A microwave signal generation method and a microwave signal source based on an optoelectronic oscillation loop

Abstract

The present invention discloses a microwave signal generation method and microwave signal source based on an optoelectronic oscillation loop. The method comprises: adjusting an intensity modulation unit to enable the optoelectronic oscillation loop to operate in a multimode oscillation state; injecting a linear frequency modulation signal or a step-frequency agility signal into the optoelectronic oscillation loop in the multimode oscillation mode, performing de-skewing processing on the loop oscillation signal, and obtaining frequency and phase information of the loop oscillation signal; and controlling a phase delay control unit after processing by a detection and feedback system so that each discrete frequency component of the linear frequency modulation signal or the step-frequency agility signal coincides with the oscillation mode of the optoelectronic oscillation loop. The technical solution provided by the present invention can simultaneously generate a linear frequency modulation signal or a step-frequency agility signal with large bandwidth, low phase noise, and high coherence in both the electrical and optical domains.

Description

Technical Field

[0001] The present invention relates to the field of signal processing technology, and in particular to a microwave signal generation method and a microwave signal source based on a photoelectric oscillation loop. Background Art

[0002] Wideband periodic signals are signals with a certain bandwidth and whose amplitude, frequency, or phase repeatedly changes over time. They are widely used in fields such as RF radar detection, wireless sensing, microwave imaging, and lidar. Common broadband periodic signals include linear frequency modulation (LFM), frequency agility (FAG), frequency hopping (FH), and phase-coded signals. LFM and step-FAG are microwave signals whose frequency varies with time according to a specific function. They are crucial pulse compression signal forms in radar detection, imaging, and sensing systems. Their large time-bandwidth product effectively addresses the conflict between range and range resolution in radar systems. To further improve radar detection performance, the LFM or step-FAG pulse waveforms emitted by radars must possess extremely high coherence. This coherent pulse waveform allows for pulse accumulation, optimizing the pulse compression signal-to-noise ratio (SNR), and increasing dynamic range. Previously, LFM and step-FAG signals were primarily generated in the microwave domain using voltage-controlled oscillators or direct frequency synthesis. However, due to the limitations of electronic bottlenecks, the linear frequency modulation signals and step-agile frequency conversion signals generated based on traditional microwave technology have disadvantages such as low center frequency, narrow bandwidth, poor phase noise, and low signal-to-noise ratio, and their performance is difficult to further improve.

[0003] Photonic technology offers significant advantages in low noise, low loss, and wide bandwidth, providing a novel approach for achieving high-performance linear frequency modulation (LFM) and step-agile frequency conversion (AGV) signals. Currently, optoelectronic oscillator (OEO) loops are an effective method for generating high-frequency, low-phase-noise, and high-SNR signals. OEOs utilize ultra-low-loss, low-noise, long optical fibers as energy storage media, resulting in a very high loop Q value. Under steady-state conditions, OEOs can generate signals with high spectral purity and low phase noise [X. Steve Yao and Lute Maleki, "Optoelectronic microwave oscillator," J. Opt. Soc. Am. B. 13, 1725-1735 (1996)]. Furthermore, due to the broadband nature of photonic systems, the phase noise of OEO output signals is independent of frequency. However, it is worth noting that conventional OEO loops often incorporate narrowband filters to filter out modes other than the oscillation frequency, resulting in only single-frequency oscillation and outputting low-phase-noise, single-frequency signals, making them incapable of generating broadband signals such as LFM and step-agile frequency conversion signals.

[0004] In order to solve the technical problem that traditional optoelectronic oscillators cannot realize broadband linear frequency modulation signals and step-fast frequency modulation signals, people have proposed an optoelectronic oscillator based on laser frequency sweeping [Hao T, Cen Q, Dai Y, et al. Breaking the limitation of mode building time in an optoelectronic oscillator [J]. Nature communications, 2018, 9(1): 1-8.]. This scheme uses laser frequency sweeping combined with phase modulation and notch optical filtering to realize a dynamically adjusted microwave photon filter in the optoelectronic oscillator loop, generating a linear frequency modulation signal with a large time-bandwidth product. Using the same principle, an optoelectronic oscillator based on two tunable lasers, a phase modulator and a notch filter can generate a bandwidth-tunable dual-chirped linear frequency modulation signal [Tengfei Hao, Jian, et al. Dual-chirp Fourierdomain mode-locked optoelectronic oscillator. [J]. Optics letters, 2019, 44(8): 1912-1915.]. However, these solutions all suffer from critical issues such as poor linearity, phase noise, and incoherence between preceding and succeeding pulses. The fundamental reason for this is that they all achieve broadband signal generation by dynamically changing the resonant cavity state (filter response, delay response, etc.) of the optoelectronic oscillator in real time. This dynamic adjustment of the optoelectronic oscillator's oscillation state prevents the signal in the loop from maintaining a steady state for long periods of time, resulting in frequency and phase drift with each cycle. This significantly degrades the phase noise, linearity, and coherence of the output broadband signal.

