CN111157101A - Weak grating array distributed vibration sensing system and method - Google Patents
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Abstract
Description
技术领域technical field
本发明涉及光纤光栅传感技术领域,尤其是涉及一种弱光栅阵列分布式振动传感系统及方法。The invention relates to the technical field of fiber grating sensing, in particular to a weak grating array distributed vibration sensing system and method.
背景技术Background technique
对于分布式弱光栅振动传感解调系统的信号采集及解调端;根据光纤光栅的振动传感机制,振动信号实质是被调制到干涉信号中,进行振动信号的解调实际上是进行相位解调;目前,分布式传感系统常用的相位解调方式有正交(IQ)解调算法、相位载波生成(PGC)检测法以及3×3耦合器解调算法;For the signal acquisition and demodulation end of the distributed weak grating vibration sensing demodulation system; according to the vibration sensing mechanism of the fiber grating, the vibration signal is essentially modulated into the interference signal, and the demodulation of the vibration signal is actually the phase Demodulation: At present, the commonly used phase demodulation methods in distributed sensing systems include quadrature (IQ) demodulation algorithm, phase carrier generation (PGC) detection method and 3×3 coupler demodulation algorithm;
对于分布式弱光栅振动传感解调系统的信号解调,目前常用的干涉仪为Mach-Zehnder干涉仪、Sagnac干涉仪、Michelson干涉仪;脉冲光被连续的弱光栅反射回来,最终到达干涉仪中,经过两个不等长干涉臂后在耦合器中发生干涉,从而使相邻弱光栅的反射光产生干涉现象;具有敏感双臂的干涉仪容易受到外界环境的干扰,如机箱温度、风扇、外界噪声、振动等影响,造成信号解调的底噪声很大,从而影响系统的信噪比。另外,现有大部分振动传感系统对频率响应的带宽较窄,对低频响应难度大。For the signal demodulation of the distributed weak grating vibration sensing demodulation system, the commonly used interferometers are Mach-Zehnder interferometer, Sagnac interferometer and Michelson interferometer; the pulsed light is reflected back by the continuous weak grating and finally reaches the interferometer The interference occurs in the coupler after passing through two unequal length interference arms, so that the reflected light of the adjacent weak grating produces interference phenomenon; the interferometer with sensitive arms is easily disturbed by the external environment, such as chassis temperature, fan , external noise, vibration and other influences, resulting in a large noise floor of signal demodulation, thereby affecting the signal-to-noise ratio of the system. In addition, most of the existing vibration sensing systems have a narrow bandwidth for frequency response, and it is difficult to respond to low frequencies.
发明内容SUMMARY OF THE INVENTION
本发明的目的在于至少克服上述一种技术不足,提出一种弱光栅阵列分布式振动传感系统及方法。The purpose of the present invention is to overcome at least one of the above-mentioned technical deficiencies, and to propose a weak grating array distributed vibration sensing system and method.
一方面,本发明提供了一种弱光栅阵列分布式振动传感系统,包括窄线宽激光器、声光调制器、环形器、弱光栅阵列和3×3耦合器和光电探测器;In one aspect, the present invention provides a weak grating array distributed vibration sensing system, comprising a narrow linewidth laser, an acousto-optic modulator, a circulator, a weak grating array, a 3×3 coupler and a photodetector;
所述窄线宽激光器,用于产生中心波长一定的连续光,并发送至所述声光调制器;所述声光调制器,用于将所述连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至环形器;所述环形器,用于接收所述双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列,所述弱光栅阵列将所述双脉冲信号反射至环形器;所述环形器还用于将经过反射的双脉冲信号传送至所述3×3耦合器;所述3×3耦合器,用于使经过反射的双脉冲信号形成干涉,生成干涉信号;所述光电探测器,用于获取所述干涉信号,并将所述干涉信号转换为电信号。The narrow linewidth laser is used to generate continuous light with a certain center wavelength and send it to the acousto-optic modulator; the acousto-optic modulator is used to modulate the continuous light into a corresponding double-pulse signal, and sending the double-pulse signal to a circulator; the circulator is configured to receive the double-pulse signal and transmit the double-pulse signal to a weak grating array, and the weak grating array reflects the double-pulse signal to the circulator; the circulator is also used to transmit the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler is used to cause the reflected double-pulse signal to form interference to generate interference signal; the photodetector is used for acquiring the interference signal and converting the interference signal into an electrical signal.
进一步地,所述弱光栅阵列分布式振动传感系统还包括数据采集与FPGA处理单元,所述数据采集与FPGA处理单元,用于生成电脉冲,以使声光调制器将所述连续光调制为相应的双脉冲信号;所述数据采集与FPGA处理单元还用于对所述电信号进行采集并解调,形成解调后的信号。Further, the weak grating array distributed vibration sensing system also includes a data acquisition and FPGA processing unit, the data acquisition and FPGA processing unit is used to generate electrical pulses, so that the acousto-optic modulator modulates the continuous light. is a corresponding double-pulse signal; the data acquisition and FPGA processing unit is also used to collect and demodulate the electrical signal to form a demodulated signal.
