AVS 64th International Symposium & Exhibition
    Electronic Materials and Photonics Division Thursday Sessions
       Session EM-ThP

Paper EM-ThP27
Manipulation of Elliptical Polarization and Modulation of Optical Activity using Terahertz Stereo-metamaterial Reflectors

Thursday, November 2, 2017, 6:30 pm, Room Central Hall

Session: Electronic Materials and Photonics Poster Session
Presenter: Elizabath Philip, The University of Alabama
Authors: E. Philip, The University of Alabama
S. Pal, The University of Alabama
S.E. Stephens, The University of Alabama
P. Kung, The University of Alabama
S.M. Kim, The University of Alabama
Correspondent: Click to Email
Metamaterials (MMs) are playing a vital role in the development of the field of photonics. These are artificial materials made by repeated arrays of meta-atoms of subwavelength size, and can be controlled to manipulate the electromagnetic (EM) waves interacting with them. With appropriate designing of these meta-atoms, it is possible to achieve unique EM properties such as perfect absorption, negative permittivity, negative permeability, electromechanically induced transparency, etc. Recently, in terahertz (THz) frequency regime, MMs are being employed to replace conventional polarization converters. Conventional polarizers, retarders, rotators, etc. are usually made using dichroic crystals and optical gratings that are bulky, less efficient and operate in narrow bandwidths. Whereas with MMs they can be made thin, compact, easily combinable and even flexible. Much of the current THz polarization converters made of MMs function only in the transmission mode [1]. Though there are a few that function in the reflection mode, these are mostly linear polarization converters [2]. Evidently, there is a lack of linear to elliptical or circular reflective polarizers in the THz regime. In this work, we take advantage of an interesting category of MMs called stereo-metamaterials (SMMs) to develop a linear to elliptical polarization converter. SMMs utilize the same meta-atom, but are arranged at different spatial positions. They are analogous to stereo-isomers, which are molecules constituting of the same atoms but have different spatial arrangements. Six separate devices with varying spatial arrangements are first optimized through simulations with finite element method using Comsol. By tailoring the spatial arrangement of the meta-atom, we manipulate the polarization of the reflected light to become elliptically polarized, achieving a maximum ellipticity angle of 20.5° at 0.240 THz. Furthermore, we modulate the optical activity of the device, and a pure optical rotation of 37.0° at 0.246 THz is attained from the simulation results. The devices are fabricated using standard photolithography techniques and their linear to elliptical polarization conversion and optical activity is successfully verified through THz ellipsometry measurements. The device sensitivity to incident polarization modulation and its corresponding reflective phase retardation response is also analyzed. Lastly, the influence of the dipole coupling and current distribution is studied in order to explain the microscopic origin for the manipulation of the reflected light. Such SMM with linear to elliptical polarization conversion and optical activity modulation properties in the reflection mode has promising applications in THz sensing and communication devices. [1] J.W. He, Z.W. Xie, S. Wang, X.K. Wang, Q. Kan, Y. Zhang, Journal of Optics. 2015;17(10):8. [2] N.K. Grady, J.E. Heyes, D.R. Chowdhury, Y. Zeng, M.T. Reiten, A.K. Azad, et al. Science. 2013;340(6138):1304-7.