Free space optical communication system based on structured optical frequency comb

Abstract

The invention discloses a free space optical communication system based on a structured optical frequency comb, and belongs to the field of optical communication. Comprising an optical frequency comb generation system, a signal coding system, a spatial light modulation and demodulation system and a signal receiving system. The optical frequency comb generation system is used for modulating input continuous laser into an adjustable optical frequency comb with high repetition frequency, short pulse width and high power; the signal coding system is used for separating the light with different wavelengths in the optical frequency comb, independently coding the light with each wavelength, and finally combining the light with different wavelengths again; the spatial light modulation and demodulation system is used for coupling the Gaussian beam in the optical fiber into a free space and converting the Gaussian beam into structured light, demodulating the structured light after the structured light is transmitted to a receiving end and re-coupling the structured light back to the optical fiber; the signal receiving system is used for receiving and analyzing the optical signals. According to the invention, the optical frequency comb and the structured light are combined, and the problem that optical signals are easily influenced by atmospheric turbulence in free space optical communication can be effectively solved on the premise of ensuring large communication capacity.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of optical communication, and more particularly relates to a free space optical communication system based on structured optical frequency comb. BACKGROUND

[0002] Under the background of the continuous development of modern communication technology, free space optical communication emerges as a kind of advanced communication means. With the acceleration of global informatization, people's demand for high-speed, high-bandwidth, low-delay and secure and reliable communication is rising, and traditional communication technology gradually exposes its limitations in some specific scenarios. Free space optical communication, with its unique advantages, has become one of the important solutions to meet these emerging communication needs.

[0003] The working principle of free space optical communication is based on light wave as carrier to realize information transmission in free space. It loads the information-carrying electrical signal onto the light wave after modulation, and transmits information in free space or atmosphere with light wave as carrier. This technology uses laser as information carrier and does not need to rely on any wired channel. This communication mode skillfully combines the advantages of traditional wireless microwave communication and optical fiber communication, and has the characteristics of large capacity and high-speed transmission of optical fiber communication, and the flexibility and advantage of not needing to lay physical lines of wireless communication.

[0004] Free space optical communication technology has many significant advantages, making it popular in many application scenarios. First, it does not need spectrum license, effectively avoiding the problem of spectrum resource shortage in traditional wireless communication, and has the advantages of high bandwidth, protocol transparency and low cost. Secondly, its unique advantages of high security, low power, small size and low delay make it irreplaceable in scenarios with high requirements for communication security and real-time performance.

[0005] However, free space optical communication technology also faces some challenges and difficulties. When the optical signal is transmitted in the atmospheric environment, it will be affected not only by weather conditions such as fog, rain and snow, but also by atmospheric turbulence, resulting in signal attenuation, which makes it difficult to realize stable communication in bad weather conditions. SUMMARY

[0006] In view of the defects of the prior art, the purpose of the present application is to provide a free space optical communication system based on structured optical frequency comb, which modulates the optical frequency comb signal into a structured optical frequency comb signal, aiming to realize large-capacity optical communication through the characteristics of optical frequency comb suitable for wavelength division multiplexing technology, and to weaken the influence of atmospheric turbulence and bad weather on optical signal attenuation through the non-diffraction characteristics of the structured light including Bessel beam and other light beams.

[0007] To achieve the above object, the application provides a free space optical communication system based on structured light frequency comb, comprising a light frequency comb generating system, a signal coding system, a spatial light modulation and demodulation system, and a signal receiving system; continuous light is converted into light frequency comb signals after passing through the light frequency comb generating system; a plurality of different comb teeth of the light frequency comb signals are independently coded in the signal coding system and combined into an optical signal; in the spatial light modulation and demodulation system, the optical signal is coupled into free space and modulated into structured light, demodulated after being transmitted to the receiving end, and coupled into an optical fiber; the signal receiving system is used for receiving and analyzing the optical signal. The light frequency comb generating system is used for modulating continuous laser into light frequency comb, and the light frequency comb has a series of discrete, equally spaced linear spectral distribution and coherent phase relationship. The signal coding system is used for splitting the light frequency comb into a plurality of comb tooth signals with different wavelengths according to wavelength, and independently coding information of each wavelength comb tooth signal, and then combining the coded signals into an optical signal. The spatial light modulation and demodulation system is used for coupling the optical signal into free space, modulating it into a structured light frequency comb signal, demodulating it after being transmitted to the receiving end, and re-coupling it into an optical fiber. The signal receiving system is used for amplifying, filtering and converting the light frequency comb signal into an electrical signal, and analyzing it through an oscilloscope.

