Optoelectronic oscillator capable of being used for generating double-frequency microwave pulse

Abstract

The invention provides a photoelectric oscillator capable of being used for dual-frequency microwave pulse generation. The photoelectric oscillator mainly comprises a laser, a polarization controller, a dual-parallel Mach-Zehnder modulator, a single-mode fiber, a photoelectric detector, an electric amplifier, an equivalent dual-band filter and a microwave source, wherein the equivalent dual-band filter is obtained by connecting two narrow-band filters in parallel and serves as a frequency selection device of the optoelectronic oscillator system; a microwave source is utilized to excite double-frequency oscillation of a photoelectric oscillator loop, loop gain modulation is realized through active mode-locking modulation, the form of an output signal is changed, and then a pulse signal is output; compared with a traditional pulse output photoelectric oscillator, the photoelectric oscillator has the advantages of being simple in structure and tunable in dual-frequency, meanwhile, the output pulse has two center frequencies, and the photoelectric oscillator has good application in the aspects of pulse Doppler radar, detection and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of signal generation and processing, and particularly relates to an optoelectronic oscillator that can be used for dual-frequency microwave pulse generation. Background Art

[0002] Microwave pulse signals are commonly used signals in the detection field. Due to their advantages in instantaneous energy, anti-interference, etc., they have been widely used in the detection field at present. In the fields of radar, short-range detection, imaging, etc., microwave pulses have become the main signals. However, limited by the electronic bottleneck, there is still a lack of effective means for generating high-frequency and low-phase-noise pulse signals. Microwave photonics has great advantages in generating large bandwidth and high-quality microwaves. At present, there are already some studies on generating pulse signals based on microwave photon methods, such as mode-locked lasers, actively mode-locked optoelectronic oscillators, etc.

[0003] An optoelectronic oscillator (OEO) has the characteristics of generating high-frequency and low-phase-noise microwave signals and is widely used in the fields of signal generation and processing, radar, etc. The output signal of a traditional OEO is a single-frequency signal, and its signal has the characteristic of low phase noise. In 2020, a research team from Hangzhou Dianzi University proposed a microwave pulse generation system based on OEO. The microwave pulse generation system based on OEO performs intensity modulation on the loop gain, resulting in periodic oscillation of the OEO loop gain. Since the OEO loop is a positive feedback loop, when the loop gain is less than a certain threshold, no signal will be output. This process is called active mode-locking modulation, and the injected signal is called an active mode-locking signal. Therefore, the OEO after gain periodic modulation will output a pulse signal, and the repetition rate of the pulse signal is related to the frequency of the active mode-locking signal. In order to ensure the phase consistency of each mode component of the OEO loop, the frequency of the generally used active mode-locking signal is an integer multiple of the OEO loop mode spacing. Therefore, by changing the fiber length of the OEO loop and the frequency of the active mode-locking signal, the tuning of the pulse repetition rate can be achieved.

[0004] Currently, the main research directions of microwave pulse generation systems based on OEO are the tuning of the center frequency of microwave pulses, the suppression of supermode noise in optoelectronic oscillators, direct modulation, multi-center frequencies, etc. In 2022, a research team from the Air Force Early Warning Academy designed an actively mode-locked optoelectronic oscillator system based on the stimulated Brillouin effect, which can be used to generate a microwave pulse system with a center frequency of 5.23 - 24.58 GHz, and the phase noise can reach -92.25 dBc / Hz@10 kHz; in the same year, a research team from Beijing Jiaotong University designed a supermode noise suppression microwave pulse generation system based on a dual-ring OEO; in 2024, a research team from the University of Electronic Science and Technology of China designed a microwave pulse generation system based on a directly modulated laser, which has a more compact structure compared to traditional actively mode-locked optoelectronic oscillators; in the same year, a research team from the Air Force Early Warning Academy achieved a microwave pulse generation system with dual center frequencies using dual-frequency injection. However, the above dual-frequency microwave pulse systems are all relatively complex. Summary of the Invention

[0005] To solve the above problems, the present invention provides an optoelectronic oscillator that can be used for dual-frequency microwave pulse generation, with output pulses having two center frequencies, and having the advantages of simple structure and tunable dual-frequency.

