variations in channel loading, including those due to power transient events (see the
section on Transient Control below). Constant power can be used if the unplanned
changes in channel powers are within the system power tolerance or if other
techniques are used to minimize the impact of gain saturation, such as using saturat-
ing lasers [56] or gain clamping [57]. Even with constant gain control, however, an
amplifier will exhibit a constant power response until the action of the control system
can adapt to a rapid input power change.
In ROADM systems, the amplifier control is complicated by the wavelength
dependence of the channel loading. Here we focus on EDFA control, which is
predominantly used in today’s optical communication systems. With