Second Harmonic Generation in Deeply Sub-Wavelength Waveguides
  We theoretically investigate second harmonic generation in extremely narrow, sub-wavelength semiconductor and dielectric waveguides. We discuss a novel guiding mechanism characterized by the inhibition of diffraction and the suppression of cut-off limits in the context of a light trapping phenomenon that sets in under conditions of general phase and group velocity mismatch between the fundamental and the generated harmonic. 
V. Roppo, M. A. Vincenti, D. de Ceglia, M. Scalora
physics.optics