Interferometric Fiber Devices and Their Applications in Optical Fiber Communications and Sensors

干涉型光纤器件是一种基于光纤的无源器件，在光通信与光传感领域都得到了广泛的应用。基于锥形光纤与特种光纤的内联型马赫-曾德尔干涉仪结构是其中两种比较新颖的技术，它们各自具有独特的性质，可以实际应用在许多场合，因此，研究它们具有重要的理论和实际意义。 本文主要的研究工作体现在四个方面： 一、基于锥形光纤的内联型M-Z干涉仪在传感技术应用中的研究。首先，借助光纤熔接机电弧放电拉锥在常规单模光纤上制作双锥内联型的M-Z干涉仪结构，并将其用于实现准分布式横向应力测量；其次，利用程序化的焰刷拉伸技术在常规单模光纤上制作微纳光纤型M-Z干涉仪结构，并利用该结构实现空气/甘油水溶液两种不同介质分界面的折射...Interferometric fiber-optic devices are one kind of fiber-based passive devices, and have been widely applied in optical fiber communications and sensors. In-line Mach-Zehnder interferometer based on tapered fibers and specialty fibers are two types of novel techniques, which can be applied in various areas for their special properties. Therefore, it is really important to investigate them theoret...学位：工学博士院系专业：信息科学与技术学院_电路与系统学号：2312010015403

Gain Flattening Filter with Twin-Core Fiber

对现有放大自发辐射(ASE)光源与掺铒光纤放大器(EdfA)增益平坦的方法做了分析和讨论,采用双芯光纤和光纤波分复用(WdM)耦合器组合的方法设计了一种新的增益平坦滤波器。由于双芯光纤的传输谱特性可以通过弯曲、扭转以及拉伸等方式调节,从而这种全光纤的增益平坦滤波器具有实现简便、可调谐性好等优点,平坦化后的出射光谱在1527.36--1561.04 nM的带宽内只有±0.5 db的起伏。结果表明,采用双芯光纤与其他器件一同制作的滤波器,在光通信与光纤传感领域有较大的应用前景。Methods related to the design of gain flattening filters for amplified spontaneous emission(ASE) and erbium-doped fiber amplifier(EDFA) are reviewed.A novel scheme to realize the gain flattening filter by using a piece of twin-core fiber and a wavelength division multiplexing(WDM) coupler is proposed and verified experimentally.The spectrum of the twin-core fiber can be adjusted by bending,twisting and stretching to meet the filter requirement.The flexibility and tunable properties make the proposed all-fiber device a good candidate for gain flattening filter.The experimental results show that the ASE spectrum can be flattened in the wavelength region of 1527.36～1561.04 nm with ripples within ±0.5 dB.The results show the filters with twin-core fiber may offer great potential for optical communications and sensing applications

Research on fiber gas sensor system based on average filtering algorithm

数字平均滤波是信号处理中一种常用的方法。在小信号检测中,使用数字平均滤波可以获得较高的信噪比,提高检测的灵敏度。本文提出了一种利用光学器件来实现数字平均滤波的新方法,应用于基于差分吸收检测原理的窄带扫描光源光纤气体传感系统。系统的输出是一段连续的光谱,包含有被测乙炔气体的多个特征吸收峰。系统使用法珀标准具ETAlOn和参考光栅提供波长参考,完成对输出信号的光谱重建。对相同波长范围的信号进行平均滤波,使气体的相同特征吸收峰重合,提高检测的灵敏度。利用光谱重建,克服了可调谐fAbry-PErOT滤波器驱动电压和透射波长不稳定因素的影响。实验结果表明,本系统可以方便有效地实现光谱意义上的数字平均滤波,检测到较低浓度的乙炔气体,比较适用于工业化气体检测系统。Digital average filtering is a widely used signal processing method.In small signal detection,digital average filtering can obtain higher signal-to-noise ratio and can improve the detection sensitivity.This paper puts forward a new method using optical device to realize the digital average filtering.Basing on difference absorption principle,a new optical fiber gas sensor system based on a scanning light source is presented,and a novel optical gas sensor system is designed.By utilizing ETALON and reference grating,it can provide reference wavelength,and realize the spectrum reproducing of the output signal.Therefore,the same spectral signals can be superposed.This method is able to overcome the uncertainty effect caused by the transmission wavelength of tunable Fabry-Perot filter and filter′s driving voltage.Experimental results show that the gas detection sensitivity is remarkably improved and can detect fairy low concentration acetylene gas.The system is suitable for industrial gas monitoring.国家自然科学基金项目(No.61077031);厦门大学“985”与“211”工程项目资

A High-Precision Method for Determining the FBG Peak Wavelength Shift Based on FBG Actual Reflection Spectrum Match

