A method and device for accelerator microwave reference line based on photoelectric mixing

Abstract

The present invention provides an accelerator microwave reference line device based on optoelectronic hybrid, including a radio frequency signal providing system, a phase reference distribution system, and a control and measurement system; the phase reference distribution system includes a synchronous transmitter and a remote synchronous receiver, an optical fiber and a phase compensation device therebetween; the control and measurement system includes a first and a second phase detection processor, the first phase detection processor realizes phase compensation according to a reference signal demodulated from the synchronous transmitter and a returned radio frequency signal; the second phase detection processor receives a low-temperature drift reference signal demodulated from the synchronous receiver and a low-noise reference signal transmitted by the signal providing system, and calibrates the low-noise reference signal according to the low-temperature drift reference signal to obtain a final reference signal. The present invention also provides a corresponding method. The device of the present invention combines the advantages of both optoelectronic transmission schemes, significantly reducing the noise introduced in the optoelectronic conversion and laser transmission processes while ensuring low-temperature drift transmission of the signal.

Description

Technical Field

[0001] The invention relates to the field of particle accelerators, and in particular to an accelerator microwave reference line method and device based on photoelectric mixing. Background Art

[0002] The high-performance operation of particle accelerators requires high-precision synchronization between multiple distributed subsystems. In the prior art, traditional synchronization schemes usually rely on pure electrical or pure optical transmission methods. Pure electrical schemes do not introduce additional phase noise, but there are problems such as large transmission loss over long distances and sensitivity to environmental temperature and humidity, which makes it difficult to meet the high-precision synchronization requirements of hundreds of femtoseconds. The solution based on continuous laser carrier has the advantages of low insertion loss, low price, and no electromagnetic interference. However, the modulation and demodulation of microwave signals through electrical and optical signals will introduce additional noise, and the bidirectional transmission of single-wavelength lasers in optical fibers will also introduce Rayleigh scattering noise. Therefore, how to design a hybrid system that combines the advantages of optics and electronics to solve the above problems has become a research hotspot in current technology. Summary of the invention

[0003] The object of the present invention is to provide an accelerator microwave reference line method and device based on optoelectronic mixing to obtain a final reference signal with low output noise and low temperature drift.

[0004] In order to achieve the above-mentioned purpose, the present invention provides an accelerator microwave reference line device based on optoelectronic hybrid, comprising a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system; the phase reference distribution system comprises a synchronous transmitter and a remote synchronous receiver, and an optical fiber and a phase compensation device arranged therebetween; the control and measurement system comprises a first phase detection processor and a second phase detection processor; the first phase detection processor is configured to output a phase compensation control signal to the phase compensation device according to a reference signal and a returned radio frequency signal demodulated from the synchronous transmitter, so as to achieve phase compensation; the second phase detection processor is configured to receive a low-temperature drift reference signal demodulated from the synchronous receiver and a low-noise reference signal transmitted from the radio frequency signal providing system through a coaxial cable, and calibrate the phase of the low-noise reference signal according to the phase of the low-temperature drift reference signal to obtain a final reference signal.

[0005] The RF signal providing system includes a RF signal source and a frequency synthesis system connected to the output end of the RF signal source. The RF signal source is configured to generate a low-noise RF signal and send it to the frequency synthesis system. The frequency synthesis system is configured to output the RF signal as a low-noise reference signal to a synchronous transmitter and a remote synchronous receiver, and provide a clock and local oscillator signal for a phase detection processor.

[0006] The synchronous transmitter includes a laser, an electro-optical intensity modulator and an optical amplifier which are sequentially arranged on a first optical path.

[0007] The synchronous transmitter also includes a first signal demodulation device arranged downstream of its optical amplifier, the first signal demodulation device includes a first splitter and a circulator arranged in sequence on a first optical path downstream of the optical amplifier, a first photodiode located on a second optical path downstream of the first splitter, and a second photodiode located at a port outside the first optical path of the circulator, each of the first photodiode and the second photodiode is connected to a first phase detection processor through a combiner with a low-noise reference signal.

[0008] The synchronous receiver includes a second beam splitter and a Faraday rotator arranged in sequence on a first optical path, and a third photodiode located on a third optical path downstream of the second beam splitter. The third photodiode and a low-noise reference signal are connected to a second phase detector processor via a third combiner.

[0009] The phase compensation device includes a servo-controlled optical fiber delay line and / or a voltage-controlled optical fiber delay line.

[0010] The first phase detection processor is configured to utilize the reference signal amplitude information feedback to control the digital-to-analog converter to output a modulator control signal, thereby performing real-time control on the operating point of the electro-optical intensity modulator.

