Free space vector anti-turbulence chaotic secure optical communication system

Abstract

The patent discloses a free space vector anti-turbulence chaos secret light communication system and relates to the technical field of communication.The scheme breaks the restriction of traditional chaos encryption technology that uses chaos signals as light carriers, uses chaos signals as synchronous driving signals and information phase control signals, and realizes time-frequency phase three-dimensional superimposed encryption of each channel through spectrum widening and time domain stretching of original light information signals under the action of chaos phase modulation spread spectrum and dispersion element phase-intensity conversion.Meanwhile, the scheme uses vector light field control mechanism to convert linear polarization Gaussian light field transmitted in free space into full Poincare vector light field with uneven polarization distribution, improves the signal-to-noise ratio of the communication system, and realizes free space anti-turbulence communication.

Description

Technical Field

[0001] This invention relates to the field of communication technology, and in particular to a free-space vector anti-turbulence chaotic secure optical communication system. Background Technology

[0002] Space laser communication boasts significant advantages such as high speed, strong resistance to electromagnetic interference, no spectrum limitations, small terminal size, and ease of deployment, making it a core communication system for scenarios like "last-mile communication," emergency communication, space-to-ground communication, and inter-satellite communication. However, with the rapid increase in transmission capacity demands, space laser communication technology faces severe challenges. On the one hand, after lasers are transmitted over long distances in free space, beam divergence leads to an increase in the size of the receiver's spot, increasing the risk of information eavesdropping and threatening the security of integrated space-ground communication networks. On the other hand, optical signals transmitted in free space are affected by various atmospheric conditions. Suspended particles, aerosols, and atmospheric turbulence can damage or even lose the information carried by the beam to varying degrees, becoming a key technical challenge hindering the practical application and development of space laser communication.

[0003] Traditional optical network information security protection methods typically employ cryptographic encryption techniques at the MAC layer and higher. However, with the development of quantum computers, encryption algorithms can be cracked in a very short time, posing a significant challenge to traditional encryption schemes through brute-force attacks. To address the challenges faced by traditional encryption algorithms, chaotic physical layer secure communication technology, with its characteristics such as broadband noise and initial value sensitivity, is widely used in the field of fiber optic secure communication.

[0004] However, as research has deepened, encryption technology using chaotic lasers as signal carriers has been limited by the low bandwidth of chaotic carriers, making it difficult to support high-speed, high-capacity communication systems and to meet compatibility requirements in existing commercial communication systems. At the same time, research on atmospheric turbulence-based secure communication systems in chaotic free space is still scarce.

[0005] Therefore, it is necessary to propose a free-space vector anti-turbulence chaotic secure optical communication system to solve the above-mentioned technical problems. Summary of the Invention

[0006] The purpose of this invention is to provide a free-space vector anti-turbulence chaotic secure optical communication system to solve the defects of encryption technology using chaotic lasers as signal carriers mentioned in the background art, achieve multi-dimensional and efficient encryption and decryption of high-speed wavelength division multiplexing optical signals, and effectively be compatible with existing optical communication systems; at the same time, reduce the impact of atmospheric turbulence on the performance of chaotic space communication systems.

[0007] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0008] This invention provides a free-space vector anti-turbulence chaotic secure optical communication system, characterized in that: the secure optical communication system includes a signal transmitting system, a free-space link, and a signal receiving system;

[0009] The signal transmission system includes a chaos driving module, a chaos encryption module, a wavelength division multiplexer, and a vector optical field control module.

[0010] The chaotic driving module can output a first optical signal and a second optical signal. The first optical signal can be injected into the chaotic encryption module as a chaotic synchronization driving signal at the transmitting end; the second optical signal serves as a chaotic synchronization driving optical signal at the decryption end (receiving end).

[0011] The chaotic encryption module can generate optical information signals and a third optical signal. The third optical signal is a chaotic control signal, which can be used as a control signal to encrypt the optical information signal. The chaotic encryption module finally emits an encrypted optical information signal.

[0012] The encrypted optical information signal and the second optical signal are simultaneously injected into the wavelength division multiplexer to generate a multiplexed fourth optical signal. The fourth optical signal is injected into the vector optical field modulation module, modulated into a vector beam, and then incident on the free space link and transmitted to the signal receiving system.

