Plasmon Laser  (Source: Courtesy of Xiang Zhang Lab, UC Berkeley)
Breakthrough will advance optical computing

Researchers from the University of California, Berkeley have reached a new milestone by creating the world's smallest semiconductor laser. The tiny laser can generate visible light in a space smaller than a single protein molecule.

The new laser breakthrough may one day usher in a new era in computing power by providing CPU makers with the ability to use light rather than electronic circuitry in processors. The key breakthrough was a method that the researchers devised to squeeze the light into a space smaller than its wavelength and keep the light from dissipating as it moved along.

"This work shatters traditional notions of laser limits, and makes a major advance toward applications in the biomedical, communications and computing fields," said Xiang Zhang, professor of mechanical engineering and director of UC Berkeley's Nanoscale Science and Engineering Center, which is funded by the National Science Foundation (NSF), and head of the research team behind this work.

The scientists say that the breakthrough will help usher in innovations like nanolasers that can probe and manipulate DNA molecules, optics based telecommunications and optical computing. Traditionally it is accepted that light can be compressed into a space smaller than half the size of its wavelength. Researchers have been able to compress light down to a couple nanometers by binding it to electrons that oscillate collectively along the surface of metals, otherwise known as plasmons.

Zhang and his team improved on this technique by pairing a cadmium sulfide nanowire with a silver surface separated by an insulating gap only 5nm wide or about the size of a protein molecule. The structure is able to store the light within an area 20 times smaller than the wavelength of the light. The light energy is reportedly stored mostly in the insulating gap between the wire and the silver surface loss is diminished significantly.

"When you are working at such small scales, you do not have much space to play around with," said Rupert Oulton, the research associate in Zhang's lab who first theorized this approach last year and the study's co-lead author. "In our design, the nanowire acts as both a confinement mechanism and an amplifier. It's pulling double duty."

Trapping and sustaining light in the very tight quarters creates conditions where the interaction of light and matter is strongly altered. The researchers say the sign of this altered interaction is a six-fold increase in the emission rate of light in the 5nm gap.

"What is particularly exciting about the plasmonic lasers we demonstrated here is that they are solid state and fully compatible with semiconductor manufacturing, so they can be electrically pumped and fully integrated at chip-scale," said Volker Sorger, a Ph.D. student in Zhang's lab and study co-lead author.

"We are going to continue to work with them to make sure they understand the reality of the Internet.  A lot of these people don't have Ph.Ds, and they don't have a degree in computer science." -- RIM co-CEO Michael Lazaridis

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