Electro-optic(EO) modulators are essential components of all high-speed optical telecommunication networks and offer unrivalled means of modulating light beams with electrical signals. In this way, the “information highway” can carry dense amounts of information. In regard to achieving the goal of increased bandwidth (the information density that can be transmitted), new materials are needed for electo-optic modulators. EO modulators fabricated with many of the new ultra-high-performance materials that have emerged in the past several years are constrained because the metal electrodes used to modulate the signal strongly absorb the modulated light beam (accompanying figure at left). This requires the insertion of special “buffer” layers between the electrodes and active region, which unfortunately increases the voltages needed to modulate the light signal (expressed as VPi, the voltage needed to shift the phase of light by Pi), hence decreases the maximum possible bandwidth.
Professors Seng-Tiong Ho and Tobin J. Marks at Northwestern, working in collaboration with Professor Alex Jen of the University of Washington, have addressed this problem by replacing metal electrodes in proximity to the active region by transparent conducting oxide electrodes (ZnO and In2O3; accompanying figure at right). In this way, VPi of an polymer electro-optic modulator was decreased by a factor of 5.3. This approach should be general and represents a completely new and cost-effect way of enhancing the performance of optical data transmission networks.
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