Coherent Nonlinear Phenomena in Subwavelength-Grating Based Microcavities
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Bose-Einstein condensation of microcavity exciton-polaritons has shown remarkable phenomena such as coherent lasing below population inversion, quantized vortices, superfluidity, and Josephson effects in a semiconductor platform. With nonlinear interaction between exciton-polaritons, it has also drawn great interests for nonlinear photonic devices. To control nonlinear interaction strength, many efforts to confine polariton condensates have been made. In this work, we use a subwavelength-grating (SWG) mirror to confine exciton-polaritons in a lithographically defined area. By careful design, we achieve single-mode polariton lasing in SWG-DBR microcavities and show fully coherent emissions measured by first- and second-order coherence functions. A fully coherent polariton lasing up to second-order hasn't been reported in conventional DBR-DBR microcavities, where single-mode lasing in both energy and polarization is nearly impossible. Optimization of the degree of coherence in polariton lasers are shown by engineering interaction strength. We also realize coupling between polariton condensates by spatial control of exciton-photon detuning. From two coupled polariton condensates with complex coupling constants, multifrequency components are generated from limit-cycle oscillations. This new type of frequency comb mechanism is originated from dynamic interplay between intra-site nonlinearity and inter-site complex couplings. Spectroscopic and interferometric measurements are performed. Also, numerical simulation of the driven-dissipative coupled polariton equation shows good agreement with the experimental results. Finally, we present polariton optomechanics, generation of orbital angular momentum, and vector beam generation in SWG-based microcavities.