Optical nonlinearities in GaAs-GaAlAs multiple quantum-well hetero-nipi waveguides

The authors report on measurements of large optical nonlinearities in GaAs-GaAlAs multiple quantum-well hetero-nipi (MQW-H nipi) waveguides using a Mach-Zender interferometer. At normal operational powers and absorption levels the lateral spreading of the photogenerated carriers is so large that the nonlinearity must be defined from the ratio between the total optical power and the width of the MQW-H nipi region rather than from the optical intensity alone. The study concludes that the nonlinearity measured in a GaAs-GaAlAs MQW-H nipi waveguide at a wavelength far below the absorption edge where the absorption coefficient is in the range 10-20 cm^-1, is on the order of 10 ^-5 cm²/W. This value is two to three orders of magnitude larger than the optical nonlinearity measured in a typical MQW p-i-n diode waveguide at similar absorption, but the increased nonlinearity is obtained at the expense of speed