[0011] The first phase-detection processor calculates the phase difference between the reference signal obtained by the first photodiode and the returned RF signal obtained by the second photodiode, and uses the PID algorithm to control the phase compensation device to change the optical fiber length to minimize the phase difference between the reference signal and the returned RF signal to compensate for the phase drift; and / or the second phase-detection processor is configured to calculate the phase difference between the low-temperature drift reference signal and the low-noise reference signal, and then adjusts the vector regulator in the second phase-detection processor according to the phase difference to calibrate the phase of the low-noise reference signal, so that the phase of the low-noise reference signal is consistent with the phase of the low-temperature drift reference signal to obtain a final reference signal; and / or the first phase-detection processor and the second phase-detection processor adopt a phase-detection control system or phase-detection chip based on low-level RF.

[0012] On the other hand, the present invention provides an accelerator microwave reference line method based on photoelectric mixing, comprising:

[0013] S1: Build an accelerator microwave reference line device based on optoelectronic hybrid, which includes a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system; the phase reference distribution system includes a synchronous transmitter and a remote synchronous receiver, and an optical fiber and a phase compensation device arranged therebetween; the control and measurement system includes a first phase detection processor and a second phase detection processor;

[0014] S2: using the first phase detector to output a phase compensation control signal to the phase compensation device according to the reference signal and the return RF signal demodulated from the synchronous transmitter, so as to achieve phase compensation, so that the synchronous receiver demodulates to obtain a low temperature drift reference signal;

[0015] S3: Using a second phase detector, receiving a low-temperature drift reference signal demodulated from a synchronous receiver and a low-noise reference signal transmitted from the RF signal providing system through a coaxial cable, calibrating the phase of the low-noise reference signal according to the phase of the low-temperature drift reference signal, and obtaining a final reference signal.

[0016] In the step S2, the first phase-detection processor calculates the phase difference between the reference signal obtained by the first photodiode of the synchronous transmitter and the returned radio frequency signal obtained by the second photodiode, and uses the PID algorithm to control the phase compensation device to change the optical fiber length to minimize the phase difference between the reference signal and the returned radio frequency signal, so as to compensate for the phase drift, so that the synchronous receiver demodulates to obtain a low-temperature drift reference signal; and / or in the step S3, the second phase-detection processor calculates the phase difference between the low-temperature drift reference signal and the low-noise reference signal, and then adjusts the vector regulator in the second phase-detection processor according to the phase difference to calibrate the phase of the low-noise reference signal, so that the phase of the low-noise reference signal is consistent with the phase of the low-temperature drift reference signal, and obtains the final reference signal; and / or the first phase-detection processor and the second phase-detection processor adopt a phase-detection control system or phase-detection chip based on low-level radio frequency; and / or the first phase-detection processor is configured to use the reference signal amplitude information feedback to control the digital-to-analog converter to output a modulator control signal, thereby performing real-time control on the working point of the electro-optical intensity modulator of the synchronous transmitter.

[0017] The accelerator microwave reference line device based on optoelectronic hybrid of the present invention transmits the radio frequency signal modulated on the continuous optical carrier to the receiving end through a single-mode optical fiber, which is used to transmit the low-temperature drift reference signal that has been phase-compensated by the phase compensation device; at the same time, the radio frequency signal transmitted from the radio frequency signal providing system is transmitted to the receiving end through a coaxial cable, which is used to transmit the low-noise reference signal. The first phase detector completes the compensation of the phase drift in the signal transmission path to obtain the low-temperature drift reference signal, and the second phase detector at the receiving end completes the phase calibration of the low-temperature drift reference signal to the low-noise reference signal, and finally outputs the final reference signal with low noise and low temperature drift, which can fully combine the advantages of the two optoelectronic transmission schemes, and significantly reduce the noise introduced in the optoelectronic conversion and laser transmission process while ensuring the low-temperature drift transmission of the signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 4 is a device structure diagram of an accelerator microwave reference line device based on optoelectronic mixing according to a first embodiment of the present invention.

[0019] Figure 2 Yes Figure 1 The schematic diagram of the optical path part of the accelerator microwave reference line device based on optical-electrical mixing is shown.

[0020] Figure 3 This is a diagram of the experimental setup used for Rayli backscatter noise testing.

[0021] Figure 4 This is the experimental result of the Rayli backscatter noise test.

[0022] Figure 5 This is a diagram of a test device for the accelerator microwave reference line device of the present invention.

[0023] Figure 6 This is a test result diagram of the accelerator microwave reference line device of the present invention.

