The strong interaction between turbulent structures arising from a plane mixing layer impinging a circular cylinder is studied using P.I.V. and analysed by means of the Proper Orthogonal Decomposition (P.O.D). Experiments are performed in the wake of a circular cylinder placed across an air/air 2D plane turbulent mixing layer (velocity ratio r=0.65). The cylinder axis is normal to the splitting plate. The Reynolds number, based on the averaged velocity of the mixing layer is Rem=7920 (Um=14.85,D=8 mm). The cylinder is placed so that the local vorticity thickness of the mixing layer, is equal to the diameter of the cylinder D. To study this complex 3D configuration, a POD approach is proposed. The three spatial directions being strongly inhomogeneous and no experimental way being presently available to get a fully 3D, three components instantaneous description of the flow, a snapshot POD approach is not possible and a 'classical' POD has to be used. Experiments are carried out to supply the correlation tensor, necessary for applying this last POD approach. A two 2D-plane PIV is set-up. The two PIV planes are arranged perpendicularly to the splitting plate and are parallel. Measurements are performed for a set of spanwise separations between the PIV-planes (over a mesh of 21 planes locations). Due to the inhomogeneity in this direction, all the combinations of the two planes over this mesh, are to be considered, leading to a set of 231 configurations. By this procedure, the full correlation tensor Rij (X, X') where X = (x,y,z), is supplied for the longitudinal and vertical velocity components only. The POD eigenfunctions are then obtained by solving an integral eigenvalue problem. The contribution of the third velocity component is obtained a posteriori by considering the continuity equation. In this paper, after a quick review of the industrial and fundamental aspects of this flow configuration, the experimental procedure is described. In a preliminary validation analysis, the one point statistics obtained from PIV measurements are compared to that obtained, in a comparable flow configuration, by means of hot-wire anemometry. Then the practical aspects of POD calculation, related to the resolution of a very large size eigenvalue problem are addressed. Finally the flow organisation issued from the POD approach is obtained. The resulting structures show that some kind of a dislocation process is involved that is comparable to the one described for example in [Williamson(1989)].