All-Fiber In-Line Mach-Zehnder Interferometer for High-Resolution Sensing

The design of an in-line Mach-Zehnder interferometer (MZI) based on an S-taper structure in a fluoride optical fiber is illustrated. The tailored taper geometry promotes efficient mode coupling and interference within the transition regions, enabling a compact design with high sensitivity. The interferometer operating principle is investigated through numerical simulations using the Beam Propagation Method (BPM), focusing on modal evolution and interference behavior along the taper. An optimization process is conducted to determine the optimal waist diameter, lateral offset, and taper length for fringe visibility and stability. The simulation results demonstrate well-defined and stable interference patterns, confirming the viability of the proposed structure for integration into advanced fiber-optic sensing platforms.