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New Fiber Development
Maaaac writes "Just read this on GMSV: 'British researchers are developing a new kind of optical fiber that could surpass the known data transmission limitations of fiber. Augmented with a pattern of microscopic air holes that runs their entire length, these aptly-named holey fibers have a variety of surprising optical properties, not the least of which is single mode operation at all wavelengths and the ability to withstand the transmission of huge amounts of energy or data. To produce the fibers, researchers aligned an array of thin glass tubes, melted them together, and then stretched them to make a single fiber several kilometers long and about 125 microns across. While it's previously been suggested that such fibers would be predominantly used to transmit power -- or even matter -- their data transmission capabilities could be instrumental to the development of optical computers.' Now if only they would run this to my curb..."
It allows multiple frequencies to pass as if they were going down a mono-modal fibre.
It changes the refractive index without requiring strange doping of the glass.
More energy can be pumped down as the waves spread out. This means that fewer repeaters are required.
New Scientist had a good article on these fibres a year or so ago, and I talked to some of the researchers at the Royal Society.
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Theoretically, yes, but the path length for each mode doesn't vary much, only by roughly 0.01% - 0.2% between successive modes. On the other hand, a difference of 0.015 between the indices of refraction of the core and cladding creates speed differences of around 2000km/sec between the two materials, or about 1% for standard glass. Higher modes have a longer path difference, but they also penetrate further into the cladding and get sped up more. The effect of the speedup in the cladding is more pronounced than the effect of path length, so higher modes reach the end faster.
In an optical fiber, light rays traveling through the core can bounce off of the outer boundary between the cladding (lower index of refraction) and the core via total internal reflection. However, interference only allows rays at certain angles with respect to the fiber propagate. Each of these valid ray directions represents a mode.
Single mode operation means only the axial mode, where the ray travels straight down the core, is valid. The reason single mode operation is desired is because the higher modes do penetrate into the lower-index cladding where the speed of light is higher when they reflect off of it, which causes the higher-index modes to propagate faster than lower modes. Basically, if you fire a very sharp pulse of light of all modes into an optical fiber, the modes will all reach the other end of the fiber at different times. Since your sharp impulse has been spread over time, there is a limit to how many different pulses can be resolved over a certain period of time. Single mode operation means that there are no higher modes and hence less spread and higher bandwidth. (There are other causes of spread, but not much can be done about most of them).
Because the size and positioning of the holes can be specified, the fibre can be designed to confine the light it is sending to a small central region of, say, a micron square, or a "big" region of several thousand square microns. If this central region is small, it is possible to operate an optical switch using very low light intensities, which is important for the future development of optical computers. (Indeed, optical switching has recently been demonstrated in a holey fibre by researchers at Southampton University.) In a "large mode" holey fibre, the cable can send lots of power, which makes these fibres useful for applications such as laser welding and machining, as well as the development of high-power fibre lasers. Being able to tailor the way light is guided by a holey fibre could revolutionise the way data is transmitted and there are likely to be many other exciting applications which have yet to be discovered
The optical computing aspects are exciting, however.
"It is a greater offense to steal men's labor, than their clothes"
Confirmed... You can be sure that whenever someone has to dig the ground, they lay fibers (along pipes, copper wires, whatever) since what is costly in installing optical fibers is not the fibers themselves, it's burying them. Why aren't they used? There is a bunch of answers to this question. These fibers are laid to be rented by someone else. 'Dark fiber' does not refer to the fact that no signal goes through them, but to the fact that they are rented 'as is' without the lasers and detectors necessary to build the whole optical network. So you need someone to rent them... That would be telecom companies, but those only use backbones and WAN/MANs (Wide/Metropolitan Area Networks) and are not interested yet by the FTTH (Fiber To The Home) concept, and they won't be unless the copper wire network's cost has been written off.
Big whoop. We already have some pretty fat honkin' pipes. The real hold up and cost is not the fiber or the fiber's capabilities, it's the machines at the ends of the fiber. Certainly, when laying fiber you want to lay the best fiber you can for future needs. But even now most fiber is enormously underutilized. Most high speed connections (faster than oh about OC-3) currently requires multiple computers to handle the bandwidth. And it takes even more equipment to bridge between the fiber and all the other networks (most of which use different protocols). That is where the major setup and operations costs are. The nature of the situation has resulted in the fastest connections (OC-128 or OC-256) being limited to only a smattering of locations. We would be far better off if the equipment to use these connections was much streamlined and lower cost. That would result in many more high speed connections and a much faster and much more robust internet.