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.
IBM found that by patterning the graphene/insulator microdisks in arrays, it was able to tune their resonant frequency by varying the size of the microdisks, the number of layers, their spacing, and the doping of the graphene layers. Upon analysis, IBM discovered a unique carrier density scaling law for its graphene/insulator superlattices that, unlike conventional semiconductor superlattices, is based on laws governing Dirac fermions (such as quarks, leptons, baryons and hadrons).
As a result, IBM has been able to demonstrate patterned graphene/insulator stacks implementing a widely tunable notch filters with a 8.2-dB rejection ratio, and a terahertz linear polarizer with 9.5-dB extinction ratio. Implemented by laying down wafer scale alternating layers of graphene and a polymer insulator, then patterning them into microdisks, IBM demonstrated that these graphene/insulator superlattices shielded 97.5 percent of electromagnetic radiation at frequencies below 1.2 terahertz.
For the future, the research group intends to tune its graphene/insulator superlattices for the infrared frequencies used by optical communications equipment today