Equalizer-free 2-km SMF transmission of 106-Gbit/s 4-PAM signal using optical transmitter/receiver with 50 GHz bandwidth

Using a fabricated optical transmitter and receiver with a 50-GHz bandwidth, we obtained a bit-error rate of less than 2 × 10⁻⁴ under error-free conditions using KP4 FEC without an equalizer.

I. Introduction

Recently, data-center traffic has been increasing explosively because of the rapid growth of cloud services. To cope with this trend, 400 gigabit Ethernet (400GbE) is currently being standardized by an IEEE task force [1]. 8 × 26.6-Gbaud 4-level pulse amplitude modulation (4-PAM) signals are sure to be used for 400GbE long-reach (such as 2-and 10-km) applications and optical transmitters operating at 50 Gbit/s have been reported [2]–[3]. However, there is a strong demand for a compact transceiver with low power consumption. And a smaller number of lanes is desirable if we are to reduce the power consumption and downsize the transceiver. Therefore, 100-Gbit/s/λ operation is needed.