Abstract

Second harmonic generation in the form of Cerenkov radiation has been used to make direct, contact-free measurements of the effective indices of guided modes in LiNbO₃ channel waveguides. X-cut substrates were used and channels, oriented along the y axis, were formed either by proton exchange or titanium indiffusion. For end-fire TE excitation, the Cerenkov harmonic is forward radiated at a shallow angle into the substrate, exits the output facet of the channel, and appears as bright bands in the far field. These bands are seen to form a one-to-one correspondence with the m-lines of the fundamental modes when a prism coupler is simultaneously clamped to the guide surface. The effective indices of the guided modes can be obtained by a simple calculation which involves only the substrate index and the angle at which the Cerenkov harmonic is radiated into the substrate.

© 1986 Optical Society of America