Electromagnetic resonances of a multilayer metal-dielectric stack

The electromagnetic resonances of multilayer metal–dielectric stacks are investigated. These structures support periodic bandpass regions, whose band edges may be predicted by considering the character of the fields inside the different layers. It is shown that the response of the structure is largely independent of its overall length, and that only the geometry of the unit cell is important. In the metal layers, the fields may have either a cosh or a sinh distribution function and match to standing waves inside the adjacent dielectric cavities at the metal–dielectric interface. It is shown that the different boundary conditions, imposed by the evanescent fields, result in the dielectric layers having a different effective length for the two modes. The sinh fields result in an effective length being very close to that of the physical length, and adjacent cavities oscillating out of phase, while the cosh fields may result in a significantly larger effective dielectric length and adjacent cavities oscillating in phase. A bandpass region is opened, with its high frequency edge always being near the dielectric Fabry–Perot limit, while the low frequency band edge is significantly redshifted.