Dispersion-based control of modal characteristics for parametric   down-conversion in a multimode waveguide
  We report generation of near-infrared photon pairs in fundamental spatial modes via type-II spontaneous parametric down-conversion in a periodically poled potassium titanyl phosphate (KTiOPO4) nonlinear waveguide supporting multiple transverse modes. This demonstrates experimentally a versatile scheme for controlling the spatial characteristics of the produced nonclassical light based on exploitation of intermodal dispersion. The down-converted photons are characterized by the measurement of the beam quality factors in the heralded regime. 
Michal Karpinski, Czeslaw Radzewicz, Konrad Banaszek
quant-ph