We investigate generalized asymmetric left-handed (LH) slab waveguides that constitute an extension to the symmetric structure initially proposed by Pendry. By utilizing the asymmetry it has been shown that they have the potential for increased image resolution. This is due to the amplification of the formed surface waves (SWs) that is able to compensate material losses. Some preliminary studies in this direction have been reported in the literature but, to the best of our knowledge, there is no complete study of all possible S W eigenmodes supported by such LH waveguides. A rigorous theoretical investigation is presented herein that offers clear mathematical explanation and detailed physical insight into the formation of surface polaritons (SPs) in these heterostructures and provides the conditions for their existence. It is found that a rich variety of SP modes can exist (30 in total) that depend critically on the combination of the different refractive indices, constitutive parameters ε(ω) and μ(ω) the sample geometry. For each case we provide the geometric dispersion diagram and the profile of the corresponding stable field configuration from which the various characteristics of the mode (enhancement, phase reversal) are apparent, An interesting result of the above analysis is that, for certain choices of the material parameters, the coupling between the interfaces allows the existence of new 'supermodes' when no stable solutions exist at the isolated interfaces of the slab alone. Finally, the modes that give rise to negative group velocity are identified and key features of the dispersion diagrams are discussed, most of which are unique to the structures studied herein and have not been previously recovered with symmetrical studies.

A robust methodology is presented for the accurate modal analysis of three-dimensional dielectric waveguides with the finite-difference time-domain (FDTD) method. We investigate the propagation of well-defined vector modes along strongly guiding rectangular waveguides. Eigensolutions of the vectorial wave equation are utilized in the simulations to accurately launch the fundamental and higher order eigenmodes. Results for their FDTD-computed propagation constant are found to be in excellent agreement with existing mode-solving techniques. Improved accuracy or significant computational savings are achieved when the nonstandard FDTD concepts are incorporated in the context of the present analysis. © 2005 IEEE.