  The possibility to generate short spin waves is of great interest in the
field of magnonics nowadays. We present an effective and technically affordable
way of conversion of long spin waves, which may be generated by conventional
microwave antenna, to the short, sub-micrometer waves. It is achieved by
grating-assisted resonant dynamic dipolar interaction between two ferromagnetic
layers separated by some distance. We analyze criteria for the optimal
conversion giving a semi-analytical approach for the coupling coefficient. We
show by the numerical calculations the efficient energy transfer between layers
which may be either of co-directional or contra-directional type. Such a system
may operate either as a short spin wave generator or a frequency filter, moving
foreward possible application of magnonics.
