Optical frequency comb repetition frequency control system and locking method

Abstract

The present invention belongs to the technical field of optical frequency comb repetition frequency, and discloses an optical frequency comb repetition frequency control system and locking method, comprising a light source module, a signal detection module, a frequency measurement module, a comparison frequency generation module, and a feedback control module. The light source module generates an optical frequency comb; the signal detection module converts the optical signal into an electrical signal, and performs noise reduction and amplification processing through a signal processor, wherein the noise reduction adopts a wavelet transform method; the frequency measurement module accurately measures the repetition frequency using a dual measurement method of a frequency counter and a spectrum analyzer; the comparison frequency generation module provides a high-precision reference frequency; and the feedback control module performs closed-loop regulation based on the difference between the measured frequency and the reference frequency. By optimizing signal processing and adopting dual frequency measurement and closed-loop feedback control, the present invention effectively solves the problems of weak electrical signals, large noise interference, and low frequency control accuracy in the prior art, thereby improving the stability and accuracy of the optical frequency comb repetition frequency.

Description

Technical Field

[0001] The present invention relates to the technical field of optical frequency comb repetition frequency, and in particular to a system for precisely controlling and locking the repetition frequency of an optical frequency comb and an implementation method thereof. Background Art

[0002] Optical frequency comb ( 光学频率梳 ) is a special spectrum that appears in the frequency domain as a series of discrete and equally spaced frequency components, like the teeth of a comb, hence the name. Optical frequency combs are usually generated by devices such as mode-locked lasers. In the cavity of a mode-locked laser, ultrashort light pulses propagate back and forth at a fixed period. Through the mode-locking mechanism, these pulses form a highly stable periodic sequence in time, and their corresponding manifestation in the frequency domain is the optical frequency comb. The frequency interval between adjacent "comb teeth" is called the repetition frequency of the optical frequency comb ( 重复频率 ).

[0003] The repetition rate of an optical frequency comb is extremely stable and precise, making it of great value in numerous high-precision scientific research and application fields. For example, in precision spectroscopy and frequency metrology, the repetition rate of an optical frequency comb can be used as an accurate frequency reference scale. By comparing the measured frequency with the comb tooth frequency of the optical frequency comb, unprecedented frequency measurement accuracy can be achieved. Furthermore, in the field of time standards, optical frequency combs can accurately transfer atomic clock frequency standards from microwave bands to optical bands, and vice versa, greatly promoting the development of optical atomic clocks and the advancement of high-precision time synchronization technology.

[0004] However, the repetition rate of an optical frequency comb is susceptible to drift due to environmental factors (such as temperature changes and mechanical vibrations) and fluctuations in the laser's internal parameters (such as cavity length and pump power). To maintain high stability and precision, the repetition rate must be precisely controlled and locked.

[0005] Existing optical frequency comb repetition rate control systems typically employ a feedback control loop. The basic principle is to detect the repetition rate of the optical frequency comb's output signal, compare the measured value with a highly stable reference frequency, and generate an error signal. This error signal is then used to adjust a laser parameter (such as cavity length or pump power) to lock the repetition rate to the reference frequency.

[0006] However, the existing technology still has some shortcomings in the implementation process:

[0007] 1. Difficulty in signal detection: After the optical pulse signal output from the optical frequency comb is converted into an electrical signal by a photodetector, the signal strength is often weak, especially at high repetition rates. This weak electrical signal is not conducive to subsequent precise frequency measurement and processing.

[0008] 2. Severe noise interference: The photoelectric conversion process and subsequent electronic circuits will inevitably introduce various noises. These noises will be superimposed on the repetitive frequency signal, reducing the signal-to-noise ratio and seriously affecting the accuracy of frequency measurement and the stability of the control system.

[0009] 3. Limited control accuracy: Traditional control systems may rely solely on a single frequency measurement method, or the feedback control algorithm may not be optimized enough, resulting in limited control accuracy and response speed of the repetition frequency, making it difficult to completely suppress frequency jitter and compensate for environmental disturbances.

