Periodically poled materials for miniature light sources

The quasi-phase matching (QPM) scheme has during the last few years been frequently used in the development of new coherent light sources. This has primarily been made possible by the introduction, and continuous improvement, of the electric field poling technique for ferroelectric crystals. Established nonlinear crystals, like LiNbO3 and KTiOPO4, can be engineered to fit with specific wavelengths at the same time as an enhanced effective nonlinearity is obtained. This allows longer crystals to be used and gives significantly reduced thresholds for optical parametric oscillators as well as higher efficiencies for the nonlinear conversion in general. In this paper an overview of QPM in periodically poled crystals is given and the status for waveguide and bulk frequency conversion is reviewed. (C) 1999 Elsevier Science B.V. All rights reserved.