Optics

Nonlinear metamaterial generates, reflects second-harmonic radiation, may benefit terahertz technology

Aug. 2, 2011

A bulk metamaterial created by researchers at Duke University serves as a nonlinear-optical mirror that reflects second-harmonic radiation back towards the source of the pump light.

John Wallace

Durham, NC--A bulk metamaterial created by researchers at Duke University serves as a nonlinear-optical mirror that reflects second-harmonic radiation back towards the source of the pump light. As with many prototypical metamaterials, this one operates in the microwave region, although the researchers anticipate that similar devices can be made to operate in the terahertz region.The device, which measures six inches by eight inches and about an inch high, is made of individual pieces of fiberglass circuit-board material arranged in parallel rows. Each piece is etched with copper circles. Each copper circle has a small gap that is spanned by a diode, which when excited by radiation passing through it, breaks its natural symmetry, creating nonlinearity.“Normally, this frequency-doubling process occurs over a distance of many wavelengths, and the direction in which the second harmonic travels is strictly determined by whatever nonlinear material is used,” noted Alec Rose, a graduate student and one of the researchers. “Using the novel metamaterials at microwave frequencies, we were able to fabricate a nonlinear device capable of 'steering' this second-harmonic. The device simultaneously doubled and reflected incoming waves in the direction we wanted.”The metamaterial has a unit cell size of 1.5 cm and has a negative refractive index. Its conversion efficiency reached a maximum of 1.5%. In another orientation, alrernating layers were rotated by 180 degrees, creating a periodically poled nonlinear material (in this case, the second-harmonic transmission was enhanced). The metamaterial's ready adaptability will be key to the creation of practical terahertz nonlinear mirrors and other devices for communications.Follow us on TwitterSubscribe now to Laser Focus World magazine; it’s free!

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.