Three figures of merit, useful as quality measures for 2D surface plasmon waveguides, are discussed and applied to help trade-off mode confinement against attenuation for the symmetric mode propagating along metal stripes. Different stripe geometries are considered, and Au, Ag and Al are compared as the stripe metal over the wavelength range from 200 to 2000 nm. Depending on which figure of merit is used, and on how mode confinement is measured, different preferred designs emerge. For instance, given a mode area, narrow thick stripes are better than wide thin ones, but given a distance from the light line, the opposite is true. Each of the metals analyzed show wavelength regions where their performance is best. The figures of merit are generally applicable and should be useful to help compare, assess and optimize designs in other 2D surface plasmon waveguides or in other absorbing waveguides.

Passive elements operating with long-range surface plasmon polaritons and constructed as Au stripes embedded in Cytop were investigated theoretically and experimentally at wavelengths near 1310 nm. The elements investigated consist of straight waveguides, S-bends, Y-junctions, couplers, and Mach-Zehnder interferometers. The measured performance of these devices is close to theoretical expectations, although uniformity issues were noted, likely because of fabrication imperfections. Cytop is a low-index polymer suitable for biosensing applications involving aqueous buffers. The elements demonstrated thus could form the basis of integrated biosensing devices operating with long-range surface plasmons.

Two-dimensional surface plasmon-polariton waveguides must generally be analysed using numerical methods. However, accurate analysis is challenging due to large permittivity contrasts and to strong localisation of mode fields, especially near corners where they tend to diverge. These difficulties impact the convergence of numerical methods, yet understanding convergence is essential if accuracy is to be claimed. The convergence and accuracy of two vectorial numerical methods commonly used, the method of lines and the finite element method, were assessed by computing the propagation constant of modes supported by the metal slab, the metal stripe and the 90 metal corner. A discretisation strategy that yields smooth monotonic convergence is demonstrated for both methods. More accurate results are then extrapolated from the convergence histories and anticipated errors (relative to extrapolated results) are computed. Both methods yield similar anticipated errors for a comparable discretisation spacing, with the finite element method yielding slightly lower errors but the method of lines requiring less computational effort. Convergence was slower for highly confined modes, particularly those having fields localised near corners. Convergence to within an anticipated error of ±2% was readily achieved with both methods, except for the attenuation of modes that are highly confined to corners which remained in error by 10 to 20%. However, the percentage difference between the extrapolated results computed from both methods ranged from 3 75 to 0 012%. The convergence and accuracy of the methods of lines for curves was also investigated, and it was found that the absorbing boundary condition used along the radiating side of the curve introduces errors that can further limit the accuracy of the computations.

A waveguide structure capable of aggressive bends (r(0)-->0) and long-range propagation (approximately 1.2 dB/mm) is described here. The structure uses a step-index slab to create the vertical confinement and a pair of metallic parallel plates on either side of the core for lateral confinement. The parallel plates are dimensioned to ensure that all modes that would cause radiation loss in a bend are cut off.

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