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Modal analysis of a step index fiber with a parabolically decreasing refractive index grading in the core along the direction of propagation
Author(s) -
Singh D. B.,
Khastgir P.,
Singh O. N.
Publication year - 1998
Publication title -
microwave and optical technology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 76
eISSN - 1098-2760
pISSN - 0895-2477
DOI - 10.1002/(sici)1098-2760(19981220)19:6<444::aid-mop16>3.0.co;2-x
Subject(s) - modal , superposition principle , refractive index , mathematical analysis , propagation constant , mathematics , physics , azimuth , optics , materials science , polymer chemistry
We make an analytical study of the modal characteristic equation of a step index fiber with a parabolically decreasing refractive index grading in the direction of propagation. We choose the cylindrical polar coordinates (ρ, ϕ, z ) and, assuming that the propagation is along the z ‐direction, we use the boundary conditions under the weak guidance approximation to obtain the modal characteristic equation. The propagation constant β depends on the z ‐coordinate, and a typical numerical computation for the azimuthal modal index ν=1 shows local modes with an oscillatory dependence of β with z . The oscillatory behavior of β is expected to be due to a superposition of the forward wave with partially reflected backward waves. © 1998 John Wiley & Sons, Inc. Microwave Opt Technol Lett 19: 444–448, 1998.