Broadband chaos generation method based on dual-drive Mach-Zehnder modulator

Abstract

The invention discloses a broadband chaos generation method based on a dual-drive Mach-Zehnder modulator, and the method specifically comprises the steps: employing two chaos generation systems, firstly building a conventional photoelectric oscillation system through employing a continuous wave semiconductor laser, an MZM, a photoelectric detector, and a radio frequency amplifier; chromatic dispersion is introduced into the photoelectric feedback loop to enhance the chaos complexity and reduce the time delay characteristic of the generated chaos; and then, small-bandwidth chaos generated by a traditional optoelectronic oscillator is used as a radio frequency modulation signal of the DDMZM in a second chaos generation system, and the bias voltage of the DDMZM is adjusted to enable the DDMZM to work in a nonlinear region, so that the bandwidth of the modulated intensity chaos is broadened under the action of high nonlinearity. According to the invention, broadband chaotic signals can be generated, time delay characteristics can be hidden in background noise, the complexity of the chaotic signals is effectively increased, the chaotic power spectrum is flat, the spectrum energy is uniform, and ultra-high-speed physical random numbers can be generated.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of chaotic signals, and particularly relates to a wideband chaotic signal generation method based on a double-drive Mach-Zehnder modulator. BACKGROUND

[0002] In 1975, researchers found the relationship between the laser model and the Lorenz chaos theory through practice, and laser chaos attracted the attention of physicists due to its relatively simple theoretical model, sensitivity to initial state, short time scale of chaotic behavior, and natural high-speed characteristics. Laser chaos has entered an era of rapid development. The research and development of optical chaos have shown broad application prospects in chaos secure communication, random number generation, information storage, and dynamic routing.

[0003] The generation of optoelectronic chaotic signals is often realized by means of an optoelectronic oscillator (OEO), the core of which is to utilize the nonlinear characteristics of an intensity or phase optical-electric modulator. In 1982, Neyer A and Voges E first constructed an optoelectronic feedback loop based on a laser source, an electro-optic modulator, a long delay optical fiber, and an optical-electric detector, and completely proposed an OEO scheme for converting continuous light energy into a high-purity stable microwave signal, laying the foundation for the field. With the in-depth research, the expansion of the bandwidth of chaotic signals and the improvement of the power spectrum flatness gradually become the focus. With the development of science and society, researchers gradually shift their focus to the bandwidth and power spectrum flatness of chaos. In 2021, Taiyuan University of Technology generated a highly nonlinear XNOR logic gate by changing the bias voltage of the IQ modulator, and successfully obtained a wideband chaotic source with a 10 dB bandwidth of 29.1 GHz by combining two delay feedback loops. The two loops with different delays are equivalent to introducing two different oscillation modes, and the beat frequency effect can effectively expand the bandwidth of the chaotic signal. In 2023, Southwest Jiaotong University combined a chirped fiber grating with a traditional optoelectronic oscillator, introduced chirped dispersion in the feedback loop of the traditional optoelectronic oscillator, adjusted the center wavelength of the laser to match the center wavelength of the chirped fiber grating, successfully improved the complexity of the chaotic signal, and weakened the weak periodicity of the chaotic signal. The experiment obtained a chaotic signal source with an effective bandwidth of 15 GHz. In 2025, Nanjing University of Aeronautics and Astronautics cascaded a low-frequency pseudo-random modulator with a traditional optoelectronic oscillator, increased the randomness of the light input to the oscillator, and significantly reduced the weak periodicity of the chaotic signal. Finally, a wideband complex chaotic signal source with a 3 dB bandwidth of 21.33 GHz was obtained. SUMMARY

[0004] To realize the generation of wideband chaotic signals and the generation of high-speed random bit sequences, the application provides a wideband chaotic signal generation method based on a double-drive Mach-Zehnder modulator.

[0005] The application discloses a broadband chaos generation method based on a dual-drive Mach-Zehnder modulator.

[0006] Step 1: build a first chaotic optoelectronic oscillation device: first, a continuous wave semiconductor laser emits a laser signal, which is divided into two paths by a beam splitter as the optical carrier signal of two chaotic optoelectronic oscillation systems; the upper path is composed of a MZM and a feedback loop to form a traditional optoelectronic oscillator: the laser signal is output by the MZM and divided into two paths by the beam splitter, one path is converted into a radio frequency signal by an optical-electricity detector after passing through a fiber dispersion, and the other path is used as the chaotic output of the traditional optoelectronic oscillator.

