【作者】 马凤；

【导师】 汪曣；

【作者基本信息】 天津大学 ， 生物医学工程， 2009， 硕士

【摘要】 工业上的需要和人们对环境的关注使气体检测技术得到了长足的发展,迄今已经有很多种气体检测的方法和仪器应用于各种领域。但出于对灵敏度、作业环境、成本等因素的考虑,人们一直都在不断地创新和研究新型的气体监测技术。本课题所研究的内容是利用近些年出现的激光内腔气体检测技术,将环腔掺铒光纤激光器应用于气体传感,实现了全光纤气体传感器。本文首先介绍了气体检测方法以及光纤气体传感器,详细讨论了光谱吸收法的原理和优点,同时介绍了光谱吸收型光纤气体传感技术的研究现状。研究了环腔掺铒光纤激光器的工作原理以及铒离子的能级结构,由三能级速率方程组对环腔掺铒光纤激光器输出特性进行了理论推导。引入气体灵敏度因子概念,推导出气体传感灵敏度因子与泵浦功率和系统损耗之间的关系。分析了环腔掺铒光纤激光器可调谐光谱范围的影响因素。利用环腔掺铒光纤激光器的工作原理,设计了气体传感系统。将气室置于激光谐振腔内,激光达到稳定前多次经过气室,增加了有效光程长;利用光纤可调谐滤波器实现了波长扫描技术;采用虚拟仪器技术完成了波长调制光谱技术,并利用软件实现了二次谐波的提取。搭建了实验平台,进行环腔掺铒光纤激光器输出特性实验。对比了在不同条件下激光器输出激光的光强和光谱范围,激光器输出特性实验结果与理论推导一致。通过实验验证了气体灵敏度因子与泵浦电流以及环腔损耗的关系。然后,利用气体传感系统进行了气体浓度实验,在不同的波长调制参数条件下,二次谐波强度不同,确定了较佳的参数后,进行了乙炔气体浓度标定实验,最后分析了气体检测浓度误差、重复性、检测极限以及波长准确性。更多还原

【Abstract】 Gas detection is necessary in many situations, such as industrial production and environmental protection. So far there are many methods and apparatus of gas detection applied in various fields, but new types of techniques for gas detection have been researching and innovating as a result of considering the facts of sensitivity, operating environment, cost, and so on. The main content of this project is to apply erbium-doped fiber ring laser to gas sensor based on laser inter-cavity technique for gas detection and to realize all-fiber gas.First, the methods of gas detection as well as fiber-optic gas sensors are introduced. The principles and advantages of spectrum absorption technology are discussed .Moreover, the present situation of fiber-optic gas sensor with the type of spectrum absorption technology is detailed.Secondly, The working principle of erbium-doped fiber ring laser and the energy level structure of Er3+ are analyzed. The output characteristics of erbium-doped fiber ring laser are theoretically derived from three-level rate equations of Er3+. The relationship between the sensitivity, the pump power, the cavity loss and other systems parameters of gas absorption sensor is investigated by introducing the concept of gas sensitivity factor.Thirdly, the gas sensor system is designed with the characteristic of gas cell placed in laser resonator. When laser reaches steady state, it has been passing the gas cell many times to increase the effective optical path. Fiber Fabry-Perot tunable filter is used to change the laser wavelength and to implement wavelength scanning technology. Wavelength modulation spectroscopy technology which is based on virtual instrument is also applied in the system.Finally, experiments about output characteristics of erbium-doped fiber ring laser and gas concentration detection were taken by established Experimental platform. The results of output characteristics of laser are consistent with the theoretical derivation. The second harmonic intensity and signal to noise rate change in different parameters of wavelength modulation. So it is important to determine the parameters of wavelength modulation. Then, the relationship between sensitivity factor, pump power and cavity loss is experimentally verified. Furthermore, the concentration of error, repeatability and detection limit are analyzed.更多还原