By modifying Marcuse's Focusing Method, a new method to reconstruct the refractive index profile of optical fibers is proposed. It eliminates the need of the index matching oil by analyzing ray-optically the effect of the cladding-air interface, and thus enabling to compensate the light power distribution on the observation plane to be appropriate for the reconstruction when the index matching oil is absent.
Computer simulation is made to show a good agreement to the order of $10^{-3}$.
Then the reconstruction of the refractive index profile of several actual optical fibers is performed.
For the experiment, to show the possibility of a realtime, automatic measurement, a data fetch system is built.
The System has a Z-80 microprocessor within and links the video camera to the minicomputer NOVA 830.
