CN118362538A - Optical frequency domain reflectometer salinity measurement device and method based on polyimide optical fiber - Google Patents
Optical frequency domain reflectometer salinity measurement device and method based on polyimide optical fiber Download PDFInfo
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Abstract
Description
技术领域Technical Field
本发明涉及光纤传感技术领域,具体是一种基于聚酰亚胺光纤的光频域反射仪盐度测量装置及方法。The invention relates to the technical field of optical fiber sensing, and in particular to a salinity measuring device and method of an optical frequency domain reflectometer based on polyimide optical fiber.
背景技术Background technique
随着全球工业和技术的快速发展,盐度传感器被广泛应用于海洋渔业与水产养殖、自然环境的监测与治理、工业生产与制造等领域。目前常见的盐度测量方法包括电导率法、折射率法、微波遥感技术和表面等离子共振法等。然而这些检测方法普遍存在检测设备体积较大、操作复杂、易腐蚀、长期稳定性差的缺点。近年来随着光纤传感技术的快速发展,与传统的电传感技术相比,在很多方面有不可替代的优势。光纤传感器具有耐腐蚀,传感测量时能抗电磁干扰,可以长距离、分布式测量等。光纤光频域反射技术是一种基于瑞利散射效应的分布式光纤传感技术,该技术能实现对盐度的高精度和分布式测量,为产业化提供了广阔的应用前景。With the rapid development of global industry and technology, salinity sensors are widely used in marine fisheries and aquaculture, natural environment monitoring and management, industrial production and manufacturing, and other fields. At present, common salinity measurement methods include conductivity method, refractive index method, microwave remote sensing technology, and surface plasmon resonance method. However, these detection methods generally have the disadvantages of large detection equipment, complex operation, easy corrosion, and poor long-term stability. In recent years, with the rapid development of fiber optic sensing technology, it has irreplaceable advantages in many aspects compared with traditional electrical sensing technology. Fiber optic sensors are corrosion-resistant, can resist electromagnetic interference during sensing and measurement, and can perform long-distance and distributed measurements. Fiber optic frequency domain reflectometry technology is a distributed fiber optic sensing technology based on the Rayleigh scattering effect. This technology can achieve high-precision and distributed measurement of salinity, providing broad application prospects for industrialization.
发明内容Summary of the invention
本发明的目的是针对现有技术的不足,而提供一种基于聚酰亚胺光纤的光频域反射仪盐度测量装置及方法。这种光频域反射仪具有抗电磁干扰能力强、耐腐蚀性好、结构简单,这种方法能实时监测盐度值的变化,能实现相对盐度分布式的精确测量。The purpose of the present invention is to provide a device and method for measuring salinity using an optical frequency domain reflectometer based on polyimide optical fiber in view of the shortcomings of the prior art. The optical frequency domain reflectometer has strong anti-electromagnetic interference capability, good corrosion resistance, and a simple structure. The method can monitor the change of salinity value in real time and can achieve accurate measurement of relative salinity distribution.
实现本发明目的的技术方案是:The technical solution for achieving the purpose of the present invention is:
一种基于聚酰亚胺光纤的光频域反射仪盐度测量装置,包括互联的窄线宽激光器和第一光纤耦合器,其中:An optical frequency domain reflectometer salinity measurement device based on polyimide optical fiber, comprising an interconnected narrow linewidth laser and a first optical fiber coupler, wherein:
第一光纤耦合器的输出端分成两路,其中一路输出端连接第二光纤耦合器,第二光纤耦合器的输出端再次分成两路,第二光纤耦合器的一路输出端顺序连接偏振控制器、第四光纤耦合器;第二光纤耦合器的另一路输出端连接环形器的a端口、环形器的b端口连接聚酰亚胺光纤、环形器的c端口连接第四光纤耦合器,第四光纤耦合器的输出端顺序连接第一平衡光电探测器、高速示波器;第一光纤耦合器的另一路输出端连接第三光纤耦合器,第三光纤耦合器的输出端再次分成两路,第三光纤耦合器的一路输出端采用单模光纤连接第五光纤耦合器,第三光纤耦合器的另一路输出端顺序连接延时光纤、第五光纤耦合器,第五光纤耦合器的输出端顺序连接第二平衡光电探测器、高速示波器;The output end of the first optical fiber coupler is divided into two paths, one of which is connected to the second optical fiber coupler, and the output end of the second optical fiber coupler is divided into two paths again, and one output end of the second optical fiber coupler is connected to the polarization controller and the fourth optical fiber coupler in sequence; the other output end of the second optical fiber coupler is connected to the a port of the circulator, the b port of the circulator is connected to the polyimide optical fiber, and the c port of the circulator is connected to the fourth optical fiber coupler, and the output end of the fourth optical fiber coupler is connected to the first balanced photodetector and the high-speed oscilloscope in sequence; the other output end of the first optical fiber coupler is connected to the third optical fiber coupler, and the output end of the third optical fiber coupler is divided into two paths again, one output end of the third optical fiber coupler is connected to the fifth optical fiber coupler using a single-mode optical fiber, and the other output end of the third optical fiber coupler is connected to the delay optical fiber and the fifth optical fiber coupler in sequence, and the output end of the fifth optical fiber coupler is connected to the second balanced photodetector and the high-speed oscilloscope in sequence;
所述环形器和偏振控制器构成主路干涉仪单元,延时光纤和单模光纤构成辅路干涉仪单元,聚酰亚胺光纤构成聚酰亚胺光纤单元,第一平衡光电探测器和第二平衡光电探测器构成平衡光电探测器单元;The circulator and the polarization controller constitute a main interferometer unit, the delay optical fiber and the single-mode optical fiber constitute an auxiliary interferometer unit, the polyimide optical fiber constitutes a polyimide optical fiber unit, and the first balanced photodetector and the second balanced photodetector constitute a balanced photodetector unit;
所述聚酰亚胺光纤为普通单模光纤用剥线钳除去丙烯酸酯层后,将光纤浸入酒精中,并用气流纸擦拭干净,最后,将光纤浸入聚酰亚胺溶液中,采用提拉法和涂刷法处理后的光纤放置在110℃的加热炉中烘干三十分钟,再以每分钟1℃的速率升高温度至180℃,最后在180℃下加热三十分钟,得到涂敷厚度为50um的聚酰亚胺光纤;The polyimide optical fiber is a common single-mode optical fiber. After removing the acrylate layer with a wire stripper, the optical fiber is immersed in alcohol and wiped clean with air flow paper. Finally, the optical fiber is immersed in a polyimide solution. The optical fiber treated by the pulling method and the brushing method is placed in a heating furnace at 110°C for 30 minutes, and then the temperature is increased to 180°C at a rate of 1°C per minute. Finally, it is heated at 180°C for 30 minutes to obtain a polyimide optical fiber with a coating thickness of 50um.
