CN105806380A - Multiplexing demodulation equipment based on long-cycle fiber grating reflective sensor - Google Patents
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Abstract
本发明涉及一种基于长周期光纤光栅反射型传感器的复用解调设备，其中，多个长周期光纤光栅反射型传感器具有不同的光程差；所述宽带光源与三端口环形器的第一端口相连，所述三端口环形器的第二端口与串联有所述多个长周期光纤光栅反射型传感器的光纤相连，第三端口与第一光纤耦合器的输入端相连；所述第一光纤耦合器的一个输出端与偏振控制器的输入端相连，另一个输出端与电动可调延迟线的输入端相连；所述偏振控制器的输出端和电动可调延迟线的输出端分别连接第二光纤耦合器的两个输入端；所述第二光纤耦合器的输出端与光电探测器的输入端相连，所述光电探测器的输出端与数据采集卡相连。本发明使得系统空间分辨率高、可复用数目大、成本低廉。
The invention relates to a multiplexing demodulation device based on long-period fiber grating reflective sensors, wherein multiple long-period fiber grating reflective sensors have different optical path differences; the broadband light source and the first three-port circulator The ports are connected, the second port of the three-port circulator is connected with the optical fiber with the plurality of long-period fiber grating reflective sensors connected in series, and the third port is connected with the input end of the first fiber coupler; the first optical fiber One output end of the coupler is connected to the input end of the polarization controller, and the other output end is connected to the input end of the electrically adjustable delay line; the output end of the polarization controller and the output end of the electrically adjustable delay line are respectively connected to the first Two input ends of the second optical fiber coupler; the output end of the second optical fiber coupler is connected with the input end of the photodetector, and the output end of the photodetector is connected with the data acquisition card. The invention enables the system to have high spatial resolution, large reusable number and low cost.
Description
技术领域technical field
本发明涉及光纤传感技术领域，特别是涉及一种基于长周期光纤光栅反射型传感器的复用解调设备。The invention relates to the technical field of optical fiber sensing, in particular to a multiplexing demodulation device based on long-period optical fiber grating reflective sensors.
背景技术Background technique
在光纤传感领域，长周期光纤光栅由于其对温度、应力和应变、环境折射率等变化的高度敏感性，而成为一种十分重要的传感器件。与布拉格光栅相比，长周期光纤光栅对温度、应力等具有更高的灵敏性，并且它的包层模式对外界环境折射率敏感，可以适用于液体折射率的高精度测量。虽然具有优秀的单点传感性能，长周期光纤光栅在应用领域的实用化进程远远落后于布拉格光栅。布拉格光栅由于其频域反射频宽很窄，一般小于1nm，可以很方便的构建成分布式的传感系统并用波分复用或时分复用技术来解调。长周期光纤光栅的频谱特征为多个透射损耗峰共存，且每个损耗峰的频谱带宽很大，对环境折射率灵敏度较高的高阶模的带宽至少有几十纳米，因此它的频域无法采用波分复用系统解调。长周期光纤光栅是同向传输的芯层模和包层模耦合，几乎没有反射频谱，因此它无法采用目前技术成熟的时分复用系统解调。由于缺乏针对长周期光纤光栅分布式传感的复用和解调方法的研究，具有优良传感特性的长周期光纤光栅的实用化进程大受影响。In the field of optical fiber sensing, long-period fiber gratings have become a very important sensing device due to their high sensitivity to changes in temperature, stress and strain, and environmental refractive index. Compared with Bragg gratings, long-period fiber gratings have higher sensitivity to temperature, stress, etc., and its cladding mode is sensitive to the refractive index of the external environment, which can be applied to high-precision measurement of the refractive index of liquids. Although it has excellent single-point sensing performance, the practical progress of long-period fiber gratings in the application field lags far behind Bragg gratings. Due to its narrow frequency-domain reflection bandwidth, generally less than 1nm, Bragg gratings can be easily constructed into a distributed sensing system and demodulated by wavelength division multiplexing or time division multiplexing technology. The spectral characteristics of long period fiber gratings are the coexistence of multiple transmission loss peaks, and the spectral bandwidth of each loss peak is very large. The bandwidth of the high-order mode with high sensitivity to the ambient refractive index is at least tens of nanometers, so its frequency domain cannot be used. WDM system demodulation. The long-period fiber grating is coupled with the core mode and the cladding mode of the same direction transmission, and has almost no reflection spectrum, so it cannot be demodulated by the current mature time division multiplexing system. Due to the lack of research on multiplexing and demodulation methods for distributed sensing of long-period fiber gratings, the practical progress of long-period fiber gratings with excellent sensing characteristics is greatly affected.
