Ultrafast two-photon absorption optical thresholding of spectrally coded pulses

We report studies on two-photon absorption (TPA) GaAs p-i-n waveguide photo detectors as optical thresholders for proposed ultrashort pulse optical cod e-division multiple-access (CDMA) systems. For either chirped optical pulse s or spectrally phase coded pseudonoise bursts, the TPA photocurrent respon se reveals a strong pulseshape dependence and shows good agreement with the oretical predictions and results from conventional SHG measurements. The pe rformance limits of the TPA optical thresholders set by the encoded bandwid th in the spectral encoding-decoding process are also discussed based on nu merical simulations. Our results show the feasibility of applying such devi ces as nonlinear intensity discriminators in ultrahigh-speed optical networ k applications. (C) 1999 Elsevier Science B.V. All rights reserved.