Polarisation separation element, a polarisation conversion system, an optical element, and a projection display system

The present invention provides a polarization separation element comprising a first array of prisms having a wedge-shaped cross-section, and a second array of prisms also having a wedge-shaped cross section. One of the prism arrays is an array of birefringent prisms. The present invention also provides a polarization conversion system having a polarization separation element of the above type for directing light having a first polarization in a first direction and for directing light having a second polarization different from the first polarization in a second direction different from the first direction; and one or more polarization conversion elements for converting light having the first and second polarizations to light having a substantially common output polarization. The polarization conversion system of the invention is suitable for use in a projection display system.