In the last decades, attention has been focused in obtaining periodically poled ferroelectric crystals to get efficient nonlinear frequency conversion processes using Quasi-Phase-Matching (QPM). Periodic inversion of the ferroelectric domains is classically obtained by electric field poling, which enables the precise control of the grating periodicity but which does not allowed thick samples along the direction of the spontaneous polarization to be fabricated. The typical widths obtained are: 500 µm for periodically-poled-LiNbO3 (PPLN), 5 mm for periodically-poled-MgO:LN and between 1 and 3 mm for periodically-poled-KTiOPO4 (PPKTP). The limited aperture size of the samples forbids the use of beams with high energy according to the damage threshold of the crystals. To date, large size crystals of PPLN and PPKTP had been obtained by crystal growth techniques, Czochralski and Top Seeded Solution Growth, from single domain seeds. The grating periodicity regularity of the obtained crystals was not sufficient to get efficient QPM frequency conversion. We propose a new protocol, based on an epitaxial growth process onto thin periodically-poled plates previously obtained by electric field poling, the goal being to get large size PPKTP crystals with a controlled regular grating period.