上述连接均采用FC/PC光连接器连接。The above connections are all made using FC/PC optical connectors.
所述窄线宽激光器的型号为TSL-550、波长扫描范围为1540nm-1560nm、扫频速度为20nm/s。The model of the narrow linewidth laser is TSL-550, the wavelength scanning range is 1540nm-1560nm, and the scanning speed is 20nm/s.
所述第一光电探测器和第二光电探测器型号均为PDB430C。The first photodetector and the second photodetector are both of model PDB430C.
所述高速示波器的型号为MSOS254A、采样率为10MHz/S。The model of the high-speed oscilloscope is MSOS254A, and the sampling rate is 10 MHz/S.
所述第一光纤耦合器的分光比为90%:10%,第一光纤耦合器中90%的一路光进入第二光纤耦合器、10%的一路光进入第三光纤耦合器。The splitting ratio of the first optical fiber coupler is 90%:10%, 90% of the light in the first optical fiber coupler enters the second optical fiber coupler, and 10% of the light enters the third optical fiber coupler.
所述第二光纤耦合器的分光比为99%:1%,第二光纤耦合器中99%的一路光进入环形器的a端口、1%的一路光进入偏振控制器。The splitting ratio of the second optical fiber coupler is 99%:1%, and 99% of the light in the second optical fiber coupler enters the a port of the circulator, and 1% of the light enters the polarization controller.
所述第三光纤耦合器的分光比为50%:50%,第四光纤耦合器的分光比为50%:50%;第五光纤耦合器的分光比为50%:50%。The splitting ratio of the third optical fiber coupler is 50%:50%, the splitting ratio of the fourth optical fiber coupler is 50%:50%, and the splitting ratio of the fifth optical fiber coupler is 50%:50%.
所述聚酰亚胺光纤为涂敷厚度50um、长度为20m。The polyimide optical fiber has a coating thickness of 50 um and a length of 20 m.
所述延时光纤5为普通单模光纤、长度为100m。The delay optical fiber 5 is a common single-mode optical fiber with a length of 100m.
本技术方案中光的传播方式如下:窄线宽激光器的光源进入第一光纤耦合器,第一光纤耦合器输出光分成两路,第一光纤耦合器的其中一路输出光经过第二光纤耦合器再次分成两路,第二光纤耦合器的其中一路输出光作为参考光经过偏振控制器到达第四光纤耦合器,第二光纤耦合器的另一路输出光从环形器的a端口进入,从b端口输出,进入到聚酰亚胺光纤,从而产生的瑞利后向散射光作为信号光从环形器的c端口输出到达第四光纤耦合器,与参考光发生干涉,产生拍频信号,经第一平衡光电探测器转成电信号后由高速示波器采集数据;第一光纤耦合器的另一路输出光经过第三光纤耦合器再次分成两路,第三光纤耦合器的其中一路输出光直接到达第五光纤耦合器,与第三光纤耦合器的另一路输出光经过一段延时光纤后发生干涉,产生频率大小为1.5MHz的拍频信号,经第二平衡光电探测器转成电信号后由高速示波器采集数据,作为外部采样时钟信号。The light propagation mode in the technical scheme is as follows: the light source of the narrow linewidth laser enters the first fiber coupler, the output light of the first fiber coupler is divided into two paths, one of the output lights of the first fiber coupler is divided into two paths again through the second fiber coupler, one of the output lights of the second fiber coupler is used as a reference light and passes through the polarization controller to reach the fourth fiber coupler, the other output light of the second fiber coupler enters from the a port of the circulator, outputs from the b port, enters the polyimide fiber, and the Rayleigh backscattered light generated is output from the c port of the circulator as a signal light and reaches the fourth fiber coupler, interferes with the reference light, generates a beat signal, and is converted into an electrical signal by the first balanced photodetector and then collected by a high-speed oscilloscope; the other output light of the first fiber coupler is divided into two paths again through the third fiber coupler, one of the output lights of the third fiber coupler directly reaches the fifth fiber coupler, interferes with the other output light of the third fiber coupler after passing through a delay fiber, generates a beat signal with a frequency of 1.5 MHz, and is converted into an electrical signal by the second balanced photodetector and then collected by a high-speed oscilloscope as an external sampling clock signal.
一种基于聚酰亚胺光纤的光频域反射仪盐度测量方法,采用上述基于聚酰亚胺光纤的光频域反射仪盐度测量装置,所述方法包括如下步骤:A method for measuring salinity using an optical frequency domain reflectometer based on polyimide optical fiber, using the above-mentioned optical frequency domain reflectometer salinity measuring device based on polyimide optical fiber, the method comprising the following steps:
1)窄线宽激光器1发出的扫频光进入第一光纤耦合器分为两路光,一路光进入主路干涉仪单元,一路进入辅路干涉仪单元,进入主路干涉仪单元的光被第二光纤耦合器分为两路光,进入环形器的一路为信号光,进入偏振控制器的一路为参考光;1) The frequency-sweeping light emitted by the narrow linewidth laser 1 enters the first fiber coupler and is divided into two paths of light, one path of light enters the main interferometer unit, and the other path enters the auxiliary interferometer unit. The light entering the main interferometer unit is divided into two paths of light by the second fiber coupler, one path entering the circulator is the signal light, and the other path entering the polarization controller is the reference light;
2)在主路干涉仪中,将聚酰亚胺光纤浸在纯水中两个小时后,聚酰亚胺层在吸水膨胀的应力变化传递到光纤上,光波在光纤内传播时产生的瑞利散射信号发生改变,产生的信号沿路返回,通过所述环形器的c端口进入第四光纤耦合器,与主路干涉仪的参考光在第四光纤耦合器处发生拍频干涉,产生拍频干涉信号,拍频干涉信号经第一平衡光电探测器转换为电信号,被高速示波器采集;2) In the main interferometer, after the polyimide optical fiber is immersed in pure water for two hours, the stress change of the polyimide layer due to water absorption and expansion is transmitted to the optical fiber, and the Rayleigh scattering signal generated when the light wave propagates in the optical fiber changes. The generated signal returns along the way and enters the fourth optical fiber coupler through the c port of the circulator, and generates beat frequency interference with the reference light of the main interferometer at the fourth optical fiber coupler to generate a beat frequency interference signal. The beat frequency interference signal is converted into an electrical signal by the first balanced photodetector and collected by a high-speed oscilloscope;
3)在辅路干涉仪中,延迟光纤和单模光纤的光在第五光纤耦合器中产生干涉信号,干涉信号经第二平衡光电探测器转换为电信号,被高速示波器采集,依据辅助干涉仪产生的干涉信号的频率,采用反正切和相位展开算法计算出激光光源的瞬时频率,对主干涉仪的拍频干涉信号应用插值算法和重新采样,得到均匀光频间隔的拍频信号假设为参考态信号;3) In the auxiliary interferometer, the light of the delayed optical fiber and the single-mode optical fiber generates an interference signal in the fifth optical fiber coupler, and the interference signal is converted into an electrical signal by the second balanced photodetector and collected by a high-speed oscilloscope. According to the frequency of the interference signal generated by the auxiliary interferometer, the instantaneous frequency of the laser light source is calculated by using the inverse tangent and phase unwrapping algorithms, and the beat frequency interference signal of the main interferometer is applied with an interpolation algorithm and re-sampling to obtain a beat frequency signal with a uniform optical frequency interval, which is assumed to be a reference state signal;
4)然后往纯水中加入盐溶液使混合溶液盐溶液浓度为0.3mol/L,在混合溶液中放置盐度计,依据盐度计获取的盐度对传感器进行修正,这时盐度增加,聚酰亚胺层会发生缩聚的现象,在0.3mol/L浓度下静置二十分钟待聚酰亚胺失水后,此时用示波器采集主路干涉仪和辅路干涉仪产生的干涉拍频信号,依据辅助干涉仪产生的干涉信号的频率,通过反正切和相位展开算法计算出激光光源的瞬时频率,对主干涉仪的拍频干涉信号应用插值算法和重新采样,得到均匀光频间隔的拍频信号假设为测量态信号;4) Then, a salt solution is added to the pure water to make the salt solution concentration of the mixed solution 0.3 mol/L, a salinity meter is placed in the mixed solution, and the sensor is corrected according to the salinity obtained by the salinity meter. At this time, the salinity increases, and the polyimide layer will undergo polycondensation. After standing for twenty minutes at a concentration of 0.3 mol/L to allow the polyimide to lose water, an oscilloscope is used to collect the interference beat frequency signals generated by the main interferometer and the auxiliary interferometer. According to the frequency of the interference signal generated by the auxiliary interferometer, the instantaneous frequency of the laser light source is calculated by the inverse tangent and phase unwrapping algorithms, and the beat frequency interference signal of the main interferometer is applied with an interpolation algorithm and re-sampled to obtain a beat frequency signal with a uniform optical frequency interval, which is assumed to be a measurement state signal;
5)将参考态信号与测量态信号分别进行快速傅里叶变换转换到距离域信号,然后以200个点的窗口大小对距离域信号进行固定滑动后,将距离域划分为多个窗口信号,再将每个滑动窗口的信号经过傅里叶逆变换转换到波长域,得到参考态信号和测量态信号的瑞利散射光谱;5) The reference state signal and the measurement state signal are respectively converted into distance domain signals by fast Fourier transform, and then the distance domain signal is fixedly slid with a window size of 200 points, and the distance domain is divided into multiple window signals, and then the signal of each sliding window is converted into the wavelength domain by inverse Fourier transform to obtain the Rayleigh scattering spectra of the reference state signal and the measurement state signal;
