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Process and apparatus for controlling the alignment of a transmit laser beam of a coherent detection optical communications transmitter/receiver terminal
| Details |
Inventors: Grant, Michael A.; Robson, David;
Assignee: British Aerospace Public Limited Company (London, GB2)
Primary Examiner: Rosenberger; Richard A.
Assistant Examiner:
Attorney, Agent or Firm: Cushman, Darby & Cushman
A process and apparatus are provided for controlling the alignment of a transmit laser beam (1a) of a first coherent detection optical communications transmitter/receiver terminal with a further coherent detection optical communications transmitter/receiver terminal relative to a receive laser beam (8). The first terminal incorporates a transmit laser beam generator (1) operable to form and pass the transmit beam (1a) through a point ahead mechanism (2) to a telescope assembly (6) operable to receive the receive laser beam (8). The apparatus includes a detector/receiver unit, means (3) for taking a component (1b) of the transmit laser beam (1a) from the transmit laser beam (1a) for receiving the receive laser beam (8) from the telescope assembly (6) and for feeding the transmit laser beam (8) to the detector/receiver unit (10), and means (16, 17, 18, 19, 20 ,21, 22, 23, 24) for detecting, separating and processing the received transmit laser beam component (1b) and received receive beam (8) at the detector/receiver unit (10) to provide signals indicative of the actual alignment of the transmit and receive beams (1a, 8), means (25) for comparing the actual alignment signals with desired alignment values to generate difference signals and means for operating the point ahead mechanism (2) in dependence upon the generated difference signals variably to control the alignment of the transmit beam (1a) relative to the receive beam (8). |
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DETAILED DESCRIPTION What is claimed is: 1.
A process for controlling the alignment of a transmit laser beam of a coherent detection optical communications transmitter/receiver terminal with a further coherent detection optical communications transmitter/receiver terminal relative to a receive laser beam received from said further terminal, including the steps of taking a component of the transmit laser beam from the transmit laser beam, which transmit laser beam primary polarisation is orthogonal to the polarisation of the receive laser beam, feeding the transmit laser beam component with the receive laser beam to a detector/receiver unit, detecting, separating and processing the received transmit laser beam component and received receive beam at said unit to provide signals indicative of the actual alignment of the transmit and receive beams, comparing the actual alignment signals with desired alignment values to generate difference signals and using the generated difference signals variably to control the alignment of the transmit beam relative to the receive beam.
2.
A process according to claim 1, in which the component of the transmit laser beam is cross-polarised with respect to the receive laser beam, and in which the transmit laser beam component and the receive laser beam are combined and mixed with a local oscillator laser beam prior to feeding to the detector/receiver unit.
3.
A process according to claim 2, in which the combined and mixed transmit laser beam component, receive laser beam and local oscillator beam are received on an at least four quadrant detector portion of the unit and the resulting quadrant output signals amplified, filtered, and processed to provide a summed communications output signal, transmit beam alignment control signals and receive beam tracking control signals.
4.
A process according to claim 3, in which the transmit beam alignment control signals provided are a sum, and azimuth and elevation difference signals, and in which the azimuth and elevation difference signals are frequency discriminated, with reference to the desired point ahead angle of the transmit beam relative to the receive beam, to provide absolute relative values for variably controlling the alignment of the transmit beam relative to the receive beam
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LCD 
