Nyquist folded reception method and system with dual parallel mach-zehnder modulators

Abstract

The present application belongs to the technical field of microwave signal measurement, and particularly relates to a Nyquist folding receiving method and system of a double parallel Mach-Zehnder modulator. The method comprises: inputting a continuous optical carrier into a double parallel Mach-Zehnder modulator and distributing it to two parallel modulation paths; loading a to-be-measured radio frequency signal to the first path to generate a signal light through small signal linear modulation, and loading a narrowband frequency modulation signal to the second path to generate multi-order optical sidebands through nonlinear modulation, thereby realizing integrated parallel control. After the two optical signals are combined, square law detection is performed, and beat frequencies between signal sidebands and multi-order optical sidebands are used to generate an electrical signal; after low-pass filtering, an intermediate frequency signal containing Nyquist interval mapping information is extracted; after low-speed sampling of the intermediate frequency signal, interval identification, frequency solving and signal reconstruction are performed, thereby recovering the original radio frequency signal. The present application does not require an optical pulse source and a multi-stage optical link, and has a simple system and high integration degree, and can realize wideband radio frequency signal receiving at a low sampling rate.

Description

Technical Field

[0001] This invention belongs to the field of microwave signal measurement technology, specifically relating to a method and system for receiving Nyquist folded signals using dual parallel Mach-Zehnder modulators. Background Technology

[0002] In modern electromagnetic information environments, efficient acquisition of wideband radio frequency (RF) signals has become a key issue in fields such as wireless communication, radar systems, and spectrum monitoring. With the continuous increase in signal operating frequency and instantaneous bandwidth, traditional direct digital reception methods based on Nyquist sampling theory are limited by high-speed analog-to-digital converters in terms of sampling rate, power consumption, storage capacity, and real-time processing capabilities, making it difficult to meet the real-time acquisition requirements of ultra-wideband RF signals. Therefore, how to achieve effective reception and reconstruction of wideband RF signals under relatively low sampling rates has become an important research direction in the field of wideband signal processing.

[0003] The Nyquist Folding Receiver (NYFR), a typical undersampled broadband reception technique, introduces a position-modulated pulse sequence local oscillator to mix with the target signal. Through pulse modulation, high-frequency signals from different Nyquist intervals are folded and mapped onto a unified low-frequency observation bandwidth while retaining Nyquist interval identification information, thus achieving low-speed sampling reception of broadband signals. However, this method is highly dependent on high-speed electronic pulse sources, and its achievable bandwidth is limited by the bandwidth of the electronic devices and the pulse width, making it difficult to meet the requirements for receiving higher-frequency broadband signals.

[0004] To enhance system bandwidth, researchers have gradually extended Nyquist folded receiver structures to the optical domain. They utilize photonic devices or structures such as electro-optic modulators, mode-locked lasers, and multi-stage modulation structures to construct optically positioned modulation pulses or optical local oscillators, thereby leveraging the high bandwidth of photonic systems to achieve broadband signal reception. Among these, the mode-locked laser-based approach overcomes the electronic pulse width limitation through ultra-narrow optical pulses, but its pulse position depends on pulse selection or dispersion modulation. The former is limited by discrete-time resolution, easily introducing quantization errors and limiting system bandwidth; the latter has strict requirements for dispersion parameter matching, resulting in poor system flexibility and complex implementation. Another approach, based on optical frequency combs, constructs an equivalent local oscillator in the frequency domain to achieve Nyquist interval marking, avoiding complex time-domain pulse control. However, it typically relies on multi-stage optical processing links and complex frequency control structures, making system integration difficult.

[0005] Therefore, while existing Nyquist folding reception technology has made some progress in broadband reception capabilities, it still has certain shortcomings in terms of system complexity, device integration, and engineering feasibility. Especially for broadband band marking technologies that do not rely on additional optical pulse sources, how to further simplify the system implementation process, reduce the complexity of parameter coordination due to multi-stage optical processing structures, and achieve efficient folding reception of broadband RF signals at low sampling rates while maintaining its broadband band marking capabilities remains a crucial technical problem that urgently needs to be solved. Summary of the Invention

[0006] This invention aims to overcome the problems of existing Nyquist folding reception technologies, where the local oscillator signal generation relies on optical pulse sources or complex optical frequency comb structures, resulting in complex system structures, low device integration, and poor engineering feasibility. It provides a dual-parallel Mach-Zehnder modulator Nyquist folding reception method and system that integrates parallel control of the modulation of the signal under test and the generation of multi-order optical sidebands through a single dual-parallel Mach-Zehnder modulator, thereby simplifying the system structure and improving integration.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] The Nyquist folding receiver method for dual parallel Mach-Zehnder modulators includes the following steps:

[0009] S1, a continuous optical carrier is input into a dual parallel Mach-Zehnder modulator, and distributed to two parallel modulation paths within the dual parallel Mach-Zehnder modulator; the radio frequency signal to be tested is loaded onto the first modulation path for small-signal linear modulation to generate signal light carrying the radio frequency information to be tested; a narrowband frequency-modulated signal is loaded onto the second modulation path for nonlinear modulation to generate multi-order optical sidebands, thereby realizing integrated parallel control of the modulation of the signal to be tested and the generation of multi-order optical sidebands within a single dual parallel Mach-Zehnder modulator;

[0010] S2, the signal light carrying the radio frequency information to be tested is combined with the multi-order optical sideband into a composite modulated optical signal through the dual parallel Mach-Zehnder modulator;

[0011] S3, the composite modulated optical signal is subjected to square-law detection, and a beat frequency electrical signal is generated by the beat frequency interaction between the signal sideband and the multi-order optical sideband in the signal light; the beat frequency electrical signal is low-pass filtered to extract the intermediate frequency signal folded into the observation bandwidth, and the intermediate frequency signal contains spectral mapping information characterizing the Nyquist interval number;

[0012] S4, the intermediate frequency signal is sampled at low speed, and the sampled signal is subjected to Nyquist interval identification, frequency calculation and signal reconstruction to recover the original radio frequency signal.

[0013] Preferably, the first modulation path operates in a small-signal linear modulation state at an orthogonal bias point, wherein the small-signal linear modulation state causes the first-order sideband to dominate in the signal light output by the first modulation path.

[0014] Preferably, the narrowband frequency modulation signal is any one of linear frequency modulation signal, sinusoidal frequency modulation signal, or periodic frequency modulation signal.

[0015] Preferably, in step S3, the effective beat frequency component generated in the square law detection is formed by the difference frequency interaction between the first-order signal sideband generated by the first modulation path and the multi-order optical sideband generated by the second modulation path.

[0016] Preferably, the frequency spacing of the multi-order optical sidebands is equal to the center frequency of the narrowband frequency-modulated signal, and the different orders of optical sidebands correspond to the spectral mapping relationships of different Nyquist intervals.

[0017] Preferably, in step S3 and step S4, the sampling frequency of the low-speed sampling is equal to the center frequency of the narrowband FM signal; in step S3, the cutoff frequency of the low-pass filter is set to half of the sampling frequency to retain the effective spectral components folded into the baseband range.

[0018] Preferably, in step S3, the intermediate frequency signal includes the center frequency, bandwidth, and spectral direction information of the folded spectrum, wherein the Nyquist interval number is determined based on the center frequency, bandwidth, and spectral direction information of the folded spectrum and in combination with the center frequency of the narrowband FM signal.

[0019] Preferably, in step S4, the Nyquist interval identification, frequency calculation and signal reconstruction are achieved by performing time-frequency analysis on the sampled signal to extract the center frequency, bandwidth and spectral direction features of the folded spectrum.

