F-P腔相干测量模型的建立与测量精度分析

RESEARCH ON COHERENT DETECTION MODE AND ANALYSIS OF MEASUREMENT ACCURACY ON F P CAVITY

研究了应用法布里－珀罗（简称Ｆ－Ｐ）干涉仪实现气体或透明液体折射率和浓度相干检测的原理，给出了检测系统的主要设计方法和技术参数．该系统主要由光纤Ｆ－Ｐ传感器、ＣＣＤ光电转换器、接口电路和微机组成，主要特点是实现了对折射率和浓度的实时、连续、动态跟踪和高精度测量．我们导出了待测介质的折射率或浓度的变化量随干涉条纹的变化量变化的函数关系式，提出了干涉条纹的“中心位置定位法”，设计了干涉条纹动态跟踪的完整算法，并进一步导出了折射率或浓度的变化量随干涉条纹扫过的ＣＣＤ象元的数量变化的函数关系式．最后，具体计算了干涉条纹的检测精度和折射率或浓度的测量精度，分析了影响测量精度的因素，给出了提高测量精度的方法．

This paper covers the coherent detective principle, which is mainly applied to reach coherent detection for the refraction index and concentration of gas or transparent liquid with Fabry Perot (F P) etalon, and also gives the main design procedures and technique parameters for the detective system. The system is composed of optical fiber F P sensor, CCD photoelectric converter, interface circuit and microcomputer, and it has such features as realtime, continuous, dynamic tracing and high accurate measurement for refraction index and concentration. We derive the function relationship that delta of refraction index or concentration for the medium varies with delta of interference fringes, put forword the “Central Fixing Position Method” of interference fringes design the perfect algorithm for dynamic tracing interference fringes, and further give the function relationship that delta of refraction index or concentration varies with quantities of CCD image element scanned by interference fringes. At last, we calculate the detection accuracy for interference fringes and measurement accuracy for refraction index or concentration, analyze the factors affecting the accuracy, and give the method for perfecting the accuracy.