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