A low-noise microwave generation system and method based on microcavity vernier double comb

Abstract

The application discloses a low-noise microwave generation system and method based on a microcavity vernier double comb, and relates to the technical field of microwaves.The system comprises an optical frequency comb generation unit, a feedforward signal processing unit and a microwave signal output unit.The optical frequency comb generation unit generates first and second optical frequency combs with unequal comb tooth frequency differences through single-frequency pumping light, and obtains first and second double optical combs after the two combs are combined and then split.The feedforward signal processing unit receives the first double optical comb, selects two comb tooth pairs in an asymmetric mode based on a vernier effect, performs beat and mixing, and obtains a reference microwave signal.The microwave signal output unit receives the second double optical comb, filters comb tooth pairs at a target mode, performs photoelectric conversion, and obtains a target microwave signal.The microwave signal output unit further performs feedforward mixing on the target and reference microwave signals, and outputs a low-noise microwave signal after noise cancellation.The application not only solves the problems of large size, high power consumption and high dependence on an ultra-stable cavity of the existing system, but also solves the problems of low spectral purity and poor system robustness of the existing system.

Description

Technical Field

[0001] This invention relates to the field of microwave technology, and in particular to a low-noise microwave generation system and method based on a microcavity vernier dual comb. Background Technology

[0002] With the rapid development of cutting-edge fields such as cold atom interferometry, radar navigation, radio astronomy, and superconducting quantum computing, precision measurement technology has placed extremely stringent requirements on the phase noise, frequency stability, volumetric power consumption, and system integration of microwave sources. Traditional microwave sources are mainly based on electronic oscillators, such as electrical resonant cavities and phase-locked loop frequency synthesizers. Their performance is limited by the inherent noise floor of electronic devices, and their phase noise is difficult to meet the requirements of ultra-low noise measurement. At the same time, such systems usually rely on a large number of discrete components, resulting in complex structures, large sizes, high power consumption, and weak anti-interference capabilities, making it difficult to adapt to the trend of precision measurement systems towards miniaturization, low power consumption, and portability. Therefore, there is an urgent need to develop an integrable, low-noise, highly stable microwave source with frequency hopping capability.

[0003] To overcome the aforementioned "electronic bottleneck," microwave photonics technology has emerged and become a research hotspot. This method leverages the extremely high frequency stability of optical frequency references to transfer the excellent coherence of the optical frequency domain to the microwave frequency band, thereby effectively circumventing the inherent limitations of electronic oscillators in generating high-frequency, low-noise signals. Among numerous optically generated microwave schemes, optical frequency division (OFD) technology based on ultrastable lasers and optical frequency combs stands out. The core of this technology lies in utilizing the frequency chain synthesis process to efficiently transfer the high frequency stability and low phase noise characteristics of high-frequency optical reference sources to the microwave frequency band, thereby obtaining high-quality microwave signals.

[0004] However, traditional optical frequency division systems still face many challenges, such as large system size, high power consumption, and susceptibility to phase jumps or even loss of lock due to environmental disturbances, which seriously reduces the robustness of the system; the closed-loop feedback mechanism based on servo-locked loops introduces additional "servo bumps" at the edge frequencies of the locked bandwidth, affecting the spectral purity. Summary of the Invention

[0005] This invention provides a low-noise microwave generation system and method based on a microcavity vernier dual comb, which not only solves the problems of large size, high power consumption and high dependence on ultra-stable cavities in existing microwave generation systems, but also solves the problems of low spectral purity and poor system robustness caused by the closed-loop feedback mechanism of existing systems.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a low-noise microwave generation system based on a microcavity vernier dual comb, the system comprising an optical frequency comb generation unit, a feedforward signal processing unit, and a microwave signal output unit. The optical frequency comb generating unit is used to generate a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth by using the same single-frequency pump light, and then combine the first optical frequency comb and the second optical frequency comb and split them to obtain a first dual optical comb and a second dual optical comb. The feedforward signal processing unit is used to receive the first dual optical comb, and select two comb tooth pairs of asymmetric mode based on the vernier effect to perform beat frequency and mixing, and output a reference microwave signal carrying the system noise characteristics. The microwave signal output unit is used to receive the second dual optical comb, filter out the comb tooth pairs at the target mode for photoelectric conversion, and output the target microwave signal; the target mode corresponds to the linear superposition position of the vernier frequencies of the two comb tooth pairs of the selected asymmetric mode; The microwave signal output unit is also used to receive the reference microwave signal, and to perform feedforward mixing on the target microwave signal and the reference microwave signal to output a low-noise microwave signal after noise cancellation.

[0007] In one possible implementation, the optical frequency comb generating unit includes a pump source, a first optical microcavity, a second optical microcavity, a beam combiner, and a first beam splitter. The pump light source is used to generate single-frequency pump light and to divide the single-frequency pump light into a first pump light and a second pump light. The first pump light is coupled into the first optical microcavity to generate a first optical frequency comb, and the second pump light is coupled into the second optical microcavity to generate a second optical frequency comb. The first optical frequency comb and the second optical frequency comb are combined by the beam combiner, and then split into a first dual optical comb and a second dual optical comb by the first beam splitter.

[0008] In one possible implementation, the two comb pairs of the asymmetric mode include a comb pair at the m-th mode and a comb pair at the n-th mode, where m and n are non-zero integers and |m|≠|n|; the feedforward signal processing unit includes a second beam splitter, a first bandpass filter, a first photodetector, a second bandpass filter, a second photodetector, and a first mixer; The second beam splitter is used to split the first dual optical comb into a first optical signal and a second optical signal; The first bandpass filter is connected in series with the first photodetector, and the first optical signal is filtered out by the first bandpass filter to extract the comb pair at the m-th mode. The first photodetector is used to generate the first beat frequency electrical signal. The second bandpass filter is connected in series with the second photodetector, and the second optical signal is filtered out by the second bandpass filter to remove the comb pair at the nth mode. The second photodetector is used to generate the second beat frequency electrical signal. The first mixer is used to mix the first beat frequency electrical signal and the second beat frequency electrical signal, and output a reference microwave signal carrying the system noise characteristics.

[0009] In one possible implementation, the comb tooth pair at the target mode is the comb tooth pair at the (n-m)th mode.

[0010] In one possible implementation, the feedforward signal processing unit further includes a frequency divider connected to the first mixer.

[0011] In one possible implementation, the division coefficient of the frequency divider is |n-m|, and the comb tooth pair at the target mode is the comb tooth pair at the +1 mode or the comb tooth pair at the -1 mode.

[0012] In one possible implementation, the microwave signal output unit includes a third bandpass filter, a third photodetector, and a second mixer connected in series. The third bandpass filter is used to receive the second dual optical comb and filter out the comb tooth pairs at the target mode. The third photodetector is used to convert the photoelectric signal of the comb teeth at the target pattern into a target microwave signal. The second mixer is used to perform feedforward mixing on the received reference microwave signal and the target microwave signal, and output a low-noise microwave signal after noise cancellation.

[0013] In one possible implementation, the first optical microcavity and the second optical microcavity have different physical ring lengths, so that the first optical microcavity and the second optical microcavity have different free spectral ranges.

[0014] In one possible implementation, the pump source includes a pump laser and an optical splitter connected in sequence; the pump laser is used to generate single-frequency pump light, and the optical splitter is used to uniformly divide the single-frequency pump light into a first pump light and a second pump light.

[0015] Secondly, the present invention provides a low-noise microwave generation method based on a microcavity vernier dual-comb, wherein the method generates microwave signals using the low-noise microwave generation system based on a microcavity vernier dual-comb as described in any one of the above claims, and the method includes: The optical frequency comb generating unit generates a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth by using the same single-frequency pump light. The first optical frequency comb and the second optical frequency comb are combined and then split to obtain a first dual optical comb and a second dual optical comb. The feedforward signal processing unit receives the first dual optical comb and selects two comb pairs of asymmetric mode based on the vernier effect to perform beat frequency and mixing, and outputs a reference microwave signal carrying the system noise characteristics. The microwave signal output unit receives the second dual optical comb, filters out the comb teeth at the target mode for photoelectric conversion, outputs the target microwave signal, and then performs feedforward mixing on the received reference microwave signal and outputs a low-noise microwave signal after noise cancellation.

[0016] In practical applications, the low-noise microwave generation system and method based on a microcavity vernier dual comb provided in this invention involves an optical frequency comb generation unit generating a first optical frequency comb and a second optical frequency comb with unequal frequency differences between their comb teeth. After beam combining and then beam splitting, the two combs are output as a first dual optical comb and a second dual optical comb. A feedforward signal processing unit receives the first dual optical comb and, based on the vernier effect, selects two comb tooth pairs of an asymmetric mode for beat frequency and mixing processing, outputting a reference microwave signal carrying the system noise characteristics. A microwave signal output unit receives the second dual optical comb, extracts the comb tooth pairs at the target mode, performs photoelectric conversion to obtain a target microwave signal, and then feedforward mixes the target microwave signal with the reference microwave signal to cancel noise, resulting in a low-noise microwave signal. This invention utilizes an optical frequency comb generation unit, a feedforward signal processing unit, and a microwave signal output unit to construct a microcavity vernier dual-comb open-loop feedforward system architecture without active feedback. This not only eliminates the system's dependence on ultra-stable optical cavities and complex closed-loop servo-locked electrical links, avoiding the "servo bump" caused by closed-loop feedback mechanisms, but also significantly improves the spectral purity of the output microwave signal, reduces system size, power consumption, and system complexity, and enhances the system's resistance to environmental interference and robustness. Furthermore, it can flexibly suppress noise in stages, outputting high-quality, low-noise microwave signals. Attached Figure Description

[0017] Figure 1 This is an overall system block diagram of a low-noise microwave generation system based on a microcavity vernier dual comb according to the present invention; Figure 2 This is a schematic diagram of a low-noise microwave generation system based on a microcavity vernier dual comb, provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the feedforward noise compensation principle of a low-noise microwave generation system based on a microcavity vernier dual-comb, provided in Embodiment 1 of the present invention. Figure 4This is a schematic diagram of a low-noise microwave generation system based on a microcavity vernier dual comb, provided in Embodiment 2 of the present invention. Figure 5 This is a schematic diagram illustrating the principle of vernier dual-comb frequency division feedforward noise compensation in a low-noise microwave generation system based on a microcavity vernier dual-comb, as provided in Embodiment 2 of the present invention. Figure 6 This is a flowchart illustrating the overall steps of a low-noise microwave generation method based on a microcavity vernier dual comb according to the present invention.

[0018] Figure labels and descriptions: 1. Optical frequency comb generation unit; 11. Pump light source; 12. First optical microcavity; 13. Second optical microcavity; 14. Beam combiner; 15. First beam splitter; 2. Feedforward signal processing unit; 21. Second beam splitter; 22. First bandpass filter; 23. First photodetector; 24. Second bandpass filter; 25. Second photodetector; 26. First mixer; 27. Frequency divider; 3. Microwave signal output unit; 31. Third bandpass filter; 32. Third photodetector; 33. Second mixer. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0021] To address the problems of large size, high power consumption, and high dependence on ultra-stable cavities in existing microwave generation systems, as well as the problems of low spectral purity and poor system robustness caused by the closed-loop feedback mechanism of existing systems, this invention provides a low-noise microwave generation system and method based on a microcavity vernier dual comb.

[0022] like Figure 1As shown, in a first aspect, embodiments of the present invention provide a low-noise microwave generation system based on a microcavity vernier dual comb, the system comprising an optical frequency comb generation unit 1, a feedforward signal processing unit 2, and a microwave signal output unit 3.

[0023] Specifically, the optical frequency comb generating unit 1 has two optical signal output terminals, and the microwave signal output unit 3 has an optical signal input terminal and an electrical signal input terminal. The first optical signal output terminal of the optical frequency comb generating unit 1 is optically coupled to the input terminal of the feedforward signal processing unit 2, and the second optical signal output terminal of the optical frequency comb generating unit 1 is optically coupled to the optical signal input terminal of the microwave signal output unit 3. At the same time, the output terminal of the feedforward signal processing unit 2 is connected to the electrical signal input terminal of the microwave signal output unit 3, thus constructing an open-loop feedforward system architecture for generating low-noise microwave signals.

[0024] like Figure 2 , Figure 3 As shown, the optical frequency comb generating unit 1 is used to generate a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth by using the same single-frequency pump light, and then combine the first optical frequency comb and the second optical frequency comb and split them to obtain a first dual optical comb and a second dual optical comb.

[0025] The first dual optical comb is input to the input terminal of the feedforward signal processing unit 2 through the first optical signal output terminal of the optical frequency comb generation unit 1; the second dual optical comb is input to the optical signal input terminal of the microwave signal output unit 3 through the second optical signal output terminal of the optical frequency comb generation unit 1.

[0026] The feedforward signal processing unit 2 is used to receive the first dual optical comb, and select two comb pairs of asymmetric modes based on the vernier effect to perform beat frequency and mixing, and output a reference microwave signal carrying the system noise characteristics.

[0027] The reference microwave signal is input to the electrical signal input terminal of the microwave signal output unit 3 through the output terminal of the feedforward signal processing unit 2.

[0028] The selection of two comb pairs with asymmetric patterns is to avoid generating a zero-frequency signal with DC after beat frequency detection of comb pairs with the same pattern.

[0029] System noise includes common-mode repetition rate noise and non-common-mode ASE-independent noise.

[0030] The microwave signal output unit 3 receives the second dual optical comb through the optical signal input terminal, filters out the comb tooth pairs at the target mode, performs photoelectric conversion, and outputs the target microwave signal.

[0031] The microwave signal output unit 3 receives the reference microwave signal through the electrical signal input terminal, performs feedforward mixing on the target microwave signal and the reference microwave signal, and outputs a low-noise microwave signal after the noise is canceled out.

[0032] like Figure 3 As shown, the target mode corresponds to the linear superposition position of the two comb teeth of the selected asymmetric mode relative to the vernier frequency, so that the reference microwave signal and the target microwave signal contain the same common-mode repetition frequency noise. During the mixing process, the reference microwave signal and the target microwave signal are subjected to difference frequency subtraction, and the common-mode repetition frequency noise in the two signals is completely canceled out. Finally, a low-noise microwave signal is output at the output terminal of the microwave signal output unit 3.

[0033] like Figure 2 , Figure 3 As shown, optionally, the optical frequency comb generating unit 1 includes a pump light source 11, a first optical microcavity 12, a second optical microcavity 13, a beam combiner 14, and a first beam splitter 15.

[0034] The pump light source 11 is used to generate single-frequency pump light and to divide the single-frequency pump light into a first pump light and a second pump light.

[0035] Specifically, the pump light source 11 includes a pump laser and an optical splitter connected in sequence.

[0036] The pump laser is used to generate single-frequency pump light, and the optical splitter is used to evenly divide the single-frequency pump light into a first pump light and a second pump light.

[0037] In this embodiment, the pump laser outputs a single-frequency narrow-linewidth pump light, and the optical splitter is a 1×2 optical splitter used to split the single-frequency narrow-linewidth pump light into two paths.

[0038] The first pump light is coupled into the first optical microcavity 12 to generate the first optical frequency comb, and the second pump light is coupled into the second optical microcavity 13 to generate the second optical frequency comb.

[0039] The first optical microcavity 12 and the second optical microcavity 13 have different physical ring lengths, so that the first optical microcavity 12 and the second optical microcavity 13 have different free spectral ranges. This allows the first optical microcavity 12 and the second optical microcavity 13 to generate inter-tooth frequency differences (repetition frequencies) under the same pump source excitation. f r1 The first optical frequency comb, and the frequency difference (repetition frequency) between the comb teeth are: f r2 The second optical frequency comb, and f r1 ≠f r2 .

[0040] The first optical frequency comb and the second optical frequency comb are combined by the beam combiner 14, and then split by the first beam splitter 15 into the first dual optical comb and the second dual optical comb.

[0041] The input end of the first beam splitter 15 is connected to the output end of the beam combiner 14. The first output end of the first beam splitter 15 is connected to the input end of the feedforward signal processing unit 2 for transmitting the first dual optical comb. The second output end of the first beam splitter 15 is connected to the optical signal input end of the microwave signal output unit 3 for transmitting the second dual optical comb.

[0042] Optionally, the microwave signal output unit 3 includes a third bandpass filter 31, a third photodetector 32, and a second mixer 33 connected in series.

[0043] The input of the third bandpass filter 31 is connected to the second output of the first beam splitter 15, and is used to receive the second dual optical comb and filter out the comb tooth pairs at the target mode.

[0044] The input terminal of the third photodetector 32 is connected to the output terminal of the third bandpass filter 31, and is used to convert the photoelectric signal of the comb pair at the target mode into the target microwave signal.

[0045] The two input terminals of the second mixer 33 are connected to the output terminal of the third photodetector 32 and the output terminal of the feedforward signal processing unit 2, respectively, and are used to perform feedforward mixing on the received reference microwave signal and the target microwave signal, and output a low-noise microwave signal after the noise is canceled out.

[0046] Optionally, the two comb pairs in the asymmetric mode include the comb pair at the m-th mode and the comb pair at the n-th mode, where m and n are non-zero integers and |m|≠|n|, thereby avoiding the generation of a zero-frequency signal with DC after the beat frequency detection of comb pairs of the same mode.

[0047] The feedforward signal processing unit 2 includes a second beam splitter 21, a first bandpass filter 22, a first photodetector 23, a second bandpass filter 24, a second photodetector 25, and a first mixer 26.

[0048] The input of the second beam splitter 21 is connected to the first output of the first beam splitter 15, and the two outputs of the second beam splitter 21 are connected to the inputs of the first bandpass filter 22 and the second bandpass filter 24, respectively, for splitting the first dual optical comb into a first optical signal and a second optical signal.

[0049] The first bandpass filter 22 is connected in series with the first photodetector 23, and the first optical signal is filtered out by the first bandpass filter 22 to obtain the comb pair at the m-th mode. The first photodetector 23 is used to generate the first beat frequency electrical signal.

[0050] The second bandpass filter 24 is connected in series with the second photodetector 25, and the second optical signal is filtered out by the second bandpass filter 24 to obtain the comb pair at the nth mode. The second photodetector 25 is used to generate the second beat frequency electrical signal.

