Abstract

There has been considerable interest in all-optical switching devices which utilize the nonresonant contribution to the nonlinear refractive index, n₂. The nonresonant nature of the effects puts the response time in the femtosecond regime. We think that using semiconductors right below their two-photon edge allow use of the two photon enhanced n₂. We present the first experimental demonstration of an all-optical switch, in a semiconductor waveguide, where the transmission of the device is not limited by linear or nonlinear absorption. The waveguides consist of a strip loaded waveguide. A 4 μm isolation layer of Al_0.25Ga_0.75As was grown on a n+ GaAs Substrate. The guiding layer consisted of 1.5 μm thick layer of Al_0.18Ga_0.82As and a cladding of 1.5 μm of Al_0.25Ga_0.75As. The cladding was etched 1.2 μm to produce 5 μm ridges for the guide spaced by 4 μm. The coupling region was 6.25 mm. The experiment were done using a color-center laser producing 10 psec pulses in the 1.55 μm spectral region. The particular directional coupler used was 0.63 coupling lengths long. Calculations using an instantaneous nonlinearity agreed very well with the experiments. Using our model we were able to estimate the n₂ at 7.0- 9.0x10^-14cm²/W.

© 1991 Optical Society of America