[0005] Therefore, in order to break through the fundamental dilemma faced by existing technologies, that is, the optoelectronic oscillator can only output a single-frequency signal in steady state and the signal quality will be greatly deteriorated during dynamic adjustment, a new technical approach is adopted to achieve ultra-low phase noise, broadband, high linearity and high coherence linear frequency modulation signals and step-agile frequency conversion signals, which is extremely critical to the development of modern radar systems, wireless communication systems, high-resolution imaging systems and other fields. Summary of the Invention

[0006] The object of the present invention is to provide a microwave signal generation method and a microwave signal source based on an optoelectronic oscillation loop, which can generate high-quality linear frequency modulation signals or step-agile frequency modulation signals.

[0007] The present invention provides a method for generating a microwave signal based on a photoelectric oscillation loop, the method comprising:

[0008] The photoelectric oscillation loop is made to work in a multi-mode oscillation state by adjusting the intensity modulation unit;

[0009] Injecting a linear frequency modulation signal or a step-agile frequency modulation signal into the optoelectronic oscillation loop in the multi-mode oscillation mode, and performing de-skewing processing on the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal;

[0010] The broadband phase delay control unit is controlled after processing by the detection and feedback system so that the discrete frequency components of the linear frequency modulation signal or the step-agile frequency conversion signal respectively coincide with the oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions:

[0011] g k >=1 and

[0012] Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, N is an integer, and τ is the total delay in the loop.

[0013] Furthermore, the method further comprises:

[0014] The repetition frequency of the linear frequency modulation signal or the step-frequency agility signal is adjusted to the free spectrum range of the optoelectronic oscillation loop, so that the linear frequency modulation signal or the step-frequency agility signal is locked with the interval oscillation mode to generate a low phase noise linear frequency modulation signal with an integer multiple period; wherein the repetition frequency of the generated low phase noise linear frequency modulation signal or the step-frequency agility signal can be step-tuned, and the tuning step is an integer multiple of the oscillation mode interval.

[0015] Furthermore, the free spectrum range of the optoelectronic oscillation loop is changed by adjusting the optical delay, and the repetition frequency of the injected linear frequency modulation signal or the stepped frequency agility signal is kept consistent with an integer multiple of the free spectrum range, so as to achieve continuous tunability of the generated microwave signal.

[0016] Furthermore, the method further comprises:

[0017] After the optoelectronic oscillation loop is started, the obtained frequency information is detected, and the adjustable optical delay line or the optical fiber temperature control device is controlled based on the detection result to achieve loop delay control.

[0018] Furthermore, the method further comprises:

[0019] After the optoelectronic oscillation loop enters a stable state, the obtained phase information is detected, and feedback control is performed on the stabilized phase relationship based on the detection result.

[0020] Furthermore, the method further comprises:

[0021] Replacing the intensity modulation unit in the optoelectronic oscillation loop with a phase modulator and an optical filter to generate a microwave photon filter;

[0022] The passband width of the microwave photon filter can be tuned by changing the optical carrier wavelength of the light source or the center frequency of the optical filter passband; the center frequency of the microwave photon filter can be tuned by changing the bandwidth of the optical filter.

