Optical frequency comb repetition frequency locking device and method based on automatic power control

Abstract

The invention discloses an optical frequency comb repetition frequency locking device and method based on automatic power control, and relates to the technical field of optical frequency combs, the device comprises an optical frequency comb optical system, an optical fiber length automatic control system and an automatic power control system, the optical frequency comb optical system is used for generating optical frequency comb repetition frequency, the optical fiber length automatic control system locks the optical frequency comb repetition frequency output by the optical frequency comb optical system, and the automatic power control system is used for adaptively adjusting the signal power in a corresponding link when the optical frequency comb optical power or the reference source power changes. The input power of the mixer local oscillator and the radio frequency port is maintained at the preset power; according to the technical scheme of the invention, the stability and accuracy of the input power of the radio frequency and local oscillation port of the mixer are improved, the suppression of noise in a link is enhanced, a phase-locked loop of an optical fiber length automatic control system can be maintained in an optimal working state for a long time, and the practicability of an optical frequency comb product is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of optical frequency combs, and in particular to an optical frequency comb repetition frequency locking device and method based on automatic power control. Background Art

[0002] The emergence and development of optical frequency combs have greatly promoted the development of science and technology such as ultrafast optics, spectral precision measurement, optical frequency synthesis and optical frequency standards. With its ultra-stable and precise comb spectrum, the optical frequency comb simply couples the optical frequency with the microwave frequency like a transmission gear, putting an end to the history of optical frequencies being difficult to measure accurately and stably, and at the same time nurturing the development and application of optical clocks; in addition, due to the specific relationship between frequency and parameters such as time and spatial distance, optical frequency combs are also widely used in the fields of precision ranging and optical frequency transmission, and have huge market prospects in satellite launch and recovery, navigation, electronic countermeasures and precision CNC manufacturing.

[0003] The effective application of optical frequency combs is inseparable from their stable and accurate repetition frequency control. At present, the domestic and international precision optical frequency comb repetition frequency control adopts the traditional analog phase-locked loop. The device block diagram is shown in the attached figure. Figure 2As shown. The traditional analog phase-locked loop usually uses a photodetector to convert the optical frequency comb signal into a radio frequency electrical signal with a repetition frequency. The radio frequency electrical signal is transmitted to the mixer after passing through a low-pass amplifier module. At the same time, the reference electrical signal output by the ultra-stable reference source is also transmitted to the mixer after passing through a low-noise amplifier. The mixer obtains a frequency difference signal after frequency discrimination between the radio frequency electrical signal and the reference electrical signal. The frequency difference signal is used to adjust the repetition frequency output by the optical frequency comb optical system to complete the locking of the repetition frequency of the optical frequency comb. The inventors noticed that the transfer function of the traditional analog phase-locked loop is designed to obtain the best loop performance based on the loop transfer parameters measured at a certain moment. When the working environment of the optical frequency comb changes, the device ages, and the reference source is replaced, on the one hand, the loop transfer parameters will change. At this time, the performance of the phase-locked loop is no longer in the best state, and even the unstable state will cause loss of lock, which will affect the use of the optical frequency comb and the accuracy of the measurement results. On the other hand, the instability of the state will also introduce more amplitude noise to the phase-locked loop. These amplitude noises directly affect the repetition frequency of the optical frequency comb through the control signal output by the phase-locked loop, seriously deteriorating the stability and accuracy of the repetition frequency. At present, those skilled in the art usually maintain and adjust the frequency locking device by replacing aged components, adjusting phase-locked loop control parameters, controlling the operating temperature to reduce parameter drift caused by environmental changes, etc., and these methods can only play an auxiliary role in maintaining the stability of the locking device, and require real-time detection of the state of the locking device and corresponding adjustments based on the state. The process is cumbersome and cannot fundamentally solve the problem of poor phase-locked loop performance. In addition, the reasons for the decline in phase-locked loop performance are extremely complex. At present, no method has been found that can effectively improve the repetition frequency locking capability of the optical frequency comb. Summary of the invention

[0004] The purpose of the present invention is to provide an optical frequency comb repetition frequency locking device and method based on automatic power control, so as to solve the problems of large amplitude noise and low stability and accuracy of repetition frequency when the optical frequency comb repetition frequency is controlled in a closed loop in the prior art.

[0005] The technical solution of the present invention is to provide an optical frequency comb repetition frequency locking device based on automatic power control, the device comprising:

[0006] The optical frequency comb optical system is used to generate an optical frequency comb repetition frequency, and output the optical frequency comb repetition frequency to an optical fiber length automatic control system;

[0007] The optical fiber length automatic control system is used to lock the repetition frequency of the optical frequency comb output by the optical frequency comb optical system;

[0008] The optical fiber length automatic control system includes a photodetector, an ultra-stable reference source, a mixer and a PID controller. The photodetector is used to convert an optical frequency comb optical signal into an RF electrical signal with a frequency that is consistent with the repetition frequency of the optical signal, and provide it to the RF port of the mixer; the ultra-stable reference source is used to generate a reference electrical signal with high frequency stability, and provide it to the local oscillator port of the mixer; the mixer is used to perform frequency discrimination on the RF electrical signal and the reference electrical signal to obtain a frequency difference signal; the PID controller is used to perform proportional, integral and differential operations on the frequency difference signal, and convert the frequency difference signal into a smooth first control signal, the first control signal is used to adjust the repetition frequency of the optical frequency comb, and the voltage of the control signal is inversely proportional to the repetition frequency of the optical frequency comb;

[0009] The first automatic power control system is used to adjust the input signal power at the RF port of the mixer to keep it at a predetermined power value;

[0010] The second automatic power control system is used to adjust the input signal power at the local oscillator port of the mixer to keep it at a predetermined power value.

[0011] Furthermore, the optical fiber length automatic control system also includes an impedance matching network, a first low-pass amplification module, an adjustable digital frequency divider and a second low-pass amplification module;

[0012] The impedance matching network is used to adjust the output impedance of the photodetector to a preset impedance value so that it matches the input impedance of the subsequent circuit;

[0013] The first low-pass amplifier module is used to extract and amplify the fundamental wave component in the first radio frequency electrical signal output by the photodetector, and filter out the remaining high-order harmonic components;

[0014] The adjustable frequency divider is used to divide the fundamental wave component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal with the same frequency as the output signal of the ultra-stable reference source;

[0015] The second low-pass amplifier module is used to extract and amplify the fundamental wave component in the second radio frequency electrical signal and filter out the remaining high-order harmonic components.

