Efficient coupling into THz PCF fibres using specially designed lenses

In this paper we present the combination of a pair of specially designed symmetric-pass (s-p) UHMWPE lenses and a THz waveguide made of the cyclo-olefin polymer Zeonex with a core diameter of about 1.4 times the wavelength to achieve coupling efficiencies in excess of 50%. The s-p lens is designed to have no spherical aberrations and the same angle of deviation for both surfaces of the lens. The surfaces are calculated numerically, starting at the outer edge. This lens has shown superior performance compared to more traditional lens designs. To achieve sub-wavelength resolution we used a lens with a focal length of 25 mm and a numerical aperture of NA=1. The combination of s-p lenses and Zeonex waveguides offer a promising THz transmission system. Characterisation of the waveguide losses and the dispersion of the waveguide are ongoing.