MULTIMODE FIBER FOR ENTERPRISE NETWORKS
FOCUS on CONNECTIVITY
Multimode fi ber for enterprise networks
Some of the long-standing advantages of using optical fiber are its superior reach at high data rates and high reliability; its immunity to electromagnetic interference; the simplicity of its connectorisation; and operation at high data rates, which provides high security and reduces system downtime. The smaller, lighter cables enabled by optical fiber also greatly improve pathway and space utilization relative to copper equivalents and increase port density, which can also increase cooling efficiency.
But nothing is ever perfect, and over time in any enterprise network, moves, adds and changes can lead to mismanaged cable, which in turn can result in congestion in the ducts, restricted airflow with associated impacts on cooling efficiency and reduced flexibility of the system for upgrades.
Mismanaged cable scenarios can also place cable under tight bend conditions which, with standard multimode or single-mode fiber cable, can result in significant power loss through macrobending of the fiber (see Figure 1).
Such power loss can place a strain on the integrity of the end-to-end optical power budget such that system reach extensions are made difficult, or not enough optical power reaches the receivers causing optical system failure, resulting in downtime.
Such impacts are significant at a time when network operators are looking for: • More reach and flexibility for data rate upgrades;
• Reduced maintenance costs;
or margin after typical connector and transmission losses are accounted for.
Over time, moves, adds and changes can lead to mismanaged cable, which can place cables under tight bend conditions
• Better cooling and space usage efficiency; • The ability to make moves and add connectors with ease; and
• Reduced cable fuel load for fire safety and environmental reasons.
Multimode optical fiber has many modes (or optical paths) of light travelling along its central core. The closer that a mode travels to the edge of the fiber core the more likely some of its light or signal power will escape into the fiber cladding, where it will no longer be guided by the core resulting in signal power loss.
As you bend multimode fiber, the modes are guided along a path that takes them closer to the edge of the core, so the amount of light that leaks out of the core (and the amount of power loss from the signal) increases significantly.
In many scenarios where cables are installed in restricted environments, such as in racking or congested areas within ducts, sharp bends of radii down to 7.5mm are observed.
A typical power budget for a 300 meter OM3 system operating at 10Gb/s is in the region of 2.8dB, of which only 1dB remains as headroom
There are two standards relating to multimode optical fiber that give guidelines for macrobend loss in multimode fibers – IEC 60793-2-10 and ITU G.651.1. These standards only specify macrobend loss for bend radii of 37.5mm and 15mm, and so do not stipulate performance requirements for tighter bend scenarios that occur in many enterprise networks.
In addition, the macrobend loss limit set by the existing standards at their lowest defined bend radius of 15mm is as much as 1dB for two turns. For a basic standards compliant 50µm multimode fiber, supporting a 10Gb/s system over 300m, these two 15mm turns may well absorb all the power budget headroom on the system, pushing it into optical power budget system failure and downtime. Hence, a multimode fiber with greatly improved macrobend performance than stipulated in the existing standards is greatly needed.
Improved macrobend performance can also enable smaller, lighter cable designs that can be more compactly stored, thereby increasing airflow and reducing energy costs. Cables made with bend-insensitive multimode fiber are capable of being bent into much tighter loops than traditional 50µm fiber.
IN SUMMARY Bend insensitive multimode fibers address key issues faced by enterprise network managers: they provide increased system reliability and reduced downtime (through increased system margin) and introduce significant value into an enterprise network.
The closer that a mode travels to the edge of the fiber core the more likely some of its light or signal power will escape into the fiber cladding
This article was written by Corning Optical Fiber and is edited for publication.
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