低相干干涉技术是使用宽谱光作为光源，根据白光相干原理，利用零级干涉条纹作为参考位置，从而在较大的范围内获得精确测量绝对位置信息的一种干涉系统。低相干干涉系统用于获得探测信号的传感器结构为干涉仪，解调部分是扫描型的干涉仪，不同的传感器采用不同的光程差设计，可以实现多路传感复用。由于低相干系统中采用干涉仪方式来解调各个传感器信息量，可以避免光源不稳定等因素引入的环境噪声，具有较高的抗干扰性；充分利用干涉图的所有数据来评定被测信号，具有精密测量理论所青睐的平均效应的效果，获得较高的测量精度；构建光纤低相干干涉系统，不需要高相干干涉系统所使用的可调谐激光光源，信号分析处理也不需要光谱仪、网络分析仪、矢量分析仪等贵重精密设备，系统成本远远低于目前广泛使用的波分复用、时分复用等系统。基于低相干原理的复用解调系统是一个性能优良且成本低廉的复用系统，但是目前这个系统的应用研究还远远落后于时分复用系统、波分复用系统等。Low-coherence interferometry is an interferometric system that uses broad-spectrum light as a light source, and uses zero-order interference fringes as a reference position according to the principle of white light coherence, so as to obtain accurate measurement of absolute position information in a large range. The sensor structure used to obtain the detection signal in the low-coherence interference system is an interferometer, and the demodulation part is a scanning interferometer. Different sensors adopt different optical path difference designs, which can realize multiple sensing multiplexing. Since the interferometer mode is used in the low-coherence system to demodulate the information of each sensor, it can avoid the environmental noise introduced by factors such as unstable light sources, and has high anti-interference; fully utilize all the data of the interferogram to evaluate the measured signal, It has the effect of the average effect favored by precision measurement theory, and obtains high measurement accuracy; the construction of optical fiber low-coherence interference system does not require tunable laser light sources used in high-coherence interference systems, and signal analysis and processing do not require spectrometers and network analysis Instruments, vector analyzers and other expensive precision equipment, the system cost is far lower than the widely used wavelength division multiplexing, time division multiplexing and other systems. The multiplex demodulation system based on the principle of low coherence is a multiplex system with excellent performance and low cost, but the application research of this system is still far behind the time division multiplex system and wavelength division multiplex system.
发明内容Contents of the invention
本发明所要解决的技术问题是提供一种基于长周期光纤光栅反射型传感器的复用解调设备，使得系统空间分辨率高、可复用数目大、成本低廉。The technical problem to be solved by the present invention is to provide a multiplexing demodulation device based on a long-period fiber grating reflective sensor, so that the system has high spatial resolution, large number of multiplexing, and low cost.
