Numerical model to aid in nanophotonic designs

Computer manufacturers nowadays face the challenge of cramming processing power onto tiny chips. A growing problem of manufacturers is that connections between electronic components measuring just a few billionths of a meter across allow electrons to leak. The leakage reduces the quality of the signal they carry, wastes energy and causes the device to overheat.

One solution seen to resolve this problem is to replace the electrons with photons of light. Hong-Son Chu and Er-Ping Li of the A*STAR Institute of High Performance Computing in Singapore and co-workers have now developed a numerical model to simulate the performance of circuits that rely on light, which could be an invaluable tool for designers in the burgeoning field of nanophotonics.

Devices that manipulate photons of light are typically many times larger than conventional circuit components, and this limits their use. In contrast, "plasmonic technology promises to overcome the size mismatch between microscale photonics and nanoscale electronics," said Li.

When light hits the interface between a metal and a dielectric insulator, it creates ripples in the density of the electric charge. These ripples, known as plasmons, are bound to the electromagnetic field of the incoming light, and travel along the interface. The plasmons have a shorter wavelength than the light, so the components that guide and manipulate them can be smaller than those used to control light directly. "This emergent technology is a potential platform for the next generation of optical interconnects that enables the deployment of small-footprint and low-energy integrated circuitry," Chu said.

Microelectronics researchers have previously relied on time-consuming and expensive computer simulations to fine-tune the designs of their plasmonic nanocircuits. Li's team has developed a much simpler model that includes a library of different plasmonic components such as waveguides, modulators and photodetectors, and can integrate their properties to predict how the whole system will behave.

Li and his co-workers used their model to quickly design and improve a compact Mach-Zehnder plasmonic modulator, a commonly used component that enables an electrical signal to control a beam of light. The device relies on an electro-optic material whose refractive index changes when a voltage is applied.

The simulation showed how the size and shape of the device could be optimized to lower its operating voltage, as well as increasing the difference between its two switching states to reduce signal noise.

The researchers now plan to improve their design software so that it includes many more properties of nanocircuits, "including mechanical, thermal, optical and electrical characteristics," said Chu.