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Plastic Optical Fibre: Cheap and Bendy
Motivator_Bob writes: "The Sydney Morning Herald has an article on making optical fibres from plastic rather than the traditional glass."Advances in optical-fibre making at the Australian Photonics research centre could bring communications at the speed of light into Australian homes and businesses in the next few years. The advance - microstructured polymer optical fibres (MPOF) - allows the manufacture of optical fibres that are much smaller, cheaper, more rugged and easier to make than glass fibres..."
50 years after Einstein, and people still don't realise that the electrons in a piece of copper wire travel at the speed of light? In fact, as light in fibre optic cabling bounces off the insides of the plastic tubing, it takes a less direct route and thus technically has a _higher_ latency than copper wire.
actully it is very bendable and isnt as fragile as you might think.
--- Sig test. 1...2...3...
This plastic optics fiber must have a higher index of refraction than glass, which increases Brewster's angle, which increases the amount of bend allowed before the signal is lost. This is no biggie, technologically speaking. The only reason it hasn't been done before is cost. Glass is very cheap and we know how to make thin strands of it already.
With LEO sats, you could get that down to something more reasonable. My current satellite service gets minimum 600ms latency real world, in geostationary orbit, 35,000km or so up. LEO sats can be much much lower, 300-800km. At LEO, the latency is no longer an issue, in fact, you might get better latency than land lines under some circumstances!
I've had enough abrasive sigs. Kittens are cute and fuzzy.
The relevant quantity in fibers is the critical angle, beyond which all light is reflected inside the higher-index core. (Actually, the whole ray-optics picture is not completely accurate for fibers with features, like the core size, comparable to the wavelength...but it's qualitatively the right idea.) (Which, by the way, has nothing to do with the reflection disappearing from the puddle, since that is a reflection into the lower-index medium, air. The puddle effect has more to do with your shadow blocking the light.)
Note also, by the way, that it's not so much that the index of the polymer fiber core has been increased, its that the effective index of the cladding is decreased (by adding lots of thin holes/veins, hence the name microstructured fiber). And you can do the same thing with glass fibers. (Because of the higher effective contrast, you can confine light more tightly and e.g. enhance nonlinear effects.
(You were on the right track that it's the bending light loss, and the advantage therein of higher index contrast, that the article was referring to.)
Microstructuring can also go in the other direction to photonic crystal fibers and guiding light in air.)
If a thing is not diminished by being shared, it is not rightly owned if it is only owned & not shared. S. Augustine
Actually, electrical signals in the neighborhood of 10-100MHz propagate through copper at about 0.1C or (18,600 mi/sec or 30,000 km/sec).
That depends on the geometry. Use thicker copper and/or space it farther apart and the signal goes faster. A less lossy dilectric helps, too.
At low frequencies - i.e. where the stray resistance of the line's copper is small compared to the characteristic impedence - the speed is dominated by the dilectric constant of the space between the conductor - and you get your approximate 70% of lightspeed. At higher frequencies (or longer wire) the line acts progressively more like a series-resistors-parallel-capacitors delay line cum low-pass filter. This slows and attenuates the signal, the higher frequencies more than the lower ones.
Selective slowing (phase shift) of the higher frequencies smears out pulses, while selective attenuation weakens them compared to noise.
This can be compensated for to some extent (by amplifying and phase shifting the higher frequencies before transmission and after reception). But there's a limit to how much of that can be done: Too much at the transmitter and you exceed the allowable signal level for the wire (causing cross-talk into the weaker signals going the other way nearby). Go far enough out and the high-frequency signals get down near the noise level, so amplification at the far end just jacks up the noise, too, and they're lost. That's why DSL will only go so far (without a repeater/regenerator).
Telephone wiring was designed for audio of only a few kilohertz, distances of a medium-sized town (rural wiring is a special case), and MANY wires in a bundle. So it uses very thin copper. Central offices were spaced in urban areas so that everybody they feed would be close enough to get a good audio signal. But DSL uses higher frequencies which peter out closer to the source.
Within the distances and frequencies where a copper structure will act as a transmission line rather than being ruined by this effect you're still talking about 70% of c.
But when the poster said "propagate through copper" he MIGHT have been talking about the "skin effect". Eddy currents in the copper due to changes in magnetic fields produce a compensating field, and the result is the field doesn't enter the copper until the eddy currents die due to the copper's resistance. (That's why magnetic fields won't enter a superconductor - to a first approximation.)
But that confuses "propagating through copper" with "propagating along a copper transmission line". In a transmission line (or any other waveguide) the signal and energy don't propagate
through the conductor(s). They propagate through the SPACE BETWEEN the conductor(s). Raise the resistance of the conductors and you increase the speed of penetration of signals into the conductor, but slow its propagation along the line.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way