[0020] The present invention also provides a dual parallel Mach-Zehnder modulator Nyquist folded receiver system comprising:

[0021] LD light source, used to generate continuous optical carriers;

[0022] Radio frequency signal generator, used to generate the radio frequency signal to be tested;

[0023] Narrowband frequency modulation signal generator, used to generate narrowband frequency modulation signals;

[0024] A dual parallel Mach-Zehnder modulator, with its input connected to the LD light source, its first modulation path connected to the radio frequency signal generator, and its second modulation path connected to the narrowband frequency modulation signal generator, is used to internally perform parallel modulation of the radio frequency signal under test and multi-order optical sideband generation, and to combine the two optical signals into a composite modulated optical signal.

[0025] A photodetector, connected to the output of the dual parallel Mach-Zehnder modulator, is used to perform square-law detection on the composite modulated optical signal and generate a beat frequency electrical signal.

[0026] A low-pass filter, connected to the output of the photodetector, is used to filter out high-frequency components and extract the intermediate frequency signal folded into the observation bandwidth.

[0027] An analog-to-digital converter, connected to the output of the low-pass filter, is used for low-speed sampling of the intermediate frequency signal;

[0028] The signal processing module is connected to the output of the analog-to-digital converter and is used to perform Nyquist interval identification, frequency calculation and signal reconstruction on the sampled signal.

[0029] Preferably, the dual parallel Mach-Zehnder modulator includes an input beam splitter structure, a first sub-Mach-Zehnder modulator, a second sub-Mach-Zehnder modulator, and an output beam combiner structure.

[0030] Compared with the prior art, the beneficial effects of this invention are: (1) This invention uses a single dual parallel Mach-Zehnder modulator to realize the modulation of the radio frequency signal under test and the generation of multi-order optical sidebands, without the need for a mode-locked optical pulse source and a multi-level optical processing link, making the system structure simpler and more compact; (2) This invention uses two parallel modulation paths to realize the loading of radio frequency signals and the driving of narrowband frequency modulation, realizing independent control of the modulation function and improving the system adjustment flexibility; (3) This invention directly completes the spectrum folding and Nyquist interval mapping of broadband radio frequency signals through the difference frequency beat frequency between the signal sideband and the multi-order optical sideband, with a clear and explicit physical mechanism; (4) This invention can realize the sub-Nyquist reception and reconstruction of broadband radio frequency signals under low-speed sampling conditions, and is suitable for the detection and recovery of single-tone, multi-tone, linear frequency modulation signals, frequency shift keying signals and binary phase shift keying signals. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of an architecture of the dual parallel Mach-Zehnder modulator Nyquist folded receiver system in this invention; Figure 2 A schematic diagram of a first sub-modulation arm, a second sub-modulation arm, and a combined spectrum provided in an embodiment of the present invention; Figure 3A schematic diagram of a simulation result of the receiving time and frequency of a single-tone radio frequency signal located in different Nyquist zones, as provided in an embodiment of the present invention; Figure 4 This is a schematic diagram illustrating a simulation result of the time and frequency of multi-tone radio frequency signal reception provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of a simulation result of LFM signal reception time and frequency provided in an embodiment of the present invention; Figure 6 A schematic diagram illustrating a simulation result of simultaneous reception of FSK signal and single-tone combined signal according to an embodiment of the present invention; Figure 7 This is a schematic diagram illustrating a simulation result of the simultaneous reception of BPSK signal and single-tone combined signal according to an embodiment of the present invention. Detailed Implementation

[0032] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0033] like Figure 1 As shown, the present invention provides a dual parallel Mach-Zehnder modulator Nyquist folded receiver system, the system comprising:

[0034] The system comprises an LD light source, an RF signal generator, a dual parallel Mach-Zehnder modulator, a narrowband FM signal generator, a photodetector, a low-pass filter, an analog-to-digital converter, and a signal processing module. The continuous light source is connected to the input of the dual parallel Mach-Zehnder modulator. The RF signal generator is connected to the first sub-modulation arm of the dual parallel Mach-Zehnder modulator. The narrowband FM signal generator is connected to the second sub-modulation arm of the dual parallel Mach-Zehnder modulator. The output of the dual parallel Mach-Zehnder modulator is sequentially connected to the photodetector, the low-pass filter, the analog-to-digital converter, and the signal processing module.

