Brazilian Journal of Physics
On-line version ISSN 1678-4448
SILVA, Humberto Filomeno da and NUNES, Frederico Dias. Analysis of cut-off conditions for coaxial fibers. Braz. J. Phys. [online]. 2001, vol.31, n.1, pp. 51-57. ISSN 1678-4448. http://dx.doi.org/10.1590/S0103-97332001000100010.
This paper reports the analysis of modal normalized frequency cut-off of coaxial fibers having four dielectric layers. The cut-off curves are obtained for four different structures and several modes as a function of the several parameters of the fibers (refractive index and layer dimension). The calculation is done using a transcendental equation obtained in this work. The analysis pays a special attention to the fundamental mode HE11 showing that for two structures (W1 and M1) the normalized frequency always is null as is the case of the standard rod fibers. For the other two structures (W2 and two regions), the normalized frequency may not be null, depending on the set of values of the fiber parameters. For this last case a loci diagram is obtained showing the regions where the normalized frequency is equal to zero and different from zero for several sets of fiber parameters. From the transcendental equation, we have an expression to calculate the curve of separation between these two regions.