[0007] Step 2: build a second chaotic optoelectronic oscillation device: the lower path is composed of a DDMZM and a chaotic output of the previous path to form an optoelectronic oscillation device based on the DDMZM: the laser signal is used as the optical carrier of the DDMZM, and the chaotic signal generated by the previous traditional optoelectronic oscillator is converted into a radio frequency signal by an optical-electricity detector, then the radio frequency signal is divided into two paths by a 50:50 power divider, and the two paths are used as the upper and lower arm modulation signals of the DDMZM; the modulation depth and bias voltage of the DDMZM are adjusted to obtain a broadband chaotic output.

[0008] Step 3: build a random number generation model: first, the broadband chaotic signal obtained is subjected to analog-digital conversion and normalization processing, and the signal randomness and complexity are preliminarily enhanced by delay subtraction processing, then the signal is divided into two paths, one path is converted into a binary number by a digital-analog converter after delay processing and x least significant bits are selected, and the other path is directly converted into a binary number by a digital-analog converter without delay operation; finally, the two paths are subjected to XOR processing to generate a high-speed random binary bit sequence.

[0009] Wherein, the value of x depends on the randomness of the signal, the larger the value of x, the stronger the randomness of the signal, and the higher the speed of the chaotic random number generated, which also means that when the randomness of the signal is not strong enough, the value of x is usually small.

[0010] The application builds a high-speed physical random number generation model based on the scheme, utilizes the method of delay subtraction, least significant bit extraction and XOR, and the generated chaotic signal has the following characteristics: 1. breaking through the minimum device bandwidth in the feedback loop of optoelectronic devices within a certain range; 2. the side peak of the autocorrelation function is weakened, and the time delay characteristic is low; 3. the power spectrum is flat, and the frequency spectrum energy is uniform, which is beneficial to chaotic secure communication; 4. the system can realize chaotic signal extraction of three channels, and the correlation of the chaotic signals of the three channels is low; 5. after a series of post-processing, high-speed random number generation with a single wave speed of more than 5THz bit / s can be realized.

[0011] Compared with the prior art, the application has the beneficial technical effects that:

[0012] The application can generate a multi-channel chaotic signal source. In the case that the equipment bandwidth of the experimental equipment is large enough, a wideband chaotic signal can be generated. The time delay characteristic can be hidden in the background noise. The complexity of the chaotic signal is effectively increased. The chaotic power spectrum is flat, and the frequency spectrum energy is uniform. Ultra-high-speed physical random numbers can be generated. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is a structure diagram of the application based on a double-drive Mach-Zehnder modulator wideband chaotic signal generation device.

[0014] In the figure: 101-continuous wave semiconductor laser; 102-beam splitter; 103-polarization controller; 104-Mach-Zehnder modulator; 105-erbium-doped fiber amplifier; 106-fiber dispersion; 107-beam splitter; 108-optical power attenuator; 109-optoelectronic detector; 110-radio frequency power amplifier; 111-optical power attenuator; 112-optoelectronic detector; 113-radio frequency power amplifier; 114-radio frequency beam splitter; 115-polarization controller; 116-double-drive Mach-Zehnder modulator; 117-optoelectronic detector; 118-oscilloscope.

[0015] Figure 2 It is a chaotic time sequence diagram of a traditional optoelectronic oscillator combined with fiber dispersion in the application.

[0016] Figure 3 It is an autocorrelation function of a traditional optoelectronic oscillator combined with fiber dispersion in the application.

[0017] Figure 4 It is a frequency spectrum diagram of a traditional optoelectronic oscillator combined with fiber dispersion in the application.

[0018] Figure 5 It is a DDMZM wideband chaotic time sequence diagram under the bandwidth limitation of 18GHz in the application.

[0019] Figure 6The DDMZM wideband autocorrelation function under the 18GHz bandwidth limit of the application.

[0020] Figure 7 The DDMZM wideband spectrum diagram under the 18GHz bandwidth limit of the application.

[0021] Figure 8 The change of the chaotic 80% bandwidth with the DDMZM feedback power under the 18GHz bandwidth limit of the application.

[0022] Figure 9 The change of the time delay characteristics with the DDMZM feedback power under the 18GHz bandwidth limit of the application.

[0023] Figure 10 The change of the chaotic 80% bandwidth with the DDMZM bias voltage under the 18GHz bandwidth limit of the application.

