title: Direct generation of polarization-entangled photon pairs in a poled fiber.
abstract: We experimentally demonstrate the direct generation of polarization-entangled photon pairs in an optical fiber at room temperature by exploiting type-II phase-matched spontaneous parametric down-conversion. A second-order nonlinearity is artificially induced in the 17-cm-long weakly birefringent step-index fiber through the process of thermal poling, and quasi-phase-matching allows for the generation of entangled photons in the 1.5-micron telecom band when the fiber is pumped at 775 nm. A greater-than 80:1 coincidence-to-accidental ratio is achieved, limited mainly by multiphoton pair generation. Without the need to subtract accidentals or to compensate for walk-off, the raw two-photon interference visibility is found to be better than 95%, and violation of Bell's inequality is observed by more than 18 standard deviations. This makes for a truly alignment-free, plug-and-play source of polarization-entangled photon pairs.
authors.affiliation: Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario, Canada. eric.zhu@utoronto.ca
authors.forename: Eric Y
authors.initials: EY
authors.lastname: Zhu
authors.forename: Zhiyuan
authors.initials: Z
authors.lastname: Tang
authors.forename: Li
authors.initials: L
authors.lastname: Qian
authors.forename: Lukas G
authors.initials: LG
authors.lastname: Helt
authors.forename: Marco
authors.initials: M
authors.lastname: Liscidini
authors.forename: J E
authors.initials: JE
authors.lastname: Sipe
authors.forename: Costantino
authors.initials: C
authors.lastname: Corbari
authors.forename: Albert
authors.initials: A
authors.lastname: Canagasabey
authors.forename: Morten
authors.initials: M
authors.lastname: Ibsen
authors.forename: Peter G
authors.initials: PG
authors.lastname: Kazansky