7
\$\begingroup\$

From the recent Lightwave article ASSIA exec touts terabit-speed DSL:

In a keynote address delivered earlier this week at the G.fast Summit in Paris, Dr. John Cioffi, chairman and CEO of DSL management optimization software supplier Adaptive Spectrum and Signal Alignment, Inc. (ASSIA) and Emeritus Professor at Stanford, asserted that his company has figured out a way to support terabit speeds over 100 m of existing twisted-pair copper lines. The techniques also can enable 100-Gbps transmission at more than 300 m and 10 Gbps over 500 m, according to the company.

The secret to such high speeds is the use of significantly higher frequencies than currently employed 300 GHz or higher, potentially. "Fiber-like speeds of 1000s of gigabits/second are possible by using the previously unexploited waveguide modes of current copper infrastructure," stated Dr. Cioffi via a press announcement. "Waveguide-mode use is similar to use of millimeter-wave transmissions in advanced wireless and 5G. Waveguides can enable use of frequencies above 100 GHz for extraordinary speeds." (emphasis added)

At current speeds, "existing twisted-pair copper lines" can be treated as standard transmission lines as is covered in many RF and communications texts.

I'd like to have some idea what the "previously unexploited waveguide modes of current copper infrastructure" refers to. There are dielectric waveguides, hollow conductor waveguides and coaxial waveguides, and those are also well described in standard texts.

Is there a twisted pair waveguide mode?

Is it possible to find a link, reference, or even a sketch of the fields of such modes?

Note: Leakage of signal between adjacent paris due to spatially overlapping modes would be a problem, but not necessarily lethal. Just as in multi-core optical fibers, there are mathematical techniques to even exploit this phenomenon, but that's beyond the scope of this question.

\$\endgroup\$
  • \$\begingroup\$ don't confuse 100Gbps with 100Ghz in short cables. in a noise free lab he only demonstrated " terabit speeds over 100 m of existing twisted-pair copper lines." The rest is hype ignoring EMI \$\endgroup\$ – Sunnyskyguy EE75 May 17 '17 at 12:23
1
\$\begingroup\$

Read for yourself and see fibre to the hub is explained with TDSL for the last 100m or so. Judging by covered numbers in illustration, patent was just approved. Maybe in 5~10 yrs (IMHO)

Lots of unknowns, not easy to achieve cost goals.

Read the presentation here enter image description here enter image description here

other references

\$\endgroup\$
  • \$\begingroup\$ Yes! This is exactly the answer to my question! :) It will take me some time now to digest all of this, there's clearly a lot going on behind the bullets. Thank you for the direct link! Once I do I'll ask a new question and leave a note here to be sure you know about it. I really appreciate your persistence! \$\endgroup\$ – uhoh May 18 '17 at 1:26
3
\$\begingroup\$

At a certain frequency, you start getting issues because you can fit more than one wavelength in between the wire pairs. This is also the reason coaxial cable and it's connectors get smaller as we go up in frequency (to 0.8mm connectors Anritsu is working on).

I've give an short explanation of 2 unconventional modes they might be referring to. Ofcourse, I've not seen the actual presentation, so this is just a guess on my part. I've never heard of anything like a "twisted pair" mode. The only thing that might be somewhat similar is a slotline, but I'm not very familiar with slotlines.

Surface Waves

Surface waves have been known about for a long time now, however, I've not seen them used outside of research. When using these, you are using the copper more as a optical-fiber style wave guide, and not a pair. The wave would be trapped between either the copper and the polymer covering it, or (but I don't think this is possible in telephone twisted pairs) the oxide forming on top of the conductor could server as the trapping dielectric. If my memory serves this right, Sommerfeld first came up with a description of these waves. The topic was later popularized by Goubau, which is why they are still sometimes called Goubau waves or the Goubau mode. The lines carrying these are then refered to G-lines.

Some references to look at on this topic:

  • Goubau’s paper On the Excitation of Surface Waves, Proceedings of the IRE, vol. 40, Issue 7, 1952.

  • G. Goubau, Open wire lines, IRE Trans. Microw. Theory Tech., vol. MTT-4, no. 10, pp.197-200, Oct. 1956.

  • M. J. King and J. C. Wiltse, Surface-wave propagation on coated or uncoated metal wires at millimeter wavelengths, IRE Trans. Antennas Propag., vol. AP-10, no. 5, pp. 246-254, May 1962.

There are also some more recent papers on the topic, I believe one of the researchers on the topic is/used to be Tahsin Akalin, but I don't know if he is still working on them. The main issue are losses that tend to still be quite strong. There is also the matter that in any research I've seen, coupling losses are quite high, and the launching structures are big or expensive, and would need to be installed at the users home to use this. There is also the matter that at any frequency this high, you are going to loose large amounts of signal whenever there is any significant bend, and from how I've seen the telephone twisted pair lines treated in average homes...

Polymer Waveguide mode

Another interesting development in research is the polymer waveguide (note, I'm working on this myself soon, so I might be more excited about this than it actually is).

In short, at mm-wave frequencies, copper (and any metal really) become poor performing cariers. However, we can start using polymers (the ones I've commonly seen used are PTFE, Styrene and LCP) as our waveguides. Problems here are the launching structures and fabrication of the high-quality polymer carriers. While these modes can be excited in hollow polymer waveguides, I don't know if it will still work/how things change when we introduce a copper core. (I suspect not because of the high losses within the metal).

Dielectric waveguides (the family of waveguides that polymer waveguides belong to) have been studied for a long time, and optical fiber is the most common member of this family. However, in recent years interest has turned to polymer waveguides for mm-wave applications as they provide flexible alternatives to rigid waveguides, and seem to be able to perform as well or better than coaxial cable (and, to higher frequency). Another advantage over rigid waveguides is that they tend to be higher bandwidth. One of the main issues now if finding launching structures that are good, and potentially integrating these into connectors.

There are a lot of papers on polymer waveguides, so I'm not going to list my favorites.

\$\endgroup\$
  • \$\begingroup\$ OK thanks for the thoughts on short-wavelength waveguide issues. Just googling for surface waves finds an un-paywalled copy of THz Sommerfeld wave propagation on a single metal wire, Jeon et al. 2005 which is a simple demonstration of a pulse traveling at least a meter. I don't know if it's conclusive but at least it's an illustration of the concept. For this question I think discussion of dielectric waveguides is off topic. I think the focus here is still the twisted copper pair to the home. \$\endgroup\$ – uhoh May 17 '17 at 7:06
  • \$\begingroup\$ I added the part on polymer waveguides because I was wondering if a wave constrained within the insulating polymer around the conductors in TP cables could be used as a polymer waveguides (although I doubt it) \$\endgroup\$ – Joren Vaes May 17 '17 at 7:13
  • 1
    \$\begingroup\$ Ya I see what you mean, ok sounds good! We'll have to keep on eye on this subject to see if anything is announced or published after the G.Fast Summit. Thanks! \$\endgroup\$ – uhoh May 17 '17 at 7:16
  • \$\begingroup\$ this not about surface waves!, but agile use of spread spectrum with group delay calibration and echo cancellation on existing copper network. \$\endgroup\$ – Sunnyskyguy EE75 May 17 '17 at 12:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.