{HEAD ~ The first optical waveguide} is formed of {TAIL ~ a single mode optical fiber} and outputs a single mode optical signal 
is formed of
{ HEAD ~ The first optical waveguide } is formed of { TAIL ~ a single mode optical fiber } and outputs a single mode optical signal
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH