Fourier decomposition method for mode characterization in metal-clad fiber with complex index profile

Fourier decomposition method in the cylindrical coordinates is used to characterize LP0x, mode effective indexes in a step fiber with complex index profile under material dispersion, from the guided modes to the radiation mode. The method help sorting the modes in function of physical properties associated to a particular mode type LP0x, etc. The main findings of this work are: (1) The imaginary part of effective indexes of the guided modes and lower order cladding modes is several orders of magnitude smaller than the real part. (2) Both real and imaginary parts of metal-clad refractive indexes around the fiber have a strong influence on the real part of LP0x, mode effective indexes. (3) In some regions of the wavelength, the fundamental mode LP01 in an aluminum-clad fiber disappears, but the higher order cladding modes still exist and propagate. (C) 2004 Elsevier B.V. All rights reserved.