Posted by Gene E. Bloch on 11/14/06 18:10

On 11/14/2006, dmaster posted this:
> Guest wrote:
> ...
>> How well will that optical cable work without shielding?
> ...
>
> Well, since the plastic cover on the cable is opaque, no "shielding" in
> the sense the word is normally applied needs to be added. In fact, I
> would suspect that the optical cable would work just fine with a
> transparent outer layer and a bright light shining on it. So, to
> answer your question: "That optical cable would work perfectly without
> shielding."
>
> Dan (Woj...)

You're absolutely correct.

1. The signal inside the fiber is laser light of a very narrow
frequency band and relatively high power. To interfere, you'd have to
get a signal which has a lot of power within the given frequency band
(as well as appropriate modulation) into the cable. Even if several
frequencies are in use (frequency-division multiplexing), each one has
the same properties.

2. The light is confined within the cable by a well-known optical
property called "total internal reflection" (also used in prism
binoculars and single-lens-reflex camera prisms). To get any light into
the cable along its length, you'd have to get around the flip side of
that phenomenon. The only places it's really possible to get light into
the cable and propagated along the cable is at the open ends.

--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")

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