Interference signal analysis for bi-tapered fiber sensor

In this paper the characteristics of bi-tapered optical fibers for biomolecular sensing are considered. This highly sensitive fiber sensor can be used for the label-free detection of biomolecules and for refractive index sensing. The presence of bi-tapered region with small diameter leads to the transformation of the fundamental mode energy into the energy of higher-order modes. The availability of multiple modes creates an interference pattern in the output signal. The magnitude of the interference output signal depends on the geometric sizes of the sensor and on the refractive index of the surrounding medium. In this paper, Maxwell's equation for step-index fiber is considered and its numerical solution is performed. Based on the obtained numerical solution, the magnitude of the output signal is calculated depending on the refractive index of a biological solution. It is shown that the sensor studied has a high sensitivity to the change in the refractive index.