[0016] Further, the first automatic power control system is used to automatically control the power of the fundamental wave component of the second radio frequency electrical signal output by the second low-pass amplification module, so that the input power at the radio frequency port of the mixer remains unchanged, and the first automatic power control system includes a voltage-controlled attenuator, a radio frequency coupler, a power detector, a voltage comparator, an adjustable reference voltage source and a PI controller;

[0017] The voltage-controlled attenuator is used to adjust the attenuation degree of the fundamental wave component of the second radio frequency electrical signal according to the signal fed back by the PI controller, so that the input signal power of the mixer radio frequency port is constant, wherein the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the feedback signal of the PI controller;

[0018] The radio frequency coupler is used to couple the power of the fundamental wave component of the second electrical signal to the power detector for subsequent power detection;

[0019] The power detector is used to receive the radio frequency power signal output by the radio frequency coupler and convert the radio frequency power signal into a direct current voltage signal;

[0020] The voltage comparator is used to receive the ultra-stable reference voltage output by the adjustable reference voltage source, compare the DC voltage signal with the ultra-stable reference voltage, and output a voltage difference signal.

[0021] The adjustable reference voltage source is used to provide an adjustable ultra-stable reference voltage for the voltage comparator;

[0022] The PI controller is used to perform proportional integral operation on the voltage difference signal to convert the voltage difference signal into a smooth second control signal, and the second control signal is used to adjust the attenuation degree of the voltage-controlled attenuator on the fundamental wave component of the second radio frequency electrical signal.

[0023] Furthermore, the optical fiber length automatic control system also includes a low noise amplifier, which is used to amplify the power of the reference electrical signal output by the ultra-stable reference source;

[0024] The second automatic power control system is used to perform automatic power control on the reference electrical signal output by the low noise amplifier, so that the input power at the local oscillator port of the mixer remains unchanged.

[0025] Furthermore, the optical fiber length automatic control system also includes a high voltage driving module and an optical pump source;

[0026] The high-voltage driving module is used to amplify the voltage of the first control signal to a predetermined high voltage, so that the voltage-amplified first control signal can completely drive the piezoelectric ceramic in the optical frequency comb system;

[0027] The optical pump source is used to provide a short-wave pump light source for the optical frequency comb optical system, and the optical frequency comb optical system uses the short-wave pump light source to generate an optical frequency comb repetition frequency.

[0028] The technical solution of the present invention further provides an optical frequency comb repetition frequency locking method for the above-mentioned optical frequency comb repetition frequency locking device based on automatic power control, characterized in that the method comprises:

[0029] Step 1, using an optical pump source to provide short-wave pump light for the optical frequency comb optical system, and the optical frequency comb optical system generates an optical frequency comb signal based on the short-wave pump light;

[0030] Step 2, using a photodetector to convert the optical frequency comb signal into a first radio frequency electrical signal with a repetition frequency, dividing the fundamental wave component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal with the same frequency as the output signal of the ultra-stable reference source, and inputting the fundamental wave component of the second radio frequency electrical signal into the radio frequency port of the mixer through a first automatic power control system;

[0031] Step 3, using a first automatic power control system to adaptively adjust the input power at the RF port of the mixer so that the input power at the RF port remains unchanged;

[0032] Step 4, using an ultra-stable reference source to generate a reference electrical signal, using a noise amplifier to amplify the power of the reference electrical signal, and inputting the amplified reference electrical signal into the local oscillator port of the mixer through a second automatic power control system;

[0033] Step 5, using a second automatic power control system to adaptively adjust the input power at the local oscillator port of the mixer so that the input power at the local oscillator port remains unchanged;

[0034] Step 6, using a mixer to perform frequency discrimination on the fundamental component of the second RF electrical signal and the reference electrical signal to obtain a frequency difference signal, the frequency difference signal is shaped and filtered by a PID controller into a smooth first control signal, the first control signal is amplified by a high-voltage driving module, and the amplified first control signal is input into the optical frequency comb optical system;

[0035] Step 7: The piezoelectric ceramic inside the optical frequency comb optical system adjusts the length of the fiber ring cavity according to the amplified first control signal, wherein the voltage of the first control signal is inversely proportional to the repetition frequency of the optical frequency comb.

[0036] Furthermore, step 3 specifically includes the following steps:

[0037] Step 3.1, the voltage-controlled attenuator attenuates the fundamental wave component of the second radio frequency electrical signal according to the second control signal output by the PID controller, separates the fundamental wave component of the second radio frequency electrical signal with a predetermined power ratio by using a radio frequency coupler, and couples it to the power detector as a radio frequency power signal;

[0038] Step 3.2, using a power detector to convert the RF power signal into a DC voltage signal, and transmitting the DC voltage signal to a voltage comparator, the voltage comparator receives an ultra-stable reference voltage output by an adjustable reference voltage source, and subtracts the DC voltage signal from the ultra-stable reference voltage to obtain a voltage difference signal, and transmits the voltage difference signal to a PI controller;

[0039] Step 3.3, use the PI controller to smooth and filter the voltage difference signal to obtain a second control signal, and use the second control signal to adjust the attenuation degree of the voltage-controlled attenuator, wherein the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the PI controller feedback signal.

[0040] Furthermore, the expression for the attenuation of the power of the fundamental component signal of the second RF electrical signal by the voltage-controlled attenuator in step 3.1 is:

[0041] AT=α·V T

[0042] Where AT is the attenuated power in dB, α is the attenuation coefficient of the voltage-controlled attenuator, α = 5.2dB / V, V T It is the voltage value of the second control signal output by the PI controller.

[0043] Furthermore, in step 3.2, the RF power signal is converted into a DC voltage signal using a power detector, which is expressed as:

[0044] V P =γ·(P i -P s )

[0045] Where V P is the converted DC voltage, γ is the conversion coefficient of the power detector, γ=0.032V / dBm, P i is the power of the RF power signal in dBm, P s It is the power of the RF power signal when the conversion voltage is 0V, in dBm.