[0013] The signal receiving system includes a vector optical field demodulation module, a wave demultiplexer, and a chaos decryption module;

[0014] The vector light field demodulation module is used to receive a vector beam, demodulate the vector beam into a fourth optical signal, inject it into a wave demultiplexer, separate the encrypted optical information signal and the second optical signal, and then inject them together into the chaotic decryption module.

[0015] The second optical signal is injected into the chaotic decryption module as a driving signal, which drives the chaotic decryption module to generate a fifth optical signal as a chaotic control signal, which decrypts the encrypted optical information signal injected into the chaotic decryption module to obtain the decrypted original signal.

[0016] As a preferred embodiment, the signal transmission system further includes a power adjustment module for adjusting the spatial transmission power of the fourth optical signal and injecting the fourth optical signal with adjusted power into the vector light field control module.

[0017] As a preferred embodiment, the power regulation module is an optical fiber amplifier.

[0018] As a preferred embodiment, the chaotic driving module includes a main laser (Drive Laser, DL), a first polarization controller (PC1), a first fiber coupler (FC1), a second fiber coupler (FC2), a first tunable optical attenuator (VOA1), a fiber mirror (M1), and a first optical isolator (ISO1).

[0019] The laser signal emitted from the main laser, after passing through the first polarization controller, is split into two paths by the first fiber coupler according to a certain ratio.

[0020] One optical signal is reflected back to the main laser through the first adjustable optical attenuator and the fiber optic mirror to generate a chaotic driving signal.

[0021] The other optical signal is split into the same first optical signal and second optical signal after passing through the first optical isolator and the second optical fiber coupler in sequence. The first optical signal is injected into the chaotic encryption module as the chaotic synchronization drive signal at the transmitting end, and the second optical signal is used as the chaotic synchronization drive optical signal at the receiving end.

[0022] As a preferred embodiment, the first fiber coupler splits the laser signal into two paths at a ratio of 1:9, with 10% of the optical signal returning to the main laser and 90% of the optical signal entering the first optical isolator.

[0023] As a preferred embodiment, the chaotic encryption module includes a multi-channel optical transmitter, a multiplexer (MUX), a first slave laser (SL1), a third fiber coupler (FC3), a second tunable optical attenuator (VOA2), a third tunable optical attenuator (VOA3), a second optical isolator (ISO2), a second polarization controller (PC2), a first photodetector (PD1), a first radio frequency amplifier (RF1), a first phase modulator (PM1), and a first chromatic dispersion element (DCF1).

[0024] The laser signal emitted by the first slave laser is split into two signals after passing through the third fiber coupler. One signal receives the first optical signal output from the chaos driving module. The first optical signal passes through the second optical isolator, the second polarization controller and the second adjustable optical attenuator in sequence before being input into the first slave laser as the transmitting end chaos synchronization driving signal.

[0025] The other optical signal is sequentially amplified by the third adjustable optical attenuator, the first photodetector, and the first radio frequency amplifier, and then converted into a third optical signal before being injected into the first phase modulator.

[0026] After multiplexing the optical information signals of different wavelengths emitted from the multiplexer, the output optical information signal is injected into the first phase modulator. Under the action of the third optical signal, the first phase modulator performs phase spectrum perturbation encryption on the optical information signal and outputs the modulated optical signal.

[0027] The modulated optical signal is injected into the first dispersive element for phase-intensity conversion and time-domain expansion, which can realize time-domain aliasing encryption of the modulated optical signal and finally output encrypted optical information signal.

[0028] As a preferred embodiment, the vector light field manipulation module includes a first fiber collimator (COL1), linear polarizers (LP), a first beam splitter (BS1), a first spatial light modulator (SLM1), a first quarter-wave plate (QWP1), and a beam expander telescope (Telescope1).

[0029] The fourth optical signal emitted from the wavelength division multiplexer passes sequentially through the first fiber collimator, the linear polarizer, and the first optical beam splitter before being reflected onto the first spatial light modulator for modulation. The modulated signal, after being modulated by the first spatial light modulator, is reflected back to the first optical beam splitter and then projected onto the first quarter-wave plate before being emitted as a lemon vector beam or a star vector beam.

[0030] As a preferred embodiment, the linear polarizer forms a 45° angle with the liquid crystal molecule alignment direction of the first spatial light modulator.

