Tunable single phase-shifted and superstructure gratings using microfabricated on-fiber thin film heaters

Tunable optical filters have applications in wavelength-division multiplexing, optical sensing, and fiber lasers. Fiber gratings that are tuned by resistive Joule heating of a thin metal film deposited onto the fiber are attractive because of their compactness, low power consumption, and controllable optical characteristics. In particular, the small effective axial thermal diffusion lengths in these systems allow complex heating profiles to be defined simply by controlling the local film thickness. In this paper, we demonstrate devices with single and multiple thermally actuated phase-shifted elements. The measured reflection spectra of these devices compare favorably with simulations based on a one-dimensional model of heat flow and confirm the heat flow characteristics expected from theory.