THE 2-PHOTON ABSORPTION SEMICONDUCTOR WAVE-GUIDE AUTOCORRELATOR

In this paper, we report a novel semiconductor waveguide autocorrelato r that employs two-photon absorption (TPA), rather than the more commo nly used-second-harmonic generation, as its nonlinear mechanism. An in troduction to TPA is given, and the reasons for its use in the autocor relator are explained with reference to nonlinear absorption experimen ts. We then describe the fabrication of the p-i-n GaAs/AlGaAs waveguid e. The initial experiments carried out with a single beam in the waveg uide are described and fitted to theory. Autocorrelation traces for bo th a CW modelocked Nd3+:YAG laser at 1.06 mum and a Q-switched InGaAsP /InP laser at 1.3 mum are presented and their pulsewidths obtained by means of a theoretical model. The sensitivity and resolution of the TP A waveguide autocorrelator are then discussed, as is a proposal for a multiple-contact TPA waveguide autocorrelator, designed so that the tw o pulse trains are counter-propagating. This would result in an autoco rrelator from which the laser pulsewidth could be obtained in a single measurement, with no moving parts, and which could be integrated with a semiconductor laser.