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 the 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 simply follow, to a remarkably good approximation, the thickness profile of the film. This temperature distribution produces a chirp with the same geometry and at a rate that can be adjusted by changing the current. Finite element modeling illuminates essential aspects of the flow of heat in the structure, and optical measurements demonstrate some of the important characteristics of the devices.