[0035] The specific functions of each module are as follows:

[0036] LD light source, used to generate continuous optical carriers;

[0037] Radio frequency signal generator, used to generate the radio frequency signal to be tested;

[0038] Narrowband frequency modulation signal generator, used to generate narrowband frequency modulation signals;

[0039] The dual parallel Mach-Zehnder modulator has its input connected to the LD light source, its first modulation path (corresponding to the first sub-modulation arm) connected to the radio frequency signal generator, and its second modulation path (corresponding to the second sub-modulation arm) connected to the narrowband frequency modulation signal generator. It is used to perform the modulation of the radio frequency signal under test and the generation of multi-order optical sidebands in parallel inside, and to combine the two optical signals into a composite modulated optical signal.

[0040] A photodetector, connected to the output of the dual parallel Mach-Zehnder modulator, is used to perform square-law detection on the composite modulated optical signal and generate a beat frequency electrical signal.

[0041] A low-pass filter, connected to the output of the photodetector, is used to filter out high-frequency components and extract the intermediate frequency signal folded into the observation bandwidth.

[0042] An analog-to-digital converter, connected to the output of the low-pass filter, is used for low-speed sampling of the intermediate frequency signal;

[0043] The signal processing module is connected to the output of the analog-to-digital converter and is used to perform Nyquist interval identification, frequency calculation and signal reconstruction on the sampled signal.

[0044] In addition, the present invention also provides a method for receiving Nyquist folded receivers with dual parallel Mach-Zehnder modulators, comprising the following steps:

[0045] 1. A continuous optical carrier is input into a dual-parallel Mach-Zehnder modulator, and distributed to two parallel modulation paths within the dual-parallel Mach-Zehnder modulator; the radio frequency signal to be tested is loaded onto the first modulation path for small-signal linear modulation to generate signal light carrying the radio frequency information to be tested; a narrowband frequency-modulated signal is loaded onto the second modulation path for nonlinear modulation to generate multi-order optical sidebands, thereby realizing integrated parallel control of the modulation of the signal to be tested and the generation of multi-order optical sidebands within a single dual-parallel Mach-Zehnder modulator;

[0046] 2. The signal light carrying the radio frequency information to be tested is combined with the multi-order optical sidebands into a composite modulated optical signal by means of the dual parallel Mach-Zehnder modulator;

[0047] 3. The composite modulated optical signal is subjected to square-law detection, and a beat frequency electrical signal is generated by utilizing the beat frequency interaction between the signal sideband and the multi-order optical sideband in the signal light; the beat frequency electrical signal is low-pass filtered to extract the intermediate frequency signal folded into the observation bandwidth, and the intermediate frequency signal contains spectral mapping information characterizing the Nyquist interval number;

[0048] 4. The intermediate frequency signal is sampled at low speed, and the sampled signal is subjected to Nyquist interval identification, frequency calculation and signal reconstruction to recover the original radio frequency signal.

[0049] Specifically, such as Figures 2 to 7 As shown, the following describes the Nyquist folding reception method of the dual parallel Mach-Zehnder modulator in this invention, taking a narrowband sinusoidal frequency modulation (SFM) signal with a center frequency of 6 GHz, a modulation frequency of 10 MHz, and a modulation coefficient of 4 as an example, based on the dual parallel Mach-Zehnder modulator structure:

[0050] 1. Modulation of the RF signal under test and generation of multiple optical sidebands:

[0051] In this embodiment, the present invention outputs a continuous wave optical carrier signal through an LD light source. ,in For the amplitude of the light field, For optical carrier frequency, For time, The imaginary unit satisfies The signal is distributed to the first and second sub-modulation arms via the input beam splitter. The first sub-modulation arm is loaded with the signal to be measured: , The amplitude of the signal, The frequency of the signal to be measured. It carries phase information. The first sub-modulation arm operates in a small-signal linear modulation state at the quadrature bias point, and its output signal light... Represented as: ;

[0052] in, and These represent the DC bias and half-wave voltage of the first sub-modulation arm, respectively, and the modulation depth. bias phase shift , For zero-order Bessel functions, the amplitude of the optical carrier component is given. This is a first-order Bessel function, corresponding to the amplitude of the first-order sideband component generated after modulation. The output signal mainly consists of the carrier wave and the first-order sideband.

