Break Through the Limitation of Malus' Law with Plasmonic Polarizers

Abstract

723wileyonlinelibrary.com COMMUNICATION www.MaterialsViews.com www.advopticalmat.de bandwidth. [ 14 ] Very recently, Xiao et al. attempted theoretically to use a pair of nonorthogonal plasmonic polarizers to rotate the linear polarization. [ 16 ] Nonetheless, the reported working bandwidth was very narrow (∼1%). Their results also showed that, when the two polarizers are orthogonal, the transmission and conversion effects are still ineffi cient.In this paper, we suggest that the aforementioned longstanding problem can be solved: two specially designed linear plasmonic polarizers, which are orthogonally oriented to each other, can induce both high transmission and 90-degree polarization conversion. We also present the fi rst experimental demonstration of such an effect in both optical frequencies and the microwave regime. The working system is of simple confi guration, high effi ciency, and larger bandwidth. Moreover, based on this effect, a super polarization converter that switches the incident polarization to an arbitrary direction has been designed and realized in the microwave band. The results represent a breakthrough of conventional effects and open the door for constructing new types of plasmonic devices, e.g., the polarization converters, one-way transmitters, subwavelength switches, modulators, etc.Figure 1 a-c show the schematic view of our design, where two linear plasmonic polarizers M with the thickness t are separated by a spacer layer I of thickness h (the spacer layer can be dielectric or air; the qualitative conclusion does not depend on the medium of spacer, unlike the case in a liquid crystal display). The linear polarizer is constructed by a metal fi lm milled with periodic rectangular holes (the lattice constant is d , the hole length is l , and the hole width is w ), with the polarization axis perpendicular to the long hole edges. If projected onto the xy plane, the rectangular holes in the two polarizers become orthogonal and form the L-shaped "crossing" (see Figure 1 c). Thus, the two perforated metal fi lms comprise a pair of orthogonal linear polarizers. Such a system can ensure that only the x -polarized component of electromagnetic wave can be coupled into the inlet and that only the y -polarized component can be produced from the exit. Hence, if there is any transmission in the system, it will inevitably lead to a rotation of linear polarization of 90 degrees.We start from one experiment carried out in the optical range. Because of the asymmetrical confi guration of the two polarizers with respect to the spacer layer, it may be a challenge to fabricate the system working in optical frequencies. By preparing a free-standing Au/SiN/Au sandwich structure, we successfully constructed the system with focused-ion-beam milling. Here, the thickness of the SiN fi lm is 50 nm, and the thickness of each gold fi lm is 100 nm. Figure 1 d Control of the polarization state represents an important ability for manipulating light and has great importance for practical applications such as photography,...

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Broadband integrated polarization rotator using three-layer metallic grating structures

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