CN113589236A - Double-chirp waveform signal generator based on photoelectric oscillation loop structure - Google Patents
Double-chirp waveform signal generator based on photoelectric oscillation loop structure Download PDFInfo
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Abstract
A double-chirp waveform signal generator based on a stimulated Brillouin scattering effect and a photoelectric oscillation loop structure belongs to the technical field of microwave photonics. The optical fiber laser device comprises a first laser, a first optical coupler, an optical phase modulator, an optical isolator, a high nonlinear optical fiber, an optical circulator, an erbium-doped optical fiber amplifier, a first optical filter, a second optical coupler, a photoelectric detector, a radio frequency amplifier, a radio frequency power divider, a low-pass filter, a second laser, a Mach-Zehnder modulator, a second optical filter, an arbitrary waveform generator and a direct current stabilized power supply. The method generates a single-sideband modulation signal with modulation sideband equal to optical carrier power and mixed beat frequency of sweep-frequency laser by a photoelectric oscillator based on the stimulated Brillouin scattering effect to generate a double-chirp waveform signal, wherein the generated double-chirp signal has smaller harmonic component; the bandwidth and the period of the double chirp signal can be adjusted by adjusting the bandwidth and the period of the single chirp signal generated by the arbitrary waveform generator.
Description
Technical Field
The invention belongs to the technical field of microwave photonics, and particularly relates to a double-chirp waveform signal generator based on a stimulated Brillouin scattering effect and a photoelectric oscillation loop structure.
Background
With the development of wireless communication and detection technologies, radar technology has been widely applied to various aspects of military and civil fields. In the radar technology, radar waveforms are an important part determining the performance of a radar system, and in various radar waveforms, double chirp signals can provide a large detection range and high range resolution for the radar system, and meanwhile, range-Doppler coupling can be reduced, and the range-Doppler resolution of the radar system is improved; in addition, the double chirp signal can reduce power fading during signal transmission. Therefore, the generation of the double-chirp waveform signal has important significance for improving the performance of the radar system and has important practical value. Dan Zhu et al uses a dual-drive mach-zehnder modulator to mix a fundamental frequency signal with a chirp signal, and filters a clutter component by a high-pass filter to obtain a dual-chirp signal. The center frequency of a double Chirp signal generated by the structure is 6GHz, and the bandwidth can reach 2GHz (Dan Zhu, Jianping Yao, Dual-Chirp Microwave Waveform Generation Using Dual-Parallel Mach-Zehnder Modulator, IEEE photon, technique, Lett., vol.27, No.13, pp.1410-1413, Jul.2015).
Disclosure of Invention
The invention aims to provide a large-bandwidth double-chirp waveform signal generator based on a stimulated Brillouin scattering effect and a photoelectric oscillation loop structure.
The structure of the double-chirp waveform signal generator is shown in figure 1 and comprises a first laser, a first optical coupler, an optical phase modulator, an optical isolator, a high nonlinear optical fiber, an optical circulator, an erbium-doped optical fiber amplifier, a first optical filter, a second optical coupler, a photoelectric detector, a radio frequency amplifier, a radio frequency power divider, a low-pass filter, a second laser, a Mach-Zehnder modulator, a second optical filter, an arbitrary waveform generator and a direct-current stabilized power supply; the optical fiber amplifier comprises a first laser, a first optical coupler, an optical phase modulator, an optical isolator, a high nonlinear optical fiber, an optical circulator, an erbium-doped optical fiber amplifier, a first optical filter, a second optical coupler, a photoelectric detector, a radio frequency amplifier, a radio frequency power divider and a low-pass filter, wherein the first laser, the first optical coupler, the optical phase modulator, the optical isolator, the high nonlinear optical fiber, the optical circulator, the erbium-doped optical fiber amplifier, the first optical filter, the second optical coupler, the photoelectric detector, the radio frequency amplifier, the radio frequency power divider and the low-pass filter form a photoelectric oscillation loop.