[0010] Therefore, how to effectively enhance the detected repetition frequency electrical signal, suppress noise interference, and achieve higher precision and stability in repetition frequency control and locking is a technical problem that needs to be urgently solved in the current field of optical frequency comb technology. Summary of the Invention

[0011] To overcome the above-mentioned defects existing in the prior art, namely, the problem that the optical frequency comb repetition frequency signal is weak and has large noise interference after photoelectric conversion, resulting in inaccurate subsequent frequency measurement and low control precision, the purpose of the present invention is to provide an optical frequency comb repetition frequency control system and locking method, aiming to improve the signal detection quality, measurement accuracy, and stability and response speed of the control system.

[0012] To achieve the above object, the present invention provides the following technical solutions:

[0013] An optical frequency comb repetition frequency control system includes a light source module, a signal detection module, a frequency measurement module, a comparison frequency generation module and a feedback control module.

[0014] The light source module generates ultrashort pulse lasers through a light source. When the laser pulses pass through nonlinear materials, new frequency components are generated, thereby forming an optical frequency comb.

[0015] The signal detection module includes a photodetector and a signal processor. This module receives the optical pulse signal from the optical frequency comb. The photodetector converts it into an electrical signal. The signal processor performs noise reduction and amplification on the electrical signal to improve signal quality.

[0016] The frequency measurement module includes a frequency counter and a spectrum analyzer. This module uses the frequency counter and spectrum analyzer to perform dual measurements of the frequency of the electrical pulse signal processed by the signal processor (i.e., the repetition frequency of the optical frequency comb) to improve the accuracy and reliability of the measurement results.

[0017] The comparison frequency generation module includes a crystal oscillator and an atomic clock. This module uses the energy level transition frequency of the atomic clock as a high-precision frequency standard and uses the crystal oscillator to provide a stable reference frequency to generate a reference frequency for comparison with the measured frequency.

[0018] The feedback control module, comprising an error amplifier, a controller, and a driver, receives the actual repetition frequency obtained by the frequency measurement module and the reference frequency provided by the comparison frequency generation module, calculating the difference between the two (an error signal). The controller generates adjustment instructions based on the error signal and uses the driver to adjust relevant parameters of the light source module (such as pump power or intracavity components), thereby achieving closed-loop control and regulation of the optical frequency comb repetition frequency.

[0019] In a preferred embodiment, the light source module includes a laser source and a nonlinear medium. The laser source is used to generate ultrashort laser pulses with high peak power and narrow pulse width, serving as the initial light source for the optical frequency comb. The nonlinear medium (e.g., a highly nonlinear optical fiber) is used to cause nonlinear effects (such as self-phase modulation and four-wave mixing) when the ultrashort laser pulses pass through it, thereby broadening the spectrum, generating new frequency components, and forming a broadband optical frequency comb.

[0020] In a preferred embodiment, the photodetector (e.g., high-speed PIN Photodiode or Avalanche Photodiode 雪崩光电二极管 ) converts the optical pulse sequence of the optical frequency comb into a sequence of electrical pulses with a corresponding repetition frequency. The signal processor amplifies the electrical signal to ensure that the signal amplitude is sufficient for subsequent processing, while also taking measures (such as noise reduction processing as described below) to suppress the introduction of noise. Preferably, the noise suppression performance of the signal processor (e.g., as reflected by filtering parameters or algorithm parameters) is related to the transmission delay of the signal in the system. As the delay time increases, more noise may be introduced or signal distortion may occur. In this case, it is necessary to dynamically adjust the relevant noise suppression parameters (such as filter bandwidth, wavelet threshold, etc.) to maintain a stable noise reduction effect.

[0021] In a preferred embodiment, the signal processor in the signal detection module adopts a specific noise reduction algorithm, such as wavelet transform noise reduction. Specifically, first, the noisy electrical signal output by the photodetector (set as a discrete signal ) to perform discrete wavelet transform ( 离散小波变换 ), decompose it into different scales and pan The wavelet coefficients under The transformation formula is: ,in is the wavelet basis function Then, the conjugate complex number of the wavelet coefficients obtained is Perform threshold processing. The commonly used hard threshold processing method is: set a threshold , if the absolute value of the wavelet coefficient Greater than , then keep the coefficient; if it is less than or equal to , then set it to 0. The processing formula is: . (Other processing methods such as soft thresholding can also be used). Finally, the processed wavelet coefficients are subjected to inverse discrete wavelet transform ( 逆离散小波变换 ), reconstruct the denoised signal The inverse transformation formula is: This noise reduction process can effectively remove the noise components in the signal while better retaining the main features of the signal. After the noise reduction process, the signal is amplified.

[0022] In a preferred embodiment, the signal processor in the signal detection module amplifies the noise-reduced signal to achieve the input level required by the subsequent frequency measurement device. Assume that the input voltage of the amplifier is , the output voltage is , the magnification is , then the amplification relationship is: The amplifier should have sufficient bandwidth to process the high-frequency electrical signals corresponding to the repetition rate of the optical frequency comb and have a low noise figure.

[0023] In a preferred embodiment, the frequency measurement module adopts a dual measurement mechanism. 频率计数器 ) by using a precisely defined time window Number of electrical pulses input to the internal Count and then calculate the frequency This method has high accuracy when measuring stable signals. Spectrum Analyzer ( 频谱 分析仪 ) performs a Fourier transform on the input electrical signal, displaying its spectrum in the frequency domain. The repetition frequency of the optical frequency comb corresponds to the fundamental peak frequency in the spectrum and can also be determined by observing the intervals between harmonic peaks. A spectrum analyzer provides information on the signal's spectral purity and helps identify noise and interference. Comparing and combining the measurement results of a frequency counter and a spectrum analyzer can improve the accuracy and reliability of repetition frequency measurements.

[0024] In a preferred embodiment, the comparison frequency generation module uses a high-stability frequency source. 原子钟 ) uses the energy level transition frequency inside the atom as a reference, has extremely high long-term stability and accuracy, and can be used as the ultimate frequency standard. 晶体振荡器 , referred to as crystal oscillator), especially the constant temperature crystal oscillator ( 恒温晶体振荡器 ) or temperature compensated crystal oscillator ( 温补晶体振荡器 ), with excellent short-term stability. The frequency of the crystal oscillator output can be controlled by a phase-locked loop ( 锁相环) is locked to the atomic clock signal, or the output frequency of a high-stability crystal oscillator is directly used, and then multiplied, divided or directly digitally synthesized ( 直接数字频率合成器 ) and other technologies to generate a reference frequency signal precisely equal to the target optical frequency comb repetition rate. Using both an atomic clock and a crystal oscillator as reference sources, the long-term accuracy of the atomic clock and the short-term stability of the crystal oscillator can be leveraged to provide a more reliable baseline for subsequent error calculations, making the error signal more sensitive to frequency deviations.

[0025] In a preferred embodiment, the feedback control module realizes closed-loop locking. The error amplifier converts the actual repetition frequency measured by the frequency measurement module into Compared with the reference frequency provided by the frequency generation module A comparison is performed (e.g., by a mixer or digital subtractor) to produce a frequency difference = The error signal is proportional to the error signal. This error signal is usually weak and needs to be amplified by an error amplifier. 比例积分微分 The controller of the algorithm receives the amplified error signal and adjusts the control parameters (proportional P ,integral I ,differential D ) calculates the control signal. The driver converts the control signal (usually a voltage or digital signal) into a physical quantity that can directly drive the actuator in the light source module, such as changing the driving current or voltage of the pump laser, or driving the piezoelectric ceramic ( 压电陶瓷 ) fine-tune the cavity length, etc., thereby adjusting the actual repetition frequency of the optical frequency comb so that it approaches and locks on the reference frequency.

