The extraordinary light transmission through double-hole and elliptical nanohole arrays in a thin gold film is investigated for different orientations of the holes relative to the lattice. Even though these bases have similar symmetry characteristics, the polarization follows the orientation of the basis for the ellipse but remains fixed along a lattice vector for the double holes. Furthermore, the maximum transmitted intensity for linearly polarized light is constant for the ellipse, but decreases for the double holes as they are rotated away from being aligned with the lattice. Finite-difference time-domain simulations agree well with the experimental findings. These experiments show how the basis determines both the coupling into the surface plasmon waves and the evanescent transmission through the nanoholes. Both of these effects need to be considered when designing nanophotonic devices using the extraordinary transmission phenomenon.Light transmission through subwavelength holes can be increased by several orders of magnitude with respect to Bethe's theory 1 when the holes are periodically arranged in a thin metal film. 2 This extraordinary transmission is the result of resonant coupling to surface plasmon (SP) waves at the metal-dielectric interface via the array of holes. 3,4,5,6,7 As with other periodic systems, the optical response of the hole array is determined by both the lattice and the basis. The SP waves are longitudinal, so the polarization is collinear with their direction of propagation. 8 This means that the polarization direction of the incident field selects which resonance of the lattice is excited. Recent works have shown that changing the basis shape from circular holes to elliptical 9,10 and rectangular 11 holes has a strong influence on the polarization and resonance properties; as the aspect ratio is increased, the polarization perpendicular to the broad edge of the hole has enhanced transmission and the resonance peaks shift in wavelength. Those works focused on the situation in which the elongated basis was aligned with the array's lattice vector. As a result, they did not separate the contributions of the basis and the lattice. Furthermore, both the ellipses and the rectangles considered in those works have a strongly polarized (evanescent) transmission mode through the holes, which was not distinguishable from the other polarization effects.In this work, we investigate the effect of the array basis and its orientation on the transmission. By comparing the behavior of ellipses to double-hole arrays, the contributions of the lattice and basis are distinguished. When the ellipses and the double holes are aligned with the lattice, they both show enhanced transmission for light polarized perpendicular to their long axis. Upon rotation of the basis, however, the transmission of the ellipses and double holes have different polarization behaviors. These experimental results are in good agreement with theoretical simulations based on finitedifference time-domain (FDTD) calculations....

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An algorithm is developed for the identification of Wiener systems, linear dynamic elements followed by static nonlinearities. In this case, the linear element is modeled using a recursive digital filter, while the static nonlinearity is represented by a spline of arbitrary but fixed degree. The primary contribution in this note is the use of variable knot splines, which allow for the use of splines with relatively few knot points, in the context of Wiener system identification. The model output is shown to be nonlinear in the filter parameters and in the knot points, but linear in the remaining spline parameters. Thus, a separable least squares algorithm is used to estimate the model parameters. Monte-Carlo simulations are used to compare the performance of the algorithm identifying models with linear and cubic spline nonlinearities, with a similar technique using polynomial nonlinearities.Index Terms-Block structured models, cubic spline, Levenberg-Marquardt algorithm, nonlinear system identification, separable least squares optimization.

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The increasing computational demands of finite-difference time-domain simulations for studying optical phenomenon requires codes with very high performance. This paper introduces a new hybrid parallel code using standard MPI and OpenMP technologies. The code is portable to a variety of high performance systems. The transmission of light through an isolated sub-wavelength in an optically thick silver film is outlined as an example application of the code.