  We investigate the switching of the coherent emission mode of a bimodal
microcavity device, occurring when the pump power is varied. We compare
experimental data to theoretical results and identify the underlying mechanism
to be based on the competition between the effective gain on the one hand and
the intermode kinetics on the other. When the pumping is ramped up, above a
threshold the mode with the largest effective gain starts to emit coherent
light, corresponding to lasing. In contrast, in the limit of strong pumping it
is the intermode kinetics that determines which mode acquires a large
occupation and shows coherent emission. We point out that this latter mechanism
is akin to the equilibrium Bose-Einstein condensation of massive bosons. Thus,
the mode switching in our microcavity device can be viewed as a minimal
instance of Bose-Einstein condensation of photons. We, moreover, show that the
switching from one cavity mode to the other occurs always via an intermediate
phase where both modes are emitting coherent light and that it is associated
with both superthermal intensity fluctuations and strong anticorrelations
between both modes.
