CN113900065A - Microwave signal generation method based on photoelectric oscillation loop and microwave signal source - Google Patents
Microwave signal generation method based on photoelectric oscillation loop and microwave signal source Download PDFInfo
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Abstract
The invention discloses a microwave signal generation method based on a photoelectric oscillation loop and a microwave signal source, wherein the method comprises the following steps: the photoelectric oscillation loop works in a multimode oscillation state by adjusting the intensity modulation unit; injecting a linear frequency modulation signal or a stepping frequency agile signal into the photoelectric oscillation loop in a multimode oscillation mode, and performing deskew processing on the linear frequency modulation signal or the stepping frequency agile signal and the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal; and after the processing of the detection and feedback system, the phase delay control unit is controlled, so that each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal is respectively superposed with the oscillation mode of the photoelectric oscillation loop. The technical scheme provided by the invention can generate linear frequency modulation signals or stepping frequency agility signals with large bandwidth, low phase noise and high phase coherence in an electric domain and an optical domain simultaneously.
Description
Technical Field
The invention relates to the technical field of signal processing, in particular to a microwave signal generation method based on a photoelectric oscillation loop and a microwave signal source.
Background
The broadband periodic signal is a signal with a certain bandwidth and with amplitude, frequency or phase repeatedly changing along with time, and is widely applied to multiple fields of radio frequency radar detection, wireless sensing, microwave imaging, laser radar and the like. Common broadband periodic signals mainly comprise linear frequency modulation signals, frequency agility signals, frequency hopping signals, phase coding signals and the like, wherein the linear frequency modulation signals and the stepping frequency agility signals refer to microwave signals with frequencies changing along with time according to a specific functional relation, are pulse compression signal forms which are very important in radar detection, imaging perception and other systems, have the characteristic of large time-width bandwidth product, and can effectively solve the contradiction between the acting distance and the distance resolution of the radar and other systems. In order to further improve the detection performance of the radar, the linear frequency modulation or stepping frequency agility pulse waveform transmitted by the radar needs to have extremely high coherence, and the pulse waveform with the coherence can be used for pulse accumulation, so that the pulse compression signal-to-noise ratio is optimized, and the dynamic range is improved. Previously, chirp signals and step-down chirp signals were generated primarily in the microwave domain by means of a voltage controlled oscillator or direct frequency synthesis. However, due to the limitation of the electronic bottleneck, the chirp signal and the step frequency agility signal generated based on the conventional microwave technology have the disadvantages of low center frequency, narrow bandwidth, poor phase noise, small signal-to-noise ratio and the like, and the performance is difficult to further improve.
The photon technology has the great advantages of low noise, low loss and large bandwidth, and provides a brand new idea for realizing high-performance linear frequency modulation signals and stepping frequency agility signals. At present, a photoelectric oscillation loop is an effective way for generating signals with high frequency, low phase noise and high signal-to-noise ratio. The Optoelectronic oscillator uses a long fiber with ultra-low loss and low noise as an energy storage medium, so that the loop Q value is very large, and under the condition of satisfying a steady state, the signal generation with high spectral purity and low phase noise can be realized [ 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 the optoelectronic oscillator output signal is independent of frequency. However, it is worth noting that a narrow-band filter is often introduced into a conventional photoelectric oscillation loop to filter out other modes except the oscillation frequency, so that the conventional photoelectric oscillation loop can only realize single-frequency oscillation, output a low-phase-noise single-frequency signal, and cannot realize generation of broadband signals such as a chirp signal and a step-down frequency agile signal.