[0023] The present invention also provides a microwave signal source based on a photoelectric oscillation loop, the microwave signal source comprising:

[0024] A light source module, used for generating an optical carrier;

[0025] A broadband signal generation module is used to generate a linear frequency modulation signal or a step-agile frequency modulation signal as a reference signal injected into the optoelectronic oscillation loop;

[0026] The optoelectronic oscillation loop module includes an intensity modulation unit, a photodetector, a broadband microwave amplifier, a broadband microwave bandpass filter, a broadband phase delay control unit, and a coupler; wherein the intensity modulation unit is adjusted to enable the optoelectronic oscillation loop to operate in a multi-mode oscillation state;

[0027] A broadband phase delay control unit, comprising a phase stabilization module and a delay stabilization control module, is configured to cause each discrete frequency component of the linear frequency modulation signal or the step-agile frequency conversion signal to coincide with an oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions:

[0028] g k >=1 and

[0029] Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, N is an integer, and τ is the total delay in the loop.

[0030] Furthermore, the phase stabilization module controls the electrically controlled phase shift unit through feedback from the microcontroller, and the electrically controlled phase shift unit includes an electrically controlled phase shifter or an adjustable optical delay line.

[0031] Furthermore, the delay stabilization control module controls the delay stabilization unit through a microcontroller feedback, and the delay stabilization unit includes an adjustable optical delay line or a long optical fiber temperature control.

[0032] Furthermore, the intensity modulation unit is implemented by a phase modulator and an optical filter.

[0033] The technical solution of the present invention has at least the following beneficial effects:

[0034] The present invention can optimize the performance of injected linear frequency modulation signals and step-agile frequency conversion signals, mode-lock the injected reference signal through multi-mode oscillation in the optoelectronic oscillation loop, and utilize the high Q value of the optical fiber in the optoelectronic oscillation loop to reduce the phase noise of the injected reference signal and improve the signal-to-noise ratio of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The structure and principle block diagram of a microwave signal source based on a photoelectric oscillation loop in one embodiment of the present invention;

[0036] Figure 2 This is a principle block diagram of an embodiment of the present invention when the injected reference signal and the loop oscillation signal are not locked;

[0037] Figure 3 This is a principle block diagram of locking the injected reference signal and the loop oscillation signal in one embodiment of the present invention;

[0038] Figure 4 A block diagram showing the principles of linear frequency modulation signal de-skewing processing according to one embodiment of the present invention;

[0039] Figure 5 This is a spectrum diagram of a linear frequency modulation signal output by a photoelectric oscillation loop in one embodiment of the present invention;

[0040] Figure 6 A spectrum diagram of linear frequency modulation signals with different bandwidths outputted by a reconfigurable device in one embodiment of the present invention;

[0041] Figure 7 A comparison diagram of the frequency spectra of linear frequency modulation signals output by a microwave signal source and a broadband reference signal generating module in one embodiment of the present invention;

[0042] Figure 8 A comparison diagram of the phase noise of the linear frequency modulation signal generated by the microwave signal source and the broadband reference signal in one embodiment of the present invention;

[0043] Figure 9 The schematic diagram of the device principle of a broadband photogenerated microwave source based on a reconfigurable optoelectronic oscillation loop in one embodiment of the present invention. DETAILED DESCRIPTION

[0044] In order to more clearly illustrate the embodiments of the present invention, specific implementations of the present invention will be described below with reference to the accompanying drawings.

[0045] Example 1:

[0046] In view of the shortcomings of existing technologies, such as Figure 1 As shown, this embodiment proposes a broadband optically generated microwave signal source based on an optoelectronic oscillation loop, which can achieve the generation of linear frequency modulation signals or step-agile frequency conversion signals with high signal-to-noise ratio and low phase noise. Specifically, the low phase noise broadband optically generated microwave signal generation device and method based on an optoelectronic oscillation loop of the present invention mainly include:

[0047] A light source module, used for generating an optical carrier;

[0048] A broadband signal generation module is used to generate a linear frequency modulation signal or a step-agile frequency modulation signal as a reference signal injected into the optoelectronic oscillation loop;

[0049] The optoelectronic oscillation loop module includes an intensity modulation unit, a photodetector, a broadband microwave amplifier, a broadband microwave bandpass filter, a broadband phase delay control unit, and a coupler; wherein the intensity modulation unit is adjusted to enable the optoelectronic oscillation loop to operate in a multi-mode oscillation state;

[0050] A broadband phase delay control unit, comprising a phase stabilization module and a delay stabilization control module, is configured to cause each discrete frequency component of the linear frequency modulation signal or the step-agile frequency conversion signal to coincide with an oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions:

[0051] g k >=1 and

[0052] Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, N is an integer, and τ is the total delay in the loop.

