  Cold plasma of power 13W has been applied on step index plastic optical
fibers. It is used to study the ability for any variations in the optical
parameters that are effective in communication. The effect of plasma on the
optical parameters, such as core index profile, cladding index and the
numerical aperture, has been studied by multiple beam interference fringes. The
interference fringes have been processed using a homemade Matlab written
program to get more accurate measurements. It is found that there is an
increase of 1.5839 in core index, at core-clad interface, with a plasma
exposure time of 150 sec.