[0024] Figure 11 The change of the time delay characteristics with the DDMZM bias voltage under the 18GHz bandwidth limit of the application.

[0025] Figure 12 The random number generation device principle diagram of the application.

[0026] Figure 13 The result diagram of the chaotic random number passing the NIST test of the application. DETAILED DESCRIPTION

[0027] The application will be further described in detail below in combination with the drawings and specific embodiments.

[0028] The application discloses a broadband chaos generation method based on a dual-drive Mach-Zehnder modulator (DDMZM). The method comprises two chaos generation systems. First, a traditional optoelectronic oscillator is built by using core devices such as a continuous wave semiconductor laser, a Mach-Zehnder modulator (MZM), a photodetector and a radio frequency amplifier, and dispersion is introduced into an optoelectronic feedback loop to enhance the complexity of chaos and reduce the time delay characteristics of the generated chaos. Then, the small-bandwidth chaos generated by the traditional optoelectronic oscillator is used as a radio frequency modulation signal of a DDMZM in a second chaos generation system, and the bias voltage of the DDMZM is adjusted to make the DDMZM work in a nonlinear region, so that the bandwidth of the intensity chaos is widened under the action of high nonlinearity. Due to the small half-wave voltage of the DDMZM, compared with the MZM, the DDMZM can more effectively improve the nonlinearity in the chaos dynamics under the condition of the same radio frequency input power. Whether the radio frequency power condition required to enter the chaos state or the bandwidth and complexity of the generated chaos signal, the DDMZM is superior to the MZM. The method can break through the bandwidth of the optoelectronic device in the optoelectronic oscillator loop within a certain range, and break the disadvantage of the chaos generation scheme of the optoelectronic oscillator, that is, the chaos bandwidth is limited by the minimum device bandwidth in the feedback loop. In the method, a complex chaos signal source with a wide bandwidth and a low time delay characteristic can be obtained by using small-bandwidth and low-cost electrical devices. In addition, a high-speed physical random number generation model based on the method is built, and a single-wave rate of more than 5Tbit / s of a high-speed random binary bit sequence is successfully obtained by using the method of delay subtraction, least significant bit extraction and XOR. The method comprises the following steps.

[0029] Step 1: building a first chaos optoelectronic oscillation device: first, a continuous wave semiconductor laser emits a laser signal, which is divided into two paths by a beam splitter as optical carrier signals of two chaos optoelectronic oscillation systems. The upper path comprises a traditional optoelectronic oscillator composed of an MZM and a feedback loop: the laser signal is output by the MZM and divided into two paths by the beam splitter, one path is converted into a radio frequency signal by a photodetector after passing through a fiber dispersion, and the other path is used as the chaos output of the traditional optoelectronic oscillator.

[0030] Step 2: building a second chaos optoelectronic oscillation device: the lower path comprises a DDMZM and a chaos output of the first path to form a DDMZM-based optoelectronic oscillation device: the laser signal is used as the optical carrier of the DDMZM, the chaos signal generated by the traditional optoelectronic oscillator of the first path is converted into a radio frequency signal by a photodetector, and then the radio frequency signal is divided into two paths by a 50:50 power divider, and the two paths are used as the upper and lower arm modulation signals of the DDMZM. The modulation depth and bias voltage of the DDMZM are adjusted to obtain a wideband chaos output.

[0031] Step 3: build a random number generation model: first, the obtained broadband chaotic signal is subjected to analog-digital conversion and normalization processing, the randomness and complexity of the signal are preliminarily enhanced through delay subtraction processing, the signal is divided into two paths, one path is converted into a binary number through a digital-to-analog converter after delay processing and x least significant bits are selected, and the other path is directly subjected to digital-to-analog conversion to obtain x least significant bits. Wherein, the value of x depends on the randomness of the signal, the greater the value of x, the stronger the randomness of the signal, and the higher the speed of the generated chaotic random number, which also means that when the randomness of the signal is not strong enough, the value of x is usually small. Finally, the two signals are subjected to XOR processing to generate a high-speed random binary bit sequence.

