Time-resolved optical nonlinearity measurement by a two color pump-probe ellipsometry in InAs quantum dot waveguide

We have developed a two color pump-probe ellipsometry for the measurement of the optical nonlinear phase shift in a waveguide with quantum dot (QD) core layers. The key point of the method is to utilize the large polarization-dependent property in the optical nonlinearity arising from a flat-dome-like shape of the QDs. In this paper we report the time resolved behavior of the nonlinear response in the QD waveguides obtained by this method. Optical phase shift of more than π/2 rad was obtained by a pumping of 30 pJ/μm². Delay time dependence of the phase shift is discussed in connection with the carrier dynamics.