Ultra-low phase noise microwave signal generation method and system based on electro-optical comb

Abstract

The invention discloses an ultra-low phase noise microwave signal generation method and system based on an electro-optical comb. The method comprises the following steps: 1) locking two lasers with continuously tunable wavelengths in the same FP cavity through two links with different modulation frequencies to realize a dual-wavelength laser with a frequency interval of (v2-v1); 2) reducing the electronic noise of each link to a quantum noise limit by using a residual amplitude modulation noise control technology; 3) coupling the lasers with the center frequencies of v1 and v2 into one path, inputting the laser into an electro-optical frequency comb generator, and generating two sets of electro-optical frequency combs with spectrum overlapping; (4) beat frequency signals of the two electro-optical frequency combs are obtained; the beat frequency signal and a reference signal from a reference signal source are accessed to a phase discriminator for phase discrimination; an output signal of the phase discriminator is sent to a proportional-integral-differential control circuit; and 5) controlling the phase noise of the radio frequency source by using the output feedback of the proportional-integral-differential control circuit to obtain an ultra-low phase noise microwave signal.

Description

Technical Field

[0001] The present invention relates to the field of microwave photonics, and in particular to a method and system for generating ultra-low phase noise microwave signals based on an electro-optical comb. The present invention uses an electro-optical comb as a frequency divider to transfer the ultra-low relative phase noise of a high-coherence dual-wavelength laser to a microwave signal. The ultra-low phase noise microwave signal generated by the method is suitable for use in the fields of time measurement, radio astronomy, radar, navigation, etc. Background Art

[0002] Ultra-low phase noise microwaves are widely used in basic scientific research and industrial applications. In basic scientific research, ultra-low phase noise microwaves are expected to replace the local oscillator signal in the current fountain atomic clock system and promote the development of time-frequency science. In the field of industrial applications, the phase noise of microwaves in the Doppler radar system will directly determine the positioning accuracy of the system. Ultra-low phase noise microwaves can meet the detection requirements of the Doppler radar system for "low, slow and small" targets. The microwave signal generated by the traditional purely electrical method is generated by the frequency doubling of the low-frequency crystal oscillator, and the frequency doubling process will inevitably make the phase noise power spectral density worse. The space for lowering the phase noise of the crystal oscillator is very limited, and the challenge of further generating ultra-low phase noise microwave signals by the traditional frequency doubling scheme is very great. With the development of optoelectronic technology, many low-noise photogenerated microwave schemes have been proposed and developed. Common photogenerated microwave schemes include optoelectronic hybrid oscillators and optical frequency division technologies.

[0003] Due to the limitation of 1 / f noise and Leeson effect, the phase noise of near-carrier frequency deviation is usually 1 / f. 3The slope of the signal decreases, so the phase noise at close carrier frequency deviation (1Hz) is often poor [Reference: D. Eliyahu, et al., "Phase noise of a high performance OEO and an ultra-low noise floor cross-correlation microwave photonic homodyne system," in Proceedings of 2002 IEEE International Frequency Control Symposium (2008), pp. 811–814.]. Optical frequency division technology uses an optical frequency comb as a large coefficient divider to divide the low-noise laser into microwaves. The generated microwave signal can have ultra-low phase noise at both close carrier frequency deviation (1Hz) and far carrier frequency deviation (10kHz). The traditional optical frequency division scheme uses a fiber optical frequency comb to divide a single-wavelength laser into microwaves. In 2017, the Paris Observatory in France and the German company Menlo cooperated to achieve a record ultra-low phase noise 12GHz microwave, with single-sideband phase noise better than -107dBc / Hz@1Hz, -173dBc / Hz@10kHz [Reference: Xie, Xiaopeng, et al. "Photonic microwave signals with zeptosecond-level absolute timing noise." Nature Photonics 11.1(2017):44-47.]. However, the traditional optical frequency division scheme requires the optical frequency comb to cover an octave, and requires a highly nonlinear photodetector, and the frequency of the optical frequency comb is not adjustable. The two-point frequency division method based on the electro-optical comb can overcome the above difficulties. In 2014, the California Institute of Technology and the National Institute of Standards and Metrology of the United States cooperated to use the electro-optical comb to divide the dual-wavelength Brillouin laser into microwaves to achieve low phase noise microwaves [reference: J. Li, et al., "Electro-optical frequency division and stable microwave synthesis," Science 345 (2014): 309–313.]. Later, this solution was developed into a product by hQphotonics of the United States. In 2017, it was reported at the International Frequency Control Forum Conference that the 30GHz microwave signal generated by the product had a phase noise of -87dBc / Hz@10Hz and -151dBc / Hz@10kHz. However, due to the limitation of the Brillouin laser, its near-carrier frequency deviation (1Hz) phase noise is poor. Summary of the invention

