| 摘要 |
The present invention relates to a method of detecting external influence on an optical cable. According to the method, for the purpose of monitoring, coherent radiation is transmitted in at least one single-mode fibre, with a wavelength below the limit wavelength of the fibre, which results in the radiation being propagated in a number of modes. On the receiving side, the monitoring radiation is then divided into two pencils of rays, each comprising the entire interference pattern which is formed during transmission in the fibre. These pencils of rays are then plane-polarized in two different directions, and the amplitude and/or content in terms of frequency of each pencil of rays is detected. From this, a signal is produced, which is a measure of their condition in terms of amplitude and/or frequency. Finally, an alarm function is initiated when the signal exceeds predetermined values with regard to time and/or level. <IMAGE> |
