  A spin-wave (SW) directional coupler comprised of two laterally parallel
nano-scale dipolarly-coupled SW waveguides is proposed and studied using
micromagnetic simulations and analytical theory. The energy of a SW excited in
one of the waveguides in the course of propagation is periodically transferred
to the other waveguide and back, and the spatial half-period of this transfer
is defined as the coupling length. The coupling length is determined by the
dipolar coupling between the waveguides, and the fraction of the SW energy
transferred to the other waveguide at the device output can be varied with the
SW frequency, bias magnetic field, and relative orientation of the waveguide's
static magnetizations. The proposed design of a directional coupler can be used
in digital computing-oriented magnonics as a connector (multiplexer) of
magnonic conduits without a direct contact, or in the analog microwave signal
processing as a reconfigurable nano-scale power divider and/or frequency
separator.