[0006] An optoelectronic oscillator that can be used for dual-frequency microwave pulse generation, comprising a laser, a polarization controller, a dual-drive Mach-Zehnder modulator, a single-mode fiber, a photodetector, an equivalent dual-band filter, and a microwave source;

[0007] The polarization controller is used to tune the polarization state of the laser signal output by the laser, so that the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator;

[0008] The microwave source is used to output different microwave signals to the dual-drive Mach-Zehnder modulator;

[0009] The dual-drive Mach-Zehnder modulator is used to modulate the laser signal parallel to its main axis under the control of the microwave signal output by the microwave source and the dual-frequency filtering signal output by the equivalent dual-band filter. Among them, when the microwave signals output by the microwave source are different, the modulated optical signals output by the dual-drive Mach-Zehnder modulator are also different;

[0010] The single-mode fiber is used to transmit the modulated optical signal to the photodetector;

[0011] The photodetector is used to convert the modulated optical signal into a modulated electrical signal;

[0012] The equivalent dual-band filter is used to perform dual-band filtering on the modulated electrical signal to obtain a filtered signal. Among them, the microwave signals output by the microwave source are different, and the filtered signals are also different. When the microwave signal is 0, the filtered signal is a single-frequency sine signal. When the microwave signal is an excitation signal, the filtered signal is a dual-frequency continuous wave signal. When the microwave signal is an excitation signal and an active mode-locking signal, the filtered signal is a dual-frequency pulse signal.

[0013] Further, when the microwave signal output by the microwave source is 0, the modulated optical signal E MZM1 (t) output by the dual-drive Mach-Zehnder modulator is as follows:

[0014]

[0015] where E0 is the optical intensity of the laser signal, ω c is the center frequency of the laser signal, s(t) is the filtered signal output by the equivalent dual-band filter, is the phase shift introduced by the filtered signal s(t), is the phase shift introduced by the bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V B is the bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V π is the half-wave voltage of the dual-drive Mach-Zehnder modulator;

[0016] When the microwave signal output by the microwave source is an excitation signal , the modulated optical signal E MZM2 output by the dual-drive Mach-Zehnder modulator is as follows:

[0017]

[0018] where V2 is the amplitude of the excitation signal, ω2 is the angular frequency of the excitation signal, is the phase shift of the excitation signal;

[0019] When the microwave signal output by the microwave source is an excitation signal and an active mode-locking signal , the modulated optical signal E MZM3 (t) output by the dual-drive Mach-Zehnder modulator is as follows:

[0020]

[0021] where V3 is the amplitude of the active mode-locking signal, ω3 is the angular frequency of the active mode-locking signal, is the phase shift of the active mode-locking signal.

[0022] Further, an optoelectronic oscillator that can be used for dual-frequency microwave pulse generation further includes an electrical amplifier;

[0023] The electric amplifier is used to amplify the modulated electric signal output by the photodetector, and then input the amplified modulated electric signal into the equivalent dual-band filter.

[0024] Furthermore, an optoelectronic oscillator applicable to dual-frequency microwave pulse generation further includes a mixer;

[0025] The mixer is used to mix the amplified modulated electric signal output by the electric amplifier when the filtered signal is a dual-frequency continuous filtered signal and a dual-frequency pulse filtered signal, and then input the mixed modulated electric signal into the equivalent dual-band filter.

[0026] Furthermore, an optoelectronic oscillator applicable to dual-frequency microwave pulse generation further includes a directional coupler;

[0027] The directional coupler is used to directionally couple the filtered signal output by the equivalent dual-band filter to the dual-drive Mach-Zehnder modulator.

