小直径光纤光栅的研制及传感交叉敏感研究

Development of a Simultaneous Strain and Temperature Sensor with Small-Diameter FBG

研究了小直径光纤光栅的研制以及传感中的温度应变交叉敏感问题。首先根据耦合模理论,分析了小直径光纤Bragg光栅光谱特性,确定了包覆层为80μm的单模光纤加工成中心波长为1 528nm的Bragg光栅的栅长及周期,并研究了小直径光纤光栅与解调设备之间的连接方式。其次利用等强度梁的变形特点,结合矩阵法,提出基于等强度悬臂梁双Bragg光纤光栅矩阵算法,对小直径光纤Bragg光栅的交叉敏感问题进行研究。温度和应变的实验辨别误差分别为5%和6%。实验结果表明,该方法可以分离温度和应变对光纤Bragg光栅传感的影响。采用该方法去除交叉影响,K矩阵始终存在逆矩阵,因此对所采用的光栅无特殊要求,从而扩大了光纤光栅选用范围,并将温度和应变识别出来。

Manufacture of the small diameter FBG was designed.Cross sensitivity of temperature and strain at sensing point was solved.Based on coupled-mode theory,optical properties of the designed FBG were studied.The reflection and transmission spectra of the designed FBG in small diameter were studied A single mode optical fiber,whose cladding diameter is 80 μm,was manufactured to a fiber Bragg grating（80FBG）.According to spectrum simulation,the grating length and period were chosen as the wavelength was 1 528 nm.The connector of the small diameter FBG with demodulation was designed too.In applications,the FBG measures the total deformation including strain due to forces applied to the structures as well as thermal expansion.In order to overcome this inconvenience and to measure both parameters at the same time and location,a novel scheme for simultaneous strain and temperature sensor was presented.Since the uniform strength beam has same deformation at all points,a pair of 80 FBG was attached on a uniform strength cantilever.One of the FBG was on the upper surface,with the other one on the below.Therefore,the strains at the monitoring points were equal in magnitude but of opposite sign.The strain and temperature in sensing point could be discriminated by matrix equation.The determination of the K is not null and thus matrix inversion is well conditioned,even the values for the K elements are close.Consequently,the cross sensitivity of the FBG with temperature and strain can be experimentally solved.Experiments were carried out to study the strain discriminability of small-diameter FBG sensors.The temperature and strain were calculated and the errors were,respectively,5% and 6%.