Research Of Metal-coated And Sensing Technology Applications On FBG

Fiber grating is a new type passive optical component with the refractive index modulated along the fiber length. It has attracted considerable interest due to its high wavelength selectivity, low insertion loss, and electromagnetism interference immunity (EMI). Fiber grating can also be easily coupled with optical fiber systems. Therefore, it has widely applied in fiber communication systems including wavelength division multiplexed (WDM), erbium-doped fiber amplifier (EDFA), optical add-drop multiplexer (OADM), and dispersion compensator and so on. Recently fiber grating has become a very important component for optical sensing field considering its many merits such as high sensitivity, light weight, small size, easily array and wavelength encoded. Although the applications in temperature and pressure measurement have been achieved, it is well known that the application in harsh environments (eg. high temperature and high pressure) with high resolution and sensitivity remains a big challenge.Systematic investigation on the fabrication and metal-coated technology of fiber Bragg grating (FBG) was presented in this dissertation. The sensing principle and interrogation technique were studied theoretically and experimentally. And the applications of FBG sensors in high pressure and high temperature measurements were successfully realized. The main results are listed as follows:The general aspects of FBG, including development, classification, cross-sensitivity problem, sensing application and interrogation, have been systematically reviewed.The fundamental sensing theory and fabrication technology of FBG are also demonstrated. Based on orthogonal design, FBGs have been fabricated using UV-writing and phase mask technology. Mathematical statistical method is employed to analyze the experimental results that derived from the measurements. The optimal fabrication parameters are concluded. The well adaptation of our FBGs to sensing measurement was confirmed by the actual application in building model vibration tests. In order to achieve the most effective integration between FBG and sensor devices, and the better result in high-temperature environment measurement, metal-coated technology is developed. The metal-coated FBGs (MFBGs) are obtained by combining the technology of electroless plating nickel and electroplating tin. The effects of metal-coated parameters on the quality of metal plating are studied. At the same time, the optimal conditions are obtained. MFBG strain gauges are fabricated and used in the real-time health monitoring on the bridge. The results indicated that all of the sensors have good reliability and stability, which are essential for the safety of the bridge.Using elasticity strain canister principle, a MFBG pressure sensor has been designed and fabricated, which can be used in the measurement of high temperature and high pressure enviorment. Moreover, the designed system structures are demonstrated in detail. Special thin-wall strain cylinder structure is introduced in the sensor system, and it enhanced the measuring range of pressure and temperature. The most theoretical result of pressure for stainless steel material Crl8Ni9 is 63MPa, calculated by finite element analysis software ANSYS. The measurement ranges of actual pressure and temperature are 0～42MPa and 20~230℃, respectively. Meanwhile, the cross-sensitivity of pressure and temperature is solved effectively.Finally, based on matching filtering interrogation method, a simple and cantilever beam tuning scheme is put forward. This interrogation system is analyzed and designed. The fabricated interrogation device has the advantage of high-resolution and low cost.