The Research Of Optic Fiber Sensor Based On The Fiber Optical White-light Interferometry

Faced with tough environment, measurement of modern sensor requires increasingly high demands of its performance, such as accuracy, reliability, dynamic range. At the same time, mature and reliable measurement technology is also in urgent demand. Optical fiber sensor has its own characteristics such as higher accuracy and sensitivity, resistance to high temperature and pressure. It is wildly used in structural health monitoring of composite materials, large-scale structures(such as bridges, etc.) and aircraft.Using phase modulation method of optical fiber sensing technology provides a reference to optical fiber sensors in the application research of fabrication, cost, and practicality.The article described the basic principles of phase modulation method of optic fiber sensor, and also discussed the basic principles of Fabry-Perot(F-P) interferometer and Michelson interferometer, and introduced typical structure of them. The above theory laid foundation for the fabrication and study of Extrinsic Fabry Perot Interferometer(EFPI) and Michelson Interferometer. Finally we observed the principle of white-light interferometry which is used in the interferometer measured system.Based on the white-light interferometry technique, an all-fiber EFPI of refractive index measuring guage is designed. The experiments of F-P cavity fabrication are conducted in-depth, and gained a 7mm F-P cavity of EFPI. This interferometer finished measurement of refractive index of the transparent materials, and has a lot of advantages such as small device size, higher accuracy, easy to operate, and easy to carry. The experimental results indicated that the deviation between measured value and the reference value given in the literature is very small, and the error is maintained about 1%.Based on the white-light interferometry technique, an optical fiber Michelson interferometry strain sensing device is obtained. Length difference of the two interferometer arms varies with the deformation of sensitive element which can stretch out and draw back fiber interferometer arms. The phase change is detected by the white light interference technique. This experimental study changed Michelson length difference between the interferometer arms by changing the size of the weight applied to the elastic sensing element, strain is proportional to the optical path difference, theory strain and experiment strain are in good agreement.