【作者】 张卫华；

【导师】 董孝义； 刘波；

【作者基本信息】 南开大学 ， 光学， 2009， 博士

【摘要】 光纤光栅是一种新型的光子器件,它的出现,使许多复杂的全光纤通信网络和传感网络成为可能,并极大地拓宽了光纤技术的应用范围。倾斜光纤光栅(TFBG)是光纤光栅的一种,它除了具有普通光纤布喇格光栅(FBG)的特点之外,还有许多独特的优点。本论文主要以TFBG为研究对象,对其传感及解调特性进行了理论与实验研究。根据TFBG所体现出来的不同于FBG的传感特性,利用数据融合理论对被测量进行了更加准确的估测。结合传感器技术、嵌入式计算技术、现代通信与网络技术,将光纤光栅应用到传感器网络中,设计了一种小区制蜂窝传感器网络。本论文是在国家“八六三计划”项目(No.2006AA01Z217)、国家自然科学基金重点项目(No.60736039)的支持下完成的。本论文的主要内容为:1.阐述了光纤光栅的几种分析方法,并利用耦合模理论与体电流理论分别对FBG与TFBG进行了理论分析。这将为以后的工作打下基础,为实验提供理论依据。2.对TFBG的传感特性及应用进行了研究,并且取得诸多进展,包括:(1)TFBG的纤芯模与包层模随着温度升高,波长偏移量是基本一致的,通过粘贴热膨胀系数不同的基底材料,可以提高其对温度的敏感度。(2)应变可以引起TFBG纤芯模和包层模谐振峰的漂移,而且应变对纤芯模与包层模的影响是不同的。根据TFBG的这一应变特性及温度特性,设计了一种能同时对温度和应变进行感测的系统。(3)对简支梁的弯曲进行了理论分析,首次提出了一种利用TFBG的不同模式来测量弯曲半径的方法。简支梁的弯曲只让TFBG各模式的谐振峰波长发生了漂移,而各模式的谐振峰的幅度没有改变。因此可以用TFBG波长来定义简支梁的弯曲半径。TFBG各模式对简支梁弯曲半径的响应是不同的,利用这一特性及TFBG的温度特性,可将TFBG用于温度、弯曲等多参量同时测量。(4)在TFBG纯弯曲的实验中发现,TFBG的纤芯模、包层模谐振波长对弯曲不敏感,不同的弯曲半径会使得包层模谐振峰透射功率与曲率成线性关系,纤芯模、包层模透射功率对温度变化不敏感。利用这些性质,可以采用一个TFBG分别测量纤芯模谐振波长和透射谱功率的变化实现对弯曲和温度的同时测量。3.对光纤光栅复用解调技术进行了研究,并取得了若干成果,包括:(1)在一些工程应用中,往往对系统分辨率没有太高的要求,而是要求结构简单且成本低廉的解调方案。因此,我们设计实现了一种双边沿滤波器构成的解调系统,这种系统具有成本低、响应速度快、使用方便等优点。(2)设计实现了一种基于TFBG的温度不敏感的FBG应变解调系统。当周围环境温度变化时,无需另加温度补偿,就可以利用TFBG实现FBG应变信号的动态解调,可以消除温度噪声对应变信号的影响。(3)在高双折射光纤环境的透射谱中,有多个边沿呈现线性,因此可将这些线性边沿作为边沿滤波器组来使用。设计了一种基于高双折射光纤环境的复用解调系统,这种系统具有结构简单,线性边沿较宽,易于调节等优点。4.利用TFBG的多个模式进行了应变传感的实验,首次提出了一种基于多传感器参数估计数据融合的应变测量方法,这种方法首次采用了TFBG的不同模式作为多个传感器。这种方法计算简便,编程容易,可以获得比有限个传感器的算术平均值更准确的测量结果,具有较高的可靠性,可用于其它测量结果具有正态分布特性的多传感器测量系统。5.简单介绍了传感器网络的一般概念,首次提出了一种基于光纤光栅的小区制蜂窝传感器网络。传统的光纤光栅传感器网络在设计时只是考虑了其复用能力,我们设计的蜂窝传感器网络在提高复用能力的情况下,将原来简单的传感器变成一个智能传感器模块。这种传感器能同时测量多个参量,提高了信道的利用率,能与环境中的其它设备进行通信,还可以向中心控制计算机发出请求。采用排队论理论对传感器网络性能进行分析,计算出平均等待时间,提高了传感器系统的可靠性。更多还原

