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