Phase-balanced differential vector modulation by laser and electroabsorption modulator

Directly modulated laser can be used as phase modulator due to chirp effect. However, accompanying amplitude modulation also results. By using EA Modulator in combination, light amplitude may be compensated enabling both amplitude and phase modulation of lightwave, which is an alternative method to conventional IQ modulator. Since light phase is proportional to intensity, we propose cumulative phasebalance coding to solve the limitation in the laser operating range for differential M-PSK and M-QAM modulation. The technique applies parallel DC-balance coding with phase-balance symbol mapping. The cumulative phase in high-order differential modulation is always bounded, it is for the first time, to our knowledge