A security enhanced chaotic communication system and method based on external time domain self-feedback encryption

Abstract

The application provides a security-enhanced chaotic communication system and method based on external time-domain self-feedback encryption, and relates to the technical field of chaotic communication carrier. The application utilizes two dispersion components and a phase modulator in the middle of dispersion to form an encryption module, and under the joint action of the encryption module, the encrypted chaotic signal is processed in time domain and phase. At the receiving end, the encrypted information is recovered in time domain and phase by using a symmetric decryption structure. Since the encryption module suppresses the time delay characteristics embedded in the chaotic carrier and the time delay characteristics in the electro-optical self-feedback phase loop, the eavesdropper cannot crack the time delay information by calculating the autocorrelation and mutual information, so the key parameters of the system cannot be intercepted, and since the dispersion value and the phase modulation depth in the encryption module are controllable variables, the key space of the system is further increased, so the security of the system is ensured.

Description

Technical Field

[0001] This invention relates to the technical field of chaotic communication carriers, and more specifically, to a security-enhanced chaotic communication system and method based on external time-domain self-feedback encryption. Background Technology

[0002] Chaotic communication has attracted widespread attention due to its advantages in physical layer encryption. Given the noise-like, non-periodic, and continuous broadband spectrum characteristics of chaos, using chaos as an encryption method for secure optical communication is very promising. The successful proposal of chaotic synchronization systems has led to a focus on chaos in protecting optical communication data exchange, seeking more secure communication methods. The feasibility of chaotic secure optical communication has been experimentally verified in the Athens commercial optical network, and the success of this experiment has strengthened various innovative researches in chaotic optical communication. In a typical chaotic optical communication system, the chaotic transmitter is the key optical device for generating a noise-like broadband chaotic optical carrier for signal concealment. External cavity semiconductor lasers are a very popular and simple transmitter for generating chaos, producing the chaotic optical carrier by using an external feedback cavity. However, since the feedback light is a linear copy of the output light, the generated chaos will have a certain periodicity, which represents the length of the external feedback cavity, thus leading to time delay characteristics in the laser. By analyzing the autocorrelation function, delay mutual information, and power spectrum of chaos generated in an external cavity semiconductor laser, time delay characteristics can be easily obtained, allowing the extraction of the external cavity length and thus posing a security risk for hacking. Traditional methods for suppressing time delay characteristics generally involve altering the external cavity structure of the chaotic laser or randomly modulating the feedback signal to break the inherent time delay characteristics of the feedback chaotic signal within the external cavity, or adding hardware modules within the chaotic transmitter cavity. Since the feedback signal reflected within the cavity is no longer a simple copy of the chaotic signal output by the laser, time periodicity and the corresponding time delay characteristics can be significantly suppressed. However, these methods may suffer from high implementation complexity, reduced robustness and stability of chaotic synchronization, directly limiting the application of chaotic communication systems. Besides the time delay characteristic problem, traditional chaotic communication systems also face several other potential security threats. Research shows that when optical chaos is used as the information carrier and information is transmitted at a low transmission rate, a direct linear filtering attack can be employed. When the cutoff frequency of the low-pass filter is set equal to the transmission bit rate, an eavesdropper can intercept some confidential information. Another attack method is a synchronization exploitation attack, which first separates the chaotic modulated signal from the public transmission link and then injects it into the cavity of an attack laser that resembles a legitimate receiver. Due to the injection locking mechanism, this illegitimate attack laser will also be able to generate a chaotic synchronization signal, making it possible to intercept messages by subtracting this synchronization signal from the signal separated from the public link.

