Free space laser communication system and method based on dynamic optical matched filtering

Abstract

The present application relates to a free space laser communication system and method based on dynamic optical matching filtering, the system comprising: a transmitting end, for providing a coherent pulse signal, loading communication information onto the coherent pulse signal, and outputting the coherent pulse signal carrying the communication information to a transmission optical path; a receiving end, comprising: a coherent receiving unit, for coherently detecting the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulating the distorted pulse signal and the target communication signal, sending the distorted pulse signal to the dynamic filtering unit, and outputting the target communication signal to the application end; a dynamic filtering unit, for demodulating the distorted pulse signal to obtain an error signal, and performing phase and amplitude modulation on a reference pulse signal with the same frequency as the coherent pulse signal according to the error signal to obtain a new local oscillator pulse signal. The present application can reduce the influence of atmospheric turbulence on the carrier signal, and at the same time improve the real-time performance of the distortion of the supplementary signal.

Description

Technical Field

[0001] The present application relates to the field of satellite laser communication technology, and in particular to a free-space laser communication system and method based on dynamic optical matching filtering. Background Art

[0002] Laser satellite communication uses optical frequency as a carrier wave, which can send and receive massive amounts of data. At the same time, laser communication has the characteristics of low power consumption and high efficiency, and the transmission speed is one order of magnitude higher than microwave communication. With the support of quantum technology, laser satellite communication is also safer than radio communication, so this technology has attracted the attention of many research and security agencies. Among them, the establishment and implementation of laser links between satellites and the ground is an important link in realizing laser communication networks. Unlike the mutual communication between satellites, the communication link between satellites and the ground exists in a complex atmospheric environment. It not only faces the influence of the stratosphere, atmospheric circulation, and various cloud groups, but also faces the disturbance of atmospheric turbulence, resulting in the polarization state, laser intensity, and beam distribution. Constantly changing with the increase of transmission distance. At the receiving end, it is reflected as irregular "flickering" of laser polarization, spatial distribution, and signal intensity. Therefore, reducing the influence of laser parameters with atmospheric turbulence is crucial to building reliable free-space optical links.

[0003] Under the existing technical framework, pre-compensation technical solutions represented by adaptive optics technology, such as maximum ratio combining, multi-plane light conversion, wavefront sensing and adaptive correction, have been applied in satellite-to-ground laser communications. These pre-compensation adaptive optics technologies first require the receiving end of the ground laser base station to use a wavefront sensor to analyze the phase distortion of the transmitted signal. Then, in the transmitting system of the ground station, a deformable mirror or spatial light modulator is introduced to perform pre-distortion compensation on the wavefront transmitted from the ground to the satellite. Although this pre-compensation scheme can ensure the integrity of communication in a static environment, for complex environments, it is not reasonable to assume that the uplink and downlink are reciprocal. The wavefront sensor is usually located at the receiver end, and when the signal is transmitted to the transmitter, a delay is inevitably generated, resulting in poor real-time compensation. Summary of the invention

[0004] Based on the above description, the present application provides a free-space laser communication system and method based on dynamic optical matching filtering to reduce the influence of atmospheric turbulence on laser parameters and improve the real-time performance of laser parameter compensation.

[0005] According to a first aspect, the present application provides a free-space laser communication system based on dynamic optical matched filtering, comprising: a transmitting end, a transmission optical path, and a receiving end;

[0006] The transmitting end is used to provide the coherent pulse signal required for laser communication, load the communication information onto the coherent pulse signal, and output the coherent pulse signal carrying the communication information to the transmission optical path;

[0007] A receiving end, comprising a coherent receiving unit and a dynamic filtering unit;

[0008] A coherent receiving unit, used to perform coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulate the distorted pulse signal and the target communication signal, send the distorted pulse signal to the dynamic filtering unit, and output the target communication signal to the application end;

[0009] A dynamic filtering unit is used to demodulate the distorted pulse signal to obtain an error signal, modulate the phase and amplitude of the reference pulse signal according to the error signal, obtain the modulated reference pulse signal and use it as a new local oscillator pulse signal; the frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

[0010] In one or more embodiments, the transmitting end includes an ultrashort pulse source and a communication modulation unit;

[0011] The ultrashort pulse source is used to provide a coherent pulse signal required for laser communication and is input into the communication modulation unit so that the communication modulation unit modulates the coherent pulse signal to obtain a coherent pulse signal carrying communication information and inputs it into the transmission optical path.

[0012] In one or more embodiments, the ultrashort pulse source includes a first ultrashort pulse laser and an ultrashort pulse frequency controller;

[0013] The ultrashort pulse frequency controller is used to control the repetition frequency of the pulse output by the first ultrashort pulse laser to be synchronized with the main clock frequency of the communication system, so that the first ultrashort pulse laser outputs the coherent pulse signal to the communication modulation unit.

[0014] In one or more embodiments, the communication modulation unit includes a first comb filter, a spectrum encoder, an IQ modulator, and a digital signal processor;

[0015] The first comb filter is used to filter out the key frequency teeth of the coherent pulse signal according to a preset frequency interval, obtain the filtered coherent pulse signal and output it to the spectrum encoder;

[0016] The spectrum encoder is used to adjust the phase and intensity of the filtered coherent pulse signal according to a preset spectrum bandwidth, obtain the adjusted coherent pulse signal and transmit it to the IQ modulator;

[0017] The IQ modulator is used to obtain the communication information generated by the digital signal processor, load the communication information into the adjusted coherent pulse signal, obtain the coherent pulse signal carrying the communication information and output it to the transmission optical path.

