Self-Guiding Effects in Gallium Arsenide Semiconductor Optical Amplifiers

摘要

The realization of all optical devices requires identification and characterization of materials possessing large nonlinearities and low loss. Although gallium arsenide aluminum gallium arsenide (GaAs-AlGaAs) quantum well structures have very large third order resonant nonlinearities just below the bandgap, the absorption in this region makes them unusable for all optical processing devices. Using these materials at below 1/2 of the bandgap reduces the losses, but also reduces the nonlinearity. In this research, we investigate a different method of accessing the nonlinearity. By fashioning GaAs-AlGaAs double heterostructure devices into semiconductor optical amplifiers, a strong positive nonlinearity correlated to the gain of the device was identified and characterized. This nonlinearity is all the more valuable as these devices can provide gain to the signal as opposed to loss thereby boosting the effective nonlinearity of the devices. The detriment in using this type of carrier induced effect is that the nonlinearity is not instantaneous and requires over 1 ps to stabilize. Standard interferometric techniques were used to characterize the nonlinearity in these forward biased devices. The resulting measurements when compared to Kerr nonlinearity of generic form nr = no + n2I, returned an effective nonlinear coefficient of refractive index n2 on the order of 5x10(exp -10) sq cm(exp 2)/W.