  Robust laser sources are a fundamental building block for contemporary
information technologies. Originating from condensed-matter physics, the
concept of topology has recently entered the realm of optics, offering
fundamentally new design principles for lasers with enhanced robustness. In
analogy to the well-known Majorana fermions in topological superconductors,
Dirac-vortex states have recently been investigated in passive photonic systems
and are now considered as a promising candidate for single-mode large-area
lasers. Here, we experimentally realize the first Dirac-vortex topological
lasers in InAs/InGaAs quantum-dot materials monolithically grown on a silicon
substrate. We observe room-temperature continuous-wave single-mode linearly
polarized vertical laser emission at a telecom wavelength. Most importantly, we
confirm that the wavelength of the Dirac-vortex laser is topologically robust
against variations in the cavity size, and its free spectral range defies the
universal inverse scaling law with the cavity size. These lasers will play an
important role in CMOS-compatible photonic and optoelectronic systems on a
chip.
