Efficient quantum key distribution with stable and expansible differential phase shift schemes

The stable differential phase shift-quantum key distribution (DPS-QKD) schemes were proposed by using Faraday mirrors to autocompensate for the phase drifts and polarization-mode dispersions in long-distance fibers. It was shown that a Faraday mirror composed of a high-reflection mirror and Faraday rotator, which gives rise to a total reflection and a rotation of the input photon polrization by π/2. The number of the interfering pulses was increased by using parallel and serial Mach-Zahnder (MZ) interferometers with multifeedback servo-systems to equalize the pulse energies, in long-distance fibers. By adding more parallel MZ interferometers, this scheme can be simply expanded to possess higher efficiencies.