System and method for generating electro-optical chaos based on mutual injection feedback loop

Abstract

This invention belongs to the field of optical communication security equipment, specifically relating to a system and method for generating electro-optical chaos based on a mutual injection feedback loop. It includes a first feedback branch and a second feedback branch. The first feedback branch includes a Mach-Zehnder modulator 1 and an optical fiber delay line 1. The second feedback branch, corresponding to the first feedback branch, includes a Mach-Zehnder modulator 2 and an optical fiber delay line 2. A chaotic signal output port is provided between the Mach-Zehnder modulator 1 and the optical fiber delay line 1, or between the Mach-Zehnder modulator 2 and the optical fiber delay line 2. The delay times of the optical fiber delay lines 1 and 2 are different. When the system is in use, the initial phases of the Mach-Zehnder modulator 1 and 2 are different. This invention has the advantages of simple structure, good delay feature suppression effect, and higher security for chaotic signals. The receiving end establishes a chaotic synchronization system corresponding to the above system, resulting in strong security for the entire communication system.

Description

Technical Field

[0001] This invention belongs to the field of optical communication security equipment, specifically relating to a system and method for generating electro-optic chaos based on mutual injection feedback loop. Background Technology

[0002] Optical communication forms the core architecture of the Internet and telecommunications networks, with almost all long-distance data transmission relying on fiber optic networks. With the rapid development of optical communication technology and the increasing demand for high-speed, long-distance, high-capacity communication and information security, optical communication networks have become the backbone of global information transmission. At the same time, with the emergence of various eavesdropping and attack incidents against optical communication networks, their security issues have become increasingly prominent. People are paying more and more attention to the security of optical communication systems.

[0003] Chaotic signals possess wideband spectrum, are non-periodic, and are highly sensitive to initial conditions. Furthermore, chaotic signals exhibit characteristics similar to random noise. However, unlike random noise, chaos is a quasi-random signal generated by a deterministic system and can be controlled through synchronization methods. Optical chaos can be used for chaotic secure optical communication, effectively concealing message signals and possessing excellent security characteristics. Even if the chaotic signal is obtained or intercepted by unauthorized eavesdroppers, it is difficult to extract any useful information. Therefore, applying chaos to secure optical communication has become a research hotspot in recent years. Electro-optic chaotic systems generate electro-optic chaotic lasers through nonlinear effects introduced by external devices. Obtaining the time delay of the electro-optic feedback loop is a crucial approach to breaking chaos; however, the time delay of the electro-optic feedback loop is easily calculated using the autocorrelation function, making it difficult to suppress. Increasing the loop feedback coefficient, which is affected by the laser output power, photodetector amplification gain, and RF amplifier gain, can increase the nonlinearity of the modulator output optical signal, thereby suppressing the time delay characteristic. Traditional electro-optic feedback loops can suppress time delay characteristics by increasing the feedback coefficient. However, due to limitations in the devices themselves, the maximum feedback coefficient in existing technologies can only reach 5.1, making it difficult to suppress the time delay characteristics. To suppress the time delay characteristics of electro-optic feedback loops and the resulting highly complex chaos, numerous solutions have been proposed. These include adding multiple feedback loops, simultaneously introducing optical and electrical feedback loops, introducing pseudo-random binary sequences into the feedback loops, and introducing nonlinear functions through digital signal processing modules. However, while the time delay is suppressed, the system structure becomes more complex, the actual cost is higher, and subsequent synchronization of signal reception becomes more difficult. Summary of the Invention

[0004] One of the objectives of this invention is to provide a system for generating electro-optic chaos based on a mutual injection feedback loop that has a simple structure and good time delay suppression effect.

[0005] The technical solutions for achieving the above objectives include the following:

[0006] A system for generating electro-optic chaos based on a mutual injection feedback loop includes a first feedback branch and a second feedback branch. The first feedback branch includes a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, an RF amplifier 1, and a subtractor 1 connected in series. The second feedback branch, corresponding to the first feedback branch, includes a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, an RF amplifier 2, and a subtractor 2 connected in series. The signal output terminal of the subtractor 1 is connected to the signal input terminal of the Mach-Zehnder modulator 2, and the signal output terminal of the subtractor 2 is... The RF amplifier 1 is connected to the wire signal input terminal of the Mach-Zehnder modulator 1. It has two electrical signal output ports, one of which is connected to the minuend input terminal of the subtractor 1 and the other is connected to the subtrahend input terminal of the subtractor 2. The RF amplifier 2 has two electrical signal output ports, one of which is connected to the minuend input terminal of the subtractor 2 and the other is connected to the subtrahend input terminal of the subtractor 1. A chaotic signal output port is provided between the Mach-Zehnder modulator 1 and the fiber delay line 1 or the Mach-Zehnder modulator 2 and the fiber delay line 2. The delay times of the fiber delay line 1 and the fiber delay line 2 are different.

