# Fiber Optic Cable Capacity

1. Nov 16, 2012

### zplizzi

I am trying to design a system that will carry light for illumination along a fiber optic cable. I see that there are many thicknesses of fiber optic cable - however I am unsure of the purpose of this. I've never heard of a 'density' of light that you can put into a cable - is there such a thing? Ie. is there a certain 'amount' of light that you can put through a certain diameter of fiber optic cabling, kind of like there is a maximum amperage you can put through a certain diameter wire? (I know it's due to resistance in electrical wire, which is very minimal in fiber.. which would lead to a negatory answer)

If not, then why the different thicknesses of fiber? (I'm talking about single strands for simplicity)

Thanks!

2. Nov 17, 2012

### Claude Bile

Light density = Light Intensity (or, more correctly, irradiance).

There are upper limits on the intensity that can be put through an optical fibre, which limits are relevant depend on the application. The "hard" limit is material damage that arises due to high intensity light, though other "softer" limits such as Stimulated Brillouin Scattering can also arise, which can affect applications that use coherent light.

Claude.

3. Nov 17, 2012

### sophiecentaur

Could the different thicknesses available relate to the minimum radius of bend that you can get? (As with copper cables)
Fibre width is very relevant for digital signalling, of course, but pulse spreading is not a problem in lighting applications.

4. Nov 17, 2012

### zplizzi

Hmm.. I'm having trouble finding data on what kinds of irradiance fiber optics cables can handle.

My application will require something like 1-2kW of sunlight to be focused into the fiber.. I'm not sure if this is easily handled by most fiber cables or not.

I can see where bend radius might affect it - luckily my application won't need any tight bends so that isn't a major issue.

5. Nov 17, 2012

### zplizzi

Ok, I've done some more thinking; here's what I've come up with.

A high quality APF (All Plastic Fiber) cable of some radius has an attenuation of about .15 db/m

Since attenuation is defined as $att = 10*log(power_f/power_i),$ my power transmission would be about 97% per meter.

For 1kw of power transmitted over 1m of cable, this equates to about 30W of power dissipated.. is this something a decently thick fiber optic cable can handle continuously?

Or am I on the completely wrong track?