  The transmission properties through a saturable cubic-quintic nonlinear
defect attached to lateral linear chains is investigated. Particular attention
is directed to the possible non-reciprocal diode-like transmission when the
parity-symmetry of the defect is broken. Distinct cases of parity breaking are
considered including asymmetric linear and nonlinear responses. The spectrum of
the transmission coefficient is analytically computed and the influence of the
degree of saturation analyzed in detail. The transmission of Gaussian
wave-packets is also numerically investigated. Our results unveil that spectral
regions with high transmission and enhanced diode-like operation can be
achieved.