[0053] The second sub-modulation arm is loaded with a narrowband SFM signal: ,in, , The signal amplitude and center frequency are given. Modulation frequency Modulation index The second sub-modulation arm operates in the nonlinear modulation region, and its output signal light can be unfolded as follows: ;

[0054] in, and These represent the DC bias and half-wave voltage of the second sub-modulation arm, respectively, and the modulation depth. bias phase shift , , These are second-order and third-order Bessel functions, respectively, corresponding to the amplitudes of the second- to third-order sideband components generated after modulation. Due to the nonlinear response characteristics of the modulator, under SFM signal modulation, multiple-order optical sidebands with equally spaced frequencies and a modulation bandwidth that is multiplied can be generated. Their instantaneous frequency and modulation slope change linearly with the sideband order, thus forming a spectral mapping relationship corresponding to different Nyquist intervals.

[0055] 2. Generation of composite modulated optical signals:

[0056] The output signal light from the first sub-modulation arm and the multi-order optical sidebands from the second sub-modulation arm are linearly superimposed through the output beam combiner, and the total output optical field is: ;

[0057] During this process, the two signals maintain independent modulation paths.

[0058] 3. Spectrum folding and low-speed sampling:

[0059] When the combined optical signal is input into the photodetector, according to the square-law response, the output electrical signal is: ;

[0060] The effective beat frequency signal is formed by the difference frequency term between the first-order signal sideband generated by the first sub-modulation arm and the multi-order optical sideband generated by the second sub-modulation arm. The output electrical signal is then passed through a low-pass filter with a 3 GHz cutoff frequency to obtain a folded signal within the observation bandwidth. The intermediate frequency signal is generated by the difference frequency interaction between the sideband of the signal under test and the corresponding optical sideband of the Nyquist interval. Therefore, the folded signal within the observation bandwidth can be expressed as: ;

[0061] in, Indicates the modulation scaling factor. Indicates the center frequency of the folded signal within the observation band. Indicates the spectral direction of the folded signal within the observed frequency band. This indicates the Nyquist Zone (NZ) number related to the folding interval of the original signal carried by the folded signal within the observation frequency band. As shown in the above formula, the bandwidth of the folded signal corresponds to both the Nyquist Zone index M and the bandwidth of the baseband SFM signal, and the initial phase in the folding time-frequency diagram of the observed frequency band SFM signal reflects the spectral direction. It is -1 or +1. The filtered electrical signal is sampled at a low speed by an analog-to-digital converter. The sampling rate is significantly lower than the highest frequency of the target RF signal, thus achieving sub-Nyquist sampling.

[0062] 4. Signal Processing and Frequency Reconstruction:

[0063] The sampled digital signal is input into the signal processing module, where time-frequency analysis is used to extract characteristic parameters such as the center frequency, bandwidth, and spectral direction of the folded signal. Based on the correspondence between the signal folding bandwidth and the Nyquist zone index M, combined with the spectral direction... Criterion and center frequency of folded signal It can uniquely determine the NZ number and its true frequency of the original radio frequency signal. This enables accurate identification and reconstruction of the original radio frequency signal.

