Fig. 1
From: Complementarity in single photon interference – the role of the mode function and vacuum fields
Scheme of the emitted light cone in type I SPDC: The entangled signal (red) and idler (green) photons occur at opposite sides of the cone (left side of the figure). In the middle of the figure a photo of the cone emission is shown. It is investigated, how the visibility (coherence) decreases if the interfering TEM00-modes signal 1 and signal 2 of a single photon are separated within the light cone e.g. tangentially as shown on right of the figure