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Networking Technology

Passive Optical Diode Created At Purdue University 92

wbr1 writes "Researchers at Purdue University have managed to create a silicon device that acts as a passive diode for infrared optical signals. From the Purdue news release: 'The diode is capable of "nonreciprocal transmission," meaning it transmits signals in only one direction, making it capable of information processing, said Minghao Qi (pronounced Chee), an associate professor of electrical and computer engineering at Purdue University. "This one-way transmission is the most fundamental part of a logic circuit, so our diodes open the door to optical information processing," said Qi.' One of the same researchers had already (using similar technology) created a way to convert laser pulses to RF."
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Passive Optical Diode Created At Purdue University

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  • by KClaisse ( 1038258 ) on Wednesday December 28, 2011 @03:45AM (#38512588)

    Both the summary and TFA are devoid of anything concrete on how this is actually done. It basically says what the title does, they created a diode. Telling me that light entering the opposite side doesn't make it through really doesn't tell me anything the word "diode" in the title doesn't. I'm sure the science behind this particular device is both clever and interesting but you'd never be able to tell since that information is completely missing. Reporting on stories is nice, but shouldn't journalists actually strive to make their articles contain actual information on what they are covering? You'd think a story about a new discovery would actually contain information about how it actually works (since that's the actual "new" part anyway).

  • Holy Entropy (Score:3, Interesting)

    by physburn ( 1095481 ) on Wednesday December 28, 2011 @03:46AM (#38512592) Homepage Journal
    It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon. Now convert it a transistor, and with a maxwell daemon, (Quantum Weak Measurement, + Quantum Computer, + Classical Prediction Logic) and we have (possibly) a free entropy device, capable of turning waste (heat) energy back to useful energy.


    Third Magic [] @ Blogspot

    • by Penguinshit ( 591885 ) on Wednesday December 28, 2011 @03:57AM (#38512652) Homepage Journal
      Entropy is always free. The Universe has been doing it without charge for billions of years.
    • Re:Holy Entropy (Score:4, Interesting)

      by XiaoMing ( 1574363 ) on Wednesday December 28, 2011 @04:03AM (#38512686)

      It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon.
      Now convert it a transistor, and with a maxwell daemon, (Quantum Weak Measurement, + Quantum Computer, + Classical Prediction Logic)
      and we have (possibly) a free entropy device, capable of turning waste (heat) energy back to useful energy.

      From TFA:

      Depending on which ring the light enters first, it will either pass in the forward direction or be dissipated backward, which creates one-way transmission.

      It seems to more just act as a nonlinear lens, dissipating (or more likely scattering) preferentially in the backwards direction.

    • It lets heat go in one direction only! That the biggest change in Thermodynamical Law since Claude Shannon.

      Are you thinking that infrared mirrors are not possible? Does the article claim that his device does work without increasing entropy?

    • Re:Holy Entropy (Score:5, Informative)

      by kubernet3s ( 1954672 ) on Wednesday December 28, 2011 @05:14AM (#38512982)
      Infrared light is not heat. I don't know where people got this idea. It is light. When it is absorbed, it may cause certain molecules to gain heat energy, but it is still light. This is a device which absorbs or scatters when you shine light on one side of it, and transmits when you shine light on the other side of it. I assume when heat energy is generated within the device, it diffuses isotropically from the point of matter-light interaction throughout the material until a definite temperature is reached, as thermodynamics predicts. If you believe that materials with different absorption cross sections at different spatial orientations allow you to violate the second law of thermodynamics, then you hardly need to construct something so elaborate: a board painted two different colors on either side should suffice. Lasers themselves, whose cavities emit a lot more in one direction than in the other (and which generate a good deal of heat in their lasing medium in a largely homogeneous fashion, but let's not get bogged down in reality) should constitute a huge violation. You should let everyone in the physics community know, as this seems like a fairly large oversight in our model of reality /sarcasm

      If you're going to go around with a name like physburn, please ensure you understand what you're talking about
      • Re:Holy Entropy (Score:4, Insightful)

        by CODiNE ( 27417 ) on Wednesday December 28, 2011 @08:19AM (#38513682) Homepage

        Infrared light is not heat. I don't know where people got this idea. It is light. When it is absorbed, it may cause certain molecules to gain heat energy, but it is still light.

        I think it comes from a basic lack of understanding of how heat is given off by fires. If all you know is something about photons and light... and that light absorption causes heat, you fill in the blanks and reason out that fire must release most of it's energy in the non-visible light spectrum. Also infrared cameras show hot and cold, therefore many may reason that infrared = heat.

