The invention provides a step index optical fiber which presents cladding having
an index lower than the index of silica and a core with an index higher than the
index of silica. The fiber is obtained by drawing a preform made by chemical vapor
deposition using a deposition tube of index lower than the index of silica. Inner
cladding of index substantially equal to the index of the deposition tube, and
then a core of index higher than the index of the inner cladding are deposited
in succession therein. The invention makes it possible to obtain a fiber having
a large effective area, reduced attenuation, and suitable for being fabricated
at low cost by chemical vapor deposition.
