A cycloidal diffractive waveplate (50) comprising first and second substrate layers (52, 54), a liquid crystal layer (60C, 60H) provided between the first and second substrate layers, and transparent positive electrodes (56) and transparent negative electrodes (58) provided on the first substrate layer. The liquid crystal layer has a diffractive state (60C) in which the optical axes of the liquid crystal molecules are periodically rotated across a plane of the waveplate and a non-diffractive state (60H) in which the optical axes of the liquid crystal molecules are all orientated in the same direction in the plane of the waveplate. The electrodes (56, 58) are arranged in an alternating series, such that when an electric voltage is applied to the electrodes an electric field is produced in the plane of the waveplate and the liquid crystal layer is switched from the diffractive state to the non-diffractive state. A method of manufacturing the cycloidal diffractive waveplate is also provided.