Abstract: A free space optical communications terminal (100) including an optical arrangement of a quarter-wave plate (105), a Faraday rotator (110), a polarisation splitter (115), a first arm (120) comprising a receiver (126) and a transmitter (128), and a second arm (130) comprising a component (132) configured to utilise a received beam. The optical arrangement apportions a circularly polarised beam between the first and second arm.

Abstract: A pointing unit (100) for use with a free space optical (FSO) communications terminal (105). The pointing unit (100) includes an optical arrangement of a first (101) and second (102) pair of rotatable steering elements (101a, 101b, 102a, 102b). The steering elements are controlled according to a control scheme (10) to steer a beam (107b) towards a target (110).

Abstract: A pointing unit (100) for use with a free space optical (FSO) communications terminal (105) including an optical arrangement (101) of one or more optically transmissive steering elements (101a, 101b). The steering elements (101a, 101b) are arranged in an optical path of an incident beam (107) entering the optical arrangement (100), and the orientation of at least one element (101a, 101b), and the refractive index of at least one element (101a, 101b), are controllable to steer a beam (107b) towards a target (110).

Abstract: A pointing unit (100) for use with a free space optical (FSO) communications terminal (105) that includes an optical arrangement (101) of one or more optically transmissive steering elements (101a, 101b). The steering elements (101a, 101b) are arranged in an optical path of an incident beam (107) entering the optical arrangement (100), and the orientation of at least one element (101a, 101b), and the refractive index of at least one element (101a, 101b), are controllable to steer a beam (107b) towards a target (110).

Abstract: An electro-absorption modulator 100 including a quantum well 102 configured to provide a variable electromagnetic absorption spectrum in response to an applied electric field, wherein the quantum well is a type-II quantum well comprising two material layers, each material layer having a graded material composition, such that the potential in each material layer varies as a function of position.

Abstract: A pointing unit 102 is for use with a free space optical communications terminal 100 including an optical source 104. The pointing unit 102 includes a first portion 106 having a mirrored surface 108, the first portion 106 being orientatable relative to an optical beam 110 produced by the optical source 104 and incident on the mirrored surface 108 in use to direct a reflection 112 of the optical beam 110 from the mirrored surface 108 towards a target 107. The first portion 106 further includes a directional radio frequency antenna 114.

Abstract: A free space optical receiver including a multi-mode transmission medium configured to receive a light beam comprising a plurality of modes, the light beam having been propagated through a free space path. The free space optical receiver also includes a mode separating means configured to separate the plurality of modes for transmission through a corresponding first plurality of transmission media as a corresponding plurality of single-mode light beams, and a combining means configured to combine two or more of the plurality of single-mode beams into a combined beam for transmission through a further transmission medium.

Abstract: A free space optical communications transmitter terminal including an optical source arranged to provide a first beam of light encoding information to be communicated; an optical source arranged to provide photons encoding bits of a key of a Quantum Key Distribution protocol; and an optics arrangement. The first beam and the photons are linearly polarised. The optics arrangement is configured to combine the first beam and the photons into a single, second, beam to be transmitted to a receiver terminal; and transform the linear polarisation of the first beam into one of left and right circular polarisation and transform the linear polarisation of the photons into the other of left and right circular polarisation. A receiver terminal receives the second beam, transforms the circular polarisations into orthogonal linear polarisations, and filters out the linear polarisation of the first beam to allow the photons to pass to a single photon detector.

Abstract: A free space optical communications transmitter terminal including an optical source arranged to provide a first beam of light encoding information to be communicated; an optical source arranged to provide photons encoding bits of a key of a Quantum Key Distribution protocol; and an optics arrangement. The first beam and the photons are linearly polarised. The optics arrangement is configured to combine the first beam and the photons into a single, second, beam to be transmitted to a receiver terminal; and transform the linear polarisation of the first beam into one of left and right circular polarisation and transform the linear polarisation of the photons into the other of left and right circular polarisation. A receiver terminal receives the second beam, transforms the circular polarisations into orthogonal linear polarisations, and filters out the linear polarisation of the first beam to allow the photons to pass to a single photon detector.

Abstract: A free space optical receiver including a multi-mode transmission medium configured to receive a light beam comprising a plurality of modes, the light beam having been propagated through a free space path. The free space optical receiver also includes a mode separating means configured to separate the plurality of modes for transmission through a corresponding first plurality of transmission media as a corresponding plurality of single-mode light beams, and a combining means configured to combine two or more of the plurality of single-mode beams into a combined beam for transmission through a further transmission medium.

Abstract: A pointing unit 102 is for use with a free space optical communications terminal 100 including an optical source 104. The pointing unit 102 includes a first portion 106 having a mirrored surface 108, the first portion 106 being orientatable relative to an optical beam 110 produced by the optical source 104 and incident on the mirrored surface 108 in use to direct a reflection 112 of the optical beam 110 from the mirrored surface 108 towards a target 107. The first portion 106 further includes a directional radio frequency antenna 114.