Multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback

Abstract

This invention discloses a multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback. Specifically, the chaotic signal undergoes self-phase modulation to generate a large number of new frequency components, which interact with the dispersion of a chirped fiber grating (FBG) and are then fed back into a semiconductor laser. Detuning the chirped fiber grating's central wavelength shifts the reflection spectrum, redistributing the chaotic signal's energy. This invention can generate a multi-channel chaotic signal source and, if the experimental equipment bandwidth is sufficiently large, produce ultra-wideband chaotic signals. It can also hide delay characteristics within background noise, effectively increasing the complexity of the chaotic signal.

Description

Technical Field

[0001] The present invention belongs to the field of laser technology, and in particular relates to a multi-channel broadband chaotic source based on self-phase modulation feedback and a random number generation method. Background Art

[0002] Chaotic optical secure communication technology uses chaotic laser signals as carriers to conceal information and exploits chaotic synchronization for information demodulation. It offers numerous advantages, including hardware encryption, high transmission rates, long distances, and compatibility with existing fiber optic networks. The hardware parameters in its link structure are all key parameters, and the security of these parameters, combined with the size of the space, determines the security of the chaotic security. Mirror-feedback semiconductor lasers are widely used as chaotic transceivers due to their simple structure and ease of integration. However, chaotic optical secure communication systems based on mirror-feedback semiconductor lasers present security risks. Firstly, due to the laser's relaxation oscillation, most of the energy is concentrated near the relaxation oscillation frequency in the chaotic signal's radio frequency spectrum, limiting the effective bandwidth of the chaotic signal to a few GHz. Secondly, in conventional optical feedback—that is, using mirror feedback from a semiconductor laser to generate chaotic signals—the feedback light is a linearly delayed signal output by an external-cavity semiconductor laser. This induces periodic resonances of the feedback delay, resulting in a distinct time-delay signature in the chaotic signal. Spectral analysis, autocorrelation function calculations, and digital mutual information calculations have demonstrated that the time-delay signature in the chaos generated by conventional external-cavity semiconductor lasers is easily discernible. The exposure of time delay characteristics reduces the randomness of the bits generated by chaotic signals, threatening the confidentiality of the chaotic source in secure communication systems. Therefore, increasing bandwidth and suppressing time delay characteristics are of great significance for improving the performance of chaotic applications in external cavity semiconductor lasers.

[0003] In recent years, people have done a lot of research on improving the bandwidth of chaotic light and suppressing the delay characteristics of chaotic light. Improving the bandwidth of chaotic signal sources can be roughly divided into three categories. One is to increase the bandwidth through light injection or composite feedback. In 2008, Wang Anbang's research group at Taiyuan University of Technology injected a steady-state master laser into a slave laser with a feedback loop, and used the beat frequency effect between light injection and the semiconductor laser to obtain a chaotic signal with a bandwidth of about 17 GHz; the second type is to introduce nonlinearity into the feedback loop and convert the phase dynamics into intensity dynamics, thereby achieving bandwidth enhancement. In 2020, Zhang Mingjiang's research group at Taiyuan University of Technology used a highly nonlinear feedback structure in the experiment to increase the bandwidth of the chaotic signal to 38.9 GHz. The third method is to use a laser with a flat small-signal modulation curve and directly use mirror feedback to increase the bandwidth of the chaotic signal. In 2020, Wang Anbang's research group used a new type of arc-edge hexagonal microcavity semiconductor laser. Due to its low threshold current, it can compensate for the low-frequency energy of the microcavity laser under a higher bias current, and obtained a chaotic signal with a bandwidth exceeding 14 GHz in the simulation. Summary of the Invention

[0004] In order to achieve safe and efficient transmission, the present invention provides a multi-channel broadband chaotic source and a random number generation method based on self-phase modulation feedback.

[0005] The present invention is a multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback. After self-phase modulation, the chaotic signal generates a large number of new frequency components, which interact with the dispersion of a chirped fiber grating and are then fed back into the semiconductor laser. The chirped fiber grating's central wavelength detuning shifts the reflection spectrum, redistributing the chaotic signal's energy and significantly expanding its bandwidth. Specifically, the method includes the following steps:

[0006] Step 1: A semiconductor laser emits a laser signal, which passes through a polarization controller and a 50:50 coupler to a phase modulator. A 50:50 beam splitter is connected after the phase modulator. A portion of the signal passes through a photodetector and an erbium-doped fiber amplifier and returns to the phase modulator as its driving signal. The remaining portion enters a chirped fiber Bragg grating (FBG). Since the phase modulator has no driving signal at this point, it is inoperative. The laser signal directly interacts with the chirped fiber Bragg grating (FBG) and feeds back into the semiconductor laser, generating a chaotic signal. The chaotic signal generated by the semiconductor laser then passes through a polarization controller and a 50:50 coupler to the phase modulator again. The chaotic signal generated by the previous feedback serves as the driving signal for the phase modulator. The chaotic signal emitted by the semiconductor laser undergoes self-phase modulation with the phase modulator, then interacts with the chirped fiber Bragg grating and feeds back into the semiconductor laser. At this point, due to self-phase modulation, the chaotic signal entering the chirped fiber Bragg grating has a rich frequency component. The dispersion generated by the chirped fiber Bragg grating causes different frequency components to propagate at different speeds, resulting in pulse broadening. Since the energy of the chaotic signal is concentrated near the relaxation oscillation, the central wavelength detuning of the chirped fiber Bragg grating is set to 0.9nm, and its reflection spectrum shifts toward the forward direction. When the chirped fiber Bragg grating reflects the chaotic signal back to the semiconductor laser, the reflectivity of the signal near the relaxation oscillation is small, while the reflectivity of the remaining frequency components is large, which weakens the relaxation oscillation and further increases the bandwidth of the chaotic signal.

[0007] Step 2: In order to generate multiple chaotic sources, a 50:50 beam splitter is added after the semiconductor laser. One path is connected to the polarization controller according to the method in step 1, and the other path is connected to a 50:50 beam splitter. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Similarly, a 50:50 beam splitter is connected after the phase modulator and then passes through a Mach-Zehnder interferometer to generate a chaotic signal source as output. A 50:50 beam splitter is added to the chirped fiber Bragg grating feedback loop. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Thus, a total of five different chaotic signal sources are generated.

[0008] Step 3: The five chaotic signals are sampled and normalized, and after delayed and subtracted, they are divided into two channels by a 50:50 beam splitter. One channel is converted into a binary number through an 8-bit digital-to-analog converter after delay processing and the least significant bit is selected. The other channel does not undergo delay operation and directly passes through the 8-bit digital-to-analog converter to obtain the least significant bit. Finally, the two signals are XORed to improve the randomness of the random number signal. In this way, five different random number signals are obtained.

[0009] The multi-channel broadband chaotic source based on self-phase modulation feedback and the random number generation method of the present invention can be applied as a chaotic signal source.

[0010] The beneficial technical effects of the present invention compared to the prior art are:

[0011] The present invention can generate multiple chaotic signal sources. If the experimental equipment bandwidth is sufficiently large, it can also produce ultra-wideband chaotic signals. It can also hide time delay characteristics within background noise, effectively increasing the complexity of chaotic signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a principle block diagram of the present invention based on self-phase modulation feedback multi-channel broadband chaotic source and random number generation.

[0013] Figure 2 This is a chaotic timing diagram of the output end of the present invention based on self-phase modulation feedback multi-channel broadband chaotic source and random number generation.

[0014] Figure 3 This is a spectrum diagram of the chaotic signal at the output end of the present invention based on self-phase modulation feedback multi-channel broadband chaotic source and random number generation.

[0015] Figure 4 This is a diagram of the autocorrelation function of the chaotic signal at the output end of the present invention based on the self-phase modulation feedback multi-channel broadband chaotic source and random number generation.

[0016] Figure 5This is a diagram showing how the chaotic signal permutation entropy at the output end of the self-phase modulation feedback multi-channel broadband chaotic source and random number generation according to the present invention changes with the feedback intensity.

[0017] Figure 6 This is the schematic diagram of the random number generator.

[0018] Figure 7 This is the result of random numbers passing the NIST test. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] The present invention is a multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback. After self-phase modulation, the chaotic signal generates a large number of new frequency components, which interact with the dispersion of a chirped fiber grating and are then fed back into the semiconductor laser. The chirped fiber grating's central wavelength detuning shifts the reflection spectrum, redistributing the chaotic signal's energy and significantly expanding its bandwidth. Specifically, the method includes the following steps:

