CN113777402A - Photon-assisted microwave signal time-frequency analysis device and method based on stimulated Brillouin scattering effect - Google Patents
Photon-assisted microwave signal time-frequency analysis device and method based on stimulated Brillouin scattering effect Download PDFInfo
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Abstract
The invention discloses a photon-assisted microwave signal time-frequency analysis device and method based on stimulated Brillouin scattering effect, wherein the device comprises a continuous wave laser, a first optical isolator, a second optical isolator, an optical coupler, an electric coupler, a 90-degree electric mixer, a first radio frequency signal source, a second radio frequency signal source, a first arbitrary waveform generator, a second arbitrary waveform generator, a first double-parallel Mach-Zehnder modulator, a second double-parallel Mach-Zehnder modulator, a first erbium-doped optical fiber amplifier, a Mach-Zehnder modulator, a single-mode optical fiber, an optical circulator and an optical photodetector. The method comprises modulating the signal to be detected onto stepped optical carrier, performing frequency-time mapping on the side band by using stimulated Brillouin, and processing the electric pulse after photoelectric detection to obtain signal time-frequency distribution. The microwave signal analysis device has a compact, simple and effective structure, can perform high-frequency resolution time-frequency analysis on the microwave signal, has reconstructability on the analyzed bandwidth and frequency band, avoids using a high-speed analog-to-digital converter, reduces the complexity and cost of the system, and has better feasibility and application prospect.
Description
Technical Field
The invention belongs to the technical field of microwave signal measurement, and particularly relates to a photon-assisted microwave signal time-frequency analysis device and method based on a stimulated Brillouin scattering effect.
Background
Microwave parameter measurement is widely applied to the fields of communication, radar, radio astronomy and the like, and the performance of a microwave parameter measurement system often influences the performance of the whole radio frequency microwave system. The time-frequency distribution measurement of unknown microwave signals belongs to one of microwave parameter measurement. The time-frequency distribution of a signal can provide a lot of information, including: 1. the position of the signal to be measured in the whole radio frequency spectrum and occupied spectrum resources; 2. identifying a signal to be detected and an interference signal or other undesired signals; 3. dynamic change of the signal to be detected, real-time monitoring of time-frequency information of the signal to be detected and the like. Therefore, the time-frequency distribution of the unknown signals can be obtained accurately and truly, and the method has important practical significance and is actively researched.
Common time-frequency analysis methods include short-time Fourier transform, wavelet transform, Viger distribution, etc., where the short-time Fourier transform and wavelet transform are linear time-frequency analysis methods and the Viger distribution is nonlinear (Proc. IEEE, 77(7): 941-. Although these methods have been widely used, implementing the above methods in the electrical domain requires first sampling the signal with an analog-to-digital converter. The analog-to-digital converter with high precision and high sampling rate has high manufacturing difficulty, and the bandwidth and the speed of time-frequency analysis are often limited. Furthermore, digital signal processing is performed after sampling, and therefore these methods are inefficient at tracking spectral changes in excess of a few microseconds, and face challenges in measuring signals with bandwidths in excess of the GHz range (IEEE J. select. Areas Commun., 17(4): 539-550, 1999). The compressed sensing technology can realize signal reconstruction under the condition of undersampling, reduce data transmission quantity, and can be used for improving the bandwidth of time-frequency analysis, but the complex algorithm also limits the real-time property of the time-frequency analysis (IEEE trans. Signal Processing, 59(9): 4053 + 4085, 2011). Therefore, a time-frequency analysis means different from the traditional electric domain needs to be explored to measure the microwave signal.
