title: Single mode fiber birefringence compensation in Sagnac and "plug & play" interferometric setups.
abstract: Single mode fiber (SMF) birefringence effects have been a limiting factor for a variety of Sagnac applications over longer distanceSMF links. In this report, we present a new concept of the SMF birefringence compensation in a Sagnac interferometric setup, based on a novel polarization control system. For the destructive interference, our control system guarantees a perfect compensation of both the SMF birefringence and imperfect propagation times matching of the setup's components. For the stabilization of the constructive interference, we have applied a fiber stretcher and a simple proportional-integral-derivative (PID) controller. The enclosed experimental data of the setup's visibility confirm validity of our polarization control system. We have also showed that the SMF birefringence model used in a "plug & play" interferometric setup [19], widely cited in the papers on quantum key distribution [11, 12, 13], cannot be applied in SMF Sagnac interferometric setup. However, the SMF birefringence model based on the Kapron equivalence well describes SMF Sagnac.
authors.affiliation: Department of Physics, Stockholm University, S-10961 Stockholm, Sweden. janbog@physto.se
authors.forename: Jan
authors.initials: J
authors.lastname: Bogdanski
authors.forename: Johan
authors.initials: J
authors.lastname: Ahrens
authors.forename: Mohamed
authors.initials: M
authors.lastname: Bourennane