[0018] In one or more embodiments, the communication modulation unit also includes an optical fiber amplifier, which is connected between the IQ modulator and the transmission optical path, so that the IQ modulator outputs the coherent pulse signal carrying communication information to the optical fiber amplifier, and the optical fiber amplifier amplifies the coherent pulse signal carrying communication information and outputs it to the transmission optical path.

[0019] In one or more embodiments, the coherent receiving unit includes an optical beam splitter, a polarization beam splitter, a coherent mixer, a balanced detector, and a signal demodulator;

[0020] The optical beam splitter is used to split the distorted pulse signal according to the channel requirements of the coherent mixer to obtain two split pulse signals, and input each of the split pulse signals into an input channel corresponding to the coherent mixer;

[0021] The polarization beam splitter is used to split the local oscillator pulse signal according to a preset polarization state to obtain two polarized pulse signals, and input each of the polarized pulse signals into another input channel corresponding to the coherent mixer;

[0022] The coherent mixer is used to separate the received split beam pulse signal and polarized pulse signal into two groups of optical signals according to in-phase and orthogonal phase relationships, and inject each group of optical signals into a balanced detector;

[0023] The balanced detector is used to perform differential processing on each group of optical signals to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal serves as a distorted pulse signal;

[0024] The signal demodulator is used to demodulate the orthogonal component signal to obtain the target communication signal.

[0025] In one or more embodiments, the dynamic filtering unit includes a phase-locked controller, a second ultrashort pulse laser, a second comb filter, and a spectral phase modulator;

[0026] The phase-locked controller is used to compare the frequency of the distorted pulse signal with the frequency of the coherent pulse signal to extract a synchronization signal and an error signal, and output the synchronization signal to the second ultrashort pulse laser, and output the error signal to the spectral phase modulator;

[0027] The second ultrashort pulse laser is used to synchronize the repetition frequency of the pulses output by the second ultrashort pulse laser with the master clock frequency of the communication system based on the synchronization signal, and output a reference pulse signal;

[0028] The second comb filter is used to filter out the key frequency teeth of the reference pulse signal according to a preset frequency interval to obtain a filtered reference pulse signal;

[0029] The spectrum phase modulator is used to perform phase and amplitude modulation on the filtered reference pulse signal according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

[0030] According to a second aspect, the present application provides a communication method of a free-space laser communication system based on dynamic optical matched filtering according to any one of the aforementioned embodiments, comprising:

[0031] The transmitting end provides the coherent pulse signal required for laser communication, loads the communication information onto the coherent pulse signal, and outputs the coherent pulse signal carrying the communication information to the transmission optical path;

[0032] The coherent receiving unit at the receiving end performs coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulates the distorted pulse signal and the target communication signal, sends the distorted pulse signal to the dynamic filtering unit, and outputs the target communication signal to the application end;

[0033] The distorted pulse signal is demodulated by a dynamic filtering unit to obtain an error signal, and the phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal; the frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

[0034] In one or more embodiments, the coherent receiving unit includes an optical beam splitter, a polarization beam splitter, a coherent mixer, a balanced detector, and a signal demodulator;

[0035] The coherent receiving unit at the receiving end performs coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulates the distorted pulse signal and the target communication signal, including:

[0036] Splitting the distorted pulse signal according to the channel requirement of the coherent mixer through the optical beam splitter to obtain two split pulse signals, and inputting each of the split pulse signals to a receiving end corresponding to the coherent mixer;

[0037] Splitting the local oscillator pulse signal according to a preset polarization state through the polarization beam splitter to obtain two polarized pulse signals, and inputting each of the polarized pulse signals into an input channel corresponding to the coherent mixer;

[0038] The coherent mixer is used to separate the received split beam pulse signal and polarized pulse signal into two groups of optical signals according to in-phase and orthogonal phase relationships, and each group of optical signals is injected into a balanced detector;

[0039] Performing differential processing on each group of optical signals through the balanced detector to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal is used as a distorted pulse signal;

[0040] The orthogonal component signal is demodulated by the signal demodulator to obtain the target communication signal.

[0041] In one or more embodiments, the dynamic filtering unit includes a phase-locked controller, a second ultrashort pulse laser, a second comb filter, and a spectral phase modulator;

[0042] The distorted pulse signal is demodulated by a dynamic filtering unit to obtain an error signal, and the phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal, including:

[0043] The frequency of the distorted pulse signal is compared with the frequency of the coherent pulse signal by the phase-locked controller to extract a synchronization signal and an error signal, and the synchronization signal is output to the second ultrashort pulse laser, and the error signal is output to the spectral phase modulator;

[0044] Based on the synchronization signal, the repetition frequency of the pulse output by the second ultrashort pulse laser is synchronized with the master clock frequency of the communication system, and a reference pulse signal is output through the second ultrashort pulse laser;

[0045] Filtering out the key frequency teeth of the reference pulse signal according to a preset frequency interval by a second comb filter to obtain a filtered reference pulse signal;

[0046] The filtered reference pulse signal is phase- and amplitude-modulated by a spectrum phase modulator according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

[0047] Compared with the prior art, the technical solution of this application has the following beneficial technical effects:

[0048] In the above-mentioned free-space laser communication system and method based on dynamic optical matching filtering, the coherent receiving unit at the receiving end compares the frequencies of the distorted pulse signal and the coherent pulse signal, extracts the error signal from the distorted pulse signal, modulates the phase and amplitude of the reference pulse signal according to the error signal, obtains the modulated reference pulse signal and uses it as a new local oscillator pulse signal, and outputs the new local oscillator pulse signal to the coherent receiving unit to adjust the phase and amplitude of each communication frequency in the output signal of the transmission optical path, corrects the influence of atmospheric turbulence in real time, and the dynamic filtering unit performs closed tracking of the output signal of the transmission optical path through the local oscillator pulse signal until the target communication signal achieves the preset high signal-to-noise ratio and low bit error rate. In this way, the delay problem caused by the traditional pre-compensation technical solution can be avoided, and the real-time performance of correcting signal distortion can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A principle block diagram of a free-space laser communication system based on dynamic optical matched filtering provided in an embodiment of the present application;

[0050] Figure 2 for Figure 1 The principle block diagram of the transmitter;

[0051] Figure 3 for Figure 1 Schematic diagram of the receiving end.

