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