Large-aperture periodically poled Rb-doped KTP with a short-period via coercive field engineering

We demonstrate periodic poling of large aperture Rb-doped KTP (RKTP) crystals with a QPM period of 3.43 pm via coercive field engineering. The periodically-poled RKTP has excellent pattern-fidelity, with a second harmonic generation (SHG) conversion efficiency of 1.4%/Wcm at 405 nm. We use ion-exchange (IE) to fabricate grating of high-and-low coercive fields and establish that the depth of the in-diffused Rb+ is the main parameter to achieve sufficiently large coercive field contrast that enables uniform periodic poling in the thick crystal. Furthermore, we demonstrate that our robust coercive field grating allows multiple cycles of polarization-switching which can be employed to decrease the refractive-index change along the polar axis, induced during the IE process.