CN104776923B - External clock signal frequency oscillation measurement method based on frequency scanning interference - Google Patents
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Abstract
本发明公开了一种基于频率扫描干涉的外时钟信号频率振荡测量装置及方法，该装置包括可调谐激光器(1)、基于迈克尔逊干涉仪的外时钟拍频信号产生系统(9)、光电探测系统(4)和数据采集卡(8)和计算机(10)；通过实时采集频率扫描干涉系统的外部时钟信号，并采用相关算法提取外部时钟信号的实时频率，进而获得拍频信号的频率振荡信息，实时准确的获得外部时钟实时的频率振荡情况。相比于其他频谱分析仪器，本发明能够通过相关算法消除高频噪声带来的影响，为降低采样时钟的频率振荡幅度，提高频率扫描干涉系统的空间传感分辨率提供了理论保证。
The invention discloses a device and method for measuring the frequency oscillation of an external clock signal based on frequency scanning interference. System (4), data acquisition card (8) and computer (10); through real-time acquisition of the external clock signal of the frequency scanning interference system, and using a correlation algorithm to extract the real-time frequency of the external clock signal, and then obtain the frequency oscillation information of the beat frequency signal , Real-time and accurate acquisition of the real-time frequency oscillation of the external clock. Compared with other spectrum analysis instruments, the present invention can eliminate the influence of high-frequency noise through correlation algorithms, and provides a theoretical guarantee for reducing the frequency oscillation amplitude of the sampling clock and improving the spatial sensing resolution of the frequency scanning interference system.
Description
技术领域technical field
本发明属于分布式光纤传感仪器技术领域，具体涉及一种基于频率扫描干涉系统的外时钟信号频率振荡的测量方法。The invention belongs to the technical field of distributed optical fiber sensing instruments, in particular to a method for measuring the frequency oscillation of an external clock signal based on a frequency scanning interference system.
背景技术Background technique
频率扫描干涉技术(SWI,Sweep-wavelengthinterferometry)凭借其具有非接触损伤、信号噪声小、响应速度快、测量范围大、信噪比高、受光强变化影响等优点,得到了广泛的研究和应用。其典型应用包括：用于光纤通讯网络及器件测试及应力、温度、扰动传感领域的光频域反射技术(OFDR,Optical FrequencyDomainReflectory)和用于生物医学成像及工业材料检测等领域的光学相干层析技术(OCT，optical coherent tomography)。该技术采用高相干激光器进行高速和线性波长扫描，利用参考臂上由法拉第反射镜反射的光与单模光纤背向散射光进行干涉。由于二者的光程不同，干涉端实际上是不同频率两束光进行干涉，形成拍频。通过探测不同的拍频信号，就可以探测传感光纤不同位置的背向散射信息。Sweep-wavelength interferometry (SWI, Sweep-wavelength interferometry) has been widely researched and applied due to its advantages of non-contact damage, low signal noise, fast response speed, large measurement range, high signal-to-noise ratio, and being affected by changes in light intensity. Its typical applications include: optical frequency domain reflection technology (OFDR, Optical Frequency Domain Reflectory) for optical fiber communication network and device testing and stress, temperature and disturbance sensing, and optical coherence layer for biomedical imaging and industrial material detection. Analysis technology (OCT, optical coherent tomography). The technology uses highly coherent lasers for high-speed and linear wavelength scanning, and uses the light reflected by the Faraday mirror on the reference arm to interfere with the backscattered light of the single-mode fiber. Because the optical paths of the two are different, the interference end is actually the interference of two beams of light with different frequencies to form a beat frequency. By detecting different beat frequency signals, the backscatter information at different positions of the sensing fiber can be detected.
