On the biphoton wavelength

We report on an experiment showing that the wavelength of a biphoton is cle arly dependent on the measurement scheme and on the way it is defined. It i s shown that it can take any value, depending on the control of the interfe rometer phase differences. It is possible to identify the interference of t he single and two-photon wavepackets as particular cases of the most genera l interference process. The variable wavelength has no implication on the e nergy of the individual photons neither on the total energy of the biphoton .