[0008] Preferably, the light frequency comb generating system comprises a continuous light laser, an electro-optical modulation module, a first polarization controller, a linear compression module, a nonlinear compression module, and a nonlinear optical ring mirror module connected in sequence; the continuous light emitted by the continuous light laser generates a preliminary light frequency comb after passing through the electro-optical modulation module; the polarization mode of the preliminary light frequency comb is changed after passing through the first polarization controller; the linear compression module is used for linearly compensating the light frequency comb after the polarization mode is changed, so that the signal exhibits pulse width narrowing in the time domain; the nonlinear compression module utilizes self-phase modulation effect to realize spectrum broadening of the light frequency comb after pulse width narrowing, which is equivalent to pulse width narrowing in the time domain; the nonlinear optical ring mirror module is used for filtering low-power side lobes in the time domain of the light frequency comb after spectrum broadening, and making the spectrum more flattened in the frequency domain.

[0009] Preferably, the electro-optical modulation module comprises a radio frequency source, an intensity modulator, a first phase shifter, a first phase modulator, a second phase shifter, and a second phase modulator; the radio frequency source is used to control the intensity modulator, the first phase modulator, and the second phase modulator; the intensity modulator is used to intensity modulate the input continuous light, providing conditions for subsequent generation of a flat optical frequency comb spectrum; the first phase modulator is used to convert the intensity-modulated continuous light into an optical frequency comb; the second phase modulator is used to strengthen the modulation depth and increase the number of spectral lines of the optical frequency comb; the first phase shifter is located between the radio frequency source and the first phase modulator, and is used to adjust the phase relationship between the first phase modulator and the intensity modulator and the second phase modulator; the second phase shifter is located between the radio frequency source and the second phase modulator, and is used to adjust the phase relationship between the second phase modulator and the first phase modulator and the intensity modulator.

[0010] Preferably, the linear compression module comprises a first single-mode fiber; the optical frequency comb signal passing through the first polarization controller generates a negative chirp in the first single-mode fiber with negative dispersion, achieving pulse width narrowing.

[0011] Preferably, the nonlinear compression module comprises a first optical amplifier and a second single-mode fiber; the first optical amplifier is used to amplify the optical frequency comb signal, so that the optical frequency comb signal can reach a power that can generate a significant nonlinear effect in the second single-mode fiber; the second single-mode fiber serves as a nonlinear medium, and the optical frequency comb signal is affected by self-phase modulation therein, achieving spectral broadening.

[0012] Preferably, the nonlinear optical loop mirror module comprises an optical coupler, a second polarization controller, and a third single-mode fiber; the optical frequency comb signal passing through the nonlinear compression module is split into two beams by the optical coupler, one of which first passes through the third single-mode fiber and then passes through the second polarization controller, and the other of which first passes through the second polarization controller and then passes through the third single-mode fiber; finally, the two beams of light pass through the optical coupler again and leave the nonlinear optical loop mirror module; the transmittance of the optical frequency comb signal entering the nonlinear optical loop mirror module is positively correlated with the power thereof, and the nonlinear optical loop mirror module plays a role in flattening the spectrum of the optical frequency comb signal.

[0013] Preferably, the signal encoding system comprises a first wavelength selection switch, N (N>1) electro-optical modulators, a signal generator, and a second wavelength selection switch; the first wavelength selection switch is used to separate the input optical frequency comb signal into N independent signals of different wavelength comb teeth; the signal generator is used to connect the N electro-optical modulators and independently encode the optical signals of different wavelengths; and the second wavelength selection switch is used to combine the N encoded comb signals of different wavelengths into one optical signal.

[0014] Preferably, the spatial light modulation and demodulation system comprises a first optical fiber collimator, a half-wave plate, a first spatial light modulator, a second spatial light modulator, and a second optical fiber collimator; the first optical fiber collimator is used for coupling the optical signal into free space; the half-wave plate is used for adjusting the polarization state of the optical signal in free space to match the requirements of the first spatial light modulator and the second spatial light modulator for the polarization state of light; the first spatial light modulator is used for modulating the Gaussian light in the spatial light passing through the half-wave plate into structured light; the structured light reaches the second spatial light modulator after propagating in free space for a distance, and the second spatial light modulator is used for demodulating the structured light; and the second optical fiber collimator is used for coupling the demodulated structured light back into an optical fiber.

