Carrier-dependent nonlinearities and modulation in an InGaAs SQW waveguide

We report measurements of optically induced carrier-dependent refractive index changes and their saturation in an InGaAs single quantum well centered within a linear multiple quantum well guided-wave Fabry-Perot resonator using diode laser sources. A low-excitation nonlinear refractive cross-section s_n = -1 × 10^-19 cm³ was deduced for probe wavelengths near the TM absorption edge, falling only to s_n = -3.1 × 10^-20 cm³, over 0.16 µm from the bandedge. For an incident irradiance of 18 kW / cm², refractive index changes in the InGaAs quantum well as large as -0.16 were deduced near the absorption edge, while the index change at a wavelength 0.16 µm from the absorption edge was -0.055. This large off-resonant index change is attributed to an enhanced free-carrier contribution within a 2-D system.