Electrically tunable efficient broad-band fiber filter

We demonstrate a new type of fiber-optic electrically tunable filter that enables a tuning range of 60 mm with an electrical power of 0.17 W, corresponding to a tuning efficiency of approximately 320 nm/W. The device is based on a metal coated long-period fiber grating written in a specially designed "air-clad" fiber that is filled with a polymer whose index of refraction is a sensitive function of temperature. Resistive heating, caused by current flowing through the metal coating, heats the polymer and induces changes in its index of refraction; these changes induce shifts in the position of the attenuation dip associated with the long-period grating. The air-clad structure has two benefits: (1) it enables the introduction of temperature sensitive materials into the fiber thus enabling power efficient operation of the device and (2) ensures that the cladding modes are insensitive to the surrounding environment and thus are unaffected by the metal coating on the surface of the fiber.