【作者】 姜明顺；

【导师】 隋青美；

【作者基本信息】 山东大学 ， 检测技术与自动化装置， 2010， 博士

【摘要】 随着光纤及光子器件制造技术的不断完善,光纤光栅已成为目前最具有代表性和最具有发展前途的光纤无源器件之一,广泛应用于光通信和光传感等领域。长周期光纤光栅(LPFG)作为一种新型的光纤光栅,由于其插入损耗小、带宽宽、后向反射低、对外界环境变化的反应灵敏度高、制作简单、成本低廉等优点,受到国内外广大学者的关注。发展短短数年,已经显示出了极为广阔的应用前景。另外,由于对光纤光栅功能需求标准的不断提高,新结构、新特性、多功能光纤光栅的研制已经成为开发新型光子器件的必然发展趋势,在保偏光纤上制作的布拉格光栅以及长周期光纤光栅以其独特的光谱特性获得了重要的应用。长周期光纤光栅在通信领域主要用作EDFA增益均衡器、ASE噪声滤波器、光纤耦合器、束状滤波器以及WDM通道隔离器等。在传感领域,由于LPFG的周期相对较长,满足相位匹配条件的是同向传输的纤芯基模和包层模,这一特点决定了LPFG的谐振波长和峰值对外界环境变化非常敏感,具有比布拉格光栅更好的温度、应变、弯曲、扭曲、横向负载、浓度和折射率灵敏度。因此,LPFG具有比布拉格光栅和其他传感器件更多的优点和更加广泛的应用。本文在前期对布拉格光纤光栅(FBG)等光子器件的研究基础上,深入分析了长周期光纤光栅的耦合模原理及不同写制方法,对不同方法下写制的长周期光纤光栅的温度和应力特性进行了实验研究；设计并实现了基于长周期光纤光栅的振动和横向负载检测系统；利用机械感生长周期光纤光栅的谐振峰值和谐振波长可调谐性设计了灵敏度可调谐系统；并将可调谐长周期光纤光栅串入光纤激光器环形腔中实现了L波段可调谐激光器的设计；另外,通过在保偏光纤上写制光栅,对保偏布拉格光栅(PM-FBG)以及保偏长周期光纤光栅(PM-LPFG)进行了特性和传感技术应用研究。本文的主要内容包括：1.根据三层光纤模型,分析了光纤波导中的模式分布,并合理简化,分析研究了长周期光纤光栅中的纤芯基模与一阶低次包层模式的耦合,用耦合常数描述了模式耦合的强弱。同时,对长周期光纤光栅的光谱特性进行分析和数值模拟,为LPFG的制作和传感应用研究提供理论基础。2.分析研究了写制长周期光纤光栅的多种方法,其中包括紫外光写入法、CO2激光写入法、腐蚀刻槽法、电弧放电法、离子束注入法、机械微弯变形法等方法。采用机械感生法,紫外光写入法及CO2激光写入法写制了长周期光纤光栅,研究了写制周期、折射率调制深度、光栅长度与长周期光纤光栅透射谱的谐振波长,谐振峰值深度以及带宽等参数间的关系,并研究了不同写制方法下的温度和应变特性。3.在全面深入研究MLPFG写制模板周期与透射谱谐振波长之间的关系的基础上,将MLPFG串入环形腔中,设计了一种新颖的L波段可调谐环形掺铒光纤激光器。通过调整待写制光纤与周期性压力槽之间的夹角,改变MLPFG的写制周期,调整MLPFG透射谱,影响环形腔增益最高点,调谐光纤激光器的输出波长。可调谐范围可达42nm(1562.465nm～1604.280nm),激光光谱3dB带宽小于0.04nm,20dB带宽均小于0.08nm,边模抑制比大于45dB。长时间观测,激光功率稳定性优于0.3dBm。具有波长易调谐、线宽窄、调谐范围大、边模抑制比高、性能稳定、及成本低廉等特点。4.通过对光纤光栅振动传感解调方案的比较,从有效性、校准简便性、复用性以及成本上考虑,选择长周期光纤光栅作为解调滤波器,设计了光纤光栅振动传感解调系统。在对悬臂梁振动传感理论分析的基础上,探究了梁长、宽、厚与传感器共振频率的关系,设计了新型布拉格光纤光栅高、低频振动振动传感器,结合光电转换,放大,滤波电路设计,实现了高、低频振动传感信号的无失真信号检测,并对传感器的频率,振幅和冲击响应性能进行了分析。低频振动传感器实现了频率范围20～200Hz的无失真振动检测,并将实验结果与其他技术设计的振动传感器进行了性能比较。高频振动传感器实现了频率范围1KHz～5KHz的无失真振动检测,频率检测误差低于0.5%。5.在对CO2激光脉冲及紫外光引入的长周期光纤光栅横向负载特性研究的基础上,设计并实验研究了基于机械微应变引入长周期光纤光栅的横向负载传感系统。利用机械线加工技术制作周期性不锈钢压力槽板,测定了槽板对待写制光纤施加的横向压力与长周期光纤光栅谐振峰峰值之间的关系,并借助布拉格光纤光栅搭建了高精度横向压力解调系统,进一步提高了检测实用性。实验表明,在0～60N的范围内,横向压力与MLPFG透射谱深度有很好的线性关系,线性度达0.9950,灵敏度约为0.35dB／N,保持45 N的压力20小时,MLPFG谐振峰峰值最大波动小于0.2dB,具备良好的稳定性。采用中心波长为1542.890nm的FBG实现了系统解调,系统灵敏度为0.12μw／N。6.利用机械感生长周期光纤光栅(MLPFG)的谐振边带倾斜度易调谐性,设计了解调灵敏度可调谐的光纤布拉格光栅应变传感系统。紫外激光写入技术制作的光纤布拉格光栅的中心波长位于LPFG的谐振边带范围内时,利用该LPFG作为透射滤波器实现了一种新型的灵敏度可调谐FBG应变传感系统。当施加在LPFG上的压力由20N调节至60N时,测试对FBG施加0～3000με轴向应变(每步调整200με)的灵敏度可调谐传感实验。结果表明,FBG应变传感系统检测灵敏度光功率变化率由0.802nW／με增加到1.204nW／με。7.利用保偏光纤光栅和偏振控制器设计了一种线性腔可开关双波长掺铒光纤激光器。通过增设偏振分束器,分别得到了对应保偏布拉格光栅快轴和慢轴的单偏振激光。另外,对保偏LPFG进行了理论研究,并采用机械感生法在熊猫型保偏光纤上写制了LPFG。通过对其温度实验的分析研究,探究了机械感生保偏LPFG在横向负载及温度同时测量,以及在可调谐起偏器中的应用。更多还原

【Abstract】 With the optical fiber and photon device fabrication technology improving continually, fiber grating has become one of the most representative and promising fiber-optic passive components. And it has been widely used in optical communication, optical sensing and other fields. The long-period fiber grating (LPFG) as a new kind of fiber grating has been studied by many researchers all around the world recently, and has gotten great progresses in a few years. It attracts home and abroad scholars for its advantages, such as low insert-loss, broad-band, low back-reflection, sensitive to the changes of environments, low-cost and easy to be fabricated. It has shown a very broad application prospects within recent development. Futhermore, new structure, new features, and multi-function photonic device design have become an