针对目前光纤布拉格光栅(fbg)解调方案中采用低分辨率CCd测量fbg峰值波长时存在的问题,提出一种采用基于fbg实际反射谱构建基函数匹配CCd测量获得的有限测量点确定fbg峰值波长偏移量的新方法。分别在理论和实测上对这种方法的有效性和可行性进行了研究,证明这种采用fbg实际反射谱函数匹配有限测量数据的方法比采用特定函数拟合测量数据的方法能够更准确地获得fbg峰值波长的偏移量。实现了在CCd采样点数少、光谱分辨率较低的情况下对fbg峰值波长偏移量的高精度确定,有效地提高了实际工程应用中基于低成本CCd解调fbg峰值波长及其微小偏移量的准确性。Referring to the problems in using low-resolution charge coupled device(CCD) to measure fiber Bragg grating(FBG) peak wavelength,a high-precision method for determining the FBG peak wavelength shift by matching basis function based on the FBG actual reflection and sampling data measured by CCD is proposed.The effectiveness and feasibility of the new method are studied theoretically and experimentally.It is proved that compared with fitting sampling data by specific functions,the matching method based on FBG actual reflection spectrum can determine FBG peak wavelength shift more accurately.In the case of few sampling data and low resolution of CCD measurement,the high-precision determination of FBG peak wavelength shift is achieved.The accuracy of demodulation of FBG peak wavelength shift using low-cost CCD in the practical applications is improved effectively.国家自然科学基金(61077031);国家质检总局科技计划项目(2010IK077)资助课

Design of broadband LP01 <-> LP02 mode converter based on special dual-core fiber for dispersion compensation

A novel broadband LP01 LP02 mode converter for dispersion compensation based on special dual-core fiber is theoretically investigated by using the coupled-mode theory. The simulated mode converter has similar to 22 nm bandwidth with a conversion efficiency of over 80%. Furthermore, this noncomplete conversion only introduces the insertion loss rather than multipath interference resulting from the residual LP01 mode. Finally, one optimal scheme for broadening the bandwidth of high-efficiency conversion has been proposed by longitudinally tapering the dual-core fiber. The simulation results show that the conversion bandwidth can be improved to similar to 31 nm by tapering with a scaling range of only 2%. (C) 2012 Optical Society of AmericaNational Natural Science Foundation of China [61077031

An Algorithm of Filtering Background Noise of Optical Fiber Gas Sensor

在光纤气体传感系统中,为提高检测的灵敏度,需要采取措施抑制系统的各类噪声。通过设计低噪声的前置放大器和光源驱动电路可有效地降低系统的噪声;但对于因光路变化和光在传输过程中偏振态发生变化引起的背景噪声的处理一直是光纤气体传感系统测量灵敏度提高的难点。提出一种基于最小二乘拟合的背景噪声滤除算法。利用参考光栅和法布里-珀罗标准具实现对输出信号的光谱重建。在此基础上,利用气体特征吸收峰两边的输出拟合整个输出曲线。将系统的输出与拟合曲线相除,实现系统输出的归一化,有效地滤除了系统的背景噪声,避免了当传感系统背景噪声发生变化时,需要重新采集背景气的繁琐工作,为测量带来方便。In fiber gas sensor systems,in order to improve the detection sensitivity,it is vitally necessary to make intensive efforts to restrain various noises of the system.Designing low-noise preamplifier and light driving circuit can effectively reduce the system noise,but cannot reduce the noise caused by the changes of optical path.This kind of noise is called background noise,which influences the measuring sensitivity of fiber gas sensor system.Therefore,how to filter the background noise affects the improvement of measurement accuracy.This paper puts forward a method based on least logarithm square method which can easily reduce the background noise of optical gas sensor system.By using reference grating and Fabry-Perot etalon,it can reconstruct the output spectra.A modified least square method is used to fit the envelope of gas absorption lines by using the data of absorption peaks on both sides.Dividing the gas absorption lines by the envelope line of absorption lines,the normalization of output is realized and thus the drift of the background noise curve due to the change of experimental environment can be reduced.This method can avoid data collection again when the background noise is drifting,and brings convenience to measurement.国家自然科学基金(61077031);厦门大学985和211工程资助课

Lateral stress detection using a tapered fiber Mach-Zehnder interferometer

In this letter, a novel approach to measure local lateral stress using a tapered fiber Mach-Zehnder interferometer (TFMZI) is proposed and demonstrated. The transmission spectra of the TFMZI are measured under different transverse pressures and loading positions. The responses of the TFMZI are analyzed in a spatial frequency domain by fast Fourier transform of the corresponding transmission spectra. The proposed approach allows an effective detection of lateral stress-induced fiber deformation at different positions along a TFMZI. 漏 1989-2012 IEEE