The structure includes {TAIL ~ a first polymeric sleeve} having a refractive index numerically lower than the refractive index of {HEAD ~ the exterior cylindrical surface} of the glass core 
The structure includes { TAIL ~ a first polymeric sleeve } having a refractive index numerically lower than the refractive index of { HEAD ~ the exterior cylindrical surface } of the glass core
OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH