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