Metal grating terahertz polarizers on substrate

The rapid growth of the terahertz industry nowadays requires the development of new effective low-loss optical elements. THz polarizers are one type of such a fundamental element. They are required for polarization-sensitive material studies, characterizing polarization of different THz sources, polarization dependence of THz detectors and other purposes. Powerful THz sources are still a big challenge for the industry, which requires THz polarizers to have low losses along with effective extinction of undesired polarization. Several approaches for developing THz polarizers exist. Free-standing wire-grid polarizers can have high extinction ratio and low losses, but are fragile and hard to manufacture [1]. Robust polarizers with high extinction ratio exist but usually have considerable losses [2]. One of the approaches suggested for developing an effective THz polarizer is development of metal wire-grid polarizers on a substrate. A wire-grid provides high extinction ratio while a substrate facilitates easier manufacturing and enhances robustness of a polarizer; however, it may increase losses. In recent work [3] a multi-layer wire-grid on polymer polarizer has been shown with an extinction coefficient as high as 90 dB at 1 THz at a cost of losses of about 1.4 dB. Different fabrication technologies vary in parameters they provide such as spatial resolution of resulting structures and have different financial costs. For this reason, it is important to know how sizes of the fabricated structures affect performance of the polarizer. In this work one-layered and multilayered polarizers for terahertz radiation made of metal grating on a substrate are studied via numerical simulations. The dependencies of extinction ratio and transmission losses on wire grid dimensions (period, thickness, fill factor), metal type and number of layers of a polarizer have been obtained. The results of the study can be used for development of an optimal THz polarizer design with acceptable losses and within limits of the chosen fabrication technology. Based on results of the numerical simulations an optimal single-layer THz polarizer design is proposed with extinction ratio of about 90 dB and losses of less than 0.5 dB at 1 THz.