[0003] Chinese patent application CN107483174A, published on December 15, 2017, discloses a method using a chirped fiber Bragg grating as the feedback component of a semiconductor laser to generate a chaotic carrier. Because the chirped fiber Bragg grating-feedback semiconductor laser is sensitive to parameters, it is difficult for an eavesdropper to generate a chaotic synchronization signal through strong injection when reconstructing a semiconductor laser similar to a legitimate receiver, thus improving system security. However, this method still suffers from high implementation complexity and difficulty in integration; the chaotic synchronization is too sensitive to parameters, making it difficult to generate a high-quality chaotic synchronization signal. Summary of the Invention

[0004] To overcome the aforementioned technical problems, this invention provides a method for hardware encryption of data outside a laser, which is highly compatible with existing commercial optical components. This not only eliminates the time delay characteristics of chaotic signals but also achieves high-quality chaotic synchronization, thereby improving system security.

[0005] To solve the above-mentioned technical problems, the technical solution of the present invention is as follows:

[0006] This invention provides a device for a security-enhanced chaotic communication system with external time-domain self-feedback encryption, comprising a transmitting end, a transmission optical fiber, and a receiving end;

[0007] The transmitting end includes: a chaos generation module, a signal generation module, and an encryption module; the chaos generation module includes a first external cavity semiconductor laser, a first optical coupler, and a first optical feedback mirror; the signal generation module includes a carrier intensity modulator and a data generation module; the encryption module includes a first dispersion component, a first phase modulator, a second optical coupler, a first photodetector, a first radio frequency amplifier, and a second dispersion device, specifically:

[0008] A chaos generation module generates a chaotic carrier wave, a signal generation module emits a carrier wave of the optical information to be encrypted, and an encryption module encrypts the chaotic modulated signal. Specifically, the first dispersion component distorts the amplitude of the optical signal to achieve time-domain encryption, the first phase modulator scrambles the phase of the optical signal to achieve phase encryption, and the second dispersion component causes a phase-intensity conversion in the chaotic modulated signal, further distorting the signal amplitude to achieve time-domain encryption. The transmitting end sends the encrypted optical signal to the receiving end via a transmission optical fiber. After receiving the encrypted optical signal, the receiving end decrypts the encrypted optical signal using a decryption module. The third dispersion component restores the time-domain disturbances of the optical signal, the second phase modulator restores the phase-domain disturbances of the optical signal, and the fourth dispersion component restores the time-domain disturbances of the optical signal to obtain the decrypted optical signal. Then, the decrypted optical signal is passed through a chaotic synchronization module, in which the second external cavity semiconductor laser and the second optical feedback mirror generate synchronized chaos. Finally, the decrypted optical signal is passed through an optical fiber delay line to achieve the same delay for both paths, and then through a second photodetector. Another path passes through a second reverse photodetector, and the two electrical signals are added together to obtain the original confidential information.

[0009] This technical solution proposes a security-enhanced chaotic communication system based on external time-domain self-feedback encryption. An encryption module is composed of two dispersive components and a phase modulator. Under the combined action of the dispersive and phase modulators, information is encrypted in both the time and phase domains. A symmetrical decryption module recovers the phase and amplitude of the chaotic modulated signal. A synchronized chaotic carrier wave is generated by a chaotic synchronization module, and the information is recovered by the recovery module. Because the encryption module suppresses the time delay characteristics embedded in the chaotic carrier wave and also suppresses the time delay characteristics in the self-phase feedback loop, and because the loop delays for encryption and decryption must be consistent in the self-phase feedback loop for signal decryption, the security of signal transmission is improved.

[0010] Furthermore, the chaotic modulated signal generation module includes a first external cavity semiconductor laser, a first optical coupler, a first optical feedback mirror, a carrier intensity modulator, and a data generation module;

[0011] The first external cavity semiconductor laser emits a chaotic carrier wave to carry the data to be encrypted. The chaotic carrier wave is input to a carrier intensity modulator. The driver of the carrier intensity modulator is electrically connected to the output of the data generation module. The carrier intensity modulator modulates the data to be encrypted generated by the data generation module onto the optical carrier wave, thereby emitting an optical signal carrying the data to be encrypted.

[0012] Furthermore, the carrier intensity modulator is a Mach-Zehnder modulator.

