| 摘要 |
1474370 Photo-electric detectors PLESSEY CO Ltd 17 May 1974 [22 May 1973] 24268/73 Heading G1A An arrangement for detecting various constituent modes of a transmitted light beam comprises: a central light detector and at least one annular light detector disposed coaxially with an axis intersecting the central detector; and electrical delay means associated with at least one of the light detectors. Portions of a light beam transmitted by an optical fibre 6, Fig. 1, undergo delays dependent upon the number of internal reflections within the fibre and characterized by the angles of emergence from the end 5. Thus the fast, direct mode emerges axially while the slow, indirect modes emerge at angles which increase with the delay. An array 1 comprising a central circular photo-cell 2 surrounded by coplanar concentric annular cells 3, 4 &c., detects the various modes. Distortion due to the delays may be minimized by compensating electrical delays 10, 11 between the photo-cell outputs. The arrangement may also be applied to e.g. a Fresnel lens by positioning it between the lens and its focal plane. |
