One of the main factors involved in the laryngeal dynamic's non-linearity is the coupling between the two vocal folds. Evaluation of the different coupling elements requires various investigations. The present work evaluate the non-linearity effects in clinical situations such as unilateral laryngeal paralysis using Lyapunov's coefficients. It also demonstrate the coupling effects on excised larynx made experimentally asymmetrical, using a specially designed device to measure vibrations from each vocal fold (opto-reflectometer).