| 摘要 |
An optical fibre cable has an optical fibre with a core and cladding embraced by a cover of polymer material. In a temperature detection range (T1-T2) the polymer material has a negative coefficient of heat expansion ( alpha 0), the absolute value of which is larger than the coefficient of heat expansion ( alpha ) in neighbouring temperature ranges (T0-T1, T2-T3). When subjected to an increase in temperature (T), the cover will contract and cause microbending of the optical fibre. Light travelling in the fibre is attenuated and reflected, and the reflected light will be attenuated further in a heated domain of the fibre. The size of the domain and its position along the fibre can be determined by measuring the running time of the light. The polymer cover has a coefficient of heat expansion such as to enable several heated domains to be detected. The fibre attenuates the light in a range of 0.01-0.1 dB/m in the heated state of the fibre. |
