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Communications Technology

Nano-Scale Optical Co-Axial Cables Announced 157

toybuilder writes "Reuters reports that scientists have published their work on nano-scale optical coax in the most recent issue of Applied Physics Letters. The coax cable is only about 300nm wide, and is able to transmit optical signals using a carbon center conductor, transmitting light at about 90% the speed of light."
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Nano-Scale Optical Co-Axial Cables Announced

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  • by ArcherB ( 796902 ) * on Monday January 08, 2007 @05:34PM (#17514390) Journal
    The coax cable is only about 300nm wide,...

    How do you plug it in?
  • huh? (Score:5, Funny)

    by macadamia_harold ( 947445 ) on Monday January 08, 2007 @05:35PM (#17514406) Homepage
    The coax cable is only about 300nm wide, and is able to transmit optical signals using a carbon center conductor, transmitting light at about 90% the speed of light.

    methinks the speed of light is whatever speed the light travels at.
    • Re:huh? (Score:4, Informative)

      by mandelbr0t ( 1015855 ) on Monday January 08, 2007 @05:38PM (#17514440) Journal

      The physics constant c refers to the speed of light in a vacuum. Read here [] to find out why this statement isn't stupid.

      • Re: (Score:2, Funny)

        by kfg ( 145172 )
        the speed of light in a vacuum.

        Appears to be zero. Now if you'll excuse me I have to go blow my nose and take a shower.

      • Re:huh? (Score:5, Insightful)

        by Incongruity ( 70416 ) on Monday January 08, 2007 @06:40PM (#17515654)
        Hardly -- the statement is a little stupid because it doesn't mention the constant c nor "the speed of light in a vacuum", it simply says "the speed of light" -- most people will recognize the error, but it's still an error.
        • The light will always travel at the speed of light, but it is absorbed and re-emitted by the medium, which takes a certain amount of time. This causes the average speed to be slower than the speed of light. So no, quoting the average speed as a percentage of the speed of light is not really an error.
        • by Instine ( 963303 )
          Actually, in physics, there's no such thing as "speed". Only Velocity. Speed, strictly speeking, is meaningless.
          • Well, that's not the physics I was taught...velocity is a vector quantity and speed is a scalar quantity... essentially velocity without a direction. That doesn't make it any less real -- it makes it less informative, sure, but no less real. A rate of change is a rate of change, regardless -- the sign (i.e. +/-) or direction, as those can be arbitrary in some cases and in most others, it's only important that they're correct relative to other related rates.
      • by solitas ( 916005 )
        So, the material's 'n' would be around 1/0.9 = 1.1111 (n=c/v). I wonder what form of "carbon" it is - crystalline and amorphous diamond are in the range of 2.42-2.57...
    • Re:huh? (Score:5, Insightful)

      by Anonymous Coward on Monday January 08, 2007 @05:38PM (#17514458)
      Light always travels at 100% of the speed of light. However, in this cable, light travels at about 90% of the speed of light in a vacuum.
    • by stigin ( 729188 )
      Well you are right in some sense... the individual photons always travel at the speed of light. The phase velocity however can be slower (and in fact also be faster) tha the speed of light. It is the later al these articles refer to since this is the classically measured propagation of a coherent bunch of photons aka a beam of light.
    • methinks it is like a weasel
    • What happens is that it gets gradually slower as each photon realises "Oh, I should be going 90% slower" with every Planck length that passes. Thus the speed of light through this fibre asymptotically tends to zero. It's actually pretty damn clever stuff. For a practical application, see "The Light of Other Days", by Arthur C. Clarke.
  • Wowsers. An index of refraction of only 1.1 is damned impressive.

    The fibers are k3w1, but what I really want to know is how they got the silly things to be so much less of a "drag" than teflon. If they can extend that, it has a lot more immediate applications as a low- material than as a fast lightpipe.

  • As soon as I read that, it occurred to me that half of the comments were going to focus on that one sentence. And what do you know? I was right.
    • You might want to cancel the pointy wizard hat you just ordered from, the summary is only two sentences long so half of the comments focusing on the second sentence isn't particularly odd. ;)
  • by JesseL ( 107722 ) on Monday January 08, 2007 @06:07PM (#17515000) Homepage Journal
    From TFA:
    "It's not quite the speed of light, but it's probably 90 percent the speed of light. That's still thousands of times faster than electronics," Naughton said in an interview.

