Reconfigurable Silicon Photonics Integrated 16-QAM Modulator Driven by Binary Electronics

A novel silicon photonics integrated reconfigurable nested Mach-Zehnder interferometer including tunable splitters and four independent phase modulators has been designed and fabricated. The architecture enables the generation of offset-free phase-amplitude constellations such as QPSK and 16-QAM by employing simple binary signals with equal peak-to-peak amplitude. The adoption of tunable splitters introduces novel features such as reconfiguration of the output constellation without modification of the RF waveform settings, as well as compensation for imperfections related to fabrication tolerances. The solution presented in this paper is based on travelling wave MZIs and thermally tunable splitters based on doped rib waveguides heated by Joule effect. The scheme minimizes the complexity of the employed architecture together with one of the driving signals. Numerical analysis has been also conducted to better investigate the system behavior and parameter optimization, evaluating the impact of suboptimum settings that might occur in a real implementation. Experimental results show the generation of QPSK signals up to 28 Gbd and 16-QAM signals up to 20 Gbd with measured bit error rate below the conventional FEC level.