Integrating a QPSK Quantum Key Distribution Link

Abstract

We present the integration of the optical and electronic subsystems of a BB84-QKD fiber link. A high speed FPGA MODEM generates the random QPSK sequences for a fiber-optic delayed self-homodyne scheme using APD detectors. IntroductionIn fiber-optic quantum key distribution (QKD) at telecommunications wavelengths, QPSK encoding of Alice's Qbits constitutes an attractive modulation format [1, 2] since it could be detected in differential interferometric schemes that need only one fiber, thus relaxing the requirements in phase and polarization stability and providing a more reliable long distance QKD link, and at the same time simplifies the system's integration and control.

Auto-compensating Quantum Cryptosystem using Homodyne Detection

“…As shown in Fig.1(a), QPSK encoding is implemented in our system as 4 data representations of the 2 different symbols in 2 conjugated bases [4,5]. Alice (Φ A : π/4 and -3π/4 in Base A 1 ; -π/4 and 3π/4 in Base A 2 ) and Bob (Φ B : π/4 in Base B 1 , -π/4 in Base B 2 ) establish a QKD link of 11km length in a standard telecom single mode fiber.…”