inevitable trend as the requirements of the fiber Bragg grating functional standard improves. The fiber Bragg grating (FBG) and LPFG, which are fabricated in polarization fiber, gain important applications depending on there unique spectral characteristics.LPFG is mainly used as EDFA gain equalizer, ASE noise filter, optical fiber coupler, beam filter, and WDM channel isolator in fiber communication. In the sensing field, LPFG has more advantages than FBG. The phase matching conditions are met by the gundermental core mode and cladding modes in the same direction due to its large period. So its resonance wavelength and peak strength are all very sensitive to external environmental changes. And LPFG has higher sensitivity than FBG to temperature, strain, bend, twist, lateral load, concentration and refractive index.In this paper, based on the early research of FBG and other photon devices, the coupler-mode theory and fabricated methods of LPFG are investigated in-depth. Furthermore, its temperature and stress characteristics are experimentally studied, and its application in vibration detection, lateral load testing, and sensitivity tunable system as well as in tunable laser manufacture are designed and implemented. Additionally, physical properties and sensing technique applications of PM-FBG and PM-LPFG are also discussed.The main contents of this article include: 1. According to three-layer cylindrical fiber model, the fiber mode distribution is analyzed. And the coupling of fiber core-mode and low first-order cladding mode is also further studied. Then coupling constants are used to describe the strength of mode coupling. Meanwhile, long period fiber grating characteristics analysis and numerical simulation provide a theoretical basis for LPFG fabricated and sensing application development.2. A variety of LPFG fabricated methods are described, including UV-fabrication method, high-frequency CO2 laser-fabrication method, corrosion-groove method, arc discharge method, ion beam implantation method, mechanical-induced micro-bend method and et al. UV-fabrication method, CO2 laser-writing method and mechanical-induced micro-bend method are adopted in this paper. The relation of fabricated period, grating length, refractive index modulation depth and resonant wavelength, resonant peak, bandwidth is researched. And the temperature and stress characteristics are experimentally studied.3. A tunable L-band ring Er(3+)-doped fiber laser (EDFL) is designed through inserting a mechanically induced long-period fiber grating (MLPFG) into Fiber ring cavity. The gratings period is altered by adjusting the angle between the periodic pressure plate and fiber. Above operation will directly influence the highest gain point of the fiber ring cavity, and make the output laser tunable. Optical fiber laser wavelength-tunable range 42nm (1562.465nm-1604.280nm) is achieved. Output laser’s 3dB line-width is less than 0.04nm and the 20dB line-width is less than 0.08nm. While the side mode suppression ratio (SMSR) is more than 45dB. Prolonged observation, laser power stability is better than 0.3dBm.Experimental results show that the tunable EDFL has the advantages of wide bandwidth, narrow line-width and stable performance.4. A novel FBG vibration sensor demodulation system is designed