Device and method for improving anti-noise performance of vortex optical multiplexing communication system

Abstract

The invention discloses a device and method for improving the anti-noise performance of a vortex optical multiplexing communication system, and the device comprises a signal transmitting module which loads a signal to signal light through an optical coupler, and achieves the decorrelation of two paths of signals through an optical fiber delay line. The vortex light multiplexing and demultiplexing module couples signal light to a free space, generates linearly polarized light through a Glan prism, generates left-handed and right-handed circularly polarized light through a wave plate, generates vortex light beams through a metasurface for coaxial multiplexing transmission, and a receiving end demultiplexes signals through the metasurface and recouples through an optical fiber-space coupler. And the multiple-input multiple-output diversity gain module is used for carrying out polarization conversion on the demultiplexed signal, carrying out electric signal conversion through a photoelectric detector, and finally carrying out signal equalization processing through a computer. According to the invention, the anti-interference capability is effectively improved, the signal transmission quality is improved, and the method has relatively strong anti-noise performance and higher communication sensitivity.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technology, and in particular to a device and method for improving the anti-noise performance of a vortex optical multiplexing communication system. Background Art

[0002] Vortex light has become an important research direction in large-capacity optical communication systems because it carries an infinite number of orthogonal orbital angular momentum modes. By utilizing the multimode multiplexing characteristics of vortex light, the transmission capacity of optical communication systems can be effectively improved. However, the transmission channel of vortex light (such as free space or multimode optical fiber) is often disturbed by atmospheric turbulence or multimode optical fiber mode dispersion, resulting in phase distortion of the vortex light beam, which in turn causes the signal power to decay. In severe cases, it may cause a sharp increase in the communication bit error rate or even communication interruption. Solving this problem is a key technical difficulty for the widespread application of vortex optical communication systems.

[0003] In order to solve the problem of vortex light phase distortion caused by atmospheric turbulence in free space, researchers in related fields have proposed several main solutions, including beam quality compensation, digital signal processing, optical domain signal enhancement and other technologies. Specifically, the existing technical solutions mainly include the following:

[0004] 1. Beam quality compensation method: This method mainly includes adaptive optics and optical neural network technology. Adaptive optics technology obtains prior information about atmospheric turbulence and compensates for the phase distortion of the signal, thereby reducing the impact of turbulent noise. The optical neural network solution does not need to detect the beam wavefront, but instead compensates for the phase distortion caused by turbulence by training the neural network model.

[0005] 2. Digital signal processing solution: This solution mainly uses the multiple-input multiple-output (MIMO) equalization method to compensate for signal fading and crosstalk through channel coding and matrix calculation, especially to solve the signal crosstalk problem caused by mode dispersion in multimode optical fiber. However, this method is often difficult to effectively deal with signal fading caused by atmospheric turbulence or long-distance propagation, and it is difficult to reduce the probability of communication interruption.

[0006] 3. Optical domain multimodal transmission scheme: By superimposing multiple vortex optical modes, the signal can achieve better transmission performance when affected by atmospheric turbulence or multimode fiber mode dispersion. This scheme can alleviate the power fading problem encountered in single-mode transmission and improve the reliability of the communication system. However, this method still faces the problem of channel crosstalk and lacks an optimal strategy for signal power allocation.

[0007] Although the above technical solutions have alleviated the interference problem in vortex optical communication to a certain extent, each technical solution still has certain limitations. For example, the adaptive optics solution is highly complex and expensive; the optical neural network requires a large number of training samples and is difficult to compensate in real time; and although the digital signal processing solution can handle mode crosstalk, it cannot effectively reduce the risk of signal fading; the multimodal transmission solution effectively alleviates the power fading problem, but the suppression effect of channel crosstalk is poor, and its power superposition strategy is not optimal. Therefore, it is urgent to propose a new solution to improve the performance of the vortex optical multiplexing system, especially in terms of anti-interference ability and signal fading control. Summary of the invention

[0008] In view of the defects of the prior art, the present invention provides a device and method for improving the anti-noise performance of a vortex optical multiplexing communication system.

[0009] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0010] A device for improving the anti-noise performance of a vortex optical multiplexing communication system, comprising:

[0011] The signal transmission module is used to load the QPSK-OFDM signal transmitted by the signal source onto the signal light, and after splitting by a 1×2 optical coupler, decorrelation of the two signals is achieved through an optical fiber delay line;

[0012] The vortex optical multiplexing, transmission and demultiplexing module is used to couple the signal light into free space, generate linearly polarized light using a Glan prism and generate left-handed circularly polarized light and right-handed circularly polarized light through a quarter-wave plate, generate vortex beams with topological charges of -2 and +2 through a metasurface with a quality factor of 1, and perform coaxial multiplexing transmission. The receiving end uses a metasurface for demultiplexing and recouples the signal through a fiber-space coupler.

