{TAIL ~ A coupler} includes input, output and {HEAD ~ interface points} for routing the optical signal 
{ TAIL ~ A coupler } includes input , output and { HEAD ~ interface points } for routing the optical signal
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH