Creating an optical antenna

Coupling a gold antenna to a InGaAsP nanorod, isolated by TiO2 and embedded in epoxy, greatly enhanced the spontaneous light emission of the InGaAsP. Credit: Michael S. Eggleston et al./PNAS

We are used to the idea of radio antennas, we see them everywhere. On the contrary the concept of an optical antenna sounds unusual. As a matter of fact optics is about waves, similar to radio. It just looks into waves at a higher frequency (and it prefers to talk about them in terms of wavelength, rather than frequency but a we know one is related to the other through the speed of light!).

Antennas are all about emission and reception of waves. In the case of optical ways, ray beams, since the invention of the laser most of the studies and of applications have been on stimulated light emission (LASER: Light Emission by Stimulated Electromagnetic Radiation) and the spontaneous emission has been basically forgotten.

Now a team of researchers at Berkely have found a way to create an antenna that can enhance the spontaneous emission of optical radiation from atoms, molecules and semiconductor quantum dots. This is nothing new, LED, Light Emitting Diodes, are exactly that but their "efficiency" is low in comparison to a Laser. 
By inventing this antenna the researchers are able to create much more efficient LED that can replace a Laser in an electronic circuit to send information inside a chip. The advantage is twofold: the spontaneous emission is much faster than Laser and the antenna is much much smaller so that it can be embedded hundreds of millions of times in a single chip.

Spontaneous emission occurs ... spontaneously, but to make use of it you need to harvest many of these spontaneous emission. This is what the researchers have done by covering a square shaped nanorod made of InGaAsP with titanium dioxide isolating the rod from a gold wire placed perpendicularly to the rod that works as an antenna. The emission is provided by the InGaAsP rod.

Optical communication in a chip (or as a substitute of a printed board to connect chips) can dramatically reduce power consumption (hence heat generation) thus fostering increasing density and miniaturisation....

Author - Roberto Saracco

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