Aiming at the technical problem that the traditional photoelectric oscillator can not realize broadband linear frequency modulation signals and stepping frequency agility signals, people provide a laser frequency sweeping-based photoelectric oscillator [ 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 ]. Using the same principle, a photonic oscillator based on two tunable lasers, a phase modulator and a notch filter can generate a bandwidth tunable dual chirped chirp signal [ Tengfei Hao, Jian, et al, dual-chip Fourier domain mode-locked electronic oscillator, J. However, the schemes have the key problems of poor linearity, poor phase noise and non-coherent front and back pulses. The fundamental reason is that the broadband signal is generated by dynamically changing the resonant cavity state (filter response, delay response and the like) of the optoelectronic oscillator in real time. The dynamic adjustment of the oscillation state of the optoelectronic oscillator prevents the signals in the loop from being in a steady state for a long time, and frequency and phase drift exist in each cycle, so that the phase noise, the linearity and the phase coherence of the output broadband signals of the optoelectronic oscillator are greatly deteriorated.
Therefore, the principle dilemma that the photoelectric oscillator can only output single-frequency signals in a steady state and can greatly deteriorate the signal quality in dynamic adjustment in the prior art is broken through, and the generation of linear frequency modulation signals and stepping frequency agility signals with ultra-low phase noise, broadband, high linearity and high coherence is realized by adopting a brand-new technical mode, so that the method is very critical to the development of the fields of modern radar systems, wireless communication systems, high-resolution imaging systems and the like.
Disclosure of Invention
The invention aims to provide a microwave signal generation method and a microwave signal source based on a photoelectric oscillation loop, which can generate high-quality linear frequency modulation signals or stepping frequency agility signals.
The invention provides a microwave signal generation method based on a photoelectric oscillation loop, which comprises the following steps:
the photoelectric oscillation loop works in a multimode oscillation state by adjusting the intensity modulation unit;
injecting a linear frequency modulation signal or a stepping frequency agile signal into the photoelectric oscillation loop in a multimode oscillation mode, and performing deskew processing on the linear frequency modulation signal or the stepping frequency agile signal and the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal;
after being processed by a detection and feedback system, the broadband phase delay control unit is controlled, so that each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal is respectively superposed with an oscillation mode of the photoelectric oscillation loop, and each mode meets the following amplitude-phase conditions:
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakN is an integer and τ is the total delay in the loop.
Further, the method further comprises:
adjusting the repetition frequency of the chirp signal or the step frequency-agile signal to the free frequency spectrum range of the optoelectronic oscillation loop, so that the chirp signal or the step frequency-agile signal is locked with the oscillation mode of the interval to generate a low-phase-noise chirp signal with an integral multiple of the period; wherein the generated repetition frequency of the low phase noise chirp signal or step agility signal is step tunable and the tuning step is an integer multiple of the oscillation mode interval.
Further, the free frequency spectrum range of the photoelectric oscillation loop is changed by adjusting the optical time delay, and meanwhile, the repetition frequency of the injected linear frequency modulation signal or the stepping frequency agility signal is kept consistent with the integral multiple of the free frequency spectrum range, so that the generated microwave signal is continuously tunable.
Further, the method further comprises:
after the oscillation of the photoelectric oscillation loop is started, the obtained frequency information is detected, and an adjustable light delay line or an optical fiber temperature control device is fed back and controlled based on the detection result, so that the loop delay control is realized.
Further, the method further comprises:
and after the photoelectric oscillation loop enters a stable state, detecting the obtained phase information, and performing feedback control on the stable phase relation based on a detection result.
Further, the method further comprises:
replacing an intensity modulation unit in the optoelectronic oscillation loop with a phase modulator and an optical filter to generate a microwave photonic filter;
the tunable passband width of the microwave photonic filter is realized by changing the wavelength of an optical carrier of a light source or the central frequency of the passband of the optical filter; the tunable central frequency of the microwave photon filter is realized by changing the bandwidth of the optical filter.
The invention also provides a microwave signal source based on the photoelectric oscillation loop, which comprises:
the light source module is used for generating optical carriers;
the broadband signal generating module is used for generating a linear frequency modulation signal or a stepping frequency agility signal as a reference signal injected into the photoelectric oscillation loop;
the photoelectric oscillation loop module comprises an intensity modulation unit, a photoelectric detector, a broadband microwave amplifier, a broadband microwave band-pass filter, a broadband phase delay control unit and a coupler; wherein, the photoelectric oscillation loop works in a multi-mode oscillation state by adjusting the intensity modulation unit;
the broadband phase delay control unit comprises a phase stabilizing module and a delay stabilizing control module, and is used for respectively superposing each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal with an oscillation mode of the photoelectric oscillation loop, wherein each mode meets the following amplitude-phase conditions:
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakN is an integer and τ is the total delay in the loop.