[0064] like Figure 2 The figures show the simulated spectral results after modulation with the RF signal of the first sub-modulation arm, the simulated spectral results after modulation with the SFM signal of the second sub-modulation arm, and the simulated spectral results before photodetection. The optical field spectrum of the first sub-modulation arm shows that under small-signal modulation, the output signal contains only the carrier and first-order sidebands. The optical field spectrum of the second sub-modulation arm shows that intensity modulation can obtain multiple frequency components with equal intervals, doubled bandwidth, and cosine envelope attenuation in amplitude. The optical field spectrum before photodetection indicates that the output signal is obtained by linearly adding the signals from both arms, and the simulation results are as expected.

[0065] like Figure 3 The diagram shows the simulation results of the received time-frequency diagrams for single-tone radio frequency signals located in different Nyquist zones. The signals under test are 7.5 GHz and 32.5 GHz single-tone signals. Taking the 7.5 GHz signal on the left as an example, the time-frequency characteristics of its folded signal are as follows: center frequency... =1.5GHz, bandwidth 80MHz corresponding modulation scaling factor The spectral direction corresponding to an initial phase of 0 Therefore, M is +1, thus obtaining the reconstruction frequency. Similarly, the center frequency of the folded time-frequency diagram of the 32.5GHz single-tone signal on the right is 2.5GHz, the bandwidth is increased to 400MHz, and other parameters remain the same, with M being +5, consistent with the expected image parameters. The RF signals from different Nyquist zones exhibit different bandwidth and frequency modulation direction characteristics after folding, verifying the present invention's ability to distinguish signals from multiple Nyquist zones and its 33GHz reception range.

[0066] like Figure 4The diagram shows the simulation results of the time-frequency diagram during multi-tone radio frequency (SFM) signal reception. The input signals are 8 GHz and 23 GHz dual-tone signals, corresponding to center frequencies of 2 GHz and 1 GHz, bandwidths of 80 MHz and 320 MHz respectively within a single cycle, and initial phases of [missing information]. and The spectral directions are +1 and -1, respectively, therefore M is +1 and -4, resulting in reconstructed frequencies of 8GHz and 23GHz, which is completely consistent with expectations. Multiple cross-Nyquist zone signals form multiple distinguishable time-frequency trajectories within the observation bandwidth, proving that the present invention has the ability to simultaneously receive and identify multiple signals.

[0067] like Figure 5 The diagram shown illustrates the simulation results of the time-frequency diagram for LFM signal reception. The center frequency of the LFM signal under test is 7.5 GHz, the bandwidth is 1 GHz, the period is 1 μs, and the corresponding chirp rate is 1000 MHz / μs. Figure 5 The center frequency of the folded signal can be extracted as 1.5 GHz, the slope of the folded signal is 1000 MHz / µs, and the bandwidth of the SFM signal in a single cycle is 80 MHz with an initial phase of 0, therefore M is +1. The center frequency of the recovered signal is 7.5 GHz, corresponding to a chirp rate of 1000 MHz / µs. Simulation results show that the bandwidth and frequency modulation slope of the folded signal are consistent with the theoretical analysis, and accurate reconstruction of the broadband LFM signal can be achieved.

[0068] like Figure 6 The diagram shows the simulation results of the time-frequency diagram for receiving a combination of FSK and single-tone signals. The signals under test are a 13GHz single-tone signal and an FSK signal encoded using '0' and '1' sequences to represent frequency information, where '0' and '1' represent two different carrier frequencies, 7.75GHz and 8.25GHz, respectively. The frequency encoding sequence within one cycle is set to {1100110011}, with a symbol duration of 0.1µs. Each cycle consists of 10 symbols, spanning 1µs. The continuous sinusoidal frequency-modulated waveform at the bottom of the figure corresponds to a single-tone radio frequency signal. From this, the center frequency of its folded signal can be extracted as 1 GHz, the bandwidth as 160 MHz, and the initial phase as 0, corresponding to a spectral direction of +1. Therefore, M is +2, resulting in a reconstructed frequency of 13 GHz. The discontinuous alternating waveform at the top of the figure corresponds to an FSK signal. From this, the center frequency of its folded signal can be extracted as alternating between 2.25 GHz and 1.75 GHz, corresponding to the original signal carrier frequencies of 8.25 GHz and 7.75 GHz, respectively, which closely match the target FSK signal. Simulation results show that the center frequency distribution, alternation pattern, and additional SFM characteristics of the folded signal are consistent with the theoretical analysis, proving that this method can effectively separate overlapping multi-band signals in space and achieve accurate detection and reconstruction of FSK and single-tone combined signals.

