| 摘要 |
PURPOSE:To obtain a cloud-to-ground discharge section detecting method by using an optical fiber conserving a plane of polarization, and detecting cloud-to-ground discharge without any power source, monitoring the cloud-to-ground discharge under centralized control. CONSTITUTION:A light wave from an optical transmission line 3 travels in the order of a microlens 5, Faraday circuit element 6, polarization beam splitter 7a, microlens 12, polarization-plane conserving optical fiber 13, microlens 14, polarization beam splitter 7b, microlens 8, and optical transmission line 3 in case of cloud-to-ground discharge. Then, the output of the light wave received at a reception terminal 2 goes to zero owing to a break of the light for the duration of t1 seconds of a lightning current and returns thereafter to a normal value when no cloud-to-ground discharge occurs, but a light wave passed through a by-pass part is also photodetected after a time t2 determined mainly by the length l of the polarization-plane conserving optical fiber 13 of the by-pass part, so it is superposed upon the normal light output. For this purpose, the polarization-plane conserving optical fibers 13 of the by-pass parts of optical systems provided to respective steel towers 41-4n are varied in length to make the time t2 different. Then, the time t1 is measured to decide on which steel tower cloud-to- ground discharge occurs to. |