[0026] The present invention also provides a method for locking the repetition frequency of an optical frequency comb, which is implemented using the above system and includes the following steps:

[0027] S1: Obtain the optical signal output by the optical frequency comb optical system and convert it into an electrical signal through the photodetector in the signal detection module;

[0028] S2: Using the signal processor in the signal detection module, the converted electrical signal is subjected to noise reduction (e.g., wavelet noise reduction) and amplification processing to obtain a high-quality electrical signal. Furthermore, the time interval information of the processed electrical signal (e.g., a pulse train) can be converted into amplitude values (e.g., using a time-to-amplitude converter) to facilitate subsequent comparison.

[0029] S3: Compare the time amplitude value obtained in step S2 (or directly use the processed frequency measurement value) with a preset standard amplitude value (or the standard value corresponding to the reference frequency) to obtain an amplitude difference value (or a frequency difference value);

[0030] S4: Determine whether the difference satisfies the preset locking condition (for example, whether the difference is within the allowable error range). If the difference does not meet the condition, indicating that the frequency has not been locked or has drifted, the feedback control module adjusts the target adjustment parameters in the light source module (such as pump power or cavity length) based on the magnitude and polarity of the difference to reduce the frequency deviation. After the adjustment is completed, return to step S1, reacquire the optical signal, and perform a new round of detection and adjustment.

[0031] S5: If the difference meets the preset locking condition (for example, if the difference is less than a certain threshold and remains so for a period of time), the repetition frequency is considered to be locked. At this point, the system maintains the current adjustment state and continues to monitor the frequency. The repetition frequency corresponding to the optical signal currently output by the frequency comb optical system is the locked repetition frequency.

[0032] The technical effects and advantages of the optical frequency comb repetition frequency control system and locking method of the present invention are as follows:

[0033] 1. Improve signal detection quality: The signal processor in the signal detection module, particularly advanced noise reduction algorithms such as wavelet transform, effectively filters out noise interference in electrical signals, then performs low-noise amplification, significantly improving the signal-to-noise ratio and laying the foundation for subsequent accurate measurements. A mechanism for dynamically adjusting noise reduction parameters adapts to varying delays, ensuring the stability of the noise reduction effect.

[0034] 2. Improve frequency measurement accuracy: Using a dual measurement mechanism of a frequency counter and a spectrum analyzer, the two methods, each with its own focus, complement each other and can more accurately and reliably determine the repetition frequency of the optical frequency comb and evaluate the signal's spectral quality.

[0035] 3. Improve control stability and accuracy: Use highly stable atomic clocks and crystal oscillators as reference frequency sources, combined with optimized feedback control algorithms (such as 比例积分微分 ), enabling precise and rapid closed-loop locking of the repetition frequency. The system monitors frequency deviations in real time and rapidly adjusts to effectively suppress frequency jitter and compensate for environmental factors (such as temperature and vibration), ensuring the frequency comb maintains a highly stable repetition frequency output over extended periods of operation.

[0036] 4. Improved system efficiency: The fast adjustment response capability shortens the time required for the optical frequency comb to stabilize from startup, as well as the transition time when switching operating states (such as changing the repetition frequency setting), thereby improving the efficiency of the entire optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for describing the embodiments.

[0038] Figure 1 1 is a flow chart of a method for locking the repetition frequency of an optical frequency comb proposed by the present invention;

[0039] Figure 2 This is a simplified flow chart of an optical frequency comb repetition frequency control system proposed by the present invention;

[0040] Figure 3 This is a detailed system composition block diagram of an optical frequency comb repetition frequency control system proposed by the present invention. DETAILED DESCRIPTION

[0041] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0042] It should be noted that, in this document, relational terms such as "first", "second", etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further limitations, an element defined by the sentence "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device that includes the element.

[0043] Example 1

[0044] Reference Figure 3 This embodiment provides an optical frequency comb repetition frequency control system. The system includes: a light source module, a signal detection module, a frequency measurement module, a comparison frequency generation module, and a feedback control module.

