How can light propagate through Hollow optical fiber.

[KT KIM]

Now I am studying a bit of optical fibers. And of course generally optical fiber works because of total reflection property of the light, which happens when the light from higher medium hits the lower medium material.

However I recently found out that there also is a thing 'Hollow optical fiber' which the core is hollowed out, filled with an air. I think the propagation should not happen because total reflection won't work here, but it works perfectly fine. I've hit some papers and got some keywords like 'band gap waveguide', 'photonic crystal' etc... but still can not understand it.

Can you give me a brief explanation, or just let me know where should I start with first?

 

[CWatters]

Not my field but I would ask...in a hollow fibre does the light propagate in the air or the glass?

Edit: Seems it's the air...

https://www.extremetech.com/extreme...ber-for-faster-networks-more-accurate-sensors

 

[sophiecentaur]

@KT KIM: How about a few references about this idea? If you've been reading then save us from having to search for what you're describing.

The hollow fibre seems to avoid the path loss through the glass so, if reflections can be made to rival the efficiency of TIR, the net loss over a long path could be less. We tend to assume that TIR is the only reflection worth considering. The above link seems to stress the improved transmission speed so, perhaps it's not so much aimed at long distance paths but at local connections. 3.5dB per km is not going to take you across the Atlantic easily.

 

[Andy Resnick]

Can you give me a brief explanation, or just let me know where should I start with first?

It's not clear to me if you are talking about photonic bandgap fibers (which can have a cavity in the center) or some sort of hollow 'light pipe'.

Photonic bandgap fibers are best analyzed in terms of wave optics, not ray optics. The interior is very inhomogeneous and is designed to allow only certain field modes to propagate. Having air (or vacuum) in the center is useful for high-power applications because there's no damage to the material.

 

[KT KIM]

Not my field but I would ask...in a hollow fibre does the light propagate in the air or the glass?

Edit: Seems it's the air...

https://www.extremetech.com/extreme...ber-for-faster-networks-more-accurate-sensors

in the air it is.

 

[KT KIM]

It's not clear to me if you are talking about photonic bandgap fibers (which can have a cavity in the center) or some sort of hollow 'light pipe'.

Photonic bandgap fibers are best analyzed in terms of wave optics, not ray optics. The interior is very inhomogeneous and is designed to allow only certain field modes to propagate. Having air (or vacuum) in the center is useful for high-power applications because there's no damage to the material.

More exact to say, I wanted to talked about, Photonic crystal fiber (including photonic bandgap fiber), maybe 'hollow optical fiber' was not a good word choice, excuse me.

 

[Andy Resnick]

More exact to say, I wanted to talked about, Photonic crystal fiber (including photonic bandgap fiber), maybe 'hollow optical fiber' was not a good word choice, excuse me.

Try starting with this:

OPTICS LETTERS / Vol. 25, No. 2 / January 15, 2000
Analysis of air-guiding photonic bandgap fibers
Jes Broeng, Stig E. Barkou, Thomas Søndergaard, and Anders Bjarklev

We present what is to our knowledge the first theoretical analysis of air-guiding photonic bandgap fibers. The
fibers are characterized by a large hollow core and a microstructured cladding exhibiting photonic bandgap
effects. Using an efficient, full-vectorial numerical method, we explain the operational principle of the fibers
and obtain detailed information about the properties of the air-guided modes. This information includes
accurate determination of the modes’ spectral extent, cutoff properties, and mode-field distributions.

 

[tech99]

I presume the photonic action gives us a hollow tube with reactive walls, which therefore reflect nearly all the energy. It seems equivalent to a metal waveguide with deep corrugations.