[0024] Figure 7 4 is a device structure diagram of an accelerator microwave reference line device based on optoelectronic mixing according to another embodiment of the present invention. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific examples. It should be understood that the following examples are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0026] like Figure 1 and Figure 2 The figure shows an accelerator microwave reference line device based on optoelectronic mixing according to the first embodiment of the present invention, which is used to maintain low noise of the receiving end signal under the condition of low temperature drift.

[0027] The accelerator microwave reference line device based on optoelectronic hybrid includes a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system. The phase reference distribution system based on a continuous laser carrier includes a synchronous transmitter 30 and a remote synchronous receiver 40, as well as an optical fiber and a phase compensation device 70 arranged therebetween; the control and measurement system includes a first and a second phase detection processor connected to the synchronous transmitter 30 and the synchronous receiver 40 respectively; the radio frequency signal providing system includes a radio frequency signal source 10 and a frequency synthesis system 20 connected to the output end of the radio frequency signal source 10, and the output signal thereof is used for both the phase reference distribution system and the control and measurement system.

[0028] The RF signal providing system includes a RF signal source (RMO) 10 and a frequency synthesis system 20 connected to the output end of the RF signal source 10. The frequency synthesis system 20 is used to provide a signal of a required frequency to a synchronous transmitter 30, a synchronous receiver 40 and a phase detector processor. The RF signal source 10 is configured to generate a low-noise RF signal and send it to the frequency synthesis system 20. In this embodiment, the model of the RF signal source 10 is SMA100B. The frequency synthesis system 20 is configured to output the RF signal generated by the RF signal source 10 as a low-noise reference signal low jitter to the synchronous transmitter 30 and the remote synchronous receiver 40, and provide a clock and a local oscillator signal to the phase detector processor.

[0029] The synchronous transmitter 30 includes a laser 31, an electro-optical intensity modulator 32, and an optical amplifier 33, which are sequentially arranged on the first optical path. Therefore, the synchronous transmitter 30 uses the laser 31 to generate a single-mode narrow-linewidth laser (i.e., a continuous laser carrier CW) as a carrier signal, and uses the electro-optical intensity modulator (EOM) 32 to modulate the amplitude of the radio frequency signal onto the continuous laser carrier to generate an optical signal including synchronous phase information, and then the optical signal is amplified by the optical amplifier 33, i.e., an erbium-doped fiber amplifier (EDFA), to obtain the output signal of the synchronous transmitter 30, and the output signal of the synchronous transmitter 30 will be phase compensated in the following steps, so that the synchronous receiver demodulates the output signal of the synchronous transmitter 30 to obtain a low temperature drift reference signal low drift.

[0030] In this embodiment, the laser 31 is a distributed feedback laser DFB, which generates a single-mode narrow-linewidth laser with a wavelength of 1550nm; the electro-optical intensity modulator 32 is a lithium niobate electro-optical intensity modulator, so that the RF signal is amplitude modulated by the laser, and the RF signal providing system provides the electro-optical intensity modulator 32 with an ultra-low phase noise RF signal.

[0031] like Figure 1 and Figure 2As shown, the synchronous transmitter 30 also includes a first signal demodulation device 34 arranged downstream of its optical amplifier 33, and the first signal demodulation device 34 includes a first optical splitter 341 and a circulator 342 arranged in sequence on a first optical path downstream of the optical amplifier 33, a first photodiode PD1 located on a second optical path downstream of the first optical splitter 341, and a second photodiode PD2 located at a port outside the first optical path of the circulator 342, and each photodiode and a low-noise reference signal low jitter are connected to a first phase detector 51 through a combiner. Thus, the first photodiode PD1 is used to demodulate the output light of the optical amplifier 33, and the second photodiode PD2 is used to demodulate the optical signal reflected back by the circulator of the synchronous receiver 40. Among them, the combiner includes a first combiner 343 and a second combiner 344. The first combiner 343 amplifies the output signal of the first photodiode PD1 and the low-noise reference signal provided by the frequency synthesis system, combines them and outputs them to the phase-detection processor. The second combiner 344 amplifies the output signal of the second photodiode PD2 (i.e., the demodulated reflected signal) and the low-noise reference signal provided by the frequency synthesis system, combines them and outputs them to the phase-detection processor.

[0032] The synchronous receiver 40 includes a second beam splitter 41 and a Faraday rotator (FRM) 42 sequentially arranged on the first optical path, a third photodiode PD3 located on the third optical path downstream of the second beam splitter 41, and the third photodiode PD3 and the low noise reference signal low jitter are connected to the second phase detector 52 through a third combiner 43. Thus, the second beam splitter 41 divides the input optical signal into two paths, one of which is reflected by the Faraday rotator 42 and then returns to the synchronous transmitter through the same optical fiber, and the other is demodulated by the third photodiode PD3 to output a low temperature drift reference signal low drift.

