OF LIGHTWAVE TECHNOLOGY, VOL.
Equivalent Step-Index-Fiber Method
for Multicladding Fibers
this paper, an equivalent step-index-fiber method
extended to multicladding fibers.
the refractive-index prome for the multicladding preform, the
transmission parameters, especially the cutoff wavelength of the
Sber drawn from the preform can
time, and energy. Comparison between the
theory and results from experimental fibers shows an accuracy
of 5% in predicted cutoff wavelengths.
N general, if the refractive-index profile of a single-mode
step-index fiber preform is measured and plotted, the cutoff
wavelength of the fiber drawn from the preform with standard
pm) can be accurately determined. How-
ever, if the fiber investigated is a graded-core fiber, the same
problem can be settled by using the equivalent stepindex fiber
Consequently, the method is developed to
fibers with cladding index variation such as fibers with raised
inner cladding, fibers with raised inner cladding and bamer
layer, fibers with depressed inner cladding, and so on
In recent years, with the development and application of the
HB special fibers (double-cladding elliptical fiber, panda fiber
and bow-tie fiber), the fiber with multicladding structure have
brought people wide interests. Therefore, if the fiber diameter
or cutoff wavelength can not be calculated in advance, the
fiber-drawing process will not be carried out. So, the only
method one can do for finally deterinining the parameter
mentioned above should be done by “trial and error” between
fiber-drawing and cutoff-wavelength measuring procedures. In
that case, much vigor and financial resources are wasted.
Thus, it is necessary to extend the equivalent step-index
fiber method into multicladding fibers in order to determine
the fiber-drawing diameter or cutoff wavelength in advance
while avoiding extra heavy and complicated
this, the method extended is required to meet the needs of
engineering application, to guarantee enough accuracy and to
calculate conveniently, which is the object of this paper.