[0013] The MIMO diversity gain module is used to input the demultiplexed signal into the polarization controller to perform polarization conversion on the signal, and convert the signal into an electrical signal through a photoelectric detector, and finally perform MIMO diversity gain equalization signal processing through a computer.

[0014] Furthermore, the MIMO diversity gain module is used to optimize the received signal by using a MIMO diversity gain equalization algorithm, wherein the MIMO diversity gain equalization algorithm uses a normal mode algorithm to perform diversity gain equalization processing on the received signal.

[0015] Furthermore, the MIMO diversity gain equalization algorithm optimizes channel weights by calculating the extreme value of the error vector amplitude of the received signal, and performs signal equalization by updating tap coefficients through a finite length filter.

[0016] Furthermore, the channel weight is calculated by the following formula:

[0017]

[0018] Where n is the number of channels, ω k is the channel weight, w k (m) is the channel matrix, x k (m) is the transmitted signal.

[0019] Furthermore, the MIMO diversity gain equalization algorithm performs adaptive channel equalization by updating the tap coefficients of the finite length filter, and the updating formula is as follows:

[0020]

[0021] Among them, w ij (m) is the tap coefficient of the filter, which represents the relationship between the received signal and the transmitted signal. The filter coefficient of the i-th row and j-th column at time step m, μ i is the iteration step length, e i is error control, is the conjugate value of the signal, y i is the received signal.

[0022] The present invention also discloses a method for improving the anti-noise performance of a vortex optical multiplexing communication system. The method is implemented based on the above device and comprises the following steps:

[0023] The QPSK-OFDM signal emitted by the signal source is loaded onto the signal light, and after being split by a 1×2 optical coupler, decorrelation processing of the two signals is realized by an optical fiber delay line;

[0024] The signal light is coupled into free space through a fiber-space coupler, linear polarized light is generated using a Glan prism, and left-handed circularly polarized light and right-handed circularly polarized light are generated through a quarter-wave plate;

[0025] The left-handed circularly polarized light and the right-handed circularly polarized light are respectively converted into vortex beams with topological charge numbers of -2 and +2 through the metasurface for coaxial multiplexing transmission.

[0026] At the receiving end, a metasurface with the same quality factor is used to demultiplex the multiplexed vortex light and restore it to two signal lights, and the signal light is recoupled into the optical fiber through a fiber-space coupler.

[0027] The two demultiplexed signals are input into the MIMO diversity gain module, and polarization conversion is performed through the polarization controller, photoelectric conversion is performed using the photodetector, and finally MIMO diversity gain equalization processing is performed through the computer.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] 1. The present invention effectively reduces the mode crosstalk and power fading caused by atmospheric turbulence or multimode fiber dispersion in the vortex optical multiplexing system through a multi-input multi-output diversity gain equalization algorithm, thereby improving the stability and reliability of the communication system.

[0030] 2. By introducing the diversity gain function, the present invention can achieve signal enhancement in multiple channels and effectively combat the vortex light phase distortion caused by atmospheric turbulence, thereby improving the system's robustness to free-space atmospheric turbulence noise or multimode fiber dispersion.

[0031] 3. The present invention can improve the communication sensitivity by 6dB to 10dB by optimizing signal processing and weight allocation, significantly improve the signal-to-noise ratio of the system, reduce the bit error rate, and improve the communication quality.

[0032] 4. The present invention is not only applicable to the phase distortion caused by free-space atmospheric turbulence, but can also be effectively applied to the mode dispersion problem in multi-mode optical fiber transmission, and is widely applicable to large-capacity optical communication systems, free-space optical communication and other optical communication systems.

[0033] 5. Through channel equalization processing of the MIMO system, the present invention realizes more efficient vortex optical multiplexing system transmission, reduces the probability of communication interruption, and improves the overall performance of the communication system. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural diagram of a device for improving the anti-noise performance of a vortex optical multiplexing communication system according to an embodiment of the present invention;

[0035] Figure 2 It is a flow chart of a method for improving the anti-noise performance of a vortex optical multiplexing communication system according to an embodiment of the present invention. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0037] The present invention provides a device for improving the anti-noise performance of a vortex optical multiplexing communication system, and the corresponding structure is as follows: Figure 1 shown.

