Abstract: A direction sensor (200) includes sensor cells (215) that respectively correspond to different directions. Each of the sensor cells (215) includes a light sensor (130, 140) and a grating (120) that couples incident light into the light sensor (130, 140) when the incident light has a specific wavelength and is incident on the grating (120) along the direction corresponding to the sensor cell (215).

Abstract: A handheld device includes: a transmitter or receiver of a signal beam for quantum key distribution; and a source of alignment beams that diverge from each other in a pattern that matches sensors on a station containing a receiver or transmitter for the quantum key distribution. The alignment beams from the handheld device are of sufficient intensity to produce on the station visible spots that facilitate manual alignment of the handheld device. The station can measure a position and a direction of respective alignment beams and dynamically steer the signal beam according to the measurements.

Abstract: A direction sensor (200) includes sensor cells (215) that respectively correspond to different directions. Each of the sensor cells (215) includes a light sensor (130, 140) and a grating (120) that couples incident light into the light sensor (130, 140) when the incident light has a specific wavelength and is incident on the grating (120) along the direction corresponding to the sensor cell (215).

Abstract: In order to facilitate alignment of a QKD transmitter and QKD receiver, the transmitter is provided with a retro-reflector for returning to the receiver a photon beam originating at the latter. The transmitter is arranged to polarization modulate the retro-reflected beam. The transmitter is provided both with an intensity detector for generating an indication of retro-reflected photon intensity, and an intensity-dependent controller for controlling the QKD transmitter in dependence on the detected photon intensity. In one embodiment, this control involves aborting operation of the QKD transmitter 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.

Abstract: A handheld device (310) includes: a transmitter or receiver (410) of a signal beam (340) for quantum key distribution; and a source (412, 414) of alignment beams (312, 314, 316, 318) that diverge from each other in a pattern that matches sensors (322, 324, 326, 328) on a station (320) containing a receiver or transmitter (430) for the quantum key distribution. The alignment beams from the handheld device (310) are of sufficient intensity to produce on the station visible spots that facilitate manual alignment of the handheld device (310). The station (320) can measure a position and a direction of respective alignment beams and dynamically steer the signal beam (340) according to the measurements.

Abstract: In order to facilitate alignment of a QKD transmitter and QKD receiver, the transmitter is provided with a retro-reflector for returning to the receiver a photon beam originating at the latter. The transmitter is arranged to polarization modulate the retro-reflected beam. The transmitter is provided both with an intensity detector for generating an indication of retro-reflected photon intensity, and an intensity-dependent controller for controlling the QKD transmitter in dependence on the detected photon intensity. In one embodiment, this control involves aborting operation of the QKD transmitter 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.

Abstract: QKD receiving apparatus is provided with an alignment-correction system for correcting misalignment of a quantum signal received at an optical port of the apparatus relative to a quantum-signal detector of the receiving apparatus. The alignment-correction system comprises a misalignment measuring subsystem for making multiple different misalignment measures, and a misalignment compensation subsystem for adjusting the relative alignment of the quantum signal and quantum-signal detector in dependence on the misalignment measures made. The misalignment measuring subsystem comprises an alignment-beam source, an alignment-beam detector arrangement, and optical components for guiding an alignment beam from the alignment-beam source to the optical port, and for guiding the alignment beam, after external retro-reflection at a cooperating QKD transmitting apparatus from the optical port to the alignment-beam detector arrangement.

Abstract: A quantum key distribution (QKD) system is provided that makes use of a quantum signal of polarized photons and comprises a QKD device and complimentary QKD apparatus. The QKD device has a QKD subsystem comprising one of a QKD transmitter and receiver for inter-working with a complimentary QKD receiver or transmitter of said apparatus. The device also has an alignment subsystem arranged to wirelessly interact with the QKD apparatus to enable generation of user feedback and/or adjustment signals for use in aligning the QKD transmitter and receiver such that the QKD transmitter is pointing at the QKD receiver and the polarization axes of the QKD transmitter and receiver are aligned.