Advances and challenges in vector modulation technologies

This paper describes recent progress of high-speed vector optical modulation technologies based on Mach- Zehnder interferometer devices. Multi-level quadrature amplitude modulation signal can be synthesized by using parallel Mach-Zehnder modulators. We can generate complicated multi-level optical signals from binary data streams, where binary modulated signals are vectorially summed in optical circuits. Modulation speed can be higher than 80 Gbaud by using a dual parallel Mach-Zehnder modulator with thin lithium niobate substrate.