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Optical Control of Light on a Silicon Chip

Posted by samzenpus on from the light-turns-it-on dept.

An anonymous reader writes "Researchers at Cornell University have demonstrated a device that allows one low-powered beam of light to switch another on and off, on silicon, a key component for future "photonic" microcircuits in which light replaces electrons for propagating signals. It is highly desirable to use silicon--the dominant material in the microelectronic industry--as the platform for these photonic chips. The approach developed confines the beam to be switched in a circular resonator, greatly reducing the footprint required on the chip and allowing a very small change in refractive index to shift the material from transparent to opaque."

12 of 129 comments (clear)

  1. Optronic gates by lisaparratt · · Score: 5, Interesting

    I thought diffraction and interference was to be the answer to switching light. Does anybody know what happened to this technology?

  2. Can somebody explain ... by YeeHaW_Jelte · · Score: 2, Interesting

    What is the exact use for this? Is it's advantage that there's no need to switch back & forth between electric signals & optic signals in e.g. a optical router, or is a computer based on solely optical signals faster than one based on electrical signals?

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    1. Re:Can somebody explain ... by frankvl · · Score: 5, Interesting

      Light travels about 10x faster than electrons in their optimal medium, so the potential processing speed limit is increased.

      Also, light processing does not necessarily generate heat, so there is no cooling needed to preserve the hardware, unlike the electro solution.

    2. Re:Can somebody explain ... by Antique+Geekmeister · · Score: 5, Interesting

      "Think again" is right. The electrons are involved in propagating a wave of electromagnetic energy, in ways that are fun to examine. But what you are describing is the average rate of travel of an electron, much like the average rate of travel of a lake: only a little bit of water goes in and out of it, on the average, so the average speed is very slow.

      The *wave* in the lake, however, is much faster, carried by particles that bounce around each other much faster. Typical propagation speeds of electrical signals in network cable is a significant fraction of the speed of light, roughly 75% of the speed of light for 75-Ohm coax cable as one example.

      Optical propagation in fiber-optic cable, which is what this new technology will be used for, is also limited to less than the speed of light. There, you get interesting effects because it's being transmitted through glass (or plastic for short cables), but still a significant fraction of the speed of light in vacuum.

    3. Re:Can somebody explain ... by CRepetski · · Score: 2, Interesting

      Additionally, an optical circuit has the advantage that two beams of light can cross each other without interfering harmfully with each other. Obviously you couldn't do this with in an electric circuit. This allows optical circuit designers to make more compact designs, and it's a lot easier to do. With circuits on microchips today being so complicated, you need some pretty hefty programs to actually to the designing. The same optical circuit could be much smaller and eaiser to design.

  3. Why silicon? by ChrisMDP · · Score: 2, Interesting
    It is highly desirable to use silicon...

    What the poster and the article both neglect to mention for us simpler types is why silicon is desirable.

    Is it simply because it requires less modification to the production pipeline, or is there another more scientific reason?

    Perhaps a scientific slashdotter can enlighten us. Ahem.

    1. Re:Why silicon? by amalcon · · Score: 2, Interesting

      IANA...well, I am not a person whose speculation on this matter should be taken seriously. Nonetheless, I would wager that the reason for this is: Silicon is very common on Earth. As I recall, it's the most common element which is solid at room temperature. This makes it inexpensive.

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      -Amalcon
  4. How good? by F'Nok · · Score: 3, Interesting

    These structures will find their first application in routing devices for fiber-optic communications.
    That's a fantastic use...

    But I'm more interested in optical computing.

    In theory extrememly low power chips should be possible, but what is the absorption rate like, especially in terms of heat, and quantity of reused light.

    That is ofcourse, assuming that this CAN be used for more sophistication chip design.

    Has there been any suggestion of other uses, and if so, what possibilities are there available for such technology?

  5. Re:Light switching CPU mentioned before? by amalcon · · Score: 3, Interesting

    (must need a huge heatsink).

    Actually, one of the major benefits of optical computing is that you don't need a heatsink at all. This is because the heat put out by a CPU is due to inefficiency (in other words, because they are not room-temperature superconductors). There is little to no inefficiency in modern optical cable, especially compared to copper wiring.

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    -Amalcon
  6. Switching time?? by TooTechy · · Score: 2, Interesting

    What's the darn switching time? Can't find it. The really important measurement and I can't find it.

    Herriot-Watt were doing this on a physically bigger scale back in the 80s and managed something like a 10ms switch speed.

  7. A Fair comparison by slackerny · · Score: 2, Interesting

    I do not see any use for optics in processing even though photons theoritically travel faster than light. (Remember photons also do not travel at 3*10^8 in a waveguide eg silicon: velocity = c/refractive index and refractive index of silicon ~= 3.5)

    although this would boost the oppurtunity for optics in processing... I do not believe it would be usefull in high speed processing simply because it would be drain lot of power (wall-plug efficiency is being worked on to improve right now!) but this could change..But one thing that cannot change is that the waveguides and devices (need to be atleast as big as the wavelength) are very big compared to the electronic devices...

    here is a fair comparison of wavelengths.
    -optical wavelength = 1.1 microns. electronic wavelength
    -(electrons can be compared in energy to an x-ray photons and so wavelength of x-ray photon - this concept is used in electron microscopy) this is in nanometers 2 orders smaller.

    so the electronic device sizes are 2 orders smaller and so lot more dense.

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  8. Interesting, utility in question by Anonymous Coward · · Score: 1, Interesting

    Nonlinear switching and wavelength conversion in
    small rings has been shown before, perhaps not in
    silicon. The use of absorption here is going to
    give you a significant switching recovery time and switching energy (power consumption and heat dissipation). You will also probably find that the repetition rate was quite low, because the absorption-induced heating of the ring will also shift the resonance and cause a long-time-constant shift that can be troublesome. At a minimum this will induce bit pattern dependence.
    Although I think the resonator enhancement of these nonlinear effects can be large and useful, one also needs to be aware that the ultimate speed is limited by the bandwidth of the resonance being used. The sharper the resonance, the higher the enhancement, but then the smaller the bandwidth. You are using the energy storage of the resonator to help you, but it takes time to "charge" and "discharge" it.
    Anyway, good luck to them. I am a bit bemused
    by the press splash, since there is quite a bit of
    related work out there over a number of years.
    But hey, keep at it.