DAC-less and DSP-free 20 Gb/s PAM-4 transmission based on a dual modulation scheme using DML and external modulation

The generation of DAC-less 20 Gb/s PAM-4 using a DML and an external modulator is demonstrated. This dual modulation scheme has been transmitted up to 75-km SSMF with similar performance to PAM-4 DAC transmitter.