本发明解决其技术问题所采用的技术方案是：提供一种基于长周期光纤光栅反射型传感器的复用解调设备，包括宽带光源和多个长周期光纤光栅反射型传感器，所述多个长周期光纤光栅反射型传感器具有不同的光程差；所述宽带光源与三端口环形器的第一端口相连，所述三端口环形器的第二端口与串联有所述多个长周期光纤光栅反射型传感器的光纤相连，第三端口与第一光纤耦合器的输入端相连；所述第一光纤耦合器的一个输出端与偏振控制器的输入端相连，另一个输出端与电动可调延迟线的输入端相连；所述偏振控制器的输出端和电动可调延迟线的输出端分别连接第二光纤耦合器的两个输入端；所述第二光纤耦合器的输出端与光电探测器的输入端相连，所述光电探测器的输出端与数据采集卡相连。The technical solution adopted by the present invention to solve the technical problem is to provide a multiplexing demodulation device based on long-period fiber grating reflective sensors, including a broadband light source and multiple long-period fiber grating reflective sensors, the multiple long-period fiber grating reflective sensors Periodic fiber grating reflective sensors have different optical path differences; the broadband light source is connected to the first port of the three-port circulator, and the second port of the three-port circulator is connected to the multiple long-period fiber grating reflectors connected in series. The optical fiber of the type sensor is connected, the third port is connected with the input end of the first fiber coupler; one output end of the first fiber coupler is connected with the input end of the polarization controller, and the other output end is connected with the electric adjustable delay line The input end of the polarization controller and the output end of the electrically adjustable delay line are respectively connected to the two input ends of the second fiber coupler; the output end of the second fiber coupler is connected to the photodetector The input end is connected, and the output end of the photodetector is connected with the data acquisition card.
所述长周期光纤光栅反射型传感器通过耦合强度为3dB的长周期光纤光栅制备而成，所述长周期光纤光栅的一端光纤保留以便接入系统，另一端的光纤用切割刀切断并采用溅射方法镀上金属反射膜。The long-period fiber grating reflective sensor is prepared by a long-period fiber grating with a coupling strength of 3dB. One end of the long-period fiber grating is reserved for access to the system, and the other end of the fiber is cut with a cleaver and sputtered. The method is to coat the metal reflective film.
所述多个长周期光纤光栅反射型传感器通过第三光纤耦合器串联接入到同一根光纤中。The multiple long-period fiber grating reflective sensors are serially connected to the same optical fiber through a third fiber coupler.
所述宽带光源的光源范围覆盖所述长周期光纤光栅传感器的谐振损耗峰的带宽。The light source range of the broadband light source covers the bandwidth of the resonance loss peak of the long period fiber grating sensor.
所述长周期光纤光栅反射型传感器的单模光纤芯层和包层有效折射率差为10-2。The effective refractive index difference between the single-mode fiber core layer and the cladding layer of the long-period fiber grating reflective sensor is 10 -2 .
相邻的长周期光纤光栅反射型传感器中光栅中心到端面的距离差大于或等于2.7mm。The distance difference between the center of the grating and the end face of adjacent long-period fiber grating reflective sensors is greater than or equal to 2.7mm.
所述宽带光源的光谱范围为60nm。The spectral range of the broadband light source is 60nm.
所述长周期光纤光栅反射型传感器的中心波长为1550nm，损耗峰带宽为20nm。有益效果The central wavelength of the long-period fiber grating reflective sensor is 1550nm, and the loss peak bandwidth is 20nm. Beneficial effect
由于采用了上述的技术方案，本发明与现有技术相比，具有以下的优点和积极效果：本发明利用数据采集和处理系统对干涉信号进行傅里叶变换提取频率即可获得干涉光的中心波长，从而得到传感器的温度信息的解调。利用电动可调延迟线往复扫描，实现了长周期光纤光栅反射型传感器的多路复用。本发明具有系统空间分辨率高、可复用数目大、成本低廉的优点。Due to the adoption of the above-mentioned technical solution, the present invention has the following advantages and positive effects compared with the prior art: the present invention uses the data acquisition and processing system to perform Fourier transform on the interference signal to extract the frequency to obtain the center of the interference light wavelength, thereby obtaining the demodulation of the temperature information of the sensor. The multiplexing of the long-period fiber grating reflective sensor is realized by using the electric adjustable delay line to scan back and forth. The invention has the advantages of high system spatial resolution, large reusable number and low cost.
附图说明Description of drawings
图1是本发明的结构示意图。Fig. 1 is a structural schematic diagram of the present invention.
