Laser autocalibration for qkd systems

A method of exchanging a key in a quantum key distribution (QKD) system having a laser and an SPD unit both operably coupled to a controller, comprising:

• exchanging photon signals between encoding stations in the QKD system, where the photon signals are generated by the laser;
• performing a first laser gate scan by sending laser gating signals from the controller to the laser over a range R1 of laser gating signal arrival times T;
• establishing from the first laser gate scan a first optimal arrival time TMAX for the laser gating signal corresponding to a first maximum number of photon counts NMAX from the SPD unit;
• terminating the first laser gate scan when the first TMAX is established;
• and
• performing a first laser gate dither by altering the arrival time T over a range of arrival times R2 about the first TMAX to maintain either the first maximum number of photon counts NMAX or a different maximum number of photon counts N′MAX over the range R2.

A computer-readable medium having instructions embodied therein to direct a computer in a quantum key distribution (QKD) system adapted to control the operation of the QKD system to perform the following method autocalibrating of a QKD system, the method comprising:

• sending photon signals between encoding stations in the QKD system, wherein the photon signals are generated by a laser in response to laser gating signals having associated arrival times T at the laser;
• performing a first laser gate scan by varying the arrival time T over a first range of arrival times R1 to establish a first optimal arrival time TMAX corresponding to a first maximum number of photon counts NMAX from a detector unit in one of the QKD stations;
• terminating the first laser gate scan when the first TMAX is established;
• and
• performing a first laser gate dither by altering the arrival time T over a second range of arrival times R2<R1 about the first TMAX to maintain either a) the first maximum number of photon counts NMAX, or b) a different maximum number of photon counts N′MAX over the second range R2.

A method of autocalibrating a quantum key distribution (QKD) system having a laser, a single-photon detector (SPD) unit and controller operably coupled to the laser and the SPD unit, comprising:

• generating photon signals with the laser by activating the laser with laser gating signals sent from the controller, the laser gating signals having an associated laser gating signal timing T;
• sending the photon signals between encoding stations in the QKD system;
• performing a first laser gate scan to determine an optimum arrival time TMAX for the laser gating signals to arrive at the laser by obtaining a first optimum number of photon counts at the SPD unit;
• terminating the first laser gate scan when TMAX is established;
• and
• periodically dithering the laser gating signal arrival time about TMAX to maintain either the first optimum number of photon counts or a second optimum number of photon counts.

A method of autocalibrating a quantum key distribution (QKD) system having two encoding stations, and a laser coupled to a controller in one of the encoding stations, the method comprising:

• performing a laser gate scan to establish an optimum arrival time of a laser gating signal at the laser that corresponds to first optimum number of photon counts from a single-photon detector (SPD) unit in one of the encoding stations when exchanging photon signals between the encoding stations;
• terminating the laser gate scan;
• and
• performing a laser gate dither process by varying the arrival time of the laser gating signal around the optimal arrival time in order to provide minor adjustments to the arrival time that lead to the SPD unit yielding either the first optimum number of photon counts, or a second optimum number of photon counts.