| 摘要 |
Particularly in the case of optical heterodyne receivers, there is the problem that before the superposition of the received light and the light generated in a local laser it is necessary to bring the polarisations of the two into agreement. This requires an arrangement for controlling polarisation which compensates temporal variations in the polarisation without the occurrence of variations in optical intensity, and thus without signal failures, during the control process. For this purpose, five elements are provided which have adjustable birefringence and are realised, for example, by relays whose movable armatures exert a more or less intense pressure on an optical fibre having a circular cross-section. <IMAGE>
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