【作者】 赵燕杰；

【导师】 王青圃； 常军；

【作者基本信息】 山东大学 ， 光学工程， 2014， 博士

【摘要】 光纤传感技术是以光波为载体,光纤为媒质,感知和传输外界被测量信号的新型传感技术。光纤具有传输损耗低、不带电、抗电磁场干扰等优点,适用于高温、高压、易燃、易爆、强腐蚀等恶劣环境,光纤传感器的研究一直都是一个热门课题。近年来,光纤传感器不仅在高、精、尖领域得到了应用,在传统工业领域也被迅速推广,已开始应用在矿山、桥梁、建筑、石化、电力、钢铁、核工业、飞机、船舶、医疗等领域之中。光纤传感器被国内外公认为是传感技术发展的一个主导方向,最具有发展前途的高新技术产业之一本论文研究内容主要包括两部分：一部分是窄线宽低噪声光纤光栅激光器,主要研究了相移光纤光栅的光谱特性和光纤激光器输出特性,设计了基于注入锁模结构的环形腔掺铒光纤光栅激光器和复合腔结构的线型腔掺铒光纤光栅激光器；另一部分是光纤气体检测技术,研究了基于吸收光谱的光纤气体检测技术,设计了基于可调谐激光吸收光谱的光纤气体检测系统和基于双波长差分吸收光谱的有源光纤ring-down气体检测系统。本文具体研究内容为：1.采用耦合模理论和传输矩阵法对光纤光栅以及相移光纤光栅的光谱特性进行了数值模拟,获得了光栅设计参数,为优化分布反馈式光纤激光器的设计提供了理论指导；研究了基于氩离子倍频激光器以及相位抖动法的光纤光栅制作系统,制作了π相移光纤光栅。2.设计了一种自注入锁模结构的光纤光栅激光器。通过将分布反馈式光纤激光器产生的部分输出光经过一个偏振控制器形成单偏振激光,然后重新注入其谐振腔进行再放大,利用光纤的交叉相位调制效应实现模式的锁定,形成稳定的单偏振激光输出,与锁模之前相比,偏振度从0.165提高到0.989,线宽被压缩了一半,输出功率的自脉动从4dBm降低到0.1dBm。3.通过上述自注入锁模技术可以有效降低光纤激光器的相对强度噪声。当泵浦光为25mW时,在弛豫振荡频率附近相对强度噪声被压缩16dB/Hz,并且观察到弛豫振荡峰向低频移动,从74.5kHz移动到41kHz；不仅在弛豫振荡峰附近的噪声得到抑制,在中频波段的相对强度噪声也得到有效抑制；研究了不同泵浦功率下弛豫振荡频移的规律。该研究可有效提高激光器的输出特性,有利于具体应用中选择有效频率区间,提高应用的信噪比。4.设计了一种新型复合腔结构的光纤光栅激光器。通过将一个π相移光纤光栅引入传统的DBR谐振腔作为选波器件,可以增加作为增益介质的掺杂光纤长度,提高泵浦吸收率,同时获得单模窄线宽激光输出；使用低掺杂浓度的铒纤,降低了相对强度噪声。该结构实现了线宽为900Hz,强度噪声为-95dB/Hz的激光输出,泵浦阈值为几个mW,边模抑制比大于67dB。5.设计了基于可调谐激光吸收光谱技术的光纤气体检测系统,采用内部参考气室实现了对甲烷吸收光谱的实时定位和自适应调整；通过对吸收谱基线归一化,实时修正了光源功率起伏及光路损耗变化的影响；开展了光纤气体检测系统在一些工业生产中的工程应用。6.采用在甲烷传感器气室内置入光纤光栅的方法设计了甲烷气体浓度与温度双参数检测系统,不仅可以同时检测气体浓度和温度,还可以对两参数进行修正。通过光纤光栅波长的变化获取温度信息,实时校正不同温度下气体吸收系数变化导致的浓度测量误差,同时气体吸收峰的位置可以准确定位光栅波长,从而修正了温度的测量误差。7.设计了一种基于双波长差分吸收方法的新型有源光纤环形Ring-down气体检测系统。选择两个不同波长的激光器作为光源,其中一个波长覆盖被测气体的吸收峰,作为传感信号；另一个波长不覆盖被测气体的吸收峰,作为参考信号。两激光器通过脉冲信号进行强度调制,由驱动控制交替产生光脉冲信号注入到同一个光纤环Ring-down腔中。通过比较传感信号和参考信号,可有效消除腔净损耗变化以及系统中光电器件引起的信号起伏影响。选用带有自动增益控制的EDFA补偿光信号在ring-down腔中的损耗,可以增加光脉冲在环形腔中的绕行次数,提高气体检测的灵敏度。该方法为光纤ring-down腔气体检测技术在工业中应用,尤其长距离传感提供了有效手段。本文主要创新点如下：1.设计了一种自注入锁模结构的光纤激光器,通过将分布反馈式光纤激光器产生的部分输出光经过一个偏振控制器形成单偏振激光,然后将其作为种子源重新注入谐振腔进行再放大,利用光纤的交叉相位调制效应实现模式的锁定,形成稳定的单偏振激光输出。与锁模之前相比,偏振度从0.165提高到0.989,线宽被压缩了一半,相对强度噪声被压缩16dB/Hz。2.通过将一个π相移光纤光栅引入传统的DBR谐振腔作为选波器件,可以增加作为增益介质的掺杂光纤长度,提高泵浦吸收率,同时还保证单模窄线宽激光输出；使用低掺杂浓度的掺铒光纤实现功率为mW量级、线宽为900Hz、强度噪声为-95dB/Hz的激光输出。3.采用在甲烷传感器气室内置入光纤光栅的方法设计了甲烷气体浓度与温度双参数检测系统。该系统不仅可以同时检测气体浓度和温度,还可以对两参数进行修正。通过光纤光栅波长的变化获取温度信息,实时校正不同温度下气体吸收系数变化导致的浓度测量误差,同时气体吸收峰的位置可以准确定位光栅波长,从而修正了温度的测量误差。4.首次将光纤气体检测系统用于煤矿采空区、瓦斯抽采发电、垃圾发电等工业生产中,传感探头不带电,本质安全,可远距离传输,工作人员不必去现场即可轻松实现对多点气体浓度的远程实时在线监测。5.首次设计了双波长差分吸收的有源光纤环形Ring-down气体检测系统。通过选择两个不同波长的光源进行检测,其中一个波长覆盖被测气体的吸收峰,作为传感信号；另一个波长不覆盖被测气体的吸收峰,作为系统腔固有损耗的参考信号。通过两信号对比,能够有效消除腔净损耗变化及系统中光电器件引起的信号起伏影响,保证了气体检测的精确度。该方法为光纤ring-down腔气体检测技术在工业中应用,尤其长距离传感提供了有效手段。更多还原

【Abstract】 Optical fiber sensing technology is a new sensor technology by fiber as a media to measure and transfer signal. Optical fiber sensors have attracted considerable attention in recent years because of their high precision, remote detection capability, electric insulation and anti-electromagnetic interference, safety in high temperature, highly pressure, flammable, explosive and highly corrosive circumstance. Recently, optical fiber sensor are not only used in high-grade, precision and advanced area, but also in coal mine, bridge, building, petrifaction, electric, steel, nuke industry, plane, ship, medical science etc.. Optical fiber sensor is universally accepted as a leading developing direction of sensor technology, and it has an excellent development future.There are two parts in this dissertation:one is narrow linewidth low noise optical fiber laser. Spectral characteristics of phase-shifted fiber grating, and output characteristics of fiber laser are described in first part. Then a self-injection locking Er3+doped fiber laser and a novel composite structure Er3+doped DBR fiber laser with a π-phase shifted FBG are proposed with emphasis. Another is fiber gas sensor. Optical fiber gas detection method based on absorption spectrum is studied. And tunable laser absorption spectrum gas detection method and active fiber loop ring-down gas sensor based on dual wavelengths differential absorption method are described in detail. The main contents of this dissertation are as follows:1. Optical fiber grating and phase shift grating are simulated by using coupling-mode theory and transfer matrix method. Design parameters of fiber gratings are obtained which can optimize its design and manufacture. Optical fiber grating manufacture system based Argon ion laser and phase dither method are studied.2. A self-injection locking fiber laser is designed in this paper. By injecting a part of output laser back into its cavity to amplify again, it can realize a stable output. The degree of polarization (DOP) is improved from0.165to0.989, and its linewidth is compressed in half. The self-pulsation of output light is reduced from4dBm to0.1dBm.3. By self-injection locking, the relative intensity noise (RIN) of fiber laser can be reduced efficiently. When pump power is25mW, the RIN of the DFB fiber laser is suppressed about16dB/Hz by the self-injection method around the relaxation oscillation frequency. And the resonance peak of the DFB fiber laser shifts to lower frequencies obviously from74.5kHz to41kHz. By this method, the RIN are suppressed not only around relaxation frequency, but also at medium frequency. It can improve the quality of output laser, which is useful to select effective frequency range and improve the signal noise ratio in application.4. A novel composite structure fiber laser is proposed in this paper. By introducing a π-phase shifted FBG into the DBR cavity as a selective wavelength component, it can increase the length of active fiber and lasing in a single mode and narrow linewidth. Efficiency of pump is increased. The proposed composite structure fiber laser obtaines narrow linewidth of900Hz and low RIN of-95dB/Hz. The pump threshold is about several mW. The SMRS is more than67dB.5. Optical fiber gas detection system based tunable laser absorption spectrum is designed. A inside reference gas cell is introduced to wavelength positioning and adaptive adjustment for the methane gas detection. Normalizing for absorption spectrum by base line can correct the influence of light power and optical loss. Engineering applications of gas detection system are described.6. A dual-parameters optical fiber sensor is proposed by introducing a FBG into the gas cell, which can measure methane concentration and temperature simultaneously and revise them. Temperature can be obtained by the shift of FBG wavelength, which can regulate the deviation of methane detection caused by temperature changing, meanwhile, methane’s absorbing line can locate FBG’s wavelength in order to make temperature monitoring more accurate. 