Reaserch On An Intensity-modulated Sensing Technology On Fiber-loop Ring-down Spectroscopy

In recent years, Fiber Cavity Ring-Down Spectrocopy technology has developedquickly. It is a kind of high sensitive absorption spectroscopy with a high sensivity. It isconsisted of fiber sensing technology and Cavity Ring-Down Spectroscopy (CRDS)technology. So it has not only the advantages of fiber sensor and CRDS, b ut its ownsuperiority. This technology has a good application prospect in a lot of areas s uch aschemical detection, environment monitoring and physical measurement.In this paper, a constuction of Fiber-Loop Ring-Down Spectrocopy (FLRDS)sensor system is proposed. Firstly, the article represents the sensing priciple of fiberring-down spectrocopy sensor system. Then it describes the working priciple ofintensity-modulated fiber sensor and fiber bend loss intensity modulation, and discussesthe superiority that the fiber (CRDS) contracts with other sensor technology.Secondly, a FLRDS sensor system scheme which the wavelength of fiber is1550nm is designed based on the theory analysis. In this scheme, a tunable laser and asignal generator are loaded on the Electro-Optic Intensity Modulator (EOIM) togenerates the optical pulse that the pulse width is1μs. The pulse is detected by theAPD detector after it goes through the fiber loop. The sensitivity of the detector is-50dBm. The result of this experiment shows that the ring-down time of the FLRDS sensorsystem is128μs. After that, a simple displacement sensor is made according to thepriciple of fiber bend loss, and is applied into the FLRDS sensor system. It proves thatthe system has a good stability and feasibility after a series of experiments.At last, a scheme that there are two fiber-loops in the system is proposed on thebasis of one fiber-loop. Two schemes of a dual-channels FLRDS sensor system basedon time divition multiplex is designed and simulated. The simulation picture shows thering-down curve of the two fiber-loops can be divided obviously. At the same time, thisappearance illustrates that this system can make measuring two different measurandssimultaneously perfectly come true. The successful simulation result of dual-channelsmultiplexing syestem gives rise to the thought of multi-channels FLRDS sensor system.This thought is able to mearsure several physical parameters at the same time. In thispaper, the problems which are needed to noticed are discussed when the multi-channelssystem is designed in detail. Go so far as to the practice of dual-channels system and thespecific design of multi-channels, they will be explored and proved at the future.The research above indicates the design of intensity-modulated sensor systembased on the FLRDS is practical. It can not only improve the sensing precisionefficiently, but also the disadvantage that the intensity-modulated sensors are alwaysaffacted by the light source seriously. This article also put forward a scheme which canmeasure several physical paraments at the same time. After some discussion and research, it turns out that the scheme has a good practicalness.