This paper discusses hybrid fiber optic access network architectures combining baseband wireline and mm-wave channels. We focus on mm-wave radio over fiber (RoF) optical access network architectures which combine radio subcarrier multiplexing techniques to improve system efficiency with fiber dispersion mitigation provided by optical single sideband modulation techniques. Besides discussing the network architecture we focus on the intermodulation effects arising from the nonlinear characteristics of the optical modulator and the reflective semiconductor optical amplifier. Keywords: radio over fiber, reflective semiconductor optical amplifiers, optical single side band, optical access networks, wavelength division multiplexing.
INTRODUCTIONThe mm-wave fiber radio networks operating in the 60 GHz region are considered key players in the future telecommunication scenario [1]. The abundant unlicensed spectrum around 60 GHz offers the potential for multi-gigabit/s indoor Wireless Personal Area Networking (WPAN) removing the bandwidth limitation of the present wireless networks. Recently it was demonstrated that it is possible to produce low cost CMOS components and circuits operating at 60 GHz [2]. These advances combined with the increasing consumer demands for high-speed multimedia data communications, such as huge data file transmission and video services with high-definition TV have already lead to standardization activities such as the. IEEE 802.15.3c working group.The standard for 60GHz WPAN networks cover relatively short distances (10 -30 m) and supports high data rate applications (480 Mbit/s -3 Gbit/s). Due to the small coverage area, 60 GHz networks require a large number of base stations (BSs) to cover a service area. This requirement has led to the development of system architectures where functions such as signal/routing/processing, handover and frequency allocation are carried out at the central office (CO). The best solution for connecting the CO with BSs in such radio network is via an optical fiber network, now known as radio over fiber (RoF) network [3]. By exploiting high bandwidth wavelength-division multiplexing (WDM) networks, an integrated efficient fiber radio backbone network can be realized, where mm-wave carriers are modulated with data and placed on a particular wavelength channel and delivered to a specific BS.Currently, wired and wireless services are separately provided by two independent physical networks. However, with the fast evolution of wireless technology, ubiquitous and always on wireless systems in buildings are expected to emerge in the near future. Hybrid broadband access networks combining wireless and wireline Wavelength Division Multiplexed Passive Optical Networks (WDM-PONs) networks can support the requirement of these future broadband ubiquitous networks. The target of a converged hybrid architecture is to connect, via a common optical WDM-PON infrastructure, both wireline and wireless users. Several hybrid wireless WDM-PON architecture have been proposed recently [4] i...