Project blurb: The project presents two passive optics structures operating at terahertz frequencies. One is a Wollaston prism the other is a broadband terahertz waveplates. Both structures rely on birefringence, where the propagation speed of two polarisations are different. The prism separates two polarisations into different directions. For the broadband waveplate, the designs include half- and quarter- waveplates, which are designed and optimised via genetic algorithm. The operating frequency range is from 220GHz to 330GHz. Both structures are fabricated via 3D printing of cyclic olefin copolymer.Big text