阅读说明：本技术 一种安全性增强和湍流缓解的oam传输装置及方法 (OAM transmission device and method for security enhancement and turbulence mitigation ) 是由 毛雅亚 刘博� 忻向军 任建新 黄景瑞 王瑞春 沈磊 吴泳锋 孙婷婷 赵立龙 于 2021-08-13 设计创作，主要内容包括：本发明公开了一种安全性增强和湍流缓解的OAM传输装置及方法,包括发送端结构、MPLC系统以及接收端结构,发送端结构用于将用户的数据进行加密调制后形成OAM光束,该OAM光束经大气湍流区域后,进入MPLC系统,MPLC系统包括具有多个具有不同相位模式的相位平面、反射镜、准直器、反馈回路以及控制器,反馈回路接在MPLC系统与接收端结构的连接通道上,监控分离后的光束之间的串扰,控制器能接收反馈回路的信号,并调整相位平面的至少一个相位模式,以纠正畸变光束的波前,降低串扰程度。本发明具有能即提高安全性又减缓湍流影响的优点。(The invention discloses an OAM transmission device and a method for enhancing safety and relieving turbulence, which comprises a sending end structure, an MPLC system and a receiving end structure, wherein the sending end structure is used for carrying out encryption modulation on user data to form an OAM light beam, the OAM light beam enters the MPLC system after passing through an atmospheric turbulence area, the MPLC system comprises a plurality of phase planes with different phase modes, a reflecting mirror, a collimator, a feedback loop and a controller, the feedback loop is connected on a connecting channel of the MPLC system and the receiving end structure, the crosstalk between the separated light beams is monitored, the controller can receive signals of the feedback loop and adjust at least one phase mode of the phase plane to correct the wavefront of a distorted light beam and reduce the crosstalk degree. The invention has the advantages of improving the safety and reducing the influence of turbulence.)

1. An OAM transmission device with enhanced security and turbulent flow relief is characterized in that: the optical fiber network interface device comprises a sending end structure (1), an MPLC system (2) and a receiving end structure (3), wherein the sending end structure (1) is used for carrying out encryption modulation on user data to form an OAM light beam, the OAM light beam enters the MPLC system (2) after passing through an atmospheric turbulence area, the MPLC system (2) comprises a plurality of phase planes (21) with different phase modes, a reflecting mirror (22), a collimator (23), a feedback loop (24) and a controller (25), the OAM light beam influenced by turbulence is reflected back and forth between the phase planes (21) and the reflecting mirror (22) to be separated in space and inclined at different angles, and enters the receiving end structure (3) after being coupled through the collimator (23), the feedback loop (24) is connected to a connecting channel between the MPLC system (2) and the receiving end structure (3) to monitor crosstalk between the separated light beams, the controller (25) is capable of receiving the signal from the feedback loop (24) and adjusting at least one phase pattern of the phase plane (21) to correct the wavefront of the distorted beam and reduce the crosstalk, and the receiving end structure (3) is capable of performing the inverse process of the encryption and modulation of the transmitting end structure (1).

2. The OAM transmission device with enhanced security and turbulence mitigation as recited in claim 1, wherein: the phase plane (21) has six different phase modes.

3. The transmission method of the OAM transmission apparatus for security enhancement and turbulence mitigation as recited in claim 1, wherein: the method comprises the following steps:

a. a sending end step: distributing user data to channels with different optical wavelengths simultaneously, encrypting the data by an optical switch under the control of a frequency hopping sequence, further transmitting the encrypted data by randomly distributed channels with different OAM states, generating the frequency hopping sequence by a Chua's chaotic model, performing electro-optical modulation on binary data to be transmitted and an optical signal in a Mach-Zehnder modulator MZM after the binary data to be transmitted is modulated and constellation encrypted in a DSP flow, accessing the modulated signal to an OAM generator, and modulating the data to an OAM light beam;

b. the transmission process comprises the following steps: the OAM light beam is incident on the analog turbulence plate, the vortex light beam influenced by turbulence enters an MPLC system (2), the MPLC system (2) receives a signal of a feedback loop (24) by using a controller (25), adjusts the phase mode of a phase plane (21), performs turbulence relieving and mode demultiplexing on the light beam,

c. a receiving end step: vortex light carrying information is decomposed and multiplexed to be changed into a Gaussian beam, the Gaussian beam is converted into an electric signal by a photoelectric detector, and then the electric signal is subjected to decryption and demodulation opposite to the encryption and modulation of a sending end to obtain decrypted data.

4. The OAM transmission method for security enhancement and turbulence mitigation as recited in claim 3, wherein: the specific method for encrypting data by the optical switch under the control of the frequency hopping sequence comprises the following steps:

an NxN optical switch selector is adopted to encrypt the physical layer, a chaos sequence generated by a Chua model is used as a key, and a recursive frequency hopping method is adopted: LDi → MZMi; LDi → MZMi + 1; ③ LDi → MZMi + 2; … …, respectively; wherein the equation for the Chua model is:

wherein the number of the first and second groups is a constant number,are variables.

