title: A high-brightness source of polarization-entangled photons optimized for applications                     in free space.
abstract: We present a simple but highly efficient source of polarization-entangled photons based on                     spontaneous parametric down-conversion (SPDC) in bulk periodically poled                     potassium titanyl phosphate crystals (PPKTP) pumped by a 405 nm laser diode.                     Utilizing one of the highest available nonlinear coefficients in a                     non-degenerate, collinear type-0 phase-matching configuration, we generate                     polarization entanglement via the crossed-crystal scheme and detect 0.64 million                     photon pair events/s/mW, while maintaining an overlap fidelity with the ideal                     Bell state of 0.98 at a pump power of 0.025 mW.
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, 08860 Castelldefels (Barcelona), Spain. fabian.steinlechner@icfo.es
authors.forename: Fabian
authors.initials: F
authors.lastname: Steinlechner
authors.forename: Pavel
authors.initials: P
authors.lastname: Trojek
authors.forename: Marc
authors.initials: M
authors.lastname: Jofre
authors.forename: Henning
authors.initials: H
authors.lastname: Weier
authors.forename: Daniel
authors.initials: D
authors.lastname: Perez
authors.forename: Thomas
authors.initials: T
authors.lastname: Jennewein
authors.forename: Rupert
authors.initials: R
authors.lastname: Ursin
authors.forename: John
authors.initials: J
authors.lastname: Rarity
authors.forename: Morgan W
authors.initials: MW
authors.lastname: Mitchell
authors.forename: Juan P
authors.initials: JP
authors.lastname: Torres
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter
authors.forename: Valerio
authors.initials: V
authors.lastname: Pruneri
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D054023:Lasers, Semiconductor; D008029:Lighting / Q000295:instrumentation*; D017785:Photons; D012031:Refractometry / Q000295:instrumentation*