  We demonstrate a new generation mechanism for polarisation- and
colour-entangled photon pairs. In our approach we tailor the phase-matching of
a periodically poled KTP crystal such that two downconversion processes take
place simultaneously. Relying on this effect, our source emits entangled
bipartite photon states, emerging intrinsically from a single, unidirectionally
pumped crystal with uniform poling period. Its property of being maximally
compact and luminous at the same time makes our source unique compared to
existing photon-entanglement sources and is therefore of high practical
significance in quantum information experiments.