[0033] Since the phase compensation device 70 is located between the synchronous transmitter 30 and the synchronous receiver 40, the output light on the first optical path of the first optical splitter 341 passes through the circulator 342 and the phase compensation device 70 and is transmitted to the synchronous receiver 40 through a long optical fiber. In this embodiment, the phase compensation device 70 includes a servo-controlled optical fiber delay line VODL and / or a voltage-controlled optical fiber delay line piezo. The servo-controlled optical fiber delay line VODL changes the optical fiber length through the servo, and is used for low-precision large-range coarse adjustment; the voltage-controlled optical fiber delay line piezo changes the length of the optical fiber wound on the metal by changing the voltage to cause the metal to deform, and is used for high-precision low-range fine adjustment.

[0034] The phase detector processor is configured to respectively detect amplitude and phase and calculate the received radio frequency signal. The phase detector processor comprises a first phase detector processor 51 at the synchronous transmitter 30 and a second phase detector processor 52 at the synchronous receiver 40 .

[0035] The first phase detection processor 51 is configured to output a phase compensation control signal to the phase compensation device 70 based on the reference signal and the return RF signal demodulated from the synchronous transmitter 30 to achieve phase compensation; at the same time, the output modulator control signal is used to control the working point of the electro-optical intensity modulator (EOM) 32 in real time, so that the output optical power of the electro-optical intensity modulator (EOM) 32 remains stable.

[0036] The specific working principle of the first phase detector 51 for performing phase compensation on the optical fiber length is as follows:

[0037] The modulated optical path is divided into two parts. The first part is directly demodulated by the first photodiode PD1 and used as the phase reference signal of the entire system. The second part passes through the circulator 342 and the phase compensation device 70 and is transmitted to the synchronous receiver 40 through a long optical fiber. The synchronous receiver 40 demodulates a part of the received optical signal into a radio frequency signal and outputs it to the second phase detector 52. The other part is reflected back to the synchronous transmitter 30 through the same optical fiber through the Faraday rotator (FRM). After being output from the circulator 342 of the synchronous transmitter 30, it is demodulated by the second photodiode PD2 to obtain a returned radio frequency signal.

[0038] The first phase-detection processor 51 performs phase compensation, which specifically includes: the first phase-detection processor 51 calculates the phase difference between the reference signal obtained by the first photodiode PD1 and the returned RF signal obtained by the second photodiode PD2, and uses the PID algorithm to control the phase compensation device 70 to change the optical fiber length to minimize the phase difference between the reference signal and the returned RF signal to compensate for the phase drift.

[0039] In order to eliminate the phase drift introduced by the laser and RF signals from generation to modulation by the electro-optical intensity modulator 32, we synchronize the phase of the reference signal demodulated directly by the first photodiode PD1 of the transmitter 30. As the phase reference of the whole system. Therefore, the phase of the input signal is the phase of the reference signal After transmission, the phase of the output signal at the third photodiode PD3 is obtained at the synchronous receiver 40. out, reflected back to the synchronous transmitter 30 and the phase of the returned RF signal is obtained at the second photodiode PD2 back, the delay introduced by the phase compensation device 70 corresponds to the delay phase feedback, then without the delay introduced by the phase compensation device 70, the phase of the output signal Phase of out and return RF signals back satisfies:

[0040] ,

[0041] ,

[0042] in, 1. 3 is the error introduced by the optical splitter and circulator of the synchronous transmitter due to environmental changes. The delay introduced by the optical fiber, 2 is the error introduced by the optical splitter of the synchronous receiver.

[0043] In order to introduce the delayed phase of the phase compensation device 70 After feedback, back = ref, then the delayed phase of the phase compensation device 70 The feedback is:

[0044] ,

[0045] It should be noted that 1. 3. The value of cannot be directly measured, and the present invention can only adjust the delay phase according to the current phase difference between the reference signal and the returned RF signal. feedback, thereby minimizing the phase difference between the reference signal and the returned RF signal.

[0046] Therefore, the phase of the output signal after phase compensation is out' is:

[0047] ,

[0048] Based on the above principle, phase compensation of the output signal (ie, the low drift reference signal demodulated from the synchronous receiver 40 ) is achieved.

[0049] In this embodiment, the synchronous transmitter 30, the synchronous receiver 40, the optical fiber therebetween, and the phase compensation device 70 are all placed in a constant temperature box to reduce the impact of temperature drift of passive components on system stability.

[0050] The electro-optical intensity modulator (EOM) 32 needs a DC bias voltage when working, and the RF signal to be modulated is superimposed on this DC voltage. In theory, this DC bias voltage can be a fixed DC voltage, but environmental changes such as temperature and humidity cause this DC bias voltage to drift, resulting in changes in the working curve. Therefore, the first phase-detection processor 51 detects the relevant parameters of the electro-optical intensity modulator 32 (such as by detecting the reference signal amplitude information) and uses the reference signal amplitude information as a feedback signal to feedback control the digital-to-analog converter to output the modulator control signal (i.e., the value of the DC bias voltage) of the electro-optical intensity modulator 32, thereby controlling the working point of the electro-optical intensity modulator in real time, so that the working curve of the electro-optical intensity modulator 32 remains stable, and the output optical power of the electro-optical intensity modulator 32 remains stable.

[0051] The second phase detector 52 is configured to receive the low-temperature drift reference signal low drift demodulated from the synchronous receiver 40 and the low-noise reference signal low jitter transmitted from the frequency synthesis system 20 of the radio frequency signal providing system through a coaxial cable (the low-noise reference signal low jitter is used as an input signal), and calibrate the phase of the low-noise reference signal low jitter according to the phase of the low-temperature drift reference signal low drift to obtain a final reference signal. The phase of the calibrated low-noise reference signal low jitter is consistent with the phase of the low-temperature drift reference signal low drift (i.e., the two signals are phase-locked by a vector modulator) to generate a final reference signal with low jitter and low slow drift. Therefore, the present invention reduces the noise introduced by the optical path part through the optoelectronic hybrid solution, and the signal achieves phase-stable transmission.

[0052] The low drift reference signal "low drift" is a signal transmitted through an optical fiber. This signal is compensated by the phase detector processor and the phase compensation device 70, so it has low temperature drift but noise and is not affected by ambient temperature changes, so as to provide a low temperature drift phase reference. The corresponding low noise reference signal "low jitter" is a signal directly transmitted through a coaxial cable, which has not been phase compensated, has relatively small noise (or jitter), but is affected by the environment and has temperature drift.

[0053] In this embodiment, the second phase-detection processor 52 is configured to calculate the phase difference between the low-temperature drift reference signal low drift and the low-noise reference signal low jitter, and then adjust the vector modulator (VM) in the second phase-detection processor 52 according to the phase difference to calibrate the phase of the low-noise reference signal low jitter, so that the phase of the low-noise reference signal low jitter is consistent with the phase of the low-temperature drift reference signal low drift, so that the receiving end outputs a final reference signal with low jitter and low drift.

[0054] Thus, the accelerator microwave reference line device based on optoelectronic hybrid of the present invention transmits the radio frequency signal modulated on the continuous optical carrier CW to the receiving end through a single-mode optical fiber, which is used to transmit the low-temperature drift reference signal low drift that has been phase-compensated by the phase compensation device 70; at the same time, the radio frequency signal transmitted from the radio frequency signal providing system to the receiving end through a coaxial cable is used to transmit the low-noise reference signal low litter. The first phase-detection processor 51 at the transmitting end completes the compensation of the phase drift in the signal transmission path to obtain the low-temperature drift reference signal low drift, and the second phase-detection processor 52 at the receiving end completes the phase calibration of the low-noise reference signal low drift by the low-temperature drift reference signal low drift, and finally outputs the final reference signal with low noise and low temperature drift, which can fully combine the advantages of the two optoelectronic transmission schemes, and significantly reduce the noise introduced in the optoelectronic conversion and laser transmission process while ensuring the low-temperature drift transmission of the signal. In addition, the system of the present invention includes a radio frequency signal source, a frequency synthesis system, a synchronous transmitter, a phase-detection processor and a synchronous receiver, and has the characteristics of high stability, high scalability, high cost performance and strong environmental adaptability.

[0055] Experimental results verification:

[0056] 1. Demonstrating the influence of Rayleigh backscatter noise

[0057] This application uses 2998.2MHz signal as the experimental signal and designs the following Figure 3The experimental device shown in the figure is used for demonstration. The device includes a laser Laser, an electro-optic intensity modulator EOM, an erbium-doped fiber amplifier EDFA, a controllable optical attenuation Att, a first optical splitter 11', a first circulator 12', a first optical fiber and a second optical splitter 13', a Faraday rotator FRM, and a photodiode PD and a signal amplifier AMP connected to the first optical splitter 11' via a second optical fiber having the same length as the first optical fiber, a photodiode PD and a signal amplifier AMP connected to the second optical splitter 13' via a short optical fiber, a phase noise analyzer R&S FSWP connected to all the signal amplifiers AMP, and a radio frequency signal source 14' connected to the electro-optic intensity modulator EOM and the phase noise analyzer R&S FSWP.

