  Nonreciprocity of spin wave propagation is a well-known consequence of
antisymmetric exchange contributions possible in magnetic spin systems that
lack inversion symmetry. In this case, it is possible for the energy of a state
to depend on the sign of its momentum as {\omega}(k) ${\neq}$ {\omega}(-k). We
discuss here the consequences of this nonreciprocity on counterpropagating
travelling spin wave states. In a confined geometry we find states with
well-defined nodes but with amplitudes that are modulated such that inversion
symmetry of the mode profile is lost. This feature leads to the suggestion that
additional features may become visible in, for example, ferromagnetic resonance
studies of ferromagnetic micro-elements with DMI, allowing a quantification of
the amplitude and direction of the DMI. Moreover, this interference between
nonreciprocal modes forms the basis for a generalized concept of mode
confinement.
