  The diffraction of a plane wave by a magneto-optical cavity located on a
metal interface is investigated theoretically. We show that the excitation of
localized eigenmodes of the cavity allows one to efficiently excite the surface
plasmon polariton (SPP). We exploit the polarization and symmetry properties of
the cavity modes to propose an efficient approach for controlling the SPP
intensity through an external magnetic field. The presented theoretical
predictions are in good agreement with the rigorous computations based on the
generalized Lorentz reciprocity theorem and aperiodic Fourier modal method. The
magnetization-induced relative intensity variation of the excited SPP
demonstrated in numerical computations varies from a few percent to 100%
depending on the polarization of the incident wave. Such large modulation opens
new possibilities for efficient SPP modulation with considered magneto-optical
intensity effect.
