Investigation of the Cladding Modes of Metal-Coated Fibers

In order to know well the characteristics of the metal-coated long-period fiber gratings, it is necessary to investigate the cladding modes of the metal-coated fibers. The eigenvalue equation for cladding modes of metal-coated fiber was obtained and the method of solving the complex equation was discussed. The influences of different kinds of metals on the propagation constants and losses of cladding modes were investigated. For the metals with low resistivity such as gold, silver and copper, the imaginary part of the complex dielectric constants has a slight influence on the propagation constants and losses, especially on the HE cladding modes. For other metals such as aluminum and nickel, the influences are comparatively greater. The losses are related to the wavelength, mode orders and the kinds of the metals. The loss is greater when the imaginary part of the complex dielectric constant is bigger and the mode order is higher.