[0051] The two input terminals of the first mixer 26 are connected to the output terminals of the first photodetector 23 and the second photodetector 25, respectively. The output terminal of the first mixer 26 is connected to the second input terminal of the second mixer 33. The mixer 26 is used to mix the first beat frequency electrical signal and the second beat frequency electrical signal, and input the generated reference microwave signal carrying the system noise characteristics to the electrical signal input terminal of the microwave signal output unit 3.

[0052] The comb tooth pair at the target pattern is the comb tooth pair at the (n-m)th pattern.

[0053] like Figure 4 , Figure 5 As shown, in order to further suppress non-common-mode noise, the feedforward signal processing unit 2 also includes a frequency divider 27, which is connected to the first mixer 26.

[0054] The division coefficient N of the frequency divider 27 is set to |n-m|, and the comb tooth pair at the target mode is the comb tooth pair at the +1 mode or the comb tooth pair at the -1 mode.

[0055] In practical applications, the low-noise microwave generation system and method based on a microcavity vernier dual comb provided in this invention involves an optical frequency comb generation unit generating a first optical frequency comb and a second optical frequency comb with unequal frequency differences between their comb teeth. After beam combining and then beam splitting, the two combs are output as a first dual optical comb and a second dual optical comb. A feedforward signal processing unit receives the first dual optical comb and, based on the vernier effect, selects two comb tooth pairs of an asymmetric mode for beat frequency and mixing processing, outputting a reference microwave signal carrying the system noise characteristics. A microwave signal output unit receives the second dual optical comb, extracts the comb tooth pairs at the target mode, performs photoelectric conversion to obtain a target microwave signal, and then feedforward mixes the target microwave signal with the reference microwave signal to cancel noise, resulting in a low-noise microwave signal.

[0056] This invention utilizes an optical frequency comb generation unit, a feedforward signal processing unit, and a microwave signal output unit to construct a microcavity vernier dual-comb open-loop feedforward system architecture without active feedback. This not only eliminates the system's dependence on ultra-stable optical cavities and complex closed-loop servo-locked electrical links, avoiding the "servo bump" caused by closed-loop feedback mechanisms, but also significantly improves the spectral purity of the output microwave signal, reduces system size, power consumption, and system complexity, and enhances the system's resistance to environmental interference and robustness. Furthermore, it can flexibly suppress noise in stages, outputting high-quality, low-noise microwave signals.

[0057] Example 1 like Figure 2 , Figure 3 As shown, in the optical frequency comb generation unit of the low-noise microwave generation system based on a microcavity vernier dual comb provided in Embodiment 1, the pump laser outputs a single-frequency narrow-linewidth pump light, which is split into a first pump light and a second pump light by a 1×2 optical splitter. The first pump light is coupled to the optical input end of the first optical microcavity 12, and the second pump light is coupled to the optical input end of the second optical microcavity 13.

[0058] Because the first optical microcavity 12 and the second optical microcavity 13 have different physical ring lengths, their free spectral ranges (FSRs) are different. Therefore, under the excitation of the same pump source, the first optical microcavity 12 and the second optical microcavity 13 generate a comb-tooth frequency difference of [value missing]. f r1 The first optical frequency comb, and the frequency difference between the comb teeth are f r2 The second optical frequency comb, and f r1 ≠f r2 .

[0059] After the first optical frequency comb and the second optical frequency comb are combined by the beam combiner 14, they are split into two paths by the first beam splitter 15: the first dual optical comb and the second dual optical comb. The first dual optical comb is connected to the input terminal of the feedforward signal processing unit 2, and the second dual optical comb is connected to the optical signal input terminal of the microwave signal output unit 3.

[0060] In the feedforward signal processing unit 2, the received first dual optical comb is split into a first optical signal and a second optical signal by the second beam splitter 21.

[0061] The first optical signal is input to the first bandpass filter 22. The first bandpass filter 22 is configured to filter out the comb pair at the m-th mode distance from the center pump mode in the spectrum. The comb pair is detected by the first photodetector 23 and converted into the first beat frequency electrical signal.

[0062] The second optical signal is input to the second bandpass filter 24. The second bandpass filter 24 is configured to filter out the comb pair at the nth mode distance from the center pump mode in the spectrum. The comb pair is detected by the second photodetector 25 and converted into a second beat frequency electrical signal.

[0063] Among them, the m-th mode and the n-th mode satisfy the condition that their absolute values ​​are not equal, that is, |m|≠|n|, and m, n≠0, thereby avoiding the generation of a zero-frequency signal with DC after the comb teeth of the same mode generate beat frequency detection.

