Polarization tomography of metallic nanohole arrays

Abstract

We report polarization tomography experiments on metallic nanohole arrays with square and hexagonal symmetry. As a main result we find that a fully polarized input beam is partly depolarized after transmission through a nanohole array. This loss of polarization coherence is found to be anisotropic; i.e., it depends on the polarization state of the input beam. The depolarization is ascribed to a combination of two factors: (i) the nonlocal response of the array as a result of surface-plasmon propagation and (ii) the non-plane-wave nature of a practical input beam. © 2005 Optical Society of America OCIS codes: 230.3990, 240.6680, 260.3910. Currently there is much interest in the optical properties of thin metal films perforated with arrays of subwavelength holes, or nanohole arrays. The optical transmission of these arrays shows a strongly peaked spectrum with anomalously large transmission peak values; this is usually ascribed to resonant excitation of propagating surface electromagnetic waves or surface plasmons (SPs). -3In this Letter we focus on the polarization properties of the anomalous transmission and show that these are strongly inf luenced by the propagating nature of the SPs.So far, polarization properties of nanohole arrays have been studied in a limited context: a beam with a given uniform state of polarization (SOP in ) is transformed by an anisotropic array or an isotropic array with nonspherical holes into a different uniform state of output polarization (SOP out ). 4 -6 This corresponds to a mapping of the Poincaré sphere onto itself; for instance, a rectangular array or a square array with elliptical holes acts as a birefringent and (or) a dichroic element that may convert a linear SOP into an elliptical SOP, conserving polarization coherence. In the present Letter we focus instead on cases where the degree of polarization (DOP) is reduced, DOP out , DOP in , corresponding to a reduction in radius and, in general, a deformation of the Poincaré sphere. 7,8 To underline this point we have chosen for our experiments square and hexagonal arrays, i.e., arrays that, for symmetry reasons, 9 cannot modify the SOP for plane-wave illumination at normal incidence. As we will show, depolarization occurs when two (quite common) conditions are simultaneously fulfilled: (i) the response of the array is nonlocal because of SP propagation, and (ii) the input beam is not a plane wave [but, e.g., a Gaussian beam, with a finite numerical aperture (NA)].In general, depolarization occurs when an optical system acts nonuniformly on polarization within the (spatial or temporal) bandwidth of the incident wave, thereby coupling polarization to other degrees of freedom. Experimentally, a study of depolarization requires a measurement of the Mueller matrix by a tomographic method. 7,8Here we report such polarization-tomography experiments on nanohole arrays and interpret the results in the context of SP propagation.We start by recapitulating the essence of our theoretical model. 9The input and output optical fields ...

Extraordinary IR Transmission with Metallic Arrays of Subwavelength Holes

“…The SPs propagate along the surface of the mesh, perhaps on both sides, to another hole where they decouple, producing photons that emerge in the same direction as the incident beam. Studies of ultrafast behavior, entangled photons, polarization effects, and SP propagation between separated subwavelength arrays have indicated that, fundamentally, the phenomena are single-photon processes that can preserve phase and polarization, at least under some conditions (13)(14)(15)(16)(17).…”

Influence of unsymmetrical periodicity on extraordinary transmission through periodic arrays of subwavelength holes

“…Polarization properties of nanohole arrays have been studied in many works [10,11,12]. Recently, orbital angular momentum of photons were explored to investigate the spatial mode properties of surface plasmon assisted transmission [13,14].…”

Polarization scramblers with plasmonic meander-type metamaterials

“…The dielectric function was derived from the Drude model and should be complemented with material data of Johnson and Christy [20] if higher frequencies are of interest. We used the plasma frequency ω p = 1.37 × 10 16 rad/s and the scattering frequency ν = 8.5 × 10 13 rad/s [21] for deriving the dispersion of Ag. Both the single and double meander structure are placed in vacuum although another permittivity configuration can be easily obtained.…”

“…Such materials could advantageously replace bulky standard optical components by a thin layer to achieve the same functionality but with higher efficiency and a lower mass and volume. Large birefringence and plasmonic anisotropy have been demonstrated in plasmonic metamaterials [8][9][10][11][12][13][14][15][16][17]. Therefore, the polarization state of light can be manipulated effectively, depending on the size and shape of the metallic nanostructures [8][9][10].…”

“…They can be used to realize phase retarders [9][10][11][12][13], polarization rotators [14] or polarization converters [15] by using structured thin metallic layers. Depolarization effects in metamaterials have also been discussed frequently [16,17]. However, a metamaterial pseudodepolarizer has, to our knowledge, not been investigated yet.…”