中文摘要
基于光纤环腔激光技术的气体传感方法因为具有很高的检测灵敏度，受到了国内外的广泛关注。采用该方法进行气体检测时由于系统不稳定、噪声大等问题使传感效果远不及理想情况。为了使该气体检测方法能够尽快从实验室阶段走向实用化，进行基于光纤环腔激光技术的气体传感仪器化研究意义重大。
本课题针对仪器化气体传感器系统，进行了如下主要工作：
1、对EDFA特性及掺铒光纤的能级理论进行了研究，基于速率方程构建了光纤环腔激光系统的理论模型，搭建了光纤环腔激光系统，利用该系统得到了光纤环腔激光器输出与泵浦电流、系统损耗和输出耦合比的关系，并获得了光纤环腔激光器的优化参数。
2、基于光纤环腔激光技术的理论和实验构建了气体传感系统理论模型，理论模拟了系统损耗、泵浦功率与气体谱线吸收度的关系；在气体传感系统理论模型的基础上，从以下几方面设计了光纤环腔激光气体传感系统的原理样机：
光学设计：采用F-P标准具实现了可调谐光滤波器非线性的实时标定；优化了系统光路使气体传感灵敏度增强系数提高了5倍以上。
机械设计：设计了仪器外壳及10cm、20cm和50cm长度的系列化气室。
电路设计：完成了低噪声的光电探测电路，并以STC单片机为核心设计了光源功率测量显示电路及智能选频电路。
算法设计：利用小波去噪方法对吸收光谱进行了预处理；采用洛伦兹拟合对气体吸收谱线进行了拟合；设计了气体吸收谱线的提取算法。
软件系统构建：以labview为基础构建了集原理样机控制、数据采集与处理和结果显示等功能为一体的软件系统。
3、对设计完成的原理样机进行了测试，该仪器可以实现对1525nm-1565nm气体吸收谱线的测试，采样误差<11×10-7，波长定位误差<80pm，气体浓度测试的累积重复性CV<0.015，可探测乙炔气体的最低浓度达到200ppm。利用该原理样机研究了内腔法与外腔法的不同以及气室长度、系统损耗、气体浓度与灵敏度增强的关系，测试结果与理论结果吻合。
基于光纤环腔激光技术气体传感系统原理样机的设计完成为深入研究该方法以及使该技术尽早实用化奠定了坚实基础。
关键词： 光纤环腔激光技术 气体传感 仪器化研究 原理样机
ABSTRACT
The gas sensing method based on intra-cavity optical fiber ring laser (ICOFRL) technology is subjected to wide attention at home and abroad because of its high sensitivity, low detectable concentration and other features. But there is no instrument based on this sensing technology now, so the sensing effect is far less than ideal due to system instability, noise and other issues.
The topic for the problems carried out the following main tasks:
1、The characteristic of EDFA and the theory of EDF energy levels have been studied. The theoretical model of ICOFRL was constructed based on rate equation and the practical optical fiber ring laser system was built. The relationships between laser output and pump current, system loss, output coupling ratio were obtained based on the model. The optimized parameters of the system were also gained.
2、The theoretical model of gas sensing system was built based on the theory and experiment of ICOFRL technology. Prototype was designed from following aspects:
(a) Optical design: By using F-P etalon the non-linearity of tunable optical filter was calibrated. Optimizing the optical system made the sensitivity enhancement coefficient increase by 5 times.
(b) Mechanical design: A series of gas cells which are 10cm, 20cm and 50cm were desiged, and the designing of instrument shell was completed.
(c) Circuit design: Low-noise optical detection circuit was designed. The optical power measurement and display circuit were designed by using the STC SCM as core. The intelligent frequerncy selection circuit was designed.
(d) Algorithm design: The wavelet denoising was used on the absorption spectrum. Lorentzian fitting algorithm was adopted to realize gas demodulation and absorption lines extraction algorithm was developed.
(e) Software system: Built the labview-based software system which can realize prototype controlling, data acquisition and processing, and result display.
