Fiber refractive index profile determination from the measured near field intensity

The main geometric parameters of optical fibers, bandwidth, mode field diameter, condition of single mode propagation, inter-waveguide coupling coefficient can be, related with their refractive index profile. In determination these parameters it's necessary to have the precision method for refractive index profile measurement. The optic fiber small geometric sizes and low difference of refractive index is caused by this problem realization difficulty.