RoF-Based Mobile Fronthaul Networks Implemented by Using DML and EML for 5G Wireless Communication Systems

We investigate the feasibility of implementing a mobile fronthaul network (MFN) based on the radio-over-fiber (RoF) technology for the fifth generation wireless communication systems cost effectively by using either directly modulated lasers (DMLs) or electroabsorption modulated lasers (EMLs) operating in the 1.55-μm window. The results show that the performance of the RoF-based MFN implemented by using DMLs is primarily limited by the composite second-order (CSO) distortions arising from the interplay between the DML's adiabatic chirp and fiber's chromatic dispersion. Thus, when we implement the RoF-based MFN by using the currently available commercial DML, its reach could be limited to ~5 km due to the CSO distortions. To increase this reach, we can utilize the DML having a very small adiabatic chirp (or the optical dispersion compensation or CSO cancelation technique). On the other hand, when we implement the RoF-based MFN by using EML, its performance is limited mostly by the relatively poor linearity and low output power of EML rather than the chirp. For example, if we increase the optical modulation index to compensate for the low output power of EML, the distortions caused by the EML's nonlinear transfer curve can also be increased. Thus, for the use in the RoF-based MFN, it would be highly desirable to increase the output power of EML as much as possible. For a demonstration, we successfully transmit 24 100-MHz-bandwidth filtered orthogonal-frequency-division-multiplexing signals over 20 km of the standard single-mode fiber by using an EML transmitter with 7-dBm output power.