1 Feasibility of two-way polarization encoded quantum communication in an optical fiber populated with telecom traffic G. B. Xavier, 1,* G. Vilela de Faria, 1 T. Ferreira da Silva, 1,2 , G. P. Temporão 1 and J. P. von der Weid 1 1 Center for Telecommunication Studies, Pontifical Catholic University of Rio de Janeiro, R. Marquês de São Vicente 225 – Rio de Janeiro - Brazil 2 National Institute of Metrology, Standardization and Industrial Quality, Av. Nossa Sra. das Graças, 50 - Duque de Caxias - Brazil *Corresponding author: guix@opto.cetuc.puc-rio.br We experimentally show a two-way transmission of polarization encoded pseudo-single photons between two remote parties separated by a single 23 km optical fiber spool. Two optical classical channels are wavelength multiplexed in the same fiber and used as feedback to an active polarization drift compensation scheme. One of the classical channels contains a 10 Gb/s data stream simulating real telecom traffic. The feasibility of quantum communication is demonstrated in the fiber’s two opposite directions of propagation over 6 hours of continuous operation, as well as a classical error rate in the data channel better than 1.0 x 10 -9 . The results are extended to show the estimated maximum transmission distance for the quantum signals based on the noise generated through Raman spontaneous scattering by up to 16 classical channels present in the fiber. OCIS codes: 060.2330, 060.5565.