A characterisation technique for packaged Er/Yb-codoped waveguides based on the analysis of laser transient behaviour is studied. A ring laser configuration was used and measurements on the evolution of laser output power during transient regime were carried out. An approximate analytical method was developed for the analysis of this behaviour. A good agreement is obtained for the relevant damped oscillation parameters. The use of this technique for active waveguides characterisation is discussed.© (2006) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.