[0004] The two-point frequency division method based on the electro-optic comb can overcome the limitations of the traditional optical frequency division scheme, but requires a dual-wavelength laser with low relative phase noise. In order to improve the performance of microwaves generated by the two-point frequency division method based on the electro-optic comb, the present invention provides an ultra-low phase noise microwave signal generation method and system based on the electro-optic comb. The present invention uses the Pound-Drever-Hall technology to lock two semiconductor lasers to the same Fabry–Pérot cavity to realize a dual-wavelength laser. The relative phase noise of the dual-wavelength laser is reduced to the quantum noise limit by using the residual amplitude modulation noise control technology. The output laser of the dual-wavelength laser (center frequencies are ν1 and ν2, respectively) is sent to an electro-optic comb generator composed of several phase modulators to obtain two sets of electro-optic combs, and the center frequencies ν1 and ν2 of the dual-wavelength laser are separated by n electro-optic comb teeth (such as n=21). The overlapping comb teeth are filtered out by an optical filter and sent to a fiber photodetector to obtain a difference frequency signal, the frequency of which is the frequency difference of the dual-wavelength laser minus n times the repetition frequency of the electro-optic comb. After detecting the frequency of the difference frequency signal, the reference source frequency is set to be the same as it. The error signal is obtained by phase detection between the difference frequency signal and the reference signal of the same frequency and is fed back to the electro-optic comb driving source to form a phase-locked loop. At this time, the phase noise of the driving source is the relative phase noise of the dual-wavelength laser minus 20*log(n), thus achieving ultra-low phase noise microwave signal generation.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A method for generating an ultra-low phase noise microwave signal based on an electro-optical comb, the steps comprising:

[0007] 1) Two independent wavelength continuously tunable lasers are locked in the same Fabry–Pérot cavity through two Pound–Drever–Hall links with different modulation frequencies to realize a dual-wavelength laser with a frequency interval of (v2-v1). The two links are each driven by a dual-channel RF signal source with a different modulation frequency to drive the phase modulator;

[0008] 2) Use the residual amplitude modulation noise control technique to control the phase modulator to reduce the electronic noise of the two-way Pound-Drever-Hall link to the quantum noise limit;

[0009] 3) Coupling the output of the dual-wavelength laser to an input electro-optical frequency comb generator to generate two sets of electro-optical frequency combs with overlapping spectra, otherwise the difference frequency signal cannot be obtained; wherein the electro-optical frequency comb generator is composed of a frequency of f r Driven by an RF source, the RF driving power of the electro-optic frequency comb generator should be large enough to ensure that the two sets of electro-optic combs can have overlapping comb teeth.

[0010] 4) Using an adjustable optical filter to filter out a pair of electro-optical frequency comb teeth of the overlapping part, and sending the output of the optical filter to a fiber photodetector to obtain a beat frequency signal; where n is the total number of comb teeth between the center wavelengths of the two independent lasers;

[0011] 5) The beat frequency signal output by the optical fiber photoelectric detector and the reference signal from the reference signal source are connected to the phase detector for phase detection; the output signal of the phase detector is sent to the proportional-integral-differential control circuit; the beat frequency signal is theoretically the same as the reference signal, both of which are (ν2-ν1-nf r );

[0012] 6) Feed the output of the proportional-integral-differential control circuit back to the RF source controller of the electro-optical frequency comb generator to implement a phase-locked loop to control the RF source phase noise, and obtain a frequency of f r Ultra-low phase noise microwave signal.

