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Simple, low fluctuation voltage signal generation for 8-Gb/s quadrature amplitude modulation using dual-parallel Mach-Zehnder modulator

Optical quadrature amplitude modulation (QAM) has attracted considerable attention because of its high spectral efficiency. For high capacity, the modulation rate should also be enhanced, which requires the generation of high-baud-rate multilevel electric signals with high precision in amplitude. In this paper, we describe a method to reduce the amplitude fluctuation of the electric signal by adopting a return-to-zero (RZ) format. We also demonstrate 2.0-Gbaud optical QAM signal generation with a conventional dual-parallel MachZehnder modulator (DPMZM) driven by the electric RZ data signals.