Three-dimensional printed achromatic λ/4 waveplate for the terahertz frequency range

A design of a three-dimensional printed achromatic $\lambda$/4 waveplate based on form-birefringence targeting the lower terahertz (THz) frequency range is proposed. For the waveplate a stratified structure is employed which gives rise to form-birefringence. Furthermore, experimental results in the frequency range from 75 GHz to 110 GHz show that the proposed waveplate causes a $\pi$/2 phase shift of incident linearly polarized light with a deviation from optimal behaviour not exceeding 5% for the entire range.