频率扫描干涉技术的关键是需要激光器光源提供较大的光频扫描范围，并且光频在扫描过程中保持高速和线性特性。这是因为在频率扫描干涉技术中的信号处理需要将信号转换到频域，通常使用快速傅里叶算法(FFT,Fast FourierTransform)实现，而FFT算法要求自变量采取等间隔采样，由于频率扫描干涉技术的自变量不是时间而是激光器的瞬时光频率，如果激光器输出光存在相位噪声，即使采用FFT算法，由于自变量非等间隔采样，会造成频率扫描干涉系统的空间分辨率严重恶化。针对这一问题，可以考虑采用附加干涉仪作为系统的外时钟进行采样的方案解决，但这种方案要求作为采样时钟的拍频信号频率稳定。而实际的采样时钟的拍频信号的频率并不稳定，其振荡的幅度大小对系统的空间分辨率及测试稳定性有很大的影响。The key to frequency scanning interferometry is that the laser light source is required to provide a large optical frequency scanning range, and the optical frequency maintains high-speed and linear characteristics during the scanning process. This is because the signal processing in the frequency scanning interferometry needs to convert the signal to the frequency domain, which is usually implemented by using the Fast Fourier Transform (FFT, Fast FourierTransform), and the FFT algorithm requires the independent variables to be sampled at equal intervals. Due to the frequency scanning interference The independent variable of the technology is not time but the instantaneous optical frequency of the laser. If there is phase noise in the output light of the laser, even if the FFT algorithm is used, the spatial resolution of the frequency scanning interferometry system will be severely deteriorated due to the non-equally spaced sampling of the independent variable. In view of this problem, it can be considered to use an additional interferometer as the external clock of the system to sample, but this solution requires the frequency of the beat signal as the sampling clock to be stable. However, the frequency of the beat frequency signal of the actual sampling clock is not stable, and the amplitude of its oscillation has a great influence on the spatial resolution and test stability of the system.
在频率扫描干涉系统中，光源的相位噪声会严重影响系统的空间分辨率及测试距离，利用外时钟采样技术在一定程度上可以消除相位噪声的影响，其原理是实现每个采样周期内的等光频采样。而实际系统外时钟的拍频信号的频率并不稳定，且其振荡的幅度会严重影响系统的空间分辨率及测试稳定性。In the frequency scanning interference system, the phase noise of the light source will seriously affect the spatial resolution of the system and the test distance. Using the external clock sampling technology can eliminate the influence of the phase noise to a certain extent. Optical frequency sampling. However, the frequency of the beat frequency signal of the external clock in the actual system is not stable, and the amplitude of its oscillation will seriously affect the spatial resolution and test stability of the system.
目前，克服激光器光源相位噪声的主要方法就是利用外时钟采样的方法获得拍频信号。但实际系统中的外时钟频率不稳定，对信号的空间分辨率和测试的稳定性都造成了很大的影响，只有通过相关的技术手段，检测出外时钟实时的频率振荡情况，才能够探索相应的方法降低其影响。At present, the main method to overcome the phase noise of the laser light source is to use the external clock sampling method to obtain the beat frequency signal. However, the frequency of the external clock in the actual system is unstable, which has a great impact on the spatial resolution of the signal and the stability of the test. Only by detecting the real-time frequency oscillation of the external clock through relevant technical means can we explore the corresponding ways to reduce its impact.
发明内容Contents of the invention
基于上述现有技术上的不足，本发明提出了一种基于频率扫描干涉的外时钟信号频率振荡测量方法，通过实时采集频率扫描干涉系统的外时钟信号，并采用相关算法提取外时钟信号的实时频率，进而获得拍频信号的频率振荡信息，实时准确的获得外时钟实时的频率振荡情况。Based on the above-mentioned deficiencies in the prior art, the present invention proposes a method for measuring the frequency oscillation of the external clock signal based on frequency scanning interference, which collects the external clock signal of the frequency scanning interference system in real time, and uses a correlation algorithm to extract the real-time value of the external clock signal. Frequency, and then obtain the frequency oscillation information of the beat frequency signal, and obtain the real-time frequency oscillation of the external clock in real time and accurately.
