QKD system with common-mode dithering

Abstract

A QKD system (10) having two QKD stations (Alice and Bob) optically coupled by an optical fiber link (FL), wherein Bob includes a variable timing delay arranged between Bob's controller (CB) and modulator (MB) or detector unit (40). A set-up and calibration procedure is performed wherein delay DL2 is adjusted until the timings for the modulator and detector unit (TSB and TS42, respectively) are established. Delay DL2 is then fixed so that the detector unit and modulator operate in a common timing mode that is not changed if the synchronization signal is changed. The timing TSS of the synchronization (sync) signals (SS) sent from Alice to Bob is adjusted to arrive at optimum system performance. Once the QKD system is in operation, because the sync signal can drift, the sync signal timing TSS is dithered maintain optimum QKD system performance. Since the modulator and detector unit timing is tied together, dithering the sync signal also dithers the modulator and detector unit together in a “common mode,” rather than varying the timing of each of these elements separately.

Dependencies are inferred from the claim text.