© 2006 ACS

With the rapid development of high-density optical integrated circuits, the demand for waveguides with subwavelength dimensions that can guide light without loss at sharp bends is vital. Achievement of this goal has been hindered by diffraction and difficulties in integrating optical and electronic components on a chip. Using metal nanoparticle arrays to take advantage of plasmonic effects is a promising approach; but here too, optical transmission is limited by resistive heating. Now, a research group from the University of Washington1 has extended this concept by replacing the lossy metal with quantum dots — semiconductor nanostructures that exhibit three-dimensional electrical charge confinement.

The new waveguide is composed of an array of densely packed quantum dots fixed to a substrate, and is fabricated in such a way that allows for rapid prototyping. Not only do the dots reduce transmission losses, but the team demonstrates the possibility of a net gain in intensity. They have shown that photons can be generated through stimulated emission, and subsequently amplified by the cascaded quantum-dot structure, with an output determined by the inter-dot coupling efficiency and the gain of each dot. This simple approach that not only allows light transmission around sharp bends and through confined spaces without loss, but also results in gain, could provide an important building block for nanophotonic systems.