[0007] Based on the above system, this invention provides a method for generating electro-optic chaos based on a mutual injection feedback loop, comprising the following steps: a laser 1 emits an optical signal, the electrical signal input to a subtractor 2 is used as the modulation signal, a Mach-Zehnder modulator 1 modulates the laser signal input to the laser 1, the output optical signal of the Mach-Zehnder modulator 1 is delayed by an optical fiber delay line 1, then converted into an electrical signal by a photodetector 1, amplified by an RF amplifier 1 and split into two paths, one of which is input to the minuend input of the subtractor 1, and the other is input to the subtrahend input of the subtractor 2. The output of the subtractor 1 is used as the Mach-Zehnder modulator signal. The modulation signal of the Mach-Zehnder modulator 2 modulates the signal emitted by the laser 2 and outputs an optical signal. After being delayed by the fiber delay line 2, it is converted into an electrical signal by the photodetector 2. After being amplified by the radio frequency amplifier 2, it is split into two paths. One electrical signal is input to the minuend input of the subtractor 2, and the other electrical signal is input to the subtrahend input of the subtractor 1. The output modulation signal of the subtractor 2 enters the Mach-Zehnder modulator 1. The two feedback branches are connected in series to form a mutual injection feedback loop. After continuous feedback excitation and iteration of the feedback loop, a chaotic signal is finally output at the chaotic signal output port.

[0008] Furthermore, the different initial phases used in Mach-Zehnder modulator 1 and Mach-Zehnder modulator 2 can further increase the complexity of chaos, which is beneficial to improving the ability to suppress time delay features.

[0009] The system and method for generating electro-optic chaos based on a mutual injection feedback loop provided by this invention utilizes a series mutual injection structure of two feedback branches. A subtractor is used to subtract two electrical signals, increasing the nonlinearity of the feedback loop and generating chaos with high complexity and time delay suppression characteristics. This invention uses a purely physical structure (no digital signal processing module, no processor module, and no need to consider complex timing). The output chaotic signal and message signal are coupled together before being transmitted. The corresponding receiving end uses the same open-loop structure (with identical hardware parameters) to achieve synchronous demodulation for decryption.

[0010] Compared with existing technologies, this invention has the following advantages: First, compared with existing complex electro-optic feedback loops, the structure of this invention is simpler and easier to apply in practice; second, by adding a subtractor to the feedback branch, this invention can increase the nonlinearity of the feedback loop, which can be achieved using devices such as differential amplifiers that have analog signal subtraction capabilities, without the need to introduce additional nonlinear function modules, making it easier to implement; third, by using fiber delay lines with different time extensions, this invention can suppress time delay characteristics and increase chaotic complexity, resulting in chaos with higher security. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the system structure of the electro-optic chaos generation method based on mutual injection feedback loop of the present invention;

[0012] Figure 2 This is a preferred embodiment of the present invention.

[0013] Figure 3 A comparison chart of the correlation functions that generate chaos in the mutual injection feedback loop of the embodiments and the prior art;

[0014] Figure 4 This is a schematic diagram of the system structure for receiver synchronization based on the present invention.

[0015] In the diagram, solid lines represent optical signal paths, dashed lines represent electrical signal paths, and arrows indicate the direction of signal flow. Detailed Implementation

[0016] The present invention will be specifically described below with reference to embodiments.

[0017] See Figures 1 to 4A system for generating electro-optic chaos based on a mutual injection feedback loop includes a first feedback branch and a second feedback branch. The first feedback branch includes a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, an RF amplifier 1, and a subtractor 1 connected in series. The second feedback branch, corresponding to the first feedback branch, includes a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, an RF amplifier 2, and a subtractor 2 connected in series. The signal output terminal of the subtractor 1 is connected to the signal input terminal of the Mach-Zehnder modulator 2, and the signal output terminal of the subtractor 2 is connected to the signal input terminal of the Mach-Zehnder modulator 2. The input terminals of the subtractor 1 and the RF amplifier 2 are connected. The RF amplifier 1 has two electrical signal output ports, one connected to the minuend input of the subtractor 1 and the other connected to the subtrahend input of the subtractor 2. The RF amplifier 2 has two electrical signal output ports, one connected to the minuend input of the subtractor 2 and the other connected to the subtrahend input of the subtractor 1. A chaotic signal output port is provided between the Mach-Zehnder modulator 1 and the fiber delay line 1 or the Mach-Zehnder modulator 2 and the fiber delay line 2. The time delay parameters of the fiber delay line 1 and the fiber delay line 2 are different. The method for generating chaos in the above system is as follows.

