Environment Refractive Index Sensor Based on Microfiber Coupler
微米光纤耦合型环境折射率传感器

An environment refractive index sensor composed of two identical subwavelength-diameter tapered optical fibers is proposed. Due to the presence of large part of evanescent-wave close to the surface of microfiber, a slight change of the refractive index of the ambient medium will result in an evident change of the power ratio at output ends of two microfibers closely coupled. In the experiment, the sensor coupling region is immersed in a glucose solution and the solution concentration variation is detected by measuring the output ratio of light power at two ends of the coupler. The experiment result shows that the sensor is with a sensitivity as high as 1.58/mol L-1. In addition, the theory indicates that the sensitivity of this sensor can be further enhanced by reducing the diameter of microfiber, or by increasing the wavelength of the incident light, or by increasing the length of coupling region.