| 摘要 |
PURPOSE:To improve the reliability of signal transmission by performing loop-back, reverse transmission, etc., when a transmission line is troubled by using a two-wire looped optical fiber transmission line and by setting a changeover mode effectively by an optical switch. CONSTITUTION:A center device 211 and terminal devices 212-215 are coupled in a loop shape by optical fiber transmission lines 201 and 202; the devices 212-215 are provided with optical switches 241-244 and optical transmitting circuits 223- 226 and 233-236, and the center device 211 with optical transmitting circuits 221 and 222, and optical receiving circuits 231 and 232. Then, the optical transmitting and receiving circuits 221 and 231 of the center device 211 are connected to devices 212-215 by the transmission line 201, and the others 222 and 232 are connected to the transmission line 202 in the opposite direction to be coupled with the devices 215-212. Optical switches 241-244 of the devices 212-215 are changed over effectively to set modes, thereby performing loop-back, reverse transmission, etc., when the transmission lines 201 and 202 are troubled. |
