An optically amplified wavelength division multiplexing network has the
functionality to add/drop channels at the optical add/drop multiplexing
(OADM) nodes. The OADM node includes a receiver amplifier, an OADM
module, and a transmitter amplifier. Once the OADM node detects a loss of
signal (LOS) due to a fiber cut or network element failure upstream, the
receiver amplifier is kept in operation as a noise source. The output of
the receiver amplifier is immediately raised by increasing pump power to
compensate for the LOS. The noise power received at the transmitter
amplifier from the receiver amplifier is substantially equal to the
signal power expected before LOS. The transient effect of downstream
optical amplifiers is therefore completely suppressed and the
inter-channel stimulated Raman scattering (SRS) induced spectrum tilt
does not change. After the noise power is raised, the receiver amplifier
may be shut down at a speed much slower than the speed of downstream
amplifier control circuitry.