Metamaterials as the design concept and umbrella name have demonstrated a broad range of useful
properties in different ranges of frequencies. The main advantage of the metamaterial-based devices is
the possibility to broaden both passive and active photonic component functionalities. While in the
visible, near infrared or microwave regimes these issues in principle have strong alternatives via a
conventional optics or electromagnetic approaches, at terahertz (THz) frequencies metamaterials are
often considered as being the unique solution for the encountered problems. Several approaches
involving metamaterials-based THz components have been proposed and show good potential for
applications [1,2]. Especially fruitful appears to be two-dimensional metamaterials or metasurfaces due
to fabrication simplifications and practically the same as bulk metamaterials functionalities.
In the talk we will focus on employment of THz metasurfaces as polarizers and polarization converters,
absorbers and conducting layers with enhanced transmittance, dichroic and chiral reconfigurable
systems, waveplates and broadband filters.
As the unified approach we employ the transmission line theory providing a needed level of the
generalization. We demonstrate its applicability in optical problems by analyzing the theoretical limits
of a metasurface converter with orthogonal linear eigenpolarizations that allows for linear-to-elliptical
polarization transformation with any desired ellipticity and ellipse orientation. Our analysis reveals that
the maximal conversion efficiency with a single metamaterial surface is 50 % in transmission and up to
90% in reflection. However, a double layer transmission converter and a single layer with a metallic
mirror can have 100% polarization conversion efficiency. We tested our conclusions numerically
reaching the designated limits of efficiency using a simple metamaterial design and checking them
against the numbers reported in literature.
The metasurfaces performance was characterized by exemplifying them with free-standing membranes
patterned with a grid of air slits perforated in a uniform large area (up to several cm2) 2μm-thick Ni
film. Depending on arrangement of both slits and their sizes different optical properties of such
metasurface can be acquired. We demonstrate linear polarization filtering with the parallel slits
dimmers, and more complex chiral behaviour of dimers, when non-equal slits are non-parallel. In
particular, strong optical activity and circular polarization conversion are reported.
|Conference||2015 Progress In Electromagnetics Research Symposium |
|Period||06/07/2015 → 09/07/2015|
Progress in Electromagnetic Research Symposium, PIERS 2015, July 6-9, 2015, Prague, Czech Republic, Proceedings, p.38. Session: SC2: THz Metamaterials: Fundamentals and Applications.