[0052] Description of reference numerals:

[0053] Communication system 100;

[0054] Transmitting end 10, ultrashort pulse source 11, first ultrashort pulse laser 111, ultrashort pulse frequency controller 112, communication modulation unit 12, first comb filter 121, spectrum encoder 122, IQ modulator 123, digital signal processor 124, optical fiber amplifier 125;

[0055] Transmission optical path 20;

[0056] Receiver 30;

[0057] Coherent receiving unit 31, optical beam splitter 311, polarization beam splitter 312, coherent mixer 313, balanced detector 314, signal demodulator 315;

[0058] Dynamic filtering unit 32 , phase-locked controller 321 , second ultrashort pulse laser 322 , second comb filter 323 , spectral phase modulator 324 . DETAILED DESCRIPTION

[0059] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0061] It should be noted that when an element is considered to be "connected" to another element, it can be directly connected to the other element, or connected to the other element through an intermediate element. The "connection" in the following embodiments should be understood as "electrical connection", "communication connection", etc. if the connected circuits, units, units, etc. have electrical signals or data transmission between each other.

[0062] See also Figure 1 , Figure 1 The principle block diagram of a free-space laser communication system based on dynamic optical matched filtering provided by an embodiment of the present application is shown. A free-space laser communication system 100 based on dynamic optical matched filtering provided by an embodiment of the present application includes: a transmitting end 10, a transmission optical path 20 and a receiving end 30. The transmitting end 10 is used to provide a coherent pulse signal required for laser communication, load communication information onto the coherent pulse signal, and output the coherent pulse signal carrying the communication information to the transmission optical path 20. The receiving end 30 includes a coherent receiving unit 31 and a dynamic filtering unit 32. The coherent receiving unit 31 is used to perform coherent detection on the output signal of the transmission optical path 20 according to the local oscillator pulse signal generated by the dynamic filtering unit 32, and demodulate the distorted pulse signal and the target communication signal, send the distorted pulse signal to the dynamic filtering unit 32, and output the target communication signal to the application end. The dynamic filtering unit 32 is used to demodulate the distorted pulse signal to obtain an error signal, modulate the phase and amplitude of the reference pulse signal according to the error signal, obtain the modulated reference pulse signal and use it as a new local oscillator pulse signal. The frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

[0063] It should be noted that the transmitting end 10, the transmission optical path 20 and the receiving end 30 are connected in communication in sequence. The receiving end 30 includes a coherent receiving unit 31 and a dynamic filtering unit 32. The coherent receiving unit 31 and the dynamic filtering unit 32 are connected in communication with each other.

[0064] Both the transmitting end 10 and the receiving end 30 are provided with an ultrashort pulse laser, and the ultrashort pulse laser of the receiving end 30 and the ultrashort pulse laser of the transmitting end 10 operate synchronously to generate corresponding reference pulse signals and coherent pulse signals. The frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal. In this way, the frequency of the local oscillator pulse signal is the same as the frequency of the coherent pulse signal, which is used to realize coherent detection.

[0065] Specifically, the coherent pulse signal carrying the communication information is transmitted in the atmosphere. During the transmission process, the coherent pulse signal carrying the communication information is affected by the atmospheric turbulence, and the frequency domain and polarization state change. The coherent pulse signal carrying the communication information output by the transmission optical path 20 is received by the coherent receiving unit 31, and the coherent receiving unit 31 uses the local oscillator pulse signal with the same frequency as the coherent pulse signal for coherent detection and demodulation. The local oscillator pulse signal is generated by the dynamic filtering unit 32.

[0066] The output signal of the coherent receiving unit 31 includes two types, one is a digital signal, that is, the target communication signal, and the other is a low-frequency analog signal, which represents the change signal generated by the coherent pulse signal under the influence of atmospheric turbulence, that is, the distorted pulse signal. The distorted pulse signal is input into the dynamic filtering unit 32, and the frequency of the distorted pulse signal and the coherent pulse signal are compared, and the error signal is extracted from the distorted pulse signal. The phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain the modulated reference pulse signal and use it as a new local oscillator pulse signal, and the new local oscillator pulse signal is output to the coherent receiving unit 31 to adjust the phase and amplitude of each communication frequency in the output signal of the transmission optical path 20, and correct the influence of atmospheric turbulence in real time. The dynamic filtering unit 32 performs closed tracking on the output signal of the transmission optical path 20 through the local oscillator pulse signal until the target communication signal achieves the preset high signal-to-noise ratio and low bit error rate. In this way, the delay problem caused by the traditional pre-compensation technical solution can be avoided, and the real-time performance of the correction signal distortion can be effectively improved.

[0067] Continue reading Figure 1 , and combined with Figure 2 , Figure 2 Shows Figure 1 The principle block diagram of the transmitter.

