Reflective optical stack for privacy display

A switchable display device for use in ambient illumination comprising:

• a spatial light modulator arranged to output light;
• wherein the spatial light modulator comprises a display polariser arranged on the output side of the spatial light modulator;
• an additional polariser arranged on the output side of the display polariser;
• a reflective polariser arranged between the display polariser and the additional polariser;
• and
• plural retarders arranged between the additional polariser and the reflective polariser,
• wherein the plural retarders comprise:
• a switchable liquid crystal retarder comprising:
• a layer of liquid crystal material having a positive dielectric anisotropy and having a retardance for light of a wavelength of 550 nm in a range from 500 nm to 1000 nm;
• and two surface alignment layers disposed adjacent to the layer of liquid crystal material and on opposite sides thereof, each of the surface alignment layers being arranged to provide homogeneous alignment in the adjacent liquid crystal material and each of the surface alignment layers having a pretilt having a pretilt direction with a component in the plane of the layer of liquid crystal material that is parallel or anti-parallel or orthogonal to an electric vector transmission direction of the reflective polariser;
• and
• at least one passive compensation retarder that comprises either:
• a passive uniaxial retarder having its optical axis perpendicular to the plane of the retarder and having a retardance for light of a wavelength of 550 nm in a range from −300 nm to −700 nm;
• or
• a pair of passive uniaxial retarders having optical axes in the plane of the retarders that are crossed and having a retardance for light of a wavelength of 550 nm in a range from +300 nm to +800 nm.