[0013] Furthermore, the encryption module further includes: a second optical coupler, a first photodetector, and a first radio frequency amplifier; the decryption module further includes a third optical coupler, a first reverse photodetector, and a second radio frequency amplifier; the receiving end further includes an optical isolator and an optical circulator;

[0014] A first external cavity semiconductor laser is connected to the input of a first optical coupler. The first output of the first optical coupler is connected to the input of a first optical feedback mirror. The first external cavity semiconductor laser generates a chaotic optical carrier in the form of optical feedback. The second output of the first optical coupler is connected to a carrier intensity modulator. A data generation module serves as the driving signal for the carrier intensity modulator, modulating information onto the carrier and transmitting it over the link. The output of the carrier intensity modulator is connected to the input of a first dispersion component. The first dispersion component scrambles the waveform of the chaotic modulated signal and suppresses the time delay characteristics embedded in the chaotic carrier. The output of the first optical coupler is connected to the input of the first phase modulator, the second optical coupler is connected to the output of the first phase modulator, the input of the first photodetector is connected to the first output port of the second optical coupler, the output of the second photodetector is connected to the input of the first radio frequency amplifier, the first radio frequency amplifier serves as the driving signal for the first phase modulator to form an electro-optic self-feedback phase loop, the second output port of the second optical coupler is connected to the second dispersion component, the second dispersion component realizes the phase-to-intensity conversion, further disturbs the waveform distribution, and realizes a chaotic modulated signal with no time delay characteristics, and the output of the second dispersion component is connected to the transmission optical fiber;

[0015] The encrypted chaotic modulated signal is transmitted via an optical fiber link and then connected to the input of the third dispersion component. The value of the third dispersion component is required to be opposite to that of the second dispersion component to restore the signal's time-domain disturbance. The output of the third dispersion component is connected to the input of the third optical coupler. The first output port of the third optical coupler is connected to the input of the first reverse photodetector. The input port of the second RF amplifier is connected to the output port of the first reverse photodetector. The second RF amplifier serves as the drive signal for the second phase modulator. The feedback delay of the encryption / decryption loop must be consistent, and the drive signal amplitude must be the same but opposite, thus erasing the phase encryption of the chaotic modulated signal. The input of the second phase modulator is connected to the second output port of the third optical coupler. The fourth dispersion component is connected to the output port of the second phase modulator, further restoring the time-domain disturbance of the chaotic signal, thereby decrypting the signal. The fourth dispersion component is connected to the fourth optical coupler. The input port of the optical isolator is connected to the first output port of the fourth optical coupler. The input port of the optical circulator is connected to the output port of the optical isolator. The first output port of the optical circulator is connected to the first input port of the fifth optical coupler. The input port of the second external cavity semiconductor laser is connected to the first output port of the fifth optical coupler. The input port of the second optical feedback mirror is connected to the second output port of the fifth optical coupler, thereby generating a chaotic synchronization signal. The input port of the second reverse photodetector is connected to the second output port of the optical circulator. The second output port of the fourth optical coupler is connected to the input port of the fiber delay line. The fiber delay line is used to compensate for the delay of another signal. The output port of the fiber delay line is connected to the input port of the second photodetector. The output ports of the second reverse photodetector and the second photodetector are connected to the input ports of the adder. Finally, the confidential information is recovered at the receiving end.

[0016] Furthermore, the first and second radio frequency amplifiers generate electrical drive signals with the same amplitude but opposite magnitudes; the first dispersion component has opposite dispersion values ​​to the fourth dispersion component, and the second dispersion component has opposite dispersion values ​​to the third dispersion component.

[0017] Furthermore, the first dispersion component, the second dispersion component, the third dispersion component, and the fourth dispersion component all use dispersion optical fiber.

[0018] A security-enhanced chaotic communication method based on external time-domain self-feedback encryption includes the following steps:

[0019] S1. Generate a chaotic carrier wave to carry the data to be encrypted;

[0020] S2. Modulate the data to be encrypted onto a chaotic carrier wave to generate a chaotic modulated signal carrying the data to be encrypted;

[0021] S3. Time-domain encryption is achieved by distorting the amplitude of the chaotic signal using the first dispersive component (106).

