Vector modulation technologies for high-speed optical transmission

We present lightwave modulation techniques for high-speed signal generation in digital and analogue applications. Advanced modulation formats, such as differential quadrature phase-shift-keying, amplitude- and phase-shift-keying, quadrature-amplitude-modulation etc, were investigated to obtain enhanced spectral efficiency, where Mach-Zehnder modulators (MZMs) are commonly used to control optical amplitude or phase in lightwave signals. In this presentation, we describe lightwave modulation techniques for high-speed signal generation based on integrated MZMs. By using quad-parallel MZM, high-speed optical 16-QAM signals can be synthesized, where the baud rate and bit rate were 12.5 Gbaud and 50 Gb/s. Impact of extinction-ratio (ER) of MZMs on advanced modulation formats is also discussed. Imbalance in the MZMs due to fabrication error can be compensated by using a dual-parallel MZM. ER can be higher than 70 dB.