Experimental Study on Gaussian-Modulated Coherent States Quantum Key Distribution Over Standard Telecom Fiber

In this paper, the authors present a fully fiber-based one-way Quantum Key Distribution (QKD) system implementing the Gaussian-Modulated Coherent States (GMCS) protocol. The system employs a double Mach-Zehnder Interferometer (MZI) configuration in which the weak quantum signal and the strong Local Oscillator (LO) go through the same fiber between Alice and Bob, and are separated into two paths inside Bobs terminal. To suppress the LO leakage into the signal path, which is an important contribution to the excess noise, they implemented a novel scheme combining polarization and frequency multiplexing, achieving an extinction ratio of 70dB.