A simple method of prediction of fractional modal power guided inside the core, excitation efficiency of the mode by uniform light source and Petermann I and II spot sizes: All for first higher order mode in graded index fibers

Employing the series expression for first order modal field of graded index fiber, we present simple but accurate analytical expressions for the fractional modal power guided inside the core, the excitation efficiency of the mode by uniform light source and Petermann I and II spot sizes as well in case of graded index fiber. This method uses prescription of a linear relation of the ratio of first and zero-order modified Bessel function with reciprocal of cladding decay parameter. The cladding decay parameter estimated from an equation containing a third order determinant and thereafter the first higher order modal field from two simple equations are utilized for formulation and evaluation of the said propagation parameters. Choosing step and parabolic index fibers as examples, we show that our predictions match excellently with the available exact results. The concerned calculations require very little computations. This accurate but simple formalism will benefit the system engineers in practical technical problems.