[0064] The output terminal of the first photodetector 23 is electrically connected to the first input terminal of the first mixer 26, and the output terminal of the second photodetector 25 is electrically connected to the second input terminal of the first mixer 26. The first mixer 26 is configured to mix the first beat frequency electrical signal and the second beat frequency electrical signal to output a reference microwave signal, and the output terminal of the first mixer 26 is directly used as the output terminal of the feedforward signal processing unit 2 and electrically connected to the electrical signal input terminal of the microwave signal output unit 3.

[0065] In the microwave signal output unit 3, the second dual optical comb split by the first beam splitter 15 is filtered by the third bandpass filter 31 to extract the nth optical signal on the spectrum. The comb teeth at the m) mode are then converted into target microwave signals after being detected by the third photodetector 32.

[0066] The output of the third photodetector 32 is connected to the first input of the second mixer 33, while the second input of the second mixer 33 receives the reference microwave signal from the feedforward signal processing unit 2. The second mixer 33 performs feedforward mixing on the target microwave signal and the reference microwave signal, outputting a low-noise microwave signal.

[0067] like Figure 3 As shown in the figure, the solid line represents the first optical frequency comb (Comb 1), the dashed line represents the second optical frequency comb (Comb 2), the two circled positions at the bottom of the figure represent the comb tooth pairs at the selected m-th and n-th modes, respectively, and the circled position at the top of the figure represents the comb tooth pairs at the n-m-th mode.

[0068] Due to the characteristics of the same pump drive, the first beat frequency electrical signal at the m-th mode includes not only the frequency difference between optical combs, but also... In addition, it also includes the system common-mode repetition rate noise term. m(δf r1 +δf r2 ) and non-common-mode independent noise terms caused by spontaneous emission (ASE), etc. δf diffm Similarly, the second beat frequency electrical signal at the nth mode includes the frequency difference between optical combs. In addition, it also includes the system common-mode repetition rate noise term. n(δf r1 +δf r2 ) and non-common-mode independent noise terms caused by spontaneous emission (ASE), etc. δf diffn Therefore, after the first and second beat frequency electrical signals are input into the first mixer 26, the output reference microwave signal... f refThe frequency and noise components can be analyzed as follows: ; in, and These are the optical beat frequencies at the nth and mth modes, respectively, obtained using the vernier effect beat frequency.

[0069] The center frequency of the third bandpass filter 31 is configured to filter the (n)th bandpass filter in the spectrum. The comb pairs at the m) mode are filtered out and input to the third photodetector 32 to be converted into target microwave signals. f target Target microwave signal f target The frequency and noise terms can be analyzed as follows: ; from Figure 3 It can be clearly seen in the spectrum that the (n)th The m) mode corresponds to the linear superposition of the vernier frequencies of the m-th and n-th modes. Therefore, both the reference microwave signal and the target microwave signal contain the same common-mode repetition rate noise term. .

[0070] When the second mixer 33 performs difference frequency subtraction on the reference microwave signal and the target microwave signal, the common-mode repetition frequency noise term... The noise is completely canceled out, and the output of the second mixer 33 outputs a low-noise microwave signal after canceling the common-mode repetition frequency noise.

[0071] In other words, the residual noise in the final low-noise microwave signal output in Example 1 is only affected by the non-common-mode ASE independent noise, i.e. .

[0072] Embodiment 1 of the present invention utilizes the open-loop feedforward structure of the vernier double comb to successfully get rid of the dependence on the ultra-stable cavity locking loop, and eliminate the "servo bump" noise and loss of lock risk generated by the traditional closed-loop locking.

[0073] Example 2 like Figure 4 , Figure 5 As shown, unlike Example 1, Example 2 optimizes the configuration of the feedforward signal processing unit 2 and the microwave signal output unit 3 based on Example 1 in order to further suppress non-common-mode noise.

[0074] The output of the first mixer 26 is no longer directly connected to the electrical signal input of the microwave signal output unit 3, but is connected to the electrical signal input of the microwave signal output unit 3 through the frequency divider 27.

[0075] Frequency divider 27 is configured to divide the received reference microwave signal by a factor of N, where the division factor N is limited to... The output of the frequency divider 27 serves as the final output of the feedforward signal processing unit 2 and is connected to the second input of the second mixer 33 in the third bandpass filter 31.

[0076] Since the reference microwave signal has been reduced to the fundamental frequency after frequency division, the third bandpass filter 31 no longer filters the nth (nth) bandpass signal. Instead of filtering the comb pairs at the m) mode, it is configured to filter the comb pairs at the ±1 mode.