    It was my understanding that electric fields propagate through copper at about 1/3 C.
    • It's actually about 2/3 the speed of light (depending on the dielectric constant). The TFA might be referring to the drift velocity of electrons in the wire (on the order of a centimeter/s), which is not a particulary useful comparison.
    • by KokorHekkus ( 986906 ) on Monday January 08, 2007 @06:27PM (#17515388)
      I thought it was a bit higher than that (still not 90% though). Did some digging and wikipedia came up with that the velocity of propagation was about .79 for a coax cable according to it. Checked a supplier of coax cables and they quoted velocity of propagation at .66 C to .84 C (latter for 1.13 mm copper KTV cable with PE insulation)

      Source: on []
      • 90%+ is possible for waveguides, and for open-wire feedline, but is usually lower for coaxial feedline.
        VF is 1/sqrt(dielectric constant). Interestingly, the velocity itself is VF*c=1/sqrt(L*C) where c=speed of light in a vacuum, and L and C are the series inductance and shunt capacitance of the feedline, so those values are directly related to the velocity factor. Finally, given L and C we can calculate the characteristic impedance Z=sqrt(L/C).

        The characteristic impedance of the coax is important to achie
  • by rjdegraaf ( 712353 ) on Monday January 08, 2007 @06:08PM (#17515004)
    The 300nm wide fiber is the key issue.

    The thinner the fiber, the less the digital light pulses are spread (due to reflections on the fiber shell) per unit distance, the more information can be sent through per unit time.

    Thinner means more bandwidth.

    • Re: (Score:2, Funny)

      by sexybomber ( 740588 )
      I guess "fat pipes" is a misnomer, then.
  • I think the thing we need to think about is when this may be useful to us. Right now it has to cost around elevenity billion dollars to make just enough to test... I think I will stick with the current speed of light through fiber.
  • Wake me up when they announce nano-scale HDMI.
  • by smellsofbikes ( 890263 ) on Monday January 08, 2007 @07:16PM (#17516224) Journal
    Will someone tell me *why* they did this? Yes, it's very cool. But the whole and only point of coax, as they talk about in TFA, is that it minimizes electrical influence.
    If you're using light, there *isn't* any electrical interference, either as a transmitter or a receiver. That's one of the major benefits of using light.
    So it's kind of pointless to make a coax, unless you really want a two-channel transmitter where one's a funny ring-shape. In which case, why not make optical ribbon cable?
    Which brings up a wholly separate question: one reason industry has moved from parallel to very-high-speed serial is that you don't have to worry about timing and synchronicity, which are primarily due to impurities in copper. Is this an issue with optical? Coz the engineering is generally easier to run ten existing lines in parallel than to make one line ten times faster, if you don't have to worry about synchronizing them.
    • Re: (Score:2, Informative)

      by fluffy99 ( 870997 )
      You obviously didn't read the entire article. The whole point is that they are shoving something with a wavelength of 375 nm down a 300 nm pipe. They explained that this is the exact same issue with shoving RF down a coax (ie 1-meter wavelengths down a 1/4" coax).
      • I must've missed that part, and I did read it. hm, weird.
      • kay, I've thought about it some more. So the wavelength's 375 nm: so what? Light's a longitudinal wave, not transverse. I'm not sure light *has* a diameter.

        The issue with shoving RF down coax is one of minimizing impedance, not wavelength, which is why the same coax works well across a decade or so of RF. Antenna length *does* need to scale with wavelength, but unless you want your waveguide to act like an antenna, you probably don't want it to be tuned, or to need to be tuned, to the wavelength in ques
        • OK, two important points about coax.