本发明提出了一种基于频率扫描干涉系统的外时钟信号频率振荡的测量方法，包括可调谐激光器1、基于迈克尔逊干涉仪的外时钟拍频信号产生系统9、光电探测系统4和数据采集卡8和计算机10；可调谐激光器1采用超窄线宽线性调谐激光光源，其光频能够实现高速线性扫描，用于为系统提供光源；基于迈克尔逊干涉仪的外时钟拍频信号产生系统9，用于产生测量装置的外时钟拍频信号，包括50:50耦合器3、第一法拉第旋转镜5和第二法拉第旋转镜6、延迟光纤7；50:50耦合器3用于光干涉，光从50:50耦合器3的a端口进入，从50:50耦合器3的c端口和d端口出射，分别被基于迈克尔逊干涉仪的外时钟拍频信号产生系统的两臂的第一法拉第旋转镜5和第二法拉第旋转镜6反射，并返回到50:50耦合器3的c端口和d端口，两束光在50:50耦合器3中发生干涉，从50:50耦合器3的b端口输出；第一法拉第旋转镜5和第二法拉第旋转镜6利用迈克尔逊干涉仪的外时钟拍频信号产生系统提供反射；延迟光纤7用于实现非等臂的拍频干涉；光电探测器4，用于将基于迈克尔逊干涉仪的外时钟信号产生系统9产生的光信号转换为电信号以及消除进入探测器两路信号存在的共模噪声；数据采集卡8，同于采集平衡探测器4输出的模拟电信号；计算机10，对数据采集卡8采集的干涉信号进行数据处理，实现基于外时钟采样技术的时钟拍频信号频率振荡的测量；该方法包括以下步骤：The present invention proposes a method for measuring the frequency oscillation of an external clock signal based on a frequency scanning interference system, including a tunable laser 1, an external clock beat frequency signal generation system 9 based on a Michelson interferometer, a photoelectric detection system 4 and a data acquisition card 8 and a computer 10; the tunable laser 1 adopts an ultra-narrow linewidth linearly tunable laser source, and its optical frequency can realize high-speed linear scanning, and is used to provide a light source for the system; an external clock beat frequency signal generation system 9 based on Michelson interferometer, Used to generate the external clock beat frequency signal of the measuring device, including a 50:50 coupler 3, a first Faraday rotating mirror 5 and a second Faraday rotating mirror 6, and a delay fiber 7; the 50:50 coupler 3 is used for optical interference, and the optical Entering from the a port of the 50:50 coupler 3, exiting from the c port and the d port of the 50:50 coupler 3, they are respectively rotated by the first Faraday of the two arms of the external clock beat frequency signal generation system based on the Michelson interferometer Mirror 5 and the second Faraday rotating mirror 6 reflect, and return to the c port and d port of the 50:50 coupler 3, the two beams interfere in the 50:50 coupler 3, from the b port of the 50:50 coupler 3 Port output; the first Faraday rotating mirror 5 and the second Faraday rotating mirror 6 utilize the external clock beat frequency signal generation system of the Michelson interferometer to provide reflection; the delay fiber 7 is used to realize non-equal arm beat frequency interference; photodetector 4 , used to convert the optical signal generated by the external clock signal generation system 9 based on the Michelson interferometer into an electrical signal and eliminate the common mode noise that enters the two-way signal of the detector; the data acquisition card 8 is the same as the acquisition balance detector 4 The analog electric signal of output; Computer 10, carries out data processing to the interference signal that data acquisition card 8 collects, realizes the measurement based on the frequency oscillation of the clock beat frequency signal of external clock sampling technology; The method comprises the following steps:
步骤201，基于迈克尔逊干涉仪光路产生外时钟信号A1；Step 201, generating an external clock signal A1 based on the Michelson interferometer optical path;
步骤202，对信号A1进行希尔伯特变换得到信号A1的复指数表达A2；Step 202, performing Hilbert transform on the signal A1 to obtain the complex exponential expression A2 of the signal A1;
步骤203，对得到的复指数信号A2实部和虚部做正切运算，得到相位信号的正切表达式A3；Step 203, performing a tangent operation on the obtained real and imaginary parts of the complex exponential signal A2 to obtain a tangent expression A3 of the phase signal;
步骤204，对A3做反正切和相位展开运算解卷绕得到外时钟信号的相位累计信号A4；Step 204, performing arctangent and phase unwrapping operations on A3 to obtain the phase accumulation signal A4 of the external clock signal;
步骤205，对信号A4的相位累计信号转化为周期累计信号A5；Step 205, converting the phase accumulation signal of the signal A4 into a period accumulation signal A5;
步骤206，逐个寻找信号A5的每个整数周期时刻对应的时间点，得到时间点信号序列A6；Step 206, looking for the time points corresponding to each integer cycle moment of the signal A5 one by one, to obtain the time point signal sequence A6;
步骤207，对信号A6进行前向差分运算得到信号A7，即信号A1每个信号周期对应的时间间隔；Step 207, performing a forward differential operation on the signal A6 to obtain the signal A7, that is, the time interval corresponding to each signal period of the signal A1;
步骤208，利用采集卡初始设定的内部时钟采样频率除以信号A7，得到系统外时钟信号A1的实时频率A8，即可提取A1频率振荡信息。In step 208, divide the sampling frequency of the internal clock initially set by the acquisition card by the signal A7 to obtain the real-time frequency A8 of the external clock signal A1, and then extract the frequency oscillation information of A1.
