CERENKOV-TYPE 2ND-HARMONIC GENERATION IN KNBO3 CHANNEL WAVE-GUIDES

Cerenkov-type second-harmonic generation using KNbO3 channel waveguide s produced by MeV He+-ion implantation is presented from the viewpoint of device design, We derive the Cerenkov phase-matching condition for multimode waveguides and utilize Cerenkov-angle analysis as a tool fo r contact-free measurement of the effective indexes of guided modes of ion-implanted KNbO3 channel waveguides at a wavelength of 860 nm. The measured mode indexes are in full agreement with calculations based o n the effective-index method and the refractive index-depth profiles o f ion-implanted KNbO3 waveguides. The efficiency of Cerenkov-type seco nd-harmonic generation is modeled using analytical approximations of t he field distributions of the fundamental and the Cerenkov-radiation m odes in embedded-channel waveguides. The acceptance width for Cerenkov -type frequency doubling in these ion-implanted waveguides is about on e order of magnitude wider than for noncritical phase-matched second-h armonic generation in bulk KNbO3 crystals. Based on the theoretical si mulations, guidelines for optimum device design are given, and the pos sibility to increase the ultimate conversion efficiency to about 30% W -1 cm(-1) through lateral-resonance enhancement of the second-harmonic field in KNbO3 channel waveguides is demonstrated.