  The nonlinear interaction of waves in PT-symmetric periodic stacks with an
embedded nonlinear anisotropic dielectric layer illuminated by plane waves of
two tones is examined. The three-wave interaction technique is applied to study
the nonlinear processes. It is shown that the intensity of the three-wave
mixing process can be significantly enhanced in resonant cavities based on
PT-symmetric periodic structures, especially as the pumping wave frequency is
near the coherent perfect absorber-lasing resonances. The main mechanisms and
properties of the combinatorial frequency generation and emission from the
stacks are illustrated by the simulation results and the effect of the layer
arrangement in PT-symmetric walls of resonator on the stack nonlinear response
is discussed. The enhanced efficiency of the frequency conversion at Wolf-Bragg
resonances is demonstrated. It has been shown that Wolf-Bragg resonances of
very high orders may lead to the global maxima and nulls of the scattered
field. The analysis of the effect of losses in nonlinear dielectric layer on
the combinatorial frequency generation efficiency has shown that the rate of
losses may amplify the intensity of the frequency mixing process.
