Chaotic signal generation method and device based on chaotic sequence modulation

Abstract

The application discloses a chaotic signal generation method based on chaotic sequence modulation and belongs to the technical field of microwave photonics. The method is characterized in that: a chaotic time sequence signal is used to modulate the intensity of a continuous light signal, and the obtained modulated light signal is input into an optoelectronic oscillation loop, so that a chaotic signal with eliminated time delay characteristics is output from the optoelectronic oscillation loop; the chaotic time sequence signal is a periodic signal with an ideal chaotic signal waveform in a single period. The application further discloses a chaotic signal generation device based on chaotic sequence modulation. Compared with the prior art, the application can solve the problem that a chaotic optoelectronic oscillator has obvious time delay characteristics at a low cost, and the generated signal characteristics are stable and are not affected by the bias point drift of a modulator.

Description

Technical Field

[0001] This invention relates to a method and apparatus for generating chaotic signals, belonging to the field of microwave photonics technology. Background Technology

[0002] Chaotic signals exhibit noise-like characteristics, strong anti-interference capabilities, and are not easily affected by other signals in the environment. They also possess strong randomness, making them widely used in radar, sensing, and secure communications. Common methods for generating chaotic signals include optical injection based on semiconductor lasers. This method injects light into the semiconductor laser and adjusts the injection intensity and frequency to generate a stable chaotic signal. However, this method is structurally complex, easily affected by environmental changes, and produces unstable signals. Recently developed optoelectronic oscillators utilize optoelectronic hybrid positive feedback technology, effectively avoiding the relaxation oscillation phenomenon of semiconductor lasers and generating broadband chaotic signals. Compared to optical injection, this method has a simpler structure, higher signal complexity, and greater stability. However, chaotic signal sources built based on photoelectric oscillators, due to their fixed-length positive feedback external cavity, exhibit weak periodicity and significant time delay characteristics in their output chaotic signals, leading to the following impacts: 1. Affecting the statistical disorder of the generated random numbers; 2. Eavesdroppers can obtain the cavity length information of the photoelectric oscillator through time delay characteristic analysis, reconstructing the chaotic photoelectric oscillator and severely impacting the security of secure communications; 3. The autocorrelation curve exhibits significant sidelobes, which can cause false alarms or misjudgments in chaotic radar. Furthermore, in practical applications of chaotic photoelectric oscillators, the DC bias voltage of the modulator is easily affected by ambient temperature, causing drift and making it difficult to stably control at the set operating point. This easily leads to a decrease in the frequency flatness of the chaotic signal, increased periodicity, and a reduction in chaotic complexity and randomness.

[0003] To address the significant time delay characteristics of chaotic signals output by existing chaotic optoelectronic oscillators, researchers have proposed a series of technical solutions. Chinese invention patent CN115133379 A discloses a random signal generation device and method based on stimulated Brillouin scattering amplification, which solves the aforementioned problem by utilizing the randomness of the cavity length in Rayleigh scattering. However, it requires an additional pump module and optical amplifier to amplify Rayleigh scattering, increasing system complexity and cost. Chinese invention patent CN116053930 A introduces a chirped fiber Bragg grating passive optical device in the dispersion loop implementation, using the grating reflection effect to form a loop in the optical path to generate chaos. Simultaneously, it utilizes the group velocity dispersion caused by the grating chirp effect to suppress time delay characteristics. While these solutions address the time delay problem to some extent, they generally suffer from system complexity and high implementation costs. Furthermore, none of them can solve the problem of chaotic signal performance degradation caused by the drift of the modulator's DC bias voltage due to environmental influences. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for generating chaotic signals based on chaotic sequence modulation. This method can solve the problem of obvious time delay characteristics in chaotic photoelectric oscillators at low cost, and the generated signal characteristics are stable and are not affected by the drift of the modulator bias point.

