Distributed on-fiber thin film heaters for Bragg gratings with adjustable chirp

This letter describes a fiber Bragg grating device that has tunable chirp. It relies on a distributed on-fiber resistive heater that consists of a thin metal film deposited onto the outer surface of a bare fiber; the thickness of this film varies continuously with position along the fiber. The physics of heat flow and diffusion in these structures leads to temperature gradients that follow, to a remarkably good approximation, the local resistance of the tapered metal film. This temperature distribution produces a chirp with a geometry that is defined by the thickness profile of the film and at a rate that can be adjusted by changing the current. Finite element modeling illuminates aspects of the flow of heat in these structures, and optical measurements demonstrate important characteristics of the devices. (C) 1999 American Institute of Physics. [S0003-6951(99)02221-4].