7. A novel active fiber loop CRD system based on dual wavelengths differential absorption method is designed. Two DFB Laser Diodes (LDs) with different wavelengths are employed, which are modulated by taking pulse signals. And they are controlled by a driver alternately to insure only one laser signal run in the loop. By comparing the sensing signal with reference signal, it can eliminate the influence the cavity loss variety and photoelectric device drift in the system efficiently. An EDFA with Automatic Gain Control is used to compensate the power loss of the laser in the ring-down cavity, in order to increase the cavity round trips and improve the precision of gas detection.. The method provides an effective way for fiber loop ring-down system application in industry, especially in long distance sensing. The main innovations of this dissertation are as follows:1. We investigated a simple self-injection locking (SIL) fiber laser. By injecting a part of output laser back into its cavity to amplify again, it can realize a stable single-polarization lasing. And its linewidth is compressed in half; RIN is suppressed about16dB/Hz and relaxation oscillation frequency of laser shifts to lower frequencies obviously from74.5kHz to41kHz.2. By introducing a π-phase shifted FBG into the DBR cavity as a selective wavelength component, it can increase the length of active fiber and lasing in a single mode and narrow linewidth. Efficiency of pump is increased. Several mW output power is realized using low Er3+doped fiber, and a narrow linewidth of900Hz and low RIN of-95dB/Hz is obtained, respectively.3. A dual-parameters optical fiber sensor is proposed by introducing a FBG into the gas cell, which can measure methane concentration and temperature simultaneously and revise them. Temperature can be obtained by the shift of FBG wavelength, which can regulate the deviation of methane detection caused by temperature changing, meanwhile, methane’s absorbing line can locate FBG’s wavelength in order to make temperature monitoring more accurate. 4. Optical fiber methane detection system is developed and used in coal mine gob, methane drainage, garbage plant and other industrial processes. It is insulation and intrinsic safety. Capacity of remote sensing makes duty officer can get enough information easily needn’t going to spot.5. A novel active fiber loop CRD system based on dual wavelengths differential absorption method is designed for the first time. It can calibrate the inherent loss of the system in real time by employing two DFB LDs with different wavelengths, which can improve the precision of gas detection. The method provides an effective way for fiber loop ring-down system application in industry, especially in long distance sensing.更多还原