6)将每个对应窗口参考态信号与测量态信号的瑞利散射光谱进行互相关运算,得到各个位置的互相关峰偏移量,结合应变频移系数,得到最终的位置-应变曲线图,之后将定位获取的传感光纤每一段位置的应变大小反推得到盐度,实现盐度的测量;6) Perform cross-correlation calculation on the Rayleigh scattering spectra of the reference state signal and the measurement state signal of each corresponding window to obtain the cross-correlation peak offset of each position, and combine it with the strain frequency shift coefficient to obtain the final position-strain curve. Then, the strain size of each section of the sensing optical fiber obtained by positioning is reversed to obtain the salinity, thereby realizing the measurement of salinity;
7)之后每次浓度间隔0.5mol/L,静置二十分钟,用示波器采集主路干涉仪和辅路干涉仪产生的干涉拍频信号重复步骤4)操作得到均匀的光频间隔信号均为测量态信号,然后将在纯水中采集的参考态信号和其它盐溶液浓度下采集到的测量态信号分别依次重复步骤5)-步骤6);7) After that, the concentration interval is 0.5 mol/L each time, and the mixture is allowed to stand for 20 minutes. The interference beat frequency signals generated by the main interferometer and the auxiliary interferometer are collected by an oscilloscope, and step 4) is repeated to obtain uniform optical frequency interval signals, which are all measurement state signals. Then, the reference state signals collected in pure water and the measurement state signals collected at other salt solution concentrations are repeated in steps 5) to 6) respectively;
8)结合标准商用盐度计获取的盐度对传感器进行修正。8) The sensor is calibrated based on the salinity obtained using a standard commercial salinometer.
瑞利散射光的强度与入射光波长的四次方成反比关系,可表示为如公式(1)所示:The intensity of Rayleigh scattered light is inversely proportional to the fourth power of the wavelength of the incident light, which can be expressed as shown in formula (1):
其中,I0为入射光的强度;λ为入射光的波长;θ是一种散射角,Where I0 is the intensity of the incident light; λ is the wavelength of the incident light; θ is a scattering angle,
瑞利散射系数表达如公式(2)所示:The Rayleigh scattering coefficient is expressed as shown in formula (2):
其中,n代表有效的光纤折射率;K为玻尔兹曼常数;T代表温度;p代表物质的弹光系数;βT在温度T下代表等温压缩率,由公式(2)可知,当温度或者应变变化,瑞利散射系数会发生改变,瑞利散射谱偏移;将受到温度或者应变时的瑞利散射谱与无外界扰动时的初始瑞利散射谱做互相关,会得到频谱的偏移量,偏移量对应于光纤受到温度或者应变的改变量,Where n represents the effective optical fiber refractive index; K is the Boltzmann constant; T represents temperature; p represents the elastic coefficient of the material; β T represents the isothermal compressibility at temperature T. It can be seen from formula (2) that when the temperature or strain changes, the Rayleigh scattering coefficient will change and the Rayleigh scattering spectrum will shift. The Rayleigh scattering spectrum under temperature or strain is cross-correlated with the initial Rayleigh scattering spectrum without external disturbance to obtain the offset of the spectrum. The offset corresponds to the change in the temperature or strain of the optical fiber.
假定满足主路干涉仪相干条件的信号光Es(t)和参考光Er(t)的光场分别为公式(3)、公式(4)所示:Assume that the light fields of the signal light Es (t) and the reference light Er (t) satisfying the coherence condition of the main interferometer are as shown in formula (3) and formula (4) respectively:
其中f0是可调谐激光器的初始频率,表示参考光的随机相位,表示在时间延迟位置处的反射率,表示背向瑞利散射信号在t时刻的随机相位,where f0 is the initial frequency of the tunable laser, represents the random phase of the reference light, represents the reflectivity at the time delay position, represents the random phase of the backscattered Rayleigh signal at time t,
根据光电探测器的平方律特性,光电探测器输出的光电流假设为I(t),考虑到光电探测器对高于截止频率的部分不作响应,且直流项部分会被过滤掉,则第一平衡光电探测器输出信号I(t)为公式(5)所示:According to the square law characteristics of the photodetector, the photocurrent output by the photodetector is assumed to be I(t). Considering that the photodetector does not respond to the part above the cutoff frequency and the DC part will be filtered out, the output signal I(t) of the first balanced photodetector is as shown in formula (5):
其中,项表示在t时刻两束光的相位差,它随时间非线性变化,fb表示两束光的拍频,它随时间线性变化,且是传感光纤上散射点位置的函数。in, The term represents the phase difference between the two beams of light at time t, which varies nonlinearly with time. fb represents the beat frequency of the two beams of light, which varies linearly with time and is a function of the position of the scattering point on the sensing optical fiber.
本技术方案基于聚酰亚胺敏感材料和光频域反射技术实现分布式相对盐度测量,在单模光纤上涂覆聚酰亚胺材料,利用聚酰亚胺吸水膨胀、失水收缩的特性,将盐度的变化转化为光纤上的应力变化,这些变化会使单模光纤中表征光波特征的参量发生变化,对这些信号参量进行傅里叶变换和互相关运算来获取光纤应变变化信息,进而反推测量出溶液盐度值。This technical solution realizes distributed relative salinity measurement based on polyimide sensitive materials and optical frequency domain reflection technology. Polyimide material is coated on the single-mode optical fiber. The characteristics of polyimide swelling when absorbing water and shrinking when losing water are used to convert the change of salinity into stress change on the optical fiber. These changes will cause the parameters characterizing the characteristics of light waves in the single-mode optical fiber to change. Fourier transform and cross-correlation operation are performed on these signal parameters to obtain the optical fiber strain change information, and then the salinity value of the solution is measured by reverse calculation.
这种光频域反射仪具有抗电磁干扰能力强、耐腐蚀性好、结构简单,这种方法能实时监测盐度值的变化,能实现相对盐度分布式的精确测量。This optical frequency domain reflectometer has strong anti-electromagnetic interference ability, good corrosion resistance and simple structure. This method can monitor the changes in salinity values in real time and can achieve accurate measurement of relative salinity distribution.
附图说明BRIEF DESCRIPTION OF THE DRAWINGS
图1为实施例的结构示意图。FIG. 1 is a schematic structural diagram of an embodiment.
图中,1.窄线宽激光器2.第一光纤耦合器3.第三光纤耦合器4.第二光纤耦合器5.延时光纤6.光纤环形器7.偏振控制器8.单模光纤9.聚酰亚胺光纤10.第四光纤耦合器11.第五光纤耦合器12.第二光电探测器13.第一光电探测器14.高速示波器。In the figure, 1. narrow linewidth laser 2. first fiber coupler 3. third fiber coupler 4. second fiber coupler 5. delay fiber 6. fiber circulator 7. polarization controller 8. single mode fiber 9. polyimide fiber 10. fourth fiber coupler 11. fifth fiber coupler 12. second photodetector 13. first photodetector 14. high speed oscilloscope.
具体实施方式Detailed ways
下面结合附图和实施例对本发明的内容作进一步的阐述,但不是对本发明的限定。The content of the present invention is further described below in conjunction with the drawings and embodiments, but the present invention is not limited thereto.
实施例:Example:
参照图1,一种基于聚酰亚胺光纤的光频域反射仪盐度测量装置,包括互联的窄线宽激光器1和第一光纤耦合器2,其中:1 , a polyimide optical fiber-based optical frequency domain reflectometer salinity measurement device includes an interconnected narrow linewidth laser 1 and a first optical fiber coupler 2, wherein:
第一光纤耦合器2的输出端分成两路,其中一路输出端连接第二光纤耦合器4,第二光纤耦合器4的输出端再次分成两路,第二光纤耦合器4的一路输出端顺序连接偏振控制器7、第四光纤耦合器10;第二光纤耦合器4的另一路输出端连接环形器6的a端口、环形器的b端口连接聚酰亚胺光纤9、环形器的c端口连接第四光纤耦合器10,第四光纤耦合器10的输出端顺序连接第一平衡光电探测器13、高速示波器14;第一光纤耦合器2的另一路输出端连接第三光纤耦合器3,第三光纤耦合器3的输出端再次分成两路,第三光纤耦合器3的一路输出端采用单模光纤8连接第五光纤耦合器11,第三光纤耦合器3的另一路输出端顺序连接延时光纤5、第五光纤耦合器11,第五光纤耦合器11的输出端顺序连接第二平衡光电探测器12、高速示波器14;The output end of the first fiber coupler 2 is divided into two paths, one of which is connected to the second fiber coupler 4, and the output end of the second fiber coupler 4 is divided into two paths again, and one output end of the second fiber coupler 4 is sequentially connected to the polarization controller 7 and the fourth fiber coupler 10; the other output end of the second fiber coupler 4 is connected to the a port of the circulator 6, the b port of the circulator is connected to the polyimide fiber 9, and the c port of the circulator is connected to the fourth fiber coupler 10, and the output end of the fourth fiber coupler 10 is sequentially connected to the first balanced photodetector 13 and the high-speed oscilloscope 14; the other output end of the first fiber coupler 2 is connected to the third fiber coupler 3, and the output end of the third fiber coupler 3 is divided into two paths again, one output end of the third fiber coupler 3 is connected to the fifth fiber coupler 11 using the single-mode fiber 8, and the other output end of the third fiber coupler 3 is sequentially connected to the delay fiber 5 and the fifth fiber coupler 11, and the output end of the fifth fiber coupler 11 is sequentially connected to the second balanced photodetector 12 and the high-speed oscilloscope 14;
本例中环形器6和偏振控制器7构成主路干涉仪单元,延时光纤5和单模光纤8构成辅路干涉仪单元,聚酰亚胺光纤9构成聚酰亚胺光纤单元,第一平衡光电探测器13和第二平衡光电探测器12构成平衡光电探测器单元;In this example, the circulator 6 and the polarization controller 7 constitute a main interferometer unit, the delay fiber 5 and the single-mode fiber 8 constitute an auxiliary interferometer unit, the polyimide fiber 9 constitutes a polyimide fiber unit, and the first balanced photodetector 13 and the second balanced photodetector 12 constitute a balanced photodetector unit;
本例中聚酰亚胺光纤为普通单模光纤用剥线钳除去丙烯酸酯层后,将光纤浸入酒精中,并用气流纸擦拭干净,最后,将光纤浸入聚酰亚胺溶液中,采用提拉法和涂刷法处理后的光纤放置在110℃的加热炉中烘干三十分钟,再以每分钟1℃的速率升高温度至180℃,最后在180℃下加热三十分钟,得到涂敷厚度为50um的聚酰亚胺光纤;In this example, the polyimide optical fiber is a common single-mode optical fiber. After removing the acrylate layer with a wire stripper, the optical fiber is immersed in alcohol and wiped clean with airflow paper. Finally, the optical fiber is immersed in a polyimide solution. The optical fiber treated by the pulling method and the brushing method is placed in a heating furnace at 110°C for 30 minutes, and then the temperature is increased to 180°C at a rate of 1°C per minute. Finally, it is heated at 180°C for 30 minutes to obtain a polyimide optical fiber with a coating thickness of 50um.
本例中连接均采用FC/PC光连接器连接。In this example, FC/PC optical connectors are used for connection.
本例中窄线宽激光器的型号为TSL-550、波长扫描范围为1540nm-1560nm、扫频速度为20nm/s。In this example, the model of the narrow linewidth laser is TSL-550, the wavelength scanning range is 1540nm-1560nm, and the scanning speed is 20nm/s.
本例中第一光电探测器13和第二光电探测器12型号均为PDB430C。In this example, the first photodetector 13 and the second photodetector 12 are both of model PDB430C.
本例中高速示波器14的型号为MSOS254A、采样率为10MHz/S。In this example, the model of the high-speed oscilloscope 14 is MSOS254A, and the sampling rate is 10 MHz/S.
本例中第一光纤耦合器2的分光比为90%:10%,第一光纤耦合器2中90%的一路光进入第二光纤耦合器4、10%的一路光进入第三光纤耦合器3。In this example, the splitting ratio of the first optical fiber coupler 2 is 90%:10%, and 90% of the light in the first optical fiber coupler 2 enters the second optical fiber coupler 4 , and 10% of the light enters the third optical fiber coupler 3 .
本例中第二光纤耦合器4的分光比为99%:1%,第二光纤耦合器4中99%的一路光进入环形器6的a端口、1%的一路光进入偏振控制器7。In this example, the splitting ratio of the second optical fiber coupler 4 is 99%:1%, and 99% of the light in the second optical fiber coupler 4 enters the port a of the circulator 6 , and 1% of the light enters the polarization controller 7 .
本例中第三光纤耦合器3的分光比为50%:50%,第四光纤耦合器10的分光比为50%:50%;第五光纤耦合器11的分光比为50%:50%。In this example, the splitting ratio of the third optical fiber coupler 3 is 50%:50%, the splitting ratio of the fourth optical fiber coupler 10 is 50%:50%, and the splitting ratio of the fifth optical fiber coupler 11 is 50%:50%.
本例中聚酰亚胺光纤为涂敷厚度50um、长度为20m。In this example, the polyimide optical fiber has a coating thickness of 50 um and a length of 20 m.
本例中延时光纤5为普通单模光纤、长度为100m。In this example, the delay optical fiber 5 is a common single-mode optical fiber with a length of 100 m.
本例中中光的传播方式如下:窄线宽激光器1的光源进入第一光纤耦合器2,第一光纤耦合器2输出光分成两路,第一光纤耦合器2的其中一路输出光经过第二光纤耦合器4再次分成两路,第二光纤耦合器4的其中一路输出光作为参考光经过偏振控制器7到达第四光纤耦合器10,第二光纤耦合器4的另一路输出光从环形器6的a端口进入,从b端口输出,进入到聚酰亚胺光纤,从而产生的瑞利后向散射光作为信号光从环形器6的c端口输出到达第四光纤耦合器10,与参考光发生干涉,产生拍频信号,经第一平衡光电探测器13转成电信号后由高速示波器14采集数据;第一光纤耦合器2的另一路输出光经过第三光纤耦合器3再次分成两路,第三光纤耦合器3的其中一路输出光直接到达第五光纤耦合器11,与第三光纤耦合器3的另一路输出光经过一段延时光纤5后发生干涉,产生频率大小为1.5MHz的拍频信号,经第二平衡光电探测器12转成电信号后由高速示波器14采集数据,作为外部采样时钟信号。In this example, the propagation mode of the light is as follows: the light source of the narrow linewidth laser 1 enters the first fiber coupler 2, the output light of the first fiber coupler 2 is divided into two paths, one of the output lights of the first fiber coupler 2 is divided into two paths again through the second fiber coupler 4, one of the output lights of the second fiber coupler 4 is used as a reference light to reach the fourth fiber coupler 10 through the polarization controller 7, and the other output light of the second fiber coupler 4 enters from the a port of the circulator 6, outputs from the b port, and enters the polyimide fiber, thereby generating Rayleigh backscattered light as a signal light, which is output from the c port of the circulator 6 to the fourth fiber coupler 10. The first fiber coupler 10 interferes with the reference light to generate a beat frequency signal, which is converted into an electrical signal by the first balanced photodetector 13 and then collected by a high-speed oscilloscope 14; the other output light of the first fiber coupler 2 is divided into two paths again by the third fiber coupler 3, and one of the output lights of the third fiber coupler 3 directly reaches the fifth fiber coupler 11, and interferes with the other output light of the third fiber coupler 3 after passing through a delay fiber 5, generating a beat frequency signal with a frequency of 1.5 MHz, which is converted into an electrical signal by the second balanced photodetector 12 and then collected by a high-speed oscilloscope 14 as an external sampling clock signal.