具体实施方式detailed description
下面结合具体实施例，进一步阐述本发明。应理解，这些实施例仅用于说明本发明而不用于限制本发明的范围。此外应理解，在阅读了本发明讲授的内容之后，本领域技术人员可以对本发明作各种改动或修改，这些等价形式同样落于本申请所附权利要求书所限定的范围。Below in conjunction with specific embodiment, further illustrate the present invention. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the teachings of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.
如图1所示，宽带光源1与三端口环形器2的第一个端口光信号连接，长周期光纤光栅反射型传感器4通过一个光纤耦合器3串联到同一根光纤上，串联了n(n≥2)个不同光程差传感器的光纤与环形器的第二个端口光信号连接，环形器的第三个端口与光纤耦合器5的输入端光连接。光纤耦合器5的一个输出端与偏振控制器6的输入端光连接，光纤耦合器5的另一个输出端与电动可调延迟线7的输入端光连接，偏振控制器6的输出端和光纤耦合器8的输入端光连接，电动可调延迟线7的输出端和光纤耦合器8的另一个输入端光连接。光纤耦合器8的输出端与光电二极管9输入端光信号连接。光电二极管9与数据存储和处理设备10电信号连接。将上述多个长周期光纤光栅反射型传感器4作为温度传感器预置在被监测的环境中，宽带光源1、环形器2和信号解调部分都在监测中心，宽带光通过环形器2进入多个传感器4，再由单模光纤将信号光传回监测中心进行信号解调与处理。As shown in Figure 1, the broadband light source 1 is connected to the first port optical signal of the three-port circulator 2, and the long-period fiber grating reflective sensor 4 is connected in series to the same optical fiber through a fiber coupler 3, and n(n ≥ 2) optical fibers of different optical path difference sensors are optically connected to the second port of the circulator, and the third port of the circulator is optically connected to the input end of the fiber coupler 5 . One output end of the fiber coupler 5 is optically connected to the input end of the polarization controller 6, the other output end of the fiber coupler 5 is optically connected to the input end of the electrically adjustable delay line 7, and the output end of the polarization controller 6 is connected to the optical fiber The input end of the coupler 8 is optically connected, and the output end of the electrically adjustable delay line 7 is optically connected to the other input end of the fiber coupler 8 . The output end of the fiber coupler 8 is optically connected to the input end of the photodiode 9 . The photodiode 9 is electrically connected to the data storage and processing device 10 . The above-mentioned multiple long-period fiber grating reflective sensors 4 are preset in the monitored environment as temperature sensors, the broadband light source 1, the circulator 2 and the signal demodulation part are all in the monitoring center, and the broadband light enters multiple The sensor 4 transmits the signal light back to the monitoring center through a single-mode optical fiber for signal demodulation and processing.
所述长周期光纤光栅反射型传感器通过耦合强度为3dB的长周期光纤光栅制备而成，长周期光纤光栅的一端光纤保留以便接入系统，另一端的光纤用切割刀切断并采用溅射方法镀上金属反射膜，形成长周期光纤光栅反射型传感器。不同的长周期光纤光栅反射型传感器中光栅中心到反射端之间的距离不同。The long-period fiber grating reflective sensor is prepared by a long-period fiber grating with a coupling strength of 3dB. One end of the long-period fiber grating is reserved for access to the system, and the other end of the fiber is cut with a cutter and sputtered. A metal reflective film is applied to form a long-period fiber grating reflective sensor. The distance from the center of the grating to the reflective end is different in different long-period fiber grating reflective sensors.
