for a cross section of an optical fibre it is the region between the circle concentric with the cladding centre circumscribed about the cladding and the largest circle, concentric with the first one, that fits into the cladding Found on http://www.electropedia.org/iev/iev.nsf/display?openform&ievref=731-02-38
for a cross section of an optical fibre it is the region between the circle concentric with the cladding centre circumscribed about the cladding and the largest circle, concentric with the first one, that fits into the cladding