Simulations shine light on optical wire

19 Nov 2007

US researchers believe that tiny optical versions of capacitors, resistors and inductors can be made by adjusting the size, shape and composition of sub-wavelength nanoparticles.

Full-wave simulation

Nader Engheta and colleagues at the University of Pennsylvania are laying down plans for optical nanocircuits that could replace conventional electronics. Apart from being much smaller, optical nanocircuits have the potential to offer more bandwidth and increase data handling capacity thanks to their higher operating frequency.

As Engheta explained, developers will have to get to grips with a different way of thinking to make the most of the technology. Specifically, this means considering a material's local permittivity rather than its conductivity.

"At lower frequencies, the substrate of a classic circuit board is very poorly conducting and elements are connected with each other only through the shorting metallic wires attached to their terminals," he told nanotechweb.org. "When you move into the infrared and visible spectrum, the displacement current that enables optical nanocircuits may also flow in the surrounding background material and connect elements in an unwanted manner."

Engheta's proposal for optical shorting wires involves the use of a special class of nanowaveguides formed by a core with a relatively large permittivity surrounded by a thin concentric shell of low permittivity. The team has considered a cylindrical waveguide just over 83 nm in diameter with a core measuring 50 nm across, and the simulation results are encouraging.

"We looked at the distribution of optical displacement current density on a transverse cross section of a straight (850 nm) optical shorting wire and the model shows that the current is confined within the core," said Engheta. "What's more, the longitudinal component of the optical electric field in the core is very small, which means that the potential drop between the two ends of our interconnecting structure is low – another key requirement."

Critics will point out that the work to date is purely computational, but the group is taking steps towards realizing a prototype circuit. Engheta is keeping the design under wraps, but he did reveal that the team has started working with the university's nanofabrication group and plans to begin its proof-of-concept experiments early next year.

The researchers presented their work in Optics Express.