CN114785422B - A system for radially polarized vortex beam interference and transmission under water - Google Patents

Abstract

The embodiment of the present invention relates to a system for radially polarized vortex beam interference for underwater transmission, which includes a vortex beam generation module for generating a radially polarized abnormal vortex beam and a radially polarized perfect vortex beam. Underwater turbulent environment modules that form turbulent environments of different strengths and an interference pattern receiving module for receiving light intensity information after interference of two vortex light beams; the vortex beam generating module is sequentially connected to the underwater turbulent environment module and the interference pattern Receive module connection. The interference superposition of the radially polarized abnormal vortex beam and the perfect vortex beam is realized. After passing through the underwater turbulent environment, the light intensity information is obtained through the CCD camera, and the topological charge is judged by the light intensity flickering degree of the interference pattern on the PC. Several different interference superposed vortices are affected by the turbulent environment.

Description

A system for radially polarized vortex beam interference and transmission under water

Technical field

The invention relates to the technical fields of laser communication and underwater optical communication, and in particular to a system for underwater transmission of radially polarized vortex beam interference.

Background technique

In recent years, the continuous development of laser technology has made it widely used in many fields, such as information and communications, biology, materials, chemistry, national defense, etc. During the research, a vortex beam with orbital angular momentum (OAM) attracted the attention of scholars. Unlike ordinary Gaussian beams, OAM can provide a considerable number of multiplexed channels for information transmission. Photons carrying OAM have higher security, confidentiality and concealment, so vortex beams have high research significance in the field of optical communications.

With the rise of underwater optical communications, underwater target detection and other fields, the transmission characteristics of laser beams in water environments have become a research hotspot in recent years. Compared with the atmospheric environment, underwater optical communications face huge challenges. When a vortex beam is transmitted in turbulence, the irregular and random motion of the turbulent environment will cause beam expansion, depolarization effect, decoherence effect, beam jitter and other negative effects on the beam, thus affecting the transmission quality of the vortex beam. Therefore, it is necessary to find Suitable methods to improve the turbulence resistance of vortex beams. For this reason, many scholars have carried out research on polarization control at the wave source, and radially polarized beam is one of them. In existing research, there are few studies on the underwater transmission characteristics of the interference between anomalous vortex beams and other vortex beams, and there are few studies on radially polarized anomalous vortex beams and perfect vortex beams.

Based on the above problems, the present invention studies the transmission characteristics of the interference of radially polarized anomalous vortex beams and perfect vortex beams in underwater turbulence. This has important practical significance for improving the transmission performance of vortex beams under water, and has potential guiding significance and engineering value in applications in the fields of underwater optical communications and underwater target detection.

It is noted that this section is intended to provide background or context for the embodiments of the invention set forth in the claims. The description herein is not admitted to be prior art by inclusion in this section.

Contents of the invention

The purpose of the embodiments of the present invention is to provide a method for radially polarized vortex beam interference for underwater transmission, which realizes the interference superposition of radially polarized abnormal vortex beams and perfect vortex beams, thereby determining the interference superposition of different topological charges. The size of the vortex affected by the turbulent environment.

The technical solution of the present invention is as follows:

The system for radially polarized vortex beam interference and transmission under water includes a vortex beam generation module for generating radially polarized abnormal vortex beams and radially polarized perfect vortex beams, and a water turbulent environment for forming different intensities. The lower turbulent environment module and the interference pattern receiving module used to receive the light intensity information after the interference of the two vortex lights;

The vortex beam generating module is connected to the underwater turbulent environment module and the interference pattern receiving module in sequence.

Further, the above-mentioned vortex beam generating module includes a He-Ne laser, a collimating beam expander, a first beam splitter, a first polarizer, a spatial light modulator, a first radial polarization converter, a reflecting mirror, a third Second polarizer, depolarizing beam splitter, reflective spatial light modulator, second calculator, Fourier lens, second radial polarization converter and second beam splitter);

The output end of the He-Ne laser is connected to the input end of the collimated beam expander, and the output end of the collimated beam expander is connected to the input end of the first beam splitter; the first splitter The output end of the beam device is divided into two beams, one of which is sequentially connected to the first polarizer), spatial light modulator, first radial polarization converter, reflector and second beam splitter, and the other is sequentially connected to the The second polarizer, the depolarizing beam splitter, the second radial polarization converter and the second beam splitter are connected;

The depolarizing beam splitter is connected to the Fourier lens, the reflective spatial light modulator and the second calculator in sequence.

Further, the above-mentioned vortex beam generating module further includes a first calculator, and the first calculator is connected to the spatial light modulator.

Further, the above-mentioned collimating beam expander is composed of two convex lenses with coincident focal points.

Further, the above-mentioned turbulent environment module includes a water tank and a turbulence generator; the water tank is connected to the output end of the second beam splitter, and the turbulence generator is arranged on the water tank.

Further, the above-mentioned interference pattern receiving module includes a polarizer for adjusting the polarization angle, an aperture for adjusting the spot size, and a CCD camera;

The input end of the polarizer is connected to the water tank (16), and the output end of the polarizer is connected to an aperture and a CCD camera in sequence.

