Tunable optical fiber filters with magnetic fluids

This letter presents a tunable optical fiber filter based on a long-period grating (LPG) by applying a magnetic field on a magnetic nanoparticle fluid. The movement of the magnetic fluid jacket surrounding the fiber cladding controlled by an applied magnetic field results in a variation of the external index between that of the magnetic fluid and air. As a result, the attenuation band of the LPG is shifted. The observed center wavelength shift of the attenuation band is as large as 7 nm, which can cover eight dense wavelength division multiplexing channels (100 GHz channel spacing). Repeatable transport of a magnetic fluid at a switching rate of 1 Hz is demonstrated.