相比于其他频谱分析仪器，本发明能够通过相关算法消除高频噪声带来的影响，为降低采样时钟的频率振荡幅度，提高频率扫描干涉系统的空间传感分辨率提供了理论保证。Compared with other spectrum analysis instruments, the present invention can eliminate the influence of high-frequency noise through correlation algorithms, and provides a theoretical guarantee for reducing the frequency oscillation amplitude of the sampling clock and improving the spatial sensing resolution of the frequency scanning interference system.
附图说明Description of drawings
图1是一种基于频率扫描干涉系统的外时钟信号频率振荡的测量装置示意图；Fig. 1 is a kind of schematic diagram of the measurement device of the frequency oscillation of the external clock signal based on the frequency scanning interference system;
其中：1、可调谐激光器，2、环形器，3、50:50耦合器，4、光电探测器，5、第一法拉第旋转镜，6、第二法拉第旋转镜，7、延迟光纤，8、数据采集卡，9、基于迈克尔逊干涉仪的外时钟拍频信号产生系统，10、计算机；Among them: 1. Tunable laser, 2. Circulator, 3. 50:50 coupler, 4. Photodetector, 5. First Faraday rotating mirror, 6. Second Faraday rotating mirror, 7. Delay fiber, 8. Data acquisition card, 9. An external clock beat frequency signal generation system based on Michelson interferometer, 10. Computer;
图2是基于频率扫描干涉系统的外时钟信号频率振荡的测量算法框图；Fig. 2 is the measurement algorithm block diagram of the frequency oscillation of the external clock signal based on the frequency scanning interference system;
图3是基于外时钟采样技术获得的时钟信号曲线；Fig. 3 is the clock signal curve obtained based on the external clock sampling technology;
其中：(A)为基于迈克尔逊干涉仪光路的产生的外部时钟信号，(B)图为外时钟信号拍频细节图。Among them: (A) is the external clock signal generated based on the optical path of the Michelson interferometer, and (B) is a detailed diagram of the beat frequency of the external clock signal.
图4是基于外时钟采样技术的时钟信号对应拍频周期示意图；Fig. 4 is a schematic diagram of a clock signal corresponding to a beat frequency period based on an external clock sampling technique;
图5是在的延迟光纤长度为1000m，光源的扫描速率为40nm/s的条件下测得的外时钟信号实时频率图。Fig. 5 is a real-time frequency diagram of the external clock signal measured under the condition that the delay fiber length is 1000m and the scanning rate of the light source is 40nm/s.
具体实施方式Detailed ways
以下结合附图及具体实施方式，进一步详述本发明的技术方案。The technical solution of the present invention will be described in further detail below in conjunction with the accompanying drawings and specific embodiments.