5. The OAM transmission method for security enhancement and turbulence mitigation as recited in claim 3, wherein: the DSP flow is divided into three steps: a constellation mapping step, an up-sampling step and a shaping filtering step;

the constellation mapping step is as follows: adopting a 16QAM constellation diagram, using a Chua model as chaotic mapping to generate a masking vector, and masking 16QAM constellation points to obtain an encrypted constellation point diagram;

the up-sampling part comprises the following steps: inserting numerical values after the constellation point coordinates, wherein the numerical value of N is the number of the inserted numerical values;

the shaping and filtering steps are as follows: the coordinates of two dimensions of the data after up-sampling are respectively sent to two filters which are orthogonal with each other for shaping and filtering, and then two paths of signals are combined by an adding unit and finally sent to an Arrayed Waveguide Grating (AWG);

in the step of receiving end, the process of deciphering and demodulating electric signal includes inverse DSP flow, the inverse DSP flow is composed of matched filter part, down sampling part and constellation demapping part, each part is corresponding to DSP flow and has opposite action.

6. The OAM transmission method for security enhancement and turbulence mitigation as recited in claim 3, wherein: in the transmission process step, a crosstalk threshold value at each measurement is given to the controller (25), and the particle swarm optimization PSO is applied to optimize the graphs of the first two planes of the phase plane (21) so as to correct the wave front of the distorted light beam in consideration of the crosstalk at each measurement.

Technical Field

The invention relates to an optical transmission technology in the technical field of communication, in particular to an OAM transmission device and method for enhancing safety and relieving turbulence.

Background

In the multimedia and big data era of the current high-speed development, along with the emergence of the emerging fields of big data, artificial intelligence, internet of things and the like, high speed, low energy consumption, intellectualization and security are inevitable trends of the future communication technology development. The increasing and popularizing of information transmission media such as video conference, network live broadcast, remote education and the like and the continuous and rapid increase of communication service volume and user number lead to the frequent and urgent need of traditional radio frequency RF resources, and the development of high-capacity and high-safety information transmission modes is urgent. Free space optical communication FSO technology has recently been widely studied worldwide because of its advantages such as high electromagnetic interference resistance, good security, and low manufacturing cost.

However, atmospheric turbulence can severely affect the performance of free-space optical communication systems, which can cause absorption scattering, beam spreading, drift, phase distortion, etc. of the transmitted vortex beam. Atmospheric turbulence, i.e., the movement of gas molecules in the atmosphere, temperature fluctuations, pressure variations, etc., can cause the refractive index of atmospheric channels to randomly change. In fact, some laser beams carry not only spin angular momentum, but also orbital angular momentum, OAM. In recent years, the introduction of a vortex beam with orbital angular momentum into an FSO system has been one of the hot spots of research. Due to the special spatial distribution characteristic of vortex light, vortex optical rotation light waves are dispersed by atmospheric turbulence, an OAM mode carried by the vortex light is diffused to an adjacent OAM state, so that crosstalk occurs between the OAM modes, and when the received light power is low, a light beam is distorted, and thus an error code occurs in a system. Therefore, it is of great significance to study and overcome the influence of atmospheric turbulence on high-order free-space coherent optical communications. In recent years, with the development of multimedia technology, a lot of information is publicly spread on the internet, but some sensitive information is not encrypted in the spreading process. Therefore, protection of information from unauthorized access during dissemination has attracted increasing attention during the last 20 years. However, in the current research, there are few directions for both improving safety and reducing the effect of turbulence. Designing a transmission method that both improves safety and mitigates the effects of turbulence has become a hot issue in many areas of research.

Disclosure of Invention

An object of the present invention is to provide an OAM transmission apparatus and method with enhanced security and turbulence mitigation, in order to solve the problems mentioned in the background art.

In order to achieve the technical purpose, the technical scheme adopted by the invention is as follows:

an OAM transmission device with enhanced security and turbulence mitigation, wherein: comprises a sending end structure, an MPLC system and a receiving end structure, wherein the sending end structure is used for encrypting and modulating user data to form an OAM light beam, the OAM beam after passing through the atmospheric turbulence zone enters an MPLC system, the MPLC system includes a plurality of phase planes having different phase patterns, mirrors, collimators, a feedback loop, and a controller, the OAM beam affected by the turbulence is reflected back and forth between the phase planes and the mirrors to spatially separate the OAM beam, and inclined at different angles, coupled by a collimator, and then enters a receiving end structure, a feedback loop is connected on a connecting channel between the MPLC system and the receiving end structure, crosstalk between the separated light beams is monitored, a controller can receive signals of the feedback loop and adjust at least one phase mode of a phase plane, the wave front of the distorted light beam is corrected, the crosstalk degree is reduced, and the receiving end structure can implement the inverse process of the encryption and modulation of the transmitting end structure.

