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