Nonlinear optical response and optical coherence time of excitons localized to quantum islands in a
GaAs∕AlGaAs single quantum well are studied by the three-pulse photon echo technique. At low temperature, the optical coherence time is estimated to be
1.8ns from the decay of the photon echo signal. The decay profile for short time delay shows the strong dependence on the input pulse area of the third pulse. Rabi oscillations are also observed. The oscillations show nonlinear behavior affected by the pre-excited polarization. Such behavior can be qualitatively explained by the local field effect due to the exciton-exciton interaction between the localized excitons.