G - Physics – 02 – B
Patent
G - Physics
02
B
G02B 6/10 (2006.01)
Patent
CA 2314723
The purely bound electromagnetic modes of propagation supported by symmetric waveguide structures comprised of a thin lossy metal film of finite width embedded in an infinite homogeneous dielectric have been characterized at optical wavelengths. The modes supported are divided into four families depending on the symmetry of their fields. In addition to the four fundamental modes that exist, numerous higher order ones are supported as well. A nomenclature suitable for identifying all modes is discussed. The dispersion of the modes with film thickness and width has been assessed and the effects of varying the background permittivity on the characteristics of the modes determined. The frequency dependency of one of the modes has been investigated. The higher order modes have a cut-off width, below which they are no longer propagated and some of the modes have a cut-off thickness. One of the fundamental modes supported by the structure exhibits very interesting characteristics and is potentially quite useful. It evolves with decreasing film thickness and width towards the TEM wave supported by the background (an evolution similar to that exhibited by the sb mode in symmetric metal film slab waveguides), its losses and phase constant tending asymptotically towards those of the TEM wave. Attenuation values can be well below those of the sb mode supported by the corresponding metal film slab waveguide. Low mode power attenuation in the neighbourhood of 10 to 0.1 dB/cm is achievable at optical communications wavelengths, with even lower values being possible. Carefully selecting the film's thickness and width can make this mode the only long-ranging one supported. In addition, the mode can have a field distribution that renders it excitable using an end-fire approach. The existence of this mode renders the finite-width metal film waveguide attractive for applications requiring short propagation distances and 2-D field confinement in the transverse plane.
Adams Thomas
Berini Pierre Simon Joseph
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