All-optical short-time fourier transforms offer the possibility of capturing and identifying spectral components of fast rare or transient events in near real-time, enabling one to observe the time-frequency evolution of non-stationary signals, but currently there is little research on all-optical short-time fourier transforms. In an early all-optical time-frequency analysis scheme, a microwave signal to be measured is modulated on a series of chirped light pulses, a specific frequency is extracted by using a cascaded linear chirped fiber bragg grating array as a band-pass filter, and chromatic dispersion is provided to separate different frequencies in a time domain (IEEE photon, technol. lett., 23(20): 1439-. Currently, some researchers have proposed a dynamic waveform time-frequency analysis scheme with a simple structure, in which a measured signal is modulated on an optical pulse and then loaded on a dispersion compensation optical fiber with a length of about 50 km. Optical pulses of different frequencies are separated in the time domain after transmission in a dispersion compensating fiber, and the frequency resolution is experimentally proved to be about 340MHz (nat. Commun, 11(1): 2020, art. No. 3309.). On the basis, researchers adopt bandwidth-amplified electro-optic conversion, which greatly reduces the dispersion requirement on high-frequency-resolution all-optical short-time Fourier transform and transmission delay, and the frequency resolution for time-frequency analysis can reach 60MHz (J. light. Technol., 39(6): 1051-. The scheme for performing time-frequency analysis meets the real-time requirement, but the frequency resolution cannot reach a higher level, so that how to perform large-bandwidth high-resolution time-frequency analysis on microwave signals is a problem with great practical significance and application value.
Disclosure of Invention
In order to solve the technical problems in the background art, the invention provides a device and a method for photon-assisted microwave signal time-frequency analysis based on a stimulated Brillouin scattering effect. By setting a reasonable sideband modulation mode, the frequency position of the stimulated Brillouin gain spectrum and the parameters of the step frequency signal, the microwave signal can be subjected to time-frequency analysis with large bandwidth and high resolution without a high-speed analog-to-digital converter. The invention reduces the cost of the whole system, increases the tunability and feasibility of the system, and has important practical significance and application value.
The invention adopts the following scheme for solving the technical problems:
a photon-assisted microwave signal time-frequency analysis device based on a stimulated Brillouin scattering effect is characterized by comprising a continuous wave laser, a first optical isolator, an optical coupler, a first double-parallel Mach-Zehnder modulator, a first arbitrary waveform generator, a first erbium-doped optical fiber amplifier, a Mach-Zehnder modulator, an electric coupler, a first radio-frequency signal source, a second arbitrary waveform generator, a second optical isolator, a single-mode optical fiber, a second double-parallel Mach-Zehnder modulator, a second radio-frequency signal source, a 90-degree electric mixer, a second erbium-doped optical fiber amplifier, an optical circulator and a photoelectric detector; the output port of the continuous wave laser is connected with the input port of a first optical isolator, the output port of the first optical isolator is connected with the input port of an optical coupler, and the output port of the optical coupler is respectively connected with the optical input ports of the first and second double-parallel Mach-Zehnder modulators; the radio frequency input port of the first dual-parallel mach-zehnder modulator is connected to the output port of the first arbitrary waveform generator, the optical output port of the first double-parallel Mach-Zehnder modulator is connected with the input port of the first erbium-doped fiber amplifier, the output port of the first erbium-doped fiber amplifier is connected with the optical input port of the Mach-Zehnder modulator, the radio frequency input port of the Mach-Zehnder modulator is connected with the output port of the electric coupler, the input port of the electric coupler is respectively connected with the output ports of the second arbitrary waveform generator and the first radio frequency signal source, the optical output port of the mach-zehnder modulator is connected to the input port of a second optical isolator, the output port of the second optical isolator is connected with one end of a single-mode optical fiber, and the other end of the single-mode optical fiber is connected with a port II of the optical circulator; the radio frequency input port of the second double-parallel Mach-Zehnder modulator is connected with the output port of the 90-degree electric mixer, the input port of the 90-degree electric mixer is connected with the output port of the first radio frequency signal source, the optical output port of the second double-parallel Mach-Zehnder modulator is connected with the input port of the second erbium-doped optical fiber amplifier, and the output port of the second erbium-doped optical fiber amplifier is connected with the port I of the optical circulator; the port III of the optical circulator is connected with the optical input port of the photoelectric detector; and the time-frequency characteristic diagram of the signal to be detected can be obtained by segmenting the waveform output by the photoelectric detector.
