Since the inception of fibre optics, the best minds in the business have focused on one thing – how to create the optimum fibre optic connection. AFC Group national business development manager Michele Hart explains.

Advances in design and manufacture aim for perfect core alignment and physical contact, minimising reflection, insertion loss and risk of damage. But at the end of the day, all this work can be undone by the most humble of culprits – a tiny speck of dirt.

It’s not glamorous, but the most basic and important procedure for the maintenance of fibre optic systems is cleaning. Failure to adhere to strict fibre hygiene standards can cause major malfunction in a network.(See Figure 1.)
 
Studies have repeatedly found that connector contamination is the most common cause of network failure. Not only that, research has also shown that the repeated mating of connectors creates electrostatic discharge on the connector end-face, which actually causes dust particles to migrate toward the fibre end-face.

Common types of contamination include dirt, dust, oil and other residues, and all can cause a variety of problems for optical connections. A particle that partially or completely blocks the core generates strong back reflections. (See Figure 2 and 3.)
 
Particles trapped between two fibre faces can scratch or chip the surfaces irreparably. Even if a particle is only on the cladding or the edge of the end-face, it can cause an air gap or misalignment between the fibre cores which will degrade the optical signal. (See Figure 4.)

 
The difficulty is that to the naked eye, the fibre can look clean. A typical human hair is about 60 micrometres in diameter – but it only takes a 9 micrometre speck of dust, too small to see without a microscope, to completely obscure a fibre core.

Consequences of fibre contamination:

• failed ORL and connector reflectance/loss
• laser ‘chirping’ and high RIN caused by reflections
• high link loss and connector loss
• ISI and other endeared defects in the WDM system
• Intermittent bit/block/FEC errors and protection switches
• Error packets or cells at layer 2/3
• Data re-transmission requests at higher layers
• Loss of time, Network outages, increased failure rate

Observing good fibre hygiene starts with correct and careful handling of the fibre optic equipment. Dust caps should always be fitted to protect unused connectors and couplers.

Prior to connection, the fibre should be inspected using an objective method such as an inspection scope. If contamination is detected, the fibre should be cleaned using either a dry method, such as a one-click-cleaner, or a wet method, such as cleaning sticks and travel-safe solution, or both. (See Figure 5.)

Re-inspection is vital – some contaminants can be difficult to remove and may require more than one clean. Once the inspection scope shows a pristine surface, the connection can be made. (See Figure 6.)

Adherence to this simple procedure will significantly reduce the instance of network disruption and save time and effort in the long run.

Visit www.afcgroup.com.au.