        In my memory of high school physics we didn't go in depth into heat transfer nor radiation. If that was the standard curriculum of the time then many people of gen X could believe that heat transfer is due to infrared light. It's interesting that the wikipedia page on Heat [] shows that many science textbooks use the term in confusing ways. Also

        They found the predominant use among physicists to be as if it were a substance.

        So one could be a competent scientist and still use the term in a semantically incorrect way, unknowlingly passing on disinformation.

        It would be interesting to do a little informal polling of what heat is and how it transfers. What percentage of people know how it really works? What percentage of scientists?

        • Heat was actually believed to be a substance, until the middle of the 19th century.

          True, it is a fairly subtle concept. I am much more concerned about the lay confusion between temperature and heat than between light and heat. However, it should be fairly well reinforced that light does not interact with something unless it interacts: windows heat up less than asphalt in the presence of energetic radiation in the optical regime.
          • Heat was actually believed to be a substance, until the middle of the 19th century. Not by everyone, Francis Bacon , Robert Boyle , and Robert Hooke didn't believe that in the 16th century, and Benjamin Thompson (Lord Rumford) proved it wasn't in the late 18th century.
            • Dammit, I keep misremembering my science history. If only there was some kind of large database of this kind of information that I could interface with remotely
  • by gweihir ( 88907 ) on Wednesday December 28, 2011 @03:54AM (#38512628)

    Why do so many researchers lie so shamelessly to the press? This may be a step in that direction, but it is a rather small one. Key components are missing and a lot depends on the actual characteristics of this device.

    • by Melkman ( 82959 )

      And even if major components like a light transistor are developed I don't see optical computing taking off in the foreseeable future. This "diode" is kind of weak since it stops reverse light by dissipating the energy. So any non trivial computing function made with it will consume a non trivial amount of energy in the form of input light. Compare this to electronics where a switch in the on or off state doesn't use energy apart from leakage. The major thing consuming energy there is switching states, and

  • Finally, we got the Pixel Qi

  • Bad news for us who have no idea what this means or implies. What could this do if this thing were real? I haven't seen a laymen explanation.
    We're not all smart guys you know.

    • by kubernet3s ( 1954672 ) on Wednesday December 28, 2011 @05:35AM (#38513082) [] []

      All those degrees in looking things up online finally paid off. You're welcome, citizen!
    • by Anonymous Coward on Wednesday December 28, 2011 @05:46AM (#38513102)

      A transistor acts as an electrical switch. Basically, it means that when an input is provided, the rest of the circuit can do something, but at the same time the input is electrically isolated from the rest of the circuit.

      Before transistors, there were relays and tubes which accomplished the same thing. They were slower, larger, hotter, and used a lot more electricity. And they were prone to burning out. As a result, computers were hopelessly complicated, the size of small rooms, and were programmed with a screwdriver. And "bugs" in the computer program were sometimes, literally, bugs. A moth, in at least one story. And an IBM chairman famously stated that he saw a world-wide market for about 5 computers.

      Then the digital transistor came along and revolutionized that. They were smaller, faster, and required much less power. And they were cheaper, too. The integrated circuit - millions of transistors etched onto a single silicon die - revolutionized that further.

      A transistor also acts like a diode, in that it only lets current flow in one direction. But note that this isn't really even necessary: relays, for instance, didn't prevent current from flowing backward. The main thing is that the input is electrically isolated from the output, not that it allows current to flow in only one direction.

      So basically, they have everything required to build an optical transistor, except for the switching part. Which is kind of the more important part anyway.

      • "As a result, computers were hopelessly complicated,"

        That doesn't follow. Computers were hopelessly simple back then. Or are you claiming the latest quad core CPU with a billion transistors is simple compared to a relay adder?

      • by LoRdTAW ( 99712 )

        To be fair, you can build logic gates using diodes. The only drawback is that the devices operate on the principal of voltage drops across diodes and level shifting, bad for complex circuits.

        • by tibit ( 1762298 )

          It does not operate on the principle of voltage drops, it's like saying that cars operate on the principle of heating up their environment (65%+ of your gasoline heats up the air around you). Diode logic operates, obviously enough, utilizing the large ratio of forward-to-backward current flow across an isolated semiconductor junction. Voltage polarity across a diode turns it on/off, but what is turned on is the current flow. I don't know where the idea about level shifting came from, it's not necessary at a

    • So assuming that they could build the pre-requisite components this would be a part in a purely 'optical' computer. Basically right now data goes through a basic flow like this: Computer generates data. Computer transfers data to network card. Network card converts electrons into 'light' and 'beams' it across the fiber optic cable to its destination. At its destination it is reconverted into electrons from 'light' and that destination does whatever. That conversion from electrons to light takes time. A
  • by _0xd0ad ( 1974778 ) on Wednesday December 28, 2011 @05:29AM (#38513064) Journal

    The "most fundamental part" of logic isn't one-way transmission, it's the ability to control that transmission by applying a voltage to the transistor's gate. The fact that current will only flow one direction between the emitter and the collector is really not that important by comparison.

    You can't build logic from diodes.

    • Yes, but controlling how much light goes through a device easy. Like caveman easy.

      Actually, I'm not an expert on photonics, the analogue of voltage could be wavelength, in which case upconversion can provide the same function. There's a lot of fluff on the Purdue site but this is actually a fairly interesting device and the research isn't bad.

      • by Electricity Likes Me ( 1098643 ) on Wednesday December 28, 2011 @07:40AM (#38513536)

        Actually it's really really hard. The optical transistor is the current holy grail of photonics and optical computing. The person who invents it will be incontinently rich.

        • Realistically the person who invents it will get a nobel prize, write a book or two, and thats it. The company he works for that paid the hundreds of millions(probably billions) of dollars for his equipment and personnel will become richER.
        • by tibit ( 1762298 )

          An optically controlled switch is easy. Any medium where you get optical saturation lets you implement a light-controlled switch. You can also have media that, say, change opacity when exposed to light of one wavelength, so you can control transmission of say red light using UV. You can also have a light-controlled-gain device, like, say, a light-pumped laser -- turn off the pumping light and gain drops below 1. Turn on pumping light and you have positive gain. The power levels involved are not very practic

        • but isn't half that challenge the construction of a diode? Once you have the diode, it's as simple as fluorescence, no? At least, in princple.
    • Not voltage, signal. Maybe there's a way for the signal to be light (creating an all-light computer) or maybe it's a voltage - or maybe it is something else. But it has to be something we can control.

      • by _0xd0ad ( 1974778 ) on Wednesday December 28, 2011 @05:52AM (#38513128) Journal

        My point was that the signal is the important part. They have no way of switching this optical diode.

        The diode effect is fairly irrelevant and unimportant. As a matter of fact, digital logic doesn't require something to act like diode at all: relay logic doesn't use diodes.

    • by tibit ( 1762298 )

      You can't build logic from diodes.

      You most definitely can, even complex logic like multipliers []:

      A static multiplier, capable of simultaneously multiplying two 4-bit binary numbers, was designed and built to demonstrate the practicability of current-operated diode logic gates. Approximately 270 diodes were required to construct the twenty gates used in the static multiplier. Dynamic tests of the assembled system indicated a reliable capability of 333,000 multiplications per second.

      Just google for some ideas. You can even build voltage-controlled multiplexers using nothing but diodes -- quite good ones, even. Your basic high-frequency sampler (going up to tens of GHz) is nothing but a sampling capacitor in a sampling diode bridge. Such bridges maintain symmetry that preserves integrity of the sampled differential signal and are the simplest way to quite accurately sample a quickly changing signal. They have incredible bandw

      • That's a pretty interesting concept, but it uses an entirely different binary representation (current polarity switch for 0/1, rather than voltage potential). In essence, it means that every signal is 2 leads rather than 1, and switching them creates a NOT gate.

        You might be right, but I'd want to see a working flip-flop before I'd accept that diodes could be used for digital logic.

        • by tibit ( 1762298 )

          The paper shows that the current representation is merely a faster dual of the voltage representation. The circuits be mechanically transformed from one form to another. Current-driven diodes do work as flip-flops, but this logic of course needs external active components to inject input currents and to propagate currents between combinatorial stages. That's how you get flip-flops or any other function that requires feedback: you put a current mirror between output and the input.

          If you want purely diode-bas

      • Oh, and I should mention... optical signals only have 1 lead (fiber), not 2. My brain is too tired to try to figure out what that would mean as far as trying to use optical diodes to accomplish anything similar to the current-direction-based logic used for that multiplier.

        • by tibit ( 1762298 )

          With two fibers you can encode information in phase difference, and I bet that would "polarize" a two-input optical diode OK.

  • Forget this minor improvement of losing optical to digital i/o's. Doesn't this mean optical Cpu's ? Which I'm sure would be magnitudes faster (cooler?).
  • It's the most expensive 1 way mirror, ever.
  • 'The diode is capable of "nonreciprocal transmission,"

    I thought any diode only allowed transmission one way.

No problem is so large it can't be fit in somewhere.