[0068] In some embodiments, the transmitting end 10 includes an ultrashort pulse source 11 and a communication modulation unit 12. The ultrashort pulse source 11 is used to provide a coherent pulse signal required for laser communication, and input it to the communication modulation unit 12, so that the communication modulation unit 12 modulates the coherent pulse signal to obtain a coherent pulse signal carrying communication information and input it to the transmission optical path 20.

[0069] Specifically, the output end of the ultrashort pulse source 11 is connected to the input end of the communication modulation unit 12, and the output end of the communication modulation unit 12 is connected to the input end of the transmission optical path 20. The ultrashort pulse source 11 and the communication modulation unit 12 constitute the transmitting end 10 of the communication system 100. The ultrashort pulse source 11 provides a coherent pulse signal required for laser communication, which is input into the communication modulation unit 12, and the frequency domain distribution and the communication channel are encoded and modulated to meet the requirements of laser communication, and carry communication information.

[0070] Continue reading Figure 2 In some embodiments, the ultrashort pulse source 11 includes a first ultrashort pulse laser 111 and an ultrashort pulse frequency controller 112. The ultrashort pulse frequency controller 112 is used to control the repetition frequency of the pulse output by the first ultrashort pulse laser 111 to be synchronized with the master clock frequency of the communication system 100, so that the first ultrashort pulse laser 111 outputs a coherent pulse signal to the communication modulation unit 12.

[0071] Specifically, the output end of the ultrashort pulse frequency controller 112 is electrically connected to the input end of the first ultrashort pulse laser 111, and the output end of the ultrashort pulse laser is electrically connected to the communication modulation unit 12. The first ultrashort pulse laser 111 can provide optical signals covering various communication frequency points of the laser communication band, which are represented as equally spaced frequency teeth in the frequency domain; the ultrashort pulse frequency controller 112 can control the repetition frequency of the output pulse of the first ultrashort pulse laser 111 to be synchronized with the main clock frequency of the communication system 100, and the clock signal can be a radio frequency signal or an optical frequency signal.

[0072] Continue reading Figure 2 In some embodiments, the communication modulation unit 12 includes a first comb filter 121, a spectrum encoder 122, an IQ modulator 123 and a digital signal processor 124. The first comb filter 121 is used to filter out the key frequency teeth of the coherent pulse signal according to a preset frequency interval, obtain the filtered coherent pulse signal and output it to the spectrum encoder 122. The spectrum encoder 122 is used to adjust the phase and intensity of the filtered coherent pulse signal according to a preset spectrum bandwidth, obtain the adjusted coherent pulse signal and transmit it to the IQ modulator 123. The IQ modulator 123 is used to obtain the communication information generated by the digital signal processor 124, load the communication information into the adjusted coherent pulse signal, obtain the coherent pulse signal carrying the communication information and output it to the transmission optical path 20.

[0073] It should be noted that the output end of the first ultrashort pulse laser 111 is connected to the input end of the first comb filter 121, the first comb filter 121, the spectrum encoder 122, and the IQ modulator 123 are connected in sequence, and the output end of the digital signal processor 124 is connected to an input end of the IQ modulator 123. The first comb filter 121 can be an FP cavity composed of two mirrors, or a comb filter composed of a ring microcavity waveguide can be used. The spectrum encoder 122 can be a spatial light modulator, or a micromechanical filter reflector. The IQ modulator 123 can use a parallel electro-optical modulator, or use any electro-optical modulator whose optical path topology is consistent with this parallel structure.

[0074] Specifically, the first ultrashort pulse laser 111 outputs a coherent pulse signal to the first comb filter 121. The first comb filter 121 filters out the key frequency teeth of the coherent pulse signal according to the frequency interval required by the communication system 100, and the remaining frequency teeth represent noise signals, so that it is easy to filter out the noise signal. The first comb filter 121 outputs the filtered coherent pulse signal to the spectrum encoder 122. The spectrum encoder 122 adjusts the phase and intensity of the frequency tooth signal corresponding to each communication frequency in the filtered coherent pulse signal according to the spectrum bandwidth requirements required by the laser communication system 100. The spectrum encoder 122 transmits the adjusted coherent pulse signal to the IQ modulator 123. The IQ modulator 123, driven by the digital signal processor 124, loads the RF digital signal (i.e., the communication signal) onto the laser carrier frequency of the adjusted coherent pulse signal to obtain a coherent pulse signal carrying communication information.

[0075] Furthermore, the communication modulation unit 12 also includes an optical fiber amplifier 125, which is connected between the IQ modulator 123 and the transmission optical path 20, so that the IQ modulator 123 outputs a coherent pulse signal carrying communication information to the optical fiber amplifier 125, and the optical fiber amplifier 125 amplifies the coherent pulse signal carrying communication information and outputs it to the transmission optical path 20.

[0076] It should be noted that the output end of the IQ modulator 123 is connected to the input end of the optical fiber amplifier 125. Specifically, the IQ modulator 123 inputs the coherent pulse signal carrying the communication information into the optical fiber amplifier 125, and the optical fiber amplifier 125 amplifies the coherent pulse signal carrying the communication information and outputs it to the transmission optical path 20, so as to facilitate long-distance spatial transmission.

[0077] Continue reading Figure 1 and Figure 2 , and combined with Figure 3 , Figure 3 Shows Figure 1 Schematic diagram of the receiving end.

