Abstract

Recently there has been a great interest in quasiphase-matching (QPM) waveguides for frequency conversion. Such waveguides have been fabricated in lithium niobate, lithium tantalate, KTP, and organic materials. In LiNbO₃ and LiTaO₃ a number of different fabrication techniques have been employed to obtain the required periodic reversal of the ferroelectric domain orientation. We have demonstrated generation of blue light by frequency doubling in QPM waveguides, fabricated in LiNbO₃ as well as in LiTaO₃. In the latter case, domain inversion was obtained by proton exchange in combination with a heat treatment. We now report on a comparison, based on simulations and experiments, between these two types of QPM waveguide. For the LiTaO₃ the domain inverted regions show an approximately semicircular cross-section, compared with a more triangularly shaped cross-section in LiNbO₃ more promising for a high conversion efficiency. In particular it should be more easy in LiTaO₃ to come close to the theoretical limit when using third-order quasiphase matching. To utilize the possibility of a more efficient interaction by going to first-order QPM, it is, however, critically important to obtain a very tight mode confinement. It is also concluded that the duty cycle is an essential parameter to optimize.

© 1991 Optical Society of America