Customized nonlinearity shaping in imperfect or variable waveguides

Abstract

Generation of high-quality single photons via heralded parametric downconversion re- quires careful design of spectral correlations in down-converted photon pairs. One step in this design process involves customized engineering of ferroelectric domains. In this thesis, we explore two aspects of such customized domain engineering.

We first explore the impact of fabrication imperfections on two main domain engineering methods, by simulating domain variations in domain engineered structures. We quantify the impact by calculating the purity and amplitude of the generated photon. We conclude that realistic fabrication imperfections do not impair purity and amplitude significantly for the studied methods. However, high variations of the dispersion relations in the crystal impact purity and amplitude significantly.

We then introduce two new domain engineering methods designed for mediums with varying dispersion relations. The first is a generalization of an existing algorithm used to design the domain configurations. The second method relies on varying the domain sizes. We show that the first method yields modest improvement, while the second one works remarkably well, even in conditions with extreme change in dispersion.