The schematic of the proposed refractive index sensor set-up is
shown in Fig. 1a. It uses a dual-core fiber having refractive-index
profile shown in Fig. 1b. The dual core fiber consists of two cores:
the inner core of width ain and the outer core of width aout, two de-
pressed cladding regions: inner cladding of thickness bin and outer
cladding of thickness bout. Both the cores have refractive index n1
that corresponds to the RI of pure silica. The inner and outer clad-
ding regions of the fiber have refractive index n2 and n3 respec-
tively, which can be attained by using fluorine doping into pure
silica using modified chemical vapor deposition (MCVD) or plasma