The first laser output frequency is fcThe optical signal of the optical fiber is divided into two branches by a first optical coupler, wherein the optical signal of one branch enters an erbium-doped fiber amplifier and is marked as a first branch 101; the optical signal of the other branch enters the optical phase modulator as an optical carrier, which is marked as a second branch 201; after power amplification is carried out on an optical signal of the first branch 101 through the erbium-doped fiber amplifier, the optical signal enters the high nonlinear fiber through a port 1 of the optical circulator to be used as pump light of a stimulated Brillouin scattering effect; the optical carrier of the second branch 201 is modulated by the output signal from the rf power divider, the output signal of the rf power divider is originally from the background noise of the rf amplifier, the phase-modulated optical signal spectrum is as shown in fig. 2(1), and the phase modulation forms modulation sidebands with equal power on both sides of the optical carrier. The modulated optical signal enters the high-nonlinearity optical fiber after passing through the optical isolator, the frequency of the optical signal cannot be changed by the optical isolator, the optical isolator has smaller optical loss for forward transmission optical signals, and has larger loss for reverse input light, so the optical isolator can block the transmission of reverse optical signals, and the optical fiber is used for preventing the optical circulator 2 port from injecting optical signals to the output end of the optical phase modulator to influence the working state of the phase modulator. When the frequency f is input into the port of the circulator 1cWhen the power of the pump light reaches the brillouin threshold of the high nonlinear optical fiber, a stimulated brillouin scattering effect occurs in the high nonlinear optical fiber, and the stimulated brillouin scattering effect generates a gain spectrum and a loss spectrum, as shown in a curve in fig. 2 (2); the gain spectrum appears in the down-conversion region of the pump light, the loss spectrum appears in the up-conversion region of the pump light, and the frequency difference between the central frequency of the gain spectrum and the loss spectrum and the pump light is defined as Brillouin frequency shift fb(ii) a After the stimulated Brillouin scattering effect, the lower sideband of the optical phase modulation signal is amplified, the upper sideband is suppressed, and the power balance relation of the sidebands of the phase modulation signal is broken; the gain spectrum and the loss spectrum of the stimulated Brillouin scattering effect have good narrow-band characteristics, and can be used for frequency selection of a photoelectric oscillator, and only frequency components meeting the requirement that the open-loop gain is more than 1 can be in an oscillator loop in the photoelectric oscillation loopStable oscillation is formed in the path, so that when the system reaches a steady state, only the frequency components in the brillouin gain spectrum are selected to form stable oscillation, while other frequency components do not have enough loop gain, so that stable oscillation cannot be formed in the photoelectric oscillation loop, the spectrogram in stable oscillation is shown in fig. 2(3), the frequency components in the gain spectrum generate stable modulation sidebands, and other noise components are suppressed in the photoelectric oscillation loop; in the invention, the power of the radio frequency modulation signal is smaller, the modulation depth is lower, so that the power of the high-order sideband is smaller and can be ignored, therefore, only positive and negative first-order sidebands are considered in theoretical analysis, the left side sideband of the optical carrier is marked as a negative first-order sideband, and the right side sideband of the optical carrier is marked as a positive first-order sideband. In addition, the gain of the stimulated Brillouin scattering effect is related to the power of the pump light, the power of the pump light in the stimulated Brillouin scattering effect can be set by adjusting the gain of the 101-branch erbium-doped fiber amplifier, so that the Brillouin gain of the stimulated Brillouin scattering effect can be adjusted, and the power of a negative first-order sideband of an optical signal after the stimulated Brillouin scattering effect of the 201-branch amplifier is equal to the power of an optical carrier by reasonably setting the power of the 101-branch amplifier injected into the high nonlinear optical fiber through the port of the optical circulator 1, so that two radio frequency components chirped in opposite directions have the same power when a double chirp signal is subsequently generated; outputting the optical modulation signal subjected to the stimulated Brillouin scattering from a port 3 of the circulator to a first optical filter; the first optical filter is a band pass filter with a pass band between the optical carrier and the negative first order sideband, as shown by the curve in fig. 3; the first optical filter is used for filtering optical frequency components except for the optical carrier and the negative first-order sideband, and simultaneously restraining spontaneous radiation noise generated by stimulated brillouin scattering to a certain extent, and a filtered spectrogram is shown in fig. 3. At the same time, the emitting frequency of the second laser is fcThe optical carrier of (a) is input into the mach-zehnder modulator as a third branch, which is marked as branch 301; the DC stabilized power supply is used for providing a DC bias voltage for the Mach-Zehnder modulator, and the voltage value of the DC bias voltage is set to be VπThe Mach-Zehnder modulator is made to work at the