title: Generation of polarization entangled photon pairs at telecommunication wavelength using cascaded χ2 processes in a periodically poled LiNbO3 ridge waveguide.
abstract: We report the generation of high-purity correlated photon-pairs and polarization entanglement in a 1.5 μm telecommunication wavelength-band using cascaded χ((2)):χ((2)) processes, second-harmonic generation (SHG) and the following spontaneous parametric down conversion (SPDC), in a periodically poled LiNbO(3) (PPLN) ridge-waveguide device. By using a PPLN module with 600%/W of the SHG efficiency, we have achieved a coincidence-to-accidental ratio (CAR) higher than 4000 at 7.45×10(-5) of the mean number of the photon-pair per pulse. We also demonstrated that the maximum reach of the CAR was truly dark-count-limited by the single-photon detectors used here. This indicates that the fake (noise) photons were negligibly small in this system, even though the photon-pairs, the Raman noise photons, and the pump photons were in the same wavelength band. Polarization entangled photon pairs were also generated by constructing a Sagnac-loop-type interferometer which included the PPLN module and an optical phase-difference compensator to observe maximum entanglement. We achieved two-photon interference visibilities of 99.6% in the H/V basis and 98.7% in the diagonal basis. The peak coincidence count rate was approximately 50 counts per second at 10(-3) of the mean number of the photon-pair per pulse.
authors.affiliation: Corporate Research & Development Center, Oki Electric Industry Co., Ltd., 1-16-8 Chuou, Warabi-shi, Saitama 335-8510, Japan. arahira335@oki.com
authors.forename: Shin
authors.initials: S
authors.lastname: Arahira
authors.forename: Naoto
authors.initials: N
authors.lastname: Namekata
authors.forename: Tadashi
authors.initials: T
authors.lastname: Kishimoto
authors.forename: Hiroki
authors.initials: H
authors.lastname: Yaegashi
authors.forename: Shuichiro
authors.initials: S
authors.lastname: Inoue