[0018] Laser 1 emits continuous laser signals, which are output to the optical signal input terminal of Mach-Zehnder modulator 1.

[0019] The Mach-Zehnder modulator 1 modulates the optical signal input from the laser 1 through the electrical signal input from the subtractor 2 and outputs it to the optical signal input end of the fiber delay line 1.

[0020] The fiber delay line 1 delays the modulated optical signal input to the Mach-Zehnder modulator 1 and outputs it to the optical input end of the photodetector 1.

[0021] The photodetector 1 converts the optical signal input from the fiber delay line 1 into a photoelectric signal and outputs it to the electrical input terminal of the radio frequency amplifier 1.

[0022] The radio frequency amplifier 1 amplifies the electrical signal input from the photodetector 1 and splits it into two electrical signals with the same power. The first electrical signal is output to the minuend port of the subtractor 1, and the second electrical signal is output to the subtraction port of the subtractor 2.

[0023] Subtractor 1 performs a differential operation on the first electrical signal output from RF amplifier 1 and the second electrical signal output from subtractor 2, and then outputs the result to the electrical modulation signal input port of Mach-Zehnder modulator 2.

[0024] Laser 2 emits continuous laser signals, which are output to the optical signal input terminal of Mach-Zehnder modulator 2;

[0025] The Mach-Zehnder modulator 2 uses an initial phase different from that of the Mach-Zehnder modulator 1 to modulate the electrical signal input to the subtractor 1 onto the optical signal input to the laser 2, forming a modulated optical signal output to the optical signal input end of the fiber delay line 2;

[0026] The fiber delay line 2 delays the modulated optical signal input to the Mach-Zehnder modulator 2 and outputs it to the optical input end of the photodetector 2.

[0027] The photodetector 2 performs photoelectric conversion on the optical signal input from the fiber delay line 2 and outputs it to the electrical input terminal of the radio frequency amplifier 2;

[0028] The radio frequency amplifier 2 amplifies the electrical signal input from the photodetector 2 and splits it into two electrical signals with the same power. The first electrical signal is output to the minuend port of the subtractor 2, and the second electrical signal is output to the subtraction port of the subtractor 2.

[0029] Subtractor 2 performs a differential operation between the first electrical signal output from RF amplifier 2 and the second electrical signal output from subtractor 1, and then outputs the result to the electrical modulation signal input port of Mach-Zehnder modulator 1.

[0030] Fiber optic delay line 1 is sequentially connected to photodetector 1, RF amplifier 1, subtractor 1, and Mach-Zehnder modulator 2, forming one feedback branch of the system structure. Fiber optic delay line 2 is sequentially connected to photodetector 2, RF amplifier 2, subtractor 2, and Mach-Zehnder modulator 1, forming another feedback branch of the system structure. The two feedback branches are connected in series to form a mutual injection feedback loop. Through continuous feedback excitation iteration of the feedback loop, a chaotic signal is finally output at the chaotic output port.

[0031] The chaotic signal output by the above system is coupled with the original message signal through an optical coupler and then output to the communication channel. The receiving end establishes a chaotic synchronization system corresponding to the above system. The receiver system structure in this embodiment is shown in [reference needed]. Figure 4Its working method is as follows: After receiving the signal from the transmitting end through the transmission channel (communication channel), the optical coupler 2 outputs two paths. The first optical signal is connected to the optical signal output end of the photodetector 5 and converted into an electrical signal, which is then input to the minuend port of the subtractor 5. The second optical signal is delayed by the fiber delay line 3 and then converted into an electrical signal by the photodetector 3. After being amplified by the RF amplifier 3, it is split into two paths. The third electrical signal is input to the minuend port of the subtractor 3, and the other is input to the subtraction port of the subtractor 4. The output of the subtractor 3 serves as the modulation signal of the Mach-Zehnder modulator 4. The Mach-Zehnder modulator 4 modulates the signal emitted by the laser 4. The signal is then delayed by fiber delay line 4, converted into an electrical signal by photodetector 4, amplified by radio frequency amplifier 4, and split into two paths. The third electrical signal is input to the minuend of subtractor 4, and the fourth electrical signal is input to the subtraction end of subtractor 3. The output of subtractor 4 returns to Mach-Zehnder modulator 3. Laser 3 inputs continuous laser signal to Mach-Zehnder modulator 3 for modulation, and the output is the same chaos as the transmitter. The optical signal is then converted into an electrical signal by photodetector 6 and connected to the subtraction input port of subtractor 5. The signals at both ends of subtractor 5 are subtracted, and finally the message signal is recovered at the output port of subtractor 5.

