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Title: Nonlinear propagating exciton-polaritons in microcavity wires and waveguides
Author: Tapia-Rodriguez, Lucy E.
ISNI:       0000 0004 7970 275X
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2019
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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.
Supervisor: Krizhanovskii, D. N. ; Skolnick, M. S. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available