Designing and understanding directional emission from spiral microlasers.

The availability of microlasers with highly directional far-field characteristics is crucial for future applications. To this end we study the far-field emission of active microcavities with a spiral shape using the Schrödinger-Bloch model. We find that they can provide directional emission under the conditions of (i) pumping along the resonator boundary and (ii) for specific resonator geometries. We systematically study the far-field characteristics under variation of the pumped area and the cavity geometry and identify a directionality optimized regime. Our results consistently explain previously obtained experimental results.