[0045] The light source module is used to generate an optical frequency comb. In this embodiment, the light source module includes a laser source and a nonlinear medium. The laser source can be a mode-locked fiber laser or a solid-state laser, which is used to generate a central wavelength in the communication band (such as 1550 nm). Near infrared) or near infrared band, the pulse width is in the order of femtoseconds or picoseconds, and the repetition frequency is in the order of tens to a few The ultrashort laser pulse sequence in the range of 100 nm is generated. The laser has a high peak power and a narrow pulse width. The generated ultrashort laser pulse is then injected into a nonlinear medium. The nonlinear medium can be a section of highly nonlinear optical fiber ( 高非线性光纤 ) or periodically poled lithium niobate ( 周期极化铌酸锂 ) waveguides, etc. When a strong laser pulse passes through a nonlinear medium, nonlinear effects such as self-phase modulation and four-wave mixing occur, which greatly broadens the laser spectrum and forms an optical frequency comb with a wide coverage range.

[0046] The signal detection module is used to receive the optical frequency comb signal generated by the light source module and convert it into an electrical signal suitable for subsequent processing. In this embodiment, the signal detection module includes a photodetector and a signal processor. A portion of the optical signal output by the optical frequency comb (which can be extracted by a beam splitter) is irradiated onto the photodetector. The photodetector uses a high-speed response photodiode (e.g. 铟镓砷PIN The photodetector converts the periodic optical pulse sequence into a sequence of electrical pulses at the same frequency.

[0047] The signal processor processes the original electrical signal output by the photodetector. First, noise reduction is performed. Suppose the original noisy electrical signal is (After sampling and discretization). Using wavelet transform denoising method:

[0048] 1. Yes Perform multi-layer discrete wavelet decomposition to obtain the wavelet coefficients of each layer For example, a 3-layer decomposition is performed using the db4 wavelet basis.

[0049] 2. Decompose the high-frequency detail coefficients obtained from each layer ( 细节系数 ) Apply thresholding. Choose an appropriate threshold λ (e.g., based on signal energy or noise level estimation, such as using 视觉收缩 、 Sure收缩 Threshold selection rules). Apply a hard threshold function: , low-frequency approximation coefficient ( 近似系数 ) Usually no thresholding is performed or a smaller threshold is used.

[0050] 3. Use the processed approximate coefficients and detail coefficients to perform inverse discrete wavelet transform to reconstruct the denoised signal , .

[0051] Experimental verification shows that the use of wavelet noise reduction processing can reduce the input signal noise ratio ( 信噪比 ) from 20 before noise reduction Increased to 42 (Test conditions: 1 Bandwidth, input noise power -80 ), significantly improving signal quality.

[0052] After noise reduction, the signal processor Amplify. Use a low-noise broadband amplifier and set the appropriate amplification factor. , so that the output voltage (in correspond The voltage amplitude) reaches the input level range required by the frequency measurement module (for example, several hundred V to V). The amplifier must ensure that it does not introduce excessive additional noise while amplifying the signal.

[0053] Furthermore, noise suppression parameters within the signal processor (such as the wavelet threshold λ or the filter cutoff frequency) can be correlated with the delay time along the signal transmission path. For example, by measuring or estimating the delay of the signal from the photodetector to the processor. , dynamic adjustment Values, such as ,in is the baseline threshold, is the adjustment coefficient. When the delay increases, the threshold is appropriately increased to more effectively suppress possible noise accumulation and maintain a stable noise reduction effect.

[0054] Example 2

[0055] Based on Example 1, this example further describes a frequency measurement module, a comparison frequency generation module, and a feedback control module.

[0056] The frequency measurement module measures the frequency of the noise-reduced and amplified electrical pulse signal output by the signal processor. This embodiment adopts a dual measurement method, including a frequency counter and a spectrum analyzer. The frequency counter (e.g. 安捷伦 53230A ) Set appropriate gate time (For example, 1 or 10 ), the number of pulses of the input signal Count and calculate the repetition frequency . Spectrum analyzer (e.g. 罗德与施瓦茨FSW ) receives the same signal and performs spectrum analysis. On the spectrum graph, you can directly read the frequency of the fundamental peak or measure the frequency interval between adjacent harmonic peaks, both of which are equal to the repetition frequency of the optical frequency comb. and spectrum analyzer measurement results If the two are consistent (for example, the difference is less than a preset tolerance), the measurement result can be considered reliable, and the average value or one of them is taken as the current actual repetition frequency. If the difference is large, it may indicate a measurement error or signal quality problem, and the system can issue an alarm.

