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

Abstract

The invention belongs to the field of optical communication security equipment, and particularly relates to a system and a method for generating electro-optical chaos based on a mutual injection feedback loop, the system comprises a first feedback branch and a second feedback branch, the first feedback branch comprises a Mach-Zehnder modulator 1 and an optical fiber delay line 1; the second feedback branch corresponding to the first feedback branch comprises a Mach-Zehnder modulator 2 and an optical fiber delay line 2, a chaotic signal output port is arranged 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, and the delay time of the optical fiber delay line 1 and the delay time of the optical fiber delay line 2 are different. The initial phase of the Mach-Zehnder modulator 1 and the initial phase of the Mach-Zehnder modulator 2 are different, the system has the advantages of being simple in structure, good in delay characteristic suppression effect and higher in chaos safety, a chaos synchronization system corresponding to the system is established at the receiving end, and the secrecy capacity of the whole communication system is high.

Description

Technical Field

[0001] The invention belongs to the field of optical communication security equipment, and in particular relates to a system and method for generating electro-optical chaos based on a mutual injection feedback loop. Background Art

[0002] Optical communication constitutes the core architecture of the Internet and telecommunications networks. Almost all long-distance data transmission relies on optical fiber networks. With the rapid development of optical communication technology, people's demand for high-speed, long-distance, large-capacity communication and information security has increased. Optical communication networks have become the backbone of global information transmission. At the same time, with the emergence of various eavesdropping and attack incidents on optical communication networks, the security issues of optical communication networks have become increasingly prominent. People are paying more and more attention to the security issues of optical communication systems.

[0003] Chaotic signals have broadband spectrum, are non-periodic, and are highly sensitive to initial conditions. Chaotic signals have characteristics similar to random noise. Unlike random noise, chaos is a quasi-random signal generated by a deterministic system and can be controlled by synchronization methods. Optical chaos can be used for chaotic secure optical communication, which can hide message signals very well and has good confidentiality characteristics. Even if chaotic signals are obtained or intercepted by illegal eavesdroppers, it is difficult to obtain any effective information from them. Therefore, the application of chaos to optical secure communication has become a hot topic in recent years. Electro-optical chaotic systems generate electro-optical chaotic lasers through nonlinear effects introduced by external devices. Obtaining the delay of the electro-optical feedback loop is an important way to crack chaos. However, the delay of the electro-optical feedback loop can be easily calculated by the autocorrelation function, making it difficult to suppress. By increasing the loop feedback coefficient affected by the laser output power, the photodetector amplification gain, and the RF amplifier gain, the nonlinearity of the modulator output optical signal can be increased, thereby achieving the effect of suppressing the delay characteristics. The traditional electro-optical feedback loop can increase the feedback coefficient to suppress the time delay characteristics, but due to the limitation of the device itself, the maximum feedback coefficient of the existing technology can only reach 5.1, making it difficult to suppress the time delay characteristics. In order to suppress the time delay characteristics of the electro-optical feedback loop and generate highly complex chaos, many solutions have been proposed. For example, by adding multiple feedback loops, introducing optical feedback loops and electrical feedback loops at the same time, introducing pseudo-random binary sequences in the feedback loop, and introducing nonlinear functions through digital signal processing modules; but as the delay is suppressed, the structure of the system becomes complicated, the actual cost is high, and it is also difficult to synchronize the signal reception in the subsequent process. Summary of the invention

[0004] One of the purposes of the present invention is to provide a system for generating electro-optical chaos based on a mutual injection feedback loop, which has a simple structure and good delay suppression effect.

[0005] The technical solution for achieving the above-mentioned purpose includes the following contents.

