**4.4 Nonlinear plasmonic metamaterials**

Plasmonic metamaterials have potential prospects for all optical switching by tailoring the constituent's plasmonic resonances and the electromagnetic coupling between them. Both individual plasmonic resonances and their interactions can be altered as a function of variation in refractive index of the embedding dielectric or substrate, resulting in better nonlinear reactions. By controlling the binding power of molecular excitons, plasmonic excitations will result in effective all-optical modulation, and plasmonic metamaterials give a novel way to increase nonlinearity using epsilon-near-zero regime 'nonlocal' effects [53].

## **4.5 Quantum dot lasers and optical amplifiers**

Quantum Dot (QD) based semiconductor optical amplifiers (SOA's) demonstrate ultrafast gain dynamics and pattern effect free amplification, both theoretically and experimentally [55]. Mode-locked (ML) lasers can be used as optical comb generators for high-frequency applications including time domain multiplexing because of its low alpha factor and wide spontaneous emission range of the quantum dot gain medium [56].