[0031] As a preferred embodiment, the modulation of the encrypted optical information signal by the first spatial light modulator includes the following steps: the x-polarization component parallel to the liquid crystal molecules of the first spatial light modulator is modulated into a first-order vortex beam, while the y-polarization component perpendicular to the liquid crystal molecules of the first spatial light modulator is not modulated and remains a Gaussian beam.

[0032] As a preferred embodiment, the first quarter-wave plate is parallel or perpendicular to the fast axis direction of the linear polarizer.

[0033] As a preferred embodiment, the modulation of the modulation signal by the first quarter-wave plate includes the following steps: when the first quarter-wave plate is parallel to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré lemon vector beam composed of a right-handed first-order vortex beam and a left-handed Gaussian beam; when the first quarter-wave plate is perpendicular to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré stellar vector beam composed of a right-handed Gaussian beam and a left-handed first-order vortex beam.

[0034] As a preferred embodiment, the vector optical field demodulation module includes: a telescope 2, a second quarter-wave plate (QWP2), a second beam splitter (BS2), a second spatial light modulator (SLM2), and a second fiber collimator (COL2).

[0035] After the beam shrinker receives the vector beam transmitted from the free space link, it passes through the second quarter-wave plate and the second optical beam splitter in sequence and is then projected onto the second spatial light modulator for demodulation. The vector beam is demodulated into a fourth optical signal and then passes through the second fiber collimator to couple the fourth optical signal into the optical fiber.

[0036] As a preferred embodiment, the vector optical field demodulation module further includes a small-signal amplifier, and the fourth optical signal is injected into the wave demultiplexer after passing through the small-signal amplifier.

[0037] As a preferred embodiment, the chaotic decryption module includes: a fourth tunable optical attenuator (VOA4), a fifth tunable optical attenuator (VOA5), a third optical isolator (ISO3), a third polarization controller (PC3), a fourth fiber coupler (FC4), a second slave laser (SL2), a fiber delay line (DL), a second photodetector (PD2), a second radiofrequency amplifier (RF2), a second chromatic dispersion element (DCF2), a second phase modulator (PM2), a demultiplexer (DMUX), and a multi-channel optical receiver;

[0038] After the fourth signal is demodulated by the wave demultiplexer, the encrypted optical information signal and the second optical signal are separated. The encrypted optical information signal is injected into the second phase modulator after being compressed in the time domain and inversely transformed in the phase-intensity domain by the second dispersive element.

[0039] The second optical signal is sequentially injected into the second slave laser through the fourth adjustable optical attenuator, the third optical isolator, and the third polarization controller. The laser signal output from the second slave laser is split into two paths after passing through the fourth fiber coupler.

[0040] One of them receives the second optical signal;

[0041] Another optical signal is sequentially converted into a chaotic modulation signal by an optical fiber delay line and a second photodetector, and then injected into the second radio frequency amplifier as the input to the second phase modulator as the fifth optical signal. The modulated optical signal injected into the second phase modulator is decrypted in the phase frequency domain to obtain the decrypted optical information signal.

[0042] The decrypted optical signal is injected into each optical receiver after the demultiplexer to obtain the original decrypted signal.

[0043] The technical effects and advantages of this invention are as follows:

[0044] 1. A free-space vector anti-turbulence secure optical communication scheme based on chaotic time-frequency aliasing encryption can effectively achieve encryption and decryption of optical information in the optical domain by using chaotic signals to perform three-dimensional time-frequency phase aliasing disturbance on the original WDM optical information signal; at the same time, combined with vector optical field modulation to achieve high-fidelity transmission of optical field information, it can significantly enhance the physical layer information security and reliability of the space optical communication system.

[0045] 2. In the encryption and decryption scheme of this invention, the problem of limited transmission rate caused by using chaotic signals as optical information carriers is avoided. Instead, it is used as a three-party synchronous driving signal and a control disturbance signal for the phase modulator. Therefore, it can support encryption and decryption of different rates and arbitrary modulation formats.

