Parameters Design And Analysis Of Optical Fiber Evanescent Wave Absorbing Sensor

In recent years, optical fiber evanescent wave absorbing sensor has made rapid progress. Comparing with the traditional direct absorption cell, it has several advantages, such as remotely sensing, high sensitivity, in-situ measuring, simply designing, small volume and low cost. It is widely used as chemical sensor and biosensor. The evanescent wave absorbing sensor is based on attenuated total reflectance (ATR). Sensors were made by single mode and multimode Silica fiber and Plastic-Clad Silica fiber according to sensitivity requirement. Single mode optical fiber is brittle because core diameter is too small, so multimode optical fiber is selected. In fact most of the studies were trying to get better sensitivity.Less-mode optical fiber evanescent wave absorbing sensor was studied based on optical waveguide theory. A theoretical way to show the effect of the main parameters was described. The core radius in the sensing region, the refractive index of absorbing medium, and the refractive index of core affect field distribution of the mode. When the core radius is smaller, and the refractive index of absorbing medium is few different with refractive index of core,the modal power in the cladding will be higher and more energy react with absorbing medium. The percentage power of mode and the excited coefficient of the light source were affected by beam's radius and slope angle. Furthermore the sensitivity of sensor was affected.Sensor was made by micromachine technologies. The sensitivities under different refractive index of absorbing medium, different core radius and different slope angle are measured through the experiments. The experimental results correspond with the theory ones.