[0005] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0006] A method for generating chaotic signals based on chaotic sequence modulation involves intensity modulation of a continuous optical signal using a chaotic time sequence signal, and inputting the resulting modulated optical signal into an optoelectronic oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the optoelectronic oscillation loop; the chaotic time sequence signal is a periodic signal that exhibits an ideal chaotic signal waveform within a single period.

[0007] Based on the same inventive concept, the following technical solutions can also be obtained:

[0008] A chaotic signal generation device based on chaotic sequence modulation includes a modulation optical module and a photoelectric oscillation loop. The modulation optical module is used to intensity modulate a continuous optical signal with a chaotic time sequence signal and inputs the obtained modulated optical signal into the photoelectric oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the photoelectric oscillation loop. The chaotic time sequence signal is a periodic signal that presents an ideal chaotic signal waveform within a single period.

[0009] Preferably, the chaotic time series signal is obtained using the following method: based on the mathematical model of the chaotic photoelectric oscillator, the ideal chaotic signal waveform output by the chaotic photoelectric oscillator is obtained through simulation; then, a segment is extracted from the ideal chaotic signal waveform as the target signal waveform, and the chaotic time series signal is generated by an arbitrary waveform generator.

[0010] More preferably, the chaotic photoelectric oscillator is a bandpass filter type photoelectric oscillator, and its mathematical model is as follows:

[0011]

[0012]

[0013] Where x(t)=πV(t) / 2V πRF β=πsgkP0 / 2V πRF , y(t)=∫ t x(t′)dt′,τ H =1 / 2πf H , τ L =1 / 2πf Lf H It is the Qualcomm cutoff frequency, f L It is the low-pass cutoff frequency, β represents the feedback coefficient, and V πRF V represents the RF half-wave voltage of the modulator. πDC V(t) represents the DC half-wave voltage of the modulator, and V(t) represents the RF input signal of the modulator. B denoted by DC bias voltage of modulator, s represents response coefficient of photodetector, g represents amplifier gain, k represents loop loss, P0 represents loop input optical power, x(t) represents input electrical signal, T represents oscillation loop period, and t represents time.

[0014] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0015] This invention increases the complexity of the injected light source by adding a modulation optical module modulated by a chaotic time series, thereby completely suppressing the weak periodicity and time delay characteristics of the chaotic photoelectric oscillation loop itself. It increases the complexity of the chaotic signal, thus improving the security of secure communication. It also eliminates the side peaks of its autocorrelation image, significantly reducing the false alarm rate of chaotic radar detection. Furthermore, this solution is highly resistant to environmental changes. Once the system enters a chaotic state, any change in the bias voltage in the photoelectric oscillation loop will generate a high-quality chaotic signal with a wide bandwidth and a very flat spectrum. It can adapt to harsh external environmental changes, has simple operation steps, and the chaotic signal is easy to generate. Attached Figure Description

[0016] Figure 1 This is a structural block diagram of a specific embodiment of the chaotic signal generation device based on chaotic sequence modulation of the present invention.

[0017] Figure 2 The chaotic time series is obtained from simulation based on a bandpass filter-type optoelectronic oscillator;

[0018] Figure 3 Normalized autocorrelation curve of chaotic signal generated by traditional optoelectronic oscillator;

[0019] Figure 4 This is a normalized autocorrelation curve of the chaotic signal generated by the present invention.

