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Communications Networking

Graphene Sheath Modulates Fiber-Optic Transmission At 200 GHz 18

Posted by timothy
from the let's-go-straight-to-x-rays dept.
An anonymous reader writes "Researchers in China have shown that a graphene sheath can modulate light transmission through an optical fiber at 200 GHz. The graphene, even crudely draped over the optic fiber on a microscope slide, absorbed some of the light passing through the fiber. But a preceding short-wavelength light pulse could temporarily disable the effect, enabling an all-optical infrared fiber-optic switch. Recovery was fast enough to enable modulation of transmitted light at 200 GHz using conventional fiber-optic communication wavelengths and thinned commercial telecommunications fibers. The findings could have use in telecommunications industry and future high-speed on-chip optical interconnects."
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Graphene Sheath Modulates Fiber-Optic Transmission At 200 GHz

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  • And on the far end? (Score:5, Interesting)

    by Shatrat (855151) on Thursday January 16, 2014 @12:19PM (#45976687)

    It sounds like this is just very high speed On Off Keying, which is not only limited by modulation but also by the ability to clearly receive that signal on the far end.
    This could be an alternative to coherent phase shift keying as a short range 100G+ interconnect though, where dispersion and noise aren't an issue.

    • by kaiser423 (828989) on Thursday January 16, 2014 @12:33PM (#45976845)
      It's modulation depth (per the abstract) is only 38%, so it's not quite a broad-band as on-off-keying. More like a non-optimal AM modulation. Still, if you can do it at those speeds that's head and shoulders above and beyond what we have now.

      Another key benefit would be the simplification of encoding/decoding hardware. Using coherent PSK, QAM and other schemes there's quite a bit of effort put into determining the channel, etc to be able to know your current place in the constellation which can be a problem in the presence of noise sources. There's the well-known algorithms, tons of proprietary ones and new research papers every day on ways to betermine estimate the transmission channel to allow for more points (bits) in a constellation. Some of the QAM's, after disruption take over 100,000 symbols to re-lock to the bit stream. But that's the price you pay to shove more data down the pipe. If this works well though, you can get rid of all of that logic, stringent requirements on the transmission media and improve immunity to noise because with a simple AM, it only takes one symbol to re-lock onto the bit stream. They're dead simple to implement and robust as can be.

      I can definitely see some really big uses for this if all goes well.
      • It's modulation depth (per the abstract) is only 38%, so it's not quite a broad-band as on-off-keying.

        Once you've got that it's trivial to use beam splitters and destructive interference to change the modulation from 62% vs. 100% to 38% vs. essentially 0% amplitude.

        • It's modulation depth (per the abstract) is only 38%, so it's not quite a broad-band as on-off-keying.

          Once you've got that it's trivial to use beam splitters and destructive interference to change the modulation from 62% vs. 100% to 38% vs. essentially 0% amplitude.

          Not that it matters: The receiver is AC coupled, anyhow. As long as the modulation is sufficiently deep that the signal is substantially above the noise floor, you're fine. Switching a third of the amplitude is nearly as good as switching all

    • If this is an all-optical switch that doesn't require high-powered lasers or other difficult to achieve non-linear optics, wouldn't this have applications for all-optical computing gates, as well? Basically use something like this to construct an all-optical transistor, and have a logic circuit powered by light instead of electricity?
      • by swschrad (312009) on Thursday January 16, 2014 @01:20PM (#45977413) Homepage Journal

        you also have to dissipate the heat of conversion in the source and detector, which means large chunks of silicon in relation to the transistors. but I can see using this to cut distortion cross-chip, or up a stack of chips in Cray-ish constructions, and maintain internal speed.

        there is of course the usual last line of the study document, on behalf of the lead and the graduate assistants who have several years to go in their degree yet, that "this effect needs more study."

  • Proof that "it works" will come after peer review and not be fully vetted til we see some solid&stable term results.

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