[0013] Furthermore, the operating wavelength of the wavelength continuously tunable laser is around 1550 nm, and the central wavelength of the Fabry–Pérot cavity is also around 1550 nm.

[0014] Furthermore, the optical part of the Pound-Drever-Hall link includes a dual-channel RF signal source, a phase modulator, a collimator, a half-wave plate, a polarization beam splitter prism, a quarter-wave plate, and a spatial light photodetector; the laser generates a pair of sidebands with opposite phases after passing through the phase modulator driven by one output of the dual-channel RF signal source. After the laser passes through the phase modulator, the phase modulator is connected to the collimator, and the optical fiber light through the collimator is converted into free-space light. The polarization state of the free-space light is adjusted to P light through the half-wave plate and input into the polarization beam splitter prism. The light outputted by the polarization beam splitter prism passes through the quarter-wave plate and is incident on the Fabry–Pérot cavity. The reflected light after the light beam is reflected by the Fabry–Pérot cavity will carry the frequency shift information; the reflected light passes through the quarter-wave plate again and becomes S light, which is reflected by the polarization beam splitter prism to the spatial light photodetector for reception.

[0015] Furthermore, the electrical part of the Pound-Drever-Hall link includes a phase detector and a proportional-integral-differential control circuit; the output of the spatial light photodetector carries frequency offset information, and generates an error signal through a phase detector with another output of the dual-channel RF signal source, which is input into the proportional-integral-differential control circuit, and the output of the proportional-integral-differential control circuit is fed back to the laser to achieve locking.

[0016] Furthermore, the performance of the electro-optical frequency comb generator should be such that the two sets of electro-optical frequency comb spectra generated by the dual-wavelength laser have overlapping parts, that is, the single-side bandwidth of the electro-optical frequency comb should reach (v2-v1) / 2; the electro-optical frequency comb generator includes a plurality of cascaded phase modulators, all of which are controlled by an external frequency of f r The plurality of cascaded phase modulators used to form the electro-optical frequency comb generator are used to spread the seed light output by the laser to obtain a multi-tooth electro-optical frequency comb.

[0017] Furthermore, the tunable optical filter should be able to achieve a bandwidth of f r Optical filtering.

[0018] Furthermore, the reference signal having the same frequency as the output signal of the optical fiber photoelectric detector should have the characteristic of low phase noise.

[0019] Furthermore, the phase detector and the proportional-integral-differential circuit should have the characteristic of low additional phase noise.

[0020] An ultra-low phase noise microwave signal generation system based on an electro-optical comb, characterized in that it includes a laser, a dual-channel radio frequency signal source, a phase modulator, a fiber coupler, a collimator, a half-wave plate, a polarization beam splitter prism, a quarter-wave plate, a Fabry–Pérot cavity, a spatial light photodetector, a phase detector, a proportional-integral-differential control circuit, an electro-optical frequency comb generator, a fiber photodetector, a reference signal source, and a radio frequency source; wherein

[0021] The laser is used to generate a seed light source;

[0022] The dual-channel RF signal source has one output for driving a phase modulator and one output for phase discrimination of an optical fiber photoelectric detector output; the modulator is connected to one output of the dual-channel RF signal source and is used to modulate the input seed light source to generate a pair of sidebands with opposite phases; wherein the modulation frequencies of the two links are different;

[0023] The fiber coupler is used to couple the outputs of two lasers; the collimator is used to convert fiber light into free-space light; the collimator, half-wave plate, polarization beam splitter prism, and quarter-wave plate are used to implement the Pound-Drever-Hall technique;

[0024] The electro-optical frequency comb generator is used to convert dual-wavelength lasers into two sets of electro-optical frequency combs; the tunable optical filter is used to filter out the crossed comb teeth; the optical fiber photodetector is used to detect the frequency information of the crossed comb teeth; the reference signal source is used to provide a frequency reference;

[0025] The phase detector and proportional-integral-differential circuit are used for phase detection of two Pound-Drever-Hall links and phase detection of the optical fiber photoelectric detector output and the reference source;

[0026] The output of the radio frequency source is divided into two parts, one part is used as a driving source of the electro-optical frequency comb generator, and the other part is used as an ultra-low phase noise microwave signal output.

