Researchers have realized one of the long-standing theoretical predictions in nonlinear optical metamaterials: creation of a nonlinear material that has opposite refractive indices at the fundamental and harmonic frequencies of light. Such a material, which doesn’t exist naturally, had been a research goal for nearly a decade.
Observation of “backward phase matching” — a phenomenon also known as the “nonlinear mirror” — provided evidence that this new type of metamaterial had been created in a waveguide material.
“Nonlinear optics is critically important to controlling light for information processing, sensing, and signal generation,” said Wenshan Cai, an associate professor in the Georgia Tech School of Electrical and Computer Engineering, who led the research team. “Our effort substantially expands the scope of nonlinear light-matter interactions in artificially structured media with engineered, unconventional linear and high-order material parameters.”
Engineered metamaterials could be especially useful in nonlinear optics, where materials with unconventional properties could make a difference anywhere light must be actively controlled.
“The linear responses of metamaterials have substantially augmented the linear properties available from naturally occurring materials,” noted Shoufeng Lan, a graduate student in Cai’s laboratory. “In the same way, studies of nonlinear metamaterials may have a revolutionary impact on the field of nonlinear optics.
The unconventional electromagnetic parameters made possible by metamaterials will provoke us to rethink and re-evaluate many of the established rules of nonlinear optics.” The research was reported in the journal Nature Materials. —JOHN TOON