New fibre for cost-effective multimode technology up to 10 Gbps

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14 August 2002 Interconnection

Stefan Ries, Private Networks Business Unit

The coming standardisation of 10 Gbps Ethernet calls for fibres that have been designed to meet future requirements. The OM3 fibre with its 50 µm fibre core and its improved gradient profile is a powerful yet cost-effective solution for modern, high-performance building cabling systems.

Hardly two years have passed since the standardisation of 1 Gbps Ethernet building cabling systems, and now, standardisation of the much more powerful 10 Gbps cabling system is imminent. The first devices were announced at the Cebit 2002 in Hannover. They will mainly be applied in powerful computer centre applications.

High data rates using multimode

However, in 10 Gbps Ethernet systems the data rates are so high that the maximum length that can be achieved with conventional multimode fibres is a mere 84 m. This capacity is just sufficient for the reliable operation of 1 Gbps transmission lines. The logical solution of simply using singlemode fibres in buildings has certain drawbacks. For one thing, the production of singlemode cable assembly systems is very costly. In addition, singlemode fibres require suitable components, which are more expensive to purchase. To achieve the necessary data rates, operators must therefore decide what price-to-performance ratio they accept and what media they want to apply.

To solve the problem, the multimode fibre has been 'outwitted'. By excitation of part of the modes, it is possible to also use multimode fibres at high frequencies. Huber + Suhner's OM3 fibre has been developed. It eliminates the production-related DMD (Differential Mode Delay) problems that relate to multimode fibres. DMD refers to the nonideality of the refraction index in the centre of the fibre, which leads to massive propagation time differences.

The DMD problem is minimised in OM3 fibres by applying special production processes in the core region. This enables such cables to be used in 10 Gbps applications. Additional optimisation for 850 nm applications allows a transmission length of 300 m to be achieved. The OM3 fibre reduces costs substantially because it allows simpler and less expensive multimode terminal devices to be used. In addition, the cable assembly requirement is reduced during cable installation.

Since transmission rates exceeding 1 Gbps are only possible with optical fibres, the UGV standardisation system has created different fibre classes. Classes OM1 to OM3 define the possible transmission length besides the defined data transmission rate. As a result, the system prescribes which fibre must be used in a given application.

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New fibre for cost-effective multimode technology up to 10 Gbps

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