[0058] Therefore, a part of the optical signal after the intensity modulation of the 2998.2MHz radio frequency signal is transmitted to the remote end through the first optical fiber with a length of 50m and demodulated by the photodiode PD. The noise of the first remote end signal obtained by this demodulation does not include the Ruili backscattering noise. The other part is transmitted through the second optical fiber with the same length of 50m. After reaching the remote end, a part is demodulated by the photodiode PD to obtain the second remote end signal, and the other part is reflected back to the transmitting end through the Faraday rotator FRM and demodulated. The noise of the demodulated reflected signal will include the Ruili backscattering noise.

[0059] The formation principle of Rayleigh backscattering noise is that when the laser is transmitted in the optical fiber, due to the uneven distribution of atoms in the optical fiber, the forward light will produce elastic collisions with these particles, and a part of the backward transmitted photons will be captured by the optical fiber to form reverse light and maintain the same wavelength and polarization state. The forward transmitted light A will produce a backward scattering a, and the backward transmitted light B will also produce a forward scattering b. However, the backward transmitted light B is weaker than the forward transmitted light A, so b is weaker than a and can be ignored. The main part is that there will be interference between the scattering a and the backward transmitted light B, thus generating Rayleigh backscattering noise. In the above description, one part is directly transmitted to the receiving end without reflection, only the forward transmitted light A without the backward transmitted light B, so there is no Rayleigh backscattering noise, and the other part will be reflected back to the transmitting end at the receiving end, so it includes Rayleigh backscattering noise.

[0060] The first remote signal and the second remote signal obtained after the two demodulations are respectively amplified by the amplifier AMP (i.e., the amplifier ZX60-83-LN of Mini Company) to amplify the RF power. The phase noise analyzer R&S FSWP is used to measure the phase noise of the signal source signal and the first remote signal and the second remote signal respectively.

[0061] Test results such as Figure 4As shown. The phase noise of the source signal is 13.5fs (10Hz-10MHz), the phase noise of the signal without Rayleigh backscattering noise (i.e., the first far-end signal) after long optical fiber transmission is 19.7fs (10Hz-10MHz), and the phase noise of the signal with Rayleigh backscattering noise (i.e., the second far-end signal) reaches 31.1fs (10Hz-10MHz). It can be seen that the additional noise caused by Rayleigh backscattering is about 24fs. Therefore, Figure 3 The experimental device shown proves that the noise jitter of the signal output by the single-fiber bidirectional transmission scheme will be very large, and Rayleigh scattering noise accounts for a large part of the reason. Therefore, it is feasible for the present invention to reduce this noise by adding a coaxial cable.

[0062] The present invention is designed as Figure 5 The test device shown in the figure is used to test the reference signal outputted by the receiving end after passing through the accelerator microwave reference line device of the present invention, and the test device comprises a phase noise analyzer R&S FSWP connected to the RF signal source 10 and the second phase detector processor 52. Figure 5 As shown, the RF signal generated by the RF signal source 10 and the RF signal output by the second phase detector 52 (ie, the final reference signal output by the microwave reference line device of the present invention) are respectively measured for phase noise by a phase noise analyzer.

[0063] Test results such as Figure 6 As shown in the figure, under the condition of measuring bandwidth of 10Hz-10MHz, the phase noise of the RF signal source is 13.5fs, and the phase noise of the final reference signal output after passing through the accelerator microwave reference line device of the present invention is 17fs, and the additional phase noise is about 10.33fs. It can be seen that the phase noise of the output signal is obviously suppressed.

[0064] like Figure 7 As shown, according to another embodiment of the present invention, for the STCF beam test platform, the specific structure of the accelerator microwave reference line device of the present invention is Figure 1 The accelerator microwave reference line device shown is exactly the same, and the only difference is the number of synchronous receivers 240 and second phase-detection processors 252. The accelerator microwave reference line device of the present invention includes a synchronous transmitter 30 and four synchronous receivers 240, the synchronous transmitter 230 corresponds to a first phase-detection processor 251, and each synchronous receiver 240 corresponds to a second phase-detection processor 252. Each second phase-detection processor 252 is used to provide a final reference signal to the S-band klystron 201 of the STCF beam test platform through a solid-state amplifier SSA, and then output a high-power radio frequency signal through the klystron 201 to control the accelerating tube 202 to accelerate electrons.

[0065] In this embodiment, the first phase detector 251 and the second phase detector 252 use a phase detector control system based on a low-level radio frequency (LLRF) system. However, in other embodiments, the first phase detector 251 and the second phase detector 252 can be replaced by a phase detector chip, but the accuracy is relatively low and the degree of environmental influence will be relatively large. Moreover, the klystron of the beam test platform can be directly controlled by the low-level radio frequency (LLRF) system, reducing the overall system complexity, and the overall cost performance is higher.

[0066] In this embodiment, the RF signal modulated onto the CW optical carrier output by the synchronous transmitter 230 is transmitted to four synchronous receivers 240 via optical fiber to transmit the compensated low-temperature drift reference signal; four RF signals are transmitted from the RF signal source 210 to the four synchronous receivers 240 via coaxial cables, thereby transmitting the low-noise reference signal. The first phase detector 251 completes the compensation of the phase drift in the signal transmission path, and the second phase detector 252 completes the calibration of the low-temperature drift signal to the low-noise signal, and finally outputs a low-noise, low-temperature drift reference signal.

[0067] Based on the above-mentioned accelerator microwave reference line device based on photoelectric mixing, an accelerator microwave reference line method based on photoelectric mixing is implemented, which specifically includes:

[0068] Step S1: constructing an accelerator microwave reference line device based on optoelectronic hybrid as described above, which includes a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system; the phase reference distribution system includes a synchronous transmitter and a remote synchronous receiver, and an optical fiber and a phase compensation device arranged therebetween; the control and measurement system includes a first phase detection processor and a second phase detection processor;

[0069] The structure of the accelerator microwave reference line device based on optoelectronic mixing is completely consistent with the structure of the accelerator microwave reference line device based on optoelectronic mixing of the first embodiment of the present invention.

[0070] Step S2: using the first phase detector to output a phase compensation control signal to the phase compensation device according to the reference signal and the return RF signal demodulated from the synchronous transmitter, so as to achieve phase compensation, so that the synchronous receiver demodulates to obtain a low temperature drift reference signal;

[0071] Step S3: using a second phase detector to receive a low-temperature drift reference signal demodulated from a synchronous receiver and a low-noise reference signal transmitted from the RF signal providing system through a coaxial cable, and calibrating the phase of the low-noise reference signal according to the phase of the low-temperature drift reference signal to obtain a final reference signal.

[0072] In step S2, the first phase detection processor calculates the phase difference between the reference signal obtained by the first photodiode of the synchronous transmitter and the returned radio frequency signal obtained by the second photodiode, and uses the PID algorithm to control the phase compensation device to change the optical fiber length to minimize the phase difference between the reference signal and the returned radio frequency signal to compensate for the phase drift, so that the synchronous receiver demodulates to obtain a low-temperature drift reference signal.

[0073] In step S3, the second phase-detection processor calculates the phase difference between the low-temperature drift reference signal and the low-noise reference signal, and then adjusts the vector regulator in the second phase-detection processor according to the phase difference to calibrate the phase of the low-noise reference signal, so that the phase of the low-noise reference signal is consistent with the phase of the low-temperature drift reference signal, thereby obtaining a final reference signal.

[0074] The first phase detection processor and the second phase detection processor adopt a phase detection control system or a phase detection chip based on low-level radio frequency.

[0075] The first phase detection processor is configured to utilize reference signal amplitude information feedback to control a digital-to-analog converter to output a modulator control signal, thereby performing real-time control on the operating point of the electro-optical intensity modulator of the synchronous transmitter.

[0076] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. The above embodiments of the present invention can also be modified in various ways. All simple, equivalent changes and modifications made according to the claims and the description of the present invention fall within the scope of protection of the claims of the present invention. The contents not described in detail in the present invention are all conventional technical contents.

Claims

1. An accelerator microwave reference line device based on optoelectronic mixing, characterized in that: The invention comprises a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system; the phase reference distribution system comprises a synchronous transmitter and a remote synchronous receiver, and an optical fiber and a phase compensation device arranged therebetween; the control and measurement system comprises a first phase detection processor and a second phase detection processor; The first phase detection processor is configured to output a phase compensation control signal to the phase compensation device according to the reference signal and the return radio frequency signal demodulated from the synchronous transmitter to achieve phase compensation, so that the synchronous receiver demodulates to obtain a low temperature drift reference signal; The second phase detection processor is configured to receive a low-temperature drift reference signal demodulated from a synchronous receiver and a low-noise reference signal transmitted from the radio frequency signal providing system through a coaxial cable, and calibrate the phase of the low-noise reference signal according to the phase of the low-temperature drift reference signal to obtain a final reference signal; The first phase detector calculates the phase difference between the reference signal obtained by the first photodiode and the returned radio frequency signal obtained by the second photodiode, and uses the PID algorithm to control the phase compensation device to change the optical fiber length to minimize the phase difference between the reference signal and the returned radio frequency signal, so as to compensate for the phase drift; The second phase detector processor is configured to calculate a phase difference between a low temperature drift reference signal and a low noise reference signal, and then adjust a vector regulator in the second phase detector processor according to the phase difference to calibrate the phase of the low noise reference signal, so that the phase of the low noise reference signal is consistent with the phase of the low temperature drift reference signal, thereby obtaining a final reference signal; The first phase detection processor and the second phase detection processor adopt a phase detection control system or a phase detection chip based on low-level radio frequency.

