Two-Photon Polarization Interference for Pulsed SPDC in a PPKTP   Waveguide
  We study the spectral properties of Spontaneous Parametric Down Conversion in a periodically poled waveguided structure of KTP crystal pumped by ultra-short pulses. Our theoretical analysis reveals a strongly multimode and asymmetric structure of the two-photon spectral amplitude for type-II SPDC. Experimental evidence, based on Hong-Ou-Mandel polarization interference with narrowband filtering, confirms this result. 
Malte Avenhaus, Maria V. Chekhova, Leonid A. Krivitsky, Gerd Leuchs,   Christine Silberhorn