Patent ID: 7720228

Claim:
A method of calibrating a quantum key distribution (QKD) system having a first QKD station (Bob) with a first modulator (MB) and a second QKD station (Alice) with a second modulator (MA), comprising: a) operating the QKD system with a first modulator basis voltage value V B ( 1 ) for the first modulator and varying a basis voltage V A for the second modulator to establish a first basis voltage value V A ( 1 ) for the second modulator that yields constructive interference of detected quantum pulses; b) operating the QKD system with the first modulator basis voltage value V B ( 1 ) for the first modulator while varying the basis voltage V A for the second modulator to establish a second basis voltage value V A ( 2 ) for the second modulator that yields destructive interference of detected quantum pulses; c) operating the QKD system with a second modulator basis voltage value V B ( 2 ) for the first modulator and varying the basis voltage V A for the second modulator to establish a third basis voltage value V A ( 3 ) for the second modulator that yields constructive interference of detected quantum pulses; and d) operating the QKD system with the second modulator basis voltage value V B ( 2 ) for the first modulator while varying the basis voltage V A for the second modulator to establish a fourth basis voltage value V A ( 4 ) for the second modulator that yields destructive interference of detected quantum pulses.