[0022] S4. A self-phase electro-optical feedback loop is formed using a first phase modulator (107), a second optical coupler (108), a first photodetector (109), and a first radio frequency amplifier (110) to encrypt the phase of the chaotic modulated signal;

[0023] S5. The second dispersive component (111) is used to make the chaotic signal undergo phase-intensity conversion, and the amplitude distortion of the chaotic modulated signal is further made into time-domain encryption.

[0024] S6. The transmitting end (1) sends the encrypted chaotic signal to the receiving end (3) through the transmission optical fiber (2);

[0025] S7. Time-domain recovery of the encrypted optical signal is performed using the third dispersion component (301);

[0026] S8. The first reverse photodetector (303), the second radio frequency amplifier (304), and the second phase modulator (305) are used to form an electro-optic phase feedback loop again to recover the phase of the encrypted optical signal.

[0027] S9. The encrypted optical signal is recovered in the time domain again using the fourth dispersion component (306);

[0028] S10. A chaotic synchronization signal is generated using a second external cavity semiconductor laser (311).

[0029] S11. The chaotic synchronization signal is passed through the second reverse photodetector (313), and the optical signal recovered by the fourth dispersion component (306) is passed through the optical fiber delay line (314) and the second photodetector (315).

[0030] S12. The two electrical signals are processed by an adder (316) to obtain the original optical signal.

[0031] This technical solution proposes a security-enhanced chaotic communication system and method based on external time-domain self-feedback encryption. Compared with existing technologies, the advantages of this invention are: An encryption module composed of two dispersive components and a self-phase electro-optic feedback loop encrypts information through the combined effects of dispersion and phase modulation. A symmetrical decryption module recovers the phase and amplitude of the information. Because the encryption module suppresses the time delay characteristics embedded in the chaotic carrier and the time delay characteristics in the feedback loop, and requires that the time delays within the encryption and decryption loops remain consistent to decrypt the chaotic signal, the security of encryption and decryption is guaranteed. Even if an eavesdropper understands the structure of this invention, their decryption process cannot confirm the time delay within the loop, thus preventing decryption and the determination of the feedback cavity length of the semiconductor laser, and preventing the generation of a chaotic synchronization signal, thereby improving the security of signal transmission. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a security-enhanced chaotic communication system based on external time-domain self-feedback encryption. Detailed Implementation

[0033] To clearly illustrate the security-enhanced chaotic communication system with external time-domain self-feedback encryption of the present invention, the present invention will be further described in conjunction with embodiments and accompanying drawings, but this should not be construed as limiting the scope of protection of the present invention.

[0034] Example 1

[0035] A security-enhanced chaotic communication system based on external time-domain self-feedback encryption, the system comprising: a transmitter 1, a receiver 3, and a transmission optical fiber 2;

