The widening horizon for multimode fibre

While singlemode fibre gets the headlines, mulitmode is the real workhorse.

Connected and efficient buildings and data centres increasingly rely on a state-of-the-art physical layer infrastructure to support growing bandwidth needs over copper, fibre and wireless technologies. When it comes to optical fibre transmission, singlemode fibre often gets the headlines with high-speed transmission records over long distances; however, multimode fibre is the workhorse media of local area network (LAN) backbones and storage area networks (SAN) in buildings and data centres.

The reason is because multimode fibre offers the lowest cost means of transporting high data rates for the distances aligned with the needs of these environments. We can expect multimode fibre’s dominance in buildings and data centres to continue because of recent developments in multimode technology and international standardisation that will extend the value proposition offered by multimode fibre for today’s and tomorrow’s networks.

Since its original inclusion in the international cabling standard ISO/IEC 11801, multimode fibre has evolved from supporting multimegabit per second transmission using light emitting diode (LED) light sources to being optimised for multigigabit transmission using 850 nanometre (nm) vertical cavity surface emitting lasers (VCSELs). With the introduction of laser optimised multimode fibre in the late 1990s, a significant update to the ISO/IEC 11801 standard included the addition of cabled optical multimode (OM) fibre categories — OM1, OM2 and OM3.

OM1 and OM2 were defined for legacy LED optimised fibres. OM3 was defined for multimode fibre optimised for laser transmission at 850 nm. A few years later, an OM4 category was added, to recognise multimode fibre with more than double the effective bandwidth at 850 nm, supporting extended distances for gigabit and multigigabit applications.

Another significant update to the multimode fibre categories is currently underway with the development of the third edition of ISO/IEC 11801 (expected for publication next year). Due to the success and prevalence of 850 nm VCSELs in today’s networks, the third edition will ‘grandfather in’ the LED optimised OM1 and OM2 fibre categories. They may only be used for changes and additions to existing installations. As a result, OM3 will be the minimum requirement for new installations.

Today, OM3 and OM4 fibres are increasingly being used in parallel fibre infrastructures using MPO connectors. They support speeds up to 100 gigabit per second (Gbps) using multiple parallel VCSELs with standards in development to support up to 400 Gbps using parallel technology.

The most significant optical fibre development in the third edition of ISO/IEC 11801 is the recent addition of a wideband multimode fibre (WBMMF) category allowing simultaneous transmission of at least four different wavelengths over each fibre, expanding per-fibre capacity with support for short wave division multiplexing (SWDM). The new WBMMF category will be included in the standard’s final draft to be circulated shortly. The naming of the new WBMMF category will be selected by national votes. The choices proposed are OM4W, OM5 and OM5W.

Regardless of the name selected, one thing is clear: WBMMF is set to widen the applications horizon for multimode fibre in connected and efficient buildings and data centres worldwide.

*Matias Peluffo is Vice President, Intelligent Buildings, Asia Pacific. He has overall responsibility for CommScope’s strategy to deliver breakthrough innovations and customer value in the building segment with a broad range of solutions. He has more than 25 years’ experience in the telecommunications industry. He plays a leading role in CommScope’s contribution to the international organisations that develop standards for cabling systems and contributes to the strategic direction and establishment of industry governing standards.