3、Tested the prototype. The spectral range can be measured is 1525nm-1565nm. Sampling error, wavelength positioning error and gas concentration reproducibility are less than 11×10-7, 80pm and 0.015 respectively. The minimum detectable concentration of acetylene is 200ppm. Using the prototype studied the differences of the cavity method and external cavity method, and also studied the relationship between the sensitivity enhancement and gas cell length, system loss, gas concentration. Test results consitented with the theoretical results.
The gas sensing prototype base on fiber ring cavity laser technology laid the foundation for studying the technology and pratical use of the technology as early as possible.
KEY WORDS：ICOFRL Technology, Gas Sensing, Instrumented Reaserch, Prototype
目 录
第一章 绪论 2
1.1 本课题研究的目的及意义 2
1.2 近红外光谱吸收气体检测技术介绍 2
1.3 基于近红外光谱技术的气体传感方法比较 3
1.4 基于光纤环腔技术的气体传感方法 6
1.4.1 国内外研究现状 6
1.4.2 研究重点 7
1.5 仪器化设计概述与要求 8
1.6 课题的主要研究内容 9
第二章 光纤环腔激光技术研究 10
2.1 光纤环腔激光技术理论研究 10
2.1.1 EDFA光源 10
2.1.2 掺铒光纤能级理论 12
2.1.3 基于速率方程的光纤环腔激光系统模型 12
2.1.4 基于SOA和EDFA的激光技术比较 15
2.2 光纤环腔激光技术实验研究 18
2.2.1 光纤环腔激光系统实现 18
2.2.2 光纤环腔激光器输出与泵浦电流的关系 18
2.2.3 光纤环腔激光器输出与系统损耗的关系 21
2.2.4 光纤环腔激光器输出与输入耦合比的关系 25
2.3 本章小结 28
第三章 基于光纤环腔激光技术的气体传感仪器化研究 29
3.1 基于光纤环腔激光技术的气体传感理论模型 29
3.2 仪器化气体传感系统总体设计 33
3.2.1 仪器化气体传感系统总体设计要求 33
3.2.2 仪器化气体传感系统总体结构设计 34
3.3 仪器化气体传感系统光学设计 35
3.3.3 光学系统结构设计 35
3.3.4 光学系统关键器件特性研究 36
3.3.4.1 EDFA光源特性研究 37
3.3.4.2 可调谐光滤波器的非线性标定方法研究 39
3.3.4.3 电控可调衰减器的标定方法研究 41
3.3.5 基于传感灵敏度增强的光路优化设计 43
3.4 仪器化气体传感系统机械设计 47
3.4.1 仪器外壳设计 47
3.4.2 传感气室设计 49
3.5 仪器化气体传感系统电路设计 50
3.5.1 低噪声光电探测电路 50
3.5.2 光功率测量及显示电路 52
3.5.3 智能选频电路 56
3.5.4 系统电源设计及选择 59
3.6 仪器化气体传感系统算法设计 60
3.6.1 气体吸收光谱数据的滤波去噪 60
3.6.2 气体吸收谱线线型 65
3.6.3 气体吸收谱线提取 67
3.7 仪器化气体传感系统软件系统构建 69
3.8 本章小结 71
第四章 基于仪器化光纤环腔激光系统的气体传感实验研究 72
4.1 仪器化光纤环腔激光气体传感系统指标测试 72
4.1.1 系统扫描频率测试 72
4.1.2 系统采样误差测试 73
4.1.3 气体谱线测量范围测试 74
4.1.4 智能选频模块切换时间测试 75
4.1.5 波长定位精度测试 76
4.2 系统损耗与吸收谱线吸收度增强关系实验研究 77
4.3 气室长度与吸收谱线吸收度增强关系实验研究 79
4.4 气体浓度与吸收谱线吸收度增强关系实验研究 81
4.5 气体浓度传感重复性实验研究 82
4.6 乙炔气体最小可探测浓度实验研究 85
4.7 外腔法和内腔法比较实验研究 86
4.8 气体传感系统原理样机性能指标总结 88
4.9 本章小结 89
第五章 总结与展望 90
参考文献 92
发表论文和科研情况说明 97
致 谢 98
