Carrier-dependent nonlinearities and modulation in an InGaAs SQW waveguide

The authors 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, σ_n=-1×10^-19 cm³, was deduced for probe wavelengths near the TM (transverse magnetic) absorption edge, falling only to σ_n=-3.1×10^-20 cm³, at over 0.16 μm from the band edge. For an incident irradiance of 18 kW/cm ², 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 2D system