{TAIL ~ A controller} is used for monitoring intensity of {HEAD ~ the beam} of light emerging from the optical switch and for providing a feedback signal to the phase shifters 
{ TAIL ~ A controller } is used for monitoring intensity of { HEAD ~ the beam } of light emerging from the optical switch and for providing a feedback signal to the phase shifters
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH