Novel Materials for the Information Highway

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Novel Materials for the Information
Highway Tobin J. Marks and Seng-Tiong Ho
Northwestern University, DMR-0520513/DMR-0076097
(MRSEC IRG 1)
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
electro-optic modulators. Electro-optic
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 Vp, the voltage needed
to shift the phase of light by p), 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, Vp 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.