200 Gb/s FSO WDM Communication System Empowered by Multiwavelength Directly Modulated TOSA for 5G Wireless Networks

In this paper, a 200-Gb/s free-space optical (FSO) wavelength division multiplexing (WDM) transmission architecture based on multiwavelength directly modulated transmitter optical sub-assemblies for 5G wireless networks has been proposed and demonstrated experimentally. Pulse amplitude modulation-4 (PAM-4) modulation format is adopted in our scheme to further improve system capacity. In order to demonstrate the feasibility of our scheme, the outdoor experiments with 25 Gb/s PAM-4 are tested in free space. With 8 × 25 Gb/s ~50-m outdoor transmission between the two buildings, the eye diagrams and bit error rates (BERs) are tested for one-hop system and forwarding system, respectively. For one-hop system, clear eye diagrams and stable BER performance are demonstrated in all the wavelengths. For the forwarding system, the values of BER with eight channels are measured lasting for 30 min that range from 1E-2 to 1E-3. The experimental results show that the scheme is feasible in FSO transmission system for 5G wireless networks. The advantages of integration, channelization, miniaturization, and low power consumption of the FSO WDM scheme present a promising result on constructing the future fronthaul/backhaul link for wireless cellular networks and optical access network extension.