[0046] Furthermore, step 3.3 specifically includes:

[0047] The PI controller performs proportional and integral operations on the voltage difference signal, specifically:

[0048]

[0049] Where V c (s) is the Laplace transform of the second control signal, V e (s) is the Laplace transform of the voltage difference signal, G is the proportional factor, p is the differential operator, and s is the complex frequency variable in the Laplace transform, indicating that the dynamic characteristic integral bandwidth of the proportional-integral controller is 1 / 2πp;

[0050] The attenuation degree of the voltage-controlled attenuator is adjusted by using the second control signal. When the voltage value of the PI controller feedback signal increases, the attenuation of the voltage-controlled attenuator increases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal decreases. When the voltage value of the PI controller feedback signal decreases, the attenuation of the voltage-controlled attenuator decreases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal increases.

[0051] Principle description:

[0052] The technicians of the present invention monitored the changes in the internal parameters of each module and the changes in the radio frequency signal during the operation of the existing optical frequency comb repetitive frequency locking device, and found that when the working environment of the optical frequency comb changes, the device ages, or the reference source is replaced, it will cause changes in optical power, radio frequency amplifier device gain, reference source power, radio frequency signal power, etc., and the changes in these parameters will cause changes in loop transfer parameters, especially reference source power and radio frequency signal power. When their power is unstable, it will cause phase noise to increase, which will interfere with the output of the mixer, making it impossible for the phase-locked loop to accurately track the frequency error, thereby causing the phase-locked loop performance to be unstable and difficult to maintain in the best working state, which will eventually lead to loss of lock, which is an important factor affecting the use of the optical frequency comb and the accuracy of the measurement results; therefore, in order to ensure that the phase-locked loop can accurately detect the frequency error, it is necessary to ensure that the reference source power and radio frequency signal power input to the mixer are stable. The stability of the reference source power and radio frequency signal power can enable the phase-locked loop of the optical fiber length automatic control system to maintain the working state of the best loop characteristics for a long time, and have stronger tolerance to changes in the working environment, product aging, and replacement of the reference source.

[0053] The beneficial effects of the present invention are:

[0054] First, the technical solution in the present invention sets an automatic power control system in the front stage of the mixer local oscillator port and the radio frequency port, and uses the automatic power control system to automatically control the power of the input second electrical signal fundamental component and the reference power, so that the signal power output to the mixer local oscillator port and the radio frequency port is maintained at a predetermined power value, thereby improving the input power stability at the mixer radio frequency port and the local oscillator port. Compared with the existing technical solutions, the closed-loop adjustment process of the technical solution in the present invention is more stable, and the phase-locked loop of the optical fiber length automatic control system can be maintained in the working state of the best loop characteristics for a long time. It has a stronger tolerance to changes in the working environment, product aging, and replacement of the reference source, and can be better applied to outdoor or sports scenes, making the optical frequency comb product more practical.

[0055] Second, the automatic power control system in the technical solution of the present invention can also suppress the amplitude noise of the input signal at the local oscillator port and the radio frequency port, thereby reducing the amplitude noise; the technical solution in the present invention also sets an impedance matching network, an adjustable digital divider and a low-pass amplifier module in the optical fiber length automatic control system, and the impedance matching network can adjust the output impedance of the photodetector to match it with the input impedance of the subsequent circuit, thereby avoiding reflection of the radio frequency electrical signal and improving the transmission efficiency; the adjustable digital divider and the low-pass amplifier module cooperate with each other to further adjust the radio frequency electrical signal to make it consistent with the frequency of the output signal of the ultra-stable reference source, and at the same time filter out the high-order harmonics in the link, further strengthen the suppression of noise in the link, and improve the performance of the entire radio frequency link; compared with the existing technical solutions, the technical solution in the present invention can make the repetition frequency of the optical frequency comb more stable and accurate, and can be applied to the field of high-precision measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] The advantages of the above and / or additional aspects of the present invention will become apparent and easily understood in the description of the embodiments in conjunction with the following drawings, in which:

[0057] Figure 1 is a schematic diagram of the overall structure of an optical frequency comb repetition frequency locking device based on automatic power control according to an embodiment of the present invention;

[0058] Figure 2 Schematic diagram of the overall structure of a traditional analog phase-locked loop according to an embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0060] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0061] like Figure 1 As shown, this embodiment provides an optical frequency comb repetition frequency locking device based on automatic power control, which includes: an optical pump source, an optical frequency comb optical system, an automatic optical fiber length control system, a first automatic power control system and a second automatic power control system.

[0062] The optical pump source is used to provide a short-wave pump light source for the optical frequency comb optical system.

[0063] The optical frequency comb optical system is used to generate an optical frequency comb repetition frequency (repetition frequency is a certain performance index of the optical frequency comb light signal, which changes with the length of the optical fiber) using a short-wave pump light source, and output the optical frequency comb repetition frequency to an automatic optical fiber length control system.

[0064] The optical frequency comb optical system includes piezoelectric ceramics (Piezoelectric ceramics, PZT), gain fiber and fiber ring cavity; the fiber ring cavity is formed by a ring-shaped fiber loop, the gain fiber is arranged in the fiber loop forming the fiber ring cavity, and the piezoelectric ceramic is bonded to the outer surface of one section of the fiber in the fiber ring cavity.

[0065] The piezoelectric ceramic is used to receive a first control signal output by a high-voltage driving module, and adjust the length of the optical fiber bonded thereto according to the first control signal, thereby changing the length of the optical fiber ring cavity in the optical frequency comb optical system, so that the repetition frequency of the optical frequency comb generated by the optical frequency comb optical system changes to a preset frequency, which is the frequency of the reference electrical signal output by the ultra-stable reference source.

[0066] Specifically, the first control signal is ≥ 0V, the voltage of the first control signal is inversely proportional to the repetition frequency of the optical frequency comb, when the voltage of the first control signal increases, the piezoelectric ceramic stretches, the length of the fiber ring cavity increases, and the repetition frequency of the optical frequency comb generated by the optical frequency comb optical system decreases, and when the voltage of the first control signal decreases, the piezoelectric ceramic shortens, the length of the fiber ring cavity decreases, and the repetition frequency of the optical frequency comb generated by the optical frequency comb optical system increases.

[0067] In this embodiment, the piezoelectric ceramic can adjust the length of the optical fiber bonded thereto by electrostriction based on the first control signal output by the high-voltage driving module, so as to change the length of the optical fiber ring cavity in the optical frequency comb system. The optical frequency comb optical system can form a closed loop with the optical fiber length automatic control system, and the closed loop can adaptively adjust the repetition frequency of the optical frequency comb and lock it to a preset frequency that is arranged identically to the output signal of the ultra-stable reference source.