[0015] Preferably, the signal receiving system comprises a second optical amplifier, a filter, a photodetector, and an oscilloscope; the second optical amplifier is used for amplifying the structured light to compensate for the loss of the structured light during transmission; the filter is used for filtering out signals other than the required wavelength band signals; the photodetector is used for converting the received structured light into an electrical signal; and the oscilloscope is used for displaying the received signal data, and the bit error rate can be calculated by using the data received by the oscilloscope.

[0016] As a further preferred embodiment of the present application, the central axes of the optical lenses in the spatial light path coincide with the central axis of the light beam.

[0017] As a further preferred embodiment of the present application, the structured light modulated by the first spatial light modulator is a high-order Bessel beam, which has the characteristics of no diffraction and carries orbital angular momentum.

[0018] As a further preferred embodiment of the present application, the optical amplifier is an erbium-doped fiber amplifier.

[0019] As a further preferred embodiment of the present application, the intensity modulator, the first phase modulator, and the second phase modulator are lithium niobate modulators.

[0020] As a further preferred embodiment of the present application, the electro-optical modulator is a Mach-Zehnder modulator.

[0021] By means of the above technical scheme conceived by the present application, the following beneficial effects can be achieved compared with the prior art: 1. The present application provides a free space optical communication system based on structured light frequency comb, in which an optical frequency comb is used as a communication light source in an optical frequency comb generation system. Since the spectrum of the optical frequency comb is a series of equidistant spectral lines with phase coherence, the system cost can be effectively reduced compared with the traditional multiple lasers as light sources.

[0022] 2. The application provides a free space optical communication system based on a structured optical frequency comb, in an optical frequency comb generation system, an electro-optical modulation module is used, and the optical frequency comb generation system is a full optical fiber structure. The comb structure of the optical frequency comb can be effectively adjusted through the electro-optical modulation module, and the demand of the light source for optical communication can be flexibly met. By using the optical frequency comb generation system with a full optical fiber structure, compared with other structures such as a micro ring, a high-power optical frequency comb signal can be generated, the power of the optical signal received at the receiving end is effectively improved, the signal noise ratio is improved, and the bit error rate is reduced.

[0023] 3. The application provides a free space optical communication system based on a structured optical frequency comb, by simultaneously introducing an optical frequency comb generation system and a spatial light modulation and demodulation system, the advantages of the optical frequency comb and the structured light are combined. The optical frequency comb signal propagating in space is modulated into a structured optical frequency comb with orbital angular momentum and non-diffraction property, and the structured light includes a high-order Bessel beam. Since the high-order Bessel beam has the non-diffraction property, it has stronger anti-interference ability when propagating in the atmosphere, and can effectively resist the influence of bad weather and atmospheric turbulence; since the high-order Bessel beam carries orbital angular momentum, multiple Bessel beams carrying different orbital angular momenta can be superimposed to realize mode division multiplexing, thereby further improving the communication capacity, and the one-to-many communication effect can also be realized by this method. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a free space optical communication system based on a structured optical frequency comb of an embodiment of the application.

[0025] Figure 2 is an optical frequency comb generation system of an embodiment of the application.

[0026] Figure 3 is an electro-optical modulation module of an embodiment of the application.

[0027] Figure 4 is a linear compression module of an embodiment of the application.

[0028] Figure 5 is a nonlinear compression module of an embodiment of the application.

[0029] Figure 6 is a nonlinear optical ring mirror module of an embodiment of the application.

[0030] Figure 7 is a signal encoding system of an embodiment of the application.

[0031] Figure 8 is a spatial light modulation and demodulation system of an embodiment of the application.

[0032] Figure 9The signal receiving system is a specific embodiment of the present application.

[0033] In all the drawings, the same reference signs are used to represent the same elements or structures, wherein 1 is a light frequency comb generation system, 2 is a signal encoding system, 3 is a spatial light modulation and demodulation system, 4 is a signal receiving system, 5 is a continuous light laser, 6 is an electro-optical modulation module, 7 is a first polarization controller, 8 is a linear compression module, 9 is a nonlinear compression module, 10 is a nonlinear optical ring module, 11 is an intensity modulator, 12 is a radio frequency source, 13 is a first phase modulator, 14 is a first phase shifter, 15 is a second phase modulator, 16 is a second phase shifter, 17 is a first single-mode optical fiber, 18 is a first optical amplifier, 19 is a second single-mode optical fiber, 20 is an optical coupler, 21 is a third single-mode optical fiber, 22 is a second polarization controller, 23 is a first wavelength selective switch, 24 is an electro-optical modulator, 25 is a signal generator, 26 is a second wavelength selective switch, 27 is a first optical fiber collimator, 28 is a half-wave plate, 29 is a first spatial light modulator, 30 is a second spatial light modulator, 31 is a second optical fiber collimator, 32 is a second optical amplifier, 33 is a filter, 34 is a photoelectric detector, and 35 is an oscilloscope. DETAILED DESCRIPTION