          1. For any given size of coax there is a maximum permitted frequency. This occurs when the average circumference of the dielectric equals the wavelength in that dielectric material. This means that as the frequency goes up the diameter of the cable must go down. We see this clearly in the development of coax connectors for mmwave applications, where diameters are now around 1mm in some cases. If one operates above the maximum frequency, then the outer of the coax will
    • "Coax," short for coaxial, is defined as "having or mounted on a common axis." In cables, it is any design in which a central conductor is surrounded by a shielded cladding -- they both encircle a common "axis" or center. All fiber cables are coax, except those used in toys and art. Most have multiple levels of shielding to protect against energy loss/insertion, physical stresses and environmental hazards, in order from inner to outer.
      • Except that 99% of the time, coax means signal down the center, and signal return path (or guard, or whatever you want to call a conduction path) back through the cladding, which is the point of the shielding. That's why we use coax for RF, because it minimizes the loop area and coaligns the signal with the return, rather than just a signal path and a current return path running out to the antenna separately, each with a 20mm outdoor-exposure-rated rubber casing.

        • Re: (Score:3, Insightful)

          by StikyPad ( 445176 )
          That's only because 99% of coax in common use is single conductor electrical shielded cable, which is to coax as sheep are to mammals. Electrical shielded cable is just a type of coax cable. Also the function of the shielding is to eliminate EMI, not to provide any sort of return path. That it is typically connected at both ends is incidental -- it's just the simplest method of grounding the insulation.
          • Here's an unbelievably cool demo of why return paths matter so very, very much. Unfortunately it takes some expensive equipment.
            Take about 50-100' of coax. Strip the ends, and put a 50 ohm resistor between the center and the braid on one end. Attach the braid on one end to the braid on the other end with a 2" wire. Put DC on it and put a current probe around the 2" wire. 99.9% of the electricity flowing, is flowing through the 2" wire. Now put a 1 MHz square wave down the center conductor and measure
    • Re: (Score:3, Insightful)

      by Goldsmith ( 561202 )
      They use coaxial wires so that their waveguide can be long and skinny.

      It's thinner than the wavelength of the light, which is not possible with fiberoptics. There are other ways of making subwavelength waveguides, but they don't work over long distances. In the co-ax, light is transmitted basically as if it were in free space, and doesn't attenuate very much. In most nanostructures used for optics, light is transmitted as a plasmon (a rather quickly attenuating surface bound state).

      There's a bonus third e
      • Re: (Score:3, Insightful)

        You're closer to convincing me than anyone else.
        So tell me why the wavelength of light matters: it's longitudinal, not transverse, so what limits it? Does light have a diameter at all? I guess there's an amplitude, some function of the electronic/magnetic components. I know they're 90 degrees to one another. Are the two the same amplitude? Does it matter that it runs into things? I guess an electric field shouldn't be able to cross a conductor, but is that absolute, or is there some penetration into t
        • So tell me why the wavelength of light matters: it's longitudinal, not transverse, so what limits it?

          Uh, WHAT? Light is certainly transverse. The reason people get confused is when they look at a graph of an EM wave they see things WAVING up and down. Light doesn't do that. The waves drawn in diagrams only mean that the amplitude of the electric/magnetic field is increasing/decreasing as the wave travels along its path.

          However, a light wave isn't (can't be) a perfect mathematical ray with changing ele

        • There are a lot of solutions to Maxwell's equations beyond the version taught in introductory electromagnetism. In a co-ax, there are different states allowed than if there was just a metal tube. I don't really want to get more technical than that, because I'll get things wrong. You could think of this system as changing light from photons to electrons and back.
  • When we're working on quantum physics and teleportation, why are we focusing on something as slow as the speed of light? If we've already teleported information via cables in the sewers beneath the Danube [], why care about the speed of light, let alone anything less than it?
  • c the constant (Score:2, Informative)

    by H0D_G ( 894033 )
    Actually, the speed of light in a vacuum is not constant at all, according to several current theories. Professor R.T. Cahill's process physics theory(i mention this one, cause i've had some lectures on it, but there are others) states that the speed of light is actually inconstant, and depends on the flow of space around it. I don't claim to understand it, being a humble chemist, but it's interesting stuff [] for a cahill paper
  • Every time I try to solder a connector on a piece of 300nm-thick coax I wind up trying to strip off the shielding, but cutting off the inner conductor as well. Either that, or I forget to put the connector shell onto the cable first....

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