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Identifier

000384097

Title

Manipulation of excition polariton condensates in 1D waveguides

Author

Gao, Tingge

Thesis advisor

Σαββίδης, Παύλος

Abstract

Abstract This thesis investigates exciton polaritons in GaAs microcavity. Exciton polaritons are the eigenstates of the microcavity in strong coupling regime. In this thesis, we realize polariton lasing in a high Q microcavity and micropillars; and to manipulate polariton condensate flow along a 1D waveguide by using optical/spin method. A high Q microcavity is investigated at low temperature and high temperature. Polariton lasing is observed only at low temperature. Micropillars are etched from the high Q microcavity. Polariton lasing threshold decreases with reducing pillar size due to strong lateral confinement, which favors polariton energy relaxation, thermalization and avoidance of exciton diffusion. A monotonic increase of the polariton lasing threshold with temperature is found which is consistent with the relation between the critical density of polariton condensate and temperature in quasi-thermalization regime. By using polariton lasing at high wave vector states observed in the planar microcavity, we realize a polariton condensate flow along a microcavity ridge. The propagation of the condensate occurs due to polariton exciton reservoir interaction. In addition, we can manipulate the polariton condensate flow through a much weaker gate beam. The above transistor switch could be employed to make spin devices. Firstly, we observe spin polarization oscillation of the polariton condensate flow due to the effect magnetic field generated by the TE-TM mode splitting. Secondly, a polariton condensate flow without spin polarization oscillation is found when the laser is in pulse mode. Finally, a spin dependent blueshift is introduced by making the gate beam circular polarized. The polariton condensate in different spin polarization could be reflected or transmitted through the gate spot. The gate beam acts as a spin filter to separate the polariton condensate with different spin polarization. All these work paves the way to the application of polariton circuits or spin circuits. The spatial control of the polariton condensate flow in the waveguide allows the implementation of polariton transistors or spin filters suitable in both optoelectronic and all-optical/spin schemes.

Language

English

Subject

Condensation

Exciton

Lasing

Microcavity

Polariton

Ridge

Spin

Issue date

2014-04-04