金属包层光纤的包层模式

为了研究金属包层长周期光纤光栅(LPFGs)的特性，需要研究金属包层光纤的包层模．根据金属包层光纤的特点，给出了金属包层光纤包层模的本征方程，讨论了这一复本征方程的求解方法，并研究了不同金属包层对包层模传播常数和损耗的影响．结果表明，对低电阻率的金属如金、银等，介电常数的虚部对低阶模的传播常数影响较小，尤其是对HE模影响更小，对铝、镍等影响稍大．金属包层对包层模的损耗，与光波长、包层模序和金属类型有关．介电常数虚部大(绝对值)，而且包层模序也大时，损耗较大．

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.