[0021] Step 1: A semiconductor laser emits a laser signal, which passes through a polarization controller and a 50:50 coupler to a phase modulator. A 50:50 beam splitter is connected after the phase modulator. A portion of the signal passes through a photodetector and an erbium-doped fiber amplifier and returns to the phase modulator as its driving signal. The remaining portion enters a chirped fiber Bragg grating (FBG). Since the phase modulator has no driving signal at this point, it is inoperative. The laser signal directly interacts with the chirped fiber Bragg grating (FBG) and feeds back into the semiconductor laser, generating a chaotic signal. The chaotic signal generated by the semiconductor laser then passes through a polarization controller and a 50:50 coupler to the phase modulator again. The chaotic signal generated by the previous feedback serves as the driving signal for the phase modulator. The chaotic signal emitted by the semiconductor laser undergoes self-phase modulation with the phase modulator, then interacts with the chirped fiber Bragg grating and feeds back into the semiconductor laser. At this point, due to self-phase modulation, the chaotic signal entering the chirped fiber Bragg grating has a rich frequency component. The dispersion generated by the chirped fiber Bragg grating causes different frequency components to propagate at different speeds, resulting in pulse broadening. Since the energy of the chaotic signal is concentrated near the relaxation oscillation, the central wavelength detuning of the chirped fiber Bragg grating is set to 0.9nm, and its reflection spectrum shifts toward the forward direction. When the chirped fiber Bragg grating reflects the chaotic signal back to the semiconductor laser, the reflectivity of the signal near the relaxation oscillation is small, while the reflectivity of the remaining frequency components is large, which weakens the relaxation oscillation and further increases the bandwidth of the chaotic signal.

[0022] Step 2: In order to generate multiple chaotic sources, a 50:50 beam splitter is added after the semiconductor laser. One path is connected to the polarization controller according to the method in step 1, and the other path is connected to a 50:50 beam splitter. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Similarly, a 50:50 beam splitter is connected after the phase modulator and then passes through a Mach-Zehnder interferometer to generate a chaotic signal source as output. A 50:50 beam splitter is added to the chirped fiber Bragg grating feedback loop. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Thus, a total of five different chaotic signal sources are generated.

[0023] Step 3: The five chaotic signals are sampled and normalized, and after delayed and subtracted, they are divided into two channels by a 50:50 beam splitter. One channel is converted into a binary number through an 8-bit digital-to-analog converter after delay processing and the least significant bit is selected. The other channel does not undergo delay operation and directly passes through the 8-bit digital-to-analog converter to obtain the least significant bit. Finally, the two signals are XORed to improve the randomness of the random number signal. In this way, five different random number signals are obtained.

[0024] like Figure 1As shown, the present invention generates a laser signal by a semiconductor laser module 101; passes through a polarization controller module 102; and then is split into two paths through a 50:50 beam splitter module 1031, one path passes through a 50:50 beam splitter 1032, and the other path is connected to a 50:50 coupler module 104; wherein, one path of the signal passing through the 50:50 beam splitter 1032 module is directly output to be connected to the spectrometer 1141, recorded as the channel 1 output signal, and the other path passes through the Mach-Zehnder interferometer module 1131 and then output to be connected to the spectrometer 1142, recorded as the channel 2 output signal. The signal passing through the 50:50 coupler 104 module then passes through the erbium-doped fiber amplifier module 1061 to the phase modulator module 105 for self-phase modulation; after passing through the 50:50 beam splitter 1033, one path enters the Mach-Zehnder interferometer module 1133 and is output, recorded as the channel 3 output signal, and the other path passes through the 50:50 coupler module 1034, one path enters the photodetector module 110 and the erbium-doped fiber amplifier module 1063 for linear amplification as the driving signal of the phase modulator; the other path passes through the erbium-doped fiber amplifier 1062 and is output. The signal enters the chirped fiber Bragg grating module 109 through the circulator module 108, and the signal fed back by the chirped fiber Bragg grating enters the attenuator module 112 and the optical isolator module 111 through the circulator module 108, and is then fed back to the semiconductor laser through the 50:50 coupler module 104. Among them, the 50:50 beam splitter 1035 is connected after the 50:50 coupler 104, and one path is directly output to the spectrometer 1144, recorded as the output signal of channel 4, and the other path is connected to the Mach-Zehnder interferometer module 1132 and then output, recorded as the output signal of channel 5.

[0025] Figure 2 The following is a chaotic timing diagram of the output signal when the dispersion is 200ps / nm, the feedback strength is -10dB, and the self-phase modulation index is 3. It can be seen from the figure that the signal has entered a chaotic state.

[0026] Figure 3 The following is a spectrum diagram of the output signal when the dispersion is 200 ps / nm, the feedback strength is -10 dB, and the self-phase modulation index is 3. Compared with the chaotic signal generated by traditional mirror feedback semiconductor lasers, the present invention makes the chaotic signal spectrum flatter, completely eliminating relaxation oscillations, and greatly improving the bandwidth of the chaotic signal.

