Broadband multi-service in-house networks using mode group diversity multiplexing

Abstract: Multiple broadband services are carried independently in a highly multimode polymer optical fibre network by selectively launching and detecting several mode groups, while counteracting mode-mixing by adaptive electrical signal processing. With cheap integrated signal processors, mode group diversity multiplexing can offer the same functionality as wavelength multiplexing at lower costs. © 2002 ICPOF 1. Introduction Optical fibre is an excellent medium for providing high bandwidth and service format transparency. It has brought tremendous data transport capabilities in core telecommunication networks, and it is now conquering the metropolitan area networks and subsequently it is moving into access networks. Coming closer to the end user and penetrating his residential area, however, the costs of installing and maintaining the fibre network become ever more important. Polymer Optical Fibre (POF) offers distinct advantages regarding cost-effective installation and maintenance in in-building business and residential areas, as compared with the commonly used single-mode fibre. The POF’s large core considerably eases coupling and splicing, and its flexibility and ductility enables fast installation in often less accessible customer locations. It offers also distinct advantages in comparison to traditional fixed wiring media such as coaxial copper cable and twisted pair copper cable: it offers significantly more bandwidth and lower losses, it is immune for electromagnetic interference, and it offers complete transparency to signal format and protocol. Similar advantages are obtained with silica large-core fibres, although these fibres are less flexible and ductile and thus less easy to install. However, in comparison to standard single-mode silica fibre, POF has per unit of length a higher attenuation, and a lower bandwidth (due to its higher dispersion caused by its multimode waveguiding behaviour). Therefore its applicability for broadband data communication is limited. POF material compositions and index profiles are being explored to improve the fibre characteristics. Perfluorinated (PF) polymers have reduced the losses to below 10 dB/km in the wavelength range of 800 to 1300 nm [1]. PF graded-index polymer optical fibres (PF GI-POF) have reached bandwidthlength ⋅products of 5 GHz⋅km. In conjunction with these improvements in polymer fibre technology, research is needed regarding system techniques to extend the data transport capabilities of POF-based networks. Next to improvements in the POF characteristics, a lot of progress has been made also on high-speed POF system techniques [2] [3] [4]. Recently, the TUE-ECO group has reported a Gigabit Ethernet PF GI-POF link with a length of about 1 km [5]. However, to further advance the capabilities of POF-based networks, new signal transport techniques have to be devised. In this paper, mode group diversity multiplexing is proposed as an approach to increase the fibre’s data transport capability. By selectively launching and detecting subsets of the large total number of guided modes in the POF, and by using electrical signal processing in order to unravel the mode mixing incurred in the POF, mode group diversity multiplexing enables to create several independent communication channels in a single fibre infrastructure, and thus allows to integrate multiple services independent of each other in this infrastructure. Its functionality is comparable to wavelength multiplexing, but without requiring the more costly wavelength-specific sources and wavelength (de-)multiplexing system functions. Mode group diversity multiplexing may outperform wavelength multiplexing, when the costs of the electrical signal processing required are lower than the costs for wavelength multiplexing. Moreover, sets of mode-group-diversity multiplexed signals may be stacked in a next hierarchical level with wavelength multiplexing, thus creating independent service groups in a unified POF-based transparent in-house