Liquid crystal filled optical fibers offer multiple ways to control optical signals by actively modulating the optical properties of the liquid crystal. This thesis describes the coupling of light guided inside a solid glass core fiber with liquid crystal filled inclusions. By applying an external electric field, the interaction of the guided light with the liquid crystal can be controlled. The first part of this thesis is concerned with microstructured optical fibers, which consist of a solid glass core and a single liquid crystal inclusion. The investigation of these microstructured fibers is focused on the characterization of electrically induced polarization effects of light in the visible and infrared spectrum. The experimental results are compared to the predictions of the coupled mode theory. In the second part, photonic crystal fibers are investigated. These fibers possess a central glass core, which is surrounded by a periodic array of liquid crystal inclusions. The main focus lies on the propagation characteristics of optical pulses such as group velocity and dispersion. These properties can be influenced by an external electric field. Finally, the possibility of four wave mixing in these fibers is discussed, which would allow for an electrically tunable frequency conversion.