2. The accelerator microwave reference line device based on optoelectronic mixing according to claim 1, characterized in that: The RF signal providing system includes a RF signal source and a frequency synthesis system connected to the output end of the RF signal source. The RF signal source is configured to generate a low-noise RF signal and send it to the frequency synthesis system. The frequency synthesis system is configured to output the RF signal as a low-noise reference signal to a synchronous transmitter and a remote synchronous receiver, and provide a clock and local oscillator signal for a phase detection processor.

3. The accelerator microwave reference line device based on optoelectronic mixing according to claim 1, characterized in that: The synchronous transmitter includes a laser, an electro-optical intensity modulator and an optical amplifier which are sequentially arranged on a first optical path.

4. The accelerator microwave reference line device based on optoelectronic mixing according to claim 3, characterized in that: The synchronous transmitter also includes a first signal demodulation device arranged downstream of its optical amplifier, the first signal demodulation device includes a first optical splitter and a circulator arranged in sequence on a first optical path downstream of the optical amplifier, a first photodiode located on a second optical path downstream of the first optical splitter, and a second photodiode located at a port outside the first optical path of the circulator, each of the first photodiode and the second photodiode is connected to a first phase detection processor through a combiner with a low-noise reference signal.

5. The accelerator microwave reference line device based on optoelectronic mixing according to claim 3, characterized in that: The synchronous receiver includes a second beam splitter and a Faraday rotator arranged in sequence on a first optical path, and a third photodiode located on a third optical path downstream of the second beam splitter. The third photodiode and a low-noise reference signal are connected to a second phase detector processor via a third combiner.

6. The accelerator microwave reference line device based on optoelectronic mixing according to claim 1, characterized in that: The phase compensation device includes a servo-controlled optical fiber delay line and / or a voltage-controlled optical fiber delay line.

7. The accelerator microwave reference line device based on optoelectronic mixing according to claim 3, characterized in that: The first phase detection processor is configured to utilize the reference signal amplitude information feedback to control the digital-to-analog converter to output a modulator control signal, thereby performing real-time control on the operating point of the electro-optical intensity modulator.

8. An accelerator microwave reference line method based on optoelectronic mixing, characterized in that: include: Step S1: constructing an accelerator microwave reference line device based on optoelectronic hybrid according to any one of claims 1 to 7, which comprises a radio frequency signal providing system, a phase reference distribution system based on a continuous laser carrier, and a control and measurement system; the phase reference distribution system comprises a synchronous transmitter and a remote synchronous receiver, and an optical fiber and a phase compensation device arranged therebetween; the control and measurement system comprises a first phase detection processor and a second phase detection processor; Step S2: using the first phase detector to output a phase compensation control signal to the phase compensation device according to the reference signal and the return RF signal demodulated from the synchronous transmitter, so as to achieve phase compensation, so that the synchronous receiver demodulates to obtain a low temperature drift reference signal; Step S3: using a second phase detector to receive a low-temperature drift reference signal demodulated from a synchronous receiver and a low-noise reference signal transmitted from the RF signal providing system through a coaxial cable, and calibrating the phase of the low-noise reference signal according to the phase of the low-temperature drift reference signal to obtain a final reference signal.

9. The accelerator microwave reference line method based on optoelectronic mixing according to claim 8, characterized in that: In step S2, the first phase detector calculates the phase difference between the reference signal obtained by the first photodiode of the synchronous transmitter and the returned radio frequency signal obtained by the second photodiode, and uses the PID algorithm to control the phase compensation device to change the optical fiber length to minimize the phase difference between the reference signal and the returned radio frequency signal, so as to compensate for the phase drift, so that the synchronous receiver demodulates to obtain a low temperature drift reference signal; and / or In step S3, the second phase-detection processor calculates the phase difference between the low-temperature drift reference signal and the low-noise reference signal, and then adjusts the vector regulator in the second phase-detection processor according to the phase difference to calibrate the phase of the low-noise reference signal, so that the phase of the low-noise reference signal is consistent with the phase of the low-temperature drift reference signal, thereby obtaining a final reference signal; The first phase detection processor and the second phase detection processor adopt a phase detection control system or a phase detection chip based on low-level radio frequency; The first phase detection processor is configured to utilize reference signal amplitude information feedback to control a digital-to-analog converter to output a modulator control signal, thereby performing real-time control on the operating point of the electro-optical intensity modulator of the synchronous transmitter.

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