Integrated Reconfigurable Coherent Transmitter Driven by Binary Signals

A novel InP monolithically integrated transmitter composed of a tunable distributed Bragg reflector laser and a reconfigurable IQ modulator with tunable power splitters has been designed, fabricated and tested. The transmitter architecture allows, in principle, 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 enables reconfiguration of the output constellation and compensation for imperfections related to fabrication. The solution presented in this paper minimizes the complexity of the employed architecture together with the one of the driving signals. Numerical analysis has been conducted to predict system behavior and evaluate the impact of sub-optimum settings that might occur in a real implementation. Experimental results show the generation PM-QPSK signals at 10 Gbaud when using the integrated DBR laser and at 32 Gbaud when using an external low-phase-noise laser. Unfortunately, the generation of 16-QAM signals, which can be in principle realized with this novel PIC, was not possible in practice because of significant spurious amplitude modulation in the electro-optic phase modulators.