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