Achieving Higher Modulation Efficiency in Electrooptic Polymer Modulator With Slotted Silicon Waveguide

Journal of Lightwave Technology (Impact Factor: 2.97). 12/2011; 29(21):3310 - 3318. DOI: 10.1109/JLT.2011.2168385
Source: IEEE Xplore


Silicon slot waveguide based Mach-Zehnder interferometric modulators with electrooptic polymers in the slot have the advantage of low half-wave voltage-length product (Vπ *L). Several key aspects of this unconventional electrooptic polymer modulator design to optimize the modulator performance are studied in this work. Both computer simulation and experiments have been conducted to understand the relationship between modulator performance such as modulation efficiency, optical loss and the waveguide design parameters. Techniques to achieve efficient poling of electrooptic polymers in the silicon slot waveguide have been developed. The doping of the silicon to enhance conductivity for efficient poling and the trade-off between conductivity and optical loss are experimentally investigated. Surface passivation of silicon nanophotonic structures has been found to be effective in improving poling efficiency. By applying these techniques to a silicon slot waveguide Mach-Zehnder modulator, a low Vπ*L of 0.52 V ·cm has been achieved. Finally travelling wave electrode designs have been evaluated and the results show that the bandwidth is mainly limited by the attenuation of the radio frequency signal in the electrode and a standard coplanar waveguide electrode design is able to reach 20 GHz in modulators of silicon slot waveguide embedded in electrooptic polymer.

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    • "Ω·m, respectively [25]. The relatively lower concentration of 1×10 17 cm -3 in the waveguide region is chosen to avoid significant impurity-induced scattering optical loss [26] [27]. Fig. 1 (d) shows a simplified equivalent circuit, in which the slot can be represented by a capacitor C and the silicon PCW region by R. Based on this equivalent circuit, as the modulation frequency increases, the percentage of electric potential dropped across the slot is supposed to decrease due to the reduced slot impedance. "
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