  Two-dimensional graphene plasmon-based technologies will enable the
development of fast, compact and inexpensive active photonic elements because,
unlike plasmons in other materials, graphene plasmons can be tuned via the
doping level. Such tuning is harnessed within terahertz quantum cascade lasers
to reversibly alter their emission. This is achieved in two key steps: First by
exciting graphene plasmons within an aperiodic lattice laser and, second, by
engineering photon lifetimes, linking graphene's Fermi energy with the
round-trip gain. Modal gain and hence laser spectra are highly sensitive to the
doping of an integrated, electrically controllable, graphene layer.
Demonstration of the integrated graphene plasmon laser principle lays the
foundation for a new generation of active, programmable plasmonic metamaterials
with major implications across photonics, material sciences and nanotechnology.