two sides of the optical carrier suppressionWith modulated state, in which VπIs the half-wave voltage of the mach-zehnder modulator; arbitrary waveform generator for emitting a single chirp fundamental frequency modulation signal fchirpAs the radio frequency modulation signal of the Mach-Zehnder modulator, the spectrum of the optical signal modulated by the Mach-Zehnder modulator is shown in FIG. 4(1), because the power of the high-order modulation sideband is very small, the influence of the high-order sideband is ignored, and the frequency of the two first-order sidebands is fc±fchirpEach modulation sideband is a frequency sweep optical sideband of linear chirp, and the frequency sweep bandwidth and the frequency sweep period of each modulation sideband are the same as those of a single chirp signal generated by an arbitrary waveform generator; the second optical filter is used for selecting the down-converted modulation sideband and suppressing other spectral components, so that a swept optical signal output is obtained as shown in fig. 4 (2); the sweep frequency optical signal output by the second optical filter is recorded as fFSAs can be seen from FIG. 4(2), fFS＝fc-fchirp(ii) a The output signal of the second optical filter is coupled with the output signal of the first optical filter in the second optical coupler to form a single-path signal, the spectrum diagram of the combined optical signal is shown in fig. 5(1), the combined optical signal has three spectral components, which are respectively the optical carriers fcNegative first-order sideband f of optical phase modulation signalc-fbAnd swept optical signal fFS(ii) a The output light of the second optical coupler is sent to a photodetector for beat frequency, the photodetector outputs the difference frequency of each spectral component, and the spectral components of the radio frequency signal generated after photoelectric conversion by the photodetector are shown in fig. 5 (2); the spectral components of the resulting RF signal have three components, namely a fixed frequency component and two chirp components f1、f2(ii) a Wherein the constant frequency component is an optical carrier f from the first optical filtercAnd the negative first-order sideband fc-fbA radio frequency component generated by a beat frequency having a frequency equal to the Brillouin frequency shift fb(ii) a Frequency sweep optical signal f output by second optical couplerFSRespectively with the optical carriers f from the first optical filtercAnd negative first order sideband fc-fbBeat frequency generates two chirp components f with chirp directions opposite to each other1、f2Two chirp minutesQuantity f1、f2The frequency of (d) may be expressed as:
as can be seen from the formula, the two chirp components have opposite frequency chirp directions, and the sweep bandwidth thereof is determined by the bandwidth of the sweep optical signal; a radio-frequency signal output by the photodetector is subjected to radio-frequency amplification and then divided into two paths of electric signals with equal power by the radio-frequency power divider, one path of electric signal is fed back to the optical phase modulator to form a closed loop, which is marked as a branch 401, when the gain of the radio-frequency amplifier is large enough to enable the open-loop gain of the loop of the photoelectric oscillator to be larger than 1, the radio-frequency signal shown in (2) of fig. 5 forms stable oscillation in the loop of the photoelectric oscillator, and when the system reaches a steady state, two output ports of the radio-frequency power divider can continuously output the radio-frequency signals shown in (2) of fig. 5 with certain power; the other path of the electric signal is used as an output signal of the system, and is input into a low-pass filter, and is marked as a branch 501; the cut-off frequency of the low-pass filter is set between the highest frequency of the chirp signal and the brillouin frequency shift, and is used for filtering out the fixed-frequency component in the radio-frequency signal, so as to obtain the dual-chirp waveform signal, and the output of the low-pass filter is shown in fig. 5 (3).
The device of the invention has the characteristics that:
(1) a single sideband modulation signal with modulation sideband equal to optical carrier power and a sweep-frequency laser mixed beat frequency are generated by a photoelectric oscillator based on a stimulated Brillouin scattering effect to generate a double-chirp waveform signal, and the generated double-chirp signal has smaller harmonic component.
(2) The bandwidth and the period of the double chirp signal can be adjusted by adjusting the bandwidth and the period of the single chirp signal generated by the arbitrary waveform generator.
(3) The system can generate double chirp signals only by one frequency sweep signal source, simplifies the system structure and omits the time synchronization process in a multi-frequency sweep source system.
Drawings
FIG. 1: the structural schematic diagram of the double-chirp signal generator based on the photoelectric oscillation structure;
FIG. 2: obtaining a spectral diagram of a signal by the stimulated Brillouin scattering effect;
FIG. 3: obtaining a spectrum schematic diagram of a signal after passing through a first optical filter;
FIG. 4: obtaining a spectrum schematic diagram of the signal after passing through a second optical filter;
FIG. 5: the double chirp signal generation process is schematically illustrated;
FIG. 6: the time-frequency diagram of the double chirp signals with different bandwidths generated by the double chirp signal generator;
FIG. 7: time-frequency graphs of the double chirp signals with different periods generated by the double chirp signal generator;
FIG. 8: the autocorrelation function curve of the generated double chirp signal.
Detailed Description
Example 1:
the first laser is a TSL-510 tunable laser of Santec company and has the frequency of 193.4145THz, the second laser is a TSL-550 tunable laser of Santec company and has the frequency of 193.4145 THz; the optical phase modulator is MPZ-LN-40 of the company Photoline, the bandwidth of the optical phase modulator is 38GHz, and the half-wave voltage is 6.5V; the photoelectric detector is KG-PD-50G-A-FC of Beijing Kangguan company, the bandwidth is 50GHz, and the conversion rate is 0.55A/W; the optical isolator is PISO-SA-1550 of Phoenix photonics in England, and the isolation is more than 40 dB; the high nonlinear optical fiber is produced by long-flying optical fiber cable company Limited, and the Brillouin gain linewidth of the high nonlinear optical fiber is gammaBBrillouin frequency shift f at 30MHzb9.387 GHz. The Mach-Zehnder modulator is MXAN-LN-20 of a photo company, and the bandwidth is 20 GHz; the arbitrary waveform generator is Keysight M8196A with a bandwidth of 25 GHz. The first optical filter and the second optical filter are XTM-50 optical filters of EXFO company, the central frequency tuning range is 1450nm-1650nm, and the bandwidth tuning range is 50pm-950 pm. The RF amplifier is a MWLA-010265G27 manufactured by full wave electronics, Inc., with a signal gain of 27dB and a saturated output power of 18 dBm. The radio frequency power divider is an AV81311 power divider produced by the forty first research institute of Chinese electronic technology group company, the frequency range is 0-26.5GHz, the power dividing ratio is 50: 50; direct currentThe voltage tunable range of the regulated power supply is 0-30V. The erbium-doped fiber amplifier is an EDFA-ILA of Ruili corporation, and has a maximum output power of 17 dBm. The first optocoupler coupling ratio was 20: 80, wherein, the 101 branch is divided into 20% optical power, and the 201 branch is divided into 80% optical power. The coupling ratio of the second optical coupler is 50: 50; the test equipment for the output signal was a Keysight corporation MSOV254A oscilloscope.
The corresponding test equipment is connected according to fig. 1, the wavelength of the first laser and the second laser is set to 1550nm, i.e. the frequency fc193.4145THz, the output power of the first laser is 10mW, and the output power of the second laser is 15 mW; the output power of the erbium-doped fiber amplifier is set to be 14.25 mW; the passband of the first optical filter is set to 193.4000 THz-193.4165 THz, and the passband of the second optical filter is set to 193.4053 THz-193.4130 THz; the output voltage of the DC stabilized power supply is 6.5V, and the cut-off frequency of the low-pass filter is set to be 8 GHz. The single chirp signal generated by the arbitrary waveform generator has a center frequency of 4.6GHz, a period of 5.28 μ s, and bandwidths set to 1GHz, 3GHz, 5GHz, and 7GHz, respectively (corresponding to fig. 6(1), 6(2), 6(3), and 6(4), respectively). The generated double chirp signal is sampled by an oscilloscope, and the sampled time domain waveform data is subjected to short-time fourier transform to obtain a time-frequency diagram of the signal, which is shown in fig. 6.
The period of the double chirp signal generated by the system can be changed by changing the period of the single chirp signal generated by the arbitrary waveform generator. The center frequency of a monocycle signal generated by an arbitrary waveform generator is set to 4.6GHz, the bandwidth is set to 3GHz, the period is set to 2.64 mus and 1.32 mus (corresponding to fig. 7(1) and fig. 7(2)) respectively, after the generated double chirp signal is sampled by an oscilloscope, the sampled time domain waveform data is subjected to short-time fourier transform, and a time-frequency diagram of the signal is obtained as shown in fig. 7.
The pulse compression performance of the double chirp signal can be obtained by calculating the autocorrelation function of the generated signal, and fig. 8 is an autocorrelation function image of the double chirp signal generated by the system, the center frequency of which is 4.6GHz, the bandwidth of which is 3GHz, and the period of which is 5.28 mus. Fig. 8(1) is in the range of 1000ns, fig. 8(2) is in the range of 30ns, the autocorrelation bandwidth of the signal is 1.45ns, and the sidelobe suppression ratio is 5.2 dB.