进一步地,所述弱光栅阵列分布式振动传感系统还包括掺铒光纤放大器,所述掺铒光纤放大器,用于将所述双脉冲信号放大;所述声光调制器将所述双脉冲信号传送至环形器,具体包括,所述声光调制器将所述双脉冲信号传送至掺铒光纤放大器,经掺铒光纤放大器放大后,传送至环形器。Further, the weak grating array distributed vibration sensing system further includes an erbium-doped fiber amplifier for amplifying the double-pulse signal; the acousto-optic modulator amplifies the double-pulse signal. The transmitting to the circulator specifically includes that the acousto-optic modulator transmits the double-pulse signal to the erbium-doped fiber amplifier, and after being amplified by the erbium-doped fiber amplifier, the signal is transmitted to the circulator.
进一步地,所述声光调制器将所述连续光调制为相应的双脉冲信号,具体包括,所述声光调制器将所述连续光调制成前后两上升沿的时间延迟为Tps、脉冲脉宽为Tw、脉冲重复频率为Fp的双脉冲信号,Further, the acousto-optic modulator modulates the continuous light into a corresponding double-pulse signal, which specifically includes that the acousto-optic modulator modulates the continuous light into a time delay of two rising edges before and after T ps , and a pulse. A double-pulse signal with a pulse width of Tw and a pulse repetition frequency of Fp ,
其中,Fp≤v/2L,v为光在弱光栅阵列中的传播速度,d为弱光栅阵列光栅距离,ne为弱光栅阵列的折射率,L为弱光栅阵列的长度,c为光速。in, F p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.
进一步地,所述3×3耦合器使经过反射的双脉冲信号形成干涉,当t=0时双脉冲信号输入传感光纤,第i与i+1个光栅反射信号形成干涉强度为I(t)的干涉信号;Further, the 3×3 coupler causes the reflected double-pulse signal to form interference. When t=0, the double-pulse signal is input into the sensing fiber, and the interference intensity formed by the i-th and i+1 grating reflection signals is I(t ) interference signal;
其中,Ei,Ri,τi,分别为第i个光栅的振幅、反射率、时间;φ(t)为第i+1与i个光栅之间的相位差,σ偏振失配因子。Among them, E i , R i , τ i , are the amplitude, reflectivity, and time of the i-th grating, respectively; φ(t) is the phase difference between the i+1-th grating and the i-th grating, and the σ polarization mismatch factor.
进一步地,所述弱光栅阵列分布式振动传感系统还包括根据所述第i与i+1个光栅反射信号形成的干涉强度为I(t)的干涉信号,获取三个探测器的电流Further, the weak grating array distributed vibration sensing system also includes an interference signal with an interference intensity of I(t) formed by the i and i+1 grating reflection signals to obtain the currents of the three detectors.
并使用标准的反正切算法,可以得到电信号的电压,And using the standard arctangent algorithm, the voltage of the electrical signal can be obtained,
其中,D为直流分量,φ0是相邻弱光栅阵列的初相位差,Δφ是外界环境引起的相位差。Among them, D is the DC component, φ 0 is the initial phase difference of adjacent weak grating arrays, and Δφ is the phase difference caused by the external environment.
另一方面,本发明还提供了一种弱光栅阵列分布式振动传感方法,包括以下步骤:On the other hand, the present invention also provides a weak grating array distributed vibration sensing method, comprising the following steps:
将中心波长一定的连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列;所述弱光栅阵列将所述双脉冲信号反射,使经过反射的双脉冲信号形成干涉,生成干涉信号;获取所述干涉信号,并将所述干涉信号转换为电信号。The continuous light with a certain central wavelength is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the weak grating array; the weak grating array reflects the double-pulse signal, so that the reflected double-pulse signal forms interference , generating an interference signal; acquiring the interference signal, and converting the interference signal into an electrical signal.
进一步地,所述弱光栅阵列分布式振动传感方法还包括对所述电信号进行采集并解调;对解调后的信号使用反正切算法得到相邻两光栅之间的相位变化。Further, the weak grating array distributed vibration sensing method further includes collecting and demodulating the electrical signal; using an arctangent algorithm on the demodulated signal to obtain a phase change between two adjacent gratings.
进一步地,所述弱光栅阵列分布式振动传感方法还包括在将所述双脉冲信号传送至弱光栅阵列前,对所述双脉冲信号进行放大。Further, the method for distributed vibration sensing of the weak grating array further includes amplifying the double pulse signal before transmitting the double pulse signal to the weak grating array.
