112-Gbit/s PDM-PAM4 transmission over 80-km SMF using digital coherent detection without optical amplifier

In this work, we experimentally demonstrated a 112 Gbit/s polarization-division-multiplexed (PDM) four-level pulse amplitude modulation (PAM4) transmission over 80-km single mode fiber (SMF) using digital coherent detection without optical amplifier and CD compensation for the short reach applications. Here, a signal-phase aided least-mean-square (SP-LMS) equalization algorithm is proposed to avoid the effects of carrier frequency offset and phase noise. Without additional carrier recovery algorithms, the PDM-PAM4 system shows good transmission performance. The received optical power (ROP) penalty is only about 0.2 dB after 80 km transmission comparing to back-to-back (BTB) transmission. A receiver sensitivity of −20dBm (at 7% FEC limit) can be reached after 80-km transmission.