In Radio Astronomy, receiving systems are sensitive to a given polarization mode. Splitting the incoming electromagnetic radiation into these modes allows simultaneous multicolor-imaging or spectroscopy in different frequency windows. The required devices - i.e., wire-grids reflecting one plane of polarization and transmitting the orthogonal one - are manufactured in the Terahertz Technology Division. They are also used to improve the sensitivity of our receivers, to inject local oscillator signals, or to perform polarization-sensitive observations tracing cosmic magnetic fields. A recent promising development in this field is the use of dichroic filters, made of custom-tailored metamaterials.