[0032] The embodiment in this case generates chaos, such as Figure 2 As shown, the generated chaos exhibits high randomness, closely resembling a Gaussian distribution. A subtractor is added to the feedback loop, which subtracts the signals from the two feedback terminals and modulates the loop with Mach-Zehnder modulators of different initial phases. This increases the nonlinearity of the feedback loop and suppresses the time delay characteristics of the chaos. Figure 3 This is a comparison chart of the correlation functions of the mutual injection feedback loop that generates chaos in the embodiment and the prior art. This embodiment is... Figure 3 As shown on the left, (a1), (a2), and (a3) ​​are the autocorrelation functions when the feedback coefficients are 3, 4, and 5, respectively; existing technologies such as Figure 3 As shown on the right, (b1), (b2), and (b3) are the autocorrelation functions when the feedback coefficients are 3, 4, and 5, respectively. The horizontal axis represents the delay time, and the vertical axis represents the normalized autocorrelation coefficient. As can be seen from the figure, the delay characteristics of the chaos generated in this embodiment are significantly lower than those in existing technologies. The chaos generated by this invention exhibits stronger delay characteristic suppression as the feedback coefficient increases. When the feedback coefficient reaches 5, the delay characteristics of the feedback loop can be completely suppressed, greatly increasing the system's security. The comparison figures clearly demonstrate the advantages of this invention: better delay characteristic suppression and higher security in chaotic behavior. When used in conjunction with a receiver-side chaotic synchronization system, the entire communication system has strong security capabilities.

Claims

1. A system for generating electro-optic chaos based on a mutual injection feedback loop, characterized in that, The system includes a first feedback branch and a second feedback branch. The first feedback branch comprises a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, an RF amplifier 1, and a subtractor 1 connected in series. The second feedback branch, corresponding to the first feedback branch, comprises a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, an RF amplifier 2, and a subtractor 2 connected in series. The signal output terminal of the subtractor 1 is connected to the electrical signal input terminal of the Mach-Zehnder modulator 2, and the signal output terminal of the subtractor 2 is connected to the Mach-Zehnder modulator 1. The RF amplifier 1 is connected to the electrical signal input terminal of the subtractor 1 and the subtractor input terminal of the subtractor 2. The RF amplifier 2 is also connected to the electrical signal output terminal of the subtractor 1 and the subtractor input terminal of the subtractor 2. A chaotic signal output port is provided between the Mach-Zehnder modulator 1 and the fiber delay line 1 or the Mach-Zehnder modulator 2 and the fiber delay line 2. The delay times of the fiber delay line 1 and the fiber delay line 2 are different.

2. A method for generating electro-optic chaos based on a mutual injection feedback loop, characterized in that, The system for generating electro-optic chaos based on a mutual injection feedback loop as described in claim 1 includes the following steps. Laser 1 emits an optical signal, which is modulated by the electrical signal input to subtractor 2. Mach-Zehnder modulator 1 modulates the laser signal input to laser 1. The output optical signal of Mach-Zehnder modulator 1 is delayed by fiber delay line 1 and then converted into an electrical signal by photodetector 1. After being amplified by RF amplifier 1, it is split into two paths. One path is input to the minuend input of subtractor 1, and the other path is input to the subtrahend input of subtractor 2. The output of subtractor 1 serves as the modulation signal of Mach-Zehnder modulator 2. Mach-Zehnder modulator 2 modulates the signal emitted by laser 2 and outputs an optical signal. After being delayed by fiber delay line 2, it is converted into an electrical signal by photodetector 2 and amplified by RF amplifier 2. After being split into two paths, one path is input to the minuend input of subtractor 2, and the other path is input to the subtrahend input of subtractor 1. The output modulation signal of subtractor 2 enters Mach-Zehnder modulator 1. The two feedback branches are connected in series to form a mutual injection feedback loop. Through continuous feedback excitation and iteration of the feedback loop, a chaotic signal is finally output at the chaotic signal output port.

3. The method for generating electro-optic chaos based on a mutual injection feedback loop according to claim 2, characterized in that, The initial phases of Mach-Zehnder modulator 1 and Mach-Zehnder modulator 2 are different.

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