本实施方式中选用光谱范围为60nm的宽带光源，光源范围要覆盖长周期光纤光栅谐振损耗峰的带宽，光源输出的光通过一个三端口的环形器将光能量引入到串联在一根光纤上的传感器中。传感器中长周期光纤光栅把50％的光能量耦合到光纤包层高阶模中，剩余的光能量在光纤芯层传输，经过一段光纤后，传输在芯层和包层的光均被光纤端面的反射膜反射，反射回的光再次经过长周期光纤光栅时，传输在包层的部分光会被重新耦合回芯层，与在芯层传输的光能量汇合。光纤芯层的有效折射率和光纤包层高阶模的有效折射率不同，传感器中一直在芯层传输的光和被耦合到包层后又耦合回芯层的光之间会引入光程差为In this embodiment, a broadband light source with a spectral range of 60nm is selected. The light source range should cover the bandwidth of the long-period fiber grating resonance loss peak. in the sensor. The long-period fiber grating in the sensor couples 50% of the light energy into the high-order mode of the fiber cladding, and the remaining light energy is transmitted in the fiber core layer. After passing through a section of fiber, the light transmitted in the core layer and cladding layer is reflected by the fiber end face When the reflected light passes through the LPFG again, part of the light transmitted in the cladding layer will be recoupled back to the core layer and merged with the light energy transmitted in the core layer. The effective refractive index of the fiber core layer is different from the effective refractive index of the high-order mode of the fiber cladding layer. In the sensor, the optical path difference will be introduced between the light that has been transmitted in the core layer and the light that is coupled to the cladding layer and then coupled back to the core layer.
δ＝2(nco-ncl)·d(1)δ＝2(n co -n cl )·d(1)
其中nco和ncl分别表示光纤芯层和包层高阶模的有效折射率，d表示传感器中长周期光栅中心到反射端面的距离。预设不同传感器中光栅中心到反射端距离不同，则每个传感器中光信号引入的光程差就不同。Among them, n co and n cl represent the effective refractive index of the high-order modes of the fiber core and cladding, respectively, and d represents the distance from the center of the long-period grating in the sensor to the reflective end face. If the distance from the center of the grating to the reflective end is different in different sensors, the optical path difference introduced by the optical signal in each sensor will be different.
传感器反射回的传感信号再经过光纤收集传输回来后，经过环形器第三个端口进入一个干涉仪解调系统中。光纤耦合器将光信号分成等光强的两束，其中的一束光通过一个电动可调延迟线，使两路光之间引入可变的光程差，随着可调延迟线的扫描，引入的光程差可以补偿不同传感器引入的光程差。另一束光纤光程不变，接入一个偏振控制器的作用是让系统获得最佳的干涉信号。补偿后的两路光在另一个光纤耦合器汇合后产生干涉。干涉信号由光电二极管探测转换成电信号，再由数据采集卡采集和存储，数据处理设备对采集下来的干涉信号进行数据分析和信息解调。The sensing signal reflected by the sensor is collected and transmitted through the optical fiber, and then enters an interferometer demodulation system through the third port of the circulator. The optical fiber coupler divides the optical signal into two beams of equal light intensity, one of which passes through an electrically adjustable delay line, so that a variable optical path difference is introduced between the two beams, and as the adjustable delay line scans, The introduced optical path difference can compensate the optical path difference introduced by different sensors. The optical path of the other optical fiber remains unchanged, and the function of connecting a polarization controller is to allow the system to obtain the best interference signal. After the compensation, the two paths of light are combined by another fiber coupler to produce interference. The interference signal is converted into an electrical signal by photodiode detection, and then collected and stored by the data acquisition card. The data processing equipment performs data analysis and information demodulation on the collected interference signal.