[0053] The high Q value and low loss characteristics of long optical fibers are used to optimize the phase noise of the signal. When the open-loop gain in the loop is greater than 1, the noise in the loop will begin to be amplified. After passing through the optoelectronic oscillation loop with a fixed delay, due to the positive feedback of the loop and the characteristics of gain greater than 1, the signal will be continuously amplified and eventually tend to be stable. At this time, the loop presents many frequency components with fixed frequency intervals. Their frequency intervals are the frequency values corresponding to the loop delay. At this time, the optoelectronic oscillation loop is in a multi-mode oscillation state. Figure 2 As shown in , when the delay phase between the loop oscillation mode and the injected linear frequency modulation signal mode does not match, the injected signal cannot be locked with the oscillation signal. Figure 3As shown in the figure, by calculating the total loop delay, the repetition frequency of the injected linear frequency modulation signal is set so that its repetition frequency matches the loop delay. Through the injection locking mechanism, the phase shifter is adjusted to match the phase of the linear frequency modulation signal with the multi-mode oscillation mode so that the modes reach a locked state, thereby achieving ultra-low phase noise broadband signal generation, as shown in the figure. Figure 5 As shown in Figure 3, the signal-to-noise ratio of the linear FM signal spectrum is greatly improved.

[0054] A method for generating broadband optical microwave signals with low phase noise based on an optoelectronic oscillation loop is used to generate a central frequency of ω c The linear frequency modulation signal with a bandwidth of BW modulates the optical carrier in the electro-optical modulation module, performs photoelectric conversion through the photodetector in the optoelectronic oscillation loop, and re-converts it into the microwave domain. By adjusting the bias voltage of the electro-optical modulator to make it work at the linear transmission point, the passband of the bandpass filter can cover the broadband periodic signal, so that its signal can completely pass through the optoelectronic oscillation loop. By adjusting the bias voltage, the gain in the optoelectronic oscillation loop is greater than 1, forming a stable positive feedback oscillation, and forming a stable multi-mode oscillation within the filter bandwidth. The frequency interval between the spectral components of the discretized linear frequency modulation signal pulse is matched with the free spectrum range of the optoelectronic oscillation loop, and the phase of the self-oscillating multi-mode signal and the injected linear frequency modulation signal is matched by the phase shifter in the optoelectronic oscillation loop, so that the injected linear frequency modulation signal is locked to the self-oscillating signal of the optoelectronic oscillation loop, forming a stable oscillation mode. From Figure 7 and Figure 8 It can be seen that the signal-to-noise ratio and phase noise of the output signal are greatly improved, thereby obtaining a stable linear frequency modulation signal with high signal-to-noise ratio, high linearity and low phase noise.

[0055] Among them, the electro-optical modulation module can be implemented through various existing or future methods, for example, using a push-pull Mach-Zehnder modulator, a phase modulator plus a filter, a polarization modulator plus an analyzer, etc. The present invention preferably uses a push-pull Mach-Zehnder modulator.

[0056] For ease of understanding, the technical solutions and principles of the present invention are described in detail below.

[0057] The self-oscillating signal generated by an optoelectronic oscillator loop is typically characterized by single-mode oscillation. In this process, since only a small, narrowband gain energy competes, the competition for modes above the oscillation threshold is significantly greater than that for modes below the threshold, resulting in single-mode oscillation. In multi-mode oscillation, all oscillation modes within the broadband bandpass filter are amplified and exceed the oscillation threshold. Gain competition cannot offset the amplification of the oscillation modes within the loop, resulting in stable multi-mode oscillation.

[0058] The multi-mode oscillation process of the optoelectronic oscillation loop in this embodiment is mainly analyzed through the time domain model, such as Figure 1 As shown, the input and output of the bandpass filter in the optoelectronic oscillation loop have the following relationship:

[0059]

[0060] Among them, V in (t) is the output signal of the photodetector, V out (t) is the output signal of the bandpass filter, ΔΩ and Ω0 are the bandwidth and center frequency of the bandpass filter respectively.

