  A drawback of high-quality modes in optical microdisks is their isotropic
light emission characteristics. Here we report a novel, robust, and general
mechanism that results in highly directional light emission from those modes.
This surprising finding is explained by a combination of wave phenomena (wave
localization along unstable periodic ray trajectories) and chaotic ray dynamics
in open systems (escape along unstable manifolds). The emission properties
originating in the chaotic ray dynamics permit directional light output even
from microlasers operating in the common multi-mode regime. We demonstrate our
novel mechanism for the limacon billiard family and find directional emission
with narrow angular divergence for a significant range of geometries and
material parameters.
