基于旋光色散效应的光纤光栅传感解调方法研究

【作者】 沈永良；

【导师】 叶红安；

【作者基本信息】 黑龙江大学 ， 微电子学与固体电子学， 2012， 博士

【摘要】 光纤光栅是目前发展最快的光纤传感器之一，由于光纤光栅是以波长编码的方式进行测量的，可用于对外界参量的绝对测量，应用范围非常广泛。光纤光栅传感信号的解调，即检测出敏感光纤光栅中心波长的移位，是光纤光栅传感系统中最关键的技术环节。对于利用单个光纤光栅实现的传感检测系统，例如光纤光栅加速度、流量传感器等，目前已报道的解调方法通常是针对传感系统中所使用光纤光栅的中心波长进行解调的，因此相应的解调装置不具有通用性。对于分布式光纤光栅传感网络，目前最广泛采用的是F-P扫描滤波法，由于扫描波长与电压间存在着迟滞、非线性和漂移，必须对F-P扫描滤波器进行实时标定。在保证标定精度的前提下，如何扩大标定装置的工作范围，以满足复用更多敏感光纤光栅的需求，也是需要解决的问题。本论文将采用基于旋光色散效应的波长检测方法，研制出具有通用性的单光纤光栅传感解调装置；研制出工作范围达到100nm以上的扫描F-P滤波器标定装置。为了适应未来发展需求，我们还将研制出同时适用于1310nm波段和1550nm波段的波长检测装置。特别是，我们将结合实际使用条件，在装置的实用化方面开展系统的研究工作。论文将主要开展下述几个方面的研究工作：我们将利用石英晶体作为旋光色散介质，搭建出基于旋光色散效应的波长检测装置。为了消除入射光源功率不稳定性对检测精度的影响，我们将采用双光束偏振检测系统，并且针对该系统设计出相应的机械装置，以保证光路调整的精确性和机械稳定性。利用石英晶体的热膨胀系数和热光系数进行估算，石英晶体所处环境温度的变化应控制在±0.1℃，此时由温度变化引入的波长检测误差小于±0.4pm。我们自制了一个400×400×200mm3的小型恒温箱，并利用廉价的致冷片和加热器实现上述温控目标，由于恒温箱具有大惯性、大滞后、非线性等特点，因此我们选择对这样的对象控制有效的广义预测控制原理，并设计了预测控制递推算法，使恒温箱的控制精度达到了±0.1℃。同时，又用光源、耦合器、光电转换器、A/D转换器和信号处理单元组成系统，测量电路系统的对称性。研制基于旋光色散效应的光纤F-P可调谐滤波器的标定装置。利用石英晶体作为旋光色散介质，并采用双光路偏振检测系统研发了相应的标定装置。利用石英晶体在C-Band的旋光色散效应，获得了线偏振光偏振面旋转角度与波长间的一一对应关系。将拟合的波长-旋转角关系作为波长参考基准，实现了对扫描F-P的标定，波长检测偏差与光谱仪测量值相比小于±6pm。还重点研究了如何提高标定装置的重复性、长期稳定性和可靠性问题。研制了同时适用于1310nm波段和1550nm波段的波长计。通过恰当地选择石英晶体的长度，保证了双光路偏振检测系统在1310nm波段和1550nm波段同时满足正交偏置条件。避免了在用于不同波段检测时，由于重新调整起偏器的方位角引起的测量误差。通过实验，我们自行研制的波长计在1310nm波段和1550nm波段的波长检测偏差与光谱仪测量值相比均小于±6pm。利用我们研制的基于旋光色散效应，可同时用于1310nm和1550nm波段的波长计。设计了光纤光栅解调装置，对1550nm波段的光纤光栅进行了温度传感解调。同时，为了使波长计能够适用于对不同功率级别的光源进行检测，将光纤准直器与光源间的光纤绕制成偏振控制器，通过调整偏振控制器与起偏器间的角度，可使进入到波长计的光功率实现从10%到80%的调变。这样，当对具有不同光功率级别的激光器进行检测时，在光电探测器上能够保持一个合适的、固定的光强。使用本装置测得的光纤光栅一阶温度灵敏度系数为8.04×106/oC，跟理论值相比，本装置一阶温度灵敏度系数误差为0.76×106/oC。可以看出使用本文设计的光纤光栅解调装置获得的光纤光栅热光系数和光纤光栅热膨胀系数与实际测的光纤光栅热光系数和光纤光栅热膨胀系数十分接近，而且和理论值基本一致，数量级相同，我们研究的实验装置是可行的。更多还原

