Tunable photonic devices using microstructured optical fibers

Microstructured optical fibers display unique optical capabilities for manipulating light. These fibers, typically all-silica, incorporate numerous airholes that run along the length of the fiber in the cladding region. By gaining insight into the properties of these modes, we demonstrate fiber designs whose characteristics are unique and provide a platform for future photonic devices. By introducing certain materials into the airholes and by engineering the fiber, it is possible to actively manipulate light, creating the potential for novel hybrid all-fiber optical devices in which tunability is incorporated into the fiber itself.; To manipulate light propagating in the microstructured optical fiber, an efficient interaction between the field and tunable materials infused in the airholes is required. This interaction can be achieved by creating sections along the fiber where the optical mode field is sensitive to the presence of active materials. One way is to spread the mode field out of the core and into the cladding by tapering the fiber. The mode field then interacts with the airholes and its guiding properties become sensitive to materials infused into the airholes and along the tapered section. The other method involves coupling the core and cladding modes using a grating written in the core of the fiber. The cladding modes have their field distribution in the cladding and therefore are sensitive to any change in the cladding/airhole interface.; To obtain tunability, materials such as polymers with a temperature dependent refractive index or microfluids are incorporated into the airholes of the microstructured optical fiber. Tunability is achieved by changing the refractive index of the polymer or by displacing the microfluids along the airholes to certain locations where overlap with the mode field occurs.; In this work, devices such as tunable filters and attenuators, based on the dynamic position of fluids along the length of the fiber or on local changes of the refractive index of polymers are demonstrated. Tunable polarizers are also achieved by introducing active materials into specific airholes to break the symmetry of the waveguide. One may tune the asymmetry by changing the index of the material (polymer) or displacing the material (micro-fluid) along the fiber. Further, gratings formed by periodic structures introduced in the airholes of the microstructured optical fiber are described in the context of tunable filters.