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