Optical amplifying repeater with monitor and control function

Abstract

An optical amplifying repeater having a monitor and control function maintaining the index of modulation of a response signal relative to the main signal to be constant. The optical amplifying repeater includes a monitor and control portion for outputting the response signal in response to a supervisory control signal, a pair of erbium-doped fibers for optically amplifying an input optical signal by stimulating action of a pumping laser diode and outputting the amplified optical signal, a pair of optical output stabilization portions for outputting a DC current ID.sub.C driving the pumping laser diode such that the optical output level of the erbium-doped fiber becomes constant, and a pair of amplification portions supplied with the response signal output from the monitor and control portion for outputting an AC current I.sub.AC driving the pumping laser diode. The optical amplifying repeater further includes a pair of gain control portions for outputting a control signal V.sub.CONT controlling the gain of each of the amplification portions such that the DC current I.sub.DC and the AC current I.sub.AC Satisfy the relationship I.sub.AC =a.times.I.sub.DC +b (a, b: constants). With such arrangement, the main signal and the response signal are amplified at the same rate and, hence, the index of modulation of the response signal component relative to the main signal can be kept virtually constant even when there is produced a change in the input signal level to the optical amplifying repeater, the temperature of the same, and the like.