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Network Hardware Science

MIT Researchers Make Advance Toward Photonic Circuits 55

MrSeb writes with this excerpt from an article in Extreme Tech: "Light-emitting diodes are a cornerstone of consumer tech. They make thin-and-light TVs and smartphones possible, provide efficient household, handheld, and automobile illumination, and, of course, without LEDs your router would not have blinkenlights. Thanks to some engineers from MIT, though, a new diode looks set to steal the humble LED's thunder. Dubbed a diode for light, and crafted using standard silicon chip fabrication techniques, this is a key discovery that will pave the path to photonic (as opposed to electronic) pathways on computer chips and circuit boards. The diode for light — which is made from a thin layer of garnet — is transparent in one direction, but opaque in the other. Garnet is usually hard to deposit on a silicon wafer, but the MIT researchers found a way to do it."
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MIT Researchers Make Advance Toward Photonic Circuits

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  • New we need a real one way mirror.
    • This would have been an excellent time for this post:

      First! (using photonic circuits).

      Or some crap like that.

  • by Zouden ( 232738 ) on Wednesday November 23, 2011 @12:23PM (#38149414)

    The summary (taken from the first article) implies that these new diodes are going to supersede LEDs, but they have completely different purposes. LEDs make lights, these things don't.

  • by bigredradio ( 631970 ) on Wednesday November 23, 2011 @12:25PM (#38149430) Homepage Journal
    From the article -

    The whole system could be made using standard microchip manufacturing machinery, Ross says. “It simplifies making an all-optical chip,” she says. The design of the circuit can be produced “just like an integrated-circuit person can design a whole microprocessor. Now, you can do an integrated optical circuit.” That could make it much easier to commercialize than a system based on different materials, Ross says. “A silicon platform is what you want to use,” she says, because “there’s a huge infrastructure for silicon processing. Everyone knows how to process silicon. That means they can set about developing the chip without having to worry about new fabrication techniques.”

    It is good to see someone is coming up with an innovation that can "actually" be introduced. Seems like I read about new innovations every day on slashdot that never get off the ground because completely new manufacturing processes need to be created. Hopefully this will actually make it because it requires fewer changes by manufacturers (which can be significant barriers to innovation).

  • light transistor (Score:5, Interesting)

    by greywire ( 78262 ) on Wednesday November 23, 2011 @12:26PM (#38149444) Homepage

    Does this mean a light transistor is coming soon?

    I am wondering if there is any material that acts as a mirror and can be switched from reflective to transparent electronically? I assume there is not or you wouldn't have devices like MEMS displays. I'm thinking if you had such a material it would be essentially a light transistor.

    • Re: (Score:2, Interesting)

      by Anonymous Coward

      Well we currently have devices that can become opaque or transparent depending on signal.

      Also, couldn't metamaterials technically be used in this way?
      That EM blackhole that was created could be turned in to a one-way channel for light instead of just an infinite spiral to absorption
      Reflective could be a mirror that punts it back through another channel that comes out at the same input, shift mirror to allow it through.
      Of course, that involves mechanical stuff (even if incredibly tiny), but the use of photon

      • Just because you can use it to store data doesn't mean it will make a good processor any time soon.
        how long does it take to switch states. That's why flash ram is not used in primary memory.

    • by Calos ( 2281322 )

      Light transistors? Not exactly as you describe, that I'm aware... But things that fit a more general description of "light transistor" do exist. They're basically optical ring resonators, but add some standard silicon doping and bias it, you can change the refractive index to stop the resonance. I'm not exactly up on my photonics, but I think in theory you could couple the ring resonator to another pathway which would ultimately go to the display, with the applied voltage controlling whether or not the s

      • by greywire ( 78262 )

        I'd like to be able to reflect something back and forth, essentially keeping it in a holding pattern until such time as I wanted to release it through one side. The length of time of course would be very very short, and the switching time from transparent to reflective would need to be fast.

    • I am wondering if there is any material that acts as a mirror and can be switched from reflective to transparent electronically? I assume there is not or you wouldn't have devices like MEMS displays

      Maybe a DLP mirror system ?

      • by greywire ( 78262 )

        Yeah, thats the MEMS I was referring to. I was wonder if there was a purely solid state way of doing it.

  • by Hentes ( 2461350 ) on Wednesday November 23, 2011 @12:26PM (#38149446)

    Could someone with expertise in the topic tell me:

    • How does this replace a LED? It's not a light source.
    • How does this allow creating optical circuits? You need more than just diodes for a logic gate.
    • If I make a sphere out of this, will it act like a black hole?
    • Making a sphere out of this should be no different than making any type of black colored sphere. The light is converted to heat and the sphere warms up. If the heat is allowed to slowly escape, then equilibrium is reached. Otherwise, the sphere melts and potentially destroys its heat absorbing properties. Or the liquid sphere radiates heat away. In a black hole, heat cannot escape at all.
      • My reading of the summary says that they claim that is opaque in one direction and transparent in the other.

        Consider the following thought experiment:
        Assume that this material works the same way for far-infrared as it does for visible light.

        In a well insulated cylinder place a sheet of this material across the interior of the cylinder so that light can pass to the left, but not to the right.