[0006] A system for generating electro-optical chaos based on a mutual injection feedback loop comprises a first feedback branch and a second feedback branch, wherein the first feedback branch comprises a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, a radio frequency amplifier 1 and a subtractor 1 connected in series in sequence, and the second feedback branch corresponds to the first feedback branch and comprises a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, a radio frequency amplifier 2 and a subtractor 2 connected in series in sequence, wherein the signal output end of the subtractor 1 is connected to the wire signal input end of the Mach-Zehnder modulator 2, and the signal output end of the subtractor 2 is connected to the wire signal input end of the Mach-Zehnder modulator 2. The radio frequency amplifier 1 is connected to the electric signal input terminal of the Mach-Zehnder modulator 1, and is provided with two electric 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 radio frequency amplifier 2 is provided with two electric 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 optical fiber delay line 1 or between the Mach-Zehnder modulator 2 and the optical fiber delay line 2, and the delay times of the optical fiber delay line 1 and the optical fiber delay line 2 are different.

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

[0008] Furthermore, the initial phases adopted by Mach-Zehnder modulator 1 and Mach-Zehnder modulator 2 are different, which can further increase the complexity of chaos and help improve the delay feature suppression capability.

[0009] The system and method for generating electro-optical chaos based on a mutual injection feedback loop provided by the present invention uses a series mutual injection structure of two feedback branches and uses a subtractor to subtract two electrical signals, thereby increasing the nonlinearity of the feedback loop, and the generated chaos has the characteristics of high complexity and suppressed delay, etc. The present invention uses a pure physical structure (no digital signal processing module, no processor module, and no need to consider complex timing), and the output chaotic signal and the message signal can be sent out after coupling, and the corresponding receiving end uses the same open-loop structure (with the same hardware parameters) to achieve receiving synchronous demodulation to achieve decryption.

[0010] Compared with the prior art, the present invention has the following advantages. First, compared with the existing complex electro-optical feedback loop, the present invention has a relatively simple structure and is convenient for practical application; second, the present invention adds a subtractor to the feedback branch to increase the nonlinearity of the feedback loop, which can be achieved by using a differential amplifier or other device with analog signal subtraction, without the need to introduce additional nonlinear function modules, making it easier to achieve; third, the present invention uses optical fiber delay lines with different time delays to suppress the delay characteristics and increase the complexity of chaos, and the generated chaos has higher security. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the system structure of the electro-optical chaos generation method based on the mutual injection feedback loop of the present invention; Figure 2 This is a preferred example result diagram of the present invention; Figure 3 A comparison diagram of correlation functions of chaos generated by mutual injection feedback loops in the embodiment and the prior art; Figure 4 The figure is a schematic diagram of the system structure of the receiving end synchronization based on the present invention.

[0012] In the figure, the solid line represents the optical signal path, the dotted line represents the electrical signal path, and the arrow indicates the direction of signal flow. DETAILED DESCRIPTION

