{HEAD ~ A time delay unit} is coupled to {TAIL ~ the coupler interface point} for receiving the optical signal, directing it along a path, and reflecting the signal back to the coupler interface point 
is coupled to
{ HEAD ~ A time delay unit } is coupled to { TAIL ~ the coupler interface point } for receiving the optical signal , directing it along a path , and reflecting the signal back to the coupler interface point
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH