Wednesday, September 22, 2010

#Optical #Antenna Boosts Signals by Millions

Optical signals transmit billions of bits per second for telecommunication applications and can sense incredibly small amounts of substances when crafted into sensors. Most optical materials, however, are of the clear plastic variety, formed into optical fibers, or into transparent semiconductors used for advanced on-chip lasers and photodetectors. Others, however, are learning to harness optical effects using electromagnetic materials, since in principle optical signals are just super high-frequency electromagnetic radiation the same as any other EM source. Rice University researchers are using an angstrom-scale air-gap between gold electrodes to harness the amplification effects of plasmons, but at optical frequencies. Although such effects have been demonstrated before, this group claims to be the first to explain why the technique works as well as the first to measure how much optical signals can be amplified by angstron-scale nanogaps. Look for incredibly tiny antennas to be used for sensors capable of detecting as little as a single molecule of nearly any substance within four years. RColinJohnson @NextGenLog

Scanning electron microscope (SEM) image of gold tips in a nanogap device used in experiments to capture and amplify light. (Image courtesy Natelson Lab/Rice University)

Here is what EETimes says about optical antennas: Optical antennas can amplify signals by a million times or more using lasers to induce quantum tunneling between sub-nanometer gaps between metal electrodes, according to researchers at Rice University who say they have accurately characterized optical antennas, which promise to enable single-molecule sensors and other advanced non-linear optical application...Sensors using the effect could sense even single molecules by harnessing the radiation intensity in the sub-nanometer gap between electrodes...Closely spaced metal electrodes act as optical antennas because their electrons can be excited with a laser, inducing plasmons—collective oscillations of the free electrons—whose evanescent electromagnetic fields are thousands of times stronger than the incident light. Unfortunately, these fields have been very difficult to measure and characterize. Now Natelson and doctoral candidate Dan Ward have found a relatively easy way to measure the fields between sub-nanoscale electrodes on optical antennas...
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