In this paper, we approximate the fundamental mode in single mode step and graded index optical fiber by a single parameter Lorentzian function within scalar variational framework. We show that it works in a low V region, a region important for evanescent wave coupling, more accurately in terms of propagation constant in comparison to single parameter Gaussian for linear and nonlinear fibers. Furthermore, we show that the low V variations of normalized propagation constant b(V ), group delay d(V ), and waveguide dispersion g(V ) with V based on Lorentzian approximation match more accurately with the results for linear optical fiber in comparison to Gaussian approximation in the low V region. C 2011 Society of Photo-Optical Instrumentation Engineers (SPIE).
We vary the refractive index of second core of dual concentric cores of a single mode Fiber Raman Amplifier (FRA), having a step profile. Based on well known scalar 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 -1 to 700 cm -1 , our interesting observation is that values of refractive indices 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 refractive indices keeping the outer core radius, core gap radius and refractive index of the first core fixed. These promising criteria should attract the attention of system designers engaged in fabrication of FRA.
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