[0020] Figure 5 This is the spectrum corresponding to the chaotic signal generated by the present invention;

[0021] Figure 6 This is the spectrum of the chaotic signal generated by this invention. Detailed Implementation

[0022] A chaotic signal generation system based on an optoelectronic oscillator typically consists of an optoelectronic oscillation loop comprising an intensity modulator, a delay fiber, a polarization controller, a microwave amplifier, an optical amplifier, an electrical power divider, an optical coupler, and a photodetector. It utilizes the nonlinear effect of the intensity modulator and the filtering effect provided by the effective bandwidth of the radio frequency devices to generate a broadband, highly complex chaotic signal. The optoelectronic oscillator is essentially a closed-loop feedback system; the chaotic signal generated by the system is fed back into the loop after passing through the modulator once. Based on its generation mechanism, such chaotic signals inevitably exhibit weak periodicity, meaning that the autocorrelation curve of the signal has multiple peaks, with the distance between any two adjacent peaks being exactly equal to the loop length. Therefore, the side peaks in the autocorrelation curve, besides the main peak, reflect the time delay characteristics of the chaotic system; the larger the side peaks, the more pronounced the time delay characteristics. Three main metrics are used to measure the quality of chaotic signals: bandwidth, time delay characteristics, and chaotic complexity. The signal bandwidth determines the radar's resolution, which is mainly determined by the bandwidth of the electrical components that make up the system. The time delay characteristics and chaotic complexity determine the radar's detection accuracy and anti-interference capability, which can be improved by increasing the loop gain. However, due to the losses of optoelectronic devices, the time delay characteristics cannot be completely suppressed or eliminated simply by increasing the loop gain.

[0023] To address the shortcomings of existing technologies, the present invention addresses this by adding a modulation optical module modulated by a chaotic time series to increase the complexity of the injected light source. This suppresses the weak periodicity and time delay characteristics of the chaotic photoelectric oscillation loop itself, while simultaneously enhancing its resistance to environmental changes.

[0024] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems:

[0025] A method for generating chaotic signals based on chaotic sequence modulation involves intensity modulation of a continuous optical signal using a chaotic time sequence signal, and inputting the resulting modulated optical signal into an optoelectronic oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the optoelectronic oscillation loop; the chaotic time sequence signal is a periodic signal that exhibits an ideal chaotic signal waveform within a single period.

[0026] Based on the same inventive concept, the following technical solutions can also be obtained:

[0027] A chaotic signal generation device based on chaotic sequence modulation includes a modulation optical module and a photoelectric oscillation loop. The modulation optical module is used to intensity modulate a continuous optical signal with a chaotic time sequence signal and inputs the obtained modulated optical signal into the photoelectric oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the photoelectric oscillation loop. The chaotic time sequence signal is a periodic signal that presents an ideal chaotic signal waveform within a single period.

[0028] Preferably, the chaotic time series signal is obtained using the following method: based on the mathematical model of the chaotic photoelectric oscillator, the ideal chaotic signal waveform output by the chaotic photoelectric oscillator is obtained through simulation; then, a segment is extracted from the ideal chaotic signal waveform as the target signal waveform, and the chaotic time series signal is generated by an arbitrary waveform generator.

[0029] To facilitate public understanding, the technical solution of the present invention will be described in detail below through a specific embodiment and in conjunction with the accompanying drawings:

[0030] The chaotic signal generation device based on chaotic sequence modulation in this embodiment, such as Figure 1 As shown, it includes an optoelectronic oscillation loop consisting of a polarization controller 2, an intensity modulator 2, an optical amplifier, a delay fiber, an optical coupler, a photodetector, a low-noise microwave amplifier, and an electrical power divider, as well as a modulation optical module consisting of a narrow-linewidth laser, an arbitrary waveform generator, an intensity modulator 1, and a polarization controller 1.

[0031] The chaotic time-series signal generated by the arbitrary waveform generator is modulated onto the continuous optical signal output by the narrow linewidth laser through intensity modulator 1. The resulting modulated optical signal is injected into the photoelectric oscillation loop through the optical input port of intensity modulator 2. Since the chaotic time-series signal is a periodic signal that presents an ideal chaotic signal waveform within a single period, modulating it onto the continuous optical signal can obtain a modulated optical signal with randomly changing intensity within a single period. Finally, the output from the photoelectric oscillation loop is a broadband, highly complex chaotic signal with completely suppressed time delay characteristics.

