  Hamiltonian of a parametric process describing the interaction of a finite
number of optical cavity modes, with the microwave field is proposed.
Three-boson interaction is due to electro-optical effect. Analysis of the model
is based on the algebraic properties of multimode field operators who, under
certain assumptions, are su (2) algebra generators. The features of the
transformation of the quantum states of signal photons in the electro-optical
modulator are investigated. The limit on the number of interacting modes from
the proposed (restricted) model to the traditionally used (unrestricted) model
of electro-optical modulator is investigated.