The technical solutions provided by the embodiments of the present invention may include the following beneficial effects:

The invention provides a system for radially polarized vortex beam interference for underwater transmission, which realizes the interference superposition of radially polarized abnormal vortex beam and perfect vortex beam. After passing through the underwater turbulent environment, the light intensity is obtained through a CCD camera. Information can be used to determine the extent of the interference superposition vortices with different topological charges affected by the turbulent environment through the degree of light intensity flickering of the interference pattern on the PC.

Description of the drawings

Figure 1 is a diagram of the working principle of the present invention.

Figure 2 is a grayscale phase diagram of the Bessel vortex beam required in the vortex light generation module of the present invention;

Figure 3 is a grayscale phase diagram of the anomalous vortex beam required in the vortex light generation module of the present invention.

In the figure, 1.He-Ne laser, 2.Collimated beam expander, 3.First beam splitter, 4.First polarizer, 5.Spatial light modulator, 6.First calculator, 7. A radial polarization converter, 8. Reflector, 9. Second polarizer, 10. Depolarizing beam splitter, 11. Reflective spatial light modulator, 12. Second calculator, 13. Fourier lens , 14. Second radial polarization converter, 15. Second beam splitter, 16. Water tank, 17. Turbulence generator, 18. Polarizer, 19. Diaphragm, 20. CCD camera.

Detailed ways

The present invention will be described in detail below with reference to the drawings and specific embodiments.

As shown in Figure 1, the system for underwater transmission of radially polarized vortex beam interference includes a vortex beam generation module (generation of radial polarization anomalous vortex and radial polarization perfect vortex), turbulent environment module, and interference pattern receiving module . Among them: the vortex beam generating module is used to generate radially polarized abnormal vortex beams and radially polarized perfect vortex beams; the underwater turbulent environment module is used to form turbulent environments of different intensities; and the interference pattern receiving module Used to receive the light intensity information after the interference of two vortex lights (radial polarization abnormal vortex beam + radial polarization perfect vortex beam).

Among them, the vortex beam generation module includes He-Ne laser 1, collimated beam expander 2, beam splitter 3, second polarizer 4, spatial light modulator 5, first calculator 6, radial polarization converter 7. Second polarizer 9, depolarizing beam splitter 10, reflective spatial light modulator 11, second calculator 12, Fourier lens 13, radial polarization converter 14 and second beam splitter 15.

The collimating beam expander 2 is composed of two convex lenses with coincident focal points. It is used to improve the directionality of the beam, reduce the additional phase caused by the interference of the vortex beam, compress the divergence angle of the beam, and make the vortex observed on the computer The light intensity of the rotating beam is evenly distributed.

The radial polarization converter 7 and the radial polarization converter 14 are used to convert linearly polarized light into a radially polarized vortex beam.

The first calculator is used to load the helical phase pattern of the anomalous vortex beam onto the spatial light modulator 5 . The second calculator 12 is used to load the spiral phase pattern of the perfect vortex beam onto the reflective spatial light modulator 11 .

The reflective spatial light modulator 11 , which allows a maximum reflection angle of ±5°, is used to reflect the formed vortex beam onto the Fourier lens 13 .

After the light beam is incident on the first polarizer 4 and the second polarizer 9, the transmitted light will obtain horizontal linearly polarized light.

Turbulence generator 17 is used to generate turbulent flow environments of different intensities. (The rotation angle of the knob is used to characterize the intensity of turbulence. The greater the rotation angle, the stronger the turbulence intensity, and vice versa).

The polarizing plate 18 is used to adjust the polarization angles of the two vortex beams so that their polarization directions are perpendicular to each other and interfere with each other.

Diaphragm 19 is used to adjust the spot size.

The interference receiving module is a CCD camera 20, which is used to receive the light intensity information of the interference superimposed radial polarization vortex, and then transmits it to the computer after imaging.

After the helium-neon laser outputs the fundamental mode Gaussian beam, it passes through a collimator composed of two coincident convex lenses, and then is divided into two beams of light by a beam splitter: one beam is incident on the first polarizer 4, and the generated linearly polarized light is incident on pure The phase liquid crystal spatial light modulator 5 loads the anomalous vortex beam grayscale image through the control end of the first calculator 6 to perform phase modulation on the linearly polarized light to obtain the corresponding anomalous vortex beam. The anomalous vortex light is incident on the first radially polarized light. Converter 7 generates a radially polarized anomalous vortex beam; another beam is incident on the second polarizer 9 and then incident on the depolarizing beam splitter 10 and reaches the reflective spatial light modulator 11 (reflective pure phase liquid crystal space The optical modulator loads the Bessel Gaussian vortex beam phase diagram) to generate the Bessel Gaussian vortex beam, which forms a perfect vortex beam after passing through the Fourier lens 13, and the perfect vortex beam is incident on the second radial polarization in turn. The converter 14 produces a radially polarized perfect vortex beam.

As shown in Figures 2 and 3, the software matlab is used to simulate the grayscale phase diagram required by the vortex beam generation module in the present invention.