[0078] In some embodiments, the coherent receiving unit 31 includes an optical beam splitter 311, a polarization beam splitter 312, a coherent mixer 313, a balanced detector 314 and a signal demodulator 315. The optical beam splitter 311 is used to split the distorted pulse signal according to the channel requirements of the coherent mixer 313 to obtain two split pulse signals, and input each split pulse signal to an input channel corresponding to the coherent mixer 313. The polarization beam splitter 312 is used to split the local oscillator pulse signal according to a preset polarization state to obtain two polarized pulse signals, and input each polarized pulse signal to another input channel corresponding to the coherent mixer 313. The coherent mixer 313 is used to separate the received split pulse signal and polarization pulse signal into two groups of optical signals according to the in-phase and orthogonal phase relationships, and inject each group of optical signals into a balanced detector 314. The balanced detector 314 is used to perform differential processing on each group of optical signals to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal is used as a distorted pulse signal. The signal demodulator 315 is used to demodulate the orthogonal component signal to obtain a target communication signal.

[0079] It should be noted that the coherent mixer 313 includes two beam splitters. The polarization beam splitter 312 can achieve 90-degree polarization. Two balanced detectors 314 are provided, and each balanced detector 314 includes two diodes and a differential amplifier. The signal demodulator 315 can use a digital signal processor. One output end of the optical beam splitter 311 is connected to an input channel of a beam splitter of the relevant mixer, and the other output end of the optical beam splitter 311 is connected to an input channel of another beam splitter of the coherent mixer 313. One output end of the polarization beam splitter 312 is connected to another input channel of a beam splitter of the coherent mixer 313, and the other output end of the polarization beam splitter 312 is connected to another input channel of another beam splitter of the coherent mixer 313. Each output channel of a beam splitter of the coherent mixer 313 is connected to the input end of each diode in a balanced detector 314, and each output channel of another beam splitter of the coherent mixer 313 is connected to the input end of each diode in another balanced detector 314. The output end of a balanced detector 314 is connected to a signal demodulator 315, which is used to output the orthogonal component signal to the signal demodulator 315, thereby demodulating the target communication signal. The output end of another balanced detector 314 is connected to a dynamic filtering unit 32, which is used to output the in-phase component signal (i.e., the distorted pulse signal) to the dynamic filtering unit 32. The closed-loop tracking feedback control process involved in this embodiment only uses the in-phase component signal, and the orthogonal component signal participates in the demodulation process and is used to demodulate the target communication signal. The target communication signal refers to a digital signal that has been corrected and carries communication information.

[0080] Specifically, the optical beam splitter 311 splits the distorted pulse signal according to the channel requirements of the coherent mixer 313 to obtain two split pulse signals, and inputs each split pulse signal into an input channel corresponding to a beam splitter of the coherent mixer 313. The polarization beam splitter 312 splits the local oscillator pulse signal according to the preset polarization state (90 degrees polarization) to obtain two polarized pulse signals, and inputs each polarized pulse signal into another input channel corresponding to a beam splitter of the coherent mixer 313, wherein one polarized pulse signal is delayed by π / 2 in phase compared to the other polarized pulse signal. Each beam splitter of the coherent mixer 313 receives a split pulse signal and a polarized pulse signal. The coherent mixer 313 separates the split pulse signals and polarized pulse signals received by the two beam splitters into two groups of optical signals according to the in-phase and orthogonal phase relationships, and each group of optical signals includes two optical signals with different energy intensities. In this way, the coherent mixer 313 outputs four optical signals with different energy intensities, and each beam splitter outputs two optical signals with different energy intensities. Further, each optical signal outputted by each beam splitter of the coherent mixer 313 is injected into a diode corresponding to a balanced detector 314. Among the two balanced detectors 314, one balanced detector 314 performs differential processing on the two optical signals outputted by one beam splitter corresponding to the coherent mixer 313 to obtain an in-phase component signal, and the other balanced detector 314 performs differential processing on the two optical signals outputted by the other beam splitter corresponding to the coherent mixer 313 to obtain an orthogonal component signal and outputs it to the signal demodulator 315. The in-phase component signal is used as a distorted pulse signal. The signal demodulator 315 demodulates the orthogonal component signal to obtain a target communication signal.

[0081] Continue reading Figure 3 In some embodiments, the dynamic filtering unit 32 includes a phase-locked controller 321, a second ultrashort pulse laser 322, a second comb filter 323, and a spectral phase modulator 324. The phase-locked controller 321 is used to compare the frequency of the distorted pulse signal with the frequency of the coherent pulse signal to extract the synchronization signal and the error signal, and output the synchronization signal to the second ultrashort pulse laser 322, and output the error signal to the spectral phase modulator 324. The second ultrashort pulse laser 322 is used to synchronize the repetition frequency of the pulse output by the second ultrashort pulse laser 322 with the main clock frequency of the communication system 100 based on the synchronization signal, and output a reference pulse signal. The second comb filter 323 is used to filter out the key frequency teeth of the reference pulse signal according to a preset frequency interval to obtain a filtered reference pulse signal. The spectral phase modulator 324 is used to perform phase and amplitude modulation on the filtered reference pulse signal according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

[0082] It should be noted that the second ultrashort pulse laser 322 and the first ultrashort pulse laser 111 are lasers with the same parameters. Among the two balanced detectors 314, the output end of one balanced detector 314 is connected to the input end of the phase-locked controller 321, one output end of the phase-locked controller 321 is connected to the input end of the second ultrashort pulse laser 322, and the other output end of the phase-locked controller 321 is connected to an input end of the spectral phase modulator 324. The output end of the second ultrashort pulse laser 322 is connected to the input end of the second comb filter 323, and the output end of the second comb filter 323 is connected to the other input end of the spectral phase modulator 324. The output end of the spectral phase modulator 324 is connected to the input end of the polarization beam splitter 312.

