After introducing fronthaul requirements in Centralized Radio Access Network architecture, different fronthaul solutions are presented. Perspectives for medium term evolution including fronthaul supervision are hinted as well as challenges for future mobile evolution towards 5G.

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Optical fiber is the required technology for Radio Access Network (RAN) backhaul and fronthaul. We report the evolution of RAN equipment including the advent of virtualization and an investigation of the required architecture and optical access technologies.

A DWDM self-seeded source achieves transmission in the O-band up to 90km SSMF at 2.5Gbps. Moreover, a "face-to-face" self-seeded architecture permits to realize transmissions at 2.5Gbps with extra-long optical cavities reaching 70km of SSMF.

Operation of a network-embedded colorless selftuning transmitter for wavelength division multiplexing (WDM) networks is experimentally demonstrated at 10-Gb/s data rate. Colorless operation is achieved by self-seeding an O-band reflective semiconductor optical amplifier (RSOA) with the feedback signal reflected at the remote node WDM multiplexer filter. In particular, the transmitter exploits a 2-Faraday rotators configuration to ensure polarization insensitive operation and allowing for the exploitation of high gain O-band RSOAs, which present a very high polarization dependent gain. Two different multiplexers and various lengths of drop fibers constituted the network-embedded transmitters. Transmission up to 72 km of standard single mode fiber has been demonstrated at 10 Gb/s, confirming the absence of chromatic dispersion penalties as expected from the choice of the O-band operation. Index Terms-Passive optical network (PON), reflective semiconductor optical amplifier (RSOA), colorless transmitter, fronthaul.