FAYETTEVILLE, Ark. Using the nonlinear optical properties of indium-phosphide crystals, researchers at the University of Arkansas have discovered a new wrinkle on optical switching. In a paper delivered at the recent Conference on Lasers and Electro-Optics meeting in Baltimore, Scot Hawkins and Greg Salamo detailed experiments showing that applied electric fields can channel light inside the crystal to create virtual optical fibers.
"We have demonstrated that an electrical field can confine a beam of light inside a crystal to form optical wires that stay the same size without the need for a waveguide," said researcher Hawkins. According to the report, optical circuitry can be reconfigured instantly in indium-phosphide crystals via an electrical field. The virtual wires used to interconnect such optical circuitry can be created on the fly, and switching can be done instantly without physical waveguides like optical fibers. The optical wires can even pass through each other with no crosstalk.
"We have determined experimentally that optical wires which pass through each other at angles greater than about 5 degrees have virtually no crosstalk," said Hawkins. One of the objectives of the research was to determine the conditions that would result in crosstalk between adjacent virtual fibers.
Virtual optical waveguides are generated in indium-phosphide crystals by externally applied EM fields.
In their paper, Hawkins and Salamo report that crosstalk only became significant when wires were 20 microns in diameter and separated by less than 40 microns. Optical wires separated by more than 40 microns were virtually crosstalk-free, a situation that bodes well for creating dense, multiport optical switches with the technique.
Optical wires are created on the fly within the indium-phosphide crystals as the result of a nonlinear interaction between the light and the crystal in the presence of an appropriate electrical field. The electrical field can be uniformly applied across the surface of the crystal while the beam is focused on its edge. Ordinarily, a 20-micron beam would spread as it propagates, like any other noncoherent beam. But when the correct electrical field is applied, the beam remains focused by virtue of an electrical reconfiguration of the atoms in the crystal. In effect, the beam creates a virtual wire as it plows through the crystal.
"The electrical field changes the electronic structure of the crystal to keep the beam the same diameter. When excited by light, the electrical field causes charges and holes in the crystal to migrate and become trapped in the shape of a wire," Hawkins explained.
According to Salamo, optical wires can carry more information using less space than electronic wires and they create no interfering fields, making them ideal for computers and telecommunications equipment. In fact, optical wires contain no physical material at all, since they are created by the beam of light itself and since they disappear as soon as the beam is stopped.
The optical wires can be instantly switched by merely changing the angle at which they enter the crystal. And even when the angle between two wires is less than 5 degrees, the crosstalk is dependent on the relative phase of the two beams. For instance, two optical wires can use exactly the same path without interfering with one another, as long as their phases are opposite.
Much research remains to be done before optical wires can be deployed in commercial electronics, the researchers cautioned. But potentially, their "virtual" nature could solve many of the density problems of 21st-century electronics.