In the device, the step period of the step frequency signal loaded to the first double-parallel Mach-Zehnder modulator is integral multiple of the period of the signal to be measured, the frequency resolution and analysis bandwidth of time-frequency analysis are controlled by controlling the parameters, namely step frequency interval and step times, of the step frequency signal generated by the first arbitrary waveform generator, and the signal frequency components extracted in different step periods are determined by the difference value between the frequency of the step frequency signal in the period and the center frequency of the stimulated Brillouin gain spectrum.
In the device, the central frequency position of a stimulated Brillouin gain spectrum generated by the interaction of pump light output by the second erbium-doped fiber amplifier and probe light output by the Mach-Zehnder modulator in the single-mode fiber corresponds to the frequency of a single-tone signal modulated on the second double-parallel Mach-Zehnder modulator one by one, and the frequency value of the single-tone signal is adjusted to control the frequency band of time-frequency analysis.
In the device, the frequency-time mapping pulse generated by the photoelectric detector comprises the following information: stepping cycle sequence number, generation time and amplitude; the frequency represented by the pulse generated in different step periods is different, the generation time of the electric pulse represents that the signal to be measured has measurable frequency components at the time, and the amplitude of the electric pulse is in positive correlation with the strength of the frequency component of the signal to be measured at a certain time.
A microwave signal time-frequency analysis method adopting the device comprises the following steps:
1) output frequency of continuous wave laser isf 0The linearly polarized light of (1) is first passed through a first optical isolator, then is equally divided into two parts by an optical coupler, and then is respectively injected into a first double-side light source and a second double-side light sourceIn parallel Mach-Zehnder modulators;
2) the two paths of orthogonal step frequency signals sent by the first arbitrary waveform generator are respectively used for driving two sub-modulators of the first double-parallel Mach-Zehnder modulator, the bias voltage of the modulators is adjusted, so that the two sub-modulators are biased at the minimum bias point, meanwhile, 90-degree phase shift is introduced into the main modulator by the bias voltage, and the first double-parallel Mach-Zehnder modulator can output a carrier-restraining single-sideband modulation signal of the step frequency signals;
3) the carrier-restraining single-sideband modulation signals output by the first double-parallel Mach-Zehnder modulator are amplified by the first erbium-doped fiber amplifier and then injected into the Mach-Zehnder modulator, the signals to be measured and the reference signals with specific frequency are coupled by the electric coupler and then driven, and the bias point of the Mach-Zehnder modulator is adjusted to carry out carrier-restraining double-sideband modulation;
4) injecting the optical signal output by the Mach-Zehnder modulator into the single-mode optical fiber through the second optical isolator to serve as detection light of the stimulated Brillouin scattering effect;
5) injecting a single-tone signal for controlling an analysis frequency band into a 90-degree electric mixer, dividing the single-tone signal into two paths, respectively driving two sub-modulators of a second double-parallel Mach-Zehnder modulator, adjusting bias voltage of the modulators to enable the two sub-modulators to be biased at a minimum bias point, and simultaneously introducing 90-degree phase shift to a main modulator by the bias voltage, so that a suppressed carrier single-sideband modulation signal corresponding to the single-tone signal frequency one to one is obtained from the output of the second double-parallel Mach-Zehnder modulator;
6) after a carrier-restraining single-sideband modulation signal output by the second double-parallel Mach-Zehnder modulator passes through the second erbium-doped fiber amplifier, the carrier-restraining single-sideband modulation signal is reversely injected into the single-mode fiber through the port I of the optical circulator to serve as pump light of the stimulated Brillouin scattering effect;
7) and injecting the optical signal output by the port III of the optical circulator into a photoelectric detector for photoelectric conversion, and segmenting the waveform output by the photoelectric detector to obtain a time-frequency characteristic diagram of the signal to be detected.