如图1所示，本发明为一种基于频率扫描干涉系统的外时钟信号频率振荡的测量装置，包括：可调谐激光器1、基于迈克尔逊干涉仪的外时钟拍频信号产生系统、光电探测系统、和数据采集卡、和计算机；As shown in Figure 1, the present invention is a measurement device for frequency oscillation of an external clock signal based on a frequency scanning interference system, including: a tunable laser 1, an external clock beat signal generation system based on a Michelson interferometer, and a photoelectric detection system , and data acquisition card, and computer;
1、可调谐激光器，2、环形器，3、50:50耦合器，4、光电探测器，5、第一法拉第旋转镜，6、第二法拉第旋转镜，7、延迟光纤，8、数据采集卡，9、基于迈克尔逊干涉仪的外时钟拍频信号产生系统，10、计算机；1. Tunable laser, 2. Circulator, 3. 50:50 coupler, 4. Photodetector, 5. First Faraday rotating mirror, 6. Second Faraday rotating mirror, 7. Delay fiber, 8. Data acquisition Card, 9. An external clock beat frequency signal generation system based on Michelson interferometer, 10. Computer;
可调谐激光器1，用于为系统提供光源，光源采用超窄线宽线性调谐激光光源，其光频能够实现高速线性扫描；Tunable laser 1 is used to provide a light source for the system. The light source adopts an ultra-narrow linewidth linearly tunable laser light source, and its optical frequency can realize high-speed linear scanning;
基于迈克尔逊干涉仪的外时钟拍频信号产生系统9用于产生测量装置的外时钟拍频信号，其结构包括：50:50耦合器3、第一法拉第旋转镜5和第二法拉第旋转镜6、延迟光纤7；50:50耦合器3用于光干涉，光从50:50耦合器3的a端口进入，从50:50耦合器3的c端口和d端口出射，分别被基于迈克尔逊干涉仪的外时钟拍频信号产生系统的两臂的第一法拉第旋转镜5和第二法拉第旋转镜6反射，并返回到50:50耦合器3的c端口和d端口，两束光在50:50耦合器3中发生干涉，从50:50耦合器3的b端口输出；第一法拉第旋转镜5和第二法拉第旋转镜6基于迈克尔逊干涉仪的外时钟拍频信号产生系统提供反射；延迟光纤7用于实现非等臂的拍频干涉；The external clock beat frequency signal generation system 9 based on Michelson interferometer is used to generate the external clock beat frequency signal of the measuring device, and its structure includes: 50:50 coupler 3, first Faraday rotating mirror 5 and second Faraday rotating mirror 6 , Delay fiber 7; 50:50 coupler 3 is used for light interference, light enters from port a of 50:50 coupler 3, exits from port c and port d of 50:50 coupler 3, and is respectively based on Michelson interference The external clock beat frequency signal of the instrument is reflected by the first Faraday rotating mirror 5 and the second Faraday rotating mirror 6 of the two arms of the system, and returns to the c port and the d port of the 50:50 coupler 3, and the two beams of light are at 50: Interference occurs in the 50 coupler 3, output from the b port of the 50:50 coupler 3; the first Faraday rotating mirror 5 and the second Faraday rotating mirror 6 provide reflection based on the external clock beat frequency signal generation system of the Michelson interferometer; delay The optical fiber 7 is used to realize non-equal arm beat frequency interference;
光电探测器4，用于将基于迈克尔逊干涉仪的外时钟信号产生系系统9产生的光信号转换为电信号，光电探测器4采用的是低噪声平衡探测器，用于消除进入探测器两路信号存在的共模噪声；The photodetector 4 is used to convert the optical signal generated by the external clock signal generation system 9 based on the Michelson interferometer into an electrical signal. The photodetector 4 is a low-noise balanced detector, which is used to eliminate the The common mode noise existing in the signal;
数据采集卡8，同于采集平衡探测器4输出的模拟电信号；The data acquisition card 8 is the same as the analog electrical signal output by the acquisition balance detector 4;
计算机10：对数据采集卡8采集的干涉信号进行数据处理，实现基于外时钟采样技术的时钟拍频信号频率振荡的测量。The computer 10: performs data processing on the interference signal collected by the data acquisition card 8, and realizes the measurement of the frequency oscillation of the clock beat signal based on the external clock sampling technology.