Claims (5)
1. A double-chirp waveform signal generator based on a stimulated Brillouin scattering effect and a photoelectric oscillation loop structure is characterized in that:
(1) the optical fiber laser device comprises a first laser, a first optical coupler, an optical phase modulator, an optical isolator, a high nonlinear optical fiber, an optical circulator, an erbium-doped optical fiber amplifier, a first optical filter, a second optical coupler, a photoelectric detector, a radio frequency amplifier, a radio frequency power divider, a low-pass filter, a second laser, a Mach-Zehnder modulator, a second optical filter, an arbitrary waveform generator and a direct current stabilized power supply; the optical fiber amplifier comprises a first laser, a first optical coupler, an optical phase modulator, an optical isolator, a high nonlinear optical fiber, an optical circulator, an erbium-doped optical fiber amplifier, a first optical filter, a second optical coupler, a photoelectric detector, a radio frequency amplifier, a radio frequency power divider and a low-pass filter, wherein the first laser, the first optical coupler, the optical phase modulator, the optical isolator, the high nonlinear optical fiber, the optical circulator, the erbium-doped optical fiber amplifier, the first optical filter, the second optical coupler, the photoelectric detector, the radio frequency amplifier, the radio frequency power divider and the low-pass filter form a photoelectric oscillation loop;
(2) the first laser output frequency is fcThe optical signal of the optical fiber is divided into two branches by a first optical coupler, wherein the optical signal of one branch enters an erbium-doped fiber amplifier and is marked as a first branch 101; the optical signal of the other branch enters the optical phase modulator as an optical carrier, which is marked as a second branch 201; after power amplification is carried out on an optical signal of the first branch 101 through the erbium-doped fiber amplifier, the optical signal enters the high nonlinear fiber through a port 1 of the optical circulator to be used as pump light of a stimulated Brillouin scattering effect; the optical carrier of the second branch 201 is modulated by the output signal from the radio frequency power divider, phase modulation forms modulation sidebands with equal power on two sides of the optical carrier, and the modulated optical signal enters the high nonlinear optical fiber after passing through the optical isolator; when the frequency f is input into the port of the circulator 1cWhen the pumping light reaching power reaches the Brillouin threshold value of the high nonlinear optical fiber, a stimulated Brillouin scattering effect can occur in the high nonlinear optical fiber, and the stimulated Brillouin scattering effect can generate a gain spectrum and a loss spectrum; the gain spectrum appears in the down-conversion region of the pump light, the loss spectrum appears in the up-conversion region of the pump light, and the frequency difference between the central frequency of the gain spectrum and the loss spectrum and the pump light is defined as Brillouin frequency shift fb(ii) a After the stimulated Brillouin scattering effect, the lower sideband of the optical phase modulation signal is amplified, the upper sideband is suppressed, and the optical modulation signal after the stimulated Brillouin scattering is output to a first optical filter from a port 3 of the circulator; the first optical filter is a band-pass filter, and the pass band is between an optical carrier and a negative first-order sideband;
(3) the emitting frequency of the second laser is fcThe optical carrier of (a) is input into the mach-zehnder modulator as a third branch, which is marked as branch 301; the Mach-Zehnder modulator works in a double-sideband modulation state of optical carrier suppression; arbitrary waveform generator for emitting a single chirp fundamental frequency modulation signal fcHirpThe high-order sideband is ignored as the radio frequency modulation signal of the Mach-Zehnder modulator, and the frequency of two first-order sidebands is fc±fcHirpEach modulation sideband is a frequency sweep optical sideband of linear chirp, and the frequency sweep bandwidth and the frequency sweep period of each modulation sideband are the same as those of a single chirp signal generated by an arbitrary waveform generator;
(4) the second optical filter selects the modulation sideband of the down-conversion, suppresses other spectral components, and records the frequency-sweeping optical signal output by the second optical filter as fFS＝fc-fcHirp(ii) a The output signal of the second optical filter is coupled with the output signal of the first optical filter in the second optical coupler to form a signal, and the combined optical signal has three spectral components which are respectively an optical carrier fcNegative first-order sideband f of optical phase modulation signalc-fbAnd swept optical signal fFS(ii) a The output light of the second optical coupler is sent to a photoelectric detector for beat frequency, the photoelectric detector outputs difference frequency of each spectral component, and the spectral components of the generated radio frequency signal have three components, namely a fixed frequency component and two chirp components f1、f2； wherein ,
(5) a radio-frequency signal output by the photoelectric detector is subjected to radio-frequency amplification and then divided into two paths of electric signals with equal power by the radio-frequency power divider, and one path of electric signal is fed back to the optical phase modulator to form a closed loop which is marked as a branch 401; when the gain of the radio frequency amplifier is large enough to enable the open loop gain of the photoelectric oscillator loop to be larger than 1, the radio frequency signal forms stable oscillation in the photoelectric oscillator loop, and when the system reaches a stable state, two output ports of the radio frequency power divider can continuously output radio frequency signals with certain power; the other path of the electric signal is used as an output signal of the system, and is input into a low-pass filter, and is marked as a branch 501; the cut-off frequency of the low-pass filter is set between the highest frequency of the chirp signal and the Brillouin frequency shift, and is used for filtering fixed-frequency components in the radio-frequency signal, so that a double-chirp waveform signal is obtained.
2. The dual-chirp waveform signal generator based on the stimulated brillouin scattering effect and the photoelectric oscillation loop structure as claimed in claim 1, wherein: the output signal of the rf power divider is initially from the noise floor of the rf amplifier.
3. The dual-chirp waveform signal generator based on the stimulated brillouin scattering effect and the photoelectric oscillation loop structure as claimed in claim 1, wherein: the first laser is a tunable laser with the frequency of 193.40 THz; a second laser tunable laser, the frequency of the laser being 193.40 THz; the optical phase modulator has the bandwidth of 38GHz and the half-wave voltage of 6.5V; the bandwidth of the photoelectric detector is 50GHz, and the conversion rate is 0.55A/W; the isolation degree of the optical isolator is more than 40 dB; brillouin gain linewidth of high-nonlinearity optical fiber is gammaBBrillouin frequency shift f at 30MHzb9.387 GHz; the bandwidth of the Mach-Zehnder modulator is 20GHz, the bandwidth of the arbitrary waveform generator is 25GHz, the central frequency tuning ranges of the first optical filter and the second optical filter are 1450nm-1650nm, and the bandwidth tuning ranges are 50pm-950 pm; the signal gain of the radio frequency amplifier is 27dB, and the saturated output power is 18 dBm; the frequency range of the radio frequency power divider is 0-26.5GHz, and the power dividing ratio is 50: 50; the voltage tunable range of the direct-current stabilized power supply is 0-30V; the maximum output power of the erbium-doped fiber amplifier is 17dBm, and the coupling ratio of the first optical coupler is 20: 80,wherein, the 101 branch circuit is divided into 20% of optical power, and the 201 branch circuit is divided into 80% of optical power; the coupling ratio of the second optical coupler is 50: 50; the test equipment for outputting signals is an oscilloscope.
4. The dual-chirp waveform signal generator based on the stimulated brillouin scattering effect and the photoelectric oscillation loop structure as claimed in claim 3, wherein: the first and second lasers are set to 1550nm, i.e. frequency fc193.4145THz, the output power of the first laser is 10mW, and the output power of the second laser is 15 mW; the output power of the erbium-doped fiber amplifier is set to be 14.25 mW; the passband of the first optical filter is set to 193.4000 THz-193.4165 THz, and the passband of the second optical filter is set to 193.4053 THz-193.4130 THz; the output voltage of the direct current stabilized power supply is 6.5V; the cut-off frequency of the low-pass filter is set to 8 GHz; the center frequency of a single chirp signal generated by an arbitrary waveform generator is 4.6GHz, the period is 5.28 mu s, the bandwidth is respectively set to be 1GHz, 3GHz, 5GHz and 7GHz, and after the generated double chirp signal is sampled by an oscilloscope, the sampled time domain waveform data is subjected to short-time Fourier transform to obtain a time-frequency diagram of the signal.
5. The dual-chirp waveform signal generator based on the stimulated brillouin scattering effect and the photoelectric oscillation loop structure as claimed in claim 4, wherein: the center frequency of a single-period signal generated by an arbitrary waveform generator is set to be 4.6GHz, the bandwidth is set to be 3GHz, the period is set to be 2.64 mu s and 1.32 mu s, and after the generated double-chirp signal is sampled by an oscilloscope, the sampled time domain waveform data is subjected to short-time Fourier transform to obtain a time-frequency graph of the signal.
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