The invention provides a device and a method for photon-assisted microwave signal time-frequency analysis based on a stimulated Brillouin scattering effect. By reasonably setting the sideband modulation mode, the frequency position of the stimulated Brillouin gain spectrum and the parameters of the step frequency signal, the microwave signal can be subjected to time-frequency analysis with large bandwidth and high resolution without a high-speed analog-to-digital converter. The invention reduces the cost of the whole system, increases the tunability and feasibility of the system, and has important practical significance and good application prospect.
Drawings
FIG. 1 is a schematic view of the apparatus of the present invention;
FIG. 2 is a time-frequency analysis diagram of a chirp signal with a bandwidth of 3.9GHz using the present invention;
FIG. 3 is a frequency resolution graph of a time-frequency analysis performed using the present invention;
fig. 4 is a time-frequency analysis diagram for a non-chirp signal, a random frequency-hopping signal, a step frequency signal and a double-chirp signal, respectively, using the present invention.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. The present embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation manner and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.
Referring to fig. 1, the apparatus of the present invention comprises: the optical coupler comprises a continuous wave laser 1, a first optical isolator 2, an optical coupler 3, a first arbitrary waveform generator 4, a first double-parallel Mach-Zehnder modulator 5, a first erbium-doped optical fiber amplifier 6, a second arbitrary waveform generator 7, a first radio frequency signal source 8, an electric coupler 9, a Mach-Zehnder modulator 10, a second optical isolator 11, a single-mode optical fiber 12, a second radio frequency signal source 13, a 90-degree electric mixer 14, a second double-parallel Mach-Zehnder modulator 15, a second erbium-doped optical fiber amplifier 16, an optical circulator 17 and a photoelectric detector 18.
The output port of the continuous wave laser 1 is connected with the input port of a first optical isolator 2, the output port of the first optical isolator 2 is connected with the input port of an optical coupler 3, the output port of the optical coupler 3 is respectively connected with the optical input ports of a first double-parallel Mach-Zehnder modulator 5 and a second double-parallel Mach-Zehnder modulator 15, the radio frequency input port of the first double-parallel Mach-Zehnder modulator 5 is connected with the output port of a first arbitrary waveform generator 4, the optical output port of the first double-parallel Mach-Zehnder modulator 5 is connected with the input port of a first erbium-doped optical fiber amplifier 6, the output port of the first erbium-doped optical fiber amplifier 6 is connected with the optical input port of the Mach-Zehnder modulator 10, the radio frequency input port of the Mach-Zehnder modulator 10 is connected with the output port of an electric coupler 9, an input port of the electric coupler 9 is respectively connected with output ports of a second arbitrary waveform generator 7 and a first radio frequency signal source 8, an optical output port of the mach-zehnder modulator 10 is connected with an input port of a second optical isolator 11, an output port of the second optical isolator 11 is connected with one end of a single-mode fiber 12, and the other end of the single-mode fiber 12 is connected with a port II of an optical circulator 17; two radio frequency input ports of the second double-parallel Mach-Zehnder modulator 15 are connected with two output ports of the 90-degree electric mixer 14, and an input port of the 90-degree electric mixer 14 is connected with an output port of the second radio frequency signal source 13; an optical output port of the second double-parallel Mach-Zehnder modulator 15 is connected with an input port of a second erbium-doped fiber amplifier 16, and an output port of the second erbium-doped fiber amplifier 16 is connected with a port I of an optical circulator 17; and a port III of the optical circulator 17 is connected with an optical input port of the photoelectric detector 18.
