“We needed a strategy that would allow us to put a high concentration of derivatized buckyballs into a convenient, processable polymer,” Ted Sargent of the University of Toronto told nanotechweb.org. “We saw an opportunity to engineer two molecules - buckyballs and polymers - to demonstrate molecular tailoring in the service of a useful function: optical nonlinearity for ultrafast switching and signal processing.”
To make the material, Sargent and colleagues reacted trihydroxyl-containing C60 molecules with a triisocyanate compound. The result was a cross-linked C60-containing polyurethane system with about 19% C60 moieties by weight. The scientists tested the optical properties of thin films of the material in the wavelength range 1150-1600 nm using the Z-scan technique.
“Our materials exhibit strong, ultrafast nonlinear optical response with good engineering figures of merit,” said Sargent. “We showed a factor of 10-100 times larger nonlinear optical response per unit length in our films than in previous works.” The scientists believe this proves that their molecular engineering strategy was a success - they achieved a high degree of charge transfer between derivatized buckyballs and polymer, resulting in large nonlinearity per molecule, and produced a material with high solubility, allowing them to make densely packed films of buckyballs within a processable polymer matrix. Earlier studies have tried to make solid-state materials containing C60 by doping glasses or using sol-gel techniques, but have only achieved doping levels of up to about 0.1 wt%.
According to Sargent, the films “enable light to change its own phase through nonlinear interactions with minimal absorption of the light within the material.” The polymer has applications in devices such as nonlinear gratings, nonlinear interferometers, and nonlinear directional couplers for optical switching and signal processing.
Now the researchers, who reported their work in Applied Physics Letters, plan to incorporate the material into nonlinear periodic devices and to demonstrate ultrafast optical signal processing. “Ultimately, the research is slated to enable an agile optical network: one in which signals can be routed and processed on the fly within the optical domain,” said Sargent.