Furthermore, the phase stabilizing module controls the electric control phase shifting unit in a feedback mode through the microcontroller, and the electric control phase shifting unit comprises an electric control phase shifter or an adjustable light delay line.
Further, the delay stabilization control module controls the delay stabilization unit in a feedback mode through the microcontroller, and the delay stabilization unit comprises an adjustable light delay line or a long optical fiber temperature control unit.
Further, the intensity modulation unit is implemented by a phase modulator and an optical filter.
The technical scheme of the invention at least has the following beneficial effects:
the invention can optimize the performance of the injected linear frequency modulation signal and the stepping frequency agility signal, lock the mode of the injected reference signal through the multimode oscillation in the photoelectric oscillation loop, and reduce the phase noise of the injected reference signal and improve the signal to noise ratio of the signal by utilizing the high Q value of the optical fiber in the photoelectric oscillation loop.
Drawings
FIG. 1 is a schematic block diagram of a microwave signal source based on a photoelectric oscillation loop according to an embodiment of the present invention;
FIG. 2 is a schematic block diagram illustrating the timing of an unlocked reference signal and an unlocked loop oscillator signal in accordance with an embodiment of the present invention;
FIG. 3 is a schematic block diagram of an embodiment of the present invention illustrating locking of the injected reference signal with the ring oscillator signal;
FIG. 4 is a block diagram illustrating the relevant principles of the dechirping process of the chirp signal in accordance with one embodiment of the present invention;
FIG. 5 is a graph of the spectrum of the output chirp signal of the optoelectronic oscillator loop in one embodiment of the present invention;
FIG. 6 is a graph of a spectrum of a chirp signal output at different bandwidths based on a reconfigurable device according to an embodiment of the present invention;
FIG. 7 is a graph illustrating a comparison of the frequency spectra of the output chirp signals of the microwave signal source and the broadband reference signal generating module according to an embodiment of the present invention;
FIG. 8 is a graph illustrating phase noise comparison of an output chirp signal generated by a microwave signal source and a broadband reference signal in accordance with one embodiment of the present invention;
fig. 9 is a schematic block diagram of a broadband photo-generated microwave source based on a reconfigurable photoelectric oscillation loop in an embodiment of the invention.
Detailed Description
In order to more clearly describe the embodiments of the present invention, the following description will be made with reference to the accompanying drawings.
The first embodiment is as follows:
in view of the defects in the prior art, as shown in fig. 1, the present embodiment provides a broadband photo-generated microwave signal source based on a photoelectric oscillation loop, which can generate a chirp signal or a step frequency agile signal with a high signal-to-noise ratio and low phase noise. Specifically, the device and the method for generating the low-phase-noise broadband photo-generated microwave signal based on the photoelectric oscillation loop mainly comprise the following steps:
the light source module is used for generating optical carriers;
the broadband signal generating module is used for generating a linear frequency modulation signal or a stepping frequency agility signal as a reference signal injected into the photoelectric oscillation loop;
the photoelectric oscillation loop module comprises an intensity modulation unit, a photoelectric detector, a broadband microwave amplifier, a broadband microwave band-pass filter, a broadband phase delay control unit and a coupler; wherein, the photoelectric oscillation loop works in a multi-mode oscillation state by adjusting the intensity modulation unit;
the broadband phase delay control unit comprises a phase stabilizing module and a delay stabilizing control module, and is used for respectively superposing each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal with an oscillation mode of the photoelectric oscillation loop, wherein each mode meets the following amplitude-phase conditions:
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakN is an integer and τ is the total delay in the loop.