进一步地,将所述连续光调制为相应的双脉冲信号,具体包括,将所述连续光调制成时间延迟为Tps、脉冲脉宽为Tw、脉冲重复频率为Fp的双脉冲信号,Further, modulating the continuous light into a corresponding double-pulse signal specifically includes: modulating the continuous light into a double-pulse signal with a time delay of T ps , a pulse width of Tw , and a pulse repetition frequency of F p ,
其中,Fp≤v/2L,v为光在弱光栅阵列中的传播速度,d为弱光栅阵列光栅距离,ne为弱光栅阵列的折射率,L为弱光栅阵列的长度,c为光速。in, F p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.
与现有技术相比,本发明的有益效果包括:通过所述窄线宽激光器,产生中心波长一定的连续光,并发送至所述声光调制器;声光调制器将所述连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至环形器;环形器接收所述双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列,所述弱光栅阵列将所述双脉冲信号反射至环形器;所述环形器将经过反射的双脉冲信号传送至所述3×3耦合器;所述3×3耦合器使经过反射的双脉冲信号形成干涉,生成干涉信号;所述光电探测器获取所述干涉信号,并将所述干涉信号转换为电信号;未使用常规的双臂干涉仪来解调相邻光栅之间的相位差,系统不会受外界环境干扰,提高了系统的稳定性,降低了系统的底噪声、提高了信噪比和频率响应范围。Compared with the prior art, the beneficial effects of the present invention include: the narrow linewidth laser generates continuous light with a certain center wavelength and sends it to the acousto-optic modulator; the acousto-optic modulator modulates the continuous light is the corresponding double-pulse signal, and transmits the double-pulse signal to the circulator; the circulator receives the double-pulse signal, and transmits the double-pulse signal to the weak grating array, and the weak grating array transmits the double-pulse signal to the circulator. The pulse signal is reflected to the circulator; the circulator transmits the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler interferes the reflected double-pulse signal to generate an interference signal; The photodetector acquires the interference signal and converts the interference signal into an electrical signal; the conventional double-arm interferometer is not used to demodulate the phase difference between adjacent gratings, and the system will not be disturbed by the external environment, improving the The stability of the system is improved, the noise floor of the system is reduced, and the signal-to-noise ratio and frequency response range are improved.
附图说明Description of drawings
图1是本发明实施例1所述弱光栅阵列分布式振动传感系统的结构示意图;1 is a schematic structural diagram of the weak grating array distributed vibration sensing system according to
图2是本发明实施例1所述弱光栅阵列分布式振动传感系统的工作原理示意图;2 is a schematic diagram of the working principle of the weak grating array distributed vibration sensing system according to
图3(a)是本发明实施例1所述的施加扰动下基于Michelson结构的传感系统的解调信号频谱图;Figure 3(a) is the Michelson-based structure under the applied disturbance described in
图3(b)是本发明实施例1所述的施加扰动下基于Michelson结构的传感系统的解调信号波形图;Figure 3(b) is the Michelson-based structure under the applied disturbance described in Example 1 of the present invention. The waveform diagram of the demodulation signal of the sensing system;
图4(a)、(b)分别是本发明实施例1所述的电信号解调后的频域和时域信号图;4 (a) and (b) are respectively the frequency domain and time domain signal diagrams after the demodulation of the electrical signal according to
图5是本发明实施例1所述的解调40kHz和0.1Hz的频率响应图。FIG. 5 is a frequency response diagram of demodulation of 40 kHz and 0.1 Hz according to
具体实施方式Detailed ways
为了使本发明的目的、技术方案及优点更加清楚明白,以下结合附图及实施例,对本发明进行进一步详细说明。应当理解,此处所描述的具体实施例仅仅用以解释本发明,并不用于限定本发明。In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.
实施例1Example 1
本发明实施例提供了一种弱光栅阵列分布式振动传感系统,其结构示意图,如图1所示,所述系统包括窄线宽激光器、声光调制器、环形器、弱光栅阵列和3×3耦合器和光电探测器;An embodiment of the present invention provides a weak grating array distributed vibration sensing system, the schematic diagram of which is shown in FIG. 1 , the system includes a narrow linewidth laser, an acousto-optic modulator, a circulator, a weak grating array, and 3 ×3 couplers and photodetectors;
所述窄线宽激光器,用于产生中心波长一定的连续光,并发送至所述声光调制器;所述声光调制器,用于将所述连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至环形器;所述环形器,用于接收所述双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列,所述弱光栅阵列将所述双脉冲信号反射至环形器;所述环形器还用于将经过反射的双脉冲信号传送至所述3×3耦合器;所述3×3耦合器,用于使经过反射的双脉冲信号形成干涉,生成干涉信号;所述光电探测器,用于获取所述干涉信号,并将所述干涉信号转换为电信号。The narrow linewidth laser is used to generate continuous light with a certain center wavelength and send it to the acousto-optic modulator; the acousto-optic modulator is used to modulate the continuous light into a corresponding double-pulse signal, and sending the double-pulse signal to a circulator; the circulator is configured to receive the double-pulse signal and transmit the double-pulse signal to a weak grating array, and the weak grating array reflects the double-pulse signal to the circulator; the circulator is also used to transmit the reflected double-pulse signal to the 3×3 coupler; the 3×3 coupler is used to cause the reflected double-pulse signal to form interference to generate interference signal; the photodetector is used for acquiring the interference signal and converting the interference signal into an electrical signal.