[0068] The gain fiber is used to convert the short-wave pump light provided by the optical pump source into long-wave light, and at the same time enhance the long-wave light propagating in the fiber ring cavity to compensate for the loss caused by the transmission and reflection of light, ensuring that the intensity of the long-wave light signal remains stable during multiple reflections in the ring cavity.

[0069] The fiber ring cavity is used to circulate long-wave light to form an optical frequency comb signal with a fixed comb tooth interval (i.e., repetition frequency).

[0070] The optical fiber length automatic control system is used to lock the repetition frequency of the optical frequency comb output by the optical frequency comb optical system.

[0071] The optical fiber length automatic control system includes a photoelectric detector, an impedance matching network, a first low-pass amplifier module, an adjustable digital divider, a second low-pass amplifier module, an ultra-stable reference source, a low-noise amplifier, a mixer, a PID controller and a high-voltage drive module.

[0072] Among them, the output end of the optical frequency comb optical system is connected to the input end of the photodetector, the photodetector, the impedance matching network, the first low-pass amplifier module, the adjustable digital divider, and the second low-pass amplifier module are connected in sequence, and the output end of the second low-pass amplifier module is connected to the RF port of the mixer through the first automatic power control system; the output end of the ultra-stable reference source is connected to the input end of the low-noise amplifier, and the output end of the low-noise amplifier is connected to the local oscillator port of the mixer through the second automatic power control system; the output end of the mixer is connected to the piezoelectric ceramic through the PID controller and the high-voltage drive module in sequence.

[0073] The photodetector is used to convert the optical frequency comb optical signal output by the optical frequency comb optical system into a first radio frequency electrical signal having a frequency that is consistent with the repetition frequency of the optical signal.

[0074] In this embodiment, the photodetector may be a silicon photodiode, an InGaAs photodiode, or the like.

[0075] The impedance matching network is used to adjust the output impedance of the photodetector to a preset impedance value so that it matches the input impedance of the subsequent circuit.

[0076] In this embodiment, the preset impedance value is 50 ohms, and the impedance matching network can adjust the output impedance of the photodetector to 50 ohms so that it matches the input impedance of the first low-pass amplifier module at the back end, so that the first RF electrical signal can be efficiently transmitted in the subsequent circuit and avoid reflection of the first RF electrical signal, thereby improving the performance of the entire RF link.

[0077] In this embodiment, the impedance matching network adjusts the transmission conditions of the first RF electrical signal according to the output characteristics of the photodetector, thereby improving the quality of subsequent signal processing. The RF link is a circuit that generates and processes RF electrical signals, such as Figure 1 As shown, the radio frequency link includes a first automatic power control system and a photodetector, an impedance matching network, a first low-pass amplifier module, an adjustable digital divider, a second low-pass amplifier module, a mixer, a PID controller and a high-voltage drive module.

[0078] The first low-pass amplifier module is used to extract and amplify the fundamental wave component in the first radio frequency electrical signal and filter out the remaining high-order harmonic components.

[0079] The adjustable digital divider is used to divide the fundamental component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal having the same frequency as the output signal of the ultra-stable reference source, that is, the divided signal is used as the second radio frequency electrical signal to make the divided signal frequency consistent with the output signal frequency of the ultra-stable reference source.

[0080] It should be noted that, in specific operations, frequency division can be achieved by setting the division ratio of an adjustable digital divider. For example, if the repetition frequency of the optical frequency comb is approximately 100 MHz and the frequency of the ultra-stable reference source is approximately 10 MHz, the division ratio of the adjustable digital divider is set to 10.

[0081] The second low-pass amplifier module is used to extract and amplify the fundamental wave component in the second radio frequency electrical signal and filter out the remaining high-order harmonic components.

[0082] In this embodiment, when the adjustable digital divider is used for frequency division, higher harmonics will be generated due to its nonlinear characteristics. The second low-pass amplifier module can filter out the higher harmonics generated by the frequency division and amplify the fundamental component of the second RF electrical signal.

[0083] The ultra-stable reference source is used to provide a reference electrical signal with high frequency stability for the RF link.

[0084] In this embodiment, the ultra-stable reference source is a device that can generate a very stable and accurate signal frequency. It is usually used in high-precision applications such as communication, measurement, metrology and frequency standards to provide a reliable reference signal; the ultra-stable reference source can be a hydrogen clock, a rubidium clock, etc.

[0085] In order to achieve efficient signal processing and system stability, the frequency of the reference electrical signal output by the ultra-stable reference source needs to be close to the frequency of the fundamental component of the second RF electrical signal. This matching frequency relationship is an important basis for selecting or customizing the reference source. That is, after determining the frequency of the fundamental component of the second RF electrical signal by measurement, the ultra-stable reference source is selected or customized according to the frequency of the fundamental component of the second RF electrical signal.

[0086] The low noise amplifier is used to amplify the power of the reference electrical signal output by the ultra-stable reference source.

[0087] The mixer is used to perform frequency discrimination on the fundamental wave component of the second RF electrical signal and the reference electrical signal to obtain a frequency difference signal (ie, mix the two signals, identify and extract the frequency information in the two signals to obtain the frequency difference between the two signals).

[0088] The PID controller (i.e., proportional-integral-differential controller) is used to perform proportional-integral-differential operations on the frequency difference signal, and convert the frequency difference signal into a smooth first control signal.

[0089] The high-voltage driving module is used to amplify the voltage of the first control signal to a predetermined high voltage, so that the voltage-amplified first control signal can completely drive the piezoelectric ceramics in the optical frequency comb system, wherein the predetermined high voltage is 150V.

[0090] The first automatic power control system is used to automatically control the power of the second RF electrical signal fundamental component output by the second low-pass amplifier module, so that the input power at the mixer RF port remains unchanged; specifically, the second RF electrical signal fundamental component is transmitted to the mixer RF port through the first automatic power control system, and the first automatic power control system can adaptively adjust the second RF electrical signal fundamental component to a predetermined power value, which is consistent with the input power value required at the mixer RF port.

[0091] In this embodiment, the first automatic power control system is set at the front end of the mixer RF port, which can timely and adaptively adjust the power value of the fundamental component of the second RF electrical signal when the optical frequency comb light power changes, which is equivalent to adaptively adjusting the gain of the RF link, so that the input signal power at the mixer RF port with a frequency detection function remains constant, thereby ensuring that the transfer parameters of the phase-locked loop do not change.

