Usability of a 5G Fronthaul Based on a DML and External Modulation for M-QAM Transmission Over Photonically Generated 40 GHz

In this paper, we numerically and experimentally present the bandwidth constraints of a cost-effective 5G mobile fronthaul based on a directly-modulated laser for data modulation and a Mach-Zehnder modulator-based optical double sideband with carrier suppression scheme for optical millimeter wave (mmW) signal generation. The effect of chirp, fiber dispersion and a combination of both on different bandwidth M-Quadrature Amplitude Modulation (M-QAM) signals, i.e. M = 4, 16 and 64, at 40 GHz has also been investigated. Simulation results are first carried out to evaluate the impact of higher chirp of the directly-modulated laser on the link performance as a function of modulation format and signal bandwidth. We then experimentally demonstrate the same scheme transmitting M-QAM signals with bandwidths ranging from 50 to 1000 MHz over a 10 km long single mode fiber. Both experimental and simulation results show that larger signal bandwidths lead to higher optical power penalties due to the combined effect with the error vector magnitudes (EVMs), however still satisfying the required limits of 3GPP standard for all QAM signals. Experimental measurements also show the feasibility of including free space optics links in the optical distribution network with no further significant penalties. Finally, a multiband signal (three-band) transmission is demonstrated leading to an increase of the total bitrate with the measured EVMs are well below the EVM requirement.