提出了一种测量液体折射率的光纤液体分析仪。利用液体表面张力的作用,在光纤探头端形成一个液滴。该液滴的作用相当于一个平凸透镜,发射光纤出射的光经液滴表面折射、未扰液面的反射和液滴表面的再次折射后进入接收光纤。根据菲涅耳公式,光线在各个界面的透射系数和反射系数与液体的折射率有关,且对于不同的液体,光线的传输路径不同。基于球面折射成像和反射式强度调制原理,分析了光线的传输路径,并建立了接收光纤接收到的光强与液体折射率的关系模型。对不同浓度的NaCl溶液进行了测量,实验结果符合理论预期,表明该方法可以用于液体折射率的测量。

A novel method for measuring refractive index of liquids based on a liquid drop formed at the end of fiber sensing probe is reported. The effect of the drop is like a plane-convex lens whose refractive index equals to that of the tested liquid. The light from transmitting fiber successively experiences refraction of the liquid drop to air interface,the air to liquid drop plane interface and the air to liquid drop,and is finally collected by the receiving fiber. According to Fresnel′s formula,the transmission coefficient and reflection coefficient at these interfaces dependes on the refractive index of the tested liquid. Based on spherical refraction imaging and reflective intensity modulation,the light transmission path is analyzed,and the mathematical mode between the intensity of the collected light and refractive index is set up. NaCl solutions with different concentrations are tested. The experimental results indicate that the method can be used for measuring the refractive index of the liquid.