Low-Pattern-Dependence Prechirp Optical Modulation by Using Saturation Behaviors of SOA-Integrated EAM

Low-pattern-dependence and chirp-control optical modulation using a monolithic integration of devices is proposed and demonstrated in this study. The monolithic integration consisting of semiconductor optical amplifier (SOA) and electroabsorption modulator (EAM) is used. As high enough optical power is coupled into a device to reach saturation condition, the field driving operation in an EAM (reversed-bias diode) and the current injection operation in an SOA (forward-bias diode) will have mutually complementary optical properties because of the reversed carrier dynamics, enabling optical waveform and its phase control. A 100 μm long EAM integrated with a 700 μm long SOA is fabricated for the device under test. A 10 Gb/s non-return-to-zero pattern trains are used for examining time-evolution optical waveform. A distorted waveform by gain saturation of SOA can be corrected by reversely predistorted signal modulated by EAM, sending out a nondistorted optical waveform. An improved signal-to-noise ratio (SNR) of data pattern from 8.8 to 10.8 is obtained by adjusting bias points of EAM and SOA, confirming pattern waveform enhancement. Total negative chirp of 6.2 GHz is also obtained from EAM and SOA, where -2.6 GHz frequency shift from SOA is extracted. Setting EAM and SOA in a negative chirp regime, a successful 43 km (photoreceiver limit) error free data transmission is found, suggesting that such an integration chip can enable simultaneously amplitude, pattern and prechirp optical processing, and showing high potential in the application of metro-area optical network.