Characterization and Modeling of Laser Micro- Machined Periodically Corrugated Metallic Terahertz Wire Waveguides

Abstract

Following the first demonstration of cylindrical metal wires as low-loss/low-dispersion terahertz (THz) waveguides, it was proposed that surface corrugations of a metal wire with radial grooves would manipulate the energy confinement, dispersion, and loss dynamics of the propagating surface plasmon polariton. We present here the first characterization of such a wire. Finite element method (FEM) simulations are used to simulated and define the design of the periodic corrugation. Parameters are chosen such that loss, operating frequency, and electric-field confinement can be optimized. An engineered copper waveguide is accomplished via laser micromachining yielding a corrugated wire with grooves 20 um wide, 40 um deep, and spaced at 250 um. Parameters were chosen for an operational frequency of 250 GHz. THz pulses from a fiber-coupled THz time-domain source are focused onto a sub-wavelength coaxial aperture that is used to couple the linearly polarized THz light to the primary radial mode of the wire waveguide. A THz detector is placed at the end of the waveguide such that the frequency- dependent diffraction can be characterized. Control tests are made on the same type of 0.6 mm radius copper wire that is laser machined into corrugated wires. Characterization of the far- field diffraction pattern at the same detector position shows differences between the plain wire and corrugated waveguide. Other characterization measurements that will be presented include the diffraction at the end of the waveguide, the loss, and the electric-field confinement.