Impedance-Matched Planar Metamaterial Beam Steerer for Terahertz Waves

TL;DR

This paper presents the design, fabrication, and experimental validation of an impedance-matched planar metamaterial for terahertz waves, enabling efficient beam steering with high transmission and low reflection.

Contribution

It introduces a novel metamaterial with tunable refractive index and impedance matching, and demonstrates a functional terahertz beam steerer with accurate wave deflection.

Findings

Achieved over 90% amplitude transmission at 0.444 THz.

Demonstrated a beam deflection angle of approximately 6 degrees.

Realized a gradient index beam steerer with high efficiency.

Abstract

Planar metamaterials with tailorable electromagnetic properties in the terahertz domain offer customized optics solutions that are needed for the development of imaging and spectroscopy systems. In particular, metamaterials carry the potential to substitute conventional bulky optics or can be basic building blocks for completely novel devices. In this respect it is advantageous that metamaterials can be devised to be impedance-matched to another material regarding their electromagnetic properties. Here, we design, fabricate and investigate a metamaterial with tailorable refractive index and impedance-matching to free space. The unit cell is comprised of two different pairs of cut-wires that provide almost independent control over the electric and magnetic response to an electromagnetic wave. For the example of a metamaterial with a uniform effective refractive index of 1.18, we experimentally demonstrate an amplitude transmission of more than 90% and a reflectivity of about 5% at a working frequency of 0.444THz. As a more functional device, we fabricate a terahertz gradient index beam steerer with a linear refractive index gradient from 1.14 to 2.66. We numerically simulate the electromagnetic wave propagation through the beam steerer and compare the electric field amplitude of the deflected wave with the terahertz field distribution that is measured behind the beam steerer in an imaging terahertz time-domain spectroscope. The numerically simulated deflection angle of 6.1{\deg} agrees well with the measured deflection angle of 5.95{\deg}. The measured peak amplitude transmission of the beam steerer amounts to almost 90%, which also agrees well with a simulated value of approximately 88%.