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Fibre-optic cabling has other benefits, such as the ability to have longer link lengths and a greater resilience to external environmental factors. For example, the problem of near-end crosstalk, which is common in copper cabling, is non-existent in fibre optics. It is also very hard to tap, so is ideal for high security applications, which is one reason why fibre is already very common in military and City applications.

The growth of fibre means that the contractors who have previously left this part of the market to others, can no longer afford to do so. In the past, the perceived complexity of fibre installation meant that many companies simply outsourced this work. In the future, it is more likely that contractors will want to carry out this work in-house, particularly when faced with tight profit margins.

While many contractors will be familiar with Category 5e copper cabling, installing fibre-optic cabling is another matter. Category 5e cabling is quite forgiving, but fibre optics allow little room for error. The good news is that once the basics of fibre optics installation and testing are understood it is straightforward. Like any form of cabling, these basics are governed and described in a set of industry standards.

The need for standards
There are three kinds of fibre optic cable standards for lans: European, international and American. These cover design, specification and installation. The first two are similar, while the latter has some clear differences. In essence, they all cover the same issues: link length, bandwidth and attenuation (the decrease in signal power between two points). These are the three main areas for contractors to understand.

But why bother learning about the standards? Couldn’t a contractor just use common sense and their knowledge gained through dealing with copper cabling?

There are some very clear reasons why this is not an option. Firstly, fibre is very different to copper cabling, using light to carry data, not electricity. Therefore, its performance is governed by a different set of properties and parameters. Further, high data-rate fibre optics provide very little headroom, so installation needs to be more precise and closely matched to the application that the customer wants to run over the lan.

Of course, contractors could simply choose to over specify, but this could prove expensive. A contractor who understands fibre will be able to provide a more competitive and tailored quotation.

  Testing is also very important. An installer needs to be able to set the correct limits, otherwise there is a strong chance of false pass or fail rates. While it is possible – although not advisable – to bend the rules with Category 5e cabling, try the same with fibre and there is a risk that the system will not work when handed over to the end-user. A contractor who appreciates fibre standards can significantly reduce snagging and testing time, leading to greater profitability and client satisfaction.

So what are the main standards? There is a range of fibre standards, each relating to a different application or bandwidth, with a specified wavelength, maximum operating distance and attenuation.

The main terms to become familiar with are ISO/IEC 11 801, OM1, OM2 and OM3. ISO/IEC 11 801 also includes OS1, which covers single-mode cable, although few installers will need to concern themselves with this kind of fibre, more commonly used in wide area networks.

ISO/IEC 11801 is the governing standard for fibre and copper lans. It was updated last year to include cable specifications for ten Gigabit Ethernet. OM refers to optical multi- mode, which is the classification of the cable involved in most fibre lan installations. OM1, OM2 and OM3 are the three kinds of optical fibres designed to support various classes of application specified within ISO/IEC 11801.

Each application will have a required bandwidth. This must be provided by the fibre optics: too little bandwidth will mean that the application may not work. Link bandwidth depends on the type and length of the fibre and is rarely measured in the field, so must be correct at the design stage.

Standard properties
It is very important for contractors to understand the properties of each kind of multi-mode cable because they have differing bandwidth levels, with OM3 having much higher bandwidth than OM2 or OM1. OM1 is sufficient for the lowest capacity, at 10 and 100 Mbit/s, while OM3 can be used at 10 000 Mbit/s. Since any contractor becoming involved in fibre optics is likely to hear the term OM3 or even be asked about it, it makes sense to describe this development.

Multi-mode fibre was not initially designed for high speed applications such as ten Gbit Ethernet. For high data-rate lans one option is to install single-mode fibre, but this has cost implications. The decision was taken to improve multi-mode fibre, leading to the bandwidth levels of OM1, OM2 and OM3 being specified in ISO 11801 in 2002.

High data-rate applications require lasers to be used rather than the light emitting diodes used previously, which cannot switch light on and off quickly enough for ten Gigabit Ethernet. Multi-mode fibres are graded index fibres ie the refractive index changes gradually across the core. This is the speed at which light is carried and relates to how it bounces or refracts along the cable length. Until high speed applications were developed, fibre cabling was optimised to work well across a range of wavelengths. OM3 has tightened up the manufacturing of the refractive index profile and optimised the fibre to work at 850 nm, ensuring that the bandwidth of OM3 is three times that of OM2 at this wavelength.

Contractors must be aware that the maximum link length for OM2 fibre is 550 m for 1 Gbit/s Ethernet, reduced to 86 m metres for 10 Gbit/s Ethernet. This means a contractor must really know what a client expects to achieve from a lan right from the beginning. There is no point installing fibre link lengths of up to 550 m if a customer plans to run ten Gbit Ethernet within the year.

Fortunately, there are plenty of resources available to help contractors learn how to design and install fibre optic data networks (see ‘training’, above). And while the various standards and issues to be aware of may initially seem daunting, anyone who is skilled at handling copper cabling will find it easy to work with fibre. In this part of the cabling industry, a little knowledge can go a long way.