We demonstrate that 3D printing, commonly associated with the manufacture of large objects, allows for the fabrication of high quality terahertz (THz) plasmonic structures. Using a commercial 3D printer, we print a variety of structures that include abrupt out-of-plane bends and continuously varying bends. The waveguides are initially printed in a polymer resin and then sputter deposited with ~500 nm of Au. This thickness of Au is sufficient to support low loss propagation of surface plasmon-polaritons with minimal impact from the underlying layer, thereby demonstrating a useful approach for fabricating a broad range of plasmonic structures that incorporate complex geometries. Using THz time-domain spectroscopy, we measure the guided-wave properties of these devices. We find that the propagation properties of the guided-wave modes are similar to those obtained in similar conventional metal-based waveguides, albeit with slightly higher loss. This additional loss is attributed to roughness associated with limitations that currently exist in commercial 3D printers.

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We present the first experimental observation of Anderson localization in the terahertz frequency range using plasmonic structures. To accomplish this goal, we designed THz waveguides consisting of a one-dimensional array of rectangular apertures that were fabricated in a freestanding metal foil. Disorder is introduced into the waveguide by offsetting the position of each aperture by a random distance within a prescribed range. For example, for a waveguide with apertures spaced by 250 μm in a periodic waveguide, 10% disorder would correspond to the apertures being shifted by a random value between ±25 μm along the waveguide axis. We find that for disorder levels below 25%, there is only an increase in the propagation loss along the device. However, for two specific waveguides with 25% disorder, we observe a spatially localized mode that lies just within the stop band of the device and exhibits a double-sided exponential spatial decay away from the maximum.

Shape memory alloy foils that are appropriately patterned are cycled between two different metal foil geometries resulting in two different terahertz (THz) plasmonic responses. This is accomplished by using patterned foils of a nickel-titanium alloy (Nitinol) that switches between the martensite phase below 31° C, yielding one physical geometry, and the austenite phase, when the foil is heated above 51° C, yielding a second physical geometry. In order to enable this reproducible switching, the sample is initially put through a two-way training procedure, through which the two different This article is protected by copyright. All rights reserved. 2 desired physical geometries are imprinted. Specifically, the metal foils are trained to switch between a sinusoidal corrugation, either one-dimensional (1D) or two-dimensional (2D), at close to room temperature and a flat metal sheet above the austenite phase transition temperature. The foils are found to switch reproducibly between geometries over at least 100 thermal cycles. Using THz timedomain spectroscopy, the transmission properties of the foils are measured as a function of incident polarization and foil geometry. The changes in spectrum are explained qualitatively and through numerical simulation.