[0046] 3. The encryption / decryption scheme and vector light field modulation / demodulation scheme proposed in this invention are effectively compatible with existing WDM communication network systems, enabling plug-and-play functionality and supporting bidirectional transmission. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the structure of a free space vector anti-turbulence chaotic secure optical communication system provided in one embodiment of the present invention;

[0048] Figure 2 This is a comparison diagram of the original WDM signal spectrum and eye diagrams of each channel provided in one embodiment of the present invention;

[0049] Figure 3 This is a comparison diagram of the encrypted signal spectrum and eye diagrams of each channel provided in one embodiment of the present invention;

[0050] Figure 4 The image shows the full Poincaré light field and polarization distribution of the stellar beam generated by vector light field modulation in one embodiment of the present invention.

[0051] Figure 5 This is a diagram showing the full Poincaré light field and polarization distribution of lemon light generated by vector light field modulation in one embodiment of the present invention. Detailed Implementation

[0052] The features and exemplary embodiments of various aspects of this application will be described in detail below. To make the objectives, technical solutions, and advantages of this application clearer, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only intended to explain this application and not to limit it. For those skilled in the art, this application can be implemented without some of these specific details. The following description of the embodiments is merely to provide a better understanding of this application by illustrating examples.

[0053] like Figure 1 As shown, in one embodiment of the present invention, a free-space vector anti-turbulence chaotic secure optical communication system is provided, characterized in that: the secure optical communication system includes a signal transmitting system, a free-space link, and a signal receiving system;

[0054] The signal transmission system includes a chaos driving module, a chaos encryption module, a wavelength division multiplexer, and a vector optical field control module.

[0055] The chaotic driving module can output a first optical signal and a second optical signal. The first optical signal can be injected into the chaotic encryption module as a chaotic synchronization driving signal at the transmitting end; the second optical signal serves as a chaotic synchronization driving optical signal at the decryption end (receiving end).

[0056] The chaotic encryption module can generate optical information signals and a third optical signal. The third optical signal is a chaotic control signal, which can be used as a control signal to encrypt the optical information signal. The chaotic encryption module finally emits an encrypted optical information signal.

[0057] The encrypted optical information signal and the second optical signal are simultaneously injected into the wavelength division multiplexer to generate a multiplexed fourth optical signal. The fourth optical signal is injected into the vector optical field modulation module, modulated into a vector beam, and then incident on the free space link and transmitted to the signal receiving system.

[0058] The signal receiving system includes a vector optical field demodulation module, a wave demultiplexer, and a chaos decryption module;

[0059] The vector light field demodulation module is used to receive a vector beam, demodulate the vector beam into a fourth optical signal, inject it into a wave demultiplexer, separate the encrypted optical information signal and the second optical signal, and then inject them together into the chaotic decryption module.

[0060] The second optical signal is injected into the chaotic decryption module as a driving signal, which drives the chaotic decryption module to generate a fifth optical signal as a chaotic control signal, which decrypts the encrypted optical information signal injected into the chaotic decryption module to obtain the decrypted original signal.

[0061] The technical solution provided in this application is a free-space vector anti-turbulence secure optical communication scheme based on chaotic time-frequency aliasing encryption. In the signal transmission system, by using chaotic signals to perform time-frequency phase three-dimensional aliasing disturbance on the original WDM optical information signal, encryption and decryption of optical information in the optical domain can be effectively achieved. At the same time, combined with vector optical field modulation to achieve high-fidelity transmission of optical field information, the physical layer information security and reliability of the space optical communication system can be significantly enhanced.

[0062] This application avoids the problem of limited transmission rate caused by using chaotic signals as optical information carriers. Instead, it uses them as a three-way synchronous driving signal and a control disturbance signal for the phase modulator, thus enabling encryption and decryption with different rates and arbitrary modulation formats.

[0063] In one embodiment of this application, the signal transmission system further includes a power adjustment module, which can be used to adjust the spatial transmission power of the fourth optical signal and inject the adjusted fourth optical signal into the vector light field control module.

[0064] In one embodiment of this application, the power adjustment module is an optical fiber amplifier, which is a commercially available module with various options.

[0065] In one specific embodiment of this application, the fiber amplifier is a first erbium-doped fiber amplifier.

[0066] As a preferred embodiment, the chaos driving module includes a main laser, a first polarization controller, a first fiber coupler, a second fiber coupler, a first tunable optical attenuator, a fiber mirror, and a first optical isolator.

[0067] The laser signal emitted from the main laser, after passing through the first polarization controller, is split into two paths by the first fiber coupler at a certain ratio.