The phase noise of the signal is optimized by using the characteristics of high Q value and low loss of the long optical fiber, when the open loop gain in the loop is greater than 1, the noise in the loop starts to be amplified, and after the photoelectric oscillation loop with fixed time delay passes through, the signal is continuously amplified due to the positive feedback of the loop and the characteristic that the gain is greater than 1, and finally the signal tends to be stable. In this case, a plurality of frequency components having a fixed frequency interval are present in the loop, and their frequency intervals are frequency values corresponding to the loop delay, which is the multi-mode oscillation state of the optoelectronic oscillation loop. As shown in fig. 2, when the delay phase between the oscillation mode of the loop and the injection chirp mode is not matched, the injection signal cannot be locked to the oscillation signal. As shown in fig. 3, the repetition frequency of the injected chirp signal is set by calculating the total delay of the loop, so that the repetition frequency is matched with the loop delay, and the phase of the chirp signal is matched with the phase of the multimode oscillation mode by adjusting the phase shifter by an injection locking mechanism, so that the modes reach a locked state, thereby realizing the generation of a broadband signal with ultra-low phase noise, and as shown in fig. 5, the signal-to-noise ratio of the frequency spectrum of the chirp signal is greatly improved.
A low-phase-noise broadband photo-generated microwave signal generation method based on a photoelectric oscillation loop is used for enabling the center frequency to be omegacThe BW linear frequency modulation signal modulates the optical carrier in the electro-optical modulation module, and carries out photoelectric conversion and reconversion through a photoelectric detector in a photoelectric oscillation loopTo the microwave domain. By adjusting the bias voltage of the electro-optical modulator to enable the electro-optical modulator to work at a linear transmission point, the passband of the band-pass filter can cover a broadband periodic signal, and the signal can completely pass through the photoelectric oscillation loop. By adjusting the bias voltage, the gain in the photoelectric oscillation loop is larger than 1, stable positive feedback oscillation is formed, and stable multi-mode oscillation is formed in the bandwidth of the filter. The frequency interval between the frequency spectrum components after the discretization of the chirp signal pulse is matched with the free frequency spectrum range of the photoelectric oscillation loop, and the phase of the self-oscillation multimode signal is matched with the phase of the injection chirp signal through a phase shifter in the photoelectric oscillation loop, so that the injection chirp signal is locked to the self-oscillation signal of the photoelectric oscillation loop to form a stable oscillation mode. As can be seen from fig. 7 and 8, the signal-to-noise ratio and the phase noise of the output signal are both greatly improved, so that a stable chirp signal with a high signal-to-noise ratio, high linearity and low phase noise is obtained.
The electro-optical modulation module may be implemented by various existing or future methods, for example, by using a push-pull mach-zehnder modulator, a phase modulator plus filter, a polarization modulator plus analyzer, or the like.
For the sake of easy understanding, the technical solutions and principles of the present invention will be described in detail below.
In the self-oscillation signal generated by the photoelectric oscillation loop, what is generally needed is a single-mode oscillation process, in which, because only a small part of narrow-band gain energy can compete, the competition capability of the mode above the oscillation threshold is obviously higher than that of the gain below the threshold, and single-mode oscillation is formed. During the multi-mode oscillation, all oscillation modes in the broadband band-pass filter are amplified and exceed the oscillation threshold, and the gain competition cannot counteract the process that the oscillation modes are amplified in the loop, so that stable multi-mode oscillation can be formed.
In this embodiment, the multimode oscillation process of the optoelectronic oscillation loop is mainly analyzed through a time domain model, as shown in fig. 1, the input and the output of the bandpass filter in the optoelectronic oscillation loop have the following relationships:
wherein, Vin(t) is the output signal of the photodetector, Vout(t) is the output signal of the band-pass filter, Δ Ω and Ω0The bandwidth and the center frequency of the band pass filter, respectively.