需要说明的是,本发明实施例所使用的光纤为全同低反射率的弱光栅阵列,光栅为啁啾光栅,3dB带宽超过3nm,反射率为-50dB,光栅阵列间隔为3m或者5m可选;It should be noted that the optical fiber used in the embodiment of the present invention is an isotactic weak grating array with low reflectivity, the grating is a chirped grating, the 3dB bandwidth exceeds 3nm, the reflectivity is -50dB, and the grating array interval is 3m or 5m optional ;
优选的,所述弱光栅阵列分布式振动传感系统,还包括数据采集与FPGA处理单元,所述数据采集与FPGA处理单元,用于生成电脉冲,以使声光调制器将所述连续光调制为相应的双脉冲信号;所述数据采集与FPGA处理单元还用于对所述电信号进行采集并解调,形成解调后的信号。Preferably, the weak grating array distributed vibration sensing system further includes a data acquisition and FPGA processing unit, the data acquisition and FPGA processing unit is used to generate electrical pulses, so that the acousto-optic modulator Modulated into a corresponding double-pulse signal; the data acquisition and FPGA processing unit is also used to collect and demodulate the electrical signal to form a demodulated signal.
优选的,所述弱光栅阵列分布式振动传感系统,还包括掺铒光纤放大器,所述掺铒光纤放大器,用于将所述双脉冲信号放大;所述声光调制器将所述双脉冲信号传送至环形器,具体包括,所述声光调制器将所述双脉冲信号传送至掺铒光纤放大器,经掺铒光纤放大器放大后,传送至环形器。Preferably, the weak grating array distributed vibration sensing system further comprises an erbium-doped fiber amplifier, which is used to amplify the double-pulse signal; the acousto-optic modulator amplifies the double-pulse signal. Sending the signal to the circulator specifically includes that the acousto-optic modulator sends the double-pulse signal to an erbium-doped fiber amplifier, and after being amplified by the erbium-doped fiber amplifier, the signal is sent to the circulator.
一个具体实施例中,所述弱光栅阵列分布式振动传感系统工作原理示意图,如图2所示;窄线宽DFB激光器产生中心波长一定(如,1550.15nm)的连续光,通过上位机对数据采集与FPGA处理单元(可利用数据采集卡进行数据采集)写入控制,数据采集与FPGA处理单元根据编译的程序生成相应电脉冲,将所述相应电脉冲用于调制AOM声光调制器,AOM声光调制器将连续激光光源(连续光)调制为对应的双脉冲光(信号),经过EDFA(掺铒光纤放大器)前置放大后进入从环形器的1端口进入,然后进入到与2端口串联的弱光栅光纤阵列中,双脉冲光被连续的弱光栅反射回来,从环形器的3端口出来后到达3×3耦合器中,由于脉冲延迟,后脉冲从第m个弱光栅反射光与前脉冲从第m+1个弱光栅反射光的光程相同,从而使相邻弱光栅的反射光产生干涉现象,即相邻弱光栅的反射光在3×3耦合器中会形成干涉;一系列的反射光脉冲就会产生出一系列的干涉脉冲信号;如果在两相邻光栅之间有振动产生,这样光在两光栅之间的传输光程差发生变化,从而导致相位变化,因而引起干涉强度就会发生变化;干涉信号(干涉脉冲信号)通过3个PD光电探测器转换成电信号;所述电信号通过数据采集与FPGA处理单元进行采集和解调,最终将信号通过PCIe传入上位机进行显示和存储处理;上位机PC主要用于人机交互;同时上位机还负责控制FPGA采集的基本设置。In a specific embodiment, a schematic diagram of the working principle of the weak grating array distributed vibration sensing system is shown in Figure 2; the narrow linewidth DFB laser generates continuous light with a certain center wavelength (eg, 1550.15nm), Data acquisition and FPGA processing unit (data acquisition card can be used for data acquisition) write control, data acquisition and FPGA processing unit generate corresponding electrical pulses according to the compiled program, and the corresponding electrical pulses are used to modulate the AOM acousto-optic modulator, The AOM acousto-optic modulator modulates the continuous laser light source (continuous light) into the corresponding double-pulse light (signal), which is pre-amplified by the EDFA (Erbium-Doped Fiber Amplifier) and then enters from the 1 port of the circulator, and then enters and 2 In the weak grating fiber array whose ports are connected in series, the double-pulse light is reflected back by the continuous weak grating, and reaches the 3×3 coupler after exiting from the 3 ports of the circulator. Due to the pulse delay, the post-pulse reflects light from the mth weak grating. The optical path of the reflected light from the m+1th weak grating is the same as that of the previous pulse, so that the reflected light of the adjacent weak grating will interfere, that is, the reflected light of the adjacent weak grating will interfere in the 3×3 coupler; A series of reflected light pulses will generate a series of interference pulse signals; if there is vibration between two adjacent gratings, the optical path difference of light transmission between the two gratings will change, resulting in phase changes, so The interference intensity will change; the interference signal (interference pulse signal) is converted into an electrical signal by three PD photodetectors; the electrical signal is collected and demodulated by the data acquisition and FPGA processing unit, and finally the signal is transmitted through PCIe. Enter the host computer for display and storage processing; the host computer PC is mainly used for human-computer interaction; at the same time, the host computer is also responsible for controlling the basic settings of FPGA acquisition.
