56-Gbit/s 40-km optical-amplifier-less transmission with NRZ format using high-speed avalanche photodiodes

We present the world's first demonstration 56-Gbit/s 40-km transmission with NRZ format using a high-speed avalanche-photodiode-based optical receiver. The receiver exhibited a minimum sensitivity of -20.8 dBm after 40-km transmission at the BER of 2.3×10-4.