes a third lens 130, a second beam splitter 131, a plano-convex lens 132, a second total reflection mirror 133, and a fourth lens 134; the third lens 130 converges the parallel light to become a diverging light beam; the plano-convex lens 132 and the second total reflector 133 interfere the diverged orbital angular momentum beams to obtain required orbital angular momentum interference beams; the second beam splitter 131 receives the light beam, reflects the light beam and enters a fourth lens 134; the fourth lens 134 reconverges the diverging light into parallel light to obtain a desired interference pattern and is used for measurement of the topological charge value.
The splitting ratio of the second beam splitter 131 is 50: 50; the second holophote 133 is a holophote plated with a high reflection film; the third lens 130 and the fourth lens 134 are both converging lenses; the position of the plano-convex lens 132 is behind the focal point f of the third lens; the plano-convex lens 132 is closely coupled to the second total reflecting mirror 133.
The same or similar reference numerals correspond to the same or similar parts;
the positional relationships depicted in the drawings are for illustrative purposes only and are not to be construed as limiting the present patent;
it should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (10)
1. A system for measuring orbital angular momentum light beam topological charge values is characterized by comprising a pump light source (10), an orbital angular momentum light beam generating unit (11), an orbital angular momentum light beam coupling unit (12), an orbital angular momentum light beam interference unit (13) and a light detector (14) which are connected in sequence;
the pump light source (10) generates a continuous Gaussian beam; the orbital angular momentum light beam generating unit (11) generates an orbital angular momentum light beam carrying required topological charges; the orbit angular momentum light beam coupling unit (12) is used for splitting and coupling the orbit angular momentum light beam to obtain a coherent orbit angular momentum light beam; the orbital angular momentum light beam interference unit (13) performs secondary interference on the orbital angular momentum light beam to obtain a required interference pattern; and the optical detector (14) observes the interference pattern to obtain the magnitude and the positive and the negative of the orbit angular momentum topological charge value.
2. The system for measuring orbital angular momentum beam topology charge values according to claim 1, wherein the orbital angular momentum beam generating unit (11) comprises a first lens (110), a second lens (111), a polarizer (112), a liquid crystal Spatial Light Modulator (SLM) (113) and a computer PC (114) connected in sequence; the pumping light source (10) is connected with the first lens (110), and the first lens (111) and the second lens (112) form a lens group for expanding and collimating the input pumping light; the polarizing plate (112) converts the Gaussian beam into linearly polarized light; and the computer PC (114) transmits a calculation hologram to the liquid crystal spatial light modulator SLM (113) to convert the linearly polarized light into a required orbital angular momentum beam.
3. The system for measuring orbital angular momentum beam topology charge values according to claim 2, wherein the orbital angular momentum beam coupling unit (12) comprises a first beam splitter (120), a first total reflecting mirror (121) and a faraday mirror (122); the first beam splitter (120) splits the passing orbital angular momentum light beam into a first light beam and a second light beam; the first light beam is reflected at a first total reflection mirror (121), and the second light beam is rotated by 180 degrees and reflected at a Faraday mirror (122); the first light beam and the second light beam reenter the first beam splitter (120) to be coupled into a light beam and then exit.
4. The system for measuring orbital angular momentum beam topology charge values according to claim 3, characterized in that the first total reflecting mirror (121) is equidistant from the Faraday mirror (122) and the first beam splitter (120); the first total reflector (121) and the Faraday reflector (122) are all total reflectors plated with high reflective films; the first beam splitter (120) has a splitting ratio of 50: 50.
5. The system for measuring orbital angular momentum beam topology charge values according to claim 4, characterized in that the orbital angular momentum beam interference unit (13) comprises a third lens (130), a second beam splitter (131), a plano-convex lens (132), a second total reflection mirror (133) and a fourth lens (134); the third lens (130) converges the parallel light into a divergent light beam; the plano-convex lens (132) and the second total reflector (133) interfere the diverged orbital angular momentum light beam to obtain a required orbital angular momentum interference light beam; the second beam splitter (131) receives the light beam and reflects the light beam to enter a fourth lens (134); the fourth lens (134) reconverges the diverging light into parallel light, obtains a desired interference pattern, and is used for measurement of the topological charge value.