[0068] One optical signal is reflected back to the main laser by the first adjustable optical attenuator and the fiber optic mirror in sequence.

[0069] The other optical signal is split into the same first optical signal and second optical signal after passing through the first optical isolator and the second optical fiber coupler in sequence. The first optical signal is injected into the chaotic encryption module as the chaotic synchronization drive signal at the transmitting end, and the second optical signal is used as the chaotic synchronization drive optical signal at the receiving end.

[0070] Here, the first tunable optical attenuator can be used to control the laser power, the fiber optic mirror reflects the optical signal back into the main laser to disturb the internal state of the laser, causing the laser to emit chaotic signals, and the first optical isolator can be used to control the direction of optical signal transmission.

[0071] In one specific embodiment of this application, the first fiber coupler splits the laser signal into two paths at a ratio of 1:9, with 10% of the optical signal returning to the main laser and 90% of the optical signal incident on the first optical isolator. This ratio is the result of experimental optimization.

[0072] In one specific embodiment of this application, the chaotic encryption module includes a multi-channel optical transmitter, a multiplexer, a first slave laser, a third fiber coupler, a second tunable optical attenuator, a third tunable optical attenuator, a second optical isolator, a second polarization controller, a first photodetector, a first radio frequency amplifier, a first phase modulator, and a first dispersive element.

[0073] The laser signal emitted from the first slave laser is split into two signals after passing through the third fiber coupler. One of the signals receives the first optical signal output from the chaos driving module. The first optical signal passes through the second optical isolator, the second polarization controller and the second adjustable optical attenuator in sequence before being input back into the first slave laser as a control signal.

[0074] The other optical signal is sequentially amplified by the third adjustable optical attenuator, the first photodetector, and the first radio frequency amplifier, and then converted into a third optical signal before being injected into the first phase modulator.

[0075] After multiplexing the optical information signals of different wavelengths emitted from the multiplexer, the output optical information signal is injected into the first phase modulator. Under the action of the third optical signal, the first phase modulator performs phase spectrum perturbation encryption on the optical information signal and outputs a modulated optical signal. Here, the output of the multiplexer is a WDM signal, and the third optical signal is used as the driving signal for the first phase modulator to drive the first phase modulator to work.

[0076] The modulated optical signal is injected into the first dispersive element for phase-intensity conversion and time-domain expansion, which can realize time-domain aliasing encryption of the modulated optical signal and finally output encrypted optical information signal.

[0077] The encrypted optical information signal and the second optical signal are simultaneously injected into the wavelength division multiplexer to generate a multiplexed fourth optical signal, which is then injected into the vector optical field control module.

[0078] The multi-channel optical transmitter can output multiple optical signals according to the actual working conditions. In this embodiment, four optical signals are selected for transmission, so a total of four optical transmitters, λ1-λ4, are selected. The signals transmitted by the optical transmitters can be optical signals of any modulation format, such as on / off keying (OOK), quadrature amplitude modulation (QAM), four-level pulse amplitude modulation (PMA4), etc.

[0079] In one specific embodiment of this application, a first laser-selected distributed feedback semiconductor laser is used.

[0080] In one specific embodiment of this application, the vector light field modulation module includes a first fiber collimator, a linear polarizer, a first optical beam splitter, a first spatial light modulator, a first quarter-wave plate, and a beam expander telescope.

[0081] The fourth optical signal emitted from the wavelength division multiplexer passes sequentially through the first fiber collimator, the linear polarizer, and the first optical beam splitter before being reflected onto the first spatial light modulator for modulation. The modulated signal, after being modulated by the first spatial light modulator, is reflected back to the first optical beam splitter and then projected onto the first quarter-wave plate before being emitted as a lemon vector beam or a star vector beam.

[0082] In one specific embodiment of this application, the linear polarizer forms a 45° angle with the liquid crystal molecule alignment direction of the first spatial light modulator.

[0083] In one specific embodiment of this application, the modulation of the encrypted optical information signal by the first spatial light modulator includes the following steps: the x-polarization component parallel to the liquid crystal molecules of the first spatial light modulator is modulated into a first-order vortex beam, while the y-polarization component perpendicular to the liquid crystal molecules of the first spatial light modulator is not modulated and remains a Gaussian beam.

[0084] In one specific embodiment of this application, the first quarter-wave plate is parallel or perpendicular to the fast axis direction of the linear polarizer.

