We present a fiber-based Quantum Cryptography (QC) system in which data is acquired by utilizing a new Time-Correlated Single Photon Counting (TCSPC) instrument. This device captures single photon events on two synchronized channels with picosecond resolution over virtually unlimited time spans and with extremely short dead-times (<95ns). The QC system operates at a wavelength of 1550nm and employs an interferometric approach in which quantum-level information is encoded in the relative phase shift between pairs of faint optical pulses generated by a strongly attenuated semiconductor laser. The QC channel and three additional conventional data channels are carried over a single transmission fiber using a coarse wavelength division-multiplexing (CWDM) scheme with a 20nm channel separation. We assess the impact of the various sources of errors in the system, such as imperfect interference visibility, detector dark counts and Raman scattering in the transmission fiber. Secure key distributions with mean photon numbers of 0.1 and 0.2 per pulse pair were demonstrated for transmission distances up to 25km and 38km respectively.

Date Published: 3 November 2006
PDF: 9 pages
Proc. SPIE 6372, Advanced Photon Counting Techniques, 637210 (3 November 2006); doi: 10.1117/12.686152

Published in SPIE Proceedings Vol. 6372:
Advanced Photon Counting Techniques
Wolfgang Becker, Editor(s)