Full Poincaré sphere coverage with plasmonic nanoslit metamaterials at Fano resonance

Abstract

A form-birefringent plasmonic metamaterial of the subwavelength thickness is used to convert the light's polarization state in a way to cover the whole Poincaré sphere's surface by adjusting the experimental configuration. This optical anisotropy is induced by grating surface plasmon polaritons of a nanoslit array made in a thin golden film with the narrow spectral Fano resonance. Phase delay between linearly polarized states introduced by the sample reaches the value of 0.85 in the visible corresponding to the effective ordinaryextraordinary refractive index difference of ⌬n Ӎ 10.4. Thin metallic films shaped at the nanoscale have become of exceptional interest due to their electromagnetic response being highly dependent on the pattern configuration which allows one to pre-engineer their optical properties. Extraordinary optical transmission 1 media, negative refractive index metamaterials, 2 and artificially anisotropic 3,4 and chiral 5,6 metamaterials are the few examples of plasmonic objects acquiring their unusual optical properties through nanostructuring. Optical response of such materials is often defined by the excitation of propagating surface plasmon polaritons ͑SPPs͒ which are coupled onto the metallic surface through the periodicity of the structure itself. 7,8 In some cases, these excitations give rise to sharp Fano-type spectral lines 9-11 which have been recently intensively used for manipulation of transmittance of the nanostructured metal films from almost perfect 12,13 to suppressed transmission. 14 Controlling the polarization state of transmitted or reflected light with anisotropic plasmonic nanostructures has been studied for a long time 15 and contemporary results in this area include giant specific linear birefringence and dichroism [16][17][18][19][20] in the spectral vicinity of plasmonic resonances. However, high phase delays between ordinary and extraordinary waves could not be achieved with broad spectral lines of about 100 nm full width at half maximum used in preceding works for the reasons given in the discussion section of this paper.In this Brief Report we show how a narrow Fano resonance in a plasmonic metamaterial could be utilized to induce huge phase delay between transmitted linearly polarized eigenstates. It is demonstrated that the resulting birefringence can be controlled by varying the angle of incidence in the range of only 8°from ⌬n = 4.4 to ⌬n = 10.4, where ⌬n is the difference between effective refractive indices of ordinary and extraordinary waves. It is shown that the polarization state of the light output from a system with a Fano resonance could cover the whole Poincaré sphere which was unattainable with previously concerned structured films of subwavelength thicknesses.A system which optical response consists of a coherent superposition of Lorentz-resonance response and background signal would possess a spectral line shape called Fano resonance. 21 The general expression for the complex transfer function of a Fano-resonance system can be written as follows:where...

Polarization scramblers with plasmonic meander-type metamaterials

“…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.…”

“…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].…”

“…This high-transmission pass band is the main reason for using meander structures for the proposed depolarizer. Other plasmonic nanostructures such as nanowire arrays show a stop band behavior, while nanoslit arrays or nanohole arrays exhibit only one narrow and lowtransmission pass band induced by a single resonance [9,16,17].…”

“…The conversion is stronger at higher frequencies where the phase retardation is larger as well. In order to describe the meander structure analytically, we use the same formalism as the authors in [17] for a plasmonic nanoslit metamaterial at Fano resonance. For an anisotropic medium under normal incidence with the optical axis oriented along the x-coordinate of the Cartesian laboratory system, its Jones matrix can be expressed as:…”

Optical Curtain Effect: Extraordinary Optical Transmission Enhanced by Antireflection

“…Usually, exotic phenomena, e.g., the well-known EOT [1,[5][6][7], Fano resonance [8,9], hot spot effect [10,11], etc., accompany with the desired metallic nano-structures. In advantage of state-of-the-art nanofabrication techniques, the metallic nano-structures are playing remarkable roles in current nano-science and have been used in many aspects including extracting more light from light emitting diodes [12,13], harvesting solar energy [14,15], improving sensitivity of biosensors [16,17], focusing light with sub-diffraction limit resolution [18][19][20] and so on.…”