[0032] The present invention uses the following method to obtain the chaotic time series signal: based on the mathematical model of the chaotic photoelectric oscillator, the ideal chaotic signal waveform output by the chaotic photoelectric oscillator is obtained by simulation; then a segment is extracted from the ideal chaotic signal waveform as the target signal waveform, and the chaotic time series signal is generated by an arbitrary waveform generator.

[0033] The chaotic photoelectric oscillator can employ various existing schemes. The following example, using the photoelectric oscillation loop in the chaotic signal generation device of this embodiment, illustrates the method for generating chaotic time-series signals. In this embodiment, the modulator bandwidth in the photoelectric oscillation loop is 20 GHz, the low-noise microwave amplifier operates within a frequency range of 40 kHz to 20 GHz, and the photodetector bandwidth is 20 GHz. Although this photoelectric oscillation loop does not have an internal filter structure, due to the limited operating frequency range of the microwave devices, it can be equivalently considered to have an added 40 kHz to 20 GHz bandpass filter. Therefore, this photoelectric oscillation loop can be regarded as a bandpass filter-type photoelectric oscillator.

[0034] A bandpass filter-type photoelectric oscillation loop can be represented by the following formula:

[0035]

[0036] Where τ H =1 / 2πf H , τ L =1 / 2πf L f H It is the high-pass cutoff frequency of the system, f L β is the low-pass cutoff frequency of the system, β represents the feedback coefficient of the system, the differential term in formula (1) represents the low-pass filter, the integral term represents the high-pass filter, x(t) represents the input electrical signal of the system, f represents the nonlinear transformation, and T represents the oscillation loop period. Since the intensity modulator is a Mach-Zehnder modulator, its transfer function can be expressed as:

[0037]

[0038] Among them, P in P represents the input optical power of the modulator. out V represents the output optical power. πRF V represents the RF half-wave voltage of the modulator. πDC V(t) represents the DC half-wave voltage of the modulator, and V(t) represents the RF input signal of the modulator. B The DC bias voltage of the modulator. Substituting equation (2) into equation (1), we get:

[0039]

[0040] Where s represents the response coefficient of the photodetector, g represents the amplifier gain, k represents the loop loss, and P0 represents the loop input optical power.

[0041] Make the following transformation, let

[0042] x(t)=πV(t) / 2V πRF (4)

[0043] β=πsgkP0 / 2V πRF (5)

[0044]

[0045] y(t)=∫ t x(t′)dt′ (7)

[0046] Substituting (4)(5)(6)(7) into (3), we obtain the second-order differential equation of the photoelectric oscillation loop as follows:

[0047]

[0048]

[0049] Solving the aforementioned differential equations using simulation software yields the ideal chaotic signal waveform of the bandpass filter-type photoelectric oscillation loop. The autocorrelation curve of this ideal chaotic signal waveform has only one correlation peak (value 1) at a time delay of 0, with all other values ​​being 0. By arbitrarily selecting a segment (e.g., 1000 sampling points) from the simulated ideal chaotic signal waveform and inputting it as the target signal waveform into an arbitrary waveform generator, the generator can output a periodic signal exhibiting the ideal chaotic signal waveform within a single period—the chaotic time series signal. Using this chaotic time series signal to intensity-modulate the continuous optical signal output from a narrow-bandwidth laser, a modulated optical signal with randomly varying intensity within a single period can be obtained. Inputting this signal as a light source into the photoelectric oscillation loop can significantly reduce the weak periodicity of the generated signal caused by the feedback signal in the loop, and may even completely eliminate the time delay characteristic of the output signal, thereby increasing the chaotic complexity and randomness of the signal.

[0050] Figure 3 This is a normalized autocorrelation curve of the chaotic signal generated by a traditional photoelectric oscillator. Figure 4 The image shows the normalized autocorrelation curve of the chaotic signal generated by this invention. As can be seen from the comparison, the method of this invention can completely eliminate the time delay characteristics introduced by the feedback signal of the photoelectric oscillation loop, so that the autocorrelation of the chaotic signal presents a more ideal single-peak curve.

