JTu5A.107.pdf CLEO:2015 © OSA 2015 Negative-index Polarization-independent Metamaterial Morteza Karami*, Christopher Rosenbury, Steven Kitchin, and Michael A. Fiddy Center for Optoelectronics and Optical Communications, University of North Carolina at Charlotte, 9201 University City Blvd, Charlotte, North Carolina 28223, USA * e-mail: mkarami@uncc.edu Abstract: We introduce a polarization-independent left-handed metamaterial, and describe its electromagnetic properties using numerical techniques. Conventional mirrored S-shaped resonators are shown to exhibit a negative refractive index; and in this work a crossed design based on these resonators is demonstrated as a polarization insensitive metamaterial with negative effective index. OCIS codes: (160.3918) Metamaterials; (350.3618) Left-handed materials; (260.2065) Effective medium theory; (260.5430) Polarization; (260.5740) Resonance; (230.4110) Modulators 1. Introduction Electromagnetic metamaterials have received attention increasingly in recent years, and they have found their place in current technologies since their relatively recent introduction to the community. One of the needs in practical use of metamaterials has been designing a polarization insensitive structure. Here, we propose a 3D metamaterial design which has a polarization-independent transmission spectra. 2. Design and Analysis Figure 1. (a) Unit cell design of mirrored S-resonator metamaterials. (b) Transmission spectrum for different angles of linearly polarized normal incident wave (propagation in z) for the case where g=1.5mm. (c) Extracted refractive index of normal incident for polarization along y; based on reference [4], extracted index values should be valid for frequency range of 6.1-7.3 GHz. The design of polarization insensitive metamaterial is based on S-shaped resonator whose electromagnetic properties have been thoroughly studied before [1–3]. One can achieve negative effective parameters using a double mirrored S-shaped resonator as depicted in Figure 1(a), where aluminum is used to make S-features and they are embedded with a dielectric spacer of polyethylene with ɛ=2.25. The S-shaped resonator has dimensions of dz=4.48 mm, dy=4.18 mm, and g=1.5 mm; its trace width is 0.34 mm for side arms and 0.64 mm for elsewhere, and it has thickness of 0.04 mm. The mirrored S-resonator is in the center of the dielectric unit cell with dimensions of 3 mm, 8.9 mm, and 6.4 mm in x, y, and z directions. The transmission spectrum of the bulk metamaterial constructed with this unit cell is shown in Figure 1(b); a strong magnetic resonance is observed at frequency 5.7 GHz for p- polarization of normal incident excitation propagating along z direction, and it vanishes gradually by tilting the polarization from y to x direction. Therefore the constructed structure is birefringent and only exhibits strong left- handed properties for p-polarization of the incident wave; consequently, its spectra depends on the polarization of incoming wave. To improve the design to achieve polarization independency, we can use crossed pairs of mirrored S-resonators to cover both orthogonal polarizations and hence all of their superpositions. In order to do that, we simulated a series of this element with different lateral periodicity, Ʌx, using a finite-element solver (Ansys HFSS), and retrieved effective parameters by following a commonly used retrieval process [4]. To design a crossed structure, an optimum lateral periodicity is found where the bulk medium exhibits acceptable negative index in frequency range of 7.3-8 GHz according to criteria for choosing correct interpretation of extracted effective parameters [4], Figure 2. As can be seen in Figure 2(b), by increasing lateral periodicity of the structure, a blueshift occurs in its strong magnetic resonance which is seen at 7.3 GHz. (a) (b) (c)