GaAs traveling-wave electrooptic (EO) modulators based on capacitively loaded coplanar strips (CPSs) have been extensively modeled, and near-optimal designs are presented. The modulator operates in a push-pull mode, and the electrodes are coupled capacitively in series via the doped under layer. The best design reported herein has asymmetric CPSs 2 cm long and generated a figure of merit of about 9.36 GHz/V. This figure of merit is an improvement by a factor of about 2.5 over the best design reported to date for this modulator architecture. Modulator bandwidths in the range of 40-70 GHz (3 dB electrical) are predicted for various designs; the corresponding optical bandwidths are in the range of 75-110 GHz (3 dB optical).
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