一种基于聚酰亚胺光纤的光频域反射仪盐度测量方法,采用上述基于聚酰亚胺光纤的光频域反射仪盐度测量装置,所述方法包括如下步骤:A method for measuring salinity using an optical frequency domain reflectometer based on polyimide optical fiber, using the above-mentioned optical frequency domain reflectometer salinity measuring device based on polyimide optical fiber, the method comprising the following steps:
1)窄线宽激光器1发出的扫频光进入第一光纤耦合器2分为两路光,一路光进入主路干涉仪单元,一路进入辅路干涉仪单元,进入主路干涉仪单元的光被第二光纤耦合器4分为两路光,进入环形器6的一路为信号光,进入偏振控制器7的一路为参考光;1) The frequency-sweeping light emitted by the narrow linewidth laser 1 enters the first fiber coupler 2 and is divided into two paths of light, one path of light enters the main interferometer unit, and the other path enters the auxiliary interferometer unit. The light entering the main interferometer unit is divided into two paths of light by the second fiber coupler 4, one path of light entering the circulator 6 is the signal light, and the other path of light entering the polarization controller 7 is the reference light;
2)在主路干涉仪中,将聚酰亚胺光纤9浸在纯水中两个小时后,聚酰亚胺层在吸水膨胀的应力变化传递到光纤上,光波在光纤内传播时产生的瑞利散射信号发生改变,产生的信号沿路返回,通过所述环形器6的c端口进入第四光纤耦合器10,与主路干涉仪的参考光在第四光纤耦合器10处发生拍频干涉,产生拍频干涉信号,拍频干涉信号经第一平衡光电探测器13转换为电信号,被高速示波器14采集;2) In the main interferometer, after the polyimide optical fiber 9 is immersed in pure water for two hours, the stress change of the polyimide layer due to water absorption and expansion is transmitted to the optical fiber, and the Rayleigh scattering signal generated when the light wave propagates in the optical fiber changes. The generated signal returns along the way and enters the fourth optical fiber coupler 10 through the c port of the circulator 6, and generates beat frequency interference with the reference light of the main interferometer at the fourth optical fiber coupler 10, generating a beat frequency interference signal, which is converted into an electrical signal by the first balanced photodetector 13 and collected by the high-speed oscilloscope 14;
3)在辅路干涉仪中,延迟光纤5和单模光纤8的光在第五光纤耦合器11中产生干涉信号,干涉信号经第二平衡光电探测器12转换为电信号,被高速示波器14采集,依据辅助干涉仪产生的干涉信号的频率,采用反正切和相位展开算法计算出激光光源的瞬时频率,对主干涉仪的拍频干涉信号应用插值算法和重新采样,得到均匀光频间隔的拍频信号假设为参考态信号;3) In the auxiliary interferometer, the light of the delayed optical fiber 5 and the single-mode optical fiber 8 generates an interference signal in the fifth optical fiber coupler 11, and the interference signal is converted into an electrical signal by the second balanced photodetector 12 and collected by the high-speed oscilloscope 14. According to the frequency of the interference signal generated by the auxiliary interferometer, the instantaneous frequency of the laser light source is calculated by using the inverse tangent and phase unwrapping algorithms, and the beat frequency interference signal of the main interferometer is applied with the interpolation algorithm and re-sampling to obtain a beat frequency signal with uniform optical frequency interval, which is assumed to be a reference state signal;
4)然后往纯水中加入盐溶液使混合溶液盐溶液浓度为0.3mol/L,在混合溶液中放置盐度计,依据盐度计获取的盐度对传感器进行修正,这时盐度增加,聚酰亚胺层会发生缩聚的现象,在0.3mol/L浓度下静置二十分钟待聚酰亚胺失水后,此时用示波器14采集主路干涉仪和辅路干涉仪产生的干涉拍频信号,依据辅助干涉仪产生的干涉信号的频率,通过反正切和相位展开算法计算出激光光源的瞬时频率,对主干涉仪的拍频干涉信号应用插值算法和重新采样,得到均匀光频间隔的拍频信号假设为测量态信号;4) Then, a salt solution is added to the pure water to make the salt solution concentration of the mixed solution 0.3 mol/L, a salinity meter is placed in the mixed solution, and the sensor is corrected according to the salinity obtained by the salinity meter. At this time, the salinity increases, and the polyimide layer undergoes polycondensation. After the polyimide is left to stand for 20 minutes at a concentration of 0.3 mol/L to lose water, an oscilloscope 14 is used to collect the interference beat frequency signals generated by the main interferometer and the auxiliary interferometer. According to the frequency of the interference signal generated by the auxiliary interferometer, the instantaneous frequency of the laser light source is calculated by the inverse tangent and phase unwrapping algorithms, and the beat frequency interference signal of the main interferometer is applied with an interpolation algorithm and re-sampled to obtain a beat frequency signal with a uniform optical frequency interval, which is assumed to be a measurement state signal;
5)将参考态信号与测量态信号分别进行快速傅里叶变换转换到距离域信号,然后以200个点的窗口大小对距离域信号进行固定滑动后,将距离域划分为多个窗口信号,再将每个滑动窗口的信号经过傅里叶逆变换转换到波长域,得到参考态信号和测量态信号的瑞利散射光谱;5) The reference state signal and the measurement state signal are respectively converted into distance domain signals by fast Fourier transform, and then the distance domain signal is fixedly slid with a window size of 200 points, and the distance domain is divided into multiple window signals, and then the signal of each sliding window is converted into the wavelength domain by inverse Fourier transform to obtain the Rayleigh scattering spectra of the reference state signal and the measurement state signal;
6)将每个对应窗口参考态信号与测量态信号的瑞利散射光谱进行互相关运算,得到各个位置的互相关峰偏移量,结合应变频移系数,得到最终的位置-应变曲线图,之后将定位获取的传感光纤每一段位置的应变大小反推得到盐度,实现盐度的测量;6) Perform cross-correlation calculation on the Rayleigh scattering spectra of the reference state signal and the measurement state signal of each corresponding window to obtain the cross-correlation peak offset of each position, and combine it with the strain frequency shift coefficient to obtain the final position-strain curve. Then, the strain size of each section of the sensing optical fiber obtained by positioning is reversed to obtain the salinity, thereby realizing the measurement of salinity;
7)之后每次浓度间隔0.5mol/L,静置二十分钟,用示波器14采集主路干涉仪和辅路干涉仪产生的干涉拍频信号重复步骤4)操作得到均匀的光频间隔信号均为测量态信号,然后将在纯水中采集的参考态信号和其它盐溶液浓度下采集到的测量态信号分别依次重复步骤5)-步骤6);7) After that, the concentration interval is 0.5 mol/L each time, and the mixture is left to stand for 20 minutes. The interference beat frequency signals generated by the main interferometer and the auxiliary interferometer are collected by using an oscilloscope 14, and the operation of step 4) is repeated to obtain uniform optical frequency interval signals, which are all measurement state signals. Then, the reference state signals collected in pure water and the measurement state signals collected at other salt solution concentrations are respectively repeated in steps 5) to 6);
8)结合标准商用盐度计获取的盐度对传感器进行修正。8) The sensor is calibrated based on the salinity obtained using a standard commercial salinometer.