[0092] The first automatic power control system includes a voltage-controlled attenuator, a radio frequency coupler, a power detector, a voltage comparator, an adjustable reference voltage source and a PI controller; the voltage-controlled attenuator, the radio frequency coupler, the power detector, the voltage comparator and the PI controller are connected in sequence to form a loop, and the adjustable reference voltage source is connected to the voltage comparator.

[0093] The voltage-controlled attenuator is used to adjust the attenuation degree of the fundamental component of the second RF electrical signal (i.e., adjust the RF link gain) according to the signal fed back by the PI controller to keep the power of the fundamental component of the second RF electrical signal constant, so that the input signal power of the mixer RF port is constant.

[0094] Specifically, the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the PI controller feedback signal. When the voltage value of the PI controller feedback signal increases, the attenuation of the voltage-controlled attenuator increases, and the signal power of the fundamental component of the second RF electrical signal decreases. When the voltage value of the PI controller feedback signal decreases, the attenuation of the voltage-controlled attenuator decreases, and the signal power of the fundamental component of the second RF electrical signal increases.

[0095] The radio frequency coupler is used to couple the power of the fundamental wave component of the second electrical signal to the power detector for subsequent power detection.

[0096] In this embodiment, the RF coupler extracts a part of the signal from the main signal path by coupling, usually a part of the fundamental component of the second electrical signal. This extraction does not affect the transmission process of the main signal, but only separates a small part of the signal and transmits this part of the signal to the power detector.

[0097] The power detector is used to receive the radio frequency power signal output by the radio frequency coupler and convert the radio frequency power signal into a direct current voltage signal.

[0098] The voltage comparator is used to receive the ultra-stable reference voltage output by the adjustable reference voltage source, compare the DC voltage signal with the ultra-stable reference voltage, and output a voltage difference signal.

[0099] The adjustable reference voltage source is used to provide an adjustable ultra-stable reference voltage for the voltage comparator.

[0100] It should be noted that the ultra-stable reference voltage corresponds to the magnitude of the signal power input to the mixer's RF port, that is, when the signal power input to the mixer's RF port is determined, the voltage of the adjustable reference voltage source is determined accordingly, so that after the automatic power control of the first automatic power control system, the power value of the signal can remain unchanged when the fundamental wave component of the second RF electrical signal is transmitted to the mixer's RF port.

[0101] The PI controller is used to perform proportional-integral operation on the voltage difference signal, and convert the voltage difference signal into a smooth second control signal. The second control signal is used to adaptively adjust the attenuation degree of the voltage-controlled attenuator, that is, to adjust the attenuation degree applied by the voltage-controlled attenuator when performing power attenuation on the fundamental component of the second electrical signal.

[0102] The second automatic power control system is used to perform automatic power control on the reference electrical signal output by the low-noise amplifier so that the input power at the mixer local oscillator port remains unchanged; specifically, the reference electrical signal is transmitted to the mixer local oscillator port through the second automatic power control system, and the second automatic power control system can adaptively adjust the reference electrical signal to a predetermined power value, which is consistent with the input power value required at the mixer local oscillator port.

[0103] In this embodiment, similarly, the second automatic power control system is set at the front end of the mixer local oscillator port, which can timely and adaptively adjust the power value of the reference electrical signal when the reference source power changes, so that the input signal power at the mixer local oscillator port remains constant, thereby ensuring that the transfer parameters of the phase-locked loop do not change.

[0104] The structural system of the second automatic power control system and the first automatic power control system also includes a voltage-controlled attenuator, a radio frequency coupler, a power detector, a voltage comparator, an adjustable reference voltage source and a PI controller; the signal processing process is the same as that of the first automatic power control system and will not be repeated here.

[0105] The present application also provides an optical frequency comb repetition frequency locking method based on automatic power control, the method also includes automatic control of the input power of the mixer local oscillator port and the radio frequency port, the optical frequency comb repetition frequency locking method based on automatic power control specifically includes the following steps:

[0106] Step 1: Use an optical pump source to provide short-wave pump light to the optical frequency comb optical system, and the optical frequency comb optical system generates an optical frequency comb signal based on the short-wave pump light.

[0107] Specifically, the optical pump source inputs short-wave pump light into the optical frequency comb optical system. The short-wave pump light is pumped by the gain fiber to be enhanced long-wave light. The long-wave light is circulated in the fiber ring cavity to form an optical frequency comb with a fixed comb tooth interval (ie, repetition frequency).

[0108] Step 2, using a photodetector to convert the optical frequency comb signal into a first radio frequency electrical signal with a repetition frequency, dividing the fundamental wave component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal with the same frequency as the output signal of the ultra-stable reference source, and inputting the fundamental wave component of the second radio frequency electrical signal into the radio frequency port of the mixer through the first automatic power control system, specifically comprising:

[0109] The optical frequency comb signal output by the optical frequency comb optical system is converted into a first radio frequency electrical signal with a repetition frequency by a photodetector; the first radio frequency electrical signal is transmitted to the first low-pass amplifier module through an impedance matching network, and the impedance matching network adjusts the output impedance of the photodetector to a preset impedance value so that it matches the input impedance of the first low-pass amplifier module, which is expressed as:

[0110]

[0111] In the formula, R' P is the output impedance of the photodetector after being adjusted by the impedance matching network, R P The output impedance of the photodetector before adjustment is preset to 50Ω.

[0112] In this embodiment, the photodiode in the photodetector works in a reverse bias state, and its output impedance is a high impedance state. Assume that its output impedance is R p , R p>>50Ω, the impedance value needs to be adjusted to the preset impedance value of 50Ω to match the subsequent circuit module, and the input impedance of the low-pass amplifier module is 50 ohms, so impedance matching is achieved. When setting the impedance matching network here, a 50Ω resistor can be connected in parallel to the output port of the photodetector, and the 50Ω resistor is grounded, so the output impedance of the photodetector can be adjusted; the first RF electrical signal is matched with the impedance of the low-pass amplifier module through the impedance matching network, which can avoid signal reflection, improve the transmission efficiency of the first RF electrical signal in the subsequent circuit, and improve the performance of the entire RF link.

