  The manipulation of light emitted by two-dimensional semiconductors grounds
forthcoming technologies in the field of on-chip communications. However, these
technologies require from the so elusive out-of-plane photon sources to achieve
an efficient coupling of radiated light into planar devices. Here we propose a
versatile spectroscopic method that enables the identification of the
out-of-plane component of dipoles. The method is based on the selective
coupling of light emitted by in-plane and out-of-plane dipoles to the
whispering gallery modes of spherical dielectric microresonators, in close
contact to them. We have applied this method to demonstrate the existence of
dipoles with an out-of-plane orientation in monolayer WSe2 at room temperature.
Micro-photoluminescent measurements, numerical simulations based on finite
element methods, and ab-initio calculations have identified trions as the
source responsible for this out-of-plane emission, opening new routes for
realizing on-chip integrated systems with applications in information
processing and quantum communications.