具体实施时,窄线宽激光器的连续光的中心波长、输出光功率、3dB线宽分别为1550.15nm、30mw、3kHz;双脉冲包括两个光脉冲,分别为前脉冲和后脉冲;所述双脉冲信号单次脉冲脉宽为Tw,后脉冲相对于前脉冲的脉冲延迟为Tps,In specific implementation, the central wavelength, output optical power, and 3dB linewidth of the continuous light of the narrow linewidth laser are 1550.15nm, 30mw, and 3kHz, respectively; the double pulse includes two optical pulses, which are respectively a pre-pulse and a post-pulse; The pulse width of a single pulse of the pulse signal is Tw , and the pulse delay of the post-pulse relative to the pre-pulse is T ps ,
优选的,所述声光调制器将所述连续光调制为相应的双脉冲信号,具体包括,所述声光调制器将所述连续光调制成前后两上升沿的时间延迟为Tps、脉冲脉宽为Tw、脉冲重复频率为Fp的双脉冲信号,Preferably, the acousto-optic modulator modulates the continuous light into a corresponding double-pulse signal, which specifically includes: the acousto-optic modulator modulates the continuous light into a time delay of two rising edges before and after T ps , pulse A double-pulse signal with a pulse width of Tw and a pulse repetition frequency of Fp ,
其中,Fp≤v/2L,v为光在弱光栅阵列中的传播速度,d为弱光栅阵列光栅距离,ne为弱光栅阵列的折射率,L为弱光栅阵列的长度,c为光速。in, F p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.
具体实施时,假设后脉冲经过第i个光栅的反射后到达3×3耦合器前光强为,In specific implementation, it is assumed that the light intensity before the post pulse reaches the 3×3 coupler after being reflected by the ith grating is,
其中,E0,Rm,ω,ne,k,Lm,τm分别为入射光的光强振幅、第m个光栅的反射率、光频率、光纤的折射率、波数、第i个光栅的光纤距离及反射光到耦合器的传输时间;Among them, E 0 , R m , ω, ne , k, L m , τ m are the light intensity amplitude of the incident light, the reflectivity of the m-th grating, the optical frequency, the refractive index of the fiber, the wave number, and the i-th grating, respectively. The fiber distance of the grating and the transmission time of the reflected light to the coupler;
前脉冲透射后经过第i+1个光栅并反射后达到3×3耦合器前光强为,After the pre-pulse is transmitted, it passes through the i+1th grating and is reflected to reach the 3×3 coupler before the light intensity is,
Ei(t)和Ei+1(t)刚好同时到达耦合器,从而在PD中产生干涉,因此干涉信号的干涉强度为E i (t) and E i+1 (t) arrive at the coupler just at the same time, causing interference in the PD, so the interference intensity of the interference signal is
上式中,前两项均为直流项,第三项中的余弦函数随时间变化,其相位为φ(t),没有外界扰动时其相位为φ0(t),外界引起的光纤的相位变化为φ1(t),因此φ(t)=φ1(t)+φ0(t),因此上式可以写为,In the above formula, the first two terms are both DC terms, and the cosine function in the third term changes with time, and its phase is φ(t), and its phase is φ 0 (t) when there is no external disturbance. changes to φ 1 (t), so φ(t)=φ 1 (t)+φ 0 (t), so the above formula can be written as,
I(t)∝D+I0cos[φ(t)]I(t)∝D+I 0 cos[φ(t)]
因此,由于3×3耦合器其输出相位相差120°,经过耦合器与三个PD后,其强度为,Therefore, since the output phase of the 3×3 coupler is 120° out of phase, after passing through the coupler and the three PDs, its intensity is,
通过光电探测器对耦合器中的三路信号进行采集,并通过数据采集与FPGA处理单元进行反正切算法解调,可得到信号电压V与相位变化的关系:The three-way signal in the coupler is collected by the photodetector, and the arc tangent algorithm is demodulated by the data acquisition and FPGA processing unit, and the relationship between the signal voltage V and the phase change can be obtained:
其中,D为直流分量,φ0是相邻弱光栅阵列的初相位差,Δφ是外界环境引起的相位差,通过电压值可以线性得到相邻弱光栅阵列的相位变化,从而实现分布式的相位变化解调;从上式中可知,信号电压V与相位变化成线性关系,通过测量电压值,从而可以得到相邻光栅之间的相位变化,通过整列光栅,实现全分布式振动监测。Among them, D is the DC component, φ 0 is the initial phase difference of adjacent weak grating arrays, Δφ is the phase difference caused by the external environment, and the phase change of adjacent weak grating arrays can be obtained linearly through the voltage value, so as to realize the distributed phase Change demodulation: From the above formula, it can be seen that the signal voltage V has a linear relationship with the phase change. By measuring the voltage value, the phase change between adjacent gratings can be obtained, and fully distributed vibration monitoring can be realized by arranging the gratings.
