dear damain,
if its possible means, how we can define for example i add 3 regions and 1 cladding region having n1 ,n2 ,n3, and n4 respectively,in which, if core is silica with germanium doped having value 1.46(approx), then n1=n2=n3=1.46, and cladding have n2<n1 term , is this correct , or any other property we need to consider for design like 3 core fiber