The polariser comprises an array of prismatic elements (2) arranged into a plate shaped assembly with plane sides facing each way. The hypotenuses of the prisms form a zigzag pattern and carry two dielectric layers which transmit the P component of the light while the S component is reflected. By selection of the refractive indices and angle of the prisms the S component is reflected twice and directed back along the incident direction. The reflective layers are designed to be near the Brewster angle for maximum effect. The prismatic elements can be made from smaller strips which are cemented together at butting faces (10) which lie in a plane parallel to the incident or polarised light.
