The case for using gap plasmon-polaritons in second-order optical nonlinear processes.

We show that using metal-insulator-metal (MIM) waveguides to carry out various second-order nonlinear optical processes not only provides highly desired tight optical confinement but also facilitates the phase-matching due to their inherently large anisotropy. This fact allows one to take advantage of otherwise inaccessible large nonlinear susceptibilities of the cubic zinc blende semiconductors. Our efficiency estimates show that since only the longer wavelength infra-red radiation propagates in the surface-plasmon-polariton (SPP) mode, the losses in the metal, while significant, do not preclude development of highly compact nonlinear optical devices on this integration-friendly semiconductor platform.