[0036] It should be noted that the dashed lines in the structural diagram represent circuits, and the solid lines represent optical paths. The transmitting end 1 includes a chaos generation module, a signal generation module, and an encryption module. The first external cavity semiconductor laser with a center wavelength of λ generates chaos in the form of optical feedback after passing through the first optical feedback mirror. This chaos serves as the optical carrier carrying the non-return-to-zero (NRZ) signal to be encrypted. The pseudo-random bit sequence is pre-encoded into an electrically non-NRZ signal, which is then modulated by a carrier intensity modulator. The modulated NRZ signal enters the encryption structure composed of a first dispersion component, a first phase modulator, a first photodetector, a first radio frequency amplifier, and a second dispersion component to encrypt the signal. The first dispersion component distorts the amplitude of the information. The first phase modulator is split into two paths by an optical coupler. One path passes through the first photodetector and the first radio frequency amplifier to generate a driving signal for the first phase modulator, thereby disrupting the phase of the optical signal. The second dispersion component causes the chaotic modulated signal to undergo a phase-intensity conversion, further disrupting the information distribution in the time domain. Under the combined action of these three optical devices, the information is encrypted in both the time domain and the phase. At the transmission fiber end, the encrypted signal enters the transmission link consisting of single-mode fiber and dispersion-compensating fiber with a dispersion value matching its own for transmission. At the receiving end, the encrypted signal is recovered using a decryption structure symmetrical to that at the transmitting end. This decryption structure comprises a third dispersion component with a dispersion value opposite to that of the second dispersion component at the transmitting end, a second phase modulator with the same half-wave voltage and bandwidth as the first phase modulator, and a fourth dispersion component with a dispersion value opposite to that of the first dispersion component at the transmitting end. First, the third dispersion component is used to recover the effect of the chaotic signal being disturbed in the time domain by the second dispersion component. Then, the second phase modulator is used to recover the phase of the information after being disturbed at the encryption end. Finally, the fourth dispersion component with a dispersion value opposite to that of the first dispersion component is used to recover the intensity. The recovered signal is isolated from the feedback light by an optical isolator, then passes through an optical circulator and enters the fifth optical coupler. After passing through the second optical feedback mirror, it is injected into the cavity of the second external cavity semiconductor laser to generate a chaotic synchronization signal. The decrypted chaotic signal and the chaotic synchronization signal are then converted by photoelectric conversion and subtracted in the electrical domain. The result is then sent to a sampling oscilloscope for signal quality recovery testing. In this embodiment, the driving signals of the first and second phase modulators have the same amplitude but opposite values. The first, second, third, and fourth dispersion components can be selected from various sources, such as chirped fiber gratings or dispersion fibers.

[0037] As illustrated by specific examples, this invention proposes a security-enhanced chaotic communication system and method based on external time-domain self-feedback encryption. An encryption module composed of first and second dispersive components and a first phase modulator encrypts information through the combined effects of dispersion and phase modulation. A symmetrical decryption module recovers the phase and intensity of the information. Because the encryption module can suppress the time delay characteristics embedded in the chaotic carrier and the time delay characteristics within the electro-optic feedback loop, the system's security is guaranteed. Even if an eavesdropper uses classic eavesdropping attack schemes, the bit error rate of the intercepted signal is far higher than the hard-decision forward error correction threshold. Although the eavesdropper understands the structure of this invention, without the same second semiconductor laser as the legitimate receiver, and unable to generate a chaotic synchronization signal, they cannot recover the encrypted signal, thus improving the security of signal transmission.

[0038] Example 2

[0039] This embodiment provides a security-enhanced chaotic communication method based on external time-domain self-feedback encryption, including the following steps:

[0040] S1. Generate a chaotic carrier wave to carry the data to be encrypted;

[0041] S2. Modulate the data to be encrypted onto a chaotic carrier wave to generate a chaotic modulated signal carrying the data to be encrypted;

[0042] S3. Time-domain encryption is achieved by distorting the amplitude of the chaotic signal using the first dispersive component (106).

[0043] S4. A self-phase electro-optical feedback loop is formed using a first phase modulator (107), a second optical coupler (108), a first photodetector (109), and a first radio frequency amplifier (110) to encrypt the phase of the chaotic modulated signal;

[0044] S5. The second dispersive component (111) is used to make the chaotic signal undergo phase-intensity conversion, and the amplitude distortion of the chaotic modulated signal is further made into time-domain encryption.

[0045] S6. The transmitting end (1) sends the encrypted chaotic signal to the receiving end (3) through the transmission optical fiber (2);

[0046] S7. Time-domain recovery of the encrypted optical signal is performed using the third dispersion component (301);

[0047] S8. The first reverse photodetector (303), the second radio frequency amplifier (304), and the second phase modulator (305) are used to form an electro-optic phase feedback loop again to recover the phase of the encrypted optical signal.

