  Spin-controlled lasers are highly interesting photonic devices and have been
shown to provide ultra-fast polarization dynamics in excess of 200 GHz. In
contrast to conventional semiconductor lasers their temporal properties are not
limited by the intensity dynamics, but are governed primarily by the
interaction of the spin dynamics with the birefringent mode splitting that
determines the polarization oscillation frequency. Another class of modern
semiconductor lasers are high-beta emitters which benefit from enhanced
light-matter interaction due to strong mode confinement in low-mode-volume
microcavities. In such structures, the emission properties can be tailored by
the resonator geometry to realize for instance bimodal emission behavior in
slightly elliptical micropillar cavities. We utilize this attractive feature to
demonstrate and explore spin-lasing effects in bimodal high-beta quantum dot
micropillar lasers. The studied microlasers with a beta-factor of 4% show
spin-laser effects with experimental polarization oscillation frequencies up to
15 GHz and predicted frequencies up to about 100 GHz which are controlled by
the ellipticity of the resonator. Our results reveal appealing prospects for
very compact, ultra-fast and energy-efficient spin-lasers and can pave the way
for future purely electrically injected spin-lasers enabled by short injection
path lengths.
