Design of Tunable Couplers Using Magnetic Fluid Filled Three-Core Optical Fibers

In this letter, we propose a novel concept to achieve tunable coupling characteristics in three-core optical fiber couplers, where two cores with 8 /im in diameter acting as input and output ports are separated by a magnetic fluid filled hollow- channel which acts as a resonator, by externally varying the magnetic field. Numerical simulations carried through the finite element method and the coupled mode theory reveal that a short coupling length of 4.1 mm is required to achieve a complete transfer of power from the input core to the output core at a magnetic field of ~ 82 Oe. As the external magnetic field is varied, the resonant condition is changed which affects the fraction of power at the output port. A good agreement between derived analytical results and numerical results is found.