Information on Fibre Optic Technologies?
Q. I was just passing by your website & found it really good for newcomers as well as experienced users.

I am working with an internetworking & ISP company right now. I work with most of the cabling technologies used. Can you suggest a good website from which I can get more information on Fibre Optic Technologies & it's use in current situations.

A. Thanks for your email and the kind comments about the website, it's nice to know when people find the site useful.

Try this site for more info on fibre optics http://www.cableu.net/, and in particular the link to Fotec.

Three questions regarding fibre optics?
Q. How can a beam of light possibly carry information?
A. The one's and zero's of the binary data are converted to light pulses and sent down the fibre at very high frequencies.

Q. For every pulse of light that is sent down a fibre optic cable there is some light which is lost because it is beyond critical angle and cannot be reflected. If part of this mode is lost then doesn't that mean the data is sent as incomplete? How can the computer make sense of an incomplete signal? Could you explain this situation.
A. The data is sent as a stream of bits and so the amount of light that is lost merely reduces the strength of the signal. The pulses of light that reach the other end will have lost some of their strength but they will still be large enough to reassemble into bytes of information. Multi-mode transmission simply means that the light travelling down the fibre will take multiple paths, it does not mean that each mode is transmitting different data. Each pulse of light comprises all modes.

Q. Finally, I know that the time between transmitting each pulse must be enough so that the first pulse completely arrives at the receiver before the second pulse does. What happens if two pulses do crossover one another? Do they mix to create a different pulse, does the PC say transfer error, or the screen freezes etc.?
A. The pulses all travel at the same speed so it is not possible for one to overtake another. The main reasons for errors in a fibre system are too much attenuation (reduction in signal strength), and reflections or backscatter at poor connections which if large enough will interfere with the signal.

I hope this answers your questions and if you would like to know more why not try http://www.cableu.net or the Techweenies website. There are some more useful links on the 'Links Page'.

Fibre cable testing?
Q. Could you please tell me what is used for fibre cable testing?

A. An OTDR (Optical Time Domain Reflectrometer) is commonly used to test fibre cables although for data networks it is easier these days to use a fibre certification tool.

OTDR results can be difficult to interpret and involve some mathematics, fibre certification tools simply tell what networks the fibre is good for, for example 10Base-FX and 1000-BaseSX etc.

For basic testing a simple light source and power meter can be used but this only gives a dB loss reading and does not test for maximum bandwidth or distance.