The phase expression of the spiral phase plate is Passing a Gaussian beam through this phase element can introduce a spiral phase delay and cause a phase singularity at the center of the beam. A grayscale image written in MATLAB, with grayscale values distributed in

Between 0-255, the information loaded onto the spatial light should be distributed from 0-1 corresponding to the phase modulation of 0-2π, so the written hologram needs to be normalized. Loading the spiral phase diagram generated by simulation onto the spatial light modulator can simulate its phase distribution diagram, thereby generating the required vortex beam.

Using matlab for simulation, Figure 2 generates the grayscale phase diagram of the Bessel Gaussian vortex beam required by the present invention. After accurately controlling the phase diagram, it is loaded into the liquid crystal spatial light modulator to generate the required Bessel Gaussian vortex beam. Through the Fourier lens, the perfect vortex beam required by the present invention can be generated.

Using matlab for simulation, Figure 3 generates the grayscale phase diagram of the anomalous vortex beam required by the present invention. The required anomalous vortex beam is generated by accurately controlling the phase diagram and loading it into the liquid crystal spatial light modulator. (For example: the figure shows a vortex beam with a topological charge of 4).

In the description of this specification, reference to the terms "one embodiment," "some embodiments," "an example," "specific examples," or "some examples" or the like means that specific features are described in connection with the embodiment or example. , structures, materials or features are included in at least one embodiment or example of the invention. In this specification, the schematic expressions of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, those skilled in the art may join and combine the different embodiments or examples described in this specification.

Other embodiments of the invention will be readily apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary technical means in the technical field that are not disclosed in the invention. . It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims (3)

1. A system for transmission under water by interference of radially polarized vortex beams, characterized in that:

the device comprises a vortex beam generating module for generating radial polarized abnormal vortex beams and radial polarized perfect vortex beams, an underwater turbulence environment module for forming different intensity turbulence environments, and an interference pattern receiving module for receiving light intensity information after interference of the two vortex beams;

the vortex beam generation module is sequentially connected with the underwater turbulence environment module and the interference pattern receiving module;

the vortex beam generation module comprises a He-Ne laser (1), a collimation beam expander (2), a first beam splitter (3), a first polarizer (4), a spatial light modulator (5), a first radial polarization converter (7), a reflecting mirror (8), a second polarizer (9), a depolarizing beam splitter (10), a reflection spatial light modulator (11), a second calculator (12), a Fourier lens (13), a second radial polarization converter (14) and a second beam splitter (15);

the output end of the He-Ne laser (1) is connected with the input end of the collimation beam expander (2), and the output end of the collimation beam expander (2) is connected with the input end of the first beam splitter (3); the output end of the first beam splitter (3) is divided into two paths of light beams, one path of the light beams is sequentially connected with the first polarizer (4), the spatial light modulator (5), the first radial polarization converter (7), the reflecting mirror (8) and the second beam splitter (15), and the other path of the light beams is sequentially connected with the second polarizer (9), the depolarizing beam splitter (10), the second radial polarization converter (14) and the second beam splitter (15);

the depolarizing beam splitter (10) is sequentially connected with the Fourier lens (13), the reflective spatial light modulator (11) and the second calculator (12);

the vortex beam generation module further comprises a first calculator (6), wherein the first calculator (6) is connected with the spatial light modulator (5);

the interference pattern receiving module comprises a polaroid (18) for adjusting the polarization angle, a diaphragm (19) for adjusting the size of a light spot and a CCD camera (20);

the input end of the polaroid (18) is connected with the water tank (16), and the output end of the polaroid (18) is sequentially connected with a diaphragm (19) and a CCD camera (20);

after the He-Ne laser (1) outputs a Gaussian beam of a fundamental mode, the Gaussian beam passes through a collimator formed by two convex lenses with coincident focuses, and is split into two beams of light by a beam splitter: one beam is incident to a first polarizer (4), the generated linear polarized light is incident to a pure phase liquid crystal spatial light modulator (5), the linear polarized light is subjected to phase modulation by loading an abnormal vortex light beam gray scale image at a control end of a first calculator (6) to obtain a corresponding abnormal vortex light beam, the abnormal vortex light is incident to a first radial polarization converter (7), and a radial polarization abnormal vortex light beam is generated; the other beam is incident to the second polarizer (9) and then is incident to the depolarizing beam splitter (10) to reach the reflective spatial light modulator (11) to generate Bessel Gaussian vortex beams, the Bessel Gaussian vortex beams pass through the Fourier lens (13) to form perfect vortex beams, and the perfect vortex beams are sequentially incident to the second radial polarization converter (14) to generate radial polarized perfect vortex beams.

2. The system for transmission under water of radially polarized vortex beam interference of claim 1 wherein: the collimation beam expander (2) consists of two convex lenses with coincident focuses.

3. A system for transmission under water of radially polarized vortex beam interference according to claim 1 or 2 wherein:

the turbulent environment module comprises a water tank (16) and a turbulent generator (17); the water tank (16) is connected with the output end of the second beam splitter (15), and the turbulence generator (17) is arranged on the water tank (16).