Scattering Amplitude of Surface Plasmon Polariton Excited by a Finite Grating.

Unusual optical properties of laser-ablated metal surfaces arise from the excitation of local plasmon resonances in nano- and microstructures produced by laser-processing and from the mutual interaction of those structures through surface plasmon polariton (SPP) waves. This interaction provides a synergistic effect, which can make the optical properties of the composite nanostructure drastically different from the properties of its elements. At the same time, the prediction and analysis of these properties are hampered by the complexity of the analytical solution to the problem of SPP excitation by surface objects of arbitrary configuration. Such a problem can be reduced to a simpler one if one considers the geometry of a structured surface as a superposition of harmonic Fourier components. Therefore, the analytical solution to the problem of surface plasmon polariton excitation through the scattering of light by a sinusoidally perturbed plasmonic metal/vacuum boundary becomes very important. In this work, we show that this problem can be solved using a well-known method for calculating guided-mode amplitudes in the presence of current sources, which is used widely in the waveguide theory. The calculations are carried out for the simplest 2D cases of (1) a sinusoidal current of finite length and (2) a finite-length sinusoidal corrugation on a plasmonic metal surface illuminated by a normally incident plane wave. The analytical solution is compared with the results of numerical simulations. It is shown that, in the first case, the analytical and numerical solutions agree almost perfectly. In the second case, the analytical solution correctly predicts the optimum height of the corrugation xopt, providing the maximum SPP excitation efficiency. At the same time, the analytical and numerical values of the SPP amplitude agree very well when the corrugation height x turns out to be x≪xopt or x≫xopt (at least up to 3xopt); at x=xopt, the mismatch of those does not exceed 25%. The limitations of the analytical model leading to such a mismatch are discussed. We believe that the presented approach is useful for modeling various phenomena associated with SPP excitation.

Analytical Calculations of Scattering Amplitude of Surface Plasmon Polaritons Excited by a Spherical Nanoantenna.

Since surface plasmon polaritons (SPPs) are surface waves, they cannot be excited by an incident plane wave, because free-space photons do not possess a sufficient in-plane momentum. Phase matching between the incident light and SPP can be achieved using a high-refractive-index prism, grating, or nanoantennas. In this work, we found an expression for the amplitude of SPP excited by an arbitrary 3D current distribution placed near a metal interface. The developed method is based on the well-known technique used in waveguide theory that enables finding the amplitudes of waveguide modes excited by the external currents. It reduces the SPP excitation problem to the summation of the set of emitters. As a particular example, we considered a spherical dipole nanoantenna on a metal substrate illuminated by a normally incident plane wave. The analytical calculations were in good agreement with the full-wave numerical simulations.

Tunable Fano-like resonances in bent single-mode waveguide-based Fabry-Perot resonator: erratum.

In this erratum, we correct an error in the numerical simulation results published in Opt. Lett.44, 231 (2019)OPLEDP0146-959210.1364/OL.44.000231. The error arose from disregarding cladding modes in the straight input and output waveguide sections [Fig. 2(a) in the original paper]. Although these modes do not contribute directly to the calculated power in the reflected and transmitted fundamental modes in those sections, they do, nevertheless, play a significant role in shaping the reflection and transmission spectra of the bent resonator, as was found after the paper had been published. While the main findings of the original paper remain largely intact, quantitatively the spectra in Figs. 3-6 are inaccurate and must be replaced with the correct ones given in this erratum. Some minor modifications to the conclusions of the original paper that are required in view of the corrected results are also discussed.

Tunable Fano-like resonances in a bent single-mode waveguide-based Fabry-Perot resonator.

Tunable Fano-like resonances are demonstrated numerically in a single Fabry-Perot resonator made of a bent single-mode waveguide. The resonances are shown to arise from the strong coupling between the fundamental mode of the core and a whispering gallery mode of the cladding. The tuning is realized by changing the bend radius of the waveguide. The influence of all major parameters of the resonator on its transmission and reflection spectra is illustrated and discussed. We believe that the presented results open up a new degree of freedom in designing bent waveguide-based refractometers, as well as other photonics elements utilizing cladding modes in bent single-mode waveguides.