As light is sent through the waveguide, the photons interact with electrons at the interface between the gold and the silicon dioxide. Those electrons oscillate, and the oscillations propagate along the device as wavessimilarly to how vibrations of air molecules travel as sound waves. Because the electron oscillations are directly coupled with the light, they carry the same information and propertiesand they therefore serve as a proxy for the light.
Instead of focusing the light alonewhich is impossible due to the diffraction limitthe new device focuses these coupled electron oscillations, called surface plasmon polaritons (SPPs). The SPPs travel through the waveguide and are focused as they go through the pointy end.
Because the new device is built on a semiconductor chip with standard nanofabrication techniques, says Choo, the co-lead and the co-corresponding author of the paper, it is easy integrate with today's technology
Previous on-chip nanofocusing devices were only able to focus light into a narrow line. They also were inefficient, typically focusing only a few percent of the incident photons, with the majority absorbed and scattered as they traveled through the devices.
With the new device, light can ultimately be focused in three dimensions, producing a point a few nanometers across, and using half of the light that's sent through, Choo says. (Focusing the light into a slightly bigger spot, 14 by 80 nanometers in size, boosts the efficiency to 70 percent). The key feature behind the device's focusing ability and efficiency, he says, is its unique design and shape.
"Our new device is based on fundamental research, but we hope it's a good building block for many potentially revolutionary engineering applications," says Myung-Ki Kim, a postdoctoral scholar and the other lead author of the paper.
For example, one application is to turn
|Contact: Lawren Markle|
California Institute of Technology