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The Fiber Bragg grating(FBG) sensors have a lot of advantages such as electrically passive operation,EMI immunity,high sensitivity,wavelength-encoded,and multiplexing capabilities.The FBG sensors have been widely applied in civil engineering,oil production, military and navigation by measuring parameters such as load,strain,temperature,and vibration.Hermetic encapsulation of FBG sensors is very important because the silica glass fiber is fragile.Traditionally,FBG sensors are sealed with macromolecule glue.The polymer-coated layer of FBG provides high short-term strengths.However,when the normal FBG is stressed in a humid or high-temperature environment,long-term strength degradation occurs because of the slow crack growth.It greatly limits the applicable fields of FBG sensors. However,the metal-coating of glass fiber has many advantages which polymer does not have. For instance,it has better wear resistance,corrosion resistance,thermal stability,electrical resistance.There are many methods to achieve metallization of optical fiber,including sputtering, plasma deposition,chemical vapor deposition(CVD),and electroless plating.The electroless plating method is extensively used because it’s advantages such as low cost,low processing temperature,good ability to form alloys and high fatigue resistance.The aim of this article is to investigate an approach of deposit Ni-Cu-P ternary alloy on silica glass fiber with electroless plating method,and discuss the effect of activation,additives, dispergation process,plating solution and pH value on the quality of the coating layer.And the temperature sensitivity of metalized FBG was measured,a method to solve cross-sensitivity is discussed.Following experiments have been performed:(1) Pretreatment of silica fiberThe silica fiber was cleaned,roughed and activated through pretreatment,thus the autocatalysis reacted continuously.Pretreatment includes cleaning,roughing,heat treatment, sensitizing and activating.Each step would have a significant influence on the coating layer.(2) Electroless Ni-Cu-P plating on the surface of FBGThe optimal plating solution was determined and affects of each ingredients on the coating layer is discussed.(3) Measuring temperature sensitivity of metalized FBGThe temperature sensitivity of metalized FBG was measured and comparison between bare FBG,Ni-P coated FBG and Ni-Cu-P coated FBG was made.
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