[0061] Since the output optical power of the laser is amplified by the voltage signal V=κGV out Performing electro-optical modulation, we can obtain the following relationship:

[0062]

[0063] Among them, T is the delay corresponding to the photoelectric loop, V πRF is the modulator's RF half-wave voltage, V πDC is the modulator DC half-wave voltage, V B is the applied bias voltage, P is the power of the continuous light output by the laser, and S is the photoelectric conversion factor. Therefore, the input voltage V(t) of the electro-optic modulator can be expressed as:

[0064]

[0065] Let the input of the electro-optic modulator be The simplified formula can be obtained:

[0066]

[0067] in, is the phase shift, is the normalized feedback gain coefficient. Near the center frequency Ω0, the complex slowly changing envelope of the quasi-sinusoidal microwave signal variation x(t) is θ(t) = |θ(t)|e iψ(t) Follow this formula:

[0068] θ=-μθ+2μγJc1[2θ T |] T (5)

[0069] Where μ = ΔΩ / 2 is half the bandwidth of the filter, γ = βsin2φ is the effective gain of the feedback loop, and θ T ≡θ (t-T), Jc1 is defined as Jc1(x)=J1(x) / x, J1(x) is the first order Bessel function of the first kind. In this formula, the phase matching condition is

[0070] When simulating formula (5), two different initial states are considered: the smooth state and the abrupt start state. The smooth state corresponds to the Hopf bifurcation, where the conditions below the threshold and above the threshold intersect as the single-mode amplitude continues to increase. The abrupt start state corresponds to the interval [-T, 0] with Gaussian random numbers as the initial conditions. At this time, the output of the optoelectronic oscillator is a highly multi-mode signal.

[0071] When the photoelectric oscillation loop appears continuous multi-mode oscillation, Figure 1 As shown in the structural block diagram, the linear frequency modulation signal generated by the broadband signal generation module is used as the injection reference source. The linear frequency modulation signal can be written as:

[0072]

[0073] Where t is the time variable, T is the pulse duration (period), k is the linear frequency modulation slope, f c is the center frequency of the linear FM signal.

[0074] The cosine expression of the linear frequency modulation signal is:

[0075] S(t)=cos(2πf c t+πkt 2 ) (7)

[0076] like Figure 1 As shown in the structural block diagram, when part of the reference signal passing through the coupler and part of the loop signal passing through the coupler enter the mixer for mixing:

[0077]

[0078] After low-pass filtering, the required difference frequency component is filtered out:

[0079] G(t)=cos[2πkτt+(2πf c τ-πkτ 2 )] (9)

[0080] Let Δf = kτ, and the above formula becomes:

[0081] G(t)=cos[2πΔft+(2πf c τ-πkτ 2 )] (10)

[0082] Combine Figure 4From the de-skewing principle block diagram, after de-skewing, a low-frequency component corresponding to Δf in the figure and a related delayed phase component are generated.

[0083] The frequency information and delayed phase information generated after de-skewing are sent to the detection and feedback system. When the discrete mode components of the injected signal and the loop signal in the spectrum are not aligned, such as Figure 4 As shown, a low-frequency component is generated after de-skewing. By detecting this frequency component, when this low-frequency component exists, the operation of the adjustable optical delay line or the optical fiber temperature control device is adjusted through the feedback mechanism to achieve a wide range of loop delay control.

[0084] When only the DC component remains after mixing, it indicates that there is only a small phase difference between the injected signal and the oscillation signal after the system becomes stable. By analyzing the phase in the above formula and controlling the phase through feedback, the phase relationship after the system stabilizes can be finely controlled.

[0085] It can be seen that by adjusting the intensity modulation unit, the optoelectronic oscillation loop is operated in a multi-mode oscillation state. A linear frequency modulation signal or a step-frequency agility signal is injected into the optoelectronic oscillation loop in the multi-mode oscillation mode, and de-skewed with the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal. After processing by the detection and feedback system, the phase delay control unit is controlled so that each discrete frequency component of the linear frequency modulation signal or the step-frequency agility signal coincides with the oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions:

[0086] g k >=1 and

[0087] Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, N is an integer, and τ is the total delay in the loop.