The voltage signal V ═ kGV after the output optical power of the laser is amplifiedoutWith electro-optical modulation, the following relationship can be obtained:
wherein T is the corresponding time delay of the photoelectric loop, VπRFIs the radio frequency half-wave voltage, V, of the modulatorπDCFor the modulator DC half-wave voltage, VBFor the applied bias voltage, P is the power of the continuous light output by the laser, and S is the photoelectric conversion factor. Thus, the input voltage v (t) of the electro-optic modulator can be expressed as:
let the input of the electro-optical modulator be
A simplified formula can be obtained:
wherein the content of the first and second substances,
for the amount of phase that is offset,
is a normalized feedback gain factor. At a central frequency omega0Near complex slowly varying envelope θ (t) | e) of quasi-sinusoidal microwave signal variation x (t)iψ(t)The following formula is followed:
θ＝-μθ+2μγJc1[2|θT|]T (5)
where μ ═ Δ Ω/2 is one-half of the bandwidth of the filter, γ ═ β sin2 Φ is the effective gain of the feedback loop, θT≡θ(t-T)，Jc1Is defined as Jc1(x)＝J1(x)/x，J1(x) Is a first order bessel function of the first kind. In the formula, the phase matching condition is
When the equation (5) is simulated, two different initial states are considered, namely, a smooth state and an abruppt start state, the smooth state corresponds to a hopf split, conditions below and above the threshold intersect with increasing single-mode amplitude, and the abruppt start state corresponds to an initial condition of a gaussian random number in the interval [ -T, 0], when the output of the optoelectronic oscillator is a highly multimode signal.
After the optoelectronic oscillation loop has continuous multi-mode oscillation, as shown in the structural block diagram in fig. 1, a chirp signal generated by the broadband signal generation module is used as an injection reference source, and the chirp signal may be written as:
where T is the time variable, T is the pulse duration (period), k is the chirp slope, fcIs the center frequency of the chirp signal.
The cosine expression of the chirp signal is:
S(t)＝cos(2πfct+πkt2) (7)
as shown in the block diagram of fig. 1, when a part of the reference signal passing through the coupler and a part of the loop signal passing through the coupler enter the mixer for mixing:
after low-pass filtering, the required difference frequency component is filtered out:
G(t)＝cos[2πkτt+(2πfcτ-πkτ2)] (9)
let Δ f be k τ, which is changed from the above equation:
G(t)＝cos[2πΔft+(2πfcτ-πkτ2)] (10)
in view of the schematic diagram of fig. 4, the deskew operation produces a low frequency component corresponding to Δ f in the diagram and an associated delayed phase component.
The frequency information and the delay phase information generated after the deskew are sent to a detection and feedback system, when the discretization mode components of the injection signal and the loop signal in the frequency spectrum are not aligned, as shown in fig. 4, a low-frequency component is generated after the deskew, and by detecting the frequency component, when the low-frequency component exists, the operation of an adjustable optical delay line or an optical fiber temperature control device and the like is adjusted through a feedback mechanism, so that the loop delay control in a large range is realized.
When only a direct current component is left after the frequency mixing, it is shown that only a small phase difference exists between the injection signal and the oscillation signal after the system tends to be stable, and the phase relation after the system is stable is finely controlled by analyzing the phase in the formula and controlling the phase through feedback.
Therefore, the photoelectric oscillation loop works in a multi-mode oscillation state by adjusting the intensity modulation unit; injecting a linear frequency modulation signal or a stepping frequency agile signal into the photoelectric oscillation loop in a multimode oscillation mode, and performing deskew processing on the linear frequency modulation signal or the stepping frequency agile signal and the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal; after being processed by a detection and feedback system, the phase delay control unit is controlled, so that each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal is respectively superposed with an oscillation mode of the photoelectric oscillation loop, and each mode meets the following amplitude-phase conditions:
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakN is an integer and τ is the total delay in the loop.
