CERENKOV 2ND-HARMONIC GENERATION REVISITED - EXISTENCE OF PHASE-MATCHING

We show that in Cerenkov second harmonic generation the phase-matching condition is not automatically satisfied. The new concept of a Cerenk ov phase-matching surface is introduced and the expression of the Cere nkov phase-matching condition is derived. We also show that the Cerenk ov scheme includes second harmonic generation at distributed couplers. For example, use of grating couplers leads to grating-assisted Cerenk ov second harmonic generation. These are important results which modif y the understanding of the physics underlying Cerenkov frequency doubl ing.