Within a well-defined pass band, meander structures behave like almost ideal linear polarizers, can induce large phase retardation between s- and p-polarized light and show a high polarization conversion efficiency. In this respect, meander structures behave similar to plasmonic nanoslits at Fano resonance [1, 2] (Fig. 1) but over a wider frequency range and with a higher transmission. Due to these properties, meander structures can interact effectively with polarized light and can be used for different, non-imaging applications such as polarization scramblers [2, 3].
Fig. 1: (a) Transmittance spectra of p-polarized (Tp) and s-polarized light (Ts) as a function of the azimuth angle ϕ at normal incidence for f = 600 THz, 630 THz and 650 THz. The fit curves are indicated by markers and were obtained from a model using plasmonic nanoslits at Fano resonance (b) Phase retardation δ as a function of the azimuth angle ϕ. (c) Transmittance of p-polarized light as a function of the azimuth angle ϕ for incident s-polarized light. The investigated meander structure has the geometry parameters Px = 400 nm, D = 40 nm and t = 30 nm.
The proposed polarization scrambler consists of spatially distributed metallic meander structures with random angular orientations. We describe the polarization properties of meander structures or meander stacks with the Mueller matrix (Fig. 2a). The whole device has an optical response averaged over all pixel orientations within the incident beam diameter. Averaging over all azimuth angles leads to a more intuitive representation of the depolarization properties of the proposed polarization scrambler (Fig. 2b).
Fig. 2: (a) Mueller matrix (elements mij with row index i = 0-3 and column index j = 0-3) of a double meander structure at 600 THz with period Px = 400 nm, corrugation depth D = 40 nm and thickness t = 30 nm. The structures are stacked on top of each other separated by a layer of air with thickness Dspa = 600 nm. (b) Mueller matrix elements from (a) averaged over the azimuth angle ϕ from 0° to 180°.
One can see that for small angles all off-diagonal Mueller matrix elements are zero whereas the diagonal elements are reduced to values below one. In this angle regime, the device represents a partial depolarizer. With our preliminary design, we achieve depolarization rates larger than 50% for arbitrarily polarized monochromatic and narrow-band light. Circularly polarized light could be depolarized by up to 95% at 600 THz. The presented polarization scrambler can be flexibly designed to work at any wavelength in the visible and infrared range with a bandwidth of up to 100 THz. The proposed device might prove advantageous for optical setups with monochromatic light sources and is desirable for space applications due to its low weight and large-scale manufacturability.
- M. Shcherbakov, M. Dobynde, T. Dolgova, D.-P. Tsai, and A. Fedyanin, "Full Poincaré sphere coverage with plasmonic nanoslit metamaterials at Fano resonance," Phys. Rev. B 82, 193402 (2010).
- P. Schau, L. Fu, K. Frenner, M. Schäferling, H. Schweizer, H. Giessen, L. M. Gaspar Venancio, and W. Osten, "Polarization scramblers with plasmonic meander-type metamaterials", Opt. Express 20, 22700 (2012).
- P. Schau, L. Fu, K. Frenner, H. Schweizer, M. Schaferling, T. Weiss, H. Giessen, L. M. Gaspar Venancio, S. Hannemann, and W. Osten, "Polarization scrambling with metallic meander structures for space applications," Proc. SPIE 8423, 842314, (2012).