  Graphene is a 2D material with appealing electronic and optoelectronic
properties. It is a zero-bandgap material with valence and conduction bands
meeting in a single point (Dirac point) in the momentum space. Its conductivity
can be changed by shifting the Fermi level energy via an external electric
field. This important property determines broadband and tunable absorption at
optical frequencies. Moreover, its conductivity is a complex quantity, i.e.
Graphene exhibits both electro-absorption and electro-refraction tunability,
and this is an intriguing property for photonic applications. For example, it
can be combined as an active material for silicon waveguides to realize
efficient detectors, switches and modulators. In this paper, we review our
results in the field, focusing on graphene-based optical modulators integrated
on Silicon photonic platforms. Results obtained in the fabrication of single-
and double-layer capacitive modulators are reported showing intensity and phase
modulation, resilience of the generated signals to chromatic dispersion because
of proper signal chirp and operation up to 50 Gb/s.