6. The system for measuring an orbital angular momentum beam topology charge value of claim 5, characterized in that the second beam splitter (131) has a splitting ratio of 50: 50; the second total reflection mirror (133) is a total reflection mirror plated with a high reflection film; the third lens (130) and the fourth lens (134) are both convergent lenses; the position of the plano-convex lens (132) is behind the focal point f of the third lens; the plano-convex lens (132) is closely connected with the second total reflecting mirror (133).
7. A method of measuring an orbital angular momentum beam topology charge of a system for measuring an orbital angular momentum beam topology charge of claim 6, comprising the steps of:
s1: using a pump light source (10) to generate a continuous Gaussian beam, and enabling the Gaussian beam to enter an orbital angular momentum beam generating unit (11);
s2: gaussian beams entering the orbital angular momentum beam generating unit (11) pass through a lens group consisting of a first lens (110) and a second lens (111) respectively, are expanded and collimated after passing through the lens group, and then pass through a polarizing film (112) and are converted into linearly polarized light; under the modulation of a computer PC (114), linearly polarized light enters a liquid crystal spatial light modulator SLM (113) and then is converted into an orbital angular momentum beam with l topological charges; the orbital angular momentum light beam enters an orbital angular momentum light beam coupling unit (12);
s3: the orbital angular momentum light beam entering the orbital angular momentum light beam coupling unit (12) is divided into a first light beam and a second light beam at the first beam splitter (120), the first light beam and the second light beam are coupled into a light beam at the first beam splitter (120) again through the reflection of a first total reflecting mirror (121) and the rotation and reflection of a Faraday reflecting mirror (122), and the light beam exits and enters the orbital angular momentum light beam interference unit (13);
s4: the orbital angular momentum light beam entering the orbital angular momentum light beam interference unit (13) is changed into divergent light from parallel light at a third lens (130), then is transmitted into a plano-convex lens (132) at a second beam splitter (131), the light refracted by the plano-convex lens (132) reenters the plano-convex lens (132) to generate interference phenomenon after being reflected by a second total reflection mirror (133) close to the bottom of the plano-convex lens (132), then the interfered orbital angular momentum light beam returns to the second beam splitter (131), is reflected at the second beam splitter (131) to enter a fourth lens (134), is changed into parallel light again, and leaves the orbital angular momentum light beam interference unit (13);
s5: and the orbital angular momentum light beam leaving the orbital angular momentum light beam interference unit (13) enters the optical detector (14) to obtain an interference pattern of the orbital angular momentum light beam after system modulation, so that the size and the positive and negative of the orbital angular momentum light beam topological charge value are respectively judged according to the interference pattern interference great bright spot number and the interference fringe rotation direction.
8. The method for measuring orbital angular momentum beam topology charge value according to claim 7, wherein in step S2, a computer PC (114) provides a computer hologram projected onto a liquid crystal Spatial Light Modulator (SLM) (113) to generate a desired orbital angular momentum beam by changing the liquid crystal array.
9. The method for measuring orbital angular momentum beam topology charge value according to claim 8, wherein in step S4, the plano-convex lens (132) generates the required interference phenomenon by refraction phenomenon caused by different refractive indexes of different media and optical path difference caused by height difference between the cambered surface of the plano-convex lens (132) and the total reflection mirror.
10. The method of claim 9 wherein the relationship between the number of interference maxima and the topology charge value is n 2| l |, and the relationship between the direction of the interference fringe rotation and the positive or negative value of the topology charge value is positive for clockwise rotation and negative for counterclockwise rotation.
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