A new and efficient algorithm is proposed for calculating directly and accurately the refractive index profile of cylindrical waveguides from knowledge of the mode near field. This inverse problem is solved using transmission line techniques. From Maxwell’s equations, we derive an equivalent transmission-line circuit for a cylindrical dielectric waveguide. Based on an analytical method, that computes the error in the reconstructed refractive index due to inaccuracy in the propagation constant ß. The proposed analytical method computes the refractive index error directly without the need for curve fitting or numerical differentiation. Subsequently we work out the exact value of the propagation constant ß. The calculation of the propagation constant ß is vital for the refractive index reconstruction and we show that it implies error minimization in the refractive index synthesis from near field. We demonstrate this algorithm with example reconstructions for step, triangular and parabolic optical fiber refractive index profiles. Furthermore we present example reconstructions for step optical fiber refractive index profiles using higher order modes near electric field. This technique is exact, fast and rapidly convergent.