Quadratic non-linear optical effects, specifically the phase-shift that a fundamental frequency wave experiences through cascading during second-harmonic-generation and the successive down-conversion, are a viable route to all-optical signal processing in integrated optics geometries. We review the most relevant device concepts and their potential applications, with examples of experimental results and prospects for implementation in non-linear thin films. (C) 1998 Elsevier Science S.A. All rights reserved.