To improve a power balance of an optical add/drop multiplexer, an add amplifier
is optically coupled to an add path of an optical add/drop module. A through loss
associated with a signal passing through the add/drop module, a drop loss associated
with a signal travelling a drop path of the add/drop module, and an add loss associated
with a signal travelling an add path of the add/drop module are known or otherwise
calibrated values. A dropped channel power measurement is used in conjunction with
the through loss, add loss, drop loss, number of dropped channels and number of
added channels to determine an add path amplification value. The gain of the add
amplifier is controlled according to add path amplification value so that the power
level of the added channel(s) substantially matches the power level of the WDM
signal output from the add/drop multiplexer. Furthermore, the gain profile of the
add amplifier preferably matches a gain profile of a signal input to the add/drop
module. In this way, the power level and gain profile of the added channel(s) can
be controlled to match the power level and gain profile of the signal passing through
the add/drop module.