The further optimization scheme of the invention is as follows:

the phase plane described above has six different phase modes.

A transmission method of an OAM transmission apparatus with enhanced security and turbulence mitigation, comprising the steps of:

a. a sending end step: distributing user data to channels with different optical wavelengths simultaneously, encrypting the data by an optical switch under the control of a frequency hopping sequence, further transmitting the encrypted data by randomly distributed channels with different OAM states, generating the frequency hopping sequence by a Chua's chaotic model, modulating binary data to be transmitted in a DSP flow, carrying out electro-optical modulation on the binary data and an optical signal in a Mach-Zehnder modulator MZM after modulation and constellation encryption are carried out on the binary data, accessing the modulated signal to an OAM generator, and modulating the data to an OAM light beam;

b. the transmission process comprises the following steps: the OAM light beam is incident on the simulated turbulence plate, the vortex light beam influenced by turbulence enters the MPLC system, the MPLC system receives a signal of a feedback loop by using a controller, adjusts the phase mode of a phase plane, performs turbulence mitigation and mode de-multiplexing on the light beam,

c. a receiving end step: vortex light carrying information is decomposed and multiplexed to be changed into a Gaussian beam, the Gaussian beam is converted into an electric signal by a photoelectric detector, and then the electric signal is subjected to decryption and demodulation opposite to the encryption and modulation of a sending end to obtain decrypted data.

The specific method for encrypting data by the optical switch under the control of the frequency hopping sequence comprises the following steps:

an NxN optical switch selector is adopted to encrypt the physical layer, a chaos sequence generated by a Chua model is used as a key, and a recursive frequency hopping method is adopted: LDi → MZMi; LDi → MZMi + 1; ③ LDi → MZMi + 2; … …, respectively; wherein the equation for the Chua model is:

whereinIs a constant value, and is characterized in that,are variables.

The DSP flow is divided into three steps: a constellation mapping step, an up-sampling step and a shaping filtering step;

the constellation mapping step is as follows: adopting a 16QAM constellation diagram, using a Chua model as chaotic mapping to generate a masking vector, and masking 16QAM constellation points to obtain an encrypted constellation point diagram;

the up-sampling part comprises the following steps: inserting numerical values after the constellation point coordinates, wherein the numerical value of N is the number of the inserted numerical values;

the shaping and filtering steps are as follows: the coordinates of two dimensions of the data after up-sampling are respectively sent to two filters which are orthogonal with each other for shaping and filtering, and then two paths of signals are combined by an adding unit and finally sent to an Arrayed Waveguide Grating (AWG);

in the step of receiving end, the process of deciphering and demodulating electric signal includes inverse DSP flow, the inverse DSP flow is composed of matched filter part, down sampling part and constellation demapping part, each part is corresponding to DSP flow and has opposite action.

In the transmission process, a crosstalk threshold value of the controller (25) during each measurement is given, crosstalk during each measurement is considered, a Particle Swarm Optimization (PSO) is applied to optimize graphs of the first two planes of the phase plane to correct the wavefront of a distorted beam, the first two graphs are defined as a particle of the PSO, the particle can be continuously adjusted according to the optimal position and the global extreme value during operation, then the optimal solution is obtained, and Mean Square Error (MSE) is used as a fitness function of the particle. To measure the crosstalk matrix between the two channels, the mode on the transmitter side would be switched between ℓ =0 and + 1. After the MPLC mode is optimized, signals carried by the two transmitting OAMs are received and detected with low crosstalk.

The OAM transmission method for enhancing safety and relieving turbulence has the following advantages:

1. by utilizing the MPLC system, crosstalk information among signals influenced by atmospheric turbulence is obtained in time through a feedback loop, and the phase mode of a phase plane is adjusted by utilizing a controller so as to correct the wave front of a distorted light beam and effectively reduce the crosstalk problem caused by the turbulence.

2. A turbulent flow relieving frequency hopping system based on OAM multiplexing is realized by using an optical switch and a multi-plane optical converter. When data is transmitted in a physical layer, encryption processing is sequentially carried out in two stages of optical frequency hopping and constellation modulation, and the safety of user data transmission is effectively improved. Therefore, on one hand, the influence of atmospheric turbulence on high-order free space coherent optical communication is effectively overcome, and the OAM multiplexing technology is realized; on the other hand, new safety encryption is introduced to the traditional optical frequency hopping system based on wavelength or polarization, the capacity of a space optical communication channel and the safety of a physical layer are improved simultaneously, and a new way is provided for exploring the communication safety of OAM multiplexing in free space optical communication.

