Asymmetric photoluminescence spectra from excitons in a coupled microcavity

Asymmetric photoluminescence (PL) emission from a coupled semiconductor mic rocavity, containing quantum wells in the upper cavity only, is reported. O n resonance, the central polariton mode is Found to emit strongly in the di rection towards the empty lower cavity, whereas in the opposite direction, towards the cavity containing the quantum wells, no central-mode PL is obse rved. At the same time, the spectra from the other modes in the system are independent of direction. The optical field resulting from the central mode is shown to be only strong at macroscopic distances away from the opticall y active excitons. A good fit to the spectra is obtained assuming elastic s cattering of uncoupled excitons into the optically active polariton states.