[0038] In the signal transmission module, the 24Gbit / s QPSK-OFDM signal emitted by the signal source is loaded onto the signal light through intensity modulation. After the signal light is split by the 1×2 optical coupler, it passes through the optical fiber delay line to realize the decorrelation of the two signals. The two signals are data of the same sequence that are decorrelated in the time domain and are carried and transmitted by different vortex optical mode channels. In this way, both diversity gain research and multi-input multi-output equalization research can be realized at the receiving end, that is, two vortex optical mode channels are used to complete the multi-input multi-output diversity gain equalization verification work proposed in the present invention. The above realizes the generation of two optical signals carrying 24Gbit / s QPSK-OFDM signal data.

[0039] In the vortex light multiplexing, transmission, and demultiplexing module, a fiber-space coupler is used to couple the optical signal into free space, and a Glan prism is used to generate linearly polarized light. The angle between the linearly polarized light and the fast axis of the 1 / 4 wave plate is adjusted to +45° (or -45°) to generate left-handed circularly polarized light (or right-handed circularly polarized light), respectively. After the left-handed circularly polarized light and the right-handed circularly polarized light pass through the metasurface with a quality factor of 1, vortex beams with topological charges of -2 and +2 are generated, respectively. In this optical path system, a beam splitter / combiner is used to realize the coaxial multiplexing transmission of vortex beams with topological charges of -2 and +2. When the two multiplexed vortex beams are transmitted through the calculated atmospheric turbulence, the system uses a Glan prism to convert the circularly polarized vortex light into linearly polarized vortex light (usually the spatial light modulator only responds to linearly polarized beams), and then uses a 1 / 4 wave plate to convert the linearly polarized vortex light into circularly polarized vortex light. If the transmission channel is a multimode optical fiber, the above "circular polarization-linear polarization-circular polarization" conversion is not required. At the demultiplexing end of the vortex light, a beam splitter / combiner is first used to divide the optical path into two paths, and then the multiplexed vortex light is demultiplexed and restored using a metasurface with the same quality factor (the corresponding quality factor in this system device is 1). The two restored light beams both contain a Gaussian beam as the target signal light and a vortex beam of order 4 as the noise light. Two pairs of lens groups are introduced to aggregate the Gaussian light respectively, and at the same time, an aperture is used to filter out the noise vortex light of order 4, and the two signal lights are respectively coupled from free space to the optical fiber through a fiber-space coupler. The above realizes the multiplexing of two vortex light beams, transmission in a turbulent channel (or multimode optical fiber), demultiplexing and other optical paths.

[0040] In the MIMO diversity gain module, the two demultiplexed signal lights are input into a polarization controller respectively, so that the signal light is converted from circular polarization to linear polarization to improve the response efficiency of the photodetector. After the signal light undergoes photoelectric conversion by the photodetector, the electrical signal is input into a real-time oscilloscope to complete diversity reception. Finally, the MIMO diversity gain equalization signal processing is performed on a computer.

[0041] Based on the theory of MIMO diversity gain equalization, the formula is derived. The implementation of this algorithm is mainly based on the normal mode algorithm. The time domain form y(m) of the receiving end signal m can be written as the following formula (1):

[0042] y(m)=w(m)*x(m) (1)

[0043] Among them, m is the name of the vortex optical channel corresponding to different modes, x(m) is the transmitter signal before transmission through the channel, w(m) is the channel matrix, and * is the convolution operator symbol. Affected by atmospheric turbulence or power fading caused by multimode optical fiber, that is, the channel matrix w(m) undergoes random changes, causing the receiving end signal y(m) to deviate from the target value, reducing communication performance and even causing communication interruption.

[0044] In order to solve the problem of signal fading, the present invention first incorporates the diversity gain function into the algorithm. After the diversity gain equalization, the received signal y n (m) can be expressed as:

[0045]

[0046] In formula (2), n represents the number of vortex light channels used for diversity gain, k is the subscript of the channel used to achieve diversity, and ω k is the weight of the corresponding channel table k, channel weight ω k It is calculated by evaluating the extreme value of the error vector amplitude. The above achieves the diversity gain of the vortex optical mode channel.

[0047] Updating the tap coefficients of a finite-length filter based on a constant-mode algorithm The invention integrates a multi-input multi-output equalization algorithm into the diversity gain algorithm, where the coefficients The subscript ij represents the tap coefficient of finite length filter i in finite length filter j, and the corresponding coefficient update formula can be written as formula (3):

[0048]

[0049] In formula (3), μ i is the iteration step length that makes the formula converge, which is usually adjustable for different mode channels; i =|y n (m)| 2 -p r is the error control equation of adaptive channel equalization; p r It is the normalized reference power of the QPSK-OFDM signal.

