What are optic fibres/cables in simple words?

physea
I suppose there's tons of information about optic fibres, but what are they really, their functions, their limitations, pros and cons?

Staff Emeritus
I suppose there's tons of information about optic fibres, but what are they really, their functions, their limitations, pros and cons?

russ_watters
physea
So basically optic fibers are hollow cables with mirror-like inner surfaces that reflect light so that light is transmitted?

Are there losses? Are they used for information transfer?

So basically optic fibers are hollow cables with mirror-like inner surfaces that reflect light so that light is transmitted?
I guess you could think of it that way. The more technical description is that fiber optic cables are a type of waveguide (https://en.wikipedia.org/wiki/Waveguide) for visible light.
Are there losses?
Yes, but they are low for good cables. I think I've seen cables where the loss is around 1dB/km.
Are they used for information transfer?
Of course. Telecommunication companies use these for internet traffic.

physea
I guess you could think of it that way. The more technical description is that fiber optic cables are a type of waveguide (https://en.wikipedia.org/wiki/Waveguide) for visible light.

Yes, but they are low for good cables. I think I've seen cables where the loss is around 1dB/km.

Of course. Telecommunication companies use these for internet traffic.

Thanks
Other applications?

Mentor
Thanks
Other applications?
The wiki article has a long section on applications.

Mentor
Thanks
Other applications?
Communications is just a small application. This is the largest application of fiber optic cables to date, I believe...

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Tolklein, lekh2003 and NFuller
physea
Yes, but they are low for good cables. I think I've seen cables where the loss is around 1dB/km.

Interesting, from that value, can we save the % loss for 2500km? or per km?

Interesting, from that value, can we save the % loss for 2500km? or per km?
I'm not sure what you mean by saving a percent loss. Do you mean how much light intensity will be lost over a 2500km cable?

Homework Helper
So basically optic fibers are hollow cables with mirror-like inner surfaces that reflect light so that light is transmitted?
For the ones used in actual applications, not quite so. It's true that a hollow cable having reflective inner surface can also transmit light from one end to the other but such scheme proves to suffer from high amount of loss per unit distance (I either read it somewhere or heard it from someone else, too bad it was long time ago I can't remember the source). In reality, generally speaking optical fibers take the form of a coaxial dielectric and flexible tube tube. It is coax because it consists of at least two 'layers'. The innermost tube is called core and the outer one is called cladding. One of the condition for it to be able to guide light is to have the core having higher refractive index than the cladding. In this way, rays hitting the core-cladding interface will undergo total internal reflection provided the incoming angle is bigger than the critical angle between the two media. As the others have mentioned, there is a wealth of information on optical fiber and a forum thread is by no means sufficient to even cover the basic, you will need an introductory textbook on this topic at the very least. As subfields of optics, optical fibers and lasers pose the same level of breadth and development.

physea
physea
I'm not sure what you mean by saving a percent loss. Do you mean how much light intensity will be lost over a 2500km cable?

Yeah sorry typo. I mean how much % will be lost.

Yeah sorry typo. I mean how much % will be lost.
Over 2500km, using the example given, 2.5dB of the signal is lost. The fraction ##f## of power transmitted is then
$$f=10^{-2.5/10}=0.56$$
So the fraction of power lost is ##44\%##.

physea
physea
Over 2500km, using the example given, 2.5dB of the signal is lost. The fraction ##f## of power transmitted is then
$$f=10^{-2.5/10}=0.56$$
So the fraction of power lost is ##44\%##.

Mmm very interesting.
Do we know how much light energy is released per gram of petrol or natural gas burned?

Do we know how much light energy is released per gram of petrol or natural gas burned?
I don't know, you will probably have to do some googling to find the answer. Since this question is not directly related to the original question though, it is probably more appropriate in a separate thread.

Chris Riccard
I'd start by looking up candela def, then lumens. Assuming a perfect burn you can measure the light output by heat temp during combustion. Prob take two pages of equations to get the answer.

Tolklein
Communications is just a small application. This is the largest application of fiber optic cables to date, I believe...

Yeah it is interesting how commercial applications of technology so easily overtake industrial applications, and then, hopefully, lead to rapid advances in said tech.

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