Study On Fiber Loop Ring-down Spectrosopy Application In The Measurement Of Concentration

Industrial production does not only offer people needed products but also produce allkinds of industrial dust. The study shows that dust content increases more than twice asmuch during the past century and the noticeable change has affected the global climateand ecosystem. Recent epidemiological evidence suggests that airborne particulate have acorrelation with mortality. So an on-line, real-time, fast, high sensitive monitoringtechnology is badly in need for monitoring the extinction coefficient and concentration ofdust.Fiber loop ring-down spectroscopy is developed based on optical fiber sensingtechnology and cavity ring-down spectroscopy as a high sensitive measuring technology.After doing plenty of investigation work, combined with the current research status ofdust measuring, in order to improve measuring precision of dust, fiber loop cavityring-down spectroscopy is first applied to dust measurement field in paper.Firstly, dust particles is consider generally as a single spherical particle in study，butthe shape of most particles are irregular. So particle average diameter values is adopted asparticle size. Several commonly distribution functions and particle average size functionsare introduced. Interaction of particles with light is analyzed. Parameters which are neededin measurement are deduced based on Beer-Lambert Law. Sensing principle of fiber ringcavity ring-down spectroscopy is introduced. System can adjust gain at equilibrium on thebasis of cavity total optical power loss self-adaptively, and dust concentration is singlevariable function of ring-down time using gain characteristics of erbium-doped fiberamplifier.Secondly, dust measuring system based on fiber loop ring-down spectroscopy isconstructed. Components which made up system are introduced. And erbium-doped fiberamplifier is mainly analyzed and is difficult to achieve the stability of the gain nearwavelength 1550 nm. So a light feedback loop is designed to control the stability of theerbium-doped fiber amplifier.Finally, the influences of dust particle size, refractive index, incidence light wavelength on extinction efficiency parameter and attenuation coefficient are analyzed bysimulation. The experiments which polystyrene particles and corn dust act as measuringobject are performed with the system. The extinction coefficients of polystyrene particlesat wavelength 1550nm in different particles size are measured, and the measuring resultsare compared with Mie calculated values. The mass concentration of corn dust of particlessize 7.6μm at wavelength 1550 nm are measured, and the results were compared with theones which the available instrument measured. The feasibility and advantage of thissystem are verified.