[Corvettaholic]

Anyone know stuff about fiberoptics? I know fiberoptic cables have a bunch of glass threads in them, and they transmit light over distance very well. Now remember how some kids used to fry ants with magnifying glasses? What do magnifying glasses focus? The light or the UV radiation? What actually does the frying? I wouldn't think photons alone could do much damage. And how do you put light into a fiberoptic cable so it comes out the other end? Could I shove some magnifying-glass-assisted light into a fiberoptic cable and point it wherever I want?

Also, how exactly does a photon travel down glass? Anything I know about atomic structure never makes any mention about photons.

[Mitch]

The cause of the light transmission doesn't come from atomic structure, it is from very old classical optics. The phonomena is called total internal reflection if I'm not mistaken.

[Scratch-]

Its like when you look into still water at different angles, as your angle gets closer to zero more and more light is reflected by the surface of the water from the spot your looking at.

[Corvettaholic]

OK, so the photon just keeps bouncing around in the fiber until it reaches the end. Seems easy enough. Now how do you stick photons in the fiber in the first place? Lets say I wrapped a fiber optic cable from my garage to my living room, shined a flash light into one end, would light come out the other?

[Scratch-]

Some would, I think they use lasers with fiber optics.

[Corvettaholic]

So, lets say I have a fiberoptic cable sitting outside, and goes into my garage pointed at a piece of paper. On the outside end, its pointing skyward, and there's me with a magnifying glass trying to focus some high quality arizona sun into the poor thing. Will the output end be able to burn the paper if I can get enough focused light into it?

[Scratch-]

Its hard to say what the focus of it would be when it comes out. It doesn’t come out exactly the same unless you have parallel light rays.

[Mitch]

OK, so the photon just keeps bouncing around in the fiber until it reaches the end. Seems easy enough. Now how do you stick photons in the fiber in the first place? Lets say I wrapped a fiber optic cable from my garage to my living room, shined a flash light into one end, would light come out the other?

yes

[Donaldson Tan]

not only u wont get parallel sunlight rays, but also u wont get be able to focus sunlight into the fiberoptic cable.. its diameter is so freaking small, how do u plan to perform this deed?

 

[gregpawin]

So, they have this glass in the middle of the fiber optic and a small layer of a different glass on the outside.  The outside glass has a higher refractive index than the glass inside, which makes the total internal reflection possible.  There's problems with bending the fibers which can make them less efficient, not work, or make their efficiency deteriorate even if you bend it back.

A huge problem is with making a clear signal over a long distance.  Over time, an exteremely short light pulse can spread out over time and requires expensive repeaters to go over long distances.

[Scratch-]

Hmmm... I read somwhere that fiber optics have surprisingly little signal loss with distance.

[Corvettaholic]

Unless you bend them. In the computer industry, fiberoptics are BIG due to much better data integrity over distance than copper. Still, its very expensive and you do need repeaters often, but not as often as copper.

As far as finding the focal point, I can find that with trial and error, or I can bust out my old highschool physics book. Figure I just stick the cable right at the focal point and hope for the best.

[Mitch]

Or you can just use the lens equation http://www.glenbrook.k12.il.us/gbssci/phys/Class/refrn/u14l5f.html

[Corvettaholic]

Yes! Thats EXACTLY what I was looking for! Thanks mitch, you just saved me a lot of hunting time!

[Seymor-Omnis]

Ah, I remember fiberoptic discussions in Physics, those were the days.  The lens equation, refraction angle, yes...that stuff hurts your head.