Drawings

Fig. 1 is a flow diagram of an OAM transmission system with security enhancement and turbulence mitigation;

FIG. 2 is a flow chart of a DSP and inverse DSP system;

fig. 3 is a conventional 16QAM constellation;

fig. 4 is a constellation diagram after masking 16QAM constellation points;

FIG. 5 is a decrypted binary bit stream diagram;

fig. 6 is a flowchart of the MPLC system.

The label names in the figure: a transmitting end configuration 1, an MPLC system 2, a phase plane 21, a mirror 22, a collimator 23, a feedback loop 24, a controller 25, and a receiving end configuration 3.

Detailed Description

Embodiments of the present invention are described in further detail below with reference to the accompanying drawings.

In the OAM transmission method with enhanced security and turbulence mitigation according to this embodiment, a system flowchart is shown in fig. 1. The whole system can be divided into three parts, namely a sending end step, a transmission process step and a receiving end step.

a. A sending end step: distributing user data to channels with different optical wavelengths simultaneously, encrypting the data by an optical switch under the control of a frequency hopping sequence, further transmitting the encrypted data by randomly distributed channels with different OAM states, generating the frequency hopping sequence by a Chua's chaotic model, modulating binary data to be transmitted in a DSP flow, carrying out electro-optical modulation on the binary data and an optical signal in a Mach-Zehnder modulator MZM after modulation and constellation encryption are carried out on the binary data, accessing the modulated signal to an OAM generator, and modulating the data to an OAM light beam;

b. the transmission process comprises the following steps: the OAM light beam is incident on the simulated turbulence plate, the vortex light beam influenced by turbulence enters the MPLC system, the MPLC system receives a signal of a feedback loop by using a controller, adjusts the phase mode of a phase plane, performs turbulence mitigation and mode de-multiplexing on the light beam,

c. a receiving end step: vortex light carrying information is decomposed and multiplexed to be changed into a Gaussian beam, the Gaussian beam is converted into an electric signal by a photoelectric detector, and then the electric signal is subjected to decryption and demodulation opposite to the encryption and modulation of a sending end to obtain decrypted data.

The specific workflow of various aspects of the system is as follows:

detailed description of optical frequency hopping:

the patent adopts NXN optical switch selector to encrypt the physical layer, theoretically, if transmitting laser with N wavelengths, there can be N! The selection mode greatly improves the transmission safety. We use the chaos sequence generated by Chua model as the key to select different frequency hopping modes. We use the recursive frequency hopping method: phi LD_i→MZM_i ；②LD_i→MZM_i+1 ；③LD_i→MZM_i+2(ii) a … … are provided. Wherein the equation for the Chua model is:

whereinIs a constant value, and is characterized in that,are variables.

Details of the DSP flow:

the DSP and inverse DSP flow in the system is shown in FIG. 2:

the DSP flow can be divided into three parts: a constellation mapping part, an up-sampling part and a shaping filtering part.

(1) Constellation mapping section

The traditional 16QAM constellation diagram adopted in this patent is shown in fig. 3, and we use a Chua model as chaotic mapping to generate a masking vector, and mask 16QAM constellation points to obtain an encrypted constellation diagram shown in fig. 4.

(2) Upsampling section

In order to make the mapped signal decision-making above the shaping filtering, a N-fold upsampling is performed before entering the filter. And inserting numerical values after the coordinates of the constellation points, wherein the numerical value of N is the number of the inserted numerical values.

(3) Shaping filter part

The coordinate of two dimensionalities of the data after up sampling is respectively sent to two filters which are orthogonal with each other for shaping and filtering, and then two paths of signals are combined by an adding unit and finally sent to an Arrayed Waveguide Grating (AWG).

The inverse DSP flow is composed of a matched filter part, a down-sampling part and a constellation demapping part. Each portion of which corresponds and acts in reverse in the DSP flow. Fig. 5 is a constellation diagram of gaussian white noise after decryption.

MPLC system flow details:

in the MPLC system, the optical fiber branches encrypted in the first two steps are fed into a customized OAM generator to generate multiple OAM beams. And the OAM light beam is incident on the simulated turbulence plate at a distance of 1 m. The light beam affected by the turbulence is then projected onto a first plane of the spatial light modulator SLM, where it bounces between the mirror and the same SLM, through 6 different phase modes, after passing through a 6-plane MPLC, the two beams will be spatially separated and tilted at different angles. The two beams are then coupled to an array of optical fibers using collimators. After the two ports collect power, a feedback loop is designed to monitor the crosstalk between the two channels. Given the crosstalk at each measurement, a particle swarm algorithm is applied to update the patterns of the first two planes to correct the wavefront of the distorted beam.

The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention. It should be noted that modifications and embellishments within the scope of the invention may be made by those skilled in the art without departing from the principle of the invention.