Abstract : Using as a model system Quantum Cascade Lasers the Principal investigator demonstrated the performance limitations of spiral shaped cavities as far as their inability to achieve high directionality; he showed that suitably deformed (Lima on shaped) resonators can partially circumvent this problem and also achieve higher optical power. He then invented notched elliptical resonators demonstrating for the first time highly unidirectional whispering gallery mode microcavity lasers with divergence as small as 5 deg. These lasers have lower threshold current density and far greater beam quality than ridge lasers, and single mode behavior in a limited range of currents. The PI found that the beam divergence is insensitive to the pumping current and to the notch geometry, demonstrating the robustness of notched elliptical resonators. Simulations have also shown that this device efficiently collimates also TE polarized modes that are typical of diode lasers. Thus this resonator can also be used to design highly unidirectional low threshold near-infrared and visible microcavity diode lasers.