[0027] The invention uses the Pound-Drever-Hall technology to lock two semiconductor lasers in the same Fabry-Pérot cavity to realize a dual-wavelength laser; uses the residual amplitude modulation noise control technology to reduce the electronic noise of two Pound-Drever-Hall links to the quantum noise limit; the output of the dual-wavelength laser is passed through an electro-optic comb generator composed of a plurality of phase modulators to obtain two sets of electro-optic combs, and the two sets of electro-optic combs have interleaved parts; uses an optical filter to filter out the beat frequency of one pair of comb teeth and then detects the phase with a reference source, obtains an error signal and then feeds it back to a radio frequency driving source to form a phase-locked loop, thereby realizing phase compression of the radio frequency driving source.

[0028] The beneficial effects of the present invention are:

[0029] The present invention provides a convenient and robust method for generating microwaves with ultra-low phase noise, which is suitable for applications such as time and frequency measurement, radio astronomy, radar, and navigation, and is used to support more accurate, precise, and precise detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The schematic diagram of the dual-wavelength laser based on the Pound-Drever-Hall technology of the present invention;

[0031] Figure 2 This is the relative phase noise test diagram of the dual-wavelength laser, where the Fabry–Pérot cavity with a longitudinal mode spacing of 1.5 GHz is taken as an example;

[0032] Figure 3 It is the principle diagram of the phase-locked loop of the present invention;

[0033] Figure 4 This is a spectrum diagram of the electro-optical comb of the present invention, where a dual-wavelength laser with a spacing of 525 GHz and an electro-optical comb tooth repetition frequency of 25 GHz is taken as an example;

[0034] Figure 5 The phase noise of the microwaves generated by the present invention is shown in FIG. 1 . Here, taking a dual-wavelength laser with a spacing of 525 GHz and an electro-optic comb tooth repetition frequency of 25 GHz as an example, the microwave phase noise is reduced by 26 dB compared with the relative phase noise of the dual-wavelength laser.

[0035] Among them, 1. continuous wave laser, 2. phase modulator, 3. collimator, 4. half-wave plate, 5. polarization beam splitter, 6. quarter-wave plate, 7. Fabry–Pérot cavity, 8. spatial light photodetector, 9. dual-channel RF signal source, 10. phase detector, 11. proportional-integral-differential control circuit, 12. electro-optic comb generator, 13. fiber photodetector, 14. reference signal source, 15. RF source, 16 tunable optical filter. DETAILED DESCRIPTION

[0036] The scheme of the present invention is further described in detail below with reference to the accompanying drawings.