[0050] In order to alleviate the mode crosstalk and power fading in the vortex optical multiplexing system, the working process of the multi-input multi-output diversity gain strategy in the present invention is described as follows: Figure 2 As shown. First, the QPSK-OFDM signal emitted by the signal source is loaded onto the light wave through intensity modulation. After the optical signal is split into two paths, one of the paths is delayed using a short-distance optical fiber to achieve decorrelation of the two signals, and then further loaded onto the vortex light with topological charges of +2 and -2. If the two vortex light modes carry the same signal, it is vortex light multiplexing; if the vortex light carries different signals, it is vortex light emission diversity. After the two vortex light signals of coaxial transmission (multiplexing / diversity) are transmitted through the atmospheric turbulence / multimode optical fiber channel, they are affected by mode crosstalk and power fading, and the system performance is seriously deteriorated. The two demultiplexed vortex lights are directly detected and demodulated, and then the received signal x 信号1 With signal x 信号2 Input the MIMO diversity gain equalization system for processing. First, the optimal solution of the channel weight is searched by solving the error vector amplitude extreme value of the signal after the two-way signal gain, and the gain signal x is obtained. 信号 . Further, the received signal x 信号2 With the gain signal x 信号 2×2 multiple-input multiple-output equalization is performed, and finally the multiple-input multiple-output diversity gain equalization of the received signal is completed, realizing the alleviation of mode crosstalk and power fading in the vortex optical multiplexing communication system.

[0051] The above results show that the present invention can be used to improve the anti-noise performance of vortex optical multiplexing communication systems.

[0052] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. A device for improving the anti-noise performance of a vortex optical multiplexing communication system, characterized in that: include: The signal transmission module is used to load the QPSK-OFDM signal transmitted by the signal source onto the signal light, and after splitting by a 1×2 optical coupler, decorrelation of the two signals is achieved through an optical fiber delay line; The vortex optical multiplexing, transmission and demultiplexing module is used to couple the signal light into free space, generate linearly polarized light using a Glan prism and generate left-handed circularly polarized light and right-handed circularly polarized light through a quarter-wave plate, generate vortex beams with topological charges of -2 and +2 through a metasurface with a quality factor of 1, and perform coaxial multiplexing transmission. The receiving end uses a metasurface for demultiplexing and recouples the signal through a fiber-space coupler. The MIMO diversity gain module is used to input the demultiplexed signal into the polarization controller to perform polarization conversion on the signal, and convert the signal into an electrical signal through a photoelectric detector, and finally perform MIMO diversity gain equalization signal processing through a computer.

2. The device according to claim 1, characterized in that: The MIMO diversity gain module is used to optimize the received signal through a MIMO diversity gain equalization algorithm, wherein the MIMO diversity gain equalization algorithm uses a normal mode algorithm to perform diversity gain equalization processing on the received signal.

3. The device according to claim 2, characterized in that: The MIMO diversity gain equalization algorithm optimizes channel weights by calculating the extreme value of the error vector amplitude of the received signal, and performs signal equalization by updating tap coefficients through a finite length filter.

4. The device according to claim 3, characterized in that: The channel weight is calculated by the following formula: Where n is the number of channels, ω k is the channel weight, w k (m) is the channel matrix, x k (m) is the transmitted signal.

5. The device according to claim 1, characterized in that: The MIMO diversity gain equalization algorithm performs adaptive channel equalization by updating the tap coefficients of the finite length filter. The update formula is as follows: Among them, w ij (m) is the tap coefficient of the filter, which represents the relationship between the receiving signal and the transmitted signal. The filter coefficient of the i-th row and j-th column at time step m, μ i is the iteration step length, e i is error control, is the conjugate value of the signal, y i is the received signal.

6. A method for improving the anti-noise performance of a vortex optical multiplexing communication system, characterized in that: The method is implemented based on the device according to any one of claims 1 to 5, and comprises the following steps: The QPSK-OFDM signal emitted by the signal source is loaded onto the signal light, and after being split by a 1×2 optical coupler, decorrelation processing of the two signals is realized by an optical fiber delay line; The signal light is coupled into free space through a fiber-space coupler, linear polarized light is generated using a Glan prism, and left-handed circularly polarized light and right-handed circularly polarized light are generated through a quarter-wave plate; The left-handed circularly polarized light and the right-handed circularly polarized light are respectively converted into vortex beams with topological charge numbers of -2 and +2 through the metasurface for coaxial multiplexing transmission. At the receiving end, a metasurface with the same quality factor is used to demultiplex the multiplexed vortex light and restore it to two signal lights, and the signal light is recoupled into the optical fiber through a fiber-space coupler. The two demultiplexed signals are input into the MIMO diversity gain module, and polarization conversion is performed through the polarization controller, photoelectric conversion is performed using the photodetector, and finally MIMO diversity gain equalization processing is performed through the computer.

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