| 摘要 |
<p>The invention allows the refractive - index profile to be obtained by phase - difference measurements. A Zeeman- effect laser (1) generates a light beam of plane waves comprising two radiations with slightly different frequencies. The beam is split into the component radiations (2d, 2e); the beats between the first radiation, which is made to follow a path outside the fibre or preform (6), and the second radiation, which is made to follow a path crossing the fibre or preform (6), are generated by a photodetector; the phase differences between said beats and a reference beat are measured, and the refractive - index profile is obtained from the phase difference values by suitable computing means.</p> |