        Now the material in the right end of the cylinder is emmitting infra-red radiation. It can pass through the material.

    • Could someone with expertise in the topic tell me:

      • How does this replace a LED? It's not a light source.
      • How does this allow creating optical circuits? You need more than just diodes for a logic gate.
      • If I make a sphere out of this, will it act like a black hole?

      From TFA:

      Basically, it’s now possible, with regular chip-fab tools, to create an integrated silicon circuit with optical, rather than electronic, interconnects — both internally, and between other chips.

      TFA makes it confusing by bringing up blinking lights used to convey various status to humans via light, which does not appear to be related.

      In the near term, though, garnet-on-silicon chips are likely to be used in networking — first in backbone routers, which are physically huge and very power hungry because of the current size of optical switching hardware, and then hopefully at home and in the office (100Gbps home networks!)

      It's all in the poorly written article.

    • by Anonymous Coward on Wednesday November 23, 2011 @01:09PM (#38149916)

      It's not a Light Emitting Diode, it's basically a Light Diode. Light can only pass through in one direction. The way this is normally done is by rotating the polarization of light through two polarizers. [] Any light of the wrong polarization cannot return back to the light source. This is usually used to protect laser sources and their modulators from return loss reflections in fiber optic systems that make use of polarization maintaining fibers.

      Anyway, a 'true' optical transistor can be fashioned out of this if coupled with an optically controlled gain medium. If you have optical transistors, you can create optical NOR or NAND gates, and all basic logic functions can be created solely from these gates.

      Just skimming the actual Nature paper itself, it appears they've basically created an optical isolator on a planar optical waveguide circuit.

      To answer your last question: no.

      You'd be better off with black construction paper for that.

    • by Anonymous Coward

      If I make a sphere out of this, will it act like a black hole?

      No. Black hole studies typically utilize Dark Emitting Arsenic Diodes, (DEADs), not Light Emitting Diodes, (LEDs.)
      DEADs don't really emit darkness, but rather just absorb light. The more current that's applied, the more light they absorb.
      Originally developed by the Department of Defense for use as a type of energy absorbing material coating, (e.g. a laser weapon shield).
      As laser research produced more and more powerful lasers, DEADS were tuned to absorb a more powerful beam but of a narrower frequency ran

  • Assuming you don't `leak' light like you do with electricity thought a traditional transistor gate when scaling way down this technology could provide a method of continued packing of high speed transistor like elements. The next interesting question would be how hot the chips would actually run, considering we're really no longer resisting, resulting in high temperatures.
    • by Semptimilius ( 917640 ) on Wednesday November 23, 2011 @12:50PM (#38149734)

      Well, much of the leaking in traditional electronic transistors is due to quantum mechanical effects, which would still apply to photonic devices. (With differences arising from such things as spin.) Some people are using evanescent fields from thin fibre lines to actually couple the signals in the line to other devices.

    • You surely leak light by the same mechanisms you leak electrons (tunneling), it is just that with light we are used to it, but still don't have a useful workaround. Optical elements also disperse light in a way that is quite similar to a conductor dispersing elecrons, and they also absorb the light (what have no equivalent for electrons).

      The biggest advantage of an optical device is that it can act on several signals at once, in a SIMD way.

  • by divisionbyzero ( 300681 ) on Wednesday November 23, 2011 @12:47PM (#38149692)

    It doesn't go off and start talking about LEDs and WDM which just confuses the issue. []

  • So if I make a 'photonic circuit'... doesn't some kind of electrical impulse have to modulate the light pathways, i.e. turning them on and off to allow light through, in order to create logic structure? i.e... doesn't this still require transistors? Or does this material actually *change* like a transistor gate when subjected to light, and change back when the light is taken away... Now that I could see making logic gates with.
    • by HiThere ( 15173 )

      Not if it's a real photonic circuit. Of course, we don't have many of those right now. A few telescopes, but not the ones with photon amplifiers. A few microscopes, but not many of them, either. Mainly the only current "photonic circuits" are experimental. (To be photonic rather than just optical you need to have light intentionally modifying the signal that other light carries. Usually this only happens by accident, and degrades the signal.)

      Most of the things that we have that approach photonics are

  • We get at least one of these overhyped materials science articles each month. This time, someone has figured out how to deposit a garnet layer in a wafer fab. This is blown up into "photonic computing real soon now". It's not.

    There's a lot of work in progress (PowerPoint) [] on optical on-chip interconnects. This is not "photonic computing". It's clusters of CPUs with a network of optical interconnects, all on one IC. The CPUs are still made of transistors. IBM has a very active research program [] in this ar

  • by CCarrot ( 1562079 ) on Wednesday November 23, 2011 @03:41PM (#38151358)

    This could be great for long term, non volatile data storage, I suppose, but unless they develop an efficient method of changing the state (i.e., which direction is opaque), I can't see this being much use for processing in general.

    On the plus side, maybe we'll finally get to see those data cubes/crystals that popular SF books are always referring to...:-)

The party adjourned to a hot tub, yes. Fully clothed, I might add. -- IBM employee, testifying in California State Supreme Court