{HEAD ~ An optical coupler} is affixed to an optics plate and configured to receive {TAIL ~ the third reflected beam} 
configured to receive
{ HEAD ~ An optical coupler } is affixed to an optics plate and configured to receive { TAIL ~ the third reflected beam }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL