MadSci Network: Physics Query:

### Subject: Does diffraction occur inside a fiberoptic cable? At its exit?

Date: Wed Aug 9 08:48:13 2006
Posted by John
Grade level: grad (science) School: University of Memphis
City: Memphis State/Province: TN Country: US
Area of science: Physics
ID: 1155138493.Ph
Message:
```
The subject of diffraction interests me beyond what my textbook explains.  One
part has me very confused.

1.  Do you normally (in an ordinary thin pipe with collimated light parallel
to it going through it) lose more and more light the longer the pipe is due to
diffraction (or does it just affect you at the entrance and exit of non TIR
pipes?

2. Does TIR, even in a very, very thin fiberoptic, make diffraction "not
happen" in the middle of the fiberoptic?

3. Does light diffract as light exits the fiberoptic?  I know it diverges
(since light exiting isn't collimated) but is some of that divergence due to
diffraction?  (i.e. if the light were collimated would it still diffract at
the fiberoptic exit?)  It would seem that it might not diffract at the exit if
the boundary at the exit was TIR.

4. My textbook just shows that wavelength/diameter determines the diffraction
(kind of a ratio) -- but how would you calculate
a. the maximum degree of divergence of collimated light leaving a pipe?
b. the amount of light lost at a given angle of that divergence?  For
example, with a pipe of diameter D and light of wavelength L, what percentage
of the light would be lost being difracted 10 degrees off the central axis? 5
degrees etc.?

This is a very interesting thing but my textbook says nothing about it.

Thank you very much for whatever light you can shed!

John

Thank you very much.

```

Re: Does diffraction occur inside a fiberoptic cable? At its exit?

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