Pre-filtering on signal fading effect for radio-over-fiber distribution systems

Abstract

With the increasing demand for broadband services, it is expected that radio-over-fiber (RoF) systems may be employed to provide high capacity wireless access networks. A major problem with the system is that standard amplitude modulation of the optical carrier generates Double Side-Band (DSB) signals. When these signals are transmitted over fiber, chromatic dispersion causes each side band to experience a different phase shift. If the phase difference at the receiver equals pi, the two side bands interfere destructively causing fading of the received signal. Using an optical filter to filter out one side band can reduce chromatic dispersion effects. Another problem in RoF systems may come from Stimulated Brillouin Scattering (SBS). SBS is an interaction between light and sound waves in the fiber, which causes frequency conversion and reversal of the propagation direction of the light. SBS severely limits the optical power that could be transmitted through a fiber and it is detrimental for optical communication systems. It can also be reduced by the filtration carried out at the transmitter (pre-filtering). Since the optical filer functions to eliminate one sideband and induces insertion loss, the optical power to be launched into the transmission fiber falls sharply and so does the risk of SBS. In this paper, we investigate the possibility of performing SSB filtering to simultaneously overcome the effects of dispersion and SBS in the transmission fibre. The results show that the pre-filtering can filter out one side band as well as reduce the effect of SBS.