[0027] Figure 4The following figure shows the autocorrelation function of the output signal when the dispersion is 200 ps / nm, the feedback strength is -10 dB, and the self-phase modulation index is 3. Due to the external cavity resonance of the semiconductor laser, the chaotic signal generated by traditional mirror-feedback semiconductor lasers exhibits a periodic time delay characteristic. The autocorrelation function clearly shows a correlation peak of this time delay characteristic near the feedback delay, which greatly reduces the security of chaotic optical secure communication. This invention hides this time delay characteristic within the background noise, improving transmission security.

[0028] Figure 5 The permutation entropy of a broadband chaotic signal generated by chirped fiber Bragg grating and self-phase modulation feedback at different feedback intensities can be used to predict the complexity of a chaotic signal. As the feedback intensity increases, the permutation entropy of the signal increases, and its complexity also increases.

[0029] Figure 6 This is a schematic diagram of the principle of generating random numbers from chaotic signals. The signals from each channel of the multi-channel broadband chaotic device based on chirped fiber Bragg gratings and self-phase modulation dual feedback are normalized and delayed and subtracted before being split into two signals. One signal passes through a delay line and enters an 8-bit digital-to-analog converter, converting the chaotic signal into an 8-bit binary signal. The least significant bit is then selected. The other signal is not delayed and is directly connected to the 8-bit digital-to-analog converter to convert the chaotic signal into an 8-bit binary signal. The least significant bit is then selected. The two signals are then XORed to generate the random number signal.

[0030] Figure 7 The random number signals of each channel of the present invention were tested using different least significant bits (LSBs) to pass NIST standard tests. The NIST random number test set includes 15 test items: frequency test, frequency within block test, run test, longest 1 length test, binary matrix rank test, discrete Fourier transform test, non-overlapping template matching test, overlapping template matching test, number of bits between matching patterns test, linear complexity test, serial test, approximate entropy test, cumulative sum test, random offset test, and random offset change test. These items are used to test the randomness of binary sequences generated by hardware- or software-based encrypted random number or pseudo-random number generators. When the random number signals generated according to the present invention have a LSB of 5 or less, the random numbers of the five channels all passed the above 15 tests.

Claims

1. A multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback, characterized in that: After self-phase modulation, the chaotic signal generates a large number of new frequency components, which interact with the dispersion of the chirped fiber Bragg grating and are then fed back into the semiconductor laser. The detuning of the central wavelength of the chirped fiber Bragg grating is used to shift the reflection spectrum, allowing the energy of the chaotic signal to be redistributed. The specific steps include: Step 1: A semiconductor laser emits a laser signal, which passes through a polarization controller and a 50:50 coupler to a phase modulator. The chaotic signal emitted by the semiconductor laser undergoes self-phase modulation with the phase modulator. A 50:50 beam splitter is connected after the phase modulator. Part of the signal passes through a photodetector and an erbium-doped fiber amplifier and returns to the phase modulator as its driving signal. The other part of the signal enters a chirped fiber Bragg grating (FBG). The laser signal directly interacts with the chirped fiber Bragg grating and is fed back to the semiconductor laser to generate a chaotic signal. Step 2: Add a 50:50 beam splitter after the semiconductor laser. Connect one path to the polarization controller as in step 1, and connect the other path to a 50:50 beam splitter. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Similarly, connect a 50:50 beam splitter after the phase modulator and pass it through a Mach-Zehnder interferometer to generate a chaotic signal source as output. Add a 50:50 beam splitter to the chirped fiber Bragg grating feedback loop. One path is directly used as a chaotic signal source, and the other path is used as a chaotic signal source after passing through a Mach-Zehnder interferometer. Thus, a total of five different chaotic signal sources are generated. Step 3: The five chaotic signals are sampled and normalized, and after delayed and subtracted, they are divided into two channels by a 50:50 beam splitter. One channel is converted into a binary number through an 8-bit digital-to-analog converter after delay processing and the least significant bit is selected. The other channel does not undergo delay operation and directly passes through the 8-bit digital-to-analog converter to obtain the least significant bit. Finally, the two signals are XORed to improve the randomness of the random number signal. In this way, five different random number signals are obtained.

2. An application of the multi-channel broadband chaotic source and random number generation method based on self-phase modulation feedback as claimed in claim 1, characterized in that: Application is chaotic signal source.

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