一个具体实施中,双脉冲信号脉冲周期为90ns,脉冲脉宽为40ns,两次脉冲间隔为10ns,两个双脉冲光发射间隔为100us,所述光电探测器为雪崩二极管(APD);In a specific implementation, the pulse period of the double-pulse signal is 90ns, the pulse width is 40ns, the interval between two pulses is 10ns, and the interval between two double-pulse light emission is 100us, and the photodetector is an avalanche diode (APD);
优选的,所述3×3耦合器使经过反射的双脉冲信号形成干涉,生成干涉信号,具体包括,所述3×3耦合器使经过反射的双脉冲信号形成干涉,当t=0时双脉冲信号输入传感光纤(弱光栅阵列),第i与i+1个光栅反射信号形成干涉强度为I(t)的干涉信号;Preferably, the 3×3 coupler causes the reflected double-pulse signal to form interference to generate an interference signal. Specifically, the 3×3 coupler causes the reflected double-pulse signal to form interference, and when t=0, the double-pulse signal forms interference. The pulse signal is input into the sensing fiber (weak grating array), and the reflection signals of the i and i+1 gratings form an interference signal with an interference intensity of I(t);
其中,E0,Rm,ω,ne,k0,Lm,τm分别为入射光的光强振幅、第m个光栅的反射率、光频率、光纤的折射率、波数、第m个光栅的光纤距离及反射光到耦合器的传输时间。Among them, E 0 , R m , ω, ne , k 0 , L m , τ m are the light intensity amplitude of the incident light, the reflectivity of the mth grating, the optical frequency, the refractive index of the fiber, the wavenumber, the mth The fiber distance of a grating and the transit time of the reflected light to the coupler.
优选的,所述弱光栅阵列分布式振动传感系统还包括根据所述第i与i+1个光栅反射信号形成的干涉强度为I(t)的干涉信号,获取三个探测器的电流Preferably, the weak grating array distributed vibration sensing system further comprises an interference signal with an interference intensity of I(t) formed by the reflection signals of the ith and i+1 gratings to obtain the currents of the three detectors
并使用标准的反正切算法,可以得到电信号的电压,And using the standard arctangent algorithm, the voltage of the electrical signal can be obtained,
其中,D为直流分量,φ0是相邻弱光栅阵列的初相位差,Δφ是外界环境引起的相位差。从上式中可知,信号电压V与相位变化成线性关系,通过测量电压值,从而可以得到相邻光栅之间的相位变化,通过整列光栅,实现全分布式振动监测。Among them, D is the DC component, φ 0 is the initial phase difference of adjacent weak grating arrays, and Δφ is the phase difference caused by the external environment. It can be seen from the above formula that the signal voltage V has a linear relationship with the phase change. By measuring the voltage value, the phase change between adjacent gratings can be obtained. By arranging the gratings, fully distributed vibration monitoring is realized.