[0034] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and should not be used to limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035] In order to achieve the above-mentioned purpose, the present application provides a free space optical communication system based on a structured light frequency comb, which has excellent adjustability and can adjust the structure of the light frequency comb according to the needs of communication; it can realize large-capacity free space optical communication while also having excellent anti-interference ability.

[0036] In order to achieve the above-mentioned purpose, the present application provides a free space optical communication system based on a structured light frequency comb, which has excellent adjustability and can adjust the structure of the light frequency comb according to the needs of communication; it can realize large-capacity free space optical communication while also having excellent anti-interference ability. Figure 1 As shown in the figure, it comprises a light frequency comb generation system, a signal encoding system, a spatial light modulation and demodulation system, and a signal receiving system; continuous light is converted into a light frequency comb signal after passing through the light frequency comb generation system; a plurality of different comb teeth of the light frequency comb signal are independently encoded in the signal encoding system and combined into an optical signal; in the spatial light modulation and demodulation system, the optical signal in the optical fiber is coupled into free space and modulated into structured light, which is demodulated after being transmitted to the receiving end and coupled into the optical fiber; the signal receiving system is used for receiving and analyzing the optical signal; The optical frequency comb generation system is used to modulate continuous laser light into an optical frequency comb. The optical frequency comb is characterized by having a series of discrete, equally spaced linear spectral distributions and having a coherent phase relationship. The signal encoding system is used to split the optical frequency comb into multiple comb tooth signals with different wavelengths according to wavelength, and to encode the signal of each wavelength comb tooth separately, and then combine the encoded signals into one optical signal. The spatial optical modulation and demodulation system is used to couple optical signals into free space, modulate them into structured optical frequency comb signals, and demodulate them after the structured optical frequency comb signals are transmitted to the receiving end and recouple them into the optical fiber. The signal receiving system is used to amplify and filter the optical frequency comb signal and convert it into an electrical signal, which is then analyzed using an oscilloscope.

[0037] In this embodiment, refer to Figure 2 , 3 The continuous-wave laser 5 is specifically a distributed feedback laser, characterized by its narrow linewidth and good wavelength stability. The continuous light emitted by the continuous-wave laser 5 enters the electro-optic modulation module 6. In the electro-optic modulation module 6, the signal emitted by the radio frequency source 12 is a 20 GHz sinusoidal signal. This signal is not only directly loaded onto the intensity modulator 11, but also loaded onto the first phase modulator 13 after passing through the first phase shifter 14, and further loaded onto the second phase modulator 15 through the second phase shifter 16. The intensity modulator 11 first modulates the input continuous light to provide conditions for generating a flat optical frequency comb spectrum. The first phase modulator 13 converts the intensity-modulated continuous light into an optical frequency comb, and the second phase modulator 15 enhances the modulation depth, resulting in a greater number of optical frequency comb spectral lines. The first phase shifter 14 adjusts the phase of the signal emitted by the radio frequency source 12 as it reaches the first phase modulator 13, ensuring that the signal controlling the first phase modulator 13 is synchronized with the signals controlling the intensity modulator 11 and the second phase modulator 15. The second phase shifter 16 is used to adjust the phase of the signal emitted by the radio frequency source 12 to reach the second phase modulator 15, so that the signal controlling the second phase modulator 15 is synchronized with the signal controlling the intensity modulator 11 and the signal controlling the first phase modulator 13. The continuous light emitted by the continuous light laser 5 is modulated sequentially by the intensity modulator 11, the first phase modulator 13, and the second phase modulator 15 in the electro-optic modulation module 6, and then its polarization state is adjusted by the first polarization controller 7.

[0038] In this embodiment, refer to Figure 4 The optical signal is linearly compressed after entering the linear compression module 8. The linear compression module 8 is a 1km long first single-mode optical fiber 17, in which the optical signal is in a negative dispersion state.

[0039] In the embodiments, reference is made to Figure 5After entering the nonlinear compression module 9, the optical signal is nonlinearly compressed. In the nonlinear compression module 9, the optical signal first passes through the first optical amplifier 18, specifically an erbium-doped fiber amplifier, whose power is amplified to a level sufficient to produce significant self-phase modulation in the second single-mode fiber 19; then the optical signal passes through the second single-mode fiber with a length of 500m.