The invention carries out photon-assisted microwave time-frequency analysis, and comprises the following specific steps:
step one, the output frequency of the continuous wave laser isf 0The linearly polarized light firstly passes through a first optical isolator, then is evenly divided into two parts by an optical coupler and then is respectively injected into a first double-parallel Mach-Zehnder modulator and a second double-parallel Mach-Zehnder modulator;
step two, two paths of orthogonal step frequency signals sent by the first arbitrary waveform generator are respectively used for driving two sub-modulators of the first double-parallel Mach-Zehnder modulator, the bias voltage of the modulators is adjusted, so that the two sub-modulators are biased at the minimum bias point, meanwhile, 90-degree phase shift is introduced to the main modulator by the bias voltage, and the first double-parallel Mach-Zehnder modulator can output a carrier-restraining single-sideband modulation signal of the step frequency signals;
injecting a carrier-restraining single-sideband modulation signal output by the first double-parallel Mach-Zehnder modulator into the Mach-Zehnder modulator after passing through the first erbium-doped fiber amplifier, driving the signal to be detected and a reference signal after being coupled through the electric coupler, and adjusting a bias point of the modulator to carry out carrier-restraining double-sideband modulation;
injecting the optical signal output by the Mach-Zehnder modulator into the single-mode optical fiber through a second optical isolator to serve as the detection light of the stimulated Brillouin scattering effect;
injecting a single-tone signal with required specific frequency into the 90-degree electric mixer, dividing the single-tone signal into two paths, respectively driving two sub-modulators of the second double-parallel Mach-Zehnder modulator, adjusting bias voltage of the modulators to enable the two sub-modulators to be biased at a minimum bias point, introducing 90-degree phase shift to the main modulator by the bias voltage, and outputting the single-sideband modulation signal by the second double-parallel Mach-Zehnder modulator to obtain a carrier-suppressed single-sideband modulation signal of the signal;
step six, enabling the suppressed carrier single-sideband modulation signal output by the second double-parallel Mach-Zehnder modulator to pass through a second erbium-doped fiber amplifier, then entering a port I of the optical circulator and being reversely injected into the single-mode fiber through a port II to serve as pump light of the stimulated Brillouin scattering effect;
step seven, injecting the optical signal output by the port III of the optical circulator into a photoelectric detector for photoelectric conversion, and processing the waveform output by the photoelectric detector according to the following principle:
1. in a stepping period, the difference between the optical carrier frequency modulated by the stepping frequency signal and the center frequency of the stimulated Brillouin gain spectrum is the frequency of the pulses mapped in frequency and time in the stepping period, and it can be known that in different stepping sequences, the frequency of the stepping frequency signal is different, but the position of the stimulated Brillouin is unchanged, so that the relative positions of the two are different, and further, if in different stepping sequences, the photoelectric detection generates the electric pulses mapped in frequency and time, and the signal frequencies represented by the pulses are different.
2. The frequency-time mapping occurs at the time when the optical sideband modulated by the signal to be measured is aligned with the stimulated brillouin, so that if a plurality of electric pulses are generated at different times in one stepping period, it is indicated that the signal has a frequency component with a frequency difference between the optical sideband frequency and the stimulated brillouin gain spectrum center frequency in the stepping period at the time corresponding to the generated pulse.
3. If the optical sideband modulated by the signal to be measured is aligned with the gain spectrum of the stimulated Brillouin and the component of the signal to be measured at the frequency is strong, the frequency-time mapping can generate a strong pulse, and the positive correlation between the amplitude of the pulse and the strength of the frequency component of the signal can be known.
In summary, extracting the pulse of the whole step signal period can completely represent the time and frequency distribution of the signal, and the pulse is segmented according to the step period to obtain a matrix containing time-frequency information, so as to obtain a time-frequency characteristic diagram of the signal to be detected.
Examples
The specific implementation process of this embodiment is:
step one, a light source generates single-frequency light with the working wavelength of about 1553.349nm and the power of about 15dBm, the single-frequency light passes through a first optical isolator, is evenly divided into two parts by an optical coupler and then is respectively input into optical input ports of a first double-parallel Mach-Zehnder modulator and a second double-parallel Mach-Zehnder modulator.