In summary, the present embodiment can realize a low-phase-noise broadband photo-generated microwave signal generation based on the optoelectronic oscillation loop. Compared with the traditional generation mode of the broadband periodic signal, the invention optimizes the phase noise by utilizing the high Q value of the photoelectric oscillation loop and carries out mode locking on the injected broadband periodic signal by utilizing the multimode oscillation process, thereby improving the signal-to-noise ratio of the linear frequency modulation signal or the stepping frequency agility signal. As shown in fig. 7 and 8, the optimization method of the present invention achieves high signal-to-noise ratio and low phase noise chirp signal generation.
Example two:
the embodiment mainly realizes the broadband photo-generated microwave source based on the reconfigurable photoelectric oscillation loop.
The present embodiment is different from the broadband optical microwave source based on the photoelectric oscillation loop in the first embodiment in that:
referring to fig. 1 and 9, in a second embodiment, compared with the first embodiment, the modulator module is replaced by the phase modulator from the intensity modulator, the filter module is replaced by the microwave broadband filter to the optical filter, and the microwave photonic filter formed by combining the phase modulator, the optical filter and the photodetector realizes the filtering function, and the main structure of this embodiment further includes:
the light source module is used for generating optical carriers;
the broadband signal generating module is used for generating a linear frequency modulation or stepping frequency agility signal as a reference signal injected into the photoelectric oscillation loop;
the photoelectric oscillation loop module comprises a microwave photon filter, a broadband band-pass microwave amplifier, a broadband phase delay control unit and a coupler, wherein the microwave photon filter consists of a phase modulator, an optical filter and a photoelectric detector.
The structure mainly realizes the effect of a microwave photon filter based on the combination of a phase modulator and an optical filter, and has the advantages of tunable bandwidth and tunable center frequency.
The microwave photon filtering method is mainly realized as follows:
in order to realize the tunable center frequency, tunable bandwidth and reconfigurability in the microwave photon filtering method of the present invention, 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.
Assuming that the center frequency of the optical bandpass filter differs from the frequency of the optical carrier by Δ f, the passband width is BWOBandwidth of the modulated chirp signal is BWeWhen the frequency difference between the center frequency of the chirp 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 bandwidth of the filter, after the beat frequency of the photoelectric detector, the positive and negative first order sidebands and the carrier frequency beat signal to be offset, and along with the increase of f, when f is too large
When the phase of the signal is increased, one of the first-order sidebands reaches the edge of the bandwidth of the filter, so that the positive and negative first-order sidebands are asymmetric, the phase rotation intensity is realized, a signal can be generated after the beat frequency of the photoelectric detector is increased
While the other first-order sideband reaches the outside of the filter's passband so that both the positive and negative sidebands are presentOut-of-band, no signal can be tapped. Therefore, is at
A passband of output response is realized, the passband having a bandwidth of fBW＝BWe+2 Δ f, center frequency fc＝BWo。
The tunable passband width of the microwave photonic filter can be realized by changing the wavelength of the optical carrier of the light source or the central frequency of the optical passband; by changing the bandwidth of the optical filter, the center frequency of the microwave photonic filter can be tunable. Therefore, the reconfigurability of the microwave photon filter can be realized, and the reconfigurability of generating a linear frequency modulation signal or a stepping frequency agile signal can be realized. In FIG. 6, (a), (b), (c), and (d) correspond to bandwidths of 2GHz, 1GHz, 500MHz, and 100MHz, respectively.
Compared with the prior art, the invention has the following beneficial effects: the invention locks the discrete component of the injected broadband reference signal by the multimode oscillation in the photoelectric oscillation loop, realizes the generation of broadband signals with low phase noise, high linearity and high coherence by utilizing a static stability mechanism in the photoelectric oscillation loop with high Q value, and breaks through the principle dilemma that the photoelectric oscillator can only output single-frequency signals under a static stable state or the performance of the broadband photoelectric oscillator is greatly deteriorated under a dynamic stable state in the prior art.
