QKD TRANSMITTER AND TRANSMISSION METHOD

摘要

In order to facilitate alignment of a QKD transmitter (12) and QKD receiver (22), the transmitter (12) is provided with a retro-reflector (53) for returning to the receiver (22) a photon beam (51 F) originating at the latter. The transmitter (12) is arranged to polarization modulate the retro-reflected beam (51R). The transmitter (12) is provided both with an intensity detector (57) for generating an indication of retro-reflected photon intensity, and an intensity-dependent controller (58) for controlling the QKD transmitter (12) in dependence on the detected photon intensity. In one embodiment, this control involves aborting operation of the QKD transmitter (12) upon an unexpectedly high photon intensity being detected; in another embodiment, the intensity indication is used to control the attenuation of the retro-reflected beam so as stabilize the average retro-reflected photon count per unit time.