  This work aims to design a CMOS compatible, low-electrical power consumption
modulator assisted by plasmons. For compactness and reduction of the electrical
power consumption, electro-absorption based on the Franz-Keldysh effect in
Germanium was chosen for modulation. It consists in the change of the
absorption coefficient of the material near the band edge under the application
of a static electric field, hence producing a direct modulation of the light
intensity. The use of plasmons allows enhancing the electro-optical effect due
to the high field confinement. An integrated electro-optical simulation tool
was developed to design and optimize the modulator. The designed plasmonic
modulator has an extinction ratio of 3.3 dB with insertion losses of 13.2 dB
and electrical power consumption as low as 20 fJ/bit, i.e. the lowest
electrical power consumption reported for silicon photonic modulators. In- and
out-coupling to a standard silicon waveguide was also engineered by the means
of an optimized Si-Ge taper, reducing the coupling losses to only 1 dB per
coupler. Besides, an experimental work was carried out to try to shift the
Franz-Keldysh effect, which is maximum at 1650 nm, to lower wavelength close to
1.55 {\mu}m for telecommunication applications.