[0040] In the embodiments, reference is made to Figure 2 6. In the nonlinear optical ring mirror module 10, the optical signal is split into two paths after passing through an optical coupler with a coupling ratio of 90%:10%. One optical signal first passes through the third single-mode fiber 21 and then through the second polarization controller 22; the other optical signal first passes through the second polarization controller 22 and then through the third single-mode fiber 21. The two optical signals then pass through the optical coupler 20 again and enter the signal encoding system 2.

[0041] In this embodiment, refer to Figure 7 In signal encoding system 2, the optical signal is first split into nine signals after passing through the first wavelength selection switch 23. Signal generator 25 generates a 20 Gaud / s four-level pulse amplitude modulation (PAM4) signal to control nine electro-optic modulators 24, specifically Mach-Zehnder modulators. Each of the nine electro-optic modulators 24 modulates one of its corresponding nine signals. The modulated signals are then combined into a single signal through the second wavelength selection switch 26.

[0042] In this embodiment, refer to Figure 8 In the spatial light modulation and demodulation system 3, the optical signal is first coupled into the atmosphere through the first fiber collimator 27, and then, after passing through a half-wave plate 28 rotated to a suitable angle, its polarization state is adjusted to a polarization state suitable for the first spatial light modulator 29. Subsequently, the optical signal is modulated by the phase-type first spatial light modulator 29 loaded with a 6th-order Bessel beam phase diagram, which can be specifically described as... ,in =6 For the topological charge of a Bessel beam. k r =5000 It represents the radial phase change rate on the phase diagram. r The polar radius on the phase diagram. θ The polar angle on the phase diagram is shown. The optical signal, modulated into a 6th-order Bessel beam, propagates through the atmosphere to the communication transmission distance and reaches the receiving end, where it is demodulated into a Gaussian-like beam by the second spatial optical modulator 30 with a demodulated phase diagram. Subsequently, the Gaussian-like beam signal is recoupled into the optical fiber through the second fiber collimator 31.

[0043] In this embodiment, refer to Figure 9In the signal receiving system 4, the optical signal is amplified to a suitable optical power by the second optical amplifier 32. Specifically, the second optical amplifier is an erbium-doped fiber amplifier. The amplified optical signal is filtered out by filter 33 to remove signals from bands other than the carrier band to be detected, and then converted into an electrical signal by photodetector 34. Finally, the electrical signal is displayed on oscilloscope 35.

[0044] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A free-space optical communication system based on a structured optical frequency comb, characterized in that, The system includes an optical frequency comb generation system, a signal encoding system, a spatial light modulation and demodulation system, and a signal receiving system. The optical frequency comb generation system modulates continuous laser light into a series of discrete, equally spaced linear spectral distributions with coherent phase relationships. The signal encoding system divides the optical frequency comb signals into multiple comb signals with different wavelengths, independently encodes each wavelength, and then combines the encoded signals into a single optical signal. The spatial light modulation and demodulation system couples the optical signal into free space, modulates it into a structured light frequency comb signal, demodulates it after transmission to the receiving end, and recouples it into the optical fiber. In the spatial light modulation and demodulation system, the optical signal is coupled into free space and modulated into structured light, demodulated after transmission to the receiving end, and coupled into the optical fiber. The signal receiving system receives and analyzes the structured light.

2. The free-space optical communication system based on a structured optical frequency comb according to claim 1, characterized in that, The optical frequency comb generation system includes a continuous-wave laser, an electro-optic modulation module, a first polarization controller, a linear compression module, a nonlinear compression module, and a nonlinear optical ring mirror module connected in sequence. The continuous light emitted by the continuous-wave laser generates a preliminary optical frequency comb after passing through the electro-optic modulation module. The polarization mode of the preliminary optical frequency comb is changed after passing through the first polarization controller. The linear compression module is used to linearly compensate for the optical frequency comb after the polarization mode change, so that the signal appears as pulse width narrowing in the time domain. The nonlinear compression module uses the self-phase modulation effect to make the optical frequency comb after the pulse width narrowing achieve spectral broadening, which is equivalent to pulse width narrowing in the time domain. The nonlinear optical ring mirror module is used to filter out low-power side lobes in the time domain of the optical frequency comb after spectral broadening, making the spectrum flatter in the frequency domain.