[0057] Experimental verification shows that after the noise reduction processing of the signal processor, the measurement error of the frequency counter can be reduced from ±50 Reduced to ±15 (For 10 Repetition frequency, 1 The peak interval detection resolution of the spectrum analyzer is improved by 20%.

[0058] The contrast frequency generation module provides a high stability reference frequency In this embodiment, the module includes a GPS disciplined rubidium atomic clock and a high-stability oven-controlled crystal oscillator ( 恒温晶体振荡器 ). Rubidium atomic clocks provide extremely high long-term stability of 10 Standard frequency signal. OCXO42 Provides excellent short-term stability 100 signal. A phase-locked loop (PLL) can be used 锁相环 ) circuit, will OCXO42 The output frequency is locked to 10 of the atomic clock Signal, get both long-term accuracy and short-term stability 100 Then, according to the target optical frequency comb repetition frequency (e.g. =250 ), using a frequency synthesizer (e.g. 直接数字频率合成器 ) or frequency division / multiplication circuit, from 100 The reference frequency is generated exactly equal to Reference frequency signal .

[0059] The feedback control module realizes closed-loop frequency locking. It includes an error amplifier, a controller, and a driver. The actual repetition frequency obtained by the frequency measurement module is converted to Compared with the reference frequency provided by the frequency generation module Input to a mixer or digital phase detector to generate a frequency difference = The error amplifier amplifies and filters the error signal. 比例积分微分 Control algorithm. It receives the amplified error signal and adjusts it according to the set proportional gain. , integration time and differential time Parameters, calculate the control output signal , ,in Is the error signal. The driver converts the digital control signal output by the controller into 数模转换器 ) is converted into an analog voltage signal. This voltage signal is used to control an actuator in the light source module. For example, if the light source module is a mode-locked fiber laser, this voltage can drive a piezoelectric ceramic ( 压电陶瓷 ) actuator to change the repetition rate by fine-tuning the cavity length. Alternatively, this voltage can adjust the drive current of the pump laser, indirectly affecting the repetition rate by changing the pump power. Through this closed-loop feedback loop, the system can automatically adjust the light source module so that Approaching , and finally the repetition frequency of the optical frequency comb is accurately locked at the target value.

[0060] Experimental verification shows that the closed-loop control system of the present invention and the high-precision frequency data provided by the dual measurement module are used. 比例积分微分 The controller's response time can be shortened from the traditional 20ms to 2.5ms (adjustment parameter example: =0.8, =0.1s, =0.05s), overshoot is reduced by 80%. In the electromagnetic interference environment of 30V / m, the repetition frequency deviation of the system is ±30 Optimized to ±5 , and the stable recovery time is only 2ms. In 24 hours of continuous operation, the long-term stability of the repetition frequency is better than ±0.1 (The traditional solution is ±1 ), the short-term stability (Allan variance) reaches 5×10 at 1 second integration time −12 .

[0061] Example 3

[0062] This embodiment describes a method for locking the repetition frequency of an optical frequency comb using the system described in Embodiment 1 and Embodiment 2. Figure 1 Flowchart:

[0063] Step S1: Acquire an optical signal and convert it into an electrical signal. The optical frequency comb system is activated, and the light source module generates an optical frequency comb. A portion of the frequency comb's output light is directed through a beam splitter into the signal detection module, where it is converted into an electrical pulse train signal by a photodetector.

[0064] Step S2: Electrical signal noise reduction, amplification and processing. The electrical signal is input to the signal processor. First, wavelet transform noise reduction is performed to remove noise. Then, amplification is performed to bring the signal to an appropriate level. Afterwards, the processed periodic electrical signal (whose period is the inverse of the repetition frequency) can be input to a time-amplitude converter ( 时间幅度转换器,TAC 时间幅度转换器,TAC ) or similar circuits / algorithms, converting the time interval information (such as the interval between adjacent pulses) into a voltage or digital amplitude value that is proportional to the time interval.

