Nonlinear čerenkov radiation in nonlinear photonic crystal waveguides

We study nonlinear čerenkov radiation generated from a nonlinear photonic crystal waveguide where the nonlinear susceptibility tensor is modulated by the ferroelectric domain. Nonlinear polarization driven by an incident light field may emit coherently harmonic waves at new frequencies along the direction of čerenkov angles. Multiple radiation spots with different azimuth angles are simultaneously exhibited from such a hexagonally poled waveguide. A scattering involved nonlinear čerenkov arc is also observed for the first time. čerenkov radiation associated with quasi-phase matching leads to these novel nonlinear phenomena.