Four-wave interaction as a controlled frequency filter

Shown is a possibility of system development with controlled frequency characteristics on the basis of almost degenerated four-wave interaction. Several cases are considered. In the media with inertialess mechanism of cubic linearity two almost contrary base wave of ω and ω2 frequencies are spread. The signal wave of ω3 frequency, subjected to reversal, interfering with the base waves, brings nonlinear polarization of the medium. Medium polarization irradiates the wave reversed to the signal. The criterion of synchronism should be provided for the effective reflection of the signal. 1) Medium polarization should be synchronous with the reversed wave in the whole volume of interaction. 2) Base waves are strictly contrary, ω1ω0, ω2=ω0+Λ. The signal wave of ω3=ω2+delta frequency falls to the base one at THETA angle. The reversed wave is irradiated at ω=ω0-delta frequency. 3) The base waves have the same frequency ω0, but they are not strictly contrary. The angle between base waves equals to 2α. Synchronism criterion of the four-photon parametric process is provided for the signal at ω0(1+sin α) frequency. The reversed wave is irradiated at ω0(1-sin α) frequency. Thus, the process of almost degenerated four-wave interaction offers wide possibilities for the control over reversal of the signal wave front