METHOD FOR DESIGNING OF DISPERSION FLATTENING FIBER FOR WDM OPTICAL TRANSMISSION SYSTEM

The field of present invention relates to an optimal dispersion flattened optical fiber (DFF) carrying the fundamental LPoi mode, which when used in wavelength division multiplexing (WDM) system, the dispersion can be kept confined within ± 1 ps/nm-km over the entire wavelength span ranging from 1290 nm to 1550 nm (260 nm). The R. I. profile of the DFF generated by the generalized R. I. profile is easier to optimize as a result of its dependence on less profile parameters, is also feasible from fabrication point of view. The core of the said fiber (DFF) has four segments with varying R. I. profile comprising of: core segment having positive R. I. ∆1, inner trench segment having negative R. I. ∆2, the ring core having positive R. I. A3, outer trench having negative R. I. ∆4 which are radially adjacent to each other, and then a cladding with a constant index profile satisfying the condition . The cut-off wavelength for LP01 mode in said DFF of the present invention is 2410 nm which is far away from the longer wavelength of operation (1550 nm), therefore the bending losses are negligible. The optimized R. I. profile of the DFF shows that the best dispersion flattened characteristic for profile parameters 'n1' = 1.55, 'ncl' = 1.5297, 'a' (core radius) = 5.3399 nm, 'Z' (no. of average level crossings 'ncl' with in core radius) = 4 and ' x' (profile parameter) = 0.020157 are achieved, when operated over the wide wavelength span of 260 nm and exhibits the chromatic dispersion ranging from -1 ps/nm-km to +1 ps/nm-km (approx.) with very small dispersion slope in particular and effective area > 12 μm2. The designed DFF in particular exhibits following typical values at 1550 nm wavelength: dispersion = -0.98 ps/nm-km, and dispersion slope = -0.02 ps/nm -km.