[0028] Furthermore, the method for the optoelectronic oscillator to obtain the dual-frequency pulse filtered signal is as follows:

[0029] Utilize the laser to output a single-wavelength laser signal, and after passing through the polarization controller, the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator;

[0030] Adjust the bias voltage of the dual-drive Mach-Zehnder modulator to make it work at the quadrature transmission point; at this time, the filtered signal output by the equivalent dual-band filter is a single-frequency sine signal;

[0031] Turn on the microwave source to make the output signal of the microwave source be the excitation signal, so that the filtered signal output by the equivalent dual-band filter is a dual-frequency continuous wave signal;

[0032] Adjust the output signal of the microwave source to be the excitation signal and the active mode-locking signal, so that the filtered signal output by the equivalent dual-band filter is a dual-frequency pulse signal, and the entire optoelectronic oscillator realizes the generation of the dual-frequency pulse signal.

[0033] Beneficial effects:

[0034] The present invention provides an optoelectronic oscillator that can be used for generating dual - frequency microwave pulses, which mainly consists of a laser, a polarization controller, a dual - parallel Mach - Zehnder modulator, a single - mode fiber, a photodetector, an electrical amplifier, an equivalent dual - band filter, and a microwave source. Among them, the equivalent dual - band filter is obtained by connecting two narrow - band filters in parallel and serves as a frequency - selection device for the optoelectronic oscillator system. The microwave source is used to excite the dual - frequency oscillation of the optoelectronic oscillator loop, and then the loop gain modulation is achieved through active mode - locking modulation to change the output signal form, and thus a pulsed signal is output. Compared with the optoelectronic oscillator with traditional pulsed output, the optoelectronic oscillator of the present invention has the advantages of simple structure and tunable dual - frequency. At the same time, the output pulse of the present invention has two center frequencies and has good applications in pulsed Doppler radars, detection, etc. Description of the Drawings

[0035] Figure 1 It is a system block diagram of an optoelectronic oscillator for generating dual - frequency microwave pulses provided by the present invention.

[0036] Figure 2 It is a schematic diagram of the transfer - function curve of the equivalent dual - band filter provided by the present invention.

[0037] Figure 3 It is the frequency - domain graph of the signal output when the optoelectronic oscillator provided by the present invention oscillates freely.

[0038] Figure 4 It is the frequency - domain graph of the signal output after the optoelectronic oscillator provided by the present invention is injected with an excitation signal.

[0039] Figure 5 It is the time - frequency analysis graph of the signal output after the optoelectronic oscillator provided by the present invention is injected with an excitation signal.

[0040] Figure 6 It is the frequency - domain graph of the signal output after the optoelectronic oscillator provided by the present invention is injected with an excitation signal and an active mode - locking signal.

[0041] Figure 7 It is the time - frequency analysis graph of the signal output after the optoelectronic oscillator provided by the present invention is injected with an excitation signal and an active mode - locking signal. Detailed Embodiments

[0042] In order to enable those skilled in the art to better understand the solutions of the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application.

[0043] The present invention proposes an optoelectronic oscillator that can be used for generating dual - frequency microwave pulses. The system structure is as Figure 1As shown, it includes a laser, a polarization controller, a dual-drive Mach-Zehnder modulator, a single-mode fiber, a photodetector, an electrical amplifier, a mixer, an equivalent dual-band filter, a directional coupler, and a microwave source;

[0044] The laser is used to generate a laser signal and send the laser signal into the single-mode fiber;

[0045] The polarization controller is used to tune the polarization state of the laser signal output by the laser so that the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator, enabling the laser signal to obtain the highest modulation efficiency;

[0046] The microwave source is used to output different microwave signals to the dual-drive Mach-Zehnder modulator;

[0047] The dual-drive Mach-Zehnder modulator is used to modulate the laser signal parallel to its own main axis under the control of the microwave signal output by the microwave source and the dual-frequency filtering signal output by the equivalent dual-band filter. Among them, different microwave signals are output by the microwave source, and different modulated optical signals are output by the dual-drive Mach-Zehnder modulator; it should be noted that the dual-drive Mach-Zehnder modulator has two radio-frequency input interfaces. One radio-frequency input interface is used for injecting the loop feedback signal, that is, the dual-frequency filtering signal output by the equivalent dual-band filter; the other radio-frequency input interface is used for injecting the signal output by the microwave source;

[0048] The single-mode fiber is used to transmit the modulated optical signal to the photodetector; it should be noted that the single-mode fiber plays a role in increasing the loop optical cavity length and improving the quality factor of the output signal in the entire optoelectronic oscillator;

[0049] The photodetector is used to convert the modulated optical signal into a modulated electrical signal to detect the modulated optical signal;

[0050] The electrical amplifier is used to amplify the modulated electrical signal output by the photodetector and then input the amplified modulated electrical signal into the equivalent dual-band filter to increase the loop gain and achieve the output of the optoelectronic oscillator;

[0051] The equivalent dual-band filter is used to perform dual-band filtering on the amplified modulated electrical signal to obtain a filtered signal. Among them, the microwave signals output by the microwave source are different, and the filtered signals are also different. When the microwave signal is 0, the filtered signal is a single-frequency sine signal. When the microwave signal is an excitation signal, the filtered signal is a dual-frequency continuous wave signal. When the microwave signal is an excitation signal and an active mode-locking signal, the filtered signal is a dual-frequency pulse signal. That is to say, there are three cases for the output of the microwave source. The first is not to output any signal. The second is to only output an excitation signal to excite the loop to generate dual-frequency oscillation. The third is to output both an excitation signal and an active mode-locking signal at the same time, which is used to perform active mode-locking modulation on the loop.

[0052] The mixer is used to mix the amplified modulated electrical signal output by the electrical amplifier when the filtered signal is a dual-frequency continuous filtered signal and a dual-frequency pulse filtered signal, and then input the mixed modulated electrical signal into the equivalent dual-band filter.

[0053] The directional coupler is used to directionally couple the filtered signal output by the equivalent dual-band filter to the dual-drive Mach-Zehnder modulator.

[0054] It should be noted that the equivalent dual-band filter is composed of two band-pass filters, a 50:50 power splitter and a combiner. The modulated electrical signal enters from the power splitter and is evenly distributed, and then enters the two parallel band-pass filters respectively, and then is combined in the combiner through the output ends of the band-pass filters. That is to say, as Figure 2 shown, the equivalent dual-band filter can be used to filter the loop microwave signal, and only the signals within the passbands of the two band-pass filters can pass through.

[0055] The principle of the optoelectronic oscillator provided by the present invention to obtain a dual-frequency pulse filtered signal is as follows:

[0056] The laser signal output by the laser can be expressed as: E(t) = E0e jωt ;

[0057] The laser signal enters the dual-drive Mach-Zehnder modulator for intensity modulation. Due to the positive feedback characteristic of the optoelectronic oscillator, assuming that the feedback signal received by port ① of the dual-drive Mach-Zehnder modulator is s(t), and no signal is injected into port ②, that is, the microwave signal output by the microwave source is 0, then the output signal E MZM1 (t) can be expressed as:

[0058]

[0059] Among them, E0 is the optical intensity of the laser signal, ω c is the center frequency of the laser signal, s(t) is the filtered signal output by the equivalent dual-band filter, The phase shift introduced for the filtered signal s(t), The phase shift introduced for the bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V B The bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V π The half-wave voltage of the dual-drive Mach-Zehnder modulator;

[0060] At this time, the output signal of the dual-drive Mach-Zehnder modulator is transmitted through a long optical fiber and finally undergoes beat frequency in a photodetector. The photodetector signal can be expressed as:

[0061] V PD (t) ∝ s(t)

[0062] Therefore, when no signal is injected into port ②, the microwave signal in the entire optoelectronic oscillator loop oscillates stably.

[0063] Due to the limited loop gain of the optoelectronic oscillator OEO, when the microwave signal received by port ② of the dual-drive Mach-Zehnder modulator is set to where the frequency ω2 of this signal is equal to the difference between the center frequencies of the two narrowband bandpass filters in the equivalent dual-band filter. Therefore, the modulated optical signal E output by the dual-drive Mach-Zehnder modulator at this time MZM2 can be expressed as:

[0064]

[0065] where V2 is the amplitude of the excitation signal, ω2 is the angular frequency of the excitation signal, is the phase shift of the excitation signal; the modulated optical signal at this time is transmitted and then undergoes beat frequency in a photodetector. The photodetector signal can be expressed as:

[0066] V PD (t) ∝ k1s(t) + k2m1(t) + k3s(t)·m1(t)

[0067] where k1, k2, and k3 are intensity coefficients respectively, which are fixed constants representing the relative intensity relationship between each frequency. Then, this signal is filtered using the equivalent dual-band filter. Due to the dual-bandpass characteristic, the output signal of the equivalent dual-band filter is a dual-frequency signal, that is, signals with frequencies f1 and f2 (i.e., |ω1 - ω2| / 2π), which are returned and injected into port ① of the dual-drive Mach-Zehnder modulator and continuously enhanced. Therefore, the loop is converted from single-frequency oscillation to dual-frequency oscillation.

[0068] When the output of the microwave source is further changed such that the injected signal is At this time, the modulated optical signal E output by the dual-drive Mach-Zehnder modulator MZM3(t) is:

[0069]

[0070] wherein, V3 is the amplitude of the actively mode-locked signal, ω3 is the angular frequency of the actively mode-locked signal, is the phase shift of the actively mode-locked signal; after transmission through a long optical fiber, beating at the photodetector gives:

[0071] V PD (t) ∝ k1s(t) + k2m2(t) + k3s(t)·m2(t)

[0072] It can be seen that the present invention can first output a dual-frequency microwave signal, and on this basis, change the output state of the microwave source so that the output signal at port ② is m2(t) = m1(t) + m aml (t), where m aml (t) is called the actively mode-locked signal and can be expressed as V3 is the amplitude of this signal, ω3 is the angular frequency of this signal, which is related to the time delay of the loop and can usually be expressed as ω3 = 2π / τ, where τ is the loop time delay of the entire optoelectronic oscillator system; when the actively mode-locked signal is introduced, the loop gain of the optoelectronic oscillator will be modulated. Since the optoelectronic oscillator is a positive feedback loop, when the gain is less than a certain threshold, there is no output from the loop, so the conversion of the loop output signal from a continuous wave to a pulsed wave is achieved.

[0073] Furthermore, the method for the optoelectronic oscillator to obtain a dual-frequency pulsed filtering signal is:

[0074] Utilize a laser to output a single-wavelength laser signal. After passing through a polarization controller, the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator, and this optical signal will obtain the maximum modulation efficiency in the dual-drive Mach-Zehnder modulator;

[0075] Adjust the bias voltage of the dual-drive Mach-Zehnder modulator to make it work at the quadrature transmission point; at this time, the optoelectronic oscillator is in a single-mode oscillation state, and the filtering signal output by the equivalent dual-band filter is a single-frequency sine signal, which shows as single-frequency in the frequency domain and the side modes are suppressed;

[0076] Turn on the microwave source so that the output signal of the microwave source is the excitation signal Make the filtering signal output by the equivalent dual-band filter be a dual-frequency continuous wave signal, where ω2 = 2πf Δ , f Δ is the frequency difference between the two band-pass filters;