[0048] S9. The encrypted optical signal is recovered in the time domain again using the fourth dispersion component (306);

[0049] S10. A chaotic synchronization signal is generated using a second external cavity semiconductor laser (311).

[0050] S11. The chaotic synchronization signal is passed through the second reverse photodetector (313), and the optical signal recovered by the fourth dispersion component (306) is passed through the optical fiber delay line (314) and the second photodetector (315).

[0051] S12. The two electrical signals are processed by an adder (316) to obtain the original optical signal.

[0052] The method described in this embodiment is applied to a security-enhanced chaotic communication system based on external time-domain self-feedback encryption. A schematic diagram of the system structure is shown below. Figure 1 As shown, in this embodiment, the chaotic carrier in step S1 is generated by an external cavity semiconductor laser (101). In step S2, a carrier intensity modulator (104) is used to modulate the data to be encrypted on the chaotic carrier. The carrier intensity modulator (104) is a Mach-Zehnder modulator. In step S3, the first dispersion component (106) is of the same type as the first dispersion component (306) in step S9. In step S5, the second dispersion component (111) is of the same type as the third dispersion component (301) in step S7. Both are chirped fiber gratings or dispersion fibers, and their dispersion values ​​are opposite.

[0053] Although the illustrative specific embodiments of the present invention have been described above to enable those skilled in the art to understand the present invention, it should also be noted that the present invention is not limited to the specific details in the above embodiments, and various simplifications and modifications within the scope of the principles and methods of the present invention are all within the scope of protection of the present invention.

Claims

1. A security-enhanced chaotic communication system based on external time-domain self-feedback encryption, characterized in that, The system includes: a transmitter (1), a transmission optical fiber (2), and a receiver (3); The transmitting end (1) includes: a chaos generation module, a signal generation module, an encryption module, a synchronization module, and a recovery module; the chaos generation module includes a first external cavity semiconductor laser (101), a first optical coupler (102), and a first optical feedback mirror (103); the encryption module includes a first dispersion component (106), a first phase modulator (107), a second optical coupler (108), a first photodetector (109), and a first radio frequency amplifier (110) and a second dispersion component (111); the receiving end (3) includes a decryption module and a synchronization module; the decryption module includes a third dispersion component (301), a third... The optical coupler (302), the first reverse photodetector, the second radio frequency amplifier (304), the second phase modulator (305), and the fourth dispersion component (306) are shown. The synchronization module shown includes a fourth optical coupler (307), an optical isolator (308), an optical circulator (309), a fifth optical coupler (310), a second external cavity semiconductor laser (311), and a second optical feedback mirror (312). The recovery module shown includes a second reverse photodetector (313), an optical fiber delay line (314), and a second photodetector (315). The transmitting end (1), the transmission optical fiber (2), and the receiving end (3) are connected in sequence, specifically: The chaos generation module generates a chaotic carrier wave in the form of optical feedback. The signal generation module (105) emits an optical signal to be encrypted. The encryption module encrypts the optical signal. The first dispersion component (106) scrambles the waveform of the signal to achieve time-domain encryption and suppresses the time delay characteristics embedded in the chaotic carrier wave. The first phase modulator (107) forms an electro-optic feedback phase loop through the first photodetector (109) and the first radio frequency amplifier (110). This loop scrambles the phase of the optical signal to achieve phase encryption. The second dispersion component (111) makes... The optical signal achieves phase-intensity conversion, further encrypting the optical signal in the time domain, and can completely suppress the time delay characteristics embedded in the chaotic carrier and the time delay characteristics in the electro-optic feedback phase loop. The optical signal is encrypted with no time delay characteristics after time domain and phase encryption. The transmitting end (1) sends the encrypted optical signal to the receiving end (3) through the transmission optical fiber (2). After receiving the encrypted optical signal, the receiving end (3) decrypts the encrypted optical signal. The third dispersion component (301) restores the disturbance effect of the encrypted optical signal in the time domain. The optical signal split from the third optical coupler passes through the first reverse photodetector (303) and the second RF amplifier (304) and serves as the driving signal for the second phase modulator (305). It requires the same time delay within the encryption and decryption loops. The phase of the encrypted optical signal is recovered using a driving signal with the opposite amplitude to that of the encryption end. The fourth dispersion component (306) then recovers the amplitude of the encrypted optical signal. The decrypted optical signal is then unidirectionally injected into the second external cavity semiconductor through the optical isolator (308) and optical circulator (309). The bulk laser (311) generates a synchronous chaotic signal after the optical signal passes through the second optical feedback mirror (312). One of the signals is generated by the second output port of the fourth optical coupler (307), which modulates the time delay of the two signals through the fiber delay line (314) and then converts them into an electrical signal through the second photodetector (315). The other signal is generated by the chaotic synchronization signal sent to the second reverse photodetector (313) through the third output terminal of the optical circulator (309) and converted into an electrical signal. Finally, the two signals are used to recover the original confidential information through the adder.