瑞利散射光的强度与入射光波长的四次方成反比关系,可表示为如公式(1)所示:The intensity of Rayleigh scattered light is inversely proportional to the fourth power of the wavelength of the incident light, which can be expressed as shown in formula (1):
其中,I0为入射光的强度;λ为入射光的波长;θ是一种散射角,Where I0 is the intensity of the incident light; λ is the wavelength of the incident light; θ is a scattering angle,
瑞利散射系数表达如公式(2)所示:The Rayleigh scattering coefficient is expressed as shown in formula (2):
其中,n代表有效的光纤折射率;K为玻尔兹曼常数;T代表温度;p代表物质的弹光系数;βT在温度T下代表等温压缩率,由公式(2)可知,当温度或者应变变化,瑞利散射系数会发生改变,瑞利散射谱偏移;将受到温度或者应变时的瑞利散射谱与无外界扰动时的初始瑞利散射谱做互相关,会得到频谱的偏移量,偏移量对应于光纤受到温度或者应变的改变量,Where n represents the effective optical fiber refractive index; K is the Boltzmann constant; T represents temperature; p represents the elastic coefficient of the material; β T represents the isothermal compressibility at temperature T. It can be seen from formula (2) that when the temperature or strain changes, the Rayleigh scattering coefficient will change and the Rayleigh scattering spectrum will shift. The Rayleigh scattering spectrum under temperature or strain is cross-correlated with the initial Rayleigh scattering spectrum without external disturbance to obtain the offset of the spectrum. The offset corresponds to the change in the temperature or strain of the optical fiber.
假定满足主路干涉仪相干条件的信号光Es(t)和参考光Er(t)的光场分别为公式(3)、公式(4)所示:Assume that the light fields of the signal light Es (t) and the reference light Er (t) satisfying the coherence condition of the main interferometer are as shown in formula (3) and formula (4) respectively:
其中f0是可调谐激光器的初始频率,表示参考光的随机相位,表示在时间延迟位置处的反射率,表示背向瑞利散射信号在t时刻的随机相位,where f0 is the initial frequency of the tunable laser, represents the random phase of the reference light, represents the reflectivity at the time delay position, represents the random phase of the backscattered Rayleigh signal at time t,
根据光电探测器的平方律特性,光电探测器输出的光电流假设为I(t),考虑到光电探测器对高于截止频率的部分不作响应,且直流项部分会被过滤掉,则第一平衡光电探测器输出信号I(t)为公式(5)所示:According to the square law characteristics of the photodetector, the photocurrent output by the photodetector is assumed to be I(t). Considering that the photodetector does not respond to the part above the cutoff frequency and the DC part will be filtered out, the output signal I(t) of the first balanced photodetector is as shown in formula (5):
其中,项表示在t时刻两束光的相位差,它随时间非线性变化,fb表示两束光的拍频,它随时间线性变化,且是传感光纤上散射点位置的函数。in, The term represents the phase difference between the two beams of light at time t, which varies nonlinearly with time. fb represents the beat frequency of the two beams of light, which varies linearly with time and is a function of the position of the scattering point on the sensing optical fiber.
本例采用光频移反射仪结合敏感材料聚酰亚胺,将聚酰亚胺吸水膨胀、失水收缩时的应力变化传递到光纤上,通过解调光纤光信号的变化情况得到应变的大小,进而反推得到对应的盐度值,本例方法有效的实现了盐度的连续测量,此外,本例光纤传感器具有体积小、与电解液不反应、可分布式测量等优势,可实现对盐度的精准监测,实验结果与盐度计一致性良好。In this example, an optical frequency shift reflectometer is used in combination with the sensitive material polyimide to transmit the stress changes of polyimide when it absorbs water and expands, and loses water and shrinks to the optical fiber. The strain size is obtained by demodulating the changes in the optical fiber optical signal, and then the corresponding salinity value is obtained by reverse calculation. This method effectively realizes the continuous measurement of salinity. In addition, this optical fiber sensor has the advantages of small size, no reaction with electrolyte, and distributed measurement, which can realize accurate monitoring of salinity. The experimental results are in good agreement with the salinity meter.
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