[0013] The present invention is specifically described below in conjunction with the embodiments. See also Figures 1 to 4A system for generating electro-optical chaos based on a mutual injection feedback loop comprises a first feedback branch and a second feedback branch, wherein the first feedback branch comprises a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, a radio frequency amplifier 1 and a subtractor 1 connected in series in sequence, and the second feedback branch corresponds to the first feedback branch and comprises a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, a radio frequency amplifier 2 and a subtractor 2 connected in series in sequence, wherein the signal output end of the subtractor 1 is connected to the signal input end of the Mach-Zehnder modulator 2, and the signal output end of the subtractor 2 is connected to the signal input end of the Mach-Zehnder modulator The radio frequency amplifier 1 is connected to the electric signal input end of the subtractor 1, the radio frequency amplifier 1 is provided with two electric signal output ports, one of which is connected to the minuend input end of the subtractor 1, and the other is connected to the subtrahend input end of the subtractor 2, the radio frequency amplifier 2 is provided with two electric signal output ports, one of which is connected to the minuend input end of the subtractor 2, and the other is connected to the subtrahend input end of the subtractor 1, a chaotic signal output port is provided between the Mach-Zehnder modulator 1 and the optical fiber delay line 1 or the Mach-Zehnder modulator 2 and the optical fiber delay line 2, and the time delay parameters of the optical fiber delay line 1 and the optical fiber delay line 2 are different; the method for generating chaos in the above system is as follows, Laser 1 emits a continuous laser signal, which is output to the optical signal input end of Mach-Zehnder modulator 1. Mach-Zehnder modulator 1 modulates the optical signal input from laser 1 by the electrical signal input from subtractor 2 and then outputs the modulated signal to the optical signal input end of optical fiber delay line 1; The optical fiber delay line 1 delays the modulated optical signal input by the Mach-Zehnder modulator 1 and then outputs it to the optical input end of the photodetector 1; The photodetector 1 performs photoelectric conversion on the optical signal inputted by the optical fiber delay line 1 and outputs the converted signal to the electrical input end of the radio frequency amplifier 1; The radio frequency amplifier 1 amplifies the electrical signal input by the photodetector 1 and divides 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 subtrahend port of the subtractor 2. Subtractor 1 performs differential operation on the first electrical signal output by radio frequency amplifier 1 and the second electrical signal output by subtractor 2, and then outputs the differential signal to the electrical modulation signal input port of Mach-Zehnder modulator 2; Laser 2 emits a continuous laser signal, which is output to the optical signal input end of Mach-Zehnder modulator 2; The Mach-Zehnder modulator 2 modulates the electrical signal input from the subtractor 1 onto the optical signal input from the laser 2 using an initial phase different from that of the Mach-Zehnder modulator 1, thereby forming a modulated optical signal which is output to the optical signal input end of the optical fiber delay line 2; The optical fiber delay line 2 delays the modulated optical signal input by the Mach-Zehnder modulator 2 and then outputs it to the optical input end of the photodetector 2; The photodetector 2 performs photoelectric conversion on the optical signal inputted by the optical fiber delay line 2 and outputs the converted signal to the electrical input end of the radio frequency amplifier 2; The radio frequency amplifier 2 amplifies the electrical signal input by the photodetector 2 and divides the amplified electrical signal 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 subtrahend port of the subtractor 2. The subtractor 2 performs a differential operation on the first electrical signal output by the radio frequency amplifier 2 and the second electrical signal output by the subtractor 1, and then outputs the differential signal to the electrical modulation signal input port of the Mach-Zehnder modulator 1; The optical fiber delay line 1 is connected to the photodetector 1, the radio frequency amplifier 1, the subtractor 1, and the Mach-Zehnder modulator 2 in sequence, forming a feedback branch of the system structure; the optical fiber delay line 2 is connected to the photodetector 2, the radio frequency amplifier 2, the subtractor 2, and the Mach-Zehnder modulator 1 in sequence, forming a feedback branch of the system structure; the two feedback branches are connected in series to form a mutual injection feedback loop. After continuous feedback excitation iteration of the feedback loop, a chaotic signal is finally output at the chaotic output port.

[0014] 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 receiving end system structure of this embodiment is shown in FIG. Figure 4 The working method is as follows: after the optical coupler 2 receives the signal from the transmitting end through the transmission channel (communication channel), the output is divided into two paths. The first optical signal is connected to the optical signal output end of the photodetector 5 and then converted into an electrical signal and input into the minuend port of the subtractor 5. The second optical signal is delayed by the optical fiber delay line 3 and then converted into an electrical signal by the photodetector 3. After being amplified by the radio frequency amplifier 3, it is divided into two paths. The third electrical signal is input into the minuend end of the subtractor 3, and the other is input into the subtrahend end of the subtractor 4. The output of the subtractor 3 is used 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 the optical fiber delay line 4, converted into an electrical signal by the photodetector 4, and amplified by the radio frequency amplifier 4, and divided into two paths. The third electrical signal is input to the minuend end of the subtractor 4, and the fourth electrical signal is input to the subtrahend end of the subtractor 3; the output of the subtractor 4 returns to the Mach-Zehnder modulator 3; the laser 3 inputs the continuous laser signal to the Mach-Zehnder modulator 3 for modulation and outputs the same chaos as the transmitting end, and then the optical signal is converted into an electrical signal by the photodetector 6 and connected to the subtrahend input port of the subtractor 5, the signals at both ends of the subtractor 5 are subtracted, and finally the message signal is restored at the output port of the subtractor 5.