[0069] In this embodiment, as Figure 7 The figure shows a simulation result of the time-frequency diagram for receiving a BPSK combined single-tone signal. The signal under test is a 14GHz single-tone signal and the phase-coded sequence is { The BPSK signal has a carrier frequency of 7 GHz and a symbol duration of 0.1 μs. Each cycle consists of 10 symbols with a duration of 1 μs. The continuous sinusoidal frequency modulation waveform at the top of the figure corresponds to a single-tone radio frequency signal. From this, we can extract the center frequency of its folded signal as 2 GHz, the bandwidth as 160 MHz, and the initial phase as 0, corresponding to a spectral direction of +1. Therefore, M is +2, resulting in a reconstructed frequency of 14 GHz. The waveform with phase jumps at the bottom of the figure corresponds to a BPSK signal. From this, we can extract the center frequency of its folded signal as 1 GHz, the folding direction as +1, and the reconstructed frequency as 7 GHz. Simultaneously, the time-frequency diagram clearly shows the phase-coded sequence in... and The phase transitions between these phases are completely consistent with the pre-coded phase diagram. Simulation results show that the center frequency distribution, BPSK switching pattern, and additional SFM characteristics of the folded signal are consistent with the theoretical analysis, proving the method's ability to accurately reconstruct complex multi-component signals.

[0070] This invention eliminates the need for optical pulse sources and multi-stage optical processing links. It achieves integrated parallel control of the modulation of the signal under test and the generation of multi-order optical sidebands within a single dual-parallel Mach-Zehnder modulator, and combines photoelectric beat frequency effects to complete the spectral folding and interval mapping of broadband RF signals. Using only a low-speed analog-to-digital converter with a sampling rate of 6 GS / s, it enables real-time reception and reconstruction of single-tone, multi-tone, broadband LFM, FSK, and BPSK signals within the 0-33 GHz range. Compared to existing photonic Nyquist folding reception schemes, this invention features a simpler system structure, a clearer physical mechanism, and stronger scalability. Furthermore, it eliminates the need for high-speed PMPTs or multi-channel parallel structures, demonstrating promising engineering implementation prospects.

[0071] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A dual-parallel Mach-Zehnder modulator Nyquist folding receiver method, characterized in that, Includes the following steps: S1, a continuous optical carrier is input into a dual parallel Mach-Zehnder modulator, and distributed to two parallel modulation paths within the dual parallel Mach-Zehnder modulator; the radio frequency signal to be tested is loaded into the first modulation path for small-signal linear modulation to generate signal light carrying the radio frequency information to be tested; The narrowband frequency-modulated signal is loaded onto the second modulation path for nonlinear modulation to generate multi-order optical sidebands, thereby realizing integrated parallel control of the modulation of the signal under test and the generation of multi-order optical sidebands within a single dual parallel Mach-Zehnder modulator. S2, the signal light carrying the radio frequency information to be tested is combined with the multi-order optical sideband into a composite modulated optical signal through the dual parallel Mach-Zehnder modulator; S3, the composite modulated optical signal is subjected to square law detection, and a beat frequency electrical signal is generated by the beat frequency effect between the signal sideband and the multi-order optical sideband in the signal light. The beat frequency electrical signal is low-pass filtered to extract the intermediate frequency signal folded into the observation bandwidth. The intermediate frequency signal contains spectral mapping information characterizing the Nyquist interval number. S4, the intermediate frequency signal is sampled at low speed, and the sampled signal is subjected to Nyquist interval identification, frequency calculation and signal reconstruction to recover the original radio frequency signal.

