Propagation through Subwavelength Waveguide

[gillwill]

I've read in various places on the web and on this board discussions regarding subwavelengths, but I still can't fully comprehend how it's possible for an EM wave to transmit through an aperture and\or encased waveguide that is smaller than the given EM wave's wavelength.

I've read about tapered wave guides and such, but still don't see how that doesn't become an obstacle, yet it doesn't.


What happens to the dimension of the wave when it transmit through such a smaller enclosure?

I can visualize how it perhaps could be somehow be compressed, say like a sphere squeezed into an oval, but that would seem to make for faster than speed of light transmission.

Any insight are appreciated.

 

[Andy Resnick]

Propagating modes (traveling waves) do not transmit through a subwavelength aperture except possibly for something like tunneling. What comes out of the aperture is a nonpropagating (evanescent) mode.

 

[gillwill]

So, in regards to light transmitted via a subwavelength diameter optical fiber, it is not the actual light wave propagating through the fiber but some residual wave emission of another form induced by the light wave, similar as to with plasmons?

 

[Andy Resnick]

I'm not sure what you mean- if you are thinking of near field scanning methods, there is an evanescent electromagnetic field present (the 'covering field'):

http://en.wikipedia.org/wiki/Near-field_scanning_optical_microscope

Evanescent waves might be used to excite surface plasmons, but I'm not sure- I'm more familiar with FRET and total internal reflection methods:

http://en.wikipedia.org/wiki/Evanescent_waves

 

[gillwill]

Sorry I am not articulating better. Perhaps I was even using the wrong terminology, but what has contributed to my confusion are articles, such as the abstract below...

http://www.nature.com/nature/journal/v426/n6968/abs/nature02193.html"

...that seems to suggest that light from visible to near-infrared spectral range is being transmitted through a wire of 50 nm diameter, but maybe it's not really "optical" waves that are traveling through?

Also this article is another:
http://en.wikipedia.org/wiki/Subwavelength-diameter_optical_fibre"[/URL]

with it's statement [quote]"Subwavelength-diameter optical fibre (SDF or SDOF) is an optical fibre whose diameter is less than the wavelength of the light being propagated through the fibre"[/quote]

Documentation like this is what prompts my inquiry as to how that's possible and if so what happens to the "light" wave to make it fit into the smaller waveguide, but if I understand your first reply it is not the light waves that are traveling through the fiber?

Maybe I'm not getting a broader concept of waves & wave actions in general, which I thought I had a rudimentary understanding of.

 

[Andy Resnick]

Ah! that's interesting- I need to read the nature article before commenting further.

The Wiki article is good, tho- note the role of the evanescent field.