[0032] Figure 1 The structure diagram of the broadband chaotic signal generation device based on the double-drive Mach-Zehnder modulator of the application is shown in the figure. The continuous wave semiconductor laser 101 generates a laser signal, which is input as an optical carrier of two optoelectronic oscillators after passing through the beam splitter 102 and the polarization controller 103. In the uplink, the laser signal passes through the Mach-Zehnder modulator 104, and then passes through the erbium-doped fiber amplifier 105 for power compensation, and the fiber 106 for reducing the time delay characteristics of the chaotic signal. After that, the signal is divided into two paths by the beam splitter 107. One path passes through the optical power attenuator 108, the photodetector 109 and the radio frequency power amplifier 110, and is used as the radio frequency modulation input of the Mach-Zehnder modulator. The other path passes through the optical power attenuator 111, the photodetector 112, the radio frequency power amplifier 113 and the radio frequency beam splitter 114, and is used as the radio frequency modulation input of the second optoelectronic oscillator. In the second optoelectronic oscillator, the laser signal passes through the polarization controller 115 as the optical carrier of the double-drive Mach-Zehnder modulator 116, and after nonlinear modulation, the generated broadband chaotic signal is converted into a radio frequency signal by the photodetector 117, and is sampled by the oscilloscope 118.

[0033] Figure 2 、 Figure 3 and Figure 4 are respectively the chaotic time sequence diagram, the autocorrelation function and the spectrum diagram of the traditional optoelectronic oscillator combined with fiber dispersion in the application. The results are obtained under the conditions that the fiber dispersion is 400 ps / nm, the optical power before entering the photodetector in the optoelectronic feedback loop is 7 dBm, and the bias voltage of the Mach-Zehnder modulator is in the nonlinear region. From the chaotic time sequence diagram, it can be seen that the signal has entered the chaotic state, and the autocorrelation side peak at this time is still in a relatively high state, the time delay characteristic value is about 0.297, the chaotic power spectrum is not flat, and most of the energy is concentrated in the low frequency part. At this time, the 80% bandwidth is 22.047 GHz.

[0034] Figure 5 、 Figure 6 and Figure 7These are the timing diagram, autocorrelation function, and spectrum of the DDMZM broadband chaos under the 18GHz bandwidth limitation of this invention. While maintaining... Figures 2-4 With the basic conditions unchanged, the DDMZM bias voltage is adjusted to the nonlinear region, and the optical power before the photodetector in the DDMZM photoelectric feedback loop is -3dBm. At this point, after nonlinear modulation by the dual-drive Mach-Zehnder modulator, the randomness and complexity of the chaotic signal are further increased, the chaotic time series oscillations are more intense, and the time delay characteristic suppression effect is also better, with the time delay characteristic value reduced to 0.0415. Simultaneously, the chaotic bandwidth is further increased, with the 80% bandwidth increasing to 35.078GHz, and the chaotic power spectrum becomes flatter with a more uniform energy distribution.

[0035] Figure 8 , Figure 9 This illustrates the variation of the chaotic 80% bandwidth and delay characteristics with DDMZM modulation power under an 18GHz bandwidth constraint, as described in this invention. Figure 8 , Figure 9 As shown, with the gradual increase of the DDMZM feedback power, the suppression effect of the 80% bandwidth of chaos and the time delay characteristics are both improved. Finally, it basically stabilizes when the feedback power reaches 9dBm, possibly because the device reaches saturation output. Here, the feedback power is defined as the power value entering the photodetector within the photoelectric feedback loop.

[0036] Figure 10 , Figure 11 This illustrates the variation of the chaotic 80% bandwidth and delay characteristics with DDMZM bias voltage under an 18GHz bandwidth constraint, as described in this invention. Figure 10 , Figure 11 As shown, the suppression effect of the 80% bandwidth and time delay characteristics of chaos first increases and then decreases with the increase of the bias voltage of DDMZM. ​​Near the optimal modulation point, as shown in the figure, when the bias voltage is equal to 0.85V, its bandwidth and time delay characteristics show the best results.

[0037] Figure 12 This diagram illustrates the principle of generating random numbers from a chaotic signal. First, the chaotic signal is sampled and normalized to provide a standardized input signal for subsequent processing. Next, the preprocessed signal undergoes a delay-subtraction process to improve the randomness of the sequence. Then, the sequence is divided into two paths, each undergoing different delay operations, and then entered into step 2. M Level quantization module. Here, the amplitude value of each differential signal is mapped to 2... MOne of the discrete quantization levels outputs a corresponding M-bit integer code. Each quantized integer is then converted from decimal to binary bits. Furthermore, to extract the bit with the highest randomness, the system uses a least significant bit extraction module to truncate the least significant bit from each binary codeword, thus generating an independent binary random bit stream for each branch. Finally, to eliminate any residual correlation between the two signals, the two bit sequences are XORed bitwise, thereby improving the unpredictability of the generated random numbers.