由于不同传感器引入的光程差不同，所以当可调延迟线扫描到某一位置，某个传感器引入的光程差被补偿为零，则该传感器对应的低相干光干涉信号出现，其干涉条纹为：Since the optical path difference introduced by different sensors is different, when the adjustable delay line scans to a certain position, the optical path difference introduced by a certain sensor is compensated to zero, then the corresponding low coherent optical interference signal of the sensor appears, and its interference fringes for:
其中，A(z)是干涉条纹的幅值外包络，P是干涉条纹的周期，是干涉条纹的初相位，z是可调延迟线扫描的位置。干涉光的中心波长与干涉条纹的关系为Among them, A(z) is the amplitude outer envelope of the interference fringe, P is the period of the interference fringe, is the initial phase of the interference fringe, and z is the scanning position of the adjustable delay line. The relationship between the central wavelength of the interference light and the interference fringes is
λ＝2P(3)λ=2P(3)
通过对干涉条纹进行傅里叶变换求得干涉条纹的频率后，根据式(3)，可以获得参与干涉的光的中心波长。干涉光中心波长即是长周期光纤光栅透射损耗峰的中心波长。长周期光纤光栅的耦合损耗峰中心波长会随着温度变化发生漂移，波长飘移与温度的变化成正比关系，其比例系数可以通过实验定标获得。本系统通过测量计算出传感器的谐振损耗峰波长位置，进而解调出环境温度待测量的信息。系统中传感器的灵敏度与长周期光纤光栅的灵敏度一致。解调方案的空间分辨率取决于长周期光纤光栅损耗峰的相干长度。通过串联布置一系列不同光程差的传感器，以及通过控制电动可调延迟线扫描解调干涉仪其中一臂，可实现多路传感器的复用。After obtaining the frequency of the interference fringes by performing Fourier transform on the interference fringes, according to formula (3), the central wavelength of the light participating in the interference can be obtained. The central wavelength of the interference light is the central wavelength of the transmission loss peak of the long-period fiber grating. The central wavelength of the coupling loss peak of the long period fiber grating will drift with the temperature change, and the wavelength drift is proportional to the temperature change, and its proportional coefficient can be obtained through experimental calibration. The system calculates the resonance loss peak wavelength position of the sensor through measurement, and then demodulates the information of the ambient temperature to be measured. The sensitivity of the sensor in the system is consistent with that of the long-period fiber grating. The spatial resolution of the demodulation scheme depends on the coherence length of the loss peak of the LPFG. By arranging a series of sensors with different optical path differences in series, and by controlling one arm of the electrically adjustable delay line scanning demodulation interferometer, the multiplexing of multiple sensors can be realized.
本实施方式中长周期光纤光栅中心波长均取光通信典型波段1550nm,一般长周期光纤光栅损耗峰带宽为20nm，则长周期光纤光栅损耗峰的干涉长度为53μm。若使用电动可调延迟线的扫描范围是10cm，本系统最多可以解调1886个传感器。为了不同的传感器干涉信号不发生混叠现象，根据单模光纤芯层和包层有效折射率差约为10-2，相邻传感器中光栅中心到端面的距离差至少2.7mm。In this embodiment, the center wavelength of the long-period FBG is 1550nm, which is a typical optical communication band. Generally, the loss peak bandwidth of the long-period FBG is 20nm, and the interference length of the long-period FBG loss peak is 53 μm. If the scanning range of the electric adjustable delay line is 10cm, the system can demodulate up to 1886 sensors. In order to prevent interference signals from different sensors from aliasing, according to the effective refractive index difference between the core layer and the cladding layer of the single-mode optical fiber is about 10 -2 , the distance difference between the grating center and the end surface of adjacent sensors is at least 2.7mm.
由于温度变化会引起传感器中长周期光纤光栅谐振损耗峰波长的漂移，从而干涉光的中心波长会发生变化，利用数据采集和处理系统对干涉信号进行傅里叶变换提取频率即可获得干涉光的中心波长，从而得到传感器的温度信息的解调。电动可调延迟线往复扫描，实现了长周期光纤光栅反射型传感器的多路复用。本发明具有系统空间分辨率高、可复用数目大、成本低廉的优点。Since the temperature change will cause the shift of the peak wavelength of the long-period fiber grating resonance loss in the sensor, the center wavelength of the interference light will change. The frequency of the interference light can be obtained by using the data acquisition and processing system to perform Fourier transform on the interference signal to extract the frequency. The central wavelength, thus obtaining the demodulation of the temperature information of the sensor. The motorized adjustable delay line scans back and forth, realizing the multiplexing of long-period fiber grating reflective sensors. The invention has the advantages of high system spatial resolution, large reusable number and low cost.
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