Fabrication and Investigation of Photonic Crystal Microcavities for Solid State Quantum Optics

摘要

We review our recent progress in the fabrication and understanding of ultra-low mode volume,high Q-factor microcavities for quantum dot based cavity QED experiments. The cavities arerealized by the controlled incorporation of defects into 2D photonic crystals that consist of atriangular lattice of air holes within an active Air-GaAs-Air slab waveguide containing InGaAsself-assembled quantum dots. Two specific cavity designs are studied: the L3-cavity consisting ofthree missing holes along a line and the Y1-cavity consisting of a single missing hole with stronglyreduced symmetry. Very good quantitative agreement is obtained between the results of spatiallyresolved optical spectroscopy and 3D calculations of the photonic bandstructure and cavity modestructure. For both cavity designs, cavity Q-factors up to ~8000 are measured for specific designswith ultra-low mode volumes V_(mode)< (λ/n) 3. The relative contribution of cavity losses due to outof plane coupling to the free space continuum, in-plane losses through the photonic crystal and viascattering due to disorder and fabrication imperfections are probed for both cavity designs. Wedemonstrate that in-plane loss can be almost completely inhibited by tuning the localized cavitymodes deeper into the photonic bandgap and the potential to fine tune the out-of plane losses viasubtle modifications of the cavity design parameters. This procedure is shown to result in up to~3x improvements of the cavity Q-factor. The Y1-design is shown to be particularly suitable forQD based cavity QED experiments, due to its very low mode volume, high Q-factors achievable(~7000) and flexibility for enhancement through careful modification of the cavity design.