And step two, the initial frequency, the stepping frequency and the stepping times of the two orthogonal stepping frequency signals emitted by the first arbitrary waveform generator are respectively 50 MHz, 5MHz and 780, and the stepping period is consistent with the period setting of the signal to be measured and is set to be 2 mu s. The two orthogonal step frequency signals are loaded on two radio frequency input ports of a first double-parallel Mach-Zehnder modulator, and bias voltage on the two radio frequency input ports is adjusted to enable the modulation mode to be a single-side band under a restraining carrier. Thus, an optical carrier wave which decreases in steps with time and frequency can be obtained on the uplink.
And step three, injecting the suppressed carrier single sideband modulation signal output by the first double-parallel Mach-Zehnder modulator into the Mach-Zehnder modulator after passing through the first erbium-doped fiber amplifier. The signal to be measured is a broadband periodic signal, the period is 2 mus, the bandwidth is between 0.1 GHz and 4.0 GHz, and the signal to be measured is transmitted by a second arbitrary waveform generator. The reference signal has a frequency of 0.1 GHz and is transmitted by the first radio frequency signal source. And coupling the signal to be measured and the reference signal through the electric coupler, loading the coupled signal to a radio frequency port of the Mach-Zehnder modulator, and adjusting a bias point of the modulator to inhibit carrier double-sideband modulation.
And fourthly, injecting the optical signal output by the Mach-Zehnder modulator into the single-mode optical fiber through a second optical isolator to serve as the detection light of the stimulated Brillouin scattering effect.
Injecting a single-tone signal with the frequency of 10.85 GHz transmitted by a second radio frequency signal source into the 90-degree electric mixer, dividing the single-tone signal into two paths, respectively driving the two sub-modulators of the double-parallel Mach-Zehnder modulator, adjusting the bias voltage of the modulators to bias the two sub-modulators at the minimum bias point, introducing 90-degree phase shift to the main modulator by the bias voltage, and outputting the single-sideband modulation signal with the carrier suppression of the signal by the second double-parallel Mach-Zehnder modulator.
Step six, enabling the suppressed carrier single-sideband modulation signal output by the second double-parallel Mach-Zehnder modulator to pass through a second erbium-doped fiber amplifier, then entering a port I of the optical circulator and being reversely injected into the single-mode fiber through a port II to serve as pump light of the stimulated Brillouin scattering effect;
and step seven, injecting the optical signal output by the port III of the optical circulator into a photoelectric detector for photoelectric conversion, and processing the waveform of the photoelectric conversion to obtain a time-frequency diagram of the signal to be detected.
The signal to be tested is set as a linear frequency modulation signal with the bandwidth of 3.9GHz and the period of 2 mu s, the bandwidth of the system is tested, and the time-frequency analysis obtained by the test is shown in figure 2, so that the system can carry out the time-frequency analysis on the signal with the bandwidth within 3.9 GHz.
The step frequency of the step frequency signal is set to 5MHz, 25 MHz, 50 MHz, 100 MHz, and the same chirp signal is analyzed, so as to obtain time-frequency analysis with different resolutions, and the frequency resolution of the time-frequency analysis can be adjusted according to the actual situation, and the analysis results are shown in fig. 3, and fig. 3(a) to fig. 3 (d) are the analysis results with the step frequency set to 5MHz, 25 MHz, 50 MHz, 100 MHz, respectively. As can be seen from comparison of the four analysis result graphs in fig. 3, when the step frequency is set to be smaller, the image obtained by time-frequency analysis is smoother, i.e., has higher frequency resolution.
The link is utilized to analyze different types of microwave signals, and the time-frequency distributions shown in fig. 4 are the analysis results of the non-linear frequency modulation signal, the frequency hopping signal, the step frequency signal, and the double-chirp linear frequency modulation signal. As can be seen from fig. 4(a), when analyzing the non-chirp signal, the lower frequency component of the signal is stronger, which is consistent with the result obtained by performing time-frequency analysis on the signal through short-time fourier transform; as is clear from fig. 4(b) and 4(c), when analyzing a signal in which the frequency of the hopping signal is not continuous with that of the step frequency signal, the frequency component of the signal may not be completely aligned with the center frequency of the stimulated brillouin gain spectrum, and thus the frequency component obtained by time-frequency analysis may have different intensities; as can be seen from fig. 4(d), the analysis result of the dual chirp signal shows that the system can analyze a plurality of frequency components at the same time.
