Optimization of Micro-Optical Fiber-Based Mach–Zehnder Interferometer RI Sensor

The electric field in micro-optical fibers is affected by and is, therefore, an indicator of the ambient refractive index. Therefore, microfibers are widely used as refractive index sensors. In this paper, we studied the electric field of the microfiber, and the influence of the cladding radius was explored by using the semiweakly guide approximation. Next, the coupling ratio and the coupling radius were introduced as two indicators of the coupling efficient between the microfiber and the ordinary fiber. The results showed that the coupling ratio increases exponentially with the decrease of the cladding radius, and a sudden decrease of the coupling radius occurs when the cladding radius declines to a certain value. These results suggest that a stronger interference is available by a careful design of the cladding radius. The method introduced in this paper is also suitable to analyze the electric field under the influence of the surrounding refractive index for a given sensor.