[0113] After impedance matching is completed, a first low-pass filter amplifier module is used to amplify the fundamental component of the first RF electrical signal, and the remaining high-order harmonic components are filtered out to obtain the fundamental component of the first RF electrical signal; an adjustable digital divider is used to divide the fundamental component of the first RF electrical signal to obtain a second RF electrical signal with the same frequency as the output signal of the ultra-stable reference source, and then a second low-pass amplifier module is used to amplify the fundamental component in the second RF electrical signal, and the high-order harmonics generated in the second RF electrical signal due to the nonlinearity of the adjustable digital divider are filtered out to obtain the fundamental component of the second RF electrical signal; the fundamental component of the second RF electrical signal is input into the RF port of the mixer after passing through the first automatic power control system.

[0114] Step 3, using a first automatic power control system to adaptively adjust the input power at the RF port of the mixer so that the input power at the RF port remains unchanged, specifically includes:

[0115] Step 3.1, the voltage-controlled attenuator attenuates the fundamental wave component of the second radio frequency electrical signal according to the second control signal output by the PI controller, separates the fundamental wave component of the second radio frequency electrical signal with a predetermined power ratio by using a radio frequency coupler, and couples it to the power detector as a radio frequency power signal;

[0116] The expression for the power attenuation of the fundamental component signal of the second RF electrical signal by the voltage-controlled attenuator is:

[0117] AT=α·V T

[0118] Where AT is the attenuated power in dB, α is the attenuation coefficient of the voltage-controlled attenuator, α = 5.2dB / V, V T It is the voltage value of the second control signal output by the PI controller (ie, the input control voltage received by the voltage-controlled attenuator).

[0119] In this embodiment, the RF coupler is a three-port RF device, including an input port and two output ports, the input port is used to receive the attenuated second RF electrical signal fundamental component signal output by the voltage-controlled attenuator, one of the output ports is used to couple part of the energy separated from the second RF electrical signal fundamental component signal to the power detector, and the other output port is used to input the separated second RF electrical signal fundamental component signal to the mixer RF port; the RF coupler couples part of the energy of the input RF signal to the power detector based on the coupling of the electromagnetic field and electromagnetic induction, and the coupling ratio (i.e., the predetermined power ratio) is 1:10, i.e., the power of the output signal of the coupling port of the RF coupler is 1 / 10 of the power of the input signal.

[0120] In this embodiment, the power detector can convert the power of the second RF signal into a DC voltage signal according to a certain proportional coefficient. In actual use, the coupling ratio of the RF coupler and the conversion proportional coefficient of the power detector are determined according to the loop characteristics required by the automatic power control system, and the power detector is selected after the determination.

[0121] Step 3.2, using a power detector to convert the RF power signal into a DC voltage signal, and transmitting the DC voltage signal to a voltage comparator, the voltage comparator receives an ultra-stable reference voltage output by an adjustable reference voltage source, and subtracts the DC voltage signal from the ultra-stable reference voltage to obtain a voltage difference signal, and transmits the voltage difference signal to a PI controller;

[0122] In this embodiment, the power detector used is a logarithmic power detector, which can convert the logarithmic transformation relationship between power and voltage into a linear relationship; the power detector is used to convert the RF power signal into a DC voltage signal, which is expressed as:

[0123] V P =γ·(P i -P s )

[0124] Where V P is the converted DC voltage, γ is the conversion coefficient of the power detector, γ=0.032V / dBm, P i is the power of the RF power signal (i.e. the input signal power of the power detector), in dBm, P s It is the power of the RF power signal when the conversion voltage is 0V, in dBm.

[0125] In this embodiment, the selection of the ultra-stable reference voltage size of the adjustable reference voltage source can be determined by the measurement data of the power detector, specifically: there is a one-to-one correspondence between the input and output of the power detector, and the one-to-one correspondence table can be obtained through experimental measurement. When the power size that needs to be stable is known, the output voltage size of the power detector can be obtained accordingly, and the ultra-stable reference voltage size is set to the output voltage.

[0126] Step 3.3, use the PI controller to smooth and filter the voltage difference signal to obtain a second control signal, and use the second control signal to adjust the attenuation degree of the voltage-controlled attenuator, wherein the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the PI controller feedback signal.

[0127] The PI controller performs proportional and integral operations on the voltage difference signal, specifically:

[0128]

[0129] Where V c (s) is the Laplace transform of the second control signal, V e (s) is the Laplace transform of the voltage difference signal, G is the proportional factor, p is the differential operator, and s is the complex frequency variable in the Laplace transform, which is used to analyze the frequency domain behavior of the control system. is the transfer function of the PI controller, and the integral bandwidth is 1 / 2πp. In this embodiment, the PI controller performs proportional and integral operations on the voltage difference signal, which is equivalent to amplifying and low-pass filtering the voltage difference signal (i.e., smoothing filtering).

[0130] The second control signal is used to adjust the attenuation degree of the voltage-controlled attenuator. Specifically, when the voltage value of the PI controller feedback signal increases, the attenuation of the voltage-controlled attenuator increases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal decreases. When the voltage value of the PI controller feedback signal decreases, the attenuation of the voltage-controlled attenuator decreases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal increases.

[0131] In this embodiment, when the second control signal increases by 1V, the attenuation degree of the voltage-controlled attenuator increases by 5.2dB, and when the second control signal decreases by 1V, the attenuation degree of the voltage-controlled attenuator decreases by 5.2dB.

[0132] In this embodiment, the voltage-controlled attenuator is usually positive voltage controlled, and the voltage difference signal is in the positive and negative voltage range. Therefore, in a specific embodiment, a positive voltage bias can be introduced into the PI controller to make the output control signal in the positive voltage range.

[0133] In this embodiment, the first automatic power control system performs automatic power control on the fundamental wave component of the input second electrical signal, so that the power of the signal output to the RF port of the mixer remains unchanged according to the set power value.

[0134] Step 4, using an ultra-stable reference source to generate a reference electrical signal, using a noise amplifier to amplify the power of the reference electrical signal, and inputting the amplified reference electrical signal into the mixer local oscillator port through a second automatic power control system.

[0135] Step 5: Use the second automatic power control system to adaptively adjust the input power at the local oscillator port of the mixer so that the input power at the local oscillator port remains unchanged.

[0136] In this embodiment, the ultra-stable reference source outputs a reference electrical signal with high frequency stability to a low noise amplifier for power amplification; the amplified reference electrical signal outputs an electrical signal with a constant power to the mixer local oscillator port via the second automatic power control system. The signal processing method in step 5 is the same as the signal processing method in step 2, which will not be repeated here.