[0077] Adjust the gain of the electrical amplifier in the system so that the output signal is in the form of a dual-frequency continuous wave;

[0078] Adjust the output signal of the microwave source to an excitation signal and an active mode-locking signal \(m_2(t)=m_1(t)+m(t)\), so that the filtered signal output by the equivalent dual-band filter changes from a dual-frequency continuous wave signal to a dual-frequency pulse signal, and the whole optoelectronic oscillator realizes the generation of a dual-frequency pulse signal. aml (t), making the filtered signal output by the equivalent dual-band filter change from a dual-frequency continuous wave signal to a dual-frequency pulse signal, and the whole optoelectronic oscillator realizes the generation of a dual-frequency pulse signal.

[0079] The performance results of the optoelectronic oscillator provided by the present invention are as Figures 3 to 7 shown. The experimental parameters of this test are as follows: the output power of the laser is 12 dBm, the 3 dB bandwidth of the dual-drive Mach-Zehnder modulator is 40 GHz, the length of the single-mode fiber is 1 km, the 3 dB bandwidth of the photodetector is 33 GHz, the output bandwidth of the electrical amplifier is 20 GHz, and the gain is 20 dBmz.

[0080] Figure 3 shows the single-frequency oscillation situation of the loop when the microwave source has no output. When an excitation signal is injected into the microwave source, the spectrum of the output signal is in a dual-frequency form. Sampling and analyzing the output signal to obtain its time-domain signal, and performing time-frequency analysis on it, as Figure 4 and Figure 5 shown, it can be found that the output signal is a dual-frequency continuous wave. Further, change the output signal of the microwave source, perform active mode-locking modulation on the system, and obtain the output signal. Figure 6 is the time-domain spectrum of the output signal. It can be seen that its signal is in a pulse form. Performing time-frequency analysis on it, the Figure 7 obtained further proves the frequency component composition of the output pulse signal.

[0081] In summary, the present invention proposes an optoelectronic oscillator that can be used for dual-frequency microwave pulse generation. The optoelectronic oscillator mainly consists of a laser, a polarization controller, a dual-parallel Mach-Zehnder modulator, a single-mode fiber, a photodetector, an electrical amplifier, an equivalent dual-band filter, and a microwave source; an equivalent dual-band filter is used to output a dual-frequency continuous wave signal. The center frequencies of the two-frequency signals are respectively within the passbands of the two narrow-band filters, and when the single frequency changes to dual frequency, it is due to the injection of excitation by the microwave source, and there is a fixed phase relationship between the two signals; after the loop oscillates stably, an active mode-locking signal is injected, and the output signal changes from a continuous signal to a pulse signal. Due to the fixed phase relationship, the time-domain signal after the superposition of the two frequency components in each periodic pulse remains unchanged. Compared with other structures, the optoelectronic oscillator proposed by the present invention has a fixed phase relationship between the dual-frequency components, has the advantages of simple structure and tunable dual-frequency, and has good applications in pulsed Doppler radar, detection, etc.

[0082] Of course, the present invention may have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can certainly make various corresponding changes and deformations according to the present invention. However, these corresponding changes and deformations should all fall within the protection scope of the appended claims of the present invention.

Claims

1. An optoelectronic oscillator that can be used for dual-frequency microwave pulse generation, characterized in that, It includes a laser, a polarization controller, a dual-drive Mach-Zehnder modulator, a single-mode fiber, a photodetector, an equivalent dual-band filter, and a microwave source; The polarization controller is used to tune the polarization state of the laser signal output by the laser so that the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator; The microwave source is used to output different microwave signals to the dual-drive Mach-Zehnder modulator; The dual-drive Mach-Zehnder modulator is used to modulate the laser signal parallel to its main axis under the control of the microwave signal output by the microwave source and the dual-frequency filtering signal output by the equivalent dual-band filter. Among them, different microwave signals are output by the microwave source, and different modulated optical signals are output by the dual-drive Mach-Zehnder modulator; The single-mode fiber is used to transmit the modulated optical signal to the photodetector; The photodetector is used to convert the modulated optical signal into a modulated electrical signal; The equivalent dual-band filter is used to perform dual-band filtering on the modulated electrical signal to obtain a filtering signal. Among them, different microwave signals are output by the microwave source, and different filtering signals are obtained. When the microwave signal is 0, the filtering signal is a single-frequency sine signal. When the microwave signal is an excitation signal, the filtering signal is a dual-frequency continuous wave signal. When the microwave signal is an excitation signal and an active mode-locking signal, the filtering signal is a dual-frequency pulse signal.