如图2所示，本发明的测量算法的步骤是：As shown in Figure 2, the steps of measurement algorithm of the present invention are:
步骤201，基于迈克尔逊干涉仪光路产生外时钟信号A1；Step 201, generating an external clock signal A1 based on the Michelson interferometer optical path;
步骤202，对信号A1进行希尔伯特变换得到信号A1的复指数表达A2；Step 202, performing Hilbert transform on the signal A1 to obtain the complex exponential expression A2 of the signal A1;
步骤203，对得到的复指数信号A2实部和虚部做正切运算，得到相位信号的正切表达式A3；Step 203, performing a tangent operation on the obtained real and imaginary parts of the complex exponential signal A2 to obtain a tangent expression A3 of the phase signal;
步骤204，对A3做反正切和相位展开运算解卷绕得到外时钟信号的相位累计信号A4；Step 204, performing arctangent and phase unwrapping operations on A3 to obtain the phase accumulation signal A4 of the external clock signal;
步骤205，对信号A4的相位累计信号转化为周期累计信号A5；Step 205, converting the phase accumulation signal of the signal A4 into a period accumulation signal A5;
步骤206，逐个寻找信号A5的每个整数周期时刻对应的时间点，得到时间点信号序列A6；Step 206, looking for the time points corresponding to each integer cycle moment of the signal A5 one by one, to obtain the time point signal sequence A6;
步骤207，对信号A6进行前向差分运算得到信号A7，即信号A1每个信号周期对应的时间间隔；Step 207, performing a forward differential operation on the signal A6 to obtain the signal A7, that is, the time interval corresponding to each signal period of the signal A1;
步骤208，利用采集卡初始设定的内部时钟采样频率除以信号A7，得到系统外时钟信号A1的实时频率A8，即可提取A1频率振荡信息。In step 208, divide the sampling frequency of the internal clock initially set by the acquisition card by the signal A7 to obtain the real-time frequency A8 of the external clock signal A1, and then extract the frequency oscillation information of A1.
在频率扫描干涉系统中，设光源的扫描速率为γ，延迟光纤产生的时延为г，则系统产生的信号的频率为fb＝γτ。由于法拉第旋转镜产生的反射光的强度远大于背向散射光的强度，所以附加干涉仪产生的时钟信号的频率仅取决于于产生时钟信号的延迟光纤长度，其他位置的背向散射信号对系统的时钟基本没有影响。In the frequency scanning interference system, if the scanning rate of the light source is γ, and the time delay generated by the delay fiber is г, then the frequency of the signal generated by the system is f b =γτ. Since the intensity of the reflected light generated by the Faraday rotating mirror is much greater than the intensity of the backscattered light, the frequency of the clock signal generated by the additional interferometer only depends on the length of the delay fiber that generates the clock signal, and the backscattered signals at other positions have a significant impact on the system. The clock has basically no effect.
利用上述装置的测量方法对一段长约为1000m的延迟光纤进行测试，设定光源的扫描速率为40nm/s，利用频谱分析的方法测得系统的平均拍频为48.9M。采用上述测量方法可以得到采样时钟每个周期对应的实时频率，如图5所示。实验结果表明：该装置和方法可以较准确的测量系统的实时拍频并能够分析频率振荡的实时分布。Using the measurement method of the above-mentioned device to test a section of delay optical fiber with a length of about 1000m, set the scanning rate of the light source to 40nm/s, and use the method of spectrum analysis to measure the average beat frequency of the system to be 48.9M. The real-time frequency corresponding to each cycle of the sampling clock can be obtained by using the above measurement method, as shown in FIG. 5 . Experimental results show that the device and method can accurately measure the real-time beat frequency of the system and analyze the real-time distribution of frequency oscillation.
尽管上面结合图对本发明进行了描述，但是本发明并不局限于上述的具体实施方式，上述的实施方式仅仅是示意性的，而不是限制性的，本领域的普通技术人员在本发明的启示之下，在不脱离本发明宗旨的情况下，还可以做出很多变形，这些均属于本发明的保护之内。Although the present invention has been described above in conjunction with the drawings, the present invention is not limited to the above-mentioned specific embodiments, and the above-mentioned embodiments are only illustrative, rather than restrictive. Under the condition of not departing from the gist of the present invention, many modifications can also be made, and these all belong to the protection of the present invention.
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