The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments can be referred to each other, and each embodiment focuses on the differences from the other embodiments.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (10)
1. A method for generating a microwave signal based on an optoelectronic oscillation loop, the method comprising:
the photoelectric oscillation loop works in a multimode oscillation state by adjusting the intensity modulation unit;
injecting a linear frequency modulation signal or a stepping frequency agile signal into the photoelectric oscillation loop in a multimode oscillation mode, and performing deskew processing on the linear frequency modulation signal or the stepping frequency agile signal and the loop oscillation signal to obtain frequency information and phase information of the loop oscillation signal;
after being processed by a detection and feedback system, the broadband phase delay control unit is controlled, so that each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal is respectively superposed with an oscillation mode of the photoelectric oscillation loop, and each mode meets the following amplitude-phase conditions:
gk1 and
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakK and N are integers and τ is the total delay in the loop.
2. The method of claim 1, further comprising:
adjusting the repetition frequency of the chirp signal to the free spectral range of the opto-electronic oscillation loop such that the chirp signal is locked with the spaced oscillation modes to generate a low phase noise chirp signal of an integer multiple of the period; wherein the generated low phase noise chirp signal is step tunable in repetition frequency and the tuning step is an integer multiple of the oscillation mode interval.
3. A method according to claim 1 or 2, characterized in that the free spectral range of the opto-electronic oscillating loop is varied by adjusting the optical delay in the loop while the repetition frequency of the injected chirp signal or step-wise frequency agile signal is kept in accordance with an integer multiple of the free spectral range to achieve a continuously tunable center frequency and repetition period of the generated microwave signal.
4. The method of claim 1, further comprising:
after the oscillation of the photoelectric oscillation loop is started, the obtained frequency information is detected, and an adjustable light delay line or an optical fiber temperature control device is fed back and controlled based on the detection result, so that the loop delay control is realized.
5. The method of claim 1, further comprising:
and after the photoelectric oscillation loop enters a stable state, detecting the obtained phase information, and performing feedback control on the stable phase relation based on a detection result.
6. The method of claim 1, further comprising:
replacing the intensity modulation unit and a broadband bandpass filter in the optoelectronic oscillation loop with a phase modulator and an optical filter to generate a microwave photonic filter;
the tunable passband width of the microwave photonic filter is realized by changing the wavelength of an optical carrier of a light source or the central frequency of the passband of the optical filter; the tunable central frequency of the microwave photon filter is realized by changing the bandwidth of the optical filter.
7. A microwave signal source based on a photoelectric oscillation loop is characterized in that the microwave signal source comprises:
the light source module is used for generating optical carriers;
the broadband signal generating module is used for generating a linear frequency modulation signal or a stepping frequency agility signal as a reference signal injected into the photoelectric oscillation loop;
the photoelectric oscillation loop module comprises an intensity modulation unit, a photoelectric detector, a broadband microwave amplifier, a broadband microwave band-pass filter, a broadband phase delay control unit and a coupler; wherein, the photoelectric oscillation loop works in a multi-mode oscillation state by adjusting the intensity modulation unit;
the broadband phase delay control unit comprises a phase stabilizing module and a delay stabilizing control module, and is used for respectively superposing each discretization frequency component of the linear frequency modulation signal or the stepping frequency agility signal with an oscillation mode of the photoelectric oscillation loop, wherein each mode meets the following amplitude-phase conditions:
gk1 and
wherein, gkGain for the kth mode, ωkIs the angular frequency of the k-th mode,
is that the system has a diagonal frequency of omegakK and N are integers and τ is the total delay in the loop.
8. The microwave signal source of claim 7, wherein the phase stabilization module controls an electrically controlled phase shift unit through a microcontroller feedback, and the electrically controlled phase shift unit includes an electrically controlled phase shifter or a tunable light delay line.
9. The microwave signal source of claim 7, wherein the delay stabilization control module controls the delay stabilization unit via a microcontroller, and the delay stabilization unit comprises a tunable optical delay line or a temperature-controlled optical fiber.
10. The microwave signal source of claim 7, wherein the intensity modulation unit is implemented by a phase modulator and an optical filter.
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