The forseen operation scenario for future fusion devices like ITER and DEMO is the high confinement mode (H-mode), which is characterized by high pressure and current density gradients in the plasma edge due to an edge transport barrier (ETB). These steep gradients provide a source of free energy for magnetohydrö dynamic instabilities. One property of the H-mode are the quasi periodically occuring edge localized modes (ELMs), which lead to the degradation of the ETB. The best model so far, which describes the critical quantities driving the ELM unstable, is the peeling-ballooning model, in which peeling modes, driven by the current density and its gradients, as well as ballooning modes, driven by the pressure gradients, combine to form peeling-ballooning modes. This Master Thesis deals with non-linear coupling of magnetic modes in AS- DEX Upgrade plasma discharges. A theoretical model first shows how coupling of modes in waves, and therefore also in plasma fluctuations, develops. Bicoherence analysis delivers a method to diagnose and dispaly these couplings. Over the course of this thesis a bicoherence algorithm was developed and thoroughly tested. Windowing and dithering turned out to be useful tools to decrease the noise sensitivity and increase the stability of the algorithm. To test the capabilities of the algorithm in analyzing experimental data, signals of magnetic pick-up coils from different AUG dischages were anayzed and displayed. The magnetic signals were then synchronized to the ELM onsets to check for coupling before, during and after the ELMs. This method preserves the important properties of the ELMs while removing unimportant ones. Consequently these ELM synchronized signals were divided into distinct phases and separatly analyzed with the bicoherence algorithm. No apparent mode couplings were found in any of the ELM phases.