Research Of Fiber Optic Sensor Demodulation System Based On Compact Optical Path Scanner

As the development of fiber optic communication, fiber optic sensors have been widely used in petrochemical industry, civil engineering, aerospace industry, electrical power, medical and shipbuilding industry due to the advantages of small size, fine insulating, corrosion resistance, etc., and they have became one of the rapid development technologies. In all fiber optic sensors, the Fabry-Perot sensors and Fiber Bragg Grating (FBG) sensors are typical representatives. They have their own advantages, and both are used widely. On the basis of further research of work principle and existed demodulation technology of Fabry-Perot sensors and Fiber Bragg Grating sensors, this dissertation present a novel optical equipment-Compact optical path scanner (COPS) based on white light interferometry demodulation, and build two demodulation system according to COPS. Compared to traditional demodulation equipment having the same function, the COPS use non-mechanical scan method, which is easy for fiber accessing and has the advantages of not cost, small size, simple structure.The main research work of this paper as following:1) Introduce the design of Compact optical path scanner (COPS). Usually the traditional optical path scanners use the mechanical method, and their have complicated optical structure, huge size and costly. For COPS, mentioned in this paper, it realizes the scan by varying liquid temperature which is linear function to volume. Moreover, the COPS has small size, simple structure and strong anti-interference ability.2) Set up a CO2 laser bonding equipment. Usually the optical fiber and quartz tube are fixed by glue, but the physical properties of glue are great different from quartz. Therefore, the stability of the adhered equipment is not good. This dissertation presents a laser bonding setup which can weld optical fiber and quartz tube well. Quartz tube and fiber are the same material, so they have the same physical properties. As a result, the stability of COPS has been evidently improved. Furthermore, this bonding technique can be used in making F-P sensors, and also can improve the stability and repeatability of F-P sensors.3) Build a white light interferometry demodulation system based on COPS. Apply COPS to white-light interferometry demodulation system and use the demodulation system into temperature and strain demodulation. As experiment shown, when the OPD of sensors vary in a range of 50μm, from 410-460μm, the measuring accuracy of COPS-WLI demodulation system is about 15 nm, resolution is about 8 nm and dynamic range is up to 35 dB.4) Build a FBG wavelength demodulation system based on COPS. Use COPS into FBG wavelength demodulation, and obtain the reflective wavelength information of FBG by analyzing the frequency reflective spectrum. As experiment shown, the resolution of system is about 35 pm.