Second-harmonic generation using 4-bar quasi-phasematching in a GaAs microdisk cavity

The 4-bar crystal symmetry in materials such as GaAs can enable quasi-phasematching for efficient frequency conversion without poling, twinning or other engineered domain inversions. 4-bar symmetry means that a 90 degree rotation is equivalent to a crystallographic inversion. Therefore, propagation geometries where light circulates about the 4-bar axis produce effective domain inversions, useful for quasi-phasematching. Microdisk optical cavities also offer resonance field-enhancement and excellent spatial overlap, resulting in highly efficient frequency conversion in micrometer-scale volumes. These devices can be integrated in photonic circuits as compact sources of radiation or entangled photons. Efficient second-order frequency conversion is a new functionality for nonlinear semiconductor microdisk resonators, which have been previously explored for all-optical circuits as switches, signal routers and optical logic gates. Arrays of microresonators can produce slow light and robust optical delay lines. Here, we present the first experimental observation of efficient second-harmonic generation in a microdisk cavity utilizing 4-bar quasi-phasematching.