[0051] Figure 5 The optical signal output by the modulator when the system generates a chaotic signal. Figure 6 The image shows the spectrum of the chaotic signal generated by the device of this invention. It can be seen that after completely eliminating the time delay characteristic, the spectrum of the chaotic optical signal becomes quite smooth, and correspondingly, the spectrum of the electrical signal also becomes quite flat. Furthermore, the technical solution of this invention enables the device to continuously and stably generate a chaotic signal without time delay characteristics regardless of the setting of the modulator's bias point in the photoelectric oscillation loop. This reduces the requirements for system bias point control, improving radar detection accuracy while enhancing the anti-interference capability of chaotic radar against environmental changes.

Claims

1. A method for generating chaotic signals based on chaotic sequence modulation, characterized in that, A continuous optical signal is intensity modulated using a chaotic time-series signal, and the resulting modulated optical signal is input into an optoelectronic oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the optoelectronic oscillation loop. The chaotic time-series signal is a periodic signal that presents an ideal chaotic signal waveform within a single period, and is obtained using the following method: based on the mathematical model of the chaotic optoelectronic oscillator, the ideal chaotic signal waveform output by the chaotic optoelectronic oscillator is obtained through simulation; then, a segment is extracted from the ideal chaotic signal waveform as the target signal waveform, and the chaotic time-series signal is generated using an arbitrary waveform generator.

2. The chaotic signal generation method based on chaotic sequence modulation as described in claim 1, characterized in that, The chaotic photoelectric oscillator is a bandpass filter type photoelectric oscillator, and its mathematical model is as follows: in, , , , , , , It is the Qualcomm cutoff frequency. It is the low-pass cutoff frequency. Indicates the feedback coefficient. This represents the radio frequency half-wave voltage of the modulator. This represents the DC half-wave voltage of the modulator. This represents the radio frequency input signal of the modulator. This represents the DC bias voltage of the modulator. The response coefficient of a photodetector is represented. Indicates amplifier gain. Indicates loop loss. Indicates the loop input optical power. Indicates the input electrical signal. Indicates the period of the oscillation loop. t Indicates time.

3. A chaotic signal generation device based on chaotic sequence modulation, characterized in that, The system includes a modulation optical module and a photoelectric oscillation loop. The modulation optical module is used to intensity modulate a continuous optical signal with a chaotic time-series signal, and inputs the obtained modulated optical signal into the photoelectric oscillation loop, thereby outputting a chaotic signal with eliminated time delay characteristics from the photoelectric oscillation loop. The chaotic time-series signal is a periodic signal that presents an ideal chaotic signal waveform within a single period, and is obtained using the following method: based on the mathematical model of the chaotic photoelectric oscillator, the ideal chaotic signal waveform output by the chaotic photoelectric oscillator is obtained through simulation; then, a segment is extracted from the ideal chaotic signal waveform as the target signal waveform, and the chaotic time-series signal is generated by an arbitrary waveform generator.

4. The chaotic signal generation device based on chaotic sequence modulation as described in claim 3, characterized in that, The chaotic photoelectric oscillator is a bandpass filter type photoelectric oscillator, and its mathematical model is as follows: in, , , , , , , It is the Qualcomm cutoff frequency. It is the low-pass cutoff frequency. Indicates the feedback coefficient. This represents the radio frequency half-wave voltage of the modulator. This represents the DC half-wave voltage of the modulator. This represents the radio frequency input signal of the modulator. This represents the DC bias voltage of the modulator. The response coefficient of a photodetector is represented. Indicates amplifier gain. Indicates loop loss. Indicates the loop input optical power. Indicates the input electrical signal. Indicates the period of the oscillation loop. t Indicates time.

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