Re: Multimode Fiber Output Model

In article <1183930871.631781.247890@xxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Farsang <youzpalang@xxxxxxxxxxxx> wrote:

1- With " Object Space NA = 0.22 " and " Telecentric Object Space "
checked on if we selectec CIRCLE.MA for
the object does that mean that every point inside of the circle emits
a cone of light with cone having NA = 0.22 and all these cones are
telecentric (i.e. thier axes are parallel to the Optics Axis)?

No expertise on optical design here, and only limited experience with
fibers; but I think the *physical thinking* you have to use to approach
this problem is roughly the following:

* The large-core fiber you use can propagate a *huge* number of
independent transverse mode patterns -- the number is some constant
times the V number of the fiber, and will be given in a standard text
(like Saleh and Teich, for example).

* If you couple into the fiber in some random way at the input end,
you'll excite some random mixture of a large number of those modes; and
if you then propagate any significant distance down that fiber random
scattering and bending will ensure that the light gets divided up among
more or less *all* of them ("random mode conversion"), with random (and
time-varying, and motion-sensitive) amplitudes for each mode.

* In this situation, one way to view the output is to picture the
output face as being divided up into the *same* total number of small
spots or patches ("coherence areas"), each of them acting like a
separately emitting patch and radiating a totally independent and
randomly phased tiny plane wave across that patch, with this cone of
diffraction-limited radiation (diffraction-limited by the patch size)
being in fact telecentric with the fiber (unless the fiber end face is
cut skewed, in which case you have to take that into account).

* So, calculate roughly what sort of spot pattern each of those little
coherence areas will be imaged to at the target plane, taking into
account the size of the patch and how far off axis each spot is at the
input plane; and then just add up the *intensities* (i.e., powers, not
field amplitudes) of those target plane spots.

That's my off-the-cuff input on how this problem can be thought about;
others may want to correct or modify this.
.

Relevant Pages

  • Re: Multimode Fiber Output Model
    ... output face as being divided up into the *same* total number of small ... spots or patches, each of them acting like a ... randomly phased tiny plane wave across that patch, ... being in fact telecentric with the fiber (unless the fiber end face is ...
    (sci.optics)
  • Re: Multimode Fiber Output Model
    ... output face as being divided up into the *same* total number of small ... randomly phased tiny plane wave across that patch, ... being in fact telecentric with the fiber (unless the fiber end face is ... give the amplitudes and phases of each of the N coherence areas. ...
    (sci.optics)
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