The performance of the TW-MZM also depends on the matching between the effective index of the optical waveguide and the electrical transmission line. A similar analysis using OptSim Circuit would show that ideal matching results in nearly infinite bandwidth while even a small mismatch (say, 10%) can adversely affect the performance.
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 K. Zu, V. Saxena, X. Wu, and W. Kuang, “Design considerations for travelling-wave modulator-based CMOS photonic transmitters,” IEEE Transactions on Circuits and Systems – II: Express Briefs, vol. 62, no. 4, pp. 412-416, April 2015.