[0065] Step S3: Compare and obtain the amplitude difference. Compare the current time amplitude value obtained in step S2 with a preset standard amplitude value. The standard amplitude value corresponds to the target locking frequency. Cycle =1 / The comparison result is an amplitude difference (or time difference), which reflects the deviation between the current repetition frequency and the target frequency.

[0066] Step S4: Determine the locking condition and adjust it. Determine whether the obtained amplitude difference meets the preset locking condition. The locking condition can be set as: the absolute value of the amplitude difference is less than a certain threshold ϵ (for example, corresponding to a frequency error less than 1 ), and this situation lasts for a certain period of time (for example, 1 second). If the amplitude difference does not meet the locking condition, it means that the frequency has not been locked or has deviated from the target value. At this time, the feedback control module calculates the adjustment signal based on the size and sign of the amplitude difference. The driver adjusts the parameters of the light source module (for example, the driver) according to the adjustment signal. 压电陶瓷 After the adjustment is completed, the system returns to step S1 and enters the next detection-adjustment cycle. If the amplitude difference meets the locking condition, it proceeds to step S5.

[0067] Step S5: Lock the frequency. When the amplitude difference meets the preset locking condition, it is considered that the repetition frequency of the optical frequency comb has been successfully locked at the target frequency. The system maintains its current control state and continuously monitors the frequency through a feedback loop to resist disturbances and maintain the locked state. At this point, the repetition frequency corresponding to the optical signal output by the optical frequency comb system is the desired, precisely locked repetition frequency.

[0068] It should be noted that the formulas used in the above embodiments are exemplary only, and the specific mathematical expressions and parameters (such as wavelet basis functions, threshold selection methods, 比例积分微分 Parameters, etc.) can be selected and optimized according to the actual application scenario and performance requirements. The variables in the formula are usually normalized or dimensionless values. Preset parameters (such as standard amplitude value, lock threshold, 比例积分微分parameters, etc.) are determined by those skilled in the art based on specific system characteristics and experimental debugging.

[0069] The systems and methods described in the above embodiments may be implemented in whole or in part through hardware circuits (analog or digital), firmware, or a processor (e.g. 现场可编程门阵列 、 数字信号处理器 The present invention can be implemented by software on a processor (e.g., a microcontroller or a microcontroller), or any combination of these methods. When implemented using software, it can be implemented in the form of a computer program product and stored on a computer-readable medium.

[0070] Those skilled in the art will appreciate that the various modules and method steps described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, a combination of computer software and electronic hardware, or other forms. Exactly how these functions are performed depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of protection of this application.

[0071] In addition, the functional modules in the various embodiments of the present application may be integrated into a processing unit, or each module may exist physically separately, or two or more modules may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0072] The foregoing is merely a specific embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. An optical frequency comb repetition frequency control system, characterized in that: include: A light source module for generating ultrashort pulse lasers and forming an optical frequency comb through nonlinear materials; a signal detection module, comprising a photodetector and a signal processor, wherein the photodetector is used to convert the optical pulse signal of the optical frequency comb into an electrical signal, and the signal processor is used to process the electrical signal; a frequency measurement module, comprising a frequency counter and a spectrum analyzer, for performing dual measurements on the frequency of the electrical signal processed by the signal processor to determine the repetition frequency of the optical frequency comb; The contrast frequency generation module includes a crystal oscillator and an atomic clock to generate a high-stability reference frequency; A feedback control module, comprising an error amplifier, a controller, and a driver, is configured to receive the actual repetition frequency measured by the frequency measurement module and the reference frequency provided by the comparison frequency generation module, calculate the difference between the two to form an error signal, and adjust relevant parameters of the light source module based on the error signal to control the repetition frequency of the optical frequency comb.

