Interesting Observation on the Performance of Dual Concentric Core Fiber Raman Amplifier due to Change in Core Gap Radius in an Extended Version

We change the core gap radius, the distance between two concentric cores of a single mode Fiber Raman Amplifier (FRA), having a step profile. Based on well known scalar wave equation and its analysis, we study crucially the effects of this variation on the performance characteristics of FRA for the first time. For practically important frequency shift band of 20 cm to 700 cm , our interesting observation is that values of core gap radii in a certain higher range show better flattening of effective Raman gain in comparison to those in lower range with single pump; side by side, larger negative coefficient of dispersion is achieved in the operating range of wavelength with increase of core gap radius. These promising criteria should attract the attention of system designers engaged in fabrication of FRA.