In conclusion, the time-frequency analysis method of the microwave signal is simple and compact in structure, has large and adjustable analysis bandwidth and adjustable time-frequency analysis frequency resolution, avoids the use of high-frequency electric devices and high-speed analog-to-digital converters, reduces cost and has a good application prospect.
In conclusion, the above-described embodiments are merely preferred examples of the present invention, and are not intended to limit the scope of the present invention, it should be noted that, for those skilled in the art, many equivalent modifications and substitutions can be made on the present invention. For example, the analysis bandwidth is limited by the highest frequency that can be achieved by the step frequency signal, where only microwave signals with a bandwidth of 3.9GHz can be analyzed at the highest due to the limitation of experimental conditions, and step frequency signals with higher highest frequency can be used to achieve higher analysis bandwidth, and these equivalent modifications and substitutions and adjustment of frequency ranges should also be considered as the scope of the present invention.
Claims (5)
1. A photon-assisted microwave signal time-frequency analysis device based on a stimulated Brillouin scattering effect is characterized by comprising a continuous wave laser, a first optical isolator, an optical coupler, a first double-parallel Mach-Zehnder modulator, a first arbitrary waveform generator, a first erbium-doped optical fiber amplifier, a Mach-Zehnder modulator, an electric coupler, a first radio-frequency signal source, a second arbitrary waveform generator, a second optical isolator, a single-mode optical fiber, a second double-parallel Mach-Zehnder modulator, a second radio-frequency signal source, a 90-degree electric mixer, a second erbium-doped optical fiber amplifier, an optical circulator and a photoelectric detector; the output port of the continuous wave laser is connected with the input port of a first optical isolator, the output port of the first optical isolator is connected with the input port of an optical coupler, and the output port of the optical coupler is respectively connected with the optical input ports of the first and second double-parallel Mach-Zehnder modulators; the radio frequency input port of the first dual-parallel mach-zehnder modulator is connected to the output port of the first arbitrary waveform generator, the optical output port of the first double-parallel Mach-Zehnder modulator is connected with the input port of the first erbium-doped fiber amplifier, the output port of the first erbium-doped fiber amplifier is connected with the optical input port of the Mach-Zehnder modulator, the radio frequency input port of the Mach-Zehnder modulator is connected with the output port of the electric coupler, the input port of the electric coupler is respectively connected with the output ports of the second arbitrary waveform generator and the first radio frequency signal source, the optical output port of the mach-zehnder modulator is connected to the input port of a second optical isolator, the output port of the second optical isolator is connected with one end of a single-mode optical fiber, and the other end of the single-mode optical fiber is connected with a port II of the optical circulator; the radio frequency input port of the second double-parallel Mach-Zehnder modulator is connected with the output port of the 90-degree electric mixer, the input port of the 90-degree electric mixer is connected with the output port of the first radio frequency signal source, the optical output port of the second double-parallel Mach-Zehnder modulator is connected with the input port of the second erbium-doped optical fiber amplifier, and the output port of the second erbium-doped optical fiber amplifier is connected with the port I of the optical circulator; the port III of the optical circulator is connected with the optical input port of the photoelectric detector; and the time-frequency characteristic diagram of the signal to be detected can be obtained by segmenting the waveform output by the photoelectric detector.
