question about electric field in an optical fiber

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R@FIX - 20 Jul 2004 19:07 GMT

Hello! excuse me for my bad english I'm french:
I'm student in ingenieur school in france, and I do a project about
optical fiber. On my project I have to caculate the electric field in
an optical fiber, it is what I did whith Matlab, in a single case, I
use the besselj and besselk functions and continuity equations... to
calculate it, whith these conditions: Ncore and Ncladding are
constant,and we choose lambda and Rcore(0.15) to have one mode in the
fiber.

I would like to know if the electric profile fields in an optical
fiber depends on how the light is injected inside?

You can see the assembly for the injected light
here -> http://reptils.free.fr/forumhardware/images/shema_FO.JPG

The consequence of this assembly is the lense diffract the light, so I
do the profil of the Airy disk genereted by the opening lense
you can see the electric field(red)(without hold account of the
injection) and the Airy disk(blue)
here-> http://reptils.free.fr/forumhardware/images/profil_de_champs.JPG

is the electric field inside depends on the Airy disc in the enter of
optical fiber?
if yes, how? whith a convolution or else?

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Steve Craig - 26 Nov 2004 17:46 GMT

> Hello! excuse me for my bad english I'm french:
> I'm student in ingenieur school in france, and I do a project about
[quoted text clipped - 20 lines]
> optical fiber?
> if yes, how? whith a convolution or else?

Some things to consider...

If you are assuming that the light entering the fiber is from the maximum of
the Airy disk then there could be some noticable differences to teh electric
field, though I'm not too sure about this. The thing is is that the maximum
of the Airy disk is a single spatial frequency of the object being the laser
itself. I don't think this will have an impact at all, but I don't know for
sure.

I did an experiment several years ago involving the electric field of the
light inside a fiber and from what I can remember the field is dependent
only on the nature of the fiber itself, ie, numerical aperature, core radius
and core shape (in the case of polarized fibers). It also depends on if the
fiber is single or multi-mode, and the function describing the index of
refraction of the fiber core and cladding (step-index or gradient index.).

Try using a Gaussian optics set-up to reduce the spot size on the fiber
corre aperature. If you are doing purly theoretical work see if the
electric field is dependent on spatial frequencies of the beam itself. To
the best of my knowledge and silghtly damaged memory, I don't think they do,
but I could be wrong.

Hope this helps.
Steve

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Natural Science Forum / Physics / Optics / November 2004

question about electric field in an optical fiber