【作者】 苏觉；

【导师】 钱景仁；

【作者基本信息】 中国科学技术大学 ， 电磁场与微波技术， 2009， 博士

【摘要】 光纤激光器是指以光纤或掺杂光纤作为工作媒质的一类激光器,因为它具有低阂值、高效率、窄线宽、可调谐、稳定性可靠、紧凑小巧、重量轻和高性能价格比等众多优点,可以广泛的应用于传感、通信、医疗、军事等领域。特别是可以作为激光型光纤传感器(Polarimetric Fiber Laser Sensor),通过直接测量光纤激光器正交模式的拍频变化来监控外界扰动。由于它具有高灵敏度、易于测量等特点,近年来受到了广泛关注。目前,对激光型光纤传感器的研究主要集中在测量压力、电流、液压、温度等方面。本论文的工作主要围绕着两种用作激光型传感器的光纤激光器及其在非互易测量(包括电流传感和陀螺)中的应用来展开。在激光型光纤传感器的设计、实验现象的理论解释等方面做了如下的研究工作:光纤激光器的基本原理与设计方案概述了激光和光纤激光器的基本原理,包括光与物质的相互作用,激光振荡的条件及频谱分布等激光产生的基本原理:掺铒光纤的增益性质,空间烧孔效应和外界扰动对激光输出稳定性的影响,光纤激光器的实际极限带宽等光纤激光器的相关知识;分别讨论了双向单纵模环形腔激光器和多波长激光器的设计方案;系统地分析了掺杂光纤饱和吸收体中形成的动态光栅的反射谱特性。激光型电流传感器的实验研究利用空间烧孔和饱和吸收体设计了一种三波长光纤F-P腔激光器,给出了设计原则以及激光器的本征偏振态:采用琼斯矩阵方法分析了三波长光纤激光器用作电流传感时的理论模型。着重分析了传感区光纤双折射对电流传感的影响,同时对温度特性进行了讨论;实验验证了激光器的设计方案,得到了稳定的三波长光纤激光器;通过外加感应区,得到了线性系数为3.05KHz/A的激光型电流传感器。线偏振光光纤激光陀螺的研究提出并设计了一个光纤非互易器件—方向相关偏振器,理论上分析了器件的工作原理并给出了测试方法。样品测试的结果为插入损耗为0.61dB,消光比大于23.35dB;首次采用方向相关偏振器和由窄带薄膜滤波器与M-Z干涉型梳状滤波器组合而成的混合滤波器实现了一种新型稳定的双向单纵模掺铒光纤环形腔激光器。对存在双折射时,温度变化对零漂的影响做了分析,得出在折射率差为0.01,温度变化0.01℃时,零漂约为10KHz的数量级:实验验证了线偏振态光纤环形腔激光器的设计方案,得到了激光阈值为16mW的双向单纵模光纤环形腔激光器。当泵浦功率为20mW—70mW时,在CW和CCW方向上始终保持为单纵模工作。用于光纤环形腔激光陀螺系统中时,其拍频输出有大于30dB的信噪比。调节腔内的偏振控制器,当零频偏置分别为1.68MHz和409KHz时,均得到了较好的拍频漂移量与角速度的线性曲线,其斜率分别为1.38KHz/(deg/sec)和1.23KHz/(deg/sec),零漂约为7kHz,与理论相符。对实验中出现的零频偏置较小时陀螺的比例因子降低的现象进行了分析,并给出解决思路。得到了第一台连续波的光纤激光陀螺。圆偏振光光纤激光陀螺的研究提出一种圆偏振态工作的光纤激光陀螺。从理论上分析了互易器件—圆偏振起偏器的原理,以及圆保偏光纤—扭转光纤的保偏特性,并改进了扭转光纤的制作方法;首次推导了光纤激光陀螺闭锁现象的解析表达式,并做了数值模拟,得到在FSR=34MHz,D=38cm,λ=1.55μm情况下,闭锁阈值约为Ω≈7.3°/s;首次实现和证实了圆偏振态激光器的设计方案,得到激光阈值为35mW的双向单纵模光纤环形腔激光器。实验中的工作泵浦功率用在50mW,处于连续波工作状态,运行基本稳定,工作波长为1549.956nm,两路输出功率相当,均可大于0.1mw。用于光纤环形腔激光陀螺系统中时,其拍频输出有大于30dB的信噪比;斜率(即比例因子)为2.67KHz/(deg/sec);零漂为±1.5KHz;灵敏度为1°/s:闭锁阈值约为10°/s,与理论相符。最后对实验中存在的一些问题进行了分析,并给出解决思路。证明了圆偏振光光纤激光陀螺工作机理的正确性。更多还原

【Abstract】 Fiber laser is a kind of lasers with fibers or doped fibers as its working media. Recently much effort has devoted to the theoretical and experimental investigations of fiber lasers due to their attractive characteristics,such as low-threshold,high efficiency,narrow linewidth,tunable output frequency,compact structure,light weight,high performance and cost ratio,as well as the stability and reliability.Fiber lasers can be widely used in many fields such as sensing,communications,medical and military areas.During these applications,polarimetric fiber laser sensor(PFLS), which detects external perturbations by a direct measurement on the beat frequency’s change of the orthogonal modes in a fiber laser,has attracted more and more interests for their remarkable advantages such as high sensitivity and ease of measurement.Currently,most of the research on PFLS is to measure pressure, current,hydrostatic pressure and temperature.The research work in this thesis mainly focus on the study of two types fiber lasers for PFLS,as well as its applications in non-reciprocity measurement including current measurement and fiber laser gyro.More concretely,their design work has been carried out in a comprehensive manner and validated through experiments.The major contributions of this thesis are summarized as follows: (?)Studies on basic working principles and designs of fiber lasersThe basic working principles as well as the major characteristics of laser and fiber lasers are firstly reviewed,including the interaction between light and matter, the laser oscillation conditions and the spectrum distribution,the gain characteristic and spatial hole burning effect,the influence of external environment on the stability of laser output and the actual limits of fiber laser bandwidth;The designs of bidirectional single-mode Er-doped fiber ring laser and multi-wavelength laser is then discussed,respectively;The characteristics of dynamic grating reflection spectrum of the fiber saturable absorber is systematically analyzed. (?)Studies on polarimetric fiber laser current sensorsThree-wavelength fiber F-P cavity laser is designed by utilizing the spatial hole burning effect and the fiber saturable absorber.The design principles and eigen state of polarization of the laser is presented;The theoretical model of three-wavelength fiber lasers used as current sensors is formulated by using Jones matrix method.The analysis is emphasized on the influence of fiber birefringence at the sensing area on the current sensor,and temperature characteristics are also discussed;The design of the fiber laser is verified through experimental research,and a stable three wavelength fiber laser is thus achieved.When the laser is used in a current sensor system,a good linear relation between the beat frequency shift and the current is acquired,with a slope of 3.05KHz/A. (?)Studies on linear polarization fiber laser gyroA direction related polarizer(DRP) is proposed and designed as a non-reciprocal optical device.The theoretical analysis of the working principle and test methods of the device are introduced.Experimental results show that insertion loss is 0.61 dB,the extinction ratio is larger than 23.35 dB;A novel and stable bidirectional single-mode Er-doped fiber ring laser making use of a DRP and a combined filter based on a narrowband thin film filter and a Mach-Zehnder comb filter is realized for the first time to best of our knowledge.Taking account of the effect of fiber birefringence,the influence of the temperature change on the null-drift from the frenquency bias(NDFFB) is analyzed.When the refractive index difference is 0.01 and temperature change is 0.01℃,the NDFFB is on the order of magnitude of 10KHz;The design of linear polarization fiber laser gyro is experimentally verified.The fiber laser with a pumping power threshold of about 16 mW and a lasing wavelength of 1550 nm is realized.When the pumping power is between 20 mW and 70 mW,the fiber laser maintains single longitudinal mode operation in both CW and CCW directions.The signal to noise ratio of the CW-CCW beat signal is larger than 30dB.By adjusting the polarization controller,a good linear relation between the beat frequency shift and the cavity rotation rate is observed in a gyro system when the frequency bias is 1.68 MHz or 409 KHz respectively.The scale factor is 1.38 KHz/(deg/sec) and 1.23 KHz/(deg/sec) respectively,and the NDFFB is about 7 KHz,which are all consistent with the theoretical analysis.The phenomenon that the scale factor reduces with the decrease of the frequency bias is analyzed,and its solution is then given theoretically.A continuous-wave fiber laser gyro is achieved for the first time. (?)Studies on circular polarization fiber laser gyroA circular polarization fiber laser gyro is proposed.The principle of the circular polarizer and twisting fiber is analyzed.The fabrication methods of the twisting fiber are improved;The closed-form expression of the lock-in effect in fiber laser gyro is deduced for the first time Numerical simulation shows that the lock-in threshold of about 7.3°/s is obtained when the working wavelength is 1550 nm,the FSR and the diameter of the ring cavity is 34 MHz and 38 cm,respectively;The design of circular polarizationpolarized? fiber laser is implemented and validated for the first time.The threshold pumping power of the fiber ring laser is about 35 mW and the lasing wavelength is 1549.956 nm.A stable and continuous laser operation is observed for the bidirectional single mode Er-doped fiber laser and the laser output is larger than 0.1 mW.When the laser was used in a gym system,it is observe that the signal to noise ratio of the CW-CCW beat signal is larger than 30 dB;the scale factor is 2.67 KHz/(deg/sec);the NDFFB is about±1.5KHz;the sensitivity of the fiber laser gyro is 1°/s and the lock-in threshold is about 10°/s.These experimental results are consistent with that of the theoretical simulation,which hence validates the proposed design idea of the circular polarization fiber laser gyro Finally,the problems encountered in the experiment are analyzed and possible solutions are suggested.更多还原