Study On Fiber Cavity Ring-Down Spectroscopy Measuring Technology

The fiber based cavity ring-down spectroscopy is an emerging super sensitive spectral measurement technology. Fiber loop ring-down spectroscopy (FLRDS) system has a very high sensitivity and suit for the detection of weak absorption material very much. The system has advantages of anti-electromagnetic radiation, high temperature resistant, easy integration, high sensitivity and less demanding on the stability of light source. It can also be widely used in chemical analysis, sensor measurement, detection of biological samples, the detection of atmospheric environment, high reflectivity measurement and other fields.Fiber bending loss and different concentrations of melamine solution are detected with the system composed of continuous optical scanning laser, fiber loop cavity, the light detector and lock-in amplifier. High sensitivity measurement of the trace liquid concentration is achieved through theoretical analysis with experiments verification.Firstly, optimization in the frequency modulation, optical path length, absorption length and optical power is made on the basis of theoretical analysis of fiber ring ring-down spectroscopy system to improve the measurement accuracy of the system.Second, procedures is write based on the Lab VIEW platform to control the laser and lock-in amplifier, which also contains data collection and handling procedures. In the experiment, the measurement process can be carried out through the computer real-time control and the experimental situation can be controlled through real-time monitoring, this can improve the efficiency and accuracy of the experiment.Finally, measurement with PS-FLRDS system on the bending losses of the optical fiber ring and different concentrations of melamine solution were made, The experiments results confirmed that the system has a high sensitivity and good linearity. The detection sensitivity of melamine solution of FLRDS system reached0.317/(mg/ml),and the minimum concentration is3.15x10-8g/ml.The way to measure liquid concentration using the PS-FLRDS measurement system presented in this paper has the advantages of high sensitivity, good linearity, wide measurement range, easy to operate, and has a good application value.