紫外写入光纤光栅应变传感特性研究

Strain Sensing Properties of UV-Written Fiber Grating

采用紫外写入光纤 Bragg光栅研究其应变传感特性。光纤光栅可借助外界应力引起轴向应变和折射率变化造成光栅 Bragg反射波长移动。在温度 2 0℃ ,利用波长在 4 0 0～ 1 80 0 nm范围色散的光谱仪并用In Ga As P/ In P ELD作宽带光源 ,从实验上测量了光纤光栅的应变与 Bragg反射波长间的关系 ,结果表明Bragg反射波长移动与光纤光栅外界应力变化在 1 55.4～ 1 56.8nm波长范围呈线性。外界应力引起的光纤光栅灵敏度为 1 .2 1 1 pm/ με,与理论计算结果基本一致。利用光纤光栅的应变传感特性 ,设计并制备了压力传感头。它由上、下两金属板和上金属板上可精密调节的两螺旋组成。光纤光栅的两端被分别固定在上、下金属板的定点上。上金属板可通过精密调节螺旋产生微小升降并作为荷重台面。在光纤伸长应变范围内通过螺旋调节 ,使光纤光栅产生尽可能大的伸长 ,以保持测试有较大线性范围 ;同时在 2 0℃恒温条件下 ,确定压力传感头的测试零点。用此压力传感头 ,在同一板材的不同厚度测量了压力变化引起 Bragg反射波长的移动 ,表明 :选择不同材料或同种材料不同厚度的金属板材可设计不同量程范围。这种压力传感头可适应不同量程的压力或荷载测量。

UV written fiber Bragg gratings is adopted to study its strain sensing properties. Axial strain and refractive index changes of fiber gratings are caused by external strains so that Bragg reflected wavelength is shifted. The strain of fiber gratings vs. Bragg reflected wavelength is measured experimentally at 20℃ using spectrum analyzer that can disperse in the region of 400～1800nm wavelength and using InGaAsP/InP light emitting diode as bandwidth source. It shows that Bragg reflected wavelength shift vs. external strain changes of fiber gratings is linear in the range of 155 4～156 8nm wavelength.The sensitivity of fiber grating to the external strains is 1 211pm/με, which basically agrees with theoretical calculation. By the using strain sensing properties of fiber grating, the sensing head of pressure has been designed and made. It consists of a upper and a below metal plates and two fine adjustable screws on the upper metal plate. Two ends of fiber gratings are fixed respectively on two fixed points. The microrise and microdrop of the upper metal plate which acts as load stage can be regulated by fine adjusting screws. By adjusting the screws in stretch strain region of the fiber gratings,the fiber grating becomes as long as possible to keep larger linear region of the sensing head. And tested zero of the sensing head is determined at constant temperature of 20℃. The shift of Bragg reflected wavelength caused by pressure changes are measured with sensing head under two same material plates with different thicks. It shows that different gauge regions can be designed by chosing metal plates with different material or same material metal plates with different thicks. The sensing head of pressure can be widely applied in the measurement of different gauge regions and loads.