本发明实施例技术方案中,光路中不存在双臂干涉结构,所以系统中的光路不会受到外界环境干扰;以基于Michelson结构的传感系统为例,分别对基于Michelson结构的传感系统和本系统的光路都施加300Hz扰动和20Hz传感信号;In the technical solution of the embodiment of the present invention, there is no double-arm interference structure in the optical path, so the optical path in the system will not be disturbed by the external environment; Take the sensing system as an example, respectively for the Michelson structure-based Both the sensing system and the optical path of the system apply 300Hz disturbance and 20Hz sensing signal;
图3(a)是施加扰动下基于Michelson结构的传感系统的解调信号频谱图;即是施加扰动下基于Michelson双臂结构,单脉冲调制使用3×3耦合器方式解调相位信号的频率信号,显示频谱图在20Hz和300Hz处有两个峰值;图3(b)是施加扰动下基于Michelson结构的传感系统的解调信号波形图,即图3(a)相应的时域信号;图3(b)中解调信号的波形图存在很多毛刺,显然传感信号受到了外界环境的影响,存在明显的噪声,从而影响系统的信噪比;图4(a)、(b)分别是利用本发明技术方案得到的电信号解调后的频域和时域信号图;图4(a)、图4(b)显示解调信号中不存在扰动信号,解调信号中的毛刺不明显,所以本发明系统可以避免振动对光路的干扰,提高系统的稳定性与可靠性,系统的信噪比也明显提升;图5是本发明系统解调40kHz和0.1Hz的频率响应图(左图对应40kHz频率响应,右图对应0.1Hz频率响应),对本发明所述系统的传感器通过PZT施加震动信号,可以实现0.1Hz~40kHz的频率响应,系统的信噪比可达到42dB。可以看到,系统具有很宽的频率响应范围,仅仅受限于光纤的长度与采集卡的采样率影响。Fig. 3(a) is based on the Michelson structure under the applied perturbation The spectrum diagram of the demodulated signal of the sensing system; that is, based on the Michelson double-arm structure under the applied disturbance, the single pulse modulation uses a 3×3 coupler to demodulate the frequency signal of the phase signal, and the spectrum diagram shows that there are two frequency signals at 20Hz and 300Hz. peak; Figure 3(b) is based on the Michelson structure under applied perturbation The waveform diagram of the demodulation signal of the sensing system, that is, the corresponding time domain signal in Figure 3(a); the waveform diagram of the demodulation signal in Figure 3(b) has many burrs. Obviously, the sensing signal is affected by the external environment, and there are Obvious noise, thereby affecting the signal-to-noise ratio of the system; Figure 4 (a), (b) are the frequency domain and time domain signal diagrams of the demodulated electrical signal obtained by using the technical solution of the present invention; Figure 4 (a), Fig. 4(b) shows that there is no disturbance signal in the demodulated signal, and the burr in the demodulated signal is not obvious, so the system of the present invention can avoid the interference of vibration on the optical path, improve the stability and reliability of the system, and the signal-to-noise ratio of the system. Fig. 5 is the frequency response diagram of the demodulation system of the present invention at 40kHz and 0.1Hz (the left picture corresponds to the 40kHz frequency response, and the right picture corresponds to the 0.1Hz frequency response). The sensor of the present invention is applied with a vibration signal through PZT, The frequency response of 0.1Hz to 40kHz can be achieved, and the signal-to-noise ratio of the system can reach 42dB. It can be seen that the system has a wide frequency response range, which is only limited by the length of the optical fiber and the sampling rate of the acquisition card.
实施例2Example 2
本发明还提供了一种弱光栅阵列分布式振动传感方法,包括以下步骤:The present invention also provides a distributed vibration sensing method for a weak grating array, comprising the following steps:
将中心波长一定的连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列;所述弱光栅阵列将所述双脉冲信号反射,使经过反射的双脉冲信号形成干涉,生成干涉信号;获取所述干涉信号,并将所述干涉信号转换为电信号。The continuous light with a certain central wavelength is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the weak grating array; the weak grating array reflects the double-pulse signal, so that the reflected double-pulse signal forms interference , generating an interference signal; acquiring the interference signal, and converting the interference signal into an electrical signal.
优选的,所述弱光栅阵列分布式振动传感方法还包括对所述电信号进行采集并解调,形成解调后的信号;对解调后的信号使用反正切算法得到相邻两光栅之间的相位变化。Preferably, the weak grating array distributed vibration sensing method further includes collecting and demodulating the electrical signal to form a demodulated signal; using an arctangent algorithm on the demodulated signal to obtain the difference between two adjacent gratings phase change between.
优选的,所述弱光栅阵列分布式振动传感方法还包括在将所述双脉冲信号传送至弱光栅阵列前,对所述双脉冲信号进行放大。Preferably, the method for distributed vibration sensing of the weak grating array further comprises amplifying the double pulse signal before transmitting the double pulse signal to the weak grating array.
优选的,将所述连续光调制为相应的双脉冲信号,具体包括,将所述连续光调制成时间延迟为Tps、脉冲脉宽为Tw、脉冲重复频率为Fp的双脉冲信号,Preferably, modulating the continuous light into a corresponding double-pulse signal specifically includes: modulating the continuous light into a double-pulse signal with a time delay of T ps , a pulse width of Tw , and a pulse repetition frequency of F p ,
其中,Fp≤v/2L,v为光在弱光栅阵列中的传播速度,d为弱光栅阵列光栅距离,ne为弱光栅阵列的折射率,L为弱光栅阵列的长度,c为光速。in, F p ≤ v/2L, v is the propagation speed of light in the weak grating array, d is the grating distance of the weak grating array, ne is the refractive index of the weak grating array, L is the length of the weak grating array, and c is the speed of light.
