Exciton-polaritons are the quasiparticles resulting from the strong coupling between photons and excitons. The strong nonlinearity due to their particle-particle
interaction and the capability of accessing their spin from outside, are of great
importance for fundamental physics research and possible future applications.
In this thesis we study the nonlinear propagation of polaritons in waveguides
and microcavity wires. Both systems have inherent advantages that make them
promising building blocks for future polariton circuits. Whilst waveguides are
easier to fabricate and usually show longer propagation distances, microwires
have a characteristic energy-momentum dispersion with finite energies at k=0
which, as I will show in this thesis, is required for the formation of Cherenkov
radiation and bright conservative solitons. The study of polariton propagation
in both systems is necessary as they could be used for different technological
applications, such as amplifiers and optical processing and transmission.
Firstly, we experimentally demonstrate amplification and nonlinear modulation of pico-Joule pulses in a polariton waveguide. We achieved a maximum gain
of 4.3 dB for a pump region 0.1 mm long. We explain the interplay of nonlinearity
and gain as a result of stimulated scattering from a continuous-wave reservoir of
excitons and polaritons generated by the pump, that amplifies the polariton field.
In the second part of the thesis, we study propagation of conservative bright
solitons in microwires and its accompanying effects. We observed Cherenkov
radiation travelling in the opposite direction to the solitons emitting it. We
show that the formation and propagation direction of the Cherenkov radiation is
determined by the microwire polariton dispersion.
Finally, we study the polarization of bright solitons propagating in microwires.
We recorded polarization precession at low excitation powers and domain formation at higher powers. We explain the observed polarization domains as a result
of spin-dependent polariton-polariton interactions and an imbalance of polariton
spin populations.
