Asymmetric Localization by Second Harmonic Generation

We introduce a nonlinear photonic system that enables asymmetric localization and unidirectional transfer of an electromagnetic wave through the second harmonic generation process. Our proposed scattering setup consists of a non-centrosymmetric nonlinear slab with nonlinear susceptibility $\chi^{(2)}$ placed to the left of a one-dimensional periodic linear photonic crystal with an embedded defect. We engineered the linear lattice to allow the localization of a selected frequency $2\omega_\star$ while frequency $\omega_\star$ is in the gap. Thus in our proposed scattering setup, a left-incident coherent transverse electric wave with frequency $\omega_\star$ partially converts to frequency $2\omega_\star$ and becomes localized at the defect layer while the unconverted remaining field with frequency $\omega_\star$ exponentially decays throughout the lattice and gets reflected. For a right-incident wave with frequency $\omega_\star$ there won't be any frequency conversion and the incident wave gets fully reflected. Our proposed structure will find application in designing new optical components such as optical sensors, switches, transistors, and logic elements.