[0083] Specifically, the phase-locked controller 321 compares the frequency of the distorted pulse signal generated by the first ultrashort pulse laser 111 with the frequency of the coherent pulse signal to extract the synchronization signal (i.e., similarity signal) and the error signal, and outputs the synchronization signal to the second ultrashort pulse laser 322, and outputs the error signal to the spectral phase modulator 324. The second ultrashort pulse laser 322 synchronizes the repetition frequency of the pulse output by the second ultrashort pulse laser 322 with the master clock frequency of the communication system 100 based on the synchronization signal, and outputs a reference pulse signal, the frequency of which is the same as the frequency of the coherent pulse signal. The second ultrashort pulse laser 322 outputs the reference pulse signal to the second comb filter 323, which filters out the key frequency teeth of the reference pulse signal according to the frequency interval required by the communication system 100, obtains the filtered reference pulse signal, and filters out the frequency teeth of the noise signal. The second comb filter 323 outputs the filtered reference pulse signal to the spectral phase modulator 324. The spectral phase modulator 324 modulates the phase and amplitude of the filtered reference pulse signal according to the error signal to obtain the modulated reference pulse signal as a new local oscillator pulse signal. In this way, the local oscillator pulse signal can be used to control the phase and amplitude of each communication frequency in the coherent pulse signal received by the receiving end 30, compensate for the signal distortion caused by atmospheric turbulence, and make the demodulated target communication signal more accurate.

[0084] Continue reading Figures 1 to 3 Based on the same inventive concept, an embodiment of the present application further provides a communication method of a free-space laser communication system 100 based on dynamic optical matched filtering according to any of the aforementioned embodiments, comprising:

[0085] S10, providing a coherent pulse signal required for laser communication through the transmitting end 10, loading the communication information onto the coherent pulse signal, and outputting the coherent pulse signal carrying the communication information to the transmission optical path 20;

[0086] S20, the coherent receiving unit 31 of the receiving end 30 performs coherent detection on the output signal of the transmission optical path 20 according to the local oscillator pulse signal generated by the dynamic filtering unit 32, and demodulates the distorted pulse signal and the target communication signal, sends the distorted pulse signal to the dynamic filtering unit 32, and outputs the target communication signal to the application end;

[0087] S30. The distorted pulse signal is demodulated by the dynamic filtering unit 32 to obtain an error signal. The phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal. The frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

[0088] In this embodiment, the coherent pulse signal carrying communication information is transmitted in the atmosphere. During the transmission process, the coherent pulse signal carrying communication information is affected by atmospheric turbulence, and the frequency domain and polarization state change. The coherent pulse signal carrying communication information output by the transmission optical path 20 is received by the coherent receiving unit 31. At the same time, the coherent receiving unit 31 uses a local oscillator pulse signal with the same frequency as the coherent pulse signal to perform coherent detection and demodulation to generate a distorted pulse signal and a target communication signal. The coherent receiving unit 31 inputs the distorted pulse signal into the dynamic filtering unit 32, and compares the frequencies of the distorted pulse signal and the coherent pulse signal, extracts the error signal from the distorted pulse signal, modulates the phase and amplitude of the reference pulse signal according to the error signal, obtains the modulated reference pulse signal and uses it as a new local oscillator pulse signal, and outputs the new local oscillator pulse signal to the coherent receiving unit 31 to adjust the phase and amplitude of each communication frequency in the output signal of the transmission optical path 20, and correct the influence of atmospheric turbulence in real time, and the dynamic filtering unit 32 performs closed tracking of the output signal of the transmission optical path 20 through the local oscillator pulse signal until the target communication signal achieves the preset high signal-to-noise ratio and low bit error rate. In this way, the delay problem caused by the traditional pre-compensation technical solution can be avoided, and the real-time performance of correcting signal distortion can be effectively improved.

[0089] In some embodiments, the coherent receiving unit 31 includes an optical beam splitter 311, a polarization beam splitter 312, a coherent mixer 313, a balanced detector 314 and a signal demodulator 315. Step S20, i.e., the coherent receiving unit 31 at the receiving end performs coherent detection on the output signal of the transmission optical path 20 according to the local oscillator pulse signal generated by the dynamic filtering unit 32, and demodulates the distorted pulse signal and the target communication signal, including:

[0090] S21, splitting the distorted pulse signal according to the channel requirement of the coherent mixer 313 through the optical beam splitter 311 to obtain two split pulse signals, and inputting each split pulse signal into an input channel corresponding to the coherent mixer 313;

[0091] S22, splitting the local oscillator pulse signal according to a preset polarization state through the polarization beam splitter 312 to obtain two polarized pulse signals, and inputting each polarized pulse signal into another input channel corresponding to the coherent mixer 313;

[0092] S23, separating the received split pulse signal and polarized pulse signal into two groups of optical signals according to the in-phase and quadrature phase relationships through the coherent mixer 313, and injecting each group of optical signals into a balanced detector 314;

[0093] S24, performing differential processing on each group of optical signals through the balanced detector 314 to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal is used as a distorted pulse signal;

[0094] S25. Demodulate the orthogonal component signal through the signal demodulator 315 to obtain the target communication signal.