[0038] Figure 13 This shows the NIST standard test results for the chaotic random numbers generated in this invention. The NIST random number test suite contains 15 test items used to test the randomness of binary sequences generated by hardware- or software-based encrypted random number or pseudo-random number generators. These include frequency testing, intra-block frequency testing, runtime testing, longest-to-one length testing, binary matrix rank test, discrete Fourier transform test, non-overlapping template matching test, overlapping template matching test, bit-level test between matching patterns, linear complexity test, serialization test, approximate entropy test, cumulative sum test, random offset test, and random offset variation test. The test results show that the generated random numbers passed all fifteen tests. To test whether the chaotic random numbers generated by this invention meet the randomness requirements, 1000 sets of data were collected, ensuring that each set of generated chaotic random numbers was at least 1 Mbit long, and the total length of the tested data was at least 1000 Mbit. Figure 13 As shown, all P-values ​​of the 15 tests in the NIST standard are greater than 0.01, indicating that the chaotic random number under test passed the NIST 15 standard tests. In this test, 20 least significant bits were extracted, and the oscilloscope sampling rate was 256 Gbps. Therefore, based on the chaotic signal generated by this invention, this invention generates a random binary bit sequence with a single-wave rate as high as 5.12 Tbit / s.

[0039] The specific embodiments described are merely illustrative examples illustrating the spirit of the invention. Those skilled in the art can make various modifications or additions to the specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

Claims

1. A broadband chaos generation method based on a dual-drive Mach-Zehnder modulator, characterized in that, First, a conventional optoelectronic oscillation system is constructed using a continuous-wave semiconductor laser, a Mach-Zehnder modulator (MZM), a photodetector, and an RF amplifier. Dispersion is introduced into the optoelectronic feedback loop to enhance the complexity of the chaos and reduce its time delay characteristics. Next, the small-bandwidth chaos generated by the conventional optoelectronic oscillator is used as the RF modulation signal for the dual-drive Mach-Zehnder modulator (DDMZM) in the second chaos generation system. The bias voltage of the DDMZM is adjusted to operate it in the nonlinear region, allowing the bandwidth of the modulated intensity chaos to be broadened under the influence of high nonlinearity. The specific steps include: Step 1: Building the first chaotic photoelectric oscillator: First, a continuous wave semiconductor laser emits a laser signal, which is split into two paths by a beam splitter to serve as the optical carrier signals for two chaotic photoelectric oscillator systems; the upper path consists of an MZM and a feedback loop to form a conventional photoelectric oscillator: after the laser signal is output through the MZM, it is split into two paths by the beam splitter. One path is dispersed by an optical fiber and then converted into an RF signal by a photodetector to serve as the RF input of the MZM, while the other path serves as the chaotic output of the conventional photoelectric oscillator; Step 2: Construct a second chaotic photoelectric oscillator: The downstream circuit consists of a DDMZM and the upstream chaotic output, forming a DDMZM-based photoelectric oscillator. The laser signal serves as the optical carrier of the DDMZM. ​​The chaotic signal generated by the upstream conventional photoelectric oscillator is converted into an RF signal by a photodetector and then split into two RF signals by a 50:50 power divider, which serve as the modulation signals for the upper and lower arms of the DDMZM, respectively. By adjusting the modulation depth and bias voltage of the DDMZM, a broadband chaotic output is obtained. Step 3: Building a random number generation model: First, the obtained broadband chaotic signal is subjected to analog-to-digital conversion and normalization. Through delay and subtraction, the randomness and complexity of the signal are initially enhanced. Then, the signal is divided into two paths. One path is processed by delay and then converted into a binary number by a digital-to-analog converter, and x least significant bits are selected. The other path is not processed by delay and is directly converted into x least significant bits by a digital-to-analog converter. Finally, the two signals are XORed to generate a high-speed random binary bit sequence.

2. The broadband chaos generation method based on a dual-drive Mach-Zehnder modulator according to claim 1, characterized in that, In step 3, the value of x depends on the randomness of the signal. The larger the value of x, the stronger the randomness of the signal and the higher the rate of generating chaotic random numbers. This also means that when the randomness of the signal is not strong enough, the value of x is usually small.

3. The broadband chaos generation method based on a dual-drive Mach-Zehnder modulator according to claim 1, characterized in that, In step 3, a high-speed random binary bit sequence with a single-wave rate exceeding 5 Tbit / s is obtained.

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