Abstract
A phase-operator formalism is constructed for the Lie algebra of SU(1,1). Uncertainty relations, analogous to the usual number-phase relations, are also constructed. These relations are then evaluated for SU(1,1) coherent states, of which the squeezed-vacuum state of the electromagnetic field is an example. We argue that the new phase, in the case of single-mode fields, may be interpreted as the phase associated with the square of the field amplitude.