We show that the polarization states of electromagnetic waves can be manipulated through reflections by an anisotropic metamaterial plate, and all possible polarizations (circular, elliptic, and linear) are realizable via adjusting material parameters. In particular, a linearly polarized light converts its polarization completely to the cross direction after reflection under certain conditions. Microwave experiments were performed to successfully realize these ideas and results are in excellent agreement with numerical simulations. DOI: 10.1103/PhysRevLett.99.063908 PACS numbers: 42.25.Ja, 42.25.Bs, 78.20.Bh, 78.20.Fm Polarization is an important characteristics of electromagnetic (EM) waves. It is always desirable to have full control of the polarization states of EM waves. Conventional methods to manipulate polarization include using optical gratings, dichroic crystals, or employing the Brewster and birefringence effects, etc. [1,2]. Here we propose an alternative approach based on metamaterials [3][4][5][6]. Metamaterials have drawn much attention recently due to many fascinating properties discovered, such as the negative refraction [4], the in-phase reflection [5], and the axially frozen modes [6], etc. Here, we show that a specific metamaterial reflector can be employed to manipulate the polarization state of an incident EM wave. In particular, a complete conversion between two independent linear polarizations is realizable under certain conditions. We show the physics to be governed by the unique reflection properties of the metamaterial, and we perform experiments and finite-difference-time-domain (FDTD) simulations to demonstrate these ideas in the microwave regime.We start from studying a model system as shown in Fig. 1(a), which consists of an anisotropic homogeneous metamaterial layer (of a thickness d) with a dispersive relative permeability tensor $ 2 (with diagonal elements xx , yy , zz ) and a relative permittivity " 2 , put on top of a perfect metal substrate (with " 3 ! ÿ1, 3 1). We consider the reflection and refraction properties of the structure, when a monochromatic EM wave with a wave vectork in !=csincosx sinsinŷ cosẑ and a given polarization strikes on the surface. According to the Maxwell equations, EM waves should satisfyẼ2 k Ẽ inside the metamaterial layer withk the wave vector. Given k x and k y , the dispersion relation between ! and k z is determined by !=c 4 "ii ÿ1 jj k 2 l 0, where i; j; l x; y; z. The above equation has four roots corresponding to two refracted waves propagating forwardly and backwardly. The solution inside the second layer must be a linear combination of these four waves, manifesting the birefringence effect [1,7]. To match the boundary conditions, we must also expand the waves in other regions to linear combinations of four solutions, namely, the forward (backward) waves with s and p polarizations. The reflected beam thus generally consists of both s and p modes, even if the incident wave possesses one polarization. To solve these problems, we have extende...

We present the design, fabrication, and measurement of a dual-band planar metamaterial with two distinct electric resonances at 1.0 and 1.2 THz, as a step towards the development of frequency agile or broadband THz materials and devices. A method of defining the effective thickness of the metamaterial layer is introduced to simplify the material design and characterization. Good agreement between the simulated and measured transmission is obtained for the fabricated sample by treating the sample as multi-layer system, i. e. the effective metamaterial layer plus the rest of the substrate, as well as properly modeling the loss of the substrate. The methods introduced in this paper can be extended to planar metamaterial structures operating in infrared and optical frequency ranges.

We report the design, fabrication, and measurement of a terahertz metamaterial composed of single geometry electric field coupled resonators that has two closely spaced electric resonances near 1.0 and 1.5 THz. Due to the mutual coupling between the different resonances in the particle, the lower frequency resonance of this metamaterial is stronger than that in a metamaterial composed of identically sized single-resonant particles, leading to a larger insertion loss and broader bandwidth. This feature provides more flexibility in metamaterial design and application in the terahertz regime.

We propose large bandwidth and high fabrication-tolerance mode-order converters on the silicon-on-insulator platform based on novel compact tapers structures. Each of the converters is in a single waveguide. Designs of different symmetries with and without breaking the parities between odd and even modes are illustrated. The fabrication tolerances of the devices are also investigated. The simulation results show that high conversion efficiencies can be readily achieved over a wavelength range from 1520 nm to 1580 nm for all of the proposed devices. The average conversion efficiencies of TE1-to-TE0, TE2-to-TE0, TE3-to-TE0, TE2-to-TE1, TE3-to-TE1, and TE3-to-TE2 converters are -0.061 dB, -0.052 dB, -0.11 dB, -0.119 dB, -0.168 dB, and -0.154 dB, respectively. The conversion efficiencies have negligible degradations under normal width and thickness deviations.

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We propose and experimentally demonstrate a feasible integrated scheme to solve all-optical differential equations using microring resonators (MRRs) that is capable of solving first- and second-order linear ordinary differential equations with different constant coefficients. Employing two cascaded MRRs with different radii, an excellent agreement between the numerical simulation and the experimental results is obtained. Due to the inherent merits of silicon-based devices for all-optical computing, such as low power consumption, small size, and high speed, this finding may motivate the development of integrated optical signal processors and further extend optical computing technologies.

We report the design and experimental measurement of a powered active magnetic metamaterial with tunable permeability. The unit cell is based on the combination of an embedded radiofrequency amplifier and a tunable phase shifter, which together control the response of the medium. The measurements show that a negative permeability metamaterial with zero loss or even gain can be achieved through an array of such metamaterial cells. This kind of active metamaterial can find use in applications that are performance limited due to material losses.

We propose and experimentally demonstrate an ultra-compact multimode waveguide crossing that can process two modes simultaneously. The symmetric Y-junction is introduced to split the high-order modes into fundamental ones, easing the subsequent processing. The footprint of the proposed crossing is as compact as 21  μm×21  μm. The measured results show an insertion loss of ∼1.82  dB for the TE mode and ∼0.46  dB for the TE mode at 1550 nm, as well as a crosstalk of <-18  dB from 1510 to 1600 nm.