| 摘要 |
PROBLEM TO BE SOLVED: To obtain a transmitting means for emergency with a convenient method by using FM modulation waves having a carrier being different from the carrier frequency of FM modulation waves used in main system communication and sending emergency communication data. SOLUTION: Each slave station is provided with an FM modulating part 206 and 226 which performs FM modulation of emergency communication data in a carrier frequency F1 being different from the carrier frequency F0 of a base band used for main system communication, and a master station side is provided with a demodulating part 108 which demodulates FM modulation waves received from the slave stations. The slave stations multiplex an emergency communication data signal undergoing FM modulation in the frequency F1 and an FM modulation signal for main system communication which is used for polling access and response, perform optical intensity conversion of them through E/O converting parts 201 and 221 and send them to optical fibers 300 and 310, and the master station side separates them by utilizing the difference of use frequency bands. Thus, emergency data communication can be performed at the point of an optional time when necessity arises independently of polling access and response signals. |
