22 December 2011

Christmas cheer, lights and communication

Christmas trees are a staple at this time of year, but the optical fibre lights bring up questions for COSMOS intern Jenna.

A christmas wreath with optical fibre lights. Credit: istockphoto

~ Jenna Hanson

I was staring at the Christmas tree set up in my lounge room the other night, watching the optical fibres in the plastic branches light up the tree and turn an otherwise dark room into a child’s fantasy of colour.

I was amazed at how a tiny tube of glass could create such beautiful colours and patterns. But optical fibre is amazing for another reason as well. Not only has optic fibre been used to light up Christmas trees for years now, it’s also been used in communications. I should know, my parents have their own telecommunications business and I’ve listened to them talk about using boxes of the fibre optic cable for different jobs.

But it got me thinking: just how does optical fibre work? How can the same material that’s used to light up my Christmas tree be used to make a telephone call? I decided to do a little investigating to find out.

Light has been used in communications for hundreds of years, one example being lighthouses. Lighthouses use beams of light to signal ships so that sailors can work out how far they are from shore and be guided safely to port. The problem with using light for communications is that it spreads out after leaving the source, meaning the light signal gets weaker with distance.

One way of dealing with this dissipation is by pushing the light through a tube, which is where optical fibre comes in. Light, which prefers to travel in a straight line, travels through the optical fibre until it encounters the side of the tube. Instead of radiating through the tube and dissipating, the beam of light hit the side of the tube and bounces off, much like a mirror, and continues on until it reaches its destination.

Optical fibre is a long, thin tubule of very high-purity glass. Although thin tubes of glass had the known ability to carry light over distances, it wasn’t until 1964 that it was considered as an efficient way of transmitting light over long distances. After years of disappointing experimental results with fibre optics, the breakthrough came in 1970 when Donald Keck, Peter Schultz and Robert Maurer from Corning Glass Works – the American ceramic and glass company that developed Pyrex and Corning ware – successfully created an optical fibre hundreds of metres long with the clarity needed to reduce the loss of light.

Shortly after this, a semiconductor laser was made that would work continuously at room temperature and telecommunications companies created complex digital codes to translate the light into the appropriate signal. These discoveries made the use of fibre optics in telecommunications possible

So now I understand a little more about what lights up my tree and lets me call my family at Christmas time. Next on my things to do list: investigating the ever-reliable Christmas beetle!


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