Extended phase matching properties of periodically poled potassium titanyl phosphate isomorphs

Abstract

We theoretically investigate the properties of extended phase-matching (EPM) for spontaneous parametric down-conversion (SPDC) in four kinds of potassium titanyl phosphate isomorphs (i.e., KTiOPO4, KTiOAsO4, RbTiOPO4, and RbTiOAsO4 crystals). The technique is based on Type II 2nd-order nonlinear optic interaction in periodically poled ferroelectric domain structures, where a single photon with a frequency of 2ω generates a pair of photons with frequencies of ω that are orthogonally polarized with respect to each other. Under EPM, both quasi-phase matching (QPM) and group velocity (GV) matching between interacting waves are efficiently satisfied for the generation of a pair of polarization-entangled bi-photon states with frequencies of ω. Our simulation results show that the generated photon pairs have broad spectral bandwidths of over 69 - 95 nm in tele-communication bands, which are much broader than those of the typical non-EPM case (e.g., ~ sub-nm bandwidth when only the QPM, not the GV matching, is achieved). We will describe the EPM properties of the four kinds of KTP isomorphs in terms of interaction type, GV matching wavelength, domain poling period, and spectral bandwidth. We highlight that the KTP isomorphs have nice potential as suitable components for constituting new quantum information processing systems.