| 摘要 |
An optical fiber 2 of radius f and having a curved portion of radius of curvature R is disposed between a light source (3) and a photodetector (4) and is subjected at a number of points, equispaced along its axis, to a transverse pressure to attenuate the transmitted radiation. These pressure points are formed by turns of a substantially incompressible helix 5 of pitch p which is wound around the fiber with a separation g and which may be constituted by an internal or external rib of a surrounding flexible sheath 6. To minimise losses in the fibre, the radius of curvature R should not be less than <IMAGE> The optimum spacing of the pressure points is a function of the radius of the fibre core and of the refractive indices of its core and its envelope. The pressure may be applied by a piezoelectrical transducer and may be modulated by an electrical signal to be picked up by the photodetector. <IMAGE> |