[0095] In this embodiment, the optical beam splitter 311 splits the distorted pulse signal according to the channel requirements of the coherent mixer 313 to obtain two split pulse signals, and inputs each split pulse signal into an input channel corresponding to a beam splitter of the coherent mixer 313. The polarization beam splitter 312 splits the local oscillator pulse signal according to a preset polarization state (90 degrees polarization) to obtain two polarized pulse signals, and inputs each polarized pulse signal into another input channel corresponding to a beam splitter of the coherent mixer 313, wherein one polarized pulse signal is delayed by π / 2 in phase compared to the other polarized pulse signal. The coherent mixer 313 separates the split pulse signals and polarized pulse signals received by the two beam splitters into two groups of signals according to the in-phase and orthogonal phase relationships, and injects each group of optical signals into a balanced detector 314. One of the balanced detectors 314 performs differential processing on a corresponding group of optical signals and outputs an in-phase component signal, and the other balanced detector 314 performs differential processing on another group of optical signals and outputs an orthogonal component signal to the signal demodulator 315. The in-phase component signal is used as a distorted pulse signal and output to the dynamic filtering unit 32. The signal demodulator 315 demodulates the orthogonal component signal to obtain the target communication signal.

[0096] In some embodiments, the dynamic filtering unit 32 includes a phase-locked controller 321, a second ultrashort pulse laser 322, a second comb filter 323, and a spectral phase modulator 324. In step S30, the distorted pulse signal is demodulated by the dynamic filtering unit 32 to obtain an error signal, and the phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal, including:

[0097] S31, comparing the frequency of the distorted pulse signal with the frequency of the coherent pulse signal through the phase-locked controller 321 to extract a synchronization signal and an error signal, and outputting the synchronization signal to the second ultrashort pulse laser 322, and outputting the error signal to the spectral phase modulator 324;

[0098] S32, synchronizing the repetition frequency of the pulse output by the second ultrashort pulse laser 322 with the master clock frequency of the communication system 100 based on the synchronization signal, and outputting a reference pulse signal through the second ultrashort pulse laser 322;

[0099] S33, filtering out the key frequency teeth of the reference pulse signal according to a preset frequency interval through the second comb filter 323 to obtain a filtered reference pulse signal;

[0100] S34. The filtered reference pulse signal is phase- and amplitude-modulated by the spectrum phase modulator 324 according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

[0101] In this embodiment, the phase-locked controller 321 compares the frequency of the coherent pulse signal generated by the first ultrashort pulse laser 111 with the frequency of the distorted pulse signal, extracts a synchronization signal (i.e., a similarity signal) and an error signal from the distorted pulse signal, and outputs the synchronization signal to the second ultrashort pulse laser 322, and outputs the error signal to the spectral phase modulator 324. The second ultrashort pulse laser 322 synchronizes the repetition frequency of the pulse output by the second ultrashort pulse laser 322 with the main clock frequency of the communication system 100 based on the synchronization signal, and outputs a reference pulse signal, the frequency of which is the same as the frequency of the coherent pulse signal. The second ultrashort pulse laser 322 outputs the reference pulse signal to the second comb filter 323, which filters out the key frequency teeth of the reference pulse signal according to the frequency interval required by the communication system 100, obtains a filtered reference pulse signal, and filters out the frequency teeth of the noise signal. The second comb filter 323 outputs the filtered reference pulse signal to the spectral phase modulator 324. The spectral phase modulator 324 modulates the phase and amplitude of the filtered reference pulse signal according to the error signal to obtain the modulated reference pulse signal as a new local oscillator pulse signal. In this way, the local oscillator pulse signal can be used to control the phase and amplitude of each communication frequency in the coherent pulse signal received by the receiving end 30, compensate for the signal distortion caused by atmospheric turbulence, and make the demodulated target communication signal more accurate.

[0102] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A free-space laser communication system based on dynamic optical matched filtering, characterized in that: include: Transmitter, transmission optical path and receiver; The transmitting end is used to provide the coherent pulse signal required for laser communication, load the communication information onto the coherent pulse signal, and output the coherent pulse signal carrying the communication information to the transmission optical path; A receiving end, comprising a coherent receiving unit and a dynamic filtering unit; A coherent receiving unit, used to perform coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulate the distorted pulse signal and the target communication signal, send the distorted pulse signal to the dynamic filtering unit, and output the target communication signal to the application end; A dynamic filtering unit, used for demodulating the distorted pulse signal to obtain an error signal, modulating the phase and amplitude of the reference pulse signal according to the error signal, obtaining a modulated reference pulse signal as a new local oscillator pulse signal; The frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

2. The free-space laser communication system based on dynamic optical matched filtering according to claim 1, characterized in that: The transmitting end includes an ultrashort pulse source and a communication modulation unit; The ultrashort pulse source is used to provide a coherent pulse signal required for laser communication and is input into the communication modulation unit so that the communication modulation unit modulates the coherent pulse signal to obtain a coherent pulse signal carrying communication information and inputs it into the transmission optical path.

3. The free-space laser communication system based on dynamic optical matched filtering according to claim 2, characterized in that: The ultrashort pulse source includes a first ultrashort pulse laser and an ultrashort pulse frequency controller; The ultrashort pulse frequency controller is used to control the repetition frequency of the pulse output by the first ultrashort pulse laser to be synchronized with the main clock frequency of the communication system, so that the first ultrashort pulse laser outputs the coherent pulse signal to the communication modulation unit.

4. The free-space laser communication system based on dynamic optical matched filtering according to claim 2, characterized in that: The communication modulation unit includes a first comb filter, a spectrum encoder, an IQ modulator and a digital signal processor; The first comb filter is used to filter out the key frequency teeth of the coherent pulse signal according to a preset frequency interval, obtain the filtered coherent pulse signal and output it to the spectrum encoder; The spectrum encoder is used to adjust the phase and intensity of the filtered coherent pulse signal according to a preset spectrum bandwidth, obtain the adjusted coherent pulse signal and transmit it to the IQ modulator; The IQ modulator is used to obtain the communication information generated by the digital signal processor, load the communication information into the adjusted coherent pulse signal, obtain the coherent pulse signal carrying the communication information and output it to the transmission optical path.