[0088] In summary, this embodiment can realize a low phase noise broadband optical microwave signal generation based on an optoelectronic oscillation loop. Compared with the traditional method of generating broadband periodic signals, the present invention optimizes the phase noise by utilizing the high Q value of the optoelectronic oscillation loop and uses the multi-mode oscillation process to mode-lock the injected broadband periodic signal, thereby improving the signal-to-noise ratio of the linear frequency modulation signal or the step-fast frequency conversion signal. Figure 7 and Figure 8 As shown, the optimization method of the present invention realizes the generation of linear frequency modulation signals with high signal-to-noise ratio and low phase noise.

[0089] Example 2:

[0090] This embodiment mainly realizes a broadband photogenerated microwave source based on a reconfigurable optoelectronic oscillation loop.

[0091] The difference between this embodiment and the broadband photogenerated microwave source based on the optoelectronic oscillation loop in the first embodiment is that:

[0092] See also Figure 1 and Figure 9 Compared with the first embodiment, the second embodiment has the following features: the modulator module is replaced by a phase modulator instead of an intensity modulator, the filter module is replaced by an optical filter instead of a microwave broadband filter, and the microwave photon filter formed by the phase modulator, the optical filter and the photodetector realizes the filtering function. The main structure of this embodiment also includes:

[0093] A light source module, used for generating an optical carrier;

[0094] A broadband signal generation module is used to generate a linear frequency modulation or step-agile frequency modulation signal as a reference signal injected into the optoelectronic oscillation loop;

[0095] The optoelectronic oscillation loop module includes a microwave photon filter composed of a phase modulator, an optical filter and a photodetector, a broadband bandpass microwave amplifier, a broadband phase delay control unit, and a coupler.

[0096] This structure mainly realizes the function of microwave photon filter by combining phase modulator and optical filter, and has the advantages of tunable bandwidth and tunable center frequency.

[0097] The microwave photon filtering method is mainly implemented as follows:

[0098] In order to achieve tunable center frequency and tunable bandwidth in the microwave photon filtering method of the present invention and achieve reconfigurability, preferably, at least one of the three parameters of the optical carrier frequency, the optical filter center frequency, and the optical filter bandwidth is adjustable.

[0099] Assume that the center frequency of the optical bandpass filter differs from the frequency of the optical carrier by Δf, and the passband width is BW O , the bandwidth of the modulated linear FM signal is BW e , when the frequency difference between the center frequency of the linear frequency modulation signal and the optical carrier is f, when f is very small, the positive and negative order sidebands after phase modulation all fall within the filter bandwidth, and after the photoelectric detector beats the positive and negative first-order sidebands and the carrier frequency beat signal, they cancel each other out. As f increases, when When the filter is turned on, one of the first-order sidebands will reach the edge of the filter bandwidth, making the positive and negative first-order sidebands asymmetric, achieving phase conversion intensity, and generating a signal after passing through the photodetector beat frequency. When , another first-order sideband will reach the outside of the filter's passband, making both the positive and negative sidebands outside the passband and no signal can be captured. A passband output response will be achieved, and the bandwidth of the passband is f BW =BW e +2Δf, center frequency is f c =BW o .

[0100] The above formula shows that by changing the optical carrier wavelength or the center frequency of the optical passband of the light source, the passband width of the microwave photonic filter can be tuned; by changing the bandwidth of the optical filter, the center frequency of the microwave photonic filter can be tuned. Therefore, the microwave photonic filter can be reconfigured, and thus the generation of linear frequency modulation signals or step-agile frequency signals can be reconfigured. Figure 6 (a), (b), (c), and (d) correspond to bandwidths of 2 GHz, 1 GHz, 500 MHz, and 100 MHz, respectively.

[0101] Compared with the prior art, the present invention adopts the above technology and has the following beneficial effects: the present invention performs broadband locking on the discrete components of the injected broadband reference signal through multi-mode oscillation in the optoelectronic oscillation loop, and utilizes the static stability mechanism in the high-Q value optoelectronic oscillation loop to achieve low phase noise, high linearity and high coherence broadband signal generation, breaking through the fundamental dilemma faced by the prior art that the optoelectronic oscillator can only output a single-frequency signal in the static steady state or the performance of the broadband optoelectronic oscillator is greatly deteriorated in the dynamic steady state.