优选的,所述使经过反射的双脉冲信号形成干涉,生成干涉信号,具体包括,使经过反射的双脉冲信号形成干涉,干涉强度为I(t)为干涉信号,Preferably, the interference of the reflected double-pulse signal to generate the interference signal specifically includes: causing the reflected double-pulse signal to interfere, and the interference intensity is I(t), which is the interference signal,
其中,Ei,Ri,τi分别为第i个光栅的振幅、反射率、时间;φ(t)为第i+1与i个光栅之间的相位差,σ偏振失配因子。Among them, E i , R i , τ i are the amplitude, reflectivity, and time of the ith grating, respectively; φ(t) is the phase difference between the i+1th grating and the ith grating, and the σ polarization mismatch factor.
需要说明的是,实施例1和实施例2未重复描述之处可相互借鉴。It should be noted that, the parts not repeatedly described in
本发明公开了一种弱光栅阵列分布式振动传感系统及方法,通过所述窄线宽激光器,产生中心波长一定的连续光,并发送至所述声光调制器;声光调制器将所述连续光调制为相应的双脉冲信号,并将所述双脉冲信号传送至环形器;环形器接收所述双脉冲信号,并将所述双脉冲信号传送至弱光栅阵列,所述弱光栅阵列将所述双脉冲信号反射至环形器;所述环形器将经过反射的双脉冲信号传送至所述3×3耦合器;所述3×3耦合器使经过反射的双脉冲信号形成干涉,生成干涉信号;所述光电探测器获取所述干涉信号,并将所述干涉信号转换为电信号;未使用常规的双臂干涉仪来解调相邻光栅之间的相位差,系统不会受外界环境干扰,提高了系统的稳定性,降低了系统底噪声、提高了信噪比和频率响应范围;The invention discloses a weak grating array distributed vibration sensing system and method. The narrow linewidth laser generates continuous light with a certain center wavelength and sends it to the acousto-optic modulator; The continuous light is modulated into a corresponding double-pulse signal, and the double-pulse signal is transmitted to the circulator; the circulator receives the double-pulse signal, and transmits the double-pulse signal to the weak grating array, the weak grating array The double pulse signal is reflected to the circulator; the circulator transmits the reflected double pulse signal to the 3×3 coupler; the 3×3 coupler interferes with the reflected double pulse signal to generate interference signal; the photodetector acquires the interference signal and converts the interference signal into an electrical signal; the conventional double-arm interferometer is not used to demodulate the phase difference between adjacent gratings, and the system will not be affected by the outside world Environmental interference improves the stability of the system, reduces the noise floor of the system, and improves the signal-to-noise ratio and frequency response range;
需要说明的是,为了降低相位解调算法的复杂程度,提高信号的解调精度和解调信信噪比,解调时本发明采用反正切解调算法,相较于其他解调算法,以正反切的运算替换了积分运算,避免了因积分运算产生的噪声自激影响;本发明技术方案无需双臂干涉,使用直接探测,使得解调不会受到外界环境干扰,降低系统的底噪声,提高了系统的信噪比,同时本发明所述系统具有超宽的频率响应范围,仅仅受限于光纤的长度,最低响应频率可达0.1Hz,系统结构简单,各元器件均为常规的器件,降低了系统的复杂性,大大降低了系统成本,更适合工程应用。It should be noted that, in order to reduce the complexity of the phase demodulation algorithm, improve the demodulation accuracy of the signal and the demodulation signal-to-noise ratio, the present invention adopts the arctangent demodulation algorithm during demodulation. Compared with other demodulation algorithms, the The operation of the forward and reverse tangent replaces the integral operation, avoiding the influence of noise self-excitation caused by the integral operation; the technical scheme of the present invention does not require double-arm interference, and uses direct detection, so that the demodulation will not be disturbed by the external environment and reduce the noise floor of the system , the signal-to-noise ratio of the system is improved, and the system of the present invention has an ultra-wide frequency response range, which is only limited by the length of the optical fiber, the minimum response frequency can reach 0.1Hz, the system structure is simple, and all components are conventional The device reduces the complexity of the system, greatly reduces the system cost, and is more suitable for engineering applications.
以上所述本发明的具体实施方式,并不构成对本发明保护范围的限定。任何根据本发明的技术构思所做出的各种其他相应的改变与变形,均应包含在本发明权利要求的保护范围内。The specific embodiments of the present invention described above do not limit the protection scope of the present invention. Any other corresponding changes and modifications made according to the technical concept of the present invention shall be included in the protection scope of the claims of the present invention.
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