Study On Sensing Technology Of Metal Coating Fiber Bragg Grating

Due to the technology advantage of electromagnetic interference resistance, high sensitivity, small volume, light weight, stability, and the long distance of signal transfer, etc., fiber grating sensor have been more and more widely used in dynamics, spacecraft, marine shafting, civil engineering structures, electrical industry, medicines, chemical sensing and so on. First, due to the bad environment of adhesive which encapsulates the fiber grating, the air-tightness, adhesive strength, endurance and heat resistance become worse. What’s more, as the adhesive is aging, the reaction transmissibility will become worse. Also, because thermo-optical and thermal expansion coefficient of the fiber grating and coating material are small, the temperature sensitivity is quite low. Using fiber grating as sensor, the temperature resolution is not so high. To the optical fiber and encapsulate grating, especially metal packaging, can improve its temperature sensitivity and service life effectively. This article is focus on the research on the metal packaging, Long-term stability after encapsulated, temperature sensitivity and other sensing characteristics, and the main jobs are as follows:(1)1. Based on the features of optical fiber and grating, and existed equipment in our library, the basic process of copper surface mounting on optical fiber and grating is fixed(2) After repeated experiments and analysis, the best plating liquid ingredients and current density are defined, also, the better copper coat will be gained.(3) Research on the feasibility of laser welding on copper coated optical fiber and grating.(4) Long term stable and repeated researches on optical fiber and grating have been done, by using the cantilever and stretcher.(5) The sensitivity and stability of copper coated optical fiber and grating both under high and low temperature have been researched.Through a lot of experiments, the article draws the following conclusions:the surface of copper-coated fiber and grating is bright, uniform and fine, and adhesion between the copper layer and the fiber is strong, which protects the fiber and grating, and also can be used as a novel sensing device and researched.Laser welding experiment verifies that, using laser welding to encapsulate copper-coated fiber and grating is completely feasible.In the strain experiment, at the same load, the maximum average error of metal encapsulated copper-coated fiber and grating is2.25pm; the maximum average error of ordinary DG-4glue-encapsulated fiber and grating is7pm; the linearity degree of metal encapsulated copper-coated fiber and grating is0.9999, while the linearity degree of DG-4glue-encapsulated fiber and grating is0.9951; the initial wavelength drift value of copper-coated fiber and grating is less than3pm, and the average drift volume is2pm; the initial wavelength drift value of DG-4glue-encapsulated fiber and grating is less than6pm, and the average drift of4.75pm; the initial wavelength drift value of DG-3S glue-encapsulated fiber and grating is less than11pm, and the average drift volume is5.75pm. All the data verified that, sensor used by copper-coated fiber and grating is much more stable and repeatable.The temperature sensitivity of copper-coated fiber and grating is3.25times of ordinary fiber and grating at low temperature (liquid nitrogen); at high temperature, the sensitivity of copper-coated fiber and grating is about25pm/℃, which is2.5times of10pm/℃. Experiments verify that, for the copper-coated fiber and grating, the measurement is reliable at both low and high temperature, even its sensitivity and linearity is good.