[0085] In one specific embodiment of this application, the modulation of the modulation signal by the first quarter-wave plate includes the following steps: when the first quarter-wave plate is parallel to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré lemon vector beam composed of a right-handed first-order vortex beam and a left-handed Gaussian beam; when the first quarter-wave plate is perpendicular to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré stellar vector beam composed of a right-handed Gaussian beam and a left-handed first-order vortex beam.

[0086] In one specific embodiment of this application, the vector light field demodulation module includes: a beam shrinking mirror, a second quarter-wave plate, a second optical beam splitter, a second spatial light modulator, and a second fiber collimator.

[0087] After the beam shrinker receives the vector beam transmitted from the free space link, it passes through the second quarter-wave plate and the second optical beam splitter in sequence and is then projected onto the second spatial light modulator for demodulation. The vector beam is demodulated into a fourth optical signal and then passes through the second fiber collimator to couple the fourth optical signal into the optical fiber.

[0088] Here, the vector optical field demodulation module is a demodulation process that is symmetrical and opposite to that of the vector optical field control module. It converts the Sagittarius / Lemon vector beam into a linearly polarized Gaussian beam, and finally couples the linearly polarized Gaussian beam into a single-mode fiber through the second fiber collimator.

[0089] In one specific embodiment of this application, the vector optical field demodulation module further includes a small-signal amplifier, which performs transmission link attenuation compensation, and the fourth optical signal is injected into a wavelength demultiplexer after passing through the small-signal amplifier. In another specific embodiment of this application, the small-signal amplifier is a second erbium-doped fiber amplifier.

[0090] In one specific embodiment of this application, the chaotic decryption module includes: a fourth tunable optical attenuator, a fifth tunable optical attenuator, a third optical isolator, a third polarization controller, a fourth fiber coupler, a second slave laser, a fiber delay line, a second photodetector, a second radio frequency amplifier, a second dispersive element, a second phase modulator, a slave demultiplexer, and a multiplexer.

[0091] After the fourth signal is demodulated by the wave demultiplexer, the encrypted optical information signal and the second optical signal are separated. The encrypted optical information signal is injected through the second dispersive element for time-domain compression and phase-intensity inverse transformation, and the output is an encrypted optical signal with only phase disturbance. The output modulated optical signal is then injected into the second phase modulator.

[0092] The second optical signal is sequentially injected into the second slave laser through the fourth adjustable optical attenuator, the third optical isolator, and the third polarization controller. The laser signal output from the second slave laser is split into two identical paths after passing through the fourth fiber coupler.

[0093] One of them receives the second optical signal;

[0094] Another optical signal is sequentially converted into a chaotic modulation signal by an optical fiber delay line and a second photodetector, and then injected into the second radio frequency amplifier as the input to the second phase modulator as the fifth optical signal. The modulated optical signal injected into the second phase modulator is decrypted in the phase frequency domain to obtain the decrypted optical information signal.

[0095] The decrypted optical signal is injected into each optical receiver after the demultiplexer to obtain the original decrypted signal.

[0096] like Figure 2 , Figure 3 As shown, in one embodiment of this application, a WDM signal output from the multiplexer is provided, along with a spectrum diagram and a comparison diagram of eye diagrams for each channel of the encrypted optical information signal after phase spectrum perturbation encryption, phase-intensity conversion, and time-domain expansion.

[0097] Figure 2 It contains the original WDM signal spectrum and the eye diagrams of the four channels. Figure 3This is the signal spectrum and four channel eye diagrams of the encrypted WDM signal. As can be seen, the four channels of the original WDM signal are clearly distinguishable, and the eye diagrams are clear. After the chaotic time-frequency aliasing encryption proposed in this scheme, the spectrum is significantly broadened. The spectrum of the encrypted WDM signal resembles spontaneous emission noise, and the signal is very smooth. The channel characteristics of the four channels in the optical domain are completely hidden, and the channel eye diagrams are tightly closed. This means that for eavesdroppers, it is impossible to directly decipher the channel information (such as channel spacing, information rate, modulation format, etc.), thus fully ensuring the security of signal transmission in the link.