[0037] The dual-wavelength laser scheme of the present invention is as follows Figure 1 As shown. Two lasers 1 with a wavelength of about 1550nm are used as seed light sources. They are respectively driven by a phase modulator 2 driven by a dual-channel RF signal source 9. The frequencies used in the two seed light sources are 36MHz and 51MHz. The outputs of the two phase modulators 2 are coupled, and one part is input to the collimator 3 to become spatial light, and the other part is input to the electro-optical comb generator 12. The spatial light adjusts the polarization state through the half-wave plate 4, completely passes through the polarization beam splitter prism 5, and then enters the Fabry-Pérot cavity 7 through the quarter-wave plate 6. It is reflected by the Fabry-Pérot cavity 7 and carries the frequency offset information. The reflected light passes through the quarter-wave plate 6 again and is incident on the polarization beam splitter prism 5 and is reflected to the spatial light photodetector 8 to obtain 36MHz and 51MHz signals. The output of the spatial light photodetector 8 is divided into two paths and then input to the phase detector 10. The other end of the phase detector 10 is connected to the dual-channel RF signal source 9. The error signal is obtained by phase detection. The error signal is related to the difference between the frequency of the laser 1 and the transmission frequency of the Fabry-Pérot cavity 7. The error signal is sent to the proportional-integral-differential circuit 11, and the proportional-integral-differential circuit 11 outputs a control signal to the laser 1 to implement Pound-Drever-Hall technology locking. After the working wavelength of the laser 1 is adjusted to the vicinity of the transmission frequency of the Fabry-Pérot cavity 7, it is locked to the transmission frequency of the Fabry-Pérot cavity 7, and the frequency value is recorded as v1. Combined with the residual amplitude modulation noise control technology, the relative phase noise of the dual-wavelength laser is reduced to the quantum noise limit, such as Figure 2 The figure shows the relative phase noise of two lasers 1 when they are separated by a mode of a Fabry–Pérot cavity 7. Note that the driving frequency of the dual-channel RF signal source is not limited to the above parameter settings, and can be used as long as Pound-Drever-Hall locking is guaranteed.

[0038] The principle of the phase-locked loop solution of the present invention is as follows Figure 3The electro-optic comb generator 12 is composed of two phase modulators connected in series. The two phase modulators are connected by the same radio frequency f r =25GHz RF signal source 15 drives, the output signal of RF signal source 15 is divided into three paths after passing through the power divider, one path is used for output, and the other two paths drive the phase modulator through the phase shifter and RF amplifier. Therefore, the two lasers will generate two sets of frequency intervals of f through the electro-optic comb generator 12. r = 25 GHz electro-optical frequency comb. Figure 4 The electro-optic frequency comb spectrum is shown. A pair of teeth of the electro-optic frequency comb is fed into the optical fiber photodetector 13 to obtain a beat frequency of (v2-v1-nf r ) signal; wherein n is the total number of comb teeth between the central wavelengths of the two lasers. The signal is sent to the phase detector 10, and the phase detector 10 is also connected to a reference signal source 14 of the same frequency. The phase detector 10 outputs a phase error signal and sends it to the proportional-integral-differential control circuit 11. The proportional-integral-differential control circuit 11 outputs an error signal to control the radio frequency source 15 to achieve phase locking, and obtain an ultra-low phase noise microwave signal with a frequency of 25 GHz. Note that the output frequency of the radio frequency signal source is not limited to the above parameter settings, and it is possible as long as the two sets of electro-optical frequency combs overlap. In addition, the above-mentioned electro-optical comb generator 12 is a cascade modulator type, and the number of its phase modulators is not limited to two. The main function of the phase modulator is to widen the spectrum. More phase modulators can obtain a wider spectrum and achieve a higher frequency division coefficient. The electro-optical comb generator can also use an electro-optical comb generator integrated on a thin-film lithium niobate chip. Figure 5 This is the phase noise diagram of the low-noise microwave signal generated by this method. Here, the dual-wavelength laser interval is 525GHz and the RF signal source driving frequency is 25GHz as an example.

[0039] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. A person skilled in the art may modify or make equivalent substitutions for the technical solutions of the present invention without departing from the spirit and scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A method for generating an ultra-low phase noise microwave signal based on an electro-optical comb, the steps comprising: 1) Locking two wavelength continuously tunable lasers in the same Fabry–Pérot cavity through two Pound-Drever-Hall links with different modulation frequencies to realize a dual-wavelength laser with a frequency interval of (v2-v1); wherein the laser center frequencies output by the dual-wavelength laser are v1 and v2 respectively; 2) Using residual amplitude modulation noise control technology to reduce the electronic noise of each Pound-Drever-Hall link to the quantum noise limit; 3) The lasers with the center frequencies v1 and v2 output by the dual-wavelength laser are coupled as one input to an electro-optical frequency comb generator to generate two sets of electro-optical frequency combs with spectral overlap; wherein the electro-optical frequency comb generator is composed of a frequency of f r RF source drive; 4) using an adjustable optical filter to filter out a pair of electro-optical frequency comb teeth of the overlapping part of the spectrum of the two sets of electro-optical frequency combs and sending them into an optical fiber photodetector to obtain a beat frequency signal; wherein n is the total number of comb teeth between the two laser center frequencies output by the dual-wavelength laser; 5) The beat signal and the reference signal from the reference signal source are connected to the phase detector for phase detection; the output signal of the phase detector is sent to the proportional-integral-differential control circuit; the frequency of the reference signal is (v2-v1-nf r ); 6) Feedback the output of the proportional-integral-differential control circuit to the controller of the radio frequency source to realize phase-locked loop control of the phase noise of the radio frequency source, and obtain a frequency of f r Ultra-low phase noise microwave signal.

