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