[0137] Step 6, use a mixer to perform frequency discrimination on the fundamental component of the second RF electrical signal and the reference electrical signal to obtain a frequency difference signal, the frequency difference signal is shaped and filtered by a PID controller into a smooth first control signal, the first control signal is amplified by a high-voltage drive module, and the amplified first control signal is input into the optical frequency comb optical system.

[0138] Step 7, the piezoelectric ceramic inside the optical frequency comb optical system adjusts the length of the fiber ring cavity according to the amplified first control signal, wherein when the voltage of the first control signal increases, the piezoelectric ceramic stretches, the length of the fiber ring cavity increases, and the repetition frequency of the optical frequency comb generated by the optical frequency comb optical system decreases; when the voltage of the first control signal decreases, the piezoelectric ceramic shortens, the length of the fiber ring cavity decreases, and the repetition frequency of the optical frequency comb generated by the optical frequency comb optical system increases.

[0139] In this embodiment, the first control signal is amplified into a high-voltage control signal by the high-voltage driving module, and then input into the optical frequency comb optical system, and drives the piezoelectric ceramic (PZT) to adjust the length of the fiber ring cavity, and then adjust the repetition frequency to form a closed-loop control. When the repetition frequency of the optical frequency comb is equal to the frequency of the ultra-stable reference source, the frequency difference signal is zero, and the fiber length automatic control system enters a balanced state; if the balanced state is broken by a perturbation, the fiber length control system continues to enter the same workflow to complete the closed-loop adjustment until it is balanced again.

[0140] Example: The optical frequency comb repetition frequency locking device without automatic power control (APC) in the prior art and the optical frequency comb repetition frequency locking device with automatic power control in the present invention are used to perform closed-loop adjustment of the repetition frequency respectively. The phase noise analyzer is used to detect the amplitude noise of the input signal of the mixer RF port when the two devices are adjusted. The detection results are shown in Table 1 below:

[0141] Table 1

[0142]

[0143] It can be seen from Table 1 that when the optical frequency comb re-rate locking device without automatic power control in the prior art is used for closed-loop adjustment, the amplitude noise of the input signal at the mixer RF port is relatively large, while when the optical frequency comb re-rate locking device with automatic power control in the present invention is used for closed-loop adjustment, the amplitude noise of the input signal at the mixer RF port is relatively small. The device of the present invention has a suppression effect of about 20 dB on the amplitude noise, and the power stability is optimized by nearly 2 orders of magnitude. Compared with the device of the prior art, the device of the present invention is more conducive to noise suppression and improves the stability of the input power at the mixer RF port.

[0144] In the present invention, the terms "install", "connect", "connect", "fix" and the like should be understood in a broad sense. For example, "connect" can be a fixed connection, a detachable connection, or an integral connection; "connect" can be a direct connection or an indirect connection through an intermediate medium. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0145] The shapes of various components in the drawings are schematic, and certain differences from their actual shapes are not excluded. The drawings are only used to illustrate the principles of the present invention and are not intended to limit the present invention.

[0146] Although the present invention is disclosed in detail with reference to the accompanying drawings, it should be understood that these descriptions are merely exemplary and are not intended to limit the application of the present invention. The scope of protection of the present invention is defined by the appended claims and may include various modifications, alterations and equivalents made to the invention without departing from the scope and spirit of the present invention.

Claims

1. An optical frequency comb repetition frequency locking device based on automatic power control, characterized in that: The device includes: The optical frequency comb optical system is used to generate an optical frequency comb repetition frequency, and output the optical frequency comb repetition frequency to an optical fiber length automatic control system; The optical fiber length automatic control system is used to lock the repetition frequency of the optical frequency comb output by the optical frequency comb optical system; The optical fiber length automatic control system includes a photodetector, an ultra-stable reference source, a mixer and a PID controller. The photodetector is used to convert an optical frequency comb optical signal into a radio frequency electrical signal with a frequency that is consistent with the repetition frequency of the optical signal, and provide it to the radio frequency port of the mixer; the ultra-stable reference source is used to generate a reference electrical signal with high frequency stability, and provide it to the local oscillator port of the mixer; the mixer is used to perform frequency discrimination on the radio frequency electrical signal and the reference electrical signal to obtain a frequency difference signal; the PID controller is used to perform proportional integral differential operations on the frequency difference signal, and convert the frequency difference signal into a smooth first control signal, the first control signal is used to adjust the repetition frequency of the optical frequency comb, and the voltage of the control signal is inversely proportional to the repetition frequency of the optical frequency comb; The first automatic power control system is used to adjust the input signal power at the RF port of the mixer to keep it at a predetermined power value; The second automatic power control system is used to adjust the input signal power at the local oscillator port of the mixer to keep it at a predetermined power value.

2. The optical frequency comb repetition frequency locking device based on automatic power control according to claim 1, characterized in that: The optical fiber length automatic control system also includes an impedance matching network, a first low-pass amplification module, an adjustable digital frequency divider, and a second low-pass amplification module; The impedance matching network is used to adjust the output impedance of the photodetector to a preset impedance value so that it matches the input impedance of the subsequent circuit; The first low-pass amplifier module is used to extract and amplify the fundamental wave component in the first radio frequency electrical signal output by the photodetector, and filter out the remaining high-order harmonic components; The adjustable frequency divider is used to divide the fundamental wave component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal with the same frequency as the output signal of the ultra-stable reference source; The second low-pass amplifier module is used to extract and amplify the fundamental wave component in the second radio frequency electrical signal and filter out the remaining high-order harmonic components.

3. The optical frequency comb repetition frequency locking device based on automatic power control as claimed in claim 2, characterized in that: The first automatic power control system is used to automatically control the power of the second RF electrical signal fundamental component output by the second low-pass amplification module so that the input power at the RF port of the mixer remains unchanged, and the first automatic power control system includes a voltage-controlled attenuator, a RF coupler, a power detector, a voltage comparator, an adjustable reference voltage source and a PI controller; The voltage-controlled attenuator is used to adjust the attenuation degree of the fundamental wave component of the second radio frequency electrical signal according to the signal fed back by the PI controller, so that the input signal power of the mixer radio frequency port is constant, wherein the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the feedback signal of the PI controller; The radio frequency coupler is used to couple the power of the fundamental wave component of the second electrical signal to the power detector for subsequent power detection; The power detector is used to receive the radio frequency power signal output by the radio frequency coupler and convert the radio frequency power signal into a direct current voltage signal; The voltage comparator is used to receive the ultra-stable reference voltage output by the adjustable reference voltage source, and compare the DC voltage signal with the ultra-stable reference voltage to output a voltage difference signal. The adjustable reference voltage source is used to provide an adjustable ultra-stable reference voltage for the voltage comparator; The PI controller is used to perform proportional integral operation on the voltage difference signal to convert the voltage difference signal into a smooth second control signal, and the second control signal is used to adjust the attenuation degree of the voltage-controlled attenuator on the fundamental wave component of the second radio frequency electrical signal.