5. The free space laser communication system based on dynamic optical matched filtering according to claim 4, characterized in that: The communication modulation unit also includes an optical fiber amplifier, which is connected between the IQ modulator and the transmission optical path so that the IQ modulator outputs the coherent pulse signal carrying the communication information to the optical fiber amplifier, and the optical fiber amplifier amplifies the coherent pulse signal carrying the communication information and outputs it to the transmission optical path.

6. The free-space laser communication system based on dynamic optical matched filtering according to any one of claims 1 to 5, characterized in that: The coherent receiving unit includes an optical beam splitter, a polarization beam splitter, a coherent mixer, a balanced detector and a signal demodulator; The optical beam splitter is used to split the distorted pulse signal according to the channel requirements of the coherent mixer to obtain two split pulse signals, and input each of the split pulse signals into an input channel corresponding to a beam splitter corresponding to the coherent mixer; The polarization beam splitter is used to split the local oscillator pulse signal according to a preset polarization state to obtain two polarized pulse signals, and input each of the polarized pulse signals into another input channel corresponding to a beam splitter corresponding to the coherent mixer; The coherent mixer is used to separate the received split beam pulse signal and polarized pulse signal into two groups of signals according to the in-phase and quadrature phase relationships, and inject each group of optical signals into a corresponding balanced detector; The balanced detector is used to perform differential processing on each group of optical signals to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal is used as a distorted pulse signal; The signal demodulator is used to demodulate the orthogonal component signal to obtain the target communication signal.

7. The free-space laser communication system based on dynamic optical matched filtering according to any one of claims 1 to 5, characterized in that: The dynamic filtering unit includes a phase-locked controller, a second ultrashort pulse laser, a second comb filter and a spectral phase modulator; The phase-locked controller is used to compare the frequency of the distorted pulse signal with the frequency of the coherent pulse signal to extract a synchronization signal and an error signal, and output the synchronization signal to the second ultrashort pulse laser, and output the error signal to the spectral phase modulator; The second ultrashort pulse laser is used to synchronize the repetition frequency of the pulses output by the second ultrashort pulse laser with the master clock frequency of the communication system based on the synchronization signal, and output a reference pulse signal; The second comb filter is used to filter out the key frequency teeth of the reference pulse signal according to a preset frequency interval to obtain a filtered reference pulse signal; The spectrum phase modulator is used to perform phase and amplitude modulation on the filtered reference pulse signal according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

8. A communication method of a free-space laser communication system based on dynamic optical matched filtering according to any one of claims 1 to 7, characterized in that: include: The transmitting end provides the coherent pulse signal required for laser communication, loads the communication information onto the coherent pulse signal, and outputs the coherent pulse signal carrying the communication information to the transmission optical path; The coherent receiving unit at the receiving end performs coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulates the distorted pulse signal and the target communication signal, sends the distorted pulse signal to the dynamic filtering unit, and outputs the target communication signal to the application end; The distorted pulse signal is demodulated by a dynamic filtering unit to obtain an error signal, and the phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal; The frequency of the reference pulse signal is the same as the frequency of the coherent pulse signal.

9. The communication method of a free space laser communication system based on dynamic optical matched filtering according to claim 8, characterized in that: The coherent receiving unit includes an optical beam splitter, a polarization beam splitter, a coherent mixer, a balanced detector and a signal demodulator; The coherent receiving unit at the receiving end performs coherent detection on the output signal of the transmission optical path according to the local oscillator pulse signal generated by the dynamic filtering unit, and demodulates the distorted pulse signal and the target communication signal, including: Splitting the distorted pulse signal according to the channel requirement of the coherent mixer through the optical beam splitter to obtain two split pulse signals, and inputting each of the split pulse signals into an input channel corresponding to the coherent mixer; Splitting the local oscillator pulse signal according to a preset polarization state through the polarization beam splitter to obtain two polarized pulse signals, and inputting each of the polarized pulse signals into another input channel corresponding to the coherent mixer; The coherent mixer is used to separate the received split beam pulse signal and polarized pulse signal into two groups of optical signals according to in-phase and quadrature phase relationships, and each group of optical signals is injected into a balanced detector; Performing differential processing on each group of optical signals through the balanced detector to output an in-phase component signal or an orthogonal component signal, wherein the in-phase component signal is used as a distorted pulse signal; The orthogonal component signal is demodulated by the signal demodulator to obtain the target communication signal.

10. The communication method of a free space laser communication system based on dynamic optical matched filtering according to claim 8, characterized in that: The dynamic filtering unit includes a phase-locked controller, a second ultrashort pulse laser, a second comb filter and a spectral phase modulator; The distorted pulse signal is demodulated by a dynamic filtering unit to obtain an error signal, and the phase and amplitude of the reference pulse signal are modulated according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal, including: The frequency of the distorted pulse signal is compared with the frequency of the coherent pulse signal by the phase-locked controller to extract a synchronization signal and an error signal, and the synchronization signal is output to the second ultrashort pulse laser, and the error signal is output to the spectral phase modulator; Based on the synchronization signal, the repetition frequency of the pulse output by the second ultrashort pulse laser is synchronized with the master clock frequency of the communication system, and a reference pulse signal is output through the second ultrashort pulse laser; Filtering out the key frequency teeth of the reference pulse signal according to a preset frequency interval by a second comb filter to obtain a filtered reference pulse signal; The filtered reference pulse signal is phase- and amplitude-modulated by a spectrum phase modulator according to the error signal to obtain a modulated reference pulse signal as a new local oscillator pulse signal.

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