Optical Rectenna Converts Light To DC

Using multiwall carbon nanotubes, researchers at Georgia Institute of Technology have created what they say are the first optical rectennas–antennas with rectifiers that produce DC current. The work could lead to new technology for advanced photodetectors, new ways to convert waste heat to electricity and, possibly, more efficient ways to capture solar energy.

A paper in Nature Nanotechnology describes how light striking the nanotube antennas create a charge that moves through attached rectifiers. Challenges included making the antennas small enough for optical wavelengths, and creating  diodes small enough and fast enough to work at the extremely short wavelengths. The rectifiers switch on and off at petahertz speeds (something the Institute says is a record). 

It takes billions of rectennas to produce significant current and the efficiency of the devices is less than one percent. However, researchers believe that a rectenna with commercial potential may be available within a year. Given that the devices are made with vapor deposition nanotechnology techniques, they might be hard to make at the local hackerspace. On the other hand, hackers are a resourceful bunch and who knows what we might see in the future?

This is probably a case where used cigarette butts aren’t going to help. But it is amazing how many different kinds of things carbon nanotubes show up in.

Image from [ Rob Felt, Georgia Tech]

39 thoughts on “Optical Rectenna Converts Light To DC

  1. Very cool! Apparently rectennas in the RF range can have an efficiency of 85%-90%. Wikipedia also says that this efficiency scale down pretty well (https://en.wikipedia.org/wiki/Rectenna). Although it seems to me that an rectenna, or any antenna for that matter would have a preferential frequency (color in this case) so I don’t know how efficient it could be as, say, a solar cell. Photodetectors/diodes would be a cool application.

      1. That ‘no’ answer isn’t the best explanation… they ARE still antennas, they just aren’t optimized as well, and as such suffer from significant/severe loss. The construction of the antenna looks different, it’s bulkier and less precise and (I think) uses more types of atoms, which makes the photoelectric interaction more complex (and thus allows for more loss through things like crystal dislocations). I think.

      1. Okay, thanks, to you and everyone else that gave me helpful answers. I was pleasantly surprised with the pleasant answers to my stupid question.

        Radio is something I understand, so when you worded it that way, I understood what I should have understood all along. Thanks for the help.

  2. I realize that theory doesn’t preclude it(in fact, it outright suggests that it should be possible); but there is always something a bit mind-blowing when somebody pulls off what we think of as an RF trick; but in the visible band. Yes, intellectually, electromagnetic waves are electromagnetic waves, just with different wavelengths; but viscerally it still hits you.

    1. I have this same reaction every time.

      Sometimes I think about this transparent, glass-like world my phone must see; furiously pulsating lights of different colors to wifi routers, 4G cells, Bluetooh, etc. It’s all just waves, but “light” is just special in our heads.

    2. I once heard an astronomer describe how he built a superhet receiver for extreme IR light by mixing the light with a microwave oscillator, giving a microwave signal as a result. It all works in theory, but it’s a bit mind blowing to see it actually done.

  3. The way some radio telescopes work is by recording the raw phase data of incoming radio signals from widely separated dishes and then combining them coherently, effectively giving you the resolution of one gigantic dish as big as the distance between them.

    You ca do this at radio frequencies because radio frequencies are relatively long. But with this, could you do it with optical frequencies? Basically, can you now build an optical telescope with an effective, say, 6′ diameter lens by putting two smallish chips 6′ apart?

    1. Perhaps.
      What you’re proposing has been done already, sort of. CHARA (Near IR, at Mt. Wilson) and COAST (Visible, at Cambridge) are two such ‘astronomical intereferometer’ telescope arrays (more listed here https://en.wikipedia.org/wiki/List_of_astronomical_interferometers_at_visible_and_infrared_wavelengths).
      Given the frequency dependence sensitivity of the rectenna I wonder if it’s easier to design since you don’t have to position the chips as precisely as you would a mirror for the same telescope.

    2. Applied into a satellite (swarm) this could circumvent the bottleneck in respect of resolution (fairing inner diameter) and lead to pretty high resolution telescopes up there (no vibration and atmosphere as great plus).