2. The dual parallel Mach-Zehnder modulator Nyquist folding reception method according to claim 1, characterized in that, The first modulation path operates in a small-signal linear modulation state at an orthogonal bias point, where the first-order sideband dominates the signal light output by the first modulation path.

3. The dual parallel Mach-Zehnder modulator Nyquist folding reception method according to claim 2, characterized in that, The narrowband frequency modulation signal is any one of linear frequency modulation, sinusoidal frequency modulation, or periodic frequency modulation.

4. The Nyquist folding reception method for dual parallel Mach-Zehnder modulators according to claim 3, characterized in that, In step S3, the effective beat frequency component generated in the square law detection is formed by the difference frequency interaction between the first-order signal sideband generated by the first modulation path and the multi-order optical sideband generated by the second modulation path.

5. The Nyquist folding reception method for dual parallel Mach-Zehnder modulators according to claim 4, characterized in that, The frequency spacing of the multi-order optical sidebands is equal to the center frequency of the narrowband frequency-modulated signal, and the different orders of optical sidebands correspond to the spectral mapping relationships of different Nyquist intervals.

6. The Nyquist folding reception method for dual parallel Mach-Zehnder modulators according to claim 5, characterized in that, In step S4, the sampling frequency of the low-speed sampling is equal to the center frequency of the narrowband FM signal; in step S3, the cutoff frequency of the low-pass filter is set to half of the sampling frequency to retain the effective spectral components folded into the baseband range.

7. The Nyquist folding reception method for dual parallel Mach-Zehnder modulators according to claim 6, characterized in that, In step S3, the intermediate frequency signal includes the center frequency, bandwidth, and spectral direction information of the folded spectrum, wherein the Nyquist interval number is determined based on the center frequency, bandwidth, and spectral direction information of the folded spectrum and in combination with the center frequency of the narrowband FM signal.

8. The Nyquist folding reception method for dual parallel Mach-Zehnder modulators according to claim 7, characterized in that, In step S4, the Nyquist interval identification, frequency calculation and signal reconstruction are achieved by performing time-frequency analysis on the sampled signal to extract the center frequency, bandwidth and spectral direction features of the folded spectrum.

9. A dual-parallel Mach-Zehnder modulator Nyquist folding receiver system, used to implement the dual-parallel Mach-Zehnder modulator Nyquist folding receiver method according to any one of claims 1-8, characterized in that, The dual parallel Mach-Zehnder modulator Nyquist folded receiver system includes: LD light source, used to generate continuous optical carriers; Radio frequency signal generator, used to generate the radio frequency signal to be tested; Narrowband frequency modulation signal generator, used to generate narrowband frequency modulation signals; A dual parallel Mach-Zehnder modulator, with its input connected to the LD light source, its first modulation path connected to the radio frequency signal generator, and its second modulation path connected to the narrowband frequency modulation signal generator, is used to internally perform parallel modulation of the radio frequency signal under test and multi-order optical sideband generation, and to combine the two optical signals into a composite modulated optical signal. A photodetector, connected to the output of the dual parallel Mach-Zehnder modulator, is used to perform square-law detection on the composite modulated optical signal and generate a beat frequency electrical signal. A low-pass filter, connected to the output of the photodetector, is used to filter out high-frequency components and extract the intermediate frequency signal folded into the observation bandwidth. An analog-to-digital converter, connected to the output of the low-pass filter, is used for low-speed sampling of the intermediate frequency signal; The signal processing module is connected to the output of the analog-to-digital converter and is used to perform Nyquist interval identification, frequency calculation and signal reconstruction on the sampled signal.

10. The dual parallel Mach-Zehnder modulator Nyquist folded receiver system according to claim 9, characterized in that, The dual parallel Mach-Zehnder modulator includes an input beam splitter, a first sub-Mach-Zehnder modulator, a second sub-Mach-Zehnder modulator, and an output beam combiner.

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