[0102] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for generating a microwave signal based on an optoelectronic oscillation loop, characterized in that: The method comprises: The photoelectric oscillation loop is made to work in a multi-mode oscillation state by adjusting the intensity modulation unit; Injecting a linear frequency modulation signal or a step-agile frequency modulation signal into the optoelectronic oscillation loop in the multi-mode oscillation mode, and performing de-skewing processing on the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal; The broadband phase delay control unit is controlled after processing by the detection and feedback system so that each discrete frequency component of the linear frequency modulation signal or the step-agile frequency conversion signal coincides with the oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions: Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, k and N are integers, and τ is the total delay in the loop; The frequency and phase information generated after de-skewing is fed into the detection and feedback system. When the discrete mode components of the injected signal and the loop signal in the spectrum are not aligned, a low-frequency component is generated after de-skewing. This frequency component is detected. When it is present, the adjustable optical delay line or optical fiber temperature control device is adjusted through a feedback mechanism to achieve loop delay control.

2. The method according to claim 1, characterized in that The method further comprises: The repetition frequency of the linear frequency modulation signal is adjusted to the free spectrum range of the optoelectronic oscillation loop, so that the linear frequency modulation signal is locked with the interval oscillation mode to generate a low phase noise linear frequency modulation signal with an integer multiple period; wherein the repetition frequency of the generated low phase noise linear frequency modulation signal can be step-tuned, and the tuning step is an integer multiple of the oscillation mode interval.

3. The method according to claim 1 or 2, characterized in that The free spectrum range of the optoelectronic oscillation loop is changed by adjusting the optical delay in the loop, while the repetition frequency of the injected linear frequency modulation signal or the stepped frequency agility signal is kept consistent with an integer multiple of the free spectrum range, so as to achieve continuous tunability of the center frequency and repetition period of the generated microwave signal.

4. The method according to claim 1, wherein The method further comprises: After the optoelectronic oscillation loop is started, the obtained frequency information is detected, and the adjustable optical delay line or the optical fiber temperature control device is controlled based on the detection result to achieve loop delay control.

5. The method according to claim 1, wherein The method further comprises: After the optoelectronic oscillation loop enters a stable state, the obtained phase information is detected, and feedback control is performed on the stabilized phase relationship based on the detection result.

6. The method according to claim 1, characterized in that The method further comprises: Replacing the intensity modulation unit and the broadband bandpass filter in the optoelectronic oscillation loop with a phase modulator and an optical filter to generate a microwave photon filter; The passband width of the microwave photon filter can be tuned by changing the optical carrier wavelength of the light source or the center frequency of the optical filter passband; the center frequency of the microwave photon filter can be tuned by changing the bandwidth of the optical filter.

7. A microwave signal source based on an optoelectronic oscillation loop, characterized in that: The microwave signal source comprises: A light source module, used for generating an optical carrier; A broadband signal generation module is used to generate a linear frequency modulation signal or a step-agile frequency modulation signal as a reference signal injected into the optoelectronic oscillation loop; The optoelectronic oscillation loop module includes an intensity modulation unit, a photodetector, a broadband microwave amplifier, a broadband microwave bandpass filter, a broadband phase delay control unit, and a coupler; wherein the intensity modulation unit is adjusted to enable the optoelectronic oscillation loop to operate in a multi-mode oscillation state; A broadband phase delay control unit, comprising a phase stabilization module and a delay stabilization control module, is configured to cause each discrete frequency component of the linear frequency modulation signal or the step-agile frequency conversion signal to coincide with an oscillation mode of the optoelectronic oscillation loop, and each mode satisfies the following amplitude and phase conditions: Among them, g k is the gain of the kth mode, ω k is the angular frequency of the kth mode, The diagonal frequency of the system is ω k The extra phase introduced by the mode, k and N are integers, and τ is the total delay in the loop.

8. The microwave signal source according to claim 7, characterized in that: The phase stabilization module controls the electrically controlled phase shift unit through feedback from a microcontroller, and the electrically controlled phase shift unit includes an electrically controlled phase shifter or an adjustable optical delay line.

9. The microwave signal source according to claim 7, characterized in that: The delay stabilization control module controls the delay stabilization unit through a microcontroller feedback, and the delay stabilization unit includes an adjustable optical delay line or a temperature-controlled optical fiber.

10. The microwave signal source according to claim 7, characterized in that: The intensity modulation unit is realized by a phase modulator and an optical filter.

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