  We propose a general design strategy based on genetic optimization to realize
asymmetric reflectivity in periodic and non-periodic planar structures
containing dielectric and gain-loss layers. By means of an optimization
algorithm, it is possible to design the imaginary (or real) part of the complex
permittivity distribution from any given and arbitrary real (or imaginary)
permittivity distribution, i.e to create non-Hermitian potentials intended to
achieve on-demand light transport for a selected spectral range. Indeed, the
asymmetric response of the obtained complex permittivity distribution is
directly related to its area in the complex permittivity plane. In particular,
unidirectional light reflection can be designed in such a way that it switches
from left to right (or vice versa) depending on the operating frequency.
Moreover, such controllable unidirectional reflectivity can be realized using a
stack of dielectric layers while keeping the refractive index and gain-loss
within realistic values.