2. The security-enhanced chaotic communication system based on external time-domain self-feedback encryption according to claim 1, characterized in that, The chaos generation module includes a first external cavity semiconductor laser (101), a first optical coupler (102), and a first optical feedback mirror (103); the signal generation module includes a carrier intensity modulator (104) and a data generation module (105); The first external cavity semiconductor laser (101), the first optical coupler (102), and the first optical feedback mirror (103) emit an optical carrier for carrying the data to be encrypted. The optical carrier is input to the carrier intensity modulator (104). The driving end of the carrier intensity modulator (104) is electrically connected to the output end of the data generation module (105). The carrier intensity modulator (104) modulates the data to be encrypted generated by the data generation module (105) onto the optical carrier, thereby emitting an optical signal carrying the data to be encrypted.

3. The security-enhanced chaotic communication system based on external time-domain self-feedback encryption according to claim 2, characterized in that, The carrier intensity modulator (104) is a Mach-Zehnder modulator.

4. A security-enhanced chaotic communication system based on external time-domain self-feedback encryption according to any one of claims 2 and 3, characterized in that, The encryption module further includes: a first dispersion component (106), a first phase modulator (107), a second optical coupler (108), a first photodetector (109), a first radio frequency amplifier (110), and a second dispersion component (111); the decryption module further includes a third dispersion component (301), a first reverse photodetector (303), a second radio frequency amplifier (304), a second phase modulator (305), and a fourth dispersion component (306); the synchronization module includes a fourth optical coupler (307), an optical isolator (308), an optical circulator (309), a fifth optical coupler (310), a second external cavity semiconductor laser (311), and a second optical feedback mirror (312); the recovery module includes a second reverse photodetector (313), an optical fiber delay line (314), and a second photodetector (315); The output of the first dispersion component (106) is connected to the input of the first phase modulator (107), the input of the second optical coupler (108) is connected to the output of the first phase modulator (107), the input of the first photodetector (109) is connected to the first output port of the second coupler (108), the output of the first photodetector (109) is connected to the input of the first radio frequency amplifier (110), the output of the first radio frequency amplifier (110) serves as the driving electrical signal for the first phase modulator (107) to modulate the phase depth of the optical signal, the second output port of the second optical coupler (108) is connected to the input port of the second dispersion component (111), and the output of the second dispersion component (111) is connected to the transmission optical fiber (2). The transmission optical fiber (2) is connected to the input end of the third dispersive element (301), the output end of the third dispersive element (301) is connected to the input end of the third optical coupler (302), the first output port of the third optical coupler (302) is connected to the input end of the first reverse photodetector (303), the input end of the second radio frequency amplifier (304) is connected to the output port of the first reverse photodetector (303), and the second radio frequency amplifier (304) serves as the driving signal for the second phase modulator (305), restoring the phase disturbance effect of the encrypted optical signal. The input of (303) is connected to the second output port of the third optical coupler (302) to match the optical signal to be decrypted in phase. Then, the input of the fourth dispersion device (306) is connected to the output port of the second phase modulator (305). The fourth dispersion device (306) is further used to recover the disturbance effect of the optical signal in the time domain. After that, the output of the fourth dispersion device (306) is connected to the input of the fourth optical coupler (307). The input port of the optical isolator (308) is connected to the first output port of the fourth optical coupler (307). The optical circulator (309) The input port of the optical circulator (309) is connected to the output port of the optical isolator (308). The first output port of the optical circulator (309) is connected to the first input port of the fifth optical coupler (310). The input port of the second external cavity semiconductor laser (311) is connected to the first output port of the fifth optical coupler (310). The input port of the second optical feedback mirror (312) is connected to the second output port of the fifth optical coupler (310). The second optical feedback mirror (312) feeds back the optical signal to the second external cavity semiconductor laser (311) to generate a synchronous chaotic signal. The second reverse photodetector (313) The input port of the optical circulator (309) is connected to the second output port of the optical circulator (309), and the second output port of the fourth optical coupler (307) is connected to the input port of the optical fiber delay line (314). The optical fiber delay line (314) is used to keep the time delay of the two signals the same. The output port of the optical fiber delay line (314) is connected to the input port of the second photodetector (315). The output ports of the second reverse photodetector (313) and the second photodetector (315) are both connected to the input port of the adder (316). Finally, the original confidential information is recovered at the receiving end.