[0077] The noise characteristics of the mixed signal output from the first mixer 26 change significantly after being divided by the frequency divider 27. Therefore, the frequency and noise terms of the reference microwave signal entering the second mixer 33 can be expressed as follows: ; In other words, after frequency division by frequency divider 27, the non-common-mode independent noise term of the first dual optical comb δf diffm The non-common-mode independent noise term of the second dual optical comb δf diffn The common-mode repetition rate noise of both optical combs is reduced by a factor of N, and due to the N-fold division, the common-mode repetition rate noise is reduced to the same level as the common-mode repetition rate noise at the first-order fundamental frequency. Therefore, in Embodiment 2 of the present invention, the third bandpass filter 31 is configured to filter out the comb pairs at the ±1st mode. After conversion by the third photodetector 32, the noise term of the target microwave signal can be expressed as: ; in, The beat frequency signal of the comb tooth pair at mode ±1. This is the non-common-mode independent noise term at the ±1 mode caused by spontaneous emission (ASE) and other factors.

[0078] When the frequency-divided reference microwave signal and the first-order fundamental target microwave signal are mixed in the second mixer 33, the common-mode repetition rate noise term with a coefficient of 1 in both signals is... It is precisely canceled again, and the total amount of residual non-common-mode noise becomes: ； Compared with Example 1, Example 2 of the present invention significantly weakens the originally difficult-to-eliminate ASE independent noise to 1 / N of the previous level by introducing N times frequency division. Therefore, Example 2 can output microwave signals with higher spectral purity and lower phase noise. Moreover, the noise suppression effect of this scheme is enhanced as the selected mode interval N of m and n increases.

[0079] Compared with traditional optical frequency division techniques based on ultra-stable optical resonators and closed-loop servo locking, the low-noise microwave generation system based on microcavity vernier dual combs of this invention creatively proposes an open-loop feedforward system architecture for generating low-noise microwave signals. By driving with the same pump, the phase noise of the two optical combs is cleverly correlated in common mode. Through the feedforward signal processing unit in Embodiment 1, common-mode repetition frequency noise is accurately subtracted and canceled directly using the electrical difference frequency characteristics of the first mixer and the second mixer without any feedback closed-loop circuit. Furthermore, in Embodiment 2, an N-fold frequency division is introduced, which greatly amplifies the ability of the feedforward signal processing unit to suppress non-common-mode independent noise such as ASE.

[0080] The low-noise microwave generation system based on a microcavity vernier dual comb of the present invention eliminates the need for a cross-octave optical comb, an ultra-stable FP cavity, and a complex servo feedback link, allowing its size to be reduced to the chip level. It not only effectively avoids the risk of lock-up and servo sidelobes but also replaces closed-loop feedback with open-loop feedforward, resulting in extremely low electrical added noise for the entire system. Furthermore, the mode selection logic of Embodiments 1 and 2 is flexible and versatile; simply adjusting the center frequency of the bandpass filter allows for easy switching between different frequencies of low-noise microwave signal output.

[0081] This invention significantly improves the system's integration, environmental adaptability, output noise performance, and system robustness.

[0082] like Figure 6 As shown, in a second aspect, embodiments of the present invention also provide a low-noise microwave generation method based on a microcavity vernier dual-comb. This method utilizes any of the aforementioned low-noise microwave generation systems based on a microcavity vernier dual-comb to generate microwave signals. The method specifically includes the following steps: Step 401: The optical frequency comb generating unit generates a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth through the same single-frequency pump light, and then combines the first optical frequency comb and the second optical frequency comb and splits the beam to obtain a first dual optical comb and a second dual optical comb.

[0083] Step 402: The feedforward signal processing unit receives the first dual optical comb, selects two comb pairs of asymmetric modes based on the vernier effect, performs beat frequency and mixing, and outputs a reference microwave signal carrying the system noise characteristics.

[0084] Step 403: The microwave signal output unit receives the second dual optical comb, filters out the comb teeth at the target mode for photoelectric conversion, outputs the target microwave signal, and then performs feedforward mixing on the received reference microwave signal and outputs a low-noise microwave signal after noise cancellation.

[0085] The low-noise microwave generation method based on microcavity vernier dual comb provided in this embodiment of the invention generates microwave signals using the aforementioned low-noise microwave generation system based on microcavity vernier dual comb, thus achieving the same technical effect as the aforementioned low-noise microwave generation system based on microcavity vernier dual comb.

[0086] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working process of the method described above can be referred to the corresponding process in the aforementioned system embodiments, and will not be repeated here.

