Self-stimulation signal detection in an optical transmission system

In an optical transmission system with a plurality (N) of optical amplifiers, an apparatus for detecting a fault at each amplifier A.sub.i (i.epsilon.›1,N!) comprising:

• means for modulating a laser of said optical amplifier A.sub.i with a local dither D.sub.ij unique to the transmission system;
• means for measuring an outgoing optical signal to provide a respective transmitted dither D.sub.Oi ;
• means for measuring a respective incoming optical signal for detecting a respective received dither D.sub.li ;
• and
• means for processing said respective received dither D.sub.lj and said respective transmitted dither D.sub.Oi for determining the ratio of the energy in said respective received dither to the energy in said respective transmitted dither to detect if any local dither D.sub.fj is present in said received dither D.sub.lj, where f designates said amplifier A.sub.i and any other amplifier connected in the transmission system downstream from said amplifier A.sub.i.

A method for monitoring the performance of an optical amplifier module of a transmission system comprising the steps of:

• generating at said optical amplifier module a local dither;
• modulating the bias current of an optical source of said optical amplifier module with said local dither;
• measuring an outgoing optical signal of said amplifier module to provide a transmitted dither;
• measuring an incoming optical signal of said amplifier module for detecting a received dither;
• and
• determining the ratio of energy in said received dither to the energy in said transmitted dither for tracking-down said local dither in said incoming optical signal.

A method for monitoring the performance of a WDM optical transmission system comprising the steps of:

• at each optical amplifier A.sub.i (i.epsilon.›1, N!) of said transmission system,
• generating a local dither D.sub.ij (i.epsilon.›1, N!, (.epsilon.›1, M!) of a known energy, for identification of said optical amplifier and of a transmission channel;
• modulating the bias current of a laser of said transmission channel with said local dither to mix an outgoing signal with said local dither;
• measuring an incoming optical signal for detecting a received dither D.sub.li ;
• measuring said outgoing optical signal for detecting a transmitted dither D.sub.Oj ;
• calculating the ratio of energy in said received local dither to the energy in said transmitted dither;
• and
• determining if a local dither D.sub.fj is present in said incoming optical signal, where f designates said amplifier A.sub.i and any amplifier connected in said transmission system downstream from said amplifier A.sub.i.