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