Instabilities in the polarisation-resolved output of a vertical cavity surface emitting laser (VCSEL) subject to optical injection have been investigated experimentally. It is found that regions of chaotic behaviour exist for both positive and negative cletuning from the stable injection locking regime. Outside the chaos regimes, several nonlinear dynamical phenomena including frequency pushing, nearly degenerate four-wave mixing (NDFWM), injection locking, limit cycle and period doubling, were also observed. (C) 2002 Elsevier Science B.V. All rights reserved.