Bright source of polarization-entangled photons using periodically poled potassium titanyl phosphate (KTP)

We used two perpendicular crystals of periodically-poled potassium titanyl phosphate (KTP) to efficiently generate frequency-nondegenerate, polarization-entangled photons in a single spatial mode. The source is compact, inexpensive, and suitable for long-distance fiber-based quantum communication.