      (Also possible to use for reconnaissance satellites, just saying…)

      1. Vibration in satellites can actually end up being a pretty big deal. There’s only one place for a mechanical vibration to damp out to: heat.
        The structural dynamics of the ISS are actually a constant consideration. I hadn’t known it until I met the guys who develop the Space Station Multi-Rigid Body Simulation (SSMRBS) though.

  4. Great idea! How much does it cost to build per kw/hr? How can we store this energy to use when we need it? I hate to rain on anybody’s parade but we don’t have an ‘energy production crisis’, we’ve got an ‘energy storage and distribution ‘ crisis.

    1. Not wrong, but throwing more energy in will solve the problem. Depends on how much it costs, taking pollution into account. Currently nobody really does take pollution into account, carbon credits were a nice idea until politicians and business got involved, now they’re massively over-issued.

      Right now you could only guess how much this is gonna cost, or produce, it’s not even a prototype, it’s an experiment to prove a principle.

      Still pretty clever. It sortof answers something I was wondering about, if you built a fast enough oscillator, would it radiate light? And how?

    2. Store it kinetically FFS!

      Pressurize via pump
      Drop something via a pulley/winch
      Spin it fast (gyroscope)

      And put it underground for later retrieval.

      If that sounds too scary to the public, LEDs-Algae-some low calorie oil or add yeast to algae and make an alcohol to burn later.

      The wall is adoption and the monolithic corps that will kill it.

      1. People have thought of storing energy kinetically, usually in super-high-speed, very heavy flywheels. Store it well out of the way of anything destroyable! Of course there’s mechanical issues. As far as pressure and weights, the problem I think is storing enough energy. Huge pressure vessels are expensive and difficult, and under 1G a weight would have to be ludicrously heavy.

        There’s a place in Wales, Dinorwig, that has 2 lakes, at the top and bottom of a mountain. During the day, it works as hydro power. At night, they use off-peak electricity and run the generators in reverse, to pump water back up to the higher lake. It makes a profit, and helps balance demand, though it’s not got a huge capacity compared to the grid itself.

        It was only practical to build because the lakes happened to be there. For the price and effort, you’re probably better off with batteries. There are things called “flow batteries” where the electrolyte, which store the energy chemically, the electrolyte is stored in tanks, and is pumped through the battery to keep it powered. Uses Vanadium in 2 of it’s (I think) 5 different valence states. It powers a small island somewhere warm, can’t remember.

      2. Other thing, as far as algae, it’s cheapest to just use sunlight to grow them. Growing any sort of plant, even algae, under electric light, is not efficient. It’s only effective for, -cough- -coughcoughcoughcoughingfit- “specialist”, high-value crops. That you might wanna keep out of daylight.

  5. This is one of those things I always wondered about, albeit in the opposite way. I remember asking my physics teacher about it; As visible light etc. is just another part of the EM spectrum, what would theoretically happen if you feed a light-frequency signal on to an antenna? They couldn’t give an answer, but I guess that this kind of clears it up.

    1. I don’t see why you couldn’t grow the nanotubes into that configuration. The problem would be how to get the data out fast enough.
      Perhaps etched with a laser in an atmosphere that would produce the circuitry. Or for simplicity’s sake maybe you sweep across it with a frequency about double the size of the sensor in multiple directions. That creates a series of frequency modulated signals, that when combined with a fourier transform, would reproduce the image.
      I like your idea of varying the length of the nanotubes to determine the frequency.
      I’d still love to see nanotubes used to make an array of tesla coils. Perhaps the top load could be shared and etched with valleys and troughs to vary the capacitance.

  6. i can’t tell you what you don’t already know,

    but i CAN remind you guys that this is the big star-trek invention we’ve all been waiting for…
    what i CAN say is star-trek related, google ISOLINEAR CHIPS…

    this will make them possible, well, the processing side, not the data storage side…
    imagine a circuit that processes data, and runs on light… a glass chip with no wires or contacts to corrode or wear out.

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