[0098] One embodiment of this application also provides the distribution of the light field and polarization state generated by vector light field modulation, such as Figure 4 , Figure 5 As shown, Figure 4 The distribution of the full Poincaré vector light field and polarization state generated by vector light field manipulation. Figure 5 This embodiment presents a lemon-shaped full Poincaré vector light field and its polarization state distribution generated by vector light field manipulation. The provided beam is a first-order full Poincaré vector beam, producing a solid light field with a non-uniform polarization state distribution. The polarization insensitivity of atmospheric turbulence allows the non-uniformly distributed vector light field to be transmitted with high fidelity in real atmosphere.

[0099] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the invention, it should be understood that the invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the invention as defined and determined by the appended claims, and all inventions utilizing the concept of the present invention are protected.

Claims

1. A free-space vector anti-turbulence chaotic secure optical communication system, characterized in that: The secure optical communication system includes a signal transmitting system, a free-space link, and a signal receiving system; The signal transmission system includes a chaos driving module, a chaos encryption module, a wavelength division multiplexer, and a vector optical field control module. The chaotic driving module can output a first optical signal and a second optical signal. The first optical signal can be injected into the chaotic encryption module as a chaotic synchronization driving signal at the transmitting end; the second optical signal is used as a chaotic synchronization driving optical signal at the decryption end. The chaotic encryption module can generate optical information signals and a third optical signal. The third optical signal is a chaotic control signal, which can be used as a control signal to encrypt the optical information signal. The chaotic encryption module finally emits an encrypted optical information signal. The chaotic encryption module includes a multi-channel optical transmitter, a multiplexer, a first slave laser, a third fiber coupler, a second tunable optical attenuator, a third tunable optical attenuator, a second optical isolator, a second polarization controller, a first photodetector, a first radio frequency amplifier, a first phase modulator, and a first dispersive element. The laser signal emitted by the first slave laser is split into two signals after passing through the third fiber coupler. One signal receives the first optical signal output from the chaos driving module. The first optical signal passes through the second optical isolator, the second polarization controller and the second adjustable optical attenuator in sequence before being input into the first slave laser as the transmitting end chaos synchronization driving signal. The other optical signal is sequentially amplified by the third adjustable optical attenuator, the first photodetector, and the first radio frequency amplifier, and then converted into a third optical signal before being injected into the first phase modulator. After multiplexing the optical information signals of different wavelengths emitted from the multiplexer, the output optical information signal is injected into the first phase modulator. Under the action of the third optical signal, the first phase modulator performs phase spectrum perturbation encryption on the optical information signal and outputs the modulated optical signal. The modulated optical signal is injected into the first dispersive element for phase-intensity conversion and time-domain expansion, which can realize the time-domain aliasing encryption of the modulated optical signal and finally output the encrypted optical information signal. The encrypted optical information signal and the second optical signal are simultaneously injected into the wavelength division multiplexer to generate a multiplexed fourth optical signal. The fourth optical signal is injected into the vector optical field modulation module, modulated into a vector beam, and then incident on the free space link and transmitted to the signal receiving system. The signal receiving system includes a vector optical field demodulation module, a wave demultiplexer, and a chaos decryption module; The vector light field demodulation module is used to receive a vector beam, demodulate the vector beam into a fourth optical signal, inject it into a wave demultiplexer, separate the encrypted optical information signal and the second optical signal, and then inject them together into the chaotic decryption module. The second optical signal is injected into the chaotic decryption module as a driving signal, which drives the chaotic decryption module to generate a fifth optical signal as a chaotic control signal, which decrypts the encrypted optical information signal injected into the chaotic decryption module to obtain the decrypted original signal.

2. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 1, characterized in that: The signal transmission system also includes a power adjustment module, which is used to adjust the spatial transmission power of the fourth optical signal and inject the adjusted fourth optical signal into the vector light field control module.

3. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 2, characterized in that: The power adjustment module is an optical fiber amplifier.

4. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 1, characterized in that: The chaos driving module includes a main laser, a first polarization controller, a first fiber coupler, a second fiber coupler, a first tunable optical attenuator, a fiber mirror, and a first optical isolator. The laser signal emitted from the main laser, after passing through the first polarization controller, is split into two paths by the first fiber coupler according to a certain ratio. One optical signal is reflected back to the main laser through the first adjustable optical attenuator and the fiber optic mirror to generate a chaotic driving signal. The other optical signal is split into the same first optical signal and second optical signal after passing through the first optical isolator and the second optical fiber coupler in sequence. The first optical signal is injected into the chaotic encryption module as the chaotic synchronization drive signal at the transmitting end, and the second optical signal is used as the chaotic synchronization drive optical signal at the receiving end.

5. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 4, characterized in that: The first fiber coupler splits the laser signal into two paths at a ratio of 1:9, with 10% of the optical signal returning to the main laser and 90% of the optical signal entering the first optical isolator.

6. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 1, characterized in that: The vector light field control module includes a first fiber collimator, a linear polarizer, a first optical beam splitter, a first spatial light modulator, a first quarter-wave plate, and a beam expander telescope. The fourth optical signal emitted from the wavelength division multiplexer passes sequentially through the first fiber collimator, the linear polarizer, and the first optical beam splitter before being reflected onto the first spatial light modulator for modulation. The modulated signal, after being modulated by the first spatial light modulator, is reflected back to the first optical beam splitter and then projected onto the first quarter-wave plate before being emitted as a lemon vector beam or a star vector beam.

7. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 6, characterized in that: The linear polarizer forms a 45° angle with the liquid crystal molecule alignment direction of the first spatial light modulator.

8. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 7, characterized in that: The modulation of the encrypted optical information signal by the first spatial light modulator includes the following steps: the x-polarization component parallel to the liquid crystal molecules of the first spatial light modulator is modulated into a first-order vortex beam, while the y-polarization component perpendicular to the liquid crystal molecules of the first spatial light modulator is not modulated and remains a Gaussian beam.

9. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 8, characterized in that: The first quarter-wave plate is parallel or perpendicular to the fast axis of the linear polarizer.

10. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 9, characterized in that: The modulation of the modulation signal by the first quarter-wave plate includes the following steps: when the first quarter-wave plate is parallel to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré lemon vector beam composed of a right-handed first-order vortex beam and a left-handed Gaussian beam; when the first quarter-wave plate is perpendicular to the fast axis of the linear polarizer, the x and y linear polarization components are converted into right-handed and left-handed circular polarization components, and the first quarter-wave plate modulates the modulation signal into a first-order full Poincaré stellar vector beam composed of a right-handed Gaussian beam and a left-handed first-order vortex beam.

11. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 1, characterized in that: The vector optical field demodulation module includes a beam shrinking mirror, a second quarter-wave plate, a second optical beam splitter, a second spatial light modulator, and a second fiber collimator. After the beam shrinker receives the vector beam transmitted from the free space link, it passes through the second quarter-wave plate and the second optical beam splitter in sequence and is then projected onto the second spatial light modulator for demodulation. The vector beam is demodulated into a fourth optical signal and then passes through the second fiber collimator to couple the fourth optical signal into the optical fiber.

12. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 11, characterized in that: The vector optical field demodulation module also includes a small signal amplifier, and the fourth optical signal is injected into the wave demultiplexer after passing through the small signal amplifier.

13. The free-space vector anti-turbulence chaotic secure optical communication system according to claim 1, characterized in that: The chaotic decryption module includes: a fourth tunable optical attenuator, a fifth tunable optical attenuator, a third optical isolator, a third polarization controller, a fourth fiber coupler, a second slave laser, a fiber delay line, a second photodetector, a second radio frequency amplifier, a second dispersive element, a second phase modulator, a slave demultiplexer, and a multiplexer. After the fourth signal is demodulated by the wave demultiplexer, the encrypted optical information signal and the second optical signal are separated. The encrypted optical information signal is injected into the second phase modulator after being compressed in the time domain and inversely transformed in the phase-intensity domain by the second dispersive element. The second optical signal is sequentially injected into the second slave laser through the fourth adjustable optical attenuator, the third optical isolator, and the third polarization controller. The laser signal output from the second slave laser is split into two paths after passing through the fourth fiber coupler. One of them receives the second optical signal; Another optical signal is sequentially converted into a chaotic modulation signal by an optical fiber delay line and a second photodetector, and then injected into the second radio frequency amplifier as the input to the second phase modulator as the fifth optical signal. The modulated optical signal injected into the second phase modulator is decrypted in the phase frequency domain to obtain the decrypted optical information signal. The decrypted optical information signal is injected into each optical receiver after the demultiplexer to obtain the original decrypted signal.

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