through demodulation methods comparison. From the validity of calibration simplicity, reusability, and cost considerations, a special long period fiber grating is chosen as demodulation filter. Based on theoretical analysis of the cantilever beam vibration sensing, the relationship between beam length, width, thickness and the sensor resonant frequency is discussed. And then high-frequency and low-frequency FBG vibration sensor is designed respectively. Not only high-frequency but also low-frequency vibration signals achive exact detection without any distortion, combind with photoelectric conversion, ampliation, and filter circuit design. Furthermore, the sensor’s frequency, amplitude and impulse response performance are texperimented. The low-frequency vibration sensor is effective in range of 20-200Hz. The results are compared with vibration sensors based on other technologies. And high-frequency vibration sensor is effective in range of 1～5 kHz. The frequency detection error is less than 0.5%.5. A novel transverse load sensing system based on MLPFG is designed based on the research of transverse load characteristic of LPFG fabricated by CO2 laser-irradiation method and UV-exposure method. Mechanical-line processing technology is used to make period stainless steel pressure grooved plate. The relationship between lateral load and LPFG resonant peak is measured. Finally, the high-precision LPFG lateral load demodulation system is realized in virtue of special designed FBG The practicality of detection system is further enhanced. Experiments show that within the range of 0-60N, the lateral pressure and the MLPFG transmission peak strength have a good linear relationship. The linearity is up to 0.9950, and the sensitivity is about 0.35dB/N. Maintaining the pressure of 45 N for 20 hours, we found the fluctuation of the MLPFG resonant peak is less than 0.2dB. A special chosen FBG with center wavelength 1542.890nm is adoted to realize system demodulation. And the demodulation sensitivity 0.12μw/N is achieved.6. A demodulation sensitivity tunable system is designed depending on the easy tenability of MLPFG resonant slope. A special designed FBG which is fabricated by UV laser technology is used to make a detection sensor. The system is achieved through tuning MLPFG resonant side-band (FBG center wavelength is in the range of MLPFG resonant slope). Sensitivity tunable experiments are carried out when the pressure applied to the LPFG from 20N to 60N, and the axial strain imposed on the FBG sensor from 0μεto 3000μεwith the step interval 200με. The experiment results show that, FBG strain sensing system detection sensitivity of optical power changes from 0.802 nW/μεto 1.204nW/με.7. A linear cavity switchable dual-wavelength erbium-doped fiber laser is designed using a polarization maintaining fiber grating and a polarization controller. Through adding polarizing beam splitter into the formal system, single-polarization laser is derived, corresponding to the PM-FBG fast axis and slow axis, respectively. In addition, PM-LPFG is studied theoretically and fabricated adopting mechanical-induced method. Through temperature characteristic analysis, its application in transverse load and temperature simultaneous measurement, as well as tunable polarization is discussed.更多还原