3. A free-space optical communication system based on a structured optical frequency comb according to claim 2, characterized in that, The electro-optic modulation module includes a radio frequency source, an intensity modulator, a first phase shifter, a first phase modulator, a second phase shifter, and a second phase modulator; the radio frequency signal emitted by the radio frequency source is used to control the intensity modulator, the first phase modulator, and the second phase modulator; the intensity modulator is used to modulate the intensity of the input continuous light. The first phase modulator is used to convert intensity-modulated continuous light into an optical frequency comb; The second phase modulator is used to enhance the modulation depth and increase the number of spectral lines in the optical frequency comb; The first phase shifter is located between the RF source and the first phase modulator, and is used to adjust the phase relationship between the first phase modulator and the intensity modulator and the second phase modulator; the second phase shifter is located between the RF source and the second phase modulator, and is used to adjust the phase relationship between the second phase modulator and the first phase modulator and the intensity modulator.

4. A free-space optical communication system based on a structured optical frequency comb according to claim 2, characterized in that, The linear compression module includes a first single-mode fiber; the optical frequency comb signal after passing through the first polarization controller undergoes dispersion compensation in the negative dispersion first single-mode fiber, thereby achieving pulse width narrowing.

5. A free-space optical communication system based on a structured optical frequency comb according to claim 2, characterized in that, The nonlinear compression module includes a first optical amplifier and a second single-mode fiber; the first optical amplifier is used to amplify the optical frequency comb signal, so that the optical frequency comb signal can reach the power that produces a significant nonlinear effect in the second single-mode fiber; The second single-mode fiber, as a nonlinear medium, allows the optical frequency comb signal to be affected by self-phase modulation, thus achieving spectral broadening.

6. A free-space optical communication system based on a structured optical frequency comb according to claim 2, characterized in that, The nonlinear optical ring mirror module includes an optical coupler, a second polarization controller, and a third single-mode fiber. The optical frequency comb signal after passing through the nonlinear compression module is split into two beams by the optical coupler. One beam passes through the third single-mode fiber and then the second polarization controller, while the other beam passes through the second polarization controller and then the third single-mode fiber. Finally, both beams pass through the optical coupler again and leave the nonlinear optical ring mirror module. The transmittance of the optical frequency comb signal entering the nonlinear optical ring mirror module is positively correlated with its power. The nonlinear optical ring mirror module serves to flatten the spectrum of the optical frequency comb signal.

7. A free-space optical communication system based on a structured optical frequency comb according to claim 1, characterized in that, The signal encoding system includes a first wavelength selection switch, N electro-optic modulators, a signal generator, and a second wavelength selection switch, where N>1; the first wavelength selection switch is used to separate the input optical frequency comb signal into N comb tooth signals of different wavelengths; the signal generator is used to connect the N electro-optic modulators to encode the comb tooth signals of different wavelengths; The second wavelength selection switch is used to recombine the encoded N different wavelength comb signals into a single optical signal.

8. A free-space optical communication system based on a structured optical frequency comb according to claim 7, characterized in that, The spatial light modulation and demodulation system includes a first fiber collimator, a half-wave plate, a first spatial light modulator, a second spatial light modulator, and a second fiber collimator. The first fiber collimator is used to couple one optical signal into free space. The half-wave plate is used to adjust the polarization state of the optical signal in free space to match the polarization state requirements of the first and second spatial light modulators. The first spatial light modulator is used to modulate the Gaussian light in the spatial light passing through the half-wave plate into structured light. The structured light travels a certain distance in free space and then reaches the second spatial light modulator, which is used to demodulate the structured light. The second fiber collimator is used to couple the demodulated structured light back into the fiber.

9. A free-space optical communication system based on a structured optical frequency comb according to claim 8, characterized in that, The signal receiving system includes a second optical amplifier, a filter, a photodetector, and an oscilloscope. The second optical amplifier amplifies the structured light to compensate for losses during transmission. The filter filters out signals other than those in the desired band. The photodetector converts the received structured light into an electrical signal. The oscilloscope displays and records the received signal data and calculates the bit error rate.

10. A free-space optical communication system based on a structured optical frequency comb according to claim 3, characterized in that, The radio frequency source generates a sinusoidal signal with a frequency of 20 GHz, which is used to control the spectral structure of the optical frequency comb.

11. A free-space optical communication system based on a structured optical frequency comb according to claim 8, characterized in that, The first spatial light modulator is loaded with phase maps corresponding to non-diffraction beams, including Bessel beams and Mathieu beams, to reduce interference to the optical signal caused by atmospheric instability.

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