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