One of the most commonly used and important components in a fibre optic network, doesn’t really do much at all.

Welcome to Building Fibre where we take an inquisitive look at how creating a smart, connected world, is impacting the way we design city infrastructure.

In this episode we’re taking a closer look at how the light is managed within a fibre network and focusing on one particular component, the passive optical splitter.

A passive fibre optic splitter is a component that does exactly what it says on the box, it splits the fibre and therefore the signal that’s travelling through it, into multiple directions.

Splitters are completely passive networking components, meaning they require no electricity or power to make them operate. If they have no electricity they are not creating any heat so there’s no need to control the climate and no maintenance required whatsoever.

The fibre optic splitter is one of the most commonly used passive devices and splitters are an important part of both the GPON networks that can frequently be found in the telecoms industries, fibre-to-the-home broadband deployments and also within Passive Optical LAN that are found in buildings.

There are two main types of splitters, the first is called the Fused Biconic Taper or FBT, and the second is called the Planar Lightwave Circuit or PLC. The fused Biconic is made by twisting and melting together individual strands of optical fibre whereas the Planar Lightwave is manufactured as an optical chip, much like a computer chip but with a wave guide imprinted upon it. The Fused Biconic can be manipulated into several forms and which have different uses so we will put them to one side for now and start by focusing on the PLC version and take a look at some of the common functions that all splitters types share.

A splitter divides the POWER of the source beam. This means a splitter that, for example, divides into two EQUAL parts, will send 50% of the power down one direction and 50% down the other, without changing the nature of the signal.

Imagine water flowing through a water main and it comes to a Y shaped fitting which divides into two identical sized pipes.  All things being equal the water will divide into two different directions and 50% will go one way and 50% will go the other way.

When we divide a water pipe, we don’t change the character of the water. We don’t inject bubbles into one side and turn the other side into cherry cola.

It’s an important distinction to make because, when we use a splitter to divide the light, we don’t intentionally change the character of the signal, it doesn’t become a different colour or frequency, it just the same signal going in two different directions at slightly less power.

But the reduction of power is a very important consideration that has to be taken into account when calculating overall distance the signal can travel through the network. Every time we introduce a component into an optical network it has an effect of reducing the power passing through, in fact the sheer action of light travelling down a fibre causes the signal to be diminished and when designing any part of the network we must take this into consideration by working out how much power we have to begin with and then calculating the losses as the light passes through the network. We call this the loss budget.

The optical power is measured in decibels commonly referred to as dB, which is a ratio between how much goes in relation to how much comes out. It’s calculated using mathematical formula which give a reading using a logarithmic scale which we don’t want to get into at the moment but suffice to say that when we get a 3dB reduction it means that the signal has been reduces by a half.

At the heart of a PLC Splitter is an optical chip which uses wave ...