A proportionate signal may be split off from each channel and taken to {HEAD ~ a photodetector} to enable {TAIL ~ the gain} of the associated SOAs to be adjusted to equalize or otherwise balance the signal levels 
to enable
A proportionate signal may be split off from each channel and taken to { HEAD ~ a photodetector } to enable { TAIL ~ the gain } of the associated SOAs to be adjusted to equalize or otherwise balance the signal levels
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH