IBM demonstrates graphene devices for terahertz waves

Graphene has been courted as the miracle material of the future, since different formulations have been fabricated into conductors, semiconductors and insulators. Now IBM has added photonic to the list by demonstrating a graphene/insulator superlattice that achieves a terahertz frequency notch filter and a linear polarizer, devices which could be useful in future mid- and far-infrared photonic devices, including detectors, modulators and three-dimensional metamaterials (see paper inNature Nanotechnology: "Tunable infrared plasmonic devices using graphene/insulator stacks"

"In addition to its good electrical properties, graphene also has exceptional optical properties. In particular, it absorbs light from the far-infrared to to the ultra-violet," said IBM Fellow Phaedon Avouris. "The terahertz range was of particular interest to IBM, because these frequencies can penetrate paper, wood and other solid objects for security applications. Unfortunately, today there are very few ways of manipulating terahertz waves such as polarizing and filtering it, but because graphene operates well at terahertz frequencies we have concentrating on creating these types of devices."

Teraherz frequency oscillations can be carried in graphene by plasmons—the collective oscillation of carriers—to enable low-loss tunable filters. But in single-layer graphene, the carrier concentration and resonant frequency was too weak for photonics applications, according to IBM. However, by going to a multi-layer graphene/instulator superlattice, transparent devices can be patterned into photonic-like crystals that distribute the carriers among the layers effectively enhancing both the carrier density and the resonant frequency


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