Optical frequency up-conversion in multimode and single-mode fibre radio systems

Using a novel optical frequency multiplication technique, microwave signal carriers up to 20-GHz are delivered to a significantly simplified remote radio access unit fed by a multimode fibre link having modal bandwidth below 1-GHz, as well as standard single mode fibre. Measurement results show that the remotely generated carriers have very narrow linewidths below 20-Hz, and exhibit much lower phase noise (< -90 dBc/Hz) than even a commercially available high frequency electronic signal generator. Thus by using optical frequency multiplication, existing in-building silica multimode fibre infrastructure, and the emerging polymer optical fibres may be used to not only transport fixed data services such as gigabit Ethernet but also to transparently distribute in-doors (and for short links), signals of present WLANs as well as future broadband WLAN services leading to significant system-wide cost reduction. It also enables the radio signal processing to be consolidated in a single central site, which is beneficial for advanced signal processing such as needed in multiple-input multiple output (MIMO) systems.