Polymer could be key to faster optical switching

Kathleen G. Tatterson

SALT LAKE CITY -- Researchers have developed a technique that uses a polymer to create an ultrafast, exciton-based optical switch that operates 10 times faster than current technology.
Today optical switches apply an electric field to an inorganic crystal to change its optical properties to turn lights on and off, generating light pulses at 20 GHz. Scientists at the University of Utah in Salt Lake City and Osaka University in Japan, however, are using a material known as poly(p-phenylene-vinylene) and its derivatives to create a switch that they report could operate at a rate of 1 THz. The team believes such ultrafast switches could be the key to logic gates of future generations of computers.
Another advantage of the polymer technique is cost, said Valy Vardeny, professor of physics at the University of Utah. "Polymers can exist in solutions and thin films, so they are very cheap," he said. Also, the light absorption of the polymer is much broader than in current technology, in which semiconductor materials use an electro-optical effect.

Laser becomes a switch
Earlier, other researchers had demonstrated the use of poly(p-phenylene-vinylene) as the first polymer-based laser, but according to the team's report, published in the June 2 issue of Physical Review Letters, this is the first application of the polymer as an optical switch in the near infrared range with variable switching times. "We now have an optical switch where the time duration is controlled externally from 200 to 500 ps," Vardeny said.
The technique starts with a data-carrying beam emitting in the near infrared (1.1 to 1.7 µm) at an electron pair. To switch electrons "off," the team blocks the infrared light with a green beam from a synchronously pumped dye laser at approximately 670 nm. "It's like writing on the beam," explained Vardeny. "Our group shows that we can 'kill' excitons -- or make them disappear -- by putting another light in the visible range where they actually meet." To switch the excitons back "on," the scientists shoot a red light beam at around 670 nm.
In addition, the team says that the resiliency of modern polymers makes the technique repeatable. "You can work with the same solution for five hours without any change," Vardeny said.