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The field of plasmonics has historically been a playground exclusively for the optics community. Primarily this is because the response of metals becomes dominated by their large conductivities at much lower frequencies, making it difficult to exploit the unique properties of surface plasmon (SP) modes. Indeed SPs on flat, perfectly conducting substrates are better described as simple surface currents or grazing photons. However the realization that one can form metal-dielectric composites to support surface waves with plasmon-like properties has opened the field of plasmonics to the terahertz and microwave domains. Pendry et al. [Science, 305, 847 (2004)] were among the first to speculate about an extension of plasmonics into long wavelength regimes. They demonstrated that the perforated surface of a perfect conductor can support a SP-like mode whose behavior is determined purely by the geometry of the substrate. Beginning with our initial experimental verification of these SP-like modes excited via grating-coupling, we present an overview of some of our recent microwave studies. We progress to study the classical method of prism coupling and also consider the enhanced transmission phenomenon (mediated by plasmon-like surface modes) through hole arrays. Finally the first experimental evidence of coupled SP-like modes between two such perforated metal substrates placed in close proximity will be presented.

It is shown that microwave radiation can be transmitted through a wall of aluminum-alloy bricks even though the width of the gaps between the metallic elements is less than 5% of the radiation wavelength. Up to 90% of the radiation made incident upon the wall is transmitted, with both linear polarizations being passed. Experimental results are compared to theoretical predictions. Proving that the transmission mechanism relies upon self-coupled surface plasmon resonances in what are effectively Fabry-Perot cavities.

Surveys of the natural world reveal an extensive array of optical effects in a broad range of animal and insect species. While the aesthete may simply take delight in such phenomena, students of photonics have increasingly been prepared to look more closely; deriving understanding and inspiration from nature's optical ingenuity. By describing specific structural color examples in detail, within a general context of Lepidopteran microstructure classification, this review paper seeks to present an introduction to current work on butterfly photonics. Additionally, new but preliminary results and analysis are presented, that describe the structural color of a butterfly that exhibits a distinct 3D photonic crystal structure.

In this work sinusoidal diffraction gratings with a range of pitches and amplitudes are used to algin nematic liquid crystal layers in a twisted homogeneous configuration. The grating profiles are accurately characterized using optical surface plasmon polariton spectroscopy which then allows a calculation of the anchoring energy as predicted by the simple Berreman expression. The experimental Rapini-Papoular anchoring energy is also obtained by a measurement of the director twist away from the alignment direction at room temperature. A linear relationship is found between the two anchoring energies except when it falls below 4 X 10 -7 Jm -2 . Noticeably, the correlation between the two theories is hot unity, if room temperature elastic constants are used in the calculation. This apparent inconsistency is explained if the effect of surface memory on the system is considered. Indeed if elastic constant, corresponding to a higher temperature, at which surface memory effects are absent, are used in the Berreman expression, good agreement between the predicted and experimentally measured energies is found.

In this work, the electro-optic response of 6CB liquid crystal is studied using a sensitive differential technique. The liquid crystal layer is held at a temperature just above the nematic to isotropic (N-I) phase transition. Transverse magnetic (p) polarized light incident on the cell is coupled to guided modes in the liquid crystal layer using either grating or prism coupling. In both cases the modes manifest themselves as sharp resonances in the reflectivity as the angle of incidence is scanned. When a low frequency sinusoidal voltage is applied to the cell the resonance shapes and positions are altered at a frequency which is twice that of the applied field, resulting in a modulation of the reflectivity for a given angle of incidence. By carefully observing the modulated signal, and comparing the data with modelling generated from multilayer optics theory, two effects are quantified. The first of these is an induced birefringence, (delta) n, varying quadratically with applied voltage, which is well understood and can be expressed in terms of Landau De Gennes theory. The second is a field induced perturbation in the imaginary part of the optical permittivity, (delta) (epsilon) i, which implies a modification of the light scattering properties of the liquid crystal. The measurement of the latter effect is, as far as we know, a novel one, being only made possible by the remarkable sensitivity of the synchronous differential technique.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Electromagnetic modes may be excited by photons using grating coupling to provide the necessary extra momentum. Rotation of the grating so that the grooves are no longer perpendicular to the plane of incidence (conical diffraction) breaks the symmetry of the system and introduces polarization conversion. This conversion is strongly enhanced when a mode is excited. Reflectivity data are presented showing polarization enhancement by the excitation of surface plasmon polaritons (SPPs), long range surface plasmon polaritons, and resonant guided modes on surface modulated gratings. The dependence of this conversion on angle of incidence, azimuthal angle, and groove depth has been studied in detail. When the grooves are at 45 degree(s) to the plane of incidence, maximum conversion is recorded for the SPP. However, for guided modes the maximum conversion occurs at angles other than 45 degree(s). The conversion has been seen to rise monotonically with groove depth and efficiencies of over 50% are easily obtained via SPPs and guided modes. Theoretical comparisons with data are made using a rigorous differential method applicable for conical diffraction. This formulation uses a coordinate transformation between the grating surface and a planar system. The comparison between data and theory is very good and further theoretical modeling predicts that conversion efficiencies can approach 100% for appropriate circumstances.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.