5. A security-enhanced chaotic communication system based on external time-domain self-feedback encryption according to claim 4, characterized in that, The driving electrical signals generated by the first RF amplifier (110) and the second RF amplifier (304) have the same amplitude but opposite values; the dispersion values ​​of the first dispersion component (106) and the fourth dispersion component (306) are opposite, and the dispersion values ​​of the second dispersion component (111) and the third dispersion component (301) are opposite.

6. A security-enhanced chaotic communication system based on external time-domain self-feedback encryption according to claim 5, characterized in that, The first dispersion component (106), the second dispersion component (111), the third dispersion component (301), and the fourth dispersion component (306) can all be replaced by chirped fiber gratings or common dispersion fibers.

7. A method for enhancing the security of a chaotic communication system based on external time-domain self-feedback encryption as described in any one of claims 1 to 6, characterized in that, Including the following steps: S1. Generate an optical carrier wave for carrying the data to be encrypted; S2. Modulate the data to be encrypted onto the optical carrier to generate an optical signal carrying the data to be encrypted; S3. The first dispersive component (106) is used to distort the amplitude of the optical signal to achieve time-domain encryption, and at the same time, the time delay characteristics embedded in the chaotic carrier are suppressed. S4. Using the first phase modulator (107), the first photodetector (109) and the first radio frequency amplifier (110) to form an electro-optic phase feedback loop, the time-domain encrypted optical signal is phase-encrypted to obtain a phase-encrypted optical signal. S5. The second dispersive component (111) is used to make the optical signal undergo phase-intensity conversion, further disturbing the time domain distribution of the signal, and simultaneously suppressing the time delay characteristics embedded in the chaotic carrier and the time delay characteristics in the electro-optic phase feedback loop, so as to achieve the effect of no time delay characteristics. S6. The transmitting end (1) sends the encrypted optical signal to the receiving end (3) through the transmission optical fiber (2); S7. Time-domain recovery of the encrypted optical signal is performed using the third dispersion component (301); S8. The first reverse photodetector (303), the second radio frequency amplifier (304), and the second phase modulator (305) are used to form an electro-optic phase feedback loop again to recover the phase of the encrypted optical signal. S9. The encrypted optical signal is recovered in the time domain again using the fourth dispersion component (306); S10. A chaotic synchronization signal is generated using a second external cavity semiconductor laser (311). S11. The chaotic synchronization signal is passed through the second reverse photodetector (313), and the optical signal recovered by the fourth dispersion component (306) is passed through the optical fiber delay line (314) and the second photodetector (315). S12. The two electrical signals are processed by an adder (316) to obtain the original optical signal.

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