[0015] The embodiment of this case generates chaos such as Figure 2As shown, the generated chaos is highly random and close to Gaussian distribution; a subtractor is added to the feedback loop, and the signals at the two feedback ends are subtracted, and the Mach-Zehnder modulators with different initial phases are used for modulation, which increases the nonlinearity of the feedback loop and suppresses the time delay characteristics of the chaos. Figure 3 : is a comparison diagram of the correlation functions of the embodiment and the prior art for generating chaos by mutual injection feedback loop. Figure 3 As shown in the left part, (a1), (a2), and (a3) ​​are the autocorrelation functions when the feedback coefficients are 3, 4, and 5, respectively; the prior art is as follows Figure 3 As shown in the right part, (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. It can be seen from the figure that the delay characteristics of the chaos generated in this embodiment are significantly lower than those in the prior art. The chaos generated by the present invention has a stronger suppression of the delay characteristics 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 security of the system. The comparison diagram can clearly show that the present invention has the advantages of good delay characteristic suppression effect and higher security of chaos. When used in conjunction with the receiving end chaos synchronization system, the entire communication system has a strong confidentiality capability.

Claims

1. A system for generating electro-optical chaos based on a mutual injection feedback loop, characterized in that: The invention comprises a first feedback branch and a second feedback branch, wherein the first feedback branch comprises a laser 1, a Mach-Zehnder modulator 1, an optical fiber delay line 1, a photodetector 1, a radio frequency amplifier 1 and a subtractor 1 connected in series in sequence, and the second feedback branch corresponds to the first feedback branch and comprises a laser 2, a Mach-Zehnder modulator 2, an optical fiber delay line 2, a photodetector 2, a radio frequency amplifier 2 and a subtractor 2 connected in series in sequence, wherein the signal output end of the subtractor 1 is connected to the wire signal input end of the Mach-Zehnder modulator 2, and the signal output end of the subtractor 2 is connected to the Mach-Zehnder modulator 1. The radio frequency amplifier 1 is connected to the electric wire signal input terminal, the radio frequency amplifier 1 is provided with two electric 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 radio frequency amplifier 2 is provided with two electric 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 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 line 1 and the optical fiber delay line 2 are different.

2. A method for generating electro-optical chaos based on a mutual injection feedback loop, characterized in that: The system for generating electro-optical chaos based on a mutual injection feedback loop according to claim 1 comprises the following steps: Laser 1 emits an optical signal, and the electrical signal input by subtractor 2 is used as a modulation signal. Mach-Zehnder modulator 1 modulates the laser signal input by laser 1. The optical signal output by Mach-Zehnder modulator 1 is delayed by optical fiber delay line 1, and then converted into an electrical signal by photodetector 1. After being amplified by radio frequency amplifier 1, the optical signal is divided into two paths, one of which is input into the minuend input end of subtractor 1, and the other is input into the subtrahend input end of subtractor 2. The output of subtractor 1 is used 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, which is delayed by optical fiber delay line 2, and converted into an electrical signal by photodetector 2. After being amplified by radio frequency amplifier 2, the optical signal is divided into two paths, one of which is input into the minuend input end of subtractor 2, and the other is input into the subtrahend input end of subtractor 1. The output modulation signal of subtractor 2 enters Mach-Zehnder modulator 1, and two feedback branches are connected in series to form a mutual injection feedback loop. After continuous feedback excitation iteration of the feedback loop, a chaotic signal is finally output at the chaotic signal output port.

3. The method for generating electro-optical 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.

Images