An optical network is implemented by {TAIL ~ coupling} of {HEAD ~ node switches} to a single waveguide 
An optical network is implemented by { TAIL ~ coupling } of { HEAD ~ node switches } to a single waveguide
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH