| 摘要 |
PURPOSE:To prevent an illegal reception by providing an optical amplifier which amplifies an optical signal in the case the exciting light of specific wavelength is supplied, and functions as an attenuator in the case the exciting light is not supplied on an optical transmission line between an optical signal source and a subscriber's terminal. CONSTITUTION:On the way of an optical transmission line 7, optical amplifiers 12-1-12-3 which amplify and output an optical signal supplied from an optical signal source 6 in the case the exciting light of specific wavelength is supplied, and function as attenuators in the case of the exciting light of specific wavelength is not supplied are inserted, and also, on each subscriber's terminal 19-1-19-3, exciting light sending-out means 13-1-13-3, 14-1-14-3 for sending out the exciting light of specific wavelength to the optical transmission line 7 in accordance with a receiving request are provided. Accordingly, the optical signal can be distributed to many subscribers, and also, unless the exciting light is sent out to the signal source 6 from the subscriber's terminals 19-1-19-3, the optical signal is not transmitted. Thus, the illegal reception can be prevented. |
