Luis Aina, AlfredoSánchez Soto, Luis Lorenzo2023-06-202023-06-201993-121050-294710.1103/PhysRevA.48.4702https://hdl.handle.net/20.500.14352/59792© 1993 The American Physical Society. The authors would like to thank Professor A. Galindo and Professor R. Tanas for a critical reading of the manuscript and useful comments. They are grateful as well to Professor J.F. Carinena for helpful and enlightening discussions of some rather technical points. Finally, they benefited from the continuous interest and advice of Professor E. Bernabeu.We introduce a unitary operator representing the exponential of the phase difference between two modes of the electromagnetic field. The eigenvalue spectrum has a discrete character that is fully analyzed. We relate this operator with a suitable polar decomposition of the Stokes parameters of the field, obtaining a natural classical limit. The cases of weakly and highly excited states are considered, discussing to what extent it is possible to talk about the phase for a single-mode field. This operator is applied to some interesting two-mode fields.engjournal articlehttp://dx.doi.org/10.1103/PhysRevA.48.4702http://journals.aps.org/open access5352-photon quantum opticsHomodyne detectionStatesFormalismNumberNoiseSu(2)Óptica (Física)2209.19 Óptica Física