How to Convert Light Waves to Electricity with Optical Rectenna?

Optical Rectenna is a device that converts light waves into DC current. Optical Rectenna is a combination of an antenna and a rectifier diode used to capture light waves using the carbon nanotubes attached to it. 

The concept of wireless electricity has been floating around since a couple of years, but finally some mind-boggling technology has come up, that can truly characterize wireless electricity in its initial stages. Optical Rectenna, and before the question pops up in your mind about what is it, first you should know about Rectenna. Rectenna is a special kind of antenna which is a combination of an antenna and rectifier diode. And the term Optical is there because the light is involved.

Now, basically what this device does is, it captures light waves from its surroundings with the help of tiny carbon nanotubes attached to it. Then some oscillating charges are generated in the rectifier which are converted to DC current. Scientists have been busy since four decades, so that they can use light waves in this way.
According to one of the researcher Baratunde Cola from Georgia Institute Of Technology, the experiment they did was simple, at least for them. No, seriously, it wasn’t that simple, as they had to repeat the same experiment for almost a thousand times in order to get the work done.
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In a press release, Cola said:

“A rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode. The closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode – which is the structure we made.”

The light captured by one carbon nanotube is almost negligible, so it requires the use of many of them. For this, a conductive substrate (google it) is needed, on the top of that substrate, vertically aligned carbon nanotubes are grown in a grass like fashion. After that, these tubes are coated with aluminium oxide electrical insulator. Then some thin layers of optically transparent materials are placed above them to act as anode. This system is the fastest diode in the world, works at petahertz speeds while switching on and off.

“It’s the only diode that’s fast enough to open and close the gate at the speed of solar energy oscillating in an antenna,”Baratunde Cola

However, the current efficiency of this system is only 1 % percent, means it can only convert 1% of light falling on it to DC current. But the researchers have assured they’ll increase the capacity to almost 40% and hope to come up with a commercial product within a year.
In the press release, Cola added:

“We could ultimately make solar cells that are twice as efficient at a cost that is 10 times lower, and that is to me an opportunity to change the world in a very big way. As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture.”

Now, on a historical note, Rectenna was invented in 1964 by William C. Brown, who was an electrical engineer based in the United States. He patented it in 1969. He demonstrated his invention with the help of a model helicopter, on which he attached a Rectenna receiver and sent microwave signals to control the helicopter. Optical Rectenna is a further implementation of his invention.
  So far, the concept of Wireless electricity has not been a topic of much conversation, but with the burgeoning technologies like Optical Rectenna, there is not much time when we’ll be free from the slavery of all those chargers and cables.