2. The optoelectronic oscillator as claimed in claim 1 and applicable to dual-frequency microwave pulse generation, characterized in that, When the microwave signal output by the microwave source is 0, the modulated optical signal E MZM1 (t) is as follows: where E0 is the optical intensity of the laser signal, ω c is the center frequency of the laser signal, s(t) is the filtered signal output by the equivalent dual-band filter, is the phase shift introduced by the filtered signal s(t), is the phase shift introduced by the bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V B is the bias voltage provided by the external voltage source of the dual-drive Mach-Zehnder modulator, V π is the half-wave voltage of the dual-drive Mach-Zehnder modulator; When the microwave signal output by the microwave source is the excitation signal the modulated optical signal E output by the dual-drive Mach-Zehnder modulator is MZM2 as follows: wherein, V2 is the amplitude of the excitation signal, ω2 is the angular frequency of the excitation signal, is the phase shift of the excitation signal; When the microwave signals output by the microwave source are the excitation signal and the active mode-locking signal the modulated optical signal E MZM3 (t) output by the dual-drive Mach-Zehnder modulator is as follows: where V3 is the amplitude of the actively mode-locked signal, ω3 is the angular frequency of the actively mode-locked signal, and is the phase shift of the actively mode-locked signal.

3. The optoelectronic oscillator as claimed in claim 1, which is applicable to the generation of dual-frequency microwave pulses, is characterized in that It also includes an electrical amplifier; The electrical amplifier is used to amplify the modulated electrical signal output by the photodetector and then input the amplified modulated electrical signal into the equivalent dual-band filter.

4. The optoelectronic oscillator according to claim 2 that can be used for dual-frequency microwave pulse generation, characterized in that, It also includes a mixer; The mixer is used to mix the amplified modulated electrical signal output by the electrical amplifier when the filtering signal is a dual-frequency continuous filtering signal and a dual-frequency pulse filtering signal, and then input the mixed modulated electrical signal into the equivalent dual-band filter.

5. The optoelectronic oscillator for dual-frequency microwave pulse generation according to claim 1, characterized in that It also includes a directional coupler; The directional coupler is used to directionally couple the filtering signal output by the equivalent dual-band filter to the dual-drive Mach-Zehnder modulator.

6. The optoelectronic oscillator for dual-frequency microwave pulse generation according to claim 1, wherein, The method for the optoelectronic oscillator to obtain a dual-frequency pulse filtering signal is as follows: Use the laser to output a single-wavelength laser signal, and the polarization state of the laser signal is parallel to the main axis of the dual-drive Mach-Zehnder modulator after passing through the polarization controller; Adjust the bias voltage of the dual-drive Mach-Zehnder modulator to make it work at the quadrature transmission point; at this time, the filtering signal output by the equivalent dual-band filter is a single-frequency sine signal; Turn on the microwave source so that the output signal of the microwave source is an excitation signal, so that the filtering signal output by the equivalent dual-band filter is a dual-frequency continuous wave signal; Adjust the output signal of the microwave source to be an excitation signal and an active mode-locking signal, so that the filtering signal output by the equivalent dual-band filter is a dual-frequency pulse signal, and the entire optoelectronic oscillator realizes the generation of a dual-frequency pulse signal.

Images