Synthesis and Properties of Vanadium Dioxide Thin Films for use as Optical Switches

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The internet primarily runs on optical fibre communication networks; only optical fibers can satisfy the ever increasing demands for bandwidth. At each end of the fibre optic cable are a variety of devices for manipulating the light beam including beam multiplexers and other steering, switching, and selecting devices. There are a variety of technologies for designing these devices such as MEMS, liquid crystals, acousto-optics, etc. One of the best technologies utilizes materials whose optical properties change in response to another electrical or optical signal. For example, a material with a variable index of refraction can be used in an interferometer to change from constructive to destructive interference thereby effecting an optical switch. Or, a beam selector can be made from a material whose reflectivity changes with electric field. Materials based devices are robust, fast-acting, small, and relatively simple to manufacture compared to other technologies. The whole idea in this project is to have new-technology optical switches that will be controlled by an electrical input. These optical switches would be based on a new technology (phase transition technology described below) and would be enhancing the efficiency of optical switching in optical networks. Transition metal oxide (MO) material system that is of particular interest in this project is the oxides of vanadium. Vanadium oxide exists in a number of stoichiometries. The dioxide VO2 has a crystalline phase transition from monoclinic to tetragonal at 340K; the (low-temperature) monoclinic phase is insulating and the tetragonal phase is metallic. The metal-insulator transition in VO2 can also be induced by an applied electric field. Thus VO2 is a prime candidate for use in an electronically controlled optical switch. The research will have three parts: preparation of VO2 thin films, characterization, and prototype device development and testing. The preparation will be by vacuum deposition - sputtering from a vanadium target in the presence of oxygen gas. VO2 films be deposited by sputtering and their optical properties will be examined with and without an electric field to explore the field induced optical switching in these devices.