【Abstract】 Fiber Bragg grating sensor is currently one of the fastest growing optical fibersensors, which uses the way of wavelength encoding to measure, and it can be used onthe absolute measurement of the outside parameters, and its application range is veryextensive. Fiber Bragg grating sensing signal demodulation, that is to detect the shift ofsensitive fiber Bragg grating center wavelength, is the most key technical link of fibergrating sensing system. As to the sensor detecting system realized by a single fiberBragg grating, such as fiber Bragg grating acceleration sensor, flow sensor etc., thereported demodulation method is usually according to the fiber Bragg grating centerwavelength using in the sensing systems to demodulate, so the correspondingdemodulation devices cannot be used in common. For distributed optical fiber gratingsensor network, the F-P scanning filtering method is the most widely used, but the F-Pscanning filter must be real-time calibrated because of the hysteresis, nonlinear and driftexistence between scanning wavelength and voltage. In guarantee calibration precision,how to expand working range of calibration equipment to meet the reuse more sensitivefiber Bragg grating demand is also the problem need to be solved. This paper developedthe universal single fiber Bragg grating sensor demodulation device applied thewavelength detection method based on the optical rotatory dispersion effect; developedscanning F-P filter calibration device with the scope of work to more than100nm. Inorder to adapt to the development of future demand, we developed the wavelengthdetection device which can be applied to1310nm band and1550nm band. In particular,we do the research work on practical of the device with the actual conditions of use. Thepaper mainly did research work as follows:We used quartz crystal as rotatory dispersion medium to build the wavelengthdetection device base on the optical rotatory dispersion. In order to eliminate the influence of the detection precision caused by the instability of the incident light sourcepower, we used double optical path polarization detection system and designed thecorresponding mechanical device to ensure the accuracy and mechanical stability of theoptical path adjustment. Use thermal expansion coefficient and thermo-optic coefficientto estimate, and the error of wavelength detection is less than±0.4pm caused by thetemperature change when the environment change of quartz crystal is controlled in±0.1℃. We made a400x400x200mm3small thermostat using cheap refrigeration sliceand heater to achieve the temperature control demand. The thermostat has large inertia,delay, nonlinear characteristics, so we chose the principle of generalized predictivecontrol which is valid for this controlled plant and designed generalized predictivecontrol recursive algorithm to make the control accuracy of the thermostat reached±0.1℃. At the same time, we used the system composed of light source, couplers,photoelectric switches, A/D converter and signal processing unit to measure thesymmetry of circuit system.We developed the calibration device of fiber F-P tunable filter based on the opticalrotatory dispersion effect. Used quartz crystal as rotatory dispersion medium, andadopted double optical path polarization detection system to develop the correspondingcalibration device. Used the optical rotatory dispersion effect of quartz crystal inC-Band to obtain one to one correspondence between the rotation angle and wavelengthin the polarized plane of the linearly polarized light. We used the fittingwavelength-rotation angle relation curve as wavelength reference standard to realize thescanning F-P calibration, and wavelength detection deviation is less than±6pmcompared to measurement value of spectrometer. Also we focused on how to improvethe calibration equipment repeatability, long-term stability and reliability problems.We developed the wavemeter which can be suitable for both1310nm band and1550nm band. By properly chose the length of quartz crystal, we ensured the doubleoptical path polarization detection system to satisfy the orthogonal offset condition in 1310nm band and1550nm band at the same time. Avoid the measuring error caused bythe readjustment of polarizer azimuth angle used in different wave bands detection.Through the experiment, the wavemeter’s wavelength detection deviation we developedis less than±6pm compared to measurement value of spectrometer on the1310nmand1550nm band.We used the wavemeter based on the optical rotatory dispersion effect, which canbe used on both1310nm band and1550nm band to design the fiber Bragg gratingdemodulation device to do temperature sensing demodulation of the fiber Bragg gratingon the1550nm band. Moreover, in order to make the wavemeter suitable for thedifferent power levels of light source, the fiber collimator and the fiber in light sourcesturn to the polarization controller, the light power into the wavemeter can be from10%to80through the adjustment of the angle between the polarization controller and thepolarizer. So photoelectric detector can keep on an appropriate, fixed light intensitywhen detect the lasers of different light power levels. The first order temperaturesensitivity coefficient of optical fiber Bragg grating, measured by this device, is8.04×106/℃, compared with the theoretical value, the first order temperaturesensitivity coefficient error of this device is0.76×10-6/℃. The thermo-opticcoefficient and thermal expansion coefficient of fiber Bragg grating obtained by opticalfiber Bragg grating demodulation devices we developed, is very close to that actualmeasured, consistent with the theoretical value, has the same order of magnitude, so ourexperiment device is feasible.更多还原