2. The optical frequency comb repetition frequency control system according to claim 1, characterized in that: The light source module includes a laser source and a nonlinear medium; the laser source is used to generate ultrashort pulse laser with high peak power and narrow pulse width; the nonlinear medium is used to generate new frequency components when the ultrashort pulse laser passes through, forming an optical frequency comb.

3. The optical frequency comb repetition frequency control system according to claim 1, characterized in that: The signal processor in the signal detection module is used to amplify the electrical signal output by the photodetector and ensure that the introduction of noise is suppressed while amplifying the signal; the noise suppression performance in the signal processor is related to the delay time of signal transmission, and the noise suppression parameters are dynamically adjusted according to the increase in the delay time to maintain the noise reduction effect.

4. An optical frequency comb repetition frequency control system according to claim 1 or 3, characterized in that: The signal processor in the signal detection module first performs noise reduction processing on the electrical signal, and then amplifies the noise-reduced electrical signal; the noise reduction process adopts the wavelet transform method, assuming that the noisy discrete signal is , the processing process includes: The signal is transformed by discrete wavelet transform Decompose into different scales and pan The wavelet coefficients under , the transformation formula is: in, is the wavelet basis function The complex conjugate of is the signal length; For the wavelet coefficients Perform threshold processing and set the threshold to , the processing formula is: , the processed wavelet coefficients are transformed into Reconstruct the noise-reduced signal , the inverse transformation formula is: .

5. The optical frequency comb repetition frequency control system according to claim 4, characterized in that: The signal processor in the signal detection module processes the noise-reduced signal Perform amplification processing; set the output voltage to , the input voltage is , the magnification is , the amplification formula is: .

6. The optical frequency comb repetition frequency control system according to claim 1, characterized in that: The frequency counter in the frequency measurement module passes through the specified time window The number of internal electrical pulses Count and calculate the frequency based on the counting results and the length of the time window , the calculation formula is: .

7. An optical frequency comb repetition frequency control system according to claim 1 or 6, characterized in that: The spectrum analyzer in the frequency measurement module determines the repetition frequency of the optical frequency comb by displaying the frequency components of the electrical signal in the frequency domain and observing the peak positions and intervals in the spectrum diagram.

8. The optical frequency comb repetition frequency control system according to claim 1, characterized in that: The comparison frequency generation module uses the frequency determined by the atomic clock based on the atomic energy level transition frequency as a high-precision reference frequency, and uses the crystal oscillator to provide a stable reference frequency, and generates a reference frequency related to the target repetition frequency through frequency multiplication or division processing; and uses the two sets of reference frequencies for comparison calculation to improve the sensitivity of error detection.

9. The optical frequency comb repetition frequency control system according to claim 1, characterized in that: The controller in the feedback control module adopts proportional-integral-differential ( PID ) control algorithm, which generates a control signal by adjusting proportional, integral and differential parameters according to the error signal output by the error amplifier; the driver converts the control signal into a current or voltage signal for controlling the power supply of the pump laser in the light source module, thereby changing the pump power and achieving adjustment of the repetition frequency of the optical frequency comb.

10. A method for locking the repetition frequency of an optical frequency comb, characterized in that: Using an optical frequency comb repetition rate control system according to any one of claims 1 to 9, the method comprises the following steps: S1: Acquire the optical signal output by the optical frequency comb optical system and convert it into an electrical signal through the photodetector in the signal detection module; S2: performing noise reduction and amplification processing on the electrical signal by a signal processor in the signal detection module to obtain a processed electrical signal, and converting the time interval information of the processed electrical signal to obtain a time amplitude value; S3: Compare the time amplitude value with a preset standard amplitude value to obtain an amplitude difference; S4: Determine whether the amplitude difference satisfies a preset locking condition; if not, adjust the value of the target adjustment index of the light source module according to the amplitude difference through the feedback control module, and after the adjustment is completed, return to step S1 to reacquire the light signal; S5: If the amplitude difference satisfies a preset locking condition, the repetition frequency corresponding to the optical signal currently output by the optical frequency comb optical system is used as the locked repetition frequency.

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