  We demonstrate a compact and stable source of polarization-entangled pairs of
photons, one at 810 nm wavelength for high detection efficiency and the other
at 1550 nm for long-distance fiber communication networks. Due to a novel
Sagnac-based design of the interferometer no active stabilization is needed.
Using only one 30 mm ppKTP bulk crystal the source produces photons with a
spectral brightness of 1.13x10^6 pairs/s/mW/THz with an entanglement fidelity
of 98.2%. Both photons are single-mode fiber coupled and ready to be used in
quantum key distribution (QKD) or transmission of photonic quantum states over
large distances.
