Depending
on the line rate transmitted through the fiber one or more of these
control elements are present in the amplifier. A 40Gbps amplifier typically
provides concurrent control of all four of these elements. A 10Gbps
amplifier may only need to provide total pump power, tilt control and
perform some sort of AGC.
Output
optical power control is a direct function, within limits, of the amount
of current driven through the pump lasers. The driver circuit must provide
a clamping function to prevent overdriving the laser which will result
in damage to these expensive devices.
Operation of the driver circuit begins with the EDFA processor determining
a desired drive level. This information passes to the control circuit
either in digital or analog form. The control circuit converts the drive
level into a current and uses a feedback loop to stabilize the current.
