We show that transverse engineering of quasi-phase-matched geometries can be used to tailor the spatial mode function that describes the quantum state of photon pairs generated in spontaneous parametric downconversion. We study several geometries and reveal how properly engineered gratings affect, in particular, the spatial correlations embedded in two-photon entangled states.
Juan P. Torres, Alexandescu, A., Carrasco, S., Torner, L. Quasi-phase-matching engineering for spatial control of entangled two-photon states. "Optics letters", Febrer 2004, vol. 29, núm. 4, p. 376-378.