2. The time-frequency analysis device for photon-assisted microwave signals based on stimulated brillouin scattering effect according to claim 1, wherein the step period of the step frequency signal loaded to the first double-parallel mach-zehnder modulator is an integral multiple of the period of the signal to be measured, the frequency resolution and analysis bandwidth of the time-frequency analysis are controlled by controlling the parameters of the step frequency signal generated by the first arbitrary waveform generator, i.e. the step frequency interval and the step times, and the signal frequency components extracted in different step periods are determined by the difference between the frequency of the step frequency signal in the period and the center frequency of the stimulated brillouin gain spectrum.
3. The time-frequency analysis device for photon-assisted microwave signals based on stimulated Brillouin scattering effect as claimed in claim 1, wherein the center frequency position of the stimulated Brillouin gain spectrum generated by the interaction of the pump light output by the second erbium-doped fiber amplifier and the probe light output by the Mach-Zehnder modulator in the single-mode fiber corresponds to the frequency of the single-tone signal modulated on the second double-parallel Mach-Zehnder modulator, and the frequency value of the single-tone signal is adjusted to control the frequency band of the time-frequency analysis.
4. The time-frequency analysis device for photon-assisted microwave signals based on the stimulated brillouin scattering effect according to claim 1, wherein the frequency-time mapping pulses generated by the photodetector include information: stepping cycle sequence number, generation time and amplitude; the frequency represented by the pulse generated in different step periods is different, the generation time of the electric pulse represents that the signal to be measured has measurable frequency components at the time, and the amplitude of the electric pulse is in positive correlation with the strength of the frequency component of the signal to be measured at a certain time.
5. A method for time-frequency analysis of microwave signals using the apparatus of claim 1, the method comprising the steps of:
1) output frequency of continuous wave laser isf 0The linearly polarized light firstly passes through a first optical isolator, then is evenly divided into two parts by an optical coupler and then is respectively injected into a first double-parallel Mach-Zehnder modulator and a second double-parallel Mach-Zehnder modulator;
2) the two paths of orthogonal step frequency signals sent by the first arbitrary waveform generator are respectively used for driving two sub-modulators of the first double-parallel Mach-Zehnder modulator, the bias voltage of the modulators is adjusted, so that the two sub-modulators are biased at the minimum bias point, meanwhile, 90-degree phase shift is introduced into the main modulator by the bias voltage, and the first double-parallel Mach-Zehnder modulator can output a carrier-restraining single-sideband modulation signal of the step frequency signals;
3) the carrier-restraining single-sideband modulation signals output by the first double-parallel Mach-Zehnder modulator are amplified by the first erbium-doped fiber amplifier and then injected into the Mach-Zehnder modulator, the signals to be measured and the reference signals with specific frequency are coupled by the electric coupler and then driven, and the bias point of the Mach-Zehnder modulator is adjusted to carry out carrier-restraining double-sideband modulation;
4) injecting the optical signal output by the Mach-Zehnder modulator into the single-mode optical fiber through the second optical isolator to serve as detection light of the stimulated Brillouin scattering effect;
5) injecting a single-tone signal for controlling an analysis frequency band into a 90-degree electric mixer, dividing the single-tone signal into two paths, respectively driving two sub-modulators of a second double-parallel Mach-Zehnder modulator, adjusting bias voltage of the modulators to enable the two sub-modulators to be biased at a minimum bias point, and simultaneously introducing 90-degree phase shift to a main modulator by the bias voltage, so that a suppressed carrier single-sideband modulation signal corresponding to the single-tone signal frequency one to one is obtained from the output of the second double-parallel Mach-Zehnder modulator;
6) after a carrier-restraining single-sideband modulation signal output by the second double-parallel Mach-Zehnder modulator passes through the second erbium-doped fiber amplifier, the carrier-restraining single-sideband modulation signal is reversely injected into the single-mode fiber through the port I of the optical circulator to serve as pump light of the stimulated Brillouin scattering effect;
7) and injecting the optical signal output by the port III of the optical circulator into a photoelectric detector for photoelectric conversion, and segmenting the waveform output by the photoelectric detector to obtain a time-frequency characteristic diagram of the signal to be detected.
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