4. The optical frequency comb repetition frequency locking device based on automatic power control as claimed in claim 1, characterized in that: The optical fiber length automatic control system further comprises a low noise amplifier, which is used to amplify the power of the reference electrical signal output by the ultra-stable reference source; The second automatic power control system is used to perform automatic power control on the reference electrical signal output by the low noise amplifier so that the input power at the local oscillator port of the mixer remains unchanged.

5. The optical frequency comb repetition frequency locking device based on automatic power control according to claim 1, characterized in that: The optical fiber length automatic control system further includes a high voltage driving module and an optical pump source; The high-voltage driving module is used to amplify the voltage of the first control signal to a predetermined high voltage, so that the voltage-amplified first control signal can completely drive the piezoelectric ceramic in the optical frequency comb system; The optical pump source is used to provide a short-wave pump light source for the optical frequency comb optical system, and the optical frequency comb optical system generates an optical frequency comb repetition frequency by using the short-wave pump light source.

6. An optical frequency comb repetition frequency locking method used in the optical frequency comb repetition frequency locking device based on automatic power control according to any one of claims 1 to 5, characterized in that: The method includes: Step 1, using an optical pump source to provide short-wave pump light for the optical frequency comb optical system, and the optical frequency comb optical system generates an optical frequency comb signal based on the short-wave pump light; Step 2, using a photodetector to convert the optical frequency comb signal into a first radio frequency electrical signal with a repetition frequency, dividing the fundamental wave component of the first radio frequency electrical signal to obtain a second radio frequency electrical signal with the same frequency as the output signal of the ultra-stable reference source, and inputting the fundamental wave component of the second radio frequency electrical signal into the radio frequency port of the mixer through a first automatic power control system; Step 3, using a first automatic power control system to adaptively adjust the input power at the RF port of the mixer so that the input power at the RF port remains unchanged; Step 4, using an ultra-stable reference source to generate a reference electrical signal, using a noise amplifier to amplify the power of the reference electrical signal, and inputting the amplified reference electrical signal into the local oscillator port of the mixer through a second automatic power control system; Step 5, using a second automatic power control system to adaptively adjust the input power at the local oscillator port of the mixer so that the input power at the local oscillator port remains unchanged; Step 6, using a mixer to perform frequency discrimination on the fundamental component of the second RF electrical signal and the reference electrical signal to obtain a frequency difference signal, the frequency difference signal is shaped and filtered by a PID controller into a smooth first control signal, the first control signal is amplified by a high-voltage driving module, and the amplified first control signal is input into the optical frequency comb optical system; Step 7: The piezoelectric ceramic inside the optical frequency comb optical system adjusts the length of the fiber ring cavity according to the amplified first control signal, wherein the voltage of the first control signal is inversely proportional to the repetition frequency of the optical frequency comb.

7. The optical frequency comb repetition frequency locking device based on automatic power control as claimed in claim 6, characterized in that: The step 3 specifically includes the following steps: Step 3.1, the voltage-controlled attenuator attenuates the fundamental wave component of the second radio frequency electrical signal according to the second control signal output by the PID controller, separates the fundamental wave component of the second radio frequency electrical signal with a predetermined power ratio by using a radio frequency coupler, and couples it to the power detector as a radio frequency power signal; Step 3.2, using a power detector to convert the RF power signal into a DC voltage signal, and transmitting the DC voltage signal to a voltage comparator, the voltage comparator receives an ultra-stable reference voltage output by an adjustable reference voltage source, and subtracts the DC voltage signal from the ultra-stable reference voltage to obtain a voltage difference signal, and transmits the voltage difference signal to a PI controller; Step 3.3, use the PI controller to smooth and filter the voltage difference signal to obtain a second control signal, and use the second control signal to adjust the attenuation degree of the voltage-controlled attenuator, wherein the attenuation degree of the voltage-controlled attenuator is proportional to the voltage value of the PI controller feedback signal.

8. The optical frequency comb repetition frequency locking device based on automatic power control as claimed in claim 7, characterized in that: The expression for the attenuation of the power of the fundamental component signal of the second RF electrical signal by the voltage-controlled attenuator in step 3.1 is: AT=α·V T Where AT is the attenuated power in dB, α is the attenuation coefficient of the voltage-controlled attenuator, α = 5.2dB / V, V T It is the voltage value of the second control signal output by the PI controller.

9. The optical frequency comb repetition frequency locking device based on automatic power control as claimed in claim 7, characterized in that: In step 3.2, the RF power signal is converted into a DC voltage signal using a power detector, which is expressed as: V P =γ·(P i -P s ) Where V P is the converted DC voltage, γ is the conversion coefficient of the power detector, γ=0.032V / dBm, P i is the power of the RF power signal in dBm, P s It is the power of the RF power signal when the conversion voltage is 0V, in dBm.

10. The optical frequency comb repetition frequency locking device based on automatic power control according to claim 7, characterized in that: The step 3.3 specifically includes: The PI controller performs proportional and integral operations on the voltage difference signal, specifically: Where V c (s) is the Laplace transform of the second control signal, V e (s) is the Laplace transform of the voltage difference signal, G is the proportional factor, p is the differential operator, and s is the complex frequency variable in the Laplace transform, indicating that the dynamic characteristic integral bandwidth of the proportional-integral controller is 1 / 2πp; The attenuation degree of the voltage-controlled attenuator is adjusted by using the second control signal. When the voltage value of the PI controller feedback signal increases, the attenuation of the voltage-controlled attenuator increases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal decreases. When the voltage value of the PI controller feedback signal decreases, the attenuation of the voltage-controlled attenuator decreases, and the signal power of the fundamental wave component of the attenuated second RF electrical signal increases.

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