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Wash your Strands - Dexgreen Fibre Hygiene

October 01, 2020 4 min read

We've all grown familiar with disease transmission hygiene by now, thanks to the global pandemic, but something you may not be as familiar with is: Fibre Hygiene!

Don't worry, this type of hygiene doesn't require litres of alcohol gel, face masks or social distancing! Our fibre experts have put together a handy guide on how to care for your fibre cabling, tools and components, to help keep signal losses to a minimum.

OPTICAL FIBRE TECHNOLOGY

There's no denying it. The Second Law of Thermodynamics is a pain. This law states that "the total entropy of an isolated system can never decrease over time". In layman's terms, this means that any system will always trend towards chaos, losing energy to the environment over time.

Unfortunately, second law principles are as true for fibre optic connectivity as they are for anything else. Fibre Attenuation is the property of light signal transmission to lose strength over time and distance. Attenuation is measured in decibels per kilometre or dB/km and the expression for fibre's attenuation coefficient (α) can be seen below, where P(z) is the optical power at a position z from origin and P(0) is the power at origin.

There are many different factors that contribute to fibre attentuation, and most of these can only really be addressed in the manufacture of the fibre itself. Dexgreen source the highest quality fibre possible for our cabling, so factors like Instrinsic Material Absorption, Hydrogen Interaction, Linear and Non-Linear Scattering are minimized.

However, there are also fibre handling factors which can greatly affect the attenuation of fibre signal, and fibre hygiene is chief among these, probably second only to micro- and macro-bending problems.

MICROBENDING AND MACROBENDING

The easiest way to distinguish these two problems are to imagine a cable installation scenario. Microbends can occurs when wrapping the cable or pinning it to a surface. Microbends are little bumps or kinks in the wire that are usually created by localized mechanical stress, and result in small, cumulative power losses.

For macrobends, imagine installing fibre cable around a door frame or wall corner. Contrary to copper cable, fibre cannot be bent below a certain radius or a large power loss will occur. Dexgreen supply specially-engineered bend managers which are installed to guide fibre cable around corners with an optimal bend radius and minimal signal loss.

BARE FIBRE HYGIENE

Fibre strands are intricate, precise and delicate. Really, they are wonders of modern technology compared to older copper cabling. Because of their delicate nature, Dexgreen recommend preconnectorised fibre cable options wherever feasible - this removes a major source of signal loss when bare fibre comes into contact directly with the environment during splicing or field connector application.

However, we recognise that not every fibre installation can be the same, so we have manufactured one of the best field connector kits on the market to answer this requirement.

As with all of our equipment, we ran a host of tests on bare fibre ends when used in conjunction with these field connectors, including microscopy and interferometry, with interesting results. As you can see from the illustrations below, it's common for bare fibre ends to pick up dirt and debris from the environment very quickly once exposed.

The solution to this problem is simple, but it is often overlooked in the field: Frequent line testing and thorough fibre hygiene. Follow this simple checklist to ensure minimal signal loss:

Inspect all fibre connectors using a video scope
Always assume connectors are dirty - coming straight out of a packet is not a guarantee of cleanliness
Re-inspect and clean any connector that comes into contact with your skin or any other surface
Clean connectors using approved fibre cleaning equipment
Replace any damaged or not cleanable connectors
Test signal levels at connectors after cleaning

And remember, when working with bare fibre strands, always Inspect, Clean, then Connect!

And for more detailed analysis of signal loss faulting, you can follow these principles and carry out some of the diagnostic techniques outlined below:

TROUBLESHOOTING PRINCIPLES

Test all the way through the installation procedure rather than just at the end to ensure the quality of intermediate steps
A signal in specifications at the NTD is not a guarantee that the line fault free (Example: if the signal reading is -24db at NTD and -18 at the PCD there is a 6db fault on the premises cable)
If signal is identified as within specifications, signal must be checked again at each test point downstream prior to handing off (your actions may have fixed the issue)
Check the most likely causes first, for example, a dirty connector is more likely than a faulty factory terminated connector
Do not eliminate unexpected causes, for example, a drop fibre may have been incorrectly labelled, connected to the wrong port, or left unconnected at a MPT or SMP

DIAGNOSTIC TECHNIQUES

Measure signal strength with a PON power meter
Check for correct optical fibre path routing using a Visible Light Source
VLS is only an indication of continuity, not line quality - visible light can pass through a fault or a dirty connector
Clean or replace dirty or damaged fibre connectors
Inspect carefully for other visible problems (e.g. cable damage, kinking, incorrect connection)