Methods for establishing modulator timing for a QKD system (100) having QKD stations (Alice, Bob) with respective modulators (MA, MB) are disclosed. The timing method includes exchanging non-quantum signals (P1, P2) between the two QKD stations and performing respective coarse timing adjustments by scanning the modulator timing domain with relatively coarse timing intervals (DeltaT1 C, DeltaT2C,) and wide modulator voltage signal (W1C, W2C). Coarse timings (T1C, T2C) are established by observing a change in detector counts between single-photon detectors (32a, 32b) when modulation occurs in exchanged non-quantum signals. The method also includes performing a fine timing adjustment by scanning the modulator timing domain with respective fine timing intervals (DeltaT1R, AT2R) and respective relatively narrow modulator voltage signals (W1R, W2R), and again observing a change in detector counts for exchanged non-quantum signals. This operation is repeated until desired final modulator timings (T1F, T2F) and desired final activation signal widths (W1F, W2F) are obtained for the two modulators. |