PORTLAND, Ore. Silicon circuits traditionally don't do optics. As an "indirect bandgap" material one in which the bottom of the conduction band is shifted with respect to the top of the valence band energy
released during electron recombination with a hole is converted primarily into phonons instead of the photons. The result is a "direct bandgap" material like gallium arsenide.
Cornell University researchers have demonstrated nanoscale techniques they say enabled the world's first silicon chip that switches optical wavelengths. The key is a ring-shaped nanoscale cavity whose resonant frequency depends on its refractive index, which can be optically switched by virtue of a second light beam controlling free-carrier dispersion.
According to Cornell University engineer Michal Lipson, the technique should eventually enable terahertz switching of
signals on silicon chips with ultra-low power,
high-modulation depth picosecond optical switches. They can be fabricated alongside conventional silicon circuitry.
"Our photonic circuits are for carrying information, not for logic," said Lipson, principle investigator and an assistant professor at Cornell in its electrical and computer engineering department. The first application is likey to be all-optical routers rather than not photonic circuitry, which could come later.
The National Science Foundation is funding Lipson's quest for techniques to enable silicon to handle optics applications.