Shaping of electromagnetic fields for THz plasmonics

The material characteristics in the THz-domain are an outstanding issue that challenge the development of suitable waveguides. It was shown that a simple metallic wires can provide waveguding with low attenuation and low dispersion. However, the need of an efficient coupling of free-space radiation limits the capabilities of the metallic wires. Here we suggest a coupling method which promise a significant increase in the coupling efficiency. We use the endfire-method which allows an excitation of the waveguide modes by direct illumination to the wire's front facet. The incident field is shaped in the field distribution by a spiral axicon and the polarization is modified by a sub-wavelength grating.