A simple device is presented that serves as a secondary source of light with prescribed polarization properties. The technique employed is based on the Schmidt purification of a mixed quantum state. Such a purification can be applied to quantum and to classical polarization states. The device presented here can be used with both classical and quantum primary sources of light. It allows controlling the degree of polarization as well as the Stokes vector that enters the decomposition of a light beam in a fully unpolarized and a fully polarized component. © 2013 Optical Society of America.