Fig. 1. System structure of conventional DD-OFDM (Tx, transmitter, Rx, receiver; PRBS, pseudo random bit sequence; DAC, digital-to-analogue conversion; LPF, low-pass filter; EDFA, erbium-doped fiber amplifier).

Fig. 2. Principle of DFT-spread OFDM modulation and demodulation.

Fig. 3. Experimental setup for a 32 Gbaud OFDM-QPSK signal with 7 km SMF-28 transmission utilizing single-arm MZM in DD system (EA, electrical amplifier; OSC, oscilloscope).

Fig. 4. Constellation comparison of a 32 Gbaud QPSK after 7 km SMF-28 transmission when the input power into the PD is −6.5  dBm.

Fig. 5. Constellation comparison of a 32 Gbaud QPSK after 7 km SMF-28 transmission when the input power into the PD is −8.7  dBm utilizing different technologies.

Fig. 6. Curves of BER versus input power into a PD utilizing different techniques.