【Abstract】 Fiber gratings, as novel photonic devices, make many complicated all-fiber communication network and sensor network executable and significantly broaden the scope of the application of optical fiber technology. Tilted fiber Bragg gratings (TFBGs), a kind of fiber gratings, have many unique advantages in addition to characteristics of ordinary fiber Bragg grating (FBG).In this dissertation, we mainly study on the sensing and demodulation characteristics of TFBG in theory and experiment. Based on the sensing characteristics of TFBG different from those of FBG, we carry out a more accurate estimate on the measurands using data fusion theory. In combination with sensor technology, embedded computing technology, modern communication and network technology, we apply FBG to the sensor network and design a cellular sensor network.With the subjects supported by the National High Technology Research and Development Program of China (Grant No. 2006AA01Z217), the National Natural Science Fund projects (Grant No. 60736039) and the Key Laboratory Fund of Optoelectronic Information Technical Science, Ministry of Education of China, the main contents of this dissertation are as following:1. Analysis methods of fiber gratings are presented and FBG and TFBG are analyzed respectively in theory using mode coupling method and volume current method. This is the base of future work and will provide theory foundation for experiment.2. Sensing characteristics and applications of TFBG are mainly studied. We have make progress including:(1) The wavelength shifts of core mode and cladding modes of TFBG are nearly consistent in temperature sensing experiment .Temperature sensitivity of TFBG can be improved by using different backing material of different thermal-expansion coefficient. (2) Strain can make the resonance peaks of TFBG core mode and cladding modes shift and the influences of strain to core mode and cladding modes of TFBG are different. A kind of system of measuring temperature and strain simultaneously is designed based on strain and temperature characteristics of TFBG.(3) A kind of method to measure bending radius using different modes of TFBG is presented for the first time by analyzing the bending of simple supported beam in theory. The bending of simple supported beam make the resonance peak wavelength of each mode of TFBG shift and resonance peak amplitude unchangeableness. So the wavelength of TFBG can be used to define the bending radius of simple supported beam. The response of different modes of TFBG are different. Temperature and bending can be measured simultaneously with a single TFBG based on this characteristic and temperature characteristic of TFBG.(4) In pure bending experiment of TFBG, it can be concluded that the resonance wavelengths of TFBG core mode and cladding modes are not sensitive to bending, resonance peak transmission power of cladding modes and curvature present linear relationship with different bending radius and transmission power of core mode and cladding modes of TFBG are not sensitive to temperature. Bending and temperature can be measured simultaneously using these characteristics to respectively measure core mode resonance wavelength and transmission power with a single TFBG.3. Demodulation and Multiplexing characteristics of fiber gratings are mainly studied. We have make progress including:(1) In some project application, it is more important to design a demodulation method which has the characteristics of simple structure and low cost than to design a demodulation method with a high resolution. We design a kind of demodulation system which is composed of double edges filter and has the advantages of low cost, quick response, easy operation and so on.(2) A FBG strain demodulation system based on TFBG, which is insensitive to temperature, is designed. When ambient temperature is changed, dynamic demodulation of FBG strain using a single TFBG without additional temperature compensation, which can eliminate the influence of temperature noise to strain signal, can be achieved. (3) There are many edges presenting linearity in transmission spectrum of high birefringence fiber loop mirror which can be used as edge filter groups. A multiplexing and demodulation system based on high birefringence fiber loop mirror, which has advantages of simply structure, wide linear edge and easy modulation.4. A strain measuring method based on measurands estimation data fusion is presented using many modes of TFBG in strain sensing experiment. Different modes of TFBG are used as different strain sensors in this method for the first time. This kind of method, which can get more accurate result than the method of calculating the arithmetic mean of limited sensors and can be used in sensors measuring system with normal distribution measuring result, has the advantages of easy calculation, easy program and high reliability.5. Common concept of sensor network is simply presented and a kind of celluar sensor network based on fiber grating is put forward. The celluar sensor network not only improves the multiplex ability but also change the simple sensor to be an intelligent sensor module while traditional fiber grating sensor network only considers its multiplex ability in design. This kind of sensor can measure several parameters simultaneously, improve the use factor of channel, communicate with other devices and also can ask to the center control computer. Queuing theory is used to analyze th system performance and calculate the average waiting time which can improve the reliability of the system.更多还原