Patent ID: 6873456

Claim:
An optical amplifying/repeating transmission system including a plurality of transmitters for sending out light signals of wavelengths differing one another and carrying information, an optical multiplexer for wavelength-multiplexing said plurality of light signals, an optical demultiplexer for wavelength-demultiplexing the wavelength-multiplexed signal, a plurality of receivers for receiving said plurality of light signals of mutually different wavelengths, and a plurality of optical repeaters installed between said transmitters and said receivers for amplifying the wavelength-multiplexed signal, and optical fibers doped with laser activating substance interconnecting said transmitters and said optical repeater, said plurality of optical repeaters, and said optical repeater and said receivers, respectively, said optical repeater including a first fixed-gain optical amplifier for amplifying the received wavelength-multiplexed signal with a first predetermined gain, an adjustable optical attenuator for attenuating the wavelength-multiplexed signal outvutted from the first fixed gain optical amplifier with a predetermined attenuation factor, and a second fixed-gain optical amplifier for amplifying the wavelength-multiplexed signal outputted from the adjustable optical attenuator with a second predetermined gain, wherein said optical amplifying/repeating transmission system comprises control signal superposing means operatively connected to one of said plurality of transmitters for superposing a control signal of a specific frequency onto one of said plural light signals, control signal level detecting means connected to the output of said second fixed-gain optical amplifier for extracting a part of output of the specific wavelength of said second fixed-gain optical amplifier to thereby detect a level of an amplified control signal of the specific frequency, and optical repeater gain control means operatively connected to said adjustable optical attenuator for controlling the predetermined attenuation factor of said adjustable optical attenuator so that level of the control signal detected by said control signal level detecting means remains constant.