[0087] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-noise microwave generation system based on a microcavity vernier dual-comb, characterized in that, It includes an optical frequency comb generation unit, a feedforward signal processing unit, and a microwave signal output unit; The optical frequency comb generating unit is used to generate a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth by using the same single-frequency pump light, and then combine the first optical frequency comb and the second optical frequency comb and split them to obtain a first dual optical comb and a second dual optical comb. The feedforward signal processing unit is used to receive the first dual optical comb, and select two comb tooth pairs of asymmetric mode based on the vernier effect to perform beat frequency and mixing, and output a reference microwave signal carrying the system noise characteristics. The microwave signal output unit is used to receive the second dual optical comb, filter out the comb tooth pairs at the target mode for photoelectric conversion, and output the target microwave signal; the target mode corresponds to the linear superposition position of the vernier frequencies of the two comb tooth pairs of the selected asymmetric mode; The microwave signal output unit is also used to receive the reference microwave signal, and to perform feedforward mixing on the target microwave signal and the reference microwave signal to output a low-noise microwave signal after noise cancellation.

2. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 1, characterized in that, The optical frequency comb generating unit includes a pump light source, a first optical microcavity, a second optical microcavity, a beam combiner, and a first beam splitter. The pump light source is used to generate single-frequency pump light and to divide the single-frequency pump light into a first pump light and a second pump light. The first pump light is coupled into the first optical microcavity to generate a first optical frequency comb, and the second pump light is coupled into the second optical microcavity to generate a second optical frequency comb. The first optical frequency comb and the second optical frequency comb are combined by the beam combiner, and then split into a first dual optical comb and a second dual optical comb by the first beam splitter.

3. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 1, characterized in that, The two comb pairs of the asymmetric mode include the comb pair at the m-th mode and the comb pair at the n-th mode, where m and n are non-zero integers and |m|≠|n|; the feedforward signal processing unit includes a second beam splitter, a first bandpass filter, a first photodetector, a second bandpass filter, a second photodetector, and a first mixer; The second beam splitter is used to split the first dual optical comb into a first optical signal and a second optical signal; The first bandpass filter is connected in series with the first photodetector, and the first optical signal is filtered out by the first bandpass filter to extract the comb pair at the m-th mode. The first photodetector is used to generate the first beat frequency electrical signal. The second bandpass filter is connected in series with the second photodetector, and the second optical signal is filtered out by the second bandpass filter to remove the comb pair at the nth mode. The second photodetector is used to generate the second beat frequency electrical signal. The first mixer is used to mix the first beat frequency electrical signal and the second beat frequency electrical signal, and output a reference microwave signal carrying the system noise characteristics.

4. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 3, characterized in that, The comb tooth pair at the target pattern is the comb tooth pair at the (n-m)th pattern.

5. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 3, characterized in that, The feedforward signal processing unit further includes a frequency divider, which is connected to the first mixer.

6. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 5, characterized in that, The division coefficient of the frequency divider is |n-m|, and the comb tooth pair at the target mode is the comb tooth pair at the +1 mode or the comb tooth pair at the -1 mode.

7. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 1, characterized in that, The microwave signal output unit includes a third bandpass filter, a third photodetector, and a second mixer connected in series. The third bandpass filter is used to receive the second dual optical comb and filter out the comb tooth pairs at the target mode. The third photodetector is used to convert the photoelectric signal of the comb teeth at the target pattern into a target microwave signal. The second mixer is used to perform feedforward mixing on the received reference microwave signal and the target microwave signal, and output a low-noise microwave signal after noise cancellation.

8. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 2, characterized in that, The first optical microcavity and the second optical microcavity have different physical ring lengths so that the first optical microcavity and the second optical microcavity have different free spectral ranges.

9. The low-noise microwave generation system based on a microcavity vernier dual comb according to claim 2, characterized in that, The pump light source includes a pump laser and an optical splitter connected in sequence; the pump laser is used to generate single-frequency pump light, and the optical splitter is used to uniformly divide the single-frequency pump light into a first pump light and a second pump light.

10. A low-noise microwave generation method based on a microcavity vernier dual-comb, characterized in that, The method for generating microwave signals using the low-noise microwave generation system based on a microcavity vernier dual comb according to any one of claims 1 to 9 includes: The optical frequency comb generating unit generates a first optical frequency comb and a second optical frequency comb with unequal frequency differences between the comb teeth by using the same single-frequency pump light. The first optical frequency comb and the second optical frequency comb are combined and then split to obtain a first dual optical comb and a second dual optical comb. The feedforward signal processing unit receives the first dual optical comb and selects two comb pairs of asymmetric mode based on the vernier effect to perform beat frequency and mixing, and outputs a reference microwave signal carrying the system noise characteristics. The microwave signal output unit receives the second dual optical comb, filters out the comb teeth at the target mode for photoelectric conversion, outputs the target microwave signal, and then performs feedforward mixing on the received reference microwave signal and outputs a low-noise microwave signal after noise cancellation.

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