Direct method of determination of the equivalent refractive index profile of the multimode optical fiber by measured impulse responses due to scanning output fiber end

This paper demonstrates the possibility of determining the equivalent, in terms of the coincidence of differential mode delay diagram, refractive index profile of the multimode optical fiber by direct method and responses to pulse action, which are measured at the output through single-mode optical fiber. As an example, by using the measured data of the refractive index profile of the sample of multimode optical fiber and based on Gaussian approximation model impulse responses at the output of a short length single mode fiber, which was jointed with multimode fiber, were calculated. Multimode and single mode fibers were jointed with axial misalignment. Responses to impulse action were calculated for several values of axial misalignment of single-mode and multimode fiber. From the responses by the direct method the equivalent refractive index profile was determined. Comparison of the results of calculations of the differential-mode delay diagram for the investigated and the equivalent refractive index profiles showed their good agreement.