Fullerene/Polymer Film Penetrates 'Quantum Gap'

In a paper for the September issue of Nano Letters released online Aug. 12, a team from the University of Toronto and from Carleton University in Ottawa reports a fullerene/polymer film that displays optical properties within the nonlinear molecular susceptibility quantum gap, a range approaching the fundamental physical limit of the performance of molecular photonic materials. The achievement points to the possibility of developing practical all-optical telecommunications components with picosecond switching times.

A current bottleneck in telecom networks is the optical-to-electrical and electrical-to-optical conversion required at switches and routers. Of interest, therefore, is the development of solutions based on nonlinear optical materials to control light through its interaction with light. Until now, however, the performance of these materials had not come within a factor of 30 of the calculated quantum gap, said Edward H. Sargent of the University of Toronto.

The new material comprises cross-linked C₆₀ molecules suspended in a polyurethane film to maximize the total nonlinear susceptibility. Measurements performed using a Z-scan technique with 3.3-ps pulses of 1150- to 1600-nm laser radiation indicated a molecular second hyperpolarizability of 55 percent of the physical limit, or 17 times the lower bound of the quantum gap.