基于光纤F-P干涉波长的溶液浓度测量系统研究

为了消除光源强度波动对测量结果的影响，根据溶液浓度与其折射率的关系和光纤法布里珀罗(F—P)干涉仪透射光谱中心波长与干涉仪腔内介质折射率之间的关系，利用其透射光谱的中心波长进行透明溶液浓度的精确测量，开发出测量实验系统。采用可调光学滤波器对传感信号进行采集。对浓度为5％～80％的酒精进行了实际测量实验，浓度最大测量偏差为0．003％。该系统具有如下特点：1)与CCD测量技术相比，采用法布里-珀罗干涉系统透射光谱的波长信号进行溶液浓度测量，可实现连续大范围、高精度测量；2)消除了光源波动对测量结果的影响，可实现连续高精度测量，且测量范围宽；3)直接利用光电探测器PIN进行传感信号的检测，使系统计算简单；4)便于实现分布式遥测系统；5)直接拟合出F—P干涉波长与溶液浓度之间的关系，使其更适合于工程实际的应用。

Solution Concentration Measurement System Based on Fiber Fabry-Perot Interference Wavelength

To essentially eliminate the measurement errors arisen from light source power fluctuation, a measurement method of solution concentration was proposed. The method is based on the relationship between transmission optical spectrum central wavelength of fiber Fabry-Perot (FFP) interferometer and the refractive index of medium in the cavity, as well as the relationship between solution refractive index and its concentration. Such a measurement system was developed. A tunable fiber optical Fabry-Perot (F-P) filter was used to collect the sensing data. Different concentrations of a set of alcohol solution, with the concentration being from 5% to 80%, were measured experimentally. The maximum absolute measurement bias is no more than 0.003%. This measurement system possesses following advantages: 1) It can be used to precisely measure the resolution concentration with a large dynamic span, comparing with a system comprises CCD (charge coupled device) camera; 2) it is immune to the fluctuation of light source, and thus a wide range precise and continuous measurement can be achieved; 3) The test system is largely simplified through employing a PIN photodetector to collect the sensing signal directly; 4) It is easy to fulfill a distributed remote measurement; 5) The proposed system is quite suitable for field applications because the concentration of the measurand can be elicited from the light wavelength.