2. The method according to claim 1, characterized in that Each of the Pound-Drever-Hall links includes an optical part and an electrical part; The academic part includes a dual-channel radio frequency signal source, a phase modulator, a collimator, a half-wave plate, a polarization beam splitter prism, a quarter-wave plate, and a spatial light photodetector; One end of the phase modulator is connected to the laser through an optical fiber, and is used to receive the seed laser output by the laser. The other end of the phase modulator is connected to one output end of the dual-channel RF signal source, and is used to receive the driving signal of the dual-channel RF signal source to modulate the input seed laser to generate a pair of sidebands with opposite phases and input them into the collimator through the optical fiber coupler. The collimator converts the optical fiber light into free-space light and is incident on the half-wave plate. The half-wave plate adjusts the polarization state of the incident free-space light to P light and inputs it into the polarization beam splitter prism. The light output through the transmission of the polarization beam splitter prism is incident on the Fabry–Pérot cavity through the quarter-wave plate. The reflected light carrying the frequency shift information after being reflected by the Fabry–Pérot cavity passes through the quarter-wave plate, and the polarization state is adjusted to S light, and then reflected to the spatial light photodetector through the polarization beam splitter prism; The electrical part includes a phase detector and a proportional-integral-differential control circuit; the output signal of the spatial light photoelectric detector and the other output signal of the dual-channel radio frequency signal source are respectively input into the phase detector for phase detection to generate an error signal and then input into the proportional-integral-differential control circuit, and the output of the proportional-integral-differential control circuit is fed back to the laser to achieve locking; The dual-channel RF signal sources in the two Pound-Drever-Hall links drive the phase modulators with different modulation frequencies.

3. The method according to claim 1, characterized in that The single-sided bandwidth of the electro-optic frequency comb reaches (v2-v1) / 2.

4. The method according to claim 1, 2 or 3, characterized in that: The electro-optical frequency comb generator includes a plurality of cascaded phase modulators, each of which is driven by an external frequency of f r The RF signal source drives the 5. The method according to claim 1, characterized in that The tunable optical filter can achieve a bandwidth of f r Optical filtering.

