Graphene Plasmonics and Terahertz Photonics
The experimental discovery of two-dimensional (2D) gated graphene in 2004 by Novoselov and Geim is a seminal event in electronic materials science, ushering in a tremendous outburst of scientific activity in the study of electronic properties of this unique two-dimensional material with a gapless Dirac electronic spectrum. The lack of a traditional bandgap makes graphene an exceptionally versatile photonic material, and the ability to dope graphene through metallic contacts and tune the carrier density through the application of a gate opens possibilities for a variety of transformative photonic devices. In particular highly doped graphene has recently been recognized as a powerful plasmonic material that combines many important properties at terahertz (THz) frequencies with the ability of being electrically tunable. Terahertz radiation has uses from security to medicine. Currently, however, THz technology is notoriously underdeveloped. Graphene plasmonics has promise of filling in this conspicuous gap in the electromagnetic spectrum with a robust and radically new technology. Recently, sensitive room temperature THz detectors have been demonstrated that operate on a photo-thermo-electric principle with response times of 10s of femtoseconds. THz absorption in a graphene element raises the temperature of the graphene carriers, which then diffuse to the contacts made of dissimilar metals and produces a photo voltage proportional to the Seebeck coefficient of the graphene. A source of THz radiation based on this photo-thermo-electric effect also looks promising. A graphene element is used as an optical mixer of near IR to generate THz plasmons which are then coupled to free space radiation by an antenna. A review of graphene and these THz developments will be described.