Vincent Ginis

Harnessing near-field light

Research paves the way for high resolution microscopy, more efficient optical communication and more
By Leah Burrows

There are many types of light — some visible and some invisible to the human eye.
For example, polarized light is invisible because even though it hits our eyes, our brain doesn’t have the tools to process it. But there is another type of light that is invisible because it never reaches our eyes. When light bounces off a surface, a small part of it sticks and remains behind. This type of light is called near-field light.

If harnessed, near-field light would have enormous potential for ultra-high-resolution microscopy, particle manipulation and optical communications. But unlike far-field light — the light that does reach our eyes — researchers haven’t developed a comprehensive toolkit to harness and manipulate it. At least, not yet.

“Today, we have a lot of tools and techniques to design what far-field light looks like,” said Vincent Ginis, a visiting scholar at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS). “We have lenses, telescopes, prisms and holograms. All these things enable us to sculpt freely propagating light in three-dimensional space. We hardly have any tools to do the same thing with near-field light.”

Until now. SEAS researchers have developed a system to mold near-field light at a distance, opening the door to unprecedented control over this powerful, unexplored type of light. The research is published in Science.

In order to manipulate near-field light, the researchers developed a device in which confined light bounces back and forth between two converters. When the light hits the converter, it changes mode and bounces back. As the light modes interact with each other, the near-field component of the light, which is sticks to the surface of the device, also changes. When all the different configurations of the near-field light are superimposed on each other, it creates a specific shape. The researchers can pre-program that shape by tuning the mode and amplitude of the bouncing light.

“When all these modes exist together, they add up to create a near-field landscape on the surface of the device,” said Marco Piccardo, a research associate at SEAS and co-author of the paper. “The shape of the landscape is determined by the combined properties of the cascading light.”

It’s a bit like music, said Ginis.

“The music that you are hearing is the superposition of many notes or modes. One note alone isn’t much but taken together you can generate any type of music,” said Ginis.

Over course, music operates in time while this near-field generator operates in three-dimensional shape.

To demonstrate their design, the researchers molded near-field light into the shape of an elephant. Or, more specifically, an elephant inside a boa constructor, an homage to the play on dimensions in Antoine de Saint-Exupéry’s classic The Little Prince.

The researchers also shaped the light into a curve, a plateau and a straight line.

“This research provides a new path towards unprecedented three-dimensional control of near-field light,” said Capasso. “We show that we could eventually have the same degree of control in the near-field as we have in far-field light.”

The paper was co-authored by Michele Tamagnone, Jinsheng Lu, Min Qiu, and Simon Kheifets. It was supported in part by the Air Force Office of Scientific Research under grant no AFOSR FA9550-14-1-0389.