6. An ultra-low phase noise microwave signal generation system based on an electro-optical comb, characterized in that: It includes two lasers, two dual-channel RF signal sources, two phase modulators, fiber couplers, collimators, half-wave plates, polarization beam splitters, quarter-wave plates, Fabry–Pérot cavities, spatial light photodetectors, three phase detectors, three proportional-integral-differential control circuits, electro-optical frequency comb generators, tunable optical filters, fiber photodetectors, reference signal sources, and RF sources; in One end of the first phase modulator is connected to the first laser through an optical fiber, and is used to receive the seed laser output by the first laser; the other end of the first phase modulator is connected to one output end of the first dual-channel RF signal source, and is used to receive the driving signal of the first dual-channel RF signal source to modulate the input seed laser to generate a pair of sidebands with opposite phases and input them into the collimator through the optical fiber coupler; One end of the second phase modulator is connected to the second laser through an optical fiber, and is used to receive the seed laser output by the second laser; the other end of the second phase modulator is connected to one output end of the second dual-channel RF signal source, and is used to receive the driving signal of the second dual-channel RF signal source to modulate the input seed laser to generate a pair of sidebands with opposite phases and input them into the collimator through the optical fiber coupler; The collimator converts the fiber light into free-space light and inputs it into the half-wave plate. The half-wave plate adjusts the polarization state of the incident free-space light into P light and inputs it into the polarization beam splitter prism. The light outputted through the polarization beam splitter prism is incident on the Fabry–Pérot cavity through the quarter-wave plate. The reflected light carrying the frequency shift information after being reflected by the Fabry–Pérot cavity passes through the quarter-wave plate, and the polarization state is adjusted to S light, and then reflected to the spatial light photodetector through the polarization beam splitter prism; The first phase detector is used to perform phase detection on the output signal of the spatial light photoelectric detector and the other output signal of the first dual-channel radio frequency signal source to generate an error signal and input the error signal into the first proportional-integral-differential control circuit, and the output of the first proportional-integral-differential control circuit is fed back to the first laser to achieve phase locking; The second phase detector is used to perform phase detection on the output signal of the spatial light photoelectric detector and the other output signal of the second dual-channel radio frequency signal source to generate an error signal and input it into the second proportional-integral-differential control circuit, and the output of the second proportional-integral-differential control circuit is fed back to the second laser to achieve phase locking; The optical fiber coupler is used to couple the first laser and the laser output by the first laser phase-locked to obtain dual-wavelength lasers with laser center frequencies v1 and v2 respectively, and input them into the electro-optical frequency comb generator; The electro-optical frequency comb generator is used to convert the dual-wavelength laser into two sets of electro-optical frequency combs with spectral overlap; The electro-optic frequency comb generator consists of a frequency of f r The radio frequency source driving; The adjustable optical filter is used to filter out a pair of electro-optical frequency comb teeth of the overlapping part of the spectrum of the two sets of electro-optical frequency combs and send them into the optical fiber photoelectric detector to obtain a beat frequency signal; wherein n is the total number of comb teeth between the frequencies v1 and v2; The third phase detector is used to detect the phase of the input beat frequency signal and the reference signal from the reference signal source, and send the output signal to the third proportional-integral-differential control circuit; the frequency of the reference signal is (v2-v1-nf r ); The output feedback of the third proportional-integral-differential control circuit controls the controller of the radio frequency source to implement a phase-locked loop to control the phase noise of the radio frequency source, and obtain a frequency of f r Ultra-low phase noise microwave signal; Among them, the first phase modulator, the first dual-channel radio frequency signal source, the optical fiber coupler, the collimator, the half-wave plate, the polarization beam splitter prism, the quarter-wave plate, the Fabry–Pérot cavity, the spatial light photodetector, the first phase detector, and the first proportional-integral-differential control circuit constitute a first Pound-Drever-Hall link; the second phase modulator, the second dual-channel radio frequency signal source, the optical fiber coupler, the collimator, the half-wave plate, the polarization beam splitter prism, the quarter-wave plate, the Fabry–Pérot cavity, the spatial light photodetector, the second phase detector, and the second proportional-integral-differential control circuit constitute a second Pound-Drever-Hall link; the modulation frequency of the first dual-channel radio frequency signal source driving the first phase modulator is different from the modulation frequency of the second dual-channel radio frequency signal source driving the second phase modulator.

7. The system according to claim 6, characterized in that The single-sided bandwidth of the electro-optic frequency comb reaches (v2-v1) / 2.

8. The system according to claim 6 or 7, characterized in that: The electro-optical frequency comb generator includes a plurality of cascaded phase modulators, each of which is driven by an external frequency of f r The RF signal source drives the 9. The system according to claim 6, characterized in that The tunable optical filter can achieve a bandwidth of f r Optical filtering.

10. The system according to claim 6, characterized in that The residual amplitude modulation noise control technology is used to control the first phase modulator and the second phase modulator to reduce the electronic noise of the two-way Pound-Drever-Hall link to the quantum noise limit.

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